3:7 3 x1 5&1 Volcanic-Rich Middle and/ Upper Eoeene Sed1mentary /; Rocks Northwest of g / ' Rattlesnake Hills ’ " Central Wyoming 1‘...) LQEOLOGICAL SURVExY/‘EROFESSIONAL PAPER 274-A Prepared at part qf a program qf tfle’ Department of Me Interior far development qf tne M {smurf River basin Volcanic—Rich Middle and Upper Eocene Sedimentary Rocks Northwest of Rattlesnake Hills Central Wyoming By FRANKLYN B. VAN HOUTEN A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—A Preparea’ ay part ofa program oft/2e Department of tae [aterz'ar for development of tae Mz'syoarz' River éan’n UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director ‘s For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 65 cents (paper cover) ’ 6255755 P9 vfiafiflr‘ SCIENCES LIBRARY CONTENTS Page Page Abstract ___________________________________________ 1 Stratigraphy—Continued Introduction _______________________________________ 1 I Middle and upper Eocene rocks __________________ 6 Purpose and scope of investigation ________________ 1 Unit 1 _____________________________________ 6 Location and topography ________________________ 1 Unit 2 _____________________________________ 7 Previous work __________________________________ 3 Unit 3 _____________________________________ 8 Field work _____________________________________ 3 ‘ Unit 4 _____________________________________ 9 Laboratory work _______________________________ 3 Unit 5 _____________________________________ 9 Acknowledgments _______________________________ 3 Unit 6 _____________________________________ 10 Stratigraphy _______________________________________ 3 White River formation (Oligocene) ________________ 11 General features ________________________________ 3 Geologic history of area _____________________________ 12 Wind River formation (lower Eocene) _____________ 5 Literature cited _____________________________________ 13 ILLUSTRATIONS Page PLATE 1. Stratigraphic sections of Tertiary sedimentary rocks, Canyon Creek area, Fremont and N atrona Counties, Wyo __________________________________________________________________________________________ In pocket 2. Sedimentary features of middle and upper Eocene rocks ________________________________________________ Faces 4 3. Volcanic rock types in pebbles in middle and upper Eocene rocks ________________________________________ Faces 5 FIGURE 1. Index map showing location of Rattlesnake Hills volcanic field and measured sections A—E ____________________ 2 2. Relative abundance of volcanic minerals in middle and upper Eocene rocks, Canyon Creek area _______________ 7 3. Variation in roundness of large volcanic pebbles in unit 6, middle and upper Eocene rocks _____________________ 11 TABLES Page TABLE 1. Minerals in Tertiary sedimentary rocks, Canyon Creek area ___________________________________________ In pocket 2. Variation in composition and texture of conglomerate in unit 6, middle and upper Eocene rocks ______________ 10 747 A SHORTER CONTRIBUTION TO GENERAL GEOLOGY VOLCANIC-RICH MIDDLE AND UPPER EOCENE SEDIMENTARY ROCKS NORTHWEST OF RATTLESNAKE HILLS, CENTRAL WYOMING By FRANKLYN B. VAN HOUTEN ABSTRACT Middle and upper Eocene sedimentary rocks in southeastern Wind River Basin, Wyo., contain abundant debris derived from Rattlesnake Hills volcanic field of dacitic and alkalic igneous rocks. Eight miles northwest of Rattlesnake Hills yellowish- gray to pale-olive middle and upper Eocene rocks as much as 550 feet thick are well exposed at the head of Canyon Creek. From bottom to top of the formation pre-Cambrian metamorphic detritus decreases in abundance and Tertiary volcanic debris increases. Volcanic pebbles in the lower half are sodic trachyte; those in the upper half are predominantly andesite. The sequence comprises 6 units of different texture and composition. Unit 1, at the bottom of the sequence, is a tough ledge-forming mudstone 30 feet thick, containing a thin bed of felsic tuff that is the first indication of volcanic activity in the Rattlesnake Hills field. Unit 2, about 100 feet thick, consists of soft mudstone and arkosic sandstone with very little tuffaceous debris. The upper- most bed is a ledge-forming arkose and conglomerate containing volcanic minerals and pebbles of sodic trachyte lava composed of sanidine-anorthoclase, albite—oligoclase, very dark hornblende. sphene, and apatite. Unit 3 comprises 90 feet of very tui'faceous sandstone, sandy mudstone, and conglomerate with pebbles and cobbles of sodic trachyte pumice, pumiceous tufl’, and lava. Giant boulders of pre—Cambrian gneissic rock distributed sporadically through the lower 25 feet of unit 3 probably resulted from renewed uplift of the faulted Granite Mountains block in the Rattlesnake Hills area. Unit 4 is a 45-foot—thick biotitic lapilli tuff with pebbles and cobbles of pumice, pumiceous tuff and porphyry containing the volcanic minerals—sanidine—anorthoclase, albite—oligoclase, very dark hornblende, pale—green augite, medium—green clinopyrox- ene, sphene, and apatite. This predominantly pyroclastic unit indicates an episode of explosive activity in the Rattlesnake Hills volcanic field. Unit 5 consists of 130 feet of very poorly sorted dark-yellowish- gray tuifaceous sandstone and volcanic conglomerate composed chiefly of andesine andesite porphyry. Both sandstone and the common type of volcanic pebbles and cobbles contain abundant magnetite, pale-green ‘augite, medium-green clinopyroxene, very dark hornblende, sphene, apatite, and andesine. Unit 6 is a very coarse grained volcanic conglomerate more than 140 feet thick, containing debris that has a composition similar to that in unit 5. Uplift and deep erosion of middle and upper Eocene rocks are revealed by a rugged unconformity at the base of the White River formation of Oligocene age. INTRODUCTION PURPOSE AND SCOPE OF INVESTIGATION From 1948 to 1952 geologic studies of the Beaver Divide area, central Wyoming, were made by the Geological Survey as a part of a program of the Depart- ment of the Interior for development of the Missouri River basin. The first year’s work was published in the U. S. Geological Survey Oil and Gas Map series (Van Houten, 1950). Results obtained during the following years are summarized in U. S. Geological Survey Oil and Gas Map OM 140 (Van Houten, 1954) and in a more comprehensive report in preparation by the writer. This paper, which supplements the other reports, comprises a detailed description of nonmarine volcanic- rich middle and upper Eocene rocks exposed in the Canyon Creek reentrant in the Beaver Divide escarp- ment. Most of the Tertiary rocks of the Beaver Divide area contain some volcanic debris, but the middle and upper Eocene rocks at the eastern end of the divide are exceptionally rich in volcanic material, for they are within 8 miles of their source in the Rattlesnake Hills volcanic field. Data concerning their correlation, thickness, stratigraphic sequence, sedimentary struc- tures, composition, and relationships to enclosing rock units, provide pertinent information about the sequence of middle and late Eocene events at the place of deposition and in the source area. LOCATION AND TOPO GRAPHY The middle and upper Eocene rocks described in this paper crop out in the Canyon Creek reentrant in the Beaver Divide escarpment in southeastern Fremont and southwestern Natrona Counties, Wyo., about 8 miles northwest of the Rattlesnake Hills volcanic field and less than 2 miles northwest of Black Mountain, the north- ernmost knob of the Granite Mountains (fig. 1). The locality is about 60 miles west of Casper and 25 miles north of the Pathfinder Reservoir. The area can be reached by car on the unimproved road that leads 1 2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY RSEW RB7W RBGW DSSW RBdW EXPLANATION —- l l i X] ‘ Cheyenne' :{g m o ,H k' XPGI‘: ' _-_ ____ = ' ‘ INDEX MAP 1 \“1 Goal Mm , l l M~—\ RATTLESNAKE HuLs l PLATEAU s VOLCAMC HELD x. \ x \\ Devfls Saddle ‘ V\H_\j \ \\ z , l \\ ~- L 'J ,1 \H3 -‘ \\§\; . § ', - I DA , 3 O " \\ Locauon on Sllahglaphtc 1 U 0 kg \\ secuon w ‘ 508 («M K .\ A Z Z : >\\§ 9‘- Tuangulanon slanon O 0 §\ 2 a: "’ ‘=§~ m (-* ‘ \ a: < 2 '_ \ {.an C‘" \ > \\ V" ¢ \ W) o R \ ‘ ( 902V" . s ° \ / 1 NJ 0 % 3N0 4‘ r \ \§\\ 0 a \\ ‘- \\./@/ ' 1 E . G R Ix “ -\('r._ek ‘1‘! I 1. w" '0 2: swat” NATRogA co CARBON co V Muddy Gap l PA wuNs I 5 0 5 Miles Fromm 1.-—Index map showing location of Rattlesnake Hills volcanic field and measured sections A-E, Fremont and Natrona Counties, Wyo. VOLCANIC-RICH MIDDLE AND UPPER EOCENE ROCKS, CENTRAL WYOMING 3 northwestward from Wyoming State Highway 220 in the vicinity of the reservoir. Along the southern margin of the Wind River Basin, Beaver Divide separates northward-flowing tributaries of the Wind River from the southward-flowing tribu— taries of the Sweetwater River. The crest of the divide rises from an elevation of 7,000 feet at its southwestern end to 7,600 feet on the west flank of the Rattlesnake Hills, 55 miles to the east. Beaver Divide also marks the boundary between two distinctive types of topog- raphy. To the north the Wind River Basin is etched out of nearly horizontal Tertiary rocks, whereas the Sweetwater Plateau, which lies to the south, is relatively flat and undissected. In the north—facing Beaver Divide escarpment that rises as much as 1,200 feet above the basin, an unusually complete section of Eocene to Miocene sedimentary rocks is exposed. These strata extend southward and overlap on older rocks of the Granite Mountains and the Rattlesnake Hills. In the Rattlesnake Hills area some 35 deeply eroded volcanoes (Carey, 1954b) surmount a northern projection of the Granite Mountains and its flanking structure, the northwest-trending Rattlesnake Hills anticline. PREVIOUS WORK In 1913 and 1914 a field party directed by C. J. Hares, of the Geological Survey, mapped the Rattle- snake Hills region (Hares, 1946) as part of a geological examination of central Wyoming (Hares, 1917). In 1944 J. D. Love collected the first fossil mammals recovered from the White River formation in the vicinity of Cameron Spring, and in 1950 he discovered the first plant and mammalian fossils in the Tertiary deposits of the Canyon Creek area. Subsequently, J. F. Rachou 1 found larger collections which are the basis of present age assignments. B. D. Carey, Jr. (1954a, 1954b) made a detailed study of the Rattle— snake Hills Tertiary volcanic field, and information supplied by him has been compiled on the Geologic Map of Wyoming (Love, Weitz, and Hose, 1952). FIELD WORK During the summer of 1951 the Tertiary formations west of Rattlesnake Hills were mapped and studied with the able assistance of Colin C. McAneny. Strati- graphic sections (pl. 1) were measured by hand level, and elevations were established by aneroid barometer readings based on the triangulation stations of the Survey. The elevations and thicknesses of the sections were then adjusted to the U. S. Geological Survey topographic sheets, Gas Hills, Wyo., and Ervay Basin SW, Wyo. 1 Rachou, J. F., 1951, Tertiary stratigraphy of the Rattlesnake Hills, central W yo- ming: Unpublished Master of Arts thesis in files of Univ. of Wyo. library. rocks at least 550 feet thick. LABORATORY WORK The mineral composition of selected sedimentary rocks and pebbles of volcanic rocks recorded in table 1 is based largely on a study of magnetic separates. Minerals in the very fine sand grade (0.06 to 0.12 mm) of crushed and seived samples were separated magnet— ically at a maximum current of 0.70 amperes. The very fine sand fraction of the sedimentary rocks con- sistently contains essentially the same accessory min- erals as the coarser fractions and generally in greater abundance. Shards and volcanic biotite, however, are more abundant in the coarser sand grades of some samples. The mineral colors reported here are those seen under the petrographic microscope. Feldspars in the nonmagnetic fraction of crushed chips of volcanic pebbles have been studied by immer- sion methods and checked in thin sections of some of the pebbles. ACKNOWLEDGMENTS It is a pleasure to acknowledge information about volcanic rocks of the Rattlesnake Hills furnished by B. D. Carey, Jr. During discussions in the field and laboratory, as well as by correspondence, Mr. Carey made available unpublished data concerning the rock types and their relationships. I am also indebted to J. D. Love for his continued interest and helpful advice during the preparation of this report, and to J. R. Smith, for his careful study of the feldspars reported in this paper. A. F. Buddington and H. H. Hess helped with the igneous-rock nomenclature and mineral identification. STRATIGRAPHY GENERAL FEATURES The Tertiary deposits in the Canyon Creek area comprise four distinct formations. Variegated rocks of the lower Eocene Wind River formation, character- ized by lentieular beds of poorly sorted feldspathic mudstone, sandstone, and conglomerate, are exten— sively exposed in the Wind River Basin north of Beaver Divide. Conformably overlying the Wind River formation. is an unnamed sequence of light- yellowish-gray to pale-olive middle and upper Eocene In contrast to the lenticular deposits of the Wind River formation, the middle and upper Eocene rocks are more persistently bedded and contain abundant volcanic debris. This sequence is separated frOm the overlying White River formation of Oligocene age by a marked erosional unconformity. The light—gray to grayish-orange de- posits of the White River formation generally are massive rather well—sorted tuf‘l’aceous fine-grained sand— stone and mudstone with rare thin lenses of conglom— erate composed chiefly of pie—Cambrian metamorphic 4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY rock. Because of the topographic relief at its base, the White River formation varies in thickness. The maximum thickness in this area is about 275 feet. Massive coarse arkosic conglomerate 50 to 100 feet thick forms a conspicuous cliff at the top of the Beaver Divide escarpment west of Canyon Creek. This coarse capping unit, which locally is separated from the White River formation by an erosional unconformity, is here considered to be the basal part of an unnamed formation that yields Miocene mammalian fossils south of Rattlesnake Hills. The volcanic and nonvolcanic minerals in the mag— netic separates of the Tertiary sedimentary rocks in the Canyon Creek area are listed below. Derived from Tertiary volcanic rocks: Pale-green augite Medium-green clinopyroxene Hypersthene Oxyhornblende Dark—brown hornblende Dark-green—brown hornblende Dark-green hornblende Amber biotite Brown biotite Greenish-brown biotite Apatite Sphene Magnetite Derived from pre—Cambrian igneous and meta— morphic rocks: Muscovite Grayish—green biotite Blue-green hornblende Fibrous colorless amphibole (including anthophyllite and tremolite) Epidote (including clinozoisite) Garnet Tourmaline Sand-size pyroclastic debris in the Tertiary rocks is composed of three kinds of material: (1) crystals; (2) vitric fragments consisting of clear flat or keeled plates, or glass containing elongate bubbles and inclusions commonly giving the shard a “fibrous” appearance; and (3) lithic fragments of groundmass containing microlites. Crystals and lithic fragments are the more common pyroclastic materials in most of the volcanic- rich deposits in the Canyon Creek area although beds of vitric tuff are present. The composition of volcanic plagioclases present cannot be accurately identified by means of standard extinction or index of refraction curves. The orien— tation of the optical indicatrix of volcanic plagioclases differs from that of plutonic and metamorphic plagio— clases on which standard extinction curves are based (Kohler, 1949; Reynolds, 1952), and 2V and refractive indices of sodic plagioclases are lower in high—tempera— EXPLANATION OF PLATE 2 location of section A and triangulation t 1), Canyon Creek valley, looking northeastward toward SSW. Light-gray pumiceous tuff (unit 4) crops on A. Cliff and terrace of basal middle and upper Eocene rocks (uni t in white band on upper slope in right back- station TEE on peak. Stratain foreground dip about 3° ground (p. 6). B. Giant boulders of pre- middle and upper Eocene rocks (p. 8). op of middle and upper Eocene rocks, Cambrian metamorphic rock in basal beds of unit 3, d deposit is a poorly section B, looking southwestward. Lower finer graine C. Massive volcanic conglomerate in unit 6 at t Debris in upper coarser part is rounder and better sorted than most of the coarse conglomerate in unit 6 (p. 10). sorted tuffaceous pebble conglomerate. D. Poorly sorted volcanic conglomera Lower finer grained deposit is crudely section B, looking southward. (1 upper Eocene rocks, f unit 6 about 8 miles west of Rattlesnake Hills volcanic field te in unit 6 at top of middle an (p. 10). bedded. Range of grain size is characteristic 0 mMUO: HZMUOH fimmmp QZ< HAQQHE .mO mflflDEfimh WM I m .E UnIlG I m U 'D I: l o l O In 2 I u 8- UnitS 5 0 ' In UAn|t4 o u 3 3 'o ._ 4D: u .s: 4,0 Uni13 22:3 302° l I (D <1 Unit2 FIGURE 2.—Relative abundance of volcanic minerals in middle and upper Eocene rocks, Canyon Creek area. Wyoming. Based largely on data in table 1. pellets as much as an inch long. Throughout unit 1 there are scattered angular sand-she grains of quartz and feldspar and locally, rare partly altered shards and magnetite. ‘ Unlike any other deposit in the sec- tion, the rock contains numerous irregular cavities as much as a quarter of an inch long, which may have resulted from shrinkage of the mud during lithification. One of the softer beds is a tufl’ (table 1, sample 2) containing abundant unaltered felsic ash composed of hexagonal brown biotite, clear obsidian shards with needlelike inclusions, pale-brown platy shards, keeled shards, and fibrous shards with abundant elongate bubbles. Lithic fragments of groundmass with micro- lites are also common. Magnetite is extremely rare. The unique types of shards in unit 1 are also abundant in tuff in unit 3 in section D (pl. 1) and in unit 4 through- out the area (table 1, sample 12). The fact that there are rare partly altered shards in the tough mudstone and abundant unaltered shards in the softer tufl’ strongly suggests that the harder layers containing small irregular cavities are composed in part of clay and silica produced by alteration of ash. The cause of the marked difference in degree of altera- tion of the tufl" and mudstone is not known. UNITB Approximately 100 feet of poorly exposed soft pale- olive to greenish-yellow and yellowish-gray biotitic mudstone and arkose capped by a more resistant bed of sandstone and conglomerate is assigned to unit 2. In the vicinity of section D the unit thins to about 75 feet. Cobbles of metamorphic rock as much as 6 inches in diameter are scattered through the upper 20 feet of the sequence in section B, and, in equivalent beds in the vicinity of section A, small boulders of metamorphic rock are also present. A persistent ledge-forming layer at the top of unit 2 consists of 3 to 5 feet of yellowish-gray crossbedded arkose and pebble and cobble conglomerate with a tuffaceous mudstone matrix and calcareous cement. Although most of the coarse-grained material is light— reddish-brown-stained pre-Cambrian gneissic rock, some of the pebbles are black mica and hornblende schists and, less commonly, white and bluish-gray sodic trachyte lava. 8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY As in the ‘Wind River formation below, the minerals present throughout most of unit 2 (table 1, samples 3 to 5) were derived from pre-Cambrian metamorphic rocks. Similarly, much of the mudstone is sticky when wet and may be bentonitic. There is very little vol- canic debris in the deposits below the capping layer at the site of section B, but in section D lithic fragments and shards, as well as hexagonal brown and amber biotite (table 1, sample 6) occur in a bed of yellowish- gray bentonitic sandy claystone about 10 feet below the top of the unit. Very dark hornblendes, sphene and apatite in the uppermost ledge-forming layer (table 1, sample 7) marks the lowest occurrence of these volcanic minerals in the section. pebbles is also in the capping sandstone and conglomer- ate. All are pebbles of sodic trachyte lava (table 1, samples 7A, 7B; pl. 3, A). In most of them the ground- mass is glassy; in some it is pumiceous. This kind of volcanic pebble is present, though rare, throughout the overlying middle and upper Eocene deposits. UNITS Unit 3 consists of about 90 feet of soft, locally cal- careous, very tuffaceous sandstone and sandy mudstone, some conglomerate which generally is coarser in the lower part of the unit, and a few beds of coarse-grained lapilli tuff. The mudstone layers are greenish yellow to pale olive and very bentonitic. The poorly sorted sandstone and conglomerate are yellowish gray and contain abundant shards and lithic fragments, volcanic minerals, rather soft pebbles and small cobbles of pumice and pumiceous tuff, and rare pebbles of sodic trachyte lava. Pebbles and cobbles of metamorphic rock are also present. In the upper 15 feet several layers of sandstone well cemented with manganese oxide, form minor light- brownish-gray ledges. Coarse-grained lapilli tuff and very tufl'aceous arkosic conglomerate between these ledge-forming layers contain pebbles and small cobbles of gray sodic trachyte porphyry and vitrophyre with white feldspar phenocrysts. This is the lowest known occurrence of porphyry pebbles in the section. Locally, there is a 6-inch bed of greenish-yellow chert and silicified mudstone at the top of the unit. In section D (pl. 1), where unit 3 is 55 feet thick and consists mainly of bentonitic sandy mudstone, two tufl’ beds are present in the upper half of the unit. The lower bed is a green-brown biotite tuff with abundant lithic fragments and keeled and fibrous shards. The upper tufl" contains green-brown hornblende and biotite as well as abundant keeled and fibrous shards. The lowest occurrence of volcanic. Northeast of section B, irregular slabs, blocks, and subrounded boulders of gneissic rock as much as 12 feet long are distributed sporadically through the lower 25 feet of unit 3 (pl. 2, B). The outcrops of this unusual deposit of giant boulders are about 5 miles west of the crest of Rattlesnake Hills anticline, and they extend at least one—half mile to the northeast of section A (pl. 1). Southwestward, toward section B, the boulder conglom- erate grades laterally into a cobble conglomerate. Farther west, in the vicinity of section D, the lower 8 feet of unit 3 is predominantly sandstone and mudstone with scattered pebbles of metamorphic rock. The regional distribution of the giant boulder deposit cannot be determined from the outcrops. The great size, angularity, and limited vertical dis- tribution of the boulders suggest that they were derived from a prominent scarp, such as faulting might produce, rather than from a broadly arched area, and that they were deposited in a brief interval during Eocene aggra- dation. These gneissic boulders could not have come from Black Mountain, only 2 miles to the southeast, for it is mainly black schist. They probably were derived, instead, from intricately faulted gneissic rocks in the Rattlesnake Hills more than 5 miles east and southeast of section A. This inference agrees with the general conclusion that most of the sediments in the middle and upper Eocene sequence were eroded from the Rattlesnake Hills area and requires that the blocks were transported more than 5 miles on a gradient esti- mated to have been from 75 to 120 feet per mile. That this is an adequate gradient is indicated by a high- level deposit of giant boulders, derived from the Lara- mie Range, that were transported at least 18 miles on a gradient of not more than 75 feet per mile. Bretz and Horberg (1952) suggest that these boulders were moved by flash floods. Mudflows, which commonly transport giant blocks and boulders (Twcnhofel, 1932, p. 92-103), can also move on very low gradients. A mudflow which travelled approximately 15 miles (Sharp and Nobles, 1953) moved on a gradient as low as 75 feet per mile (less than 1°) at its outer end, in contrast to a slope of 24° to 32° in the source area and of 9° in the upper part of the course. Both nonvolcanic and volcanic minerals are present in sedimentary rocks of unit 3 (table 1, samples 8 to 10). Blue-green hornblende is more abundant here than in any other unit and, like that in the uppermost bed in unit 2, is rather distinctive. It generally has pale-bluish-green to yellowish-green pleochroism, and the grains are clear and smooth because they have poorly developed cleavage. Similar hornblende is com- mon in samples of schist from the Rattlesnake Hills but is rare in samples of gneiss, indicating that outcrops of VOLCANIC-RICH MIDDLE AND UPPER EOCENE ROCKS, CENTRAL WYOMING 9 hornblende schist supplied relatively more sand-size detritus (luring deposition of the upper part of unit 2 and unit 3 than at any other time in the Tertiary history of the Canyon Creek area. The lower beds of unit 3 contain the same volcanic minerals found in the uppermost strata of unit 2 (table 1, sample 8). In addition to these minerals, deposits in the upper half of unit 3 contain more magnetite and the lowest occurring augite in the section (table 1, sample 9). Moreover, some medium-green clinopy— roxenc occurs in the uppermost beds (table 1, sample 10). Significantly, magnetite and pyroxene persist through most of the overlying middle and upper Eocene rocks. Some pumice pebbles and pebbles of pumiceous tuff (table 1, sample 10B) as well as a few porphyry and vitrophyre pebbles in the upper 15 feet of the unit have the same mafic minerals as the sodic trachyte pebbles in unit 3 and the uppermost bed of unit 2. Other pumice pebbles (table 1, sample 9A) and porphyry pebbles (table 1, sample 10A) from the uppermost part of unit 3 are the lowest occurring fragments of pyroxene- bearing volcanic rock. UNIT 4 This is one of the most uniform stratigraphic units in the middle and upper Eocene sequence, and comprises 45 feet of light—gray to pale-yellowish-gray calcareous coarse—grained lapilli tuff and fine-grained vitric tuff, with a few layers and lenses of conglomerate containing both volcanic and metamorphic detritus. These rocks form a conspicuous scarp between the slopes of units 3 and 5. 310st of the beds in unit 4 are 1 to 2 feet thick. Locally, some are only a few inches thick, and minor channeling is common. Throughout the tuff there are abundant pebbles and cobbles of pumice and pumiceous tuff, as well as some pebbles of sodic trachyte lava. About a quarter of a mile north of section B a conglomerate lens 50 feet wide and 8 feet thick consists of very poorly sorted detritus composed largely of abundant angular fragments of porphyry and rounder pieces of pumice as much as 2 feet in diameter and some pre-Cambrian metamorphic debris. Westward, in the vicinity of section D, unit 4 is 25 feet thick and contains considerable greenish—yellow tufl’aceous mudstone like that in unit 3. . Although fine—grained vitric tuff in unit 4 (table 1, sample 12) is composed of felsic shards like those in the tuffs in units 1 and 3, the lapilli tuff (table 1, sample 11) contains the light— and dark—green pyroxenes character- istic of the deposits of units 5 and 6. All the pebbles examined in unit 4 are sodic trachyte, but few contain the same mafic minerals as the common type of sodic trachyte pebble in unit 3 and the uppermost bed of unit 2. Instead, the sodic trachyte pumice and pumi- ceous tuff pebbles in unit 4 (table 1, sample 11A; pl. 3, B) have pyroxene minerals much like those in andesite pebbles in units 5 and 6. The predominant hornblende, however, is a rather distinctive very dark green variety. UNIT 5 Approximately 130 feet of light-olive-gray to pale- olive and yellowish-gray poorly sorted bentonitic tuffaceous mudstone, sandstone, and conglomerate constitutes unit 5. Calcareous cement is common, especially in the coarser grained deposits. Equivalent beds are only 75 feet thick in section D (pl. 1). Throughout unit 5 the conglomerate, which com- ‘monly is in lenticular channel—fill deposits, consists of pebbles and cobbles of both pre-Cambrian metamorphic rock and Tertiary volcanic rock. Most of the coarsest material is metamorphic rock. In contrast to the con— glomerates in lower units, however, those in unit 5 contain abundant volcanic debris which is composed predominantly of brown-weathering medium-gray ande- sine andesite porphyry with conspicuous white feldspar phenocrysts. There are also rare pebbles and cobbles of light—gray pumice and reddish-brown aphanitic ~ andesite. A primitive titanothere, Eometarhinus erwyensis (Univ. Wyo. 928; Rachou“), was found about 9 feet above the base of unit 5 in soft poorly sorted sandstone and small pebble conglomerate. According to Rachou, this species is structurally intermediate between the middle and the late Eocene species of the genus. The middle part of unit 5 is a crumbly tuffaceous sandstone and mudstone about 55 feet thick, which contains abundant chips of pinkish-gray bentonite and white pumice fragments as much as a quarter of an inch long. At the top of the unit there are irregular patches of yellowish-gray chert and silicified mudstone several inches thick. ‘ Throughout unit 5 the sandstone matrix contains abundant volcanic minerals and rare nonvolcanic ones (table 1, sample 13). Magnetite, pale—green augite, and medium—green clinopyroxene are more abundant here than in any of the underlying units, and oxyhorn- blende, though rare, is consistently present. The me— dium—green clinopyroxene commonly is darker than it is in lower units. In contrast to the volcanic pebbles in underlying units, most of those in unit 5 are andesine andesite; a few are sodic trachyte. MoreOver, the most common rock type is andesite porphyry (table 1, sample 14B) characterized by very dark brown and green-brown hornblendes like those in the sodic trachyte porphyry pebbles in the upper 15 feet of unit 3 (table 1, sample 4 Rachou, J. F., 1951. op. cited. 10 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 10A). The rare pebbles of andesite pumice in unit 5 (table 1, sample 14A) have a similar mafic mineral com- position. UNIT 6 East of Canyon Creek unit 6 forms the prominent cliff at the top of Beaver Divide and consists of as much as 140 feet of very coarse grained light-olive-gray to pale-olive conglomerate (pl.2, 0, D) which locally lies on an erosional surface cut on unit 5. At the site of section B (pl. 1) unit 6 is rather firmly indurated, but eastward and westward along the divide it is commonly unconsolidated. Unlike the coarse deposits of under- lying units which contain much fine—grained matrix, the coarser grained beds of unit 6 are composed largely of pebbles, cobbles, and boulders with only a minor amount of mudstone and sandstone. About two— thirds of the coarse debris consists of volcanic rock, predominantly a brown—weathering medium—gray an— desite porphyry with conspicuous white feldspar phen- ocrysts. Rare pebbles of aphanitic andesite, sodic trachyte porphyry, and pumice are also present. The other third of the coarse debris is pro-Cambrian meta- morphic rock. Although most of the boulders are less than 3 feet in diameter, some are as much as 5 feet long. Many of [the boulders are rather well rounded; some are quite angular, however. Distinct bedding occurs only in the finer grained beds of pebble con- glomerate. At the site of section B a 30-foot lens of crumbly tuffaceous poorly sorted mudstone and sand— stone containing abundant crystal tuif is present in the lower half of the unit. Southeastward, deposits of unit 6 extend beyond underlying Tertiary rocks and overlap on pre-Cambrian rocks of Black Mountain. Lateral variations in the composition and texture of conglomerate in unit 6 are recorded in table 2. These data reveal a rather marked progressive change in the proportion of rock types, the common size and round- ness of fragments, and the texture and bedding. Some of the very coarse angular and unsorted detritus as much as 6 miles west of Rattlesnake Hills volcanic field may have been transported by mudflows associated With volcanic activity. Such mudflows are masses of water-soaked volcanic debris that slide rather rapidly on a relatively steep initial gradient. The smaller rounder better sorted detritus more than 8 miles west of the source area undoubtedly was transported by streams. Comparison of the large pebble fraction (16 to 64 mm) of samples of unit 6 conglomerate (fig. 3) shows that roundness of very large pebbles (32 to 64 mm) increases - markedly between 6 and 8 miles from the source area, instead of increasing uniformly over the 15-mile course. This observation accords with Krumbein’s conclusion (1940, p. 670) based on a study of flood gravel, that “pebble rounding is a rapidly increasing function at the beginning of the process and becomes progressively slower as the distance increases.” Very large pebbles are relatively rare 15 miles from the volcanic field and at this distance large pebbles (16 to 32 mm) have become rounded, Whereas nearer the source they are more angular. Throughout unit 6 the fine-grained sand fraction contains a volcanic-rich mineral assemblage (table 1, sample 15) like that of unit 5 (table 1, sample 13). Although the principal volcanic rock type, as in unit 5, is an andesine andesite porphyry, the andesite pebbles in unit 6 contain more varied suites of minerals than do the pebbles in any of the underlying units (table 1, samples 15B, 15C, 15D, 15E, pl. 3, 0; table 1, sample 15F, pl. 3, D). The rock in one dark-gray pebble consists of minute hypersthene and plagioclase phenocrysts in an aphanitic groundmass (table 1, sample 15A). No other hypersthene-bearing rock has been found in the entire section. Nevertheless, similar hypersthene-bearing rocks of intermediate chemical composition do occur in the Rattlesnake Hills volcanic field, according to B. D. Carey, Jr. (personal communi— cation, 1953). TABLE 2.—Variation in composition and texture of conglomerate in unit 6, middle and upper Eocene rocks Distance northwest of Rattle- 4-6 miles __________________________ 8 miles (sec. B, pl. 1) ______________ 9-10 miles _________________________ 13-15 miles. snake Hills volcanic field. Percentage of rock types (field {90 percent volcanic rocks .......... 65 percent volcanic rocks __________ 50 percent volcanic rocks __________ estimates). 10 percent metamorphic rocks ..... 35 percent metamorphic rocks _____ 50 percent metamorphic rocks ..... Diameter of large fragments: Maximum size _______________ 14 feet _________________ 5 feet l ____________________________ 9 feet ______________________________ 1 foot. Rare size _____________________ 3—5 feet _______________ 3—5 feet ____________________________ 1—3 feet ____________________________ i 4—8 inches. Common size ................. 1—3 feet ____________________________ 1—3 feet ____________________________ 6—10 inches ________________________ 1-3 inches. Estimated average roundness: 2 Large boulders _______________ Subangular to subrounded ________ Subrounded _______________________ Subrounded _______________________ Small boulders and cobbles... Subangular ____________________________ do _______________________________ o __________________________ Rounded. Very large pebbles ._ _ Angular to subangular ____________ Subrounded to rounded ___________ Subrounded to rounded ___________ Do. Large pebbles _____________ _-___do _____________________________ Subaugular to subrounded _____________ do _____________________________ Do. Texture and bedding ............. C oarse detritus distributed Coarse detritus in thick persistent Some conglomerate in lenses, Conglomerate in lenses in throughout deposit, largely un- stratifled. units. unstratified or crudely bedded Pebble conglomerate rather well bedded. some scattered throughout poorly sorted mudstone and sandstone. poorly sorted mudstone and sandstone. I One-half mile east, 12 feet. 1 See figure 3, A-D for average roundness at diflerent distances. YOLCANIC-RICH MIDDLE AND UPPER EOCENE ROCKS, CENTRAL WYOMING 11 .001 '0 . 7:: C O l 2 l 0 1 I_J FIGURE 3.—Variation in roundness of large volcanic pebbles in unit 6. middle and upper Eocene rocks 23456789 llllllLl 5 Inches 3 1 l 10 Centimeters l A, Subangular pebbles, sample from outcrops 4 to 6 miles northwest of Rattlesnake Hills volcanic field; B, Subrounded to rounded pebbles, sample from section B (pl. 1), about 8 miles northwest of Rattlesnake Hills volcanic field; 0, Subrounded to rounded pebbles, sample from outcrop about 10 miles northwest of Rattlesnake Hills volcanic field; D, Rounded pebbles. sample from outcrop about 15 miles northwest of Rattlesnake Hills volcanic field. WHITE RIVER FORMATION (OLIGOCENE) It is not the purpose of this paper to present a detailed description of the post-Eocene rocks in the Canyon Creek area. Nevertheless, some information about the White River formation is pertinent to an understanding of the middle and upper Eocene rocks because it, too, contains considerable volcanic debris, and also because it was deposited under a different set of environmental conditions. The White River formation in this area is of Chadronian (early Oligocene) age (Rachou; 5 see also pl. 1). 5 Rachou, J, F,, 1951,01). cited. Unlike the middle and upper Eocene rocks which lie conformably on the Wind River formation, the White River formation rests on an erosional unconformity cut at least 250 feet into the middle and upper Eocene rocks in this area. Four to six miles farther west along Beaver Divide this unconformity is cut through the entire middle and upper Eocene sequence and about 100 feet into the Wind River formation. ' Here the White River formation is about 450 to 500 feet thick. In further contrast to the unnamed middle and upper Eocene formation, which contains considerable coarse debris and consists of several distinctive and persistent subdivisions, the \Vhite River formation comprises a 12 ~ SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY maximum of about 275 feet of massive generally well- sorted fine-grained sedimentary rocks with only a subordinate amount of conglomerate. The lowest 50 feet of the formation, preserved between sections 0 and D (pl. 1.) is predominantly light-gray calcareous biotitic vitric tuff (table 1, sample 16) and very tuffa— ceous mudstone. The upper part of the formation consists chiefly of grayish-orange to yellowish—gray sandy mudstone with some layers of light-gray cal— careous vitric tuff and rare lenses of conglomerate. Most of the conglomerate lenses in the White River formation are composed of abundant somewhat angular pre-Cambrian rock fragments and rounder pebbles and cobbles of andesite porphyry (table 1, sample 16A) like those in the upper part of the middle and upper Eocene rocks. The andesite porphyry pebbles and cobbles are most numerous in the vicinity of section 0 where the upper part of the White River formation rests uncon- formably on middle and upper Eocene strata. In some of the conglomerate lenses in the White River formation rather soft rounded very light gray volcanic pebbles and small cobbles are common. Although most of these light-gray pebbles are porphy- ritic sodic trachyte lava (table 1, samples 16B, 16C), some are coarse-grained tuff of similar composition. The feldspar present is like that in pebbles in the lower half of the middle and upper Eocene rocks, but unlike these pebbles the soft porous light-gray pebbles in the White River formation contain large sanidine-anortho- clase phenocrysts. The composition and field occurrence of the coarse volcanic detritus in the White River formation suggest that the detritus was derived from middle and upper Eocene volcanic rocks. Most of the andesite porphyry pebbles and cobbles may have been reworked from the underlying volcanic conglomerate, although some may have been eroded directly from the Rattlesnake Hills area. Most of the soft very light gray sodic trachyte porphyry pebbles, on the contrary, probably were derived directly from middle and upper Eocene irrup— tive rock exposed in the volcanic field. Reworking of the underlying volcanic conglomerate in the Canyon Creek area presumably would have destroyed the rare pebbles of softer sodic trachyte, thus producing a con- glomerate composed chiefly of the tougher types of volcanic rock. Although the abundance of uncontaminated tuff in the White River formation suggests that volcanoes may have been active in the Rattlesnake Hills field during Oligocene time, present data provide no good evidence that the tuff was derived locally. Rachou6 reports the following Chadronian (early Oligocene) mammals from the lower part of the White 0 Rachou, J. F., op. cited. River formation in the vicinity of sections D and E: Hymcodon, cf. H. leidycmus (U. S. G. S. specimen); Agriochoerus intermedius (Univ. Wyo 932); Archaeothe- rium, cf. A. mortoml (Univ. Wyo., 927); Cylindrodon, cf. 0. fontis (Univ. Wye. 933); Ischyromys, cf. I. typus (Univ. Wyo. 934) ; and a titanothere. Fossil leaves of Ace?" glabroides were also collected here. A larger Chad- ronian fauna collected from the lower 200 feet of the White River formation in the vicinity of Cameron Spring, about 4% miles west southwest of Canyon Creek, in sec. 1, T. 32 N., R. 90 W., consists of the fol- lowing mammals (Hough, 1955): Paratherium beaveri, Oligoryctes cameronensis, Titanotheriomys cf. T. veterior, Cylindrodon fontis?, Cylindrodon brownii, Pseudocylin— drodon? wyomingensis, Oedromus? sp., Palaeolagus temnodon, Megalagus brachyodon, Hyaenodon sp., Pseudo— cynodictis cf. P. paterculus, Mesohippus of. M. montan— ensis, Menodus heloceras, Trigom'as sp., annopus sp., Hyracodon sp., Leptomeryx sp., Leptomeryx esulcatus, Bathygenys alpha, Merycoidodon culbertsom', and Mery- coidodon gracil’is. GEOLOGIC HISTORY OF AREA The Eocene and Oligocene history of the Canyon Creek area is summarized here in the following sequence of events. After the Granite Mountains and other structures formed during the Laramide Revolution had been de- formed and deeply eroded, prolonged aggradation of the Wind River Basin began with deposition of the lower Eocene Wind River formation. Arkosic sand and gravel accumulated in stream channels while varie- gated sandy mud was deposited on flood plains and carbonaceous layers formed in local swamps. Most of this detritus was derived from the Granite Mountains, and is coarser grained along the southern margin of the basin than it is farther north. As the deposits ac- cumulated in the lowland of the basin they gradually spread marginward across truncated Paleozoic and Mesozoic strata flanking the Granite Mountains and the Rattlesnake Hills and Dutton Basin anticlines. N o volcanic~ debris is known from the Wind River formation in the Canyon Creek area. Six miles to the west, however, some tuff is present, and, about 50 miles west of Canyon Creek, tufl’ is common in the upper part of the formation. The westward increase in amount of lower Eocene tufl’, together with the distribution, thickness, and texture of tufl’ in the Wind River forma- tion in the central and western parts of the Wind River Basin (Hay 7), indicates that this pyroclastic debris 7 Bay, R. L., 1952, Stratigraphy of the lower volcanic rocks in the southern part of the Absaroka Range: Unpublished Doctor of Philosophy thesis in files of Princeton Univ. library. VOLCANIC-RICH MIDDLE AND UPPER EOCENE ROCKS, CENTRAL WYOMING was produced by explosions during early Eocene time in the Yellowstone-Absaroka volcanic field. Accumulation of lenticular deposits of the Wind River formation was followed without significant interruption by deposition of more persistent beds of light-yellowish—gray to pale-olive mud and sand of the middle and upper Eocene sequence. The first sediment reflecting the change was a uniform and widespread layer of mud and felsic ash (unit 1) which apparently accumulated on broad flood plains or, perhaps, in broad, shallow lakes. The ash in this basal bed is the first evidence of volcanic activity in the Rattlesnake Hills volcanic field. Deposition of the succeeding flood plain and channel deposits of mud and sand with very little volcanic debris (unit 2) ended with the influx of coarse arkosic gravel derived from pre-Cambrian rocks of the Granite Mountains. The gravel was first deposited east of section B only, while coarse sand and mud and a thin bed of biotitic ash accumulated farther west. Sub- sequently, some of the streams transporting the pre- Cambrian detritus began to erode volcanic debris from the Rattlesnake Hills area, and an extensive sheet of arkosic sand and gravel containing volcanic minerals and pebbles of sodic trachyte lava was spread through- out the region. Accumulation of the coarse arkosic sediments cul- minated in the deposition of giant gneissic boulders in‘ the lower part 'of unit 3 in the vicinity of section A; tufl'aceous sand and gravel accumulated farther west. This giant boulder bed may have been deposited by flash floods or by mass flowage which moved the boulders and blocks northwestward at least 5 miles on a gradient that was less than 2° in the lower part of the course. The gneissic blocks were, perhaps, derived from scarps produced by renewed deformation of the intricately faulted pre-Cambrian rocks in the Rattle— snake Hills area. This episode of deformation may have accompanied the volcanic activity that supplied the first abundant volcanic debris deposited in the Canyon Creek area. Although some beds of vitric ash were of primary eruptive origin, most of the volcanic debris in unit 3 was brought in by streams along with detritus eroded from pre—Cambrian rocks. Pebbles of sodic trachyte pumice, pumiceous tufl’, and lava were the dominant coarse material eroded from the volcanic field. During deposition of the upper part of unit 3 sodic trachyte porphyry pebbles, as well as pyroxene and abundant magnetite grains, were transported to the Canyon Creek area for the first time. Deposition of these dominantly detrital volcanic— rich sediments was interrupted by explosive volcanic activity in the source area which produced an extensive l3 pyroclastic deposit of fine—grained vitric tufl" and lapilli tuff (unit 4). The sodic trachyte debris of this eruption contains more pyroxene than any of the material previously derived from the volcanic field. As a result of renewed uplift of the Rattlesnake Hills area and possibly the piling up of volcanic debris, streams were powerful enough to transport coarse volcanic gravel more than 8 miles northwestward. Significantly, this coarse detritus and the associated pyroclastic materials in units 5 and 6 have a distinctive composition and texture. N 0 longer were pumice, felsic shards, and sodic trachyte porphyry and lava the principal products derived from the volcanic source area. Instead, dirty yellowish-gray poorly sorted volcanic—rich mud and sand, ash of lithic fragments, abundant augite, clinopyroxene, and magnetite, and pebbles and cobbles of andesite porphyry were deposited in the Canyon Creek area. - As the slopes in the source area became steeper, mudflows and powerful streams transported a great mass of very coarse volcanic and metamorphic debris that forms the thick cobble and boulder conglomerate of unit 6 at the top of the middle and upper Eocene rocks. Following the deposition of the coarsest of all the volcanic sediments in the middle and upper Eocene deposits, uplift and deep erosion of the region inter- rupted aggradation in the southern part of the Wind River Basin. - Widespread aggradation was renewed when sedi- ments of the White River formation began to accumu- late on the rugged erosional surface in early Oligocene time. Deposition of at least 275 feet of rather well- sorted mud with local gravel lenses was accompanied by several prolonged showers of felsic ash. LITERATURE CITED Bretz, J. H., and Horberg, Leland, 1952, A high-level boulder deposit east of the Laramie Range, Wyo.: Jour. Geology, v. 60, p. 480—488. Carey, B. D., Jr., 1954a, A brief sketch of the geology of the Rattlesnake Hills, in Wyo. Geol. Assoc. Guidebook 9th Ann. Field Conf., p. 32—34. 1954b, Geologic map and structure sections of the Rattle— snake Hills Tertiary volcanic field, in Wyo. Geol. Assoc. Guidebook 9th Ann. Field Conf. Chayes, Felix, 1952, Notes on the staining of potash feldspar with sodium cobalti—nitrite in thin section: Am. Mineralo- gist, v. 37, p. 337—340. Dorf, Erling, 1953, Succession of Eocene floras in northwestern Wyoming [abs]: Geol. Soc. America, Bull., v. 64, p. 1413. Hares, C. J., 1917, Anticlines in central Wyoming: U. S. Geol. Survey Bull. 641—1, p. 233—279. 1946, Geologic map of the southeastern part of the Wind River Basin and adjacent areas in central Wyoming: U. S. Geol. Survey, Oil and Gas Inv. Prelim. Map 51. 14 Hough, Jean, 1955, A lower Oligocene fauna. from the eastern Beaver Divide area near Cameron Spring Reservoir, Fre- mont County, Wyo. [in preparation]. Kohler, Alexander, 1949, Recent results of investigation on the feldspars: Jour. Geology, v. 57, p. 592—599. Krumbein, W. C., 1940, Flood deposits of San Gabriel Canyon, Calif.: Geol. Soc. America Bull., v. 51, p. 639—676. Love, J. D., Weitz, J. L., and Hose, R. K., 1952, Geologic map of Wyoming, U. S. Geological Survey. Rachou, J. F., 1951, Tertiary stratigraphy of the Rattlesnake Hills, central Wyoming [abs]: Geol. Soc. America Bull., v. 62, p. 1541. Reynolds, D. L., 1952, The diflerence in optics between volcanic and plutonic plagioclases, and its bearing on the granite problem: Geol. Mag., v. 89, no. 4, p. 233—250. O SHORTER CONTRIBUTIONS TO ‘GENERAL GEOLOGY Sharp, R. P., and Nobles, L. H., 1953, Mudflow of 1941 at Wrightwood, southern California: Geol. Soc. America Bull., v. 64, p. 547—560. Stobbe, H. R., 1949, Petrology of volcanic rocks of northeastern New Mexico: Geol. Soc. America Bull., v. 60, p. 1041—1095. Tuttle, O. F., and Bowen, N. L., 1950, High temperature albite and contiguous feldspars: Jour. Geology, v. 58, p. 572—583. Twenhofel, W. H., 1932, Treatise on sedimentation, 2d ed.: 926 ‘p., The Williams & Wilkins Co. Van Houten, F. B., 1950, Geology of the western partof Beaver ,Divide area, Fremont County, Wyo.: U. S. Geol. Survey Oil and Gas Inv. Map OM 113. 1954, Geology of the Long Creek—Beaver Divide area, ‘Fremont County, Wyo.: U. S. Geol. Survey Oil and Gas Inv. Map OM 140. PROFESSIONAL PAPER 274 TABLE 1 GEOLOGICAL SURVEY FELDSPARS IN PEBBLES RELATIVE ABUNDANCE OF MINERALS IN 0.70—AMPERE MAGNETIC FRACTION OF VOLCANIC ROCK ROCK TYPE Q 3 03 g g Dominant 0 a) r: r: a Q S 3;:- +5 3 m 3 feldspar c Q, .fi 5 c I: _‘5 ‘3 45 w 33 g phenocrysts 0 s I: g0 a, E r» g 5 Q a 2 g E A Z a” a m U ‘I 2 $4 3 OJ :: ‘1’ 4°: ’8 5" "1 m 8 52 _ ,u o 0 E 43 ‘1’ no 0 N <9 '5‘ 3: 3 OJ —4 a, a; m *5 5 C“ m o 0 tan ‘4 5 5 g :4 g "o 'u o 4.. o :4 n o H g A: s.‘ to cu m . E a :3 ' S: ‘1’ 4: '8 b 3 i E i 5 E 3 ‘4 Em 8 0g L: 2 g 2 CL =5 Estimated 8 2 3 g g {'31) e ‘6 g g ”3% gé‘ $ 2 i 33. m {3 ‘50 g}; 3 F3 5 3 m ‘3 g g Refractive composition .,_ g 50 :3 A q, a: S >3 :5 >, :4 >3 E .o 3 cu I: E a g) 2 g .8 C‘. :5 a if? E 79. g indices (hlgh-temp- cu “3 ‘1’ 0 Tu g", R’ 5 J: as? .2 33 3 E 2 2 g "a E .3 3 as E R 0 ~43 53 3: 4% a. erature) m. E 5 IL m , O > > > <1 m o < m o m in La (5 9 Ln in A m L a, Nx min=l.533 . Very light gray sodic trachyte 3 160 \ N2 max=l.550 Ohgoclase porphyry pebble m \ Albite— Very light gray sodic trachyte =1. i 163 Ny 540 oligoclase porphyry pebble 2 " Light-gray andesite porphyry ; 16A pebble I 16 _ r I I \ \ Fine—grained tuff \ Nx min=l.536 Oligoclase- Medium-gray andesite porphyry 15F NZ max=l.554 andesine pebble 15E Nx min=l.540 Oligoclase— Medium—gray andesite porphyry Nz max=l.551 andesine pebble Nx min=l.545 . Reddish-brown aphanitic 15D N2 max=l.554 Andesme andesite pebble to *- ' =1.5 ' - d 'te o h r E 150 11:11: 1:23;:1 ~12: Andesine Medggllr: gray an e51 p rp y y :) \ .0 . pe Nx min=l. 538 Oligoclase~ Light-gray andesite porphyry 155 N2 max=l.553 andesine pebble 15 Nx min=l.540 Oligoclase- Dark-gray aphanitic andesite A N2 max=1.5651abradorite PEbble \ \ 15 \\ Tuffaceous conglomerate \ Nx min=1.546 . Reddish-brown aphanitic 14C! J I \\ Nz max=l.554 Andesme andesite pebble Nx min=l.545 . Medium-gray andesite porphyry In 148‘ i J I I Nz max=1.555I Andesme pebble g Nx min=l.543 ‘ Very light gray andesite pumice 14A 1 J Nz max=l.553 Andesme pebble i 13 \\ Tuffaceous conglomeratic o \ sandstone 12 Fine —grained tuff In C <1' a: ._ ' _ - ~ 0 E 11A \\ Ny =1 540i 11’:‘.1b1tle Very llght as? sodic trachyte o D \ o 1goc ase pumlce pe es 11 \ ‘Lapilli tuff ‘— I m g" 103 \: Pumiceous tuff pebble : \ ' Albite- Medium-gray sodic trachyte 10A Ny =l.540i I per hyr and v1troph re, very P y y ohgoclase . . light gray pumice pebbles : U \ r0 10 \\ \ Tuffaceous sandstone ‘U 3 9A \ Ny =1,540i Alblte- Very l1ght gray SOdlC trachyte ‘o ‘ \ oligoclase pumice pebbles ._ \ ~ . 2 \ \ 9 Tuffaceous sandstone R 8 Conglomerate 7B \Ny =l.540i Albite- Light-bluish-gray sodic trachyte oligoclase lava pebbles N ‘ =l.523i 7A _ N: 311.24% Albite— Very light gray sodic trachyte \ \ Nz max=l.543 ‘ oligoclase lava pebbles 7 Conglomeratic sandstone : \\ N E 6 \ Sandy Claystone :3 5 Sandstone 4 \ Sandstone 3 \ Sandy mudstone g -- 2 Fine-grained tuff Wind River formation 1 Sandy mudstone Very abundant Abundant Common Rare Very rare MINERALS IN TERTIARY SEDIMENTARY ROCKS. CANYON CREEK AREA, WYOMING 327329 0—55(Inpocket) GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 1 _ EXPLANATION LlTHOLOGlC SYMBOLS .9653» O n h J DEO'OO Volcanic conglomerate 0.0.0 ., .f’o‘s- .030 900- ~ oaao -. Oct ‘00 Conglomerate SW 5‘ sec. 33, T. 33 N., R. 89 W. NE 3‘ sec. 34, T. 33 N., R. 89 W. C Tuffa MlOCENE(?) MIDDLE AND UPPER EOCENE Carbonaceous shale \\\\\\ \\\\\\\ Fossils from lower part of White River formation south of sections D and E Ace’r glalmn'des (USGS Specimen) Hyracodzm, of H. leidyanus (USGS specimen) Agriochoe’ruis intermedius (Univ. Wyo. 932) Archaeotherium, of A. mortoml (Univ. Wyo. 927) Cylindmdoi, of c. font’is (Univ. Wyo. 933) Ischyromys, Cf I. tyms (Univ. Wyo. 934) Titanothere Bedded chert Poorly exposed C . Covered interval OLIGOCENE White River formation A Predominantly vitric tuff ® Lithologic sample; see table 1 o ’ ~ Stratigraphic position of fossils Boundary of formation, dashed where projected Boundary of minor rock unit, dashed where projected Units 5 and 6 COLOR SYMBOLS Pale reddish brown I W Wind River formation LOWER EOCENE Yellowish gray to pale grayish orange Light olive gray to pale olive MIDDLE AND UPPER EOCENE Yellowish gray to light olive gray and pale olive Quercus castaneops‘is Zizyphus cinnamomoides Legumimsites sp. Aralia sp. ____ I: .. .. Ulmws so. 6850' Sparganium antiquum Zelkovu. nervosa Light gray to light yellowish gray :Unit 1 Pale olive to greenish yellow; black square (El) indicates yellowish—gray layers m-EEN Datum is mean sea. level LOWER EOCENr I Wind River formatIon Light greenish and yellowish gray to very pale olive Light greenish gray and grayish yellow green; ”‘“°‘”““a'°‘fll‘"“‘°“esye”°“‘s""’a"aye's STRATIGRAPHIC SECTIONS OF TERTIARY SEDlMENTARY ROCKS, CANYON CREEK AREA, FREMONT AND NATRONA COUNTIES, WYOMING WNW...) CHEESE P { k1}. 1‘ l L; J 3) Dakota Group in Northern Front Range Foothills, Colorado GEaLGGICAL sunvrgg/ ZROFESSIQNAL PAPER 274—; Dakota Group in Northern Front Range Foothills, Colorado I By KARL M. WAAGE’ A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—B A re‘vz'yed médz'w'rim and termz'fiolagy for t/ze Dd/éOZd graup mm] [0661/ details qf z'z‘r stratigrapfly UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :1955 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director For sale by the Superintendent of Documents, U. 5. Government Printing Office Washington 25, D. C. - Price 45 cents (paper cover) CONTENTS Page Abstract ___________________________________________ l5 Stratigraphy—Continued Introduction, , o _______________________________________ 15 South Platte formation—Continued Dakota terminology and subdivision __________________ 16 Southern nonmarine phase—Continued .Stratigraphy ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 18 Beds between the Plainview and Kassler Lytle formation _______________________________ 7.1 19 sandstone members ___________________ Definition ___________________________________ 19 Kassler sandstone member _______________ Type locality of the Lytle ____________________ 20 Van Bibber shale member ________________ Lateral variation ______________________________ 20 First sandstone subunit and Benton con- Contact of Lytle and Morrison formations _____ 23 tact _________________________________ Eldridge type locality of the Morrison _____ 24 Lateral variation- _ , , , __________________ Alameda Parkway type section ____________ 25 Type locality ___________________________ Post-Morrison warping- _ _________________ 25 Intermediate phase—Boulder County __________ Summary ______________________________ 25 Northern marine phase ______________________ Contact of Lytle and South Platte formations__ 26 Age _______________________________________ Age ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 26 Relationship of the phases ___________________ South Platte formation ____________________________ 27 Status of the term Dakota group ______________________ Definition ___________________________________ 27 Correlation of the Lytle and South Platte formations-___ Lithology __________________________________ 27 Evaluation of unconformities _________________________ Southern nonmarine phase ___________________ 28 Literature cited ______________________________________ Plainview sandstone member _____________ 28 Index ______________________________________________ ILLUSTRATIONS FIGURE 4. Distribution of the Dakota group ______________________________________________________________________ 5. Lateral variation in the Lytle formation ________________________________________________________________ 6. Basal sandstone lens in the Lytle formation on Turkey Creek _____________________________________________ 7. Interpretations of the Morrison-Dakota contact _________________________________________________________ 8. Contact of the Lytle and South Platte formations at Spring Canyon _______________________________________ 9. Contact of the Lytle and South Platte formations at Eldorado Springs _____________________________________ 10. Composite section of the South Platte formation _________________________________________________________ 11. Plainview member of the South Platte formation at Plainview _____________________________________________ 12. Second shale subunit of the South Platte formation ______________________________________________________ 13. Base of main clay bed of the Van Bibber member of the South Platte formation _____________________________ 14. Nonmarine phase of the South Platte formation on Willow Creek __________________________________________ 15. Intermediate phase of the South Platte formation on Little Thompson Creek ________________________________ 16. Double hogback formed by marine phase of the South Platte formation ____________________________________ 17. Lateral changes in the South Platte formation ___________________________________________________________ 18. Characteristic exposure of the Dakota group in the Denver area ___________________________________________ 19. Correlation of the Lytle and South Platte formations _____________________________________________________ III Page 30 31 33 34 36 38 40 42 44 45 47 48 51 Page 16 21 22 24 26 27 28 29 30 32 34 36 4O 43 45 46 A SHORTER CONTRIBUTION TO GENERAL GEOLOGY DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO KARL M . ABSTRACT Pre-Benton Cretaceous strata throughout eastern Colorado and adjacent areas are divisible into a lower part which consists of sandstone, conglomeratic sandstone, and variegated claystone, and an upper part which consists of dark-gray shale interbedded with units of brown-weathering sandstone. A sharp discon- formity—the most pronounced lithogenetic break in the sequence of beds between the Morrison formation and the Benton shale— separates these two parts. For the northern Front Range foothills of Colorado the name Lytle formation is applied to the lower part of the pre-Benton sequence; the upper part is named the South Platte formation. The term Dakota group is retained to include these two formations. Lytle sediments were deposited on flood plains and are more closely related lithogenetically to the Morrison formation than to the overlying South Platte formation. The Morrison-Lytle contact is indefinite in many places because, (1) conglomeratic beds are not persistently present in the base of the Lytle and (2) the rocks in the upper part of the Morrison are similar to those in the Lytle. Both the old and new type sections of the Morrison have indefinite upper contacts. The Morrison-Lytle contact probably corresponds closely to Eldridge’s Morrison- Dakota contact in the Denver basin area; the prevalent belief that Eldridge included plant-bearing Dakota beds in the type locality of the Morrison is a misinterpretation of his original description. South Platte sediments were deposited in deltaic, estuarine, littoral, and neritic environments around the spreading Creta- ceous sea. The formation is largely in a nonmarine elastic phase in the southern part of the northern foothills but changes northward into a marine shale phase. Thin beds of altered volcanic ash and a single persistent marine zone facilitate cor- relation of the phases. Prominent local subunits are distinguished as members. All the South Platte formation except the beds at the top and base are in the zone of I noceramus comancheanus Cragin, and the age of the entire unit is presumed to be Early Cretaceous (Albian). In the northern Front Range foothills three distinct physical breaks occur in the sequence of beds between the undoubted Jurassic (Portlandian) part of the Morrison formation and beds of Early Cretaceous (Albian) age in the South Platte for— mation. Not enough fossil evidence is available to permit evaluation of these unconformities or to assign a greater time value to a particular unconformity. The Lytle and South Platte formations can be readily cor- related with their lithic equivalents in adjacent areas. The VVAA G if disconformity that separates them is a regional feature that lies between the Lytle sandstone and Glencairn shale members of the Purgatoire formation in southeastern Colorado. In eastern Wyoming this disconformity lies within the Cloverly formation, at or near the base of the upper sandstone member. INTRODUCTION Correlation and description of pre—Benton Creta— ceous (Dakota) rocks in eastern Colorado is made difficult by the multiplicity of names that have been applied to them. The problem is not entirely one of confused nomenclature that can be resolved by sub— mitting the different names to tests of precedence or usage; a basic difficulty is that none of the terminologies now in use accurately express the principal natural lithogenetic subdivisions and stratigraphic breaks that occur in the pre—Benton Cretaceous sequence throughout eastern Colorado. This report is a response to the need for a revised terminology which is suited to the broad natural subdivisions of the beds in question and yet is flexible enough to be adjusted to their local variations as revealed by detailed stratigraphic study. Pre-Benton Cretaceous strata exposed in the Dakota hogback of the northern Front Range foothills were studied in 1951—52 during investigations of refractory— clay deposits for the U. S. Geological Survey. Pre— vious field studies of the Dakota that contributed supplementary material include an investigation of refractory clays in the Purgatoire and Dakota forma- tions of south—central Colorado by the Survey (Waagé, 1953) and a reconnaissance study of critical Dakota localities in Colorado and adjacent states. The recon- naissance was supported by a grant from the Shell Research Fund of the Department of Geology, Yale University. The area of study here referred to as the northern Front Range foothills includes a narrow belt of pre— Benton Cretaceous exposures extending southward along the east flank of the Front Range. These expo- 15 16 sures extend from 2 miles south of the Wyoming State line, in Larimer County, where the beds emerge from under Cenozoic cover, to the fault—terminated end of the Dakota hogback just south of Indian Creek in the Kassler quadrangle, Douglas County. The belt of outcrop (fig. 4) is continuous except for a few short WYOMING Northern )’ Front Range k foothills COLORADO INDEX MAP HURSEI’OOTH RESERVO/f? EXP LAN AT ION Outcrop of the Dakota group LOCATION OF SECTIONS . Boxelder Creek .- Bellvue Spring Canyon . Handy Ditch Little Thompson Creek Eldorado Springs Plainview Van Bibber Creek 9. Alameda Parkway 10. Morrison 11. Turkey Creek 12. Deer Creek 13. South Platte River aqmmpwwp—d 14. Helmer Ranch 15. Willow Creek 16. Rainbow Creek 10 Miles FIGURE 4.~l)istribution of the Dakota group in the northernjl‘ront Range foothills, Colorado. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY gaps in which the beds are eliminated by faulting; the largest of these, a gap of about 3.5 miles, is at Golden. South of the end of the hogback at Indian Creek the pre-Benton Cretaceous rocks disappear by faulting for about 8 miles along the strike, and reappear in a short segment of hogback at Perry Park in the Castle Rock quadrangle. The northern foothills area of study corresponds with the area in which Lee (1923) applied the name Dakota group to the pre—Benton Cretaceous rocks of Colorado and divided it into five informal subdivisions. The terminology presented in this report is a revision of Lee’s Dakota group; consequently it is intended to apply only to the northern foothills area. DAKOTA TERMINOLOGY AND SUBDIVISION Pro-Benton Cretaceous strata in eastern Colorado were originally included in the Dakota group. Re— ports of the Hayden Survey, published between 1869 and 1878, used this term in the same sense in which it was first applied to the basal sandy beds of the Cre— taceous rocks (formation no. 1.) in the type area in eastern Nebraska (Meek and Hayden, 1862, p. 419— 420). King (1878, p. 298) also adopted the term Dakota group for the reports of the 40th parallel survey, but only after Hague (1877, p. 39) had used the terms Dakota Cretaceous, Dakota formation, Dakota sandstone, and Dakota group interchangeably. After the organization of the U. S. Geological Survey in 1879 successive attempts to standardize stratigraphic terminology in Survey reports (Powell, 1882, p. XL— XLVII; 1890, p. 63) led to the selection of the forma- tion as the “grand unit” for mapping. The term group gradually lost favor as a synonym for formation and was eventually reclaimed and defined (Walcott, 1903, p. 21—27) in the broader sense in which it is understood today. Consequently the original Dakota group in publications on eastern Colorado properly became the Dakota formation, or Dakota sandstone, a change that was purely taxonomic and in no way altered the meaning of Meek and Hayden’s original definition. The first attempts to subdivide the Dakota formation in eastern Colorado were informal. Gilbert (1897) distinguished an upper, fire—clay-bearing part on the economic geology sheet of the Pueblo folio. Hills was the first to emphasize a threefold division of the formation. In both the E1 Moro folio (Hills, 1899) and the W'alsenburg folio (Hills, 1900) he notes that the Dakota formation consists of a lower porous, conglomeratic sandstone, a middle shale bed, and an upper fine-grained sandstone containing some shale, Because the middle shale was locally refractory it was DAKOTA GROUP‘ IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 17 commonly referred to as fire clay. Hills mapped this fire clay on the economic geology sheet of both folios. Subsequent to Hills’ work the threefold division of the Dakota formation in the Arkansas River valley area and elsewhere in southeastern Colorado was noted by a number of geologists. In 1905 fossils of Early Cretaceous age were discovered in the middle shale in Prowers County by Darton (1905, p. 120) and along the Purgatoire River, south of La Junta, and on Oil Creek near Canon City by Stanton (1905, p. 661—663, 666*667). Up to this time the Dakota formation in Colorado had been assumed to bc Late Cretaceous (Cenomanian) in age on the basis of its fossil plants, of which the greater number were col- lected from sandstone in the upper part of the Dakota strata in eastern Kansas and Nebraska. Previous discovery of marine Early Cretaceous beds in Kansas, where the Dakota group underwent a taxonomic over- haul and subdivision completely separate from that in Colorado, apparently had not prepared the Colorado investigators to deal with a similar discovery. Pos— sibly this was because the Colorado work was largely confined to quadrangles adjacent to the Rocky Mountain front and did not include Dakota terrain in southeastern Colorado, where the beds are more obviously similar to the Kansas sequence. The recognition of the middle and, consequently, the lower part of the Dakota formation as Early Creta- ceous and the continued acceptance of the top sand— stone as Late Cretaceous did not bring about an im— mediate change in the formal terminology in Colorado, but subdivision of the Dakota on the basis of this age difference was informally expressed wherever Early Cretaceous fossils could be found in the sequence. The Early Cretaceous part of the sequence was com- monly discussed separately under the heading Coman- che series, or Comanche formation, (Darton, 1906, p. 25; Henderson, 1909, p. 172), in spite of the fact that it was included as a part of the “Dakota” forma— tion or “Dakota” sandstone. The quotation marks probably indicate the dissatisfaction of the authors with this ambiguity. The first formal subdivision of the Dakota formation was made by Stose (1912) in the Apishapa quadrangle. He named the Early Cretaceous lower sandstone and middle shale of the threefold sequence the Purgatoire formation, and re- tained the name Dakota sandstone for the upper sand- stone. Subsequently Finlay (1916), in the Colorado Springs quadrangle, named the sandstone and shale units in the Purgatoire formation the Lytle sandstone member and Glencairn shale member respectively. With the exception of the addition to the Dakota sandstone of a local refractory shale unit, the Dry Creek Canyon member (Waagé, 1953, p. 12—17), the subdivision and nomenclature have remained as designated by Stose and Finlay. The names Dakota sandstone, in its restricted sense, and Purgatoire formation have been used throughout southeastern and south-central Colorado and as far north along the Front Range foothills as Perry Park in the Castle Rock quadrangle (Richardson, 1915). In the northern Front Range foothills very little work was done on the pre-Benton Cretaceous strata be- tween 1912 and 1923. No attempt was made to extend Stose’s subdivisions of the original Dakota formation north of the Castle Rock quadrangle, although the presence of a similar sequence had previously been recognized in the foothills north of Boulder (Henderson, 1909, p. 174). Lee’s work in the northern foothills (Lee, 1923, p. 1—20) led to a fivefold rather than threefold subdivision of the Dakota formation in this area. His stratigraphic study of the Dakota was based on a section exposed in the Poudre Valley and Reservoir Company ditch along the north side of the Cache La Poudre River, 2 miles north of Bellvue, Larimer County. Lee called the Dakota formation the Dakota group and divided it into five informal subunits: the lower sandstone, lower shale, middle sandstone, middle shale~—later renamed upper shale (Lee, 1927)~—and upper sandstone. Lee used this terminology throughout the Front Range foothills north of the Castle Rock quadrangle, identifying his subunits in many measured sections and correlating them with the subdivisions of Stose and Finlay to the south and with the Wyoming terminology to the north. Later Lee (1927) elaborated on this study and extended his correlations northward into Montana. Fossils collected by Lee, and others, from the middle shale (upper shale of Lee’s 1927 report) of his Dakota group were described by Reeside (1923) who recognized that the fauna was an impov— erished representation of the Early Cretaceous (Wash— ita) fauna found in the Purgatoire formation of south- central and southeastern Colorado. No formal changes have been made in nomenclature or subdivision of Lee’s Dakota group since it was proposed, and it has existed side by side with the southern classification of Stose and Finlay. Terminologies other than that of Lee have been used in the northern Front Range foothills presumably because Lee’s Dakota group is too broad a unit for detailed work and because some of its subdivisions lack lateral cOntinuity and are difficult to apply. The Stose and Finlay terminology was used in the Denver-Golden area by Waagé (1952) but subsequent work leading to the present report has shown that it was incorrectly applied and that it is equally as unsatisfactory as Lee’s in providing a logical subdivision of the pre-Benton Cretaceous strata. George (1927, p. 63—64) called the 18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Early Cretaceous rocks throughout eastern Colorado the Purgatoire and incorrectly used the names Lakota and Fuson in the northern foothills for members of the Purgatoire that he considered equivalent, respectively, to Finlay’s Lytle and Glencairn members of the Pur— gatoire in the Colorado Springs area. This unfortunate usage, based on incorrect correlation with the Black Hills area (fig. 19), is still used in Colorado by some workers. Other workers have extended the Cioverly- Thermopolis-Muddy terminology southward from Wyoming, and some still use the term Dakota formation in the sense in which it was used in early reports of the Geological Survey. Inasmuch as Lee’s terminology is the only one based on a careful stratigraphic study, it is certainly the most acceptable and the most useful of the existing possi- bilities. The Geological Survey (Wilmarth, 1938, p. 566) provisionally accepted Lee’s Dakota group for northernnColorado with the condition that IfA‘t‘he‘Purgatoire proves to be present in the Bellevue section it will be removed from the Dakota group of W. T. Lee. Several sources of confusion in the usage of pre— Benton Cretaceous terminology are apparent in the history of subdivision and nomenclature outlined in the preceding paragraphs. The first source was the taxo- nomic change from the use of the terms formation and group as synonyms to their use as terms for separate ranks of rock units. A more critical source was the tendency to separate the Early Cretaceous from the Late Cretaceous parts of the pre—Benton Cretaceous sequence, a tendency that influenced, and is reflected in, Stose’s formal subdivision of the old Dakota formation in southeastern Colorado. The use of age as a criterion for the subdivision of rock units, a practice at the root of many nomenclatural problems, can lead only to confusion in correlation and to ambiguity in terminology when applied to complex transgressive deposits like the pre-Benton Cretaceous sequence. Much of the confusion associated with the name Dakota stems from this cause. An unfortunate nomenclatural practice, that of retaining the name Dakota for the Late Creta— ceous part of the sequence in those areas where Early Cretaceous rocks can be identified and separated, has served to crystallize the confusion. This practice has been applied in Kansas and in Colorado, making it impossible to use the name Dakota in a single sense for physical correlation between areas in which Early Cretaceous strata are separated from the Dakota and areas in which the occurrence of Early Cretaceous rocks has not been sufficiently well established to permit their separation from the Dakota. Introduction of terminologies from other areas is a recent source of confusion in the Colorado pre-Benton Cretaceous classification. It is understandable, when one considers the confused state of the local terminology and the reluctance of workers to use the name Dakota in any sense because of its ambiguity, but the practice is untrustworthy in light of our lack of knowledge about the details of regional Dakota stratigraphy. The continued use of the rather obvious incorrect correlation of the Glencairn member of the Purgatoire formation with the Fuson shale illustrates the hazard of using a foreign nomenclature to circumvent the inadequacies of the native nomenclature. It has be— come increasingly obvious, as work on the Dakota has progressed, that neither the local classifications pro— posed for the pre-Benton Cretaceous sequence in eastern Colorado nor the foreign classifications are adapted to the natural lithogenetic subdivision that characterizes the sequence throughout much of the western interior. This natural subdivision either has been overlooked or has been effectively obscured by the unquestioned acceptance of previous classifications. STRATIGRAPHY Inasmuch as none of the classifications applied to the pre—Benton Cretaceous sequence in Colorado accurately express its principal lithogenetic subunits and stratigraphic breaks, all previous systems of nomen— clature are excluded from the following discussion in order to present the general stratigraphic features of the sequence without the bias that such systems impose. The most noticeable stratigraphic feature in the sequence of Dakota strata lying between the Morrison formation and the Benton, or Graneros, shale in eastern Colorado is its divisibility into two distinctive parts. The lower part consists of irregular lenses of light—gray to gray—white, commonly porous sandstone, and con— glomeratic sandstone which are irregularly interbedded with variegated claystone similar to that in the under- lying Morrison formation. Weathered outcrops of the sandstone are highly variable in color but light values of buff and gray predominate, and pink and yellow staining is common. This lower part of the sequence is typified by its variability, both in the relative amounts of sandstone to variegated claystone and in the irregular thickness and distribution of the sandstone lenses. Contrary to common belief, the base of the lower part of the sequence is not consistently marked by a conglomerate bed. Where the lower part is a single massive unit composed chiefly of sandstone and con— glomerate, an obvious physical break occurs between it and the Morrison formation. At other localities the lower part of the sequence consists of alternating lenses DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 19 of sandstone and variegated claystone similar to the upper part of the Morrison and there is no obvious unconformity between the units. The upper part of the sequence consists of sandstone units that weather buff and brown and alternate with units of dark-gray to black shale and siltstone. The sandstone beds are dominantly fine grained, tabular to massive, cross laminated, and less porous and more resistant than those in the lower part of the sequence. The intervening dark-colored shale units are laminated, commonly silty, and contain thin layers of altered volcanic ash. Although somewhat variable in lithology and thickness, the changes in the sandstone and shale units are gradual, lateral changes in facies, and the upper part of the sequence as a Whole presents a regu— larity in its succession and a continuity of its parts that contrasts markedly with the lenticularity of‘ the lower part of the sequence. The contact between the upper and lower parts of the sequence is a persistent disconformity marking the abrupt change from the variegated claystone and gray— white sandstone below to the black shale and brown— weathering sandstone above. The disconformity is a planed surface on which rests, in many places, a thin conglomerate or conglomeratic sandstone. Beneath the disconformity the upper few feet of the lower part of the sequence commonly consists of weathered sandy clay or claystone containing local concentrations of iron oxide. The disconformity is the most obvious physical break in the section between the Morrison formation and the Benton shale; it can be traced throughout eastern Colorado and into adjacent States. The interpretation of the gross twofold lithic divi- sion within the pre-Benton Cretaceous sequence is fairly evident. The lower part of the sequence consists of flood-plain deposits more closely related lithogeneti— call y to the underlying Morrison formation than to the upper part of the pre-Benton sequence. Probably much of the sediment in the lower part of the sequence is locally derived from the NIorrison. The discon— formity separating the lower from the upper part of the sequence is a transgressive feature affording the first evidence of an invading Cretaceous sea. The initial deposits above the disconformity are chiefly fresh- and brackish-water beds presumably deposited in local deltas or in bodies of water impounded along the coastal plain by the rise in sea level. The time value of the disconformity cannot be accurately assessed at any given locality because of the lack of diagnostic fossils, but it was sufficiently long in many places to allow leaching of the top of the lower part of the sequence. The upper part of the sequence is a record of both 332778-55—42 local and regional fluctuations in strand line. In some places, presumably the larger deltaic areas, the sequence is predominantly nonmarine, in other places it is pre- dominantly marine or estuarine: everywhere it is a complex unit recording local conditions at or near the strand line from the initial impounding of coastal-plain drainage until marine conditions prevailed. The upper and lower parts of the pre—Benton Creta- ceous sequence and the disconformity that separates them are regional features useful for physical correla- tion throughout much of the interior region. In the northern Front Range foothills of Colorado, this twofold lithogenetic division affords a logical basis for separating the sequence into formational units. The name Lytle formation is here applied to the lower unit of sandstone, conglomeratic sandstone, and variegated clay, and the name South Platte formation is given to the upper unit of alternating sandstone and dark-colored shale beds. The term Dakota group is retained to include these two formations. LYTLE FORMATION DEFINITION The beds of sandstone, conglomeratic sandstone, and variegated claystone that make up the lower part of the pro-Benton Cretaceous sequence are correlated here with the Lytle sandstone member of the Purga—~ toire formation in south-central Colorado and the name Lytle, raised to the rank of formation, is applied to them throughout the northern Front Range foothills. Finlay (1916, p. 7—8) gave the name Lytle sandstone member to the lower sandy part of the Purgatoire formation in the Colorado Springs quadrangle, noting that it consists of light—colored sandstone, pebbly beds, and “scattered lenses of greenish or reddish clay near the top ;” he also mentions that the overlying Glen- cairn shale member is “rather sharply separated from the Lytle member.” Finlay did not recognize the disconformity separating the two lithogenetically dis tinct parts of the pre-Benton sequence but it is obvious from his descriptions that he intended to separate his Glencairn and Lytle members at this lithic change. VVaagé (1953, p. 7—9, 27) traced the members southward into south-central Colorado and used the disconformity as the contact between them. Correlation of the Lytle sandstone member of the Colorado Springs area with the lower part of the pre-Benton Cretaceous sequence in the northern foothills is clear cut inasmuch as the disconformity occurs in both the northern and southern Front Range foothills. Furthermore the beds beneath it are lithologically identical and show the same stratigraphic relations with the underlying Morrison formation. , 20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TYPE LOCALITY OF THE LYTLE Finlay took the name Lytle from a small settlement of a few homes along Turkey Creek in the southwestern part of the old Colorado Springs 15-minute quadrangle. Today the locality is marked by the Lytle School, situ- ated along Lytle Road just south of Turkey Creek in the SW%NW}£ sec. 2, T. 17 S., R. 67 W., Timber Mountain quadrangle. The following section was measured at the typical exposure northeast of the school on the west-facing scarp of the hogback between Turkey Creek and Little Turkey Creek. Description Purgatoire formation (in part). Glencairn shale member (in part): Sandstone, fine- to coarse-grained, tabular, Feet cross-laminated; weathers brown __________ 3. 0—7. 0 Disconformity. Lytle sandstone member: Sandstone, fine-grained, argillaceous, soft; weathers white, with local yellow stain; grades into unit below ___________________ 1. 5—6. 0 Sandstone, fine- to medium—grained, massive, cross-laminated, with scattered irregular layers of conglomeratic sandstone; weathers gray, light gray, and yellowish gray _______ 47. 0—? Remainder of section obscured by slope wash. Dinosaur bone fragments found in the slope wash 90—100 feet below the top of the type section suggest that the Lytle sandstone member is less than 100 feet thick at this place. Finlay gives an average thickness of 145 feet for the Lytle in the Colorado Springs area but this figure is excessive. No clear—cut contact between the Lytle member and the Morrison formation was seen in the type area, but conglomeratic sandstone ledges that presumably mark the base of the member crop out locally between 50 and 70 feet below the top of the unit. LATERAL VARIATION In the northern foothills abrupt lateral variation in the local dominance of its sandstone or claystone frac- tion is characteristic of the Lytle formation. At one extreme the Lytle consists almost entirely of sandstone and conglomerate and resembles its more consistently arenac‘eous southern equivalent, the Lytle sandstone member of the Purgatoire formation. At the other extreme the Lytle lacks conglomeratic beds and con- sists of approximately equal amounts of fine- to medium—grained sandstone and variegated claystone distributed in alternating lenses. Generalized graphic sections of the Lytle formation illustrating its variable lithic content and thickness are shown in figure 5. Two of these sections are given in more detail. A dominantly sandy section of the Lytle formation is exposed in the road cut along Colorado Route 186 on the south side of the dam across Spring Canyon, Horsetooth Reservoir, SEM sec. 32, T. 7 N., R. 69 W., Larimer County. Description South Platte formation. Disconformity. Lytle formation: Feet 8. Claystone, light-gray with pink and yellow stain, sandy; grades imperceptibly into unit below _____________________________ 7. Sandstone, fine-grained, massive, cross-lam- inated; weathers yellowish gray to buff with local pink and light-purple staining- _ 6. Claystone, grayish—green with red and yellow stain in uppermost foot, silty ____________ 5. Sandstone, argillaceous, and claystone, sandy; weathers with red, pink, and yellow stain__ 4. Sandstone, light-gray with pink to yellow east, fine-grained, cross-laminated, with thin irregular interbeds and lenses of greenish- gray silty claystone. Clay-pellet conglom- eratic layers throughout, thickest at base__ 3. Sandstone, as in unit 4 but fine- to coarse- grained with a few thin lenses of small chert and quartzite pebbles. Few lenses of claystone and a 22-foot bed of clay- pellet conglomerate 8 feet from top _______ 2. Sandstone and conglomerate. Upper 3—4 feet are chert and quartzite-pebble con- glomerate; remainder partially obscured by wash, apparently massive, cross-laminated, friable sandstone and conglomeratic sand- stone _________________________________ Unconformity. Morrison formation: 1. Clay and claystone, variegated, silty, upper 2 feet yellow, underlain by 4-foot zone of purplish-red claystone which grades down- ward through about 3-foot zone of maroon and bluish-purple to typical greenish-gray claystones of the Morrison ________ i ______ 1. 0—4. 0 24. 0 2. 5 1.5 22. 0 14.0 13.0 12. 0:!: In the scarp face of the Dakota hogback north of Deer Creek in SE}£NE}£SE% sec. 5, T. 6 S, R., 69 W., Indian Hills quadrangle, the Lytle consists of alter— nating units of sandstone and claystone. Description South Platte formation. Disconformity. Lytle formation: 9. Claystone, gray containing local pink stain, Feet sandy, some zones argillaceous sandstone____ 0. 3—1. 0 8. Sandstone, medium— to coarse-grained and con- glomeratic, massive, lenticular, locally cliff forming; weathers light gray and light buff. Conglomerate chiefly in lower 10 feet ________ 24. 0 Unconformity. 7. Siltstone, light-gray and greenish—gray, red mottling in lower 5 feet, some scattered lenses of silty claystone and some argillaceous sand- stone ____________________________________ 8. 0 21 DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO uoneuuo; 110511.1qu uo; 12111.10; 9an ASSESS mowing: 2: 3 tan 3332?» his: was nosafihe Bid 23 E meant: .mhmam‘w‘d mxbcE 0 0 ..0 000 o o- 00 ..... . :oflmfihow :owTEOE mo Eda “53on53 pmmmz mo ommm . ENE 98 occumhfl o mmhm- :mwcmmuw ozoamam v.8 mcgmhflo vmummoimkr 7% wcoumunam ofiameBwaoo «Ed mcofimufimw 0.0.0. 0.0.0 ZOH E E“ <31 on he. 2 :u 0a: ‘5‘” “E Es g o c. H 06% 0",} «,0 Tn‘ah' E 3‘“ “5 2:5; 2., :5 54 a: «a, o - o1: "’ ’ EB 53 “a: Morrison in) 3 2 $36- formation ‘9 8 “- 5’ ~ E 3 Z "‘ . =~ z” W Mo m “E (inpart) om f5 ’ N ._. ,E 0>a—i 0" a) :c> o hifih if}; a) OHU‘ ES mgm p~ >3 .£.=m 1: >1 E as: Emma: _. o .2 :1 «1m: 2 ‘6“ o a we: 5"] :73 Emma U FIGURE 7.—Several interpretations of the contact between the Morrison formation and the Dakota group in the Denver area. tion, but contains lithic descriptions and thickness figures that serve to refute Lee’s interpretation. Eld- ridge states (1896, p. 61) that the “upper third” of the Morrison is “a succession of sandstones and marls” which includes a conglomeratic sandstone at the base and, above it, sandstone interbedded with shale. He specifically describes the shale as “similar to those comprising the bulk of the Jura,” in other words, varie- gated shale, not gray or black shale. A comparison of the relative thicknesses of ‘ the units described by Eldridge further demonstrates that he could not have included any of the plant—bearing Dakota with his type Morrison. Eldridge gives an average thickness of 200 feet for the Morrison; consequently the part of the formation he refers to as the “upper third” can be expected to be about 60 or 70 feet thick. In the section measured by the writer at Morrison, 65 feet of varie- gated clay and sandstone, including a weakly con— glomeratic sandstone, lie between the dominantly green— ish-gray Blorrison claystones and the probable base of the Lytle formation. Actually the Morrison is about 270 feet thick at the type locality, not 200, but even a third of this larger figure would not make the upper part of the Morrison more than 100 feet thick. Yet, if Lee’s interpretation is applied to the section measured at Morrison, the “upper third” of the Morrison is 228 feet thick, and the formation as a whole is between 350 and 400 feet thick, or about double Eldridge’s figure. By Lee’s interpretation the over- lying Dakota, said by Eldridge to be between 225 and 300 feet thick, is only 78 feet thick. Certainly Eld- ridge would have mentioned local deviations of this magnitude in the thickness of his formations had they existed. Lee (1920) revised Eldridgc’s type Morrison section, placing the upper contact under the so—called Saurian sandstone which marked the base of the upper third of Eldridge’s Morrison. His stated reason for this revision was that “No obvious break was found in the section between the plant horizon and the Saurian conglomerate” (Lee, 1920, p. 185). In the Turkey Creek section 1.8 miles south of the type lVIorrison, Lee (1927, p. 28) placed his Morrison-Dakota contact at the base of the Lytle, apparently unaware that the break he had chosen as the contact at Morrison lay some 98 feet stratigraphically below. Throughout the foothills region Lee (1927) confused the two conglom- eratic zones in question and consistently placed his Morrison-Dakota contact at the base of the most obvious conglomerate zone, apparently unaware that more than one such zone existed. This is understand— able when one recalls that Lee’s study of the Dakota group along the Front Range was made with reference to the “type section” of his Dakota group at Bellvue DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 25 Where the entire upper variegated part of the Morrison is absent and the Lytle rests directly on the greenish— gray marl and claystone of the Morrison. An examination of the Morrison type section with its lack of conglomeratic beds and indefinite Morrison— Lytle contact indicates that Eldridge based his descrip- tion of the Morrison on its aspect throughout the Denver basin area rather than at Morrison, Colo. Had he presented a measured section of the type it would have been difficult for him to indicate his Morrison—Dakota contact because of the absence or obscurity of the basal conglomerate of the Dakota. Two clues to Eldridge’s conception of the position of the Morrison-Dakota contact are implicit in his descrip- tion of these two formations. The first is his recogni- tion of two horizons at which conglomeratic lenses are commonly located, one at the base of his Dakota and one at the base of the upper third of his Morrison. The second is the presence of variegated clay, rather than black shale, in the sandy strata between these two conglomeratic zones. The pattern of two con- glomeratic zones separated by beds containing varie- gated clay corresponds closely to the sequence including the basal conglomerate of the Lytle and the under- lying variegated beds of the upper part of the Morrison with their discontinuous basal conglomeratic zone. Consequently, it is most likely that the Morrison-Lytle contact of the present report corresponds to Eldridge’s Morrison—Dakota contact. ALAMEDA PARKWAY TYPE SECTION Waldschmidt and LeRoy (1944, p. 1100) in recom— mending a new type section for the Morrison formation recognize that Lee (1920) misinterpreted Eldridge’s Morrison-Dakota boundary. Nevertheless they be- lieve that Lee corrected this error in a subsequent paper (Lee, 1927), for they state that . . the Morrison lies with apparent disconformity below the conglomeratic phase of the Dakota as it was originally defined by Eldridge (1896, p. 60—62) and Lee (1927, p. 28) . . . Lee’s 1927 work offers a somewhat more accurate sec- tion of the type Morrison than the estimated section presented in his 1920 work, but the two sections are obviously much the same and can be matched to show that Lee did not change the position of his Morrison- Dakota contact in his 1927 work. Consequently the top of the Morrison as defined by Eldridge (1896, p. 60—62) and as redefined by Lee (1927, p. 28) is in differ— ent stratigraphic positions, Lee’s being at the base of the conglomeratic zone in the upper third of Eldridge’s Morrison formation. The new type section of the Morrison formation along west Alameda Parkway is better exposed than Eldridge’s type section at Morrison but the upper contact is equally obscure. None of the many thin sandstone lenses between the disconformity at the top of the Lytle formation and the greenish—gray claystones of the Morrison contain pebbles of chert and quartzite. Waldschmidt and LeRoy have chosen the base of the uppermost massive sandstone lens in the Lytle as the top of their Morrison, but this ledge thins out into variegated claystone a short distance north of the road cut. The statement (Waldschmidt and LeRoy, 1944, p. 1100) that this sandstone is conglomeratic in the Alameda exposure should be modified inasmuch as the conglomerate consists of scattered clay pellets but lacks the chert and quartzite pebbles so typical of the “conglomeratic phase of the Dakota.” Chert and quartzite pebble conglomeratic sandstones, presumably at the base of the Lytle, crop out locally along the hogback north of the Parkway and, when followed laterally toward the road cut, apparently grade into nonconglomeratic sandstone that lies between 35 and 55 feet below the Morrison—Dakota contact chosen by Waldschmidt and LeRoy. Slope wash prevents con- tinuous lateral tracing from the conglomeratic outcrops so that the exact contact of the Morrison and Lytle formations in the Alameda type section remains in doubt. POST-MORRISON WARPING The contact of the Lytle formation with both the greenish-gray part of the Morrison formation and its upper variegated sandy part suggests either local, deep, pre—Lytle channeling, slight angular unconformity, or a combination of the two. Detection of discordance in bedding at the contact is impossible because the sand- stone bodies on either side are irregularly lenticular and crossbedded. In the Canon City area and to the south in the Wet Mountains the overlap of older formations by the Lytle sandstone member of the Purgatoire formation (or Dakota) has been noted by a number of authors. Although some of these occurrences need to be corroborated by further study, there is evidence that the Morrison is locally overlapped by the Lytle. In western Oklahoma Stovall (1943, p. 60) has demon- strated gentle angular unconformity between the Morrison and Purgatoire. For the northern foothills of the Front Range all that can be said with certainty is that the Lytle rests unconformably on different parts of the Morrison which are stratigraphically as much as 100 feet apart. The fact that this crosscutting of the underlying Morrison takes place gradually along the strike rather than in abrupt local channels strongly suggests slight angular unconformity. SUMMARY The beds between the disconformity that marks the top of the Lytle formation and the greenish—gray clay- 26 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY stones of undoubted Morrison are highly lenticular and variable in thickness and lithology. They contain two horizons at which conglomeratic lenses are locally common. The upper one of these has the thicker and more persistent conglomeratic lenses and the uncon— formity at their base is taken as the Morrison-Lytlc contact. As far as can be inferred from the original description of the Morrison formation, this contact corresponds to the Morrison-Dakota contact of Eld— ridge. Slight angular unconformity is indicated at the base of the Lytlc formation in additon to local channel— ing. The conglomeratic lenses of the Lytlc are gen— erally the more resistant and consequently are more prominent on the outcrop. Where they are absent, or nonresistant, or separated into many benches by varie— gated claystone, the Morrison—Lytlc contact is indefi— nite. Throughout most of the northern foothills the local conglomeratic lenses at the base of the Lytlc crop out near enough to one another so that the position of the Morrison-Lytle contact can be interpolated between them. Where it is not possible to recognize the contact over a large area, it is expedient to map the Lytle with the Morrison as an undifferentiated unit. CONTACT OF LYTLE AND SOUTH PLATTE FORMATIONS Beneath the disconformity that marks the top of the Lytle formation the beds appear to be leached. Yellow to white, soft clay, argillaceous siltstone, and fine— grained sandstone with f erruginous panlike concretionary layers form a distinctive zone that is helpful in locating the disconformity on the outcrop. Tests made of this material where it is chiefly clay or claystone show that the alumina content is high just beneath the contact but decreases abruptly downward. Locally the clay just beneath the contact qualifies as a high heat duty refractory clay, but the clay bodies are too thin and discontinuous to be mined. Clay below this zone is generally light shades of red and green and is well below refractory grade. At a very few places the leached zone is thin or entirely lacking, but the sharp contact is nonetheless evident because of the contrasting rock types of the beds above and below it (figs. 8, 9). AGE The only organic remains found to date in the Lytle formation in the northern Front Range foothills are chertified fragments of coniferous wood. No fossils FIGURE 8.—Tabular sandstone of the I’lainview sandstone member of the South Platte formation (above) in disconformable contact (D) with massive light—colored sand. stone and claystone of the Lytlc formation at Spring Canyon dam site, Fort Collins quadrangle. DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 27 FIGURE 9.~Silty shale and basal sandstone of the Plainview sandstone member of the South Platte formation in disconformable contact (at man’s hand) with argil- laceous sandstone of the underlying Lytle formation on hogback south of Eldorado Springs. have been described from equivalents of the Lytle in eastern Colorado, but beds in a similar stratigraphic position in Wyoming (Cleverly formation in part) locally contain a sparse assemblage of fresh—water mollusks and charophytes which are considered (Yen, 1946 and 1951; Peck, 1941) Early Cretaceous in age. The mollusks and the eharophytes are distinct from similar fossils in undoubted Morrison strata. On the basis of its physical correlation with fossiliferous beds in Wyoming the Lytle formation is classified as Early Cretaceous. SOUTH PLATTE FORMATION DEFINITION The upper part of the pre—Benton Cretaceous se— quence, lying between the Lytle formation and the Benton shale, is here treated as a single unit in the northern Front Range foothills and named the South Platte formation. It is equivalent to the upper sand- stone, upper shale, middle sandstone, and uppermost black shale part of the lower shale of Lee’s Dakota group. The South Platte formation grades laterally northward from a dominantly nonmarine elastic phase in the Kassler quadrangle to a dominantly marine shale 832778—55—3 phase in Larimer County, consequently no single exposure is typical for the unit over its entire area of outcrop, and three localities rather than a single locality are necessary as standards for reference. The for- mation is named for the South Platte River inasmuch as the southernmost of the three standard sections, selected as the type because it shows the maximum number of subunits, is exposed on the north side of the gap made by the river through the Dakota hogback in the Kassler quadrangle, Jefferson County. In addition, the entire outcrop area of the formation in the northern foothills lies within the drainage basin of the South Platte River. LITHOLO GY The South Platte formation consists of 200—350 feet of alternating units of gray to black shale and brown— weathering sandstone. The sandstone is chiefly fine grained but coarser fractions are common locally in the nonmarine phase. Individual sandstone units have considerable lateral extent and vary laterally in thick- ness, nature of bedding, and amount of contained argil— laeeous matter. Quartzitie sandstone, in the sense that siliceous cement causes the rock to break across the 28 grains, is rare and is confined largely to the top of the uppermost massive sandstone bed. The shale units in the nonmarine phase consist of hard, laminated, noncalcareous, silty shale that is commonly interlaminated or thinly interbedded with siltstone and fine-grained sandstone. Differential ther- mal analyses of these shale units show that kaolinite is the dominant clay mineral. Some of the shale is rela- tively silt free and highly refractory. The transition into the marine phase is marked by (1) a change of the dominant clay mineral in the shale units to illite, (2) a decrease in the sand content of most shale units, and (3) the appearance of zones of calcareous shale contain thin beds of fossiliferous silty limestone. Thin beds of white, yellow, or light—gray claystone presumed to be altered volcanic ash are common in the shale. These beds hold fixed positions relative to other lithic units and some are very useful as key beds inas- much as they are laterally persistent and can be traced from the nonmarine phase into the marine phase. In the nonmarine phase they are dominantly kaolinitic and rarely exceed 3 inches in thickness; locally they are hard enough to be classed as porcellanite. One bed (the second key marker in fig. 10.) was sampled at intervals from the nonmarine into the marine phase; its dominant clay mineral changed along the strike from kaolinite to montmorillonite. One thin zone of slightly fossiliferous marine silt- stone extends through most of the nonmarine phase and is useful, along with the larger shale and sandstone units and the thin beds of altered volcanic ash, for correlating between the phases of the South Platte formation. SOUTHERN NONMARINE PHASE Exposures of the nonmarine phase of the South Platte formation extend from the south end of the northern foothills in the Kassler quadrangle, Douglas County, northward to about Coal Creek in the Ralston Buttes quadrangle, Jefferson County. Within this area the formation exhibits its maximum number of subunits. No single exposure of the formation shows each subunit in its entirety, either because of stratigraphic variation such as the local thickening of sandstone subunits at the expense of underlying shale subunits, or because of masking by talus and slope wash. The type section of the formation, which is also the standard for the non— marine phase, is given on a later page. This type section contains all the subdivisions but some of the shale subunits are incomplete. Consequently an anno— tated composite section, figure 10, is used for reference in describing the subdivisions of the formation. The descriptions and the annotated graphic section give only those details pertinent to the aiIns of this paper. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Lithology of subunits shale 06 C ONFORMI TY First sandstone: brown-weathering, fine- grained sandstone; interbeds of gray silty shale in upper half. Lower half chiefly massive. cross‘laminated sandstone UNCONFORM/TY . First shale: dark~gray refractory shale and First silty shale with interbeds of fine93" e ~Et o s... u: E ”’13 a) c: F: E o ‘ --I a; t“ "4 ,0 3'9 Q) m 1: O U} '5 .413 CD t... ___ ,_. c: in: m MnsE 0'0 .5: 355 a: —“' >333 I” m E m 0 h .C "‘ «In-1 0-1 In +. m w 5 m E a 5, .--_-l.‘§ 3 > [‘4 “ Due >3 gfi "-3'. "'.-'.'.'~'|I'l|l3 | 5 .85 ° " I III ' ' u. D: ' " 5 . 0.) fill? a?“ :1 .r: o I” "a m (1):: 8 >5 '9 1:: D4 3"; h a) ... G N H a! re 0) E u :5 55 0) TU 02 "57‘s {)5 a: >» 322’ 2 HHIlllll v.15. , *5 .s "*‘i’v‘dl'flizizl -. ‘- l a,» v— I] N L I g 5; ox 3‘ :: " =1a?'l'l'l'lll'i‘Illill'i‘f”'|'|I'Ii=‘|'|'l'l' 2|T:~:-1: 1, gm , ,_ . . -‘*~_l||l|=:'vl’l|I l= ||‘ ,: 95 “-3. ,_ . '.'.UIIIIIIIIIIIII'I’IZIIII'IIIIIIIIIIIIIIIIIIHI. '8 3 :5: N LI. LL LL ‘0'}: g ’4 In..¢' 3“ ._ v E O v—i an \ s i >34: I '. H :; - . 1-; :HIHA‘ [ll]l¥l:|l*|ll:l!l“IIIEIII." O k §§I|III~55 ”75H ‘ ' f];II|I|I*I IIIIIIIlIiIIImIIIIII‘IIIIIIIlIIIEIEIIl$137743 i we :- llll | NHL“ H‘I'l'lll'llll'll-s_;l-;-i ' NIL ' ~‘ ‘ ' (D -: ' O E: -m (I) Boxelder Creek II II liil'l'l'l'Il-‘l? Ill'llI 111-! ll Marine fossils Second key marker bed First key marker beds Ash beds, kaolinitic to montmorlllomtlc FIGURE 17.#Luteral changes in the South Platte formation along the northern Front Range foothills. 43. 44 The Kassler sandstone member is a southern element that lenses out northward in the northern foothills. It is widely distributed in south-central and south- eastern Colorado where it forms prominent cliffs. Lithic equivalents of the first sandstone subunit of the South Platte formation are widespread in the inte— rior region (Muddy sandstone member, Dakota sand- stone, Newcastle sandstone) where its great variability suggests complications beyond our present knowledge of the stratigraphy. In the southern plains, and foot— hills of the Rocky Mountains from east—central Colo— rado south and southeastward, this sandstone subunit is a resistant and conspicuous unit. Commonly it coalesces with the equivalent of the Kassler sandstone member below and together these two units form Stose’s Dakota sandstone. Locally they are separated by a refractory shale subunit correlative with the Van Bibber shale member. The change in phase within the South Platte forma— tion in the northern foothills reflects both local and regional events. After an initial sandy transgressive phase (Plainview sandstone member), a marine environ- ment prevailed in much of northeastern Colorado and eastern Wyoming until the withdrawal of the sea marked by the regressive, uppermost sandstone of the sequence. In east—central and southeastern Colo- rado, however, the sea withdrew earlier as deltas spread eastward and northeastward from local positive areas to form an irregular deltaic plain along what is now the southern Front Range and Wet hfountains. The Kassler sandstone and Van Bibber shale members, and their equivalents, form these deposits. Locally, near the positive areas, nonmarine sedimentation was almost continuous. The nonmarine phase in the northern foothills marks such an area; preliminary studies have revealed other similar nonmarine sequences along the north half of the Wet Mountains. Following the deposition of the marine beds to the north and the sandstone and overlying refractory shales and clays to the south there was a widespread break in sedimenta- tion, presumably caused by slight uplift over a large part of the interior. Subsequently the regressive upper sandstone, which is largely continental in the south and varies locally between marine and continental in the north, was deposited. The overlying platy silt- stone and shale at the base of the Benton were depos— ited on the upper sandstone as the sea readvanced throughout the interior region. The generalized summary above is based on exposed rocks and so pertains only to the outcrop areas along the mountains in eastern Colorado and Wyoming. Many more details of pre-Benton Cretaceous stratig- raphy have been revealed by the subsurface work in the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Denver—Julesburg basin area but little of this informa— tion is available. Fogarty1 and Hayes 2 have compiled and interpreted much well data in this area, and their work reveals that the pre-Benton Cretaceous beds thicken eastward from the mountain front into the deeper part of the basin of Early Cretaceous sedimen— tation. This basin is irregular in shape and lies ob— liquely northwest across the northeastern part of Colorado. In the deeper part of the basin the sub- units increase in number and the stratigraphy is com- plicated by the addition to the sequence of subunits of eastern provenance, at least one of which apparently lies stratigraphically above the equivalent of the first sandstone subunit of the South Platte formation. The study of the subunits that outcrop in the northern foothills supports the belief generally held that subunits of eastern provenance do not extend to the outcrop along the Front Range in Colorado. STATUS OF THE TERM DAKOTA GROUP Lee’s (1923) usage of the term Dakota group in the northern foothills is retained here to include the Lytle and South Platte formations because it is a useful map unit for reconnaissance, or for quadrangle maps of small fractional scale. The relatively thin Lytle formation is difficult to map separately at a scale less than 1: 24,000 (fig. 18). The usage follows the original definition of the Dakota group (lVIeek and Hayden, 1862, p. 419—420) inasmuch as it includes all pre-Benton Cretaceous strata. In the type area along the Missouri River in Nebraska the Dakota rests on Paleozoic rocks so its lower contact is unequivocal. The characteristic twofold lithogenetic division is present in the type area where a sharp break separates sandstone with variegated clay below from sandstone with dark-gray clay, carbonaceous clay, and lignite above. In light of previous attempts to make the name Dakota reflect opinion on the age of the rocks it includes, it must be emphasized that Dakota group, as used here, is strictly a rock term and whether or not the group contains both Lower and Upper Cretaceous rocks, is entirely Lower Cretaceous, or varies in age from region to region, is irrelevant to this definition. Because of the indefinite nature of the Morrison- Lytle contact in parts of the northern foothills it may not be convenient in some places to use the Dakota group as a unit for small—scale mapping; in such places the best map units would be the Morrison and Lytle formations undifferentiated, and the South Platte formation. lFogarty, C. H., 1952, Subsurface geology of the Denver basin. Unpublished doctorate thesis in files of 0010. School of Mines. 2 Hayes, J. R., 1950, Cretaceous stratigraphy of eastern Colerado. Unpublished doctorate thesis in files of Colo. Univ. DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 4:5 OF THE LYTLE AND SOUTH PLATTE FORMATIONS CORRELATION The correlation of the pro—Benton Cretaceous strata in the northern Front Range foothills with equivalent strata in adjacent parts of the interior region is indi— cated in the chart, figure 19. Correlation with south— central and southeastern Colorado is based on field work in those areas; for other regions it is based largely on the literature. The Dakota sandstone of south-central and south— eastern Colorado is equivalent to the combined first sandstone subunit, Van Bibber shale member, and Kassler sandstone member of the South Platte forma- tion. The Glencairn shale member of the Purgatoire formation is presumably equivalent to that part of the South Platte formation below the Kassler sandstone member, although it is considerably thinner and the possibility that beds equivalent to the Plainview sand— stone member have been at least partially overlapped by the beds in the I noceramus comancheanus zone cannot be discounted. In and southeast of the Canon City embayment area the I . comancheanus fauna is locally present in the top of the Gleneairn member. Farther to the southeast on the plains it occurs in silty layers throughout the black shaly part of the Purgatoire. The Lytle formation of the northern foothills is equiva- lent, by definition, to the Lytle sandstone member of the Purgatoire formation. The Purgatoire and Dakota terminology is objection- able because it does not conform to the major lithoge- netic units within the pre-Benton Cretaceous sequence, and because of its misuse of the name Dakota. The separation of the Dakota sandstone from the Purgatoire formation is not at the most significant break in the sequence, as was supposed when these units were defined, but at a relatively local unconformity. The old idea, based originally on the supposed Late Cre— taceous age of the Dakota flora, that this unconformity is the break between Lower and Upper Cretaceous rocks is no longer admissible inasmuch as the uncon- formity vanishes northward, in the northern foothills, within the I. comancheanus zone. The regional discon- formity in the sequence lies within the Purgatoire formation, separating it into two lithogenetically dis- tinct parts. FIGURE 18,—Characteristic exposure of the Dakota group in the Denver area, looking north in Dutch Creek gap, Indian Hills quadrangle. formations. U, approximate Morrison—Lytle contact. Us, upper sandstone subunit; K, Kassler sandstone member; and P, Plainvicw sandstone member of South Platte formation. D, discontormity between Lytle (L) and South Platte SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 46 flame“ 2:.ng .._ 33m “255254 USEOSEOEEOE tam UEEEE .203 a: XXXLLA use“??? uwwwmfl {13/ wcoumusmm van diam .onotfiim umvvwngmfifi 29.224:me soflmfipg somTCoE mgouowémp diam $5.59»? 5953 ES 229830 5328 5 $833.33 SEE gnaw ES BEA 2: E mosaitoulé “7:52; macamccdfi 33.852950 ..;....w.o. magm—ucmm :oCaEpe :omeoE coEmEpo‘HCOmEgoE. llllll poo—Em”: D oaoamccmm 95am :mm o coSmEgow 05392:? .5304 oflmhmfimfimnoo M 3331— 33 . m llllll ma, :8 Swan III 293 $304 . I IN! hmnm m 3.93 :omzm | le H H V B mfloomwwflfim .8352: m. mcogmnsdm mnemfiam 2332 u a Bwtfifiddnm ... QEOQmUCNm hummD k®>wm .3 pm loom :ofimEgS 567782 0 .\\\\«vv 1. WWW . , Udlx d. pwnEmE A . wPIInHIH m unopmucdm G Wu WWII“ u an 2%: mu m w. .lllul m m m m W n. |..|.~. u. on an W. Awmmm: Umpuflbmmb anm H :lr"..u. 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Tom B ‘ \ . m nomado . ., mnonncmm pwmmDA macaw—85m occamtcam n. xmmpu NCO .. ‘ H . ‘. ‘. u . 3352 mfimwoswz w “H.“ a HHHI r j ‘ ‘ . . ‘ IIIII o Edam wepwqmpo \ / Edam neacmm Edam :oEom \ wamnm b.2502 Edam NCBOE «mud .mmaw . . . 55.60 .SECNJ me «warm EMU ~5de .8289 when“: mEH mmmfi J .H 3 chm—$.82 cumuofioo absooufizom 25.330 62:300.“ wmcmm «30gb .sztoz mifioma ampunoo wEEomB .HZ DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 47 Correlation with the pre—Benton Cretaceous strata of eastern Wyoming largely repeats Lee’s work (1923, 1927) and follows the correlation of Lee’s Dakota group in the recent Cretaceous correlation chart (Cobban and Reeside, 1952) except for minor adjustments at the position of the disconformity separating the Lytle and South Platte formations. In southeastern Wyoming this disconformity probably lies within the shale mem- ber of the Cloverly formation where the latter contains gray or black shale in its upper part. Where the Grey- bull sandstone member of the Cloverly, or its equivalent sandstone, rests directly on variegated beds or other rocks similar to the Lytle, the disconformity would be at the base of the Greybull. In like manner the dis- conformity in northeastern Wyoming is probably in the upper part of the Fuson shale where the latter contains gray or black shale in its upper part; in other places it may be at the base of the Fall River sandstone. EVALUATION OF UNCONFORMITIES The upper contact of the Morrison formation is gener- ally accepted as marking the boundary between Jurassic and Cretaceous rocks in the western interior. Recently, Reeside (1952,p. 22—26) summari ed what is known regarding the Morrison and its age in relation to the overlying Lower Cretaceous rocks, concluding that . in the United States there is reason to infer a time interval between the Morrison formation and the succeeding beds that represents possibly part of the Portlandian, probably the Pur- beckian, the Berriasian, the Valanginian, the Hauterivian, and possibly the Barremian of the standard European sequence. However, the interpretation of the magnitude of the hiatus rests largely on the interpretation of the fresh— water mollusks, charophytes, and plants that occur in the continental beds lying between the Jurassic (Port— landian) dinosaur-bearing part of the Morrison forma— tion, and the Lower Cretaceous marine beds, such as the South Platte formation, containing the Albian Inocemmus comancheanus fauna. Neither the paleo- botanists nor the students of the fresh—water mollusks agree on the interpretation of their separate kinds of fossils, and although most favor an Early Cretaceous age for the beds in question, there is no substantial evidence to indicate what part or parts of the Lower Cretaceous is represented. The study of the pre-Benton Cretaceous beds in the northern Front Range foothills can add little to the problem of the J urassic—Cretaceous boundary other than to point out that the gap in time between the Jurassic (Portlandian?) dinosaur-bearing part of the Morrison formation and the Lower Cretaceous (Albian) beds of the South Platte formation is taken up by more than one physical break in the sequence. Threejuncon- formities are present in the interval in question: one is at the base of the dominant-1y red, variegated upper part of the Morrison, the second marks the Morrison— Lytle contact, and the third is the disconformity mark— ing the Lytle—South Platte contact. Neither the upper- most part of the Morrison nor the Lytle formation contains diagnostic fossils in the area. The fresh—water molluscan faunas described from Lower Cretaceous rocks elsewhere in the western interior (Yen, 1949) come from beds that occupy the same strati— graphic position and are lithologically similar to both the upper part of the Morrison formation and the Lytle formation along the Colorado Front Range. Whether these faunas are restricted to beds equivalent ,to the Lytle part of the sequence or whether they also occur in beds equivalent to the top part of the Morrison is not known. Most authors have considered what is here called the lower part of the Lytle as the basal Cretaceous conglomerate; if rock units so designated could be correlated on the strength of such designation alone, the beds containing the fresh-water mollusks elsewhere would indeed be equivalent to the Lytle along the Front Range. Inasmuch as a single, well- defined, and persistent conglomerate is lacking at the base of the Dakota group along the Front Range, and in other regions as well, no such generalited correlation can be made. Consequently the unconformity at the base of the Lytle could mark either the Jurassic and Cretaceous boundary or a hiatus of unknown magnitude within Lower Cretaceous rocks. Evidence is equivocal as to what part of the Lower Cretaceous the fresh—water molluscan fauna in question represents. Yen’s (1949, p. 469—470) conclusion that the mollusks are older than the British Wealden mollusks and younger than the British Purbeck is not convincing in light of the lack of a physical break between these British units (Arkell, 1933, p. 543). Moreover it has not yet been satisfactorily demonstrated that fresh- water mollusks can be used for such precise long-range correlation. Charophytes and ostracods from the beds in question (Peck, 1941) contain elements similar to both Purbeck and Wealden microfossils and have cor— roborated their Early Cretaceous age. Peck does not attempt a more precise age determination than Early Cretaceous on the basis of these fossils. Dinosaur remains in the same beds have not been studied. If Yen’s age determination based on the mollusks is correct and the Lytle formation and its genetic equiva— lents are basal Lower Cretaceous, the disconformity at the top of the Lytle is probably the larger of the three breaks and represents most of Early Cretaceous time, from early Neocomian to about middle Albian. The occurrence of more than one obvious physical break in the beds between the Morrison and South 48 Platte formations along the northern Front Range in Colorado and the possibility of similar multiple breaks in correlative beds elsewhere in the western interior suggest that more than one Early Cretaceous fresh— water molluscan fauna may be present. Yen (1951, p. 3) points out that certain molluscan faunas do sug- gest at least slight age differences between the Kootenai formation in Montana, the Cloverly formation in Wyoming, and the Peterson limestone in Wyoming and Idaho. Obviously there is insufficient evidence for evaluating any of the three unconformities between undoubted Jurassic strata and the marine Lower Cretaceous rocks in the northern foothills. If a clear-cut break exists between Jurassic and Cretaceous rocks it could be either the unconformity at the base of the Lytle for- mation or that at the base of the upper part of the Morrison formation. On the strength of Yen’s inter- pretation of the fresh-water mollusks it is also possible that the disconformity between the Lytle and South Platte formations has the greatest time value of any of the three breaks. In the absence of definitive paleontologic evidence the slight but widespread angular unconformity between the Lytle and Morrison formations seems the most reliable indication of a major time break in the sequence, but this unconformity does not necessarily mark the Jurassic-Cretaceous boundary. LITERATURE CITED Arkell, W. J., 1933, The Jurassic system in Great Britain: 681 p., Oxford, The Clarendon Press. Cobban, W. A., and Reeside, J. B., Jr., 1952, Correlation of the Cretaceous formations of the western interior of the United States: Geol. Soc. America Bull., v. 63, p. 1011—1044. Crowley, A. J., 1951, Possible Lower Cretaceous uplifting of Black Hills, Wyoming, and South Dakota: Am. Assoc. Petroleum Geologists Bull., v. 35, no. 1, p. 83—90. Darton, N. H., 1905, Discovery of the Comanche formation in southeastern Colorado: Science, new ser., v. 22, p. 120. 1906, Geology and underground waters of the Arkansas Valley in eastern Colorado: U. S. Geol. Survey Prof. Paper 52. , Eldridge, G. H., 1896, Mesozoic geology, in Eminons, S. F., Cross, Whitman, and Eldridge, G. H., Geology of the Denver basin in Colorado: U. S. Geol. Survey Mon. 27, p. 51—150. Finlay, G. I., 1916, Description of the Colorado Springs quad- rangle, Colorado: U. S. Geol. Survey Geol. Atlas, folio 203. George, R. D., 1927, Geology and natural resources of Colorado: Colo. Univ. Semicentennial Pub., p. 63-64. Gilbert, G. K., 1897, Description of the Pueblo quadrangle, Colorado: U. S. Geol. Survey Geol. Atlas, folio 36. Hague, Arnold, 1877, Colorado Range, in Hague, Arnold, and Emmons, S. F., Descriptive geology, U. S. geological exploration of the fortieth parallel (King): Prof. Papers Eng. Dept. U. S. Army, no. 18, v. 2, p. 39—41. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Henderson, Junius, 1909, The foothill formations of north- central Colorado: Colo. Geol. Survey, 1st Rept., 1908, p. 172—176. Hills, R. C., 1899, Description of the Elmoro quadrangle, Colo- rado: U. S. Geol. Survey Geol. Atlas, folio 58. ———— 1900, Description of the Walsenburg quadrangle, Colo- rado: U. S. Geol. Survey Geol. Atlas, folio 68. King, Clarence, 1878, Systematic geology, U. S. geological exploration of the fortieth parallel: Prof. Papers Eng. Dept. U. S. Army, no. 18, v. 1, p. 278—305. Knowlton, F. H., 1896, The fossil plants of the Denver basin, in Emmons, S. F., Cross, Whitman, and Eldridge, G. H., Geology of the Deliver basin in Colorado: U. S. Geol. Survey Mon. 27, p. 466—472. 1920, A dicotyledonous flora in the type section of the Morrison formation: Am. Jour. Sci., 4th ser., v. 49, p. 189—194. Lee, W. T., 1920, Type section of the Morrison formation: Am. Jour. Sci., 4th ser., v. 49, p. 183—188. 1923, Continuity of some oil-bearing sands of Colorado and Wyoming: U. S. Geol. Survey Bull. 751—A, p. 1—20. 1927, Correlation of geologic formations between east- central Colorado, central Wyoming, and southern Montana: U. S. Geol. Survey Prof. Paper 149. LeRoy, L. W., 1946, Stratigraphy of the Golden—Morrison area, Jefferson County, Colo.: Colo. School Mines Quart, v. 41, no. 2, p. 69—75. ' Lesquereux, Leo, 1883, Contributions to the fossil flora of the western territories, pt. 3, The Cretaceous and Tertiary floras: U. S. Geol. Survey Terr., rept. 8, 283 p. Meek, F. B., and Hayden, F. V., 1862, Descriptions of new Lower Silurian, (Primordial), Jurassic, Cretaceous, and Tertiary fossils, * * * : Acad. Nat. Sci. Phila., Proc., v. 13, p. 419—420. Peck, R. B., 1941, Lower Cretaceous Rocky Mountain nonmarine microfossils: Jour. Paleontology, v. 15, p. 285—304. Powell, J. W., 1882, Plan of publication: U. S. Geol. Survey 2d Ann. Rept., p. XL—XLVII. —— 1890, Conference on map publication: U. S. Geol. Survey 10th Ann. Rept., pt. 1, p. 63—79. Richardson, G. B., 1915, Description of the Castle Rock quad- rangle, Colorado: U. S. Geol. Survey Geol. Atlas, folio 198. Reeside, J. B., Jr., 1923, The fauna of the so-called Dakota formation of north-central Colorado and its equivalent in southeastern Wyoming: U. S. Geol. Suvey Prof. Paper 1317H, p. 199—208. 1952, Summary of the stratigraphy of the Morrison formation: in Yen, Teng-Chien, Molluscan fauna of the Morrison formation: U. S. Geol. Survey Prof. Paper 233—B, p. 21751. Stanton, T. W., 1905, The Morrison formation and its relations with the Comanche series and the Dakota formation: Jour. Geology, v. 13, p. 65lk669. Stovall, J. W., 1943, Mesozoic stratigraphy, in Schofl‘, S. L., Geology and ground water resources of Cimarron County, Okla.: Okla. Geol. Survey Bull. 64, p. 43—132. Stokes, W. L., 1944, Morrison formation and related deposits in and adjacent to the Colorado Plateau: Geol. Soc. America Bull. v. 55, p. 951—992. Stose, G. W., 1912, Description of the Apishapa quadrangle, Colorado: U. S. Geol. Survey Geol. Atlas, folio 186. Waagé, K. M., 1952, Clay deposits of the Denver-Golden area, Colo.: Colo. Sci. Soc., Proc., v. 15, no. 9. p. 375A381. DAKOTA GROUP IN NORTHERN FRONT RANGE FOOTHILLS, COLORADO 4:9 Waagé, K. M., 1953, Refractory clay deposits of south-central Colorado: U. S. Geol. Survey Bull. 993. Walcott, C. D., 1903, Nomenclature and classification for the Geologic Atlas of the United States: U. S. Geol. Survey 24th Ann. Rept., p. 21—27. Waldschmidt, W. A., and LeRoy, L. W., 1944, Reconsideration of the Morrison formation in the type area, Jefferson County, 0010.: Geol. Soc. America Bull. v, 55, p. 1097— 1114. Wilmarth, M. G., 1938, Lexicon of geologic names of the United States: U. S. Geol. Survey Bull. 896. Teng-Chien, 1946, On Lower Cretaceous fresh-water mollusks of Sage Creek, Wyoming: Acad. Nat. Sci. Phila., Notulae Naturae, no. 166. 1949, Review of the Lower Cretaceous fresh-water molluscan faunas of North America: Jour. Paleontology, v. 23, no. 5, p. 4654172. —— 1951, Fresh-water mollusks of Cretaceous age from Montana and Wyoming with a summary by J. B. Reeside, Jr.: U. S. Geol. Survey Prof. Paper 233—A, p. 1—20. 1952, Molluscan fauna of the Morrison formation: U. S. Geol. Survey Prof. Paper 233—B, p. 21~51. Yen, INDEX Page Abstract ______________________________________________________________________ 15 Acknowledgments ............ 15 Alameda Parkway, six subdivisions of Morrison along ________________________ 23 type section of Morrison __________________________________________________ 23, 25 unconformity at base of first sandstone subunit__ 34 Anchura kiowima _____________________________________________________________ 41 Area of study _________________________________________________________________ 15, 16 Bellvue section, type locality of Lee’s Dakota group-_,_.1._._________._.7...1 24, 25 variegated shale __________________________________________________________ 22 bellvuensis, Inoceramus ________________________________________________________ 41 Benton shale ________________________________________________________ 18, 27, 33, 35, 42 Bentonitelike clay ____________________________________________________________ 38 Bovelder Creek, stratigraphic section measured at _____ 39 typical marine phase of South Platte at ___________________________________ 40 Calycoceras ___________________________________________________________________ 41 Charophytes _______________ 27 Cloverly formation ___________________________________________________________ 42 Comanche formation _________________________________________________________ 17 comancheanus, Inaceramus..__._ _ . _ _ _ . . _ ____._. ._____.____.._.._..__ 31 Coniferous wood in Lytle ____________________________________________________ 26 Correlation of nonmarine and marine phases, South Platte ________________ ._ _ 42 Dakota group, history of terminology __________________________________ 16, 17, 18 in northern Front Range foothills ................................. 19, 44, 45 Dakota hogback. . . ..................................... _ 16, 24, 36 Deer Creek, alternating units of sandstone and claystone at ................... 20 stratigraphic section measured at ________________________________________ 20, 21 Dinosaur-bearing beds ..................................................... 20, 23, 47 Diseonformity Within pro-Benton Cretaceous sequence _______________________ 19 between Lytle and South Platte ........................ _ 26 Distribution of conglomeratic lenses in Lytle formation _______________________ 22 Dry Creek Canyon member __________________________________________________ 17 Eldorado Springs, hogback __________________________________________________ 23, 36 stratigraphic section measured at ......................................... 23 First sandstone subunit of South Platte, lithic equivalents ____________________ 44 source of fire clay ____________________________________ - 31 thickness" .................................... 30, 33 Fossils _______________________________________ 17, 40, 41 Fuson shale __________________________________________________________________ 18 Glencairn shale ____________________________________________ __ 17,19 Golden Fire Brick Co. mine.... _ 31 Graneros shale ________________________________________________________________ 18 Horsetooth Reservoir, stratigraphic section measured at ______________________ 23 Indian Creek hogback ________________________________________________________ 16 Inoeeramus bellvuensis ________________________________________________________ 41 comancheanus _______________________________________________________ 31, 37, 38, 40 distribution .............................................................. 41 Jurassic-Cretaceous boundary ..................... . .......................... 47 Kassler sandstone, composition _________________ . 28. 30, 31 distribution ___________________ __ 44 thickness ................................................................. 31 kiowtma, Anchum ............................................................. 41 Lakota sandstone ............................. . .......................... _ 18, 46 larimerensia, Ostrea ________ 41 Lateral tracing, Morrison-Lytle contact 23 Lateral variation in Lytle formation ___________________________ 20, 21 Lee, W. T., quoted ............................................ 25 Lytle formation, composition of conglomerate. 23 correlation with the pre-Benton Cretaceous ............................... 19 thickness in Bellvue section; ............................................. 22 Colorado Springs area ....................... 20 typical locality ................................ , 20 Lytle-South Platte disconformity ............................................. 29 Page Molluscan fauna ________________________________________________________ 23, 27, 40, 48 Morrison formation, angular unconformity between the Purgatoire and _______ 25 composition of conglomerate .............................................. 23 lateral variation _________________________________________________________ 21 six subdivisions along west Alameda Parkway. ........ 23 Morrison-Dakota contact __________________________ _ ______________ __ 24,25 Morrison-Lytle contact, interpretation of Eldridge’s description of ______ Morrison—Turkey Creek area, base of first sandstone unit ..................... contact of Kassler and first sandstone subunit ____________________________ 34 Newcastle sandstone _________________________________________________________ 41 noctuensis, Ostrea _____________________________________________________________ 41 Ostrea larimerensis ____________________________________________________________ 41 noctuensis ________________________________________________________________ 41 Pachydiscus ___________________________________________________________________ 41 Plainview sandstone, composition ____________________________________________ 28, 29 fourth sandstone subunit _________________________________________________ 28 stratigraphic section of typical exposure..-._... 29 stratigraphic section near tunnel entrance, Rabbit Mountain _________ ._ 37 thickness ......................................................... 30, 35 Plant-bearing beds ___________________________________________________________ 24, 41 Porcellanite __________________________________________________________________ 28 Post-Morrison warping .......................... 25 Pro-Benton Cretaceous strata, extent of exposures, _ . 15, 16 faulting ...................................... fivefold division ........ interpretation of twofold lithic division ................................... 18 lithogenetic subunits ________________________ 18 subdivision in northern Front Range foothills. ,. 19 threefold division ____________________________ 16 Ptm‘a salinensz‘s ______________________________________________________________ 31 Purgatoire formation ___________________________________________________ 17, 18, 19, 25 Reeside, J. B., Jr., quoted ................................................. 41 Refractories industry, chief source of clay for __________________________________ 31 Refractory clay ........................................................... 15,26, 31 shale, erratic distribution. in Dakota sandstone ______________________________________________________ salinensis, Pteria ______________________________________________________________ Second shale subunit _______ Shell Research Fund grant ...................... South Platte formation, composition of units _ _ extent of nonmarine phase ................................................ 28 first sandstone ____________________________________________________________ 28 pattern change _________ standard section on Rabbit Mountain _____ thickness ______________________________________ transition of nonmarine phase to marine phase ............................ 28 type section .............................................................. 27, 34 typical marine phase. _ _ _ 40 Spring Canyon, stratigraphic section measured at ............................ 20, 21 Stratigraphic section, across Spring Canyon, Horsetooth Reservoir .......... 20, 23 between Turkey Creek and Little Turkey Creek _________________________ 20 Boxelder Creek ........................................................... 39 Dakota hogback north of Deer Creek 20 Eldorado Springs _________ 23 Lytle _____________________ 20 railroad cut at Plainview ................................................ 29 Third sandstone subunit ......................................... 28, 30, 38, 40, 42 Third shale subunit ...................... 28, 38, 40 Turkey Creek, stratigraphic section measured at ______________________________ 20, 21 Van Bibber shale, composition _______________________________________________ 32 economic value of ___________ 31 first key marker.__. ............ 30, 32 thickness ................................................................. 32, 33 Vertebrate fossils _____________________________________________________________ 41 51 O § fl Basal Eagle Ford Fauna (Cenomanian) in Johnson and Tarrant Counties Texas i K GJEOLOGIC‘AL SURVEY __I_’__ROFESSIONAL PAPER 274-0 Basal Eagle Ford Fauna (Cenomanian) in Johnson and Tarrant Counties Texas By LLOYD WILLIAM STEPHENSON A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—C Descriptims aiiaI illustrations effossi/s of Late Cretaceous age, including two ia’em‘ifieaI éiva/ve species, two gastropoa’ species, and eig/zt cep/za/opeaI species UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :1955 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director For sale by the Superintendent of Documents, U. S. Government Printing Ofl‘ice Washington 25, D. C. — Price 75 cents (paper cover) CONTENTS Page Page Abstract ____________________ I: ______________________ 53 Systematic descriptions—Continued Introduction _______________________________________ 53 Gastropoda ____________________________________ 5 7 Fossiliferous localities ________________ ’ _______________ 54 Cephalopoda- - - - _ _ _ _ _ _ _ _ _ _ - _ - _ _ _ _ - _ _ _ -'_ ________ 58 Systematic descriptions ______________________________ 55 Literature cited _____________________________________ 65 Pelecypoda ____________________________________ 55 Index _____________________________________________ 67 Scaphopoda ____________________________________ 57 ILLUSTRATIONS [Plates 4-7 follow page 68] PLATE 4, Inoceramus, Pseudomelania?, Lispodesthes, Tarrantoceras, Desmoceras, and Acanthoceras. 5. Tarrantoceras. ‘ 6. Borissiakoceras, Euomphaloceras, and Tarrantoceras. 7. Euomphaloceras. III A SHORTER CONTRIBUTION TO GENERAL GEOLOGY BASAL EAGLE FORD FAUNA (CENOMANIAN) IN JOHNSON AND TARRANT COUNTIES, TEXAS By LLOYD WILLIAM STEPHENSON ABSTRACT The/basal few feet of the Eagle Ford shale in Johnson and Tarrant Counties, Tex., contains interbedded concretionary calcareous sandstones and sandy limestones, some of which are fossiliferous. The fauna obtained from the concretions includes 2 identified pelecypod species, 2 gastropod species (both new) and 8 cephalopod species (6 new). One new genus, Tarranto— ceras, of the family Acanthoceratidae, is described. The two new gastropod species are: Pseudomelam'a? basicostata and Lispodesthes lirata; the new cephalopod species are: Acanthocems johnsonanum, Tarrantocems rotatile, T. stantoni, T. lillianense, T. multicostatum, and Borissiakoceras orbiculatum. Several additional poorly preserved mollusks are identified generically but not specifically. Both the lithologic character of the beds and the composition of the fauna indicate that this zone is the northward extension of the flag member (later named Bluebonnet member by Adkins 'and Lozo) of Adkins, in Bell County, Tex. The zone is strati- graphically higher and younger than the Tarrant unit of More- man in Tarrant County, a unit that Moreman considered cor- relative with the flag member in Bell County. In terms of the classification of the Cretaceous strata of Europe the fauna here described is of late Cenomanian age. INTRODUCTION This report records a few molluscan species, mainly acanthoceratid ammonites (Cenomanian), from con- cretionary calcareous sandstones and sandy limestones interbedded with shale in the basal few feet of the Eagle Ford shale in southeastern Tarrant and north- eastern Johnson Counties, Tex. The fauna is of interest partly because it includes species not previously described and partly because it confirms evidence of the synchroniety of the containing beds with the so- called flaggy member of the Eagle Ford shale in Bell and McLennan Counties. Attention was first called to the flag member by W. S. Adkins (1923, p. 67—79), at which time he interpreted these flaggy beds as forming a middle member of the Eagle Ford shale. In a later publication Adkins (1933, p. 239, 270, 417—422) treated the shale below the flag member as a unit of uncertain age, which he called the Pepper formation. However, in a recent publication Adkins and Lozo (1951, p. 117—157) present evidence that the Pepper 339390—55 shale is a southward extension of the Lewisville mem- ber of the Woodbine formation, and this correlation is accepted by Stephenson (1953, p. 57—67). It is therefore established that the flag member, which Adkins and L020 (1951, p. 119, fig. 26), later named the Bluebonnet flag member of the Lake Waco shale, forms the basal unit of the Eagle Ford shale, as that unit is developed in McLennan and Bell Counties. These authors treat the Eagle Ford shale in that area as a group. The Lake Waco shale is the lower of two formations into which they divide the Eagle Ford group in McLennan, Bell and other counties farther south, and the South Bosque marl is the upper forma- tion. They subdivide, the Lake Waco into three subunits: the Bluebonnet flag member, about 6 feet thick in McLennan, Bell, and Williamson Counties, at the base; the Cloice shale member, 12 to 35 feet thick, in the middle, extending from McLennan County to Travis County; and the Bouldin flag member, 8 to 13 feet thick, at the top, also extending from McLennan County to Travis County. Among fossils described by Adkins (1928, p. 240—248) from the flag member (=Bluebonnet member) in Bell County are: Eucalycoceras leonense, Acanihoceras lons— dalei, A. bellense, and A. stephensoml. From the same source Moreman (1942, p. 203, 204) described Acantho- Gems valid’um and A. pepperense. Acanthocems al- vamdoense Moreman is from the same stratigraphic position at a locality 4 miles south of Alvarado, Johnson County. It appears that the type of Mantellicems sellardsi Adkins (1928, p. 239) came from the Bouldin member in Williamson County, but Adkins also re- corded it from the Bluebonnet member in Bell County. All the others were from the Bluebonnet member. It is appropriate to mention here a geologic unit in Tarrant County, originally described by Moreman (in Adkins, 1933, p. 424, 425) as the Tarrant sandy clay and limestone, and later (1942, p. 195) referred to by him as the Tarrant formation. He classed this 15- to 18-foot unit as the basal formation of the Eagle Ford 53 54 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY group, and correlated it with the flag member (=Blue- bonnet member) in Bell County. Locally the Tarrant is a sharply defined unit with a thin conglomerate at the base. Stephenson (1946, p. 1764, 1770; 1952 [1953], p. 3, 4, 30) has presented evidence that the Tarrant unit is stratigraphically lower and older than the Eagle Ford shale and forms the upper part of the Lewisville member of the Woodbine formation in Tarrant County. The correlation of the Tarrant with the flag member has led to the listing of Woodbine species with Eagle Ford species (Adkins, 1928, p. 32; 1933, p. 432—435; Moreman, 1942, p. 193—196), and consequently to confu sion (as to the stratigraphic relation of the upper Wooc bine to the lower Eagle Ford. A careful recheck of tilt Tarrant fauna shows that of 74 named species (4 quest onably identified), 37 (2 questionably identified) are mmmon to the fauna of the typical Lewisville beds )n Timber Creek in Denton County; So far as I have been able to determine, only one species, Exogg, ra columbella Meek, is common to the Tarrant and he Bluebonnet member. One other species, Inoceramus arvanus Stephenson, now known to be present in the Bluebonnet and its equivalents, was originally described from the Lewisville member in Cooke County, but it has not been recognized in the Tarrant unit. One species from the Tarrant, Euomphal- oceras eulessanum (Stephenson), is closely related to Euomphaloceras lonsdalez' (Adkins), but it appears to be specifically distinct. Another species in the Tarrant, Eucalycoceras barcusi (Jones), (=Acanthoceras barcusi Jones), appears to be closely allied to Eucalycoceras leonense Adkins from the Bluebonnet member. FOSSILIFEROUS LOCALITIES The fossils described on following pages were ob- tained from beds that represent the northward ex- tension of the flag or Bluebonnet member of the Lake Waco formation of Adkins and Lozo, and therefore belong stratigraphically above the Tarrant unit. The fossils were collected from the basal 10 feet or less of the Eagle Ford shale at two nearby localities on Walnut Creek in Tarrant County, and at two localities in Johnson County. . The two localities in Tarrant County were dis— covered by the late T. W. Stanton in 1923. They are on Walnut Creek, 4.75 miles east-northeast of Mans- field. The following is quoted from his field notes dated May 18, 1923: On Walnut Creek just below bridge (which has been washed out) a small exposure of the Eagle Ford contains many large flat concretions, one of which was very fossiliferous, containing Inocerarnus fragilis [‘3], Acanthoceras, Anchura (orig. no. 1942). One hundred yards [about 165 yards] down the creek there is a good exposure showing 15 ft. of Eagle Ford with the large con- cretions in lower 6 ft. and thin indurated sandstone bands for 5 feet higher. Some of these yielded Ostrea and a few thin pele- cypods. These exposures must be within 10 feet of the top of the Woodbine. A very good series of specimens of the Acan- thoceras was obtained here. Stanton’s collection (USGS 11740) was obtained from the large concretions.l He states that the concretions are within 6 feet of the base of the 15-foot section. In March 1929, Stanton, accompanied by J. B. Reeside, Jr., and me, visited the Walnut Creek localities. I measured and described the section at the exposure about 500 feet downstream from the bridge site, as follows: Section on left bank of Walnut Creek, 4.75 miles east-northeast of Mansfield, 500 feet downstream from an abandoned road crossing Eagle Ford shale: 7. Clay, gray, shaly, weathering in thin flakes; contains a few thin, irregularly platy calcareous sandstone seams ____________________________ 7 6. Sandstone, platy, and sand, 1 to 6 inches thick, crossbedded, containing scattered white clay balls at base _______________________________ 5. Clay, dark, shaly, gypsiferous; a few concre- tiOnary calcareous sandstone masses about 4 feet above base _____________________________ 8 4. Sandstone, thin, platy, and interbedded shale; here and there a small to large, more or less ovate, concretionary (septarian) mass of fine cal- careous sandstone reaching 1 foot in thickness, and showing effects of crushing by pressure from above; fossiliferous __________________________ 1 3. Clay, dark, shaly _____________________________ 1 2. Sandstone, thin, coarse, calcareous, containing dark phosphatic pebbles and marcasite pebbles; contains Exogyra columbella Meek, and fish teeth; noted several shark teeth, one tooth of Ptychodus and one pavement tooth ___________ $64—$42 Woodbine formation: Lewisville member: 1. Sand and sandy clay, gray, massive, fine argil— laceous, to water level ___________________ 2 Feet Total _____________________________ 20 At the lower end of the exposure sandstone of Wood- bine aspect could be seen below water level in the creek. Reeside found the internal mold of a fragment of a large ammonite (USGS 14582), here identified as Euomplm- loceras alvaradoense (Moreman), loose at the base of the preceding section, and probably weathered out of either layer 4 or layer 5 (pl. 7, fig. 1). A small collection (USGS 14580) was made from a large concretion in place 6 feet above the base of the Eagle Ford formation, about 150 feet downstream from the bridge site. In a layer of coarse calcareous sand in the Woodbine formation, 5 feet below the base of the 1 A collection made at a given locality at a given time is assigned a United States Geological Survey number (as USGS 11740). Other collections made at the same locality at later times are given separate and later collection numbers. Thus more than one collection number may pertain to the same locality. BASAL EAGLE FORD FAUNA IN JOHNSON AND TARRANT COUNTIES, TEX. Eagle Ford shale, were collected Ostrea solem'scus Meek, Exogyra columbella Meek, Protarca? tramitensis (Cra- gin), and Gymnentome valida Stephenson (USGS 14579). These are common species of the Lewisville member of the Woodbine formation. The fossils from the basal beds of the Eagle Ford shale on Walnut Creek are listed below: Fossils from basal beds of the Eagle Ford shale on Walnut Creek, about 4.76 miles east-northeast of Mansfield, Tarrant County, Tex. (USGS 11740, 14580, 14582) [The one species marked with an asterisk (*) is common to the Lewisville member of the Woodbine formation. The three species marked with a dagger (T) are common to the Bluebonnet member (=flag member) of Bell and Williamson Counties] * T Inoceramus aroanus Stephenson Ostrea sp. Brevicardium? sp. Caestocorbula? sp. Cadulus sp. Pseudomelania? basicostata Stephenson, n. sp. Lispodesthes lirata Stephenson, n. sp. Cyclichna sp. Acanthoceras johnsonanum Stephenson, n. sp. Tarrantoceras rotatile Stephenson, n. sp. stantom’ Stephenson, n. sp. lillianense Stephenson, n. sp. TEuomphaloceras lonsdalei (Adkins) TE. alvaradoense (Moreman) Borissiakoceras orbiculatum Stephenson, n. sp. One of the two localities in Johnson County, the one on the north-facing slope of Mountain Creek Valley, 2.5 miles north-northeast of Alvarado, was discovered by Stanton, Reeside, and Stephenson in March 1929. The outcrop consists of large calcareous sandstone con- cretions containing fossils, weathered out in a field. Large masses of sandstone typical of the Lewisville member of the Woodbine formation are exposed nearby in the bed of Mountain Creek topographically 20 feet lower than the fossiliferous concretions in the field. The concretions must therefore occupy a stratigraphic position low in the Eagle Ford shale, within a few feet of the top of the underlying Woodbine formation. The following fossils were obtained at this locality: Fossils from concretions near the base of the Eagle Ford shale, in a field 2.5 miles north-northeast of Alvarado, Johnson County, Tex. (USGS 14583) [The two species marked with an asterisk (‘) are common to the Lewisville member of the Woodbine formation. The three species, marked with a dagger (T) are common to the Bluebonnet member (=flag member) of the Lake Waco formation of Bell and Williamson Counties] *TInoceramus arvanus Stephenson *Exogyra columbella Meek Acanthoceras johnsonanum Stephenson, n. sp. Tarrantoceras rotatile Stephenson, n. sp. multicostatum Stephenson, n. sp. TEuomphaloceras lonsdalei (Adkins) TE. alvaradoense (Moreman) Tarrantoceras rotatile is closely related to T. sellardsi (Adkins), which is recorded from both the Bluebonnet 55 and Bouldin members of the Lake Waco formbtion.. Acanthoceras johnsonanum appears to be more closely related to A. bellense Adkins, from the Bluebonnet member, than it is to other species in the two flaggy members. The other locality in Johnson County is in an erosion gully in a cultivated field about a mile north of Lillian. This place was discovered by James P. Conlin, of Burleson, Tex. He reports finding the following fossils in a concretion from this gully: Acanthoceras cleara- doense Moreman, Acanthoceras sp., Eucalycoceras sp., and Borissiakoceras sp. I am referring Moreman’s species A. aloarad'oense to the genus Euomphalweras Spath, and Conlin’s Eucalycocems to the new genus Tarrantoceras. Conlin has sent to me from this locality one specimen that I refer to Tarrantoceras rotatile and another that I am calling T. lilllanense (USGS 24510). He has also furnished a specimen from the same sc urce, that I am making the holotype of T. stantom'. SYSTEMATIC DESCRIPTIONS Class PELECYPODA Genus INOCERAMUS Sowerby, 1822 Inoceramus arvanus Stephenson Plate 4, figures 1—3 1952 [1953]. Inoceramus arvanus Stephenson, U. S. Geol. Survey Prof. Paper 242, p. 65, pl. 12, figs. 6—9. The basal beds of the Eagle Ford shale yi elded specimens of a small Inoceramus that appear to be identical in essential shell characters with I. artanus Stephenson from the Lewisville member of the Wood- bine formation in Texas. As is generally true of this genus the shells of any given species sho‘w considerable individual variation, but the variations in form outline and surface features of the shells here under consi iera- tion agree essentially with those exhibited by the Lewisville species, and the average size is about the same. Shell rather small for the genus, roughly subcir 'ular to subquadrate in outline, moderately inflated. Form and outline showing marked individual variations. ' Anterior slope steep, in some specimens at right angles to the plane of contact of the two valves, and in some overhanging a little toward the front. The postero- dorsal, posterior and ventral slopes descend more gently and the latter may be modified by a broad, shallow radial depression. Beaks prosogyrate, strongly in- curved, situated at the anterior extremity of the hinge, and at or near the anterior margin of the shell. The anterior margin descends steeply and may be at right angles to the straight hinge line. Surface marked only with fine growth lines and with irregularly devel- oped growth undulations. 56 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The right valve shown in plate 4, figure 3, measures: Length 43 mm, height 43 mm, convexity about 13 mm. The larger left valve shown in plate 4, figure 1, measures: Length 53 mm, height 57 mm, convexity about 17 mm. None of the available specimens from the flaggy limestones forming the base of the Eagle Ford'shale show the hinge or ligamental pits. As seen in para- types from the Woodbine formation (Stephenson, 1952 [1953], pl. 12, figs. 8, 9), the ligamental area is long, 3 or 4 mm wide in adults, and is crossed trans— versely by a series of shallow ligamental pits that are nearly twice as wide as the spaces separating them. Types.—Holotype, USNM 105157; 3 figured paratypes, USNM 105158 a—c, and 12 unfigured paratypes, USNM 105159; 3 plesiotypes from basal calcareous concretions of the Eagle Ford shale, USNM 108840, 108849, and 108864. Occurrence—The species was originally recorded from the Lewisville member of the Woodbine formation, in Cooke County, Tex., at a locality half a mile north of U. S. Highway 82, half a mile west of the Grayson County line (type locality); from Grayson County on a branch of Walnut Creek, 0.7 mile north of Gordonville; and on a branch of Sandy Creek, 2.5 miles north of Sadler. The species is present in basal calcareous concretions of the Eagle Ford shale at the following localities in Texas: Walnut Creek, about 4.75 miles east-northeast of Mansfield, Tarrant County (USGS 11740 (1 figured)). Walnut Creek, 150 feet downstream from the old piers at a bridge site, about 4.75 miles east-northeast of Mansfield, Tarrant County (USGS 14580). North—facing slope of Mountain Creek Valley, 2.5 miles north- northeast of A'lvarado, Johnson County (USGS 14583 (1 figured». Bird Creek, south of Belton—Temple Highway, about 4 miles east—northeast of Belton, Bell County (USGS 11845 (1 figured), 13577). Genus 0STREA Linné, 1758 Ostrea sp. Many small and fragmentary shells of a poorly preserved, undetermined oyster are present in one of the collections from Walnut Creek, about 4.75 miles east-northeast of Mansfield, Tarrant County, Tex. The containing-matrix is a fine calcareous sandstone (USGS 11740, USNM 108839). Genus EXOGYRA Say, 1820 Exogyra columbella Meek 1876. Exogyra columbella Meek, in Macomb, Rept. Expl. Exped. Santa Fe, N. Mex., to junction of Grand and Green Rivers, p. 124, pl. 1, figs. 3 a—d. (See synonymy in U. S. Geol. Survey Prof. Paper 242, 1952 [1953], p. 77.) This species is represented by one small internal mold in basal calcareous concretions of the Eagle Ford shale at the locality on the north-facing slope of Mountain Creek Valley, 2.5 miles north-northeast of Alvarado, Johnson County, Texas (USGS 14583). It occurs at the same stratigraphic position in a branch west of the Missouri-Kansas-Texas Railroad, 1.25 miles south of Grandview, Johnson County (USGS 14145), and in a road ditch 0.75 mile east of Lloyd, 0.5 mile north of Pleasant Home School, Denton County. FOr synonymy, description, types, and occurrence and range in Texas (see Stephenson, (1952 [1953], p. 77). The basal beds of the Eagle Ford shale is the highest strati— graphic position from which this species has been recorded in Texas. USNM 108865. Genus BREVICARDIUM Stephenson, 1941 Brevicardium? sp. One shell, a right valve, from the locality on Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County, Tex. (USGS 11740), is questionably referred to Brem'cardium Stephenson. In size and form the specimen agrees well with that genus. The shell, which is thin and frail, is embedded in fine hard cal- careous sandstone in such a manner that only its interior surface and margin are observable. Obscure radial lining on the internal surface and fine crenula- tions on the margin suggest the presence on the exterior surface of fine radial ribs such as characterize the genus Brem'cardium. The hinge features are obscure. The shell measures: Length 8.4 mm, height 7.5 mm, con— vexity about 2 mm. USNM 108850. Genus CAESTOCORBULA Vincent, 1910 Caestocorbula? sp. In the collections from two localities on Walnut Creek, about 4.75 miles east-northeast of Mansfield, Tarrant County (USGS 11740 and 14580), are several internal molds of a small bivalve mollusk belonging to the family Corbulidae, and questionably referred to the genus Caestocorbula Vincent. Remnants of shell sub- stance adhere to the molds over parts of their surfaces. The molds are plump centrally and anteriorly, and strongly constricted posteriorly, with a short truncation at the posterior end. The right valve bears small distinct, rather closely spaced concentric ribs on its lateral surface; the left valve is nearly smooth, but has weak concentric ribs. The reference of the molds to Caestocorbula Vincent is based on similarity in form and on the concentric ribbing on the right valve which, though finer, resembles that on, Caestocorbula cras- siplica (Gabb) from the Ripley formation of Mississippi and Tennessee. A selected right valve measures: Length 4 mm, height 2.8 mm, convexity about 1.5 mm. USGS 108851 and 108852. BASAL EAGLE FORD FAUNA IN JOHNSON AND TARRANT COUNTIES, TEX. ' 57 Class SCAPHOPODA Genus CADULUS Philippi, 1844 Cadulus sp. One small smooth incomplete tube partly embedded in hard matrix, from Walnut Creek, about 4.75 miles east-northeast of Mansfield, Tarrant County (USGS 11740), is referred to Oadulus Philippi. The tube as preserved is about 6 mm long, about 0.5 mm in di- ameter at the small end, increases to a maximum of 1.1 mm about 4 mm from the small end, and apparently becomes slightly constricted as it nears the incomplete large end. The tube is gently and evenly curved and appears to be slightly compressed, with long axis at right angles to the plane of curvature. may be compared with the closely similar species, Oadulus praetenuis Stephenson, from the Templeton member of the Woodbine formation in Grayson County, Tex. (1952 [1953], p. 143). USNM 108860. Class GASTROPODA Genus PSEUDOMELANIA Pictet and Campiche, 1862 Pseudomelania? basicostata Stephenson, n. sp. Plate 4, figures 4, 5 The three available specimens of this species are from Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County (USGS 11740). Shell small, spire of medium height with apical angle of about 34°, decreasing to about 25° on the larger whorls below. Protoconch not preserved. Suture sharply but not deeply impressed. Whorls 6 or 7; whorls of spire nearly flat on the sides, smooth except for obscure, microscopic spiral lining. Body whorl with a weak obtuse subangulation at the periphery. Basal slope steep, rounded in cross section, bearing on its lower two-thirds 3 or 4 flattish to round-crested spiral ribs, separated by narrower interspaces. Growth lines broadly convex in trend forward on the base, broadly concave forward above the periphery, slightly deflected backward just before reaching the suture above. Aperture not well preserved but apparently rather broadly lanceolate, with an acute angle at the rear and sharply rounded, though not channeled or notched at the front. Dimensions of the incomplete holotype, the largest of the three shells: Height 10+ mm, diameter 4.5 mm. The species is very much smaller than either P.? roanokcma Stephenson or P. ? ferrata Stephenson, from the Woodbine formation of Texas, and also differs in having spiral costae on the base. Types.—Holotype, USNM 108847; 2 unfigured paratypes, USNM 108858. , 339,390—55————2 The specimen , ridge out onto this projection. Genus LISPODESTHES White, 1877 Lispodesthes lirata Stephenson, n. sp. Plate 4, figures 6—11 The individuals of this species are present in con— siderable numbers in collections from two nearby localities on Walnut Creek, about 4.75 miles east- northeast of Mansfield, Tarrant County (USGS 11740 and 14580). The shell substance is very thin and fragile and it is impossible to separate any one indi- vidual in complete form from the hard matrix. How- ever, nearly all the features needed for description can be seen in a selected series of more or less fragmentary shells. Shell small, with plump body whorl and spire of medium height. Spiral angle about 46°, though some- what variable on different individuals. Protoconch apparently low turbinate, with about 1% coils. Suture closely appressed in a shallow depression. Whorls 4 or 5, gently convex on the side, expanding rather rapidly, bearing spiral lirae that may become covered with callus in adults. The body whorl of adults bears eight to twelve thin, low, threadlike spiral lirae, ranging from distinct to obscure and on different individuals from regularly to very irregularly spaced; those low on the base are most obscure. The growth lines are sinuous, being broadly convex in trend toward the front on the base and broadly concave forward on the side above the periphery. The periphery and base are broadly rounded, the latter becoming rather steep below. Aperture long- lanceolate, acutely angular at the rear, and passing in front into a rather long, narrow curved siphonal canal (beak). Outer lip broadly arched in the younger stages, expanding in adults into two pronglike pro- jections; The upper of the projections is long and narrow and curves upward spurlike; on the body whorl one of the upper lirae, usually the third one below the suture, becomes more prominent as it approaches the aperture, and extends as a sharply upraised ridge out on the upper projection to its tip. The lower projection is broader, shorter, and may end in a blunt, inbent point; one of the basal lirae extends as a slightly raised A groove on the inner surface of each projection, the upper one the deepest, is a reflection of the ridge on the outer surface. In the adult the mantle of the living organism spread outward away from both the inner and the outer lip and se- creted a layer of callus on the outer surface; in fully mature individuals callus may cover the entire shell, concealing the spiral lirae. In mature shells an anal channel incised in callus extends from the posterior angle of the aperture up the outer side of the spire to the apex. 58 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Dimensions of the incomplete holotype; Height 14 +mm, diameter, exclusive of the expanded lip, about 8.5 mm. A larger incomplete paratype (pl. 4, fig. 9), whose expanded wing is not uncovered, measures: Height 17+mm, diameter 7 +mm. The species is similar to, and closely related to Lispodesthes panda Stephenson, from the Templeton member of the Woodbine formation, but the spire of L. lirata is a little higher, the sides of the whorls are plumper, the upper spur of the expanded lip is more slender and its degree of upward curvature is less, and there is less of a tendency for the shell to become com- pletely covered with callus in the mature stage. L. patula Stephenson, also from the Templeton member, is larger and bears more numerous, finer, and more closely spaced spiral lirae. A closely related species in the western interior is Lispodesthes nuptialis White, from beds that are correlated by J. B. Reeside, Jr., with the Carlile shale. It is there associated with the ammonite Collignonicems woolgari (Meek) (=Prionotropsis woolgam' Meek) in a paleontologic zone (Turonian) that is stratigraphically higher and younger than the basal beds of the Eagle Ford shale. Types.—H0l0type, USGS 11740, USNM 108856; 3 figured paratypes, USGS 11740, USNM 108862; 2 figured paratypes, USGS 14580, USN M 108857; 15 selected unfigured paratypes, USGS 14580, USNM 108867; 15 unfigured paratypes, USGS 11740, USNM 108837. Occurrence.——At two adjacent localities on Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County, Tex. Genus CYLICHNA Loven. 1846 Cylichna? sp. At one of the localities on Walnut Creek about 4.75 miles east—northeast of Mansfield, Tarrant County (USGS 11740) several examples of a small gastropod having the form of Cyliclma Loven occur. These are mostly internal molds with a thin film of soft calcareous shell material covering parts of them. No indication of spiral lirae can be detected. The shell is subcylindri— cal, broadly bulging in profile, the body whirl enveloping all the earlier whorls. One specimen about maximum size measures: Height 3 mm, diameter 1.5 mm. USNM 108859. Class CEPHALOPODA Family DESMOCERATIDAE Genus DESMOCERAS Zittel, 1884 _ Desmoceras? sp. Plate 4, figures 12, 13 Two small incomplete ammonites from Walnut Creek, Tarrant County (USGS 11740), appear to belong to the Desmoceratidae, but are too immature to permit of their definite assignment to any one of the many genera into which that family group has been sub- divided. The shell is rather plump and smooth. the venter rather narrowly rounded, and the umbilicus small, though the coiling is not as close as it is in some members of the group. The ventral lobe is narrow and . deep and the ventral saddle small and bluntly pointed. ’ There are four relatively narrow complexly denticulate lateral saddles and four corresponding lobes; both lobes and saddles decrease rapidly in size from the venter to the line of involution. The figured specimen measures: Greatest diameter 9.5 mm, maximum radius center to venter 5.5 mm, dorsoventral diameter about 3.5 mm, corresponding transverse diameter about 4.5 mm. USNM 108830. Family ACANTI-IOCERATIDAE Genus ACANTHOCERAS Neumayr, 1875 Acanthoceras johnsonanum Stephenson, n. sp. Plate 4, figures 14—17 This species is represented by one incomplete medium- sized specimen from Johnson County, which apparently includes little, if any, of the living chamber. The shell is plump, subsquarish in cross section, flattened a little on the flanks; the adult volution embraces one- fourth or less of the preceding one. The ribs range from weak to moderately strong, becoming more prom- inent in the adult stage; they tend to alternate in prom— inence, about half of them reaching the umbilical shoulder in strength, where each bears a radially elongated, rather prominent node; the intervening ribs become weaker inward, some of them fading out be— fore reaching the umbilical shoulder. The venter is broadly convex. Each of the stronger ribs bears seven nodes, and most of the weaker intermediate ribs bear five nodes; the weakest rib noted bears only one very low midventral node. The nodes in the median row on the venter are of medium strength and slightly elongated in the younger stages, but become very weak and scarcely observable in the late adult stages. On each ventral angle there is a pair of nodes connected by a raised part of the supporting rib; in the early stages of growth the two paired nodes are cone shaped and subequal in strength and are a little more prominent than the midventral nodes; in the adult stage the outer node of each pair is a little the stronger and is slightly elongated radially. The suture is partly and not very clearly revealed. Enough can be seen to show that it is es— sentially acanthoceratid in pattern. Diameter of holotype, as preserved 110 mm (esti- mated) maximum radius center to venter about 60 mm; the dorsoventral diameter appears to be a little less than the corresponding transverse diameter at both the early and adult stages of growth. BASAL EAGLE FORD FAUNA IN JOHNSON AND TARRANT COUNTIES, TEX. 59 The species is similar in size and form to Accmtho- cems bellense Adkins, but in general is more strongly ornamented, having more numerous and more prom- inent ribs and nodes; a striking difference is the relative smoothness of A. bellense, especially in the area of the umbilical shoulder, on which the radially elongated nodes on the larger ribs are not only very weak but are set farther out on the flank from the line of involution than are the corresponding nodes on A. johnsonanum. Another difference is the cone-shaped outer node of the ventral pair on the adult of A. bellense in con- trast to the radial elongation of the corresponding node on A. johnsommum. Holotype.——From north-facing slope of Mountain Creek Valley, 2.5 miles north-northeast of Alvarado, Johnson County, USGS 14583, USNM 108846. Occurrence.—Recorded from the type locality only. Genus TARRANTOCERAS Stephenson, n. gen. Type species: Tarrantoceras rotatile Stephenson. Etymology: Tarrant County; Greek Kepas', a horn. The features that characterize this new genus are: relatively} small size; strong lateral compression; numerous, closely spaced radiating ribs that cross the venter with little or no diminution in size; seven rows of nodes on the earlier whorls, including a Weak row of median nodes that fades out in adult stages; a row of nodes on each ventral angle; a row of weak nodes on each flank about one-third the width of the flank inward from the ventral angle, this row fading out for- ward on later stages; radially elongated nodes on the main ribs at the umbilical shoulder; suture with a mod- erately deep ventral lobe and short blunt ventral saddle, a broad, relatively low, bifid first lateral saddle with roundedj nondigitate subelements, a broad, shallow digitate lateral lobe, and a second lateral saddle similar to the first, but protruding farther forward on the flank; umbilicus one-third to two-fifths the total diameter of the shell. The shell of Tarrantoceras, though similar in form and ribbing to that of Ammonites mantelli J. Sowerby, the genotype of Mantelliceras Hyatt, is more compressed than that species and possesses a different and simpler suture pattern. According to Wright and Wright (1951, p. 24, 37), Mantellicems mantellvl is restricted to the specimen figured by Sharp (1853, p. 40) in his plate 18, figures 7a—c; the suture shown in his figure 70 includes 3+ relatively narrow, high digitate saddles and part of a fourth saddle; in contrast the exposed suture of Tarrantoceras includes only two relatively low broad lateral saddles, the elements of which are rounded (nondigitate), separated by a relatively broad, shallow digitate lobe. Apparently Mantellicems does not possess a medium row of ventral nodes. In form and Ornamentation Tarrantocems rotatile, the genotype of this new genus, is very similar to Eucalycocems pentagonum (Jukes—Browne), the geno- type of Eucalycoceras Spath. The sutures, hOWever, are markedly different in the two species, so different in fact that, in my opinion, they cannot be considered as congeneric. This opinion is based on a comparison of T. rotatile with an incomplete topotype of E. pen— tagonum from the Holaster subglobosus zone (Ceno- manian) of England; in this English species the first and second lateral saddles are high and narrow and are separated by a deep, narrow, digitate lobe; the sub- elements of the saddles are narrowly rounded, almost digitate. In strong contrast the first and second lateral saddles of T. rotatile are low and broad, with broadly rounded subelements, and the intervening lobe is broad and shallow; this type of suture is con- sistent in the holotype and in five of the paratypes of T. rotatile, and also in the three other species of Tar- rantoceras here recognized in the basal Eagle Ford of Tarrant and Johnson Counties. In other words, here is a group of four species possessing closely similar suture patterns, which differ markedly from the suture of the topotype of Eucalycocems pentagonum cited above. Tarrantdceras rotatile Stephenson, n. sp. Plate 5, figures 1—10 Shell small, coiled in one plane, each whorl em- bracing about the outer one-third of the flanks of the preceding whorl. Flanks compressed, being only slightly convex in cross section. Radial. ribs closely spaced, numbering 44 on the largest whorl of the holotype; of these only 14 reach the umbilical shoulder in strength and bearing prominent shoulder nodes; the others are intercalated between the strong ribs and either die out well down on the flank, or reach the umbilical shoulder with Weak unnoded termini. All the ribs are about equal in strength at the ventral angle. The number of smaller and weaker ribs between two strong ribs ranges from one to three. The ribs are gently sinuous, there being a slight curvature in trend backward well out on the flank and a slight bend for- ward as the ribs approach. the ventral angle. Each rib as a whole is inclined a little forward, and all the ribs cross the venter with no diminution in strength. In the earlier stages each strong rib bears seven nodes. There is a median row of ventral nodes that becomes weaker toward the front and dies out at a shell diameter of about 50 mm. Each rib bears a strong, beadlike node at, each ventral angle; in the holotype these nodes tend to become weaker in the forward direction, but are still observable at its largest stage. On the \ribs of each flank there is a row of 60 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY lateral nodes spaced about one third the width of the flank inward from the ventral angle; these nodes are much weaker than the nodes on the ventral angle and become weaker toward the front, disappearing at shell diameters of 30 mm or more on different individuals; this row is too far away from the ventral angle to be considered as paired with the row on that angle. A fairly prominent node elongated slightly in the radial direction is present on each strong rib at the umbilical shoulder. In the holotype the living chamber is nearly com- pletely represented and includes more than half the last whorl. The sutures nearest the inner end of the living chamber are Well preserved. The ventral lobe is deep and broad, and has three principal and several minor digitations on each side, the lOWer ones forming a pair embracing the ventral saddle. The ventral saddle is short, rising about one-fourth as high as the lobe is deep; it is weakly trifid on its forward blunt end. The first lateral saddle is broad and relatively short and is divided by a short, narrow sublobe; each subsaddle thus formed is weakly trifid and the elements are broadly rounded, that is, nondigitate. The lateral lobe is smaller than the ventral lobe, and is short, broad and digitate. The second lateral saddle is nearly as large as the first, is similarly divided, protrudes for- ward on the flank, and extends to the line of involution. Dimensions of the holotype: Diameter 61 mm; maximum radius center to venter 36 mm; dorsoventral diameter 21 mm; transverse diameter about 18 mm; maximum diameter of umbilicus 21 mm. The species is closely related to Tarmntoceras sellardsi (Adkins), (=Mantelliceras sellardsi Adkins), from the Bouldin member of the Lake Waco formation (of Adkins and Lozo). It differs from that species in having more prominent ribs, wider umbilicus and smaller, beadlike nodes in the median ventral row in contrast to the coarser, more elongated nodes in the median ventral row of Adkin’s species. Types.—Holotype from Walnut Creek, 4.75 miles east- northeast of Mansfield, Tarrant County, USGS 11740, USNM 108835; 2 figured paratypes from the same source, USNM 108854; 7 unfigured paratypes from the same source, USNM 108863; 1 unfigured paratype, USGS 14580, USNM 108853; 1 unfigured paratype, USGS 11740, USNM 108855. Occurrence.-—Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County, USGS 11740 (3 figured), 14580. Tarrantoceras stantoni Stephenson, n. sp. Plate 5, figures 11-21 In the collection from Walnut Creek, Tarrant County (USGS 11740) are 15 more or less incomplete and fragmentary specimens that resemble Tarrantocems rotatile Stephenson except that they differ in the details of their ornamentation, and slightly in form. The largest specimen is nearly as large as T. rotatile but the shell is plumper, the radial ribs are fewer and not so closely spaced, the nodes are stronger in all the rows, presenting a subspinose effect, especially in the younger stages. The holotype is a specimen from near Lillian, Johnson County, furnished by J. P. Conlin. The species is similar to T. rotatile in form and gen- eral appearance, in the number and spacing of the node rows, and in the pattern of the sutures. As in that species the nodes in the row on the flank become weaker forward and fade out in the later stages, and the nodes in the median row on the venter become weaker toward the front, and are wanting on the largest stage represented in the collection. The nodes on the ventral angles continue strong on all but the latest stage of adults. Several specimens representing young stages of growth indicate initial close ceiling with an envelopment of more than half the preceding coil. In late stages the envelopment is one-fourth or less of the preceding coil. Approximate dimensions of the holotype: Greatest diameter 60 mm, maximum radius center to venter 36 mm, maximum dorsoventral diameter 25 mm, cor- responding transverse diameter 18 mm. The diameter of the smallest specimen in the collection, which lacks the living chamber, is 7.5 mm. Fragments among the paratypes from Johnson County indicate that individuals may attain somewhat larger size than the holotype, and may become plumper in late stages of growth. On one fragment of the large end of an adult (plate 5, fig. 21), senility is indicated by the weakening and closer spacing of the ribs and the shortening of the dorsoventral diameter. The species is named in honor of the late Dr. Timothy W. Stanton. ' Types.—-The holotype, the most complete available specimen of‘ this species, Was generously supplied by J. P. Conlin, by exchange of the best, though less complete, specimen of the same species in the collection from Walnut Creek. Conlin found his specimen in a gully in a cultivated field about 1 mile north of Lillian, Johnson County, Tex. (USGS 24510, USNM 108866). Three figured paratypes, USGS 11740, USNM 108861; 11 unfigured paratypes, USGS 11740, USNM 108836. One figured paratype, USGS 14583, USNM 108845; 3 unfigured paratypes, USNM 108843. Occurrence—Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County, USGS 11740; north-facing slope of Mountain Creek Valley, 2.5 miles north-northeast of Alvarado, Johnson County, USGS 14583; an erosion gully in a cultivated field about 1 mile north of Lillian, Johnson County (J. P. Con- in’s 100. no. 4551). Tarrantoceras lillianense Stephenson, n. sp. Plate 5, figures 22—27 This species is represented by nine specimens that possess features of form and sculpture intermediate between those of Tarrantoceras rotatile and those of BASAL EAGLE FORD FAUNA IN JOHNSON AND TARRANT COUNTIES, TEX. 61 T. stantoni. Compared with the former the flanks are plumper, and in the adult stage the ribs are fewer, a little coarser and more widely spaced, and the nodes on the ventral angles and on the umbilical shoulders are a little coarser; the sutures are essentially identical, presenting shallow lateral lobes and broad, low saddles with rounded forward elements. Compared with T. siantom' the flanks are of about the same plumpness but the ribs are more numerous and weaker, and the nodes are much less conspicuous, lacking a spinose effect; on this species the ventrolateral rows of nodes are more closely spaced than they are on T. stantom'. The holotype is an incomplete internal mold (about half a volution) having some shell adhering, represent- ing mainly the living chamber and bearing 22 radiating ribs. The imprint of part of the venter of the pre- ceding volution is present on the inner curve of the specimen and a rubber cast of this imprint is shown in plate 5, figure 25. Dimensions of the holotype are: Greatest diameter 56 mm, dorsoventral diameter 20 mm, corresponding transverse diameter 19 mm, di— ameter of umbilicus 20 mm. The figured paratype, representing a younger stage, measures: Greatest diameter 33 mm, radius center to venter 21 mm, dorsoventral diameter about 14 mm, corresponding transverse diameter about 14 mm, diameter of umbilicus 10 mm. Types.—Holotype from a gully in a field 1 mile north of Lillian, Johnson County (J. P. Conlin, collector), USGS 24510, USNM 108841; 1 figured paratype, USGS 11740, USNM 108848; 7 unfigured paratypes, USGS 11740, USNM 108838. Occurrence.——Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County; a concretion in an erosion gully about 1 mile north of Lillian, Johnson County. Tarrantoceras multicostatum Stephenson, n. sp. Plate 6, figures 21—23 Two incomplete internal molds that possess the essential characters of Tarrantocems Stephenson, differ specifically from T. rotatile Stephenson. The adults are somewhat larger than T. rotatile, are plumper on the flanks, more rounded on the venter and have smaller and weaker ventral nodes. The most striking difference, however, is the greater number of costae; 30 costae can be counted on the large incomplete volution of the holotype (pl. 6, fig. 21), which includes ’ less than half a turn; it is estimated that the complete volution must'have possessed 60 or more costae, in contrast to the 44 connted on T. rotatile. The um- bilical nodes on the larger costae are prominent and radially elongated. In the mold of the holotype of T. multicostatum a little more than half the living chamber is represented, back of which are parts of 2 or 3 badly corroded sutures. In the paratype, which probably includes about half the living chamber, part 3.39390~55 3 of the last suture is more clearly preserved than are the sutures in the holotype; as thus revealed the sutures appear to be essentially like those of T. rotatile. Except for their greater number and the smaller size of their nodes the costae of the present species are similar to those of T. rotam'le; the number of smaller costae betWeen the larger costae ranges from 2 to 4. The approximate dimensions of the holotype as preserved are: Diameter, 67 mm, dorsoventral di— ameter 25 mm, corresponding transverse diameter, 23 mm, maximum radius center to venter 41 mm, and maximum diameter of the umbilicus 28 mm. Types.—Holotype, USNM 108844; paratype, USNM 108842. Occurrence—The holotype and paratype, the only available specimens, are from the north-facing slope of Mountain Creek Valley, 2.5 miles north-northeast of Alvarado, Johnson County, Tex. (USGS 14583). Genus EUOMPHALOCERAS Spath, 1923 Type species: Ammonites euomphalus Sharpe 1923. Euomphaloceras Spath, Great Britain Geol. Survey Summary of Progress (1922), App. 2, p. 144. 1951. Euomphaloceras Spath. Wright and Wright, Paleont. Soc., Mon., London (revision of Sharpe’s Mollusca of Chalk of England), p. 29, 36. (Includes synonymy of the genus.) Acanthocems lonsdalei Adkins (1928, p. 244) from the base of the Eagle Ford shale in Bell County, A. alvamdoense Moreman (1942, p. 205) from the same stratigraphic position in Johnson and Tarrant Counties, and A. eulessanum Stephenson (1952 [1953], p. 201) form the Lewisville member of the Woodbine formation in Tarrant County, appear to be American representa- tives of the genus Euomphaloceras Spath. The features that distinguish this genus from Acanthoceras Neumayr are: a median row of small ventral nodes that fade out in later stages; typically these nodes number two or more times as many as the nodes in either of the two adjacent rows of ventrolateral nodes; however, the comparative number of the small nodes in the median row is extremely variable in different species; the nodes in the outer ventrolateral row (farthest from the midline of the venter) are much more prominent than those of the corresponding row in Acamhoceras, and these outer nodes increase in prominence in the later stages of growth becoming strikingly prominent in large adults; in general the system of ribs and nodes in Acanthoceras is more regular than in Euomphalocems. J. P. Conlin, of Burleson, TeX., has shown me a fragment of a large ammonite (specimen 4621 in his private collection), which possesses an unusual ventral feature. The large prominent nodes of this specimen seem to ally it with the genus Euomphalocems, but its specific identity was not determined. The fragment 62 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY pertains to the living chamber probably just back of the aperture. The specimen is subquadrate in cross section, with dorsoventral diameter of about 105 mm and corresponding transverse diameter between the ribs of about 95 mm. The ribs on the flank are non- prominent and widely separated and bear moderately prominent, somewhat elongated nodes on the umbilical shoulder. The fragment includes two ribs on the flank, each bearing a large prominent node on the ventral angle, with a third rib, the one farthest forward partly broken away on the flank, but with the ventral portion intact. The two pairs of nodes farthest from the aper- ture are connected by broad, gentle swells of the other- wise smooth ventral surface. In striking contrast the two nodes farthest forward are connected by a prom- inent transverse ridge that rises wall-like across the venter. Another large specimen in Conlin’s private collection (5560), probably also a species of Euomphalocems, from the classic Bird Creek locality in Bell County, possesses a closely similar wall-like feature on the venter between the two nodes farthest forward. Conlin also reports a poorly preserved specimen, probably Euomphalocems alvaradoense (Moreman), from 4 miles south of Alva— rado, which shows the same wall—like feature between the two anterior nodes. This feature, having been observed in three specimens from three widely separated basal Eagle Ford localities, is obviously not rare in large ammonites at that stratigraphic position. The location of the feature near the aperture of the shell suggests that it may be some sort of a gerontic mani- festation; since, however, gerontic features usually take the form of constrictions, rather than expansions, the real biologic meaning of the wall-like ventral ridge connecting the two anterior ventral nodes remains to be determined. Euomphaloceras lonsdalei (Adkins) Plate 6, figures 6—20 1928. Acanthoceras lonsdalei Adkins, Tex. Univ. Bull. 2838, p. 244, pl. 26, fig. 5; pl. 27, fig. 3. Acanthoceras lonsdalei Adkins. Moreman, Jour. Pale- ontology, v. 16, no. 2, p. 204. 1942. The holotype of Euomphaloceras lonsdalei (Adkins) is a medium-sized specimen having a diameter of 110+ mm; the specimens from Tarrant and Johnson Counties are smaller than the holotype; one fragment from Bell County, a topotype, pertains to a specimen larger than the holotype. The largest available measurable topotype is 44+ mm in diameter and the diameter of the smallest specimen, from Tarrant County is 8.5 mm; the available specimens present a nearly complete range in size between these extremes. Assuming that all these specimens are correctly referred to Adkin’s species, a considerable individual variation in the size and distribution of the nodes and costae, and in minor details of the suture patterns, is indicated. The holotype as now available to me is incomplete; the anterior part of the holotype as shown in Adkins original figure presumably is lost; it probably included part of the living chamber; at any rate the broken large end of the holotype in its present condition shOWS traces of a septum that may have been the last one immediately back of the living chamber. Using the available part of the holotype, two topo— types, and 20 or more smaller specimens from sandy limestone at the base of the Eagle Ford shale in Tarrant and Johnson Counties, a more detailed description of the species may be given than was possible with the original material. The shell is medium sized, exceeding a measured diameter of 110 mm. It is plump, broad and broadly rounded on the venter, and flattish on the flanks. In the early stages of growth the advancing shell envelopes more than half of the preceding volution, but in the later stages the degree of envelopment may be one-third or less the width of the flank. The ribs are weak to medium strong except as they are made prominent by nodes on the ventral angles and flanks. The ribs present on the flanks number 14 or 15 to the volution; in adults they trend nearly directly across the flanks, but in the younger stages they bend forward at the ventral angles; 7 or 8 larger ribs extend inward in strength to the umbilical shoulder, but in larger specimens the number reaching the shoulder may in- crease to 12 or 13; intermediate smaller ribs, which may be weak or of ordinary strength at the ventral angles, die out on the flanks before reaching the umbilical shoulder, or about at the shoulder. On the venter in each space between the larger ribs of adults are one or two additional weak transverse ribs; these are few or wanting in the small, early stages of the shell. The larger ribs that reach the umbilical shoulder bear prominent, radially elongated nodes at their inner ends. Each of the larger ribs bears a pair of rather Widely separated nodes at each ventral angle; the inner node of each pair (nearest the midline of the venter) is the smaller and is slightly elongated parallel to the venter; the outer node is prominent, cone shaped, and the successive nodes of this row increase in promi- nence in the forward direction; the nodes in the median row on the venter are smaller and more numerous than those in either of the lateral ventral rows; in this median row there is one small node on each rib, whether large or small, that crosses the venter; on the smaller ribs on the venter there may or may not be a small ventro- lateral node in line with the inner lateral row of nodes. The sutures are not observable on the holotype nor on the smaller of the two topotypes. Traces only of u the sutures appear on the larger topotype. Sutures are Well preserved on the small plesiotypes and on several of the selected examples. Ventral lobe deep and rather wide, with parallel digitate sides, ending below in two longitudinal prongs that enclose a squarish ventral saddle; the latter rises about one-third as high as the lobe is deep, its blunt forward end indented with one or more small notches; first lateral saddle broad, about as high as the ventral lobe is deep, and rendered bifid by a small, narrow sublobe; each sub— saddle thus formed is subdivided into three parts by small lobules; each of the small elements of the saddle formed by the sublobe and lobules is simple and rounded on its front; the first lateral lobe is rather broad, digitate, and shallower than the'ventral lobe; the second lateral saddle is much smaller than the first and in the early stages of the shell is broken into three small, simple elements by lobules; the second lateral lobe is small with three digitations; two small, simple saddles separated by a small, pointed lobe intervene between the second lateral lobe and the line of involu- tion; in the stage reached by the largest of the four plesiotypes from Tarrant County the saddles are rendered somewhat less simple by the appearance of additional small lobules or notches. Dimensions of the part of the holotype that is avail- able for measurement: Diameter 85 mm; maximum radius from center to venter about 53 mm; dorso- ventral diameter of volution at broken end 35 mm; corresponding transverse diameter about 45 mm; diameter of umbilicus about 28 mm. The maximum diameter of the holotype, including the part at the large end that appears on the original illustration and now presumed to be lost, is 110+ mm. Types.—Holotype, Bureau of Economic Geology, Austin, Tex., 2410; 2 plesiotypes (=topotypes), USGS 11845, USNM 108831; 4 plesiotypes, USGS 11740, USNM 108824; 9 selected examples, USGS 11740, USNM 108823. Occurrence.——Holotype and two topotypes, Bird Creek near Belton—Temple Highway, about 4 miles east-northeast of Bolton, Bell County; north-facing slope of Mountain Creek Valley, 2.5 miles north-northeast of Alvarado, Johnson County, USGS 14583; Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County, USGS 11740. Euomphaloceras alvaradoense (Moreman) Plate 7, figures 1—9 1942. Acanthoceras alvaradoense Moreman, Jour. Paleontology, v. 16, no. 2, p. 205, pl. 32, fig. 6; text fig. 2, O, T. This species occurs in considerable numbers at two localities (USGS 11740, 14580) in Tarrant County and at a locality (USGS 14583) in Johnson County about 6.5 miles north of the type locality of the species. The specimens range from fragmentary to nearly complete in form, and from a minimum diameter of BASAL EAGLE FORD FAUNA IN JOHNSON AND TARRANT COUNTIES, TEX. 63 about 16 mm to about 100 mm. However, one large internal mold of about the posterior half of a living chamber, found loose in the bed of Walnut Creek at one of the outcrops of the basal beds of the Eagle Ford shale in Tarrant County (USGS 14582), is in- terpreted to represent an adult stage of the species; the dorsoventral diameter of the volution at the large end of this fragment is 78 mm and the corresponding transverse diameter is about 80 mm. The features that indicate the closer relationship of the species to Euomphalocera-s Spath than to Awn- thocems Neumayr are the large nodes composing the outer of the two ventrolateral rows of nodes, which increase regularly to large size as growth proceeds, and occasional small intermediate ribs and nodes be— tween the regular ribs on the venter. Of the two species of Euomphalocems in the basal beds of the Eagle Ford shale this species is least like the genotype, E. euom- phalum, in that there is only a meager development of small medial ventral nodes. Form plump, cross section subquadrate, flanks and venter gently convex; ribs nearly direct, 16 or more to the volution in early stages, 12 or 13 in later stages, ranging from weakly developed to medium strong on different individuals. In the early stages a pair of ventrolateral nodes is present on each ventral angle of each main rib, the inner one (nearest the midline of the venter) slightly elongated and equal to or larger than the outer one, which is cone shaped or slightly elongated; the nodes of each pair are joined by a slightly higher swelling of the rib on which it stands, and the outer node leans away from the venter at an angle of about 45 degrees; as growth proceeds the inner nodes on the inner row gradually become weaker and eventu-. ally coalesce with those in the outer row to form large cone-shaped nodes that continue to increase in strength to the largest observed stage of growth. The com- plete coalescence is accomplished on different in- dividuals at shell diameters ranging from 65 to 90 mm. A median row of ventral nodes is present in early stages; these nodes are cone shaped or slightly elongated, weak, and die out on different individuals at different stages of growth, usually at a shell diameter of 65 mm or less, but may be represented by weak swellings at diameters as great as 125 mm; most of the nodes in the median row lie in alinement with nodes in the ventrolateral rows on the main ribs, but additional weaker nodes may be present on weak intermediate ventral ribs. Nearly all the main ribs bear radially elongated nodes on the umbilical shoulders. The suture pattern is not observable on some of the specimens but may be clearly seen on others, especially on some of the smaller ones. The suture is of the acan- thoceratid pattern. There is a deep, quadrangular, . 64 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY . digitate ventral lobe; a short quadrangular ventral saddle enclosed between two straight terminal prongs of the ventral lobe, the forward end divided by one, two, or three shallow notches; first lateral saddle broad, divided into two subsaddles by a small digitate sublobe, the subsaddles further divided by lobules into three small denticulate elements rounded on the front; first lateral lobe relatively small, digitate; second lateral saddle relatively small with three or four rounded small denticulate elements; another very small lobe or lobule is followed by two or three small saddles separated by small lobes, to the line of involution. Dimensions Of holotype: Diameter 125 mm; maxi- mum radius center to venter about 76 mm; dorso- ventral diameter 45 mm; transverse diameter measured on ribs 52 mm; between ribs 45 mm; diameter of umbilicus 37 mm. A medium-sized incomplete in- dividual, with about half the living chamber repre— sented, measures: Diameter 89 mm; maximum radius center to venter about 52 mm; dorsoventral diameter at large broken end 34 mm; corresponding transverse diameter of volution measured on ribs about 40 mm; maximum diameter of umbilicus about 28 mm. The large fragment of an internal mold representing about half of the living chamber, previously mentioned, probably indicates that adults of the species attained a diameter of 270 mm or more. Types.—The holotype, from Johnson County, 4 miles south Of Alvarado, the only specimen available at the time of the original description, is in the Moreman collection at the Bureau of Economic Geology, University Of Texas, Austin, Tex. (BEG 19801). Two plesiotypes, USGS 11740, USNM 108822; 1 plesiotype, USGS 14582, USNM 108828; 1 plesiotype, USGS 14583, USMN 108825; 12 selected examples, unfigured, USGS 14583, USNM 108826; 4 selected examples, unfigured, USGS 14580, USNM 108827; 6 selected examples unfigured, USGS 11740, USNM 108829. Occurrence.—Walnut Creek, about 4.75 miles east-northeast of Mansfield, Tarrant County, USGS 11740, 14580, and 14582; north—facing slope of Mountain Creek Valley, 2. 5 miles north- northeast of Alvarado, Johnson County, USGSI14583; 4 miles south of Alvarado (holotype). Genus BORISSIAKOCERAS Arkhanguelsky, 1916 1916. Borissiakoceras Arkhanguelsky, Com. geol. Petrograd Mém., (N. S.), v. 152, p. 55, pl. 8, figs. 2, 3. 1935. Borissiakocems Arkhanguelsky. Morrow, Jour. Paleon- tology, V. 9, No. 6, p. 463—465. (Genus discussed in connection with the description of the species, B. reesidei Morrow.) In its general form, its rounded venter, the presence of a row of short, oblique nodes on the ventral angle, the essential similarity of its sutures, and the presence of lateral and ventral crests, the species Borissiakocems orbiculatum Stephenson agrees closely enough with the genotype, B. mirabile Arkhanguelsky, to indicate a con— generic relationship. In Grayson County, Tex., the genus has been recognized stratigraphically as high as the Metoicocems whitez' zone of the Eagle Ford shale (USGS 14555). One fragment of an ammonite from the Lewisville member of the Woodbine formation, identified as Euhoplit'es? sp. (Stephenson 1952 [1953], p. 198, pl. 45, figs. 5, 6) should have been referred to Borissiakoceras. Morrow (1935, p. 463—465) referred two species from the Upper Cretaceous of the western interior to Borissiakocems, one, B. reesidei, from the upper part of the Graneros shale, south of Wilson, Elsworth County, Kans., and the other, B. aplatum, from the upper part of the Blue Hill shale member Of the Carlile shale, south of Tipton, Mitchell County, Kans. As figured, both Of these species are less compressed and more rounded on the venter than B. orbiculatum, and they both lack ventrolateral nodes. Specimens from the western rim of the Black Hills in Wyoming (USGS 12649), Obtained from a dark limestone concretion in beds correlated by Cobban and Reeside (1952 cor. chart) with the lower part of the Greenhorn limestone, (pl. 6, fig. 5), are very similar in form and suture pattern to B. orbiculatum, but most of the individuals have a less conspicuous development of the ventral nodes; however, weak nodes are present and on some the nodes are stronger than on others. This difference, though slight, appears to be fairly consistent in a dozen or more individuals and with the limited available material it seems advisable to regard the Black Hills specimens as belonging to a separate undescribed species. There is also an undescribed species of Borissiakoceras from a Cretaceous locality 1 mile northeast of Wilcox, Wyo.; it has a thin disklike form, an excavated venter, a narrower umbilicus, and a more elaborate suture pat— tern, than has B. orbiculatum. Borissiakoceras orbiculatum Stephenson, n. sp. Plate 6, figures 1-4 This species is represented in the basal beds of the Eagle Ford shale by three specimens from Walnut Creek, Tarrant County, Tex. (USGS 11740). Shell small, strongly compressed, rounded on the venter, each volution enveloping about three-fifths of the pre- ceding one. Flanks fiat, diverging slightly outward; ribs represented by obscure, widely spaced, gently sigmoidal undulations, each with a short node, oblique forward, at each ventral angle. N 0 other nodes present. Venter nearly semicircular in cross section at early stages, obtusely subangular at each edge in later stages. On a juvenile stage of one of the three specimens evi- dence Of a small, threadlike ventral keel was noted on the exterior of the shell, but this keel was accidentally destroyed in preparation; it was not reflected on the underlying internal mold. Two specimens of the closely BASAL EAGLE FORD FAUNA IN JOHNSON AND TARRANT COUNTIES, TEX. 65 related, undescribed species from the western rim of Black Hills, Wyo., previously mentioned, each bears an imprint of a small, threadlike, evenly beaded ventral keel at an early stage of growth; among the 16 speci- mens from this locality these 2 are the only ones that reveal the presence of a keel. Growth lines gently sigmoidal on each flank indicate a weak lateral crest; the growth lines also indicate a rather pronounced ventral crest. Umbilicus small, about one-fourth the diameter, with steep, rounded sides. The sutures are not clearly revealed on the holotype, which is chosen for its size and perfection of form, but are uncovered on one small paratype. The ventral lobe is broad, simple, and of moderate depth; the ventral saddle is simple, broadly rounded, and about one-third as high as the lobe is deep. The lateral suture pattern is simple; the first lateral saddle is rendered bifid by a shallow notch; the first lateral lobe is much smaller than the ventral lobe and may be simple or weakly bifid; the second lateral saddle is about as broad as the first and is similarly bifid; the second lateral lobe is about as deep as the first, but is narrower and is simple; between this lobe and the line of involution are two smaller simple saddles separated by a shallow simple lobe. One specimen of the closely related species from the locality on the western rim of the Black Hills, shows the sutures at a later stage of growth perfectly preserved (pl. 6, fig. 5); they are like the suture in B. orbiculatum except that two or three additional small notches appear in the lateral saddles. Dimensions of the holotype, an individual that probably includes most of the living chamber: Diameter 22.5 mm,~maximum radius center to venter 14 mm, dorsoventral diameter of volution near the aperture about 9 mm, corresponding transverse diameter about 4.5 mm, width of volution from line of involution to venter near aperture 11 mm, maximum diameter of umbilicus about 5 mm. Types.—Holotype, USNM 108832; 2 figured paratypes, USNM 108833. Borissiakoceras sp., from western rim of Black Hills, Wyoming, figured for comparison of sutures, USGS 12649, USNM 108834. Occurrence—Found only at the type locality on Walnut Creek, 4.75 miles east—northeast of Mansfield, Tarrant County (USGS 11740). Adkins (1933, p. 433) lists the genus Boris— siakocems, n. sp., from Walnut Creek, but does not state the exact locality. LITERATURE CITED Adkins, W. S., 1923, Geology and mineral resources of McLennan County: Tex. Univ. Bull. 2340, 202 p., 4 pls., geol. map. —— 1928, Handbook of Texas Cretaceous fossils: Tex. Univ. Bull. 2838, 303 p., 37 pls. 1933, The geology of Texas; pt. 2, The Mesozoic systems in Texas: Tex. Univ. Bull. 3232, p. 239—518 (esp. p. 423—432). Adkins, W. S., and Arick, M. B., 1930, Geology of Bell County, Texas: Tex. Univ. Bull. 3016, 92 p., 2 figs., geol. map. Adkins, W. S., and Lozo, F. E., 1951, Stratigraphy of the Wood- bine and Eagle Ford, Waco area, Texas, in Adkins, W. S., and others, 1951, The Woodbine and adjacent strata of the Waco area of Central Texas: Fondren Sci., Ser. 4, [Dallas], p. 101—164, 6 pls., 26 figs. Cobban, W. A., and Reeside, J. B., Jr., 1952, Correlation of the Cretaceous formations of the western interior of the United States: Geol. Soc. America Bull., v. 63, p. 1011—1044, fold- ing chart. Jukes—Browne, A. J., and Hill, W. M., 1896, A delimitation of the Cenomanianflbeing a comparison of the corresponding beds in southwestern England and western France: Geol. Soc. London Quart. Jour. v. 52, no. 206, p. 99—178 (esp. p. 156, pl. 5, fig. 1). Moreman, W. L., 1927, Fossil zones of the Eagle Ford of north Texas: Jour. Paleontology, v. 1, no. 1, p. 89—101, pls. 13—16. ————— 1933, quoted in Adkins, W. S., The Geology of Texas; pt. 2, The Mesozoic systems in Texas: Tex. Univ. Bull. 3232, p. 425—426. ' 1942, Paleontology of the Eagle Ford group of north and central Texas: Jour. Paleontology, v. 16, no. 2, p. 192—220, pls. 31—34, 2 figs. Morrow, A. L., 1935, Cephalopods from the Upper Cretaceous of Kansas: Jour. Paleontology, v. 9, no. 6, p. 463—473, pls. 49—53, figs. 1—8. Sharpe, Daniel, 1853, Description of the fossil remains of M01- lusca found in the Chalk of England, pt. 1, Cephalopoda: Palaeont. Soc. Mon., London, 70 p., 27 pls. Spath, L. F., 1923, On the ammonite, horizons of the Gault and contiguous deposits: Great Britain Geol. Survey Summary of Progress (1922), app. 2, p. 139—149. Stephenson, L. W., 1946, Alunite at Woodbine-Eagle Ford con- tact in northeastern Texas: Am. Assoc. Petroleum Geol- ogists Bull., v. 30, no. 10, p. 1764~1770. 1952 [1953], Larger invertebrate fossils of the Woodbine formation (Cenomanian) of Texas: U. S. Geol. Survey Prof. Paper 242, 226 p., 59 pls. —— 1953, Mollusks from the Pepper shale member of the Woodbine formation: U. S. Geol. Survey Prof. Paper 243—E, p. 57—68, pl. 13. , Wright, C. W., and Wright, E. V., 1951, A survey of the fossil Cephalopoda of the Chalk of Great Britain: a revision of Sharpe (1853) Description of the fossil remains of Mollusca found in the Chalk of England, pt. 1, Cephalopoda: Palaeont. Soc. Mon., London, p. 1—40. Abstract ...... Acanthocerus" alvaradoeme .......................... 53, 55, 61, 63 burcusi ______________________________________ 54 bellense. ........ ._- 53, 59 eulessanum _________ 61 johnsonanum._ ........ 55 58, 59; pl 4 lomdalei ................................. 53, 61, 62 peppereme .................................. 53 nephemoni. 53 validum ..................................... 53 sp .......................................... 55 Acanthoceratidae .................. 58 alvaradoense, Acamhoceras... __. 53,55, 61, 68 Euomphaloceras ..... . 54, 55, 62, 65; pl. 7 Ammonites euomphalus _________________________ 61 mantelli .................................... 59 aplatum, Borissiulcoceras ....... 64 armnus, Inoceramus _________________ 54,55; pl. 4 B barcusi, Acam‘hoceras ....... ' ..................... 5 4 Euomphaloceras ............................ 54 basicostata, Peeudomelania__ __ 57; pl, 4 . bellense, Acamhoceras ......................... 53, 59 Bluebonnet flag member of Lake Waco shale- 53, 54, 55 Borisslaokceras __________________________________ 64 aplatum ____________________________________ 64 mirabile ................ 64 orbiculatum. __ ________ 55, 64, 65; pl. 6 reesidei ...................... 64 sp ................................. 55,64,65; pl. 6 Bouldin flag member ___________________________ 53, 56 Brem'cardium. . . .. 56’ 56' C Cadulus ........................................ 57 praetmuis ............................. 57 sp .................... 57 Caestocorbula. .. __________________________ 56 crasaiplica. . 56 ................ 66' Carlsile shale ........... 58, 64 Collwnomceras woolaari. 58 columbdla, Eroauru __________________________ 54, 55,56 crassiplica, Caestocorbula ________________________ 56 Cylichm ............. . 55,58 sp ................................. __- 55, 58 D Desmoacertu...._..__.__...-..__-....___-__1_._. 58 sp ....................................... 58; pl. 4 Desmoceratidae ........... . ..................... 5 8 E Eagle Ford shale ............................... 53 flag member ........................... 53 Eucalucoceras leoneme ..................... _ 53, 54 pentagmum- - . 59 55 INDEX [Italic numbers indicate descriptions] Page Euhoplz‘tea sp ................................... 64 eulessanum, Acanthoceras ....................... 61 Euomphuloceras ______________ . 54 Euomphaloceras. . ________________________ 61 aloaradoeme. __________ 54 55, 62, 6'3 pl 7 burcusi ..................................... 54 eulessanum ................................. 54 euomphalum 63 lonsdalei ____________________________ 54, 55, 02; pl. 6 euomphalum, Euomphaloceras ___________ 63 euomphalus, Ammonites .............. 1 51 Exogyra ______________________________ 56' columbella ............................... 54, 55, 56 F ferrata, Pseudomelania __________________________ 57 fragilis, Inoceramus _____________________________ 54 G _ Graneros shale .................................. 64 Greenhorn limestone ___________________________ 64 Gymnentome valida .............................. 55 H Holaater subglobosus ............................. 59 i I Inoceramus _____ L ............................... 55 armmus. fragilia ...................................... 54 i J johmonanum, Act‘amhoce‘ras ............. 55,58, 59; pl. 4 1' L Lake Waco shale _______________________________ 53 subunits 0L1 ............................... 53,55 Lewisville memlier of Woodbine formation ..... 53, 54,55, 56, 61,64 lillianense, Tarraiitoceras .................. 55, 60; pl. 5 lirata, Liapodesthéra ..................... 55,57, 58; pl. 4 Lispodesthes.. "F ______________________________ 57 limtu ________ r ........ 55, 57, 58; pl.4 nuptialis ..... T. ______ . . 58 panda ....... t ______ _ 58 patula ..................................... 58 List of fossils iromlbasal beds of Eagle Ford shale. 55 Localities, J ohnson County _____________________ 55 Tarrant County _____________ 54 Walnut Creek _______________ 54 lonsdolei, _Acanthmteras _______________________ 53, 61, 62 Euomphalocerhs ____________________ 54, 55, 69; pl. 6 ‘ M mantelli, Ammonigps ............................ 59 Mamelliceras. - ..... 59 Mantelliceras numb ..... 59 sellardsi ............... 53, 60 Metm'cocems whitei} _____________________________ 64 mirabile, Borissialc cams _________________________ 64 multicostamm. Tarrantoceras ............. 55, 61; pl. 6 i N nuptiaus, Lispodesz‘fws ........................... 53 O orbiculatum, Boriasiakoceras ____________ 55, 64, 65; pl. 6 Ostrea _________________ soleniscus. _ _ _ Sp __________________________________________ 55, 56 P panda, Lispodesthes _____________________________ 58 patula, Liapadesthes ............................. 58 pentagonum, Eucalycoceras 59 Pepper formation ............................... 53 pepperense, Acanthoceras ........................ 53 praete'nuis, Cadulus ....................... 57 Prionotropsie woolaarl ..................... 58 Protarca tramitensis" ‘55 Pseudomelama .................................. 57 basicostata _______________________________ 57; pl. 4 57 57 Ptychodus ...................................... 54 R Reeside, J. B., Jr ............................... 54 reesidel, Boriasiakoceras. . 64 Ripley formation ...... 56 roanokana, Pseudomelama. 57 rotatile, Tammtoccras _______________ 55, 59, 60,61; pl. 5 S aellardsi, Mantilliceras __________________________ 53, 60 Tarrantoceraa... ............................ 55, 6O soleniscus, Oatrea ............................... 55 South Bosque marl... _ 53 Stanton, ’1‘. W., quoted _________________________ 54 stantoni, Tarrantocerae _________________ 55, 60, 61; pl. 5 stephensoni, Acamhoceras ......... 53 Stratigraphic sections ............. 54 subglobosus, Holaster ............................ 59 T Tarrant formation .............................. 53, 54 Tarrantoceras. . . 59 lilliuneme..___.____.._..__.'_ ........ _. 55, 60; pl. 5 multicostatum ......................... 55, 61: pl. 6 motile ..... 55, 69. 60, 61; pl. 5 sellardsi. ______________________________ 55, 60 slantom' ............................ 55, 6'0, 61; pl. 5 tramitmsia, Protarca ____________________________ 55 V valida, Gymnemome _____________________________ validum, Acanthoceras ......................... 53 W whitci, Metoicocems ............................. 64 Woodbine formation .............. 53, 54, 55, 56, 57, 58 woolgari, Collignoniceraa ........... _ 58 Prionotrapsis ............................... 58 67 PLATES 4_7 FIGURES 1—3. 4—5. 6—11. 12—13. 14—17. PLATE 4 [Figures natural size except as Indicated] Inoceramus arvanus Stephenson (p. 55). 1. Internal mold from concretion in field 2. 5 miles north-northeast of Alvarado, Johnson County. USGS 14583. USN M 108840. 2. Internal mold from Walnut Creek, about 4. 75 miles east-northeast of Mansfield, Tarrant County. USGS 11740, USNM 108849. 3. Internal mold from Bird Creek, 4 miles east-northeast of Belton, Bell County. USGS 11845, USN M 108864. Pseudomelam'a? basicostata Stephenson, n. sp. (p. 57). Views of the holotype, X3, from Walnut Creek, 4. 75 miles east-northeast of Mansfield, Tarrant County. USGS 11740, USNM 108847. Lispodesthes lirata Stephenson, n.sp. (p.57). 6. Holotype, X2, from Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County. USGS 11740, USNM 108856. 7—9. Views of 3 paratypes (each X2) from the same source. USN M 108862. 10. A paratype, X2, from a, locality on Walnut Creek near the preceding locality. USGS 14580, USNM 108857. 11. Inner view' of a paratype, X2, from the same source, showing groove under upper prong of expanded lip. USNM 108857. Desmoceras? sp. (p. 58) 12. Internal mold, X3, coated for photographing, from Walnut Creek, 4. 75 miles east-northeast of Mansfield, Tarrant County. USGS 11740, USNM 108830. 13. The same specimen, uncoated, to show sutures. Acanthoceras johnsonanum Stephenson, n. sp. (p.58). 14,15. Views of holotype, from concretions in a field, 2. 5 miles north-northeast of Alvarado, Johnson County. USGS 14583, USNM 108846. 16. View of partly uncovered Inner volution of holotype. 17. Back view of inner volution of holotype. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 4 INOCERAMUS, PSEUDOMELANIAP, LISPODESTHES, TARRANTOCERAS, DESMOCERAS, AND ACANTHOCERAS GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 5 TARRANTOCERAS FIGURES 1—10. PLATE 5 [Figures natural size except as Indicated] Tarrantoceras rotatile Stephenson, n. sp. (p. 59). 1,—3 Views of the holotype, coated, from Walnut Creek, 4. 75 miles east-northeast of Mansfield, Tarrant County. USGS 11740, USNM 108835. 4. Side view of holotype, uncoated, to show sutures. 5. View of part of venter of holotype, uncoated, to show sutures. 6 7. Views of an incomplete paratype, from the same source, USNM 108854. 8—10 Views of a small paratype, from the same source, USNM 108854. 11— 21. Tarrantoceras stantom' Stephenson, n. sp. (p 60). 11— 13. Three views of the holotype, from gully in field 1 mile north of Lillian, Johnson County. USGS 24510, UNSM 108866. 14,15. Views of a small paratype, X3, from Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County. USGS 11740, USNM 108861. 16, 17. Views of a small paratype from the same source. USNM 108861. 18. A small paratype, X3, coated, from the same source, USNM 108861. 19, 20. Views of the same paratype, X3, uncoated to show sutures. 21. An incomplete specimen, from concretions in a field, 2.5 miles north-northeast of Alvarado, Johnson County, to show gerontic features near aperture. USGS 14583, USNM 108845. 22—27. Tarrantoceras lillianense Stephenson, n. sp. (p. 60). 22, 23. Views of the holotype, from gully in field 1 mile north of Lillian, Johnson County. USGS 24510, USNM 108841. 24. Back ventral view of the holotype. 25. View of rubber cast made from imprint on inner curve of holotype. 26, 27. Views of a paratype, from Walnut Creek, 4.75 miles east—northeast of Mansfield, Tarrant County. USGS 11740, USNM 108848. PLATE 6 [Figures natural size except as indicated] FIGURES 1—4. Borissiakoceras orbiculatum Stephenson, n. sp. (p. 64). 1. Holotype, X2, from Walnut Creek, 4.75 miles east-northeast of Mansfield, Tarrant County, USGS 11740, USN M 108832. 2, 3. Side and back ventral views of a paratype, X2, from the same source, USN M 108833. 4. Side View of a paratype, X4}§, showing sutures, from the same source, USNM 108833. 5. Borissiakoceras sp. (p. 64). View, X2, of specimen from western rim of Black Hills, Wyo., USGS 12649, USNM 108834. Inserted for com- parison with B. orbiculatum. 6—20. Euomphaloceras lonsdalei (Adkins), (p. 62). Six specimens shown in the order of size from largest to smallest. 6. Ventral view of fragment from septate portion of a large topotype, from Bird Creek, 4 miles east-northeast of Belton, Bell County. USGS 11845, USNM 108831. 7, 8. Views of another smaller topotype, USN M 108831. 9—11. Views of a plesiotype from Walnut Greek, 4.75 miles east-northeast of Mansfield, Tarrant County, USGS 11740, USNM 108824. 12, 13. Views, X2, of a small plesiotype, from the same source, USNM 108824. 14—17. Views of a small plesiotype, from the same source; 14, 15 side and back ventral views, X2, coated; 16, 17 back ventral and side views, X3, uncoated, to show sutures. USNM 108824. 18—20. Views, X3, of the smallest plesiotype from the same source; figures 18, 19 coated; figure 20 uncoated, to show sutures. USN M 108824. 21—23. Tarrantoceras multicostatum Stephenson, n. sp. (p. 61). 21. Holotype from concretion in field, 2.5 miles north-northeast of Mansfield, Tarrant County. USGS 14583, USNM 108844. 22, 23. Views of a paratype, from the same source, USNM 108842. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 6 ,-_ BORISSIA KOCERA S, EUOMPHALOCERA S, AND TARRANTOCERAS GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 7 EUOMPHALOCERAS PLATE 7 \ [Figures natural size] FIGURES 1—9. Euomphaloceras alvaradoense (Moreman) (p. 63). 1. Ventral view representing part of living chamber of a large plesiotype, from Walnut Creek, 4.75 miles east- northeast of Mansfield, Tarrant County. USGS 14582, USNM 108828. 2, 9. Views of a plesiotype, from concretion in a field, 2.5 miles north-northeast of Alvarado, Johnson County. USGS 14583, USNM 108825. 3—5. Side and ventral views (figs. 3, 4), coated, plesiotype, from Walnut Creek, 4.75 miles east-northeast of Mans- field, Tarrant County. USGS 11740, USNM 108822; partial view of opposite flank of same specimen (fig. 5), uncoated, to show sutures. 6—8. Side and ventral views (figs. 6, 7), coated, of a plesiotype from the same source, USNM 108822; back ventral view of same specimen (fig. 8), uncoated, to show sutures. U. 5. GOVERNMENT PRINTING OFFICE: 195! .“unnunuxmuouu a unwmmu muuuumm rnUM nunlnnnn ALADnn—ueuwgwm ourvey rrolesswnzu raper 4 I ‘_E_U lb. " 111110! J , Characteristic Jurassic Mollusks From Northern Alaska. -—(" GE’éLOGICAL SURVEY/EROFESSIONAL PAPER 274—1) BERKELEY LIBRARY UNIVERSITY OF CALIFORNIA GEOLOGICAB SGIENCES LEBRARY. Characteristic Jurassic Mollusks From Northern Alaska By RALPH w. IMLAY A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—D A stuq’y Mowing Mott t/ie flortéerrz fl/aséan fdufld/ yuccersz’on agrees wit/z t/zaz‘ e/yerw/zere 2'72 t/ze Bored! region mm] 2'72 ot/ier party of Now/1 flmerz'ca and in non/noes; Europe UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. — Price 25 cents (paper cover) CONTENTS Page Abstract _______________________________________________________________________________________________________ 69 Introduction ___________________________________________________________________________________________________ 69 Biologic analysis _______________________________________________________________________________________________ 69 Stratigraphic summary __________________________________________________________________________________________ 70 Ages of fossils _________________________________________________________________________________________________ 73 Comparisons with other faunas __________________________________________________________________________________ 75 Ecological considerations ________________________________________________________________________________________ 75 Geographic distribution _________________________________________________________________________________________ 78 Summary of results ____________________________________________________________________________________________ 81 Systematic descriptions _________________________________________________________________________________________ 82 Literature cited ________________________________________________________________________________________________ 92 Index __________________________________________________________________________________________________________ 95 ILLUSTRAITONS [Plates 8—13 follow index] PLATE 8. Inoceramus and Gryphaea 9. Aucella _ 10. Amaltheus, Dactylioceras, “Arietites,” Phylloceras, and Posidomla 11. Ludwigella, Dactylioceras, and Harpoceras. 12. Pseudocadoceras, Arcticoceras, Amoeboceras, Tmetoceras; Coeloceras, and Pseudolioceras 13. Reineckeia, Erycites, and Cylindroteuthis. Page FIGURE 20. Index map showing Jurassic fossil collection localities in northern Alaska ___________________________________ 79 TABLES 4 Page TABLE 1. Relative abundance of specimens of Jurassic molluscan genera in northern Alaska __________________________ 70 2. Geographic distribution of Jurassic macrofossils from outcrops in northern Alaska ___________________________ 77 3. Test wells from which Jurassic fossils and stratigraphic data have been obtained ____________________________ 82 4. Jurassic macrofossils from well cores in northern Alaska __________________________________________________ 82 CHARTS CHART 1. Correlation of Jurassic formations of northern Alaska .............. ‘_-___-_--__-_--_-_-----___-___,_-__ In pocket III A SHORTER CONTRIBUTION TO GENERAL GEOLOGY CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA BY RALPH W. IMLAY ABSTRAC T The fossils from the Jurassic strata of northern Alaska prove that the Lower, Middle, and Upper Jurassic series are repre- sented but suggest that certain stages or parts of stages are not represented. There is no faunal evidence for the presence of the middle and upper parts of the Bajocian, the entire Bathonian, the upper part of the Callovian, the lower Oxfordian, or the upper Portlandian. Field evidence shows that a discon- formity occurs at the stratigraphic position of the upper Port- landian. Both field and subsurface data suggest an uncon< formity immediately preceding the upper Oxfordian. The absence of faunal evidence for certain stages, or parts of stages, may be related to the fact that elsewhere in Alaska and in the western interior of North America major retreats of Jurassic seas occured during Bathonian, late Callovian, and Portlandian times. Although the Jurassic strata in northern Alaska are gen- erally impoverished faunally, nevertheless, in many places in- terpretations of the stratigraphy or the structure are based on the fossils present, or the fossils are used as supplementary evidence. Wherever the faunal succession can be determined in northern Alaska, it agrees essentially with that elsewhere in the Boreal region and in other parts of North America and in northwest Europe. Faunal and lithologic relationships suggest that the eastward- trending Jurassic seaway of northern Alaska had rather uni- form and moderately steep slopes along its northern and southern margins and that more than half of its sea bottom was stagnant and at least as deep as the lower part of the neritic zone. The existence of moderately deep water may ex- plain the presence of the ammonites Phylloceras, Lytocems, and Remeckeia, which are missing in the shallow-water Jurassic strata in the interior of North America, in east Greenland, and in the Barents Sea area. The scantiness of the fauna over much of the seaway is problably related to unfavorable bottom condi- tions and to an inadequate supply of certain materials such as phosphate. Fairly warm waters during Early Jurassic and early Middle Jurassic (Bajocian) time is indicated by the presence of ammonites that had a nearly worldwide distribution. Somewhat cooler waters and the presence'of climatic zones during the Late Jurassic in Alaska, as in other parts of the Boreal region, is indicated by the presence of molluscan genera quite distinct from those in the Late Jurassic of the Mediter- ranean region. INTRODUCTION This study of the Jurassic macrofossils from north- ern Alaska is based on collections made by E. de K. Leflingwell in 1911 and by field parties from the United States Geological Survey since 1947. During the sum- mer of 1950 the writer spent 10 days along the Canning River and 1 day along the Sagavanirktok River ex- amining J urassic outcrops. This provided some first- hand field information concerning the difliculties of mapping the Jurassic strata and of determining the stratigraphic succession. The brief descriptions of the stratigraphic and lithologic relationships presented herein as background for the ecologic and stratigraphic interpretations have been obtained mainly from dis- cussions with the geologists who have recently studied the Jurassic rocks. These geologists, including George Gryc, C. L. Whittington, I. L_. Tailleur, E. G. Sable, A. S. Keller, W. W. Patton, Jr., B. H. Kent, M. D. Mangus, J. T. Dutro, H. N. Reiser, R. L. Detterman, and R. H. Morris, have also checked or rewritten all locality descriptions and have plotted the positions of the localities on figure 20. Their efforts have contrib- uted greatly toward increasing the accuracy and value of the data in this report. It is hoped that the inter- pretations of the data will have immediate use in north- ern Alaska and will have application in other parts of Alaska. BIOLOGIC ANALYSIS The Jurassic fossils from northern Alaska that are generically identifiable include 163 specimens of am- monites, 9 belemnites, 530 pelecypods, 5 scaphopods, 9 rhynchonellid brachiopods, and more than a hundred pieces of the crinoid Pentacrinus. Of the total of 707 individual mollusks at hand, 338 belong to the pelecy- pod Aucella, and 369 belong to other genera. The Aucellas are a mere sampling of the enormous number's present in the outcrops, but the other 369 mollusks represent nearly all that could be obtained by the field geologists in the time available. This number is sur— prisingly small considering that many field parties have worked in the area during the past 50 years. It shows that the outcropping Jurassic strata are poorly fos- siliferous except for Aucella. The number of specimens 69 70 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY in the molluscan genera arranged according to their age is shown on table 1. Many of the fossils in the collections are either crushed or fragmentary. Most of the pelecypods, other than AaceZla, are so imperfectly preserved that they are not worthy of description and are merely listed generically. Most of the ammonites are merely com- pared specifically with European or American species. Three ammonites are identified specifically with am- monites occurring in southwestern Alaska. Four species of AuceZZa are identified with species that are common in Boreal Jurassic strata. Not a single species is described as new. Partly, this reflects the wretched preservation of the fossils. It is probable, however, that better preservation would allow positive identifi- cations of a number of species with named species elsewhere in North America, in the Boreal region, or in northwest Europe. TABLE l.—Relatz‘ve abundance of specimens of Jurassic molluscan genera in northern Alaska Genera Jiigsiggi‘c Bgidziiarn 03138;?“ gigigelgidgigg rocks rocks rocks Grammatodon _______ 2 _____________________________ Plicatula ___________ 40 ____________________________ C’amptonectes _______ 1 1 ____________________ Velopecten? _________ 4 ____________________________ Lima ______________________________________ 6 Gryphaea ___________ 9 ____________________________ anloma ___________ 14 10 ____________________ Aucella- ————7 ______________________________ 338 Posidonz'a __________________ 4O ____________________ I noceramus _________ 9 35 20 ____________ Pholadomya ________ 1 ____________________________ Tancredia __________________________________ 3 Dentalium ____________ 5 _____________________________ Cylindroteuthis--- _ .. _ 3 1 ________ 5 Phylloceras _________ _ _ _ _ - .. _ _ ________________ 2 Lytoeeras ___________ 1 _____________________________ “Arietites” _________ 1 ____________________________ A maltheus ___________ 15 ____________________________ Coeloceras __________ 4 ____________________________ Dactylioceras ________ 20 _____________________________ Pseudolioceras- _ _ _ _ _ ________ 48 ____________________ Erycites ____________________ 5 ____________________ Tmetoceras _________________ 2 ____________________ Arcticoceras ________________________ 9 ____________ Pseudocadoceras _____________________ 1 ____________ Amoeboceras ________ _ ______________________ 20 Reineckeia __________________________ 35 _____________ It is surprising that so few pelycypod genera are represented in the Jurassic deposits of northern Alaska. There is a complete lack of such common genera as Pleuromya, Trigom‘a, Astarte, Isocyprina, and Melea— grinella. Other equally common Jurassic pelecypods such as Grammatodon, Gryphaea, and Pholadom/ya are known by single occurrences. Actually the only fairly common pelecypods are Inoceram/as and Aacella, and these characteristically do not occur together. Among ammonites, too, very few genera are repre- sented, considering the amount of Jurassic time and strata present. It seems probable, however, that the subsurface Jurassic contains a greater variety of am- monites than the outcrops, judging by the few cores that have been obtained. Most of the ammonite genera present in Alaskan Jurassic rocks are fairly common elsewhere in Boreal Jurassic strata and in northwest Europe, but the presence of Phylloceras, Lytoceras, and Beineckeia north of the Arctic Circle in Jurassic de- posits is unique (Spath, 1932, p. 149, 151). This is probably the first record of Lytoceras and Reineckeia from Jurassic rocks bordering the Arctic Ocean. The record of a Reineckeia is particularly interesting, be- cause this genus has been considered as a characteristic element of Mediterranean faunas. STRATIGRAPHIC SUMMARY Detailed descriptions of the distribution, thicknesses, lithologic features, and subdivisions of the Jurassic strata exposed in northern Alaska are being prepared by geologists of the Alaskan Branch for publication by the Geological Survey. Completion of such detailed descriptions is essential before accurate generalized de- scriptions of the formations can be made or before well-substantiated interpretations of the origin and re- gional stratigraphic relationships of the formations can be formulated. For the present paper, therefore, only a summary of the gross features of the Jurassic strata is presented as background for the discussions con- cerning the fossils. This summary is based on discus- sions with geologists in the Alaskan Branch, on their published and unpublished papers, and on the writer’s observations. The Jurassic sedimentary rocks in northern Alaska are represented by three lithologic facies—one domi- nantly coarse elastic, another dominantly shale and silt- stone, and a third glauconitic calcareous sandstone and siltstone interbedded with considerable shale. The coarsely clastic facies has been called the Tiglukpuk formation. The other facies are included under the term “Kingak shale.” The coarsely elastic facies has been found only in the foothills north of the Brooks Range extending from near the Lupine River southwestward at least as far as the Utukok River. It ranges in thickness from a featheredge to about 2,000 feet, is highly variable in thickness along the strike, and is absent locally within its belt of outcrop. It is characterized by conglomerate, CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 71 graywaeke, sandstone, ehertlike material (possibly devitrified tuif) , tufl's, sills, pillow lavas, and a few thin beds of limestone. Interbedded with these rocks are dark siltstone and shale which constitute as much as 50 percent of some sections and as little as 10 percent of others. Such features as crossbedding and ripple marks are almost unknown. The coarser constituents of the conglomerate range in size from granules to boulders and consist mostly of chert, igneous rocks, and metamorphic rocks. The matrix of the conglom- erate is a graywacke. Sills have been identified only west of the Anaktuvuk River and lavas, only between Nuka River and Utukok River. Limestone occurs as thin eoquinas composed of the peleeypod Amella. The coarse elastic facies rests with angular discordance on Triassic and older rocks in the area between the Utukok and Ipnavik Rivers. Elsewhere, its lower contact is considered to represent an erosional surface. The shale and siltstone facies (hereafter abbreviated to shale-siltstone) crops out in the foothills north of the Brooks Range extending from the West Fork of the Ivishak River northeastward at least as far as the Sad- leroehit River and probably into Canada. It ranges in thickness from about 1,000 to 4,000 feet. It consists mainly of dark-gray to black noncaleareous shale but includes interbeds of rather hard pyritic siltstone, nodules and lenses of ironstone, and some septarian con- eretions. The shale is mostly chunky to fissile, but some is papery. Fossils occur rarely in siltstone lenses, in coneretions, and in shale. This facies rests con- eordantly but sharply on Triassic limestone and shale. A similar shale and siltstone facies about 1,000 feet thick overlies Triassic rocks from the Nuka River west- ward at least to the Kokolik River and probably extends to Cape Lisburne. This facies has not furnished fossils and could be either of Jurassic or earliest Cretaceous age (E. G. Sable, March 5, 1954, oral communication). The facies characterized by calcareous, glauconitic quartz-bearing sandstone is interbedded with consider- able dark shale and siltstone that is mostly noncal- careous. It locally contains pebbles of chert, slate, and sandstone. It has been found only in the subsurface of the Arctic Coastal Plain near Point Barrow and Cape Simpson and is entirely of Early Jurassic and early Middle Jurassic (Bajocian) age. It has been called a platform facies because it was deposited on the southern margin of an area that was probably a land mass during Paleozoic time, is much thinner than equivalent beds farther south, contains abundant microfossils and mac- rofossils, and its mineral composition indicates deriva- tion from an area of metamorphic rocks to the north. This facies differs from the equivalent part of the shale- siltstone facies exposed in the valleys of the Canning and Sadleroehit Rivers by a much greater abundance of fossils, glauconite, and calcareous material. The platform facies rests on a few hundred feet of Upper Triassic strata which in turn overlie metamorphic rocks. It is the opinion of the geologists who have mapped the Jurassic sedimentary rocks in northern Alaska that these rocks were laid down in an eastward—trending trough, about 150 miles wide, whose southern margin intersects the northern front of the Brooks Range in the area between the Ribdon and the Lupine Rivers. They consider that the elastic facies was deposited near the southern margin of the trough and that the shale- siltstone facies was deposited north of the elastic facies. The shale-siltstone facies happens to be exposed in the area between the Ivishak and Hulahula Rivers because of extensive post-Jurassic uplift in that area. The elastic facies is absent east of the Lupine River because of erosion that accompanied the uplift. The evidence for the uplift is both stratigraphic and structural and will be discussed amply in other publications being prepared by members of the AlaskanBranch of the Geological Survey. For the purpose of demonstrating the ‘relationships of the shale-siltstone to the elastic facies and the reality of the uplift, a few pertinent facts will be listed. First, the Okpikruak formation of earliest Cretaceous age thins eastward from a maximum of at least 1,500 feet near the Sagavanirktok River to only a few feet about 2 miles west of the Canning River opposite Shublik Springs and is absent on the banks of the Canning River. Fossils collected throughout this interval demonstrate that the thinning is due to erosion. Second, the overlying Torok formation of latest Early Cretaceous (Albian) age thins eastward from a maximum of 3,400 feet near the Sagavanirktok River to a featheredge in the Shaviovik Valley. Third, on the west bank of the Canning River opposite the mouths of Eagle and Cache Creeks the Jurassic strata are nearly 4,000 feet thick, contain Oxfordian. fossils at their top, and are overlain by beds of latest Early Cretaceous (Albian) age that have been correlated with the Tuktu member of the Umiat formation. Fourth, about 12 miles to the northeast in-Ignek Valley, between Red Hill and the Katakturuk River, J urassie strata are only about 1,000 feet thick, contain Toareian (late Lias) ammonites at their top, and are overlain by beds that are correlated with the Tuktu member. Fifth, on the Sadleroehit River the Jurassic is at least 3,000 feet thick, contains Callovian ammonites in its upper part, and is overlain by beds that are probably equivalent to the Tuktu member. These facts demonstrate clearly that uplift and erosion of several thousand feet of J uras- sic sediments and more than 1,500 feet of earliest Cre- taceous sediments occurred during Early Cretaceous 72 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY time. Of course, subsequent uplifts in the same area in Late Cretaceous or Cenozoic times, or both, are re- sponsible for dissection of Upper Cretaceous sedimen- tary rocks and for the present day exposures. It is interesting that, except for small outcrops of Middle Jurassic (Bajocian) age near the Kiruktagiak and Siksikpuk Rivers, the elastic facies appears to be entirely of Late Jurassic age and represents the upper Oxfordian and Kimmeridgian stages and possibly part of the Portlandian stage. In contrast, the shale-silt- stone facies includes Lower, Middle, and Upper J uras— sic at least as high as the Kimmeridgian, and in the Canning River area the beds of Oxfordian to Kimmer- idgian age probably do not form more than one-fifth of the total Jurassic sequence. These age relationships, considering the distribution of the two facies, indicate that the Upper Jurassic beds overlap the Middle and Lower Jurassic beds and that the sequence in the sub- surface may locally be as complete and as thick as in the Canning River area. Mapping by A. S. Keller and R. L. Detterman, in the area between the Sagavanirktok and Canning Rivers, has shown that the Upper Jurassic beds do overlap the older Jurassic beds but that relationships within the Jurassic sequence are probably complicated by several intervals of erosion or of nondeposition. For example, on the Lupine River a collection (Mes. loc. 22769) made about 300 feet above the base of the Jurassic strata contains Aucdla comentrica (Sowerby) A. mgosa (Fischer), and A. mosquemz's (von Buch) . This asso- ciation indicates a middle Kimmeridgian age. About 51/2 miles to the northeast, on Nose Bleed Creek, a col- lection (Mes. loc. 22747) made near the base of the Jurassic strata contains Amaltheus (Pseudoamaltlwus) and Lytooems of. L. fimbm'atum (Sowerby). These fossils are definitely of Early Jurassic age, and the pres- ence of Amaltheus indicates a Pliensbachian age. About 61/2 miles farther northeast, on the west fork of the Ivishak River, a collection (Mes. 100. 22745) made in the lower 400 feet of the Jurassic rocks contains Pseudocadocems grewingkz‘ (Pompeckj). This fossil is excellent evidence. for the middle Callovian age of the beds in which it occurs. The evidence at these three localities indicates rather strongly that the Lower Jurassic beds are overlapped by Upper Jurassic (Cal— lovian) beds and the latter by Kimmeridgian beds. Taking into consideration all the fossil evidence dis- cussed under the heading Correlation, and the strati- graphic relationships in both outcrop and subsurface, it seems probable that the Jurassic sequence in northern Alaska includes three disconformities. The oldest dis- conformity corresponds to the middle and upper Bajo- cian and the Bathonian, the next younger to the upper Callovian and lower Oxfordian, and the youngest to all or part of the Portlandian. The probable occur- rence of these unconformities throughout the Arctic Coastal Plain is indicated by the few wells that have penetrated Jurassic sedimentary rocks. (See table 3.) It is interesting that elsewhere in North America and in the Boreal region in general there is evidence for withdrawals or retreats of the seas from the continental areas during the Bathonian, the late Callovian, and the late Portlandian. As such large parts of the earth are involved, the withdrawals cannot be ascribed pri- marily to local tectonic movements, although local movements may have influenced the extent and dura- tion of the disconformities. No evidence for a disconformity exists Within the Lower Jurassic sequence. In fact, the presence of the ammonite “Arietites” of. “A.” bucklandi (Sowerby) in the Avak test well 1 at 464 feet above the base of the Jurassic rocks, as determined by lithology and microfossils, suggests that even the earliest Jurassic is represented. If an unconformity exists between the Lower Jurassic and the Triassic rocks, as is sug- gested by an abrupt lithologic change and a conspicu- ous microfaunal change, then the time represented by the unconformity is probably latest Triassic. The total thickness of the Jurassic system in northern Alaska changes greatly from place to place, owing to overlap relationships, to disconformities within the Jurassic strata, to post—Jurassic erosion, and to dif- ferences in original thickness. The maximum thickness of the Lower Jurassic strata is about a thousand feet in the valley of the Canning River, but the Lower Jurassic thins westward noticeably from the Canning River and has not been identified west of the Lupine River. In the subsurface of the Arctic Coastal Plain there are not enough faunal data to separate the Lower Jurassic rocks from the Lower Bajocian, but the Lower Jurassic strata are at least 620 feet thick in the Simp- son test well 1, at least 838 feet thick in the South Barrow test well 3, and nearly 500 feet thick in the Topagoruk test well 1. The Bajocian strata have an estimated maximum thickness of a thousand feet in the valleys of the Can- ning and Sadlerochit Rivers. Elsewhere on the out- crop, they have been identified only in small areas near the Siksikpuk and Kiruktagiak Rivers where they are probably less than 300 feet thick. In the subsurface they are at least 81 feet thick in the South Barrow test well 2 and at least 291 feet thick in the Topagoruk test well 1. The Callovian strait-a are at least 800 feet thick in the valleys of the Canning and Sadlerochit Rivers and may be as much as 2,000 feet thick. The only other exposures CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 73 known in northern Alaska are on the west fork of the Ivishak River where the minimum thickness is 400 feet. It seems probable, however, that the Callovian beds are present from the Sadlerochit River eastward into Can- ada, because the United States Geological Survey has collections of Amtz’cocems and Cadocems from the Richardson Mountains, an eastward continuation of the Brooks Range. Also, the files of the United States Geological Survey contain a report from S. S. Buck— man to E. M. Kindle that lists Uadocems and Pseudo- cadocems from the Firth River in Arctic Canada (O’Neill, 1924, p. 14a, 15a). The upper Oxfordian to lower Portlandian strata range exceedingly in thickness in the outcrop belt north of the Brooks Range. The thickness at the Canning River is probably not greater than 800 feet, but the highest beds there are probably not younger than Oxfordian. West of the Canning River, thick- nesses of 1,500 to 2,000 feet are common as far west as Driftwood Creek; although locally within the belt of outcrop, thicknesses are much less. The range in thick- ness must be due either to depositional or erosional dif- ferences in latest Jurassic time, because the underlying Triassic rocks maintain a fairly uniform thickness of 300 to 500 feet along the mountain front. AGES OF FOSSILS The Sinemurian, Pliensbachian, and Toarcian stages of the Lower Jurassic are represented faunally in north- ern Alaska, and there is an ample thickness of strata in some sections to account for the oldest stage, the Hettangian. The lower Sinemurian is identified by an ammonite “Arietites” cf. “A.” bucklcmdi (Sowerby) from the Avak test well 1 at the depth of 1,836 feet, which is 464 feet above the base of the Jurassic. The Pliensbachian is identified by the ammonite Amaltheus, which in Europe is known only from that stage and occurs mostly in its upper part (Roman, 1938, p. 146, 147) underlying the lower Toarcian beds containing finely—ribbed Dactylz'ocems (Arkell, 1933, p. 153, 165). In the subsurface of northern Alaska, Amal- theus has a comparable stratigraphic position in the South Barrow test well 3 a short distance below beds containing Dactyliocems. (See table 4.) On the out- crop the Pliensbachian is represented by Amaltheus (Pseudoamaltheus) from near the base of the Jurassic rocks on Nose Bleed Creek. It is, also, probably repre- sented from the Sadlerochit River area by a Gryphaea similar to 6‘. cymbz’um Lamarck. The lower Toarcian is identified by various specimens of Dactylz’oceras in the South Barrow test well 3 at depths of 1,7 72 feet and 2,016 to 2,018 feet. The speci- mens from depths of 2,016 to 2,018 feet are all finely 342062—55—2 ribbed and are closely comparable to species in England in the zones of Dactyliocems tenuicostatmn and Har- pocems serpentinum. The specimens from the depth of 1,772 feet are all coarsely ribbed and are similar to species in the Hildocems bifrons zone in England. Thus, the stratigraphic relation of the finely ribbed to the coarsely ribbed species is-the same in Alaska as in England. Also, the finely ribbed species of Dwtylz’o- Gems are only 51 feet above the highest occurrence of Amaltheus, so their stratigraphic position with respect to Amaltheus is the same as in England. Correlation of the beds containing the coarsely ribbed Dactylz'o- Gems With the H ildocems bifrons zone is substantiated by some ammonites from Prince Patrick Island, about 700 miles northeast of Point Barrow. These ammonites (see pl. 11, figs. 1—18) include many coarsely ribbed Ddctylz’ocems, a fragment of a keeled ammonite that is probably Hildocems, and several examples of Harpo- cems similar to H. ewamtum (Young and Bird) (Wright, 1882, pl. 6). The upper Toarcian is identified in northern Alaska only in Ignek Valley a few miles east of the Canning River by several specimens of Pseudolz'ocems similar to P. lythense (Young and Bird) (Wright, 1884, pl. 62, figs. 4—6) and P. compactile (Simpson) (Buckman, 1911, pl. 41a—c) from Europe. These species differ from species of Pseudoliocems in the lower Bajocian strata of Alaska by having the lower third of their flanks nearly smooth or only weak striate. The lower Bajocian is identified in the subsurface by fragmentary ammonites referred to Tmetocems and Pseudolz'oaems and in the outcrops in the valleys of the Canning and Sadlerochit Rivers by Pseudoliocems whiteavesé (White), E waites howellz' (White), and Inocem'm/ws chifer Eichwald. These species are common in southwestern Alaska in the lower part of the Kialagvik formation where the associated am- monites furnish a definite correlation with the lower- most Bajocian (Imlay, 1952, p. 978) rather than upper Toarcian. Of course, a fragment of Pseudoliocems such as occurs in the Topagoruk test well 1 at the depth of 8,111 feet might represent either upper Toarcian or lower Bajocian, but the Tmetocems at the depth of 8,113 feet is characteristic of the lower Bajocian and prob- ably does not occur in the Toarcian (Frebold, 1951b, p. 20). It is surprising that the middle and upper Bajocian and the entire Bathonian have not been identified faunally in northern Alaska. Part of these stages may be represented on the high west bank of the Canning River, opposite the mouths of Eagle and Cache Creeks, where about 2,000 feet of beds are exposed between the lower Bajocian shales containing Pseudolioceras and 74 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the lower Callovian siltstones containing Arctiaocems, but the beds cannot be reached because they are undercut by the swift current of the river. From a distance of a quarter of a mile it is impossible to determine whether the inaccessible part of the section is continuous or is repeated by folding. It is interesting that lower Bajo- cian beds near the Siksikpuk and Kiruktagiak Rivers and in the Topagoruk test well 1 are overlain directly by upper Oxfordian or Kimmeridgian beds. This is evidence for a major unconformity but does not date the unconformity very closely. It might represent part of the Middle Jurassic or part of the Callovian, or both. Judging by the occurrences and magnitudes of Jurassic unconformities elsewhere in North America, the un- conformity is probably mostly of late Callovian age. This receives some support by the presence of upper Bathonian beds characterized by the ammonite Arcto- cephalites in the Richardson Mountains in Canada just east of the Brooks Range. The Callovian is identified in northern Alaska by two occurrences of Arcticoceras sp., one of Pseudo- cadooems grewz'ngkz' (Pompeckj) , and one of Reineckeia (Reineckeites) of. R. stuebeli Steinmann. This species of Redneckez'a was obtained about 550 feet above Arotz'cocems sp. on the west bank of the Canning River, but the species of Pseudocadocems was found in another area within 400 feet of the base of the Jurassic rocks. Arcticoceras is considered to represent the lowest Col- lovian on the basis of its occurrence in the western interior of North America (Imlay, 1948, p. 14, 15; 1953a, p. 5) and in Greenland (Spath, 1932, p. 141,142). Pseudocadocems in Europe ranges from the zone of Sigalocems callom'ense to the zone of Erymocems coronatum. P. grewc’ngki (Pompeckj) is common in southwestern’ Alaska and in the Cook Inlet area, Alaska, in beds that are correlated with the upper part of the European zone of Sigalocems calloviense and the zone of Kosmocems jason (Imlay, 1953b, p. 50, 53). The presence of. the subgenus Reineckez'tes merely proves the Callovian age of the beds in which it occurs. If the identification with B. stuebelz' Steinmann is cor- rect, an assignment as high as the zone of Peltocems athleta is possible (Arkell, 1939, p. 199), although some of the occurrences of B. stuebelz' in Europe are probably in the underlying zone of Erym/nocems coronatwm (Spath, 1928, p. 270). The upper Oxfordian to lower Kimmeridigian strata contain Amoebocems (Prionodocems?), Aucella spi- tiensis Holdhaus, and Aucella concentrioa (Sowerby). Auoella concantm'ca (Sowerby) is considered to be a reliable marker for the parts of the stages indicated only where it occurs in abundance and is not associated with Aucella mgosa (Fischer) or A. mosquemis (von Buch). There are five such occurrences in thin lime- stone beds in the area between the Shaviovik and Kukpowruk Rivers. Amella spitz‘ensis Holdhaus has been found only near the Canning River and in the most easterly branch of the Shaviovik River. It is associated with a few specimens of A. concentrica (Sowerby) and Amoeboceras. The specimens of Amoebocems cannot be assigned definitely to any sub- genus because they are all immature. Their features, however, suggest assignment to the subgenus Prio- nodocems, which is much more common in uppeer Ox- fordian than in lower Kimmeridgian beds in the Boreal region and in northwest Europe. It is probable that the beds containing Aucella spitiensis are lower strati- graphically than the beds containing abundant A. con- centm’ca and that the latter are absent from the Canning River area owing to erosion. These probabilities are suggested by the post-Callovian (Jurassic) strata in the Canning River area being only one-third to one- half as thick as equivalent strata farther west; by ample evidence for repeated uplift and erosion in the area be- tween the Canning and Sadlerochit River, as discussed under the stratigraphic summary; and by the fact that Aucella concentrica attained its greatest abundance in early Kimmeridgian time. The middle Kimmeridgian to lower Portlandian strata in northern Alaska are identified by Aucella rugosa (Fischer) and A. mosquemz’s (von Buch). These occur together although A. rugosa is much more abundant. The same species are associated in Russia, Siberia, east Greenland, and the Barents Sea area in beds of late Kimmeridgian to early Portlandian age (zones of Subplam'tes wheatleyensz's to Zamz'skz'tes albam' inclusive). (See Pavlow, 1907, p. 25, 26, 38, chart opposite p. 84; Spath, 1936, p. 166, 167.) It seems probable, however, that their total range is much greater. In Mexico A. mosquensis has been found with the ammonites Kossmatz'a and Dummgz'tes (Burck- hardt, 1912, p. 206, 221, 236) in beds that are considered higher than the European zone of Zamz'skites albamfi (Imlay, 1952, pl. 2). A. mosquensz's has also been found much lower associated with Gloohz’oems fialar and Idocems dumngeme (Burckhardt, 1912, p. 216, 217) in beds that represent the middle Kimmeridgian and are probably equivalent to the European zone of Adam- stephtmus pseudomutabih's. In northern Alaska, like- wise, a middle Kimmeridgian age for some of the oc- currences Of Aucella mosquensis and A. mgosa (Mes. locs. 22766 and 22769) is indicated by their association with A. concentrica, which has not been recorded in Eu- rope above the middle Kimmeridgian zone of Aulaco- stephanus pseudomutabz’lés. The same association has been noted by the writer throughout several hundred CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 75 feet of beds near the middle part of the Naknek forma- tion in the Talkeetna Mountains in south central Alaska. Field evidence that the upper part of the range of A. concentm'o'a overlaps the lower part of the range of A. mgosa or A. mosquensis has been useful in mapping the Naknek formation and will be useful in interpreting the history of the Late Jurassic. The upper Portlandian has not been identified faunally in northern Alaska and is probably not rep- resented by strata. Field geologists have noted con- siderable local evidence for an erosional unconformity between the Jurassic beds and the overlying Okpikruak formation of earliest Cretaceous age. Because the Okpikruak formation contains Aucellas that represent both the Berriasian and Valanginian stages, the time of the unconformity must be latest Jurassic. COMPARISONS WITH OTHER FAUNAS The few fossils that have been obtained from the Lower Jurassic and the early Middle Jurassic (Bajo- cian) strata of northern Alaska can be matched very well specifically in the rich but mostly undescribed assemblages from Talkeetna Mountains, the Cook Inlet region, and southwest Alaska. (See chart 1.) They are similar to and probably in part identical with species in northwest Europe and the Boreal region. The resemblances of the Toarcian ammonites from South Barrow test well 3 to those on Prince Patrick Island and the resemblances of those from the latter to Toarcian ammonites from northwest Europe is strik- ing. The lower Bajocian species of Pseudoliocems and Erycz'tes in Alaska are equally similar to species in the Barents Sea area and in Europe. These genera have not been found on Prince Patrick Island, but the lower Bajocian is clearly represented there by an~ other ammonite Ludwigella maclintooké (I-Iaughton) (1857, p. 244, 245, pl. 9, fig. 2—4) which is similar to L. comm Buckman (1887, p. 20, pl. 4, figs. 1—4). Re- cent collections from that island have furnished an- other specimen of Ludwigella (pl. 11, figs. 1—3) that is similar to L. mdz’s Buckman (1888, p. 103, pl. 15, figs. 11—13). These resemblances should be expected because the faunas of the Lower Jurassic and Bajocian are cosmopolitan. Nowhere in the world is this better demonstrated than in the Cook Inlet region and the Talkeetna Mountains of south central Alaska, where the ammonites can be matched zone for zone with north- west Europe. When these fossils are described, many species will probably be identified with species in Europe. In keeping with the well—known provincial distribu- tion of mollusks during the late Middle Jurassic (Ba- thonian) and Late Jurassic, the fossils from the Upper Jurassic strata of northern Alaska are dominantly Boreal but include a few genera, such as Phyllocems, Lytocems, and Reineckez'a, that generally are consid- ered distinctive of the Mediterranean province of post- Bajocian time. As such genera also occur in southwest and south central Alaska, far north of their occurrence in Europe, it seems probable that they entered the Boreal sea from the Pacific Ocean. In the Callovian strata the ammonites Arcticooems and Pseudocadocems are Boreal elements, and Rein- eckeia is a characteristic genus of the equatorial areas. Arcticoceras has been recorded previously from the basal Callovian at a number of places in the Arctic region and in the western interior of North America. Pseudocadocems has been recorded from the middle Callovian in southwest and south central Alaska, Arctic Canada, the Barents Sea area, andEurope as far south as England and France. The presence of Reineckeia apparently identical with R. (Beineckez’tes) stuebeli Steinmann is surprising because the genus in Europe does not range north of southern England and south- ern Germany (Spath, 1932, p. 149). The species itself, or a very similar species, is widespread throughout a broad equatorial belt extending from India to Europe to Mexico and South America. In the upper Oxfordian to lower Portlandian strata the only common fossils are Aucellas. These belong to species that are abundant in the Boreal Jurassic else- where, although ranging as far south as Mexico and northern India. Amoebocems of upper Oxfordian or lower Kimmeridgian age represents another Boreal ele- ment that ranges southward into central Europe and into northern California. The occurrence of a few specimens of Lytocems? and Phyllocems probably re— flects a broad connection southward with the Pacific Ocean as these genera are common in the Upper J uras— sic of southwest and south central Alaska. ECOLOGICAL CONSIDERATIONS The Jurassic sedimentary rocks of northern Alaska, according to Payne, Gryc, and Tappan (1951), were deposited in an eastward-trending trough about 150 miles wide in the area now occupied by the northern margin of the Brooks Range, the foothills of the Brooks Range, and the southern part of the Arctic Coastal Plain. The trough was bounded on the south by a rising landmass from which most of the sediments were derived. It was bounded on the north by the Barrow Platform, whose southern margin corresponds with the present northern part of the Arctic Coastal Plain. The sediments deposited in the trough attain a thickness of at least 4,000 feet. Their areal distribution shows 76 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY that coarse clastics were deposited along the southern margin of the trough, dark pyritic noncalcareous clay and silt in the central part of the trough, and glauco- nitic calcareous sand and silt, interbedded with consid- erable clay, along the northern margin of the trough. Part of the 1,500 to 2,000 feet of coarse elastic sedi— ment was derived from the present site of the Brooks Range and part from areas as far south as the Baird Mountains. The composition of some of the conglom- erates within the facies indicates local derivation from islands or headlands within a few miles, according to the field geologists. The lack of crossbedding, ripple marks, and genera of sessile benthonic mollusks other than Aucella is probably related to rapid sedimenta- tion rather than to deposition in deep water, as chella thrived in places where thick elastic sediments were being deposited. The absence of the nearly ubiquitous pelecypod Inocemm/us from beds containing Amella and its rarity even in the same formations suggests that these genera lived under different environmental conditions. Although Auoella occurs characteristically in thin shell beds associated with clay shales and silt- stones, its presence locally in pebbly beds or even in coarse conglomerates suggests that it may have lived in waters that were too agitated or too shallow for I nocemm/us to exist. The part of the shale—siltstone facies that is of upper Oxfordian to Portlandian age was deposited north of and in deeper water than the elastic facies. It is in-' ferred that the parts older than the upper Oxfordian pass southward into coarse clastics that are overlapped by Late Jurassic strata, but evidence of this is meager. In fact, the presence of two major disconformities that have not resulted in appreciable lithologic changes in the adjoining strata suggests that there may not have been thick or extensive deposition of coarse clastics prior to the Oxfordian. Conditions on the sea bottom and in the sea during deposition of the clays and silts were probably unfa- vorable for abundant life or for its preservation con- sidering the scarcity of sessile and mud-dwelling benthos, Foraminifera, and such free-floating or swim- ming organisms as crinoids, ammonites, belemnites, and pectenids, except in a few widely separated beds. Sandstone units in the Lower Jurassic have furnished a few benthonic organisms such as Omytoma, Gryphaea, Pholadomg/a, Grammatodon?, Inward/rims, and Den- talz'um. Plicamla attached to the matted remains of Pentacm'nus has been found near the base of the Lower Jurassic. There are a few occurrences of I nocemmus and Owytoma in the lower Bajoeian and of I nocemmus and brachiopo‘ds in the Callovian. Aucella has been found in several concretions embedded in shale of late Oxfordian to Kimmeridgian age. All these fossils in the outcropping shale-siltstone facies are from only 30 localities. (See table 2.) This number is surpris- ingly small considering that nearly 4,000 feet of strata are involved, that outcrops are fairly extensive along the Canning and Sadlerochit Rivers, and that geologists have spent several thousand hours studying the area. The scarcity of outcrops in areas between the rivers can only partially explain the small number of fossils collected, as similar shales and siltstones in the Jurassic of the Cook Inlet region in south central Alaska are much more fossiliferous. ' The scarcity of benthonic organisms might be due to such slow deposition that scavengers destroyed most of the organic remains, to such rapid deposition that most organisms could not establish themselves on the sea bottom, to deposition considerably below the neritic zone, to stagnant conditions on the sea bottom, to a scarcity of certain minerals essential for abundant or— ganic growth, or to some combination of these possi- bilities. Concerning these, neither the .thickness of sediments in relation to the time involved nor the char- acteristics of the sediments indicate exceedingly slow or exceedingly rapid deposition. Depth of water much below the neritic zone seems unlikely because the shale- siltstone facies apparently contains two major discon- formities which involve some erosion in the area between the Lupine and Shaviovik Rivers as shown by the field- work of A. S. Keller and R. L. Detterman. Even if the disconformities are mostly nondepositional, the sameness of the strata throughout the shale-siltstone facies suggests that the depth of the sea did not vary by more than a few hundred feet between intervals of erosion, nondeposition, and deposition. The possibility of stagnant conditions on the sea bot— tom is suggested by the presenee of considerable dis- seminated pyrite and the absence of such mud—dwelling pelecypods as Pleuromya, Panope, Thracia, Astam‘e, and Pinna. If a major part of the sea bottom was stagnant, however, it was probably below wave base and probably at least as deep as the lower part of the neritic zone. The scarcity of ammonites, belemnites, and Forami- nifera may also be related to unfavorable bottom condi- tions or to destruction of the shells after death but probably reflects in addition an unfavorable food situa— tion in general. Perhaps the food situation is related to the deposition of graywacke nearshore, lack of or- ganic matter derived from the land, and dominance of sedimentary over metamorphic or igneous rocks in the source areas south of the Jurassic sea. CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA Fox-nation Kukpmn-uk River to Lupine River Tiglukpuk {ormtion _West Fork of 1vishak River to Sadlerochit River c Locality number on fig. 20 Nlnl v lmlolhlwlal ldlfilfllfil 33 r « Kingak shale | x N I‘Sl c r Mesozoic localily number 22127 I 22776 23577 23697 22507 22509 23598 21552 22591 22584 22585 1 22586 22582 22587 22588 22578 22579 22580 22501 22749 n F N N — r a o n a N a 772 .29 22746 17 22759 20 22739 21 21024 22596 25 22597 21023 24033 26 22595 22002 10305 10300 1o 07 3? 23747 as 23749 if 23743 ‘3'!— d ~ c w a 227 8 16 22769 22764 21028 24035 22 81 w — c p w a 22745 o m se vs at X 2401 22 X 2401 24 x 21025 Pentacrinus subanguhris var. alaska Springer XX n.2L, Brlchiopods indet ............................... X Grammatodcn sp ..... Plicatula spp. ........ >< Entolium Sp. ...... Camptonectes sp. . Lima up. 7777777777 Gryphnea ci‘. G. cymbium Lamarck A. ()xy1orna app. ....................... ><>< Auceua concentrica (Sewer-by) ,. XX XX A. wifiensis Holdhsus A. moaquensis (Von Buck) A. rugosa (Fischer) ..... XX XX Pocidonia cf. P. ornati Inoceramus 1m: Ker Eichwald. hoceramus app ............... Phohdomya w. . . . Twedia Sp. 10ernaliuxn Hp Phyuoceras (Partschiceras) P. (Macropmuoceras) sp .......... Ly‘toceraa cf. L. limbriatum (Sowerby). 14.? up. Anialtheus (Pseudoamaltheus) sp. . Pseudouoceras whiteeveai (White) .. P. cf. P. 1ythense (Young and Bird). P. of. P. compactile (Simpson) XX P. up. indet. .................... P.? 8P. ..................... -Erycites howelli (White). .. Erycites sp. indet. ,. Parkinsonia ? 5p. juv 'Arcticoceras up ...... Pseudocadoceru grewingki (Pompeckj). Amoeboceras (Prionodoceras?) app. juv. . Reineckeia (Reineckeltes) cf. R. stuebeli " Cylindroteuthis spp ..................................... X Helen-mites indet ........................................ X xix ] TABLE 2.~—Geographic distribution of Jurassic macrofossils from outcrops in northern Alaska. It has been suggested that the source for the platform facies was to the north (Payne, Gryc, and Tappan, 1951) in large areas of metamorphosed rock of possible pre- Cambrian age. This is indicated by the presence of quartz sandstone, glauconite, and considerable cal- careous material, which is rare or absent in the coarse elastic facies deposited along the southern part of the Jurassic seaway. Also, studies of the Jurassic rocks in the western interior of the United States show that glauconite is much more common in sandstones derived from areas of metamorphic or igneous rocks than from , areas of sedimentary rocks (Imlay, 1950, p. 91). The greater amount of calcareous material in the platform facies may merely reflect a greater number of shell- building organisms, but their number in turn may be related to the kind and quantity of minerals being brought into the sea. The macrofossils present in the platform facies in— clude such sedentary types as brachiopods and the pele- cypod Owytoma and the free-swimming ammonites and pectinids. This is essentially the same assemblage as in the shale-siltstone facies, and similarly there is a conspicuous absence of mollusks that are common in muds in the shallower part of the neritic zone. It seems probable that the calcareous sandstones would be firm enough for the attachment of such pelecypods as Ostrea Qr Meleagrinella, if other conditions such as depth and temperature were suitable. The absence of such mol- lusks may have little significance concerning depth of water because the Jurassic strata pinch out northward in a distance of 12 miles between the South Barrow test wells 3 and 1 (Payne, Grryc, and Tappan, 1951), owing mainly to onlap rather than to erosion, as indicated by fossils (table 4). Rapid northward thinning of the Lower Jurassic sedimentary rocks is shown by the pres- ence of lower Bajocian ammonites in the South Barrow test well 2 only 52 feet above the base of the Jurassic, whereas the Lower Jurassic in the South Barrow test well 3 is at least 838 feet thick. On the other hand, such rapid thinning might be interpreted as meaning that the sea bottom sloped steeply and that the subsurface Jurassic in the Simpson test well 1 and South Barrow test well 3, from which most of the fossils were obtained, was actually deposited in the deeper part of the neritic zone. A rapid southward change of the platform facies into the shale-siltstone facies is shown by the Jurassic se- quence in the Topagoruk test well 1, only about 27 miles south-southwest of the Simpson test well 1. In the Topagoruk well the Lower Jurassic and lower Bajocian strata consist entirely of noncalcareous pyritic siltstone and shale. The overlying upper Oxfordian to Kim- meridgian strata consist mostly of pyritic dark shale but include some limestone beds, scattered grains of quartz, chert, and glauconite; and basally are marked 78 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY by a glauconitic sandstone. This sequence differs from the typical shale-siltstone facies as exposed in the Can- ning River area by the presence of quartz and a greater abundance of Foraminifera. The writer has the impression, based on the faunal and lithologic relationships just discussed, that the sea bottoms along the northern and southern margins Of the Jurassic seaway in northern Alaska sloped uni- formly and moderately basinward and were at least in the lower part of the neritic zone at a distance of perhaps 30 miles from shore. This means quite difler- ent conditions of sedimentation than existed during the Jurassic in east Greenland (Spath, 1932, p. 154; 1936, p. 175), the Barents Sea area (Frebold, 1929, p. 23; 1932, p. 21—27; 1951a, p. 77—84), and the western interior Of North America (Imlay, 1950, p. 93—98), where both fossils and lithologic features indicate dep- osition in the littoral zone and in the shallower part of the neritic zone. Perhaps the existence of deeper water in Alaska than in the other areas explains the presence in Alaska Of such ammonites as Phylloceras, Lytocems, and Reineeheia. As the same genera are fairly common in southwestern Alaska, a marine con- nection with northern Alaska is a certainty. One such connection almost certainly existed in the area now represented by Yukon Territory, Canada, but another probably existed in eastern Siberia. Evidence of the faunas in northern Alaska indicates temperature conditions in the Jurassic sea similar to those in other parts Of the Boreal region. The tempera- ture during the Early Jurassic and the Bajocian was probably warm, as indicated by the cosmopolitan dis- tribution of the ammonite genera represented. The presence of Grg/phaea and of attached crinoids in the Lower Jurassic is considered to be a good indicator of fairly warm waters. In contrast, the Upper Jurassic rocks in northern Alaska contain such typical Boreal elements as Aacella and the Cardioceratinae and lack most elements typical Of the Upper Jurassic of the Mediterranean region. This faunal differentiation has generally been interpreted as indicating the presence of climatic zones. The poverty of molluscan genera and species in the Jurassic beds of northern Alaska may also be related to the lower temperature of the sea water than in the Mediterranean province. GEOGRAPHIC DISTRIBUTION The occurrence by area and locality of the species described in this report is indicated in tables 2 to 4. The general position of each locality is shown on figure 20. Detailed descriptions Of the individual localities are given in the following list. Localities at which fossils were collected from outcrops of the Jurassic in northern Alaska Locality number on fig. 20 Geological Survey Mesozoic locality Collection field numbers Collector and year of collection, description of locality, and stratigraphic assignment and age H 10 .10 10 10 11 12 12 13 14 22127 22126 22776 23577 23697 22507 22509 23598 21552 22591 22584 22585 22585 22586 22582 22587 22588 22579 22580 49A 8343 49A SE30 51ASa56 51ATr266 51ATr257 50ATr166 50ATI226 51ATr19 49AT1‘352 50A Ke263 50AKel32 50A K9135 50AKe93 50AKe136 50AK6121 50AKel74 50AKel75 50A K697 50AK6109 E. G. Sable, 1949. Kukpowruk River, ap- proximate lat 68°42’30” N., long 163°14’ W., eastern part of a large cut bank on southwest side of river. Sandstone and shale con- taining concretions. Stratigraphic position unknown. Upper Jurassic, Kimmeridgian to lower Portlandian. E. G. Sable, 1949. Near Kukpowruk River, on mountain ridge between first and second creeks west of large cut banks of black shale. Approximate lat 68°23’ N., long 162°43' W. Sandstone and shale beds from 50 to 100 feet above top of Triassic strata. Upper Jurassrc, upper Oxfordian or lower Kimmeridgian. E. G. Sable, 1951. West bank of easternmost fork of Driftwood Creek at first cutbank above small tributary from the west. Ap- proximate lat 68°40’ N., long 160°26’28” W. Conglomerate, conglomeratic .shale, and chert, possibly near base of ngak shale, fossils from concretions in shale. Upper Jurassic, middle Kimmeridgian to lower Portlandian. . L. Tailleur, 1951. Kill wa river, lat 68°43’ N., long 158°25’ W. oquinoid limestone overlain by shale, siltstone, and sandstone 3 feet above Triassic rocks. Upper Jurassxc, middle Kimmeridgian to lower Portlandian. I. L. Tailleur, 1951. Kiligwa River, lat 68°ll'3’ N., long 158°25’ W. Coquinoid limestone .“1 sequence of shale, chert. and chert breccxa. Probably near base of overturned sectlon. Upper Jurassic, middle Kimmeridglan to lower Portlandian. . L. Tailleur, 1950. Cutaway Creek, lat 68°36’. N.,long 157°33’ W., 3 miles NW. of Rim Butte. Coquinoid limestone 10 feet above Triassic strata. Upper Jurassic, upper Ox- fordian or lower Kimmeridgian. L. Tailleur, 1950. Let 68°40’ N., long 157°08' W., Ipnavik River, 4 miles north of Ekakevik Mountain. Coquinoid limestone 110 feet above Triassic strata. Upper Jurassic, upper Oxfordian or lower Kimmeridgian. . L. Tailleur, 1951. Lat 68°23’ N., long 157°15’ W., Ipnavik River 2 miles south of mouth of Memorial Creek. Coarse- to fine-grained graywacke from 100 to 150 feet above Triassic strata. Upper Jurassic, probably middle Kimmeridgian to lower Portlandian. . L. Tailleur, 1949. Lat 68°31’ N., long 153°03' W., cutbank on Fortress Creek about 5 miles SSW. of Fortress Mountain. Medium-dark- green fine-grained graywacke containing much volcanic material. Middle Jurassic, lower Bajocian. A. S. Keller, 1950. Tiglukpuk Creek, lat 68°22’ N., long 151°50’ W. Graywacke. Middle Jurassic, Bajocian. A. S. Keller, 1950. Peregrine Creek, lat 68°26’ N., long 150°28’ W. Fine-grained sandstone. Upper Jurassic, probably Kimmeridgian. A. S. Keller, 1950. Peregrine Creek, lat 68°26’ N ., long 150°28’ W. Same general locality as 22584. Fine-grained sandstone. Upper Jurassic, probably Kimmeridgien. A. S. Keller, 1950. East Fork of Manushuk River, NEMSEM quad. 683; lat 68°27’ N., long. 150°20’W. Coquinoid limestone. Up- per Jurassic, upper Oxfordian or lower Kimmeridgian. A. S. Keller, 1950. Peregrine Creek, lat 68°26’ N., long l50°28’ W. Same general locality as 22584. Fine-grained sandstone. Upper Ju- rassic, probably Kimmeridgian. A. S. Keller, 1950. Peregrine Creek, lat 68°28’ N., long 150°27’ W. Coquinoid limestone. Upper Jurassic, upper Oxfordian or lower Kimmeridgian. A. S. Keller, 1950. East Fork of Nanushuk River, lat 68°30' N ., long 150°24’ W. Coqui- noid limestone. Upper Jurassic, middle Kimmeridgian to lower Portlandian. A. S. Keller, 1950. East fork of Nanushuk River, lat 68°30’ N., long 150°24’ W., same location as 22587 Coquinoid limestone. Upper Jurassic, probably upper Oxfordian or lower Kimmeridgian. A. S. Keller, 1950. Lat 68°27’ N ., long 150°20’ W., same general location as locality 22578. Coquinoid limestone. Upper Jurassic, middle Kimmeridgian to lower Portlandian. A. S. Keller, 1950. May Creek, lat 68°26' N., long 150°09’ W. Coquinoid limestone. Upper Jurassic, middle Kimmeridgian to Portlandian. H H I" H H 79 CHARACTERISTICM-IJURASSIC MOLLUSKS FROM NORTHERN ALASKA .53“? 955.8: E 33:52 “838:8 :mwou 3333. 9:323 Qua NowaHIdN aha—rm _ A _ a _ _ _ _ mWI=I OO. 0 On «0‘. tfl'. com. uNh. u¢m_ uWfl. ; uDW. .00. nNW. k . / _ \ CK A. . J 0 \ m: . , I mw,’ km w / m n 4 bags, I / L .40 .w. _ #6 m 9 M x m. /,w a Xm o , 40 x Y A J \ u m 1 y w a, a0 yo / 4) r mx/W m4 \ / v. . 1 an * 4 “J4 .fl m + fl V / a 4v 4mm! ¢ ¢ ‘ r. ¢x 1oz)» \\ 2p .x \ V A \ x. a _ ,m _ m l a J ‘ v/ a a 4. J A % m A :7? * A .7 . u. . a . w , ,., ‘ m m m _ m , ,x H , x \ u r x , y ,_ m K W \k A x \ . Mxx , \\ ,1 1/, u. xx an 6 A an . w. .W a ‘Wl 7; ave/x . Q «Q co M \\ ‘ r . 0 av r l y I \\ 4, m , u. 9 L~\ \ “ A\ m. .w .2 r‘ ‘ A m \ \ ...| A A ‘ F _ \n \ (1/ I . 8 _ gaggle. _ u /l | mix \ A m :4 -i1i .zommsaa m K A 2.0; :2 «25...... £95. \V . . I [I w 35:83 :3: \ix lt|\l camngm 230‘ . . 11 J"! 8 x \\\\V\ / l: 8 332.5; :58 0 l zo_._.< N 30253 1.53 q 4/ , .K \ b 12:5 .58 ‘ F , , _ A Q A A, _ _ ,. ,,, A b _ _ A fl _ . \ A _,_ z A ‘> .3: .3. .3. .09 .3. A ll: .vn. .mm. .3. .8. .3. .ow. .0h .2. 80 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Localities at which fossils were collected from outcrops of the Jurassic in northern Alaska—Continued . Geological . . . . Geological ' - - - Locallty S . Collector and year of collectlon, description Locality . Collector and year of collection, description number urvey Collectlon of locality and stratigraphic assignment number Survey Collection of localit and strati ra hi i ment Mesozoxc fieldnumbers ' Mesozmc field numbers 5” g 1D 0 assgn on fig. 20 locality and age on fig. 20 locality and age . . .- 14 22581 50AKe114 A. S. Keller, 1950. Same general location as 25 22596 50AGr18 George Gryc, R. W. Imlay, Allan Kover,1950. Mes. loo. 22580, lat 68°26’ N., long 150°09' W. Canning River, west side, lat 69°23’30” N., Coquinoid limestone. Upper Jurassic, long 146°07’30" W. Black shale containing middle Kimmeridgian to lower Portlandian. ironstone beds, lenses and nodules about 2,300 15 22749 51ADt149 R. L. Detterman, 1951. About 1 mile west of feet above base of exposed section. Upper Lupine River on long ridge, lat 68°47' N., Jurassic, lower Callovian. long 148°25’ W. Dark siltstone and silty 25 22597 50AGr24 George Gryc, R. W. Imlay, Allan Kover, 1950. shale, weathers metallic blue, contains fossil Canning River, west bank, lat 69°23’20” N., coquinas. Upper Jurassic, middle Kim- long 146°07’30" W., same locality as Mes. meridgian to lower Portlandian. locs. 21024 and 24033. Black shale containing 15 22750 51ADt151 R. L. Detterman, 1951. Lupine River area. beds and nodules of ironstone about 200 feet Cutbank in small stream one-fifth of a mile below top of exposed section. Upper Jurassic, north of Mes. loc. 22749, lat 68°48’ N ., long middle Callovian. 148°25’ W. Dark siltstone having a blue 25 24033 52AKe37 A.S. Keller, 1952. Canning River, lat 69°25’ N., metallic luster and fissile noncalcareous silty long 146°08’ W. Fossils from slightly calcare- shale. Upper Jurassic, probably Kimmer- ous ironstone beds in up er part of Kingak idgian to Portlandian. shale, same locality as es. locs. 21024 and 15 22751 51ADtl52 R. L. Detterman, 1951. Lupine River area, 22597. Upper Jurassic, Callovian. cutbank three-tenths of a mile east of Mes. 26 21023 47AGr202 George Gryc, 1947. Canning River, west bank, loc. 22750 in same stream, lat 68°49’ N., long at mouths of Eagle and Cache Creeks, lat 148°24’ W. Siltstone and silty shale as at 69°25’ N., long 146°08’ W. From base of Mes loc. 22750. Upper Jurassic, middle pyritic black shale outcrops that contain Kimmeridgian to lower Portlandian. nodules and lenses of ironstone. Middle 16 22766 51AKel35 A. S. Keller, 1951. Lupine River, lat 68°52’ N., Jurassic, lower Bajocian. long 148°22’ W. Fissile clay to silt shale con- 26 22595 50AGr9 George Gryc, R. W. Imlay, Allan Kover, 1950. taining spheroidal concretions and sideritic Canning River, west bank, lat 69°25’ N., lenses. About 500 feet above the base of the long 146°08’ W., same locality as Mes. loc. Kingak shale. Upper Jurassic, middle 21023. 150 feet above base of exposure. Black Kimmeridgian. shale containing ironstone lenses and nodules. 16 22768 51AKe153 A. S. Keller, 1951. Lupine River, lat 68°52’ N., Middle Jurassic, lower Bajocian. long 148°22’ W. Shale as at Mes. 100. 22766 27 24013 52AMo48 R. H. Morris, 1952. Cutbank on west side of between 500 to 800 feet above base of Kingak Canning River, lat 69°30’45” N., long shale. UpperJ urassic, middle Kimmeridgian 146°18’45" W. Black fissile shale containing to lower Portlandian. limestone concretions 50 feet below top of 16 22769 51AKe154 A. S. Keller, 1951. Lupine River, lat 68°52’ N., Kingak shale. Upper Jurassic, upper 0x- long 148°22’ W. Shale as at Mes. loc. 22766. fordian or Kimmeridgian. About 300 feet above base of Kingak shale. 27 24014 52AM050 R. H. Morris, 1952. Cutbank on west side of Upper Jurassic, middle Kimmeridgian. Canning River, lat 69°32’ N., long 146°18’ W. 17 22746 51ADt136 R. L. Detterman, 1951. Small divide nine- Black shale containing limestone concretions tenths of a mile east of Nosebleed Creek, lat 50 feet below top of Kingak shale. Upper 68" 50’ N., long 148°10’ W.‘ Dark ferruginous Jurassic, upper Oxfordian or lower Kim- brittle silty shale. Upper Jurassic, middle meridgian. Kimmeridgian to lower Portlandian. 27 21028 47AGr239 George Gryc, 1947. Canning River, 2% miles 18 22747 51ADt144 R. L. Detterman, 1951. Long cutbank on west south of Black Island, NEVi NE}i quad. 682, side of Nosebleed Creek, just below ice field, lat 69°30’45" N., long 146°18’45’ W. Black lat 68°52’ N., long 148°14’ W Calcareous shale containing ironstone interbeds near top siltstone. Lower Jurassic, Pliensbachian. of Kingak shale. Upper Jurassic, upper 18 22748 51ADt145 R. L. Detterman, 1951. Nosebleed Creek, Oxfordian or lower Kimmeridglan. , about one-tenth of a mile north of Mes. 100. 27 22598 50AG1‘31 George Gryc, R. W. Imlay, Allan Kover, 1950. 22747 on same side, lat 68°52’ N., long 148°l5’ Canning River at same locality as Mes. loc. W. Siltstone and silty shale. Lower Juras- 21028. From 200 to 500 feet below top of sic. Kingak shale. Upper Jurassic, upper Ox- 19 22745 51ADtl34 R. L. Detterman, 1951. West fork of Ivishak fordian or lower Klmmeridgian. River, lat 68°58’ N., long 148°07’ W. East 28 21025 47AGr257 George Gryc, 1947. Black Island in Canning side of river south of junction of tributary River, lat 69°33’ N., long 146°15’ W. Black from east. Siltstone lenses in hard, splintery shale containing ironstone interbeds imme- silty shale. Within lower 400 feet of Kingak diately overlying the Upper Triassic Shublik shale. Upper Jurassic, middle Callovian. formation. Lower Jurassic. 19 22764 51AKe115 A. S. Keller, 1951. West fork of Ivishak River, 28 24035 52AKe46 A. S. Keller, 1952. Canning River, lat 69°33’ lat 68°58’ N., long 148°05’ W. Pyritic silt- N., long 146°15’ W. Middle Jurassic, lower stone and shale containing large spheroidal Bajocian. Ironstone beds and shales from concretions within the lower 400 feet of the 1,000 to 1,500 feet below the top of the Kingak Kingak shale. Upper Jurassic, probably - shale. - Callovian. 29' 23772 50AGr61 George Gryc, R. W. Imlay, Allan Kover, 1950. 20 22759 51AKe48 A. S. Keller, 1951. Gilead Creek, lat 69°13’ N., Near Red Hill on Ignek Creek, lat 69°36’ N., long 147°40’ W. Isolated cutbank of dark- long 146°06’ W. Shale underlying sandstone gray shale containing large lenses of light-gray at base of Ignek formation. LOWer Jurassic , ironstone. Kingak shale. Upper Jurassic, Toarcian. upper Oxfordian to lower Kimmeridgian. 30 21819 48AWh130 C. L. Whittington, 1948. North bank of Sadie- 21 22739 51ADt22 R. L. Detterman. 1951. West Fork of Sha- rochit River at mouth of tributary from viovik River, lat 69°23’ N., long 147°13' W. northwest, about 4 miles upstreagl from Interbedded siltstone and sandstone 50 feet mouth of Ignek Valley FPI‘k; lat 69 _30 N., below basal sandstone of Okpikruak forma- long 145°05' W. Thin cnnold beds m gray tion. Kingak shale. Upper Oxfordian or shale containing ironstone interbeds near Kimmeridgian, h Chaise $761112?ng shalle§48Lo§ver J uraSSlc.1 11th ‘ ' o I 30 21820 48AW 131 . . 1 ing on, . ame genera - 22 24011 52AM04 R. H. Morrls,°1952. Jumper Fork, lat 69 23 ology as Mes. loc. 21819 but about 300 yards lilfilongl 146 59 2V qu‘fi part 0‘- ngak downstream Lower Jurassic . n n . . ‘ ' ioavlfer 15335.22. 6 enses m 801‘ fiss‘le Shale“ 31 22033 48AWh132 c. L. Whlttmgton, 19408. [North bank 3f sad- 23 21026 47AGr32 George Gryc, 1947. Shaviovik River, main lerochlt 15“”?! lat 69 31 N" long 145 02 W' / About ”4 miles downstream from Mes. loc. fork or mOSt easterly branch, SEl‘NEM 21819 Dull-black earthy shale at first out- quad. 682’ lat 69°22 N" long “6°32, W‘ cro downstream from Mes 100 21820 and Black shale containing nodules and interbeds been 500 feet hi her stratigraphically unless of ironstone and some limestone. Isolated govered “1“)er conceals faults Kingak outcrops of Kingak shale. Upper Jurassic, sh 1 U er Jurassic lower Callovian upper Oxfordian or lower Kimmeridgian. 32 22081 48ASa146 E. (geéablepgms. On south-flowing tributary 23 21027 47AGr8 George Gryc, 1947. From same locality and of Sadle,5chit River two_fifths of a mile about same stratigraphic position as Mes. above mouth, approximate lat 69°32’10" N., 10921026- UPPe.’ 19185510, UPW Oxford!” long 145°55' w. Probably within middle or lower Kimmerldglan. third of Kingak shale and about 1,700 feet 24 24012 52AM036 R. H. M01115, 1952. Kavik River, lat 69°19, above 1125 basemblack earthy shale, Middle N.,long 146°18' W. Ironstone lenses in black Jurassicy lower Bajocian. pyrltic shale. Lower Jurassic. 32 22082 48ASa148 E. G. Sable, 194s. Downstream one-fifth of a 25 21024 47AGr205 George Gryc, 1947. Canning River, west bank, mile from Mes. loc. 22081, approximate lat about 2,850 feet upstream from Mes. loc. 69°32’ N.,long144°54’ W. Pyrite concretions 21023. Black shale containing ironstone beds. in black shale about 2,600 feet above base of Upper J urassic, Callovian. Kingak shale. Middle Jurassic, Bajocian. CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA ' 81 Localities at which fossils were collected from outcrops of the Jurassic in northern Alaska—Continued . Geological Egg? Survey Collection onfl 20 Mesozoic fleldnumbers g. locality Collector and year of collection, description of locality, and stratigraphic assignment and age 33 10308 114a E. de K. Leffingwell, 1911. Sadlerochit River, half a mile above mouth of Camp 263 Greek; lat 69°33’ N., long 144°47’ W. Fossils from concretions in black shale at foot of exposure and probably in lower 100 feet of Kingak shale. Middle Jurassic, lower Balocian. E. de K. Leflingwell, 1911. Sadlerochit River, north side, about a quarter of a mile down- stream from Camp 263 Greek and 1% miles upstream from mouth of Neruokpukkoonga Creek about 1,500 feet above base of Kingak shale; lat 69°33’ N., long 144°46’ W. Middle Jurassic, lower Bajocian. E. de K. Leflingwell, 1911. Sadlerochit River, cut on north side about 3,000 feet above base of Jurassic, probably lat 69°33’ N., long 144°43’ W. Friable black shale containmg pyrite concretions. Middle Jurassic, lower Bajocian. E. G. Sable, 1948. Cutbank on east side of Sadlerochit River near east end of Sadlerochit Mountains. First Cutbank north of tribu- tary stream from south; lat 69°36’20” N., long 144°27’30” W. Massive sandstone con~ taining conglomerate and ironstone lenses, probably within 75 feet of base of Jurassic. Lower Jurassic. E. G. Sable, 1948. Most prominent cliff on west side of Sadlerochit River near east end of Sadlerochit Mountains, lat 69°37’30” N. long 144°25’ W. Sequence of interbedded sandstone, shale, siltstone, and conglomerate lenses about 120 feet above outcrops of Trias- sic rocks. Lower Jurassic. E. G. Sable, 1948. Cutbank on east bank or easternmost meander of Sadlerochit River near east end of Sadlerochit Mountains, lat 69°39’ N., long 144°23’ W. Pebbly fine- grained dark-gray sandstone at base of 480 feet of sandstone, shale, and conglomerate lenses. Lower Jurassic. 33 10309 ll4b 34 10307 110 35 23747 48AS3210 36 23749 48ASa229 37 23748 48ASaZl4 SUMMARY OF RESULTS The Jurassic strata cropping out in northern Alaska are impoverished faunally in respect to genera, species, and individuals of macrofossils. Well cores from the Arctic Coastal Plain indicate that the subsurface J u- rassic is much richer in individuals and somewhat richer in genera than the outcrops. The mollusks are repre- sented by only 12 genera of pelecypods, 14: genera of cephalopods, and 1 genus of scaphopods. Other macro- fossils include 1 brittle star, 1 crinoid, and 2 or 3 genera of brachiopods. The brachiopods, the brittle star, and many of the pelecypods are too poorly preserved to merit description. Only the mollusks are described. These include 7 species of pelecypods, 23 species of am- monites, and 1 belemnite. Because of poor preserva- tion, most of these species are merely compared with European or American species. However, 4 species of Amella are identified with species common in the J u- rassic of the Boreal region, 3 species of ammonites are identified with species occurring in southwest Alaska, and 1 ammonite is identified with a species common to Europe and South America. The stratigraphic positions of many of the fossil collections have not been determined very closely be- cause of the great thicknesses of similar appearing strata involved, the lack of key beds, structural com- 342062—55—3 plications, limited exposures, and the presence of dis- conformities involving erosion and overlap. At one place or another, beds ranging in age from Early to Late Jurassic rest on Upper Triassic rocks. In many places interpretations of the stratigraphy or the struc- ture are based on the fossils present, or the fossils are used as supplementary evidence. The age determina- tions of the fossils are based on the known ranges and faunal succession of the various genera and species elsewhere in the Boreal region or other parts of North America and in northwest Europe. The succession has been proven correct for northern Alaska whenever con— ditions have permitted stratigraphic collecting. The Lower Jurassic includes no recognizable dis- conformities. In comparison with the Lower Jurassic of Europe, the oldest stage, the Hettangian, has not been identified faunally; but there is an ample thick— ness of strata in some sections to account for it. The next younger stage, the Sinemurian, is identified by the ammonite “Arietites” cf. “A.” bucklamli (Sowerby). The overlying Pliensbachian stage is identified by the ammonite Amaltheus. The lower Toarcian is identi- fied by finely ribbed species of Dactylioceras which are succeeded by coarsely ribbed species of Dactylio- ceras. The upper Toarcian is identified by certain spe— cies of Pseudoliooeras. The lower Bajocian is identified by the ammonites Tmetooeras, Pseudolioceras, and E rycites. Two species of Pseudolioceras and E rycites are also common at the base of the Middle Jurassic in southwestAlaska. The middle and upper Bajocian and the entire Ba- thonian have not been identified faunally in northern Alaska and are probably represented in part by a disconformity. The lower Callovian is identified by the ammonite Arcticocems; the middle Callovian, by Pseudocado- ceras; and the middle to upper Callovian, by Beineckeia (Reineclceites) . The highest Callovian and the lower Oxfordian have not been identified faunally and are probably repre- sented by a major disconformity. The upper Oxfordian to lower Kimmeridgian strata are identified by the ammonite Amoeboceras and the pelecypods Aucella spitiensis Holdhaus and A. con- centrica (Sowerby). The middle Kimmeridgian to lower Portlandian strata are identified by Aucella rugosa (Fisher) and A. mosquensis (von Buch). The lower part of the range of these species overlaps the highest part of the range of A. canoe/retried (Sowerby). The upper Portlandian has not been identified fau- nally in northern Alaska, and there is field evidence for an erosional unconformity during late Portlandian time. 82 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 3,—Test wells from which Jurassic fossils and stratigraphic data have been obtained Eleva- Jurassic rocks represented tion at Top of Base of Test well (See fig. 20.) Location ground Jurassic Jurassic leyéeeltm m feet in feet Lower Jurassic Lower Bajocian Up 1%fiufigli‘gggnand Simpson 1 _________ LatN70°57’05” N., long 155°21’45” 15. 0 5, 550 6, 300 Present_ _ __ (?) ___________ Absent. South Barrow 2- _ _ _ Lat 21°15’51” N., long 156°37’55” 23. 5 2, 310 2, 443 _____ do _____ Present at Do. W. 2 391. South Barrow 3- _ - _ La‘tzv71°09’40” N., long 156°34’45” 30. 0 1, 645 2, 610 _____ do _____ (?)_’ __________ Do. Topagoruk 1 _______ Lat 20°37’30” N., long 155°53’36” 27. 0 6, 910 8, 640 _____ do _____ Present at Microfauna at W. 8,111 and 6,910 to 7,820. 8 113. Avak 1 ____________ La€V71°15’02” N., long 156°28’06” 1. 8 1, 360 2, 300 _____ do _____ (?) _, __________ Absent. TABLE 4.—Jurassic macrofossils from well cores in northern Alaska Depths in test wells, in feet, from which fossils were obtained Fossil Simpson test well 1 S‘i‘gg 3331?? South Barrow test well 3 ’{gsréavggfiui‘r Ag‘agltfst Brittle star _______________________________________________________________ 2, 010 ____________________ Brachiopods ______________________________________________________________ 2, 131; 2, 132 ____________________ Velopecten? sp _____________________________________________________________ 2, 165; 2, 186; 2, 199 ____________________ Oxytoma sp _______________________________________ 6, 174; 6, 186 __________ 2, 412 ____________________ “Arietites” cf. “A.” bucklandi (Sowerby) ____________________________________________________________________ 1, 836 Amalthcus of. A. nudus (Quenstedt) __________________________________________ 2, 198 ____________________ of. A. depressus (Simpson) ________________________________________________ 2, 186 ____________________ of. A. margaritatus (Montfort) _____________________________________________ 2, 111 ____________________ sp. indet ________________________________________ 5, 680 __________ 2, 069—2, 198 ____________________ Coeloceras afl'. C’. mucronatum (D’Orbigny) ____________________________________ 2, 063 ____________________ Dactylioceras cf. D. semicelatum (Simpson) ____________________________________ 2, 017; 2, 018 ____________________ of. D. kanense McLearn ___________________________________________________ , 016 ____________________ of. D. crassiusculosum (Simpson) ___________________________________________ 1, 772 ____________________ of. D. delicatum (Bean—Simpson) ___________________________________________ 1, 772 ____________________ of. D. commune (Sowerby) _________________________________________________ l, 772 ____________________ Pseudolioceras? sp _____________________________________________________________________________ 8, 111 __________ Tmetoceras sp ___________________________________________________ 2, 391 ____________________ 8, 113 __________ Faunal and lithologic relationships suggest that much of the Jurassic sea bottom in northern Alaska sloped moderately basinward and was stagnant, and at least as deep as the lower part of the neritic zone. The existence of such depths may explain the presence of the ammonites Phylloceras, Lytoceras, and Reineclceia, which are missing from the Jurassic in the interior of North America, east Greenland, and the Barents Sea area. The scantiness of the faunas over much of the seaway is probably related to unfavorable bottom con- ditions and also to derivation of most of the associated sediment from sedimentary rocks to the south. In con- trast, the much more abundant faunas found along the northern margin of the seaway are associated with sediments derived from metamorphic rocks to the north and probably had a more ample supply of phosphate. The poverty of molluscan genera and species may also be related to a somewhat lower temperature of sea— water in the Boreal region than in the Mediterranean region. Fairly warm water, at least during Early Jurassic and early Middle Jurassic (Bajocian) time, is indicated by the presence of Gryphaea and of am- monites that have a cosmopolitan distribution. Fauna] differentiation in the Boreal region, including Alaska, during the Late Jurassic is considered evidence for the presence of climatic zones. SYSTEMATIC DESCRIPTIONS Class PELEGYPODA Genus GRYPHAEA Lamarck. 1801 Gryphaea cf. G. cymbium Lamarck Plate 8, figures 2—4 Internal molds of 9 left valves and 4 right valves represent a species that probably is identical with G. cymbium Lamarck. The right valve is slightly convex on the figured specimen and is slightly concave on the other specimens. The left valve is short, plump, and bears a sulcus on its posterior side. The beak is blunt and incurved directly and in some specimens bears an attachment scar. CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 83 The Alaskan specimens compared to G. cymbz'um were found within several hundred feet of the base of the Jurassic. In England Gryphaea cymbium is typical of the middle Lias‘ (equals upper Pliensbachian) (Arkell, 1933, p. 162) but has been recorded in the lower Pliensbachian (Arkell, 1933, p. 140, 144, 148). In central Europe it has the same range (Pfannenstiel, 1928, p. 390). Figured specimens: USNM 108752. Kingak shale, USGS Mes. loc. 23748. Genus AUCELLA Keyserling, 1846 Aucella concentrica (Sowerby) Plate 9, figures 11—16 (For synonymy see Pavlow, 1907, Soc. Impériale Naturalistes, Moscou, Nouv. Mém., v. 17, livr. 1, p. 14; Sokolov, 1908, Com. géol. [Petrograd] Mém. Nouv. sér., livr. 36, p. 8; Waterston, 1951, Royal Soc. Edinburgh Trans, v. 62, p. 40). This species has been thoroughly described and dis- cussed in several publications (Lahusen, 1888, p. 32, 33; Pavlow, 1907, p. 14—16; Sokolov, 1908, p. 8—10, 27, 28; Sokolov and Bodylevsky, 1931, p. 34, 35, under the name A. bronmi (Rouiller)). The careful work of Water- ston (1951, p. 40, 41, pl. 1, figs 2a—c) has demonstrated, however, that the species was first described by Sowerby (1827, v. 4, p. 113, pl. 559, fig. 1) as Plagiostoma con— centrica. Its valves are nearly equal, elongated ob- liquely, gently to moderately convex in the unbonal region, and flattened posteriorly. Its beaks are small, low, and curved inward. Its surface bears many sharp concentric ribs that are crossed by very fine closely spaced radial striae. Minor variations in the convexity of the shell, degree of obliquity of the valves, and strength or pattern of the ribbing have been the basis for the naming of a number of species, most of which Sokolov (1908, p. 8) includes in Aucella bronmi (Rouiller) (equals P. can— centm'ca Sowerby) as normal varieties. This is a sensi— ble procedure considering that the varieties are not known to have any stratigraphic significance. In northern Alaska about 50 specimens of Awella concentrica (SOWerby) have been collected from 11 localities in the foothills north of the Brooks Range. Some of these specimens are from thin coquinas which consist mainly of crushed and broken Aucellas. Others are from concretions and exhibit fairly complete shell outlines. The radial striae are generally better pre- served on external molds than on internal molds, where they may be visible only at the points of intersection with concentric ribs. The specimens preserved in the coquinas are identified on the basis of their flattened valves, nearly microscopic radial striae,'and rather low concentric ribs. Similar coquinas composed of A. ru— gosa (Fischer) have much more convex left valves and much higher concentric ribs. Aucella concentrica (Sowerby) in northern Eurasia and the Barents Sea area ranges from late Oxfordian into the middle Kimmeridgian and attains its maximum abundance in the early Kimmeridgian (Lahusen, 1888, p. 8, 26, 33; Pavlow, 1907, table opposite p. 84; Sokolov, 1908, p. 2; Sokolov and Bodylevsky, 1931, p. 34, 35). Its highest occurrence is in the zone of Aulacostephamos pseudomutabz’lz‘s, which probably corresponds to its occurrence in Mexico (Burckhardt, 1930, p. 80). Its lowest occurrence is Within the zone of Uardz’ocems cordatum as used by the Russians, which includes much more than the northwest European zone of Cardiocems cordatum (Arkell, 1946, p. 25). It has not been re- corded definitely below the zone of Amoebocems alter- noz’des and apparently is rare below the Russian zone of Amoebocems alternam (Lahusen, 1888, p. 26). The distribution of Auoella concentrica (Sowerby) in other parts of the Boreal region shows that it is not known below the lowest occurrence of Amoebocems. In southern Germany some small Aucellas that prob- ably represent only a variety of A. concentrica occur in the zone of Amoebocems altemans (Pompeckj, 1901 p. 23, 24, 29). In Spitzbergen A..comentm’ca occurs with Amoebocems (Prionodocems) (Sokolow and Bodylev- sky, 1931, p. 20, 83, 107, 136). It is reported to be associated there with Cardioceras afi'. C’. cordatum Sowerby, but the ammonite illustrated (Sokolov and Bodylevsky, 1931, p. 83, pl. 6, fig. 3) is an Amoebocems. In southwestern Alaska and the Cook Inlet region of Alaska, A. concentrica is abundant in beds containing Amoebocems (Prionodocems) and has never been found associated with Cardiocems. Some of the specimens of Aucella concentrica from northern Alaska are of middle Kimmeridgian age as they are associated at Mes. loos. 22769 and 22766 with A. mgosa (Fischer) and A. mosquemis (von Buch), which are not known in beds older than the middle Kimmeridgian. Most of the specimens of A. concen- tm’ca are from coquinas and are probably mainly of early Kimmeridgian age as indicated by the absence of other species of Aucella and by the fact that A. com— centm’ca attained its greatest abundance during that time. A few specimens associated with A. spitiemis Holdhaus and the ammonite Amoebocems (Prionodo- Gems) at Mes. locs. 21028 and 22598 are probably of late Oxfordian age, as Prionodocems is characteristic of the late Oxfordian and is rare in the early Kim- meridgian. Plesiotypes: USNM 108743, 108744, 108745, 108749. Kingak shale, USGS Mes. locs. 21026, 21028, 22126, 22507, 22509, 22578, 22582, 22598, 22759, 22766. 22769. 84 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Aucella spitiensis Holdhaus Plate 9, figures 1—10 Aucella spitiensis Holdhaus, 1913, Paleontologica Indica, ser. 15, v. 4, pt. 2, p. 408—410, pl. 97, figs. 7-13. Aucella, subspitiensis Krumbeck, 1934, Neues Jahrb., Beilage— Band 71B, 1). 439—448, pl. 14, figs. 1—12, pl. 15, figs. 1—8. Aucella cf. A. subspitiensis Wandel, 1936, Neues J ahrb., Beilage- Band 75B, p. 462—463. Buchia subspitiensis Teichert, 1940, Royal Soc. Australia J our., v. 26, p. 112—113, pl. 1, figs. 1—7. Western Thirty-five specimens from northern Alaska are assigned to this species. They have obliquely elongated valves; the right valve is nearly flat, and the left valve is weakly to moderately convex. The beak on the right valve is short and blunt; the beak on the left valve is short, stout, and gently incurved. The surface bears concentric ribbing of irregular strength and spacing that is superposed on irregular concentric undula- tions. Weak scattered radial striae are generally re- stricted to the umbonal region and are visible only on some external molds and on specimens that retain some shelly material. Most internal molds do not show any trace of radial striae. The appearance of the Alaskan specimens of A. spi- tiensz's Holdhaus differs from that of the Indian speci- mens only by the presence of weak radial striae. The Indian specimens, however, are nearly all internal molds (Holdhaus, 1913, p. 404, 409) on which radial striae would scarcely show if weakly developed on the shell. The Alaskan specimens of A. spétz'ensis Holdhaus appear to be identical with A. subspitiensis Krumbeck from the Malay Archipelago and Australia. The later species is reported by Krumbeck (1934, p. 445—446) to differ from A. spitz'ensis mainly by the left valve having radial striae and a more obliquely truncated anterior margin. However, concerning the weak radial striae, Krumbeck (1934, p. 443) states that they are lacking on most of the molds of the type collection of A. subspi- tiensz's and are visible only on some of the best preserved fossils. Concerning the shape of the anterior margin of the left valve, Krumbeck (1934, p. 445) notes that one of the specimens from India figured by Holdhaus (1913, pl. 97, figs. 10a—c) as A. spitiemz’s has a similar shape to A. subspitiemz’s and may represent that species. As this particular specimen was considered by Hold- haus (1913, p. 410) as typical of the majority of speci— mens in his species, A. spitiensz’s, the differences noted by Krumbeck are not valid. A. spitiensz’s Holdhaus resembles A. concentrica con- siderably in the Oblique elongation of the shell but is readily distinguished by its conspicuous, irregular con- centric undulations, by its more convex left valve, and by its irregularly developed radial striae. The range of A. spitz'ensz's Holdhaus is not known. Teichert (1940, p. 110, 111) has summarized the evi- dence and concluded that the possible maximum range is late Oxfordian to late Kimmeridgian. In northern Alaska A. spitz'ensis is associated at Mes. locs. 24014 and 22598 with the ammonite Amoeboce’ras . (Pm'nodo- ceras?), Whose presence is excellent evidence that A. spitz'ensis existed in the late Oxfordian or early Kim- m‘eridgian. Its association in Alaska with Aucella concentrica (Sowerby) at Mes. locs. 21028 and 22598 and its nonassociation with A. mosquensz's (von Buch) or A. mgosa (Fischer) suggest that it does not range as high as the middle Kimmeridgian. Plesiotypes: USNM 108746a—f, 1087 47a, b. Kingak shales, USGS Mes. locs. 21026, 21028, 22598, 24013, 24014. Aucella rugosa (Fischer) Plate 9, figures 20—27 (For synonymy see Pavlow, A. P., 1907, Soc. Impériale Natural- istes Moscou, Nouv. Mém., v. 17, livr. 1, p. 36, 37; Spath, 1936, Meddelelser om Grbnland, bind 99, nr. 3, p. 100.) Aucella mgosa (Fischer) is the most common species of Aucella in the Upper Jurassic of northern Alaska and is represented in the United States Geological Sur- vey collections by 50 well-preserved specimens and by 75 fragmentary or crushed specimens. The 75 speci- mens are a selection from coquinas that consist of enormous numbers of Aucellas. ' The species has been well described and illustrated by Pavlow (1907, p. 36— :38, pl. 1, figs. 6a—c, 7a—c). Its shape is similar to that Of A. mosque’nsz's (von Buch) , with which it is commonly associated. Most specimens are less elongated poste- riorly, are broader and flatter, and have less strongly incurved beaks. The distinguishing feature, however, is the ribbing. On A. mgosa (Fischer) the concentric ribs are high, thin, and widely and generally regularly spaced. These are crossed by extremely fine dense radial striae. In contrast, on A. mosquensis (von Buch) the concentric ribs are much lower and are ir- regular in strength and spacing; the radial markings, when present, are broader, lower, and scattered; and the surface of the shell is marked by constrictions at irregu- lar intervals. If internal molds only are compared the differences in ribbing are not so striking, and the iden- tification is based mainly on rib pattern and the density of radial striae when viewed under oblique lighting. In discussing the Aucellas of east Greenland, Spath (1936, p. 100) notes that the specimens he assigned to A. mgosa (Fischer) are connected by transitions with typical A. mosquensz's (von Buch) ; and he doubts, therefore, whether A. rugosa is a distinct species. The writer’s opinion, after handling hundreds of specimens from the Naknek formation of the Cook Inlet region, CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 85 is that most specimens are definitely referable to one species or to the other. A few specimens, such as the one shown on pl. 9, fig. 26, have ribbing characteristic of A. mgosa in the umbonal region but posteriorly develop constrictions and irregular ribbing similar to that of A. mosquensis. Such specimens are possibly transitional between the two species or are possibly a variant of A. rugosa. The latter is most likely because of the presence of ribbing characteristic of A. mgosa on the umbonal region and because constrictions and swellings have been developed on a number of species of Aucella that are otherwise very different. Plesiotypes: USN M 108740, 108741a—c, 108742a—c. Kingak shale, USGS Mes. locs. 21027, 22127, 22579— 22581, 22587, 22746, 22749, 22751, 22766, 22768, 22769, 23577, 23697. Possibly present at Mes. locs. 22584— 22586, 22776. Aucella mosquensis (von Buch) Plate 9, figures 17—19 (For most of the synonymy see Pavlow, 1907, Soc. Impériale Naturalistes Moscou, Nouv. Mém., v. 17, livr. 1, p. 22; Spath, 1936, Meddelelser on Grtinland, bind 99, no. 3, p. 98, 99.) !Aucella blanfolrdiana Stoliczka. Holdhaus, 1913, Paleontologia Indica, ser. 15, v. 4, pt. 2, p. 412—413, pl. 98, figs. 1—9. fAucella subpallasi Krumbeck. 1934, Neues Jahrb., Beilage— Band 71—B, p. 450—454, pl. 15, fig. 11; pl. 16, figs. 1—10. l‘Aucella aff. A. m‘o‘squensis (von Buch). Anderson, 1945, Geol. Soc. America Bull., v. 56, p. 966, pl. 4, figs. 12a, b; pl. 12, fig. 3. This species is represented from northern Alaska by 19 specimens, of which 13 show the features of the left valve very well. The shell is elongate, very in- equivalved and very inequilateral. During growth it becomes more elongate posteriorly, and its ventral mar- gin becomes more curved. The left valve is strongly convex; its umbo is stout; and its beak is long, much incurved, and has a slight forward twist. The right valve is gently convex, and its beak is low. The surface of the valves bears concentric ribs of irregular strength and spacing and irregularly spaced undulations and constrictions. Fine radial markings are visible on some specimens under oblique lighting. A. mosquensis (von Buch) is similar to several other species of Aucellas in both the Jurassic and Lower Cretaceous and even resembles the genus Aucellina of the Aptian and Albian stages of the Cretaceous. The combination of swollen left valve, posteriorly elon- gate form, stout umbo, strongly incurved beak, and ir- regular concentric ornamentation generally serves to distinguish A. mosquensis from other species, but only well-preserved specimens can be certainly identified. Fortunately, in Alaska A. mosquemz’s is generally asso- ciated with A. mgosa (Fischer), which is generally easily identified. The range of A. mosquensis (von Buch) in northern Europe has been shown by Spath (1936, p. 166, 167) to be between the zones of Subplam'tes wheatleyemis and Zaraz'skites albam' inclusive, that is, upper Kim- meridgian and basal Portlandian. It seems probable that the total range of the species is somewhat greater. In California and Mexico it, or a closely similar species, has been found with K ossmatz’a and Durangites (And? erson, 1945, p. 940; Burckhardt, 1912, p. 206, 221, 236) in beds that are correlated with the middle part of the Portlandian stage (Imlay, 1952, pl. 2, opposite p. 992). In Mexico it has been found also in lower beds asso- ciated with Glochicems flalar and I doceras dumngense (Burckhardt, 1906, p. 144, 155). This occurrence of A. mosquensis with Glochiceras fialar represents the middle Kimmeridgian, probably equivalent to the European zone of Aulacostephamus pseudomutabih's, and is considerably older than any known occurrence in Europe. Considering the wide distribution and fair abundance of A. mosquensig (von Buch) in Europe as far south as France and Austria and in North America as far south as Mexico, it is rather astonishing that the species has not been identified among the collections of Aucel- las from India or the Malay Archipelago. The pos- sibility that A. mosquensz's is present there but called by another name is suggested by comparisons with A. blanfordiana Stoliczka (Holdhaus, 1913, p. 412—414, pl. 98, figs. 1—9) and the statement by Holdhaus (1913, p. 414) that he cannot “establish any criteria that will in all instances clearly distinguish the two species.” Krumbeck (1934, p. 453) notes that A. blanfordz'ana may be distinguished from A. paZZasz' Lahusen (equals A. mosquemis as used herein) by its left valve having a more swollen umbonal region, more irregular concen- tric ribbing, perhaps by lacking radial striae, and prob- ably by certain apparent differences in the ears on both valves. However, if the illustrations of A. blamfordi- ana published by Holdhaus are accurate, separation of the two species from a mixed lot would indeed be diflicult. Another similar species, A. subpallasz' Krumbeck (1934, p. 450—154, pl. 15, fig. 11; pl. 16, figs. 1—10), from the Malay Archipelago and western Australia (Teich- ert, 1940, p. 113, 114, pl. 1, figs. 8—12), is distinguished from A. pallasz’ Lahusen (that is A. mosquensis), ac- cording to Krumbeck (1934, p. 452), mainly by having a more prominent umbo and a more strongly incoiled beak and by the absence of a posterior ear on the left valve, which feature is slightly developed in A. mos- quensz's. Krumbeck (1934, p. 453) considers that A. subpallasz' resembles A. blanfordz’ana even more than it resembles A. mosquemz’s but may be distinguished from 86 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the former by a more swollen right valve, a more swollen and more strongly incurved beak on the left valve, a differently shaped byssal ear, and perhaps the presence of radial striae. Comparisons of the published photographs of the type specimens of A. subpallasi Krumbeck with 11 well— preserved specimens of A. mosquensis (von Buch) from Russia leaves considerable doubt as to whether the two species are distinct. Several specimens from near Mos- cow and near Vetlanka Creek in Orenburg province have as prominent umbos and as tightly incoiled beaks as any of the specimens of A. subpallasi figured by Krumbeck. The differences in the ears noted by Krum- beck may be a matter of preservation or of individual variation and probably do not justify more than a varietal name. Plesiotypes: USNM 108748a—c. Kingak shale, USGS Mes. locs 22751, 22766, 22769, 22776. Probably present at Mes. locs 22750 and 23598. Genus POSIDONIA Bronn. 1828 Posidonia cf. P. ornata Quenstedt Plate 10, figure 21 One small slab from the basal Middle Jurassic exposed on the banks of the Canning River hears about 40 speci- mens of Posidonia that are Within the range of varia- tion of P. ornata Quenstedt as illustrated by Guillaume (1927, p. 222, pl. 10, figs. 4—13). This species has been recorded from beds of lowest Bajocian to Callovian age in many parts of the world. (See Steinmann, 1881, p. 257, pl. 10, figs. 3,5; Ravn, 1911, p. 462, pl. 33, figs. 2, 3; Roman, in Sayn and Roman, 1928, p. 114; Weir, 1930, p. 84.) The specimens from the Canning River area are smaller than the average for the species, but Guil- laume (1927 , p. 225) notes that the oldest representa- tives of the species (see Quenstedt, 1858, p. 31, pl. 42, fig. 4) are the smallest. Figured specimens: USNM 108750. Kingak shale, USGS Mes. loc. 24035. Genus INOCERAMUS .T. Sowerby, 1819 Inoceramus lucifer Eichwald Plate 8, figures 1, 5—10 Inoceramus lucifer Eichwald, 1871, Geognostisch-Palaeontolo— gische Bemerkungen fiber de Halbinsel Mangischlak und die Aleutischen Inseln, p. 194, 195, pl. 18, figs. 5—7. This species in northern Alaska is represented by 35 specimens of various sizes that show variations in sculp- ture similar to specimens from southwestern Alaska and Cook Inlet. For purposes of comparison, three speci- mens from Tuxedni Bay, the type locality, are illus- trated on plate 8, figures 5, 7, 9, 10. The species has a long mytiloid outline, terminal beaks, a fairly short‘hingeline, and a concave anterior margin below the umbones. Its surface bears concentric ribbing that ranges considerably in strength and spac- ing even on a single specimen. The umbonal region is smooth or nearly smooth and is generally separated from the remainder of the shell by a constriction. Some specimens have more than one constriction. The coarsest ribbing generally occurs near the constrictions, but the surfaces between constrictions may bear very weak ribs. In northern Alaska I. Zucifer is associated with the ammonites Erycites and Pseudolioceras. In southwest- ern Alaska at Wide Bay it occurs with these ammonites in the lowest exposed part of the Kialagvik formation but ranges to the top of the formation where it is associ- ated with Emileia, Sonm'm'a, and Stemmatoceras. In Cook Inlet on the Iniskin Peninsula in ranges as high as the siltstone underlying the Gaikema sandstone member of the Tuxedni formation. Near Fossil Point on Tux- edni Bay it occurs in units 30 to 35 of the section meas- ured by Martin and Stanton (Martin, 1926, p. 142, 143) . In its highest occurrence on the Iniskin Peninsula and on Tuxedni Bay, it is associated with the ammonites Stemmatooems, E milez'a, Sonm'm'a, Lissocems, and rare 0toz‘tes. Its range, therefore, is through the lower and middle Bajocian and not higher than the European zone of OtOites sauzei. Plesiotypes: USNM 1087 51a—c. Kingak USGS M65. 1005. 10307, 10309, 21023, 21552, 22082. shale, Class CEPHALOPDA Genus PHYLLOCERAS Suess, 1865 Subgenus PARTSCHICERAS Fucini, 1923 Phylloceras (Partschiceras) sp. Plate 10, figures 18, 19 One specimen of Partschicems is available from northern Alaska. The body chamber of this specimen appears to be complete and represents nearly a com- plete whorl. The ornamentation consists only of faint moderately dense ribs on the ventral region. At a diameter of 20 millimeters the whorl height is 14 mil- limeters, and the whorl thickness is 8.5 millimeters. This species differs from P. subobtusz‘forme (Pom- peckj) (1900, p. 247, pl. 7, figs. 1a—d), from the Callo- vian of the Cook Inlet area, Alaska, in its more com- pressed whorl section and weaker ribbing. It appar- ently differs from P. ckantrez' Munier—Chalmas (see Sayn and Roman, 1930, p. 216, pl. 21, figs. 11, 11 a; text fig. 33) from the Callovian and Oxfordian of Europe only in its finer ribbing. Figured specimen: USNM 108775. Kingak shale, USGS Mes. 100. 24013. CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 87 Subgenus MACROPHYLLOCERAS, Spath, 1927 Phylloceras (Macrophylloceras) sp. Plate 10, figure 20 The occurrence of M acrophyllocems in northern Alaska is based on one large fragment of an internal mold. Not a trace of the ornamentation is preserved, but the sutlge line shows the high external lobe and the moderately broad saddles that are characteristic of this subgenus. The lack of constrictions on the mold also confirms the assignment. Figured specimen: USNM 108774. Kingak shale, USGS Mes. loc. 21027. ‘ Genus AMALTHEUS Montfort, 1808 , Amaltheus spp. Plate 10, figures 1—5 Many strongly compressed specimens of Amaltheus have been obtained from the South Barrow test well 1 at depths ranging from 2,069 to 2,198 feet. These show clearly such generic features as the flexuous primary ribs that tend to fade on the upper parts of the flanks, the forwardly inclined indistinct secondary ribs, and the noded cordlike keel. Two specimens show weak spiral lines on the upper parts of the flanks. The speci- mens from depths of 2,177 to 2,198 feet have weaker more closely spaced ribs than the specimens from the higher beds. One specimen from the depth of 2,186 feet becomes nearly smooth anteriorly and may be compared to A. depressus Simpson (Buckman, 1911, v. 1, pl. 25). Another, from the depth of 2,198 feet, has stronger ribs on the upper parts of the flanks as in A. nudus (Quenstedt) (1858, p. 167, pl. 20, fig. 4; 1885, p. 321, pl. 41, figs. 1, 2) . Much stronger and more widely spaced primary ribs are present on a specimen from the depth of 2,111 feet. This specimen resembles A. mar- gafitatus (Montfort) as figured by Arkell (1933, pl. 31, fig. 2). Figured specimens: USNM 108765—108770. Kingak shale, South Barrow test well 3 at depths from 2,069 to 2,198 feet. Simpson test well 1 at a depth of 5,680 feet. Subgenus PSEUDOAMALTHEUS Frebold, 1922 Amaltheus (Pseudoamaltheus) sp. Plate 10, figure 17 One fragment of an ammonite shows features similar to those of A. (Pseudoamaltheus) engelhardti D’Orb- igny (1844, p. 245, pl. 66; Wright, 1882, p. 400; Wright, 1883, pl. 70) from the upper Pliensbachian of north- west Europe. The fragment belongs to a species having a fairly narrow umbilicus and flattened flanks. Its ornamentation consists of Widely spaced low spiral ribs and faint radial striae. The striae produce faint denticulations at their intersections with the spiral ribs. The venter is not preserved. ‘ Figured specimen: USNM 108764. Kingak shale, USGS Mes. 100. 22747. Genus ARIETITES Waagen, 1869 “Arietites” of. “A.” bucklandi (Sowerby) Plate 10, figures 7, 8 One ammonite is represented by parts of two whorls. It has highly evolute coiling, a subquadrate whorl sec- tion, triple keels, and prominent, widely spaced ribs that incline forward slightly on the flanks and end abruptly ventrally near the keels. The ventral ter- minations of the ribs have a slight forward twist. The median keel is a little higher than the other keels, as shown by an external mold, and is separated from them by smooth furrows. The shape and ornamentation of this ammonite greatly resemble the inner whorls of Ammwm'tes buck- Zcmdi Sowerby (Wright, 1881, p. 269, pl. 1, figs. 1—3; Buckman, 1919, pl. 131), which is a zone fossil for the lower Sinemurian stage of northwest Europe. Whether the generic name should be Ammonz'tes, Arietites, or Oomm'cems will have to be decided by the International Commission on Zoological Nomenclature. In any case, the group of species to which A. bucklandz' belongs is characteristic of the Sinemurian, and the Alaskan ammonite figured herein should represent the lower part of the Lower Jurassic. It is interesting, therefore, that the ammonite was obtained 464 feet above the base of the Jurassic as determined by litho- logic characteristics and by Foraminifera. Figured specimen: USNM 108778. Kingak shale, Avak test well 1 at a depth of 1,836 feet. Genus DACT‘YLIOGERAS Hyatt, 1867 Dactylioceras afl'. D. semicelatum (Simpson) Plate 10, figures 6, 13 Four crushed specimens are characterized by very fine fairly widely spaced ribs that arch forward on the venter and by swellings rather than tubercles at the ventral ends of the primary ribs. Many of the second- ary ribs are indistinctly connected with the primary ribs or begin below the ventral ends of the primary ribs. These specimens bear a general resemblance in rib pattern to D. semicelatum (Simpson) (Buckman, 1911, pl. 31) and to a species from east Greenland (Rosenkrantz, 1934 p. 89, pl. 5, figs. 4, 5) but have weaker and more widely spaced ribbing, especially on their inner whorls. The fineness of this ribbing re- sembles that of D. kanense McLearn (1932, p. 59, pl. 3, 88 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY fig. 5; pl. 4, figs. 1—7, 9; pl. 5, figs. 6-9) from British Columbia. Figure specimens: USNM 108763a, b. Kingak shale, South Barrow test well 3 at depths of 2,017 and 2,018 feet. Dactylioceras cf. D. kanense McLearn Plate 10, figure 14 One fragment may be compared to the internal whorls of the holotype of D. Immense McLearn (1932, p. 59, pl. 4, fig. 1) from the lower part of the Maude formation of British Columbia, or to the inner whorls of D. attenuatus (Simpson) (Buckman, 1926, pl. 655) from England. It is characterized by having fine hair— like, rather dense ribbing and by hearing small elongate tubercles at the ends of the primary ribs. Its ribbing is considerably denser than in the specimens herein shown on pl. 10, figs 6, 13 that resemble D. semicelat’wm. (Simpson). D. tenuicostatum (Young and Bird) (Buckman, 1920, pl. 157; 1927, pl. 157A) has slightly coarser and denser ribbing. In England finely ribbed Dactyliocems occur in the lower Toarcian in the zones of Dactylz'oceras temn'cos— tatum and Harpocems serpentinum. The same age for the finely ribbed Dactylz'ocems from Alaska is shown by their position in the South Barrow test well 3 only 51 feet above the highest occurrence of Amaltheus and 244 feet below a coarsely ribbed species of Dactylz'ocems. Figured specimen: USNM 108762. Kingak shale, South Barrow test well 3 at a depth of 2,016 feet. Dactylioceras spp. Plate 10, figures 9—12, 15, 16 Many fragments of immature specimens of Dactyli- ocems obtained from a well core belong to coarsely ribbed species such as occur in the Hildocems bifrom zone in Europe. The fragments shown on plate 10, figures 10—12 have a compressed whorl section and coarse ribbing similar to D. comer/mw (Sowerby) (Wright, 1884, pl. 84, figs. 1, 2; Buckman, 1927, pl. 707) . The primary ribs incline forward on the flanks, and about half of them divide high on the flanks into two ribs that arch forward considerably on the venter. The fragments (pl. 10, figs. 15, 16) have a stouter whorl section and may be compared to D. delicatum (Bean— Simpson) (Buckman, 1926, pl. 656). Their primary ribs are high, thin, fairly widely spaced, and nearly radial, and most of them bifurcate high on the flanks into two weaker secondary ribs that arch forward gently on the venter. The points of furcation are marked by tubercles that become weaker anteriorly. Another fragment (pl. 10, fig. 9) differs from the others in the same core in its coarser more widely spaced pri- mary ribs, lower whorl section, and slower rate of coil- ing. It may be compared to the inner whorls of Dac- tg/liocems crassiusculosum (Simpson) (Buckman, 1912, pl. 62) or the inner whorls of D. braum‘anum (D’Or— bigny) as illustrated by Buckman (1926, pl. 658). The correctness of the generic and age assignments of these fragments is shown by comparison with speci- mens of Dactyliocems of various sizes from Prince Patrick Island, which is about 700 miles northeast of Point Barrow, Alaska. The specimens from Prince Patrick Island (see pl. 11, figs. 4—11, 14, 16~18) may readily be compared to European species such as D. cras- siusculosum Simpson, D. commune (Sowerby) (Buck- man, 1927, pl. 707) , and D. directum (Buckman) (1926, pl. 654). One of the collections from Prince Patrick Island contains a fragment of a keeled ammonite that is probably Hildocems. Another collection contains several external molds of H arpocems (see pl. 11, figs. 12, 13, 15) that greatly resemble H. ewamtum (Young and Bird) (Wright, 1882, pl. 62, figs. 1—3). Figured specimens: USNM 108759, 108760, 1087 61a—d. Kingak shale, South Barrow test well 3 at a depth of 1,772 feet. Genus COELOCERAS Hyatt, 1867 Coeloceras afi’. C. mucronatum (D’Orbigny) Plate 12, figures 12—14 One ammonite represented by both external and in- ternal molds of four specimens is characterized by a highly evolute form and by prominent widely spaced nearly radial primary ribs that end high on the flanks in large tubercles. From these pass two or three nar- row, weak secondary ribs. The bundles of forked ribs are generally separated by single, weak ribs that begin at or just above the zone of tuberculation. The ribbing along the midventral line is not preserved. In lateral view this ammonite appears to be nearly identical with Ooelocems mucronatum (D’Orbigny) (1845, p. 328, pl. 104, figs. 4—8). In ventral View it appears to have slightly weaker and more numerous secondary ribs, although D’Orbigny figures a variety having three secondary ribs for each primary rib. Some ofthe specimens illustrated by Wright (1884, pl. 86, figs. 3, 4, pl. 87, figs. 5, 6) as “Stephanocems browni- anum” (D’Orbigny) appear to differ from the Alaskan ammonite mainly by having fewer and weaker second- ary ribs. 0. gremm'lloum’ (D’Orbigny) (1844, p. 307, pl. 96) has even sparser ventral ribbing. The Alaskan species is referred to Oerocems rather than to Dacty- liocems because of its large tubercles and the consider- able difference in size between its primary and secondary ribs. It does not have any of the button-and—loop orna— mentation that characterizes Peronocems. Buckman CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 89 (1927, p. 43) designated Ammwm'tes mucronatus D’Or- bigny as the genotype of his new genus Mucrodactylites. Except for the presence of a weak groove along the midventral line, the species appears to be a typical Coelocems. . The Alaskan species of OerOGems was obtained in the South Barrow test well 3, 6 feet above the highest occurrence of Amaltheus and 45 feet below the lowest occurrence of finely ribbed Dactyliocems. This posi- tion indicates that it is of upper Pliensbachian age, be- cause Amaltkeus does not range to the top of the Pliens- bachian and finely ribbed Dact’yliocems are typical of the lower Toarcian. In Europe Ooelocems is most com- mon in the lower Pliensbachian but has been recorded higher from beds containing Amaltheios (Beurlen, 1924, p. 150). Ooelwems mmromtum D’Orbigny is reported (Roman, 1938, p. 183) to be of Toarcian age. Such genera as Nodicoelocems and C’msm'ooelocems Buckman (1926, p. 42), which resemble Ooelocems, are common in the lower Toarcian (Daviess, in Buclnnan, 1930, p. 38— 40) . The ages of these ammonites show that the occur— rence of a erlocems in Alaska at or near the top of the local range of Amaltheus is not out of line with the occurrence of 006loce7'as in Europe. Figured specimen : USNM 1087 58a—c. Kingak shale, South Barrow test well 3 at a depth of 2,063 feet. Genus PSEUDOLIOCERAS Buckman, 1888 Pseudolioceras whiteavesi (White) Plate 12, figures 15, 16 Ammonites (Amaltheus) whitemiesi White, 1889, U. s. Geol. Survey Bull. 51, p. 69—90, pl. 13, figs. 1—5. Harpoceras whiteavesi Kellum, Daviess, and Swinney, 1945. U. S. Geol. Survey Prelim. Repts. on geology and oil possibilities of the southwestern part of the Wide Bay anticline, figs. 4e, f. This species is represented in northern Alaska by at least 15 specimens, of which some are illustrated for comparison with the type specimens from southwestern Alaska. The species is characterized by a very narrow umbilicus, a sharp raised umbilical edge, and strongly falcoid ribs. The pattern and strength of the ribs re- sembles that of P. beym’chi (Schloenbach) as figured by Buckman (1888, pl. 20, figs. 7, 8), but the raised um- bilical edge on P. whiteavesi is a possible distinction between the species. Detailed comparisons with Euro- pean species must await study of the abundant and well- preserved material from Wide Bay in southwestern Alaska. At that place P. wihiteavesz' occurs at the base , of the Middle Jurassic associated with Tmetocems, Erycites, and Hamtocems (Imlay, 1952, p. 978). Cotypes: USNM 20110; plesiotypes, USNM 108754, 108755. Kingak shale, USGS Mes. 1008. 10307 and 24035. Pseudolioceras cf. P. lythense (Young and Bird) Plate 12, figure 20 One specimen, represented by both external and in- ternal molds, greatly resembles P. lythense (Young and Bird) (Wright, 1884, p. 444, pl. 62, figs. 4—6 ; Rosen- krantz, 1934, pl. 6, fig. 1), from the Toarcian of Europe and Greenland, in character of ribbing, width of um- bilicus, and prominence of keel. The strongly falci- form moderately prominent ribs rise from the striae on the lower third of the flanks and disappear ventrally before reaching the keel. The keel is bordered by weak furrows that are separated from the ribs by a narrow smooth area. The ribbing on the lower part of the flanks is much finer than on any of the species of Pseudo- Zz'ocems in the lower part of the Kialagvik formation in southwestern Alaska. Figured specimen: USNM 108757. Kingak shale, USGS Mes. 100. 23772. Pseudolioceras cf. P. compactile (Simpson) Plate 12, figures 17, 18, 21 Two specimens from the uppermost beds of the Kingak shale in Ignek Valley have much compressed whorl sections and weak ribbing similar to that of P. compactile (Simpson) (Buckman, 1911, pl. 41 a—c) from the upper Toarcian of Europe. The smaller speci- men (pl. 12, figs. 17, 18) is smooth except for faint falciform striae near its anterior end and a low rounded keel that is bordered by weak furrows. Its posterior portion only is sutured. The larger specimen (pl. 12, fig. 21) is nearly smooth on the lower third of the flanks. The upper two-thirds of the flank bear faint broad fal- ciform ribs that disappear ventrally before reaching the keel. The keel, exposed at several places, is low, rounded, and bordered on each side by weak furrows. Figured specimens: USNM 108753, 1087 56. Kingak shale, USGS Mes. 100. 23772. Genus TMETOCERAS Buckman, 1891 Tmetoceras sp. Plate 12, figures 7—10 Small fragments of Tmtocems were obtained from both South Barrow test well 2 and Topagoruk test well 1. In the latter the genus was obtained only 2 feet higher than some molds of Pseudolz'ocems. The fragments of Tmetocems show evolute coiling, simple high thin, slightly flexuous ribs, tongue—shaped tuber- cles at the ventral ends of the ribs, and a narrow smooth midventral area. They resemble closely the inner whorls of well-preserved specimens of Tmetocems from the lowermost exposed beds of the Kialagvik formation on Wide Bay in the Alaskan Peninsula. 90 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Figured specimens: USNM 108779, 108780. Kingak shale, South Barrow test well 2 at a depth of 2,391 feet; Topagoruk test well 1 at a depth of 8,113 feet. Genus ERYCITES Gemmellaro, 1886 Erycites howelli (White) Plate 13, figures 12, 13 Ammonites (Lillie) howem White, 1889, U. S. Geol. Survey Bull. 51, p. 68—69, pl. 12, figs. 1, 2; pl. 14, figs. 1—3. Hammatoceras howelli Pompeckj, 1900, Russ. K. min. Gesell. Verh., ser. 2, Band 38, p. 275. “Hammatocems” howelli Kellum, Daviess, and Swinney, 1945, U. S. Geol. Survey Prelim. Repts. on geology and oil possibilities of the southwestern part of the Wide Bay anticline, figs. 4a, b. One fragment of the anterior part of a penultimate whorl agrees perfectly in whorl shape and ornamenta- tion with the holotype of E. howelli (White) from the basal part of the Middle Jurassic beds at Wide Bay in southwestern Alaska. The associated ammonites at Wide Bay include Pseudolioceras whitea'vesi (White) and Tmetocems. These occur directly beneath beds con- taining Emilez'a, Sonm'm'a, Erycz'tes, and Pseudo- liooems. The fragment from northern Alaska is asso- ciated with Psemdoliocems. Figured specimen: USNM 108777. Kingak shale, USGS Mes. 100. 10308. Genus ARCTICOCERAS Spath, 1932 Arcticoceras sp. Plate 12, figures 11, 19 Nine fragments of Arotz’coaems obtained from the Canning and Sadlerochit Rivers in northern Alaska are too poorly preserved for specific identification. How- ever, they show the essential generic features very well. The fragment illustrated (pl. 12, fig. 11) may be com- pared to immature densely ribbedvariety of A. 760072.71 Spath (1932, p. 55, pl. 14, figs. 2, 3) from east Green- land or to A. ishmae (Keyserling) (Spath, 1932, pl. 15, figs. 7a, b) from Pechora land. It has an extremely small umbilicus, rather sharp primary ribs that bi- furcate near the middle of the flanks, and forwardly arched secondary ribs. Another fragment (pl. 12, fig. 19) shows the characteristics of the anterior part of the adult body whorl of the genus. This part is smooth except for very faint growth lines, is retracted considerably from the remainder of the shell near the aperture, and has a deep forwardly inclined constric- tion preceding the aperture. The aperture is inclined forward more strongly than the constriction and is pro- duced into a long ventral lappet. The general appear- ance is similar to that of the adult whorl of A. koohz' (Spath) (1932, pl. 14, fig. 1) except for size. Figured specimens: USNM 108782 a, b. Kingak shale, USGS Mes. locs. 22083 and 22596. Genus PSEUDOCADOCERAS Buckman, 1919 Pseudocadoceras grewingki (Pompeckj) Plate 12, figure 1 (For synonomy see Imlay, 1953, U. S. Geol. Survey Prof. Paper 249—B, p. 93.) One external mold of P. grewz’ngki (Pompeckj) shows the form and ornamentation of the species very well. Even the imprint of the suture line is preserved. The cast of this mold is essentially identical with a specimen from the Shelikof formation figured by the writer (Imlay, 1953b, pl. 49, figs. 1, 2, 8). The species is characteristic of the middle three-fifths of the Sheli- kof formation of the Alaska Peninsula and the Chinitna formation of the Cook Inlet area. Its presence is con- sidered to be excellent evidence of the middle Callovian (Upper Jurassic) age of the beds in which it occurs. The occurrence of P. grewc’ngki in northern Alaska is of particular interest stratigraphically, because the only specimen found was within the lower 400 feet of the Kingak shale on the West Fork of the Ivishak River. It appears, therefore, that the entire Lower and Middle Jurassic, which are present in nearby areas north of the Brooks Range, have been overlapped at that point. Plesiotype: USNM 108781. Mes. 10c. 22745. Kingak shale, USGS Genus AMOEBOCERAS Hyatt, 1900 Subgenus PRIONODOCERAS Buckman, 1920 Amoeboceras (Prionodoceras?) spp. juv. Plate 12, figures 2—6 Twenty fragments from the upper few hundred feet of the Kingak shale exposed on the west bank of the Canning River are assigned to Amoebocems rather than Uardioce'ras, because some of them possess a finely denticulated keel. Definite subgeneric assignment is not possible because adult whorls are not present. Some of the fragments (pl. 12, figs. 2, 3) are com- parable to an immature specimen illustrated by Spath (1932, pl. 1, fig. 5). They have sharp ribs that incline forward gently on the flanks and curve strongly for- ward on the ventral margin. Small tubercles are pres- ent on the middle of the flanks and much stronger tubercles, near the ventral ends of the ribS. About one rib in three bifurcates near the middle of the flanks or is followed by a short secondary rib. There are at least three denticles on the keel for every ventrolateral tubercle. Other fragments (pl. 12, figs. 4—6) have much stronger ribbing, fewer secondaries ribs, and more con- CHARACTERISTIC JURASSIC MOLLUSKS FROM NORTHERN ALASKA 91 spicuous tubercles. The ventral ends of the ribs are inclined strongly forward and unite in a continuous lateral keel that is much lower than the median keel. Comparisons may be made to A. prorsum Spath (1932, p. 24, pl. 5, fig. 5) from Greenland or to a small speci- men of A. sokolovi (Sokolov and Bodylevsky) (1931, pl. 6, fig. 2) from Spitzbergen. Figured specimens: USNM 108772a—c, 108773 a, b. Kingak shale, USGS Mes. locs. 21028, 22598, and 24014. Genus REINECKEIA Bayle, 1878 Subgenus REINEGKEITES Buckman, 1924 Reineckeia (Reineckeites) cf. R. stuebeli Steinmann Plate 13, figures 1—7 ' Reineckeria anceps D’Orbigny, 1849, Pal. Franc, Terr. Jur., v01. 1, pl. 166, figs. 3, 4. Remecket‘a stuebeli Steinmann, 1881, Neues J ahrb., Beilage- Band 1, p. 290, pl. 11, fig. 7. Reineckeia douvillet Steinmann, 1881, Neues Jahrb., Beilage- Band 1, p. 289, pl. 12, figs. 2—4, 8. Remeckeia stuebeli Petitclerc, 1915, Essai sur la faune du Cal- lovien du Département des Deux-Sevres . . . etc., p. 101, pl. 6, fig. 2; pl. 9, fig. 5; pl. 10, fig. 3. Reinecketa douvtllei Petitclerc, idem, p. 83, pl. 4, fig. 5, pl. 10, figs. 2, 4, 1915. Reineckeia doum‘llet Loczy, 1915, Geologica Hungarica v. 1, p. 375, pl. 13, figs. 1, 2. ?Reineckeia stuebeli Stehn, 1924, Neues J ahrb., Beilage-Band 49, (1923) p. 111, pl. 7, fig. 2; fig. 17. Reineckeites duplew Buchman, 1924, Type Ammonites, V. 5, pl. 522. Remeckeites stuebeli Spath, 1928, Palaeontologia Indica, v. 9, p. 256, 268—270, pl. 34, fig. 6. Remeckeia stuebelt Corroy, 1932, Carte géol. France Mém., p. 119, pl. 14, figs. 1, 2, 7. Reineckeia. steubelt var. doum'llei Corroy, 1932, idem, p. 121, pl. 14, figs. 3—6. Thirty—five specimens of a fairly evolute species of Ref/neckez'a were obtained from a single, thin bed of hard siltstone exposed on the west bank of the Canning River about 550 feet stratigraphically above an occur- rence of Arcticocems. The specimens have been crushed laterally, and generally the body whorl has been crushed more than the other whorls. None of the specimens exhibit a complete view of the venter. The inner whorls at diameters of less than 40 to 45 milli- meters bear prominent primary ribs that give rise to conical spines at about one-third of the height of the flanks. From most of these pass pairs of secondary ribs that are nearly as prominent as the primaries. Rarely a primary rib does not fork at the tubercle but is continued ventrally as a single rib. At greater diameters the tubercles disappear; the points of furca- tion become less distinct and lower on the flanks; and the ribs become breader and lower. On the inner whorls the secondary ribs become slightly compressed ventrally in a manner that suggests the presence of a narrow midventral groove. On the body whorl the presence or absence of a midventral groove cannot be confirmed because of defective preservation. The specimens from the Canning River agree very. well in ornamentation and manner of coiling with the specimens from South America and Europe that have been assigned to Reineckez'a (Reineckez'tes) stuebelz' Steinmann. The suture line, fairly well exposed on two specimens, agrees in plan with that figured by Corroy (1932, p. 120). Particularly noticeable are the small oblique second lateral lobe, the greater width of the saddles than of the lobes, and the obliquity of the suture with respect to the radius of the shell. Spath (1928, p. 268—270) and Corroy (1932, p. 121) have discussed the considerable variation in ornamenta- tion and whorl shape of this species and have expressed the opinion that the associated R. doum'llez' Steinmann does not seem to be separable specifically. Corroy notes that the name R. doum’lle has generally been ap- plied to specimens having a more compressed whorl section than the type of R. stuebeli. Spath points out that the Indian species, B. wuagem' Till, differs from R. stuebelz‘ only by having less regularly bifurcating ribs in its body chamber and suggests that it is probably the Indian equivalent. The widespread distribution of B. stuebeli or of closely similar species in several continents and even north of the Arctic Circle is un- usual for ammonites. The genus Reineckez'a particu- larly has been considered a Mediterranean element (Spath, 1932, p. 148—149). P l e s i o t y p e s: USNM 108771a—f. Kingak shale, USGS Mes. locs. 21024, 22597, and 24033. Genus CYLINDROTEUTHIS Bayle, 1878 Cylindroteuthis spp. Plate 13, figures 8—11, 14—17 Eight specimens are referred to this genus because of their long, slender, nearly cylindrical guards and prob- ably short alveolar cavities. The specimen shown on plate 13, figures 9—11, 14, 15, is flattened ventrally throughout its entire length and bears a weak ventral groove near its apical end. Its sides converge slightly toward the dorsum. Its alveolar cavity is confined to the anterior third of the guard. The point of the alveolus is slightly closer to the ventral than to the dorsal side. The specimen shown on plate 13, figures 8, 16, 17, is much more cylindrical, is flattened slightly only toward the apical end, and shows the beginning of the alveolar cavity at its extreme anterior end. Figured specimens: USNM 108783a, b. Kingak shale, USGS Mes. loos. 22588 and 23772. 92 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY LITERATURE CITED Anderson, F. M., 1938, Lower Cretaceous deposits in California and Oregon: Geol. Soc. America Special Paper 16, 339 p., 85 pls., 6 figs. 1945, Knoxville Series in the California Mesozoic: Geol. Soc. America Bull., v. 56, p. 909—1014, 15 pls. Arkell, W. J., 1933, The Jurassic system in Great Britain: Oxford, Clarendon Press. 1939, The Ammonite succession at the Woodham Brick Company’s Pit, Akeman Street Station, Buckinghamshire, and its bearing on the classification of the Oxford Clay: Geol. Soc. London Quart. Jour., v. 95, p. 135—222, pls. 8—11. America Bull., v. 57, p. 1—34, 4 tables. Beurlen, Karl, 1924, Ueber einige neue und seltene ammoniten aus dem Lias 8 des schwabischen Jura: Centralbl. Min- eralogie, p. 147—160, 4 figs. Buckman, S. S., 1887—1907, A monograph of the Inferior Oolite ammonites of the British Islands: Palaeontographical Soc., 456 p., 118 pls. 1909—30, Type Ammonites, 7 v. Burckhardt, Carlos, 1906, La faune jurassique de Mazapil avec un appendice sur les fossiles du crétacique inférieur: Inst. geol. México Parergonesa B01. 23, 216 p., 3 pls. 1912, Faunes jurassiques et crétaciques de San Pedro del Gallo: Inst. geol. México, Bol. 29, 264 p., 46 pls. 1930, Etude synthétique sur le Mésozoi‘que Mexicain: Soc. paléont. Suisse Mem., v. 49, p. 1—123. Corroy, G., 1932 La Callovien de la Bordure Orientale du Bassin de Paris: Carte géol. France Mem., 337 p., 29 pls., 4 figs. Frebold, Hans, 1929, Oberer Lias und unteres Callovien in Spitzbergen: Skrifter om Svalbard Og Ishavet, Nr. 20, p. 5—24, 2 pls. 1932, Grundzfige der tektonischen entwicklung Ost- grtinlands in postdevonischer zeit: Meddelelser om Grim- land, bind 94, nr. 2, 112 p., 3 pls., 17 figs. 1951a, Geologic des Barenteschelfes: Akad. Wiss. Berlin, Math—nature. KL, Abh. 1950, No. 5,150 p., 82 figs. 1951b, Lowermost Middle Jurassic fauna in Whitesail Lake Map—area, British Columbia, m Contributions to the Paleontology and Stratigraphy of the Jurassic system in Canada: Geol. Survey Canada Bull. 18, 54 p., 18 pls., 2 figs. Guillaume, Louis, 1927, Revision des Posidonomyes J urassiques: Soc. géol. France Bull., sér. 4, v. 27, p. 217—234, pl. 10. Haughton, Samuel, 1857, Geological notes and illustrations m M’Clintock’s Reminiscences of Arctic Ice Travel, Royal Dublin Soc., Jour. 1, p. 183—250, illus., map. Holdhaus, K., 1913, The fauna of the Spiti shales, fasc. 4, La- mellibranchiata and Gastropoda: Paleontologica Indica, Mem., ser. 15, v. 4, pt. 2, p. 397—456, pls. 94—100. Imlay, R. W., 1948, Characteristic marine Jurassic fossils from the western interior of the United States: U. S. Geol. Survey Prof. Paper 214—B, p. 13:33, pls. 5—9. 1950, Paleoecology of Jurassic seas in the western in- terior of the United States: Nat. Research Council, Report of the Committee on a treatise on marine ecology and paleoecology, 1948—49, no. 9, p. 72—104, 8 figs, 1 table. 1952, Correlation of the Jurassic formations of North America exclusive of Canada: Geol. Soc. America Bull., v. 63, p. 953—992, 2 pls. 1946, Standard of the European Jurassic: Geol. Soc. . Imlay, R. W., 1953a, Callovian (Jurassic) ammonites from the . United States and Alaska, Part 1. Western Interior United States: U. S. Geol..Survey Prof. Paper 249—A, p. 1—39, pls. 1—24, 2 figs. 1953b, Callovian (Jurassic) ammonites from the United States and Alaska, Part 2. Callovian ammonites from the Alaska Peninsula and Cook Inlet regions: U. S. Geol. Sur- vey Prof. Paper 149—B, p. 41—108, pls. 25—55, 6 figs. Krumbeck, Lothar, 1934, Die Aucellen von Misol: Neues J ahrb. Beilage-Band 71, Abt. B, p. 422—469, pls. 14—16. Lahusen, J ., 1888, Uber die russischen Aucellen: Com. géol. St. Petersbourg Mem., Band 8, no. 1, p. 1-46, 5 pls. Martin, G. 0., 1926, The Mesozoic stratigraphy of Alaska: U. S. Geol. Survey Bull. 776, 493 p., 13 figs. McLearn, F. H., 1932,‘Contributions to the stratigraphy and paleontology of Skidgate Inlet, Queen Charlotte Islands, British Columbia, (2d pt) : Royal Soc. Canada Trans, 3d ser., v. 26, sec. 4, p. 51—84, 10 pls. O’Neill, J. J., 1924, The geology of the Arctic coast of Canada west of the Kent Peninsula: Canadian Arctic Expedition 1913—18, Rept., v. 11, pt. A, 107 p., 6 figs, 35 pls., 3 maps. Orbigny, Alcide (1’, 1842—51, Paléontologie Francaise. T‘errains Jurassiques, v. 1. Pavlow, A. P., 1907, Enchainement des aucelles et aucellines du Crétacé Russe: Soc. imp. naturalistes Moscou, Nouv. Mem., v. 17 (22), p. 1—93, pls. 1—6, correlation table opposite p. 84. Payne, T. G., Gryc, George, Tappan, Helen, and others, 1951, Geology of the Arctic slope of Alaska: U. S. Geol. Survey OM 126, Oil and Gas Inv. Ser., 3 sheets, colored. Pfanensteil, M., 1928, Organisation und Entwicklung der Gry- phaen: Palaeobiologica, v. 1, p. 381—418. Pompeckj, J. F., 1900, Jurafossilien aus Alaska: Russ. K. min. Gesell. Verh., St. Petersburg, 2d ser., v. 38, p. 239—278, pls. 5—7. 1901, Aucellen in Frankischen Jura: Neues J‘ahrb. 1901, Band 1, p. 18—36, pl. 4. Quenstedt, F. A. V., 1858, Der Jura: 100 pls. 1883—88, Die Ammoniten des Schwfabischen J ura: Stutt- gart, 3 V., 1140 p., 126 pls. Ravn, J. P. J., 1911, On Jurassic and Cretaceous fossils from Northeast Greenland: Meddel. om Grénland, bind 45, p. 433—500, pls. 32—38. Roman, Frederic, 1938, Les Crétacées: 554 p., 53 pls. Rosenkrantz, Alfred, 1934, The Lower Jurassic rocks of East Greenland: Meddel. om Grfinland, bind 110, Nr. 1, 122 pages, 13 pls. Sayn, G. and Roman, F., 1928—30, Monographie stratigraphique et paléontologique du Jurassique moyen de la Voulte-sur- Rhéne: Lyon Univ., Lab. géologie Travaux, mém. 11, fasc. 13, 14, 256 p., 21 pls. Sokolov, D., 1908, Aucellen von Timan und von Spitzenbergen: Com. géol. St. Bétersbourg Mem., Nouv. ser., livr. 36, p. 1—29, 3 pls. Sokolov, D., and Bodylevsky, W., 1931, Jura-und-Kreidefaunen von Spitzenbergen: Skrifter 0m Svalbard og Ishavet, Nr. 35, 151 p., 14 pls. Sowerby, James, and Sowerby, J. de 0., 1812—46, Mineral Conchology: 7 V., pls. 1—337 (1812—22) by J. Sowerby; pls. 338—648 (1822—46) by J. de G. Sowerby. Tiibingen, 842 p., atlas of Ammonites Jurassiques et CHARACTERISTIC JURASSIO MOLLUSKS FROMfNORTHERNfiALASKA 93 Spath, L. F., 1982, The invertebrate faunas of the Bathonian- Callovian deposits of J‘ameson Land (East Greenland): Meddel, om Gronland, bind 87, nr. 7, 158 p., 26 p1s., 14 figs. 1927—33, Revision of the Jurassic cephalopod fauna of Kachh (Cutch) : Paleontologia Indica, new ser. v. 9, 6 pts., 945 p., 130 pls. 1936, The Upper Jurassic Invertebrate Fauna of Cape Leslie, Milne Land. II. Upper Kimmeridgian and Port- landian: Meddel. om Gronland, bind 99, Nr. 3, 180 p., 50 p1s., 2 figs. Steinmann, G., 1881, Zur Kenntnis der J ura-und Kreideforma- tion von Caracoles (Bolivia) : Neues Jahrb., Beilage-Band 1, p. 239—301, pls. 9—14. Teichert, Curt, 1940, Marine Jurassic of East Indian affinities at Broome, Northwestern Australia: Royal Soc. Western Australia Jour., v. 26, p. 103—118, pl. 1. Wandel, Gerhard, 1936, Beitrage zur Kenntnis der jurassischen Molluskenfauna.von Misol, Ost—Celebes, Buton, Seran und Jamdena: Neues Jahrb., Beilage-Band 75, Abt. B, p. 447— 526, pls. 15—20, 13 text figs. Waterston, O. D., 1951, The stratigraphy and palaeontology of the Jurassic rocks of Eathie (Cromarty) ; Royal Soc. Edin- burgh Trans., v. 62, p. 33-52, 2 pls., 4 figs. Weir, John, 1930, Mesozoic brachiopods and mollusca from Mombosa, m Reports on geological collections from the coastlands of Kenya Colony made by Miss M. McKinnon Wood: Hunterian Mus. Mon., v. 4, pt. 4, p. 77—102, pls. 9—11. White, 0. A., 1889, On invertebrate fossils from the Pacific Coast: U. S. Geol. Survey Bull. 51, 102 p., illus. Wright, T., 1878-86, Monograph on the Lias Ammonites of the British Islands: Palaeontographical Soc, 503 p., 88 pls. A Page Abstract ...................................... 69 Age of fossils ........................... .. 73—75 alaska, Pentacrinua subangular 77 album, Zaraiakites ............................. 74, 85 altermms, Amoeboceras ________________________ 83 altemoides, Amoeboceras. 83 Amalthm .............................. 70, 73, 81, 88 deprmm ........................... 82, 87, pl. 10 margaritatua - 82, 87, pl. 10 nudus .............................. 82, 87, pl. 10 (Pseudoamaltheus) ..................... 72, 73, 77 enaclhardti... sp ................................. 87, pl. 10 sp .................................. 82, 87, pl. 10 (Amaltheua) whiteaoeai, Ammonites 89 Ammonites ................................... 76, 81 Ammonites bucklandi _________________________ 87 mucro'nams ......... 89 (Amaltheus) whiteavesi .................... 89 (Lillia) howelli ............................ 90 Amoeboceraa. _ _ . . 70, 75, 81 altemam ................................. 83 alternoides ................................ 83 91 91 (Primodoceras) ........................ 74. 83, 84 spp. juv-__. 90, pl. 12 Anaktuvuk River ............................ 71 Analysis, biologic ............................. 69—70 amps, Reineckeia. . 91 Arctic Coastal Plain .................... 71, 72, 75, 81 Arcticoceras .......................... 70, 73, 74, 75, 91 ishmae“ 90 kochi ______________________________________ 90 sp ............................... 74, 77, 90, pl. 12 Arctocephalitea 74 “Arietites” ____________________________________ 70 bucklandi .................. 72, 73,81,82, 87, pl. 10 Aslarte _______________________ 70, 76 athleta, Peltoceras ............................. 74 attenuatus, Dactylioceraa ...................... 88 Aucellu ............... 69, 70, 71, 76, 78, 81 blanfordiana .............................. 85 brmmi .................................... 83 concentrica. . - 72, 74, 75, 77, 81, 8.3, 84, pl. 9 mosqumeis ........... 72, 74, 75, 77, 81, 84, 86, pl. 9 pallasi .................................... 85 rugosa... 72, 74, 75, 77, 81, 83, 84, pl. 9 spitimsis ................... 74, 77, 81,83, 84, pl. 9 subpallasi .................... 85 subspitiemis ............. . 84 Aulacostephanus pseudomutabilia ........... 74, 83, 85 Avak test well 1 ........................... 72, 73, 82 B Baird Mountains ............................. 76 Barents Sea area ........................... 75, 78, 82 Barrow Platform ............................. 75 Belemnites ........ 76, 77, 81 beyrichi, Pseudolioceras ........................ 89 Bibliography ................................. 92—93 bifrom, Hildoceras. . _ _ 73, 88 blanfordiana, A ucella... ........... 85 Boreal region. . ..... 72, 75, 78, 81 Brachiopods ..... . . . . 77, 81, 82 braunianum, Dactylioceras. 88 Stephanocerasu 8 Brittle star ................................... 81, 82 INDEX [Italic numbers indicate descriptions] Page bronm‘, Aucella ............................... 83 Brooks Range ....................... 70, 71, 73, 75, 76 Buchia subspitimsis ........................... 84 bucklandi, Ammonites. .................. 87 “Arietites”.--_ _ _ 72, 73, 81,82, 87, pl. 10 C Cache Creek ................................. 71 Cadoceras ___________________________________ 73 callovimse, Signloceras. .................. 74 Camptonectes _______________________________ 70 sp ........................................ 77 Canning River ......................... 72, 73, 74, 78 valley of .................................. 71 Cardioceras ................................... 90 cordatum ................................. 83 Cephalopods ................................. 81 chantrei, Phylloceras .......................... 86 Coeloceras .................................... 70 arenauz’llami. . . _ ________ 88 mucronutum ______ .__ 82, 88, pl. 12 commune, Dactylioceras. . . 82,88, pls. 10,11 compactile, Pseudolioceras ..... __ 73, 77, 89, p]. 12 Comparisons with other faunas _______________ 75 concentrica, Aucella ...... 72, 74, 75, 77, 81,83,84, pl. 9 Plagiostoma ....... 83 Cook Inlet ................................... 75 cordatum, Cardioceraa ......................... 83 cornu, Ludwigella ............................. 75 coronatum, Erzmmoceras .......... ‘ 74 Oorom'cems _____________________ 87 Crassicoelocerac _____________________________ 89 craasiusculosum, Dactylioceras... . 82,88, pls. 10,11 Cylindroteuthis ............................. 70 spp .......... _... 71,91,pl. 13 cymbium, Grz/phaea ................... 73, 77, 82, pl. 8 D Dactylioceras ............................... 70, 73, 81 attenuatus ................................ 88 braunianum ............ 88 commune ....................... 82,88, pls. 10, 11 crassiusculosum ................ 82,88, pls. 10,11 delicatum _____ .__ 82,88,p1. 10 directum ............................... 88, pl. 11 kanense ......................... 82, 87, 88, pl. 10 semicelatum__ .- 82, 87, pl. 10 tmuicostatum ............................. 73, 88 spp ....................................... 88 delicatum, Dactylioceras. 82, 88, pl. 10 Dentalium ................................... 70 SD ........................................ 77 depreasus, Amaltheua... 82, 87, pl. 10 directum, Dactylioceras .................... 88, pl. 11 Distribution of fossils ......................... 78—81 douvillel, Reineckela.-. 91 Driftwood Creek ............................. 73 duplex, Reineckeites ........................... 91 durangeme. Idocema. _. 74,85 Durangites .................................... 74, 85 E Eagle Creek .................................. 71 Ecology.. .. 75—78 Emileia ...................................... 86, 90 engelhardti, Amultheus (Pseudoamaltheus).- 87', pl. 10 Entolium ..................................... 77 P380 Erycz'tes .......................... 70, 75, 81, 86, 89, 90 howellL ..- 73, 77, .90, pl. 13 sp ....................... 77 Erymnoceras coronatum. .. _. 74 ezaratum, Harpoceras ................... 73, 88, pl. 11 F Facies of Jurassic rocks ....................... 70—71 fialar, Glachicems ............................. 74,85 fimbn'atum, Lytocems ......................... 72, 77 Firth River ________ ._ 73 Foramiuifera .............................. 76, 77, 87 G Glochicems fuzlar .............................. 74, 85 Grammatodon ......... 70, 77 yrmauillouzi, Coeloceraa ....................... 88 yrewingkz', Pseudocadoceras ________ 72, 74, 77, .90, pl. 12 Graphaea ...................... 70, 78, 82 cymbium ......................... 73, 77, 82, pl. 8 H Hammatoceras ................................ 89 howelli ........ 90 Harpoceras naratum .................... 73, 88, pl. 11 serpentimtm .............................. 73, 88 whiteaveai ..... 89 Hildocems bi/rons ............................. 73, 88 howelli, Erycites ...................... 73, 77, 90, pl. 13 Hammatoceraa“ 90 Hulahula River ............................... 71 I Idoceras duranqense ........................... 74,85 ‘ Ignek Valley ..... Inoceramus ........................... ._._ 70, 76 Zucifcr ............................ 73, 77, 86, pl. 8 spp ..... 77 Introduction ................................. 69 Ipnavik River ________________________________ 71 ishmae, Arcticocems _ 90 Isocyprinu .................................... 70 Ivishak River ............................. 71, 72,73 J Jason, Kosmoceras ............................ 74 K kaneme, Dactuliocerus ................ 82, 87,88, pl. 10 Katakturuk River ............................ 71 Kialagvik formation. 73 Kingak shale ................................. 70 Kiruktagiak River ........................... 72, 74 kochi, Arcticooema._ 90 Kokolik River ................................ 71 K oomoceras jason ............................. 74 Koasmutia .................................... 74, 85 L (Lillia) howelli, Ammonitcs ................... 90 Lima _________________________________________ 70 sp ........ 77 Lisburne, Cape .............................. 71 Lissoceras ..................................... 86 lucifer, Inoceramus .................... 73, 77, 86', pl. 8 Ludwigella comu ............................. 75 maclintocki ............................... 75 rudis .................................. 75, pl. 11 95 96 Page Lupine River ________________________________ 70, 72 lyihense, Pseudolioceras. .......... 73,77, 89, pl. 12 Lytoceras ............................... 70, 75, 78, 82 fimbriatum __________________________ sp ________________________ ~__..._.j ........ M 75 Macrol‘ossils ___________ 81 (Macrophylloceras) sp, Phylloceras.. . _ 77, 87, pl. 10 margaritatus, Amaltheus ________________ 82, 87, p]. 10 Meleagrinella _________________________________ 70, 77 mosquensis, Aucella 72, 74, 75, 77, 81, 84, 85, pl. 9 Mucrodactylites ............................... 89 mucro’natum, Coeloceras _________________ 82, 88, pl. 12 mucronatus, Ammonites _______________________ 89 N Naknek formation ____________________________ 75 Nodicoeloceras. . _ . North America.“ Nose Bleed Creek. nudus, Amaltheus ....................... 82,87, pl. 10 Nuka River .................................. 71 O Okpikruak formation ......................... 71, 75 Ostrea ........................................ 77 P pallasi, Aucella ............................... 85 Panope .......... 76 Parkimania sp. juv .............. 77 (Partschiceras) sp., Phylloceras... 77, 86‘, pl. 10 Pelecypods ___________________________________ 81 Paltoceraa alhleta ______________________________ 74 Pentacrimw .................... 69 subangular alaska _________________________ 77 Peronoceras ................................... 88 Pholadomya. _ _ _ sp _______ Phylloceras. chantrei __________________________________ 86 subobtusiforme ____________________________ 86 (Macrophyllocems) 51).... 77, 87, 131.10 (Partschicerax) sp ________ 77, 86, pl. 10 Pinnu ....................... 1..- 76 Plagiostoma concentrica _______________________ 83 - Pkuromua ____________________________________ 70, 76 Plioatula“ ._ -. 70, 77 Point Barrow ................................ 71, 73 INDEX Page Posidonia _____________________________________ 70 amata. _ _ .......... 77, 86', pl. 10 Prionodoceras. . . 74 Prince Patrick Island. 73, 75 (Primodoceras) spp. juv., Amoeboceras ........ 74, 83, 84, 90, pl. 12 prormm, Amoeboceras _________________________ 91 (Pseudoamultheus), Amaltheus ............. 72, 78, 77 engelhardti, Amauheus" ......... 87, pl. 10 sp., Amultheus ........................ 87, pl. 10 Pseudocadoceraa ............................ 70, 73, 75 grewingki.... __ 72, 74, 77,90, pl. 12 Pseudolioceras _______________________ 70, 75, 81, 86, 90 beyrichi ___________________________________ 89 compactile. . 73, 77, 89, pl. 12 lytheme... ___ 73, 77,89, pl. 12 whiteavesi. 73, 77, 89, 90, pl. 12 sp ........................................ 77, 82 pseudomutabilia, Aulacostephanus .......... 74, 83, 85 R Red hill ______________________________________ 71 Remeckeia ................................. 70, 75, 82 i anceps ____________________________________ 91 “ doum‘llei. 91 stuebeli _______________________________ __ 91 doum‘llei __________________________ _ 91 waaaem’ ___________________________________ 91 (Remeckeites) ............................. 81 stuebelinn .. 74, 75, 77,91, pl. 13 Remeckeites duplex ____________________________ 91 stuebeli ......................... __ _________ 91 (Reineckeites), Reineckeia.. ______________ 81 stuebeli, Reineckeia.. .. 74,75, 77,91, pl. 13 Ribdon River __________ _ 71 Richardson Mountains ....................... 73, 74 rudis, Ludwiaella __________________________ 75, pl. 11 ruaosa, Aucclla ___________ 72, 74, 75, 77, 81, 83, 84, pl. 9 S Sadlerochit River _____________________________ 71, 73 Sagavanirktok River _________________________ 71 sauzei, Otaites ______ 86 Scaphopods ..... 81 semicelatum, Dactylioceraa ______________ 82, 87, pl. 10 serpentinum, Harpoceras ...................... 73,88 Shaviovik Valley _____________________________ 71 Shublik Springs_. _ 71 Siaaloceras callom'ense _________________________ 74 Siksikpuk River .............................. 72, 74 Simpon, Cape..-. ........ _. 71 Simpson test well 1. ________ 72, 77, 82 sokolovi, Amoebaceraa- _ ........ .. 91 So’nm'nia _____________________________________ 86, 90 South Barrow test well 1 _____________________ 77 2 ........................... ... 72, 82 72, 73, 75, 77, 82 Page spitiensis, Aucella ____________ 74, 77, 81, 83, 84, p]. 9 Stemmatoceras ________________________________ 86 Siephanoceras braunianum.. _____________ 88 Straiigraphy, summary 01.. ......... 70—73 stuebeli, Roineclceites .......................... 91 Reineckeia ________________________________ 91 (Reineckeites). 1 74, 75, 77, 91, pl. 13 douvillei, Reineckeia" ......... 91 subangular alaska, Pentatrmus. _________ 77 subobtuxiforme, Phylloceras .................... 86 subpallasi, Aucella ____________________________ 85 Subplanites wheatleyensis. _________ 74, 85 subspitiemis, Aucella __________________________ 84 Buchia .......... 84 Summary .................................... 81—82 Systematic descriptions _______________________ 82-91 ’I‘ Talkeetna Mountains ________________________ 75 Tancredia ___________ 70 SD .............. 77 tenuicostatum, Dactyliocems ................... 73,88 Test wells. (See Wells.) Thracia _______________________________________ 76 Tiglukpuk formation ......................... 7O Tmetoceras _________________ 70, 73, 81, 89, 90 sp __________________________ 82, 89, pl. 12 Topagoruk test well 1 72, 73, 74, 77,82 Trigonia ______________________________________ 70 Tuktu member ________________________________ 71 U Umiat formation, Tuktu member ____________ 71 Utukok River ________________________________ 70, 71 V Velopecten .................................... 70 sp ........................................ 82 W waagmi, Reineckeia ___________________________ 91 Wells, test, Avak 1. ........ 72, 73,82 Simpson 1. _. _ ......... 72, 77, 82 South Barrow l ........ 77 2 _____________________________________ 72,82 3 ____________________________ 72, 73,75, 77, 82 Topagoruk 1 _____________________ 72, 73, 74, 77, 82 West Fork of Ivishak River __________________ 71 wheutleyemis, Subplanites _____________________ 74, 85 whiteavcsi, Ammonites (Amaltheus)... 89 Harpoceras _______________________________ 89 Pseudolioceras ______________ 73, 77, 89, 90, p]. 12 Z Zarm‘skites albam’ ____________________________ 74, 85 PLATES 8—13 PLATE 8 [All figures natural size] FIGURES 1, 5—10. I naceramus lucifer Eichwald (p. 86). 1, 6, 8. Left valves of plesiotypes, USNM 108751, from USGS Mes. 100. 21552. 5, 7. Plesiotypes, USNM 108784, from USGS Mes. 100. 3009, Tuxedni Bay, southern Alaska. Shows variation in coarseness of ribbing. 9, 10. Left valve and dorsal view of plesiotype, USNM 108776, from USGS Mes. 100. 3005, Tuxedni Bay, south- ern Alaska. Shows highly constricted umbos. 2—4. Gryphaea of. G. cymbium Lamarck (p. 82). 2, 3. Posterior and lateral views of left valve of specimen, USNM 1087 52a, from USGS Mes. 10c. 23748. 4. Right valve of specimen, USNM 108752b, from USGS Mes. 100. 23748. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 3 INOCERA MUS AND CR YPHAEA . PROFESSIONAL PAPER 274 PLATE 9 GEOLOGICAL SURVEY A U CELLA ‘3‘ «an.» .. .1“. 1 ; 7%...- y. 4... mt“... v.2, PLATE 9 [Figures natural size unless otherwise indicated] FIGURES 1—10. Aucella spitiensis Holdhaus (p. 84) 11—16. Aucell 11, Left and right valve of plesiotype, USNM 1087468., from USGS Mes. 100. 21028. Left and right valves of plesiotype, USNM 108746b, from USGS Mes. 100. 21028. Left valves of plesiotypes, USNM 1087478., b, from USGS Mes. loo. 22598. Right valves of plesiotypes, USN M 1087460, d, from USGS Mes. 10c. 21028. eft valve of plesiotypes, USNM 1087466, f, from USGS Mes. 100. 21028. a concentrica (J. de C. Sowerby) (p. 83). 13, 4. Left and right valves of plesiotype, USNM 108745, from USGS Mes. loc. 22769. 15. 16. est Alaska. eft valve of plesiotype, USNM 108744, from USGS Mes. 10c. 22598. eft valve of plesiotype, USNM 108743, from USGS Mes. 100. 22509. 17—19. Aucell mosquensis (von Buch) (p. 85). Left valves of plesiotypes, USNM 108748, from USGS Mes. 100. 22769. 20—27. Aucelle 20, i ril 21, 2 in 27. tvs z rugosa (Fischer) (p. 84). bernal mold. 0 times to show radial ribbing. [2. Left and right valves of plesiotype, USNM 108749, from USGS Mes. 100. 10248 near Katmai Bay, south- !3—25. Left valves of plesiotypes, USNM 108741, from USGS Mes. 100. 22768. Shows the character of the )s where the shell is preserved. Fig. 24 is a ventrodorsal view showing the greater convexity of the left valve. 2, 26. Left valves of plesiotypes, USNM 108742, from Mes. 100. 22769. Shows the character of the ribs on the Small right valve and larger left valve of plesiotype, USNM 108740, from USGS Mes. loc. 22127. Enlarged FIGURE 1. 6, 13. 7, 8. 10—12. 14. 15, 16. 17. 18, 19. 20. 21. PLATE 10 [Figures natural size unless otherwise indicated] Amaltheus cf. A. dem‘essus Simpson (p. 87). USNM 108770, from depth of 2,186 feet in South Barrow test well 3. . Amaltheus sp. (1). 87). USNM 108765, from depth of 2,074 feet in South Barrow test well 3.. . Amaltheus sp. (p. 87). USNM 108766, from depth of 2,090 feet in South Bar row test well 3. Shows spiral markings on keel. . Amaltheus cf. A. margaritatus (Montfort) (p. 87). USNM 108768, from depth of 2,111 feet in South Bar row test well 3. . Amaltheus cf. A. nudus (Quenstedt) (p. 87). USNM 108769, from depth of 2,198 feet in South Barrow test well 3. Dactyliocems aff. D. semicelatum (Simpson) (p. 87). USNM 108763, from depth of 2,018 feet in the South Barrow test well 3. “Arietites” cf. “A.” buckla/mli (Sowerby) (p. 87). Lateral and ventral views of specimen, USNM 108778, from depth of 1,836 feet in the Avak test well 1. . Dactyh’ocems cf. D. crassiusoulosum (Simpson) (p. 88). USNM 108760, from depth of 1,772 feet in South Barrow test well 3. Dactyliocems cf. D. commune (Sowerby) (p. 88). USNM 108761, from depth of 1,772 feet in South Barrow test well 3. Dactylioceras cf. D. Immense (McLearn) (p. 88). USNM 108762, from depth of 2,016 feet in South Barrow test well 3. Dactyliocems cf. D. delicatum (Bean-Simpson) (p. 88). USNM 108759, from depth of 1,772 feet in South Barrow test well 3. Amaltheus (Pseudoamaltheus) cf. A. engelhardti (D’Orbigny) (p.87). Fragment of outer whorl, USNM 108764, from USGS Mes. loc. 22747. Phyllocems (Partschiceras) sp. (p. 86). USNM 108775, from USGS Mes. 10c. 24013. Phylloceras (Macrophyllocems) sp. (p. 87). USNM 108774, from USGS Mes. 10c. 21027. Posidom'a cf. P. ornata (Quenstedt) (p. 86). USNM 108750, from USGS Mes. 100. 24035. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 10 AMALTHEUS, DACTYLIOCERAS, "ARIETITES,” PHYLLOCERAS, AND POSIDONIA GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 11 LUDWIGELLA, DACTYLIOCERAS, AND HARPOCERAS PLATE 11 [All figures natural size] FIGURES 1—3. Ludwigella! cf. L. rudis (Buckman) (p. 75). USNM 108790, from elevation of 400 feet on Big Rag Mountain, about 6 miles northeast of Mould Bay Weather Station, Prince Patrick Island. 4—6. Dactylioceras cf. D. commune (Sowerby) (p. 88). 4. View of rubber cast of external mold of the same specimen shown in figs. 5 and 6, USNM 108787, from elevation of about 400 feet just east of summit of a ridge about 5 miles east-northeast of Mould Bay Weather Station, Prince Patrick Island. 7—9. Ventral and lateral views of internal mold and lateral view of rubber cast made from the external mold of 7—11.14. Dactylioceras cf. D. directum (Buckman) (p. 88). same specimen, USNM 108785, from elevation of 600 feet about 4 miles northeast of Mould Bay Weather Station, Prince Patrick Island. 10, 11, 14. Lateral and ventral views of internal mold and lateral view of rubber cast of external mold of same specimen, USNM 108786, from same locality as specimen shown in figs. 4—6. 12, 13,15. Harpoceras cf. H. ewaratu/m (Young and Bird) (p. 88). Views of rubber casts of external molds, USNM 108789, from elevation of 700 feet near summit of southeast face of main southern ridge near Crozier Channel east of the Mould Bay Weather Station, Prince Patrick Island. 16—18. Dactyh‘oceras cf. D. orassiusculosum (Simpson) (p. 88). 16. View showing internal mold of outer whorl and external mold of inner WhOI‘lS, USNM 108788a. 17. View of rubber cast of internal whorls shown in fig. 16. 18. Internal mold of an outer whorl, USNM 1087 88b. Both specimens are from the same locality as the ammonites shown in figs. 12, 13, and 15. FIGURE 1. 2—6. 7—10. 11, 19. 12—14. 15, 16. 17, 18, 21. 20. PLATE 12 [Figures natural size unless otherwise indicated] Pseudocadoceras grewmglci (Pompeckj) (p. 90). Plesiotype, USNM 108781, from USGS Mes. 100. 22745. Amoeboceras (Prionodoceras?) spp. juv. (p. 90). 2, 6. Specimens, USNM 108773, from USGS Mes. 100. 22598. 3—5. Specimens, USNM 108772, from USGS Mes. 10c. 21028. Tmetoceras sp. (p. 89). 7—9, 7, Ventural View of rubber cast. of external mold, USNM 108780; 8, 9, internal mold of part of same specimen shown in fig. 7. From depth of 2,391 feet in South Barrow test well 2. 10. Mold of specimen, USNM 108779, from depth of 8,113 feet in Topagaruk test well 1. Arcticoceras sp. (p. 90). Lateral views of ribbed inner Whorl and smooth body whorld showing apertural constriction. USNM 108782, from USGS Mes. 10c. 22596. erloceras cf. 0'. mucronatum (D’Orbigny) (p. 88). Lateral views of specimens, USNM 108758a—c, in a well core at depth of 2,063 feet in the South Barrow test well 3. Pseudoliocems whitecwesi (White) (p. 89). 15. View of rubber cast of plesiotype, USNM 108755, from USGS Mes. 10c; 24035. 16. View of rubber cast of plesiotype, USNM 108754, from USGS Mes. 100. 10307. Pseudoh'oceras cf. P. compactile (Simpson) (p. 89). 17, 18. Internal mold and suture lines of an immature specimen, USNM 108756, from USGS Mes. 100. 23772. 21. View of rubber cast of a mature specimen, USNM 108753, from USGS Mes. Loc. 23772. Pseudoh‘oceras cf. P. lythe'nse (Young and Bird) (p. 89). View of rubber cast of specimen, USNM 108757, from USGS Mes. loc. 23772. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 12 PSEUDOCADOCERAS, ARCTICOCERAS, AMOEBOCERAS, TMETOCERAS, COELOCERAS, AND PSEUDOLIOCERAS GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 13 REINECKEIA, ERYCITES, AND CYLINDROTEUTHIS PLATE 13 [All figures natural size] FIGURES 1—7. Remeclceia (Remeckeites) cf. R. stuebeli Steinmann (p. 91). Lateral View. and suture line of specimens, US NM 108771, from USGS Mes. loc. 22597. Suture line drawn from anterior end of septate whorl shown in fig. 5. ’ 8, 16, 17. Cylindroteuthis sp. (p. 91). 8. Cross section at diameter of 23 mm. 16. Ventral view. 17. Lateral view of specimen. All USNM '108783a, from USGS Mes. 100. 22588. 9-11, 14, 15. Cylindrotheuthis sp. (p. 91). 9. Cross section at alveolar end. 10. Section about 28 mm posterior to alveolar end. 11. Section at broken apical end. 14. Ventral view. 15. Lateral view of specimen, USNM 108783b,-fr0m USGS Mes. 10c. 22588. 12, 13. Erycites howelh‘ (White) (p. 90). Ventral and lateral views of plesiotype, USNM 108777, from USGS Mes.loc. 10308. “'- "‘ ak'” GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 CHART l European stages (Arkell, 1946) English formations (after Arkell, 1933) Northwest Europe standard zones (Arkell, 1946, 1951) Characteristic fossils in the western interior region Characteristic fossils in east Greenland modified after Spath (1932, 1935, 1936) Characteristic fossils in the Alaska Peninsula and Cook Inlet regions Northern Alaska Characteristic fossils in northern Alaska Foothills of the Brooks Range Arctic Coastal Plain F k . , 1 , A . Kukpowruk River to Okpi'kruak River to Anaktuvuk River to ,weSt .Or Canning River Ignek V3 1.6), Sadlerochit River Test wells in Barrow Topogoruk I'Jishak River to from Red Hill to , and Simpson area test well 1 Killik River Siksikpuk River Lupine River Shaviovik River Foothills area ‘ Katakturuk River east of Ignek Valley Lower Neocomian Lower Neocomian Lower Neocomian Lower Neocomian Middle Albian Middle Albian Middle Albian Lower Neocomian Purbeck beds Not known Titanites ? , Craspedites , and Laugeitcs I ' 1 1 1 1 11 11 i 1 11 ’ 1 i , 1 1 1 1 1 1 1 1 Titanites giganteus Aucella piochi Absent 1 1 ‘ 1 1 1 1 1 1 j 1 ‘ 1 1 1 1 1 1 1 1 1 1 1 Portlandian 1 . 1 . l\ot known 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Kerberites okusenSis 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ' ‘ 1 1 1 1 ' ‘ 1 1 1 1 1 1 1 : Portlandbeds , w . 1 1‘ 1 1 1 1‘ 11 1 111 1 1 , 1 , 1 1 1 111 11 1 1 1 1 . ‘ 1 1 1 1 1 1 1 Glaucolithiteg'gorei Crendonites 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A 1 1 1 1 1 1 1 1 1 1 1 1 _ 1 ' A 9 9 . 1 r; 1 1 o 9 1 1 1 ., ‘7‘ 1 ’ 1 1 1 1 1 ‘ 1 9 1 _ . . . , , , . 1 1 1 1 1 , Zaraiskites albani Epipallasu:eras 1 1 1 1 1 1 1 . 1 1 1 1 1 P 1 i llasioides N t k Aucella mosqueiisis Aucella mosquensis Tiglukpuk Tiglukpuk Tiglukpuk 1 1 ‘ ‘ av 0" a pa 0 nown and and form tion formation formation Present Present 1 ‘ , ‘ 1 Present _ Aucella rugosa Aucella rugosa a ‘ 1 1 1 1 Pavlovm rotunda PallaSlLIE‘I‘aS 1 1 1 1 1 1 1 1 1 1 Pectinatites pectinatus Pectinatites 1 1 1 1 1 ———‘——-'—‘——”—“ 1 1 1 Subplanites wheatleyensis '1 1 1 1 ‘ 1 1 1 Vetulonaia spp. 1 1 1 1 Subplanites sp. a and 1 1 . i I l G raulus veternus ' 1 ‘ 1 , ‘ Kimmeridge " a 1 , . . y Y 1 1 Kimmeridgian clay "fGraveSia gigas Not known 1 1 1 1 1 » 1 1 1 1 1 1 1 1 t 1 1 1 1 Gravesia gravesiana 1 1 1 1 _——— 1 1 3 '1 1 ; 1 Aulaeostephanus pseudomutabilis 1 1 1 1 U ’ 1 1 H 1 1 1 g Rasenia mutabilis w Hoplocardioceras deuipiens m n! ‘ , , , , . , 1 x 1 a) . .k U 3 C/ ot identiii d 1, " D - :33 Euprionoce as koclii '5 L1 ' , to 3 Rasenia cymodoce o if E E g Rascnia horealis 8 g . . . < #"7 C a Pietonia baylei Rasenia orhignyi 8 8 1 D4 ' _ Ainocboceras m Amoeboceras g a - ~ V :1 a :1 Ringsteadia pseudocordata lVot known 7 8 gig Overlaps 1 1 . . . . . 35 a: older 1 1 Decipia decipiens , i C 11' b d . . , N tk Amoeboceras ti’rmnodoreras) Jurassic 1 1 Ora ian e s .- _ 0 nown , ) . - , ‘Peris‘p‘hiiictes cautisni'grae and Itingstcadia OxfOrdian » . “”74" W ' * ' 7,, ,7, 1 '71 1 1 1 71 1 1 1 '? 1 1 Periephinctes plicatilis Cardioceras aft. C. ZCIlailiae 1 1 1 1 1 1 1 ‘ 1 1 1 1 1 ' ' 1- 1' ’ - -ii 1 1 1 1 1 1 - , - V V V 1 1 1 1 1 ‘ 1 1 1 . Cardioceras bondatum Cydioceras spp. Cardioreras Cai diocei as distans 1 1 1 1 1 1 1 1 1 1 1 1 A; , - 1 1 1 1 1 r' > V » _ Cardioccras cordiforme 1 1 1 1 1 1 1 1 1 1 1 1 uens‘te‘dt’oceras mariae w Not known 1 1 1 1 , 1 1 1 1 : i .' Quenstedtoceras collieri 53 Cardioceras martini 1 1 . V 1 I 1 ‘ ‘Quenstedi‘oc'eras lamberti _,,_._ '3 1 1 1' 1 ‘ 1 1 Oxford clay' i 1 1 , 1 1 ‘ ‘ ‘ 1 Peltoceras athleta :4 1 ‘ 1 1 1 1 1 1 1 ‘ 3 Not known 1 1 1 1 91 1 1 L9 1 1 Q ‘ 1 El‘ mnoceras coronatLim Absent ' ‘ 1 y g l’seudocadoceras Reineckeia cf. R. stuebeli 1 1 1 -> 1 1 1 . i3 3 ' 1 1 1 1 ‘ Kosmoceras Jason a 1 1‘ 1 1 1 1 I Z) hepgilei‘ites, Lilloettla, 8 Pseudocadoceras grewmgki 1 1 1 ‘ 1 .» 1 1 Callox ian _ _ Kepplerites nicleai‘ni U ()xycei ”95 g 1 1 1 2 g 1 Sigaloceras callovxense ‘ , fl, - ——————_ m 1 m “1 1 Kellawa 5 beds Kepplerites tychonis Kepplerites t7)" 1 , ‘ ‘adocei‘asflowericeras, Q 1 1 1 i Present ,5) 1 y 1 1 ’ ' * Xeriorx‘phalites,Kheraiceras Not known ‘ 1 1 1 V ll Present 1 Proplanulites koenigi Gowerioei’as subitum Not known 1 v 1 1 1 ifi 0L3 y i 1 . W, 1 Gulicliniceras 1 1 1 1 1 mi no 1 , 1 1 1 ‘ ‘ E E 1 1 1 1 1 ‘ ‘ . :1 1 1 1 1 1 1 1 Maoroceplialitos ma: i‘ocephalus Arcticorteras ‘1; 1 Arcticocei‘as Arcticoceras ‘ 1 1 ‘ 1 1 Cornbrash beds a ‘ 1 1 1 Present EL ‘ 1 1 1 m 1 i 1 1 N , 1 7 ____. _i__._ _,_. 1 Hj—v—w 9 {>1 1 a 1 76 1 ‘ ‘ 1 1 Clydomceras discus E 1 NM known 1 1 1 1 1 ‘1 1 1 1 ' 1 1 77;; 1 1 1 ‘ 1 1 _ ~ 1 1 1 1 1 1 1 1 1 1 1 1 1 E” 1 1 1 1 1 1 ‘ 1 1 1 1 1 1 1 Clydoniceras liollandi Arctocephalltes g Arctoc epliaittes ’ 1 1 1 ‘ 1 1 ‘ 1 1 1 1 1 ‘ 1 ‘ 1 ‘ 1 a 1 1 ‘ ' a 1 1 1 1 1 1 1 v n. - 1 ‘ 1 1 1 1 1 ‘ 1 1 1 1 F 1 1 1 Oppelia aspidOides 51 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 :2 1 1 1 Bathonian Great oolite rwr—r , '6 77777 —-~ WW , v , , 1,, ,, A”- 1,......? 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Tulites subconti‘actus 2 1 1 1 1 1 ‘ 1 1 1 1 1 1 1 1 1 1 S r 1 i: 1 1 1 1 1 1 1 1 1 ‘ 1 1 1 1 1 1 $ i’roccrites progracflis Not known (‘i‘auom 1 (,‘ranmephalitcs 1 ‘ 1 ‘ ‘ 1 ‘ 1 1 1 1 ‘ d 1 1 1 . 1 ‘ ‘ 1 ‘ 1 FE ggiceras Zi;17a;j ‘ 1 ‘ 1 Not known ‘ 1 1 1 1 1 1 1 1 1 .. , , 1 1 1 1 1 1 1 ,2 , fl, _______ W, ,i _ ,,,,,,1, , N 1,, W ,7, , , , ‘ 1 1 1 ‘ ‘ 1 1 1 1 1 1 1,» 1 1 ,1 1 1 1 1 .3 < 1 1 J1IlZiSFOI (was ._n v 1 1 1 1 1 , J} 1 1 ~ ”#7 2111 1 1 ,, 1 1 1 .1 1 111m L1 1 1 1 1 .1 1 1 1 - undroro is E 11511 1 1 1 1 7i 1 1 1 rd 336 ‘ ‘ 1 1 1 1 1 1 <4 1 1 1 >31 . 1 ‘9 ' ‘ 1 immatm‘c as 7:: 8 9"; 1 11 1 ‘ 1 1 ‘ ~ 1 1 1 . ‘V# : 21m 1 1 ‘ ‘ 1 1 1 1 T i, M 7,1 1 1 1 w 1 1 1 1 Elmileia E J ‘n 1 1 1 1 T6 1 1 , 1 7 O i 1 1 1 1 1 ’3 ‘ 1 1 1 m.:m few—iv—i—J 9 1 1 i 1 191 ‘ ‘ 1 1 c 1 - 1 1 1 '3 Lt '5 ’l'metoceras Er '(‘li ' 1 1 I ‘ m 7 7' ‘ Tmetoccras $3 9 J y es’dm 1 Present locall‘ ‘ ‘ ‘1 . , i - j 1 ,4 . 1 n . m 0 C Pscuilolioceras whiteavesi 1 1 1 1 Liocei as Opalinum 1&4: L111 1 1 1 1 1 1 1 1 1 1 1 l‘resent ) >4 1 r) 1 1 1 1 1 1 1 1 1 1 1 locally Il‘CSCHt Present Kiiigak shale Present Lytoceras Jureiise Pseiidolioceras 1 Pseudolioc ras L P. lytheiise 1 1 1 1 1 1 1 I 1 1 1 I 1 1 1 1 1 1—‘—_”— 1 1 1 1 1 1 1 1 Hildoceras bifrons Dactylioceras 1 'iémyhoieraikspg‘ 1 1 1 1 1 1 1 - oarse y D )et ‘ 1 ‘ 1 ‘ 1 1 1 1 1 , Toarciaii Upper Lias ’4 Pselldoggx‘fll‘nog‘eras ‘ 1 ‘ 1 1 ‘ ‘ ‘ “WEE-k shale llai'poceras serpentinum 1 1 1 , Dactyiioceras Spy. 1 1 Dactylioceras tenuicostatum 1 ’ (Finely ribbed) 1 1 Paltopleuroceras spinalum Present Middle Lias i I Amaltheus mar aritatus . g Arnalthcus spp. 1 1 . 1 _ Amaltlieus ‘7 , U Pliensbachian Prodactyiioceras davoei a Dei‘ocei'as, and 2 . Nonmar ine "_’-""‘ Xiphei'ocei'as fi'w ,__ 1’ i '''''' 1 £11 Ti‘agophylloceras ibex Beaniceras D 1 1-.1 1 - v ‘ Lptonia Jainesom Uptonia jamesoni E Echioceras raricostatum 1 3’ ' ‘9 I; 7 g 1 1 1 1 1 1 ’ OX noticeras ox not 1 1 ‘ 1 1 1 1 "1 y y um Not known 1 1 1 1 1 1 , Lower Lias Asteroceras obtusum 1 1 1 1 1 q . (,oroniceras 1 1 1 .inemurian 1 1 1 _ . and 1 1 Arietites turnei‘i Absent Armoccras ‘ 1 1 , 1 1 1 1 1 1 1 1 1 , , ‘ 1 1 1 1 1 1 ' i » t 1 _ _ . . . , , ’ , ’ ' Arnioceras semicostatum 1 1 1 1 1 1 1 1 Not identified Not identified Not identified Not identified ‘ 1 ‘ 1 ‘ 1 ‘ 1 ‘ i 1 1 I I 1 1 1 1 1 1 1 Co 0 ‘ ‘ ‘ 1 1 ‘ 1 ‘ 1 ‘ r niceras bucklandi ”Arietites" ct". ”A”. bimkiandi 1 ‘ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ‘ Scamnoceras angulaium 1 . 1 1 1 1 1 1 1 Hettanian 1 1 1 ‘11 1111 1 1 1 1 g Psiloceras lanoib' Wahnei'ooeras '.’ Not known 1 1 1 1 1 1 1 1 1 1 1 1 1 P ‘ 15 Plants ‘ ‘ ‘ ‘ 1 1 1 1 1 1.1 1111 1 1 , '2 Not identified a Not identified Upper Triassw to Paleozoic Upper Tl‘iaSSlC Upper Tl‘laSSlC Upper Triassic Upper Tl‘laSSiC Upper Triassic Upper Triassic Upper Triassn: CORRELATION OF JURASSH,‘ FORMATIONS OF NORTHERN ALASKA Triassic Upper 342062 0 — 55(In pocket) 1/0 :3 , :2 / 171 ~25: Owl Creek - (Upper Cretaceous) Fossils from Crowleys Ridge Southeastern Missouri L: GEOLOGICAL SURVEJ_PROFESSIONAL PAPER 274— E Owl Creek (Upper Cretaceous) Fossils from Crowleys Ridge Southeastern Missouri By LLOYD WILLIAM STEPHENSON A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—E Supplemented wit/z descriptions and illustrations of oetter preserved sfle/[s from tne type section of t/ze 0w] Creeé formation 2. 5 miles nort/zeast of Ripley, Tippan County, Miss. UNITED STATES GOVERNMENT PRINTING OFFICE,WASHINGTON : 1955 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price $1 (paper cover) CONTENTS Page Page Abstract ___________________________________________ 97 Systematic descriptions—Continued Introduction _______________________________________ 98 Mollusca—Continued Physiographic setting _______________________________ 99 Pelecypoda ________________________________ 106 Stratigraphy and lithologic character of the formations- _ 100 Prionodesrnacea ________________________ 106 Structure __________________________________________ 102 Anomalodesmacea ______________________ 1 15 Fossil localities _____________________________________ 102 Teleodesrnacea _________________________ 117 Correlation ________________________________________ 105 Gastropoda ________________________________ 124 Systematic descriptions ______________________________ 106 Ctenobranchiata ________________________ 124 Porifera _______________________________________ 106 \ Opisthobranchia ________________________ 132 Spongiae ___________________________________ 106 Cephalopoda _______________________________ 134 Annelida _______________________________________ 106 Ammonoidea ___________________________ 1 34 ChaetOpoda ________________________________ 106 Literature cited _____________________________________ 136 Mollusca-__-__________,-__- ____________________ 106 Index _____________________________________________ 139 ILLUSTRATIONS [Plates follow page 140] P age PLATE 14. Views of Clayton (Paleocene), Owl Creek and McNairy (Upper Cretaceous) formations, in Stoddard and Scott Counties, Mo. _ 15. Cliona, Hamulus, Nucula, Nemodon, Glycymeris, Nuculana, and I donearca. 16. Trigom'a, Tenm’pterz'a, Pinna, Ostrea, and Exogyra. 17. Pecten, Crenella, Cuneolus, Anatz‘mya, and Lima. 18. Veniella, Scambula, Brevicardium, and Pholadomya. 19. Cardium, Crassatella, and Liopistha. 20. Cardium, Aphrodina, Legumen, Tenea, Tellina, Leptosolen, Linearia, and Cyprimem'a. 21. Goniochasma, Napulus, Helicaulax, Polim'ces, Gyrodes, Pseudomalaxis, Gastrochaena, and Panope. 22. Liopeplum, Morea, Anchura, Fusinus, Drilluta, Turritella, and Trobus. 23. Volutomarpha, tharpa, Caveola, ancteon, Bullopsis, and Discoscaphites. 24. Sphenodiscus and Baculites. FIGURE 21. Sketch map showing Owl Creek fossil localities in Crowleys Ridge _________________________________________ 103 III A SHORTER CONTRIBUTION TO GENERAL GEOLOGY OWL CREEK (UPPER CRETACEOUS) FOSSILS FROM CROWLEYS RIDGE, SOUTHEASTERN MISSOURI By LLOYD WILLIAM STEPHENSON ABSTRACT The Owl Creek formation, which is typically developed in Tippah County, Miss, is now known to extend northward to the head of the Mississippi Embayment in southeastern Mis- souri. The formation is represented in Crowleys Ridge in Stoddard and Scott Counties, Mo., by 11 feet or less of weathered, mottled, yellowish~brown and greenish-gray, glauconitic, finely micaceous sand or sandy clay, indurated in part to ferruginous, argillaceous sandstone. In Missouri the formation is uncon- formably underlain by the McNairy sand (Upper Cretaceous), and is unconformably overlain by the Clayton formation (Paleocene). Fossils, mainly mollusks, are contained in the Owl Creek formation of Missouri in greater or less abundance; they are in the form of internal and external molds only; no shell material has escaped solution and removal by circulating ground waters, but many of the molds are identifiable. Fifty-six species are identified and described in this paper. All of them occur also in the typical Owl Creek formation of Mississippi, where their shells have been more or less com- pletely preserved, some in almost as perfect condition as the shells on a modern ocean beach. In describing the Missouri specimens it has seemed desirable in order to present their characteristic features more clearly, to include supplementary illustrations of the more perfect shells of the same species from Mississippi. Four new genera and nine new species are de- scribed. Although these new forms are present as molds in Missouri the holotypes and some of the paratypes are selected - from among the more perfect Mississippi shells. For the 4 new genera, including 1 pelecypod and 3 gastropods, the names Tenuipteria, Trobus, tharpa and ancteon are pro- posed; the new species are the pelecypods Orenella microstm‘ata, Cardium (Granocardiu‘m) lowei and Tellina buboana, and the gastropods Pseudomalawis pateriformis, Trobus buboanus, Heli- caulaa: fomosa, Morea transemm, Liopcplum rugosum, and tharpa sinuosa. The Owl Creek formation is the youngest and stratigraphi- cally the highest Upper Cretaceous formation present in out- crop in the eastern Gulf region. In terms of the European clas- sification the formation falls within the Maestrichtian stage (upper part of Upper Cretaceous). INTRODUCTION The Owl Creek formation, the uppermost Cretaceous formation at the surface in northern Mississippi, which is typically developed in Union and Tippah Counties, crops out in a narrow, irregular strip extending from the vicinity of New Albany, Union County, northward through Tippah County to and beyond the Tennessee State line (Stephenson and Monroe, 1940, p. 226—248, pl. 1A; Conant and McCutcheon, 1941, p. 25—27, pl. 1). North of the State line the belt of outcrop has been mapped about half way across Hardeman County, be- yond which in Tennessee and Kentucky the formation is concealed by overlapping Paleocene and Eocene strata (Wade, 1926, p. 7, 8, fig. 1). In Mississippi the formation typically consists of 20 to 40 feet of dark compact, fine-grained, micaceous, glau- conitic sand and sandy clay, in part calcareous; it con- tains an abundance of marine fossil organisms, chiefly mollusks, many of which are in an unusually fine and complete state of preservation. About the middle of the 19th century Dr. W. Spillman of Columbus, Miss, collected fossils at the locality that was later designated the type locality of the formation; it is on Owl Creek 3 miles [21/2 miles] northeast of Ripley, Tippah Coun- ty (El/2 sec. 7, T. 4 S., R. 4 E.). The section exposed on Owl Creek was described by Hilgard (1860, p. 88). The fossils were submitted to the pioneer American paleontologist, T. A. Conrad (1858), who described 56 new species of mollusks. A few additional species have been described by Conrad (1860), and by other authors in more recent years, but the Owl Creek fauna has never been as thoroughly studied as its importance j'ustifies. The formation is separated from the under- lying Ripley formation and from the overlying Clay- ton formation by erosional unconformities. Authors who have contributed substantially to our knowledge of the unit now called Owl Creek formation, in Mississippi and Tennessee include in chronologic order: Conrad (1858, 1860); Hilgard (1860); Crider (1906) ; Wade (1926) ; Stephenson and Monroe (1937, 1938, 1940) ; and Conant and McCutcheon (1941). (97) 98 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Strata presumed to be of Ripley (Late Cretaceous) age were known and mapped to the extreme head of the Gulf Embayment in southern Illinois as early as 1906, but no fossils were discovered in them and they were considered to be of nonmarine origin (Glenn, 1906, p. 27—29, pl. 1). More recent investigations have failed to disclose fossils in these beds in Illinois on which to base a correlation, but the geographic and stratigraphic relationship of the beds with reference to other known formations indicate that they are the northern extension of the McNairy sand member of the Ripley formation of Tennessee and Kentucky. Lamar and Sutton (1930, p. 853—854, fig. 1) state that the Ripley of southern Illinois is unconformably overlain by the Porters Creek clay. He did not recognize the Clayton formation (Paleocene) between the Ripley and the Porters Creek. At the old Olm— stead ferry landing the Porters Creek clay is 60 or 70 feet thick; the upper 30 feet is mined as fuller’s earth. Lamar reports indistinct imprints of marine fossils that are too poorly preserved for identification in the fuller’s earth in Illinois. I visited the Olmstead locality in 1936 and found paleontologic evidence in a small, poor exposure along an old abandoned road about 100 yards upstream from the 01d Olmstead ferry landing that the Clayton formation is present beneath the Porters Creek clay. The section here is as follows: Section along an old abandoned road 100 yards from the old Olmstead ferry landing, Pulaski County, Ill. Paleocene series: Clayton formation: Feet Sand, greenish-gray argillaceous, richly glauco- nitic __ ____ ___ _____ 2 Sand, weathered brown, ferruginous, argil- laceous,, glauconitic, With many chert pebbles in lower 18 inches; contains poorly preserved prints Of fossils in lower 2 feet; recognized Venericardi-a sp. (of the V. planlcosta group), Idoncarca saffordi (Gabb), anm'tella sp _____ 41A, Unconformity. Upper Cretaceous series: McNairy sand: Sand, fine white micaceous ____________________ 2 Concealed to water level ______________________________ 40: 48%: The pOsition of the preceding section is stratigraphi- cally below the Porters Creek clay, and the recognized fauna in the glauconitic sand is sufficient to identify the Clayton formation. In a later visit to the Olmstead locality when the Ohio River was at flood stage several poor exposures of the richly glauconitic sand of the Clayton formation were seen in the immediate vicinity of the old ferry landing, but no additional fossils were found. Prior to 1932 neither the Clayton formation nor the Porters Creek clay were known west of southern Illi- nois in southeastern Missouri; however, prophetic of their discovery Lamar and Sutton (1930, p. 853) said: West from Pulaski County, Illinois, the formation dips below younger sediments and is not known to occur elsewhere at the surface, unless the gray clay reported at Idalia and Bloomfield, Missouri, is Porters Creek—a conclusion which a study of well records of the region seems to justify. Lamar and Sutton also stated (p. 855—856) : Clays ascribed to the Lagrange, probably either the lower part or the dark gray upper phase described later, are also exposed near Idalia and Bloomfield, Missouri, in Crowleys Ridge. These clays have been called the Idalia shale by Mar- but [1902, p. 21—23], who describes the clays as “uniformly dark in color and, where freshly exposed, it is black, very much resembling the dark shales of the Coal Measures”. About 60 feet of this clay is exposed near Id‘alia, * * *. As previ- ously stated, it is thought that the gray clay exposed at Idalia and Bloomfield may be the upper part of the Porters Creek formation instead of one of the Lagrange clays. The clays at Idalia and Bloomfield were later mapped by Farrar (1935, pl. 6) as Midway group (Clayton formation and Porters Creek clay). Before 1932 the Owl Creek formation, as such, was not known in outcrop in the Gulf Embayment area north of Hardiman County, Tenn. .In 1932 the late F. E. Matthes, who was then engaged in physiographic studies in southeastern Missouri, discovered fossil im- prints in a thin layer of greenish-gray oolitic, glau- conitic, somewhat sandy clay, which crops out in a road bank in the southeast-facing slope of Crowleys Ridge, 0.35 mile northwest of Ardeola station, Stoddard Coun- ty, Mo. (pl. 14, A, B). He collected a chunk Of this material and submitted it to me for the determination of the fossils. I recognized several well—known Upper Cretaceous species. (Matthes, 1933, p. 1007—1009.) A collection made from the oolitic clay in J anu- ary 1933 by Willard Farrar of the Missouri Geological Survey and Water Resources showed that, in addition to the Cretaceous fossils, the clay contained several characteristic Clayton (Paleocene) fossils. Field in- vestigations in 1933 by the Missouri Survey and by the present author proved that the bed of oolitic clay is in fact the basal bed of the Clayton formation which, together with an overlying section of Porters Creek clay, represents the Paleocene series (Midway group) in the Gulf Embayment area. It was found that the Cretaceous fossils in the oolitic clay were derived by mechanical reworking from a bed of ferruginous, micaceous, fossiliferous clayey sand and sandy clay (Cretaceous) in place immediately beneath the oolitic clay. This reworking must have taken place before the calcareous material composing the shells of the or- ganisms was leached away, for the clay contains only ‘ OWL CREEK FOSSILS FROM CROWLEYS RIDGE, SOUTHEASTERN MISSOURI 99 the imprints of the fossils. The fossils in the Creta- ceous bed are also present as imprints only, but they represent an abundant fauna that includes many char- acteristic species of the Owl Creek formation of Mis- sissippi. The sand is lithologically like that of the typical Owl Creek except that the calcareous content has been removed in solution by circulating ground waters, and the iron in the glauconite has been oxidized to reddish, brownish, and yellowish hematitic and limonitic compounds. Before the discovery of Cretaceous fossils in Crow— leys Ridge the beds now known to be of that age were believed to be of Tertiary age and were so classified and mapped by Marbut (1902). One of the reasons for this erroneous correlation was the mistaken assump- tion that masses of quartzitic sandstone in the Mc- Nairy sand at Bell City in northeastern Stoddard County, and elsewhere in adjacent parts of Crowleys Ridge, were of the same age as similar quartizitic masses in the Wilcox formation farther south in Crowleys Ridge in Clay, Greene, and Craighead Counties, Ark. The discovery of the Cretaceous and Paleocene fos- sils throws new light on the geologic history of the Gulf Embayment, for it shows that the seas in which the Owl Creek and Clayton formations were de— posited extended northward to the extreme head of the embayment area. Following the discovery of Cretaceous and Paleo- cene strata in Crowleys Ridge in southeastern Mis- souri, representatives of the Missouri Geological Sur- vey and Water Resources were assigned to study the general geology, stratigraphy, and economic resources of the area, and reports, including areal geologic maps, were issued on these subjects. The report of most in— terest in connection with the present paper was pre- pared under the authorship of Willard Farrar (1935) and is entitled “The Cretaceous and Tertiary geolOgy.” The Cretaceous fossils listed in this report were iden- tified by me, and the Paleocene fossils by Julia Gard- ner. This report was followed by one entitled “The geology of Stoddard County, Missouri,” under the au- thorship of Farrar and McManamy (1937). In March 1933, it was my privilege to spend a short field sea- son in the area with Farrar and with H. S. McQueen, of the Missouri Survey. Again in April 1938, I spent 2 days in the area with H. S. McQueen, D. R. Stewart and Lyle McManamy of the Missouri Survey, and with W. H. Monroe of the United States Geological Survey. PHYSIOGRAPHIC SETTING Crowleys Ridge is an attenuated remnant of a hilly part of the Coastal Plain that has withstood the ero- sional attack- of two large rivers, the Ohio and the Mississippi. The ridge is about 200 miles long, extend- ing from Mississippi River below Cape Girardeau, Mo., to Helena, Ark. ; the ridge is extremely irregular in out- line and height, ranging in width from less than 1 mile to 18 miles, and rising to a maximum of about 580 feet above sea level and 260 feet above the surrounding low- lands. The continuity of the ridge is broken by four erosional gaps now traversed by streams. Little River traverses a gap about 9 miles wide in Scott and Stod- dard Counties, and Castor River flows through a narrow gap in Stoddard County; St. Francis River passes through a narrow gap on the Missouri State line; and L’Anguille River traverses a gap 8 miles wide in Lee County, Ark. The part of the ridge between the Little and Mississippi Rivers, Missouri, is locally known as the Benton Hills and the part in Stoddard and Dunklin Counties as Bloomfield Ridge. In his treatise on the geology of Crowleys Ridge, Call (1891, p. 128, 129) recognized that the lowland between the ridge and the Ozark province on the west was cut and partly refilled with sediments by the Mississippi River at a time when the courSe of the river was west of the ridge as far south as Helena, Ark., where it joined the Ohio River. Call says: The Mississippi entered the great emhayment just below Cape Girardeau and spreading into several considerable streams rapidly engaged in the work of denudation and removal. Two main channels. were formed, one east. and the other west of Crowley‘s Ridge. That is to say, such was their relation to what is now that ridge. The great valley through which fl0Ws the White, lower Black, Cache, and other smaller streams was then dug out. On the west the great trough of the Mississippi was then deeper and wider than that of the Ohio to the east. At length the waters of the Mississippi cut through and passed to the east of the ridge and its work west of the ridge ended. Although Call recognized some of the major facts in the geographic relationship of the Mississippi to the Ohio River his description of that relationship is some- what confused and he did not offer a detailed explana- tion of how the Mississippi was diverted from its course west of Crowleys Ridge to join the Ohio in the vicinity of Cairo. The physiography of Crowleys Ridge, as interpreted by Marbut (1902), and later with certain modifications by Matthes (1933), tells the astonishing story of the capture twice of one great river by another—the Ohio the “captor” and the Mississippi the “captured.” The story is briefly summarized in the following paragraphs. In early Quaternary time the Ohio River flowed to the southeast of a coastal-plain upland of which Crow- leys Ridge is now an attenuated erosional remnant. At the same time the Mississippi River turned to the west and southwest at Cape Girardeau, Mo., and flowed to 100 the south on the west side of the upland. The two rivers came together in the vicinity of Helena, Ark., and con- tinued as a single stream to the Gulf of Mexico. In the Cairo region near the head of the Gulf Embayment the gradient of the Ohio River was supposedly about 20 feet lower than that of the Mississippi. The drainage on the upland in the region of Scott and Stoddard Counties was to the northwest to the Missis- sippi, the small tributary valleys of course becoming deeper in that direction. The Ohio meandering in its flood plain east of the upland scoured away the south- east side of the upland, which became continuously nar- rower. The valleys of the northwestward-flowing tribu— taries thus were beheaded forming notches in the profile of the upland along its south edge and, as cutting con- tinued, the notches grew progressively deeper. Eventu— ally one of the notches corresponding to the geographic position of the present Little River became so low that the flood waters of the Mississippi spilled through it and flowed southward to the lower flood plain of the Ohio. Repeated floods continued to cut the notch deeper and wider until eventually the great Mississippi aban- doned its channel in the Advance Lowland and, follow- ing the course of the present Little River, joined the Ohio in that part of its flood plain which Marbut called the Morehouse Lowland. The Mississippi River must have followed this course for a relatively long time for the gap that it produced in Crowleys Ridge is nearly 9 miles wide. While this great shift in the course of the Mississippi was taking place another notch in the upland, south of Cape Girardeau, was being lowered in the same manner as that in the Little River area. Eventually a second capture of the river was accomplished through this notch, which diverted its course to the channel it now occupies from Cape Girardeau via Commerce to Cairo. The channel now occupied by Little River was, in its turn, abandoned by the Mississippi River. Marbut (1902, p. 3—7) named the great lowland west of Crowleys Ridge the Advance Lowland, from the vil- lage of Advance 24 miles southwest of Cape Girardeau. He applied the name to the lowland to and “‘beyond” the Arkansas State line. _ Stephenson and Crider (1916, p. 25) expanded the application of the name Advance to include the whole of the lowland in Arkansas be- tween Crowleys Ridge on the east and the Ozark province on the west. STRATIGRAPHY AND LITHOLOGIC CHARACTER OF THE FORMATIONS The sedimentary rocks composing the northern part of Crowleys Ridge include beds of Paleozoic, Late Cre- SI-IORTER CONTRIBUTIONS TO GENERAL GEOLOGY taceous, Paleocene, Eocene, Pliocene( ?), Pleistocene, and Recent ages. The following generalized section based, with modifications, on the published results of the researches of Willard Farrar and his associates on the staff of the Missouri Geological Survey and Water Resources, pertains to Scott and Stoddard Counties (Farrar, 1935, p. 10—28; Farrar and McManamy, 1937, p. 14—44). Generalized section of rocks in Crowleys Ridge, Missouri [Maximum known thicknesses are given] Quaternary system : Recent series: Fe" Silts, sands, and gravels of flood plains _________ 20 Pleistocene series: Terrace deposits ______________________________ 80 Loess ________________________________________ 70 Unconformity. Tertiary system: Pliocene series: Gravel, sand, and clay, unnamed ______________ 60 Unconformity. Eocene series: Wilcox formation 250 Unconformity. Paleocene series: Porters Creek clay ___________________________ 100 Clayton formation ____________________________ 10 Unconformity. Cretaceous system: Upper Cretaceous series: Owl Creek formation _________________________ 11 Unconformity. NcNairy sand ________________________________ 181 Unconformity. Devonian system Undifferentiated sandstones, lime- Sllurlan system . . . stones, dolomltes _________________ 120+ Ordovxcxan system 902+ The Owl Creek formation as it is exposed in the section at the discovery locality near Ardeola is typical and its stratigraphic relationship to underlying and overlying formations is shown most completely and most clearly there. The description of the Ardeola section given by Farrar (1935, p. 16) is, with certain modifications, repeated here. One important modifica- tion is the transfer of the lower 11 feet of his Owl Creek unit to the McNairy sand, and the recognition of an unconformable relationship between the McNairy sand and the Owl Creek, as here interpreted. Other sections in Stoddard and Scott Counties, in which the Owl Creek formation is present, are less completely exposed that the one near Ardeola. (See pl. 14, following p. 140.) OWL CREEK FOSSILS FROM CROWLEYS RIDGE, SOUTHEASTERN MISSOURI Section along road in southeast-facing slope of Crowleys Ridge, 0.35 miles northwest of Ardeola in NW%NW14 sec. 10, T. 27 N., R. 11 E., Stoddard County, Mo. [Altitude at‘ top of section 493: feet] Quaternary system: Pleistocene series: Loess, yellowish-brown ________________________ 5 Unconformity. ‘ Tertiary system: Pliocene series: Gravel, brown, Well-rounded pebbles, and some red sand 6 Unconformity. Paleocene series: Midway group: Porters Creek clay: Clay, dark-green on fresh surface, weath- ering to light gray, locally including interstratified beds of ferruginous clay _______________________________ 47 Clayton formation: Clay, pale-green, sandy, very glauconitic, oolitic in lower part, containing White angular sand grains near base; abun- dantly fossiliferous, including indige- nous species and reworked Owl Creek Species _____________________________ 5 Feet Unconformity. Cretaceous system: Upper Cretaceous series: Owl Creek formation: Sand, yellowish-brown, argillaceous, glauco- nitic, finely micaceous; contains many prints of fossils ________________________ 5 Clay, greenish-gray mottled with yellow and brown, sandy, sparingly glauconitic, finely and strongly micaceous; contains a few prints of fossils ________________________ 6 Unconformity, contact sharp. McNairy sand: Clay and sand, brown, laminated, cross- bedded, with parting planes of muscovite mica; contains abundant comminuted plant remains; borings in upper 8 or 10 inches are filled with sandy matrix from overlying Owl Creek formation __________ 11 Sand, grains angular, white to bright orange, crossbedded, lignitic, locally cemented with limonite ________________________________ 11 Clay, brown, light- and dark-gray to black, with interbedded sand; limonite and mus- covite mica along bedding planes _________ 27 Lignite, very sandy _______________________ 1 Sand, grains angular, white, with iron oxide stains, somewhat lignitic ________________ 11 Concealed to lowland level ________________ 38 173 A sample of the pale-green oolitic clay at the base of the Clayton formation was studied critically by R. C. Erd (written communication), whose report is quoted as follows: 1 347625—55—2 101 The sample is composed of clay oolites or pellets, ranging in size from 0.1 to 0.5 mm, and other mineral grains in a matrix of olive-green montmorillonite clay. The pellets comprise about 80% of the sample. In most instances detrital mineral grains or glauconite serve as nuclei for the oolites. The nuclei are surrounded by massive light-green montmorillonite (mean in— dex of refraction:1.555), which in turn is encased by concen- tric shells of montmorillonite. The individual montmorillonite crystals apparently lie with their plates tangential to the sphere. This oriented aggregate shows maximum birefringence (a’=1.53,r':1.56) and pleochroism ( X=pale brown, YZ=dark reddish brown). In many cases the oolite is merely a hollow shell of the oriented montmorillonite about a detrital grain, possibly as the result of shrinkage of the montmorillonite. The oolite'itself has in almost all instances shrunk (‘2) away from the surrounding clay matrix leaving a smooth and lustrous surface. The clay matrix is a light to olive-green montmorillonite with a mean index of refraction of 1.555 and appears to be similar to the massive montmorillonite in the pellets. A few detrital grains and glauconite occur directly in the matrix in addition to those found in the oolites. The light frac- tion consists of subangular water-clear quartz with a few in- clusions of biotite (‘3), apatite, and epidote; subangular to sub- round translucent quartz; angular fresh orthoclase; and microcline, some of which is being replaced by montmorillonite along cleavage cracks. The heavy fraction constitutes only a little of the sample. The minerals in approximate order of abundance in the heavy fraction are: Opaques (17,6, to 17/2 of the heavy fraction, mostly iron minerals), kyanite, zircon, staurolite, garnet, epid'ote, rutile, tourmaline, hornblende, muscovite, biotite, and chlorite. A1- most all of the detrital grains are coated with montmoril- lonite, glauconite, or limonite. Little or no phosphatic material is present and the amount of carbonate is negligible. The latter evidently has been leached from the rock for molds of shells, with delicate fea- tures well—preserved, are common. The shells are filled with both matrix clay and oolites although finer structures are pre- served by the montmorillonite matrix alone. Typical, nodular, dark-green glauconite with aggregate polarization is commonly found in the sample both as nuclei of the pellets and in the matrix. The chief occurrence of glauconite, however, is as slightly curved and twisted tubes which are polygonal in cross-section and closely resemble the faecal pellets figured by Moore (1939, p. 520, fig. 1—a, c, m). In longitudinal section the glauconite is seen to have a mica- ceous structure and to have expanded perpendicular to the basal cleavage in a manner similar to vermiculite. Optically the glauconite is biaxial negative, u':1.593, 1"=1.610, mean in- dex of refraction ea 1.61, 2V is approximately 20°. These glauconitized faecal pellets are most commonly found as nuclei of the montmorillonite oolites. A primary origin for the clay oolites, possibly coincident with the reworking of the underlying Cretaceous bed, seems likely. It is possible, however, that calcareous oolites have been partially or wholly replaced by clay and the remaining carbonate leached out. In addition to the faecal pellets mentioned by Erd there are scattered through the oolitic clay a few clusters of larger pellets that resemble in form another kind of 102 faecal pellets illustrated by Moore (1939, p. 520, fig. 1f) . In a subsequent study Erd reports on these as follows: Large faecal pellets are abundantly present in these samples but were not found in the material submitted earlier. The pellets are grouped together ulually with their long axes in sub-parallel arrangement. The pellets are normally round in cross-section but some have been squeezed together to produce a polygonal cross-section. Impressions of the oolites and detrital grains may be seen on the surface of the pellets, but they do not contain these objects. They are unique in this respect for even the matrix montmorillonite found in the molds of shells contains oolites and detrital grains. The large pellets do, however, contain about 10—20% of angular grains of quartz. The pellets are composed of gray-green montmorillonite which is similar to that in the matrix and has the same mean index of refraction. These pellets differ from the glauconitic (faecal?) pellets in composition, size (the small pellets are about 0.5 mm long by 0.15 wide), abundance (the small pellets are much more common and may make up 20% of the sample), and in grouping (they are scattered throughout the sample). It is interesting to note that the oolitic clay in the Ardeola section is at the same stratigraphic positiOn as 7 the fossil mollusks replaced by clay of the montmoril- lonite group in a railroad out half a mile south by west of Pontotoc, Pontotoc County, Miss. The latter occur- rence was recorded by Stephenson (1939, p. 96—99, pl. 16) and later by Ross and Stephenson (1939, p. 393—397, fig. 1). At the Pontotoc locality the replaced fossil shells are in the basal bed of the Clayton formation of the Midway group (Paleocene), immediately and un- conformably above glauconitic sand representing the southward extension of the Owl Creek formation. This identity of stratigraphic position is probably not accidental; it would seem to indicate a similarity in marine physical conditions in the Gulf Embayment area in early Midway time, extending from northern Missis— sippi to southeastern Missouri. STRUCTURE In structural attitude the Upper Cretaceous and Paleocene (Midway) beds, which form an important part of the body of Crowleys Ridge in southeastern Missouri, are monoclinal, dipping gently to the south- east into the synclinal basin formed by the downwarp- ing of the Gulf Embayment region. Data furnished by Farrar and McManamy (1937 geol. map, pl. 9) indi- cate that the southeast dip of the Cretaceous-Paleocene contact in the Bloomfield area in Stoddard County is between 40 and 45 feet to the mile. The map cited shows a broad upwarp accompanied by minor faulting in the Bloomfield area, but the data presented seem to justify an estimated regional dip of the Cretaceous-Paleocene SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY contact to the southeast of 35 or 40 feet to the mile. As the beds below and above the contact are nearly parallel to each other the regional dip of the Cretaceous, Paleo- cene, and Eocene beds to the southeast may be assumed to be about the same as that of the contact. Originally, and as late as late Tertiary (Pliocene) time, the Cretaceous and Paleocene strata of Crowleys Ridge in southeastern Missouri were physically con- tinuous southward through the Gulf Embayment with the beds of the same age in Mississippi. Their physical continuity was broken in Pleistocene time by erosion, first by the Ohio River before the capture of the Mis- sissippi, and later by the combined waters of the Ohio and the Mississippi, leaving the Cretaceous and Paleo- cene formations at elevated positions in the Crowleys Ridge upland. FOSSIL LOCALITIES ‘With the exception of one collection (USGS 16221), all the Cretaceous fossils from Missouri described or mentioned in this paper were obtained from the Owl Creek formation at the localities in Stoddard and Scott Counties listed below; the Cretaceous fossils in this collection (USGS 16221) were found in the basal bed of the Clayton formation, into which they had been incorporated by mechanical reworking from the under- lying Owl Creek formation. The collection bearing the number USGS 19088 consisted of one incomplete in- ternal mold of the ammonite, Sphenodiscus pleum'septa (Conrad), which was collected by Edison Shrum of Advance, Mo., and donated to the United States Geo- logical Survey, through Willard Farrar of the Missouri Survey. (See fig. 21.) The one collection (USGS 16221) from the basal bed of the Clayton formation, previously mentioned, was made by F. E. Matthes in June 1932, at the locality near Ardeola station, the description of which is given be- low; the bed is reported to be at an altitude of 430 feet, and about 110 feet above the base of the slope. This is‘ the collection that led to the discovery of the McNairy sand, and the Owl Creek formation of the Cretaceous, and the Clayton and Porters Creek formations of the Paleocene, in southeastern Missouri. All the fossils spe- cifically identified in this collection are Owl Creek (Upper Cretaceous) species derived by mechanical re- working from the underlying Owl Creek formation. Some of the genera that are not identified as to species may be indigenous to the Clayton formation. Typical Clayton (Midway) fossils were later found in the oolitic clay, associated with the reworked Cretaceous fossils. 103 OWLa CREEK FOSSILS FROM CROWLEYS RIDGE, SOUTHEASTERN MISSOURI A .wnaadfi c5 5 wowuawwums as .quH $2320 5 mac—awake“ page :a “3:53 .333 Ami—@8333. mmwoa wfizigo was 30:83an :c—uafihow Heir—m 4 .3 .E ”933 mghscwom .5335 was mwtaw Eo—Mo—oww r5832 £33m Ups—:3 53d maiden—Sn Sass»... .hwzflw E03286 535 won—ED 05 «a mw—wnaucusa :33me v5. .Eocfiegm $2.82 53.93% 95 «o 3an $032: 3:: can. .39“ :Sudoiamewzhucoofiouo air—Dy :ofldfiua “$30 :5 $5 Esau 630289 new; 353 mzmmow :93? «a vwgm $2380 5 33:53 9:32? .Esomwfia Ewumdofizom .vann—oo 38m 33 3quch no 3.3% no 92: nouoamléw auburn >h€tik0k20023 n ugh a AhEr—zm Evie—ONO .m.: D Guunflcouogvci W. m >t k kZO Z: d “0 nun—5:. :ofioozcov d Accummucoamuhcnav fl gum Paulo—a “Em n w 2 O 0 , O \CLEEOkZOOZD cataco— :mnoh W 32E 0332mm W. 5355.5.“ €qu #30 D 5555.5. 53:? m EE>==< n H 88— m n. u n w. m. x m E m 3 m 3 S V M 3 a zO:. 1861, Synopsis of the Mollusca of the Cretaceous for- mation: Am. Philos. Soc. Proc., v. 8, p. 57—257 (reprint of same date, p. 1—201). Gardner, J. A., 1916, Mollusca, Brachiopoda, and Vermes, in Clark, W. B., and others, Systematic paleontology, Upper Cretaceous deposits of Maryland, Md. Geol. Survey, Upper Cretaceous [Maryland], p. 371—733, pls. 12—45. Glenn, L. C., 1906, Underground waters of Tennessee and Ken- tucky west of Tennessee River and of an adjacent area in Illinois: U. S. Geol. Survey Water-Supply Paper 164, 173 p., 7 pls. Harbison, Anne, 1945, Upper Cretaceous mollusks of the lower Ripley formation near Dumas, Mississippi: Acad. Nat. Sci. Phila. Proc., v. 97, p. 75—92, pls. 1—6. Hilgard, E. W., 1860, Report of the geology and agriculture of the State of Mississippi: 391 p., geol. map, Jackson, Miss, E. Barksdale, State Printer. Johnson C. W., 1905, Annotated list of the types of invertebrate Cretaceous fossils in the collection of the Academy of Natu- ral Sciences of Philadelphia: Acad. Nat. Sci. Phila. Proc., v. 57, 28 p. OWL CREEK FOSSILS FROM CROWLEYS RIDGE, SOUTHEASTERN MISSOURI Lamar, J. E.,~and Sutton, A. H., 1930, Cretaceous and Tertiary sediments of Kentucky, Illinois, and Missouri: Am. Assoc. Petroleum Geologists Bull., v. 14, no. 7, p. 845—866, 4 figs. Marbut, C. F., 1902, The evolution of the northern part of. the lowlands of southeastern Missouri: Mo. Univ. Studies, v. 1, no. 3, p. 145—207 (reprint p. 1—63) . Matthes, F. E., 1933, Cretaceous sediments in Crowleys Ridge, southeastern Missouri: Am. Assoc. Petroleum Geologists Bull., v. 17, no. 8, p. 1003—1009. 1933, The Pleistocene diversion of the Mississippi River across Crowley’s Ridge, southeastern Missouri [abstracts] : Science, new ser., V. 77, p. 459—460; Washington Acad. Sci. J our., v. 23, no. 12, p. 572—573 1934, Pleistocene diversions of the Mississippi and the Ohio Rivers near Crowleys Ridge [abstract]: Geol. Soc. America Proc., 1933, p. 96—97. Meek, F. B., 1864, Check list of the invertebrate fossils of North America, Cretaceous and Jurassic: Smithsonian Misc. Coll. 7, no. 177, 40 p. Moore, H. B., 1939, Faecal pellets in relation to marine deposits, in Trask, P. D., ed., Recent marine sediments, Am. Assoc. Petroleum Geologists, p. 516—524. Morton, S. G., 1829, Description of the fossil shells which char- acterize the Atlantic Secondary formation of New Jersey and Delaware; including four new species: Acad. Nat. Sci. Phila. Jour., 1st ser., v. 6, p. 72—100, pls. 3—6. 1834, Synopsis of the organic remains of the Cretaceous group of the United States: 88 p., 19 pls., Phila., Key and Biddle. Ross, C. S., and Stephenson, L. W., 1939, Calcareous shells re- placed by beidellite: Am. Mineralogist, v. 24, p. 393—397, fig. 1. Stephenson, L. W., 1923, The Cretaceous formations of North Carolina: Pt. 1, Invertebrate fossils of the Upper Cretaceous formations: N. C. Geol. and Econ. Survey, v. 5, 592 p., 100 pls. 137 1939, Fossil mollusks preserved as clay replacements, near Pontotoc, Miss.: J our. Paleontology, v. 13, no. 1, p. 96—99, pl. 16. 1941, The larger invertebrate fossils of the Navarro group of Texas . . .: Tex. Univ. Pub. 4101, 641 p., 95 pls. 1952 [1953], Larger invertebrate fossils of the Woodbine formation (Cenomanian) of Texas: U. S. Geol. Survey Prof. Paper 242, 226 p., 59 pls. Stephenson, L. W., and Crider, A. F., 1916, Geology and ground waters of northeastern Arkansas: U. S. Geol. Survey Water- Supply Paper 399, 315 p., (esp. p. 129—132). Stephenson, L. W., and Monroe, W. H., 1937, Prairie Bluff chalk and Owl Creek formation of eastern Gulf region: Am. As- soc. Petroleum Geologists Bull., v. 21, no. 6, p. 806—809. 1938, Stratigraphy of Upper Cretaceous series in Missis- sippi and Alabama: Am. Assoc. Petroleum Geologists Bull., v. 22, no. 12, p. 1639—1657. 1940, Upper Cretaceous deposits [Mississippi] : Miss. State Geol. Survey Bull. 40, 296 p., 15 pls. Stewart, R. B., 1930, Gabb’s California Cretaceous and Tertiary type lamellibranchs: Acad. Nat. Sci. Phila. Spec. Pub. no. 3, 314 p., 17 pls. Tuomey, Michael, 1854, Description of some new fossils, from the Cretaceous rocks of the southern States: Acad. Nat. Sci. Phila. Proc., V. 7, p. 167—172. (Descriptions brief and inadequate, locality descriptions inadequate, no illustra- tions, and types lost.) Wade, Bruce, 1926, The fauna of the Ripley formation on Coon Creek, Tenn.: U. S. Geol. Survey Prof. Paper 137, 272 p., 72 pls. Weller, Stuart, 1907, A report on the Cretaceous paleontology of New Jersey: N. J. Geol. Survey, Paleontology series, v. 4, 871 p., 111 pls. (bound separately). Whitfield, R. P., 1885, Brachiopoda and Lamellibranchiata of the Raritan clays and greensand marls of New Jersey: U. S. Geol. Survey Mon. 9, 338 p., 35 pls. A Page (Acanthocardia) tippanum, Cardium ____________ 118 Actean linteua .................................. 133 acutilineata, C'te'noides ........................... 113 Lima __________________________ 104,113,114;p].17 acutilineata texana, Lima ................ 1 114 Advance Lowland _____________________ . 100 alabame'nse, Cardium (Granocardium) ___________ 119 alabamensis, Idomarca .......................... 109 alto, Cyprimeria ............ _ 105,120; pl. 20 alveata, Gyrodes ____________________ 125 Natica (Gyrodes) ............. _ 125 americana, Gastrochaena ________________________ 124 Ammonites pkurieepza .......................... 135 Anati'mya anteradiatm _ _ 104,116; pl. 17 longula. _____________________ 116 teranau ................... 116 $1) ................................. 104,116; pl. 17 (Anatimya) arteradiata, Pholadomya ____________ 116 Anati'na ___________________________ _ 115 anatinus, Solen. _____________________________ 115 A'nclmra spp ........................... 105,128; pl. 22 angulicostata, Trigom’a ....... . 104,112; pl. 16 anteradiata, Anatimya __________ _ 104, 116; pl. 17 Pholadomya (Anatimya). ...... 116 anteradiata tezana, Anatimya ___________________ 114 Aphrodma tippana _____________________ 105, 120; pl. 20 Area (Macrodon) eujalensis _____________ 108 Ardeola, stratigraphic section near. _.. _____ 100 argentea, Tenuipteria ............ 104,111; pl. 16 arge’nteus, Inoceramus _________________________ 110, 111 argillensis, Patten ............................... 113 Azinaea rotundata ______________________________ 108 B Baculitea carinatus _____________________ 105, 134; pl. 24 apillmani .................................. 134 tippaemis ................. . 134 bexaremic, C‘mssatella nudosa ____________________ 117 biplicata, Siliquaria _____________________________ 123 Solon (Leptosolen) ................... 123 biplicatus, Leptoeolen ............ . 105, 123; pl. 20 Breoiarca sp ................ 104, 10.9 Breoicardium fragile .................... 105, 120; pl. 18 buboana, Tellina ................... 105,121,122; pl. 20 buboanus, Trobus .......... . 105,127,128; pl. 22 bubonic, Peder: (Campto’nectes)- .._ 104, 118; pl. 17 Bullopsis cretacea ....................... 105, 133; pl. 23 0 Call, R. E., quoted _____________________________ 99 (Camptonectes) bubonic, Pecten. _________ 104,113 hiloardi, Pecten ____________ capaz, Oucullua ................................ 109 Idomarca ...................... 104,109, 110; pl. 15 Cardlum proteztum ............................. 116 Cardium (Acanthocardia) tippanum ............. 118 Cardium (Granocardium) «lobar/tense ____________ 119 lowci ___________________________ 105,119; pl. 19 tippanum ________ . 105,118; pl. 19 Cardium (Laem‘cardium) spill/mam. .......... 120 Cardiu'm (Pachycardium) spillmani ..... 105, 120; pl. 20 :tantoni ................................. 120 cari'natus, Baculites .................... 105, 134: pl. 24 INDEX [Italic numbers indicate descriptions] Page Cavcola producta ................................ 132 sp _________________________________ 105, 182; pl. 23 chatficldomis, Crassatella vodosa _________________ 117 Clayton formation ______________________ 98, 99, 101, 102 Ghana microtuberumd _.__ 104, 106; pl. 15 conradi, Disccscaphites __________________________ 135 Pholadomya ________________________________ 115 Scaphites ___________ 135 Vem'ella. _________________________ 105, 117; pl. 18 Coon Creek tongue of Ripley formation ________ 117, 118,122,124.125,126,130, 133 Corbula spp __________________________________ 105,123 Corsicana marl". _ 106,113,114,118,120,136 costata, Exam/1a..-. _____________ 111; pl. 16 coxtella/tus, Inoceramus. _ _____________ 111 Craasatella gqrd'nerae ............................ 117 vadoaa ____________________________________ 117, 118 bezarensis. 117 chatfieldensis.. 117 manorensis . . _ 117 ripleyana ...................... 105, 117; pl. 19 wadei ____________________________ 117 Crassutellites ripleyanus 117 vadosus _____________________________________ 117 Crenella elegantula ............................ 114,115 microstriata _________ __._ 104,111,115;p]. 17 serica ........................ 104, 114; pl. 17 Orenella (Stalaaimum) sema. 114 cretacea, Bullopsis ..................... 105, 183; pl. 23 Crowleys Ridge, description ___________________ 99,100 Czenoides acu/tilineota ................ 113 Cucullaea capar. . ___________________ 109 tippana.-. _________________ 109 vulgaris ......... 109 Cucullaea (Idomarca) tippana ___________________ 109 Cumulus tippanus _____________________ 104, 115; pl. 17 Cyclichna sp. ._ ....................... 105,134 Cyprimeria alta. ________________ 105, 120; pl. 20 ' 120 ' 120 D demote, Dosinia ................................ 120 Discoscaphites comadi ___________________ 135 iris ..................... 105, 134; pl. 23 sp......_._ .......................... 135; pl. 23 Distribution of fossils _________________________ 104—105 DonazfordiL . .... 107 Daaim'a densata" 120 Dreiasena tippana _______________________ 115 Drillum ripleyana _______________________________ 131 sp ................................. 105, 131; pl. 22 E oborea, Tellinimem ______________________________ elegamtula, Crenella. ellipticum, Leaumen .................. 105, 121; pl. 20 Enacteon _______________ linteus ............ tharpa smuosa" .. 105, 131, 132; pl. 23 Erd, R. 0., quoted_.__ .; ___________________ 101, 102 Escondido formation ......................... 113, 136 eujalensis, Arca (Macrodo'n) ..................... 108 Nemodtm. ...................... 104, 108; pl. 15 Triaonia ........................... 104, 112; pl. 16 Page (Euspz‘ra) halli, Polinices ________________________ 125 Ezogyra costata ................................. 104, 106,111, 113, 117,118, 120,121,123,126;pl.16 ponderosa ..... 106,107,111,113,114,117.118,120,126 F Farrar, Willard, cited. ._ . Ficzoaczeon ________________ Ficus octoIiratus ________________________________ 128 jordii, Donaz ____________________________________ 107 jormosa, Helicaulax ..... 105, 128; pl, 21 fragile, Brem‘cardium A _ _ _ Fusinus, sp. A __________ sp. B .............................. 105, 130; pl. 22 G Gardner, Julia, cited ___________________________ 99 gard'nerae, Crassatella __________ 117 Gastrochaena americana. _. _________ 124 ripleya'na ___________ _. 105, 124; pl. 21 Glycymeris rotundata ___________________ 104, 108; pl. 15 Goniochasma ____________________________________ 121 scaphoides ................. 124 Sp _______________________ __ 105, 124; pl. 21 (Granocardium) alabamense, Cardmm ........... 119 lowei. Cardium .................... 105, 119; pl. 19 tippanum, Cardium ................ 105, 118; pl. 19 “Green marl” ________ 134 Gyrodes alveatu" . 125 major _____________ 125 11er ......................... 125 spfllmanii ____________ ._ 105, 125; pl. 21 supraplicatus. .. 105, 125; pl. 21 sp ................................ 126‘; pl. 21 (Gyrodes) alveata, Natica ........................ 125 H halli, Poli’nices (Euspz'ra) ________________________ 125 Hamulus squamosuL.-. .. 104, 106’; pl. 16 Helicaulaz formosa ..................... 105, 128; pl. 21 hilgardi, Pecten ................................. 113 Pecten (Camptanectes).. .. 104, 113; pl. 17 Homerstown marl .............................. 134 I Idonearca alabamensis .......................... 109 capaz ____________ 104, 109, 110; pl. 15 safiord'i ......... 98 tippana _________________ 109 (Idonearca) tippana, C‘ucullaea .................. 109 Inoceramus urgemeus _________________________ 110, 111 coatellatua .................. 111 Eric, Discoccaphites" ______ 105,134; pl. 25 Scaphitea ................................... 135 J jugosa, Volula .................................. 130 K Kemp clay ....................... 106, 113, 117, 129, 136 L (Laeolcardium) splllmani, Cardium .............. 120 Lamar, J. E., and Sutton, A. E, quoted ....... 98 139 140 Page laqueata, Pimm ........................ 104,110; pl. 16 Leda longifrtms _________________________________ 107 slackiama ___________________________________ 107 Legumen ellipticmn._ .- 105, 121; pl. 20 Leptosolm biplicalus ................... 105,128; pl. 20 (Leptosolen) biplicata, Solen ..................... 123 Lima acutilineata ___________ _. 104,115, 114; pl. 17 teranu ................................. 114 Lineur‘ia ........................................ 122 metaxtriata. 105,122; pl. 20 linteus, acteon .................................. 133 ancteum ........................... 105,153; pl. 23 Solidulus _____________________ 132, 133 Liopeplum rugosum_.__..___ ........ 105,130,131; pl. 22 subjugosum ............................... 130, 131 Liopisthu protexta ........ 104,116,- pl. 19 List of collection numbers ______________________ 104 longifrons, Leda ................................. 107 Nuculana.... ‘ 104,107; pl. 15 longula, Anatimya ______________________________ 116 lowei, Cardium (Granocardium) ________ 105,119, pl. 19 (Lunatia) redilabrum, Natica ................... 125 M McManamy, Lyle, cited ....................... McNairy sand _________________________ 99,100,102,105 (Macradcm) eujalensia, Area 108 major, Cypri'meria ______________________________ 120 Gurodes ..................................... 125 manormsis, Crassatella vadosa. 117 Mal-but, C. F., cited .......................... 99,100 Marshalltown formation ________________________ 114 marglandica, Mona _____ 129 Matawan formation ____________________________ 110 Matthes, F. E., cited ........................... 98 Merchantville clay. ._ 110 Meretriz tippana ............................ 120 metastriata, Linearia ................... 105,122; pl. 20 microstriata, C‘remlla. 104, 114, 115; pl. 17 micratuberum, 0110M ................... 104, 106; pl. 15 Midway group ............................... 98, 102 Mississippi River, diversion of ............... 99. 100 Monmouth formation ............ 109, 114, 117, 124, 133 monmouthemis, Panope ................ 105,123: pl. 21 Morea margllmdicai -. 129 transenna __________________________ 105,129: pl. 22 Music parilz's ___________________________________ 121 N Nacatoch sand _________________________________ 117 Napulus octolimtus ................. 105,128,129; pl. 21 sp _____________________________________ 129; pl. 21 Natica (Gyrodes) alveata ....... 125 Natica (Lunatic) rectilabru'm ____________________ 125 Navarro group ___________ 113, 117, 120, 124, 129, 132, 136 Ne'modon eufaulensia. _ ........... 104, 108: pl. 15 Numla percmssa ___________________ 104, 106, 100; pl. 15 Nuculana longifrans .................... 104, 107: pl. 15 sp .......................................... 107 O occidentalis, Phaladomya ........................ 115 octoliratua, Ficus ................................ 128 Napulus ....................... 105, 128. 129; pl. 21 Olmstead Ferry landing, Ill., stratigraphic sec- tion ................................ 98 Oatrca tedicosta ......................... 104, 111: pl. 18 Owl Creek formation, description of, Missis- sippi ............................... 97 southeastern Missouri ______________________ 100 Tennessee __________________________________ 97 INDEX 1’ Page (Pachz/cardz'um) spillmani, Cardium_.__ 105,120: pl. 20 (Pachycardium) stantoni, Cardium ______________ 120 Pandoracea _________________________________ 115 Panope monmouthemis.. 105, 123; pl. 21 parilia, Mysia ....................... 121 T211211 ................... pateriformia, Paeudomalazz's _ . . 105, 121: pl. 20 105, 124: pl. 21 Pacten ............................ 118 argillensw- 113 hilaardi _________ 113 simplicius ____________________ 113 Pecten (Camptonectes) bubonis- 104,118; pl. 17 hthardi ___________________ _ 104,113: pl. 17 Pecten (Syncyclomma) aimplicius“ _ 104,113; pl. 17 Peedee formation _________________ 113 percraasu, Nuculu _______ perplana, Scambula. . - 104,106, 107; pl. 15 ..... 105,118; pl. 18 petrosus, Gyrodea.-.. ________ 125 Pholadomya comadi. 115 occidentalis ................ 115 tippana ....................... _ 104,115: pl. 18 Pholadomya (Anatimya) anteradiata. 116 pilsbryi, Pseudomalixis __________________ 124, 125 Pz'mm Zaqueata .......... _ 104 110' pl. 16 planicosta, Venericardiu- 98 pleurisepta, Ammonma. _ _...._-___. _____ 135 Sphenodiscus ........ . 102,105,135, 136: pl. 24 Potjnices rectilabmm ................... 105,125; pl. 21 Polinices (Euspira) hulli ........................ 125 ponderosa, Ezogyra__._ 106, 107, 111, 113, 114, 117, 118, 120 Porters Creek clay ............................. 98, 102 Prairie Blufi chalk .................... producta, Canola- proteztu, Liopistha ...................... 104. 116': pl. 19 proteztum, Cardium ..................... 116 Providence sand ......... Pseudomalaxis pateriformio ............. 105,124: pl. 21 pilsbryi ................................... 124,125 1 , , .......... -... _.. 125 R rectilabrum, Nalica (Lu/mafia) ................... 125 Polinicea ........................... 105,125: pl. 21 Red Bank sand. 114 Ripley formation ...... 105, 107, 108, 113, 116, 117, 128, 131 ripleyana, Crassatella uadosa ____________ 105,117:pl. 19 Drilluta ............... , 131 Gastrochaena _______________________ 105,124; pl. 21 Pseudomalizis .............................. 125 ripleyanus, Crassatellites. . 117 rotundatu, Azinea ............................... 108 Glycymeris _________________________ 104, 108; pl. 15 rugosum, Liopeplum ............... 105, 130,131: pl. 22 S safardi, Idlmearca _______________________________ 98 scabra, Triga'niauu _________________ 112 - 105,118,- pl. 18 ___________ 135 ................... 135 ....... 124 serica, Crenella ......................... 104,114,' pl. 17 scrim, Crenclla (Stalaymium)-. ..... 114 Serpula sp ............. _ 106 Siliquaria biplicata .............................. 123 " ’ ,mem --_ 113 Pectm (Smudonema) ............. 104,113: pl. 17 sinuosa, Eaharpo ......... 105, 131,132: pl. 23 slackiana, Leda. . ..... 107 Sale» anatimu .................. 115 Selma (Leptosolm) biplicata .................... 123 O Page Solidulus linteus .............................. 132, 133 Sphenodiscus pleurisepta... _._ 102, 105,185,136: pl. 24 spillmam'. Baculite: .......................... 134 Cardium (Laem’cardium). ........... 120 Cardium (Pachycardium) _ 105,120; pl. 20 spillmtmii, Gyrodes _________ 105,125; pl. 21 squamosus, Hamulus _______ - 104,106: pl. 15 (Stalagmium) serica, Crenella ................... 114 stanttmi, Cardium (Pachycardium) ______________ 120 stimpsom', Xylophaga ........................... 124 Stratigraphic sections___.. ..._ 98, 100, 101 subjugosum, Liopeplum.. _______ 130, 131 supraplicatus, Gyrodes ............. ._ 105, 125; pl. 21 (Syncyclonema) simplicius, Pecten _____________ 104, 113 T tecticosta, Ostrea _______ Tellina buboana. _ ._ 104,111; pl. 16 105, 121, 122; pl. 20 Tellim’mera eborea. _____________ 122 Tenea parilis _____ 105,121; pl. 20 Tenuipteria... . ......... 110 urgentea .................. 104,111;p1. 16‘ terana, Anatimuu anteradiata 116 Lima acutilimata ............ 114 tippana, Aphrodina. . .. 105, 120; pl. 20 Cucullaea ................................... 109 Cucullaea (Idtmearca) ________________ 109 Dreissena ___________________________________ 115 Idonearca ________________________ ___ 109 Meretriz ________________ 120 Pholadomya.. Turritella. _ tippaemis, Baculitea tippanu'm, Cardium (Acanthocardia).- Cardium (Granocardium). _. 105,118,- pl. 19 tippanus, Cumulus _________ 104, 115,- pl. 17 104,115; pl. 18 __ 105,126,' pl. 29 torta, Cyprimeria... _________ 120 transenna, Mona .......... 105, 129; pl. 22 Trigonia angulicostata__ .......... 104,112; pl. 16 mfaulensis _______ ._ 104,112; 111.16 scabra _________________ _ 112 Trobus ............................... 127 buboanua _____ __ 105, 127, 128; pl. 22 Turrz’tella tippana ...................... 105, 126',- pl. 22 vertebroides ..................... 105, 126‘, 127; pl. 22 sp ......................................... 98,106 V vadoaa, Craamtella ............................ 117, 118 vadosa bezarensis, C‘racsatdla .............. 117 chatfieldemis, Crascatella ............. 117 manorensis, Crassatella..- 117 ripleyana, Crassatella ............... 105, 117: pl. 19 wadei, Crussatella ........................... 117 vadosus, Crassatelliteau _ 117 Venericardia planicosta .......................... 98 sp .......................................... 98 Veniella conradi. ..... _.._ 105, 117; pl. 18 vertebroidee, Turritella .............. 105,126,127; pl. 22 Valuta juqosa ................................... 130 Volutomor'pha spp_- .105, 151: pl. 28 mlgaris, Cucuuaea ............................. 109 W wadei. Crusaatella vadoaa ....................... 117 Wenonah sand _________ 117 Woodbury clay ................................. 110 X Xylophaaa stimpetmi ............................ 124 PLATES 14—24 347625—55—4 .cooSOo—Z .m .m km mirage—cam .0: .WHEEZDCU HECUm QZ< ijwQfl—OHm 7: mZCrr Jug—:5 AHEYUSJOEU .33 .1. £53m aua33m 2.; 2:5 4930 .30.:3%:_U :: doom :1? =o€wE~3 =3k30 :o 51. m5... 2:5. 5—2 J3:ch 3a m n.— e— .m— 32 9N C cN :5: «”mmnm'lfimm :m 3:2...an .mZOHFaJZflOh ZC,_.>C .QZ<$ >=—<702 mo :0? ,__< >3 OK?“ Iflaflv—U :33 ZEm—BFm—m gulf—.2. E QBAZHQ Em mflhE>xim :{321225—6 GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 15 20 21 CLIONA, HA 1V] UL US, 5\ LC [ILA , NHJIODON, CL ) “(I ) 'MIL'R I S, Nl/‘C ULA NA , A N D I DONEA RCA FIGURES 1, 2. 8-12. 13—17. 18, 19. , 20-26.‘ PLATE 15 [Figures natural size except as indicated] Cliona microtuberum Stephenson (p. 106). - - ~ -‘ Casts of borings, X 2, in a fragment of bivalve shell (1) and in a gastropod shell (2), from a dry branch 300 feet downstream from a road crossing, 2.1 miles southwest of Ardeola station, Stoddard County, Mo. USGS 16451, USNM 128081. . Hamulus squamosus Gabb (p. 106)n Rubber cast from external mold, X 2, from ditch on north-south road 1.4 miles weSt' by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128083. ‘ ' . Nucula percrassa Conrad (p. 106). 4, 5. Views of a nearly perfect topotype, from Owl Creek, Tippah County, Miss. _ USGS 707, USNM 128084. 6. Interior of the left valve of a topotype, from the same source. ‘USNM 128084. 7. Internal mold, X 2, of part of a right Valve, from ditch on north-south'road 1.4 miles west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128085. Nemodon eufaulensz's (Gabb), (p. 108). ' 8. Left valve, X 2, of a topotype, from Eufaula, Barbour County, Ala. USNM 18830. 9, 10. Right valve, X 2, of another topotype, and hinge, X 2, of the same, from Eufaula. USNM 18830. 11, 12. Internal mold, X 2, and rubber cast of external mold, X 3, of a left valve, from ditch on north—south road 1.4 miles west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128092. Glycyrnerz's rotundata (Gabb), (p. 108). ' 13, 14. Views of a right valve, from Owl Creek, Tippah County, 'Miss. USGS 594, 'USNM 21681. 15. Interior of a juvenile left valve, from Owl Creek, Tippah County, Miss. USGS 707, USNM 128093. 16. Internal mold of a right valve, from ditch on north—south road 1.4 miles west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128095. 17. 'Internal mold of a juvenile left valve, from road on sautheast-faeing slope of Crowleys Ridge 0.35 mile northwest of Ardeola station, Stoddard County, Mo. USGS 16429, USNM 128094. Nuculoma longifrons (Conrad), (p. 107). , ‘ ' 18. A left valve, frOm 0w1 Creek, Tippah County, Miss. USGS 707, USN M 128088. 19. Internal mold, X 2, of a right valve, from ditch on north-south'road 1.4 miles west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128087. ' ‘ Idanearca capax (COnrad), (p. 109). ' " ' i 20, 21. Views of a medium-sized topotype, from Owl Creek, Tippah County, Miss. ‘USGS 707, USNM 128097. 22. Rubber cast'from the interior of an adulttopotype, for cbmparison with figures 23, 24. USGS 707, USN M 128097. ’ ‘ ' * ‘ ‘ 23, 24. Views of the internal mold of a left valve, from ditch on north-south road 1.4 miles'west by south of Ardeola station, Stoddard County, Mo. _ USGS 19090, USNM 128098., " ’ ‘ ' 25. Internal'inOId‘, X2, of a medium-sizedleft' valve, with's'urfaée sculpture impressed upon' it, ‘from the preceding localitth'SNM 128098." ' ' " ’ ‘ " 26. Rubber cast, X 1%, from the external mold of the preceding specimen. PLATE 16 [Figures natural size except as indicated] FIGURES 1—3. Trigom‘a angulicostata Gabb (p. 112). i 1. Right valve, from Owl Creek, Tippah County, Miss. USGS 707, USNM 128110. 2, 3. Internal mold of right valve (2) with sculpture impressed upon it, and rubber cast from external mold of a left valve (3), from road on southeast facing slope of Crowleys Ridge 0.35 mile northwest of Ardeola station, Stoddard County, Mo. USGS 16429, USNM 128109. 4—9. Tenuipteria argentea (Conrad), (p, 111). 4, 5. Two topotypes, a right valve (4) and binge, X 2, of a left valve (5), from Owl Creek, Tippah County, Miss. USGS 707, USNM 128104. 6. Left valve from the Owl Creek locality. USGS 6464, USNM 128102. 7. Internal mold of left valve ‘with weakly impressed sculpture, from ditch on north-south road 1.4 mile west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128103. 8. Incomplete internal mold, X 1%, of right valve, from a dry branch 300 feet downstream from a road crossing, 2.1 miles southwest of Ardeola station, Stoddard County, Mo. USGS 16451, USNM 128105. ' 9. Incomplete external mold of left valve, from road on southeast-facing slope of Crowleys Ridge 0.35 mile northwest of Ardeola station, Stoddard County, Mo, USGS 16452, USNM 128106. 10—12. Pinna laqueata Conrad (p. 110). 10. Left side of topotype, from Owl Creek, Tippah County, Miss. USGS 707, USNM 128100. 11. Left side of an incomplete topotype, from the same source. USNM 128099. _ 12. Rubber cast from incomplete external mold of right valve, from southeast-facing slope of Crowleys Ridge 0.35 mile northwest of Ardeola station, Stoddard County, Mo. USGS 16452, USNM 128101. 13, 14. Ostrea tectz'costa. Gabb (p. 111). Internal molds of two left valves, from ditch on north-south road 1.4 miles west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128107. 15—17. Trigom'a eujaulensis Gabb (p. 112). 15. A topotype, right valve, from bluff on Chattahoochee River at Eufaula, Barbour County, Ala. USGS 854, USNM 128112. 16, 17. Internal mold, X 1%, of left valve and rubber cast, X 1%, from incomplete external mold of right valve, from ditch on north-south road 1.4 miles west by south of Ardeola station, Stoddard County, Mo. USGS 19090, USNM 128111. 18. Eaagyra costata Say (p. 111). Rubber cast from external mold, X 2, of a left valve from road on southeast-facing slope of Crowleys Ridge 0.35 mile northwest of Ardeola station Stoddard County, Mo. USGS 16452, USNM 128108. mecokxi Q73» 4&5?th ”ES/iaw .vQKNRAwDZWVH JiZQUtFB m: HFm~>flpw Q.\\\ s ukL SALT‘“ 085.5\\\\\\\\\\\\\\§§tt§§§§§§§§§§\ M°mswwn w\p‘1i-FE§,‘|3‘URG “NE «0“» ' ,,,,,,. ...4.’414'/w \\\\\\\\\\\\\\\\\\\ . 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Solid blocks indicate type localities of Middle Ordovician formations. Adapted from Rodgers, 1952. ' MIDDLE ORDOVIC‘IAN ROCKS OF EASTERN TENNESSEE ANALYSIS»OF STRATIGRAPHIC NOMENCLATURE HISTORICAL BACKGROUND EARLY WORK Early geologic work in eastern [Tennessee may. be divided'into three phases: (1) that of Safford (1869) and of Safl’ord and Killebrew (1876 and later); (2) that of the U. S. Geological Survey reported in Folios of the Geologic Altas of the United States by Campbell, Hayes, and Keith (see classification below); and (3) the work of E. O. Ulrich and his associates. Safford (1869, p. 246—250) designated the outcrop belt dealt with in this report as the “Gray belt” of “the upper member of the Trenton and Nashville series, “in contrast to the “Red belt” of beds of the same age adjacent to the northwest. Within the Gray belt he recognized two details that are important in making present-day correlations: the occurrence of black shale with graptolites at the base of the shale section, and a gradual change in rock color from gray or “Sky-blue” in the northeast to dominant red in the southwest. Safiord gave the thickness of the shale between the “Clinch Mountain Sandstone” (Bays formation) and’ the “Maclurea Limestone” (Lenoir limestone) as 1,982 feet. Saflord and Killebrew (1876, p. 108, 130) intro— duced the term Lenoir limestone, the loldest term still applied to rocks of Middle Ordovician age in the Appalachian area, for blue, argillaceous limestone near Lenoir City which previously was designated the Maclurea Limestone by Safl'ord (1869). Folios of the U. S. Geological Survey covering many quadrangles in the southern Appalachians were pre— pared by several geologists working simultaneously in different areas, all under the general supervision of Bailey Willis. The earliest were published between 1894 and 1896, although some results of the work were published by Willis in 1893. Stratigraphic terminology 143 of the Middle Ordovician rocks differs from one folio to another, probably because of progressive refinement of correlation and nomenclature. Because of a delay in publication of some folios, some names first appeared in quadrangles far from their type areas. The Estillville folio (Campbell, 1894) largely in south- western Virginia, contains the names Chickamauga limestone, Sevier shale, and Bays sandstone, the first based on' outcrops in the Ringgold (Georgia) quadrangle (Hayes, 1891, 1894a), the second on outcrops in the Knoxville quadrangle (Keith, 1895), and the third on outcrops in the Morristown quadrangle (Keith, 1896b). In the Cleveland folio (Hayes, 1895), equivalents of the Sevier shale as defined in the Estillville folio were termed the Athens shale and Tellico sandstone, the first from outcrops within the quadrangle, the second from outcrops in the Loudon quadrangle (Keith, 1896a). The name Athens had, however, been used earlier in the Kingston folio (Hayes, 1894b) for supposedly equiva- lent shales now known to be of Late Ordovician age. All five of these names appear in a single section in the subsequent Knoxville and Loudon folios (Keith, 1895, 1896a), where the Sevier was restricted to the upper part of the rocks assigned to it in the Estillville folio, and the names Athens and Tellico were used for its lower part. However, the term Tellico was apparently not found to be regionally applicable, as it was not used in the adjacent Morristown folio (Keith, 1896b), where the Sevier was shown as lying directly on the Athens. Keith’s lithologic descriptions of these formations southeast of Bays Mountain in the Knoxville folio may be summarized as follows: Bays sandstone—Red calcareous and argillaceous sandstone, with some feldspathic sandstone beds; 300—l,100 feet thick. Sevier shale.—Light-blue calcareous shale with two units of bluish-gray and gray calcareous sandstone. Average thickness from top to bottom of the 5 units: shale 550 feet; sandstone 300 feet; shale 550 feet; sandstone 575 feet; shale 625 feet; “The Early classification of Middle Ordovician rocks in eastern Tennessee Safford, 1869 Hayes, 1894, Ringgold folio Hayes, 1895 Cleveland folio (east- ern part) Campbell, 1894 Estillville folio (Holston River outcrop belt) Keith, 1895 Knoxville folio (sautheast oi Bays Mountain) Clinch Mountain Sand- stone.l Rockwood forma- tion. Rockwood formation. Clinch sandstone. Clinch sandstone. Trenton and Nashville series Lenoir limestone.2 Chickamauga lime- stone. Sevier shale. Tellico sandstone. Athens shale. Chickamauga limestone. Bays sandstone. Sevier shale. Chickamauga limestone. Bays sandstone. . Sevier shale. ‘ Tellico sandstone. Athens shale. Chickamauga limestone. Knox dolomite. Knox dolomite. Knox dolomite. Knox dolomite. Knox dolomite. 1 Beds directly above the Middle Ordovician; no correlation of Clinch sandstone with Rockwood formation is implied. 2 Proposed by Safiord and Killebrew, 1876, p. 130. 144 shales are precisely like the Athens shale, and the sandstones are very similar to the Tellico sandstone.” Tellico sandstone.—Bluish—gray and gray calcareous sandstone and sandy shales, closely interbedded; these weather to a porous sandy rock with a strong red color; 800-900 feet thick. Athens shale—Black graptoliferous shales near the base, passing up into thin light-blue shaly limestone; 1,000—1,200 feet thick. Chickamauga limestone.——~Massive blue and gray and argil— laceous limestone; 0—50 feet thick. In his subsequent revision of the folio terminology, . Ulrich distinguished the Mosheim limestone below the Lenoir limestone (Ulrich, 1911). He later (in Gordon, 1924) introducedthe term Whitesburg limestone for beds between the Lenoir (Chickamauga) limestone and the Athens shale. The term Ottosee shale, which he substituted for Sevier shale as mapped in the northwest part of the Knoxville quadrangle (Keith, 1895), was never applied to the southeasternmost belt. Similarly, the Holston marble, noted as discontinous lentils by ' Keith in the Knoxville and London folios, but given formational rank by Ulrich, was not recognized in the southeastern belt. Ulrich’s classification of rocks of Middle Ordovician age in this belt was as follows: Bays sandstone Sevier shale (=Ottosee shale of northwestern belts) Tellico formation (Holston marble of northwestern belts absent) Athens shale Whitesburg limestone Lenoir limestone Mosheim limestone LATER WORK A complex classification of rocks of Middle Ordovician age was adopted in Virginia by Butts (1940), and forma- tion names that had their origins in Tennessee were extended into Virginia. B. N. Cooper and C. E. Prouty (Cooper and Prouty, 1943, Cooper, 1944) investigated in detail the Middle Ordovician rocks of southwestern Virginia. Their work disclosed that the classification of Butts was untenable, and they therefore'established a new one. As the rocks of this area are relatively fossiliferous, detailed zonation is possible, and this section may be used as a standard for correlation and classification elsewhere. The units of the southwestern Virginia section are as follows: Moccasin formation Witten limestone Bowen formation Wardell formation Gratton limestone Benbolt limestone Peery limestone Ward Cove limestone1 1 The Ward Cove, Lincolnshire, Five Oaks, and Blackford were originally (Cooper and Prouty, 1943) classed as members of the Cliflield formation. In later publications (for example, Cooper, 1945, p. 43) these units were given formation rank, and the term Cliflield formation was abandoned. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Lincolnshire limestone Five Oaks limestone Blackford formation Subsequent work (B. N. Cooper, 1950) shows that the Gratton is a partial lateral equivalent of the Wardell limestone, and that the Elway limestone is a unit of formational rank that had been included at the top of Blackford formation. C. E. Prouty extended these concepts into Tennessee. His earlier paper (Prouty, 1946) contains no reference to the southeasternmost belt other than to note the correspondence of the Sevier shale to the Ottosee shale and the Ottosee shale to the Benbolt limestone. In a later paper (Prouty, 1948, p. 1612—1613) he makes the following statements: The Lincolnshire limestone thickens from Virginia into Ten- nessee by addition at the base, resembling in appearance the more shaly Lenoir limestone facies of Tennessee, a partial equiv- alent of the Lincolnshire. The overlying Thompson Valley elastic limestone occurs throughout the southeast belts in Virginia and Tennessee, being partly equivalent of the commercial “Holston” marble of the Knoxville, Tennessee, area (Farragut limestone). The upper Cliflield (Ward Cove and Peery forma- tions) thins from Virginia into Tennessee, disappearing entirely in southwest Virginia and northeast Tennessee. * * * From Virginia into Tennessee * * * the most pro- nounced change * * * is in the grading of the Benbolt-Gratton— Wardell facies into the Sevier shale facies. The Sevier is best developed southeast of Clinch Mountain (and the Tazewell axis) * * *, the interval thinning from more than 4,400 feet in the Bays Mountain area southeast of Knoxville, Tennessee, to less than 800 feet northwest of the axis near the Cumberland escarpment. The Farragut limestone (“Holston marble”) thins northwestward and disappears northwest of the arch. The Tel- lico sandstone shows ofl‘lap relationship to the Farragut, thinning out on the southeast flank of the axis. The lower Sevier shaly limestone overlaps the Tellico toward the arch. The middle Sevier * * * thins out directly northwest of the axis. The upper Sevier * * * and the overlying Bowen formation show offlap relationships with the lower Sevier, possibly due to pre— Witten erosion. Cooper and Cooper (1946, p. 51—53), however, showed that the Mosheim and Lenoir limestones are at least partly equivalent, forming a unit that underlies the Lincolnshire limestone. Elsewhere in their paper (p. 78—80) they suggest the equivalence of the Whitesburg limestone to the Botetourt member of the Edinburg formation, and they proposed (p. 78) use of the term Liberty Hall facies of the Edinburg limestone (a revival of the term Liberty Hall limestone of Campbell, H. D., 1905) for the black shales and platy limestones long referred to as the Athens shale or limestone in Virginia. The work of Rodgers, G. A. Cooper, B. N. Cooper, and the writer in East Tennessee indicates that Keith’s MIDDLE ORDOVICIAN ROCKS 0F EASTERN TENNESSEE Athens shale, Tellico sandstone, Sevier shale, and Bays sandstone of the southeastern belt under discussion are equivalents of Keith’s Chickamauga. and Moccasin limestones of the northwestern belts. The broader outlines of this relation have been shown diagram- matically by King (1950, fig. 9, p. 660). Some differ- ences in the interpretation of the details exist between the different geologists and are presented in their re- ports. (Rodgers, 1953, p. 66; B. N. Cooper, 1953, p. 3; G. A. Cooper, 1955.) The graptolites of the Athens shale have been the subject of extensive study by C. E. Decker (1952). In the southern Appalachians, Decker accepts the strati- graphic classification of the older folios. His graptolite collections from many sections of this unit are significant contributions to our knowledge. NECESSITY FOR A REVISED CLASSIFICATION Two published geologic maps on a scale of 1: 125,000 embrace the area of this report: Keith (1895) and Rodgers (1953). The classification of rocks of Middle Ordovician age on neither map conforms with the findings of the present writer. Keith’s (1895) classification below can be recognized in the field, but several of the units of that classification seem arbitrary and unnatural. The Tellico sandstone seems to have been drawn on the basis of its topographic 145 expression, which is quite marked. The Sevier shale contains several units that can be recognized individu- ally, the lowest of which contains a fauna that is notably different from the remainder of the formation. Rodgers (1953, p. 76—82) briefly described and dis- cussed the rocks on which the present report is based. He distinguished most of the named units of the present report, but named and classified them differently. In the writer’s opinion Rodgers’ introduction of the terms Ottosee shale and Holston formation and the continued use of the Athens shale here give these terms time- stratigraphic rather than rock-unit status. Observa- tions made after the preparation of Rodgers’ report changed many of the present author’s Views on corre- lation. He now accepts the correlation of the thick sandy formation, here termed the Chota formation, with the “Holston formation of the standard belt” of Rodgers. The writer desires to present an accurate description of the stratigraphy in as much detail as is practical, by means of a rock-unit classification based primarily on the rocks of his map area. This classification is com- pared with those of Keith and Rodgers below. In the treatment of the individualunits to follow, a summary of the nomenclatural status of the formation precedes discussion of the unit itself so that problems of termi- nology are dealt with as they arise. Classification of Middle Ordovician rocks of the type Tellico-Sevier belt Present report Keith, 1895 Rodgers, 1953 Bays formation. Bays sandstone. Bays formation.1 Sevier formation: Bacon Bend member. Sevier formation, main body. Not differentiated from main body of Sevier shale. Sevier shale, upper part. Not differentiated from main body of Ottosee shale. Ottosee shale.1 Chota formation. Sandstone lentil in Sevier shale. Holston formation.l Tellico formation. Includes lower part of Sevier shale, all of Tellico sandstone, and upper part of Athens shale. Blockhouse shale: Dark shale member. Toqua sandstone member. Whitesburg limestone member. Athens shale, lower part. Not differentiated from Athens shale. Not differentiated from Chickamauga lime- stone. Athens shale.l Sandstone layers of Sand Mountain, near Etowah, Tenn. (p. 80). Whitesburg limestone. Lenoir limestone: Argillaceous limestone member. Mosheim member. Douglas Lake member. Chickamauga limestone. Lenoir limestone: Mosheim member. Basal layers with chert fragments and dolomite breccia (p. 78). 1 Units mapped by Rodgers. 346880—55————2 146 Each formation of this classification is mappable on scales of 1:62,500 or larger. The designation member is applied to two types of rock units: those so thin that. they cannot conveniently be shown on scales smaller than 124,000, and those that are lateral equivalents of part or all of a named formation. For the latter type formation rank is given to the units having the most common lithic features and member rank is applied to those having the less well known features. Older names have been retained where ambiguity seems unlikely. Reasons for departures from previous usages are given in discussions of the individual units below. New names are given to units that have not previously been recognized or named and to some units whose old names imply a lithic identity which in the writer’s view is not present. MIDDLE ORDOVICIAN SECTION The thickness of the Middle Ordovician section in the Tellico-Sevier belt averages 7,500 feet. All the rocks are calcareous—calcareous shale, calcareous siltstone, calcareous mudrock, calcareous sandstone, calcarenite, and limestone. (An exception is a thin quartzite at the top of the section.) The adjective “calcareous” will often be omitted hereafter to avoid unnecessary repetition. Limestone, 30 to 100 feet thick, forms the base of the section, overlying interbedded dolomite and limestone of the Knox group of Late Cambrian and Early Ordovi— cian age. The limestone is succeeded by dark—gray shale or gray sandstone. The rest of the sequence is a succession of interbedded shale and sandstone to the uppermost unit of maroon mudstone, siltstone, and sandstone. Black Chattanooga shale of Devonian and Carboniferous age overlies the rocks of Middle Ordovi— cian age. A stratigraphic diagram (pl. 28) is based on the writer’s mapping of rocks of Middle Ordovician age; it shows the relations of the rock units encountered. The diagram is an exaggerated downdip View of the outcrop belt. The vertical scale is twice the horizontal scale of the diagram. Churches and schools whose names appear on the topographic maps are plotted on the diagram and properly located with respect to the rock units on which their foundations lie. This diagram can be used, therefore, together with the appropriate topographic maps, to find localities in the area. Fossil localities and other noteworthy points mentioned in the text are indicated by appropriate symbols. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY STRUCTURE OF THE TELLICO-SEVIER BELT Through most of the area of this investigation rocks of Middle Ordovician age form a homocline in which the beds have an average strike of N. 45° E. and an average dip of 45° SE. In the southwestern part of the area (pl. 27), near the Little Tennessee River, two anticlines define a structural anomaly. The northernmost of these (north of Union Grove Church) brings to the sur- face rocks of Early Ordovician age in its core, and its axis plunges gently to the southwest, widening the out— crop belt of part of the section. To the southeast a gentle anticline lies athwart the general northeast- southwest structural grain of the area; the Little Tennessee River follows closely the crest of this struc— ture. These two anticlines are apparently not related, for beds may be traced between them without apparent deflection. In the northeast part of the area, the outcrop belt widens as the homocline passes into a synclinorium. This structure as defined by the limestone and lower shale units is little faulted, but in the higher sandstone and shale units many faults and much complex folding appear. Although it was not possible here to work out stratigraphic relations of the sort determined farther southwest, the complex structure aided stratigraphic work by bringing some fossiliferous beds to the surface at many places across the strike. ROCKS UNDERLYING MIDDLE ORDOVICIAN KNOX GROUP (LATE CAMBRIAN AND EARLY ORDOVICIAN)— RELATIONS WITH OVERLYING ROCKS Limestones and dolomites of the Knox group underlie rocks of Middle Ordovician age. The limestones are gray and blue gray, very fine grained, and most are marked by many thin irregular clay partings. Dolo- mite beds form less than half of the highest few hundred feet of Knox; these are usually light gray, finely crystal— line, and well laminated to platy. Fossils showing that these rocks are correlative with the Mascot dolo— mite have been found at several places. The contact of the" Lenoir limestone (the lowest formation of the Middle Ordovician sequence) with the Knox group is disconformable. Relief on the upper surface of the Knox is indicated by the lenticularity of the Douglas Lake member at the base of the Lenoir limestone. Fragmental material derived from rocks of the Knox group and incorporated in the Douglas Lake member is evidence that the upper surface of the Knox was littered with debris as a result of subaerial exposure. Outcrops are inadequate to make determinations of the MIDDLE ORDOVICIAN ROCKS OF EASTERN TENNESSEE relief of this surface within the area studied, but Bridge (1955) found relief of about 140 feet at this contact in the excellent exposures near Douglas Lake a short distance to the northeast. LENOIR LIMESTONE GENERAL FEATURES The term Lenoir limestone is here applied to lime- stones of several distinctive types that comprise the basal part of the Middle Ordovician section. The main part of the formation consists of gray cobbly argillaceous limestone with which the name Lenoir is associated by many geologists from Virginia to Ala— bama, regardless of its exact stratigraphic position or fossil content. Also included in the Lenoir of this report is dove-gray aphanitic limestone termed the Mosheim member, and a discontinuous basal unit characterized by several kinds of detrital limestone to which the term Douglas Lake member is applied. The name, Lenoir limestone, was proposed by Safford and Killebrew (1876, p. 130—131) to replace the term “Maclurea Limestone” of Safi'ord (1869). Lenoir limestone is used in preference to Chickamauga lime— stone (Hayes, 1891) because the former has priority. The type section of the Lenoir limestone near Lenoir City, Tenn, has been described by Cooper and Cooper (1946, p. 52), and their description is summarized as follows : Thickness Limestone, dark-gray, medium-grained, sparsely cherty; Maclurites “magnus” _______________________ feet__ 100—125 Limestone, impure; Mimella nucleus (Butts), Valcourea sp., Hesperorthis sp ________________________ feet__ 25—45 Mudrock, dolomitic ___________________________ do“ 7. 5 Limestone, shaly; crowded with Rostricellula pristine (Raymond) _____________________________ inches, A 2—18 Limestone, dove—gray, aphanitic _______________ feet-_ 4—9 Wherever there are exposures, the Lenoir, with a thickness ranging from 26 to 95 feet, intervenes be— tween the basal beds of the Blockhouse shale and the highest beds of the Knox group. This fact is empha- sized because Keith in his maps of the area (Keith, 1895, 1896a) showed the Athens shale resting directly on the Knox in most places. Measured sections of the Lenoir and its component members are given in table 1. The members are shown on plate 28 also, but the small scale of that diagram precludes accurate representation of thicknesses. DOUGLAS LAKE MEMBER The term Douglas Lake member of the Lenoir lime- stone was proposed by Bridge (1955) for unusual beds exposed at the base of the Lenoir on the north shore of Douglas Lake about 2 miles east of Douglas Dam. These exposures are in the Tellico—Sevier belt about 25 miles northeast of the area of the present study. on plate 28 (V0 4 and TA 5B). 147 The Douglas Lake member contains several kinds of elastic and impure limestone, the most common of which are yellow and salmon—pink silty limestone, pink and gray calcarenite, and medium- to coarse-grained limestone conglomerate that locally contains abundant fragments of chert. The fragments contained in the conglomerate are angular and many are lithologically similar to beds in the underlying Knox group. These detrital limestones and limestone conglom« erates are found in five small isolated bodies within the area studied; the locations of two of these are shown All are at the base of the Lenoir limestone but at considerable distances from one another. None is sufficiently well exposed to per- mit accurate tracing of its outlines, but the deposits are assumed to be lentieular and to lie in depressions on the upper surface of the Knox group, as they do at Douglas Lake according to Bridge. MOSHEIBI MEMBER The term Mosheim limestone was first used by Ulrich (1911). At its type section along the Southern Railroad 0.9 mile south-southwest of Mosheim, Tenn, about 60 feet of thick-bedded dove—gray aphanitic limestone is exposed, with .Macluriles magmas Lesueur in the upper 10 feet. Between the aphanitic beds and the dolomitic beds of the Knox group is a gray cobbly limestone, 2 feet thick, with large leperditiid ostracodes. Overlying the aphanitic limestone is “5—10 feet of impure, granular, crumbly-weathering limestone con— taining a few orthid brachiopods, Mimella and Val- courea, and trilobites, which correlate these beds with the middle beds of the type Lenoir” (Cooper and Cooper, 1946, p. 51). The Mosheim member of the Lenoir limestone in the Tellico—Sevier belt is identical lithologically with the aphanitic limestone in the Mosheim section. Some beds flecked with numerous calcite crystals are calcarenites (lime sandstones) in which the grains and most of the matrix are composed of the same aphanitic material; some of the filling between grains, however, is crystal- line calcite. Because of the purity and massiveness of the Mosheim limestone beds, their weathered surfaces are characteristically fluted. ARGILLACEOUS LIMESTONE MEMBER Gray to dark-gray fine—grained argillaceous limestone forms the main body of the Lenoir in the Tellico-Sevier belt. The argillaceous material concentrated betWeen nodules of limestone gives the rock its distinctive ap— pearance on weathered surfaces. Chert is sparingly present. Small crystals of pyrite are commonly dis— seminated through the rock, and freshly broken rock has a strong odor of sulfur dioxide. 148 Within the area of this study, most sections of the Lenoir limestone contain both the argillaceous lime- stone member and the more pure Mosheim member. In all these the Mosheim is overlain by the argillaceous limestone. In some sections, however, one or the other of these members occupies the whole interval between the Knox group and the overlying Blockhouse shale (see table 1). Cooper and Cooper have found sections in which rock types that resemble the Mosheim and argillaceous lime- stones are interbedded, and they conclude: “probably the type Mosheim is a calcilutite facies representing a substantial part of the true Lenoir” (1946, p. 52). It is in this sense that these terms are used here. The top of the Lenoir limestone appears as a sharp and planar contact. The overlying beds (Whitesburg limestone member of the Blockhouse shale) are similar lithologically to the argillaceous limestone member of the Lenoir, but the darker color of the Lenoir beds readily permits discrimination at most places, and there is no gradation between them. FOSSILS The Douglas Lake member of the Lenoir limestone has yielded many specimens of a small tumid rhyn- chonellid brachiopod, identical with or very similar to Rostricellula. pristine (Raymond) (pl. 25, figs. 38, 39). One specimen of Lingulafostermontensis Butts and a few specimens of leperditiid ostracodes were also collected. From the argillaceous limestone have come “Rafines- quina” champiainensis (Raymond) (pl. 25, fig. 37), Valcourea strophomenoides (Raymond), and a species each of Hesperorthis and Mimella. The Mosheim member contains only gastropods. Two forms, identified from calcite-filled cross sections, are Lophospim sp. and Madurites magnus? Lesueur. The faunas and stratigraphy of the Lenoir limestone of the Tellico—Sevier belt correspond well with those at SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Lenoir City and Mosheim, Tenn., and leave little doubt that all should be assigned to the Lenoir limestone of the type section. SOILS AND TOPOGRAPIIIC EXPRESSION The Lenoir limestone does not form a distinct soil in this area. Its outcrop belt is narrow and its content of insoluble residues is low compared to the thick forma- tions adjacent to it, so that in most places its outcrop is concealed by colluvial deposits from the neighboring formations. Nevertheless, the Lenoir has a definite, although subtle, topographic expression. Many small streams follow it closely, and elsewhere a gentle depres- sion marks its trace. BLOCKHOUSE SHALE GENERAL FEATURES Dark—gray calcareous shale with thin beds and lenses of dark-gray dense limestone forms the main body of a unit of formational rank, 150 to 950 feet thick, here given the name Blockhouse shale. In the southwestern part. of the area studied these fine—grained rocks are partly replaced by fine- to coarse-grained sandstone, named Toqua sandstone member in this report. Thin argillaceous limestone forms a basal member of the Blockhouse shale, and the term Whitesburg limestone member is applied to it. NAME The Blockhouse shale as defined in this report was included by Keith (1895) and Rodgers (1953) in the lower part of the Athens shale. The writer departs from this usage for two reasons: the rocks of this area do not have many significant characters in common with the rocks at the type section of the Athens shale, and the dark~gray shale and associated rocks, here called the Blockhouse, form a distinct mappable unit that warrants recognition as a formation. TABLE 1,—Thicknesses, in feet, of constituent units at measured sections of the Lenoir limestone [Locality numbers refer to points indicated on plate 28] Locality no ___________________________________ WD 41 WD 2 BL 9 BL 5 BL 4 BN 3 EN 5 TA 5 V0 8 . V0 22 Distance between sections, in miles ________________________ 6. 6 2. 2 3. 2 0. 9 6. 0 1. 9 2. 7 2. 6 4. 5 Argillaceous limestone member--- _ 14 15 3 40 10 45 40 45 10 Light-gray pure limestone (Mos- heim member) _________________ 12 55 50 45 60 45 30 Basal elastic limestone (Douglas Lake member) ________________ 3 55 20 MIDDLE ORDOVICIAN ROCKS OF EASTERN TENNESSEE Typical Athens shale at the town of Athens, Tenn, was described by Rodgers (1952b) as “blue, nodular, calcareous and argillaceous rock that is more nearly shaly limestone than true shale. * * * Black shale, which is supposedly typical of the Athens, does not occur in this area.” The term Athens shale has been widely extended to include black calcareous shale (Keith, 1895; Ulrich, 1911; Butts, 1940; Decker, 1952 and others); but, in the author’s opinion, refined stratigraphic nomenclature requires that this and other terms be confined to one type of rock, contiguous or demonstrably contemporaneous with the unit at its type section. Local names have been given to equivalent rocks of different facies in other parts of the stratigraphic column. The terms Copper Ridge dolomite and Conococheague limestone, for example, are applied to different lithofacies of the same Upper Cambrian interval (Howell, chm., and others, 1944), and this practice contributes to clear stratigraphic nomenclature. Thus the term Athens should be applied Only to rock comparable to that of the type section. Geologic section 1. Type section of the Blockhouse shale, Block- house quadrangle, Blount County, Tenn. [The base of this section is 800“, southwest of Bench Mark F 132Y (elevation 972 ft) extending southeastward up a guliied hillside. Attitude of bedding somewhat variable, strike averaging N. 40° E., dip 50° SE.] Tellico formation, lower shale division: Gray, brown and buff- weathering silty (shale, sandy shale, 2 ft thick, about 50 ft above base. Blockhouse shale: Dark shale member: 4. Shale, fissile, chocolate-brown weathering, without silt, interbedded with buff-weather- ing silty shale __________________________ 20 3. Shale, fissile, chocolate-brown weathering, without silt ____________________________ 30 2. Shale, dark-gray; v brown-weathering, with intercalated cobbles and beds, 2 to 6 in. thick, of dense, dark—gray limestone; no fossils seen ____________________________ 1. Shale, calcareous, fissile, dark-gray, gray- brown weathering, weathered chips paper- thin, crunchy underfoot; fragments of graptolites in all but basal 25 ft __________ 'Whitesburg limestone member: Limestone, light-gray, cobbly, upper 2 to 5 ft interbedded with dark—gray shale _________ Lenoir limestone at base of section. Feet 150 200 5-20 WIHTESBU'RG LIMESTONE MEMBER NAME The Whitesburg limestone was named by Ulrich (1929, p. 2, footnote) for dark crystalline limestone between the dark calcareous Athens shale and the Lenoir limestone. The type locality was designated as 2 miles southeast of Whitesburg, Hamblen County, 149 Tenn. (fig. 22), where the thickness was stated to be 500 feet. Cooper and Cooper (1946, p. 54) say “the type Whitesburg is composed of black limestone and inter- calated graptoliferous shales with an aggregate thick- ness of 500 feet * * * ” The writer found few exposures at this type section. Above the dolomites of the Knox group are scattered exposures of cobbly limestone that probably belongs to the Lenoir limestone. These are overlain by about 5 feet of granular limestone that contains brachiopods and abundant fragmental trilobite remains. Overlying these beds is dark-gray thin-bedded to slabby very fine grained limestone with interbedded dark-gray shale that contains graptolites. G. A. Cooper (oral communication, 1949) pointed out a locality about 6 miles north-northeast of the Whites- burg section where similar granular limestone about 400 feet thick contains the same fossils as the 5-foot unit of the type section. This thick unit of granular limestone is also overlain by dark—gray graptolite shale, with intercalated light-gray calcarenite. The variability of thickness of the granular limestone, therefore, appears to be very great here, from 5 feet to 400 feet in 6 miles. Separation of the graptolite-bearing shale and lime- stone from the granular limestone with trilobites and brachiopods seems warranted. The writer has there— fore applied the term Whitesburg limestone member of the Blockhouse shale to the granular beds. The lime- stone is considered a basal member of the graptolite- bearing beds because of the gradational contact between them. Keith (1895, 1896a) undoubtedly included the beds here classed as the Whitesburg in his Chickamauga limestone, as he did in the vicinity of Whitesburg (Keith, 1896b). LITHIC FEATURES The Whitesburg limestone member of the Block- house shale contains two contrasting phases: light-gray fine-grained argillaceous cobbly limestone and dark- gray granular ferruginous siliceous argillaceous, and commonly oolitic, limestone that occurs in even beds averaging about 2 inches in thickness. These two phases have been found in the same exposure, but in most places only one is present. The cobbly bedded rock is exposed in fresh outcrops at only a few places; where fresh it is not easily dis- tinguished from the argillaceous limestone member of the underlying Lenoir limestone. The Whitesburg is, however, lighter colored than the Lenoir, slightly more argillaceous, and contains much more fragmental organic debris. Weathering of this phase of the Whites- burg is most efiective on the shaly matrix that encloses the cobbles, commonly freeing them to litter the surface of the ground. 150 Fresh rock of the even—bedded granular phase is very hard and tough, difficult to break with a hammer. It weathers to a reddish-yellow compact saprolite in which many fossils are well preserved as molds. At one out- crop in the Vonore quadrangle (VO 4, pl. 28) the rock contains sufficient iron to weather a deep hematitic red. Much of this rock in the southwestern part of the area studied contains scattered small well-rounded quartz grains. The cobbly bedded fine-grained rock occurs in the central part of the area studied, from about the Sevier- Blount County line southwestward to the area between localities BL 5 and BN 4 of plate 28. In this area the member is from 3.5 to 20 feet thick (table 2). The even- bedded granular limestone is from 10 to 21 feet thick; it occurs in both the northeastern and southwestern parts of the area and along the limbs of the narrow syncline that parallels the main belt in the eastern part of Blount County. DARK SHALE MEMBER LITHIC FEATURES The dominant rock of the Blockhouse shale is dark- gray finely laminated calcareous shale. Parallel lam- inae spaced at intervals of from 1 to 4 millimeters set apart somewhat differently colored rock. Where slightly weathered, the laminae form closely space planes of fissility. In the upper half of the Blockhouse, gray dense fine- grained limestone forms beds and lenses Within the shale. Many are plainly marked by shrinkage cracks. The thicker limestone beds are from 6 to 8 inches thick and may be traced along outcrops for considerable distances; most, however, are only 2 or 3 inches thick and are not persistent. The limestone beds do not have the laminations of the enclosing shale. Although the shales that characterize the Blockhouse have often been referred to as black, they are actually dark gray and distinct from such black noncalcareous shales as form the Deepkill shale of New York or the Chattanooga shale of Tennessee. Weathered Blockhouse shale is gray brown or SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY chocolate brown, in contrast to the buff, yellow, and ochrous shades of higher shales of this Middle Ordo- vician section. Weathering reduces the rock to brittle thin leaves that produce a characteristic crunchy noise when walked upon. TOQUA SANDSTONE MEMBER NAME The term Toqua sandstone member of the Blockhouse shale is here given to fine- to coarse-grained gray cal- careous sandstone that occurs in the lower part of the formation in the southwestern part of the area of this study. The name is taken from Toqua Church, Vonore quadrangle, Monroe County, Tenn. (see type section, Geologic section 2). The presence of a sandstone at this horizon is not indicated in the London folio (Keith, 1896a), and the area encompassing the outcrop of this rock was mapped as the Athens shale in that folio and by Rodgers (1953, pl. 8). LITHIC FEATURES The Toqua sandstone member of the Blockhouse shale is formed of light-gray fine- to coarse—grained calcareous sandstone. The finer grained sandstone is well lam- inated, crossbedded, and occurs in beds 4 to 12 inches thick that are separated by thinner beds of dark-gray graptoliferous shale. The coarser grained rock is poorly laminated and forms beds 10 to 20 inches thick which are set apart by poorly defined bedding plane partings that do not contain shale. Poor sorting characterizes the coarse—grained sandstone: particle size ranges from clay size to rock fragments as large, as 30 millimeters in diameter. The average large size of quartz grains is from 1 to 1.5 millimeters, and the largest fragments are rounded pebbles of dense gray limestone. An unusual but rare component of the rock through- out the Toqua are fragmental graptolites that remain uncrushed. Weathered rock of the Toqua is greenish brown or olive; its saprolite is yellow brown to ochrous. These colors contrast with the dark brown and red colors of weathered sandstone units higher in this section. TABLE 2.— Thickness and type of bedding at measured sections of the Whitesburg member of the Blockhouse shale Locality no .................................. WA 2 ' WD 41 l WD 2 l BL 7 EL 5 EN 3 TA 5 V0 4 V0 22 Distance between sections, in miles ________________________ 3. 0 6. 6 2. 2 3. 2 6. 9 3. 6 1. 9 4. 9 Type bedding __________________ Even Cobbly Cobbly Cobbly Cobbly Even Even Even Even Thickness, in feet _______________ 21 3. 5 5 6 5—20 14 10 10 10 MIDDLE ORDOVICIAN BOOKS OF EASTERN TENNESSEE Geologic section 2.—Type section of the Toqua sandstone member of the Blockhouse shale (Section measured 1.15 miles southeast of Toqua Church, Vonore quadrangle, Monroe County, Tenn., near the southeast bank of the Tellico River, along and near a wagon road. Strike averages N. 65° E., dip 25° SE.] Porsion of section exposed near wagon road Blockhouse shale: Dark shale member: Feet 20. Shale, dark-gray, finely laminated, calcar- eous, silt-free; seen only in abundant float and in a few small outcrops about 500 ft northeast of wagon road; about _________ 200 Toqua sandstone member, about 400 ft thick: 19. Sandstone, fine-grained, and dark-gray shale, interbedded; poorly exposed in cultivated fields about 500 ft northeast of wagon road; about ___________________________ 18. Sandstone, fine-grained, and silty shale, interbedded; here deeply weathered to saprolite; sandstone is thin bedded in units from 6 in. to 2 ft thick, forming about one—third of the total thickness of this part of the section; exposed in gullies about 200 ft northeast of the wagon road; about____ Portion of section exposed «long wagon road 150 100 17. Sandstone calcareous, medium— to coarse- grained, with small rounded fragments of fine-grained limestone; beds from 6 in. to 2 ft thick _____________________________ 20 16. Covered in gully ________________________ 10 15. Sandstone calcareous, light-gray, weathers to greenish-brown; fine- to coarse-grained, poorly sorted; beds about 1 ft thick, with laminations about 1 in. apart; uncrushed graptolites: Climacograptus sp., Diplo- graptus sp., Glossograptus sp ____________ 20 14. Sandstone, fine- to medium-grained; weath- ered and poorly exposed ________________ 15 13. Claystone, fissile, ochrous, punky; saprolite of shale ______________________________ 1 l2. Sandstone, weathered, fine— to medium- grained; weathers to yellow-brown _______ 2 11. Shale, weathered, chocolate-brown; lacks silt __________________________________ 10. Sandstone calcareous, light-gray, weathers to greenish—brown; mostly fine grained and platy; fragmental uncrushed grapto- lites _________________________________ 6 9. Shale, weathered, chocolate-brown, fissile, silt—free; abundant graptolites: Nema— graptus gracilis (Hall), Dicellograptus maf- fatensis var. alabamensis Ruedemann, Di- dymograptus sagitticaulns Gurley, Clinto- cograptus sp., Diplograptus sp ___________ 8. Sandstone calcareous, light-gray, fine- to medium—grained; most of the unit is fine grained and platy, with a few coarser grained beds as much as 1.5 ft thick With- out laminae __________________________ 14 7. Sandstone calcareous, light-gray, fine— grained, platy, crossbedded, with a few medium-grained nonlaminated beds ______ 28 0. 5 1.5 151 Portion of section exposed on hillside to north of wagon road 6. Sandstone calcareous, light-gray, weathers Feet to greenish-brown, with gray surfaces; beds about 1 ft thick with faint parallel laminae from V2 to 1 in. apart ____________ 10 5. Siltstone, light-gray, platy; small detrital mica flakes in some bedding planes _______ 20 Whitesburg limestone member, 15 ft thick: 4. Limestone, dark-gray, granular, argillaceous; weathers to dark-brown; Christiania sub- quadrata Hall and Clarke, and other fossils ________________________________ 10 3. Limestone, gray, granular, with irregular clay partings; much fragmental fossil re- mains ________________________________ 5 Lenoir limestone, 40 ft thick: 2. Limestone, fine-grained, ‘argillaceous, nodu- lar __________________________________ 10 1. Limestone, aphanitic, dove-gray, with flecks of crystalline calcite (Mosheim member)- , 30 Limestone of Knox group at base. STRATIGRAPHIC RELATIONS INTERNAL STRATIGRAPHY The Blockhouse shale as a whole ranges in thickness from 150 feet (BN 2) to about 950 feet (TA 5A); the average for the formation is about 400 feet, the thick- ness of the type section. The contact of the Whitesburg limestone member with the dark shale member is gradational. Where these relations are best seen (100. BL 5 at Blockhouse, pl. 28) the cobbly beds of the Whitesburg thicken from 5 to 20 feet along 750 feet of strike distance, and in the thickened portion includes tongues of dark-gray shale 6 inches to 2 feet thick. ‘ The contact of the Whitesburg with the Toqua sandstone member, however, is sharp and without inter- bedding. Where the Toqua overlies the Whitesburg, the Whitesburg commonly contains scattered grains of quartz in shaly partings between limestone strata. Dark-gray shale forms the full thickness of the forma- tion above the Whitesburg in the northeastern segment of the belt. The Toqua sandstone member forms the lower part of the formation toward the southwest. The section near Mint (BN 2, same as Decker, 1952, Geo- logic section 7, p. 34) displays the interrelations of the shale and sandstone facies and is the northeasternmost exposure of the sandstone facies. A lower shale unit, here 55 feet thick, contains a few sandy beds each about 2 inches thick. This is overlain by beds of coarse— and fine-grained sandstone, some as much as a foot thick without laminae, separated by shaly partings (Toqua sandstone member), forming a unit about 20 feet thick. The overlying unit, about 85 feet thick, is composed of dark-gray shale with thin beds of fine-grained dark-gray limestone near the top. The dark-gray shale is over- lain by medium-gray buff-weathering silty shale of the Tellico formation. 152 FIGURES 1—3. 4, 5. 6—8. lO——13. 14-16. 17—19. 20, 21. 22, 23. 24—27. 28, 29. 30-33. 34—36. 37. 38, 39. PLATE 25 [Photographs by G. A. Cooper. All figures natural size except where otherwise indicated] Pionodema sp. Bacon Bend member of Sevier formation, locality TA 29A, 0.14 mile northeast of Fourmile Church, Tallassee quadrangle. 1. Impression of part of pedicle exterior from mold, X 2, USNM 117343b. 2. Mold of brachial interior, X 2, USN M 117343m. 3. Mold of pedicle interior, X 2. Counterpart of fig. 1. Sowerbyella sp. Sevier formation, upper shale division, locality EN 11, 0.53 mile east-southeast of Old Kagley Church, Binfleld quadrangle. ' 4. Mold of brachial interior, 2 specimens, X 2, USNM 123579b. 5. Mold of pedicle interior (lower specimen) and brachial exterior (upper specimen); mold of pedicle interior of Glyptorthis sp. at left center, X 2, USNM 123579a. _ Dinorthis transverse Willard. Sevier formation, middle sandstone division, locality KZ 11, 1.57 miles southwest of Rocky Branch, Kinzel Springs quadrangle. 6. Impression from mold of brachial exterior, USNM 118024b. Note branching costae.’ 7. Mold of brachial interior, USN M 118024f. 8. Mold of pedicle interior, USNM 118024a. . “Camerella” longirosm's Billings. Sevier formation, middle sandstone division, locality TA 25, 0.28 mile northwest of Fourmile Church, Tallassee quadrangle. Pedicle exterior, X 2, USNM 1170963.. Zygospira sp. 10. Several specimens partly buried in matrix, X 2, USNM 123577b. 11, 12, 13. Pedicle, brachial, and anterior views, X 3, USNM 123577a. Bacon Bend member of Sevier formation, locality B 35, 0.27 mile southeast of Christie Hill School, Blockhouse quadrangle. Gen. and sp. aff. Zygospira acutirostris (Hall). Sevier formation, 8 miles south of Cleveland, Tenn., 0.5 mile southeast of Hambright mine. This fossil is common in the Chota formation. Pedicle, brachial, and anterior views, X 3, USNM 117189a. Oligorhynchia sp. Sevier formation, west side of Guthrie Gap, 2 miles south-southeast of Whitehorn, Bulls Gap quadrangle. Pedicle, brachial, and anterior views, X 3, USNM 118017. Sowerbyites sp. Tellico formation, upper shale division, locality WA 45, Chapman Highway, 1.58 miles east-northeast of Cusick, Walden Creek quadrangle. 20. Pedicle exterior, partly exfoliated, USNM 123578a. 21. Brachial exterior, partly exfoliated, USN M 123578b. Cyrtonotella sp. Tellico formation, upper shale division, locality B 136, at bench mark LHT 1366, 1 mile southeast of Chilhowee View School, Blockhouse quadrangle. 22. Mold of pedicle interior, USNM 1235743.. 23. Mold of brachial interior, USNM 123574b. , Paurorthis catawbensis Butts. Tellico formation, upper shale division, locality V0 21, 1.6 miles south—southeast of Toqua School. 24, 25. Brachial View, X 1 and X 2, USNM 11727821. 26. Brachial interior of silicified specimen, X 2, USNM 117278b. 27. Two molds of pedicle interior and fragment of external mold, X 2, USN M 117275. “Strophomena” tennesseensis Willard. Tellico formation, middle sandstone division, locality WD 6, 0.3 mile north- west of Cold Spring Church. ‘ 28. Mold of pedicle interior, USNM 123580a. 29. Mold of brachial interior, USNM 123580b. Christiania subquadrata Hall and Clarke. Figs. 30 and 31 from Whitesburg limestone member of Blockhouse shale; figs. 32 and 33 from “Upper” Lenoir limestone, a quarter of a mile southeast of Friendsville, Concord quadrangle. 30. Mold of brachial interior, X 2, USN M 123575a. Locality BN 4, 0.8 mile southeast of Centenary Church, Binfield quadrangle. 31. Mold of pedicle interior, immature specimen, X 2, USNM 123576a. Locality TA 3, U. S. Highway 129, 1 mile north of Wellsville, Tallassee quadrangle. 32. Brachial interior of silicified specimen, X 2, USNM 117580j. 33. Brachial View of silicified specimen, X 2, USNM 110168.. Bimum'a superba Ulrich and Cooper. “Upper” Lenoir limestone. 34. Pedicle View of silicified specimen, USNM 108201. 0 Between Friendsville and Christiansburg, Tenn. 35. Brachial view of silicified specimen, USNM 108200a. 36. Brachial interior of silicified specimen, USN M 108200h. A quarter of a mile southeast of Friendsville, Concord quadrangle, Tennessee. “Rafinesquina” champlainensis (Raymond). Lenoir limestone, locality WD 45, 0.1 mile southwest of triangulation station 37 SH, Wildwood quadrangle. Brachial view. Rosm‘cellula cf. R. pristina (Raymond). Douglas Lake member of Lenoir limestone, locality TA 5, 0.65 mile south- west of Williamson Chapel, Tallassee quadrangle. Brachial and lateral views of a specimen, X 2, USNM 117238b. GEOLOGICAL SI’RYEY ' PROFESSIONAL PAPER 27-1 PLATE '25 THE TELL] CO-S EV I ER B Ii LT REPRESEN'I‘A'I‘IVE BRACIII()POI)S FROM ROCKS ()l" MIDDLE OBDOVICIAN AGE IL 1‘ \‘ “ ..= C t: tic—1; x159: 252.2:53 £05.: :51 = .1. :53. .4535? H.» u: a: 3.5,» .— . .V. :.x_ 0mm .7. in... it u «a: 25...: 1.13.2.3. nun—:55: 9—. 1,53.» == :— ZO—E42fl9n— Ivy—fizzm 3:9. EC yum—22:2 2.4m:— ZOU<2 NEH. 7; 2m: CHEMOBLOU kmkflbm A\\ Geology by R. B. Neuman, 194962. except upper boundary of Bays fonatIon in Vonore quadrangle, after Rodgers, 1952 SEVIERVI E I" a 0 346880 0—55 (In pocket). I // PROFESSIONAL PAPER 274 PLATE 27 EIXPLAN ATION DEVONIANU) AND MISSISSIPPIAN ORDOVICIAN 3 5 " 52’ 30” oszs " n4“ W‘174—t‘, Ecology of F oraminifera in North eaStorh Gulf of Mexico All: ' GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-G VUJ LLVAVUULVM‘.L Lulu.“ - l L'u Tnis report concerns woré a’one ' partiy on oe/zalf of Me U. S. Atomic Energy Commission and is pnolis/zea’ ur Ur uxunxvv uuvnvalmx tau: wit/2 Me permission of Me Commission nu LL uuu ‘ LIV“ .u vansz _. V—AWWWIWVWV" w! :Iwum Ecology of F oraminifera in Northeastern Gulf of Maxim By ORVILLE L. BANDY A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—G Frequency dz'n‘rz'énz‘z'on of Recent Foranzz'nz'fera in Me coastal waters of wen‘ern Florida. Tnz's report cencerns rworé done part/y 0n ée/m/foftne U. S. fltonzz'c Energy Caninez'yyz'on anezI 2': pnfi/z'y/zea' wz'z‘n t/ze perinz'mz'an of Me C onnn z'syz'on UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office ' Washington 25, D. C. CONTENTS Page Abstract ___________________________________________ 179 Faunal zonation—Continued Introduction ________________________________________ 179 Offshore faunal zones—Continued Previous work ______________________________________ 180 Fauna 5 (251—600 feet) ______ ' ________________ Method of study ____________________________________ 181 Planktonic species ___________________________ Faunal zonation _____________________________________ 181 Environmental analyses _______________________________ General features ________________________________ 181 General ________________________________________ Brackish habitat ________________________________ 182 Brackish habitat ________________________________ Tampa Bay ________________________________ 182 Ofl'shore area ____________________________________ Charlotte Harbor, Pine Island Sound, and Paleoecological implications __________________________ San Carlos Bay ___________________________ 183 Conclusions ________________________________________ Offshore faunal zones ____________________________ 184 Faunal reference list _________________________________ Fauna 1 (8—40 feet) __________________________ 185 Systematic paleontology ______________________________ Fauna 2 (41-105 feet) _______________________ 185 Literature cited _____________________________________ Fauna 3 (106—180 feet) _______________________ 185 Index ______________________________________________ Fauna 4 (181—250 feet) _______________________ 186 Nmmflkww PLATES 29—31. FIGURE 25. 26. 27. 28. CHART 1. . Foraminiferal distribution in Charlotte Harbor, Pine Island Sound, and San Carlos Bay, Fla. . Foraminiferal distribution off Mobile, Ala. . Foraminiferal distribution ofl" Panama City, Fla. . Foraminiferal distribution off Tarpon Springs, Fla. . Foraminiferal distribution off St. Petersburg, Fla. . Foraminiferal distribution off the Cocohatchee River, Fla. ILLUSTRATIONS [Plates follow index; charts in pocket] Foraminifera of northeastern Gulf of Mexico. Northeastern Gulf of Mexico, showing areas of sampling and biofacies __________________________________ Assemblages and ecologic factors in the river, bay, and shallow-marine habitats __________________________ Assemblages and ecologic factors in the offshore area _________________________________________________ Depth and temperature variations during Miocene to Pleistocene time in northern Florida ___________________ Foraminiferal distribution in Tampa Bay, Fla. TABLES TABLE 1. Median percentages of Foraminifera in Tampa Bay, Charlotte Harbor, Pine Island Sound, and San Carlos Bay--- FEW“ . Median percentages of significant Foraminifera in the offshore depth zones, based upon concentrate samples _________ Foraminifera in selected formations of the Miocene, Pliocene, and Pleistocene of Florida ________________ , _________ Locations and depths of samples_ _ _ _ , ,-_ _ _ _ _ _, , , ,4 A _ ___ -1 _______________________________________________ III Page 186 186 187 187 187 188 189 191 192 198 201 203 Page 180 187 188 190 Pure 183 184 190 199 A Shorter Contribution to General Geology ECOLOGY OF FORAMINIFERA IN NORTHEASTERN GULF OF MEXICO By ORVILLE L. BANDY* ABSTRACT Frequency studies of Foraminifera in the northeastern part of the Gulf of Mexico reveal basic uniform patterns of distribution. Samples for the investigation represent the area inshore from the IOU-fathom line between Mobile, Ala., and Fort Myers, Fla. Included, also, are Tampa. Bay, Charlotte Harbor, Pine Island Sound, San Carlos Bay, and the lower reaches of some rivers. Brackish waters of bays and harbors are subdivided into shoals and channels, and these in turn are separated into inner, intermediate, and outer bay areas. Faunal assemblages are as follows: river habitat and inner shoals, Ammobaculites and Streblus; inner bays and channels, Elphidium and Streblus; intermediate and outer parts of harbors and bays, Elphidium, Streblus, miliolids, and rare offshore species; and intermediate and outer shoals, abundant Streblus, with few arenaceous species. Salinity variation is the major factor controlling distribution of Foraminifera in the brackish habitat. The greatest weight percentage of Foraminifera and the greatest number of species in the sediment are in the channels and open bay areas. . Data from this study together with those from prior workers are used in presenting a classification chart of faunal assemblages for brackish-water habitats. Samples of the offshore area present the following fauna] gradation: ?feptt)h Pmckieh areas Normal-salinity environment 66 0—40 Streblus assemblage _____ Archaias angulatus 41—105 Hanzawaz‘a strattoni _____ angulatus Asterigerina carinata- _ - _ Asterigerina carinata Hanzawaia strattom' 106—180 _______________________ Planulz'na ornata Hanzawaia strattom' concentrica 181—250 ______________________ Cibicides pseudoungerianus Hanzawaia concentrica Amphistegina lessom‘i 251-400 ______________________ U vigem’na assemblage Amphistegina lesson/ii 401—600 ______________________ Uv'igerina assemblage Bolivina goésiz’ A composite analysis of the offshore assemblages resulted in the tabulation of median values for the percentages of significant species in each of the faunal zones“, The factors limiting the distribution of species in the marine environment are manifold and include temperature, food, nutrients, and other factors. Reduced salinity plays a major role in inhibiting certain species in some nearshore areas; however, turbulence and turbidity are also important. The Weight percentage of the Foraminifera in the sediment increases very gradually offshore to the edge of the continental shelf, and then it increases very rapidly beyond this “ Department of Geology, University of Southern California. point. The number of benthonic species increases from less than 20 near the shore to more than 50 on the upper part of the continental slope. Upwelling of colder waters is indicated on the outer part of the continental shelf and may be significant in restricting the distribution patterns of many species. Different upper limits of the depth ranges of planktonic species demonstrate another method of depth correlation. Globigeri- noides rubra (D’Orbigny) appeared in less than 100 feet of water, most of the other species appeared between depths of 100 and 200 feet, and Globorotalia tumida (Brady) appeared at about 400 feet. These data suggest that these species, when alive, float no higher than the minimum depths indicated. Paleoecological implications are discussed briefly, and an example is given in which the depth-to-temperature relationships are demonstrated for selected formations from the Miocene, Pliocene, and Pleistocene of Florida. INTRODUCTION An investigation was made of the distribution of Foraminifera on the continental shelf and the upper part of the continental slope between Mobile, Ala., and Fort Myers, Fla. (fig. 25). West of central Florida, the outer edge of the continental shelf averages about 210 feet below sea level, and west of northern Florida it averages about 180 feet. The lower part of fauna 4 corresponds approximately with the edge of the shelf ofi' central Florida, and the upper limit of this fauna corresponds roughly with the edge of the shelf ofl’ northern Florida. Included in the investigation were Tampa Bay, Charlotte Harbor, Pine Island Sound, San Carlos Bay, and the lower reaches of some of the rivers emptying into these areas. The primary purpose of this study was to discover significant faunal trends and to analyze these in terms of ecologic factors. In this way a better understanding of existing facies may be developed, possibly to serve as a more reliable basis for the interpretation of fossil facies. The samples were collected from the research vessels MV Pompino and MV Alaska, made available to the U. S. Geological Survey by the U. S. Fish and Wildlife Service. Inshore samples in water shallower than 30 feet were obtained with an underway sampler, Whereas those in deeper water were obtained with Pettersson and orangepeel samplers. Positions in inshore areas were obtained by sextant and dead reckoning, and positions in deeper water were obtained by loran (long- 179 180 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY W 84° 83" TEA VERSE L M’E See chart 2 0k 8210’ 92°00 si 50' DETAIL MAP OF CHARLOTTE HARBOR, ' ' 50 Nauchl mlles 50 Statute miles 1 I l _GEORGIA —-‘__.__ —_~__ a as???” "f? ETERSBURG YE 27‘ ~l| 40' ".2 ,‘ See chanl 30' “ : ”nor: ,7 ' ’TARPON SPRINGS ‘1 1AMPA O “555 a: TAIL map if, ST PETERSBURG \ 1 VENICE ‘\ ENGLEWOOD \| ‘ \\ ‘1 \ \ l I pron‘r MYERS \555 DETAIL mp COCOHATCI'IEE I? 26° PINE ISLAND SOUND AND SAN CARLOS BAY FIGURE 25.—-Northeastern part of the Gulf of Mexico, showing areas of sampling and biotacies. range navigation). The samples were taken on behalf of the Division of Raw Materials of the U. S. Atomic Energy Commission chiefly to provide data on the occurrence and distribution of phosphate in bottom sediments of the eastern Gulf of Mexico. This study was directed by H. R. Gould of the U. S. Geological Survey and was financed in part by funds made avail- able by the Atomic Energy Commission. The work on Foraminifera was undertaken by the writer as a part of the study. Mr. Gould provided much of the data on temperature, salinity, and all of the data on pH and depth. Addi— tional information on salinity and temperature was obtained from George B. Austin, Department of Oceanography, Agricultural and Mechanical College of Texas, and from J. 0. Bell, Acting Chief, Gulf Fishery Investigations, U. S. Fish and Wildlife Service. K. O. Emery, Geology Department, University of Southern California, offered many helpful suggestions in the course of the study. The foraminiferal collections at the U. S. National Museum were consulted in the taxonomic phases of the present investigation, and many courtesies were extended the writer by A. R. Loeblich of the Museum and Ruth Todd of the U. S. Geological Survey. The figures of Foraminifera were drawn by Mary E. Taylor. The research for this project was conducted in the micropaleontological laboratory, Allan Hancock Foundation, University of Southern California. PREVIOUS WORK Included in the bibliography are publications of a taxonomic nature on the Foraminifera of the Gulf of Mexico and related areas. The more important pub- lications emphasizing ecology of Foraminifera in the Gulf of Mexico commence with Norton’s study of the general trends in Florida and the West Indies regions (1930). He grouped his stations into four bathymetric zones and indicated the types of families common in these. Kornfeld (1931) reported on the Foraminifera in beach samples from 80 stations along the coast of the Gulf of Mexico between the Rio Grande and the Mis- sissippi River delta, and he indicates a prevalence of arenaceous species in embayments. Hedberg (1934) studied the distribution of Foraminifera in Lake Mara— caibo and vicinity in Venezuela and gives a considerable \ / ECOLOGY UF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO amount of salinity data in association with the trends there. Parker (1948) has published a significant analy- sis of the Foraminifera of the continental shelf along the Atlantic coast from Maine to Maryland; however, there are very few abundant species common to both the Atlantic and the coastal waters of western Florida. Lowman (1949) studied the relative frequency dis- tribution of Foraminifera in the Gulf of Mexico, pre- senting his results by graphic means and using cate- gories at the generic level for the most part. Israelsky (1949) has demonstrated a significant application of ecology to petroleum geology in his oscillation paper. Phleger and Parker (1951) have presented a wealth of data on the depth ranges of species in the northwestern part of the Gulf of Mexico. Post (1951) has analyzed the shallow-water species of Foraminifera of the south Texas coast. She distinguishes between the assem- blages of the closed bays, polyhaline bays, passes, and open gulf, and reports very few arenaceous species in these areas. Parker, Phleger, and Peirson (1953) re- port four biofacies in San Antonio Bay as follows: open- gulf, bay, marsh, and river biofacies. They conclude that the distribution patterns are the result of the re- lationships between barrier islands, passes, and runoff into the bays. The author (Bandy, 1951, 1954) has completed a study of some shallow-water Foraminifera in a limited area ofi the Louisiana coast which demon— strates interesting trends among shallow-water species, especially with respect to irregularities on the sea bot- tom. At the present time, Miss Frances Parker of the Scripps Institution of Oceanography is studying the deeper water environments in the northeastern part of the Gulf of Mexico. The area involved is essentially contiguous with that of this study. With respect to general interest, a most useful and comprehensive bib— liography of publications on the Gulf of Mexico was published recently by Geyer (1950). METHOD OF STUDY Analyses of 344 samples were used as a basis for this study. Several additional samples were analyzed but were not used because of their small size and lack of representative faunas. The samples of the two north- ern profiles were very small and are probably not as representative as those of other profiles. All of the samples were weighed dry, and those which required washing were processed on a 240-mesh screen (0.064 mm openings). Next the Foraminifera were concentrated directly from the sediments by the carbon tetrachloride method of separation, and the concentrate was weighed. Considerable error can be introduced into such a weight analysis by the large quantities of small shells and ex- traneous matter which floats with the formaminiferal concentrates. This error was eliminated or vastly re- 181 duced by estimating the percentage of Foraminifera in the concentrate and then incorporating this factor into the final weight analyses. Examination of residues following the separations showed fairly clean separa- tions in most cases. The major exception to the ade- quacy of the separation technique occurred with the Amphistegina lessonii faunas. In some samples many specimens of this species remained with the residues rather than the float; in these an estimate was made of the percentage of Amphistegimz in the residues. These values are given separately for the appropriate stations. Relative frequencies of the foraminiferal species were determined by counting representative fractions of each sample. Counts of from 200 to 500 specimens were usual; however, as many as. 1,000 specimens were counted in a few samples and as few as 100 specimens were counted for several samples. FAUNAL ZONATION GENERAL FEATURES As shown in figure 25, there are seven subdivisions of the general area. The first of these is Tampa Bay and the second is Charlotte Harbor together with Pine Island Sound and San Carlos Bay; these consist of brackish shallow-water areas (charts 1, 2) which include the associated lower reaches of several streams. Five of the subdivisions are in the offshore area and consist of 5 biofacies paralleling the shore which are based upon 5 lines of samples extending across the continental shelf and down to a depth of about 600 feet (charts 3—7). One of the 5 lines of samples is off Mobile, Ala., and is approximately 50 miles long; the remainder are off Florida, and their locations and lengths are Panama City, 65 miles; Tarpon Springs, 140 miles; St. Peters- burg, 130 miles; and the Cocohatchee River, 150 miles. The sampled depths off Mobile and Panama City are much more restricted than the others. All of the data from this analysis are incorporated in the figures of the frequency distribution of Foraminifera (charts 1—7). The first subdivision at the top of each figure, ecologic factors, is designed to show all of the available ecologic data including depth of water, tem—‘ perature range, salinity range, and the percentage by weight of Foraminifera in the sediment. In addition to the ecologic factors, an algal belt is indicated be- tween depths of 130 and 350 feet which is characterized by an abundance of bryozoans, calcareous algae, and Amphistegina lessonii. Lowman (1949) reported the presence of this algal belt in his investigation of the Gulf of Mexico. Amphistcgina lessom'i was restricted to the outer part of the algal belt, ranging in depth from about 170 to 350 feet. Abundant bryozoans were found between depths of 130 and 350 feet. According to Howard Gould (oral communication) the calcareous 182 algae were found in a nonliving state at the time of collection, and they appear to represent reef structures that developed during times of lowered sea level in the Pleistocene. Archaias assemblages Within the algal limestone corroborate this suggestion. Further, Am- phistegina limestone was found at greater depths than the Archaias limestone, showing how the faunal zones were displaced downslope during times of reduced sea level. Many of the specimens of Amphisteginc are discolored, but many are also very fresh in appearance and are considered to inhabit the reef structures at the present time. The second subdivision of the frequency figures, the composite frequency graph, is designed to show the gross relations between the arenaceous, porcelaneous, and hyaline groups of benthonic Foraminifera. Plank- tonic species are plotted as a separate category in this graph. In the third subheading, frequency distribu- tion of species, the benthonic species are segregated into depth suites and plotted against 100 percent of the total benthonic population. Arenaceous species are plotted together, separate from the other species. All values of less than 1 percent are indicated as 1 percent; all other values are to the nearest 1 percent. A summary of the distribution patterns of Forami- nifera is presented in tablesl and 2, wherein median values are given for the frequencies of species in the habitat subdivisions. Figures for each of these sub— divisions total mostly somewhat less than 100 percent except in the river habitat (fig. 25) and in a branch of the inner channel, where the totals are 116 and 107 percent respectively. This incongruity stems from the fact that there are too few samples, and Streblus is very abundant in the mouths of the rivers and is re— placed in large part in upstream areas by Ammobacu— lites. Additional samples would have resulted in better median values for this habitat. Figures 26 and 27 represent abbreviated classifications of the faunal assemblages and the available ecologic data. A group of 17 samples, collected in the offshore area between Tarpon Springs and St. Petersburg, was pre- served in alcohol. This number is in addition to the 344 samples used in compiling the frequency graphs. As determined by the rose bengale stain method (Walton, 1952), less than 1 percent of the Foraminifera were live specimens. Three of the samples contained the Planulina assemblage and represented depths ranging from 156 to 258 feet, the normal depth range indicated for this assemblage in the frequency profiles (charts 5—7). The remaining 14 samples contained the normal Archaias assemblage and represented depths ranging from 18 to 60 feet, again well within the depth zone indicated in the profiles, especially off Tarpon Springs. Estimates of the relative frequency of stained (live) SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY specimens accorded with frequencies of the dead as- semblages. Many replaced (phosphatized?) or discolored Fora- minifera occurred in the preserved samples, and all such species were represented by other specimens that were living. More complete data concerning this phase of the investigation will be included in another Geological Survey report, on sedimentation, by H. R. Gould and R. H. Stewart. BRACKISH HABITAT In the brackish inland waters, the salinity ranged from less than 0.04 to 28.14 parts per thousand. The range of pH was 6.30 — 8.22, and the temperature range was 13.9°—19.8° C. Percentages by weight of Fora— minifera in the sediments were mostly less than )4 of 1 percent, and the number of species increased generally from 5 or less in the shallow inner areas to 20 or more in the channels opening into the gulf (charts 1, 2). Are- naceous Foraminifera were dominant in the lower reaches of the rivers, whereas the porcelaneous species were of greatest importance in open bays and especially in the channels. Hyaline species were I abundant throughout most of the bay areas. TAMPA BAY In chart 1 it is apparent that there are two main sub- divisions of Tampa Bay regarding bottom configura- tion. These are shoals and channels, each of which is further subdivided into bay-head, intermediate, and bay—mouth areas. In the shallower waters of the bay— head environment there is an abundance of Ammo— baculites salsus, Streblus tepidus, and little else; in the intermediate and bay-mouth shoals occur Streblus, species of Elphidium, a few other genera, but no speci- mens of Ammobaculz'tes. The channels of the inner area exhibit an abundance of Streblus tepidus and S. sobrinus; the intermediate channels exhibit high fre- quencies of Quinqueloculi’na akneriana, Q. jugosa, Tril— oculina trigonula, Streblus tepidus, and T extularia secasensis; and the bay-mouth channels show an in- crease in the frequency of Streblus tepidus, the appear- ance of species of Elphidium which were mostly absent in the intermediate channels, and a more equal em— phasis of the miliolids and other species. Prominent trends and distinctions of faunal subdivisions include diversification of species toward the bay mouth in both shoals and channels, and a fairly distinct separation of the shoal and channel faunas. That is, the inner shoals exhibit Ammobarculites, and the inner channels have an abundance of Streblus sobrinus and S’. tepidus; porce— laneous species are rare on the intermediate and outer shoals, whereas the channels associated with these areas have abnormally high concentrations of these species. Elphidium guntem‘ appeared in minor numbers ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO ..................................... 5:33: 3:338th ................................ fiafiwmgww 3553.35 .......................................... 3:332“ ........................................ asazuasfié ............................................ Semi .......................................... 538.3 ............................................ 2239.3 .............................. garages sgtsgsssefiso ........................................ Sassamoa ......................................... EES§§ ...................................... Eases; EEESN ............................................. 3.3.2?» ......................................... 955.53. aiemtw ....................................... .2253 E:.§.§§m~ ............................................... 25$. ................................... gag» MENESQEEV. 8? :wifi Sufism caisswa “muse afiwloh innings “325% 3:3 “ma oowfiloafi ”as; a in 8? was]: ”$53 Sarah in DefimTomfi ”name 38$: “3:: use" vanom 632% 9:3 Enema 3an ”—353 $3M 538 ham 3389 L35 3:53: 5:5 Ho nonwhm «one: hm m SEES Luann €32: imam 33 3me £05530 macaw ham moiao new 655m «ESE 05m £33m 38.550 ham Saw? $6on in shoal areas near the mouths of rivers and around the N o Foraminifera were found on the shoal represented by samples 503—506 where diatoms formed the dominant part of the sedi- edges of some of the channels. Streblus sobrinus and Elphidium guntem' were especially large and well developed in the however, edges of this shoal. ment; as“ 3230 saw ESQ AYSSW 8:3,: ”Fem £2232 382380 .35 eastern S Eofigggeh kc wouswggnoa :EnwElé "Sea. A pH minimum of 6.9 was reported at one place in the Little Manatee River; excepting for this, the pH of the rivers ranged Observed variations The temperature range of 15.8°—18.1° C. in pH may be adequate to affect faunas in parts of the Measurements of temperature, pH, and salinity is probably the annual minimum. Streams entering were made in December, and the indicated ranges are representative of the variation found in the bay at that 19.4° C. In the shallow waters of the bay, temperature is probably not significant in so far as the faunal sub- divisions are concerned; however, it is probably sig— nificant in distinguishing between these faunas and between 7.07 and 8.00, thus only slightly lower than Tampa Bay exhibited a temperature range of 106°— those of the bays in colder regions. time of year. the range of 7.20—8.12 for the bay. bay, but it is unlikely that this factor is important in distinguishing between the general faunal subdivi- sions. Perhaps reduced pH is contributory to the decline of hyaline species and the disappearance of porcelaneous species in the river habitat. Salinity According sand within the bay, whereas those of the rivers were to Gould (oral communication) there is a flow of less measurements ranged from 6.6 to 24.2 parts per thou- mostly less than 0.4 parts per thousand. dense fresh water over the denser saline waters of the bay. This would tend to modify the faunal environ- ment of shoal areas in the path of such currents, pos- sibly explaining the absence of Foraminifera on some shoals such as the one mentioned above (samples The percentage of Foraminifera in the sedi- ment is much greater in the channels and open bay areas than on the shoals (chart 1), and this may well 503—506). 68 Ga .r. O. hm m amboumnw tm S fsw‘ummar : .1 a . 6 ad D .mdnhabol i N mni .aeb tn aa Vaola .E& A a mmrmahtt ma , md, mbsme 6 mm m rumimmsa rm U enOuhtirt (\ a o untStaoim .maw S f tuuimyem g Sb .ahe 0108 am Vim D ngahBtm at my ymgh d n0 A maswrflobwinn hm. SB 11 0.0 ae aon I o svum e sro s ceeioadw Pi E0 enir et. eSt NL .ld..dTne mrm IR mesnefib aWu PAH. swake Soup aC srilrihdn ewo R eoaamnYO h po tbn eulu tome B MMU%r ma yp.m R tHaeaS;0.U bmmm m FmYum t ddm mw.f1maaem mmdm 2MW0 was r .1 .mhe T tflBseeSd lamm o ra nnsd pss L ahsonenl Xer R hCOiih a ere C 1r.«bdtwn comm fa.wnnhw bmd c oCdaIcf 364220— 56‘2 184 The river habitat displays a predominance of Ammo— baculites exiguus in the upstream areas, whereas in the downstream areas there is an important influx of Streblus sobrinus and S. tepidus. The inner harbor and inner bay areas are characterized by the continued prevalence of Streblus sobrinus and S. tepidus, the absence of Ammobaculites, and the appearance of Elphidium rugulosum, E. adoenum, and an occasional Quinqueloculina (table 1). The outer harbor and outer bay areas show considerable faunal diversity with the appearance of many miliolids and the absence of Streblus sobrinus. Temperature, pH, and salinity measurements (chart 2) were made during the month of December. Tem- peratures fell as low as 13.0° C. in the rivers, whereas , the bay temperatures were between 183° and 19.1° C. Fluctuations of temperature are characteristic of these shallow waters, and, therefore, change of temperature, ~rather than the values, may be the control. The effect of temperature, however, is likely of minor importance in determining faunal differences within the area. Values of pH are mostly above 7 ; however, there is a trend toward lower, more acid conditions in the rivers. This correlates with the decrease of porcelaneous and hyaline Foraminifera in these areas. Variation in salinity is considered the most significant controlling factor in the harbors and bays. The salinity is less than 0.04 parts per thousand in the rivers, about 11 parts per thousand near the mouths of rivers, and more than 28 parts per thousand in the harbors and bays. Foram- inifera are known to be typically marine animals. Therefore, the observed salinity gradient is considered as the probable controlling factor. Maximum tolerance to variations in salinity is observed in Ammobacul'ites, somewhat less is attributed to Streblus, less yet to species of Elph’idz'um, and the least tolerance is observed in most other genera of hyaline and porcelaneous species. Percentages of Foraminifera in the sediments of Charlotte Harbor, Pine Island Sound, and San Carlos Bay were confined mostly to less than % of 1 percent, about the same as that in the adjacent offshore area. This suggests a relatively low productivity of F orami- nifera with respect to sedimentation rates. OFFSHORE FAUNAL ZONES The detailed frequency data for all of the species are presented in charts 3—7. The progressive changes in the faunal character with increase in distance from land and depth of water made it possible to segregate the species into 5 arbitrary faunal groups between the depths of 8 and 600 feet. The arenaceous species are listed separately and in sequence according to in— creasing depth. There is a patent intergradation of faunal groups, and many of the rarer species occur in SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY different faunas in the different profiles. Generally these rarer species are more widely distributed, and they are, therefore, less diagnostic of restricted depth zones. The more abundant and restricted species were analyzed statistically in an effort to determine dependable depth indices, and these data, representing a composite generalization drawn from the five offshore profiles, are presented in table 2. The figures in this table are median percentages of occurrence of signifi- cant Foraminifera for the depth ranges given. The samples in the offshore profiles demonstrate many interesting general trends. In the 3 southern profiles the number of species generally increases from TABLE 2.——Median percentages of significant Formamim‘fera in the ofishore depth zones, based upon concentrate samples Depth zones (feet) Species 8-40 41—105 106—180 181—250 25—400 401—600 Fauna 1 Elphidium guvnteri _______________ 5 1 _________________________________ poeuam'm ___________________ 19 3 3 1 ................. Streblue tepidus ................. 48 1 1 ........................ Fauna 2 ' Archaias anaulatus .............. 1 43 11 1 ________________________ Asterigen‘na carinata ____________ 5 20 1 1 ________________ Discorbis flortdanus _____________ 2 8 1 1 ________________ concinnus ................... l 13 2 1 ________________ Hanzawaz'a concentrica .......... } 18 18 13 5 ........ strattoni ___________________ l Tertulariu candetana ____________ } 4 5 3 mayari .................................. F one 3 Bigenerina irregularis ........... 1 4 10 10 4 1 Planulz’na ornata ________________________ 2 16 If) 5 ________ Fauna 4 Amphistegina lessonii ..................................... 3 1 2 1 ........ Casszaulina curvata assem- blage _________________________________________________ 2 9 Cibicides pseudoungerianus ...................... l 8 20 21 Gauerfa aegifa ................ 1 _______________ 4 12 12 3 Tertularza comm assemblage-.. 1 Fauna 5 Baliaina goesii ................................................... 1 7 daggariua ............ _.__ ........................ 1 6 14 Planulina foveolata ....... _ ................................ 1 2 Robulus calcar ______________________________ 1 1 3 Uvigerina bellula__.. _ _ _. flintii ........... .. _-__ _______________________________ 6 18 hispido-costatu ________________ 1 Representative for areas of normal salinity only; 1 percent otherwise. 2 Represents occurrence in concentrate; It would range from 10 to 70 percent of unooncentrated fauna. ECOLOGY 0F FORAMINIFERA, NORTHEASTERN GULF OF MEXICO about 20 in the nearshore area to more than 50 at the outer ends of the deeper profiles. The weight percent- age of the Foraminifera in the sediment fluctuates from less than 1 percent near the shore to about 2 percent on the outer part of the continental shelf and then increases rapidly on the continental slope, an increase which coincides with the progressive increase in planktonic tests in the sediment. Two exceptions to this general— ization include an increase in the percentage of Foram- inifera due to the abundance of porcelaneous species in less than 100 feet of water and sporadic percentage increases near the edge of the continental shelf because of the abundance of Amphistegina lessom’i. Percentages of Foraminifera in the sediments of the northern profiles are mostly less than 1 percent, a smaller value that is caused by correspondingly larger contributions of sand and silt. In the southern profiles, porcelaneous species are of very high frequency in less than 100 feet of water, whereas they are minor constituents in the shallow waters of the northern profiles. Arenaceous species show a depth zonation like that of the other types of Foraminifera. In the southern profiles these comprised less than 10 percent of the fauna in shallow water, whereas they amounted to more than 20 percent of the fauna toward the edge of the continental shelf. The arenaceous types were quite abundant throughout the northern profiles. One good example of a bottom prominence was noted in the Panama City profile (chart 4) where the offshore declivity of the bottom is interrupted at about 118 feet and shoals to about 104 feet (stations 354—359) before continuing downward again. This configuration is re- flected in the faunal trends by a decrease in the per- centage of arenaceous species and an increase in the percentage of porcelaneous species on the prominence. Quinqueloculina lamarckiana exhibits the greatest in- crease in frequency at this locality and is in large part responsible for the increase in the porcelaneous category. FAUNA 1 (8—40 FEET) The dominant species of fauna 1 are Streblus tepidus, Elphid’ium guntem', and E. poeyanum. Species which are important, but less consistently present, include Elphidium advenum, E. memlcamum, Quinqueloculina akneriana, Q. jugosa, Streblus sobrinus, and Textularia secasensis. Under some conditions Archaias, and to a lesser ex- tent Astem'geréna, occur in abundance in depths of 8— 105 feet (chart 5) whereas under other conditions they are restricted to a depth range of about 41—105 feet (charts 6, 7). Where Archaias is present in the shal- lower waters, Streblus is absent or very rare. The ex- planation of this situation may be that the Streblus fauna is developed in brackish waters, whereas Archaias 185 is restricted to inshore waters of normal salinity. Other species listed for fauna 1 are not as variable in their occurrence and are usually found at the normal depths for this fauna. FAUNA 2 (41-105 FEET) Dominant species of fauna 2 include Asterigerina carinata and Archaias angulatus in the southern profiles, whereas the following species were found in the indi- cated depth ranges in all areas: Discorbis fioridtmus, D. concinnus, Hanzawaia, strattom', Temtularia. candeicma, and T. mayom'. The last two species occur in low fre- quencies together, so they were combined for simplicity in computing median percentages of occurrence. Not shown in table 2 are other species of importance such as Peneroplis proteus, Quingueloculina agglutinata, Q. dutemplei and Q. horrida. As shown in charts 3—7, many other species occur in this fauna, but generally they are not as specific for the specified depth range. Hanzawaia, strattoml is very abundant between depths of 41 and 105 feet; however, young specimens of this species are difficult to separate from young specimens of the deeper occurring H. concentrica, so the 2 were combined in the frequency counts. H. strattom' is pre- dominant in the upper half of the depth range whereas H. concentrica is the more abundantly represented mem- ber in the lower half of the range. Hanzawaia strattoni is found in fauna 1, but it is rare. This agrees with the findings of Parker, Phleger, and Pierson (1953) that it is a rare species in very shallow waters and beach sands. In table 2 it may be noted that fauna 2 identifies the 41- to 105-foot depth in 3 ways: certain species range mostly from these depths into shallower depths, as Asterigerina carinata and Archaias angulatus; other species range mostly from these depths downward as shown by Hanzawaia strattom’, Textular’ia candeiana, and T. mayom'; and other species that are rare or absent in this fauna become very important below the depth of 105 feet, as exemplified by Planulina ornate. The two species of Discorbis given for this zone are of high frequency and are rare both above and below this zone. Archaias angulatus and Asterigem’na carinata, are re- stricted mostly to the southern profiles, being very poorly developed in the northern profiles off Panama City and Mobile. This fauna is designated as faunas 2A and 2B in chart 5 in order to subdivide the range of Archaias angulatus. As mentioned earlier, this spe- cies becomes very abundant in the depth range of fauna 1. FAUNA 3 (106-180 FEET) Overlapping characteristics of specific ranges permit the establishment of a characteristic fauna for the depths of 106—180 feet. Planulina ornata, and 186 Bigmerina irregularis are the definitely diagnostic species; the remaining species which occur with this fauna are also components of other faunas. As in fauna 2, there are 3 requisites for recognition of the depth zone given for this fauna: several species (Arch- aias angulatus, Asterigerina carinata, Discorbis flori- danus, D. concinnus) that were common and abundant in the zone above are rare or absent; the most important diagnostic species of this zone is Plamtlina ornata, although it occurs also in the next deeper zone Where it accompanies the important species of fauna 4; and the 2 species of Hanzawaia intergrade in this depth range. Species which are sporadic, but seemingly restricted to fauna 3, include Oibicides robertsom‘anas and Rotor- ln'nella basilica. A number of rare species have much greater depth ranges as shown in charts 3—7. Bryo- zoans are common in the outer half of the depths as— signed to this fauna, and abundant specimens of Amphistegina lessom'i appear sporadically at depths mostly below 170 feet. A shallower occurrence of A. lessonii was noted in sample 11 off Mobile, Ala, at a depth of 108 feet. Perhaps these are being eroded from a topographic high, where they developed during times of marine transgression during the Pleistocene. FAUNA 4 (181—250 FEET) Diagnostic features of fauna 4 consist of the abun- dance of Oibicides pseudoungerianus together with Hanzawaia concentrica, Planulina ornata, Gaadryina aequa, and the Textularia comica assemblage. The T. conica assemblage includes this species, T. pseudotrochus, T. barretm’, and Gaudryina stavensis. This assemblage of arenaceous species makes its appearance in the zone above and continues into the upper part of the fauna 5 zone. Important species of fauna 4 which range into shallower water are Hanzawaia concentrica, Planulina. ornata, Textulam'a candeiana, T. mayori, and Bige’nerina irregularis. Although many of the species of fauna 4 (table 2) become even more abundant in the next deeper zone, diagnostic species of fauna 5 are also present. As mentioned under general features of faunal zona- tion, Amphistegina lessom'i is locally abundant (10—70 percent of the fauna) in this and the following faunal zones of the southern profiles (charts 5—7). Sporadic abundant occurrences of this species indicate that it may be restricted to the fossil reef structures discussed on page 181. Many of the specimens of Amphistegina are broken and partially discolored or replaced by phos- phorite(?), and this may be the reason so many speci- mens remained in the residues in the carbon tetrachlor- ide separations. Some of the specimens always floated, and these were invariably fresh in appearance. Another species which may prove to be diagnostic of this depth SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY is Marginalina advena; however, it is relatively rare. Rare species which also range downward into the next zone include Anomalina to, Bolivina daggarius, Nom'on aflim's, Robulus calcar, and Textularia foliacea var. occidentalis. FAUNA 5 (251—600 FEET) Fauna 5 is characteristic of the upper part of the continental slope. Diagnostic species include Bolivina goésii, B. daggam'us, Planalina foveolata, Robulus calcar, Um'gerina bellula, U. flimii, and U. hispido—costata. Less abundant characteristic species include Discorbz's flori- densis, Ehrenbergiaa spinea, Hanzawaia bertheloti, Héglundina elegans, Marginulinopsis densicostata, M. subaculeata, Spiroplectammina floridana, Pseudoclavulina constans, and Karreriella bradyi. The foregoing species represent the concentrate fraction. Amphistegina les- som'i occured in many of the residues of samples from depths shallower than 350 feet in the 3 southern profiles, comprising from 10 to 70 percent of the total population there. Herein is a possible criterion for subdividing the depths of this zone; however, it is possible that a large number of specimens of this species may have been transported from the 181— to the 250-foot zone. Species of fauna 4 are quite abundant in the depth range of fauna 5; however, the species of the latter become progressively more abundant with depth, and for this reason the depth range is subdivided into 251- to 400—foot and 400- to GOO-foot categories (table 2). Trends toward increasing abundance are not only em- phasized in this way, but criteria are provided for predicting faunal positions within the zone. One of the useful lower depth-range (400—600 feet) indices is Bolivina goésit', which exhibits a median value of 7 percent in its relative proportion to the remaining benthonic species. PLANKTONIC SPECIES No plankton hauls were made in conjunction with this investigation. Hence, the analyses of planktonic species are dependent solely upon the occurrence of the tests in the bottom sediments. Charts 3—7 show several significant trends or associations. The first of these which has been noted by Lowman (1949) and by Phleger and Parker (1951) is the increase in the per- centage of planktonic species with distance offshore. A second feature of importance is the association of the break in slope at the edge of the continental shelf with an abrupt increase in the percentage of planktonic species. Generally the percentage of planktonic species rises sharply from about 30 or 40 percent to 60 or 70 percent seaward across the edge of the continental shelf. A third point of significance is the progression of appearance of the tests of different planktonic species (fig. 27). Globigerinoides rubm nearly always appears ECOLOGY OF .FORAMINIFERA, NORTHEASTERN GULF OF MEXICO first near the shallow end of the profiles between depths of about 70 and 100 feet. Globigem’na bulloides appears next, becoming common between depths of about 100 and 160 feet and increasing more or less in frequency offshore. Globorotalz'a menardii makes its appearance at about the same place as Globz'geri’na, bulloz'des, and then the following species appear and increase in abundance: Uandeina m'tida, Globigerina eggeri, G. acquilateralis, Globigerinoz'des conglobata, G. sacculifem, Globorotalia puncticulcta, G. truncatulinotdes, Orbulz'na universe, Pullem'atina oblzqmloculata, and Sphaeroidina bulloides. Finally, Globorotalia tumida makes its ap— pearance at a depth of about 400 feet. These data suggest that living specimens of the species listed float no higher than the minimum depths indicated (Emiliani, 1954, reported similar results). Observational data by Phleger (1951, tables 2— 9) bear this out He reports living specimens of Globigerinoides rubm at the same and also shallower depths than most other plank— tonic species, whereas Globorotalz'a tumida is fo nd living in the lower living range of most planktohic species. The fourth and last trend of general signifi- cance is the correlation of the relative abundance of planktonic species with the percentage of Foramiiilif- era in the sediments. Wherever the percentage? of tests in the sediments shows a marked increase, ther is an increase in the relative percentage of plankto‘nic species. } ENVIRONMENTAL ANALYSES GENERAL Many associations found in the present investiga- tions are similar to those reported from other areas; indeed, some of the same species or their homeomorphs 187 (Rottgardt, 1952), Trinidad (Cushman and Bronniman, 1948), and from elsewhere in the Gulf of Mexico. One of the better environmental analyses is that of Lowman (1949) in which he recognized free—floating, bottom— living stagnant(?), and bottom—living open-water cate- gories. Planktonic species form the first category. The second is characterized by Haplophmgmoides and Trochammina which are associated with Ammoastuta in brackish water and with Cyclammina and Bathyszphon in marine water, and the third is made up of the ben- thonic populations discussed earlier (fig. 26). The first and third categories are represented in the present study, the second is apparently absent. BRACKISH HABITAT In bays and harbors an important subdivision is that between open water and stagnant water. The chemi— cal characteristics identified with stagnant environ- ments include oxygen deficiency and the presence of toxic products as a result of organic decay. These factors are more than ample to limit the Foraminifera to those few arenaceous species which appear in such habitats (Lowman, 1949). In the open—water environ— ment the oxygen content, although variable, is probably adequate most of the time. In this region the changes in faunas are matched against the progression in salinity values. Lowman pointed out that Ammobaculites is found in a weakly brackish environment and that Streblus, Elphidium, miliolids, and others are charac- teristic of strongly brackish water. Associations of Ammobaculites and Streblus in the river habitats of this investigation suggest mixed faunas due to fluctuating conditions as a result of the interaction of tidal and river currents. However, specimens of Elphidium should occur with the faunas of weakly brackish en— are reported from Japan (Hada. 1931), Germany vironments if this were correct. . Salinity (parts pu- thousand) Habitat pH Oxygen Diatoms and Size other plants 0 9 ll 27 36 Stagnam Deficiency Deficiency Ammoaetuta Bathysiphon water ? ? ? 2 Small 7 Haplophragmoides ' Trochammina Ammohaculites 7 7 7 Normal 7 Streblue 7 Elphidium 8 Open ? Miliolidae 1 water 8. 5 Excess Excess Large 7 Other Epecies Adapted in part from data by Lowman (1949) FIGURE 26.——Assemblages and ecologic factors in the river. bay, and shallow-water habitats. 188 It was noted that in 1 or 2 instances the species of the open—water category were especially large and abundant adjacent to areas of high diatom production. The diatoms serve directly or indirectly as food, and their abundance may well explain the large size of the Foraminifera here. Another point of significance is that, excepting in the bay areas, the shoals exhibit a much higher percentage of Streblus tepidus (90 percent or more) than the channels. OFFSHORE AREA Environmental limiting factors should be more easily assessed for the offshore area than for the shallow-water areas inasmuch as the general ecology is somewhat more uniform and stable in the offshore environment. A regular procession in conditions occurs offshore with increase of depth and pressure. One of the best demonstrations of the separate effects of temperature and depth (pressure) is that of Crouch (1952). In his study of the cores of some deep basins off southern California, he found that the fauna and temperature did not change between the sill and the bottom of several deep basins, a vertical distance of several thousand feet in one case. In contrast, there is a regular succession of faunas on the open sea bottom at equivalent depths. In that environment, tempera- ture and not depth (pressure) appears to be the main limiting factor. Temperature changes are gradational from shallow depths to the deep ocean bottom, and SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY they seem to show a changing pattern that is reflected in the faunas. Natland (1933) noted that where the temperature changes most rapidly, the fauna changes rapidly. This correlation has been noted, also, by the author (Bandy, 1953) in the frequency charts for the offshore area of California. In the frequency charts of the present study (charts 3—7) there is an apparent correlation between temperature and faunal changes (see fig. 27). However, progressive restriction of tem— perature variation may be of greatest significance in the shallower waters, whereas the reduction and con- tinued restriction of temperature may be most signifi- cant in somewhat deeper water. Greater temperature variation near the upper part of the continental slope suggests the possibility of intermittent upwelling there (chart 7). The sudden dropoff of the lower limit of the bottom-temperature range in chart 3 between samples 7 and 8 also suggests intermittent periods of upwelling. Intermittent upwelling of colder waters may thus be most significant in two ways: in restriction of the depth ranges of stenothermal warm-water species and in providing nutrients for the phytoplankton on the outer part of the continental shelf; in this way abundant food is provided for foraminiferal populations that are adapted to lower temperatures. The pH of the waters of the offshore area is not considered im- portant in limiting the distribution of the species because it ranges between the narrow limits of 7.7 and 8.2 for the most part (Sverdrup, Johnson, and Depth (feet) 100 200 300 -400 500 600 Tempfigture 21—32 17-26 18.2—22.4 17. 4-22. 3 16. 7-21.1 16-19. 2 15.2-17.4 Streblus* u: Archaias * a,” _. 3 Hanzawaia __ _ "g ( fi. strattoni ) ( H. concentrica) a, Planulina ornata m 3 Amphistegina lessonii O __ _ —_—_ __ E Cibicides pseudoungerianus .r: E Uvigerina sp. m _ Bolivina gro'e'sii o Globigerinoides ruin-a .,.. m .. _ .5. 3 Other species s a» ‘ v > g % 94 Globorotalia t‘umida * If Streblus, a brackish-water assemblage, is present, the Archaias assemblage is generally absent. FIGUBE 27.—Assemblages and ecologic factors in the offshore area. ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO Fleming, 1942, p. 210). Local stagnant areas would exhibit a decrease in these values to about 7.0, perhaps less (Strom, 1936). Variation in salinity is an important ecologic factor in the shallower waters, especially along the coasts where brackish conditions exist near the debouchments of rivers. The Streblus fauna is found generally in such areas, and its tolerance of widely varying salinities has been noted by many authors. It is known to thrive, also, in typical marine waters, as in some of the lagoons along the southern California coast,- there— fore, it is clearly a euryhaline fauna. This does not imply that all species of Streblus are so categorized, but only those of the S. tepidus type. Perhaps the most important factors in explanation of the distribution patterns of Streblus are its ability to endure great fluctuations in salinity and in_the character of the sediments and associated nutrients and bottom plants. Salinity and the character of the bottom sediments appear to be two of the main factors limiting the upper depth range of Archaias. This genus is not found in depths shallower than 40 feet off the outlets of brackish bays and harbors, whereas it occurs up to the beach level in other areas such as that near Tarpon Springs. On the other hand, Archaias is not known to occur in shallow clear waters of colder regions; hence, temperature is also important. Oxygen, nutrients, and bottom plants are closely related factors which vary with increasing depth of water in large part due to decreasing light intensity. Myers (1943) has contributed much to an understand- ing of the interrelationships between foraminiferal populations and bottom plants, and it should be em- phasized that the successive changes occurring in the character of the latter with increasing depth would be expectably reflected in the benthonic populations of Foraminifera. Unfortunately, data on oxygen, nutrients, and bottom vegetation are not available. Turbidity is of little importance to some of the species of Foraminifera inasmuch as the representatives of Hanzawaia of the clear waters off Florida also occur in the turbid waters off Texas and Louisiana in com— parable numbers (Bandy, 1954). Other genera which are quite restricted to clear warm waters include, Archaias and Asteriger’ina. Amphistegina tolerates some turbidity; however, it usually occurs on bottom prominences unless the waters are clear. With the ecologic data available, temperature gradi- ent is one of the important factors limiting the distri- bution of foraminiferal species; however, other factors are or may be significant, also. Some problems are raised as a result of studying the distribution patterns of some of the species of Foraminifera. One enigma involves the question .of why Nonion afim's occurs at 189 depths as shallow as 181—250 feet in the waters off Florida and specimens of this same species occur off Point Conception in abundance only at depths of 10,000 feet (Bandy, 1953). N. afinis was erroneously desig- nated N. barleeanus in this earlier report. A second interesting problem involves Planulina ornata. Ofl’ San Diego, Calif, this species ranges to depths of more than 3,000 feet, whereas in this study, it becomes very rare below 400 feet. Explanations of these problems include the possibilities that the species lives in shallow water, and its tests are transported into deeper water in large numbers off San Diego; the species has adapted itself to different conditions in the 2 areas; and the 2 occurrences actually represent different species. The first and second explanations are probably in part cor- rect; however, the solution is impossible with present data. The tests from both areas are alike and exhibit about the same amount of variability, and, in the opinion of the author, they represent a single species. They may or may not be different physiological species, but from the standpoint of the hard parts, they are indistinguishable. PALEOECOLO GICAL IMPLICATIONS So many of the species of this investigation range back into the history of the Gulf coastal region during early Cenozoic time that they provide not only an ideal means of interpreting environments of the later Ceno- zoic but also an approach toward extrapolating even further into the geologic past of Florida. This section is not an attempt to present a complete analysis of the paleoecology of the later Cenozoic of Florida, but only an effort to exemplify how investigations of this kind may be used to express quantitative environmental changes of the geologic past. Cooke (1945) has pre— sented the best stratigraphic and paleogeographic study of Florida, and he and others have met with difficulty in using Foraminifera for stratigraphic cor— relation purposes in Florida. These difficulties were recently expressed by Schroeder and Bishop (1953), who attempted to reevaluate the foraminiferal data pre- sented by Cole (1931) and Cushman and Ponton (1932). ~. In table 3 are some of the species assigned to the faunal zones by Cushman and Ponton. Ecology of the modern representatives or homeomorphs of these species is used as a basis for reconstructing depth and temperature trends in the later Cenozoic of Florida (fig. 28). It is assumed that the water temperatures of the Gulf of Mexico have been essentially the same as those of today. If not, the picture presented herein might be modified somewhat. According to the foregoing foraminiferal species, it would seem that the early Miocene (Tampa limestone) was deposited in less than 100 feet of water, probably 190 TABLE 3.—Foraminifera in selected formations of the Miocene, Pliocene, and Pleistocene of Florida Forma- tion Foraminifera Series Group Zone Archaias ‘ cene Plio- Pleisto- cene Archaias 1 Amphislegina lessonii Bigenerina floridana Discorbis floridanus 2 Textularia foliacea var. occidentalis Globorotalia menardii Dentalina communis Discorbis floridanus 3 Robulus americanus var. spinosus Saracenaria acutam‘icularis Globorotalia menardii Uoigerina parkeri Denlalina communis Discorbis floridanus 3 Robulus americanus americanus var. spinosus Saracenaria acutauricularis Siphogenerina lamellata Valvulineria floridana Globorolalia menardii Orbulina universe 3 Dentalina communis Robulus americanus var. spinosus Saracenaria acutauricularis Uvigerina peregrina Globorotalia menardii Orbuli'rla universa 2 Cancellaria Ecphora Upper Miocene Duplin marl Arca Yoldia Miocene Dentalina communis Marginulina glabra Robulus americanus var. spinosus Saracenaria acutauricularis Globorotalia menardii (Cooke, 1945) Aslerigerina floridana 4 miocemca Bigenerina floridana Shoal River formation Oak Grove sand member Cardium' taphrium Glycymeris waltonensis (Cooke, 1945) Lower and middle Miocene Alum Bluff group Asterigerina chipolensis 4 floridana 4 Buliminella eleganlissima Nodobaculariella cassis Sorites Triloculina trigonula Chipola formation Archaias cene Tampa lime- stone Lower Mio- 1 Marine formations. 3 Common. 3 Rare. _ _ 4 These species were originally described under Amphistegma by Cushman and Ponton (1932); however, because they are not involute dorsally, they are here placed in Asterigerina. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY less than 40 .feet ; the lower Miocene (Chipola forma- tion) was deposited at depths between 40 and 100 feet; and the late Miocene (Duplin marl) is represented by a cycle of deepening and subsequent shoaling through the zonal sequences from the Cardium zone to the Pliocene. The major depth attained was probably between 250 and 600 feet. The presence of Valvuli- neria and Uvigerina suggest these depths. During Pliocene and Pleistocene times the Archaias fauna characterized many of the marine sediments which are, therefore, considered to have been deposited in less than 100 feet of water. The detailed picture may actually be much more complex; for example, forami- niferal lists of Schroeder and Bishop (1953) indicate that part of the Hawthorn formation of early and middle Miocene age was deposited in deeper water (250—600 feet) than the Chipola, and also a part of the Pliocene faunas of Cole (1931) represent a Streblus facies which suggests shallow water and variable salinity. Fre— quency analyses should be made of all of the various facies of the middle and later Cenozoic before the PLEISTO MlOCENE PLlOCENE CENE Early lEarly and middlel Laie C m o w a; c -- r: r: 2 '5 W 2 °’ 2 E’ 3 g g E .9 g on g g g a = '- E “L' N g o 2 3 ‘6 3 g 3 E .2 N 8 3 '5 'a E a \‘i 0 ‘3 ° ‘5 g f, 5 o E D 3‘ 3 S o a .. L l— 0 U 0 )- <( [U 0 < 4 C i i l I00— .— m 200~ L|J LL 3 “300 E l —30 '5 DJ E 400 D 0 FE I —25‘_9 l— l- b E Q 500“ U m uJ ~20}; 600- 3 o E 700* 45 E 3 i. < n: Lu 0. 402 L|J }_ *7 FIGURE 28.——Depth and temperature variations during Miocene to Pleistocene time in northern Florida. ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO foraminiferal evidence in the literature will have great ecologic significance. The temperature curve in figure 28 is not indicative of climatic change, but of cooling due to deepening of the seas followed by shoaling of the seas and resulting higher temperatures. Gardner (1926, p. 101) suggested reduced temperatures following the deposition of the Chipola; however, she indicates shoaling following Chipola time in contrast to the deepening indicated herein. Two particular problems of the Cenozoic stratigraphy of Florida are emphasized by investigations such as this: whether there are as many erosional unconform— ities as have been suggested, and whether biofacies maps of successive stratigraphic units of Florida should exhibit ecologic suites comparable to those indicated in this investigation. In amplification of the first prob- lem, proposed evidence of an unconformity between the Hawthorn formation and the upper Miocene strata is suspect because there is little or no evidence of shoaling in the upper part of the Hawthorn formation. Accord— ing to the foraminiferal data, this formation was deposited at depths greater than 200 feet. Similarly, the upper Miocene strata represent about the same conditions. Further analyses may either corroborate or otherwise explain this condition. The second problem involving biofacies studies of the stratigraphic units of Florida should reveal a series of ecologic zones paralleling the former shorelines, and these would duplicate their modern counterpart in a general way. Because of homotaxis, very careful speciation and identification of varieties will be necessary in order to develop stratigraphic indices that are dependable. CONCLUSIONS Brackish-water species of Foraminifera in the bays of Florida are cosmopolitan in that they are found, also, in many of the brackish—water areas of the world, especially the coastal regions of the Gulf of Mexico and the Caribbean Sea. This shallow-water environment is subdivided into shoals and channels, and these are separated into inner, intermediate, and outer bay areas. The lower reaches of some rivers are also represented, and these together with the inner shoals are character— ized by very high frequencies of Streblus and Ammo- baculites. The inner channel and bay habitats exhibit an abundance of Streblus and Elphidium, and the intermediate and outer harbor and bay areas have an abundance of these two genera together with abundant miliolids and rare marine species. The intermediate and outer shoals are marked by the presence of very high frequencies of Streblus and few if any arenaceous species. The faunal pattern is considered to correlate with the salinity gradient generally as follows: 1—9 parts per thousand, Ammobaculites and Streblus; 9—27 191 parts per thousand, Ammobaculites, Streblus, and Elphidium; 27—34 parts per thousand, Streblus, Elphi- diam, Miliolidae, and other rare marine species. The stagnant brackish habitat is not represented by the, samples of this investigation; however, from data compiled by others it is noted that foraminiferal assemblages are almost totally different, and they, too, exhibit changes that correlate with the salinity gradient. Temperature variation is an important - factor in restricting the faunas of shallow—water areas to eurythermal species. Low pH values of rivers constitute a restrictive factor to procelaneous and hya- line species. Variation in food is probably very important, but data of this type are unavailable; however, it was noted that unusually large specimens of Foraminifera occur adjacent to areas of extremely high diatom production. The percentage of tests in the sediment was found to be highest in the moderately to strongly brackish waters of channels and open bays, whereas the lowest percentages were found in the weakly brackish areas of the river and shoal habitats. The exclusion of porcelaneous and hyaline species from the latter explains the reduction in percentage. Five general faunas are indicated for the offshore area between depths of 8 and 600 feet: (1) Streblus fauna, 8—40 feet, off brackish bays; (2) Archaias fauna, 8—105 feet, in normally saline waters, and Asterigem'na carinatc fauna including Hanzawaia strattom', 41—105 feet; (3) Planulina ornate fauna, 106—180 feet; (4) Oibz'cides pseudoungerianus fauna, 181—250 feet; and (5) Um'gerina fauna, 251—600 feet (deep end of sampled profiles). In fauna 5, Bolivina goésii becomes signifi- cant below a depth of 400 feet, affording a means for subdividing the fifth depth zone. Off western Florida, an Amphistegina assemblage occurs locally between depths of 170 and 350 feet on the upper part of the continental slope. This assem— blage is almost invariably associated with fossil reefs of Bryozoa and calcareous algae. Ecologic interpretations indicate that both the pro- gressive restriction of temperature range and reduction of temperature are significant as limiting factors in the offshore area. Upwelling of colder waters is indi- cated on the outer part of the continental shelf by sudden drops of the lower limit of the bottom temper- ature. Variations in salinity are mostly significant in the shallow coastal waters; otherwise, this factor is nearly stable in deeper waters and is relatively unimportant. Variation in pH is also quite restricted in the open sea and is considered to be of little con- sequence. Turbidity is important in the shallower waters, inhibiting the development of the Archaias assemblage in some areas. Other species such as Hanzawaz'a strattom' and H. concentrica occur in both 192 clear and turbid waters and are clearly tolerant of considerable turbidity. Factors such as food, nutrients, and bottom plant distribution are considered important, but data for these are lacking. Percentages (weight) of Foraminifera in the bottom sediments increase from less than 1 percent near shore to about 2 percent on the outer part of the continental shelf. There is a rapid increase on the upper part of - the continental slope where the tests of planktonic species increase in frequency. There is also an increase in the number of benthonic species from about 20 in the nearshore area to more than 50 at a depth of 600 feet. Hyaline species are abundant over all of the off— shore region; however, porcelaneous species have the greatest frequency in less than 100 feet of water on shell bottoms, and arenaceous species, which comprise less than 10 percent of the benthonic species generally, amount to as much as 20 percent or more in many places near the edge of the continental shelf. There are four points of significance regarding the planktonic species: a general increase occurs in the percentage of planktonic tests offshore; an abrupt in- crease is observed in this percentage from about 35 to 65 percent in crossing the edge of the continental shelf; there is a progression of appearance of the planktonic species, that is, Globigerinoides rubm appears at depths of between 70 and 100 feet, most of the remaining spe- cies appear between 100 and 160 feet, and Globorotal'ia tumida makes its appearance at a depth of about 400 feet; and increase in the percentage of planktonic spe— cies correlates generally with an increase in the weight percentage of Foraminifera in the sediment. Paleoecological implications of this investigation are exemplified by a summary analysis of published fora- miniferal data on the Miocene, Pliocene, and Pleisto- cene of northern Florida. Beginning with the early Miocene, the water depth was between 0 and 100 feet. In the middle Miocene it was somewhat deeper and at‘ the beginning of the late Miocene it became even deeper, attaining depths of 250—600 feet. In the later part of the Miocene, shoaling began and con- tinued into the Pliocene in most areas. Marine Plio- cene and Pleistocene faunas represent depositional con- ditions such as those prevailing between 0 and 100 feet of depth off the present coast. Exceptions to this gen- eral trend occur southward where the Hawthorn forma— tion of early and middle Miocene time represents a deeper water facies than its time equivalent to the north. There are also some examples of brackish-water facies in the Pliocene. FAUNAL REFERENCE LIST An alphabetized reference list of the species of Fora- minifera studied during this work is given below. The SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY original and sometimes one or more subsequent refer- ences are given for each of the species. Where changes in classification have been made, the reasons for these are discussed briefly. The primary object of this list is to facilitate reference to original sources and to sys- tematic treatises. Illustrations of those species which are not figured herein will be found in the references given. The species are systematically arranged on the plates so that related species are together. The figures were made by Miss Mary E. Taylor, and the types are catalogued and deposited in the U. S. National Museum, Washington, D. C. A duplicate set is a gift to the Hancock Foundation, University of Southern Califor— nia, Los Angeles, Calif. Ammobaculites exiguus Cushman and Bronniman, 1948, Cushman Lab. Foram. Research Contr., v. 24, p. 38, pl. 7, figs. 7, 8. Gulf of Paria, Trinidad, in 0—2 fathoms. This paper, pl. 30, fig. 2. Ammobaculites exilis Cushman and Bronniman, 1948, idem, p. 39, pl. 7, fig. 9. Gulf of Paria, Trinidad, in 0—2 fathoms. This paper, pl. .30, fig. 3. Most of the specimens were broken. Ammobaculites salsus Cushman and Bronniman, 1948, idem, p. 16, pl. 3, figs. 7—9. Brackish water, west coast of Trin- idad. This paper, pl. 30, fig. 4. Amphistegina lessom'i D’Orbigny, 1826, Annales sci. nat., sér 1, tome 7, p. 304, Modeles, no. 98, L’Ile-de-France (Mauri- tius). Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 26, pl. 13, figs. 13, 14; p]. 14, fig. 1. Recent, Gulf of Mexico. Angulogerina bella Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 12, pl. 6, figs. 7—8. Gulf of Mexico, mostly between 50 and 120 meters. The occurrence of this species in the present investiga- tion accorded with the indicated range given for the type. _ » Anomalina i0 (Cushman), 1931, U. S. Natl. Mus. Bull. 104, p. 125, pl. 23, figs. 1, 2. Off Fowey Light, Florida, in 40 fathoms. This paper, pl. 31, fig. 7. Various authors have followed Cushman in assigning this species to Cibicides; however, the dorsal spire is concealed, and it tends to be bilaterally symmetrical and falls well within the definition of the genus Anoma- lz'na. The present author considers that Anomalinoides Brotzen (1942, Sver. Geo]. Unders, Sweden, Avh., ser. C, no. 451) is a junior synonym of D’Orbigny’s genus. Archaias angulatus (Fichtel and M011), 1798, Testacea micro- scopica aliaque, minuta ex generibus Argonauta et Nautilus, Wien, Osterreich, p. 113, pl. 22, figs. a—e. Recent, Arabian Sea. Cushman, 'J. A., 1930, U. S. Natl. Mus. Bull. 104, pt. 7, p. 46, pl. 16, figs. 1—3; pl. 17, figs. 3—5. Growth sequences indicate that this species is quite variable, depending on its size. Other species that have been established for variations of this species are included in the present concept of A. angulatus as illustrated by Cushman in the reference given above. ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO Articuline sagra D’Orbigny, 1839, Foraminiféres, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 183 (plates published separately), v. 8, pl. 9, figs. 23—26. Recent, Cuba. Astacolus ovatus Galloway and Heminway, 1941, New York Acad. Sci., Sci. Survey Puerto Rico and Virgin Islands, v. 3, pt. 4, p. 334, pl. 8, fig. 10. Upper Oligocene, Puerto Rico. Asterigerina‘ carinata D’Orbigny, 1839, Foraminiféres, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 118 (plates published separately), v. 8, pl. 5, fig. 25; pl. 6, figs. 1—2. Recent, Cuba and Jamaica. Bandy, O. L., 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 5. Recent, Gulf of Mexico. Bathysiphon sp. Fragments of this genus were found in a few samples. Bigenerina irregularis Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 4, pl. 1, figs. 16—21. Recent, Gulf of Mexico. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, figs. 8, 9. I Recent, Gulf of Mexico. Bolivina daggam’us Parker, 1955, Cushman Found. Foram. Research, Contr., v. 6, pt. 1, p. 52. Recent, Gulf of Mexico. This paper, pl. 31, fig. 9. Bolivina fragilis Phleger and Parker, 1951, idem, p. 13, pl. 6, figs. 14, 23, 24a, 24b. Recent, Gulf of Mexico. Bolivina goésii Cushman, 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 34, pl. 6, fig. 5. Recent, Atlantic Ocean. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 13, pl. 6, fig. 17. Recent, Gulf of Mexico. Bolivina pulchella (D’Orbigny) var. primitive Cushman, 1930, Florida Geol. Survey Bull. 4, p. 47, pl. 8, figs. 12a, 12b. Choctawhatchee marl, Florida. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 14, pl. 7, fig. 3. Recent, Gulf of Mexico. Bolivina striatula Cushman, 1922, Carnegie Inst. Washington Pub. 311, p. 27, pl. 3, fig. 10. Recent, Tortugas region. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 9. Recent, Gulf of Mexico. Bolivina subaenariensis Cushman var. mem'cana Cushman, 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 47, pl. 8, fig. 1. Recent, Gulf of Mexico. This paper, pl. 31, fig. 10. Buccella ha'rmai (Phleger and Parker), 1951, Geol. Soc. America Mem. 46, pt. 2, p. 21, pl. 10, figs. 11-14. Recent, Gulf of Mexico. This species is the genotype for Buccella Anderson, 1952. Bulimina marginata D’Orbigny, 1826, Annales sci. nat. sér. 1, tome 7, p. 269, pl. 12, figs. 10—12. Recent, Rimini, Italy. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 16, pl. 7, figs. 27, 28. Recent, Gulf of Mexico. Buliminella elegantissima (D’Orbigny), 1839, Voyage dans l’Amérique méridionale, v. 5, Foramiféres, pt. 5, p. 51, pl. 7, figs. 13, 14. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 17, pl. 8, figs. 3, 4. Recent, Gulf of Mexico. Canon's sagra (D’Orbigny), 1839, Foraminiferes, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 77, pl. 5, figs. 13—15. Recent, Cuba and Jamaica. andy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 30, fig. 9. Recent, Gulf of Mexico. 193 Candeina m'tida D’Oribigny, 1839, Foraminiferes, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 108, pl. 2, figs. 27—28. Recent, Cuba and Jamaica. Cushman, 1941, Amer. Jour. Sci., v. 239, pl. 1, fig. 1. Recent, Bartlett Deep. Cassidulina curvata Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 26, pl. 14, fig. 5. Recent, Gulf of Mexico. This species was very abundant in many of the samples near the outer ends of the profiles, and it was accompanied by small similar species, mainly C. laevigata D’Orbigny and C’. laevigata var. carinata Cushman. It is doubtful if the Gulf of Mexico speci- mens assigned to C. laem’gata are properly assigned. The Gulf of Mexico specimens are figured in the paper by Phleger and Parker. Cibicides deprimus Phleger and Parker, 1951, idem, p. 29, pl. 15, ~ figs. 16, 17. Recent, Gulf of Mexico. Cibicidcs pseudoungerianus (Cushman), 1922, U. S. Geol. Survey Prof. Paper 129—E, p. 97, pl. 20, fig. 9. Oligocene, Mississippi. This paper, pl. 31, fig. 8. A comparison of the specimens of this investigation with the types in the U. S. National Museum indicate that they fall within the scope of this species. C’z'bicides robertsom‘anus (H. B. Brady), 1881, Quart. Jour. Micros. 800., v. 21, p. 65. Brady, 1884 Challenger Rept., Zoology, v. 9, p. 664, pl. 95, figs. 4a*c. Phleger and Parker, 1951, Geol. Soc. America Mem. 46,. p. 31, pl. 16, figs. 10—13. Recent, Gulf of Mexico. Dentalina communis (D’Orbigny), 1826, Annales sci. nat., sér. 1, tome 7, p. 254. Recent, Adriatic Sea. Cushman, 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 75—76, pl. 12, figs. 3, 4, 15—17. Recent, Atlantic Ocean. Dimorphina sp. Only 2 or 3 specimens of this genus were found. Discorbis concinnus (H. B. Brady), 1884, Challenger Rept., Zoology, v. 9, p. 646, pl. 90, figs. 7—8. Recent, tropical seas. This paper, pl. 31, fig. 4. Discorbis floridtmus Cushman, 1922, Carnegie Inst. Washington Pub. 311, p. 39, pl. 5, figs. 11—12. Recent, Dry Tortugas Islands. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 1. Recent, Gulf of Mexico. Discorbis fioridensz’s Cushman, 1931, U. S. Natl. Mus. Bull. 104, pt. 8, p. 17, pl. 3, figs. 3—5. Recent, Atlantic Ocean. This paper, pl. 31, fig. 5. Ehrenbergina spinea Cushman, 1935, Smithsonian Misc. 0011., v. 91, no. 21, p. 8, pl. 3, figs. 10, 11. Recent, 011' Puerto Rico. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 27, pl. 14, fig. 18. Recent, Gulf of Mexico. Elphidium advenum (Cushman), 1922, Carnegie Inst. Wash- . ington Pub. 311, p. 56, pl. 9, figs. 11—12. Recent, Dry Tortugas Islands. This paper, pl. 30, fig. 18. Specimens of this study were found to agree perfectly , with the types of this species. Elphidium discoidale (D’Orbigny), 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 56, pl. 6, figs. 23—24. Recent, Cuba and Jamaica. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 30, fig. 4. Recent, Gulf of Mexico. 194 Elphidium gunteri Cole, 1931, Florida Geol. Survey Bull. 6, p. 34, pl. 4, figs. 9, 10. Pliocene, Florida. This paper, pl. 30, fig. 19. Some specimens of the variety E'. gunleri var. galvesto- nense Kornfeld were included in the counts of this species. Elphidium mexicanum Kornfeld, 1931, Stanford Univ., Dept. Geology, Contr., v. 1, no. 3, p. 89, pl. 16, figs. 1, 2. Recent, Texas and Louisiana. This paper, pl. 30, fig. 20. Elphidium poeyanum (D’Orbigny), 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de 1’Ile de Cuba, Foraminiferes, p. 55, pl. 6, figs. 25, 26. Recent, Cuba and Jamaica. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 30, fig. 6. Recent, Gulf of Mexico. ,Elphidr'um rugulosum Cushman and Wickenden, 1929, U. S. Natl. Mus. Proc. 2780, v. 75, art. 9, p. 7, pl. 3, fig. 8. Recent, 10—20 fathoms off Juan Fernandez Island, Chile, This paper, pl. 30, fig. 21. Eponides anlillarum (D’Orbigny), 1839, in Ramon de la Sagra, Histoire physique, politique ct naturelle de l’Ile de Cuba, p. 75, pl. 5, figs. 4—6. Recent, Cuba and Jamaica. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 30, fig. 8. Frondicularia sagittula Vanden Broeck, 1876, Annales Soc. Belgique Micros, V. 2, p. 113, pl. 2, figs. 12, 14. Recent, British West Indies. Cushman, 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 143, pl. 21, fig. 2. Recent, Gulf of Mexico. Gaudryina aequa Cushman, 1947, Cushman Lab. Foram. Re- search, Contr., v. 23, pt. 4, p. 87, pl. 18, figs. 18-21. Recent, South Carolina. _ Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 6, figs. 11, 12. Recent, Gulf of Mexico. The specimens figured by Phleger and Parker are quite typical of the species and should be identified as such. Gaudryina slavensis Bandy, 1949, Bull. Am. Paleontology, v. 32, no. 131, p. 29, pl. 3, fig. 8. Oligocene, Alabama. This paper, pl. 30, fig. 1. The specimens are remarkably similar to the types of this species. Both are quite distinctly triserial in the early portion of the test and the roughness of the surface is somewhat variable. The specimens may have been reworked from the Eocene. Glandulz'na comatula (Cushman), 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 83, pl. 14, fig. 5. Recent, Gulf of Mexico. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 10, pl. 5, figs. 7—9. Recent, Gulf of Mexico. The type of Glandulr‘na (G. laevigala) as sectioned and presented by D’Orbigny is strictly uniserial; hence, topotypes which are otherwise can hardly suffice for interpretation of the generic characters of Glandulma. The author considers the genus Pseudoglandulina Cushman to be a junior synonym of Glandulina. The types are well figured in Ellis and Messina (Catalogue of Foraminifera, 1940—54) and the synonymy presented by Galloway (1933) is excellent. Globigerina bulloides D’Orbigny, 1826, Annales sci. nat., sér. 1, tome 7, p. 277, Modeles, no. 17. Recent, Adriatic Sea. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 34, pl. 19, figs. 6, 7. Recent, Gulf of Mexico. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Globigerina eggeri Rhumbler, 1900, Nordische Plankton, pt. 14, Foraminiferan, p. 19, fig. 20. Recent, Atlantic and Pacific Oceans. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 34, pl. 19, figs. 8, 9. Recent, Gulf of Mexico. Globigerinella aeguilateralis (H. B. Brady), 1879, Quart. Jour. Micros. Sci., v. 19, p. 71. Brady, 1884, Challenger Rept., Zoology, v. 9, p. 605, p]. 80, figs. 18—21. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 35, pl. 19, fig. 14. Recent, Gulf of Mexico. Globigerr’noides conglobata (H. B. Brady), 1879, Quart. Jour. Micros. Sci., v. 19, p. 72. Brady, 1884, Challenger Rept., Zoology, v. 9, p. 603, pl. 80, figs. 1—5; pl. 82, fig. 5. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 35, pl. 19, fig. 15. Recent, Gulf of Mexico. Globigerinoides rubra (D’Orbigny), 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 82, pl. 4, figs. 12—14. Recent, Cuba and Jamaica. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 6. Recent, Gulf of Mexico. Globigerinoides saccultfera (H. B. Brady), 1877, Geol. Mag, v. 4, p. 535. Brady, 1884, Challenger Rept., Zoology, v. 9, p. 604, pl. 80, figs. 11—17; pl. 82, fig. 4. Recent, near New Guinea. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 35, pl. 19, figs. 17, 18. Recent, Gulf of Mexico. Globorotalia menardii (D’Orbigny), 1826, Annales sci. v. 7, p. 273; Modéles, no. 10. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 36, pl. 20, figs. 1,2. Recent, Gulf of Mexico. Globorotalr’a puncticulata (D’Orbigny), 1832, in Deshayes, G. P., Encyclopedia Methodique, Histoire naturelle des vers. Paris, tome 2, pt. 2, p. 170. Fornasini, 1898, Paleont. Italica, v. 4, p. 210, tf 5, “Figure inedite di d’Orbigny.” This paper, pl. 31, fig. 1. Globorotalr'a truncatulinoides (D’Orbigny), 1839, in Barker-Webb and Berthelot, Histoire Naturelle Iles Canaries, v. 2, pt. 2, “Foraminiferes”, p. 132, pl. 2, figs. 25—27. Recent, Canaries. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 36, pl. 20, figs. 3—7. Recent, Gulf of Mexico. Globorolalia lumida (H. B. Brady), 1877, Geol. Mag., v.4, p. 294. Brady, 1884, Challenger Rept., Zoology, v. 9, p. 692, pl. 103, figs. 4—6. Recent, near New Guinea. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 36, pl. 20, figs. 14, 15. Recent, Gulf of Mexico. Guttulina australis (D’Orbigny), 1839, Voyage dans l’Amérique méridionale, V. 5, pt. 5, Foraminiferes, p. 60, pl. 1, figs. 1—4. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 7. Recent. Gulf of Mexico. Guttulina regina Cushman is a junior synonym of G. austrah’s.‘ For additional information about this synonymy see Cushman and Ozawa (1930, p. 32). Gypsina vesicularis (Parker and Jones), 1860, Ann. Mag. Nat. History, ser. 3, v. 6, p. 31, no. 5. Recent, Australia. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 33, pl. 19, fig. 4. Recent, Gulf of Mexico. nat., ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO Hanzawaia bertheloti (D’Orbigny), 1839, in Barker-Webb and Berthelot, Histoire Naturelle Iles Canaries, v. 2, pt. 2, Foraminiferes, p. 135, pl. 1, figs. 28—30. This paper, pl. 31, fig. 6. The genus Hanzawaia was proposed in 1944 (Asano) for species such as this one with the dorsal spire more or less covered with flaplike extensions of the last whorl. The genus Cibicz'dma (Bandy, 1949) is a junior synonym of this genus. Hanzawaia concentric-a (Cushman), 1918, U. S. Geol. Survey Bull. 676, p. 64, pl. 21, fig. 3, Choctawhatchee marl, , Florida. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 29, pl. 15, figs. 14, 15. Recent, Gulf of Mexico. Hanzawaia strattom' (Applin), 1925, Am. Assoc. Petroleum Geologists Bull., V. 9, no. 1, p. 99, pl. 3, fig. 3. Miocene, Louisiana. Band‘y, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 4. Recent, Gulf of Mexico. Haplophragmoides mexicana Kornfeld, 1931, Stanford Univ., Dept. Geology, Contr., v. 1, no. 3, p. 83, pl. 13, fig. 4. Recent, littoral zone of Texas and Louisiana. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 6. Recent, Gulf of Mexico. Hiiglundina elegans (D’Orbigny), 1826, Annales sci. nat., v. 7, p. 276, no. 54. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 22, pl. 12, fig. 1. Recent, Gulf of Mexico. Karrem’ella bradyi (Cushman), 1911, U. S. Natl. Mus. Bull. 71, pt. 2, p. 67, text figs. 107a—c. Recent, Pacific Ocean. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 6, pl. 3, fig. 4. Recent, Gulf of Mexico. Lagena spp. Occasional specimens of this genus were of little value in this investigation. They are plotted together in the frequency graphs. Lagenonodosaria scalaris (Batsch), 1791, Sechs Kupfertafeln mit Conchylien des Seesandes, p. 5, pl. 2, fig. 4. This paper, pl. 30, fig. 16. Lingulma carinata D’Orbigny, 1926, Annales sci. nat., v. 7, p. 257, no. 1; Modeles, no. 26. Cushman, 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 95, pl. 19, figs. 1, 2. Recent, ofl Florida. Loxostomum mayori (Cushman), 1922, Carnegie Inst. Wash- ington Pub. 311, v. 7, p. 27, pl. 3, figs. 5, 6. Recent, ofl’ Florida. This paper, pl. 31, fig. 11. Loxostomum subspinescens (Cushman), 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 48, pl. 7, fig. 5. This paper, pl. 31, fig. 12. This species seems to be rather variable in the spinose character of the walls. The larger individuals are characterized almost entirely by the terminal aperture, and the species is placed, therefore, in Loxostomum rather than Bolivina, its original designation. Marginulina advena (Cushman), 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 134, pl. 39, figs. 1—4. Recent, off Florida. This paper, pl. 30, fig. 15. This species was originally placed in Vaginulina by Cushman. It is compressed in the early part, but the adult is nearly always oval in cross section. It is placed, therefore, in Marginulina. The types were examined in the U. S. National Museum, and they form the basis for the change. The variation observed in the type specimens is considered to be the result of dimorphism. 195 Marginulina hantkem' Bandy, 1949, Bull. Am. Paleontology, v. 32, no. 131, p. 46, pl. 6, fig. 9. Eocene, Alabama. Some specimens occur in the present investigation that are very similar to this species. AS noted in the original publication, M. hamkem' was a new name for the homonym M. subbullata Hantken. Marginulz'nopsz's densicostata Thalmann, 1937, Eclogae Geol. Helvetiae, Lausanne, Suisse, v. 30, p. 347, pl. 21, fig. 2. Recent, West Indies. Marginulinopsis subaculeata (Cushman), 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 123, pl. 34, fig. 2. Recent, Gulf of Mexico. This paper, pl. 30, fig. 14. Nodobaculam’ella atlantica Cushman and Hanzawa, 1937, Cush- man Lab. Foram. Research Contr., v. 13, pt. 2, p. 42, pl. 5, figs. 7, 8. Recent, eastern coast of the U. S. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 4. Recent, Gulf of Mexico. Nodobaculariella mexicana (Cushman), 1922, Carnegie Inst. Washington Pub. 311, p. 70, pl. 11, figs. 7, 8. Recent, Tortugas Islands. This paper, pl. 29, fig. 7. This species was originally described under Arliculina; however, it lacks 'the miliolid chamber arrangement in the early part, the chambers being in one plane through- out, and it is placed, therefore, in the genus Nodoba- culam’ella Cushman. Nonion afiim‘s (Reuss). 1851, Deutsche Geol. Gesell., Zeitsehr., Berlin, Band 3, p. 72, pl. 5, fig. 32. Oligocene, Germany. Bandy, 1953, Jour. Paleontology, V. 27, no. 2, p. 177, pl. 21, fig. 8 (given incorrectly as N. barleeanus). Recent, off Point Conception, Calif. This paper, pl. 30, fig. 17. Nam’onella atlantz‘ca Cushman, 1947, Cushman Lab. Foram. Research Contr., v. 23, pt. 4, p. 90, pl. 20, figs. 4, 5. Recent, Florida. ' Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 10. Recent, Gulf of Mexico. Nom'onella grateloum' (D’Orbigny), 1826, Annales sci. nat., v. 7, p. 294, no. 19; in Ramon de la Sagra, Histoire physique, politique et naturelle de 1’Ile de Cuba, 1839, p. 46, pl. 6, figs. 6—7. Recent, Cuba and Jamaica. Cushman, 1939, U. S. Geol. Survey Prof. Paper 191, p. 21, pl. 6, figs. 1—7. Orbulina universa D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 3, pl. 1, fig. 1. Recent, Cuba and Jamaica. Pavam'na atlantica Cushman, 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 51, pl. 19, fig. 1. Recent, Florida and West Indies. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 17, pl. 8, figs. 6, 7. Recent, Gulf of Mexico. Peneroplis proteus D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 60, pl. 7, figs. 7—11. Recent, Cuba and Jamaica. Cushman, 1930, U. S. Natl. Mus. Bull. 104, pt. 7, p. 37, pl. 13, figs. 1—17. Recent, western Atlantic._ Planorbulina mediterranensis D’Orbigny, 1826, Annales sci. nat., v. 7, p. 280, no. 2, pl. 14, figs. 4—6; Modeles, no. 79. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 3. Recent, Gulf of Mexico. Planulina foveolata (H. B. Brady), 1884, Challenger Rept., Zoology, v. 9, p. 674, pl. 94, fig. 1. Recent, near Bermuda. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 33, pl. 18, figs. 9, 10. Recent, Gulf of Mexico. 196 The figure of the type appears to represent a specimen that is much thicker than the average; however, speci- mens compared with the type and paratypes are reported to be the same species. Planulina ornate (D’Orbigny), 1839, Voyage dans l’Amérique p méridionale, v. 5, pt. 5, Foraminiferes, p. 40, pl. 6, figs. 7—9. Recent, off the coast of Chile. Bandy, 1953, Jour. Paleontology, v. 27, no. 2, p. 177, pl. 24, 1 fig. 4. Recent, off the coast of California. ‘ Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 2. Recent, Gulf of Mexico. Young specimens have a truncate edge, whereas adults 1 tend to develop a sharp edge. P. exorna Phleger and Parker (1951) is considered to be a junior synonym of P. ornate by this author. ‘Polymorphina pulchella (D’ Orbigny), 1839 in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 129, pl. 2, figs. 4—6. Recent, Cuba and Martinique. Cushman, 1922, Carnegie Inst. Washington Pub. 311, p. 33, pl. 4, figs. 7, 8. Recent, Tortugas region. Pmoepom‘des cr'ibrorepandus Asano and Uchio, 1951, in Stach, ‘ Illustrated catalogue of Japanese Tertiary smaller For- aminifera, pt. 14, Rotaliidae, p. 18, tfs. 134, 135. Pliocene, Japan. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 30, fig. 3. Recent, Gulf of Mexico. This species is commonly identified as Eponides repandus (Fichtel and Moll) ; however, the pores on the apertural face are distinctive of the genus Poroepam'des. The type figure of Epom’des (E. repandus) does not exhibit this character. Proteonina atlantica Cushman, Research Special Pub. 12, p. 5, pl. 1, fig. 4. the New England coast. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254~F, pl. 28. fig. 1. Recent, Gulf of Mexico. Pseudoclavulina consians Bandy, n. sp., this paper, p. 198, pl. 30, fig. 5. Pullem’a quinqueloba (Reuss), 1851, Deutsche geol. Gesell. Zeitschr., Band 3, p. 71, pl. 5, fig. 31. Oligocene, Germany. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 29, pl. 15, figs. 12, 13. Recent, Gulf of Mexico. Pulleniatina obliquz‘loculala (Parker and Jones), 1865, Philos. Trans, v. 155, p. 368, pl. 19, fig. 4. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2,p. 35, pl. 19, figs. 19, 20. Recent, Gulf of Mexico. Pyrgo comata (Brady), 1881, Quart. Jour. Micros. Soc., v. 21, p. 45. ‘ Brady, 1884, Challenger Rept., Zoology, V. 9, p. 144, pl. 3, 1 fig. 9. Recent, cosmopolitan. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 28, fig. 9. Recent, Gulf of Mexico. Pyrgo nasuta Cushman, 1935, Smithsonian Misc. Coll., ‘ no. 21, p. 7, pl. 3, figs. 1—4. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 7, pl. 3, figs. 12-14. Recent, Gulf of Mexico. ‘Pyrgo peruuitma (D’Orbigny), 1839, Voyage dans l’Amerique méridionale, v. 5. pt. 5, Foraminiferes, p. 65, pl. 9, figs. 1—3. Recent, ofi’ Peru. ‘Quinqueloculina agglutinans D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 195, pl. 12, figs. 11—13. Recent, Cuba and 1 Jamaica. 1944, Cushman Lab. Foram. Recent, off V. 91, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Many subsequent figures of this species do not show the square cross section of the chambers which is quite characteristic of this species. Quinqueloculina akneriana D’Orbigny, 1846, Foram. Fossiles Vienne, p. 290, pl. 18, figs. 16—21. Middle Miocene, Vienna. Quinquelocuh’na bicostata D’Orbigny, 1839, idem., p. 195, pl. 12, figs. 8—10. Recent, Cuba and Jamaica. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 7, pl. 3, fig. 15. Recent, Gulf of Mexico. Quinqueloculina bosciana D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 191, pl. 11, figs. 22—24, Recent, Cuba and Jamaica. This paper, pl. 29, fig. 4. Quinqueloculina compta Cushman, 1947, Cushman Lab. Foram. Research Contr., v. 23, pt. 4, p. 87, pl. 19, fig. 2 Recent, off coast of Florida. Bandy, 1954, U. S. Geol. Survey Prof. Paper, 254—F, pl. 28, fig. 2. Recent, Gulf of Mexico. This paper, pl. 29, fig. 5. Quinqueloculma dutemplei D’Orbigny, 1846, Foram. Fossiles Vienna, p. 294, pl. 19, figs. 10—12. Middle Miocene, Vienna. This paper, pl. 29, fig. 9. Quinqueloculina horrida Cushman, 1947, Cushman Lab. Foram. Research Contr., V. 23, p. 88, pl. 19, fig. 1. Recent, coastal waters of South Carolina. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 7, pl. 3, figs. 18, 19. Recent, Gulf of Mexico. Quinqueloculina jugosa Cushman, 1944, Cushman Lab. Foram. Research, Special Pub. 12, p. 13, fig. 15. Recent, ofi‘ Massachusetts. This paper, pl. 29, fig. 8. Quinqueloculina lamarckiana D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 189, pl. 11, figs. 14, 15. Recent, Cuba and‘ Jamaica. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 28, fig. 3. Recent, Gulf of Mexico. Quinqueloculina poeyana D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de 1’Ile de Cuba, p. 191, pl. 11, figs. 25—27. Recent, Cuba and Jamaica. This paper, pl. 29, fig. 6. Quinqueloculina polygona D’ Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de lI’le de Cuba, p. 198, pl. 12, figs. 21—23. Recent, Cuba and Jamaica. Cushman, 1929, U. S. Natl. Mus. Bull. 104, pt. 6, p. 28, pl. 3, fig. 5. Recent, West Indies. Quinqueloculina rhodiensis Parker, 1953, Cushman Foundation Foram. Research Special Pub. 2, p. 12, pl. 2, figs. 15—17. Recent, Gulf of Mexico. This species is recorded by many authors as Q. costata. D’Orbigny, a homonym, and Parker corrected the name in the cited reference. This paper, pl. 29, fig. 10. Raphanulina tuberculata (D’Orbigny), 1846, Foram. Fossil Vienne, p. 230, pl. 13, figs. 21, 22. Middle Miocene, Vienna. Bandy, 1949, Bull. Am. Paleontology, v. 32, no. 131, p. 70, pl. 10, fig. 6. Eocene, Alabama. Rectobolivina advena (Cushman), 1922, Carnegie Inst. Wash- ington Pub. 311 (v. 17), p. 35, pl. 5, fig. 2. Recent. Tortugas region. ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 8. Recent, Gulf of Mexico. Reophax scorpiurus Montfort, 1808, Conchylologie Systematique v. 1, p. 331, fig. p. 330. Recent, Adriatic. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 3, pl. 1, figs. 7, 8. Recent, Gulf of Mexico. Reussella atlamica Cushman, 1947, Cushman Lab. Foram. Research Contr. v. 23, pt. 4, p. 91, pl. 20, figs. 6, 7. Recent, off southeastern coast of the U. S. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 31, fig. 7. Recent, Gulf of Mexico. Robulus calcar (Linne), Systematique Naturae, ed. 10, 1758, v. 1, p. 708. Cushman, 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 115, pl. 30, fig. 7, pl. 31, figs. 4, 5. Recent, western Atlantic, Caribbean, and Gulf of Mexico. This paper, pl. 30, fig. 11. Robulus stephensoni Cushman, 1939, Cushman Lab. Foram. Research Contr., v. 15, p. 90, pl. 16, figs. 2, 3. Upper Cretaceous, Tennessee. ' This species was very rare and it is almost exactly like the types of this species from the Cretaceous. Perhaps the specimens of this investigation are reworked from Cretaceous bottom outcrops. Robulus suborbicularis Parr, 1950, British Australian, New Zealand, Antarctic Research Exped., Rept., series B (Zoology and Botany), v. 5, pt. 6, p. 321, pl. 11, figs. 5, 6. Recent, Tasmania. This paper, pl. 30, fig. 12. . Rotorbinella basilica Bandy, n. sp., this paper, p. l99,pl. 31, fig. 3. Saracenaria ampla Cushman and Todd, 1945, Cushman Lab. Foram. Research Special Pub. 15, p. 31, pl. 5, figs. 5—6. Miocene, Jamaica. Schenckiella occidentalis (Cushman), 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 87, pl. 17, figs. 1, 2. Recent, Gulf of Mexico. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 6, pl. 3, figs. 5—7. Recent, Gulf of Mexico. Sigmoilina subpoeyana (Cushman), 1922, Carnegie Inst. Wash- ington Pub. 311, p. 66; U. S. Natl. Mus. Bull. 104, pt. 6, p. 31, pl. 5, fig. 3. Recent, West Indies. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 1. Recent, Gulf of Mexico. This paper, pl. 29, fig. 1. This’species was originally described as Ouinquelo- culina, and many authors have confused it also with Spiroloculina antillarum D’Orbigny. Sigmoilina tenuis (Czjzek), 1848, Haidinger’s Naturwiss. Abh., v. 2, p. 149, pl. 13, figs. 31—34. Miocene, Austria. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 8, pl. 4, fig. 7. Recent, Gulf of Mexico. Siphom'na bradyana Cushman, 1927, U. S. Natl. Mus. Proc., V. 72, art. 20, p. 11, pl. 1, fig. 4. Recent, West Indies. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 24, pl. 12, figs. 13, 14. Recent, Gulf of Mexico. Siphotextularia olianaensis Colom and Ruiz de Gaona, 1950, Spain Inst. Inv. Geol. “Lucas Mallada,” Estud. Geol., v. 6, no. 12, p. 413, fig. p. 415, tf. 16. Eocene, Spain. This paper, pl. 30, fig. 9. Sorites crbitolitoides (Hofker), 1930, Siboga Report II, p. 149, pl. 55, figs. 8, 10, 11; pl. 37, figs. 4, 6; pl. 58, figs. 1—5; pl. 61, figs. 3, 14. Recent, Florida, South Carolina, and Netherlands Indies. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 5. Recent, Gulf of Mexico. 197 Sphaeroidina bulloides D’Orbigny, 1826, Annales sci. nat., v. 7, p. 267, no. 1, Modéles, no. 65. Gushman, 1924, U. S. Natl. Mus. Bull. 104, pt. 5, p. 36, pl. 7, figs. 1—6. Recent, northeastern coast of U. S. Spiroloculina depressa D’Orbigny, 1826, Annales sci. nat., ser. 1, tome 7, p. 298; Modeles, no. 92. Cushman and Todd, 1944, Cushman Lab. Foram. Research Special Pub. 11, p. 28, pl. 1, figs. 1, 6; pl. 5, figs. 1—9. This paper, pl. 29, fig. 2. Spiroplectammina floridana (Cushman), 1922, Carnegie Inst. Washington Pub. 311, v. 17, p. 24, pl. 1, fig. 7. Recent, Tortugas region. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 4, pl. 1, figs. 25, 26. Recent, Gulf of Mexico. Stomatorbina concentrica (Parker and Jones), 1864, Trans. Linnean Soc. Zool., v. 24, p. 470, pl. 48, fig. 14. Recent. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 22, pl. 12, fig. 2. Recent, Gulf of Mexico. Streblus sobrinus (Shupack), 1934, Am. Mus. Novitates, no. 737, p. 6, fig. 4. Pleistocene and Recent, New York Harbor. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 30, fig. 7. Recent, Gulf of Mexico. Streblus tepidus (Cushman), 1926, Carnegie Inst. Washington Pub. 344, p. 79, pl. 1. Recent, Puerto Rico. This paper, pl. 31, fig. 2. Textularia candeiana D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 143, pl. 1, figs. 25—27. Recent, Cuba and Jamaica. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 2. Recent, Gulf of Mexico. Textularia cam'ca D’Orbigny, 1839, in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, p. 143, pl. 1, figs. 19, 20- Recent, Cuba and Jamaica. This paper, pl. 30, fig. 6. Textulam'a foliacea Heron-Allen and Earland var. occidentalis Cushman, 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 16, pl. 2, fig. 13. Recent, Cuba. This paper, pl. 30, fig. 10. Textularia mayori Cushman, 1922, Carnegie Inst. Washington Pub. 311, v. 17, p. 23, p]. 2, fig. 3. Recent, Tortugas region. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 29, fig. 3. Recent, Gulf of Mexico. Textulan'a pseudotrochus Cushman, 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 21, pl. 5, figs. 1—3. Recent, off southern coast of Florida. This paper, pl. 30, fig. 7. Textularia secasensis Cushman and McCulloch, 1940, Allan Hancock Pacific Exped. Pub., v. 6, no. 2, p. 141, pl. 16, fig. 24. Recent, eastern Pacific. Textulariella barrettii (Jones and Parker), 1876, Soc. Malacolo- gique de Belgique, Annales (Mem.), tome 11 (ser. 2, tome 1), p. 99, fig. p. 99. Tertiary and Recent, West Indies. Cushman, 1922, U. S. Natl. Mus. Bull. 104, pt. 3, p. 20, pl. 3, figs. 3—6. Recent, Key West and West Indies. Triloculina afim‘s D’Orbigny, 1852, Prodrome de Paleontologie stratigraphique univ. des animaux mollusques et rayonnes, v. 3, p. 161. Cushman, 1932, U. S. Natl.‘Mus. Bull. 161, pt. 1, p. 58—59 pl. 13, fig. 4. Recent, tropical Pacific. The angular character of the edges serves to distinguish this species, although in many cases the two species have probably been included under T. trigonula. 198 Triloculina bellatula Bandy, n. sp., this paper p. 198, pl. 29, fig. 11. Probably Miliammina fusca (H. B. Brady) has been included with the frequency counts of this species; however, most of the specimens were calcareous with a bifid tooth and belong under this new species. Triloculina linneiana D’Orbigny var. comis Bandy, n. this paper, p. 198, pl. 29, fig. 12. Triloculina trigonula (Lamarck), 1807, Annales Nat. Hist. Paris Mus., v. 5, p. 351, no. 3, tome 9, pl. 17, fig. 4. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, pl. 28, fig. 5. Recent, Gulf of Mexico. Trachammina laevigata Cushman and Bronniman, 1948, Contr. Cushman Lab. Foram. Research, V. 24, pt. 2, p. 41, pl. 7, figs. 21, 22. Recent, Mangrove swamp, Trinidad. This paper, pl. 29, fig. 13. Troohammma simplissima Cushman and McCulloch, 1948, Cushman Lab. Foram. Research Contr., v. 24, p. 76. New name for T. pacified var. simplex. Recent, off Lower California. This paper, pl. 29, fig. 14. Um‘gem‘na bellula Bandy, new, name, this paper, p. 199, pl. 31, fig 13. Uvigerina flintii Cushman, 1923, U. S. Natl. Mus. Bull. 104, pt. 4, p. 165, pl. 42, fig. 13. Recent, West Indies. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 18, pl. 8, figs. 15, 16. Recent, Gulf of Mexico. Uvz'gem'na hispido-costata Cushman and Todd, 1945, Cushman Lab. Foram. Research Special Pub. 15, p. 51, pl. 7, figs. 27, 31. Miocene, Jamaica. Phleger and Parker, 1951, Geol. Soc. America Mem. 46, pt. 2, p. 18, pl. 8, figs. 17—21, 23. Recent, Gulf of Mexico. This paper, pl. 31, fig. 14. Valvulineria sp. One or two specimens of this genus were found and seem to be undescribed. Because of the lack of specimens and its lack of importance in this study, no attempt was made to establish a new species at this time. Virgulina schreibersiana Czjzek, Haidinger’s Naturwiss. Abb., Band 2, p. 11, pl. 13, figs. 18—21. Miocene, Vienna Basin. Bandy, 1954, U. S. Geol. Survey Prof. Paper 254—F, p. 139, pl. 31, fig. 10. Recent, Gulf of Mexico. var., SYSTEMATIC PALEONTOLOGY Ecologie studies of Foraminifera in the eastern Gulf of Mexico off the coast of Florida and Alabama reveal 3 new species, 1 new variety, and 1 homonym. These five are figured and described herein in order to make the names available for the ecologic studies. The types are catalogued and deposited in the U. S. National Museum, Washington, D. C. The classifica- tion used is that of Galloway (1933). Family ATAXOPHRAGMIIDAE Sehwager, 1877 Genus PSEUDOCLAVULINA Cushman, 1936 Pseudoclavulina constans Bandy, n. sp. Plate 30, figure 5. 1951. Pseudoclavulina mem'cana Phleger and Parker (not Cush- man), Geol. Soc. America Mem. 46, pt. 2, pl. 2, figs. 15, 16. Test of moderate size for the genus, averaging about 1 mm in length; early triserial portion roughly trihedral with closely appressed chambers, later uniserial part SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY with from 3 to 5 closely appressed chambers which are shorter than they are broad at first and then become about as long as they are broad near the apertural end; sutures slightly depressed in the uniserial portion, flush with the surface in the triserial portion; wall fairly roughly finished, of calcareous grains for the most part; aperture terminal, rounded to ovate with a very Short neck. Length, 1.00 mm; breadth, 0.30 mm. , This species differs from Pseudoclavulz'na mem'ccma (Cushman) (1922b, p. 83, pl. 16, figs. 1—3) in that the chambers are much more closely appressed in the uni— serial portion, the aperture is at the end of a short tubular neck, whereas there is a much coarser and eonically shaped neck in P. mexicana, and also the early trihedral portion is much smaller and much less distinct- ly trihedral than in Cushman’s species. Holotype (USNM 624349) from station 2168, 62 fathoms, off the west coast of Florida, lat. 26°08.6' N., long. 83°54.2’ W. Family MILIOLIDAE D’Orbigny, 1839 Genus TRILOCULINA D’Orbigny, 1826 Triloculina bellatula Bandy, n. sp. Plate 29, figure 11. Test elongate in side view, breadth about three-fifths the length; edges rounded in apertural View; chambers distinct; wall calcareous with arenaceous coating; apertural end does not project beyond test; aperture circular with small bifid tooth. Length, 0.55 mm; breadth, 0.30 mm; thickness, 0.20 mm. This species is rare and is quite distinctive in its small size, in that the aperture does not project, and in the presence of the small bifid tooth. Triloculina tortuosa Cushman (1921b) is larger and has a long neck without a tooth. Holotype (USNM 624397) from station 442, 28 feet, off the west coast of Florida, lat. 27°36.65’ N., long. 82°39.32’ W. Triloculina linneiana D’Orbigny var. comis Bandy, 11. var. Plate 29, figure 12 Test elongate ovate in side view, breadth about one- half the length; edges round in apertural View ; chambers distinct, rounded in cross section; wall ornamented with moderately heavy longitudinal costae, about 20 to 30 on the last chamber; apertural end projecting, and flar- ing slightly; aperture rounded with prominent bifid tooth which usually projects slightly. Length, 1.60 mm; breadth, 0.80 mm; thickness, 0.60 mm. This variety is similar in general to T. linneiana D’Orbigny (1839, p. 172). It differs from D’Orbigny’s species in possessing more costae which are not as strongly developed and in being much larger. This new variety differs from T. linneiana var. caloosahat— ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO cheensis Cole (1931, p. 25) in having a long flaring aperture with a prominent bifid tooth and the costae are not as prominent. Holotype (USNM 624398) from station 1214, 42 feet, off the west coast of Florida, lat. 27°29.6’ N., long. 82°54.0’ W. Family ROTALIIDAE Reuss, 1860 Genus ROTORBINELLA Bandy, 1944 Rotorbinella basilica Bandy, n. sp. Plate 31, figure 3 Test biconvex, dorsal side sometimes more convex and sometimes less convex than the ventral side; edge angled, may be abruptly rounded in the latter part of the final whorl; about 6 to 8 chambers in the final whorl, enlarging fairly rapidly as added; inner ends of chambers with translucent thickening on ventral side; dorsal spire with no secondary thickening, showing about 12 cham- bers in all comprising the whorl and one-half that make up the test; dorsal sutures curved, oblique, and slightly depressed, especially in the later part of the test; ventral sutures only slightly curved and oblique, much depressed, especially in the later part of the test; wall with medium—sized perforations; umbilicus‘with a fairly large distinct single boss; aperture a low arched opening extending from near the edge into the umbilicus with an upper lip. Diameter, 0.25 mm; thickness, 0.11 mm. The species differs from Rotorbinella versiformis (Bandy) (1953, p. 179) in lacking the dorsal thickening of that species, in being nearly biconvex, and in that the test is made up of only about 1% whorls. Rotorbinella. basslem' (Cushman and Cahill) (1933, p. 32) difiers in that it possesses several whorls, it is nearly planoconvex, it possesses distinct sutural reentrants, and it is larger. Rotorbinella, translucens (Phleger and Parker) (1951, p. 24) differs also in possessing several whorls and in having a small or poorly defined umbilical plug. Holotype (USNM 624375) from station 1425, 23 fathoms, off the west coast of Florida, lat. 26°17.2’ N., long. 84°03.3’ W. Family UVIGERINIDAE Galloway and Wissler. 1927 Genus Uvigerina D’Orbigny, 1826 Uvigerina bellula Bandy, new name Plate 31, figure 13 1896. Uvigerz'na auberiana D’Orbigny var. laevis Goés, Bull. Mus. Comp. Zool., V. 29, p. 51, pl. 4,. figs. 71—74, 1896. (This variety is a homonym of U. Zaevis Ehrenberg, 1845, K. Preuss Akad. VViss. Berlin, p. 377, 317.) Test small, elongate fusiform, greatest width about the middle; periphery lobulate; chambers inflated, three to a whorl in the early portion, assuming a very loose triserial arrangement in the later part; early chambers about as high as wide, later ones becoming higher than 199 wide; wall finely perforate and smooth excepting for a slight tendency to become hispid in the early part of the test; aperture terminal, round, with a prominent neck and lip. Length, 0.40 mm,; diameter, 0.10 mm. This species is well known, and its presence in the Gulf of Mexico has been reported by Phleger and Parker (1951, p. 18). Ehrenberg’s U. laem's has priority, and so this species of Goes is renamed herein. Hypotype (USNM 624402) from station 2166, 69 fathoms, off the west coast of Florida. lat. 26°07.4’ N., long. 83°57.7’ W. TABLE 4‘Locations and depths of samples Latitude Longitude Depth Sample no. (N.) (W.) (lee!) 30°03.0’ 88°03.6’ ('19 30°02.5’ 88°03.6’ 69 30°01 .8’ 88°03.6' 69 30°00.9’ 88°03.7’ (>9 29°57.8’ 88°03.7’ 78 29°54.6’ 88°03.7’ 99 29°46.7’ 88°03.8’ 108 29°43.0’ 88°03.9’ 117 29°40.4’ 88°04.0' 123 29°37.5’ 88°04.1' 120 29°35.3’ 88°04.1’ 120 29°33.7’ 88°04.2’ 129 29°32.4’ 88°04.3’ 129 29°30.8’ 88°04.3’ 129 29°29.1’ 88°04.4’ 1‘35 29°27 .3’ 88°04.5’ 159 29°24.9’ 88°04.6’ 189 29°20.3’ 88°04.9' 309 26°11.2’ 83°44.2' 249 26°11.9’ 83°39.9' 207 26°12.2’ 83°37.3’ 207 26°12.3’ 83°35.6’ 207 26°12.6’ 83°34.0’ 201 29°11.6’ 85°45.7’ 255 39°16.2’ 85°45.7’ 171 29°19.4’ 85°45.6’ 141 29°22.4’ 85°45.6’ 117 29°23.9’ 85°45.6’ 105 29°26.1’ 85°45.5’ 105 29°26.6’ 85°45.5’ 105 29°31.5’ 85°45.4’ 10:) 29°36.2’ 85°45.3’ 117 29°39.5' 85°45.3’ 117 29°46.3’ 85°45.2’ 105 29°48.1’ 85°45.1’ 111 29°52.8’ 85°45.l’ 105 30°00.2' 85°45.0’ 87 30°03. ] ’ 85°44.9’ 81 30°04.2’ 85°44.9’ 69 30°04.5’ 85°44.9’ 69 30°04.5’ 85°44.9’ 69 30°05.5’ 85°46.4’ 63 30°07.55’ 85°43.4’ 39 30°08.55’ 85°41.9’ 39 27°32.25' 82°43.46’ 10 27°33.61’ 82°43.81' 12 27°34.25' 82°43.84' 21 27°36.33’ 82°44.69’ 45 27°35.88' 82°45.23’ 30 27°35.70’ 82°45.30’ 7 27°33.37’ 82°45.36’ 8 27°35.00’ 82°45.44’ 9 27°34.62’ 82°45.19’ 21 27°34.53' 82°44.80’ 20 27°34.87' 82°39.80' 11 27°34.97' 82°39.19’ 10 27°34.18’ 82°38.89’ ll 27°33.80’ 82°39.12’ l3 27°33.41’ 82°39.37' l4 27°32.96’ 82°39.96’ 13 27°32.64’ 82°39.87’ 10 27°32.47’ 82°40.16’ 10 27°32.41’ 82°40.55’ 8 27°32.35' 83°41.04’ 11 27°32.26’ 82°41 .66’ ll 27°32.20’ 82°42.10’ 9 27°36.40’ 82°43.51’ 35 27°36.48’ 82°42.17’ 28 27°36.63’ 82°40.78’ 26 27°36.65’ 82°39.32’ 28 27°36.76’ 82°37.58’ 13 27°38.29’ 82°34.91’ 13 27°38.63’ 82°34.76’ 14 27°38.65’ 82°35.15’ 20 27°38.67’ 82°35.58’ 20 27°38.70’ 82°36.08’ 26 27°38.73’ 82°36.78’ 30 27°38.73’ 82°37.27’ 26 27°38.73’ 82°37.78’ 25 27°38.72’ 82°38.27’ 24 200 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 4—Locations and depths of samples—Continued Sample no. Latitude (NJ 27°38.73’ 27°38.64’ 27°38.06’ 27°38.83’ 27°39.29’ 27°39.73' 27°40‘31’ 27°44.30’ 27°44.43’ 27°44.56’ 27°46.39’ 27°46.66’ 27°47.06’ 27°47.74’ 27°48.94’ 27°49.97’ 27°50.95’ 27°5217fi’ 27°53.32’ 27°53.98’ 26°44‘78’ 26°44.64’ 26°44.72’ 26°44.76’ 26°45.24’ 26°45.60’ 26°45.85’ 26°46.00’ 26°46.1.5’ 26°46.23’ 26°47.31’ 26°48.63’ 26°50.64’ 26°49.15’ 26°47.64’ 26°47.53’ 26°49.34’ 26°50.69’ 26°52.81’ 26°55.33’ 26°56.03’ 26°41.00’ 26°38.35’ 26°36.82’ 26°35.38’ 26°33.17’ 26°31.92’ 26°29.39’ 26°28.55’ 26°28.12’ 26°27.53’ 26°29.41’ 26°30.88’ 26°31 .46’ 26°32.54’ 26°33.39’ 26°34.16’ 26°36.97’ 26°38.21’ 26°40.35’ 26°41 .49’ 26°20.48’ Longitude (W-) 82°38. 86' 82°39 ,34’ 82°26.97’ 82°26.66’ 82°25.79’ 82°27.30’ 82°04.18’ 82°07.48’ 82°07.92’ 82°08.52' 82°09.13’ 82°09.73’ 82°08.76’ 82°07.10’ 82°06.81’ 82°06.50’ 82°06.16’ 82°05.08’ 82°05.18’ 82°05.26' 82°05.58’ 82°06.52' 82°06.06' 82°11 .72’ 82° 12.43’ 82°12.21’ 82°11.52’ 82°10.18’ 82°09.43’ 82°07.78’ 82°03.35’ 82°03.00’ 82°01.92’ 82°00.87’ 82°00.93’ 82°00.32’ 81 °56.42’ 81 °55.92’ 81°55.34’ 81 °53.78’ 81 °53.25’ 81°50.74’ 81°49.27’ 81 °52.94’ 81 °53.49’ 81°54.05’ 81°54.60’ 81°55.15’ 81°55.69’ 81°56.91’ 81°57.92’ 82°02.89' 82°03,44’ 82°03.99’ 82°04.54’ 82°07.29’ 82°07.84’ 82°08.96' 82°03.04’ 81°59.80’ 82°12.73’ 82°11.74’ 82°10.42’ 82°46.82’ 82°47.72’ 82°49.96’ 82°53.5' 82°55.l’ 82°56.5’ Depth (feet) wamzsmsMaw23888ssgaafiaszmmssasq$5535“qu TABLE 4—Locations and depths of samples—Continued Sample no. Latitude (N) 28°07.9’ 28°07.9’ 28°07.8’ 28°07.8’ Longitude ( W. 82°57.0’ 82°57. 6’ 82°58. 7 ’ 82°59.0’ 82°59.8’ 83°01 . 8' Depth (feet) ECOLOGY OF FORAMINIFERA, NORTHEASTERN GULF OF MEXICO TABLE 4—Locat1izms and depths of samples—Continued Latitude Longitude Depth Sample no. (N.)- (W.) (feet) 27°18.7’ 84°13.5’ 276 27°18.4’ 84°17.8’ 336 27°19.0’ 84°21.5’ 387 27°18.6’ 84°25.9’ 438 26°18.4’ 82°13.4’ 42 26°18.4’ 82°15.9’ 42 26°18.9' 82°17.3’ 45 26°19.2’ 82°18.9’ 51 26°19.7' 82°20.3' 48 26°20.0' 82°22.1’ 51 26°19.7' 82°22.8’ 57 26°19.2’ 82°23.9' 60 26°18.9' 82°24.8’ 60 26°19.0’ 82°26.0’ 6O 26°19.0’ 82°26.9’ 66 26° 19.0’ 82°28.0’ 66 26°19.0’ 82°29.1’ 72 26°18.9’ 82°30.2’ 78 26°18.9’ 82°31.3’ 78 26°18.9’ 82°32.7’ 78 26°18.8’ 82°33.9’ 84 26°18.4’ 82°34.9’ 84 26°18.2’ 82°36.0' 90 26°18.0' 82°37.3’ 90 26° 17.5' 82°39.7’ 90 26°17. 2’ 82°40.8’ 90 26°17.0' 82°42.0’ 93 26°16.9’ 82°46.l’ 96 26°17.1’ 82°47.2’ 99 26°17.4’ 82°48.3’ 102 26°17.7’ 82°49.4’ 105 26°18.0’ 82°50.4’ 108 26°18.2’ 82°51.9’ 108 26°18.2’ 82°52.8’ 114 26°18.1’ 82°53.7’ 117 26°18.0’ 82°54.7’ 123 26°18.0' 82°55.5’ 126 26°17.9’ 82°56.4’ 132 26°18.2’ 82°00.0’ 138 26°18.0’ 83°01.0’ 138 26°17.6’ 83°01.7’ 138 26°17.4’ 83°02.4’ 138 26°17.2’ 83°03.3’ 138 26°17.0’ 83°04.4’ 144 26° 16.1’ 83°06.1' 147 26°15.2’ 83°07.9' 150 26° 14.9’ 83°09.5’ 156 26° 14.6’ 83°11.3’ 162 26° 14.4’ 83°13.2’ 168 26°14.4’ 83°15,2’ 171 26°14.4’ 83°17.2’ 174 26°14.5’ 83°19.2' 177 26°13.9’ 83°22.2’ 183 26°02.1’ 84°17.0’ 582 26°02.5’ 84°15.0’ 558 26°02.9’ 84°13.0’ 546 26°03.1’ 84°10.9’ 522 26°03.5’ 84°08.9’ 516 26°04.0’ 84°06.6’ 492 26°04.6’ 84°04.8’ 474 26°05.3’ 84°03.0’ 462 26°06.0’ 84°01.2’ 450 26°06.6’ 83°59.5’ 426 26°07.4’ 83°57.7’ 414 26°08.0’ 83°56.0’ 393 26°08.6’ 83°54.2’ 372 26°09.3’ 83°52.5’ 348 26°10.0’ 83°50.8’ 327 26°10.6’ 83°49.0’ 306 26°11.3’ 83°47.4’ 288 27°17.8' 84°38.0’ ' 600 LITERATURE CITED Acosta, J. T., 1940, Algunos Foraminiferos nuevos de las costas Cubanas: Torreia, Mus. Poey, Universidad de la Habana, Cuba, no. 5, p. 3—6. Andersen, H. V., 1952, Buccella, a new genus of the rotalid Foraminifera: Wash. Acad. Sci. Jour., v. 42, no. 5, p. 143-151. Asano, Kiyoshi, 1944, Hanzawaia, a new genus of Foraminifera from the Pliocene of Japan: Geol. Soc. Japan Jour., Tokyo, v. 51, no. 606, p. 97, 98. Bandy, O. L., 1949, Eocene and Oligocene Foraminifera from Little Stave Creek, Clarke County, Ala.: Bull. Paleontology, v. 32, no. 131, 210 p. 1951, Bathymetric distribution of some shallow-water Foraminifera in the Gulf of Mexico [abs]: Geol. Soc. America Bull., v. 62, no. 12, pt. 2, p. 1521. 201 1953, Ecology and paleoecology of some California Foraminifera; Part 1, The frequency distribution of Recent Foraminifera off California: Jour. Paleontology, v. 27, n0. 2, p. 161—182. 1954, Distribution of some shallow-water Foraminifera in the Gulf of Mexico: U. S. Geol. Survey Prof. Paper 254—F, p. 125-140. Brady, H. B., 1884, Challenger Rept,: Zoology, V. 9. Cole, W. S., 1931, The Pliocene and Pleistocene Foraminifera of Florida: Florida Geol. Survey Bull. 6, 79 p. Cooke, C. W., 1945, Geology of Florida: Florida Geol. Survey Bull. 29, 329 p. Crouch, R. W., 1952, Significance of temperature on Foramini- fera from deep basins off southern California: Am. Assoc. Petroleum Geologists Bull., v. 36, p. 807—843. Cushman, J. A., 1918, Some Miocene Foraminifera of the coastal plain of the United States: U. S. Geol. Survey Bull. 676. . 1921a, Foraminifera from the north coast of Jamaica: U. S. Natl. Mus. Proc., v. 59. 1921b, A monograph of the Foraminifera 0f the north Pacific Ocean: U. S. Natl. Mus. Bull. 71, pt. 6, p. 42, pl. 9, fig. 1. 1922a, Shallow-water Foraminifera of the Tortugas region: Carnegie Inst. Washington Pub. 311. 1922b, The Foraminifera of the Atlantic Ocean: U. S. Natl. Mus. Bull. 104, pt. 3, p. 83, pl. 16, figs. 1—3. 1926, Recent Foraminifera from Puerto Rico: Carnegie Inst. Washington Pub. 344. Cushman, J. A., and Bronniman, Paul, 1948, Additional new species of arenaceous Foraminifera from shallow waters of Trinidad: Cushman Lab. Foram. Research Contr., v. 24, pt. 2, p. 37—42. Cushman, J. A., and Cahill, E. D., 1933, Miocene Foraminifera of the coastal plain of the eastern United States: U. S. Geol. Survey Prof. Paper 175—A, p. 32. Cushman, J. A., and Ozawa, Yoshiaka, 1930, A monograph of the foraminiferal family Polymorphinidae, Recent and fossil: U. S. Natl. Mus. Proc., v. 77, art. 6, 185 p. Cushman, J. A., and Ponton, G. M., 1932, The Foraminifera of the upper, middle, and part of the lower Miocene of Florida: Florida Geol. Survey Bull. 9, 147 p. D’Orbigny, A. D., 1826, Tableau methodique de la classe des Céphalopodes, Annales sci. nat., v. 7, no. 19, p. 294. 1839, Foraminiferes in Ramon de la Sagra, Histoire physique, politique et naturelle de l’Ile de Cuba, A. Bertrand, Paris, France. Ellis, B. F., and Messina, A. R., 1940—54, Catalogue of Foramini— fera: New York, Am. Mus. Nat. History. Emiliani, Cesare, 1954, Depth habitats of some species of pelagic Foraminifera as indicated by oxygen isotope ratios: Am. Jour. Sci., V. 252, p. 149—158. Galloway, J. J., 1933, A manual of Foraminifera: Bloomington, Ind. , Principia Press. Gardner, Julia, 1926, The molluscan fauna of the Alum Bluff group of Florida: U. S. Geol. Survey Prof. Paper 142—0, p. 101—149. Geyer, R. A., 1950, A bibliography of the Gulf of Mexico: Texas Jour. Sci., v. 2, no. 1. Hada, Yoshine, 1931, Report of the biological survey of Mutsu Bay; No. 19, Notes on the Recent Foraminifera from Mutsu Bay: Tohoku Imp. Univ., Sci. Repts., ser. 4, v. 6, p. 45—149. Hedberg, H. D., 1934, Some Recent and fossil brackish to fresh—water Foraminifera: Jour. Paleontology, v. 8, p. 469—47 6. Israelsky, M. C., 1949, Oscillation chart: Am. Assoc. Petroleum Geologists Bull, v. 33, p. 92—98. 202 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Kornfeld, M. M., 1931, Recent littoral Foraminifera from Texas and Louisiana: Stanford Univ., Dept. Geology, Contr., v. 1, no. 3. Lalicker, C. G., and Bermudez, P. J., 1941, Some Foraminifera of the family Textulariidae collected by the first Atlantis Exped.: Torreia, Mus. Poey, Universidad de la Habana, Cuba, no. 8. Lowman, S. W., 1949, Sedimentary facies in Gulf Coast: Am. Assoc. Petroleum Geologists Bull., v. 33, no. 12, p. 1939—1997. Myers, E. H., 1943, Life activities of Foraminifera in relation to marine ecology: Am. Philos. Soc. Proc., v. 86, no. 3, p. 439—458. Natland, M. L., 1933, The temperature and depth distribution of some Recent and fossil Foraminifera in the southern Cali- fornia region: Scripps Inst. Oceanography Bull., Tech. ser. 3, no. 10, p. 225—230. Norton, R. D., 1930, Ecologic relations of some Foraminifera: Scripps Inst. Oceanography Bull., Tech. ser., V. 2, p. 331—388. Parker, F. L., 1948, Foraminifera of the continental shelf from the Gulf of Maine to Maryland: Harvard Coll. Mus. Comp. Zoology Bull., v. 100, no. 2, p. 214—241. Parker, F. L., Phleger, F. B., and Pierson, J. F., 1953, Ecology of Foraminifera from San Antonio Bay and environs, south- west Texas: Cushman Foundation Foram. Research Special Pub. 2, 75 p. Phleger, F. B., 1951, Gulf of Mexico Foraminifera, Part 1, Foraminifera, distribution: Geol. Soc. America Mem. 46. Phleger, F. B., and Parker, F. L., 1951, Gulf of Mexico Foram- inifera, Part 2, Foraminifera species: Geol. Soc. America Mem. 46. Post, R. J., 1951, Foraminifera of the south Texas coast: Inst. Marine Sci. Pub., v. 2, no. 1, p. 165—176. Rottgardt, Dietrich, 1952, Mikropaleontologisch wichtige Bestandteile recenter brackischer sedimente an der kusten Schleswig-Holsteins: Meyniana, Geol. Inst. Univ. Kiel, Band 1, p. 169—228. . Schroeder, M. C., and Bishop, E. W., 1953, Foraminifera of Late Cenozoic in southern Florida: Am. Assoc. Petroleum Geologists Bull., v. 37, no. 9, 2182—2186. Strom, K. M., 1936, Land-locked waters; hydrography and bottom deposits in badly ventilated Norwegian fjords with remarks upon sedimentation under anaerobic conditions: Norske Vidensk.-akad. Oslo, 1. Math-Naturw. Kl., hefte 7, 85 p. Sverdrup, H. U., Johnson, M. W., and Fleming, R. H., 1942, The Oceans: New York, Prentice-Hall, Inc. Vaughan, T. W., 1918, Some shoal-water bottom samples from Murray Island, Australia, and comparisons of them with samples from Florida and the Bahamas: Carnegie Inst. Washington Pub. 213. Walton, W. R., 1952, Techniques for recognition of living Foraminifera: Cushman Foundation Foram. Research Contr., v. 3, pt. 2, p. 56—60. Page Acknowledgments ______________________ 179—180, 192 acutauricularis, Saracenaria..._ 190 advena, Marqinulina ...... 186,195; charts 3—7; pl. 30 Rectobolivina _____________________ 196; charts 3—7 advenum, Elphidium_- 183,184,185; charts 1—7; pl. 30 aegua, Gaudryina __________ 184,186,194; charts 3, 5—7 aequilatcralis, Globigerina ______________________ 187 Globz'gerinella ....................... 194; chart 7 111711118, Nom'on ______ 186, 189, 195; charts 3, 5—7; pl. 30 Triloculina _________________________ 197; chart 5 agglutinam, 011inquelocul1'na.- 196; charts 4, 6, 7 agglutinala, Quinquelaculma .................. 185 akneriana, Quinqueloculina _____________________ 182, 183, 185, 196; charts 1, 2, 6, 7; pl. 29 Alaska, MV ______________________ ___ 179 Algal belt, location ................ ___ 181—182 Alum Bluff group, dominant species. _ _ _ 190 (table) amerr’canus, Robulus .......................... 190 spinosus, ROM/1113.. _ . 190 Ammoastuta ________________ .. 187 Ammobaculites. 182, 184, 187, 191 21101111: ______________________ 183, 183, 185, 184,192; charts 1,2,7; pl. 30 exilis _________________________ 192; chart 7; pl. 30 aalsus ___________ 182, 183, 192; charts 1, 2; pl. 30 Amphistegina. .......... 181, 182, 189,190, 191 lessonii. ................................... 181, 184, 185, 186, 188, 189, 192; charts 3, 5-7 ampla, Saracenaria __________________ 197; charts 5, 6 angulatus, Archaias _______ 184, 185,186,192; charts 4-7 Angulogerina bella . _______________ 192; charts 3—7 Anomalina ................................... 192 1'0 _____________________ 186,192' charts 4—7; pl. 31 Anomalinoider... 192 antillarum, Epo’nia'es _________________ 194; charts 3—6 Spiroloculma _________________________ 197; pl. 29 Arm .................................. 190 zone _____________________________________ 190 Archaic: _______________ 185, 187, 189, 190, 191 cum/Jams ............. 184,185, 186, 192; charts 4—7 sp ....... 182 zone... 190 Aracnauta. 192 Arliculina. 195 sag’ra .................................. 193 Astacolus oratus ..................... 193: charts 5—7 Asterigerim ____________________________ 185, 189 carimlla... __184 185 186 191,193; charts 3—7 chipolensis ________________________ 190 floridana ................................ 190 miocenica ................................. 190 atlamtica, Nodobacula *1‘ella. _________ 195; charts 3—7 Nonionella ....................... 195; charts 2—7 Parom‘nu ........................ 195; charts 5—7 Proteom'na ______________ 196; charts 3, 4, 7 Reusrella ...................... 197; charts 1, 3-7 auberiana laevis, Uvz'gerina ____________________ 199 auriculata, Wiesnerella ................... charts 5, 7 australis, Guttulma __________________ 194; charts 3-7 barleeanus, N 0711011.. ________________ 189, 195 barrem'i, Textularia. _ Textulariellu __________________ 197, charts 5. 7 basilica, Rotorbinella“ 186, 197, 19.9; charts 5—7; pl. 31 baasleri, Rotorbinella.. 199 Balm/siphon sp ...... ._ 187, 193; chart 2 bella, Anguloyerina ................... 192; charts 3—7 bellatula, Triloculina .................... 198; chart 1 bellula, Uvigerina.... 184,186, 198, 199; chart 7; pl. 31 bertheloti, Hanzawaia ______ 186,195; charts 6, 7; pl. 31 bicostata, Quinqueloculma____ 183,196; charts 1—3, 5—7 Bigenerina floridana ........................... 190 irregularis _______________ 184, 186, 193; charts 3—7 Bolivimz. . _-___ 195 daggarius _______ 184,186,193; charts 3, 5, 7; pl. 31 fragilis _____________________________ 193; chart 6 aoésii ____________ 184, 186,188, 191, 193; charts 5—7 pulchella primitiva... _. 193; chart 7 striatulu ............. _.._ 193; chart 2 subaenariensis maicana. _. 193; charts 3, 5; pl. 31 bascia’na, Quinqueloculina. 183,196; charts 1—7; pl. 29 Bottom plants, efiect on faunal distribution. 189, 192 Brackish habitat, dominant species _____ 190 (table) INDEX ___... [Italic numbers indicate descriptions] Page bradyana, Siphom’na ................. 197; charts 3—7 bradyi, Karreriella. . ________ 186,195; charts 5, 7 Buccella hannaL... ........ 193; charts 1, 2, 4—7 Bulimina marginatu ____________________ 193; chart 3 Buliminella elegantissima ________ 190,193; charts 1, 2 bulloides, Globigerina..- __ 187, 194; charts 3—6 Sphaeroidinc ___________________ 187,197; chart 7 colour, Robalus ________ 184, 186,197; charts 3—6; pl, 30 caloasahutcheensis, Triloculina linneiana _______ 198 Cancellaria. _ _ 190 zone ______ 190 Cancris sagra ..................... 193, charts 4—7 candeianc, Textularia..__ 184, 185,186,197; charts 4—7 Candeiana nitida. _ _ ________ 187,193; chart 7 Cardium taphrium" 190 zone ____________ 190 curmata, Asterigerina__184, 185, 186,191, 193; charts 3—7 Casxidulina laem'gata ______________________ 193 Lingulina ................. 195; chart 7 Cassidulinu curvata ............ 184, 193; charts 3, 5—7 laevigata ___________________ 193; charts 3, 5—7 111111111111 ................ 193 cassis, Nodotaculuriella. ........... 190 Charlotte Harbor, Fla ______________ 179, 181, 183, 184 Chipola formation, dominant species ..... 190(table) environment of deposition ______________ 190,191 chipolmsz's, Asterigerinc" ._ 190 Citicides ____________ 192 depn’mus _________ .. 193; charts 6, 7 pseudoungerianus _________________________ 184 186, 188,191,193; charts 3—7; pl. 31 ml ertsom'anus .................. 186, 193; chart 7 Cibicidina _____________________________________ 195 Cocohatchee River, Fla ______________________ 181 comata, Purge ___________ 196; charts 3, 4, 6 camatula, Glandulina..__ _.__ 194; charts 3, 7 comis, Triloculina linneiana. _ 198; charts 6, 7; pl. 29 cammum’s, Dentalma ............. 190, 193; charts 5, 7 compressa, Virgulina __________________________ 198 compta, Quinqueloculinu 196; charts 3—7 concentrica, Hanzawm‘a... ..... 184, 185, 186, 188, 191, 195; charts 3—7 Stomatorbina _______________________ 197; chart 5 concimtus, Discorbis .......................... 184, 185, 186, 193; charts 1, 3—7; pl. 31 conglobata, Globigerinoides ___________ 187, 194; chart 7 conica, Textularia _____ 184, 186, 197; charts 3—7; pl. 30 constans, Pseudoclavulina _____________________ 186, 196, 198; charts 5, 7; pl. 30 convergens, Robulur __________________________ chart 6 cribrorepandus, Poroeponides _________ 196; charts 4—7 curvata, Cassidulina ___________ 184, 193; charts 3, 5—7 Cyclammina __________________________________ 187 daggariur, Balivina ..184, 186, 193; charts 3, 5, 7; pl. 31 densicostata, Marginulinopsis _______ 186, 195; chart 7 Dentalina commum's ____________ 190, 193; charts 5, 7 depressa, Spiroloculina __________ 197; charts 3, 4, 6, 7 deprimus, Cibicides .............. 193; charts 6, 7 Dimorphina sp ......................... 193; chart 7 discoidale, Elphidium ..... 193; charts 2-7 Discorbis ________________________ 185 concinnus._ 184, 185, 186, 193; charts 1, 3—7; pl. 31 floridanus ______ 184, 185, 186, 190, 193; charts 1—7 floridensis. ....... 186, 193; charts 4—7; pl. 31 Duplln marl, dominant species __________ 190 (table) environment of deposition ................ 190 dutemplei, Quinqueloculina .................... 185, 196; charts 4, 5, 7; pl. 29 190 190 eggeri, Globigm'na ............... 187,194; charts 3—7 Ehrenbergina spinea ............. 186, 193; charts 5, 7 eleguns, Ho‘glundina... _ 186, 195; charts 5, 6 elegaméssima, Bulimmella ______ 190, 193; charts 1, 2 Elphidium .......................... 182,184, 137, 191 advenum" _ 183, 184, 185; charts 1—7; pl. 30 discoidale ________________________ 193; charts 2—7 gunten‘- - 182, 183, 184, 185, 194; charts 1—6; pl. 30 aalvertomme __________________________ 194 mezicanum .............. 185, 194; chart 7; pl. 30 .. 183, 184, 185, 194; charts 1—7 ruguloaum _______ 183, 184, 194; charts 1, 2; pl. 30 Page Epom’des antillarum _________________ 194; charts 3—7 repandus __________ exiguus, Ammobaculites. ___. 184, 192; charts 1, 2, 7; pl. 30 mm, Ammobaculites ............. 192; chart 7; pl. 30 exoma, Planulina._ ________________ 196 fitmii, Uvigerina... 184, 186, 198; charts 5—7 fioridana, Asteriqerim" ________________ 190 Bigenerina ................................ 190 Spiroplectammma ........... 186, 197; charts 4—7 Valvulineria _____ fiorz’danus, Discorbis" . 185, 186, 190, 193; charts 1-7 floridensis, Discorlis ______ 186, 193; charts 4—7;. pl. 31 jaliacea occidentalis, Textularia ................ 186, 190,197; charts 3—7; pl. 30 Fort Myers, Fla ______________________________ 179 foreolata, Planulina _________ 184, 186, 195; charts 5—7 ............. 193; chart 6 ._ 194; chart 5 fragilis, Bolivma _______ Frondicularia sam‘ttula... fusca, Miliammina _____________________ 198 galvestonense, Elphidium gunteri _______________ 194 Gaudruina aequa __________ 184, 186, 194; charts 3, 5—7 stavemis _________________ 186, 194; chart 5; pl. 30 glabra, Marginulina ___________________________ 190 Glandulma ................................... 194 comatula ________________________ 194; charts 3, 7 luevigata ........................... 194 Glohigerina aequiluteralis. 187 bulloides _____________________ 187, 194; charts 3—7 eggeri ........................ 187, 194; charts 3—7 Globigerinella aequilateralis. ......... 194; chart 7 Globigerinmdes conglobata ............ 187, 194; chart 7 7111111 ........... 186, 187, 188, 192, 194; charts 3—7 sacculifera ................... 187, 194: charts 5—7 Globorotalia menardii ________ 187, 190, 194; charts 3—7 puncticulata ..... __ 187, 194; chart 7; pl. 31 trunca/tulinoides“ .. 187, 194; charts 3, 5—7 tumz’da ........ _ 187, 188, 191, 194; charts 3—7 Glycz/meris waltomnsis ________________________ 190 zone ...................................... 190 110E331, Bolivimz _____ 184, 186, 188, 191, 193, charts 5—7 grateloupi, Nonimzella ________________ 195; charts 4—6 gunteri, Elphidium ............................ 182, 183, 184, 185, 194; charts 1—6; pl. 30 galvestoneme, Elphidium ........... _.- 194 Guttulimz auetralis ................... 194, charts 3-7 reama .................................... 194 Gypsina vesicularis ................... 194; charts 4—7 _ 193; charts 1, 2, 4—7 ______ 195; chart 5 hamrai, Buccella _____ hunt/16111", Marginulina.. Hanzawaia ................................. 186, 188 concentrica. 184, 185, 186, 188, 191, 195; charts 3—7 strattom' ________ 184, 185, 188, 191. 195; charts 3—7 Haplophragmoides ............................ 187 mericana _______ ___. ....... 195; charts 3, 4 Hawthorn formation, environment of deposi- tion __________________________________ 190, 191, 192 hispida-costata, Urigerina ______________________ 184, 186, 198; charts 3, 5—7; pl. 31 H6alu11d1'na elegant .............. 186, 195; charts 5, 6 horrida, Quinqueloculma ______ 185, 196; charts 3, 4, 6 186, 192; charts 4-7; pl. 31 _. 184. 185, 193; chart 3—7 io, Anomalina __________ irregularis, B1gener1'na.. jugosa, Ouinqueloculina. .................... 182, 183, 185, 196; charts 1-6; pl. 29 Karrenella bradyi ............... 186, 195; charts 5, 7 Laboratory procedure ............ 181, 182 lueriyata, Cassidulinc... _ 193; charts 3, 5—7 Glandulina .................. 194 Trachammina _______ ___. 198; chart 1; pl. 29 laevigata carinata, Oaasidulina ................. 193 laevis, Uviqerina __________ _ 199 Uviaerimz auberiama ....................... 199 Lagena spp ............................. 195; chart 5 Lageuonodosaria Malaria“ ___- 195; charts 5, 7; pl. 30 lamarckiana, Ouinqueloculma ........ 183, 185, 196; charts 1—7 lamellata, Siphogenerimz ....................... 190 lessanii, Amphistegina ......................... 181, 184, 185, 186, 188, 189, 192; charts 3, 5—7 Linyulimz carinata ...................... 195; chart 7 203 204 linneiana. Triloculina ............. calaoschatchemsis, Triloculina comis, Triloculr‘na ......... 198: charts 6, 7; pl. 29 Little Manatee River, Fla ____________________ 183 Lorostomum __________________________________ 195 mayari .............. 195; charts 1, 7; pl. 31 subspmescens ............. 195; charts 6. 7; pl. 31 marginata. Bulimina ____________________ 193; chart 3 .Marginulma .................... 195 advent: __________________ 186, 195; charts 3—7; pl. 30 190 hantkeni ____________________________ 195; chart 5 subbullata _________________________________ 195 Jttarginulinopsis demicastata ________ 186, 195; chart 7 subaculeata ........... 186, 195; charts 3, 5—7 pl. 30 mayori, Lazostomum._ _._ 195; charts 1, 7; pl. 31 Textularia ______________ 184,186,197; charts 3-7 medtterranensis, Planonbulina ______ 195; charts 1, 3-7 menardii, Globorotalia _______ 187,190, 194; charts 3—7 mezicana, Bolivina subaenarieflsis ............. 193; charts 3, 5; pl. 31 Haplophragmoides ________________ 195; charts 3, 4 Nodobaculariella __________ 195; charts 5, 7; pl. 29 Pseudoclavulma... 198 meziumum, Elphidz‘um ________ 185, 194; chart 7; pl. 30 Miliammina fusca .............. 198 miocenica, Asterigerina __________ 190 Mobile, Ala _______________________ 179, 181, 185, 186 nasuta, Pyrgo... 196; charts 3, 5, 7 Nautilus ______________________________________ 192 m‘tida, Candeiuna ___________________ 187, 193; chart 7 Nodobacularlella _______________ 195 atlantica __________ __ 195, charts 3— 7 cams __________________ 190 mexicana _______________ 195; charts 5, 7; pl. 29 Nonitm ajfimfis ________ 186, 189, 195; charts 3, 5—7 pl. 30 barleeanus. _ __ _______________ 189, 195 Noniomella atlantica. ________ 195; charts 2-7 gratelouzn' ........................ 195; charts 4—7 Nutrients, efiect on faunal distribution. 189,191, 192 Oak Grove sand member. See Alum Bluff group. obliquiloculata, Pulleniatina ....... 187,196, charts 3—7 occidentalis, Schenckiella _______________________ 197 Textularia foliacea. 186, 190,197; charts 3—7; pl. 30 Offshore zones, dominant species ________ 190 (table) olianaensis, Siphotextularia ...... 197; chart 5; pl. 30 drbitolitoides, Sarites __________ r _______ 197; charts 1—7 Orbulina universa ___________ 187,190,195; charts 3—7 amata, Planulina _____________________________ 184, 185, 186,188,189,191, 196; charts 3-7 ovatus, Astacolus .................... 193; charts 5—7 Oxygen, effect on fauna] distribution _________ 189 pacifica simpler, TrochamminaQ 198 Panama City, Fla ......... . 181,185 parkeri, Uvigerma _____________________________ 190 Pal/mine atlantica ................... 195; charts 5-7 Peneraplis proteus.... 185, 195; charts 4—7 peregrina, Uvigerina_. _______________ 190 peruviana, Pyrgo ____________ 196; charts 1, 4,6, 7 pH, effect on fauna distribution ________ 188—189, 191 Pine Island Sound, Fla _____________ 179, 181, 183, 184 Planorbulina mediterranensis. __ 195; charts 1,3—7 Planulma. . 182 aroma, . ._ 196 fal‘eolata _________________ 184, 186,195; charts 5—7 omata___ 184,185,186, 188, 189, 191, 196; charts 3—7 poeyana, Quinqueloculina ................... 183,196; charts 1—3, 5—7; pl. 29 poeyanum, Elphidium. _. 183, 184, 185,194; charts 1—7 polygonal, Quinqueloculina ______________ 196; chart 6 Polymorphina pulchella. .. 196; charts 3—7 Pompino, MV ________________________ 179 Poroeponides cribrorepandus ......... 196; charts 4—7 primitira, Bolivina pulchella ............ 193; chart 7 .. 196; charts 3,4,7 185,195; charts 4-6 Protecnina atlantica _____ proteus, Peneroplis. . . _ Pseudoclavulina constant ............... 186,196, 198; charts 5,7; pl. 30 mezicana ____________________ 198 Pseudoglandulina ............................. 194 WDEX Page pseudatrochus, Tcxtulariu...- 186,197; chart 5; pl. 30 pseudrmngerianus, Cibicides. _____ 184,186,188,193; charts 3—7; pl. 31 pulchella. Polymorphina ............. 196; charts 3—7 primitiva, Bolivina ................. 193; chart 7 Pullenia quinqueloba __________ 196; chart 7 Pulle'niatina obliquiloculata. . _..- 187,196; charts 3—7 puncticulata, Globarotalia.... 187,194; chart 7; pl. 31 Pyrgo comata ......... _._- 196; charts 3, 4, 6 nasuta ...... ._.. 196; charts 3, 5, 7 peruviana- _._ 196; charts 1, 4, 6, 7 quinqueloba, Pulle'nz'a ___________________ 196; chart 7 Qulnqueloculina ____________________________ 184, 197 ‘agglutinans. 196; charts 4, 6, 7 agglutinata... ...- 185 ukneriana. 182,183,185,196; charts 1, 2,6, 7; pl. 29 bicostata ................. 183,196; charts 1-3, 5—7 bosciana .............. 183,196; charts 1—7; pl. 29 compta. ._ ..... 196; charts 3—7; pl. 29 dutemplet ..... _._ 185,196; charts 4, 5, 7; pl. 29 horrida ____________________ 185,196; charts 3, 4, 6 17200311.... _. 182, 183,185,196; charts 1—6; pl. 29 lamarckiana __________ ‘_ .. 183,185,196; chartsl-7 poeyana. _._ _ 183,196; charts 1—3,5—7; pl. 29 polymma ........................... 196; chart 6 rhodiensis ................... 196; chart 5; pl. 29 Raphanulina tuberculata. ............. 196 Rectobolivina advma.. . 196; charts 3, 5—7 regina, Guttulina..... _________ 194 Reophaa: scorpiurus _____________________ 197; chart 3 repandus, Epamdes ........................... 196 Reusaella atlantica ......... _ 197; charts 1, 3—7 rhodiensis, Qumqueloculina ______ 196; chart 5; pl. 29 robertstmianus, Cibicidea .......... 186, 193; chart 7 Robulur americanus ___________________ 190 americunus spinosus _______________ _._- 190 calcar ............. 184, 186, 197; charts 3—7 pl. 30 convergens ______________________________ chart 6 stephensoni __________ 197; charts 4, 5; pl. 30 auborbicrtlaria ...... 197; charts 4—6; pl. 30 Rotorbimlla basilica“ 186, 197. 199: charts 5—7; pl. 31 bassleri .................... 199 tram sluscenr _______________________________ 199 versiformis ________________________________ 199 rubra, Globigerinoides __________ 187, 188, 191, 194; charts 3—6 ruaulosum. Elphidium ........................ 183, 184, 194; charts 1, 2; pl. 30 sacculifera, Globigerinoides._ 187, 194; charts 5-7 sagittula, Frondicularia ______________ 194; chart 5 score. Articulina ______________________________ 193 Canon's __________________________ 193; charts 4—7 St. Petersburg, Fla ____________________ 181,182 Salinity, eflect on fauna! distribution _______ 189, 191 salsus. Ammobaculites ........................ 182, 183, 192; charts 1, 2; pl. 30 San Carlos Bay. Fla ________________ 179, 181, 183, 184 San Diego. Calif ......... 189 Saracenaria acutuuricularis ____________________ 190 ampla ........................... 197; charts 5, 6 scalaris, Lagemmodoaaria.. 195; charts 5, 7; pl. 30 Schenckiella occidentalis. _._ ________ 197 echreibersiana, Virgulina._ 198; charts 3—7 scorpiurus, Rheophax __________________ 197; chart 3 recase‘nsis, Textularia _________________________ 182, 185, 197; chart I. 2, 4-7; pl. 30 Shoal River formation, Oak grove sand mem- ber, dominant species ................ 190 (table) sigmoilina subpoeytma ...... 197; charts 3, 5, 6, 7; pl. 29 tenuis __________________________ 197; charts 5, 7 simplex, Trochammina pacifica ________________ 198 simplissima, Trochammina..._ 198; chart 4; pl. 29 Siphoaenerina lamellata _______________________ 190 Siphom'na bradvana ________________ 197; charts 3—7 Siphoteztularia_ olianaensis..-_ 197; chart 5; pl. 30 sobrinus, Streblus. __182,183, 184, 185, 197; charts 1—3, 5 Sorites orbitolitoides ________________ 197; charts 1—7 51) .................... 190 Sphaeroidinc bulloides __________ 187. 197; chart 7 spinea, Ehrmbergina .......... 186, 193; chart 5, 7 ‘Error for Q. aglutinans. Page spinasue. Robulus americamw ................. 190 Spiroloculina antillarum ................ 197; pl. 29 depresses __________________ ._ 197; charts 3, 5-7 Spiroplcctammina floridana _____ 186, 197; charts 4-7 stuvensis, Gaudryina ......... 186, 194; chart 5; pl. 30 stephensoni, Robulus..- __ 197; charts 4, 5; pl. 30 Stomatorbma concentrica ________________ 197; chart 5 atratttmi, Hanzawaia“ 184,185, 188, 191, 195; charts 3-7 Streblus ___________ 182, 184, 185, 187, 188, 189, 190, 191 _ 182, 183, 184, 185, 197; charts l—3,5 tepidua ................................... 182, 183, 184,185,188,189, 197; charts 1-7; p. 31 striatula. Bolivina ...................... 193; chart 2 subaculeata, Marqinulinapsis .................. 186, 195; charts 3, 5-7; pl. 30 subaenariensis mezicana, Bolivina _____________ 193; charts 3. 5; pl. 31 subbullata, Marvinulim _______________________ 195 suborbicularis, Robulu8.. ._ 197; charts 4—6; pl. 30 subpoeyana, Sigmor‘lma _____ 197; charts 3, 5—7; pl. 29 subspinescms, Lozostomum..__ 195; charts 6, 7; pl. 31 Tarnpa Bay, Fla ................... 179, 181, 182, 183 Tampa limestone. dominant species _____ 190 (table) environment of deposition ______ _ . 189—190 taphrium, Cardium. __ . 190 Tarpon Springs, Fla ________________________ 181, 182 Temperature, effect on fauna] distribution. . _ - 188, 189, 191 tennis. Sigmoilina ................... 197; charts 5, 7 tepidus, Streblus .............................. 182, 183, 184,185, 188, 189, 197; charts 1—7: pl. 31 Textularia burrettii“ .......................... 186 candeiana.. _._ _._ 184,185,186,197; charts 4-7 conica... _. 184, 186, 197; charts 3-7; pl. 30 foliacea occrdentalisJSG, 190,197; charts 3—7; pl. 30 mayori .............. 184,185,186,197, charts 3—7 pseudotrochus ............ 186,197; chart 5; pl. 30 secasensis- 182,183,185, 197; charts 1, 2, 4-7; pl. 30 Textulariella barrettii ....... 197; charts 5, 7 tortuoaa, Triloculinmn. ________________ 198 transluscens, Rotorbinellc ............... __ 199 trigonula. Triloculina. _._ 182, 183, 190, 198; charts 1—7 Triloculma amnis ....................... 197; chart 5 bellatula... 1.98; chart 1 limteicma _________________________________ 198 limteiana caloosahatcheensz‘s ............... 198 comis ................. 198; charts 6, 7; pl. 29 198 _ 182,183,190, 198, charts 1—7 Trochammina. __________________________ 187 laem’gata ..................... 198; chart 1; pl. 29 pacifica simpler ........................... 198 simplissima .................. 198; chart 4; pl. 29 truncatulium'des, Globorotalia.... 187; 194: charts 3-7 tuberculata, Raphanulina ...................... 196 tumida, Globorotalia ______ 187, 188, 191,194; charts 3—7 Turbidity, effect on fauna] distribution. _ 189, 191—192 universa, 0rdulina ........... 187, 190,195; charts 3—7 Uvigerma auberiana laevis ..................... 199 bellula ........... 184, 186,198,199; chart 7; pl. 31 fiintii ____________________ 184,186,198: charts 5-7 hispido—costata. 184,186,198; charts 3, 5-7; pl. 31 - 199 _ 190 peregrina ................................. 190 sp __________________________________ 188,190, 191 Vaginulma ................................... 195 Valvulinerlu ........................ 190,198; chart 7 floridana ......................... 190 SD ......................... 198 versiformis, Rotorbinella... _______ 199 vesicularr‘s, Gupsina _______ 194; charts 4—7 Virgulina compressor .................. 198 achreibcrsiana .................... 198; charts 3—7 waltonensis, Glucymeris _______________________ 190 Wiesnerella auriculata. ._ charts 5, 7 Yoldia ......................... 190 190 "Error for Textularia barrettii. Plates 29—31 PLATE 29 FIGURE 1. Sigmoilina subpoeyana (Cushman) (p. 197). Hypotype, USNM 624378. 2. Spiroloculma depressa D’Orbigny (p. 197). Hypotype, USNM 624384. 3. Quinqueloculina akneriana D’Orbigny (p. 196). Hypotype, USNM 624356. 4. Quinqueloculina bosciana D’Orbigny (p. 196). Hypotype, USNM 624359. 5. Quinqueloculina compta Cushman (p. 196). Hypotype, USNM 624360. 6. Quinqueloculina poeyana D’Orbigny (p. 196). Hypotype ,USNM 624365. 7. Nodabaculariella mewicana (Cushman) (p. 195). Hypotype, USNM 624336. 8. Quinqueloculina jugosa Cushman (p. 196). Hypotype, USNM 624363. 9. Quinqueloculina dutemplei D’Orbigny (p. 196). Hypotype, USNM 624361. 10. Quinqueloculina rhodiensis Parker (p. 196). Hypotype, USNM 624367. 11. Triloculina bellatula Bandy, n. Sp. (p. 198). Holotype, USNM 624397. 12. Triloculina linneiana D’Orbigny var. comis Bandy, n. var. (p. 198, 199). Holotype, USNM 624398. 13. Trochammina laevigata Cushman and Bronniman (p. 198). Hypotype; a, ventral View; I), edge View; 6, dorsal view; USNM 624400. 14. Trochammina simplissima Cushman and McCulloch (p. 198). Hypotype; a, dorsal View; b, edge View; 0, ventral view; USNM 624401. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 29 13b FORAMINIFERA OF NORTHEASTERN GULF OF MEXICO GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 30 X50 19b 20b FORAMINIFERA 0F NORTHEASTERN GULF OF MEXICO FIGURE PLATE 30 . Gaudryina stavensis Bandy (p. 194). Hypotype, USNM 624307. . Ammobabulites exiguus Cushman and Bronniman (p. .192). Hypotype, USNM 624264. Ammobaculites exilis Cushman and Bronniman (p. 192). Hypotype, USNM 624265. Ammobaculites salsus Cushman and Bronniman (p. 192). Hypotype, USNM 624266. . Pseudoclavulina constans Bandy, n. sp. (p. 198). Holotype, USNM 624349. Textularia comica D’Orbigny (p. 197). Hypotype, USNM 624390. Textularia pseudotrochus Cushman (p. 197). Hypotype, USN M 624393. . Textularia secasensis Cushman and McCulloch (p. 197). Hypotype, USNM 624394. . Siphotextularia olianaensis Colom and Ruiz de Gaona. (p. 197). Hypotype, USNM 624381. . Textularia foliacea Heron-Allen and Earland var. occidentalis Cushman (p. 197). Hypotype, USNM 624391. . Robulus calcar (Linne) (p. 197). Hypotype, USNM 624372. . Robulus suborbicularis Parr (p. 197). Hypotype, USNM 624374. . Robulus cf. stephensom? Cushman (p. 197). Hypotype, USN M 624373. . M arginulinopsis subaculeata (Cushman) (p. 195). Hypotype, USNM 624334. . Marginulina advena (Cushman) (p. 195). Hypotype, USNM 624331. . Lagenonodosaria scalaris (Batsch) (p. 195). Hypotype, USNM 624327. . Nonion afiim's (Reuss) (p. 195). Hypotype, USNM 624337. . Elphidium advenum (Cushman) (p. 193). Hypotype, USNM 624297. . Elphidium gunteri Cole (p. 194). Hypotype, USNM 624300. . Elphidium mem'canum Kornfeld (p. 194). Hypotype, USNM 624301. . Elphidium rugulosum Cushman and Wickenden (p. 194). Hypotype, USNM 624303. FIGURE PLATE 31 Globorotalia puncticulata (D’Orbigny) (p. 194). Hypotype; a, ventral view; b, edge view; 0, dorsal View; USNM 624316. Streblus tepidus (Cushman) (p. 197). Hypotype; a, ventral view; 17, edge View; c, dorsal View; USNM 624388. . Rotorbinella basilica Bandy, n. sp. (p. 197, 199). Holotype; a, ventral view; b, edge view; c, dorsal view; USNM 624375. . Discorbis co'ncinnus (H. B. Brady) (p. 193). Hypotype; a, ventral View; b, oblique view; c, dorsal view; USNM 624293. . Discorbis fiom’densis Cushman (p. 193). Hypotype; a, dorsal view; b, oblique view; 0, ventral view; USNM 624295. Hanzawaia bertheloti (D’Orbigny) (p. 195). Hypotype; a, ventral view; b, edge view; 0, dorsal view; USNM 624321. Anomalina i0 (Cushman) (p. 192), Hyptoype; a, dorsal View; b, edge view; c, ventral view; USNM 624269. . Cibicides pseudoungerianus (Cushman) (p. 193). Hypotype; a, ventral view; b, edge view; 6, dorsal view; USNM 624289. . Bolivina daggan‘us Parker (p. 193). Hypotype, USNM 624278. . Bolivina subaenariensis Cushman var. mexicana Cushman (p. 193). Hypotype, USNM 624281. . Loxostomum mayom' (Cushman) (p. 195). Hypotype, USNM 624329. . Loxostomum subspinescens (Cushman) (p. 195). Hypotype, USNM 624330. . Uvigem'na, bellula Bandy, new name (p. 198, 199). Holotype, USNM 624402. . Um'gem’na hispido costata Cushman and Todd (p. 198). Hypotype, USNM 624404. 1!. l. GOVERHIEIT PRINTING OFFICE: I936 GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 31 X 115 FORAMINIFERA OF NORTHEASTERN GULF OF MEXICO PROFESSIONAL PAPER 274-6 CHART I GEOLOGICAL SURVEY If I3 'o‘—‘ . I‘.‘ Ed Em gfi 3;: EE 5' _, c_. a 0.1:: 3% a: E: "=2 £5 “5* as: 4 4g; 35 52:: 3‘ 3% ;E= 5w E5 \fi‘-E%m3‘ 6w;< ;: ;5i3 .35. gm : 2 2 t 3: E; iv .3»; g“ :5 :m 5")“; ~-. ,_,‘ij Pan—.5- ALL 4: ' r-L‘ r‘fiW—‘_“ > H‘fi’A“ ' r T 4 ' SAMPLE NUMBERS H 9‘ 3—104 7\ ”d i-O‘at Hen—mun ' =§§5§_ 5figiifiififiiiixiisitiufiiliwI33! ss§§§ §8§§a“ assfinggafiii o‘"fi1!"i“’ITIT”HIIIII‘TIr‘uIrr‘rIM I‘TIITTY‘IIIII III'I'I IIIIIII‘IIIIT1 [I]; . ._ 10 / / i. ' ‘ BOTTOM PROFILE 7/ ' ‘ Lu ‘ 7 , ‘ , . -‘ i I m/ / v ,/«=...//// : //”//// ‘2“. .r' _ “/ 3’" 1' 7’ , E 30 . u . /’_/ 'ITEMPERATURENSfi—IaJvCENTIGRADE _ m ‘ — ’/ , . 7 ’ ‘ ~ ' : 7.204112 ' _ “.40 x / . . V _ ‘ - v ' ’ ' w I sfiurmv: 6.67242 . so , » r ,_ ,»' I. 55‘" ‘v .8 ‘ ‘ oun— — V , _ 3;: as- = — -2 < . ,. , a _ E55 4- I I . _ pgfi 2: J , I Ell-E j _ L , ‘v » _ an 9 '~ \/\ 3° ‘ HYALINE SPECIES 8 PERCENTAGE OF EACH GROUP RENACE US 0x COMPOSITE FREQUENCY GRAPH Buccella hannai Buliminella elegantissima Discorbis concinnus flor idanus Elphidium gunteri PERCENTAGE SCALE rugulosum Loxostomum mayori Planorbulina mediterranensis Reussella atlantica Streblus sobrinus tepidus HYALIN E SPECIES Pyrgo peruvinna ‘I’ I I I I I I I I I I I I I II: 3 I Quinqueloculina. akneriana _‘\,\I I bicostata I bosciana II II: IIII I1 IIIIIJIIIII jugosa lamarckiana poeyana Sorites orbitolitoides Triloculina belInhxla ' I tr igonula /\ I PO RCELANEOUS SPECIES III II IIIII I l I Ammobaculites exiguua salsus Textuhria secasensis /\/\\ — Trochammina Inevigata I T I III II §§O~Ntoar v-lI-‘I‘Hv-‘v-l «Numb-nun 452 d 457 — 507 — IT I II I I I I I I I I I I I I I I I I I I I I II I I I II I do ~N In non-t ROM 04 «(wan .. H :33::!§:§:::§5§:::§s§§::::§§9 B§§§ §§§§§a§§§§§ SAMPLE NUMBERS ARENACEOUS SPECIES FREQUENCY DISTRIBUTION OF SPECIES FORAMINIFERAL DISTRIBUTION IN TAMPA BAY, FLA. 364220 0 — 56 (In pocket) No. l ILOGICAL SURVEY PROFESSIONAL PAPER 274-6 CHART 2 ND >- m :: < m a m = o ‘6’ B W 235:. §E Em 5< <> 00 < “ WE _,m xu: g o 0:91 xi» 3“ z 8 << <2 .1” N < A II >Lz m2 5 (n < u 2 an: m u I I I (OUTER) T (MOUTH) DEPTH OF WATER, IN FEET ’2 '6: g 1.9 _ > _ *- E: — .. .7 E a 9 t t t 0 2 ~ 5 a E “ E 5 - ° 3 g E ‘ m I—un Lu) - u. E 2 2 9 E E E '° 8 ECOLOGIC FACTORS 100 g _ g 1 Q a I A 2 : HYALINE SPECIES lhl u. 50— o — . {‘3 : ARENAICEOUS E ‘ SPECIES E ‘ PORCELANEOUS SPECIES ;, U - I m _ Lu _ n- S COMPOSITE FREQUENCY GRAPH Bolivina striatula Buccena hannai 100 Buliminella elegantissima Discorbis floridanus Elphidium advenum 75 5 discoidale 5’, all so E ‘ Z gunterl m g poeyanum 30 If 20 Lo -rugulosum 3 Nonionella atlantica Streblus sobrinus tepidus SPECIES Quinqueloculina akneriana. r bicostata bosciana \ \ Jugosa lamarckiana “A poeyana Sorites orbitolitoides Triloculina trigonula “m M“ ‘ PORCELAN EOUS SPECIES JIIIIIIIIIII|LILIIII IIIIIIIIIIIIIIIIIII—I’ Ammobaculites exiguus ~/\ salsus __ l Bathysiphon sp. I Textularia secasensis 715 720 — 723 — 726'- 731 734 - 74a - 749 - 750 752* 759 — 762 — 77: 77+— 776 - 753 « 7% 796 r]! I IV I I @1000 mm MON Nous sass§e$ gaggeaa 6451 l I r 0' O Ix Ix o§§w ,0, SAMPLE NUMBERS ARENACEOUS SPECIES FREQUENCY DISTRIBUTION OF SPECIES FORAMINIFERAL DISTRIBUTION IN CHARLOTTE HARBOR, PINE ISLAND SOUND, AND SAN CARLOS BAY. FLA. 364220 0 — 56 (In pocket) No. 2 GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-6 CHART 3 SAMPLE NUMBERS ‘ D I— ... N v m N on 2' ‘3 3 “.3 I: 2 2 8 Z a § 3 E 0 I I I I I I I I I I . I I I I 38 “g E — BOTTOM SALINITY (JUNE-AUGUST) — 37 E? g . 4o — " I —— 36 .2. I— z . I Amphistegina lessonii —— 35 EI E _ ~ 7/ . . n. 80 . , common In res1due (I) “ ' 7/ E 5.3") ' ‘ T / BOTTOM PROFILE m E 140 — ~ ,// 7/ _ 28 3:. E 2:6 I— — / 2 “J 16d .d _ < 22 E I 7 ~— 26 n: . ». - —— . I E 3‘200.7 . _ g3? —- S “‘3 1‘8 E T APPROXIMATE / 7 r/ : 24 E Lu 3'1 240 T/ / / , 8m 3 1.4 o —/ . . I 3» BOTTOM-TEMPERATURE é — 22 :12 I— 280 * . ‘ ' ‘ gm: 2' ‘ . RANGE a. 20 2 m 1.0 . “ :1 ///////,2 2+— g 320 ~ . 1" < E w .6 — ~ A 18 Eu “- WEIGHT PERCENTAGE D. 9 ~2 00 * OF FORA'MINIFERA IN SEDIMENT ,_ L“ - 4 I- ' ' so MILEs r; 3 ' ECOLOGIC FACTORS Globorotalia truncatulinoides, G. menardii, G. tumida Orbulina universa Pulleniatina obliquiloculata Globlgerma eggerl j Globigerindides rubra 100 é . . Globlgerma “ bulloides D. (:3 _ HYALINE SPECIES 0: L9 I __ u < Lu 50 ._ LL. 0 m _ <9 < I— a Z “J .. g E CELANEOUS . E . ,. : ”'35 ////// Asterigerina carinata Discorbis concinnus floridanus Elphidium advenum gunteri poeyanum Guttulina australis Hanzawaia concentrica, H. strattoni Nodobaculariella atlantica Pyrgo comata Quinqueloculina bosciana compta jugosa poeyana Reussella atlantica Sorites orbitolitoides StI'eblus sobrinus tepidus Amphistegina lessonii Angulogerina bella Elphidium discoidale Eponides antillarum Marginulina advena Nonionella atlantica Planorbulina mediterranensis Planulina omata Pyrgo nasuta Quinqueloculina bicostata horrida Iamarckiana Spiroloculina depressa Triloculina trigonula Virgulina schreibersiana Bolivina daggarius /// H. stratboni FAUNA COMPOSITE FREQUENCY GRAPH I [nl'llll Ill Cull-4 H. concentrica 2 FAUNA 3 subaenariensis mexicana Bulimina marginata Cassidulina laevigata, C. curvata Cibicides pseudoungerianus Glandulina comatula Marginulinopsis subaculeata Nonion aflinis Polymorphina pulchella Rectobolivina advena Robulus calcar Sigmoilina subpoeyana Siphonina bradyana Uvigerina hispido-costata Bigenerina irregularis Haplophragmoides mexicana Proteonina atlantica Textularia mayori conica assemblage Gaudryina aequa Reophax scorpiurus Textularia foliacea occidentalis -—v --4 f-t SAMPLE NUMBER ARENACEOUS SP S ECIES FREQUENCY DISTRIBUTON OF SPECIES FORAMINIFERAL DISTRIBUTION OFF MDBILE, ALA. 364220 0 - 56 (In pocket) No. 3 PERCENTAGE SCALE GEOLOGICAL SURVEY SAMPLE NUMBERS V v-i a; h In —: w v N a to <- N o: h '9‘ P 33§zsaagxaagaaaza E IIIIJ_IiIIIII|38 z 0 T I E ' BOTTOIII SAJNI'“: (AUGUST) % 4o 7// / 36 z / _ ”— < 80 é/ 7/ BOTTOM PROFILE 34 I! v I v E 120 / 7 r// // ~32 E P- " 2 "“ 160 — 30 E E _ 8 2.0 E, 200 —28 s a — g 1.6 a 240 — 25 D :5 12 280 BOTTOM TEMPERATURE (AUGUST) 24 g '3 2° WEIGHTPERCENTAGEOFFORAMINIFERA IN SEDIMENT _ D. ._ .4 380 ~20 (I; __—/\__h— _ 18 § 0 40° I‘v 65 MILES =: ECOLOGIC FACTORS Pulleniatina obliquiloculata Orbulina. universa Globigerina eggeri Globorotalia menardii, G. k tumida, G. truncatulmmdes Globigerina bulloides 100 fifilw a D. ._. D O E a: _ (D :x: — HYALINE SPECIES g _ Lu 50.. LI. 0 _ m _ (3 < |_ z ......... lu U 0: LL! A. : COMPOSITE FREQUENCY GRAPH Elphidium gunteri I I41 I I l J poeyanum I I M441 [II /\\,E Streblus tepidus a. FAUNA ‘I Archaias angulatus Asterigerina carinata , Discorbis concinnus floridanus Guttulina australis Gypsina vesicularis H. stratboni H. concentrica Hanzawaia concentrica, H. strattoni ! Nodobaculariella atlmtica Peneroplis proteus Pyrgo peruviana Quinqueloculina agglutinans compta horrida jugosa Sorites orbitolitoides , Triloculina trigonula Virgulina. schreibersiana FA U N A 2 Buccella hannai Cancris sagra Elphidium advenum diacoidale Eponides antillarum Nonionella atlantica grateloupi Planorbulina mediterranensis Planulina ornata ,,,,,, Poroeponides cribrorepandus Proteonina atlantica Pyrgo comata Quinqueloculina bosciana" ‘ dutemplei lamarckiana Reussella atlantica FA U N A 3 Angulogerina bella Anomalina i0 In. u' Cibicides pseudoungerIOi'ng .~ Discorbis floridensis Marginulina. adyena. Polymorphina Robulus calcar 1‘ cf R. 'stepHéhsoiIi 4' suborbicglagg t 1‘- Siphonina bradyana “ . r 1' ' Textularia secasensis Bigenerina irregularis Textularia candeiana mayori Haplophragmoides mexicana , Proteonina atlantica ,* ~ . A ‘ Textularia conica assembage — . V N7 Spiroplectammina floridana Trochammina simplissima Textularia foliacea occidentalis / l I I I I I | I I I I V H O on N m "4 m ‘1’ N 00 ‘D N 0! '\ V“ as an a: I\ h !\ rx 0 T m m m m m m 3 m 3 15’, - 3 :9, 3 5 c7, 3 m SAMPLE NUMBERS ARENACEOUS SPECIES FREQUENCY DISTRIBUTION OF SPECIES “FORAMINIFERAL DISTRIBUTION OFF PANAMA CITY,_ FLA. 33.4225 0 - 56 (In pocket) No. 4 PROFESSIONAL PAPER 274-6 CHART 4 SALINITY, PARTS PER THOUSAND TEMPERATURE, DEGREES CENTIGRADE [mlTlllll I 0 0| PERCENTAGE SCALE GEOLOGICAL SURVEY R SAMPLE NUMBERS m .4 n: ION m u— M 333923359333335933353$3§§§§§§E§§2§§§§EE§§§§§§§§§§§§32EEEE::::§2§2§ °°::ZZS'ZSSSZSSZZZSZZSZSHH H~~fi_~.—I—.H~- HHHSHHEHSHHH~~-_«~~~~~._I.-......‘..'I..I...... . 07710“?IIIIIIIlIIIxIIIIIIII||I|IIIITT1IIIFIIIIIIIIITrrTIIIIlIIIIT 38 D U, 150 20 ’ BOTTOM SALINITY (JIJNE) _— 32 5 E 14.0 :3 mph1stegina lessonii in residue. estinf‘lnated A 3:, g _ - 7 ' o E 130 80~ | 10 69 percent 0 . auna _33 E I5 '3 100“ x xx x xxxx — 32 z m BOI’T I - Iz m 12.0 120A /// OM pRo _ 31 .1 z 140 — W W 5/}; I l — 30 g E - 11.0 160— _ 29 w E 180 — \4 _ 28 E m 10,0 200— _ 27 ‘ E ._ 220— Abundant bryozoa and calcareous algae _‘ 26 n. E 9.0 E 240—- I ‘ __.25 E: u 260 - E BOT'r _ 24 n: 8.0 280— OM T ._ 2.3 o E, 300 — EMPERATURE (JUNE —— 22 “- 7,0 I 320— ’ _ 21 5 E 340— # 2° W m 6,0 gaeo~ I H19 5 u, 380 — >_ 18 m < 5.0 400— WEIGHT PERCENTAGE OF FORAMINIFERA IN SEDIMENI _ 17 8 w E 420— E 15 D D m 4.0 440— — 15 “5 E g 460— _ 14 a: w E 3.0 480- _ 13 a ; 500~ _ 12 < E E 2.0 520— E 11 E u 9 540— 10 0- m 1.0 560— 9 E 3 580— I 8 I— .0 60° {.7 140 MILES AI ECOLOGIC FACTORS Orbulina universa Globorotalia menardii, G. truncatulinoides, G. tumida Pulleniatina obliquiloculata Globigerina eggeri Globigerinoides sacculifera Globiger‘ma bulloides 100 g HYALINE SPECIES o c: L9 I U 5 “- 5° :2. . o z m . w _ . . . . _ < . E :3 / .. .. “4 PORCELANEOUS SPECIES / , . . . E - /// a .. . 7 .. ,, 0 .. . 4 . . Ibm/flfl/xzm .. . . “FF-”ACE?” SEFC'ES CO POSITE FREQUENCY GRAPH Elphidium gunteri F100 — 75 — a _ S m .E _. «3’ _ 3 7’5. , so g 0) ~ 2 "' — 4o {3‘ . E 5 '1? _ 30 n. Streblus tepidus, S. sobrinus I I ‘ 20 FAUNA 1 — — 1o — > 5 _ — 0 Z /\/\A _ Archaias angulatus _ Asterigerina carinata — ’— E Elphidium advenum : I— poeyanum — ‘ A \kayv Wkfl Nodobaculariena mexicana R ~/ I 4 _ Peneroplis proteuq NW Quinquelocul'ma bicostata E jugosa E / i M '— lamarckiana poeyana — I: rhodiensi's : K E _ Mb _/\_. ' Sor ites orbitolitoide q ; I Triloculina trigonula FAUNA 2A Discorbis concinnus f loridanus Guttulina Gyps ina ve s Hanzawaia concentrica, H. strattoni Nodobaculariella Nonionella. grateloupi Planorbulina mediterranensis Quinqueloculina bosciana compta FAUNA ZB Elphidium discoidale Eponides antillarum Nonione 11a Planulina ornate. Quinqueloculina dutemplei Reotobolivina advena Reussela atlantica Spiroloculina depressa Triloculina affinis Virgulina schreibersiana FAUNA 3 PERCENT OF TOTAL BENTHOS IN CONCENTRATE Amphistegina lessonii Buccella hannai Cancris sagra Cibicides pseudoungerianus Marginulina Polymorphina pulchella Poroeponides crib Pyrgo nasuta Rotorbinella Sigmoilina subpoeyana Siphonina bradyana Wiesnerella aur FAU NA 4 Angulogerhm Anomalina io Astacolus ovatus Bolivina goé’sii subaenariensis mexicana daggariusr Céssidulina curvata, C. laevigata Dentalina communis Discorbis floridensis Ehrénbergina spinea Frondicularia Héiglundina elegans Lagena spp. Lagenonodosaria scalaris Marginulina hantkeni Marginulinopsis subaculeata Nonion affinis Pavonina Planulina foveolata Robgrluwsr gialcar suborb icular is stephensoni Saracenaria ampla Sigmoilina tennis Stomatorbina concentr UMigerina flintii ‘ hispido-costata FAUNA 5 Textularia secasensis I I candeiana Q . _ - \/“ IIII IIII /\/\ Bigener ina irregfilaris" Textularia mayotji ‘ I I Gau ryina stavensis ‘ Textularia pomca, T. pseudotrochus conica assemblage ‘ Textulariella barrettii I I I I IIII _ 1.. Gaudryina aegua ' i _ Spiroplectammina floridana. Textularia foliacea occidentalis 'I’IIIE Siphotextularia olianaensis Pseudoclavulina constans Karreriella bradyi IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII NONI“) A ONInnmmn-I O m M ION In R O 3§ofl~~2fi$~~n~~m"133838393?w3$$§$8$fimzfimmfifla‘SGSSSwa‘fl$nIfiK‘IRI‘3R228538 o HEM...'04..HH—fiA—Nuuflunfijfi.‘——._—.H....—4...HHHGH~,~.«_..—_.~.—.H_I~N.......~.4..........4,._,...........fi ~HH~H~~~~H_—~~~m—._HMHH ~—HEM—”"0.“aa~~fififim~-fifim—MH~”Ha—Hadfi—I—m—Iafia SAMPLE NUMBERS ARENACEOUS SPECIES FREQUENCY DISTRIBUTION OF SPECIES FORAMINIFERAL DISTRIBUTION OFF TARPON SPRINGS. FLA. 364220 0 - 56 (In pocket) No. 5 GEOLOGICAL SURVEY Elphidium advenum WEIGHT PERCENTAGE OF FORAMINIFERA IN SEDIMENT 10 m Nw‘ua‘fl DEPTH,IN FEET PERCENTAGE OF EACH GROUP‘ PROFESSIONAL PAPER 274-G CHART SAMPLE NUMBERS m t OANM‘WONDQOHNMVID'ONQ an 0 ' to h m Mount-n B IIL IIIIIILJIIlIIIlIlIlIlII|IIlIIIlIlIJ_|_w ° 4 PP A BOTTOM-SALINITY RANGE ‘ A I < V. ‘1‘ ‘ - 4“ if; g ‘0 :§ B _AtIundan't Amplhisteglina IeEsonii'ih reéidue, :32 a so - OTTO" PR I estimated 20—70 percent of fauna~34 >: 8 _ OFILE ' A —33 I; E 120‘7/i -._ / xxx' )1 xx X :321: a: _ "'2,’ _ < “1 lcso:4/ap,‘,(I)7{///~ ,~ _323g¢n: 200 —@ ["4759 \J -' r28 E 2“) : ‘ Orro” Abundant bryozoa and‘ I :2 E _ ”Em, calcareous algae ~ 2; 2m - ER 7.”? .. — 24 - 5 ~a3 320 — Q‘NGE / m : 3: 36° : :3: 400 I— — 13 It _ , - —17 3 W 440 — WEIGHT PERCENTAGE OF FORAMINIFERA IN SEDINENT _15 a” g _ . ' -15 Lu I: 4301 —14 g 9 _ ~13 !— E 520 ~ -12 g m _ 11 u: U 560 - I: _ 8 l- SDO IL I30 MILES , >‘I ECOLOGIC FACTORS Orbuiina universa ; Globigerina eggeri Globorotalia truncatulinoides, G. menardii,. G. tumida Pulleniatina obliquiloculata Globigerinoides sadculifera . P v - Globigerina bulloides \ 100 q , _ T‘ _ HYALINE SPECIES , so — H 7 I. ' Iris: ‘ _I - .I 1/ ,./ y? — l . . ’ V - /%/// ~ N A . I COMPOSITE FREQUENCY GRAPH gunteri I l 75 IIIIIWIIT poeyanum I I Quinqueloculina akneriana jugosa l I I I 40 lamarckiana \"P E 3 I & { 3 7 30 poeyana Streblus tepidus IIIIIIILIJI IIIIIIIIIIII Triloculina trigonula ,J I—F Archaias angulatus Asterigerina car Discorbis conc f lor E lphidium discoi Guttulina austr 'Gypsina vesic is FAUNA I Hanzawaia concentrica, H. strattoni Peneroplis proteus Planorbulina mediterranens Poroeponides cribrorep Quinqueloculina agglutinans bicosta comp horr Sorites orbitolito Triloculina linneiana Buccella hannai FAUNA 2 Eponides antillarum Nodobaculariella atlantica Nonionella atlantica grateloupi Planulina orna’ra / IIIIIII IIIIIII Pyrgo peruviana I ‘Reussella atlantica Virgulina schreibersiana y» Amphistegina lessonii Angulogerina bella Anomalina io Bolivina f Cancris sagra Cassidul‘ma laevigata, C. curvata Cibicides deprimus pseudoungerianus Loxostomum subspinescens Marginulina advena Nonion affinis Pavonina atlantica Polymorphina pulchella Pyrgo comata Quinqueloculina poly Rectobolivina advena Robulus suborbicular Rotorbinella bas Sigmoilina s Siphonina bradyana Spiroloculina depres Astacolus ova Bolivina goé sii Discorbis floridensis Hanzawaia bertheloti Hb'glundina elegans Marginulinopsis subaculea Planulina foveola Robulus calcar convergens Saracenaria ampla Uvigerina flintii hispido—costata Textularia secasensis FAUNA 3 FAUNA 4 FAUNA 5 candeiana \/ Bigenerina irregularis Textularia mayori Textularia conica assemblage Sp iroplectammina floridana Textularia foliacea occidentalis Gaudryina aequa I O N N m SAMPLE NUMBERS ARENACEOUS SPECIES FREQUENCY DIS'RIBUTION OF SPECIES FORAMINIFERAL DISTRIBUTI)N OFF ST. PETERSBURG, FLA. 364220 0 - 56 (In pocket) No. 6 50 100 PERCENTAGE SCALE PROFESSIONAL PAPER 274-6 CHART 7 GEOLOGICAL SURVEY g SAMPLE NUMBERS ' A «monmmo—nNm¢mngNva-«omwngg‘tnwflsmfiifig "7 '\ mo”“““"“’°"°°$ "Nmm “S"‘L’Zflgtgegmgmmwwcvmmmmmncm mmm~:::£3£_~£22£~flfi_fi m’””” “N“ 03°": gwmmmmmma‘m‘” °°3 3v3vwvrvvvv< Triloculina trigonula FAUNA 1 Archaias angulatus Asterigerina carinata Discorbis concinnus Discorbis floridanus Guttulina australis H. *H. concentrica . . . s on' Hanzawala stratton1,,H. concentmca tratt 1 Loxostomum subspinescene ~ Nodobaculariella atlantica mexicana E Peneroplis proteus Pyrgo peruviana Quinqueloculina agglutinans dutemplei poeyana Sorites‘ orbitolitoides Triloculina linneiana comisfi FAUNA 2 Bolivina pulchella primitiva Buccella hannai Cibicides robertsonianus Eponides antillarum Lingulina carinata, 7 ,7 Nonionella atlanticai W7, 7* grateloup Planorbulina mediterranensis Planulina ornatafi Polymorphina pulchella Pyrgo nasuta Reiussella atlanticafi” Sigmoilina sybpoeyana Spiroloculina depressa Virgulina schreibersiana Wiesnerella auriculata FAUNA 3 PERCENT OF TOTAL BENTHOS IN CONCENTRATE ,, Amphistegina lessonii Angulogerina bella Anomalina io Cancris sagra Cassidulina curvata, C. laevigata m; Cibicides pse Gypsina vesicularis Loxostomum mayori Marginulina Nonion affinis Pavonina atlantica Poroeponides cribrorepandus Rectobolivina advena Robulus calcar,___\ Rotorbinella basilica Siphonina bradyana FAUNA 4 Astacolus ovatus Bolivina goésii daggarius Cibicides deprimus Dentalina communis Dimorphina sp. Discorbis floridensis Ehrenbergina spineai Glandulina comatula Hanzawaia bertheloti Hb'glundina elegans Lagenonodosaria scalaris Marginulinopsis densicostata subaculeata Planulina foveolata Pullenia quinqueloba Sigmoilina tenuis Uvigerina bellula flintii hispido—costata Valvulineria sp. FAUNA 5 Ammobaculites exiguus exilis Bigenerina irregularis Textularia secasensis candeiana mayori conica assemblage_x Textulariella barretti Gaudryina Proteonina atlantica Spiroplectammina floridanaiw Textularia foliacea occidentalis Pseudoclavulina constans Karreriella bradyi '3 a 1423 142‘ §Z€‘ 3:33 :SAMPLE NUMBERS ARENACEOUS SPECIES FREQUENCY DISTRIBUTION OF SPECIES FORAMINIFERAL DISTRIBUTION OFF THE COCOHATCHEE RIVER. FLA. 364220 0 — 56 (In pocket) No. 7 3475/ f[ a. 027 7/77‘ Palmlike Plants from the Dolores Formation (Triassic) Southwestern Colorado ég'gOLOGICAL SURVWI’ROFESSIONAL PAPER 274—H MVYVWF‘Wv—fi'vrv fi—‘.——v~.—_—__" '1 ’ —‘—— r. -A Y 4 7' — v——f__, Palmlike Plants from the Dolores F Ormation (Triassic) Southwestern Colorado By ROLAND W. BROWN A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL; SURVEY PROFESSIONAL PAPER 274—H UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY Thomas B Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Oflice Washington 25, D. C. CONTENTS Page . Page Abstract __________________________________________ 205 Relationships of Sanmigueh'a _________________________ 207 Geologic occurrence of the plants _____________________ 205 Bibliography _______________________________________ 209 Description of the specimens _________________________ 206 ILLUSTRATIONS Page FIGURE 29. Reconstruction of Sanmiguelia lewz'si Brown ___________________________________________________________ 206 PLATES 32, 33. Triassic plants from southwestern Colorado ________________________________________________ Following 206 III A SHORTER CONTRIBUTION TO GENERAL GEOLOGY PALMLIKE PLANTS FROM THE DOLORES FORMATION (TRIASSIC) IN SOUTHWESTERN -COLORADO By ROLAND W. BROWN ABSTRACT Plant remains from the Dolores formation in southwestern Colorado include a few small twigs of the conifer Brachyphyllum and large, many-ribbed leaves described as those of an angio- sperm, tentatively regarded as a primitive palm and named Sanmiguelia lewisi. This is the earliest known angiospermous flowering plant. Its occurrence in the Middle to Late Triassic, however, indicates that evidence for the origin of the angio- sperms should be looked for in the earlier Triassic or late Paleozoic. GEOLOGIC OCCURRENCE OF THE PLANTS In September 1953, G. EdWard Lewis, of the U. S. Geological Survey, searching for fossil remains in the upper part of the San Miguel River valley in south— western Colorado, found a palmlike leaf impression in the red Dolores formation near Placerville. This specimen, 38 cm long and 20 cm Wide, was fragmentary, lacking the apex and base. Therefore, further search was made at the same locality early in 1954, but Lewis found only a few more fragments, none of which gave a clue to the nature of the basal or petiolar portion of the leaves. However, in September 1954, Lewis and the writer, at an outcrop one-half mile north of the original site, succeeded in finding fairly good specimens that illustrate the salient features of these leaves, some of which were still attached to part of a structure- less cast of a stem. Further exploration of the fossil- bearing bed along its outcrop for 10 miles on both sides of the San Miguel River yielded equally good material to the writer in June, 1955. The principal locality is in SE}; sec. 12, T. 43 N ., R. 11 W., in a low cliff of reddish. calcareous sandstone, on the hillside of the right bank, 420 feet above the San Miguel River and 145 feet above the base of the Dolores formation, near the old Fall Creek post office, about 2% miles southeast of Placerville. Exposed there is the following pertinent sequence of strata, omitting the overlying 1000 feet of the Jurassic Wanakah and Morrison formations, and 250 feet of the Cretaceous Dakota sandstone: 364884—56 Partial section at old Fall Creek post ofice, Colorado I Jurassic Entrada sandstone. 50 ft. Whitish massive sandstones with few dark, shaly or limy thin-bedded strata. Triassic Dolores formation. 485 ft. Bright red, calcareous, massive and thin-bedded cliff-forming sandstones, few shales, and some conglomerates. It yields remains of meto- posaurs, phytosaurs, and plants. The lowermost whitish conglomeratic sandstone rests on an erosion surface of the Cutler formation. Permian . Cutler formation. 275 ft. Dark red shales and sandstones, with fragmentary plants. The Dolores formation, named and described by Whitman Cross (1899) from exposures in the valley of ' Dolores River in southwestern Colorado, at first included the red beds that are now known as the Cutler formation. However, the discovery in 1904 near Ouray of an angular unconformity below the fossili- ferous horizon in the Dolores caused Cross and his associates (Cross, Howe, Ransome, 1905; Cross, Ransome, 1905; Cross, Howe, Irving, 1907) to restrict the name Dolores to the Triassic strata and to name the more reddish underlying beds the Cutler formation, provisionally of Permian age. Cross reported that R. C. Hills in 1880 and 1882 had announced the dis— covery of fossils in the Dolores, including reptilian teeth, ganoid fishes, mollusks, and plants. Before these could be described, however, they were lost. Cross said that in the course of his survey of the area more reptilian teeth and a plant, identified by David White as Pachyphyllum [an error for Brachyphyllum] milnsteri, were found. All of these fossils reputedly indicated the Triassic age of the Dolores. At the Fall Creek post office locality in the Dolores the writer and Lewis in 1954 found phytosaurian teeth and the plant impressions described in the following pages, including the object of unknown identity (pl. 33, fig. 4). The nonmarine sediments of the Triassic in the “four corners” area of the southwestern States are believed 205 206 SHORTER CONTRIBUTIONS TO GENERAL ASSEMBLY FIGURE 29. Tentative reconstruction of Sanmigmlia lewisi Brown. In Me the leaves were probably somewhat stlfl, like the lower right hand leaf, rather than undulant. No sheaths or crests are shown because dlscemible evidence for them is lacking. X 115 to have accumulated on floodplains and in scattered pools and lakes at not many hundreds of feet above sea level. Such plants, therefore, as were entombed in the sediments, most likely originated in the lowlands of the basin of deposition, whereas remains of more dis- tant upland plants did not get into the fossil record. Whatever the reason, whether land vegetation was sparse on account of climatic conditions, or whether the circumstances attending the accumulation of the sediments were unfavorable, plant remains in the Dolores apparently are relatively scarce. DESCRIPTION OF THE SPECIMENS CONIFERS Brachyphyllum miinsteri Schenk Plate 33, figures 1, 3 Brachyphyllum mfinsteri Schenk, 1867, Die fossile flora. der Grenz- schichten des Keupers und Lias Frankens, p. 187, pl. 43, figs. 1—12. .The coniferous twigs from the Dolores formation, here figured, resemble closely those shown by Schenk from the Rhaetic formation at Bamberg, Germany. Neither these nor Schenk’s specimens, however, quite match the usual conception of the features of the genus Brachyphyllum with its closely appressed foliage. They can be compared with the twigs of some species of Palissya, Sequoia, Sphenolepidium, Araucarites, and others found in the Triassic and later formations. Without cones or other distinguishing features, the identification of remains of this kind is fraught with much uncertainty. Probably the specimen collected by Cross (1899) in the .Telluricb quadrangle and identi- fied by David White as Pachyphyllum mi‘msteri, was a representative of this species—the Pachyphyllum being an error for Brachyphyllum. Apparently, that specimen is now lost. Numerous species of conifers have been described from the Triassic of the United States, and particularly . from the southwestern States, notably in and around the Petrified Forest National Monument near Hol- brook, Arizona. There is, therefore, nothing especially unusual about the presence of such remains in the Triassic of southwestern Colorado. MONOCOTYLEDONS SANMIGUELIA Brown, :1. gen. Plants with alternate, simple, large, elliptic, strongly pleated, monocotyledonous, palmlike leaves. Stem rounded, tapering rapidly toward the apex, but other features unknown. Sanmiguelia lewisi Brown, n. sp. Plate 32, figures 1, 2; plate 33, figure 2 Elliptic to ovate entire, firm-textured leaves, attain- ing a length of 40 cm and width of 25 cm, conspicu- ously pleated, the strong ribs or veins converging toward the apex and the base. Midrib not differen- tiated. Between the 16 to 20 ribs are closely spaced parallel veinlets, as in all palms. The leaves are at- tached to the stem alternately by broad, thin, clasping, or probably sheathing petioles at vertical intervals of 4 cm, as shown by three leaves preserved in one block of sandstone. These permit a tentative reconstruction of the plant (fig. 29). However, neither sheaths nor crests (hastulas, ligules) are discernible, either because none existed or because the preservation around the stem is poor. The stem, now only a calcitic cast without cell structure, is rounded and in a vertical dis- tance of 10 cm narrows rapidly from a diameter of 4 cm to a blunt point, thus suggesting that it is the apical portion of a low, but mature plant. PLATE 32 FIGURES 1, 2. Sanmiguelia lewisi Brown. Fig. 1 shows the broad base of the petiole clasping the grayish, granular, rounded stem. The latter is a calcitic cast without cellular structure. X }6 GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 km; '. _ TRIASSIC PLANTS FROM SOUTHWESTERN COLORADO PLATE 32 PLATE 33 PROFESSIONAL PAPER 274 GEOLOGICAL SURVEY TRIASSIC PLANTS FROM SOUTHWESTERN COLORADO PALMLIKE PLAN TS The generic term Sanmiguelia. is feminine and is from the name of the river at the type locality. The species is named for G. Edward Lewis, vertebrate paleontologist of the U. S. Geological Survey and discoverer of the first specimens. RELATIONSHIPS OF SANMIGUELIA Sanmiguelia leun'si is regarded tentatively but credi- bly as a primitive palm. Superficially its leaves re- semble those of species of other monocotyledonous genera, such as Carludovica, Curculigo, Cypripedium, Joimn'llea, Lilium, Potamogeton, Setoria, Smilacz'na, Veratrum, and others. In some of these the plicate or accordion-pleated feature of the foliage is almost as strongly and comparably developed, and there may be no distinct midrib. Consequently, it is regrettable that no flowers, fruits, or stems with cell structure, have been found with Sanmiguelia to eliminate the foregoing genera completely and to establish its identity as a palm conclusively. Besides the suggestive morphologic appearance of its leaves, further reason for believing that Sanmiguelia represents a palm is derived from consideration of the probable ancestral features of primitive palms. The late Robert T. Jackson, from observations of the juvenile leaves of palm seedlings and with numerous lucid illustrations, discussed this phase of the subject in part, as follows (Jackson, 1899, p. 124, pl. 23): Amongst palms many species present interesting features of localized stages in development. I have studied the develop- ment of seedling palms of thirty-seven species and from published figures of von Martius and others know something of the early characters of forty-five species distributed through twenty-eight genera. Seedlings of all species have simple, early seed—leaves, and these are always one of two types. The first and most primitive type of seed-leaf is elongate, lanceolate, or oval, ter- minating more or less acutely, and with a longer or shorter rachis, usually long. This type is seen in Latam'a (pl. 23, fig. 94), Corypha (pl. 23, fig. 104), Cocos (pl. 23, fig. 102), Phoenix (pl. 23, figs. 100, 103, 103a), and many other genera. The sec- ond type of nepionic or seed-leaf is similar to the first, except that it is distally cleft. It is characteristic of Chrysalidocarpus (pl. 23, fig. 95), Kentia (pl. 23, fig. 96), Caryota (pl. 23, fig. 98), and many other genera. Very young specimens of genera which have distally cleft leaves or exceptional individuals show a trans- ient distal fusion of the apices of the leaf, as in Kentz'a (pl. 23, fig. 96), demonstrating that the cleft type is only a modification of the first or entire type. In some types as Stevensonia grandi- folia J. Dunc. (Phoenicophorum sechellarum H. Wendl.), which have distally cleft leaves, the first leaves are entire, the cleft character appearing later (third leaf of the specimen in hand). FROM DOLORES FORMATION 207 This is a further demonstration of the primitive nature of the entire type * * *. In Latam'a commersoni J. F. Gmel. (L. borbom’ca Lam.), the seed-leaf is ovate, lanceolate (pl. 23, fig. 94); during growth the later leaves become relatively broader, until, by distal tension, splits take place (pl. 23, fig. 93), and in the adult the leaf is a quite broad, fan-leaf type * * *. In the growth of a pinnate-leaved palm, when a new leaf first appears, the pinnae cling together laterally on their outer margin and to the distal leaflet, in such a way that the whole leaf simulates the entire type and demonstrates the simple dynamic genesis of this type of compound leaf from an ovate leaf like that of the young * * *. Also the distal tip of pinnate leaves repeats the form of nepionic leaves * * *. Some palms sucker from the base, and in such suckers we might expect to find localized stages in de- velopment, as is the case. In Raphis flabelliformis L’Herit., a fan-leaf palm, suckers from the base have simple leaves like pl. 23, fig. 94, and only in later growth are the typical fan—leaves of the species acquired * * *. Suckers of Chrysalidocarpus lutescens repeat the form of the seedling so closely that they are practically identical in leaf characters * * *. To Jackson’s discussion of juvenile leaf forms should now be added Eames’ recent interesting observations on the development of leaves in the mature stages of palms (1953). In general, the simple seedling leaves are succeeded, according to the kind of palm, by pin- nate or palmate leaves. Study of histological prepar- ations of leaf primordia indicates that the palmate is derived from the pinnate form, the central pinna of the palmate being the distal pinna of the pinnate leaf, and the rachis of the palmate leaf being shortened or tele- scoped. The rein or marginal flange that is present on erupting leaves of mature plants is seldom seen on the leaves of juvenile plants. Ancestral or reminiscent features have not been as definitely recognized in the lineage of the palms as they have in such genera as Ginkgo (Brown, 1939, p. 246; 1943, p. 862, figs. la—lc) and Oerm'dz‘phyllum (Brown, 1939). Until now the fossil record of the palms has dated from the Jurassic Lias. Lignier (1895, 1908), from collections in Normandy, described and illustrat- ed as Propalmophyllum liasinum, fragmentary portions of fan-shaped leaves showing chiefly the apexes of the petioles and bases of the fans, with a few ribs. Of these Seward (1931, p. 366) said— Some French fossils described by Prof. Lignier as Propalmophyl- lum bear a striking resemblance to pieces of a palm leaf, though they cannot be accepted as proof of the existence of palms in a Jurassic flora. Nevertheless, in a table on page 414 of the same book, Seward indicates Palmae as dating from the Jurassic. I, myself, see no reason for doubting Lignier’s identi- PLATE 33 FIGURES 1, 3. Coniferous twigs of Brachyphyllum mu‘nsteri Schenk. 2. Sanmiguelia lewisz‘ Brown, showing the numerous parallel veinlets between the prominent ribs. 4. Unknown object, probably an animal trail. X 1 5. Paloreodozites plicatus (Lesquereux) Knowlton, from the Paleocene Dawson arkose near Ramah, Colo. X1 Xlé X2 208 fication of his leaves as palms. True, some fragmen- tary Jurassic and later fossils, superficially somewhat resembling the fragments figured by Lignier, have been mistaken for remains of palms; but these are the egg capsules of chimaeroid fishes (Brown, 1946). The first authentic remains of palms found in the United States are from the early Upper Cretaceous. From then on, both fan and feather palms are not uncommon. The fossil wood of palms, known as Palmoxylon, is fairly abundant at some localities. When thoroughly silicified it is attractive and durable; and in Aboriginal American days it was sometimes used for making arrow-points and other artifacts. Fossil trunks, or portions thereof, that are sometimes misidentified as Palinomylon, are the Mesozoic ferns known as Tempskya. The fossil fruits of palms, par— ticularly of Nipa, are known. Others, sometimes called Palmocarpon, are somewhat indefinite and doubtful. More particularly pertinent to the discussion of the relationships of Sanmiguelia lewisi are leaves of Paloreo- doxites plicatus (Lesquereux) Knowlton (pl. 2, fig. 5) from Paleocene strata in the Denver basin, Colorado— the Denver formation at Golden; and the Dawson arkose at Ramah. The small fragment from the Raton formation at Tercio, described by Knowlton (1917, p. 287, pl. 63, fig. 1), must be regarded as doubtfully identified. These elliptic to ovate leaves (approxi- mately 20 cm in length and 7 cm in width, with 12 ribs) were called Oreodoxites plicatus by Lesquereux (1883, p. 122, pl. 18, figs. 1—4). Knowlton (1930, p. 41, pl. 11, figs. 1—4) changed the generic name of this species to Paloreodoxites because the genus Oreodoxites was founded by Goppert on an indefinite Permian seed, and because Lesquereux may not have known of Goppert’s genus but thought he was creating the name anew on the basis of similarities he saw between his leaves and those of the living Oreodom. Actually, as there appears to be no close relationship between Paloreodoacites and Oreodoxa, Knowlton’s name is not too happy a substitute. The prime question now is, Are the leaves of Paloreo- doxites plicatus leaflets of a large compound leaf, as Lesquereux seems to have conjectured; simple, mature leaves; or simple, seedling leaves? Because none of these leaves has been found attached to a rachis or stem, their exact nature is open to speculation. The leaves could be simple seedling leaves of fan or of feather palms, both kinds having been present in the Denver basin and adjoining areas during Paleocene time. The leaves could be mature leaflets of a pinnate palm, or they could be mature leaves of a primitive kind of palm, a leftover from early Mesozoic time. SHORTER CONTRIBUTIONS TO GENERAL ASSEMBLY Whatever the answer to the foregoing question, the leaves of Sanmiguelia. resemble somewhat those of Paloreodoxites and some from the Stonesfield slates in the Jurassic Oolite at Eyeford, England, called Lilia [an error for Lilium] lanceolata Buckman (in Murchison, 1845, p. 93, pl. 2, fig. 3). This is Buckman’s descrip- tion— Leaf ovato-lanceolate, with a slight acuminated point—leaf- stalk short. An elegant parallel veined endogenous leaf, having much the appearance of leaves of the liliaceous tribe of plants. On the same plate Buckman figured two somewhat similar but more fragmentary leaves as Naiadea acuminata, and Stricklandic acuminata, both of which he described as endogenous leaves. Seward (1904, p. 121, 122) synonymized “Lilia” and Naiadea with Podozamites stonesfieldensis and Stricklandia with Baiera phillipsi. As I have not seen these specimens I can form an independent opinion of them only from Buckman’s descriptions and illustrations. Considera- tion of these almost persuades me that perhaps Seward’s disposition of the specimens was not altogether appro— priate. Particularly, I am doubtful about Buckman’s pl. 2, fig. 3 of “Lilia”. How Buckman, whose other illustrations seem to be fairly accurate, could have drawn a coarsely ribbed leaf from a specimen that, if Seward is correct, should have no ribs but only nu- merous closely spaced parallel veins, as in typical Podozamites, I do not comprehend. His illustration looks too much like those of small leaves of Paloreo- doxiles, Sanmiguelia, or seedling leaves of living palms, to be dismissed too lightly as Podozamiles. Moreover, Seward (1904, p. 152, pl. 11, figs. 5, 6) described and figured as Phyllites a poplarlike leaf from the same beds. This leaf has the appearance of an authentic dicotyledonous leaf, and if it is such, it strongly sup- ports the opinion that primitive palms, or at least monocotyledons, also could have existed simulta- neously somewhere and perhaps in the same flora.1 Furthermore, the fan palms (Propalmophyllum) of Lignier were already in existence in Lias time in Normandy. The doubtful nature of “Lilia,” and the impossibility of demonstrating any but a superficial resemblance among “Lilia,” Paloreodoxites, and the specimens here being reported, necessitate a new name for the Colorado monocotyledon. Possibly Sanmiguelia lewisi represents some plant other than a palm or similar monocotyledon with parallel-veined leaves. For example, Oordaites has strap—shaped leaves whose veins are closely spaced but the leaves are not plicate or strongly ribbed. Perhaps the yuccalike leaves sometimes reported from Triassic 1Under the name Sassendorfites benkerti, Oskar Kuhn. in a report just received from Germany, describes and illustrates another dicotyledonous leaf, this from lower Jurassic strata at Sassendorf, near Bamberg. (Orion, J ahrg. 10. 110. 19—20, Oct. 1955.) PALMLIKE PLANTS FROM DOLORES FORMATION localities under the name Yuccites are cordaitean foliage. Some cycads have leaves comparable in size to those of Sanmiguelia. but the veins are not ribbed as in palms, and, if closely parallel, may fork or anasto- mose to make a notably reticulate pattern. So far as I am aware, no other extinct or living plants, except palms and species of the monocotyledons already mentioned, have leaves that match or closely resemble those of Sanmiguelia lew'isi. This species, if not a primitive palm, is a palmlike monocotyledon, whose simple leaves without midribs are fully developed, not seedling leaves, of a mature plant. If this be true, these specimens are the oldest known megascopic remains of the angiospermous flowering plants. Botanists and paleobotanists have long been looking for evidence concerning the time, place, and manner of 209 origin of the angiospermous plants. Adequate sum- 'maries of the speculations on this matter may be found in Arnold (1947, p. 333—365) and Axelrod (1952), with pertinent bibliographies. Sanmiguelia lewisi does not seem to provide answers to some of the fundamental questions involved in this speculation: Did the mono- cotyledons come from the dicotyledons or the dicotyle- dons from the monocotyledons or did both descend from a common ancestor? Did woody monocotyle- , dons derive from herbaceous ancestors? Did the ' angiosperms originate in upland areas, according to Axelrod’s thesis? As representatives of the angio- sperms existed in the early Jurassic it is not altogether surprising now to find their ancestors in the Triassic. Perhaps their ultimate origin must be sought in the Paleozoic. BIBLIOGRAPHY Arnold, C. A., 1947, An introduction to paleobotany: New York, McGraw-Hill Co. Axelrod, D. I., 1952, A theory of angiosperm evolution: Evolu- tion, v. 6, p. 29—60. Brown, Roland W., 1939, Fossil plants from the Colgate member of the Fox Hills sandstone and adjacent strata: U. S. Geol. Survey Prof. Paper 189, p. 239—275, pls. 48—63. —— 1939, Fossil leaves, fruits, and seeds of Cercidiphyllum: Jour. Paleontology, v. 13, p. 485—499. 1943, Sorne prehistoric trees of the United States: Jour. Forestry, v. 41, p. 861—868, fig. 1. . ———— 1946, Fossil egg capsules of chimaeroid fishes: Jour. Paleontology, v. 20, p. 261—266, pls. 38, 39. Buckman, James, 1845, in R. I. Murchison, Outline of the geology of the neighborhood of Cheltenham, p. 93—109, pls. 1—13. Cross, Whitman, Howe. Ernest, and Irving, J. D., 1907, Ouray quadrangle, Colorado: U. S. Geol. Survey, Geol. Atlas of the U. S., Folio 153. Cross, Whitman, HOWe, Ernest, and Ransome, F. L., 1905, Silverton quadrangle, Colorado: U. S. Geol. Survey, Geol. Atlas of the U. S., Folio 120. Cross, Whitman, and Purington, C. W., 1899, Telluride quad- rangle, Colorado: U. S. Geol. Survey, Geol. Atlas of the U. S., Folio 57. Cross, Whitman, and Ransome, F. L., 1905, Rico quadrangle, Colorado: U. S. Geol. Survey Atlas of the U. S., Folio 130. Eames, Arthur, J., 1953, Neglected morphology of the palm leaf: Phytomorphology, v. 3, no. 3, p. 172—189. Hills, R. .C., 1880, Note on the occurrence of fossils in the Triassic and Jurassic beds near San Miguel in Colorado: Am. Jour. Sci., v. 19, p. 490. 1882, Jura-Trias of southwestern Colorado: Am. Jour. Sci., v. 23, p. 243. Jackson, R. T., 1899, Localized stages in development in plants and animals, Mem. Boston Soc. Nat. Hist, v. 5, no. 4, p. 894153, pls. 16—25. Knowlton, F. H., 1917, Fossil floras of the Vermejo and Raton formations of Colorado and New Mexico: U. S. Geol. Survey Prof. Paper 101, p. 223—455. —— 1930, The flora of the Denver and associated formations of Colorado: U. S. Geol. Survey Prof. Paper 155. Lesquereux, Leo, 1883, The Cretaceous and Tertiary floras: U. S. Geol. Survey Terr. Rept., v. 8. Lignier, Octave, 1895, Vegetaux fossiles de Normandie—II, Con- tributions a la flore liasique de Sainte-Honorine—la-Guillaume (Orne.): Mem. Soc. Linn. Normandie, v. 18, p. 121—152, figs. 1—6. ——- Idem, 1908, V. Nouvelles recherches sur Ie Propal- mophyllum liasinum Lignier: Idem., v. 23, p. 1—14, pl. 1. Seward, A. C., 1904, Catalogue of the Mesozoic plants in the Department of geology British Museum (Natural History). The Jurassic flora—II, Liassic and oolitic floras of England. —— 1931, Plant life through the ages: New‘ York, The Macmillan Co. U. 5. GOVERNMENT PRINTING OFFICE: 1956 9/57.)“ Pf -.?7¢ ‘1 Additions to the Flora of the Spotted Ridge Formation in Central Oregon GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—1 Additions to the Flora of the Spotted Ridge Formation in Central Oregon By SERGIUS H. MAMAY and CHARLES E. READ A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—1 Tfle U. S. Geological Survey’s previously imdescm'éed eallectioii of fossil plants from t/te Spotted Ridge formation is fully described and illustrated, including t/zree flew species. UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Oflice ‘ Washington 25, D. C. CONTENTS Page Abstract ______________________________________________________________________________________________________ 2 1 1 Introduction __________________________________________________________________________________________________ 21 1 Stratigraphy of the Grindstone-Twelvemile Creeks Paleozoic Inlier ___________________________________________________ 212 Systematic descriptions _________________________________________________________________________________________ 214 ?Lepidodendroid branchlet __________________________________________________________________________________ 214 Genus M esocalamites Hirmer ________________________________________________________________________________ 214 Genus Phyllotheca Brongniart _______________________________________________________________________________ 216 Genus Asterophyllites Brongniart _____________________________________________________________________________ 218 Genus Pecopteris Brongniart _____________________________________________________ . ___________________________ 219 Genus Dicranophyllum Grand’ Eury __________________________________________________________________________ 219 Problematica-_______________________________-____________-__~______-_-__-____________; ____________________ 221 Discussion ____________________________________________________________________________________ _ _______________ 222 Literature cited ________________________________________________________________________________________________ 223 Index ________________________________________________________________________________________________________ 225 ILLUSTRATIONS [Plates 34—37 follow index] PLATE 34. Mesocalamites and Phyllotheca. 35. Phyllotheca pauh‘nensz’s Mamay and Read, n. sp. 36. Pecopteris, 2’Schizopten‘s, ?Cordaianthus, Asterophyllites, and 71epidodendroid branchlet. 37. Undetermined roots and Dicranophyllum rigidum Mamay and Read, n. sp. A SHORTER CONTRIBUTION TO GENERAL GEOLOGY ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION IN CENTRAL OREGON By SERGIUS H. MAMAY and CHARLES B. READ AB STRACT The U. S. Geological Survey’s previously undescribed collec— tion of fossil plants from the Spotted Ridge formation (Pennsyl- vanian) in central Oregon is fully described and illustrated. This includes three new species: Mesocalamites crooke’nsis, n. sp., Phyllotheca paulmensis, n. sp., and Dicwmophyllum rigidum, n. sp. The collection also contains an abundance of Pecoptem's oregone’nsis Arnold and Mesocalamites hespem’us (Arnold) Mamay and Read, as well as a minor representation of a few other plants, some problematical. The flora contains unusually few species, and comparisons of its components with other Pennsylvanian floras prompt the conclusion that on the basis of the fossil plants alone, the precise age of the Spotted Ridge formation within the Pennsylvanian cannot be deter- mined with any great degree of confidence. INTRODUCTION In 1938 S. A. Berthiaume and C. W. Merriam dis- covered abundant fossil plants in a sequence of upper Paleozoic sedimentary rocks exposed on the ranch of Orin Mills, about 15 miles southeast of Paulina, in Crook County, Oreg. The following year Merriam and Read revisited the locality and made a large collection of the fossil plants. The announcement of this discov— ery was published by Read and Merriam (1940) ;' this preliminary report included a tentative list of the com- ponents of the flora, along with a short discussion of their geographic relations and stratigraphic implica- tions. The geology of this region was later described in a report by Merriam and Berthiaume (1943), in which this'Paleozoic sequence was divided into three strati- graphic: units: the Coffee Creek, Spotted Ridge, and Coyote Butte formations. On the basis of marine in— vertebrate fossils, the Cotfee Creek formation was as- signed to the lower Carboniferous, and the Coyote Butte formation, to the Permian. The interposed Spotted Ridge formation, however, was found to be barren of invertebrate fossils; and consequently, the de- termination of its age was made on the basis of its fossil plant contents. This formation was assigned to the Pennsylvanian, with Pottsville age provisionally indi- . cated. A more detailed account of the stratigraphy of this region is given on page 212. In 1949 Chester A. Arnold and a group from the Uni- versity of Michigan visited this locality and made a collection of the fossil plants. This collection was re- cently described by Arnold (1953), who has advised us (1954, oral communication) that the University of Michigan collection was obtained at the site of Read and Merriam’s original excavation; thus, there is no' doubt that the two collections represent portions of the same flora. Arnold described two new species. The first, Pecop- teris oregonensis Arnold, is a delicate fernlike plant with dactylothecoid fructifications and highly variable foliage; fragments of this plant make up all but a small part of the total plant material in both the Uni- versity of Michigan and the U. S. Geological Survey’s collections. The other, Calamites hespem'us Arnold, is a calamarean stem species based on internal casts; the foliage and fructifications are unknown. Arnold also briefly described the detached vegetative and reproduc- tive parts of Phyllotheca sp.; although he made no specific determination, Arnold reiterated the opinion given by Read and Merriam that the Phyllotheoa ma— terial most closely resembles the Turkish species P. ralliz' Zeiller. ' In their preliminary analysis of this flora, Read and Merriam listed the genera Asterophyllz’tes, Gala/mites, Dactylotheca, Dicmnophylhom, Phyllotheca, and Sphe- noptem's (several species), as well as “Material referable to two new genera of cordaitalean affinities” and “some problematica not definitely assignable at present” (Read and Merriam, 1940, p. 109). Arnold, however, included the dactylothecoid fructifications, as well as sterile foliage reminiscent of certain sphenopterid species within the specific limits of Pecoptem’s orega- nensis. Arnold reported neither Asterophyllites nor cordaitalean material; and although fragments of Di- cmnophg/llum and Phyllotheca were present in the University of Michigan’s collection, they were appar- 211 212 CONTRIBUTIONS TO ently too incomplete and poorly preserved to warrant full description or specific determinations. > The U. S. Geological'Survey’s collection of Spotted Ridge plants has not yet been described in full detail; nor, to the best of the writers’ knowledge, have further collections of this material been made. It thus seems that the publication of a full description of this collec- tion and complete illustration of the flora, as a supple- ment to Arnold’s studies, should constitute a note of more than casual interest. The flora is especially sig- nificant in View of the rarity of Pennsylvanian plant records in the Western United States, as contrasted with their abundance in the Eastern and Midwestern States, and because of the presence of certain floristic components that occur only rarely in any of the known Pennsylvanian floras. A detailed knowledge of the flora ofythe Spotted Ridge formation also appears de- sirable as a complement to Merriam and Berthiaume’s description of the geology of the area involved, espe- cially since their determination of the age of the Spotted Ridge formation was so entirely dependent on this fossil—plant collection. The descriptions that fol— low are presented for the purpose of amplifying as much as possible our knowledge of the Spotted Ridge flora, primarily by discussion of those floristic elements not found by Arnold. STRATIGRAPHY OF THE GRINDSTONE-TWELVEMILE CREEKS PALEOZOIC INLIER The Grindstone-Twelvemile Creeks Paleozoic inlier, Crook County, Oreg., comprises parts of T. 18 S., Rs. 21 and 25 E., and T. 19 S., Rs. 24 and 25 E., and is about 15 miles southeast of Paulina. On the Upper Mills Ranch in an area of about 20 square miles, strongly folded Mississippian, Pennsylvanian, and Permian strata are exposed. Resting unconformably On these older rocks are less strongly folded Triassic and J was— sic strata. Nearly horizontal middle and late Tertiary extrusive volcanic and pyroclastic rocks apparently once completely overlay the Paleozoic and Mesozoic sequence but have now been locally eroded. First observed and reported by Packard (1928, 1932), the general stratigraphy and structure of the Paleozoic inlier was first described in some detail by Merriam and Berthiaume (1943). The following statement of the stratigraphic sequence is transcribed from their more detailed account. ' COFFEE CREEK FORMATION, LOWER CABBONIFEROUS General description—The Coffee Creek formation is named for exposures on a minor tributary of this name which enters Grindstone Creek south of Wade Butte. At the type section in sec. 30, T. 18 S., R. 25 E. 14 mile east of the spring at Mills sheep camp 9. line of limestone outcrops trend roughly north- east-southwest. In general the formation consists of well- bedded fairly pure limestones, carbonaceous limestones, argilla- ceous to sandy limestones, and calcareous sandstone. Expo— GENERAL GEOLOGY sures of the type Coifee Creek area were traced intermittently along the strike for a distance of about 11/4 miles from locality 93 on the south to locality 98 on the north. * * * Thickness.—~Estimates of thickness are greatly handicapped by deformation, and nowhere has the base of this formation been recognized. Conservative figures of 900 to 1000 feet are based on width of outcrop in the anticlines of Cofiee Creek, and north of Coyote Butte, where in the last instance the strata stand in nearly vertical position. Stratigraphic relations and age—The Coffee Creek formation represents the oldest Paleozoic division recognized in this region. Judging from the lithologic and paleontologic criteria its relationship to the overlying Spotted Ridge Pennsylvanian is one of disconformity. Overlap of the partly land-laid Spotted Ridge upon the Coifee Creek is suggested by distribu- tion of the two units, though stratigraphic evidence is inade- quate. In some localities the Coffee Creek is directly overlain by either Permian or Triassic beds. These unconformities are discussed below. The age of the Gtgantella horizon is based on the listed fauna and is Lower Carboniferous, roughly Viséan, in terms of the British succession. That the lower-sands of this division are not older than Lower Carboniferous is at- tested by presence of the product Striattfera, not known in strata of greater age. The preliminary faunal list is as follows: Dtbunophyllum oregonensts Merriam Lithostrotion (Lithostrotz'on) packa-rdt Merriam Lithostrotlon (Siphonodendron) oregonensts Merriam Campophyllum readt Merriam Gtgantella sp. Striatifera sp. Spirlfer cf. striatus (Martin) Tetrataxis sp. Small loxonemoid gastropods Lithistid sponge spicules All but the spirifer are very abundant, Striattfera the com- monest form ranging throughout. Gigantella has been found only in the key limestone bed about 45 feet below the top of the formation as shown at locality 2, where the bed is crowded with these shells in association with the corals listed. The Foraminifera, small gastropods, and sponge spicules are abun- dant at the same horizon ; they are silicified and can be prepared by the acid-etching treatment. SPOTTED RIDGE FORMATION,~ PENNSYLVANIAN General description—Sediments of the Spotted Ridge forma— tion are exceedingly variable in both vertical and horizontal direction, ranging from compact mudstones and cross-bedded sandstones to very coarse boulder conglomerates. Locally much bedded chert is present. The members thicken and thin in various directions or may pinch out completely within a short distance. Good exposures are rare because the outcrop belts are in alluviated valleys or somewhat depressed areas between strike ridges formed by more resistant Permian rocks. The best exposures are in the type section on the west flank of Spotted Ridge, extending south about 2 miles to locality 83. Plant-bearing sandstones and mudstones.——Sandstones with much carbonaceous material and recognizable plant remains appear to range throughout the formation, while the lenticular plant-bearing mudstones were found only in the upper part. The lowest sands with plants occur at locality 96 near the Coffee Creek contact. These basal deposits are sands of medium-grain and light neutral-gray color on fresh surface, weathering to various tones of limonite brown. Feldspar grains are abundant. Plant remains range from finely divided car- bonaceous debris to flattened stems several inches in length. ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION IN CENTRAL OREGON That a similar facies persists locally or recurs in some situa- tions is indicated by the presence of plant-bearing beds of much the same character at locality 108 within about 75 feet of the top of this division, possibly 900 feet stratigraphically above the locality first mentioned. Lenticular distribution of sedimentary types is apparent within the plant-bearing deposits. At the main plant locality on the west side of Spotted Ridge are fine sandstones, siltstones, and mudstones in varying order within a thickness of 5 feet. Intergradation from one layer to another is recognized. Fol- lowing the same approximate horizon southward a distance of 1A; mile to locality 7 one finds crossbedded sandstone lenses within a heavy conglomerate including 2-foot boulders. Some of the finer sands here contain plant remains in direct associa- tion with small nuculid bivalves, small gastropods, and what appears to be a scaphopod about 1/2 inch in length. The lenticnlar mudstones and siltstones at locality 115 are of an unusual shade of medium-grayish olive green. Lamination is usually not well defined, and fissility is undeveloped. The sediment is very compact and brittle. In general the plants lie more or less parallel to bedding though occasional leaves and stems are decidedly oblique in position. The plants occur as coaly films; stems are much flattened but retain evidences of vascular structure. Impressions of leaves below the car- bonaceous films are sharply defined. The fine state of preser- vation of the dark leaves surrounded by a relatively light matrix lends added value to the plants for study purposes. While certain tongues or lenses within the plant-bearing beds are marine or brackish it is believed that most of the sedi- ments in this facies are land—laid, though an estuarine origin in part is not unlikely. The plants do not appear to have suf— feredvtransportation; in fact, some calamite stalks with whorls of twigs appear to be essentially in position of growth. * * * Thickness—In view of intense folding and lack of continuous outcrop it was not found possible to arrive at accurate figures regarding thickness. Variability in lithology from place to place along the outcrop belts suggests great differences in thickness of the entire section and of its individual members. This ap— plies particularly to the conglomerates, and to the cherts, which last are entirely absent at certain localities in horizons where they would be expected. Judging roughly from width of out- crop the formation at the type section, extending through 10- cality 115, is probably 1000 feet thick. Southward along Twelvemile Creek the thickness is at least 1000 feet, while on the north slope of Coyote Butte it may, with the included oherts, exceed 1500 feet. Stratigraphic relations and age—The lowest exposed Spotted Ridge beds recognized lie in the vicinity of locality 96 where plant-bearing sands were found within a few feet of a well- exposed limestone bed of the Gigantella horizon and therefore near the top of the Coffee Creek Lower Carboniferous. Uplift and emergence following deposition of the purely marine upper Coffee Creek is suggested by the probable terrestrial or estuarine nature of these lower Spotted Ridge deposits. Nothing conclu- sive has, however, been determined regarding the magnitude of the break separating Coffee Creek from Spotted Ridge beyond the fact that the marine faunas of the upper Coffee Creek are of Lower Carboniferous age, while floral evidence suggests a Lower Pennsylvanian age for the upper Spotted Ridge beds. The Coyote Butte Permian is unconformable upon the Spotted Ridge. Judging from fossil evidence there is in all probability a hiatus representing a portion of the Lower Permian and per— haps most of the Upper Pennsylvanian. A sharply defined con- tact between Spotted Ridge sandstones and relatively pure lime- stone of the Coyote Butte is exposed at locality 105 in the southwestern portion of the area. There is here a slight angular 213 discordance between the two divisions. The Coyote Butte for- mation is regarded as marine in contrast to the partly estuarine, terrestrial and alluvial or delta-plain character of the under- lying Spotted Ridge. While no determinable marine fossils were discovered in the Spotted Ridge formation, reliable evidence regarding its age is provided by the flora found at locality 115 in a horizon within the upper 400 feet. * * * Read and Merriam conclude that the flora is Lower Pennsyl- vanian, stating, however, that the possibility of its being Upper Pennsylvanian cannot be completely ruled out. If the flora ultimately proves to be Lower Pennsylvanian, it is likely that no great gap exists between the Coffee Creek and Spotted Ridge formations. COYOTE BUTTE FORMATION, PERMIAN G eneral description—The youngest Paleozoic beds of the area comprise a sequence in which massive limestones form the most conspicuous exposures. These produce prominent ridges, buttes, and small circular hills or knobs subsidiary to the main ridge slopes. Steeply dipping strata forming the crest of Coyote Butte near the southern limit of the map constitute the type section of the division. The Coyote Butte beds here lie in the north limb of a tight syncline overturned toward the south. Another bold outcrop of the formation is found in the belt of limestone extending north—northeast about 4 miles from the vicinity of Tuckers Butte to the spring at locality 92. A third area of Permian beds includes the limestone exposures in the northeast portion of the map, one tongue of which extends southwest beyond Twelvemile Creek where it is covered by Tertiary lava. At the type section the lower portion of the Coyote Butte is generally a light olive-gray limestone, often crinoidal and locally containing abundant fusulinids. Higher in the section, at the summit of Coyote Butte, the limestone becomes purer, finer- grained, deep olive~gray and more distinctly bedded. In this upper portion there are fewer fusulinids, while brachiopods are common. * * * Limestones of the Coyote Butte formation are interbedded with large amounts of sandstones. Furthermore the discon- tinuous nature of some of the limestone exposures leads to the impression that these deposits are lenticular within the more arenaceous facies. Generally speaking, exposures of the sands are poor, while the limestones form prominent linear or cir- cumscribed exposures. Northeast of locality 123 in the center of the map several zones of sandstone float alternate with fusu» linid limestones. * " * Thickness.—At the type section on Coyote Butte approxi- mately 900 feet of the Permian beds is exposed. Estimates of thickness on Spotted Ridge and north of Tuckers Butte are approximately the same. However, exact thicknesses cannot be given since bedding is poor and folds within the massive limestone are difficult to work out. Where the formation is largely aLenaceous the exposures are poor. Unconformable relation of the Permian to overlying beds further eliminates true thickness estimation. Stratigraphic relations and age—The Coyote Butte forma- tion is unconformable on the Spotted Ridge Pennsylvanian, as suggested by pinching out of the Pennsylvanian strata in sec. 5, T. 19 S., R. 25 E., where the contact between Coyote Butte limestone and the Lower Carboniferous Coffee Creek formation is apparently depositional. At locality 105 north of Tuckers Butte an exposure of the lower contact of the Per- mian shows a slight angular discordance and a definite trunca- tion of the conglomeratic and sandy beds of the underlying 214 formation. On the basis of lithology and position the latter beds are presumed to be the Spotted Ridge formation. Further- more, on the west side of Spotted Ridge and at several other localities the basal Coyote Butte strata are very pebbly lime- stones and calcareous conglomerates, probably indicating re- working of subjacent Pennsylvanian clastics. Fusulinids, corals, and brachiopods from the Coyote Butte formation indicate a Permian age for these beds. Several faunal zones are undoubtedly represented but have not been differentiated in view of the complex structure and lenticularity of sedimentation. More refined studies of structure, stratig- raphy, and sedimentation will be required to work out the details of this zonation. Since the Spotted Ridge plant-bear- ing beds a short distance below the Coyote Butte formation are regarded as Lower Pennsylvanian, a hiatus of some magni- tude is indicated between the two formations. Nearly all the localities in the lower part of the formation have yielded a new species of Parafusulma. In addition, species of Sch/wage- rina are found at several localities as well as forms tentatively referred to as Fusulinella and Triticites. Field evidence shows that several of the fusulinid types are either associated or occur in almost the same horizon. The fusulines imply that the Coyote Butte is not lowest Permian. Dr. G. Arthur Cooper is now completing a detailed study of the Coyote Butte brachiopods and reports that most of the” species are of Asiatic aflinity; a few are almost exact identities with Russian forms from the Urals and Timan. According to Cooper the brachipods indicate Lower Permian. The follow- ing identifications were supplied by Cooper: Productus cf. P. mammatus Keyserling P. .aif. P. porrectus Kutorga Avom‘a tuberculata Schellwien Linoproductus cf. L. sinuata King Juresanw aft. J. juresancnsis Tschernyschew Waagc-noconcha n. sp. 1 Krotom’a pustulata Keyserling Keyserlingina sp. Mamgintfera cf. M. involuta Tschernyschew Rhynchopom n. sp. Camarophoria mutabilis n. var. U. biplicata Stuckenberg 0. karm‘nskyi Tschernyschew Notothym‘s mtcleola Kutorga Notothym‘s n. sp. Martiniopsis sp. Spiriferella n. sp. In a recent study of rugose corals from the Coyote Butte formation Merriam (1942) has described the following forms: Waagenophylmm washbumi Merriam Waagenophyllum ochocoensis Merriam Waagenophyllum sp. a. Waagenophyllum sp. b. I/ithostrotion (I/ithostrotionella) occidentalis Merriam I/ithostrotion (I/L'thostrotionellal) berthiaumi Merriam The species of Waagenophyllum support a Permian age and point to an Old World relationship of the faunas. The ammonoid ansiam‘tes merriami Miller and Furnish was found in the region covered by the present survey, but whether it came from the Spotted Ridge Pennsylvanian or the Coyote Butte is not known. According to Miller and Furnish * * * it appears to be of either Upper Pennsylvanian or Lower Permian age. CONTRIBUTIONS T0 GENERAL GEOLOGY SYSTEMATIC DESCRIPTIONS Division LYCOPSIDA iLepidodendrid branchlet Plate 36, figure 13 This small specimen represents the terminal part of a slender leafy twig, probably of lepidodendrid af- finity. It is 4.5 cm long, with a maximum diameter of 6 mm, measured so as to include the leaves in the foli— ated part. The lower half or so of the specimen bears no appendages or scars of attachment; on the upper half, however, there are a number of small (reach- ing 4 mm in length), closely imbricated leaves, whose shape cannot be made out satisfactorily. A part of the upper half of the specimen was appar- ently defoliated before preservation, and in this part a few vertically elongated, spirally arranged de- pressions may be seen faintly (pl. 36, fig. 13,); these are strongly suggestive of lepidodendrid leaf cushions. Aside from Arnold’s observation of a single impres- sion of a stigmarian rootstock in the University of Michigan’s collection, the specimen discussed here, if properly identified, represents the only suggestion of the presence of an arborescent lycopodiaceous element in the Spotted Ridge flora. Division SPHENOPSIDA Genus MESOCALAMITES Hirmer In their monograph of the calamitaleans of western Europe, Kidston and J ongmans (1917) recognized that certain species of Calamites were characterized by the occurrence of directly superposed ribs at some of the nodes, in contrast to the more typically alternating ribs of most of the species. These forms with super- posed ribs were segregated, without nomenclatural distinction, into a group referred to as i‘Section II” (1917, p. 188) ; it was pointed out that they represent a morphologically and chronologically intermediate stage between the typical Ualamz'tes and the older, sup- posedly more primitive Asterocalamz'tes, in which all the ribs are superposed. In a subsequent publication Hirmer (1927, p. 382) gave formal recognition to the six species placed in Kidston and J ongmans’ “Section II” of Calamites (0. roemem' Goeppert, 0. cistz'iformz's Stur, 0. taitz'cmus Kidston and J ongmans, 0. hauem' Stur, 0. ramifer Stur, and 0. approximatiformis Stur) , erecting the new genus Mesocalamz’tes for their accommodation. This treat- ment may prove objectionable to some paleobotonists on the grounds that there is insufficient comparative knowledge of the foliar and fruiting parts to warrant a generic separation of Mesocalamites from Calamites. In supporting Hirmer’s adoption of the name Meso- ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION 1N CENTRAL OREGON . calamites, however, the present writers feel that this is justifiable from the standpoint of convenience in re- ferring to two types of calamarian pith casts that may be readily distinguished from each other on the basis of nodal organization. It is simpler and less confusing to use the descriptive designation M esocalamz'tes than the noncommittal term “Section II of Calamites.” Mesocalamitean pith casts, in most cases not too well preserved, constitute a conspicuous element in the U. S. Geological Survey’s collection of Spotted Ridge plants. Most of these conform closely with Arnold’s description of Calamites hespem‘us, but a few specimens clearly in- dicate that more than 1 and probably 3 species are actually present in this assemblage. Although M esocalamitcs is mentioned in Arnold’s discussion of this species, it is used only as an informal group designation. In conformity with the authors’ views regarding the desirability of maintaining I-Iirmer’s distinction between pith casts of Calamites and M esocalamz'tes, the following nomenclatural adj ust- ment is proposed. Mesocalamites hesperius (Arnold) Mamay and Read, 11. comb. Plate 34, figure 3 Calamites hesperius Arnold, 1953, Palaeontgraphica, Band 93, Abt. B, p. 62—63, pl. 24, figs. 1, 6—8. Although a few specimens in the U. S. Geological Sur- vey’s collection are rather larger than any reported by Arnold, most of the specimens present nothing in the way of features that might suggest a necessity for expansion or emendation of Arnold’s original diag- nosis. A specimen of Mesocalamites hespem’us from the U. S. Geological Survey’s collection is shown in plate 34, figure 3. Mesocalamites crookensis Mamay and Read, n. sp. Plate 34, figures 4, 4a This description is based on a single specimen, which consists of one side of a flattened internal stem cast. Although the specimen is not well preserved, it none— theless clearly exhibits the more critical features upon which the identification of calamitean species is chiefly based; that is, the organization of the ribs and nodes. The specimen is a straight segment of the stem, 14 cm long, with a maximum width of 2.0 cm. It seems prob- able that the entire width of the stem is represented, for differences in width of the fragment are negligible throughout its length. Nine nodes are present, with eight complete internodes and an incomplete one at either end of the specimen. The internodes are all shorter than the width of the specimen, ranging only from 1.4 to 1.5 cm in length. The specimen shows no evidence of branch scars, tubercles, or leaves. The ribs are essentially straight. They range from 1.0 mm to more usual widths of 1.5 mm and are sep— 379717—56—2 215 arated from each other by distinct grooves. The num- ber of ribs on the exposed side of the specimen ranges from 10 to 12 on each internode. The nodes are clearly defined but lack any distinguishing features other than the transverse grooves that mark their positions. The overall aspect of this specimen is shown in plate 34, figure 4. This specimen is interesting chiefly because the ribs are preponderantly in direct superposition at the nodes, thus providing a close approach to the type of nodal organization that distinguishes Asterooalamz'tes from the true Calamites. Alternation of the ribs is, in fact, evident at only 4 of the 9 nodes present in the specimen. In each of these 4, only 3 or 4 of the total of 10 or 12 ribs may be seen to alternate with those of the next internode. The few ribs that do show alter- nation have bluntly pointed or rounded ends, while the preponderantly nonalternating ribs are distinctly trun- cated at the nodes. (See pl. 34, fig. 4a.) Some of the ribs can be traced through nearly the entire length of the Specimen without an alteration occurring; most of the ribs may, in some part of the specimen, be followed over 3 or 4 nodes before finding an alterna- tion. Among the six species included by Hirmer in Mesa- calamites, M. crookensés may be most closely compared to M. approximatifo'rmis on the basis~of the relative rarity of alternating ribs common to both of these species. However, the regular occurrence of tubercles at the ends of the ribs of M. approximatifomz's, and their apparently complete absence in M. crookensz's in itself seems to constitute a sufficient basis for distin— guishing the two species; but aside from this difference . and that of relative sizes, the holotype of M. crookcnsis compares very closely to the specimen of M. approxi— matiformz's shown in text figures 79 and 80 of Kidston and Jongmans’ monograph (1917, p. 205). M. crookemz’s is distinguished from M. hcspem'us on 'the basis of the broader (2.5—3.0 mm) ribs, longer (2.3—3.5 cm) internodes, the presence of tubercles at the apical ends of the ribs, and the apparently higher fre— quency of alternating ribs in M. hespem'us. Arnold makes no mention of the relative frequencies of alter- nating and superposed ribs, but his photographs of the holotype of M. hespem’us (1953, pl. 24, figs. 1, 6, 7, and 8) show a much more nearly equal distribution of the two than present in M. crookensis. Insofar as they are presently known on the basis of the limited amount of material at hand, the features of M esocalamz'tes (woo/semis are summarized below. Specific diagnosz'8.—Internal casts at least 2 cm in diameter; internodes reaching 1.5 cm in length, con- sistently wider than long, and differing little in length in the same specimen. Ribs straight, lacking tuber- cles, 1.0—1.5 mm wide, and separated by distinct 216 grooves. Ribs preponderantly superposed, usually continuous over several nodes; alternating ribs with bluntly pointed apices, superposed ribs truncated. Branch scars not known. Holotype.—USNM 40708. Mesocalamites sp. indet. Plate 34, figures 1, 1a, 2 The presence of still a third mesocalamitean species in this flora is indicated by a few specimens which, al- though too fragmentary for positive specific determi- nation, display some features that strongly oppose their identification with either M. hespem'us or M. crookensis. The largest specimen, shown in plate 34, figure 2, is a fragment of the flattened impression of a stem, 13 cm long; the widest part of the specimen measures 1.7 cm, but it is not clear whether this represents the entire width of the specimen or not. Only two nodes are preserved; the intervening inter- node is quite long, measuring 5.8 cm. 'The ribs are straight and very narrow in proportion to their length, in no instance exceeding 1.0 mm (and most typically from 0.5—0.7 mm) in width. The nodal relations of the ribs cannot be made out in this‘ specimen. The fragmentary specimen shown in plate 34, figures 1 and 1a, is 4.8 cm long and contains only 1 node (the 2 nearly transverse lines, 1 near each end of the specimen, are not nodes, but fractures in the matrix) ; the internodes were thus at least 2.8 cm long, measured from the single node to the farthest end of the specimen. As in the specimen described in the preceding para- graphs, the ribs of this one are proportionately narrow, measuring no more than 0.6—0.8 mm in width, and chiefly on this basis it is assumed that both specimens represent the same species. Although it is only a small fragment, this specimen clearly exhibits nodal superposition of its ribs, which limits the possibilities of its generic identity to Meso— calamz'tes. As shown in plate 34, figure 1a, all the ribs' are in direct superposition, and some of them converge toward a common point on the nodal line, as frequently occurs in the immediate area of calamitean branch scars. In this instance, however, there is no clear evi- dence of a branch scar, unless the shallow depression present at the point of convergence of the ribs may be interpreted as such. Even thOugh their superposed ribs indicate a relation- ship of these specimens to both Mesocalamites hespem'xus and M. crookensis, they appear to represent a different species by virtue of the great length of the internodes and the proportionately small width of the ribs. On the other hand, they show some resemblances to both M. ramifer (Stur) Hirmer, as illustrated by Kidston and J ongmans (1917, pl. 141, fig. 4), and M. cistiz’fmmz's (Stur) Hirmer (compare with Kidston and J ongmans, CONTRIBUTIONS TO GENERAL GEOLOGY 1917, pl. 142, fig. 2, and pl. 147, fig. 1), but more satis- factory specimens are necessary before either of these two species can be positively identified in the Spotted Ridge flora. Genus PHYLLOTHECA Brongniart Although more than 2 dozen species of Phyllotheca have been previously reported from different parts of the world, to the best of the writers’ knowledge, the Mills’ Ranch locality is the only source of this genus known in the United States at present. Phyllotheca actually constitutes a problematical and poorly understood genus, in spite of the frequency with which it has been recorded in the literature. Accord- ing to Seward’s (1898, p. 281—283) discussion of this genus, it can be distinguished from the related cala- marian genus Annulam’a only on the basis of relative development of the leaves of one whorl and the attitude of the whorls; in Phyllotkeca the basally fused leaves of any one whorl are all the same size and spread equally in all directions from the supporting axis, but those of Annularz'a are unequally developed and tend to lie in one plane. On the basis of this distinction the Oregon material is referable to Phyllothecu;1 it is described below in detail because of the unusual nature of some specimens that illustrate the actual organic continuity between stems, leaves, and fructifications. Such a continuity was apparently not demonstrable in the University of Michigan’s collection, for which reason Arnold made no definite specific determination. Phyilotheca paulinensis Mamay and Read, n. sp. Plate 34, figures 6—8, plate 35, figures 1—6 Phyllotheca sp. (cf. P. ralm Zeiller), Arnold, 1953, Palaeonto- graphica, Band 93, Abt. B, p. 63, pl, 24, fig. 2—5, 1953. With the execption of the fern Pecoptem's mega/name's Arnold, Phyllotheca paulinensz‘s appears to have been the most ubiquitous element of the Spotted Ridge flora, judging from the large number of fragments in the U. S. Geological Survey’s collection. Most of these consist of isolated leaves or parts of leaf whorls. Detached cones are abundant, and there are also a few fairly large stem fragments, some with lateral branches and fructifications attached. The general attitude of the leaves is shown in plate 34, figures 6 and 7, where they can be seen arising from 1The phyllothecoid aflinity of the Turkish species Phyllotheca rami Zeiller, which the Oregon material very closely.resembles, was ques- tioned by Gothan (1927, p. 150), primarily on the basis of the organi- zation of the cones of P. ralm. As the result of a restudy, as yet un- published, 01 the Carboniferous floras of Turkey, Jongmans has recently shared Gothan’s views; he has expressed the opinion that P. rail“ is a peculiar form of Annmarie, probably related to A. radiate (oralcom- munication delivered before the Eighth International Botanical Con- gress, Paris, 1954). The present writers, however, prefer to tentatively consider both P. rail“ and the Oregon material as truly phyllothecoid, in the absence of clearly demonstrable unequal formation of leaves or foliar mosaics. ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION IN CENTRAL OREGON the stem fragments at several of the nodes. The leaves generally stand out from the stem at a nearly perpen- dicular angle, with their tips gently bending upward to describe a shallow saucerlike whorl. . The leaves range in length from 5 mm on the smaller branchlets (pl. 34, fig. 6) to 1.5 cm on the larger axes (pl. 34, figs. 7, 8; pl. 35, figs. 3, 4). All the leaves of any given whorl, however, appear to be equally de- veloped. Their basal widths range from about 0.75 mm to 1.5 mm, but this does not seem to be con- sistently proportional to length, for the shorter leaves are usually relatively broader than the longer ones. The leaves are consistently widest at their bases and taper gently toward their tips, without any abrupt narrowing of the lamina. The basal fusion of the leaves into the collarlike structure that constitutes one of the distinguishing features of Phyllotheca is difficult to demonstrate be- cause, in instances where the leaf whorls are attached to a stem fragment, the presence of the stemitself ob- scures this feature. However, in a few whorls that were compressed in the plane of the node that bore them, the fusion can be seen between 3 or 4 members of a whorl (pl. 34, fig. 8, and pl. 35, fig. 3). The fusion is restricted to the very basalmost parts of the leaves and results in an extremely narrow collar that could easily be overlooked; the collar has not been observed to ex- ceed 1.5 mm in width. Although none of the specimens include a complete foliar whorl compressed in such a way that would fa- cilitate the determination of the exact number of leaves in a whorl, one nearly complete whorl (pl. 35, fig. 4) contains parts of 20 leaves, and less complete ones con- tain from 12 to 18. It thus seems likely that 2 dozen or more leaves constitute the full foliar complement , of a node. The venation of the leaves is not preserved. Most of the numerous cones are detached specimens, but a few were preserved in organic connection with leafy stem fragments, so that there exists no doubt con- cerning the relationship of these parts. The cones differ considerably in size; some are only 2.5 cm or so in length (pl. ‘35, fig. 2), but others reach lengths of 7 cm (pl. 35, fig. 6). The largest specimens are incomplete, suggesting that total lengths of con- siderably more than 7 cm may have been attained. The smallest specimens are only 6 or 7 mm wide, measured between the tips of the extended sterile appendages, ' while one incomplete specimen (pl. 35, fig. 5) is nearly 2 cm wide. The average width, however, is about 1 cm. The sterile appendages (bracts) are clearly shown by every cone specimen, but determining the number of bracts to a whorl has not been possible. In the larger specimens the whorls of bracts are usually spaced about 2 mm apart, and the free parts extending be- _ yond the sporangia reach 4 mm in length (pl. 35, fig. 6) . 217 They usually stand out from the cone axis at nearly a right angle, with their tips gently bent upward toward the apex of the cone. _ None of the critical details of the sporangia were ob- served; and it was impossible to isolate spores by chem- ical maceration, although several attempts were made with the more promising specimens. The fertile parts of the cones merely appear as dark masses interposed between the whorls of bracts (pl. 35, figs. 1, 5, and 6) ; in some placesvthese masses show rounded outlines or a series of rounded depressions 0r protuberances that indicate the original positions of the sporangia. In this connection, see the specimens shown in plate 34, fig- ure 5. Each specimen consists of a circularly arranged group of small rounded bodies less than 0.5 mm in diameter. In the better specimen, shown at the bottom of the photograph, there appear to be 8 or 9 of these objects, which may represent sporangia; opposite each there is a faint line which probably indicates the pres- ence of an accessory organ, perhaps a subtending bract. These two specimens quite possibly represent whorls of Pkg/Zlotheca sporangia that were compressed trans- versely to the axes of the cones that produced them, exposing the sporangia in such a way that the individ- uals may be made out fairly well. If so, however, these must have been produced by very small cones, for the circlets each measure only 2 mm or so in diameter, which is significantly smaller than the width of the smallest cone specimens present in the collection. There is also the further possibility that these represent the fructification of still another genus of articulates. The attachment of cones to vegetative parts is clearly illustrated in plate 35, figure 1. Here the terminal part of a slender branch fragment is shown, with parts of four cones attached. The largest of these is 5.5 cm long in its incomplete condition and appears to repre- sent a direct continuation of the tip of the vegetative axis; from the base of this cone arises a second, rather smaller one. The two nodes below these cones are ap- parently sterile, since only the ordinary foliar leaves are seen here. Each of the next two lower nodes, however, is fertile, one cone arising from each. In all cases where lateral cones have been seen, they are sessile, arising directly from the axil of a foliar whorl. The large specimen shown in plate 35, figure 2, is of interest in that it bears at least one slender lateral branch, to which three small cones are attached; this branch is seen arising from the left side, at about the middle of the specimen. A short distance below this branch is another, also fertile; although the actual organic connection of this branch to the main axis can— not be seen, their relative positions strongly suggest an original organic connection. At some places on the specimen, ordinary foliage arises from the nodes. The attachment of sterile foliage to the stem, however, may 218 be seen still more clearly in the specimen shown in plate 34, figure 6. This specimen is 17 cm long and contains 21 nodes, from several of which arise small sterile lateral branches; the remainder of the nodes show parts of ordinary foliar whorls. The largest stem fragment, shown in plate 35, figure 2, lacks part of its width through nearly half of its total length of approximately 24 em, but at either end the specimen appears to be nearly complete. Its width langes from 2 to 3 em, but this may be due to relative degrees of compaction at different parts of the speci- men. The internodes average about 1.5 cm in length and are thus consistently wider than long. Details of the ribbing and nodal organization are not clear. At the upper part of plate 35, figure 2, the ribs appear very narrow, but at the bottom of the same illustration they are appreciably wider; they seem to alternate at some of the nodes and continue uninterruptedly over others. The stems of Phyllotheca paulz‘nensz‘s thus display nodal features of Hirmer’s Mesooalamites, but in the absence of information regarding the relative fre- quencies of alternating and superposed ribs, there is no clear basis for a comparison to the pith casts referred to Mesocalamz'tes earlier in this paper. The proposal of the new specific name Phyllotheca paulz’nensz's for the Oregon material is based largely on comparisons with the three previously described spe- cies that are known in the fertile condition: P. deligues— cans Schmalhausen (1879) ,- P. uluguruam Gothan (1927), and P. rallii Zeiller (1899). The fructifica- tions of P. deliguescens and P. ulugmmana closely re- semble each other in the presence of elongated fertile zones between the sterile whorls of bracts, to which large numbers of fertile units were attached at random. In this feature these species stand apart from P. ralliz' and P. paulinensz's, in which the arrangement of both sterile and fertile whorls is much more compact, each internode producing only one whorl of fertile units. Although the cones of P. rallii and P. paulinensis thus show a typically calamostachyan organization in this respect, the reference of these species to Phyllotheca seems preferable on the basis of leaf characters, which are typically neither annularian nor asterophyllitean. P. paulinesis is extremely similar to P. ralliz'. How- ever, the two species are distinguishable from each other on the basis of the following points of contrast: Internodes of P. paulz'nensis do not exceed 2 cm in length and are consistently wider than long, but those of P. rallii are from 4 to 8 cm long and always longer than wide; cones of P. paulz'nemz's reach 7 cm or more in length, but those of P. rallii reach a maximum length of 4 cm; cones of P. paulinensz's ale b01ne sessile in the axils of foliar whorls, but those of P. rallii are pedicellate. CONTRIBUTIONS T0 GENERAL GEOLOGY The known characters of Phyllotheoa paulinensis are summarized below. Specific diagnosis—Largest known stem fragments to 3 cm in width; internodes averaging 1.5 cm in length, consistently wider than long; ribs apparently alternating or directly superposed at the nodes. Leaves produced as many as 20 or more in a whorl; leaves 0.5— 1.5 cm long, basally O.75—1.5 mm wide, tapering gently toward their tips; basally fused parts of leaf whorls producing a narrow sheath, usually not more than 1.5 mm wide. Cones 2.5~7 cm or more in length, 6 mm to nearly 2 cm wide, measured between tips of bracts; bracts extending to 4 mm beyond fertile units, pro- duced in whorls usually 2 mm apart; sterile whorls apparently separated by single whorls of fertile units, but mode of attachment of sporangia and nature of spores unknown; cones produced terminally on side branches or laterally, the lateral ones borne sessile in the axils of foliar whorls. Syntypes.——USNM 40710-40718. Genus ASTEROPHYLLITES Brongniart Cf. A. equisetiformis (Schlotheim) Brongniart Plate 36, figures 11 and 12 The surfaces of several slabs in the U. S. Geological Survey’s collection are covered with numerous speci- mens of this delicate foliage; the best of this material is shown in plate 36, figure 12. Most specimens consist of detached parts of foliar whorls; however, one very unsatisfactorily preserved specimen, not illustrated here, shows the attach- ment of leaves to the axis. The specimen contains 6 internodes, each about 1 cm long and 8 mm wide; each node bears a few leaves, but it is not possible to deter- mine the full number of leaves produced by a node. The ribbing and nodal organization of this specimen are obscure. The leaves range from 4 to 12 mm in length. They are very narrow, scarcely exceeding 0.5 mm in width in the larger specimens. The leaves taper gently, ter- minating in sharp points; the acicular appearance of the leaves is shown‘best in plate 36, figure 11, which shows the tip of a small branchlet, thickly clothed with small, immature leaves. Because of its imperfect preservation (and particu— larly in the absence of branching foliated axes that would demonstrate what differences exist between the leaves produced by the different orders of branches), this material cannot with any degree of confidence be specifically determined. There is little doubt, how— ever, that its reference to the genus Asterophylh’tes is correct. The specimens are somewhat reminiscent of some of the smaller leaved examples of Astemphyl- lites equ‘isetz’formz's, which is perhaps the most common species of this genus. ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION DI CENTRAL OREGON Division PTEROPSIDA Genus PECOPTERIS Brongniart Pecopteris oregonensis Arnold Plate 36, figures 1—7 This species comprises perhaps 75 percent of the plant material in the U. S. Geological Survey’s collection and is briefly mentioned here for the purpose of clarifying one point in Read and Merriam’s preliminary report of 1940. They tentatively listed “several species of Sphe- noptem‘s” and “Dactylotheca” as components of the flora ( 1940, p. 109) . Arnold, however, has treated the sphenopteroid foliar elements as variants of the more typicallypecopterid pinnules of Pecoptem’s oregonemz's, and the “Dactylotheca” as the fructification of that spe- cies. Careful reinspection of the U. S. Geological Sur- vey’s collection has revealed no basis for variance with Arnold’s treatment of these elements. It is thus ap- parent that truly sphenopterid leaves are absent from the Oregon flora, and all the fernlike foliage with its abundant fructifications almost certainly belongs to the single species Pecoptem's oregonemz's. Several speci- mens of this species are illustrated in plate 36, fig- ures 1—7. Arnold’s description of this species may be amplified by the U. S. Geological Survey’s collection with regard to one minor point. Arnold described the aphlebiae of P. oregonensis as being “only one centimeter or more long.” Several specimens in the U. S. Geological Sur- vey’s collection, however, illustrate that these append- ages were sometimes larger, more conspicuous struc- tures. While many of the specimens do fall within the size range given by Arnold, they are typically well over 2 cm in length (pl. 36, fig. 6), and 1 incomplete speci- men, shown in plate 36, figure 5, measures 3.3 cm to its broken tip. If it had been complete, this particular aphlebia would probably have been more than 4 cm long. In this respect, the aphlebiae of P. oregonensis compare much more closely with those of Dactylotheoa plmnoéa, as illustrated by Kidston (1924, pt. 5, pl. 93, figs. 2 and 3). Genus DICRANOPHYLLUM Grand’Eury This genus, still of problematical affinities, new con— tains at least 24 species, with occurrences having been reported in Asia, western Europe, Great Britain, Aus- tralia, and North America. Dicrarnophyllum is found chiefly in strata of Pennsylvanian or Permian age, al- though Dawson (1881) reported one species (D. austml- icum Dawson) from the Devonian of Australia. There is considerable doubt that the reference to Di- cmnophyllum is correct in the latter instance. Dicmnophg/llum is rare in North American rocks. Before Read and Merriam’s announcement of its pres- 219 ence in the Oregon flora, only six other occurrences had been recorded. These were D. dichotommn Lesquereux (1880, p. 553), D. dimorphum Lesquereux (1880, p. 554), D. glabrum (Dawson) Stopes (1914, p. 79; Bell, 1940, p. 132), 0.? gamettemz's Elias (1936, p. 12), and some questionable specimens doubtfully referred to Dz'm‘anophyllum by White (1899, p. 272). Dicranophyllum rigidum Mamay and Read, n. sp. Plate 37, figures 3-10a This species is represented in the U. S. Geological Survey’s collection by a fairly large number of speci- mens, including several large fragments of stout branches, apparently with most of their leaves pre-I served intact. Most of the material, however, con— sists of detached leaves and small stem fragments, some partly denuded of their leaves before preservation. None of the specimens demonstrate the fruiting habit of this plant. The branch fragments range up to about 1 cm in diameter, but most of the specimens are more slender than this, usually measuring only 2—5 mm in thickness. In only one specimen has branching been observed; however, the type of branching (sympodial or monopodial) cannot be determined from this speci- men. Details of the leaf cushions are not well preserved in this material; in only one specimen, shown in plate 37, figure 4, can they be seen at all. The exposed sur- face of this branch fragment appears to have been com- pletely decorticated before preservation and shows only a faint pat-tern of shallow leaf cushion impressions that give the specimen a superficially lepidodendroid aspect through their vertical elongation and spiral dis- position. As shown in this figure, the phyllotaxy is a fairly close spiral. The leaves were apparently persistent, for the de— corticated stem fragment shown in plate 37, figure 4, is the only specimen in the collection in which the leaves are not attached. The leaf bases are decurrent, a feature that is best seen in the smaller branches, Where the leaves are not very densely arranged. Decurrence of the leaves is illustrated in plate 37, figures 3, 9, 10, and 10a. The leaves differ considerably in length, ranging from about 1.5 to 4.5 or 5 cm long, and the stoutest specimens are about 1.5 mm wide at the base. Some ex— amples of the longer leaves may be seen in plate 37, figure 6. The branch fragment toward the right of this figure is densely covered with leaves, which makes it difficult to follow any individual leaf from its tip to the point of its attachment to the axis. However, it is quite evident that some of the leaves approach 5 cm in length. In contrast to these, the leaves shown 220 in plate 37, figures 10 and 10a, are not only much more loosely arranged on the axis but are also much shorter, measuring only 1.5 cm or so in length. The specimen shown in plate 37, figure 9, is of in- terest because it represents the apex of a branch, pre- served before complete elongation of the axis and ex- tension of the leaves. This fragment is 4 cm long, and its apical half is so densely covered with leaves that it is diflicult to distinguish the individual leaves from each other. The identity of this specimen as Dicmnophylhwn is nevertheless established by the forked tips clearly visible in some of the leaves. These leaves average about 2 cm in length, and their straight- ness gives the impression that they must have been fairly rigid in life, perhaps as much so as the needles of a spruce or fir. The same impression is lent by most of the other leaves in the collection, including the longer specimens. The chief distinguishing characteristic of Dioram— phyllmn (repeated bifurcation of the leaves) is well illustrated in plate 37, figures 7, 7a, 8, and 8a. The smaller leaves bifurcate twice, resulting in four essen- tially equal divisions at their tips. This point, how- ever is not clearly demonstrable in the longest leaves, for, it is difficult to trace the entire length of one leaf in the longest specimens. These bifurcate at least twice; in consideration of their greater length, how- ever, it is quite possible that they were more divided than the smaller leaves. Isolated leaves, each with a double bifurcation, are shown in plate 37, figures 7 and 8. The specimen shown in figure 8 probably represents part of one of the longer leaves; this fragment is 15 mm long, and each of the 4 ultimate segments is about 5 mm long. In the latter feature this specimen differs from that shown in plate 37, figure 7, for there the ultimate divisions are con- siderably shorter (less than 2 mm long), and more spinelike. Despite such differences as this, however, all the complete leaf specimens in the collection appear to be consistent in the following features: The two foliar segments resulting from each bifurcation always include a fairly narrow angle (usually between 30° and 40°), and each bifurcation of the lamina occurs above the middle of the foliar segment involved. Details of the venation are difficult to determine be- cause of faulty preservation. Some of the leaves con- tain coalified median streaks that give the impression of broad midveins when viewed with the naked eye. (See pl. 37, fig. 7.) These streaks may be as much as half the width of the lamina; they divide in accord- ance with the foliar divisions and proceed almost to the tips of the leaves. If these are vascular strands, there is no evidence that more than one was present in each laminar division. CONTRIBUTIONS T0 GENERAL GEOLOGY Although several of the previously recorded species of Dicramphyllum are too incompletely known for a satisfactory comparison to the Oregon material, the latter can be distinguished from most species primarily on the basis of leaf size, even though other points of contrast also exist. Several species have leaves that are considerably larger than those of D. rigidum; in this respect, the greatest contrast is shown by D. stria- tum Grand’Eury (1877) and D. Zatz’folz'um Sterzel (1907), leaves of which have been reported to exceed 20 cm in length. In the opposite extreme, we find the 2 species D. domimI N emej c (1929) and D.? brevifoh’wm Kawasaki (1931), whose relatively small dimensions preclude a conspecific identification with D. m'gidum; neither of these 2 species produced leaves longer than 17 mm. 1 With regard to leaf size, D. rigidum may perhaps be most closely compared to D. galliou/m, Grand’Eury (1877), the most completely understood representative of this genus. Although the leaves of these two species correspond rather closely in size, they differ in manner of foliar division, those of ‘D. rigidum displaying a con- sistently more symmetrical] pattern of bifurcation than those of D. galliomn. Dz‘cmnophyllwm figidwm is so named with reference to the generally rigid aspect of the leaves, and is diag- nosed below. 1 Specific Diagnosis.——-Foliage apparently persistent, rigid, arranged in closely crowded spiral phyllotaxy, and seated upon slightly elevated vertically elongated leaf cushions. Leaves 1.5—5.0 cm long, not more than 2 mm wide at their bases. Shorter leaves bifurcating only twice; the resultant four ultimate divisions sharply pointed, 2 mm or less in length; longest leaves possibly bifurcated more than twice, with ultimate segments reaching 5 or 6 mm in length. All bifurcations essen— tially symmetrical and occurring beyond the middle of the dividing segment; members of each division includ- ing an angle of approximately 30°—40°. Vasculariza- tion of leaves apparently consisting of a single median vein, bifurcating according to laminar divisions. Re- productive organs unknown. Syntypes.—USNM 40733—40740. It should be pointed cut here that in view of the range of leaf size, some authors may prefer the treat— ment of the two extremes as distinct species, but such a distinction cannot, in the writers’ opinions, be clearly demonstrated with the present material. The fact that several examples of leaves of intermediate length are present in the collection suggests, rather, that a single variable species is represented, possibly complicated by genetic polymorphism or by ecologically stimulated - variation of the foliage. ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION IN CENTRAL OREGON PROBLEMATIGA Mordaianthus Grand’Eury (cf. 0. longibracteatus Florin) Plate 36, figure 10 This tentative determination is offered on the basis of the single specimen illustrated in plate 36, figure 10, which appears to represent the top part of a poorly preserved cordaitean inflorescence. The axis of the fragment presents a rather slender appearance, being 5.5 cm long and only 2.5 mm wide at its base. It bears about a dozen alternately arranged bractlike append- ages, which arise from the axis at intervals of 7—11 mm. The bracts depart at wide angles and assume gently ascending positions. The largest bract, apparently complete, is 2.8 cm long; the most, however, are incom- plete, consisting of only the basal parts. A small budlike structure, 3—4 mm long, may be faintly seen in the axil of nearly every bract. The preservation of these structures is especially poor; but although their organizational details are completely ob- scured and no actual fruiting organs are preserved, they are sufficiently consistent in relationships of their size and position with the subtending bracts that they can scarcely be considered to be the results of accidental ' preservation. Even in the absence of any knowledge of the critical details, the gross appearance of this speci- men is strongly reminiscent of a Cordaianthus in- florescence, with its sterile bracts and axillary dwarf shoots. A tentative comparison to Gordaianthus Zongz'brac- teatus Florin is Suggested here, on the basis of the long bracts present in this specimen. In certain other fea- tures, such as its more slender main axis and less crowded appendages, the Oregon specimen presents a somewhat less robust, more lax aspect than that of 0. longibracteatus (cf. pl. 36, fig. 10, with Florin, 1950, pl. 1, fig. 1) ; these contrasting features suggest that the Oregon specimen might actually be determinable as a new species of Cordaianthus, were it more satisfactorily preserved. Of. Schizopteris trichomanoides Goeppert Plate 36, figures 8—9 The specimens illustrated in plate 36, figures 8 and 9, are mentioned here because of a notable similarity to a specimen figured by Zeiller (1892, pl. 1, fig. 8) under the binomial Schizoptem's trichomcmoz'des and appar- ently accepted by him as the remains of a genuine fern. The Oregon material consists of several fragments of a repeatedly bifurcated structure that are preserved as a dark stain on the surface of the rock, with only here and there a thin fleck of carbonaceous residue to suggest a truly vegetable origin. The largest fragment (pl. 36, fig. 9) is a fan-'shaped structure with a dozen or more ultimate divisions, which are the result of regularbi- ‘ 221 furcation at intervals of 3—7 mm. The individual seg- ments are narrow and straplike, not exceeding 2 mm in width, and essentially equal in dimensions to their counterparts resulting from the bifurcations. (See pl. 36, fig. 8.) In some parts of the specimens there are indications of a narrow dark band traversing the middle of the segments, suggesting a median nerve or some other type of mechanical thickening in the original organism. There is no indication of attachment to an axis, for the basal parts of the fragments are not present. Numerous examples of similarly bifurcated struc— tures have been recorded in paleobotanical literature, as, for example, Schizoptem’s dichotoma Gumbel (see Zeiller, 1892, pl. 1, fig. 7) or Marchantites érectus (Leckenby) Seward (Seward, 1898, fig. 49). However, the comparison made here is suggested because the over- all appearance of the Oregon material seems to resemble most closely Zeiller’s figure of Schizopteris trichoma- noides. The question of natural affinities of such fossils is difficult. They have been variously interpreted as lichens, liverworts, algae, and ferns, but in many in— stances, as in the present one, there has been little more than the gross outline of the plant preserved as a basis for its systematic interpretation. Roots of unknown affinity Plate 37, figures 1—2 These structures are briefly brought to attention here because they constitute a conspicuous element among the other plant fragments in the Spotted Ridge flora and because certain features of appearance could pos- sibly lead to misinterpretation and the unwarranted assumption of a nonexistent element in the flora. The collection contains numerous fragments of long, straplike organs measuring from 2 mm to 2 cm or more in width. (See pl. 37, fig. 2.) The longest fragments reach 7 cm in length; these show little difi'erence’in width throughout their length. They are preserved as very thin carbonaceous films, and one of their more conspicuous features is the finely striated nature of their surface, best shown in plate 37, figure 1. The striations are very closely spaced and run parallel to the length of the fragments. In most instances the edges of the specimens are smooth and unbroken; their overall appearance at first gives the impression that we are dealing with a group of poorly preserved small to medium parallel-veined leaves, perhaps of cordaitean affinity. Other features, however, establish these specimens as roots rather than leaves. Each specimen contains a single thick, usually centrally located strand, which is without doubt the vascular system of the root. This 222 structure is clearly shown in plate 37, figure 1. The absence of any considerable substance to the specimens suggests that compaction of the specimens was pre- ceded by nearly complete decay of the cortical tissues, with the result that the vascular system is clearly seen and is only slightly obscured by the remains of the dermal layer, represented by the parallel striations." In some specimens the central strand crosses diago- nally from one side of the root to the other, while the fine striations of the dermal layer uninterruptedly fol- low their courses parallel to the length of the root. Such a displacement in position of the vascular strand would not be unusual if, by decay of the surrounding cortical tissues, the strand were deprived of organic connection with the dermal layers. The specimen shown in plate 37, figure 1, is of fur- ther interest in that it illustrates the departure of a lateral rootlet from the right side of the specimen; the vascular strand of the lateral rootlet may be seen origi— nating from the central strand of the parent root. The surface of this specimen also contains several circular punctations that are interpreted as scars of attachment of rootlets. Although the rootlike nature of these specimens is quite obvious, it is not possible to correlate them with any of the foliar species already described. DISCUSSION The composition of the Spotted Ridge flora now may be systematically summarized as follows: Lycopsida ?Lepidodendroid branchlet ' Stigmarian rootstock Sphenopsida Asterophylh’tes sp. (cf. A. equisetiformis) Mesocalamites hespem‘us Meaooalamites crookensis Mesocalamitcs sp. indet. Phyllotheca paulinensis Pteropsida Pecoptem‘s oregomnsis fO'ordaia/nthus (cf. 0. longibracteatus) Dicranophyllwm rigidum Problematica Cf. Schxizopter'is trichomanoides Undetermined roots It again should be emphasized here that the flora is strongly dominated by four of the above—named ele- ments (Mesocalamz’tes hespem’us, Phyllotheca pauli— nemis, Pecoptem's oregonemis, and Dicranophyllum m'gz'dum) ; all the other entities are represented in the collection by single or, at the most, a very few spe- cimens. It is our opinion that this floristic picture is not an artificial one that has been distorted by insufli- ciently thorough collecting, for the U. S. Geological Survey’s collection is a large one, extremely rich in CONTRIBUTIONS TO GENERAL GEOLOGY plant fragments. The Spotted Ridge flora is, then, of primary interest from the point of view of its relatively few recognizable species as compared with the highly diversified plant assemblages that are more usually characteristic of the Pennsylvanian period. The pter— idosperms and sphenophylls are completely lacking; the lycopods and cordaitaleans are only weakly repre- sented by a few questionable specimens and a single species represents the ferns. The small number of species present in the flora stimulates even further interest when one compares the dominant forms with other Carboniferous floras— American or Europeanufor the purpose of deriving conclusions regarding the geologic age of the Spotted Ridge formation. It soon becomes apparent that, apart from the limited composition of this assemblage, it is further unique because its dominant elements cannot be compared to any American flora of well— established stratigraphic position. The problem of the geologic age of this flora is, therefore, much more com- plex than it first appears and demands a reconsidera- tion of the few identifiable species contained in the assemblage. Read and Merriam (1940) expressed the opinion that this flora is of early Pennsylvanian age; at the same time, however, they allowed the possibility of a late Pennsylvanian age designation. This opinion was based in part on negative evidence; that is, the ap- parent absence from the flora of certain genera diag- nostic of strata of late Pennsylvanian age. Arnold (1953, p. 67) also stated the opinion that the flora most likely represents early Pennsylvanian time. A consideration of the geologic occurrences of those species which can be most favorably compared with the Spotted Ridge flora reveals a conflicting and rather puzzling set of circumstances, described below. 1. Mésocalamz'tes is a genus that appears to be re- stricted to strata of Pottsville or pre-Pottsville age. Kidston and Jongmans (1917, p. 188) point out that with the exception of M. romem', which is known to occur in the basal part of the European Lower Car- boniferous, the species belonging to this group are characteristic of the upermost part of the Lower Car- boniferous (equivalent to the American Mississippian). To this may be added the evidence of known North American occurrences, cited by Arnold (1953, p. 62433); Mesocalamz'tes has been reported from the Pottsville of Pennsylvania and West Virginia, the Canso group (lower Pennsylvanian) of Nova Scotia, and the Namurian of Greenland. On the basis of simi— larities of M. hespem'ue and M. crookensz‘s to previously described members of this genus, then, one might read- ily assume a lower Pennsylvanian or even upper Mis— sissippian age for the Spotted Ridge formation, espe- cially if the associated floristic elements were not known. ADDITIONS TO THE FLORA OF THE SPOTTED RIDGE FORMATION IN CENTRAL OREGON 2. Insofar as it is presently understood, primarily on the basis of detached foliage or defoliated stem frag- ments, the genus Phyllotheca has predominantly Per- mian or early Mesozoic stratigraphic distribution. P. paulinemz’s, however, most closely resembles P. ralliz', a species that is known only from the Westphalian A of Turkey. Thus, the evidence of Phyllotheca paulin— ensis appears to support an early Pennsylvania age as- signment for the Spotted Ridge formation. 3. Pecoptewls oregomnsis is perhaps the most enig- matic element in the flora, from the standpoint of stratigraphic significance. Although it combines fea— tures reminiscent of several European species, its over- all aspect is suggestive of a closer relationship to P6- coptem's plumosa (Kidston’s Dactylotheca plumosa) than to any other species. This would seem to suggest .Pottsville age, according to present information on North American floras; White (1900, p. 884) has re- ported this species from the Sewanee coal of Tennessee, and Bell (1944, p. 84) has reported it as a common element in the Cumberland group (lower Pennsylvan- ian) of Nova Scotia. In Great Britain, where this species is much better understood, however, it is known to range throughout the entire upper Carboniferous; and, according to Kidston (1924, p. 391), “In the Rad- stock Series it occurs as a common and characteristic plant.” It thus appears that little confidence may be placed in Pecopterz's oregonemz's as an age indicator. 4. The presence of Dicmnophyllwm injects an ele- ment of decidedly late Pennsylvanian affinity into the Spotted Ridge flora. In the absence of satisfactory North American records of this genus, this again is largely based on the known stratigraphic occurrences of European species. In Europe Dicmnophyllum is well known from many localities, and although several species have been reported from Permian strata, Seward (1919, p. 93) has pointed out that it is more characteristically a Stephanian (upper Pennsylvanian) genus. Read and Merriam (1940, p. 111) suggest that the presence of Dicmnophyllwm in the Oregon flora may be interpreted as indicating a mesic upland facies instead of younger age. Although such a possibility should not be denied, the great preponderance of the fern Pecoptem's oregonensis would seem to discourage that interpretation. The set of facts presented above impresses the present writers with the apparent futility of attempting to de- termine the stratigraphic position, within the Pennsyl- vanian, of the Spotted Ridge formation. A reliable interpretation of this paleontologic situation is doubt- less hindered by imperfections in our understanding of the stratigraphic ranges of North American Paleozoic plants and their relationships with European floras and by the uniquely limited specific composition of the flora. As it now stands, however, the floristic evidence ap- 223 pears to weigh almost as heavily for a late Pennsyl- vanian age determination as for an early one. For these reasons, it is the writers’ opinion that pending the dis- covery of more complete paleontologic evidence, the age of the Spotted Ridge formation should be designated simply as Pennsylvanian, Without further speculatory qualification. LITERATURE CITED Arnold, G. A., 1953, Fossil plants of early Pennsylvanian type from central Oregon: Palaeontographica, Band 93, Abt. B, p. 61-68, pls. 24—25. Bell, W. A., 1940, The Pictou coal field, Nova Scotia: Canada Geol. Surv. Mem. 225. 1944, Carboniferous rocks and fossil floras of northern Nova Scotia: Canada Geol. Surv. Mem. 238. Dawson, J. W., 1881, Notes on new Erian (Devonian) plants: Geol. Soc. London Quart. Jour., v. 37, p. 299—308, pls. 12—13. Elias, M. K., 1936, Character and significance of the late Paleo- zoic flora at Garnett, p. 9—23, in Moore, R. C., Elias, M. K., and Newell, N. D., A “Permian” flora from the Pennsyl- vanian rocks of Kansas: Jour. Geol., v. 44, no. 1, p. 1—31. Florin, Rudolf, 1950, On female reproductive organs in the Cordaitinae: Acta Horti Bergiani, v. 15, no. 6, p. 111—134, pls. 1—6. Gothan, Walther, 1927, Fossile Pflanzen aus den Karru-Schich- ten der Umgebung des Ulugurugebirges in Deutsch-Ostra- frika: Palaeontographica, supp. 7, p. 145—152, pls. 18—19. Grand’Eury, F. C., 1877, Flore Carbonifere du departemente de la Loire et du centre de la France: Mem. Acad. Sci. Inst. France, v. 24, p. 1—624, pls. A—D, 1—34. Hirmer, Max, 1927, Handbuch der Palaobotanik: Munich and Berlin. Kawasaki, Shigetaro, 1931, The flora of the Heian system, part 2: Chosen (Korea) Geol. Surv. Bull., v. 6, no. 2, pls. 16—99. Kidston, Robert, 1924, Fossil plants of the Carboniferous rocks of Great Britain: Great Britain Geol. Surv. Mem., Paleon- tology, v. 2, pt. 5, p. 377—522, pls. 92—122. Kidston, Robert, and Jongmans, W. J ., 1915—1917, A monograph of the Calamites of western Europe: Meded. van de Rijk- sopsporing van Delfstoffen, no. 7, text, p. 1—207, 1917 ; atlas, pls. 1—158, 1915. Lesquereux, Leo, 1880, Description of the coal flora of the Car- boniferous formation in Pennsylvania and throughout the United States, Volume 2: Pennsylvania 2d Geol. Surv. Rept. P, p. 355—694. Merriam, C. W., 1942, Carboniferous and Permian corals from central Oregon: J our. Paleontology, v. 16, no. 3, p. 372—381. Merriam, C. W., and Berthiaume, S. A., 1943, Late Paleozoic formations of central Oregon : Geol. Soc. America Bull., v. 54, no. 2, p. 145—172. Miller, A. K., and Furnish, W. M., 1940, Studies of Carbonif- erous ammonoids, parts 5—7: J our. Paleontology, v. 14, no. 6, p. 521—543. Nemejc, Frantisek, 1929, On some discoveries of fossil plant remains in the Carboniferous districts of central Bohemia (II) : Bull. ,Int. Acad. Sci. Boheme, v. 30, p. 131—138, pls. 1—2. Packard, E. L., 1928, A new section of Paleozoic rocks in cen- tral Oregon: Am. Jour. Sci., 5th ser., v. 15, p. 221—224. 1932, A contribution to the Paleozoic geology of central, Oregon: Carnegie Inst. Washington Pub. 418, p. 105—113. Read, 0. B., and Merriam, C. W., 1940, A Pennsylvanian flora from central Oregon: Amer. J our. Sci, v. 238, no. 2. p. 107—111. 224 CONTRIBUTIONS TO GENERAL GEOLOGY Schmalhausen,. Johannes, 1879, Beitrage zur Juraflora Russ- White, David, 1899, Fossil flora of the lower coal measures of lands: Mem. Acad. ”Imp. Sci. St. Petersbourg (7), v. 27, Missouri: U. S. Geol. Surv. Mon. 37. no, 4, p, 1—96, p15, 1—16. 1900, The stratigraphic succession of fossil floras of the Seward, A. 0., 1898, Fossil plants, Volume 1 :/ Cambridge. Pottsville formations of the southern anthracite coal field: 1919’ ibid, Volume 4. U. S. Geol. Surv. 20th Ann. Rept, pt. 2. Zeiller, Rene, 1892, Etudes sur la flore fossile des depots Sterzel, J‘ T" 1907’ Die Karbon- und Rothegendflora 1m Gross- houillers et Permiens des environs de Brive: Etudes des herzogtum Baden: Grossh.-bad. geol. Landesanstalt Mitt., gites mineraux de la France, v. 2’ p. 1432, pls. 1_15_ Band 5, no. 2, p. 347—892, pls. 14—68. 1899, Etude sur la flore fossile de bassin houiller Stopes, 11- 0-, 1914. The “Fern Ledges” Carboniferous flora 0f d’Heraclee (Asie Mineure) : Mem. Soc. Geo]. France, St. John, New Brunswick: Canada Geol. Surv. Mem.n41. Paleont., V. 9, no. 1, p. 57—91, pls. 16—22. INDEX Page Abstract ______________________________________________________________________ 211 Annularia ___________________________________________________________ 216 approximatiformis, Calamites .................... 214 ______________________________ 215 .............................. 214 Asterophyllites _________________________________________________ ._ 211,218 equudiformle .............................................. __ 218, 222 amtralicum, Dicrunophullum __________ 219 Avonia tuberculata ____________________________________________________________ 214 Berthiaume, S. A., Merriam, O. W., quoted ________________________________ 212—214 berthiaumt, Lithostrotlon (Lithostrottomlla) ..................................... 214 Bibliography ___________________________ 223—224 biplicata, Camarophoria __________________________________ 214 brevifolium, Dicranophyllum ___________________________________________________ 220 Calamites ___________________________________________________________________ 211, 214 approximatiformts ____________________________________ _ 214 cistii/‘ormis _____________________________________________ _._ 214 haueri ..... _._. 214 heaperms ________________________________________________________ 211, 215 rumifer. . ____________________________________________________________ 214 roemeri ___________________ 214 taitianus __________________ 214 Cumarophoria biplicata ........ 214 karpinskyi _________________________________ , ______________________ 214 mutabilis _______________________________________________________ _ 214 Campophyllum readi ........ 212 cistiiformls, Mesocalamitesm 216 Coffee Creek formation ____________________________________________________ 211,212 Cooper, G1 Arthur, identifications by ______________ . 214 Cordaiamhus longibracteatus ______________ _. 221, 222, pl. 36 Coyote Butte formation. ______ 211, 213-214 cistilformta, Calamitcs _________________________________________________________ 214 crookemls, M esocalamltes _________________________________________ 215, 216, 222, pl. 34 Dadvlotheca ___________________________________________________________ 211 plumosa ______________ deliqueacem, Phyllotheca _____ Dibunophvllum oregonensis., dichotoma, Schizopteris ___________________________ dichotomum, Dicranophvllum _______________________ Dicranophyllum _____________ auatraticum _______________________________________________________________ 219 brevifolium ................ 220 dichotommn ........... 219 dimorphum ___________ 219 domim‘ ................ 220 gallicum ___________________________________________ . 220 gamdtemis ________________________________________ 219 glabrum... 219 latifolium. 220 rigidunL. ____________________________________________ 219, 222, pl. 37 striatum.. __________ 220 dimorphum, Dicranophullum_. ___________________________________ 219 Discussion _________________________________________________ 222—223 domim, Dicranophyuum ....................................................... 220 anslanites merriami __________________________________________________________ 214 equiwtiformis, Asterophyllites ............................... £18, 222 erectua, Marchamites __________________________________________________________ 221 Fusulinella ................................................................... 214 gallicum, Dicranophyllum _____________________________________________________ 220 garnattemis, Dicranophyllum ..................................... 219 Gigantella horizon ........... Page huueri, Calamltes .............................................................. 214 hesperlus, Calamfies ..................... 211,215 Mesocalamites .......................................... £16, 216, 222, pl. 34 Introduction ................................................................ 211-212 involuza, Maralmfera ............................... 214 juresanensis, Jurmmia ........................................................ 214 Juresanla juresanemis ......................... 214 karpimkul, Camarophon'a ..................................................... 214 Keyaerlingina sp_. .., ............... 214 Krotovia pustulata... latifolium, Dicranophullum‘ _ Lepidodendrid branchlet.. Limprodudus sinuata __________________________ 214 Lithostrotion (Lithostrotio'n) packardi ....... 212 (Lithostrationella) berthiuumi“ 214 Maiden/tails" 214 (Siphonodendron) oreaonemis ______________________________________________ 212 (Lithostrotion) packardi, Lahostrationu” 212 (Lithostrotionella) berthiaumf, Lithostrotion ........................... 214 occiderdalis, Lithostrotion _______________________________________ 214 longibracteatua, Cordaianthus ____________________________ _ 221, 222, pl. 36 Lycopsida .................................................................... 222 mammatus, Produdus ________________________________________________________ 214 Marchantitea creams. .................................. 221 M arginifera involuta. _ _ ........ 214 Martim'opsis sp ........... 214 Merriam, C. W., quoted ______________________________________________________ 214 Merriam, C. W., and Berthiaume, S. A., quoted. ...... 212—214 merriamz‘, ansianites __________________________ 214 Mesocalamites _______________ 214 approximatiformis ________________________________________ 215 cistiiformis _______________________________________________ 216 crookensis _____________________ . 215, 216, 222, pl. 34 hesperiua ____________________________________ 215 216, 222, p]. 34 ramifer. . . ____________________________ ._ ________ 216 roemm' .................................................... 222 sp ............................................. _._ 216, 222, pl. 34 mutabilis, Camaraphorla. . _; ........................... 214 Natothyns nucleola __________________________________________________ 214 n. sp ................................... 214 nucleola, Notothyris ___________________________________________________ 214 occidentalis, Whostration (Lithostrotlanella) ________________________________ 214 ochocoensia, Waagenophyllum ............................................ 214 aregonemz‘s, Dibunophyllum __________________________________________ . 212 Lithostroflon (Siphonodendron) Pecopteris ______________________________ packardi, Lithostrotion—(Luhostrotion) ______________________________________ 212 Parafusulina, new species of.. ........................................... 214 paulinemis, Phyllotheca ............................ 216, 222, 223, pls. 34, 35 Pecopten's oregonemis .................. 211, 216, 219, 222, 223, p]. 36 plumosa ................................................... 223 Phyllotheca ............................. 211,916 dela'quearcem....._._..._._..._..._.._.__.._._..n...“T .................... 218 paulmensis n. sp ......................................... £16, 222, 223, pls. 34, 35 rallii .................. ' ..... 2 11, 216, 218, 223 uluquruana ________ plumosu, Dadalotheca. sp ......................................... Pecopteris .................................. 223 porrectus, Productus _._. 214 Problematica ...................................................... 221, 222 Produdus mammatus. ................................................... 214 porrectus .................................................................. 214 225 22 6 INDEX Page Page Pteropslda ____________________________________________________________________ 222 Stigmarian rootstock ......................................................... 222 pustulata, Krotovia ____________________________________________________________ 214 Striatiflera ........... r ......................................................... 212 Stratigraphy, Gfind$tone-Twelvemile Creeks Paleozoic Inlier. ralm, Pin/110mm ___________________________________________________ 211, 216, 218, 223 ramffer, Calamites. _________________________________ 214 M esocalamues. _________________________________ 216 readi, Campophyllum ._ 212 Rhymhopora n. sp ____________________________________ 214 rigidum, Dicranophullum. ______________________________________ 219, 222, p]. 37 Tertiary lava ______ raemeri, Calamites ______________________________________________________ 214 Tetrataxis sp ............. Mesocalamites .................................... 222 trichamanoides, Schizopterls Roots of unknown aflinity. _____________________________________ 221—222, 111. 37 Triticites _________________ tuberculata, Ammia Schizopteris dichotoma ......................................................... 221 Tuckers Butte ................................................. 213 trichomanoidea ....................... . £21, 222, pl. 36 Schwaaerimz ____________________________ 214 ulwuruana, Phyllotheca ....................................................... 218 simmta, Linoproductus ____________________________________________________ 214 (Siphonodendron) orepommls, Lithoctration ____________________________ 212 Waagenoconchu n. sp .......................................................... 214 Sphenopsida _________________________________________ _ 222 Waaamophullum ochocoemis. 214 Sphenopteris ____________________________________________ 211 waehburnL . . _ ..‘ .......................................................... 214 Spirifer atrium ............................ 212 sp. a____.__..._‘. .......................................................... 214 Spiriferella, n. sp .................... .__ 214 sp. b .......................................................... 214 Spotted Ridge formation ___________________________________________________ 211, 212 washbumi, Waaaenophyllum ............................................. 214 PLATES 34—37 PLATE 34 [All figures natural size unless otherwise indicated on plate] FIGURES 1—2. Mesocalamz'tes sp. (p. 216). 1. Fragment of a mesocalamitean pith cast, containing one node. USNM 40705. .13. Same specimen, enlarged to show the superposed ribs and convergence of the ribs toward a common point on the nodal line. 2. Fragment of a mesocalamitean pith cast, containing two nodes and one complete internode. Note the long, narrow ribs. USNM 40706. 3. Mesocalamites hespem’us (Arnold) Mamay and Read, 11. comb. (p. 215). Fragment of pith cast, shown for comparison with Mesocalamites crookensis Mamay and Read. USNM 40707. 4, 4a. Mesocalamz'tes crookensis Mamay and Read, n. sp. (p. 215). ‘ 4. General view of the holotype. USNM 40708. 4a. Part of the holotype enlarged to show the preponderant superposition of the ribs at the nodes. 5. Two whorls of small (?) sporangia, possibly from an articulate cone. In the whorl shown at the bottom of the photo- graph, the faint lines opposite the sporangia are suggestive of subtending bracts. USNM 40709. 6——8. Phyllotheca paulinensis Mamay and Read, n. sp. (p. 216). ' 6. A large stem fragment, showing attachment of lateral branches and foliage. Syntype, USN M 40710. 7. A stem fragment with a small lateral branch attached, showing the general attitude of the leaves. Syntype, USNM 40711. 8. A specimen with four leaf whorls; basal fusion of leaves is shown in the two lowermost whorls. Syntype, USNM 40712. 34 PLATE PROFESSIONAL PAPER 274 GEOLOGICAL SURVEY A w(~ 1 4 ALA MITES AND PHYLLOTH ‘ 4 1MESO( GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 35 PHYLLOTHECA PA ULINENSIS MAMAY AND READ, N. SP. PLATE 35 [All figures natural size unlessthherwise indicated on plate] FIGURES 1—6. Phyllotheca paulinensis Mamay and Read, n. sp. (p. 216). 1. Fragment of an axis bearing a terminal cone and three lateral ones, with interposed sterile whorls. Syntype, USNM 40713. 2. Large fragment of a stem (slightly reduced), showing the attachment of leaves, lateral branches, and cones. The branch departing from about the middle of the left side of the axis bears three small cones. Syntype, USNM 40714. 3. Part of a foliar whorl, showing basal fusion of the leaves. Syntype, USN M 40715. 4. A foliar whorl containing parts of at least 20 leaves. Syntype, USNM 40716. 5. Fragment of an unusually thick cone. Syntype, USN M2407 l7. 6. An unusually long cone fragment, showing distribution and attitude of the bracts. Syntype, USN M 40718. FIGURES 1—7. 8—9. 10. ‘ 11—12. 13. PLATE 36 [All_'figures natural size unless otherwise indicated on plate], / Pecopteris oregonensis Arnold (p. 219). 1. Fragment of rachis, showing surface punctations and spinelike emergences. USNM 40719. 2, 3. Specimens of sterile foliage, illustrating differences in size and shape of pinnules. Figure 2, USNM 40720; figure 3, USNM 40721. 4. Fertile specimen; laminar tissues apparently decayed before preservation, leaving only the sporangia. USN M 40722. 5, 6. Large aphiebiae. Figure 5, USNM 40723; figure 6, USNM 40724. 7. Frond fragment, illustrating the typical aspect of this species. USNM 40725. Cf. Schizopteris trichomanoides Goeppert (p. 221). 8. Specimen showing the pattern of repeated bifurcations. USNM 40726. 9. Fragment showing fanlike general outline. USN M 40726. Cf. Cordaianthus longibracteatus Florin (p. 221). Fragment of an axis bearing several bracts and faintly preserved axillary budlike structures. USNM 40727. Cf. Asterophyllites equisetiformis Brongniart (p. 218). 11. Tip of a vegetative branch, thickly covered with young leaves. USN M 40728. 12. Rock slab bearing numerous specimens of foliage and fragments of two poorly preserved axes. USNM 40729. ?Lepidodendroid branchlet (p. 214). Slender axis bearing small leaves and showing faint surface ornamentation reminiscent of chz'dodendron leaf cushions. USNM 40730. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 a PLATE 36 PECOPTERIS, PSCHIZOPTERIS, PCORDAIANTHUS, ASTEROPHYLLITES, AND ?LEPIDODENDROID BRANCHLET PLATE 37 PROFESSIONAL PAPER 274 SURVEY GEOLOGICAL N. SP. 9 UNDETERMINED ROOTS AND DICRANOPHYLLUM RICIDUM MAMAY AND READ PLATE 37 [All figures natural size unless otherwise indicated on plate] 12. Undetermined roots (p. 22). 1. Specimen showing the median vascular strand, longitudinal striations of the dermal layer, and circular punc- tations on the surface. A lateral rootlet is shown departing from the left margin of the specimen; the con- nection of the vascular strand of the lateral rootlet with that of the parent root is also shown. USNM40731. 2. Rock slab containing several root fragments of different sizes. USNM 40732. :. Dicranophyllum rigidum Mamay and Read, n. sp. (p. 219). 3. Fragment of a foliated axis, showing decurrent leaf bases. Syntype, USNM 40733. 4. Fragment of a defoliated axis, showing vertically elongated leaf cushions. Syntype, USNM 40734. 5. Fragment of along, slender axis, bearing loosely arranged leaves. Syntype, USNM 40735. 6. Rock surface bearing two axes. The axis toward the right is densely covered with long leaves, some of which bifurcate twice toward the left. Syntype, USNM 40736. 7, 7a. Single leaf. Note the spinelike ultimate divisions, as contrasted with the longer ones shown in figures 8 and 8a. Syntype, USNM 40737. 8, 8a. Single leaf, showing twice-bifurcated lamina with four ultimate segments. Syntype, USNM 40738. 9. Tip of an axis, thickly clothed with leaves. Note the rigid aspect of the foliage. Syntype, USNM 40739. 10, 10a. Fragment of a leafy axis. Note the bifurcation of the leaves, their shortness, and their lax arrange— ment as compared with the specimen shown in figure 6. Syntype, USNM 40740. '4", , 9' P75 .2751d Fossils from the Eutaw Formation Chattahoochee River Region, Alabama-Georgia gEO'LOGICAL SURVEY PROFESSIONAL PAPER 274-J Fossils from the Eutaw Formation Chattahoochee River Region, Alabama-Georgia ByLLOYD‘WUJJANISTEPHENSON A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 27$J Descrzptz'om 5272a] z’l/mz‘rdtz'my of Late Cretaceom pe/ecypoa’s and one ammom'te UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF'THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U; S. Government Printing Office Washington 25, D. C. - Price 70 cents (paper cover) CONTENTS Page Systematic descriptions—Continued Abstract ——————————————————————————————————————————— 227 Mollusca—Con tinued Page. Introduction _______________________________________ 227 Arcidae ____________________________________ 235 Stratigraphic setting _________________________________ 228 Pteri'dae 2 7 Eutaw localities in east-central Alabama and adjacent 0 t 1d ________________________________ 23 parts of Georgia __________________________________ 228 s rein-ae ““““““““““““““““““ 38 Chattahoochee River ____________________________ 228 Anomudae --------------------------------- 242 Chattahoochee County, Ga, east of Chattahoochee Cardiidae __________________________________ 242 River --------------------------------------- 230 Veneridae ________________________ ' __________ 2 43 Russell County, A1a., west of Chattahoochee River- 231 Mactridae _________________________________ 244 Macon County, Ala _____________________________ 233 Go b l'dae 244 The Eutaw fauna and its relationships _________________ 234 Plar utl, ”EC; ___________________________ 2 Systematic descriptions ______________________________ 234 can men). 1 ae """"""""""""""" 47 Mollusca ________________________________________ 234 References _________________________________________ 248 Nuculidae _________________________________ 234 Index _____________________________________________ 249 ILLUSTRATIONS [Plates follow page 250] PLATE 38. Views of the Eutaw formation in the Chattahoochee region. 39. 40. 41. 42. 43. 44. 45. FIGURE 30. Sketch map of parts of Russell County, Ala. and Chattahoochee and Muskogee Counties, Ga, showing fossil- bearing localities _______________________________________ Nucula, Brem‘arca, and Protarca. Brem‘arca, Trigonarca, Pseudoptera, and Ostrea. Cardium (Trachycardium), G'ryphqea, Anemia, and Pseudoptera. Ostrea cretacea Morton. ‘ Ostrea (Lopha) and Ea'ogym. Cymbophora, Caryocorbula, Legumen, and Placenticeras. Corbula and Placenticeras. Page ___________________________________________ 229 A SHORTER CONTRIBUTION TO GENERAL GEOLOGY FOSSILS FROM THE EUTAW FORMATION, CHATTAHOOCHEE RIVER REGION, ALABAMA-GEORGIA By LLOYD WILLIAM STEPHENSON ABSTRACT The Eutaw formation in east-central Alabama and an adjacent area in west-central Georgia has yielded an assemblage of fossil mollusks, some of the species of which are restricted to that unit and are of value in determining the age and stratigraphic rela- tionships of the Upper Cretaceous formations in the Chatta- hoochee River region. Several of the restricted species have close relatives in younger formations in the Atlantic and Gulf Coastal Plain. Representative species are described in this paper. The Eutaw formation is estimated to be about 200 feet thick in the Chattahoochee River region; it consists mainly of more or less argillaceous and micaceous sand with interbedded layers of calcareous sandstone and concretions, but includes some im- portant layers and lenses of shale. These sediments were de- posited in relatively shallow marine offshore waters. As a con- spicuous part of their faunal content, certain layers contain vast numbers of the shells of Osirea cretacea Morton that are either scattered through the matrix or are so abundant in some beds as to form almost solid oyster reefs. Of the 16 species and 1 variety described, 10 species and the variety are new. All are bivalves except one, which is an ammonite. The described species are: Nucula prepercrassa Stephenson, n. sp. T*Protarca oblique Stephenson *Breviarca symmetros Stephenson, n. sp. T*Tn'gonarca inflate Stephenson, n. sp. Pseudoptem securifwnzis Stephenson, n. sp. Ostrea (Lopha) ucheensis Stephenson, n. sp. cretacea Morton Gryphaea wrather'i Stephenson Exogym upatoiensis Stephensoa T*Anomw preolmstedi Stephenson, n. sp. *Cardz'um (Trachycerdium) ochilleanum Stephenson, n. sp. T*Legumen aff. L. carolinense (Conrad) *Cymbophora ochilleana Stephenson, n. sp. T*Caryocorbula? veatchi Stephenson, n. sp. georgz'tma Stephenson, n. sp. longa Stephenson, 11. var. Placenticeras benm‘ngi Stephenson, n. sp. Forms marked with an asterisk in the above list are either identical with, or closely allied to, species in the Snow Hill marl member of the Black Creek formation of North Carolina and South Carolina. Five species marked with a dagger have identical or closely related representatives in the Cusseta sand in the Chattahoochee River region. It may be accepted that the indicated species are ancestral to species occurring in the strati- graphically younger Snow Hill marl member and in the Cusseta, sand. The presence of Gryphaea wratheri in the upper part of the Eutaw formation affords satisfactory evidence that the formation is synchronous with the upper part of the Austin chalk of Texas, which includes a zone of G. wratheri. The accepted Santonian age of the upper part of the Austin chalk of Texas carries with it the implication that the Eutaw of the eastern Gulf region is also of Santonian age. INTRODUCTION The type area of the Eutaw formation is in the Vicinity of Eutaw, the county seat of Greene County in west-central Alabama. As at present classified (Monroe, Conant, Eargle, 1946, p. 204—210), the Eutaw formation in central and western Alabama con- sists of 160 to 240 feet of marine sediments, including interbedded glauconitic sands and clays in its lower part and mainly massive glauconitic sand, the Tombig— bee sand member, in its upper part. There is no sharp line of separation between these two parts. Fossils are rare in the lower part and common in the Tombigbee sand member, especially so in its upper part. The Eutaw formation of west-central Alabama is un- conformably underlain by the McShan formation ,Which consists of about 200 feet of crossbedded, fine- to medium-grained marine sand that is characterized by its content of fine pale green, partly leached glauconite grains; this unit was formerly considered a part of the overlying Eutaw formation. The Eutaw formation of central and west-central Alabama is unconformably overlain by the Mooreville chalk, the lowermost forma— tion of the Selma group of Alabama and Mississippi. Traced eastward the McShan formation disappears not far west of the longitude of Montgomery, where presumably it is covered by a transgressive overlap of the Eutaw formation. From Montgomery County eastward the Eutaw formation appears at the surface in an easily traceable belt 4 to 12 miles wide to and be- yond the Chattahoochee River. Throughout this 227 228 (distance the formation is uncorformably underlain by an undifferentiated unit of the Tuscaloosa group, presumably the Gordo formation. From Montgomery County eastward to the longitude of Hardaway in ,Macon County, the Eutaw formation is unconformably overlain by the Mooreville chalk of the Selma group; ‘east of Hardaway to, and beyond, the Chattahoochee River the overlying unconformable unit is a more or ‘less argillaceous and calcareous sand facies of the Mooreville unit, to which the name Blufftown formation ‘has been given (Veatch, 1909, p. 82—90; Monroe, 1941, p. 73—88). ‘ In its eastward extension from Montgomery County ‘the Eutaw formation has not been satisfactorily divided into a lower and an upper part corresponding ‘to the two parts recognized in central and western Alabama; there is some reason to believe that the lower ‘ part of the formation is wanting and that the beds that are present belong mainly to the Tombigbee sand mem— 1her. In the Chattahoochee region fossiliferous zones occur at different stratigraphic positions in the formation ‘ from near its base to its top. Selected localities that afford exposures of the Eutaw ‘ and associated formations in the Chattahoochee region were visited by Norman F. Sohl and me in March 1955, ‘ and supplementary collections of fossils were made. Through the courtesy of Maj. Gen. Joseph H. Harper 1 and his subordinate officers, and especially by the per— sonal guidance of Capt. J. F. Rast, we were able to visit 1 several important localities in the Fort Benning Military Reservation. , i The evolution of our knowledge of the Upper Creta- ceous section of eastern Alabama is recorded in many papers, the more important of which are the following: T. A. Conrad (1860, p. 275—298) ; D. W. Langdon (1890, p. 587—606); S. W. McCallie (1903, p. 199~202); Otto Veatch (1909, esp. p. 82—106) ; L. W. Stephenson (1911, p. 66—215); L. W. Stephenson (1914, 77 p.); L. W. Stephenson and W. H. Monroe (1938, p. 1639—1657); Monroe (1941, 150 p.); Monroe (1947, p. 1817—1824); and D. H. Eargle (1950, preliminary map 105, with text). STRATIGRAPHIC SETTING The Eutaw formation of eastern Alabama and western Georgia has not been studied in detail. However, sections have been examined and fossils collected at localities along the belt of outcrop and the contacts of the unit with underlying and overlying formations have been seen at several places. The unit is uncon- formably underlain by sediments considered by Monroe (1947, p. 1,820) to be the eastward continuation of the Gordo formation of the Tuscaloosa group, and is uncon- formably overlain by the Mooreville chalk (of the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Selma group) and by the Blufftown formation, an eastern sand and clay facies of the Mooreville chalk. Although the boundaries of the Eutaw formation in Macon and Russell Counties, Ala. and in Chattahoochee County, Ga., have not been mapped in detail the approximate belt of outcrdp in the Alabama counties is shown on a map prepared by Monroe (1941, pl. 1) and the important localities on Chattahoochee River and in Chattahoochee County, Ga, are shown on an accompanying sketch map (fig. 30). The Eutaw formation is estimated to be about 200 feet thick in the Chattahoochee River valley Where it is divisible into two parts that do not correspond to the two parts recognized in central and Western Ala- bama. The lower part consists mainly of 130 feet or more of massive marine sand, indurated in certain layers, and containing in some layers vast numbers of the shells of Ostrea cretacea Morton. For convenience of reference this part of the formation is here desig— nated the 0. cretacea zone. This zone is believed to be approximately synchronous with the Tombigbee sand member of the Eutaw formation of central and western Alabama. The upper part of the formation is greenish- gray somewhat laminated clay with subordinate sand, probably attaining a thickness of 50 or more feet; the best exposure of this clay section is at Slick Bluff on Chattahoochee River 2 miles southeast of Fort Mitchell, Russell County. The clay contains the imprints of fossils. Whether this clay forms a persistent unit in the upper part of the Tombigbee sand member, or is present only as one or more lenses of local extent, has not been determined. However, the clay is recogniz- able above the 0. cretacea. zone for at least 7 or 8 miles west of the exposures on Chattahoochee River (see p. 232). This clay unit may be stratigraphically a little higher and younger than the main body of the Tombig— bee sand in central and western Alabama where pre- sumably it is overlapped and concealed by the trans- gressing Mooreville chalk. EUTAW LOCALITIES IN EAST-CENTRAL ALABAMA AND ADJACENT PARTS OF GEORGIA Descriptions of a few selected localities in Macon and Russell Counties, Ala, and in Chattahoochee County, Ga., that show the character and stratigraphic relationships of the Eutaw formation, and the zonal distribution of its fossils, are given below. CHATTAHOOCHEE RIVER. Outcrops in the bluffs and banks of Chattahoochee River, where the belt of outcrop of the Eutaw forma- tion intersects that stream, reveal the character of the strata forming the basal 28 and the upper 50 feet or more of the formation; some of the intervening beds ‘ FOSSILS OF THE EUTAW FORMATION, ALABAMA-GEORGIA 85' 05’ 85°00“ 84° 55’ \‘ ,“ PHENIX CIT\ s. s. . \ ‘ w ‘5 ~ usunc‘mfim‘ ’ " muupm ‘ Avsnoxmrr: urn oscumnm mm “54/ 32” 32’ 29 25’ ”1:0 32“ 20’ 0059, Young: 3mg: 32° 20’ 0‘ / a .J,“ 0 EXPLANATION K A 7 Fossil—bearing locality r I \ I “ma" ‘ ’ m \_’_¢ 85°05' Base from maps of Seale. Ala.—Ga,, and Columbus, GarAla” scale 1'62 500, by Army Map Service, 1945—1950 FIGURE 30,—Skctch map of parts of Russell County, Ala. and Muskogee and Chattahoochee Counties, (3a., showing fossil-bearing localities. Numbers are the collection numbers of the United States Geological Survey; each collection made at a given locality bears a separate collection number. appear in small exposures in the river banks. The first exposure of the formation is in a low bluff on the Georgia side below the mouth of Upatoi Creek, 8.5 miles by the river below Columbus, and the last expo- sure is in a bluff on the Alabama side, 200 yards above the mouth of Uchee Creek, 16.5 miles below Columbus. An account of these exposures has been given by Stephenson (1911, p. 82, 83, 117—121). In present usage the Eutaw formation is restricted to the strata exposed along the river between the points indicated in the preceding paragraph. Between the mouth of Uchee Creek and Chimney Bluff on the east side of the river 22 miles below Columbus no exposures that show the contact between the Eutaw and overlying Blufitown formations were observed. The lower 25 feet of strata exposed at Chimney Bluff consists of irregularly bedded, cross- bedded lignitic sand and clay that is interpreted to be referable to the lower part of the Blufftown formation. The most important Eutaw fossil-bearing strata ex- posed along the river are those at Broken Arrow Bend, old Burdock Landing, and Slick Bluff. The strata com-— 230 posing the Eutaw formation in the Chattahoochee area dip gently to the south at an inclination probably not exceeding 30 or 35 feet to the mile. Section at Broken Arrow Bend—At Broken Arrow Bend about 10 miles by the river (airline 6 miles) downstream from Columbus, Ga, exposures along the right and left banks of Chattahoochee River show that the contact of the Eutaw formation with the underly— ing Gordo formation of the Tuscaloosa group is a broadly undulating unconformity. The Gordo con— sists of coarse, compact, crossbedded, arkosic and micaeeous sand and interbedded light—drab to almost white clay. The thickness above water level as seen along the left bank at a medium low stage of the river is 4 or 5 feet and the upper eroded surface rises and falls through a vertical range of 5 feet or more, in places passing below water level and reappearing again farther downstream. The basal 2 to 8 feet or more of the over- lying Eutaw formation consists of medium to coarse crossbedded sand and interbedded laminated clay. These materials contain lignitized and silicified wood, including large logs, and poorly preserved fossil leaves. These basal beds are conformably overlain by 15 feet or more of slightly laminated gray micaeeous, calcar- eous sand and clay including interbedded layers of calcareous concretionary nodules 2 or 3 feet apart; these beds dip gently downstream. The calcareous beds at Broken Arrow Bend contain a late Cretaceous marine fauna, the species of which have been only partly identified and described. Among the forms present are: Pseudoptera securiformis Ste- phenson, Ostrea cretacea Morton, Exogyra upatoiensis Stephenson, Anomia preolmstedi Stephenson, Legumen of. L. carolinensis (Conrad), Caryocorbula? veatcki Stephenson and Placenticeras benningi Stephenson (USGS 00115. 847, 5384, 6409). Half a mile downstream from Broken Arrow Bend the layers of nodular limestone dip down to water level and between two of these indurated beds is a layer made up largely of the shells of Ostrea cretacea Morton (large variety) (USGS 5385). From here downstream for the next 2 miles a few low outcrops in the river banks reveal the gently southward dipping indurated beds that characterize the zone of 0. cretacea, which is estimated to be between 75 and 100 feet thick in this area. More complete exposures of the 0. cretacea zone, as it is developed west of Chattahoochee River in Russell and Macon Counties, Ala, are described on following pages. Section at old Burdock Landing—The upstream end of Uehee Shoals (or Rapids) is at a point on the river about east of Fort Mitchell, and the shoals extend from there for several miles down the river. The submerged SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY indurated layers of the Ostrea crctacea zone of the Eutaw formation are the cause of the shoals. The site of old Burdock Landing is on the Alabama side about three- fourths of a mile below the upstream end of the shoals. An exposure just below the landing reveals 30 feet of greenish-gray clay, laminated in part, with fine sand partings. From a fossiliferous bed at the water’s edge a short distance below the landing the following forms- are identified: Pseudoptera securiformis Stephenson, Ostrea cretacea Morton, 0. (Lopha) ncheensis Stephen~ son, Anomia preolmstedi Stephenson, Cyprimeria cf. 0. depressa Conrad, Legumen afl’ L. carolinense (Conrad), and Oaryocorbula? georgiana Stephenson? (USGS colls. 848 and 5386). These fossils are mainly in the form of prints in finely micaeeous clay, but 0. cretacea Morton is preserved as shells in dark-gray argillaceous, finely micaeeous sand. Section at Slick Blufi.—Slick Bluff is half a mile downstream from old Burdock Landing. The bluff exposes greenish-gray clay that has been considerably disturbed by relatively recent landslides and at some earlier time was afiected by earth movements that produced sand-filled fissures, now appearing as so— called sandstone dikes; these dikes were first described by S. W. McCallie (1903, p. 199—202). On account of the disturbed condition of the clay, the section could not be measured but the thickness was estimated to be 50 feet or more. A few fossil prints were collected from the disturbed clay among which were recognized: Ostrea ucheensis Stephenson, Cyprimeria of. C'. depressa, Conrad, Legumen aff. L. carolinensis (Conrad), and Oaryocorbula? georgiana Stephenson? (USGS colls 845, 5887). The clay section at Slick Bluff overlies the calcareous beds (=0. cretacea zone) and forms the upper part of the Eutaw formation as here interpreted. Section near mouth of Uehee Creek—Cretaceous sedimentary rocks interpreted to lie close to the upper- most part of the Eutaw formation are exposed in the right bank of the river about 200 feet upstream from the mouth of Uehee Creek. These beds consist of 25 feet of thinly laminated sand and clay with seams of finely comminuted vegetable matter; the sand is white or stained yellow and is very fine and micaeeous; the clay is dark gray. The Cretaceous beds are unconformably overlain by. 10 feet of terrace gravel, sand, and loam (Pleistocene). CHATTAHOOCHEE COUNTY, GA., EAST OF CHATTAHOOCHEE RIVER Section on Upatoi Creek—A bluff on Upatoi Creek 7 miles southeast of Columbus, Ga., formerly (1908) exposed the section described below; the section is now largely concealed by vegetation. FOSSILS OF THE EUTAW FORMATION, ALABAMA—GEORGIA Section on Upatoi Creek one—fourth mile below the old Columbus— Cusseta road crossing, 7 miles southeast of Columbus Eutaw formation: Feet Sand, marine, weathered brown, unconsolidated- _ _ 5 Sand, fine, and clay, partly weathered, greenish- gray, irregularly foliated ______________________ 5 Sandstone, fine-grained, white ___________________ 1 Sand, fine, and clay, greenish-gray, irregularly foliated _____________________________________ 2 Sand, argillaceous, dark greenish-gray ____________ 5 Sandstone, fine-grained, white ___________________ 1% Clay, with irregular dark clay foliations, and lignite fragments; includes discontinuous nodular lime- stone layers and irregularly distributed calcareous concretions; fossiliferous ______________________ 25 Unconformity, contact poorly exposed. Tuscaloosa group (Gordo formation): Sand, coarse, arkosic, crossbedded, light-gray streaked with yellow; includes subordinate layers of sandy clay ________________________________ 22 Concealed to water level ________________________ 21 :l: 87% d: Fossils described in this paper from the basal 25 feet of the Eutaw formation at the preceding locality are listed below. Fossils from the basal 25 feet of the Eutaw formation on Upatoi Creek, 7 miles southeast of Columbus, Ga. (USGS 5378 and 5377) Pseudoptera securiformis Stephenson Ostrea cretacea Morton Exogyra upatoiensis Stephenson Legumen aff. L. carolinense (Conrad) Placentieeras benningi Stephenson Additional fossils, mostly poorly preserved, belonging to the following genera, have been identified from the Upatoi Creek locality: Trigonarca,‘Pholadomya, Cardi- um, T ellina?, T urritella, Anchura, and Volutomorpha. Several species of shark teeth are present. Section on Ochillee Creek.——Strata corresponding to the basal 25 feet of the Eutaw formation in the section on Upatoi Creek are exposed on Ochillee Creek at and near the site of the dam and the old mill at Ochillee, Chattahoochee County, and for several hundred yards both downstream and upstream from the dam site. The bridge of the present roadway is approximately at the site of the dam and mill. These beds are fossilifer- ous and include some fossils that are in a more complete state of preservation than those found at other Eutaw localities in the Chattahoochee area. A list of the species described from Ochillee Creek is given below. 231. Fossils from the basal 20—25 feet of the Eutaw formation on Ochillee Creek near old Ochillee, Chattahoochee County ( USGS 5874, 5378,. 15501, and 25570) Protarca obliqua Stephenson Pseudoptera securiformis Stephenson Ostrea cretacea Morton Anomia preolmstedi Stephenson Legumen afi‘. L. carolinense (Conrad) Cymbophora ochilleana Stephenson Caryocorbula? veatchi Stephenson Placenticeras benningi Stephenson In addition to the species formally described in this paper, fossils belonging to the following genera have been recognized in the collections from Ochillee: Serpula (tubes), Idonearca, Pecten (Camptonectes), Etea, Cy—- primeria, Leptosolen, Turritella, and Anchura. Both the dam and the water mill of former years. have completely disappeared from the Ochillee locality. Upstream from the site of the dam there is now exposed in the bed of the creek marine argillaceous sand with irregularly distributed ovate concretions 4 to 8 inches in diameter; these concretions contain imprints and molds of fossils with films of adhering shell substance, among which are many individuals of Pseudoptera securiformis Stephenson and Placenticems benningi Stephenson (USGS 25570). RUSSELL COUNTY, ALA., WEST OF CHATTAHOOCHEE RIVER Section 4 miles southwest of Phenix City.—The uncon- formable contact between the Gordo formation of the Tuscaloosa group and the overlying Eutaw formation was formerly well exposed on the old Columbus-Seale road 4 miles southwest of Phenix City (opposite Colum- bus); at this locality the contact is gently and broadly undulating. This locality was described in earlier- papers (Stephenson, 1911, p. 74, 75, pl. 6—8; 1914, p. 10, 11, pl. 1—B). The Gordo formation of this paper is the same as the Lower Cretaceous of the earlier papers. The earlier correlation of this unit with the Lower Cretaceous seemed to have found partial con— firmation in E. W. Berry’s interpretation (oral com— munication) of a meager, poorly preserved fossil flora found at old Fort Decatur in Macon County, Ala. (Stephenson, 1914, p. 12). Additional plant remains collected from the same place at a later date caused Berry (1923, p. 433—435) to change his mind and refer the plants to the Upper Cretaceous, a correlation that is in agreement with the conclusions of more recent investigators. 232 Section southwest of Yans Bridge—An exposure in a cut of U. S. HighWay 431, on the northeastward- facing slope of Uchee Creek valley 0.6 mile southwest of Youngs Bridge, reveals the following section: Section in cut of U. S. Highway 431, on the northeastward—facing slope of Uchee Creek valley in SWXiNWV; sec. 26‘, T. 16’ N., R. 29 E., Russell County, Ala. Eutaw formation: Shale, gray, marine, with interbedded thin layers of light-gray sandstone in upper 15 feet, out by 2 nearly vertical sandstone dikes; a soft sandstone bed about 18 feet above base contains Inoceramus sp., Lio- pistha sp., and Placenticeras benningi Stephenson? (USGS 25462) _________________________________ 30 Sandstone, calcareous; contains many shells of Ostrea cretacea Morton ________________________________ 1 :1: 31d: The 30 feet of shale in the preceding section corre— sponds to part of the shale unit exposed at old Burdock Landing and in Slick Blufi on Chattahoochee River. 'The indurated fossiliferous bed at the base of the section marks the top of the 0. cretacea zone in this area. Sections near Uchee.—A section in a cut on the new Hurtsboro—Marvyn highway, 5.9 miles south of Lee County line, about 2.6 miles southwest of Uchee, in northwestern Russell County, is as follows: Feet Section in cut on Hurtsboro-Maroyn highway, 5.9 miles south of Lee County line, in NEMNElfi sec. 35, T. 16 N., R. 26' E., Russell County, Ala. ,Blufl’town formation: Clay, greenish-gray, sandy, marine, with a lens of sand Feet about 2.5 feet thick 8 feet below top, _____________ 30 Sand, greenish-gray massive, marine, with two inter- bedded whitish indurated layers, about ____________ 4 Conglomeratic sand; includes quartz and phosphatic pebbles, many fragments of dark bones, and water- worn shells; also many medium-sized shells of a smooth Exogyra, and some large shells of Trigonarca, Cardium, and other forms; _______________________ 1 Unconformity. Eutaw formation: Sand, gray compact argillaceous, micaceous __________ 5 Sand, darker gray than the preceding; contains many shell fragments, mainly in the upper half, and some well-preserved shells, mostly small but including a few of medium size; included among the fossils are: Trigonarca infiata Stephenson, Exogyra sp. (medium size, smooth), Cyprimeria sp. (small), and Caryo- corbula? veatchi longa Stephenson __________________ 10 50 A cut on the same highway, 0.15 mile to the north (downslope) from the preceding cut, 5.75 miles south of Lee County line, reveals an 18-foot section of marine sand, clay, and marl. A layer of coquinalike marl 4 to 6 feet above the base contains many shells of SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Ostrea cretacea Morton and a few internal molds of Pseudoptera securiformis Stephenson. This bed is near the top of the 0. cretacea zone. A section described in detail by W. H. Monroe, that reveals the greater part, if not all, of the 0. cretacea zone, is exposed along the Marvyn road 2% miles (air- line) north by west of Uchee. Section along the old M arvyn road 2% miles (airline) north by west of Uchee, near center of sec. 7, T. 16 N., R. 27 E., on northeast- ward-facing slope of a headwater branch of a small tributary of Uchee Creek, Russell County, Ala. Blufftown formation(?): 20. Sand, light-red, chert and quartz grains as much as one—fourth inch long, subangular, poorly sorted; weathered to colluvium in upper part- - 23 Eutaw formation: 19. Sand, red and gray, fine, with thin laminae of gray Feet clay ______________________________________ 5 18. Sand, gray and yellow, fine, clayey, ferruginous, micaceous; contains prints of f0ssils ___________ 5% 17. Sand, light-brown, fine, much more clayey than overlying bed; contains many prints of fossils, those in lower 2 feet retaining some white calcium carbonate __________________________ 4% 16. Sandstone, hard, fine-grained; base and top slightly irregular; contains many shells of Ostrea cretacea Morton, and some of Anemia preolmstedi Steph- enson _____________________________________ l 15. Sand, light-brown, clayey, like bed 17 above; contains many shells of 0. cretacea ____________ 3 14. Sandstone, hard, light-brown; contains many shells of O. cretacea _________________________ 1 13. Limestone, sandy, light-brown: contains shells of 0. cretacea and 0. ucheensis Stephenson (USGS 17766) ____________________________________ 3 l2. Limestone, sandy, hard, fine-grained ____________ 1 11. Clay, indurated, light-tan or buff; contains many shells of 0. cretacea and some of Anemia preolm- stedi Stephenson ___________________________ 21/ 10. Sand, light-yellow, fine, micaceous, glauconitic(?)_ 1 9. Clay (or silt), finely sandy, like bed 10; lower part contains large masses of chalklike precipitated calcium carbonate; contains many shells of 0. cretacea ___________________________________ 11 8. Limestone, finely sandy, lightabrown, largely com- posed of shells of 0. cretacea _________________ 7. Sand, light-brown, clayey; contains many shells of 0. cretacea ______________________________ 3 6. Clay, blocky, light brownish-gray, with much chalklike precipitated calcium carbonate; some shells of 0. cretacea _________________________ 5 5. Bed composed mainly of 0. cretacea shells and a few shells of Anemia sp., with a matrix of light- brown, very fine sandy clay _________________ 4 . Chalk, light-buff and white, in silt or clay _______ 3 . Boulders of hard crystalline limestone filled with shells of 0. cretacea; Anemia preolmstedi present; softer beds incompletely exposed in ditch but relationship to limestone not clear; many oyster shells appear waterworn (USGS 17776) _______ 12 \H N\ was FOSSILS OF THE EUTAW FORMATION, ALABAMA-GEORGIA Section along the old Maroyn road 2% miles (airline) north by west of Uchee, near center of sec. 7, T. 16' N., R. 27 E., on northeast- wardvfacing slope of a headwater branch of a small tributary of Uchee Creek, Russell County, Ala.—C0ntinued fEutaw formation—Continued Feet 2. Sand, clayey, light-brown, soft, and White chalk, containing many shells of 0. cretacea, alternating with light-brown chalky clay, merging down- ward into bed below ________________________ 43 1. Clay, finely sandy, blocky, light-brown and white chalk; contains shells of 0. cretacea and prints of pelecypods; this bed is slightly more sandy in lower 15 feet _______________________________ 36 Concealed to water level of creek __________________ 14 182 In the preceding section layers 17—19 compose a sandy facies probably representing part of the clay unit of the Eutaw formation exposed at Slick Bluff on Chattahoochee River. Ostrea oretacea Morton is re- corded as ranging through a thickness of 130 feet of the section (layers 1—16). The new oyster, 0. ucheensis Stephenson, is listed in layer 13, Where it is associated with 0. cretacea; this is 20 feet below the top of the Eutaw part of the section. Another lot of fossils from this locality (USGS 17585), recorded as obtained from the upper 20 feet of the 0. cretacea zone, includes 0. vcretacea and 0. ucheensis. The new species, Pseudoptera securiformis Stephenson (USGS 17211) was obtained near the top of the 0. cretacea zone at this locality. MACON COUNTY, ALA. Section north of Creek Stand.—-The zone of Ostrea rcretacea Morton, which is at least 130 feet thick in northwestern Russell County, continues westward in (comparable thickness into Macon County. A section similar, though less complete than the one described by Monroe 2% miles north by west of Uchee, is exposed on the Society Hill road 4.1 miles north by west of Creek :Stand. .Section on Society Hill road, northward-facing slope of Opintlocco Creek valley about 4.1 miles (airline) north by west of Creek Stand, A! acon County, Ala. , Eutaw formation: Feet 7. Sand, massive, greenish-gray, argillaceous, calcare- ous, partly indurated to calcareous concretionary layers that form projecting ledges on the slope; contains vast numbers of the shells of Ostrea cre- tacea Morton, more abundant in some layers than in others (USGS 17007) ,- a few shells of G'ryphaea wratheri Stephenson present in an indurated layer 10 feet below crest of hill (USGS 18312) _ _ _ _ 40 6. Sand, soft, light-greenish-gray, calcareous _________ 14 233 Section on Society Hill road, northward-facing slope of Opintlocco Creek valley about 4.1 miles (airline) north by west of Creek Stand, Macon County, Ala—Continued Eutaw formation—Continued Feet 5. Sand, dark-greenish-gray argillaceous, calcareous, glauconitic, partly indurated to nodular calcareous masses in upper 4 or 5 feet _____________________ 9 4. Sandstone, concretionary, argillaceous, calcareous- _ 1 3. Clay, greenish-gray, calcareous __________________ 4% 2. Sand, partly indurated, greenish-gray, calcareous, with a few shells of 0. cretacea Morton __________ }t 1. Sand, greenish-gray, argillaceous, calcareous _______ 4 73 Neither the base nor the top of the Eutaw formation is exposed in the preceding section. However, the base is probably not more than a few feet below the surface at the crossing of the Society Hill road over Opintlocco Creek. The top of the section is near the crest of the slope overlooking the valley of Opintlocco Creek to the north. A cut in the Society Hill road 0.85 mile south of the crest of the slope, 3.35 miles north of Creek Stand, exposes 15 feet of greenish—gray argillaceous sand with one indurated layer midway of the section. Oyster shells, apparently a large variety of Ostrea cretacea Morton, are abundant below and above the indurated layer. Assuming a uniform 10W dip of the Eutaw strata to the south, this oyster-bearing zone is strati- graphically a few feet higher than the topmost stratum of the section 4.1 miles north by west of Creek Stand. The contact of the Eutaw formation with the overlying Blufftown formation should intersect the road some- where within the next 1 or 2 miles south of the cut. The stratigraphic range of Ostrea cretacea in eastern Macon County as revealed in the preceding section, is at least 75 feet. The presence of Gryphaea wratheri Stephenson in the upper part of the section is consistent with its known occurrences elsewhere in eastern Ala- bama. Section east by north of Hardaway.—The contact between the Eutaw formation and the overlying Blufl'town formation is clearly revealed in an outcrop on a country road about 3.5 miles east by north of Hardaway station. Section in cut on country road, 3.5 miles east by north of Hardaway station in NW% sec. 7, T. 15 N., R. 23 E., Macon County, Ala. Blufftown formation (lateral merging facies from Mooreville chalk) : ‘ Feet Sand, strongly chalky, argillaceous ___________________ 9 Conglomerate, including phosphatized molds of mol- lusks and many large pebbles of phosphatized lime- stone (as much as 6 inches long) with attached shells of Exogyra, Gryphaea, and Plicatula ________________ 1—2 '234 Section in out on country road, 3.5 miles east by north of Hardaway station in NW% sec. 7‘, T. 15 N., R. 28 E., Macon County, Ala.—Continued Unconformity. Eutaw formation: Sand, greenish-gray, fine, micaceous, with many small irregular concretionary masses in the form of nodules; one indurated bed 1 foot thick is 5.5 feet below the contact and another 1 feet thick is 8.5 feet below the contact; the sand contains Ostrea cretacea Morton, Gryphaea wratheri Stephenson, and Exogyra sp _______ 11 22 THE EUTAW FAUNA AND ITS RELATIONSHIPS The fauna described in this paper includes most of the present available species in the Eutaw formation of east-central Alabama and an adjacent area in Georgia, that are well preserved or that have a useful significance in determining the stratigraphic position and relation- ships of the formation. It does not include many poorly preserved or rare fossils that, in our present knowledge, have no such significance. It may be safely assumed that thorough collecting at all available localities in the area would result in the discovery of additional new species and better preserved examples of described species based on incomplete material. A list of the species, all mollusks, described in this paper is given below. Those marked with an aster- isk(*), 61 percent of the whole, are identical with, or closely allied to, species in the Snow Hill marl member of the Black Creek formation of North Carolina and South Carolina. It may be assumed from this relation- ship that many of the species in the Snow Hill faunal assemblage have their progenitors in the fauna of the Eutaw formation. The species in the list marked with a daggerfi) are identical with or closely related to species in the Cusseta sand in the Chattahoochee region, and may be regarded as ancestral to the Cusseta species. The Cusseta sand is interpreted to be ap- proximately synchronous with the Snow Hill marl member. List of fossils described in this paper Nucula prepercrassa Stephenson, n. sp. T*Protarca oblique Stephenson Breviarca subinflata Stephenson, n. sp. symmetros Stephenson, n. sp. sp T*Trigonarca inflate Stephenson, n. sp. Pseudoptera securiformis Stephenson, n. sp. Ostrea (Lopha) ucheensis Stephenson, n. sp. cretacea Morton Gryphaea wratheri Stephenson Exogyra upatoiensis Stephenson T*Anomia preolmstedi Stephenson, n. sp. *C’ardium (Trachycardium) ochilleanum Stephenson, n. sp. T*Legumen aff. L. carolinense (Conrad) *Cymbophora ochilleana Stephenson, n. sp. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY T*Caryocorbula? veatchi Stephenson, n. sp. * veatchi longa Stephenson, 11. var. * georgiana Stephenson, n. sp. Placenticeras benningi Stephenson, n. sp. In Alabama, Gryphaea wratheri Stephenson occurs in the upper 35 or 40 feet of the Eutaw formation and also in the basal bed of the Mooreville chalk, where- it may be in part indigenous and in part reworked from the Eutaw below. In eastern Alabama a few examples of the species have been found high enough in the lower half of the Mooreville chalk to indicate that they are indigenous there, and not reworked from the Eutaw. The thickness of the beds through which the species ranges has not been accurately determined, but it may not exceed 50 feet. Gryphaea wratheri is an important index fossil in fixing the stratigraphic position of the Eutaw formation and of the Mooreville chalk and its clay and sand facies, the Blufftown formation. In Texas the species ranges through a zone within the upper half of the Austin chalk that is not known to exceed 35 feet in thickness (Stephenson, 1936, p. 1'4). The 0'. wratheri zone is there underlain by the Inocemmus undulartoplicatus zone, which also lies within the upper half of the Austin chalk. Above the G. wratheri zone are three narrowly restricted zones, in succession the zones of" Exogym tigrina, Ostrea centerensis, and 0. traviscma, the latter at the top of the Austin chalk. It is generally accepted that, in terms of European nomenclature, about the upper half of the Austin is of Santonian age. It follows that, on the indirect evidence afforded by G. wratheri, the upper part of the Eutaw formation and the overlying Mooreville and Blufl'town formations, are of Santonian age. SYSTEMATIC DESCRIPTIONS Phylum MOLLUSCA Class PELECYPODA Order PRIONODESMACEA Superfamily NUCULACEA Family NUCULIDAE Genus NUCULA Lamarck, 1799 Nucula prepercrassa Stephenson, n. sp. Plate 39, figures 1—5 Adult shell of medium size, relatively thin, moder- ately inflated, elongate, inequilateral, equivalve; great-7 est inflation above the midheight and a little anterior- to the midlength, from which point the surface rounds broadly over to the beak and broadly down to the ven- tral margin. Beaks prominent, incurved, opisthogyw rate, approximate, situated about 0.7 of the length from the anterior extremity. Escutcheon broad, relatively short, broadly excavated. Lunule long, narrow, weakly Foss1Ls OF THE EUTAW FORMATION, ALABAMA-GEORGIA 23o outlined. Anterodorsal margin long, very broadly arched, descending; anterior margin narrowly rounded; ventral margin long, broadly rounded; posterior margin subpointed; posterodorsal margin nearly straight, steeply descending. Surface with fine, weak concentric ridges, and with inconspicuous, low, flat, closely crowded, radiating ribs. Dimensions of the holotype, a right valve: Length 30 mm, height 20 mm, convexity 8 mm. Hinge taxodont, teeth numerous, sharp, in two un- equal series; in the anterior series the teeth number 30 or more and in the posterior series about 12. In one paratype, a left valve, a poorly preserved large tooth, oblique forward, is present just back of the deeply im— pressed resilifer; this tooth fits into a corresponding socket, which is well preserved in the holotype, a right valve. In the holotype, a deeply submerged spoon- shaped ehondrophore projecting obliquely inward and forward provides a support for the resilium. Adductor scars small, subovate, slightly sunken, high in the shell; pallial line entire. Inner margin finely crenulate. The few available specimens indicate that this species is similar in form and outline to Nucula, percmssa Conrad, from the Owl Creek formation of Mississippi. It differs from Conrad’s species in that the shell is much thinner, the hinge is narrower, the ehondrophore is larger and projects farther inward, and the adult shells lack the senile inbending of the ventral margins so con- spicuously developed in most of the Owl Creek shells; the latter feature in the Owl Creek shells may be a premature senile variation brought about by some in- hibiting environmental condition, for some large adult shells in both the Owl Creek and the Ripley formation, that have been referred to Conrad’s species, lack the inbending. Types.—Holotype, from Oehillee Creek near Oehillee, Chat- tahoochee County, Ga., USGS 15501, USNM 125058; I figured paratype, same source, USNM 125059; 3 unfigured paratypes, same source, USNM 12-3060; 1 figured paratype, same source, USGS 5378, USNM 125061. Distribution and Tanya—The species is known only from the lower part of the Eutaw formation at the type locality. Superfamily ARCACEA Family ARCIDAE Genus PROTARCA Stephenson, 1923 Protarca obliqua Stephenson Plate 39, figures 9—14 1923. Protarca obliqua Stephenson, N. C. Geol. and Econ. Survey, v. 5, p. 104, pl. 19, figs. 1—3. 1945. Protarca obliqua. Stephenson. Nicol, Jour. Paleontology, v. 19, no. 6, p. 619. 1950. Protarca oblique Stephenson. Nicol, Jour. Paleontology, v.24, no. 1, p. 92, pl. 21, fig. 10. .. 1954. Protarca oblique Stephenson. Nicol, Jour. Paleontology, v. 28, no. 1, p. 98. The genus Protarca and its type species, P. oblique, from the Snow Hill marl member of the Black Creek formation, of North Carolina, were described by Stephenson (1923, p. 103—105, pl. 19, figs. 1—3), and descriptions of two smaller specimens from Oehillee Creek at old Oehillee, Chattahoochee County, Ga. were given in the same paper. Two other medium- sized specimens from Oehillee Creek and one juvenile shell from the upper part of the Eutaw formation in western Russell County, Ala., have since been added to the collection. Also the largest known example of the species was recently collected from a calcareous concretion in the Cusseta sand near Peachburg, Bullock County, Ala; the Cusseta sand is approximately synchronous with the Snow Hill marl member. Although the Oehillee material is from the lower part of the Exogym ponderosa zone, and the type from the Snow Hill marl member is from the upper part of that zone, I am unable to recognize any essential differences that would justify a specific separation of the specimens from the two zones. In form, outline and internal features they seem to be identical; although the larger specimen from Oehillee (pl. 39, fig. 9) appears smooth as preserved, the small specimen (pl. 39, fig. 11) shows radial ribs well preserved all over its outer surface such as would probably be present on the young stage of the other shell from Oehillee Creek, were it well preserved in the umbonal region. The specimen from the Cusseta sand near Peachburg, a left valve (pl. 39, figs. 13, 14), is larger and thicker than the holotype from the Snow Hill marl member of the Black Creek formation in North Carolina. This is the first record of Protarca, oblique in the Cusseta sand. Types.—Holotype from Snow Hill marl member of Black Creek formation (upper part of Exogyra ponderosa zone), Snow Hill, Greene County, N. C., USGS 5348, USNM 31500; 1 plesio- type from the same zonal position, in the Cusseta sand, cut of Central of Georgia Railroad about 0.7 mile north of Peachburg, Bullock County, Ala., USGS 25478, USNM 125062; 2 plesiotypes from lower part of Eutaw formation (lower part of E. ponderosa zone), Oehillee Creek, Chattahoochee County, Ga, USGS 5378, USNM 125063; 1 plesiotype from the same source, USGS 15501, USNM 125064; 1 unfigured example from the same source, USNM 125065. . Distribution—In addition to the occurrences recorded in the preceding paragraph, one juvenile shell has been found in the upper part of the Eutaw formation in a cut on the Hurtsboro— Marvyn highway, 5.9 miles south of the Lee County line, Russell County, Ala., USGS 25567, USNM 125066. Range—Assuming the correctness of the identifications indic- ated in this paper the known stratigraphic range of the species is throughout the Exogyra ponderosa zone and the geographic range is from eastern Alabama to eastern North Carolina, in the Atlantic and Gulf Coastal Plain. 236 Genus BREVIARCA Conrad, 1872 Breviarca subinflata Stephenson, n. sp. Plate 39, figures 6—8 Shell small, thin, of medium inflation, subquadrate in outline, relatively short, subequilateral, equivalved except that the left valve slightly overlaps the right around the margin. Beaks prominent, strongly in- curved, nearly direct, slightly separated, situated slightly anterior to the midlength. Umbonal ridge prominent, rounded on the crest, broadly humped and a little sinuous in the linear direction; posterodorsal slope steep; dorsal slopes broadly excavated adjacent to the hinge. Surface rounding down regularly from point of highest inflation to the anterior and ventral margins: surface with fine concentric and faint, fine radial lining. Dimensions of the holotype, a left valve: Length 13 mm, height 10.3 mm, convexity 4.4 mm. Cardinal area amphidetic, elongate—subtrigonal; a central amphidetic, triangular ligamental area covering about half the cardinal area is minutely striated at right angles to the length. Hinge broadly arched on’ its lower margin, truncated above by the straight lower margin of the cardinal area; centrally the hinge is narrow and bears closely spaced, small transverse teeth; the hinge broadens toward the front and toward the rear, the broadened areas bearing numerous succes- sively longer teeth which, away from the center, become more oblique inward and downward, the longer ones becoming angulated in trend. Inner margin smooth; on the interior of the left valve a groove that closely parallels the inner margin marks the contact of the margin of the slightly overlapped right valve. Other internal features not uncovered. This species is closely allied, possibly ancestral to, Brezviarca umbonata (Conrad) from the Snow Hill marl member of the Black Creek formation of North Caro- lina. (See Stephenson, 1923, p. 114; 1941, p. 86.) Compared with Conrad’s species, B. subinflata, is not so strongly inflated, is higher with respect to its length, and is more definitely subquadrate, as opposed to sub— trigonal, in outline. These differences, though small, together with the lower stratigraphic position of the Georgia species, seem to justify the recognition of the latter as specifically distinct. Types.—Holotype, from Ochillee Creek below bridge at old Ochillee, Chattahoochee County, Ga., USGS 15501, USNM 125067; I figured paratype, same source, USNM 125068; 2 un- figured paratypes, same source, USNM 125069. Distribution and range.——Known only from the lower part of the Eutaw formation at the type locality. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Breviarca symmetros Stephenson, n. sp. Plate 40, figures 1, 2 Shell small, moderately inflated, nearly symmetrical, in form and in ovate outline, subequilateral, equivalve. Beaks small, subcentral, incurved, direct, slightly separated at the tips. Umbonal ridge practically wanting but the margin bulges slightly in the postero- ventral direction. Dorsal margin broadly arched, anterior margin regularly rounded, ventral margin broadly rounded, posterior margin with narrowest curve below, broadening a little above. Surface with low, slightly irregular concentric riblets and fine weak radial lining. Dimensions of the holotype, a left valve: Length 10.5 mm, height 9.2 mm, convexity 3 mm. One of the para- types, a left valve is 12 mm long. Ligamental area amphidetic, elongate-triangular, scored with transverse, fine, closely spaced grooves; the apex of the area is central below the beak. Hinge plate long, narrow centrally, broadening at each end, arched on its inner margin, set with numerous teeth; the teeth are small and transverse to the hinge line centrally, becoming successively longer and more oblique on the broadened areas in each direction away from the center, attaining horizontality at the ends. Adductor scars large, subequal, subovate, their inner margins bounded by narrow, thin, weak radial carinae. Inner surface smooth, pallial line simple and well away from the inner margin, which is smooth. Compared with Brem'arca subt'nfiata, this species is less elongated, less inflated, and lacks an umbonal ridge, in which respect it resembles B. perovalis Conrad, B. subovalis Conrad, and B. congesta. Conrad; it is smaller and less elongated than the first two named species, and is a little longer than B. congesta; it has a proportionately shorter and smaller ligamental area than either of the three species. Typea—Holotype, from the upper part of the Eutaw forma- tion in a cut of the new Hurtsboro Ma‘rvyn road 5.9 miles south of the Lee County line, in Russell County, Ala., USGS 25567, USNM 125070; 2 unfigured paratypes from the same locality, USNM 125071. Range.—Known only from the type locality. Breviarca? sp. Plate 40, figure 3 One small incomplete left valve of a bivalve mollusk (USGS 15501), probably a Brem'arca, from Ochillee Creek below bridge at old Ochillee, Chattahoochee County, Ga., is similar in form and surface features to B. subinflata but is longer in proportion to the height. The umbonal ridge is subangular, sinuous, slightly 1 i FOSSILS OF THE EUTAW FORMATION, ALABAMA—GEORGIA overhanging near the beak, becoming rounded on the crest toward the terminus: Posterodorsal slope narrow and slightly excavated. Beaks strongly incurved, nearly direct, situated about two-fifths of the length from the anterior end. Surface covered with low, weak, concentric ribs asymmetric in cross section, the lower slope of each rib gently inclined toward the venter, the upper slope steep and weakly crenulated by obscure fine radial lining. Dimensions: Length 10.5 mm, height 6.3 mm, convexity about 2.5 mm. USNM 125072. Genus TRIGONARCA Conrad, 1862 Trigonarca inflate Stephenson, n. sp. Plate 40, figures 4—8 Shell of medium size, thick-shelled, strongly convex, subtrigonal in outline. Beaks moderately prominent, incurved, opisthogyrate, widely separated, situated a little anterior to the midlength. Umbonal ridge rounded on crest, slightly curved, concave rearward in trend. The main surface rounds over regularly toward the anterior and ventral margins; posterodorsal slope steep, broadly excavated adjacent to margin. Growth lines sharp, resting stages marked by numerous con- centric undulations. Obscure radiating lines detectable on parts of surface especially on anterior slope. Dorsal margin arched, anterior margin regularly rounded, ventral margin broadly rounded to nearly straight centrally, posterior margin sharply rounded below, truncated and inclined strongly forward above. None of the adult shells is completely preserved; the holotype, a left valve, is broken away in a narrow strip around the anterior and ventral margins back to the pallial line. The approximate dimension of the holo— type are: Length 60 mm, height 50 mm, convexity 20 mm. None of the available shells exceeds these dimensions. The ligamental area forms an obtuse-angled sub- triangle with longest sideat base, shortest side at rear and the third side broadly arched along the anterodorsal margin; six ligamental grooves, chevron-shaped, with short ends of grooves at rear. Hinge taxodont, hinge plate arched on lower margin, truncated on upper margin by the lower straight edge of the ligamental area. Teeth in two series separated by a short eden— tate area opposite the beak; starting at the rear end of the anterior series, the teeth are small, numerous, closely spaced transverse to hinge line, but in the for- ward direction they gradually become longer and oblique in trend; on the broad anterior part of the hinge plate of adults the otherwise long, oblique, angulated teeth become broken into small round-topped pro— tuberances of irregular size and distribution. The posterior series of teeth is shorter than the anterior series and from front to rear includes several short 237 slightly oblique teeth, passing into longer angulated teeth and finally into successively shorter and more oblique teeth at the end of the series; all the teeth are striated on the sides at right angles to the hinge plate in the direction of movement. In a young shell (pl. 40, fig. 5) the long teeth are entire, and not broken into irregular protuberences. Anterior adductor scar large, subovate, with a weak, narrow radial ridge along its posterior side; posterior scar smaller, elongated, seated on the outer end of a pronounced radial buttress. Pallial line simple. Inner surface scored with coarse radial grooves in a wide band, bordering the inner side of the pallial line. In form this species is similar to Trigonarca maconensis Conrad but the adult shells are much smaller, appar- ently more inflated, somewhat smoother, and the liga- mental grooves are narrower and more numerous. T. inflate probably is ancestral to T. maconensis. Types.—Holotype, a left valve from upper part of Eutaw for— mation in cut of Hurtsboro-Marvyn road, 5.9 miles south of Lee County line, in Russell County, Ala, USGS 25567, USNM 125073; 1 figured paratype, a small right valve, same source, USNM 125074; 7 more or less incomplete, unfigured paratypes, 6 right valves and 1 left valve, and several fragments, same source, USNM 125075. Occurrence.—Known only from the type locality as indicated above. Ranger—Upper part of Eutaw formation. Superfamily PTERIACEA Family PTERIIDAE Genus PSEUDOPTERA Meek, 1873 Meek (1873, p. 489; 1876, p. 29) proposed the name Pseudoptem as a subgenus of Pteria Scopoli. He desig- nated as genotype Avicula anomala Sowerby, as figured by d’Orbigny (1843—47, p. 478, pl. 392). It would ap- pear that the species illustrated by d’Orbigny must be accepted as the genotype of Pseudoptera, although it is the true A. anomala Sowerby, the type of which is not illustrated by Woods (1905, p. 64, pl. 9, fig. 2a). D’Orbigny’s figured specimen is from the lower Turo— nian at Le Mans, Department of Sarthe, France; \Sowerby’s specimen, the true A. anomala is from the Upper Greensand (Albian) at Blackdown, Devonshire, England. The two species probably belong to the same genus. The specimens referred to Pseudoptera in this paper are similar in form to the one from Le Mans figured by d’Orbigny; the right valves are, however, more flatly compressed. There is also a marked difference in the surface ornamentation, the specimens from the Eutaw formation having radial lining only on the anteroventral slope of left valves. The features of the ligamental area are well shown on two of the specimens from the Eutaw formation, whereas this area was not seen by either Sowerby or d’Orbigny. '238 Pseudoptera securiformis Stephenson, n. sp. Plate 40, figures 9, 10; plate 41, figures 12—14 Shell large, subtrigonal in outline, inequivalve, strongly inequilateral, bent conspicuously to the left in the adult stage, probably slightly gaping at the rear. In some specimens the curvature to the left is not ap- parent because of subsequent mechanical flattening. 'The left valve is moderately convex, the maximum in— flation is along the umbonal ridge, which extends in a nearly straight or slightly sinuous course from the umbo to the lower posterior extremity, forming an angle to the hinge line ranging in different individuals from 500 to 65°. A narrow, sharply upraised, somewhat irregular ridge traverses the crest of the umbonal ridge from the beak to the lower posterior extremity. The surface back of the umbonal ridge forms a broad very gently convex, slightly undulating slope to the dorsal margin and to the posterior margin; near the hinge line the surface flattens out a little to form an ill-defined posterior wing or rostrum. The anteroventral slope is steep and short and toward the front flares out to form a relatively narrow anterior ear that projects about 10 millimeters in advance of the beak in adults. The right valve is nearly flat or only gently convex, conforming, however, to the curvature of the shell to the left; it is smaller than the left valve, which overlaps it conspicuously along the anteroventral margin. Dorsal margin of shell straight, about three—fourths the total length of the shell; anterior end subpointed; anteroventral margin descending, long, broadly convex; posterior margin narrowly rounded below; postero- dorsal margin broadly convex, inclined forward, curving upward slightly to meet the hinge line. The surface of the shell, especially of the left valve, bears coarse, :sharp growth lines. The surface back of the umbonal ridge of the holotype and of some other specimens bears two broad, low diverging radiating folds, but these folds appear to be wanting on many specimens. A series of narrow, obscure to moderately pronounced, irregu— larly serrated radiating ribs are present on the ante— roventral slope of most left valves the shell substance of which is preserved, but this is a variable feature. Approximate dimensions of the holotype, a left valve: Length 100 mm, height 70 mm, maximum convexity :about 25 mm. Some shells attain a length of 120 mm. The features of the ligamental area are preserved on :two of the paratypes. The area is wide and bears 5 or 6 .ligamental pits of differing width and spacing; the pits are wider than the intervening spaces. appears to lack dentition but near the anterior end of the cardinal area a little back of the beak is a narrow, nonprominent ridge extending obliquely inward to the inner edge of the area; in front of and parallel to this The hinge SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY ridge is a wide and deep channel that ends beakward in a small pit. No evidence of the position of the main adductor scar can be detected on the available internal molds but there is the clear impression of a small muscle ' scar (retractor?) 5 or 6 mm inward from the inner edge of the cardinal area and 25 or 30 mm inward from the beak. Types.—-—Georgia: Holotype, from Ochillee Creek at old Ochillee, Ga., USGS 15501, USNM 125076; 1 unfigured para- type, same source, USGS 5374, USNM 125077; 1 unfig- ured paratype, same source, USGS 5378, USNM 125078; 1 un- figured paratype, same source, USGS 15501, USNM 125079; 1 figured paratype, same source, USGS 25570, USNM 125082; 1 figured paratype, USGS 5377,. USNM 125080. Alabama: 2 figured paratypes, USGS 5384, USNM 125081; two unfigured paratypes, USGS 848, USNM 125083. Distribution.—Chattahoochee County, Ga.: Chattahoochee River, Broken Arrow Bend, left bank, about 10 miles below Columbus, USGS 847; about 0.5 mile below Broken Arrow Bend, USGS 5385; Upatoi Creek, left bank, 0.25 mile below the old Columbus-Cusseta road bridge, USGS 5373 + 5377 1; Ochillee Creek near old Ochillee, USGS 5374 + 5378 + 15501 + 25570; Russell County, Ala: Chattahoochee River, Broken Arrow Bend, right bank, about 10 miles below Columbus, Ga., USGS 5384 + 6409; just below Burdock Landing, USGS 848; Slick Bluff, USGS 845; old Marvyn road, 2.7 miles (airline) north by west of Uchee, USGS 17211; Hurtsboro—Marvyn highway 5.75 miles south of Lee County line, USGS 25575. Perry County, Ala: Road cut in northward—facing slope 1.7 miles northeast of old Hamburg, USGS 25467. Ranger—The species, as known, ranges through the Eutaw formation of east-central Alabama and adjacent parts of Georgia; one specimen has been found in the basal bed of the Mooreville chalk. Within the Eutaw formation the species ranges from the base nearly to the top. Superfamily OSTRACEA Family OSTREIDAE Genus OSTREA Linné, 1758 Subgenus LOPHA Bolten, 1798 Ostrea (Lopha) ucheensis Stephenson, n. sp. Plate 43, figures 1—5 Shell of medium size, subtrigonal to subcircular in outline, with a tendency for the steeply descending posterodorsal margin to be nearly straight. Right and left valves low—convex to nearly flat. Both valves ornamented with radiating, coarse, round-crested ribs or folds numbering 5 to 10 on different individuals, the folds of one valve corresponding to the intercostal spaces of the other valve, the two valves intermeshing around the margins. A smooth flattish area extending 15 to 30 millimeters out from the beak on each valve of most individuals is unaffected by the folds. Growth lines fine on the umbonal area, becoming coarser to 1 Numbers connected by the plus sign (+) pertain to the same locality. FOSSILS OF THE EUTAW FORMATION, ALABAMA-GEORGIA roughly imbricating toward the outer margins. Beaks nonprominent, more or less pointed With a tendency to an angulation of 90° to 115°. Dimensions of the holotype, a left valve: Length 65 mm, height 66 mm, convexity about 10 mm. The largest shell in the collection, a right valve, is 67 mm long and 75 mm high. Ligamental pit relatively small, short, triangular, straight or slightly curved, opening Widely to the interior. Inner margin smooth except for the coarse flutings caused by the intermeshing of the external folds. Adductor scar elongate, more than twice as long as Wide, curved, bean-shaped, with the convexity toward the outer margin. Types.——Holotype, from hill 3% miles north-northwest of Uchee, Russell County, Ala., beds of Eutaw formation exposed in gullies in field southwest of road, USGS 17583, USNM 125031; 7 unfigured paratypes, same source, USNM 125032; 3 figured paratypes, USGS 18317, USNM 125033; 5 unfigured paratypes from the preceding locality, USNM 125034; 6 un— figured paratypes, USGS 17585, USNM 125035. Distributiom—Russell County, Ala.: This species is found 3.2 to 3.4 miles (airline) northwest of Uchee, USGS 17583 + 18317; 2.6 to 2.9 miles north by West (airline) of Uchee, USGS 17585 + 17766 + 18309; 5 miles northwest (airline) of Scale, USGS 18308; Chattahoochee River at Burdock Landing, USGS 848, and Slick Bluff, USGS 845 + 5387. Dallas County, Ala.: One and one-half miles southeast of Summerfield, USGS 19546. Range—In Russell County, Ala., the known occurrences of this species are all in the upper part of the Eutaw formation, probably within the upper 50 feet. The one recorded occurrence in Dallas County, Ala., is in the Eutaw formation, but its exact stratigraphic position within that unit has not been determined. Ostrea cretacea Morton Plate 40, figures 11, 12; plate 42, figures 1—17 1834. Ostrea cretacea Morton, Synopsis of the organic remains of the Cretaceous group of the United States, p. 52, pl. 19, fig. 3. (See synonymy in N. C. Geol. and Econ. Survey, v. 5, pt. 1, p. 134, 1923.) The probable validity of the name Ostrea cretacea Morton for the abundant small oyster shells in the Eutaw formation (Tombigbee sand member) at Erie Blufl“, Hale County, Ala., is discussed by Stephenson (1923, p. 135). Further consideration of the subject has afforded no basis for changing the opinion expressed at that time. I believe that the types in the Academy of Natural Sciences, Philadelphia, Pa, came from the Eutaw formation at Erie Blufi, Warrior River, Hale County, Ala., and that the label attributing them to Charleston, S. C., is in error; these specimens agree closely with shells from Erie Bluff. A comparison of Morton’s original figure of Ostrea cretacea with the original figure of 0. alabamiensis Lea (1833, p. 91, pl. 3, fig. 17) fails to justify Dall’s (1898, p. 679) placing of Morton’s species in the syn— onomy of Lea’s species; the two species differ markedly 389135—58—2 239 in form and outline, and 0. cretacea is smooth on the inner margin, with the exception of a few obscure crenulations near the hinge of some shells. Ostrea cretacea Morton is a small simple nearly straight, or only slightly curved, oyster, subovate to subtrigonal in outline, both valves low-convex. Con- centric markings pronounced but variable in strength and spacing on different individuals. Radial markings practically absent, but a few obscure radial lines may be detected on some shells, including the holotype. The shells exhibit marked individual variation in out- line and convexity; the dorsal margin may be broad or narrow and pointed. Radial color markings of brownish tint are preserved on a rare specimen (pl. 40, fig. 12). The recorded dimensions of the holotype are: Length 24 mm, height 34 mm, convexity 6 mm. Among the specimens referred to the species in the present paper the largestmeasured shell, a left valve (pl. 42, fig. 14), is 43 mm long, 57 mm high, and has a convexity of about 15 mm. In Alabama Ostrea cretacea Morton is restricted in vertical range to the Eutaw formation. At Erie Bluff on Warrior River, Hale County, the type locality, the zone containing this species is about 21 feet thick; the zone is uncomformably overlain by the Mooreville chalk of the Selma group. The same zone bearing great numbers of the shells of 0. cretacea is well exposed at Choctaw Bluff, Greene County, about 6 miles (air- line) upstream from Eric Bluff, and at Wolfs Bluff, Hale County, less than a mile downstream from Erie Blufl“. In a road cut 1.7 miles northeast of old Hamburg, Perry County, Ala., the zone yielding the species is only about 10 feet thick and occupies the same strati- graphic position below the Mooreville chalk that it does at Erie Bluff. In east—central Alabama in Macon and Russell Counties the zone of Ostrea cretacea is much thicker than it is in the central and western parts of the state, attaining a measured thickness of 130 feet. In these counties the shells of the species are present in vast numbers in certain layers, especially in the upper part of the zone. In this area the shells average a little larger than at the type locality at Erie Bluff. However, the size ranges from that of the smaller more typical shells to about one and four—fifths that of the holotype, and there seems no reason to question the reference of all the shells to 0. cretacea Morton. Presumably the average greater size of the shells in some assemblages reflects the more favorable environmental conditions in which the organisms lived. Types.—Holotype and three paratypes in the collection of the Academy of Natural Sciences of Philadelphia; these are labeled “Charleston, S. C.,” but for reasons previously stated this label is believed to be in error, the true type locality being, Erie Bluff, 240 Warrior River, Ala. On the assumption that Erie Bluff is the type locality, the four shells illustrated by Stephenson (1923, pl. 28, figs. 11—13, USNM 31541731544) are topotypes. Two plesiotypes (essentially topotypes), Choctaw Bluff, 'Warrior River, Greene County, Ala., USGS 6425, USNM 125025; 2 figured topotypes, Erie Bluff, Warrior River, Hale County, Ala, USGS 6428, USNM 125026; 3 pleisotypes, 4.1 miles north of Creek Stand, Macon Co., Ala., USGS 17007, USNM 125027; 7 plesiotypes about 3.1 miles north of Creek Stand, Macon County, Ala., USGS 17006, USNM 125028; 1 plesiotype, 5 miles northwest of Seale, Russell County, Ala., USGS 18308, USNM 125029; 2 plesiotypes, left valves, half mile below Broken Arrow Bend, about 10 miles below Columbus, in Chattahoochee County, Ga, USGS 5385, USNM 125030. Distribution—The shells of Ostrea cretacea Morton may be seen in outcrops of the Tombigbee sand member of the Eutaw formation at many places between Greene County, Ala., and Chattahoochee River, and at a few places in Chattahoochee County, Ga. Only a few localities at which the shells have been collected will be recorded here. Alabama: Greene County, Choctaw Bluff, Warrior River, USGS 6425; Hale County, Warrior River at Erie Bluff, USGS 6428+ 6932 and at Wolfs Bluff, USGS 6429; Perry County, 1.7 miles northeast of old Hamburg, USGS 6441; Macon County, 2 miles north of Warrior Stand, USGS 17574, 2.3 miles north- west of Warrior Stand, USGS 17550, 3.1 miles north of Creek Stand, USGS 17006, and 4 miles (airline) north of Creek Stand, USGS 17007; Russell County, 2.5 miles north-northwest of Uchee, USGS 17766+ 17776, Hurtsboro—Marvyn road 5.85 miles south of Lee County line, USGS 25575, 3.4 miles northwest of Uchee, USGS 17775, 5 miles northwest of Scale, USGS 18308, Chattahoochee River, right bank, at Broken Arrow Bend, USGS 5384, and just below Burdock Landing, USGS 5386. Georgia: Chattahoochee River, left bank, one—half mile below Broken Arrow Bend, USGS 5385, Upatoi Creek 7 miles southeast of Columbus, USGS 5373+5377+17612, Ochillee, USGS 5374+5378+ 15501. South Carolina: Well of Charleston Consolidated Railway and Lighting Co., Charleston, at several depths between 1,725 and 2,007 feet. ' North Carolina: Well of Clarendon VVatchorks Co., \Vil— mington, at depths between 720 and 1,105 feet; well at Fort Caswell at depth of 1,365 to 1,380 feet. (See Stephenson, 1923, p. 136.) Range.-Shclls of this species occur in vast numbers in certain beds of the Eutaw formation in Alabama and in adjacent parts of Georgia. Some shells that seem indistinguishable from the species have been recorded from overlying formations in Georgia, North Carolina, and South Carolina as high as the up- per part of the Exogyra ponderosa zone. Genus GRYPHAEA Lamarck, 1801, sensu lato Gryphaea wratheri Stephenson Plate 41, figures 3~8 Gryphaea wratheri Stephenson, U. S. Geol. Survey Prof. Paper 186—A, p. 2, pl. 1, figs. 1—4. 1936. The original description of Gryphaca wratheri Ste— phenson and a record of the distribution of the species as known at that time, are given in the paper cited in the synonymy. (See also Stephenson, 1937, p. 133— 146.) The species is closely related to G. aucella Roemer but averages larger, thicker shelled, broader, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY less convex and is less strongly incurved at the beak. A consistent difference between the two species that was not mentioned in the original description pertains to a calluslike ridge or fold marking the contact between the two valves on the inner surface of the shell; in a typical example of G. wrathem' this feature appears as a conspicuous round-crested concentric ridge extending around the inner surface at the line of contact of the two valves, terminating at its two ends below the beak at the inner angles of the ligamental pit. The strength of this ridge varies markedly on different individuals. In G. aucella either no ridge is present at this line of contact, or if present is only weakly developed at the ends of the line nearest the ligamental pit. As in most species in the oyster family the shells of G. wrather’i have marked individual variation in shell characters. The left valve shown in plate 41, figure 5, measures: Length 32 mm, height about 33 mm, convexity about 12 mm. The average size of the Alabama shells is about the same as that of the more typical ones from east- central Texas. However, a few may attain a size and thickness considerably greater than the average. One such shell (pl. 4], fig. 3) from House Bluff, Alabama River, Autauga County, measures: Length 56 mm, height 58 mm. Types.-Holotype, USNM 75506; 2 figured paratypes, USNM 75507, 75507a; 36 unfigured paratypes, USNM 75508; all from a cut on Gaston Avenue just northeast of the intersection of West Shore Drive, 0.7 mile west of the dam of White Rock Reservoir, Dallas, Tex.; all are from USGS coll. 14075. Plesio- type from 0.5 mile north by east of Liberty Hill Church, Macon County, Ala, USGS 19060, USNM 125022; 2 plesiotypes from 0.75 mile north by east of Liberty Hill Church, Macon County, Ala., USGS 17576, USNM 125023. Plesiotype from House Bluff, Alabama River, Autauga County, Ala., USGS 6442—13, USNM 125024. Distribution in eastern Alabama.——Macon County, upper part of Eutaw formation: 4.25 miles N. of Chesson, USGS 17570; 2% miles northeast of Hardaway, USGS 17761 ; 2 miles north of Edwards, USGS 17572; 7 miles northeast of Hardaway, % mile(?) north-northeast of Liberty Hill Church, USGS 19060 (1 plesi- otype), 17763; 075 mile north by east of Liberty Hill Church, USGS 17576 (2 plesiotypes), 17764; about 7 miles northeast of Hardaway, 0.1 to 0.3 mile south of Mount Andrew Church, USGS 17771; Fort Davis road 6 miles south of Tuskegee, USGS 6445; 6.1 miles north by east of Fort Davis, USGS 17569; 2.5 miles north of Cotton Valley crossroad, USGS 17608; 2.35 miles north of Cotton Valley crossroad, USGS 17607; 2.25 miles north— northwcst of Warrior Stand, USGS 18306; 2 miles north of War- rior Stand, USGS 17574; 4.1 miles north by west of Creek Stand, USGS 18312. Macon County, base of Blulftown formation: 0.75 miles north by east of Chesson, USGS 17568; 2.5 miles northeast of Hardaway, USGS 17573. Russell County, upper part of Eutaw formation: Uchee Creek 200 feet upstream from crossing of U. S. Highway 241 [431], USGS 19079. Russell County, lower part of Mooreville chalk (sandy facies): 0.55 miles north of Hurtsboro, USGS 18320; 2.5 miles east by north of Hurtsboro, USGS 17604; State Highway 26, 3.4 miles east of Hurtsboro, USGS 18318+ 25583. FOSSILS OF THE EUTAW FORMATION, ALABAMA-GEORGIA Stratigraphic and geologic range—The original description of the species (Stephenson, 1936, p. 3, 4) records it from the upper part of the Tombigbee sand member of the Eutaw formation and from the basal bed of the Mooreville chalk (Selma group) at 15 localities in Alabama between the vicinity of Eutaw, Greene County, and Montgomery, Montgomery County. Part of the shells from the basal Mooreville were mechanically re- worked from the underlying Eutaw formation, but some may be indigenous to the basal Mooreville. The more recent field work of W. H. Monroe and others in eastern Alabama has resulted in the discovery of G. wratheri in Macon and Russell Counties in the upper part of the Eutaw formation in that area, where also a few indigenous examples of the species have been found in the lower part of the Mooreville chalk (sandy facies). Subsequent to the publication of the original description, the species has been recorded from the upper part of the Tombigbee sand member of the Eutaw formation in Mississippi (Stephenson and Monroe, 1940, p. 69). The species has been obtained from a core sample (USGS 25369), depth 4,324—4,326 feet, in a well of the Shell Oil Co. in the Chaperall field, Sistrunk—Chapman B1, sec. 13, T. 10 N., R. 7 W., Wayne County, Miss; this mate- rial was submitted by E. H. Rainwater November 22, 1954, and was identified by Norman F. Sohl. In east central Texas Gryphaea wratheri is present within the upper half of the Austin chalk in a zone having a maximum ob- served thickness of 35 feet; this zone .has been traced through the chalk from the type locality of the species in Dallas, Dallas County, Tex., southward and southwestward to Guadalupe County, Tex.; the species has also been recorded in a marine sand that probably represents the westward continuation of the Blossom sand (late Austin age) at two localities, one about 3 miles north by west of Dodd City, and the other about 5 miles north of Windom (north of Lone Elm Church), Fannin County, 'Tex. In recent years the species has been identified in west Texas in Jeff Davis, Reeves, and Presidio Counties. These examples possess the essential features of the species but are notable for their larger average size and their thick shells, indicating vigorous growth in a favorable habitat. Some shells attain lengths as great as 50 mm, heights as great as 64 mm, and a maximum thickness (diameter) of 15 mm. Genus EXOGYRA Say, 1920 Exogyra upatoiensis Stephenson Plate 43, figures 6—10 1914. Exogym upatoiensis Stephenson, U. S. Geol. Survey Prof. Paper 81, p. 46, pl. 13, figs. 5—7; pl. 14, figs. 1—3. 1923. Exogyra upatoiensis Stephenson. Stephenson, N. C. Geol. and Econ. Survey, v. 5, p. 164, pl. 45, figs. 1—5. Two of the three cotypes of this species came from the basal beds of the Eutaw formation at Broken Arrow Bend on Chattahoochee River, about 10 miles below Columbus and the third from a locality on Upatoi Creek 6 miles east-northeast of Broken Arrow Bend, Chattahoochee County, Ga. (7 miles southeast of Columbus). The species is described and illustrated in the two papers cited in the synonymy. The left valves of two of the cotypes are well formed and are ornamented all over with fine, closely spaced, irregular radial costae. The left valve of the larger of the three 241 cotypes shows fine radial costae in the umbonal region around a very large scar of attachment, but elsewhere is partly smooth and partly ornamented with short, irregular costae; the costae on the umbonal ridge are somewhat coarser than on other parts of the surface. West of Chattahoochee River in Russell and Macon Counties, and on to the west in Alabama, the species is represented in collections from many localities by shells, mainly in the upper part of the Eutaw formation (Tombigbee sand member), that exhibit a Wide indi- vidual range in the form and ornamentation of their left valves. Among these shells a few possess the fea- tures of the originally described shells from the type area, but most of them are irregular in form as a result of crowding or other unfavorable environmental condi- tions. Many of these nontypical shells have a minor development of fine, closely crowded typical costae in the umbonal region, away from Which the surface bears relatively coarse, irregularly distributed costae; on the crests of the costae are scattered spinelike projections formed by the sharp upfolding of concentric lamellae. Although many of these shells are nontypical in appear- ance there is a reasonable certainty that they all belong to Exogyra upatoz'ensz's Stephenson, and that they are individual variants within the species. Types.—Cotypes from basal beds of Eutaw formation, Chatta- hoochee River, Broken Arrow Bend, about 10 miles below Colum- bus, right bank (Alabama), USGS 5384, USNM 31219, 31221, and Upatoi Creek 7 miles southeast of Columbus, Chattahoochee County, Ga., USGS 5377, USNM 31220. Plesiotypes from upper part of Eutaw formation (Tombigbee sand member) 2.25 miles north-northwest of Warrior Stand, USGS 18306, USN M 125018; and 0.75 mile north by east of Liberty Hill Church, USGS 17576, USNM 125019, Macon County, Ala.; Catoma Creek 5 or 6 miles southwest of Montgomery, Montgomery County, Ala., USGS 17010, USNM 125020. Plesiotype from base of Mooreville chalk, Choctaw Bluff, Warrior River, 4 miles south by east of Eutaw, Greene County, Ala., USGS 25466, USNM 125021. Distribution—Greene County, Ala. (base of Mooreville chalk): Choctaw Bluff, Warrior River, USGS 25466 (1 plesiotype). Autauga County, Ala. (upper part of Eutaw formation): House Bluff, Alabama River, USGS 17011. Montgomery County, Ala. (upper part of Eutaw formation): Catoma Creek, 5 or 6 miles southwest of Montgomery, USGS 17010 (includes 1 plesiotype). Macon County, Ala. (Eutaw formation): 4.25 miles north of Chesson, USGS 17570; 2.5 miles northeast of Hardaway, USGS 17761; 2 miles north of Edwards, USGS 17572; 0.5 mile north- northeast of Liberty Hill Church, USGS 17763; 0.75(?) mile north by east of Liberty Hill Church, USGS 19060; 0.75 mile north by east of Liberty Hill Church, USGS 17576 (includes 1 plesiotype); 0.1 to 0.3 mile south of Mount Andrew Church, USGS 17771; 2.5 miles north of Cotton Valley crossroad, USGS 17608; 2.25 miles north-northwest of Warrior Stand, USGS 18306 (includes 1 plesiotype); 2 miles north of Warrior Stand, USGS 17574; 4.1 miles north by west of Creek Stand, USGS 11646+ 17007+ 17212. Russell County, Ala. (Eutaw formation): 3.8 miles north by west of Uchee, USGS 17585; 3.25 miles north- northwest of Uchee, USGS 17583+ 17584; Chattahoochee River, 242 Broken Arrow Bend, right bank, about 10 miles below Columbus, USGS 5384; near Fort Mitchell Landing, USGS 575. Chatta- hoochee County, Ga. (basal beds of Eutaw formation): Chatta- hoochee River, Broken Arrow Bend, left bank, about 10 miles below Columbus, USGS 847 (includes 2 cotypes), 25573; Upatoi Creek, 7 miles southeast of Columbus, USGS 5373+5377 (includes 1 cotype). Range—The species, as at present satisfactorily identified, is restricted in its stratigraphic range to the Eutaw formation in central and east-central Alabama and in Chattahoochee County, Ga., and is recorded from a well at Charleston, S. C., at a depth of 1,974 to 2,007 feet. Examples found in the basal bed of the Moorevillc chalk in Alabama are believed to have been mechani- cally reworked from the underlying Tombigbee sand member of the Eutaw formation. Superfamily ANOMIACEA Family ANOMIIDAE Genus ANOMIA Linné, 1758 Anomia preolmstedi Stephenson, n. sp. Plate 41, figure 9-11 Left valve of medium,sized shell thin, subcircular in outline, flattish, to strongly convex in different individ- uals, approximately equilateral. The beak is not preserved on most of the available shells but, as seen on two young left valves, it is small, nonprominent, and is situated about 1 millimeter away from the margin. The surface of well—preserved shells bears very fine, irregular, more or less obscure, closely spaced riblets and fine, closely spaced, overlapping concentric lamellae. The whole outer surface presents a charac- teristic soft silvery sheen. Hinge edentulus. Inner surfaces of available left valves not well enough pre- served to show the muscle scars. The inner surface of the figured paratype is lined with a thin layer of matrix filling, the outer surface of which bears the imprint of the right valve. This imprint is smooth and undulating; a little below the hinge margin is the outline of the oval opening (foramen) through which passed the byssus that provided the mechanism for the attachment of the animal to a foreign object, as for example, to the surface of an abandoned moluscan shell. No right valves are present in the material studied and the imprint just described is the only observed evidence of its presence. Although the genus Anomia is represented in our col- lections from the Cretaceous sediments of the Atlantic and Gulf Coastal Plain by several species and by many individuals, right valves are rarely seen. This is because they are thin and frail and are easily destroyed; in an exceptional example the right valve is protected by the overlying left valve which has retained its natural position on the object of attachment. Dimensions of the holotype: Length 33 mm, height 31 mm. convexity 9 mm. A large and exceptionally SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY convex left valve measures: Length 35 mm, height 36 mm, convexity about 15 mm. Shells of this species from the Eutaw and Blufftown formations in the Chattahoochee area south and south- east of Columbus, Ga., have heretofore been referred to Anemia olmstedi Stephenson (Stephenson, 1923, p. 219), but these shells present certain consistent differences from A. olmstedi, and occupy a lower stratigraphic posi- tion than that species. In A. preolmstedi Stephenson the riblets covering the outer surface of the left valve are finer and weaker than the similar riblets in A. Olmstedi and the concentric growth lamellae, although similar in appearance, are finer and more closely spaced and are not conspicuously upraised along their free margins. Types.—Holotype, from Chattahoochee River, Broken Arrow Bend, right side, about 10 miles below Columbus, in Russell County, Ala., USGS 6409, USNM 125014; I figured paratype from same source, USNM 125015; 8 unfigured paratypes (from same source), 2 mentioned, USNM 125016; 2 unfigured para— types, the large one measured, from Ochillee, Chattahoochee County, Ga, USGS 5378, USNM 125017. Distribution—Alabama, Russell County: Eutaw formation, Broken Arrow Bend, Chattahoochee River, right side, about 10 miles below Columbus, Ga., USGS 5384 + 6409 (holotype and 9 paratypes); just below Burdock Landing, Chattahoochee River about 13.5 miles below Columbus, USGS 5386 ; northeastward facing slope of small branch of Uchee Creek, 2% miles north by West of Uchee, USGS 17759 + 17765 + 17769; gullies southwest of road 3% miles north-northwest of Uchee, USGS 17584. Blufltown formation, Big Bend, Chattahoochee River, 24.5 miles below Columbus, USGS 5388. Georgia, Chattahoochee County: Eutaw formation, Ochillee Creek at old Ochillee, USGS 5378 (2 paratypes, 1 measured); Chattahoochee River, Broken Arrow Bend, left bank, about 10 miles below Columbus, Ga, USGS 847. Blufi‘town formation, just below Banks Landing, Chattahoochee River, 27 miles below Columbus, in Stewart County, USGS 5390. Range.———The species ranges through the Eutaw formation of the Chattahoochee area and upward into the lower part of the Blufftown formation (Moorcville age). Order TELEODESMACEA Superfamily CARDIACEA Family CARDIIDAE Genus CARDIUM Linné, 1758 Subgenus TRACHYCARDIUM March, 1853 Cardium (Trachycardium) ochilleanum Stephenson, n. sp. Plate 41, figures 1, 2 Shell of medium thickness, subquadrangular in out- line, length and height nearly equal, moderately con- vex, a little oblique toward the lower rear. Beaks of medium prominence, incurved, closely approximate, slightly prosogyrate, situated centrally. Umbonal ridge of medium prominence, obtusely subangular in cross section. Posterodorsal slope steep, broadly exca— FOSSILS OF THE EUTAW FORMATION, ALABAMA-GEORGIA vated. Main surface rounding down broadly to the anterior and ventral margins. Dorsal margin short, slightly arched; anterior margin semicircular, rounding into the broadly rounded ventral margin; posterior terminus subangular below the midheight; posterior margin above the terminus truncated, inclined forward. The surface bears about 38 well-developed radiating ribs; these are flattish-topped with the exception of several ribs on the umbonal ridge, which are sharp crested. On about the anterior three-fifths of the sur— face the ribs bear regularly spaced nodes elongated transversely and, where largest, numbering about 8 in a radial distance of 5 millimeters; toward the beak on each rib the nodes become regularly smaller and weaker and are scarcely observable near the tip of the beak. The nodes are in alinement from rib to rib and the rows of nodes appear to be in alinement with the fine growth lines. On the posterior two- fifths of the surface the crests of the ribs are essentially smooth with the exception of obscure irregular nodes on the posterodorsal slope. Dimensions of the holotype, a right valve: Length 28 mm, height 29 mm, convexity about 12 mm. The figured paratype, a left valve, is 24 mm long and 24 mm high. The hinge is imperfectly preserved in the holotype and the figured paratype, but the features are observ— able in part. Hinge narrow; ligamental groove short, opisthodetic; the cardinal teeth of the right valve include a small anterior tooth and a relatively large posterior tooth (broken away), separated by a deep socket; in the left valve the anterior cardinal (also broken away) is large and the posterior one small, the two separated by a deep socket; the lateral teeth are small and well removed from the cardinals. Internal features not uncovered. This species is closely related to Cardium (True/ty— camdium) carolinense Conrad (1875), in Kerr, W. C., app. A, p. 7; Stephenson, 1923, p. 286), from the Snow Hill marl member of the Black Creek formation, Snow Hill, N. C. It differs from that species in that the ribs are narrower, the interspaces are wider, and the pattern of the nodes, though similar, is much coarser. Types.—Holotype, a right valve from Ochillee Creek, below bridge at site of old Ochillee, Chattahoochee County, Ga., USGS 15501, USNM 125010; I figured paratype, same source, USNM 125012; 2 unfigured juvenile paratypes, a right and a left valve, same source, USNM 125011; 1 unfigured paratype, same source, USGS 25569, USNM 125013. Distribution and range—The only available specimens are the types from the Ochillee Creek locality. 243 Superfamily VENERACEA Family VENERIDAE Genus LEGUMEN Conrad, 1858 Legumen afl‘. L. carolinense (Conrad) Plate 44, figures 17~20 The internal and external molds of a species of Legumen Conrad are common in the Eutaw formation in the Chattahoochee River area (Georgia-Alabama). In outline and form, and in the character of the con- centric growth markings on the outer surface of the shell this species appears to be essentially like L. caro- linense (Conrad) from the Snow Hill marl member of the Black Creek formation of North Carolina (Con- rad, 1875, p. 8, pl. 2, fig. 10; Stephenson, 1923, p. 321, pl. 81, figs. 5—8). The part of the Chattahoochee River section that corresponds in age to the Snow Hill marl member is the Cusseta sand which uncon- formably overlies the Blufftown formation. Legumen carolinense is recorded from a marine facies of the Cussetta sand exposed at Woolridge Landing, Chatta— hoochee River, near the northeastern corner of Barbour County, Ala. In the Chattahoochee region the Eutaw formation forms the lower part of the zone of Exogym ponderosa, whereas the Cusseta sand forms the upper part of that zone above the Blufftown formation. If the molds and prints of Legume/n in the Eutaw are correctly referable to L. carolinense the indicated range of the- species is through the zone of E. ponderosa. Although the prints and molds of Legumen in the Eutaw formation are like L. carolinense in most of their features there are minor differences that appear to be consistent so far as the available material permits one- to judge. The pallial sinus, as obscurely preserved on several of the internal molds from the Eutaw, is narrow- er than it is in L. carolmense, and the anterior margin of the shell appears to be more narrowly rounded. If these differences should prove to be constant features they might justify a specific separation. However, granting the reality of these differences the conclusion may reasonably be drawn that the form of Legumen so. abundantly present in the Eutaw formation is ancestral to L. carolinense in the Cusseta sand and in the Snow Hill marl member of the Black Creek formation. The hinge features, which are so perfectly preserved in the cotypes of L. caroline'nse from North Carolina, are not observable 0n the molds and prints from the Eutaw formation in the Chattahoochee River area. However, imprints of the inner edges of the cardinal teeth on the 244 dorsal margin of the internal molds agree in their arrangement with the cardinal teeth of L. carolmense, and the reference of the molds to the genus L. Conrad seems well established. The internal mold shown in plate 44, figure 19, measures: Length 58 mm, height 34 mm, thickness 13 mm; the mold shown in plate 44, figure 17, measures: Length 52 mm, height 32 mm, thickness 13.5 mm. Figured specimens.—Broken Arrow Bend, Chattahoochee River, Chattahoochee County, Ga., USGS 6408, USNM 125006; Upatoi Creek,‘7 miles southeast of Columbus, in Chattahoochee County, Ga., USGS 5377, USNM 125007; just below Burdock Landing, Chattahoochee River, Russell County, Ala., USGS 848, USNM 125008; 1 unfigured specimen from the same source, USGS 25570, USNM 125009. Distribution—Russell County, Ala., Chattahoochee River: Broken Arrow Bend, right bank about 10 miles below Columbus, Ga., USGS 5348+ 6409; just below Burdock Landing, about 13.5 miles below Columbus, USGS 848 (includes I figured specimen) +5386; Slick Bluff about 14 miles below Columbus, USGS 845 +5387. Chattahoochee County, Ga.: Chattahoochee River, Broken Arrow Bend, left bank, about 10 miles below Columbus, USGS 847+ 6408 (figured); Upatoi Creek, 7 miles southeast of Colum- bus, USGS 5377 (includes 1 figured specimen); Ochillee Creek at old Ochillee, USGS 5378. Superfamily MACTRACEA Family MACTRIDAE Genus CYMBOPHORA Gabb, 1869 Cymbophora ochilleana Stephenson, n. sp. Plate 44, figures 1—3 Shell small, subtrigonal in outline, thin, subequi— lateral, equivalve, moderately inflated. Beaks promi— nent, incurved, prosogyrate, slightly separated, situated a little in advance of the midlength; umbonal area narrow. Anterodorsal and posterodorsal slopes steep, broadly excavated; umbonal ridge weakly developed, broadly subobtuse; greatest inflation central above the midheight, from which point the main surface rounds down broadly to the ventral margin. Dorsal margin broadly arched, anterior margin narrowly rounded, ventral margin very broadly rounded, posterior margin narrowly rounded a little below the midheight. Main surface contains very fine incremental lines that become a little coarser toward the ventral margin. On more than half of the anterodorsal slope bordering the margin the incrementals become sharp ridges; this ridged area is abruptly separated from the smoother surface on the slope above it. A similar ridged area is present on the posterodorsal slope where, however, it covers less than half of the slope. Dimensions of the holotype, a right valve: Length 23.5 mm, height 19 mm, convexity 7 mm. The hinge is not completely preserved in any of the available specimens; it is very thin and the calcareous SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY shell has become crystallized and is easily shattered in. the process of removing the matrix covering it. How- ever, enough of the hinge can be seen in the type ma- terial to reveal most of its features. In the left valve two cardinal teeth below the beak are fused together- at their upper ends and diverge widely below toward the interior; the posterior one is nearly direct and the anterior one oblique; a deep narrow channel separates. the latter from the thin, sharp margin. The ligamental pit is internal back of the cardinal teeth but is poorly preserved. Well-developed elongated, thin laterals, one anterior and the other posterior are present; these are transversely striated on the sides in the direction of' movement. The two cardinal teeth in the right valve are also fused above and diverge widely inward; the- separating socket is wide enough to receive both the» cardinals of the left valve. The laterals of the right valve are claspers receiving the single laterals of the- left valve. This species is similar in form to Cymbophom trig0~ nalis Stephenson (1923, p. 336) from the Snow Hill marl member of the Black Creek formation of North Carolina. It differs in that the main surface lacks: concentric ribbing and is marked only by fine increm mental lines. The hinge features of the two species. appear to be essentially identical. Types.—Holoty~pe, from the Eutaw formation, Ochillee Creek, at old Ochillee, Chattahoochee County, Ga., USGS 15501, USNM 125000; 9 unfigured paratypes, same source, USNM' 125001; I figured paratype, same source, USGS 5374, USMN 125002; 3 unfigured paratypes, same source, USNM 125003; 1 figured paratype, same source, USGS 5378, USNM 125004; 11 unfigured paratypes, same source, USNM 125005. Distribution—All the available examples are from Ochillee- Creek, at the site of old Ochillee, Chattahoochee County, Ga., as recorded above under “types.” Range.—Known only from the basal beds of the Eutaw forma— tion at the type locality. Superfamily MYACEA Family CORBULIDAE The family Corbulidae is represented in the Eutaw formation of the Chattahoochee region by many rela-- tively large specimens referable to two or more species. One of these species, Caryocorbula? veavtch'i Stephenson, n. sp., is closely related to Corbula oxynema Conrad (1875, in Kerr, app. A, p. 11), from the Snow Hill marl member of the Black Creek formation of North Caro-r lina, and another, Oaryocorbula? georgiana Stephenson, n. sp., is a species possessing a coarse type of concentric sculpture. Another probably undescribed species, rep— resented by poorly preserved specimens, has still coarser concentric ribbing and is larger than the typical 0. georgiana. Vokes has shown (1945, p. 7—10) that the genotype FOSSILS OF THE EUTAW FORMATION, ALABAMA-GEORGIA of Corbula, Lamarck (1799), C. sulcata Lamarck, a Recent species from the coast of Senegal, West Africa, posesses hinge characters sufficiently distinctive and character- istic to separate it generically from many of the Tertiary and Cretaceous species that have been referred to Corbulw. I have examined a right and a left valve labeled 0. sulcata Lamarck, presumably topotypes (USNM Ter. Coll. Moll. 614185), from the Senegal coast, and am in agreement With Vokes’ conclusion. The characters on Lamarck’s species that indicate this separation are, in the hinge of the left valve, the absence, of a chondrophore, the presence of a large cardinal tooth, the deep submergence of the ligamental pit (resilifer) and the separation of this pit from the adjacent socket by a thin septum and, in the right valve, the presence of a weak, but distinct, short posterior lateral tooth that fits into a shallow lateral socket in the left valve. For the purpose of comparison illustrations of a right and a left valve of the Recent C. sulcata Lamarck are given on plate 45, figures 1—6. The deep ligamental pit and the prominent cardinal tooth in the left valve, the lateral tooth in the right valve, and the correspond— ing lateral socket- in the left valve are clearly shown in these illustrations. A score or more of generic names have been intro- duced by Vokes and others for shells of the family Corbulidae, most of which at one time or another have been referred to Corbula. The species here described under the name, Oaryocorbula? veatchz', appears to possess most of the essential generic features of Cary— ocorbula Gardner (1926, p. 46) from the Claiborne group (Eocene) of Alabama, and is referred questionably to that genus. Genus CARYOCORBULA Gardner, 1926 1926. Caryocorbula Gardner, Nautilus, v. 40, p. 46. 1928. Caryocorbula Gardner, U. S. Geo]. Survey Prof. Paper 142—E, p. ‘230. 1945. Caryocorbula Gardner. Vokes, Am. Mus. Nat. History Bull., v. 86, art. 1, p. 11. Gardner designated Oorbula alabamiensis Isaac Lea, from the Claiborne group (Eocene) as the type species of Oaryocorbula and described the genus as follows: Shell small or of moderate dimensions; acutely keeled posteriorly ; slightly inequivalve; the right valve 3. little larger and a little higher relatively than the left; both valves concentrically rugose, the sculpture upon the right valve in some species stronger and more regular than upon the left; a microscopically fine radial lineation developed in some of the later species, particularly upon the posterior keel; ligament, dental, muscle and sinal characters similar [?] to those of Corbula s. s. The Cretaceous species here referred questionably to Oaryocorbula appear to be essentially like that genus in hinge, ligamental and internal features, but 245 they are plumper, more trigonal in outline, more pointed posteriorly and average larger. The whole group of Cretaceous and Tertiary Corbulidae is in need of critical monographic study. Caryocorbula? veatchi Stephenson, n. sp. Plate 44, figures 4—9 Shell of medium size, moderately thick, subtrigonal in outline, inflated centrally and anteriorly, compressed and subpointed posteriorly, rostrate on posterodorsal margin, very inequilateral, inequivalve, the right valve slightly larger and overlapping the left around the margins. Beaks moderately prominent, incurved, slightly prosogyrate, closely approximate, situated about 0.55 the length of the shell from the anterior extremity; right and left beaks of nearly equal height. Umbonal ridge weak but traceable as a thin, weak carina from the beak to the posterior extremity; on the right valve the space between this ridge and the dorsal margin is very narrow; on the left valve this space is slightly wider; it is slightly excavated on each valve. Dimensions of the nearly complete holotype: Length 20 mm, height 14 mm, thickness 11.6 mm. A paratype, a right valve, shown on plate 44, figure 6, measures:- Length 21 mm, height 15.5 mm, convexity 6.7 mm. The hinge of the right valve bears a strong, trigonal, pointed, upturned cardinal tooth, bordered posteriorly by a deep, wide resilial socket. On the left valve the chondrophore, which supports the ligament, is elevated and is separated from the posterior margin of the shell by a weak, narrow ridge; the middle of the chondrophore is slightly excavated. In front of' the chondrophore is a deep trigonal socket for the reception of the cardinal tooth of the right, valve. The adductor scars are slightly upraised; the posterior scar is bordered on the front side by a low, narrow ridge that, extended downward, coincides with the very shallow pallial sinus. On the inner surface of the right valve a narrow groove closely paralleling- the margin marks the contact of the margin of the overlapped left valve. The surface is ornamented with fine, subdued, somewhat irregular growth ridges that are a little coarser toward the outer margins. Senility is indicated by the abrupt inbcnding of the outer surface within 1 to 4 millimeters of the ventral and anterior margins of adult shells. Compared with the closely related Caryocorbula? oxynema (Conrad), from the Snow Hill marl member of the Black Creek formation of North Carolina, this species possesses a thicker shell, a heavier hinge, and a finer and weaker pattern of concentric growth ridges. Types.—-Holotype, from Ochillee Creek at old Ochillee, 246 Chattahoochee County, Ga., 2 unfigured paratypes, same USGS 5374, USNM 125036; source, USNM 125037; 2 fig- ured paratypes, same source, USGS 15501, USNM 125038; 14 unfigured paratypes, same source, USNM 125039; and 3 unfigured paratypes, same source, USGS 5378, USNM 125040. Named in honor of Otto Veatch, the original collector, and one time assistant State Geologist of Georgia. Distribution—Alabama, Russell County: Broken Arrow Bend, Chattahoochee River, right bank, USGS 5384. Georgia, Chattahoochee County: Broken Arrow Bend, Chat- tahoochee River, left bank, USGS 847; Ochillee Creek near old Ochillee (type locality), USGS 5374+5378+15501+25569. Range—Lower part of Eutaw formation, Chattahoochee area, Georgia—Alabama. Closely related large shells belonging to two or more species of Caryocorbula? are present at a higher stratigraphic position in the Cusseta sand (Alabama—Georgia) and in the Snow Hill marl member of the Black Creek formation of North Carolina. Caryocorbula? veatchi longa Stephenson, n. var. Plate 44, figures 10—13 This shell from the upper part of the Eutaw forma- tion resembles Oaryocorbula? veatchi but it averages a little larger, is proportinatcly longer, and is not quite so strongly inflated; its concentric surface sculpture, though weak and moderately fine, is nevertheless stronger than that of 0.? veatchi; the features of the chondrophore in the left valve are more strongly marked. Dimensions of the holotype, a right valve: Length 23 mm, height 15 mm, convexity 6.5 mm. Types.—~Holotype, a right valve, from Hurtsboro—Marvyn road 5.9 miles south of Lee County line in Russell County, Ala., USGS 25567, USNM 125041; 1 figured paratype, same source, USNM 125042; 8 unfigured paratypes, same source, USNM 125043. Distribution—In addition to the type locality (USGS 25567) poorly preserved specimens of the species have been identified from two localities on the Chattahoochee River in Russell County: just below old Burdock Landing, USGS 848, and at Slick Bluff, USGS 845+5387. Shells of comparable size but still more elongated, and having still stronger concentric sculp- ture occur at higher stratigraphic positions in the Blufftown formation and in the Cusseta sand. Range—As here restricted this variety is known only from the upper part of the Eutaw formation in Russell County, Ala. Caryocorbula? georgiana Stephenson, n. sp. Plate 44, figures 14—16 Shell of medium size, subtrigonal in outline, strongly inflated centrally and anteriorly, humped in the ante— roumbonal region, compressed and narrow posteriorly, inequilateral, inequivalve, the right valve slightly larger than the left. Beaks prominent, strongly in- curved, prosogyrate at the tips, closely approximate, situated about centrally. Umbonal ridge of the right valve narrow, sharply defined, sinuous, paralleled on SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the marginal side by a narrow radial excavation and on the other side by a broad radial excavation. Antero- dorsal slope of right valve steep, overhanging near the beak; posterodorsal slope also overhanging a little near the beak. Anterodorsal margin broadly arched, ante— rior margin evenly rounded, narrower than a semicircle, ventral margin broadly rounded, posterior margin with a short truncation below midheight, posterodorsal margin straight, strongly inclined forward. The main surface of the right valve bears concentric ridges that are small and fine in the umbonal area and increase in strength and coarseness outwardly, becom— ing Very coarse adjacent to the ventral margin; these ridges are round crested and bear fine growth lines on the sides and in the interspaces; the ridges become smaller and much finer on the dorsal slopes. The sur- face of the left valve is not preserved on the available material, but imprints of small areas indicate that this valve lacks coarse ribbing and bears only small incre- mental ridges. Dimensions of the holotype, a right valve: Length 17 mm, height 13 mm, convexity about 6 mm. Indivi- duals may attain a length of 20 mm. The hinge of the right valve includes one prominent, upcurved, trigonal cardinal tooth back of which is a deep, broad resilial depression; in front of the cardinal tooth is an oblique channel opening inward. Lateral teeth are wanting. A rubber impression made from the internal mold of a left valve (pl. 44, fig. 16) shows that the internal ligament is seated on a raised chondrophore directed obliquely to the rear and inward; in front of the chondrophore is a deep, wide socket for the reception of the cardinal tooth of the right valve. The adductor scars occupy raised platforms the impressions of which are conspicuous on internal molds; the posterior plat- form is a little higher than the anterior one. The pallial sinus is very shallow. , . In the clay facies of the Eutaw formation exposed on Chattahoochee River at old Burdock Landing and at Slick Bluff, Russell County, Ala., are many internal and external molds of Oaryocorbula? that have the form and outline of 0.? georgiana, but average larger and show a wider range in individual variation in the coarseness of their concentric sculpture. Most 'of them are flattened and distorted by mechanical pressure. They are referred questionably to 0.? georgiana. Types.—Holotype, from Ochillee Creek south of bridge at old Ochillee, Chattahoochee County, Ga., USGS 15501, USNM 125044; 1 figured paratype, same source, USNM 125045; 1 figured paratype, same source, USGS 5378, USNM 125046; 28 unfigured paratypes, same source, USNM 125047; 12 question- able examples from just below old Burdock’s Landing, Chatta< hoochee River, Russell County, Ala., USGS 848, USN M 125048. Distribution—Ochillee Creek near old Ochillee, Chattahoochee FOSSILS. OF THE EUTAW FORMATION, ALABAMA-GEORGIA County, Ga., USGS 5378+ 15501; Broken Arrow Bend, Chatta- hoochee River, left bank, USGS 847; questionably on Chatta— hoochee River, right bank just below old Burdock Landing, USGS 848; questionably on Chattahoochee River, right bank at ‘Slick Bluff, USGS 845+5387. Range—The types and duplicate specimens are from the lower part of the Eutaw formation in the Chattahoochee River area, Georgia—Alabama; questionably identified specimens are present in the upper part of the formation. Class CEPHALOPODA Order AMMONOIDEA Family PLACENTICERATIDAE Genus PLACENTICERAS Meek, 1870 Placenticeras benningi Stephenson, n. sp. Plate 44, figures 21, 22; plate 45, figures 7—11 The species, as seen in the holotype and 15 paratypes, :attains medium size for the genus; all the paratypes are smaller than the holotype. Shell strongly involute, compressed on the flanks, with greatest inflation of the volution at the umbilical shoulder, the flanks converg- ing outward toward the venter. In early stages the flanks are nearly flat but as growth proceeds they be- come broadly convex in profile. The flattened venter is narrow for the genus. In young stages retaining the shell the venter is slightly excavated and is bordered on each ventral angle by a very thin upraised rim. At a radius of 35 to 50 mm the venter begins to become rounded. In some of the smaller stages this rounding is accompanied by a smoothing out of the surface, appar- ently indicating maturity at an earlier stage than that attained by the holotype. Beginning at a radius of about 55 mm on the holotype a row of small obscure elongated nodes 8 to 10 mm apart on each ventral angle can be detected; this part of the venter is con— siderably waterworn. These nodes are wanting on the younger paratypes whose venters become rounded at early stages. The umbilicus'is small with steeply sloping sides; the umbilical shoulder is at first obtusely subangular but becomes rounded in adults. In early stages a succeed- ing whorl envelops three-fourths or more of the preced- ing whorl, but in later stages only about two-thirds of the preceding whorl is enveloped. In young shells the flanks of the whorls are nearly smooth but they exhibit :a row of gentle radially elongated undulations about two-fifths the width of the flank inward from the ventral angle; these increase in strength forward and they increase in spacing from 5 mm apart on early stages to 20 mm or more apart on adults; they do not develop into 110ch proper. At a diameter of 65 mm or less weak nodes begin to appear on the umbilical shoulder; at first these are spaced 12 to 15 mm apart but in the forward direction the spacing increases to 20 247 to 24 mm on adults, and the nodes increase in size to moderate prominence. The sutures are best seen on several of the young paratypes; the description is based on the one shown in plate 44, figure 21. The ventral lobe is broad and shallow with a pair of short digitate diverging prongs, one on either side; these prongs inclose a broad, short ventral saddle which is divided by a relatively broad very shallow lobule. The first lateral saddle is relatively very broad and short and is subdivided by four short bifid subsaddles, separated by three small sublobes; the subsaddles and sublobes are further indented with tiny lobules. The first lateral lobe is narrow and trifid, the sublobes are indented with lobules. The second lateral saddle is less than half as broad as the first, is bifid with sublobes, and is further indented with lobules. From the venter to the line of involution there are 11 saddles separated by 10 lobes, both saddles and lobes becoming simpler inward; the last saddle at the line of involution is quite small and plain. The third lateral lobe inward from the venter is larger than any of the others. The inner part of the suture beyond the line of involution is not uncovered. The holotype, chosen for its size (pl. 45, fig. 7), has suffered considerable mechanical compression and some distortion, especially the part representing the living chamber. The measurements that can be given are therefore only approximate and include the following: Maximum diameter 170 mm, maximum radius center to venter 103 mm; at a diameter of about 120 mm the transverse diameter of the volution is about 35 mm; at the same diameter the height of the volution from the line of involution to the venter is about 52 mm. A more accurate measurement of the young paratype shown in plate 44, figure 21, can be made as follows: Greatest diameter 87 mm ; maximum radius center to venter 50 mm; height of volution line of involution to venter about 40 mm; transverse diameter between nodes 21 mm; same on nodes 25 mm; maximum diameter of umbilicus measured shoulder to shoulder 30 mm; the same measured line of involution to line of involution 20 mm. This species is closely related to Placenticeras guad— alupe (Roemer) from the Austin chalk (Inocemmus undulatoplicatus zone) at the Falls of the Guadalupe, 2 miles below the highway bridge at New Braunfels, Tex. (Roemer, 1852, p. 32, pl. 2, fig. 1 a, 6.) Compared with the illustrations of Roemer’s species this species is more compressed, the nodes on the ventral angles are much weaker or absent, and instead of a row of nodes on the outer flank it possesses a corresponding row of undula- tions and this row is a little farther removed from the ad- j acent paralleling ventral angle; the saddles and lobes of the suture also seem to be consistently shorter. The 248 specimen referred by Hyatt (his collection) to Roemer’s species (Hyatt, 1903, p. 197, pl. 29), as figured, does not appear to be correctly identified. Compared with Roemer’s figured specimen it shows no indication of the presence of a row of small relatively closely spaced nodes on each ventral angle and on the adult stage the shoulder nodes become much larger, elongated and directed obliquely forward. Placenticeras sancarlosense Hyatt (1903, p. 200, pl. 30; pl. 31, figs. 1, 2), from San Carlos, Presidio County, Tex., is also nearly related to P. benmlngi, but it is stouter, more closely coiled, possesses a row of nodes instead of undulations on the outer flank, and has well developed alternating nodes on the ventral angles at an early stage (diameter of 40 mm or less). Assuming that all the specimens here referred to P. benm'ng'i are correctly identified there is considerable individual variation of form within the species. Some of the younger shells begin to thicken and round over on the venter, at the same time becoming smoother on the venter and outer flank, than is true of the holotype which represents a much later and larger stage of growth. Types.~Holotype, from basal beds of Eutaw formation Broken Arrow Bend, Chattahoochee River (Alabama side) USGS 5384, USMN 125049; I figured paratype, from the same zone on Upatoi Creek, 7 miles southeast of Columbus, USGS 5377, USNM 125050; 2 figured paratypes from same zone, on Ochillee Creek, old Ochillee (below bridge), Chattahoochee County, Ga., USGS 15501, USNM 125051; 2 unfigured paratypes, same source, USNM 125052; 6 unfigured paratypes, same source, USGS 25569, USNM 125053; 4 unfigured paratypes from old Ochillee (upstream from bridge), USGS 25570, USNM 125054. Named in honor of Brig. Gen. Henry L. Benning, a distin— guished Confederate Army officer for whom Fort Benning was named, and whose home was in Columbus, Ga. Distribution—The known occurrences of this species in the Chattahoochee region are recorded under the heading “types” above. Range.—-The species is known only from the basal beds of the Eutaw formation in the Chattahoochee region. REFERENCES Berry, E. W., 1923, The age of the supposed Lower Cretaceous of Alabama: Washington Acad. Sci. Jour., v. 13, no. 20, p. ' 433—435. Conrad, T. A., 1860, Descriptions of new species of Cretaceous and Eocene fossils of Mississippi and Alabama: Acad. Nat. Sci. Phila. Jour., 2d ser., v. 4, p. 275w298, pls. 46, 47. 1875, Descriptions of new genera and species of fossil shells of North Carolina, in Kerr, W. C., Physical geography, résumé, economical geology, N. C., Geol. Survey Rept., v. 1, app. A, p. 1—13, pls. 1, 2. Ball, W. H., 1898, Contributions to the Tertiary fauna of Florida: Wagner Free Inst. Sci. Trans, v. 3, pts. 146, 1654 p., 60 pls. D’Orbigny, Alcide, 1843—47, Description des animaux inverté- brés; Lamellibranches: Paléontologie frangaise, terraine cré- tacé, 1st ser. v. 3, 807 p. pls. 237—489. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Eargle, D. H., 1950, Geologic map of the Selma group in eastern Alabama: Oil and Gas Investigations, preliminary map 105 (with text). Gardner, Julia, 1926, The nomenclature of the superspecific groups of Corbula in the lower Miocene of Florida: Nautilus, v. 40, no. 2, p. 41—46. Hyatt, Alpheus, 1903, Pseudoceratites of the Cretaceous: U. S. Geol. Survey Mon. 44, 351 p., 47 pls. Langdon, D. W., 1890, Variations in the Cretaceous and Tertiary strata of Alabama: Geol. Soc. America Bull., v. 2, p. 587—606. Lea, Isaac, 1833, Tertiary formation of Alabama, in Lea, Isaac, 1833, Contributions to geology, Phila., 227 p., p. 29—208, pls. 1—6. ‘ McCallie, S. W., 1903, Sandstone dikes near Columbus, Georgia: Am. Geologist, v. 32, p. 199—202. Meek, F. B., 1873, Preliminary paleontological report, consisting of lists of fossils with descriptions of some new types: U. S. Geol. Survey Terr. 6th Ann. Rept., p. 429—518. 1876, A report on the invertebrate Cretaceous and Ter- tiary fossils of the Upper Missouri country: U. S. Geol. Survey Terr., 9th Ann. Rpt., 629 p., 85 figs, 45 pls. Monroe, W. H., 1941, Notes on deposits of Selma and Ripley age in Alabama: Ala. Geol. Survey Bull. 48, 150 p. 1947, Stratigraphy of outcropping Cretaceous beds of southeastern United States: Am. Assoc. Petroleum Geolo- gists Bull., v. 31, no. 10, p. 1817~1824. Monroe, W. H., Conant, L. C., and Eargle, D. H., 1946, Pre- Selma Upper Cretaceous stratigraphy of western Alabama: Am. Assoc. Petroleum Geologists Bull., v. 30, no. 2, p. 187—212, 4 figs. Roemer, Ferdinand, 1852, Die Kreidebildungen Von Texas und ihre organischen Einschliisse, Bonn, bei Adolph Marcus, 100 p., 11 pls. Stephenson, L. W., 1911 [1912], Cretaceous [of Georgia], in Veatch, Otto, and Stephenson, L. W., Geology of the Coastal Plain of Georgia, Ga. Geol. Survey Bull., no. 26, p. 66~215. 1914, Cretaceous deposits of the eastern Gulf region: U. S. Geol. Survey Prof. Paper 81, 77 p., 21 pls. 1923, The Cretaceous formations of North Carolina; pt. 1, Invertebrate fossils of the Upper Cretaceous forma- tions: N. C. Geol. and Econ. Survey, V. 5, 592 p., 100 pls. 1936, New Upper Cretaceous Ostreidae from the Gulf region: U. S. Geol. Survey Prof. Paper 186—A, p. 1—12, pls. 1—3. 1937, Stratigraphic relations of the Austin, Taylor, and equivalent formations in Texas: U. S. Geol. Survey Prof. Paper 186—G, p. 133—146, pl. 44, fig. 7. 1941, The larger invertebrate fossils of the Navarro group of Texas: Tex. Univ. Pub., Bull. 4101, 641 p., 95 pls. Stephenson, L. W., and Monroe, W. H., 1938, Stratigraphy of Upper Cretaceous series in Mississippi and Alabama: Am. Assoc. Petroleum Geologists Bull., v. 22, no. 12, p. 1639« 1657. ‘ 1940, The Upper Cretaceous deposits [Mississippi]: Miss. State Geol. Survey, Bull. 40, 296 p., 15 pls. Veatch, Otto, 1909, Second report on the clays of Georgia: Ga. Geol. Survey Bull., no. 18, 453 p. Vokes, H. E., 1945, Superspecific groups of the pelecypod family Corbulidae: Am. Mus. Nat. History Bull., v. 86, art. 1, p. 1—32, pls. 1—4. Woods, Henry, 1904—12. A monograph of the Cretaceous Lamellibranchia of England: Palaeont. Soc. Mon., v. 2, pts. 1—9, 473 p., 62 pls. INDEX [Italic numbers indicate descriptions] Acknowledgments _____________________ alabamiensis, Corbula _________________________________________________________ 245 081m: ____________________________________________________________________ 239 Ammonoidca. 247 Anchura“ . . 231 anamala, Amula. 237 Anemia olmstedi ______________________________________________ 242 prealmstedz’ .......................................... 230, 231, 232, 234, 242: pl. 41 sp ________ 232 Anomiacea. 242 Arcaeea ......... 235 aucella, Gryphaea ________________________ _ 240 Austin chalk ____________________________ _ 234 Avicula anomala ______________________________________________________________ 237 B bemzingi, Placenticeras ............................... 230, 231, 232, 234, £47, 248; pl.44 Black Creek formation. _ _ _ ______ 234, 235, 236, 243, 244, 245, 246 Blufitown formation. . _ . 229, 232, 233, 234, 240, 242, 243, 246 Brezviarca congesta _____________________________________________________________ 236 perovalis __________________________________________________________________ 236 aubin/lata. 234, 236; pl. 39 subovalis.. ......................................................... 236 symmetros, . _________________________________________________________ 234 umbonata _________________________________________________ 236 sp ........................................................ Broken Arrow Bend, fossils from Burdock Landing, fossils from ________________________________________________ 230 C (Cumplonecles) Pectm ___________________________________ 231 Cardiacea...._._.__. ___ 242 Cardium ........ . .......................................................... 231, 232 Cardium (Trachycardium) carolinenae _________________________________________ 243 ochilleanum ............................... 249; p]. 41 carolinense, Legumen ............................. 230, 231, 234, 243; pl. 44 carolinense, Cardium (’I'rachycardmm). 243 Caryocorbula ...................................................... 245 georgiana ................................................ 230, 234, 244, 246'; pl. 44 oxynema.. 245 veatchi ............................................ 230, 231, 244, 245, 246; pl. 44 Caryocorbzda ueatchi longa ............................................ 232, 246; pl. 44 centerensis, Ostrea __________________________________________________ 234 Clay section at Slick Bluff _____________________________________ 228 congesta, Breviarca .................. 236 Corbula alabamiensis __________________________________________________________ 245 ozynema __________________________________________________________________ 244 sulcatau. __ 945; pl. 45 Corbulidae. _ . . ....................... 244 Creek Stand, fossxls from near, __________________________________ 233 cretacea, Ostrea ............................. 228, 230, 231, 233, 234, 239, 240; pls. 40, 42 Cusseta sand. . _ . , _____________________________________________________ 234, 243, 246 Cymbophora ochilleana. 231, 244: pl. 44 trigonalis __________________________________________________________________ 244 Cyprimen‘a ................................................................... 231 depressa . . ..... 230 sp .................................................................... 232 D depressa, Cyprimeria .......................................................... 230 , E Page Etea .......................................................................... 231 Eutaw fauna and its relationships ____________________________________________ 234 Eutaw formation __________________ localities ___________________ ,_ Exogyra ______ ponderosa ......................................................... tigrina .................................................................... 234 upatoz‘ensis. . 230, 231, 234, 941: pl. 43 Sp ................................................................. 232, 234 F Fort Decatur, fossil plants from ............................................... 231 G Gardner, Julia, quoted _______________________________________________________ 245 georgiana, Curyocorbula ______________________________________ 230, 234, 244, 246'; pl. 44 Gordo formation of Tuscaloosa group ______________ 228, 231 Gryphaea ..................................................................... 233 aucella ____________________________________________________________________ 240 wratheri ..................................................... 234, 940, 241; pl. 41 I Idonearca _____________________________________________________________________ 231 inflata, Trigonarca ............... 234, 237; pl. 40 Inoceramm undulaioplicatus ............................. 234, 247 sp ________________________________________________________________________ 232 L . Legumen carolinense ......................................... 230, 231, 234, 243; pl. 44 Leptosolm .................................................................... 231 Liopistha sp .................................................................. 232 List of fossils .......................... 234 Location of most important fossil—bearing strata .............. 229 longa, Carycarbula reatchl .......................... ...- 246; pl. 44 (Lopha) ucheensis, Ostrea ............................................ 230, 238; pl. 43 McShan formation ______________ 227 maconensis, Trigonarca. 237 Mactraoea .................................................................... 244 Mooreville chalk ................................. 227, 228, 233, 234, 239, 240, 241, 242 Myacea ...................................................................... 244 N Nucula prepercrassa ................................................. 234, 235; pl. 39 Nuculacea .................................................................... 234 O obliqua, Protarca ................................................. 231. 234, 235; pl. 35 ochilleamz, Cymbophara ________________ .. 231,342, 244; pl. 44 ochilleanum, Cardium (Trachycardium) . .. .......... 242; pl. 41 Ochillee Creek, fossils from ............... 231 olmstedi, Anemia ............................................................. 242 Ostracea ____________________________________________________________________ 238 Ostrea alabamiensis. 239 centeremis ................................................................ 234 cremcea ...................................... 228, 230, 231, 233, 234, 289, 240; pl. 40 234 ucheensfs ............................................................ 230, 232, 233 249 250 INDEX Page Page Ostrea cretucea zone ........................................................... 228 Slick Bluff, fossils from _, ...................................................... 230 Ostrea (Lopha) uchemsia ........................................... 230, 238; pl. 43 Snow Hill marl member ________________________________ 234, 235, 236, 243, 244, 245, 246 Owl Creek formation ,,,,,,,,, 235 Stratigraphic section, east by north of Hardaway station". crynema, Caryocarbulu .......... 245 Ochillee Creek ..................... Oorbula ........................... 244 old Marvyn road, northwest of Uchee, _ _ Society Hill road, north of Greek Stand ................................... 233 Upatoi Creek ............................................................. 231 Pecten (Camptonectes) ........................................................ 231 Stratigraphic setting" .......... 228 perovalis, Bret'iarca ........ 236 mom/lam, Brem'arca. ____________________________ 234, 236; pl. 39 Pholadomya ......... 231 subovalis, Brem‘arcm. 236 Placenticeras benm‘ngi ................................ 230, 231, 232, 234, 247, 248; pl. 44 sulcula, Corbula .......................................................... 245; pl. 45 quadalupe .......................................... 247 symmetros, Berviarca .......................................................... 234 sancarlosense, _ ________ 248 Plicatula .................... 233 T ponderosa, Elam/7a,, __________________ 235, 243 Tallinn ....................................................................... 231 preolmsterli, Anemia ...................................... 230, 231,232, 234,242; 1)]. 41 tigrina, Exam/m ___________ __ 234 prepercrassa, Nucula ................................................. 934, 235; pl. 39 Tombigbee sand member ____________________ .. 227, 228, 239, 240, 241, 242 Proturca obliqua...- 231, 234. 235; pl. 39 (Trachycardium) carolineme. Cardium.. .................... 243 Pseudoptera ................................................................... 287 ochillecmum, Cardium ................................................ 242; pl. 41 securiformis .......................................... 230,231, 233, 234,238; pl. 40 tram‘sana, Ostrea .............................................................. 234 Pteriacea ..................................................................... 237 trigonulis, Cymbophorm. ................ .. 244 Trigonorca.. ................................. 231, 232 Q inflate ...................... 232,234, 237; pl. 40 quadulupe, Placenticeras ....................................................... 247 maco'nencis ................................................................ 237 Tum'tella _____________________________________________________________________ 231 R Tuscaloosa group ....................................................... 228,230,231 References ........................... - 228,248 Ripley formation ............................................................. 235 U Uchee, fossils from near ....................................................... 232 S ucheemis, Ostrea ............................... .. 230,232, 233 sancarlosense, Placenticerar ............... (Lopha) ______ 230,238; pl. 43 Santonian age ............................ umbmmta, Brem‘arca ........................................................... 236 Sections, description of, Broken Arrow Bend, _ undulatoplicatus, Inoceramus ................................................ 234, 247 Burdock Landing _____________________________________________________ 229, 230 Upatoi Creek, fossils from... .. 230—231 east by north of Hardaway station ........................................ 233 upatoinenm's, Exogyru _________________________________ _. 230, 231, 234, 241; pl. 43 Hurtsboro-Marvyn road, south of Lee County line. _ _.. ._ 232 near Uchee _______________________________________________________________ 232 V north of Greek Stand ..................................................... 233 veatchi, Caryocorbula .................................. 230, 231, 234, 244, 245, 246; pl. 44 Ochillee Creek ............................................... 231 veatchi langa, Carycorbula. .. 232,946; pl. 44 Slick Bluff .............................................. _._ 229, 230 Veneraeea ............................................................. 243 (southwest of Phenix City__ ._ 231 Volutomorpha ................................................................. 231 southwest of Youngs Bridge .............................................. 232 Uchee Creek valley _______________________________________________________ 232 . W Upatoi Creek __________ -._. ... 230,231 wrutheri, Gryphaea ............................................... 234,940, 241; pl. 41 Selma group .............................. 227, 239 securiformis, Pseudoptem. ........ ... 230, 231, 233, 234 Y .Serpula ....................................................................... 231 Youngs Bridge, fossils from near .............................................. 232 II. 5. GOVERNMENT PRINTING OFFICE' I956 PLATES 38—45 PLAT E 38 The unconformable contact of the Eutaw formation on the Gordo formation (Tuscaloosa group) in a cut of the old Columbus- Seale road (near the present U. S. Highway 431) about 4 miles southwest of Phenix City (opposite Columbus, Ga.) in Russell County, Ala. Light-gray silty, micaceous shale of the upper part of the Eutaw formation exposed in Slick Bluff on Chattahoochee River, right bank, about 14 miles below Columbus, Ga. Layers of nodular calcareous, fossiliferous concretions in dark-gray sandy marine clay in right bank (Alabama side) at Broken Arrow Bend, Chattahoochee River, about 10 miles by the river below Columbus, Ga. Calcareous fossiliferous sandstone in the bed of Ochillee Creek below the mill dam at the site of old Ochillee, about 10 miles southeast of Columbus Ga. ,the dam and mill have disappeared and the creek' is now crossed at this place by a bridge of one of the roads of the Fort Benning Military Reservation. 72:33: Ew-EUCCEAP—Lkgfiu HIE Z. ZC_,__H>mpx :«xzco‘HCHC GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 30 NUCULA. BREVIARCA, AND PROTARCA PLATE 39 [Figures natural size except as indicated] FIGURES 1—5. Nucula prepercrassa Stephenson, n. sp. (p. 234). 1. Left valve of a paratype. USGS 15501, USNM 125059. . 2, 3. Side and top views of the holotype, a right valve. USGS 15501, USNM 125058. 4. Interior view, X 1%, of holotype. 5. Internal mold, X 1%, of a paratype, a right valve. USGS 5378, USNM 125061. 6—8. Breviarca subinflata Stephenson, n. sp. (p. 236). Views, X 3, of the holotype, a left valve. USGS 15501, USNM 125067. 9—14. Protarca obliqua Stephenson (p. 235). 9, 10. Exterior and interior views of a plesiotype, a left valve. USGS 15501, USN M 125064. 11. Exterior view, X 1%, of a plesiotype, a young right valve. USGS 5378, USNM 125063. 12. Internal mold of a plesiotype, a left valve, from the same source. USNM 125063. 13, 14. Views of a large plesiotype, a left valve, from the Cusseta sand near Peachburg, Ala. USGS 25478, USNM 125062. (Inserted for comparison.) FIGURES 1, 2. 3. 4—8. PLATE 40 [Figures natural size except as indicated] Breviarca symmetros Stephenson, n. sp. (p. 236). Views, X 3, 0f the holotype, a left valve. USGS 25567, USNM 125070. Brem'arca? sp. ' View of left valve, X 3. USGS 15501, USNM 125072. Trigonarca inflata Stephenson, n. sp. (p. 237). 4. A paratype, a juvenile right valve. USGS 25567, USNM 125074. 5. Interior View, X 2, of the preceding shell. 6—8. Views of the holotype, a left valve. USGS 25567, USN M 125073. . Pseudoptera securifarmis Stephenson, n. sp. (p. 238). 9. The holotype, a left valve. USGS 15501, USNM 125076. 10. A paratype, a left valve, mechanically deformed, showing details of sculpture. USGS 25570, USNM 125082. Ostrea cretacea Morton (p. 239). 11. Interior View of a plesiotype, a left valve. USGS 17007, USNM 125027. 12. Exterior View, X 1%, of a left valve, uncoated to show color bands. USGS 18308, USNM 125029. GEOLOGICAL SURVEY YROFESSIONAL PAPER 274 PLATE 40 BREVIARCA, TRIGONARCA, PSEUDOPTERA, AND OSTREA GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 41 CARD] UM (TRA CHYCARDI UM), GR YPHA EA9 ANOMIA, AND PSE UDOPTERA FIGURES 1, 2. 3—8. 9—11. 12—14. PLATE 41 [Figures natural size except as indicated] Cardium (Trachycardium) ochilleanum Stephenson, n. sp. (p. 242). 1. View, X 1%, of a paratype, a left valve. USGS 15501, USNM 125012. 2. View, X 1%, of the holotype, a right valve. USGS 15501, USNM 125010. Gryphaea wratheri Stephenson (p. 240). . Left valve of a large plesiotype. USGS 6442—B, USNM 125024. Left valve of a plesiotype, showing a posterior wing extension. USGS 19060, USNM 125022. Left valve of a plesiotype lacking posterior wing extension. USGS 17576, USNM 125023. Right valve of a plesiotype from the same source. USNM 125023. Interior view of the preceding shell. . Interior view of the shell shown in fig. 5. Anemia preolmstedi Stephenson, n. sp. (p. 242). 9. Exterior of holotype, a left valve. USGS 6409, USNM 125014. 10, 11. Exterior and interior views of a paratype from the same source; the interior view shows the imprint of the byssal opening (foramen) of the right valve on matrix filling. USN M 125015. Pseudoptera securiformis Stephenson, n. sp. (p. 238). 12,13. Rubber casts from internal molds (paratypes) of left valves, showing hinge areas. USGS 5384, USNM 125081. 14. Right side of internal mold (a paratype), showing flattish form of right valve. USGS 5377, USN M 125080. wflgwew PLATE 42 [All figures natural size] FIGURES 1—17. Ostrea cretacea Morton (p. 239). ' 1—2. Topotypes, left valves, from Erie Bluff, Warrior River, Ala. USGS 6428, USNM 125026. 3, 4. Plesiotypes (essentially topotypes), from Choctaw Bluff, Warrior River, Ala. USGS 6425, USNM 125025. 5—17. Plesiotypes—arranged to show gradation in dorsal outline from pointed in figure 5 to squarish in figure 17. Figures 5, 13, 4.1 miles north of Creek Stand, Macon County, Ala., USGS 17007, USNM 125027; figures 6, 8—12, 14—16, from 3.1' miles north of Creek Stand, USGS 17006, USNM 125028; figures 7, 17, one-half mile below Broken Arrow Bend, Chattahoochee River, left bank, USGS 5385, USNM 125030. Figures 1—14 are left valves; figures 8, 9 are views of left and right valves of same shell; figures 15, 16 are exterior and interior views of a right valve; and figure 17 is a view of right valve. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 42 OSTREA CRETA (TEA. MORTON GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 43 'OSTREA (LOPHA) AND EXOGYRA PLATE 43 [All figures natural size FIGURES 1—5. Ostrea (Lopha) ucheensis Stephenson, n. sp. (p. 238). 1, 2. Exterior and interior views of holotype, USGS 17583, USNM 125031. 3—5. Views of 3 paratypes, USGS 18317, USNM 125033. 6—10. Exogyra upatoiensz's Stephenson (p. 241). 6. Left valve from Catoma Creek, 5 or 6 miles southwest of Montgomery, Ala, USGS 17010, USNM 125020. 7. Left valve from three-fourths mile north by east of Liberty Hill Church, Macon County, Ala., USGS 17576, USNM 125019. 8. Left valve from 2% miles north—northwest of Warrior Stand, Macon County, Ala., USGS 18306, USNM 125018. 9, 10. Views of a large shell, from base of Mooreville chalk, Choctaw Blufl', Warrior River, Greene County, Ala, USGS 25466, USNM 125021. FIGURES 1—3. 4—9. 10—13. 14—16. 1 7—20. 21, 22. PLATE 44 [Figures natural size except as indicated] Cymbaphora ochilleana Stephenson, n. sp. (p. 244). 1. View, X 1%, of holotype, a right valve. USGS 15501, USNM 125000. 2. View, X 1%, of a paratype, a left valve. USGS 5378, USNM 125004. 3. View, X 1%, of hinge of a. paratype, a right valve. USGS 5374, USNM 125002. Caryocorbula? veatchi Stephenson, n. sp. (p. 245). 4, 5. Right side and dorsal views, X 1%, of holotype. USGS 5374, USNM 125036. 6, 7. Right side and interior views, X 1%, of a paratype. USGS 15501, USNM 125038. 8, 9. Exterior and interior views, X 1%, of a paratype, USGS 15501, USNM 125038. Caryocorbula? veatchi longa Stephenson, 11. var. (p. 246). 10, 11. Exterior and interior views, X 1%, of holotype. USGS 25567, USNM 125041. 12, 13. Exterior and interior views, X 1%, of a paratype from the same source. USNM 125042. Caryocorbula? georgiana Stephenson, n. sp. (p. 246). 14. View, X 1%, of holotype, a right valve. USGS 15501, USNM 125044. 15. Interior View, X 1%, of a paratype from the same source. USNM 125045. 16. View, X 1%, of a rubber cast from internal mold of a left valve. USGS 5378, USNM 125046. Legumen afi. L. carolinense (Conrad), (p. 243). 17--18. Right side and dorsal views of an internal mold. USGS 6408, USNM 125006. 19. Left side of an internal mold (uncoated) to show pallial line and sinus. USGS 5377, USNM 125007. 20. Imprint of exterior of a left valve to show concentric markings. USGS 848, USNM 125008. Placemiceras benm’ngz' Stephenson, n. sp. (p. 247). . 21. Lateral view of a young paratype. USGS 5377, USNM 125050. 22. Lateral view of a young paratype. USGS 15501, USNM 125051. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 44 C YMBOPHORA , CAR YOCORB ULA, LEG UM EN, AND PLA (JEN TI CERA S GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 45 (IORBULA AND PLACENTICERAS PLATE 45 [Figures natural size except as indicated] FIGURES 1—6. Corbula sulcata Lamarck, inserted for comparison with Cretaceous shells (p. 245). 1—3. Views, X 2, of a Recent right valve, a topotype, from the coast of Senegal, West Africa (USNM Ter. Coll. Moll. 614185). 4—6. Views, X 2, of a left valve, a topotype, from the same collection. 7-11. Placenticeras benm'ngi Stephenson, n. sp. (p. 247). 7. Side view of the holotype. USGS 5384, USNM 125049. 8, 9. Side and front-edge views of a young paratype; note the slightly excavated ventral band. USGS 15501, USNM 125051. 10. View of inner cross section of the paratype shown in plate 44, figure 22, at a diameter of about 65 mm. USGS 15501, USNM 125051. 11. Front ventral view of the paratype shown in plate 44, figure 21. >..2)¢~/( Stratigraphy of Middle OrdOViCian Rocks in the Zinc-Lead District of Wisconsin, Illinois, and Iowa GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-K Prepared in cooperation witn tne Wisconsin Geological and Natural History Survey Stratigraphy of Middle Ordovician Rocks in the Zinc-Lead District of Wisconsin, Illinois, and Iowa By ALLEN F. AGNEW, ALLEN V. HEYL, JR., c. H. BEHRE, JR., and E. J. LYONS A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—K Preparea’ 2'72 c‘ooperaz‘z'orz wit/z Me Wz'yeomz'a Geo/agz'ea/ aaa’ Natural History Survey UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. — Price 60 cents (paper cover) CONTENTS Abstract ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Introduction ________________________________________ Purpose of the investigation ,,,,,,,,,,,,,,,,,,,,,, Location and geographic setting __________________ Field work _____________________________________ Acknowledgments ________________________________ Regional geology and stratigraphic relations ,,,,,,,,,,,,, Structure ______________________________________ Regional stratigraphic summary ,,,,,,,,,,,,,,,,,, Stratigraphic principles __________________________ Stratigraphic problems ,,,,,,,,,,,,,,,,,,,,,,,,,, Platteville—Decorah boundary _________________ Beloit dolomite ______________________________ Unnamed limestone member, Decorah forma— tion ____________________________________ Subdivisions of Galena dolomite ,,,,,,,,,,,,,,, Origin and application of the names ,,,,,,,,,,,,,,, Madison sandstone __________________________ Pecatonica dolomite member ,,,,,,,,,,,,,,,,, McGregor limestone member ,,,,,,,,,,,,,,,,, Quimbys Mill member ,,,,,,,,,,,,,,,,,,,,,,,,,, Stratigraphy of the mining district ,,,,,,,,,,,,,,,,,,,,,,, Pre-Platteville rocks ____________________________ Pre—Cambrian rocks ,,,,,,,,,,,,,,,,,,,,,,,,,, Cambrian rocks _____________________________ Ordovician rocks ,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Prairie du Chien group ,,,,,, , ____________ St. Peter sandstone ,,,,,,,,,,,,,,,,,,,,, Platteville formation ____________________________ General features ,,,,,,,,,,,,,,,,,,,,,,,,,,,, Glenwood shale member _____________________ Lithologic description and stratigraphic re- lations _______________________________ Distribution ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Fauna and correlation ,,,,,,,,,,,,,,,,,,,,, Economic products ______________________ Pecatonica dolomite member _________________ Lithologic description and stratigraphic re- lations ________________________________ Distribution ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Fauna and correlation ,,,,,,,,,,,,,,,,,,,,, Economic products ,,,,,,,,,,,,,,,,,,,,,, McGregor limestone member _________________ Lithologic description and stratigraphic re- lations ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Distribution ,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Fauna and correlation ,,,,,,,,,,,,,,,,,,,, Economic products ,,,,,,,,,,,,,,,,,,,,,, Page 251 252 252 252 252 254 254 254 254 260 261 261 262 264 265 269 269 269 269 269 271 271 271 271 272 272 273 274 274 275 275 277 277 277 277 278 278 279 279 279 279 282 282 282 Quimbys Mill member _______________________ Lithologic description and stratigraphic re- lations ________________________________ Distribution ____________________________ Fauna and correlation ,,,,,,,,,,,,,,,,,,, Economic products ________________________ Distribution of facies of the Platteville and con- ditions of deposition ,,,,,,,,,,,,,,,,,,,,,, Decorah formation ____________________________ ’_ ~ General features ,,,,,,,,,,,,,,,,,,,,,,,,,,,, Spechts Ferry shale member _________________ Lithologic description and stratigraphic re- lations ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Distribution ____________________________ Fauna and correlation ,,,,,,,,,,,,,,,,,,, Economic products ,,,,,,,,,, , ____________ Guttenberg limestone member ,,,,,,,,,,,,,,,, Lithologic description and stratigraphic re— lations ________________________________ Distribution ,,,,,,,,,,,,,,,,,,,,,,,,,,,, Fauna and correlation ,,,,,,,,,,,,, , ______ Economic products ______________________ Ion dolomite member _______________________ Lithologic description and stratigraphic re- lations _______________________________ Distribution _____________________________ Fauna and correlation ___________________ Economic products ______________________ Distribution of facies of the Decorah and con- ditions of deposition ,,,,,,,,,,,,,,,,,,,,,,,, Galena dolomite ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, General features ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Cherty unit ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Noncherty unit ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Distribution ________________________________ Distribution of facies of the Galena and condi- tions of deposition ________________________ Fauna and correlation ,,,,,,,,,,,,,,,,,,,,,,, Economic products ,,,,,,,,,,,,,,,,,,,,,,,,,,, Post-Galena rocks _______________________________ Ordovician rocks—Maquoketa shale ,,,,,,,,,,, Silurian rocks ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Post—Silurian deposits ,,,,,,,,,,,,,,,,,,,,,,, Literature cited ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Stratigraphic sections ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Index _______________________________________________ III Page 282 282 283 284 284 284 285 285 286 286 289 289 289 289 289 292 293 293 293 293 295 295 295 295 296 296 296 297 298 299 299 300 300 300 301 302 302 305 311 IV FIGURE 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. CONTENTS ILLUSTRATION Upper Mississippi Valley region showing general geology and location of the zinc—lead district _______________ Generalized stratigraphic column for zinc-lead district __________________________________________________ Bluff showing Platteville, Decorah, and Galena strata __________________________________________________ Diagrammatic cross section of Platteville, Decorah, and Galena strata eastward across the mining district____ Map of part of upper Mississippi Valley region, showing localities cited in text ____________________________ Generalized west-east cross section of Decorah formation and adjacent strata _____________________________ Correlation of Platteville, Decorah, and Galena strata with units in Minnesota ____________________________ Stratigraphic column of Platteville, Decorah, and Galena strata in zinc-lead district ________________________ Classifications of Platteville, Decorah, and Galena sequence since 1906 _____________________________________ Quarry showing Prairie du Chien group ______________________________________________________________ Crossbedded St. Peter sandstone in roadcut ___________________________________________________________ Pecatonica and McGregor members of the Platteville formation in roadcut ________________________________ Glenwood shale member and Pecatonica member of Platteville formation above St. Peter sandstone in roadcut, _ Suggested correlatives of Platteville, Decorah, and Galena strata ________________________________________ Comparative stratigraphic terminology of Platteville, Decorah, and Galena rocks in the zinc- lead district _____ Type section of Quimbys Mill member of Platteville formation __________________________________________ Type section of Spechts Ferry shale member of Decorah formation ______________________________________ Quimbys Mill member of Platteville formation and the overlying Guttenberg member of Decorah formation in a quarry at Calmine, Wis _________________________________________________________________________ Type section of Guttenberg limestone member of the Decorah formation __________________________________ Decorah formation in dolomite facies, overlain by Galena dolomite and underlain by Quimbys Mill member of Platteville formation, in quarry at York Church, \Vis ________________________________________________ Carbonaceous shale partings between wavy dolomite beds of Guttenberg limestone member of Platteville forma— tion in quarry in Green County, \Vis _______________________________________________________________ Exposure in mine showing effect of mineralizing solutions on Guttenberg member of Decorah formation ______ Honeycomb weathering of Galena dolomite in a roadcut in Grant County, Wis ____________________________ Maquoketa shale and overlying Silurian dolomite in roadcut and quarry __________________________________ Page 253 255 256 257 258 263 264 268 270 272 273 274 275 278 280 283 286 287 290 290 291 291 297 301 A SHORTER CONTRIBUTION TO GENERAL GEOLOGY STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT OF WISCONSIN, ILLINOIS, AND IOWA By ALLEN F. AGNEW, ALLEN V. HEYL, JR., C. H. BEHRE, JR., and E. J. LYONs AB STRACT Stratigraphic studies, both outcrop and subsurface, of Ordovi- cian rocks of the zinc-lead district in Wisconsin, Illinois, and Iowa form the basis for a more accurate means of delimiting potentially ore-bearing areas from less favorable localities. Detailed stratigraphic subdivisions of the Platteville, Decorah, and Galena strata have permitted the mapping of folds with structural relief of 30 feet or less in areas smaller than a quarter of a mile square. Such relatively small flexures and their associated fractures have caused the localization of the ore- bearing solutions. Lithologic characteristics provided the basis for subdividing the rocks into mappable units—formations and members. No systematic paleontologic study has been made 5 age assignments, therefore, are only general Although the investigation initially dealt with relatively local areas, certain members of the rock units and their subdivisions are mappable regionally. Rock units below the Platteville formation include sandstone and shale of the St. Peter sandstone; shale, dolomite, and sand— stone of the Prairie du Chien group, sandstone, siltstone, and dolomite of Cambrian age, and the Pre-Cambrian granitic rocks. The Galena strata are overlain by the shale and dolomite of Maquoketa age, upon which rests Silurian dolomite, Because the Platteville, Decorah, and Galena strata include the currently producing ore zone, the detailed investigation was restricted to those units. The Platteville formation regionally includes the green sandy Glenwood shale member at its base, as much as 3 feet thick; the brown Pecatonica dolomite member, 20~24 feet thick; the gray limestone and dolomite of the McGregor limestone member, totalling 30 feet; and the uppermost member, the brown limestone dolomite, and shale of the Quimbys Mill member, as much as 18 feet thick. In the mining district the Decorah formation includes at the base green shale and limestone of the Spechts Ferry shale mem- ber, with a maximum thickness of 8 feet; the brown limestone, dolomite, and shale of the Guttenberg limestone member, 12~16 feet thick; and the uppermost member, the grayish-green lime- stone, dolomite, and shale of the Ion dolomite member, 20 feet thick. In the western part of the mining district and to the west is an unnamed limestone member that underlies the Spechts Ferry. To the east, the Platteville and Decorah strata are dolomite of similar lithologic character, and have been called the Beloit dolomite. The Galena dolomite is generally coarsely crystalline massive vuggy dolomite or limestone divisible regionally into two units, a cherty lower unit 105 feet thick and a noncherty upper one 120 feet thick. The cherty unit is divided into four zones, A, B, C, and D in descending order, based primarily upon relative chert content and the presence of Receptaculites. The noncherty unit is divided on the basis of thinness of bedding and the amount of interbedded shale into Dubuque at the top and the more massive, less shaly Stewartville and zone P of the Prosser below; the latter is divided less precisely on the basis of Receptaculites which are abundant in the Stewartville, but not in zone P, below. The name Dubuque is applied much as it has been in the past; the name Stewartville is applied more or less as it has been in the past; and the name Prosser includes the cherty unit and probably all of zone P of the overlying noncherty unit. Because of paleontologic deficiencies and because of the distinct lithologic differences, in this paper the Galena is subdivided into the cherty and noncherty units rather than into the Prosser, Stewart- ville, and Dubuque members of common, although not precise usage. A bentonite layer is present near the base of the Spechts Ferry shale member; less commonly bentonite seams are found 30—32 feet below and 18 feet above the contact between the cherty and noncherty units. West of the mining district the unnamed lower member of the Decorah formation includes bentonite at its base. Locally bentonite is present in the Decorah. All members of the Platteville formation except the Glenwood decrease in thickness toward the west, whereas all members of the Decorah formation thicken toward the West. In general the Platteville, Decorah, and Galena strata represent a marine environment of a relatively shallow-water platform. Facies analysis of the Platteville, Decorah, and Galena forma- tions shows a regional change from shale (Decorah formation) and limestones (Galena and Platteville formations, excluding the Glenwood member) west of the mining district eastward into dolomite (all three formations) east of the district. Chert is characteristic of the upper two members of the Platteville forma- tion to the east. To the northwest, in southeastern Minnesota the Decorah formation is green shale, and the lower two zones of the Galena dolomite are interbedded shale and limestone; the Galena has very little chert in Minnesota. The increase in dolo- mite and chert to the east is probably due to the influence of the Wisconsin arch. Leaching, dolomitization, and silicification, due to the zinc-lead mineralizing solutions, have altered some of the carbonate strata 251 252 especially the Quimbys Mill member (“glass rock” of local usage) and the Guttenberg member (oil rock of local usage); in places either of these units may have been reduced from 15 feet of argillaceous limestone with a small amount of shale, to less than 5 feet of shale and argillaceous residuum. Zinc-lead bearing strata include the cherty unit of the Galena dolomite, the Decorah formation, and the Quimbys Mill and McGregor members of the Platteville formation; the zinc-lead ore occurs in veins and breccia along inclined fracture zones (“pitches and flats”), in more or less interconnected vugs (”brangle”), and disseminated in the more shaly beds. Lead ore is found also in vertical joints (“crevices”) especially at favorable horizons (”openings”) in the upper or noncherty member of the Galena dolomite. INTRODUCTION PURPOSE OF THE INVESTIGATION In late 1942, when lead and zinc were in great demand because of the requirements of World War II, the U. S. Geological Survey began a project in Wisconsin, Illinois, and Iowa, hoping thereby to aid prospectors and mine operators in the discovery of additional lead and zinc ore. Production from the mining district, which was con- sidered by most geologists to be almost completely worked out, was being maintained in a limited way by several small mining operations; most of the ore was being concentrated in one relatively small custom mill, and two smaller mills shipped the rest of the concen— trates from the district. None of the companies had geologists on their staffs, nor were consulting geologists working in the area. It seemed plausible that a de- tailed restudy of the geology of the district might result in a renewed interest in its ore—bearing potentialities, and thus might contribute materially to the supply of lead and zinc at that critical wartime period. LOCATION AND GEOGRAPHIC SETTING The zinc—lead district in Wisconsin, Illinois, and Iowa lies mainly within the Driftless Area (fig. 31), on gen- erally southwestward—dipping lower Paleozoic strata. As a result of the absence of glacial drift and because of the mature dissection, there are many natural exposures; they are supplemented by quarries, by roadcuts, and by railroad cuts and tunnels. Because of the regional dip the outcrop pattern of the Platteville, Decorah, and Galena strata (Middle Ordovician) is mapped as a generally nortl1westward-trending band that is limited on the southwest by the apron of Maquoketa rocks (Upper Ordovician) flanking the cuesta formed by rocks of Silurian age and on the northeast by the exposure of pre—Platteville beds. Within this band of outcropping Platteville, Decorah, and Galena strata are a few“mounds”~—knobs 0f Silurian rocks with their aprons of Maquoketa shale; in addition some upland areas contain relatively thin but rather extensive patches SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY of lVIaquoketa under the omnipresent mantle of loess and residual material. Pre-Platteville strata are ex- posed along parts of the valleys especially in the more deeply dissected areas in the district. FIELD WORK The geologic study of the zinc-lead district in VVis— consin, Illinois, and Iowa was begun by the U. S. Geological Survey in October 1942, and was still in progress in 1955. The initial investigation was an analysis of the structural control of the ore deposits in an area of many open mine workings and drill holes and some exposures and included a cooperative pros~ pecting program with the U. S. Bureau of Mines. This study was soon extended and expanded to a gen— eral geologic mapping program of the mining district, including the areal geology, stratigraphy, structure, economic geology, and the larger geologic features, which was started in 1943 and has continued without interruption since that time. It was soon evident that the rock units of Platteville, Decorah, and Galena ages, which contain the ores, should be rcstudied because the published stratigraphic work of the preceding 10 to 15 years did not agree with the rock units recognized underground by the miners and in drill cuttings by prospect drillers. Furthermore, the miners and drillers were not always consistent in the recognition of the rock units in a restricted area, nor was there adequate correlation of rock units from area to area within the mining district. The writers there- fore made a detailed examination of the Platteville, Decorah, and Galena formations and subdivided them into relatively thin units so that the rather small ore- localizing structures could be mapped more accurately. A. F. Agnew has been responsible for the direction of the stratigraphic study, the description of most of the sections, the regional stratigraphy, and the preparation of the present report. The other writers described stratigraphic sections and in addition contributed much helpful discussion. The writers jointly described stratigraphic sections and acquired additional strati— graphic information in the course of the mapping of geologic structure. The writers’ stratigraphic study included the exam— ination of exposures, mine workings, and drill—hole cuttings and cores within the mining district, by hand lens and binocular microscope. Later, more informa- tion of a regional nature was desirable; as a result exposures and cuttings from holes drilled in nearby areas of Wisconsin, Illinois, Iowa, and Minnesota were investigated in 1944 and 1945, mainly by Agnew. The stratigraphic description presented herein was originally written in 1945 and is a result principally of the work from 1942 through 1945, although additional studies by STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT EXPLANATION Younger rocks Outcrop of Platteville, Decorah, and Galena rocks Older rocks Outline of zinc-lead district Outline of driftless éFéa 50 O L>I l | 4. Rock Island 253 TRUE NORTH MAGNETIC NORTH Data in part from State geo ogic maps, Willman and Templeton, 1951? 250 Miles l l 1 FIG ['RE 311—L'pper Mississippi Valley region, showing Driftless Area, zine-lead district, and bedrock distribution of Platteville, Decorah, and Galena strata. Agnew since 1949, based in part upon his work dealing with the subsurface Ordovician rocks of Iowa in 1946 and 1947 while engaged in ground water studies for the U. 8. Geological Survey in cooperation with the Iowa Geological Survey, have modified considerably some of the earlier concepts and terminology. The report was completely rewritten in 1953—54, to incorporate a revised approach to the problem and to include per— tinent information and published references acquired since 1945. Comprehensive reports on the geology, structure, ore deposits, and mineral resources of the district have been prepared for readers interested in other phases of the study (Heyl, Lyons, Agnew and Behre, 1955; Heyl, Agnew, Lyons, Behre, in preparation). The geologic study was instigated in 1942 by C. H. Behre, Jr., who had been supervising research in the mining district by students of Northwestern University since 1933. A. F. Agnew was in charge of the work from 1942 to the end of 1945, and again since July 254 1950; A. V. Heyl, Jr., was in charge from 1946 to July 1950, except for part of 1948—49 when E. J. Lyons was in charge. A. E. Flint was in charge of the work in Iowa in 1951—1953, and since that time, C. E. Brown. The members of the party consisted of A. F. Agnew from October 1942 to December 1945 and also during the summer of 1948 and since June 1949; A. V. Heyl Jr., from February 1943 to August 1950; E. J. Lyons as a part-time member of the party from Feb— ruary 1944 to June 1948, and a full—time member from June 1948 to October 1949; C. H. Behre, Jr., as a part— time member and project advisor from October 1942 to October 1945; A. E. Flint, 1949—53; R. M. Hutch- inson, 1944—45; Dorothy J. West, 1948; J. W. Allingham, 1950—55, C. E. Brown since 1951; Percy Crosby, 1953—54, J. E. Carlson, since 1951; W. A. Broughton 1950—55; L. G. Collins, 1953. Harriette A. Burris, R. W. Chartraw, J. F. Coulthard, R. P. Crumpton, D. C. Dixon, Catherine M. Fulkerth, H. L. Hefty, Maxine L. Heyl, M. A. Husted, J. H. Moor, D. W. Ressmeyer, H. F. Seeley, J. C. Spradling, C. W. Tandy, Jr., J. J. Theiler, Mary C. Wheeler, L. A. Ziech served as field assistants, and Marge B. Hake and Mary J. MacCulloch as scientific aids, during vari- ous stages of the program until 1954. A. E. Flint and R. P. Crumpton, in particular, added to the knowledge of the Plattevillc, Decorah, and Galena sequence during their mapping of the geologic structure. ACKNOWLEDGMENTS The study of the zinc-lead district in Wisconsin, Illinois, and Iowa has been done in cooperation with the Wisconsin Geological and Natural History Survey since 1945 and the Iowa Geological Survey since 1951. The Wisconsin Survey, directed by E. F. Bean and later by G. F. Hanson, contributed funds for the work in Wisconsin and a large amount of data including strati- graphic information and logs of deep wells, supplied by F. T. Thwaites. The Iowa Geological Survey gave financial support to the work in Iowa and permitted the use of subsurface data that had been used in ground— water studies by Agnew for the U. S. Geological Sur— vey in 1946—47. A. C. Trowbridge and H. G. Hershey, State Geologists of Iowa, freely contributed information. Our work was aided by the free interchange of data with the field party of the Illinois State Geological Survey during the summer of 1943 and from the spring of 1944 until 1954. The U. S. Bureau of Mines maintained a party from December 1942 to 1954, except for a few months in 1946, to explore deposits in the district. The cores and churn-drill samples were logged by U. S. Geologi— cal Survey geologists, and in most instances the explora- tions were planned and interpreted in close cooperation SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY by members of both organizations. We wish to acknowledge their invaluable aid in carrying out our studies. Acknowledgment for their valuable aid and contribu— tions is made to Paul Herbert, Jr., and R. R. Reynolds, formerly of the Illinois State Geological Survey; H. B. Willman, of the Illinois State Geological Survey; W. C. Bell, formerly of the University of Minnesota; J. R. Ball, formerly of Northwestern University; representa- tives of mining companies, especially the Vinegar Hill Zinc Co., The New Jersey Zinc Co., and the American Zinc, Lead, and Smelting Co.; to C. W. Stoops, an ore buyer, mine operator, and geologist at Platteville; and drillers of water wells and prospect holes and the many mine operators who supplied useful data. Par— ticular thanks is due to M. A. Melcher, president of the Wisconsin Institute of Technology. The school furnished office and laboratory space for many years and gave us much valuable data and use of its facilities. We wish to thank the Geologv Departments of the University of Wisconsin and Northwestern University for use of binocular microscopes and theses. REGIONAL GEOLOGY AND STRATIGRAPHIC RELATIONS STRUCTURE The zinc-lead district in Wisconsin, Illinois, and Iowa lies on the southwestern slope of the Wisconsin arch (fig. 31). The regional dip of the rocks is to the sou th—southwest but it has been modified by folds which are directed easterly, northwesterly, and northeasterly. Joints and generally high angle faults are associated with the folds, and in the mining district bear zinc-lead ore. REGIONAL STRATIGRAPHIC SUMMARY Because this report deals primarily with rocks re— lated to the major zinc-lead ore deposits—the Platte— ville, Decorah, and Galena strata (Middle Ordovician)— pre-Platteville and post-Galena rocks are discussed only briefly. Pre-Cambrian rocks underlie the mining district, as granite gneiss and other granitic rocks have been penetrated in wells at several localities. Cambrian strata consist of sandstone, siltstone, and dolomite, of Late Cambrian age (fig. 32). The Mount Simon sandstone, which unconformably overlies the pre- Cambrian, is succeeded conformably by sandstone and siltstone of the Eau Claire sandstone, and that by the Dresbach sandstone; the latter is overlain eonformably by the glauconitic sandstone and siltstone of the Franconia sandstone, which is succeeded eonformably by sandstone, siltstone, and dolomite of the Trempealeau formation. There are many facies changes. The STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT E w Average 0 9 Group or . - - “ L - Descri tion thickness, 2% 8 formation p in feet 7/377 2 g A/ A Dolomite, buff, cherty; Pentamerus at top, 90 S N % / A / A ‘5 a 12 / 200 __, 3 2 A / A / m 3 A A Dolomite, buff, cherty; argillaceous near base 110 E : _—‘_‘ . . _ . & Maquoketa shale ,— I I Shfglsegiltszlgttmbiilgmltic, phosphatic depauperate 108—240 2 0099:.— , 1 Dolomite, yellowish-buff, thin-bedded, shaly 4o / . . . 7 / Dolomite, yellownsh-buff, thick-bedded; Receptcwulztes 80 in middle 225 Galena dolomite . . Dolomite, drab to buff; cherty; Receptaculztes 105 q, near base 1‘: E .‘E Dolomite, limestone, and shale, green and brown; (:3 2 Decorah formation phosphatic nodules and bentonite near base 35—40 > O . . Limestone and dolomite, brown and grayish; green, 3 PlatteVIlle formation sandy shale and phosphatic nodules at base 55—75 0 St. Peter sandstone Sandstone, quartz, coarse, rounded 40+ 280— ; Prairie du Chien group Dolomite, light-buff, cherty; sandy near base and 0— 320 3 (undifferentiated) in upper part; shaly in upper part 240 Trempealeau . . formation Sandstone, Siltstone, and dolomite 120-150 Franconia sandstone Sandstone and slltstone, glauconitic 110—140 2 E 3 Dresbach sandstone Sandstone $26 “2° 3 < 3 o Eau Claire sandstone Siltstone and sandstone gga 700- 1050 Mount Simon 440— sandstone Sandstone 780 389000756 2 FIGI‘RE 32.—Generalized stratigraphic column for zinc-lead district. 255 256 thickness of the Cambrian rocks increases southward across the district from 960 to 1,310 feet. Rocks of the Prairie du Chien group (Lower Ordo— vician) in many places are dolomite, with a sandstone formation or sandy zone near the middle; in other localities, however, this group is represented by a large amount of red and green shale, silicified limestone, and limestone. The overlying St. Peter sandstone (Middle Ordovician) is normally 40 feet thick, but unconformable relations between it and the Prairie du Chien below, coupled with leaching of the dolomite in the latter, cause sandstone of this type to be present to a depth of at least 320 feet below the top of the St. Peter. Because of this the Prairie du Chien reaches a maximum thickness of 250 feet; together the two units aggregate 280—320 feet. The outcropping band of the southwesterly dipping Platteville, Decorah, and Galena strata (Middle Ordo- vician), which contain the zinc-lead deposits, strikes generally northwesterly across the district; facies changes are evident both toward the northwest and toward the southeast. These changes are marked by differences in the lithologic character of the equivalent rocks, and by differences in thickness. As viewed within the confines of the mining district, especially the eastern part, the beds designated Platte— ville, Decorah, and Galena by earlier writers fall naturally, because of general lithologic similarity, into three groups, as follows: Grouping of Platlem‘lle, Decorah, and Galena rocks in district [Local terminology in parentheses] Noncherty unit (bufl‘) Cherty unit (drab) Ion dolomite member (gray and blue) Group 1 Guttenberg limestone member (oil rock) Speehts Ferry shale member (clay bed) _ _V,_ ,_Diseon1‘ormity Quimbys Mill member (“glass reek”) Group 2 MeGregor limestone member (Trenton) Pecatoniea dolomite/member (quarry beds) Glenwood shale member (shale) Group 3 Because the stratigraphic guides for the practical miner are the different lithologic characteristics, such a classification might be the most practical locally, insofar as the eastern, or main part of the mining district is concerned. Group 2 is a lithologic entity within this part of the mining district, for the rocks composing all three of its subdivisions were deposited under generally similar conditions and they also reacted similarly under the stress of later geologic solutional and structural pro— cesses. Furthermore, in the mining district the basal beds of Group 2 are distinct lithologically from the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY uppermost beds of Group 3, and the upper beds of Group 2 are equally distinct lithologically from the lowest beds of Group 1. When considered regionally, on the other hand, to the east the dolomite of the Quimbys Mill member is lithologically more similar to that of the McGregor member below than it is to the Spechts Ferry above. Moreover, the Quimbys Mill pinches out to the west as does the Pecatonica, whereas the Spechts Ferry pinches out and the Guttenberg thins to the east. Furthermore, in its western facies the shale character of the Ion member is more similar lithologically to that of the Guttenberg and Spechts Ferry below than it is to the limestone of the Galena above. In addition to the facies and convergence factors mentioned above, a disconformity marked by a corro- sion surface and associated closely with a bentonite layer lies within, rather than at the top or bottom of Group 2. Thus the available regional evidence sug- gests a different grouping of the beds, as follows (fig. 33): Regional grouping of Platteville, Decorah, and Galena rocks Galena dolomite Noncherty unit Cherty unit Ion dolomite member Guttenberg limestone member Spechts Ferry shale member *1 —l)isconformity Quimhys Mill member MeGregor limestone member Pecatonica dolomite member Glenwood shale member Decorah formation Platteville formation ,—_\" ,a' ‘5. \'_:«‘ ”f" FIGL‘RE 33.—Platteville (Op), Deeorah (0d), and Galena (0g) strata in 200 foot bluff west of State Route 81, in Grant County, Wis. (fig. 35, loo. 9). STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT Similarly, 300 miles away in Missouri, Groshskopf (1948, p. 354) has shown that the Decorah as used in eastern Missouri is coincident in extent with the over— lying Kimmswick and overlaps various parts of the Plattin; this suggested to him that the Decorah is related more closely to the Kimmswick than to the underlying Plattin and that a hiatus exists between the Decorah and the Plattin. For these reasons the classification given on the preceding page is the one used in the upper Mississippi Valley region, which includes the zine-lead mining district. Except for the Glenwood shale member the Platte— ville formation is limestone and (or) dolomite, with 257 thin shale partings. The dolomite facies as mapped generally includes part of the mining district and extends toward the east, Whereas the limestone facics extends toward the west (fig. 34). Significant regional changes in the stratigraphic char- acter of the Platteville formation are not present in the Glenwood shale (basal) member. The overlying Peca— tonica dolomite member thins northwesterly from 20—24 feet in the mining district, to 10 feet in northeastern Iowa, and less than 2 feet in southeastern Minnesota; it maintains a thickness of 26 feet in the vicinity of Beloit (fig. 35) and Janesville, Vi’is, along and east of the Wisconsin arch, although Bays and Raaseh (1935, p. 297) reported only 18 feet of Pccatonica dolomite member over the Wisconsin arch. ff WEST .CENTRAL EAST . § Guttenberg, Iowa PIattevulle, WisxGalena. Ill. Monroe, WIS. O 8 < Maquoketa shaIe 2 200'- 150’— < 2 Lu 2‘ 0 100’- < 2 Lu 2’ . A A A A _~ Cherty unit .3. .2 .:~ A — 0 50,— '3‘ ~AAA AAAAAA_ AAXAAA AAA AAAAA AAAAAAA AAAAAAAAA’EAAA 1A Alfie-£3, AA A} A ——"—-'::‘ “Z—‘* ‘— ’1' ~— ~—“ __ ‘2. "— “w 52$le ‘R’fur. .. .. _ ’ ~ ~_ _ - _ » - . 4‘ A ~:_Z‘:;ZA A “'1' A" A - A ~ A A A AA~A AAAA—‘AAAAAAAAAAAAA AAA SegézAZAAA A AAAAAAAAAAAAAAA A A AAAAAAAAAAAAAAAAAAAA A A A' A A A A A A A A A O E Limestone and shale Ion member _‘ n: 8 ' d h l ‘5’ Limestone an 5 ae A A A AAAAA A A A .— . A ‘_ uim ys Ml” membe' A A'K’m A A AAAAAAAAA O “J 50'— Spechts Ferry A A A A A A A A A A _ d —' i ' l’ =' shale member MCGregOr memb Li DO’Ormre McGregor membe m 5 er mestone j PCCatonic ‘ member 0- a dolomite . an. nnnnnnn DIICII-ID...IIIII....QI.....'.I-I ’— Glenw od, 5 100 ' shale mgmber K '- Sandstone :5 Lu LLJ e. W W a ’— . 75 Miles | EXPLANATION XXX X ...o-.-c- Bentonite Phosphatic pebbles Receptaculites Fm [IRE 34.—Diagrammatic cross section of Platteville, Decorah, and Galena strata eastward across the mining district, showing facies relationships. 258 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY I ! H O U S T O N V E R N O N _L ___ i . I 0' W A . X I _ ' _'— ‘ _ ‘ m Lansmgo RICHLAND, I . I Richland 0 0U) 14| ALLAMAKEE Center Decorah 0 LL] Waukon . . Z Wtsconsm I Z _ ' .35 __—_.______ Prairie du Chien I 25 LIJ ‘ "‘ .16 '— | m c L A Y T o N — —— - —— - >. < I Guttenber ' LL , 42 ' ttevnlle ' 31 G E E > N .26 Janesville 0 LAFAYoETTE'_k ROCK . _ - _ . '7 — Monroe I Z I < I Z I SI .45 Beioit < Sl— — _ .1. _ _ ° I D E L AW A R E "U? S ] o . , D [D l STEPHENSON WINNEBAGO ' ‘ I ' . . % Rockford L I N N .J O N E S I . J A C K S O N .1 ___._ _ 10-.9 “Was CARROLL OGLE . FIGURE 35.—Map of part of the upper Mississippi Valley region, showing outline of zinc-lead district. Localities cited in the text are listed below. 1 Bordon Whey Plant well 2. sec. 33, T. 8 N., R. 3 W., Boscobel, Wis. 27. Type section of Quimbys Mill, SE corner, sec. 11, T. 1 N., R. 1 E., Wisconsin. 2. Roadcut, sec. 22, T. 8 N., R. 3 W., junction of State Routes 60 and 61, Wisconsin. 28. Roadcut, center EM sec. 1, T. 4 N., R. 3 W., County Road A, Wisconsin. 3. Quarry, sec. 31, T. 6 N., R. 6 W., and sec. 36, T. 6 N., R. 7 W., north edge of 29. Quarry, near center sec. 23, T. 4 N., R. 5 E., County Road F, Wisconsin. Wyalusing, Wis. 30. Bautsch mine, see. 10, T. 27 N., R. 1 E., Illinois. 4. Crow Branch diggings, sec. 22, T. 5 N., R. l W., Wisconsin. 31. Quarry, NWM sec. 30, T. 3 N., R. 5 E., Wisconsin. 5. Roadcut, sec. 15, T. 2 N., R. 2 W., U. S. Highway 151, Wisconsin. 32. Ravine, center of east line sec. 4, T. 1 N., R. 1 E., Wisconsin. 6. Roadcut, secs. 1 and 12, T. 2 N., R. 2 W., U. S. Highway 151, Wisconsin. 33. Type section of Guttcnberg, SW34 sec. 5, T. 92 N., R. 2 W., Iowa. 7. USGS-Raisbeck hole 2, sec. 21, T. 2 N., R. 1 E., Wisconsin. 34. East bank of Galena River, near center sec. 34, T. 29 N., R. 1 E., Illinois. 8. City well, see. 18, T. 86 N., R. 5 E., Bellevue, Iowa. 35. Ravine, NE% sec. 32, T. 97 N., R. 5 W., State Route 51, Iowa. 9. Bluff, sec. 36, T. 4 N., R. 5 W., near State Route 81, Wisconsin. 36. Type section of Ion, NW1/4 sec. 35, T. 96 N., R. 4 W., Iowa. 10. Quarry, sec. 4, T. 90 N., R. 2 E., Spechts Ferry station, Iowa. 37. Roadcut, NWM sec. 33, T. 6 N., R. 5 W., U. S. Highway 18, Wisconsin. 11. Eagle Point Quarry, sec. 7, T. 89 N., R. 3 E., Dubuque, Iowa. 38. Quarry, SW1/4 sec. 24, T. 5 N., R. 5 W., Wisconsin. 12. Roadcut, sec. 7, T. 2 N., R. 2 W., U. S. Highway 61, Wisconsin. 39. Quarry, NEM sec. 32, T. 6 N., R. 4 W., Wisconsin. 13. Quarry, sec. 3, T. 2 N., R. 3 E., Darlington, Wis. 40. Roadcut, center sec. 21, T. 6 N., R. 3 W., U. S. Highway 18, Wisconsin. 14. Type section of Glenwood, sec. 6, T. 98 N., R. 7 W., Iowa. 41. Roadcut, SWM sec. 31, T. 5 N., R. 3 W., County Road A, Wisconsin. 15. Roadcut, sec. 18, T. 5 N., R. 2 W., U. S. Highway 61, Wisconsin. 42. Quarry, SW14 sec. 9, T. 3 N., R. 3 E., Calamine, Wis. 16. Clayton County Home well, see. 7, T. 93 N., R. 4 W., Iowa. 43. Quarry, SEM sec. 19, T. 6 N., R. 1 E., Montfort, Wis. 17. Cheese factory well, see. 6, T. 4 N., R. 5 W., North Andover, Wis. 44. Quarry, sec. 5, T. 4 N., R. 6 E., York Church, Wisconsin. 13- ‘smlagf “"3111! 569‘ 5v T- 4 N., I; 1 If; EeVIZEYTyiS. 45. Quarry, along Honey Creek, SWM sec. 23, T. 1 N., R. 6 E., Wisconsin. 19. choo we , sec. 26, T. 6 N., .1 ., o , is. . . . . 20. City well, sec. 12, T. 6 N., R. 6 E., Mount Horeb, Wis. 46' Ginte mine, scc. 30’ T' 29 N" R' 1 E" Illin01s. . _ 21. City well 1, sec. 4, T. 90 N., R. 3 W., Colesburg, Iowa. 47. Quarry, SEX sec. 18, T. 3 N., R. 3 W., County Road U, Wisconsm. 22. City well, see. 29, T. 29 N., R. 2 W., East Dubuque, Ill. 48. Roadcut, NWK sec. 34, T. 1 N., R. 2 W., State Route 11, Wisconsin. 23. Roadcut, near center NM; sec. 10, T. 4 N., R. 2 W., County Road A, Wisconsin. 49. Quarry, SEM sec. 3, T. 6 N., R. 5 E., U. S. Highway 151' Wisconsin. 24. Roadcut, near center of 8% sec. 35, T. 5 N., R. 1 E., Wisconsin. . . . 25. Type section of McGregor, NEM sec. 28, T. 95 N., R. 3 W., Iowa. 50' 01d railroad tunnel, 813% 5910. 21, T. 1 N., R. 1 E., Wisconsm. 26. Type sections (of Bays and Roasch 1935) of Magnolia, NW% sec. 26, T. 3 N., 51' T T' Redfern well, SEX sec. 34' T' 29 N" R' 2 Ev Illlnms. R. 10 E., Wisconsin. 52. Quarry, NWX sec. 5, T. 3 N., R. 1 E., Platte Mound, Wis. STRATIGRAPHY 0F MIDDLE ORDOVICIAN In southeastern Minnesota, where the Pecatonica is less than 2 feet thick, it consists of very sandy limestone above calcareous sandstone that contains phosphatic nodules. This phase is exposed in the long roadcut along U. S. Highway 16 in sec. 35, T. 103 N., R. 10 W., just south of Lanesboro, Minn. (about 40 miles north of Decorah, Iowa; fig. 35). The McGregor member, a limestone in the western and central parts of the district, changes laterally, becoming progressively more dolomitic eastward near the crest of the Wisconsin arch, where it is dolomite (fig. 34). This dolomitization affects the upper beds of the McGregor farther west than it does the lower strata. Chert is present in the McGregor from Shulls- burg, Wis, eastward. The Quimbys Mill (upper) member of the Platteville formation is limestone or limestone and dolomite in the central part of the mining district, and is cherty dolo- mite to the east (fig. 34). The unit wedges out to the west, as is shown by its thickness of only 1 foot in the roadcut 10 miles southwest of Platteville, Wis, (fig. 35, 10c. 12), and of only a few inches in a roadcut 10 miles northwest of Platteville, in sec. 1, T. 4 N., R. 3 W. (100. 28). The Quimbys Mill averages 14 feet thick in localities several miles east of the type section (100. 27) and at Mount Horeb (100. 20), and is more than 18 feet thick in an area southeast of Shullsburg. All members of the Platteville formation are conform— able except the Quimbys Mill. The Quimbys Mill strata do lie conformably on the McGregor, and a dark shale bed commonly marks the contact. However, the Quimbys Mill member and the overlying Decorah strata, Whether the Spechts Ferry shale member or the unnamed limestone member (p. 264), regionally show disconformable relationships. In the central part of the mining district the upper surface of the Quimbys Mill is corroded and pitted by solution; clots of greenish shale and of sandy limestone similar to that in the overlying Spechts Ferry fill these pits, giving the appearance of involutions in vertical cross section. East of the mining district, where the Spechts Ferry is absent, the pits are filled with sandy dolomite and phosphatic pebbles of the Guttenberg that farther west mark the upper part of the Spechts Ferry. Similar features were noted by Chamberlin (1882, fig. 8), Sardeson (1898, p. 322), and Ulrich (1924, fig. on p. 96). This corrosion surface marks the upper limit of the Quimbys Mill member. The Decorah formation at its type locality, 80 miles northwest of the mining district, is 25—30 feet of green— ish calcareous shale with nodular limestone, overlying a 2-foot basal limestone unit that wedges out to the east. In the western part of the mining district the Decorah is divisible into the following three members: at the 259 ROCKS IN THE ZINC-LEAD DISTRICT base is the 8-foot thick greenish shale with limestone nodules of the Spechts Ferry, next above is the brown limestone and some shale of the Guttenberg 15% feet thick, and at the top is the grayish limestone and shale of the Ion, 19 feet thick (fig. 34). In the eastern part of the mining district the Spechts Ferry has wedged out, the brown dolomite of the Guttenberg has thinned to 8 feet thick, and the overlying grayish buff dolomite of the Ion is only 15 feet thick and difficult to distin- guish from the lower zone of the overlying Galena dolomite. The Decorah rests disconformably on the Platteville; it grades upward into the Galena (Agnew, 1950), con- trary to previous statements (Kay, 1932; Kay and Atwater, 1935) that an unconformity exists at the latter contact. The Galena dolomite is rather uniform in thickness across the mining district—averaging 225 feet—and is generally a dolomite. The lower part, however, is limestone in the western part of the district and t0 the west, and also locally in the central part of the district; The formation is divisible regionally into two sub- divisions of about equal thickness, a cherty unit below and a noncherty one above. The cherty unit includes the lower two-thirds of the Prosser member of estab‘ lished stratigraphic usage, whereas the noncherty unit consists of the upper third of the Prosser, the Stewart- ville, and the Dubuque members. As the Prosser, Stewartville, and Dubuque members are not every- where recognizable in the regional area embraced in this study, and because the noncherty and cherty units are distinctive throughout its extent, the twofold sub- division of the Galena based on the presence or absence of chert is employed in the present report (p. 265). The Maquoketa shale (Upper Ordovician) is gener- ally grayish dolomitic shale and dolomite in the mining district, although its lower one—third is commonly brownish in color. The Maquoketa is as thin as 110 feet in the southern part of the mining district, and thickens toward the northeast to 240 feet in a locality 25 miles west of Madison, Wis. (fig. 31); it likewise thickens to the northwest, 220—260 feet being common in the area northwest of Dubuque, Iowa. The Maquo- keta is characterized by facies changes, especially west of the mining district. It appears to lie conformably on the Galena, although regionally the contact seems to be disconformable. Dolomite of Early Silurian age is present up to 200 feet thick in the mining district. The lower 20 feet or so is argillaceous dolomite; this is succeeded by 65 feet of cherty strata, 20 feet of noncherty dolo— mite, and the upper 90 feet is somewhat cherty and contains Pentamerus. Dolomite of the Silurian gener— 260 ally lies unconformably on the Maquoketa, although locally the contact appears to be gradational. Post—Silurian deposits found locally in the mining district include boulders of quartz sandstone, boulders of hematite, boulders of quartzite and greenstone, and poorly cemented conglomerate. In addition, in the southern, eastern, and western fringes of the district, glacial drift occurs generally in local patches (fig. 31). Pleistocene terrace deposits and loess are common in the mining district. STRATIGRAPHIC PRINCIPLES Because the geologic investigation that gave rise to the present report had as its major purpose the deline— ation of geologic structure, the rocks were studied in terms of mappable units-formations and members. Initially the investigation was concerned with rela- tively local areas (maximum width 10 miles), but more regional relationships were scrutinized as areas 15 or 20 miles or more distant from the initial one were -mapped. In local areas 5 to 10 miles wide, differences in lithofacies were observed, and the recognition of facies relationships was found to be even more impor- tant in the regional correlation of the strata than in local correlation. Despite these lateral changes in lithologic features, from the standpoint of the structural mapping it was desirable to picture the rocks as correlative units, pro— vided that upper and lower limits of the mapped unit were recognizable. Thus a liberal interpretation of the facies concept was applied. Regionally and even locally all lithologic criteria were evaluated and a top or base was assigned to a particular unit, although the gross lithology of that unit in places may have been atypical, as for example the regional lithology of the Guttenberg limestone member, and locally the Ion member of the Decorah— Galena contact. As another example, the Decorah formation at its type locality is indivisibly green shale with limestone nodules, overlain by limestone of the Galena, and underlain by limestone of the Platte— ville. Thirty-five miles closer to Platteville, at the type locality of the Ion the upper (Ion) member of the Decorah is still green shale and limestone in almost equivalent amounts; it is overlain by buff limestone of the Galena dolomite and underlain by tan limestone of the Guttenberg (middle member of the Decorah). At Platteville the Ion is light—brown dolomite with greenish argillaceous mottlings and partings; it is overlain by light—brown dolomite of the Galena and is underlain by light—brown Guttenberg limestone. In gross lithology the Ion at Platteville is more like the overlying than it is like the underlying strata, although 'at Decorah, Iowa, the reverse is perhaps true. The SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY recognition of one persistent and other less—persistent bentonite beds aided in the regional tracing of the strata across facies changes. A “formation” in this study is a locally mappable unit consisting of rocks mainly of one dominant litho- logic type, with boundaries based upon objective cri- teria. It is extended regionally, despite facies changes, from local areas on the basis of all the lithologic cri- teria (including fossils) available; and its boundaries, although in this extension somewhat subjective, are drawn at the same stratigraphic positions relative to units above and below, as where the formation was initially mapped. Stratigraphic purists may object, for example, to calling the Ion a part of the Decorah formation at Platteville, Wis, where actually it is more similar in lithology to the overlying Galena dolo— mite. However, the philosophy presented herein per- mits the use of workable stratigraphic units locally. permits the correlation of these units regionally, and permits the stratigraphic nomenclature to be held at a minimum. Geologic time rock classification is another matter, entirely (see the discussion of this problem as related to Cambrian strata of the upper Mississippi Valley by Bell, Feniak, and Kurtz, 1952, p. 175476). Fossils in the Platteville, Decorah, and Galena strata of the upper Mississippi Valley have not been adequately studied, nor have most of the many fossil collections been gathered with adequate attention to principles of stratigraphic geology. As a result the faunal characteristics of the strata are as yet not completely known. N0 systematic paleontologic study of the strata has been attempted during the course of the present project. However, fossils have been observed as rock characters, and it is believed that because the faunas are related closely to environmental conditions, and because they recur in succeeding strata of similar lithologic facies, they are generally facies faunas. Thus only general assignments to the larger time-stratigraphic subdivi- sions (systems and series) is made herein. Furthermore, dolomitization can destroy evidence of fossils originally entrapped in the limestone (Bucher, 1953, p. 292); therefore, relatively unfossiliferous dolo- mitic rocks such as the Pecatonica may originally have been characterized by a much greater abundance and diversity of forms. 340st of the fossils observed in the Galena, Decorah, and Platteville beds seem to be facies faunas (as should be expected, but commonly is not). As Allan so con— cisely stated (1948, p. 7), the practice of matching faunas—usually faunas determined in a museum by one person but collected by someone elsewis quite illogical; and the widely accepted views that dissimilarity of STRATIGRAPHY OF MIDDLE ORDOVICIAN faunal content indicates difference of age, and that similarity of faunal content establishes chronological equivalence, are ex- tremely unsafe generalizations. Allan’s views were forecast by Sardeson (1907, p. 190), who stated that “the identity of fossils does not prove strictly contemporaneous deposits, but only related faunas.” (See also Williams, 1952; Rich, 1951, p. 17.) Regionally these faunas transgress lithologic units, they recur with ecologically recurring rock- depositing environments, or they are absent where their particular environment was absent. For example, Bell (1950, p. 493) ventures the suspicion that the widespread Eden—)Iaysvillc “hiatus,” the physical evidence for which is so infrequently demonstrated, records the absence of a biotic environment—not the absence of a depositional record. The writers agree heartily with Bell, for there is no physical evidence that a “hiatus” exists between the Stewartville and Dubuque members of the Galena; yet because the fauna of the limestone and dolomite of the Stewartville is Trenton in aspect, and the fauna of the shale and limestone of the Dubuque is Richmond in appearance, a hiatus representing Eden and Maysville “time” is commonly postulated between the Stewart- ville and Dubuque members (see also Lattman, 1954, p. 268; McFarlan and White, 1948, p. 1642). Because the object of this study was the mapping of geologic structure, therefore, and because of the reasons stated above, the fossils have not yet been studied in detail and only general assignments to the geologic time scale are made. The faunal relationships of these strata remain to be worked out; this constitutes an extremely interesting problem whose solution will contribute materially to our knowledge of stratigraphy, paleontology, ecology, and general geologic history of the Middle Ordovician 0f the upper Mississippi Valley. STRATIGRAPHIC PROBLEMS PLATTEVILLE-DECORAH BOUNDARY Bain’s (1905, p. 19) original description of the beds of Platteville age at the type locality recorded an average thickness of 60 feet, consisting of: Feet 4. Thin beds of limestone and shale ___________________ 10—20 3. Thin-bedded brittle limestone, breaking with a con- choidal fracture ________________________________ 25—30 2. Buff to blue magnesian limestone, heavy bedded, (frequently a dolomite) __________________________ 20—25 1. Shale, blue _______________________________________ 1—5 According to Bain, unit 4 consists of limestone and shale commonly in thin alternating beds, but there is comparatively little uniformity in this member in differ- ent parts of the district * * * the shale layers are better de- 261 ROCKS IN THE ZINC-LEAD DISTRICT veloped toward the West, while the limestone is the main part or the whole of the member in the eastern portion of the lead and zinc district. The shale beds are usually green or blue in color, though some of the beds are at times yellow, chocolate colored, or even black. The green shales are especially developed in Iowa. The chocolate-colored and black shales are highly carbonaceous, and are locally termed ”oil rock,” though the main bed of chocolate-colored shale, or the Hoil rock” of the lead and zinc district, lies just at the base of the Galena. The limestone is commonly a thin-bedded, fine-grained, blue rock, rich in fossils. At times it is subcrystalline, and, while usually non- magnesian, becomes markedly magnesian toward the east, where it seems to be the equivalent of the “upper buff” of the Wisconsin section. The most marked beds of No. 4 in the type locality of the Platteville occur near the base of this member, and are termed ”glass rock.” These are the typical glass-rock beds of the lead and zinc district. These “green or blue” shales and the “thin—bedded, fine—grained, blue rock [limestone] rich in fossils” belong in the Spechts Ferry, which is here referred to the Decorah formation, as is discussed later (p. 286). The “chololate-colored and black shales” and the subcrystalline limestone that becomes dolomitic toward the east belong in the Quimbys Mill member of the Platteville formation. It is therefore evident that the grouping of the two members together as facies of the same unit led to Bain’s impression that unit 4 of his description lacked uniformity. Bain (1905, p. 21) described the Galena as follows: Generalized section of the Galena limestone, Illinois Feet 5. Dolomite, earthy, thin-bedded _____________________ 30 4. Dolomite, coarsely crystalline, massive to thick bedded ________________________________________ 60 3. Dolomite, thick to thin bedded, coarsely crystalline, chert bearing __________________________________ 90 2. Dolomite, thick bedded, coarsely crystalline _________ 60 1. Thin bedded limestone with shaly partings which are highly fossiliferous and, in part, at least, carbona- ceous—the ‘oil rock’ of the miners ________________ 2 The basal member of the Galena, No. 1 of the above section, is well known throughout the zinc district. It receives its name from the large amount of carbonaceous material which it con- tains, often sufficient to cause it to burn when lighted with a match. In the mining district it is everywhere recognized as the oil rock; and as there are usually several bands of shale interbedded with thin-bedded brittle limestone, the most important band is there discriminated as the main oil rock. Away from the mining district the horizon is occupied by a soft green clay. Usually the shaly element is most important at the top, and ordinarily—in southwestern Wisconsin, at least— a particularly bituminous parting is recognized as belonging to the oil rock. It is apparent that Bain considered the carbonaceous oil rock and the “soft green clay” as different facies, thus implying that the “glass rock,” “clay bed,” and “oil rock” are all facies of the same stratigraphic unit. They belong to three separate members (Quimbys Mill, Spcchts Ferry, Guttenberg) of two different 262 formations (Platteville, Decorah), as is demonstrated in the discussions of those units in succeeding pages. In a later publication Bain (1906, p. 22, 23) placed all of the “bluish or greenish” shale at Spechts Ferry, Dubuque County, Iowa (fig. 35, 100. 10) in the Platte- ville formation, and stated that in a quarry about 2 miles northwest of Platteville, Wis, “the equivalents of the main oil-rock horizon which marks the base of the Galena” were present, and that the unit immediately below “represents the clay bed usually found beneath it.” It is not clear from the above statement whether he meant the clay bed to be assigned to the Galena or to the Platteville, but presumably the latter. Two pages later, however, he (1906, p. 25) wrote as follows: General section of basal Galena beds Ft. In 4. Thin-bedded magnesian limestone, variable in thickness, which depends upon the extent of dolomitization _____________________________ 0‘15 15 3. Thin—bedded limestone or dolomite with partings of oil rock _________________________________ 5»8 2. Brown, shaly material, with minor lenses of lime- stone; the main oil-rock horizon ______________ }é~2 1. Shale or blue clay containing black phosphatie pebbles ___________________________________ )ée3 In places dolomitization extends down to the top of N0. 3 of the above section; in other places No. 1 of the section cannot be distinguished from the shaly limestone beds at the top of the Platteville, in which black and brown shale, indistinguishable from the oil rock of the Galena, occurs. Bain’s earlier concept that the green shales and brown carbonaceous shales are merely different facies of the same beds is thus again evident. His described section (1906, p. 28) at Eagle Point quarry, Iowa, shows 3 feet of green argillaceous fossiliferous shales as the basal unit of the Galena. Ellis (1905, p. 313), who worked closely with Bain on the Wisconsin and Iowa parts of the study, wrote as follows: The base of the Galena is marked by a constant shale bed vary— ing from 1 to 3 feet in thickness. This shale consists of blue clay and of brown carbonaceous material, which gives it the name of “oil rock” * * * [The underlying “glass rock,” which comprises the upper beds of the Platteville] carries varying amounts of magnesium carbonate, although not approaching a dolomite. Cox (1911, p. 431) likewise interpreted this relation— ship as one of facies: The base of the main body of oil rock occurring from 8 to 12 feet above the glass rock is taken as the division between the Platteville limestone below and the Galena dolomite above. * * * Interbedded with, or just below, there is often a greenish clay bed a foot or so in thickness. It is uncertain whether he meant the “greenish clay bed” to be basal Galena or uppermost Platteville. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Grant (1903, p. 35—36; 1906, p. 33) had likewise noted the stratigraphic recurrence of the oil rock, with the bluish or greenish shale between. However, he termed the oil rock above the blue shale the ”main oil rock.” He found that this bed of oil rock in every case overlies the clay bed, which in turn overlies the “glass rock.” He signified the “main oil rock” as the basal unit of the Galena, and the clay bed as the upper- most unit of the underlying Platteville. Later he was not consistent, however, for he and Burchard (1907, p. 6) placed within the Galena the green shale beds occurring below the oil rock in the Eagle Point quarry at Dubuque, Dubuque County, Iowa (fig. 35, Ice. 11), although in other sections (1907, p. 5) the blue and green shale was consistently put in the Platteville. Although Davis (1906, p. 548) had noted that the clay bed and the oil rock are separate and superimposed units and not facies, his lead was not followed until Trowbridge and Shaw (1916, p. 39) and Boericke and Garnett (1919, p. 1218—1219) likewise distinguished them. The Platteville-Decorah boundary was shown re— cently (Agnew, Heyl, 1946) to be one of regional dis— conformity. The upper member of the Platteville formation pinches out to the west, whereas the members of the Decorah formation thin and are absent to the east. Furthermore, locally the upper surface of the Quimbys Mill is pitted and corroded, and contains involutions of sedimentary rocks of the overlying unit. The presence of a bentonite layer near the base of the Spechts Ferry is evidence that these relationships are not facies, because the bentonite layer remains just above the contact of the limestone and shale as the beds are traced eastward beyond the area of Spcehts Ferry strata (fig. 36). BELOIT DOLOMITE In the eastern part of the mining district and farther east the strata of Platteville, Decorah, and Galena age are dolomite, and the gross lithology of the three for— mations is somewhat similar. A marked difference, however, is the fact that the Galena maintains its characteristic honeycomb (wormy) weathered appear- ance, which the lower two formations do not share. This eastern area is the type for Sardeson’s Beloit formation, which name he (1896b, p. 360) suggested to replace “ ‘Trenton’ or Lower Trenton,” as the overlying Galena strata are more probably the “equiv- alent to the Trenton limestone of New York.” The Beloit was made up of the four divisions: “lower buff beds,” “lower blue beds,” “upper buff beds,” and “upper blue beds” (Chamberlin, 1877, p. 293, 295, 296). The Beloit was distinguished first on lithologic criteria, having “thinner, more compact strata” in STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT WESTERN PART South»centra| Grant County CENTRAL PART Western Lafayette County 263 EASTERN PART Eastern Lafayette County Formation Member C A D; L‘ b . A A . A A . , / I 5 ii A imestone, uff, chert A A Dolomite, buff; chert A A Dolomite, buff; chert 10 —' g g l 2 b N L , . ‘5 2 D Limestone, buff Dolomite, buff Dolomite, buff 0 4’ Z 07 P P — Limestone and shale, — ‘— Dolomite, grayish-buff; trace *- Dolomite, buff;trace E greenish-gray 7— of olive shale of olive shale .10’-- 5 ]_ a. 1’ Limestone, gray, dolomitic; — .g ##_ greenish-gray shale 20" 5 — Dolomite, light-brown: g I | l i trace of brown shale 9 II Limestone, tan; chocolate shale 7 “’ , l l ‘E Limestone, tan; some 30L g reddish-brown shale I (3 . Dolorfngte. buffh; trace 0 rown s I :1! IT; Shale and limestone, olive ‘ a e x—x‘x' S echt miss-l - ' __ # 40’4 gerrys Q: Shale, green, limestone lenses Dolomite, brown; trace of brown shale _ Quimbys X—"T’x‘ _ Dolomite, buff 2 . * — Dolomite and shale, brown _ m E Ml” l l_l| . g o ! — Limestone and shale, brown 3 $ Limestone, gray _ n. h _ _ 50/“ % Limestone, grayish-buff 2 EXPLANATION AAA AA Chart 9 P P P Prasopora D Phosphatic riodules X X X X x x x Bentonite Limestone Dolomite FIGURE 36.—Gencralized west-east cross section of the Decorah formation and adjacent strata. contrast with the overlying Galena’s “thick porous ones” (Sardeson, 1897a, p. 23). Sardeson felt that a faunal distinction also was needed, however, as the lithologic differences best recognizable in the “lead re- gion” are not quite satisfactory, because “local altera— tion of the rock has produced the typical Galena facies in the top of the Beloit formation.” The addition of faunal criteria made the Beloit formation the “zone of Orthis subaequata Con. (0. perveta Con., etc), and the Galena is the zone of Receptaculi'tes oweni H.” Sarde— son’s (1897a, p. 29) correlation placed the top of the Beloit at the top of the Fucoid bed (Ion) of Minnesota (fig. 37), which he had traced to the vicinity where the 389000—56—3 Beloit is exposed by the presence of fossils including Prasopom contigua Ulrich. This makes the Beloit equivalent to the Platteville and Decorah formations of the present classification, as noted first by Sardeson (1907, p. 187, 193). The lithologic unity of the Beloit formation is characteristic eastward from the mining district to the vicinity where the Beloit is exposed. The lithologic subdivisions of the Beloit are likewise most characteristic in that area. However, certain miscorrelations (especially of the lower blue beds) which Sardeson perpetuated (1896b, p. 362) causes one to avoid those subdivisions as strati- graphic units. 264 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Classification used . in this paper Minnesota Fo mat' M Winchell and Ulrich, Sardeson, 1897a; Hall and Sardeson, ' '°" embe’ 1897, p. Ixxxw 1907, p. 185 1892, fig. 5 Dubuque Maquoketa (Utica) Triplecz'a bed * Maquoketa (Utica) Stewartville Mao-lured. zone Maclurea. bed Maclurea g Lingulelasma bed Lingulasma % Fusisp'ira, (5 Camwrella bed Camarella Prosser Nematopo'm . Orthisina bed Orthisi'na Clttambom'tes Phylloporina Zygospi‘ra lon ‘ Ctenodonta Fuc0|d bed Fucoid E g Guttenberg Rhinidz'ctya bed Stictopora bed StictOPM' a D Spechts Ferry Stictoporella bed Stictoporella bed St'ietopo'rella QuimbysMiu 'illIHllllllllllllllllllTI HWTIITUIHHIHHUIHIIIllllllllIlIIIL . Blue, or % McGregor Vanuxemza bed Bellerophon bed Blue 1) g Pecatonica a Buff limestone Buff limestone Buff Glenwood * Sardeson (1897a) also referred to the Triplecia bed as the“Transition formation" and as the Maquoketa shales FIGURE 37.~Corre1ation of Platteville, Decorah, and Galena strata with units in Minnesota. [ Furthermore, in the area Where the Beloit is exposed it is difficult to distinguish the uppermost strata of the Beloit from the overlying Galena strata. Conversely, the Platteville and Galena formations are distinct in the area of their type localities in the mining district; the Decorah formation, though mainly shale in its type locality 80 miles northwest of the mining district, and mainly dolomite at the eastern edge of the mining dis— trict, nevertheless is traceable lithologically across these facies changes; therefore, the Decorah is a distinct unit in the mining district. IVIoreover, the terms Platteville and Decorah have been in use consistently since 1906, whereas the term Beloit has been virtually forgotten. The names Platteville and Decorah are therefore used in this paper. UNNAMEDI LIMESTONE MEMBER, DECORAH FORMATION Northwest of the mining district is a thin limestone unit that is similar in lithologic character to the under- lying McGregor there, but separated from that member by bentonite. It is typically exposed in the quarry at the north end of Ice Cave Bridge (called Halloran’s 1Although the writers originally intended to name this distinctive unit the Ice Cave Bridge member from an exposure in Decorah, Iowa, because of the greater thickness in Fillmore County, Minn. (30 miles to the northwest) M. P. Weiss is naming and defining the unit from exposures near Carimona in that county. quarry by Calvin, 1906, p. 85), in NEXNWZ sec. 15, T. 98 N., R. 8 W., in Decorah, Winneshiek County, Iowa (see section 6, p. 306), where it consists of 2% feet of limestone above half a foot of bentonitic shale and siltstone. Other exposures near Decorah that show this member well are the Coon Creek ravines in SW’% sec. 13, T. 98 N., R. 7 W., the Conners roadcut along the north line of sec. 13, and the readout along the south line of the SW% sec. 13, all about 8 miles east of the Ice Cave Bridge quarry. The thickness has di— minished to 2 feet at these localities, but otherwise the strata are similar to those at Ice Cave Bridge quarry. Twelve miles to the southeast, in a ravine 2 miles north of Forest Mills (fig. 35, loc. 35) these limestone strata are thinner and have changed somewhat in color to bluish gray (see section 7, p. 307 ). Similar lithology was observed in the type section of the Ion, 11 miles farther east, in NW% sec. 35, T. 96 N., R. 4 W. (loc. 36), except that the limestone bed is only 0.9 foot thick and the bentonite bed is overlain and underlain by dark brown shale. Near McGregor, 5—8 miles farther southeast, roadcuts, in the N 13% see. 9 and the NE% sec. 34, and the (type locality of the McGregor) NEM sec. 28, T. 95 N., R. 3 W. (100. 25) showed 0.4—0.7 foot of purplish limestone overlying 0.3—0.5 foot of bentonite and bentonitic siltstonc. STRATIGRAPHY 0F MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT The bentonite bed in the Spechts Ferry member in the McGregor—Ion area is 0.3—0.5 feet above the top of the limestone of the unnamed member, whereas in the Coon Creek to Conners area east of Decorah it is 0.8—1.3 feet above the limestone; at Decorah the bentonite layer is 2.5 feet above. East of the Mississippi River the relations of this unnamed member of the Decorah with the overlying Spechts Ferry in Grant County, Wis., are not com- pletely clear, as the tabulation below shows: Relations of unnamed member of Decorah formation in Grant County, Wis. Thickness between bentonite Exposures Lithologie character beds (feet) Units Total Readout, U. S. Highway 18 (loc. 37) 1... Shale, olive, and brown 0.5 0.5 limestone. Bloomington quarry (lee. 38) 1......____, Shale, olive _________________ 1. 6 1. 6 Mount Hope quarry (loo. 39) 1 __________ Shale, olive _________________ .2 1 0 Limestone, bufi ............. .8 ' Readout, U. S. Highway 18 (100. 40) 1... Limestone, bufi _____________ .6 .6 Readout, County Trunk A (lee. 41) 1__ Shale, olive _________________ .1 8 Limestone, buff to brown... . 7 ‘ Shriners Park quany, SEMSWM sec. Shale, olive _________________ .6 1 2 4,‘.’1 5N, R. 3W (midway between Limestone, bufi _____________ .6 ‘ lees. 41 and 28). Readout, County Trunk A (lee. 28) _____ Limestone, buff _____________ . 7 Limestone, pink ____________ .1 1 5 Shale, olive _________________ .2 ' Limestone, bufl _____________ . 5 L ilberty Ridge quarry, NWl isElé see. Shale, olive __________ . 1 , ’1‘. N. R .(1 mile south of Limestone, pink _____ ___, .8 1.2 1100. 15). Shale, olive __________________ .3 1 Locality numbers and section, township, and range are given on figure 35. At the Liberty Ridge quarry lenses of limestone similar in lithology to the Quimbys Mill are present in the basal part of the lower bentonite bed. Six miles east of this quarry (readout, County Trunk E, center E}é sec. 18, T. 5 N., R. 1 W.) 1.5 feet of typical lime- stone ef the Quimbys Mill member is overlain by 0.9 feet of pinkish limestone, which may possibly represent the eastern feathering out of the unnamed member, although the lower bentonite bed is absent. Moreover, 4 miles southeast of the Bloomington quarry in a road- cut along State Route 35 (SEX sec. 8, T. 4 N., R. 4 W.), Where the Quimbys Mill is absent, the McGregor is overlain in ascending sequence by a 0.1-feot mottled brown and green shale, a 0.1-foot olive shale, a 0.1-foot greenish limestone, a 0.3—foot olive shale, and that by the bentonite bed of the Spechts Ferry. As the ben— tonite bed at the base of the unnamed limestone mem— ber is elsewhere overlain by a mottled brown and green shale, the unnamed limestone and its basal bentonite 265 bed are considered to be absent at this readout south of Bloomington. The western edge of the Quimbys Mill is an approxi— mate north-south line about 5 miles west of the east line of Grant County, Wis. (fig. 35). Recegnizable beds of the unnamed limestone unit are seen as far east as the mouth of the Wisconsin River, which is 30 miles west of the Quimbys Mill pinchout. Between the mouth of the \Visconsin River and the central part of Grant County, there are beds of indeterminate assign— ment, although presently they are recognized as having some of the characteristics of the unnamed limestone member. Although these limestone beds at Decorah were excluded from the Decorah of Calvin, in their eastern occurrences (Grant County, Wis.) they are more characteristic of Decorah strata than of the underlying Platteville. Furthermore, the members of the Platte- ville formation thin to the west whereas those of the Decorah formation thin to the east. The unnamed limestone member, therefore, is here referred to the Decorah formation. This was apparently the assign— ment made by Stauffer (1925, p. 616—619) at an ex— posure in St. Paul, Minn, as he determined the top of the Platteville to be below 1.5 feet of brown dolemitic limestone, which was overlain by a thick bentonite bed that was succeeded above by 2 feet of gray to bluish limestone. These limestone beds, which Stauf- fer placed in the Decorah, rested on a corrosion surface, probably the same as the one that Sardeson (1898, pl. 9) recognized at the top of the Bellerophon bed (fig. 37). Ne systematic paleontologie study has been made of these strata (p. 289). Such a study should be valuable, as would similar studies through the Platteville, De— corah, and Galena sequence of the upper Mississippi Valley. Because the unnamed member is better ex— posed in Winneshiek County, Iowa, and Fillmore County, Minn, than in the mining district, further study of this member should be concentrated in that general area. SUBDIVISIONS OF GALENA DOLOBIITE Galena is the name applied by Hall (1851, p. 146) to the rocks exposed in the vicinity of the town of Galena, Ill. In the upper Mississippi Valley region the Galena has been divided into the following three members on the basis principally of paleontologie criteria: Dubuque (Sardeson, 1907, p. 193)—1imestone and shale, bounded below by the “cap rock” of the Stewartville; named from Dubuque, Iowa (fig. 35). Stewartville (Ulrich, 1911b, pl. 27)—tho Maclurea 266 zone (Winchell and Ulrich, 1897, p. lXXXiii~lxxxvii) of Minnesota; named from Stewartville, Fillmore County, Minn, 65 miles northwest of Wauken, Iowa. Presser (Ulrich, 1911a, p. 257)~The Fastspira (above), Nematopora and Otitambonites (below) beds of Minnesota (Winchell and Ulrich, 1897, p. lxxxiiie lxxxvii) ,' named from Prosser’s ravine, near Wykofl', Minn, 50 miles northwest of Waukon, Iowa. The Presser member was named by Ulrich (1911a, p. 257) as including the Olitambonites (Vellamo), Nematopora, and Fusispira beds (fig. 37) of the Min- nesota reports, apparently from the exposures in “Prosser’s ravine, near Wykoff,” (sec. 20?, T. 103 N., R. 12 W). The member was not adequately described in 1911, nor is the type section properly located. However, Winchell and Ulrich (1897, p. lXXXV-lXXXVii) had previously given a section at “Prosser’s ravine,” near Wykofi', Fillmore County, “which Ulrich undoubtedly intended as the type section” (Stauffer and Thiel, 194], p. 86). About 185 feet of limestone occurs at this locality, of which the lower 110 feet or so were assigned to the Presser. As described by Staufl'er and Thiel the beds are fairly thick, composed of hard compact drab limestone with a small amount of shale. Several zones are cherty. The name Stewartville was applied by Ulrich (1911b, pl. 27) to the “Maclurea zone” of the earlier Minnesota reports, apparently from exposures near the town of Stewartville, Minn. (sec. 34?, T. 105 N., R. 14 W.). In southeastern Minnesota, as elsewhere in the upper Mississippi Valley region, the Stewartville is a dolomite or dolomitic limestone. It was originally described as having a thickness averaging 50 feet. Stauffer and Thiel (1941, p. 87) described a section from the type region of the Presser member, in Presser Creek, 2% miles west of the town of Wykofl’ (15 miles southeast of Stewartville) as follows: Maquoketa Formation: Dubuque Member: Feet 18. Limestone, shaly, gray to buff, fossiliferous ______ 20. 0 Galena Formation: Stewartville Member: 17. Dolomite, cavernous, yellow to buff, fossiliferous. Common fossils include Maclurma mant- tobensts and Hormotoma major _______________ 16. Dolomite, very porous, yellow from weathering, in thin, knotty layers. Common fossils are Receptaculttes owem’, ZVIaclum'rLa cuneata, M. mam‘tobensis, Hormotoma major, Endoceras sp., I tlaenus americanus ________________________ 15. Dolomite, thick-bedded, gray to yellow. Com- mon fossils are Receptaculites owem’, Maclurina manitobensts, Hormotoma major, W'estonoceras mtnnesotense ______________________________ 16.0 10. 5 12. 3 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Galena Formation—Continued. Stewartville Member—Continued 14. Dolomite, gray to brown, weathering yellow. Common fossils are Reoeptaculites owem', Rafi— nesquma alternate, Maclurtna manttobensis, M. crassus, Hormotoma major, H. trentonensis, Illaenus amerz’canus, Isotelus gigas ____________ 14. 5 13. Shale, argillaceous, yellow to gray ______________ 1 0 Feet 54. 3 Presser Member: 12. Limestone, compact, drab, subcrystalline, with some thin, argillaceous layers ________________ 11. 0 11. Limestone, compact, hard, drab, thin—bedded, with numerous graptolites __________________ 1. 0 10. Limestone, compact, hard, drab, very fossilifer- ous. Common fossils include Rafinesquina del- tor’dea, Catazyga uphamz', Plectambomtes gib- bosus, Byssonychia tntermedz‘a__-,, ___________ 8. 0 9. Limestone, bluish, compact, partly crystalline, thin—bedded to shaly. Common fossils include Streptelasma corniculum and Rafinesquina deltoides __________________________________ 8. 0 8. Limestone, compact, drab, with some chert or flint. Fossiliferous ________________________ 13. 3 7. Limestone, compact, drab, with numerous fossils. Common forms are Ischadites iowensz’s, Hesper- orthis tricenaria, Plectambom’tes sericeus, Ra- finesqutna alternata, Vellamo diverse, Endeceras annulatum, Isetelus gigas ____________________ 19. 3 6. Limestone, thick—bedded, compact, drab, with some chert. Common fossils include Hesper— orthis tricenaria and Plectorthis plr'catella tren- tonensis __________________________________ 10. 3 5. Limestone, compact, drab, with shaly beds at the base, forming bottom of small caves and line of springs. Graptolites common _______________ 9. 2 4. Limestone, argillaceous, massive, but weathering into thin, knotty beds, blue to gray in color. Receptaculites owem‘ common ________________ 17. 8 3. Limestone, compact, drab, passing into argil- laceous beds. Receptaculites owem' and Plec- tambom'tes sericeus common _________________ 10. 3 2. Limestone, compact, light drab in color. Abund- ant fauna includes Dinorthts meedsi germane, Rafinesquma alternate, Rhynchotrema tncrebes- certs _____________________________________ 3. 2 1. Covered interval to level of Deer Creek at outlet of Presser Creek ___________________________ 5. 3 The strata above the Stewartville and underlying the Maquoketa were named Dubuque by Sardeson (1907, p. 193) from their outcrops at Dubuque, Iowa. Sardeson described the Dubuque as consisting of those “strata of irregular limestone and interlaminated carbonaceous shales” which lie above the “cap rock” of the Stewartville and below the “blue shales of the Maquoketa proper.” Kay (19350, p. 571) stated that this “cap rock” falls within the Stewartville both lithelegically and faunally, and as the “cap rock” occurs within bed 14 of the following section (Calvin, STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT Bain, 1900, p. 429), Kay redefined the Dubuque, restricting it to bed 15: Feet 15. Thin-bedded Galena limestone, earthy, non— crystalline, the layers ranging from ten or twelve inches near the base to less than three inches in thickness near the top; upper part of this member very shaly; carries as fossils Lingula iowensz’s, Liospim lenticularis, and Conularia trentonesisuu 30 14. \Vell dolomitized Galena in layers ranging from one to two and a half feet in thickness; with softer beds near the middle, which frequently disintegrate so as to form caverns; basal part only, of this member, represented above the Receptaculitcs beds at Eagle Point ________________________________ 30 Recent work by the writers (see also Flint and Brown, 1955), however, has lent support to a sub- division based upon the deseription by Calvin and Bain. Because the descriptions of the Prosser and Stewart— ville in their type areas (southeastern Minnesota) are incomplete, these names cannot be used precisely in stratigraphic work in the general upper Mississippi Valley region without further study of the stratigraphy and paleontology of the Galena in southeastern Minne— sota. Such a study should result in the validation of the names Presser and Stewartville and thus in their continued use, because they are well-established in the literature. This is preferable to renaming these strata from different, although perhaps more representative localities regionally, as Templeton and Willman (1952, p. 6 and fig. 3) have done. During the past few years W. C. Bell and his students have been examining the rocks of this area, and NI. P. Weiss’ report, The stratig— raphy and stratigraphic paleontology of the upper Middle Ordovician rocks of Fillmore County, Minn,2 contains descriptions of type sections and additional material that give precise stratigraphic meaning to the units described by Ulrich. In the zinc—lead. district the beds of the Galena are dolomite and are only sparsely fossiliferous; the fossils that are present in exposures are poorly preserved. Furthermore, where seen in the mines and in cuttings from prospect drill holes, local rock alteration and the pulverization by drilling have destroyed most of the fossils that survived the effects of regional dolomitiza— tion. As a result, during the current study it was necessary to subdivide the Galena on the basis of lithologic criteria. The units that can be recognized in exposures in the mining district are as follows, in descending order: I Unpublished Ph. D. thesis, Minn. Univ., Minneapolis. 1953. 267 Noncherty unit: Fifi/33m Dolomite and dolomitic limestone, yellowish-gray, finely granular, argillaceous, thin— to medium-bedded; thin partings of dolomitic yellowish—gray shale; lower contact gradational ________________________ Dolomite, yellowish-buff, coarsely granular to crystal- line, vuggy, medium— to thick-bedded; Receptaculites common 35—55 ft above base _____________________ Cherty unit: Zone A. Dolomite, buff to drab, otherwise as above; chert bands common in upper 44 ft and 50—56 ft below top; locally a thin bentonite about 32 ft below top; Receptaculites 35—40 ft below top and 10 ft 35~45 75—85 above base _____________________________________ 70 Zone B. Dolomite as above, except more brownish; chert bands rare; Receptaculites common ___________ 15 Zone 0. Dolomite as above; chert bands common____ 10 Zone D. Dolomite as" above, except with streaks of greenish argillaceous material; no chert ____________ 10 Total ________________________________________ 225 By definition the Prosser extends upward to the base of the upper Receptaculites zone, which has been called the base of the Stewartville member (fig. 38). However, it has been found extremely difficult to place this boundary with any degree of reliability, especially in subsurface work. The contact is normally not char— acterized by a marked and easily recognizable lithologic change. In fact, the delimitation of the Presser member in the mining district depends solely upon the finding of Receptaculites owem’ Hall, a difficult task in weathered or largely covered outcrops and in drill cuttings and cores. Furthermore, Receptaculites individuals have been found downward to within a few feet above the topmost chert, or about 25 feet lower than the normal position of the base of the upper Receptaculites zone. The highest appearance of the chert bands within the described Prosser affords a useful lithologic key horizon (see also VVillman and Reynolds, 1947, p. 10). In many places an observable color change in the dolomite occurs at the appearance of the chert bands. This change in lithology, striking in all outcrops and even more so in subsurface study, is found in southwestern VV'sconsin, northeastern Iowa, and northwestern Illi- nois. The highest chert horizon is readily recognized farther south and west in Iowa (Agnew, 1955) and farther south in Illinois. (Workman, L. E., and Herbert, Paul, Jr., formerly with the Illinois Geological Survey, oral communication, August 18, 1945.) The stratigraphic continuity of the cherty and noneherty units is well established, and the contact between them is so dependable as a key horizon that structure contour maps using it as a datum have been prepared during 268 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY ‘ Member and Local . ‘ Unaltered Formatlon subdivision terminology Description thickness, In feet y :::::_j Shale, blue or brown, dolomitic; with dolomite Maquo- shale __ _ a lenses; phosphatic depauperate fauna in 108240 keta 30;; lower few feet 1 3 g Dolomite, yellowish-buff, thin- to medium- 35- '2 bedded; with interbedded dolomitic shale 45 D _?_. 2 v E E t 3 Dolomite, yellowishbuff, thick-bedded, vuggy; 37— ; é‘ Receptaculites‘in lower part 47 120 2 2 / "’ 8 7 o Buff or 5“ Z sandy ‘ P / , / Dolomite as above; bentonite rarely at 38 midpoint 225 Galena A A A l 4 l A ‘4 “A Dolomite, drab to buff, thick- to thin‘ A bedded; cherty; bentonite at base 32 x. f\ A A O ' A A g A /A i 9: A Dolomite as above; Receptaculites at top 6 C 3 A 4 Dolomite as above; cherty 6 3 105 a A 5 A Dolomite as above; some chert; Receptaculites 26 at midpoint 4 Drab , . . A Dolomite as above; little chert; Receptaculztes 15 B abundant A / Dolomite as above; much chert 10 i C A A Dolomite as above; 10 i D Dolomite and limestone, light-gray, argillaceous; 11* , __ grayish-green, dolomitic shale 15 20 Gray __ Dolomite, limestone, and shale as above, 579 lon but darker Blue — Limestone, brown, fine-grained, thin- 2&— Decorah 1 1 bedded, nodular, conchoidal; dark-brown 1246 Guttenberg Oil rock #1er T shale l—_ Shale, green, fossiliferous; greenish-buff, SPBChtS Ferry Clay bed fine-grained limestone; phosphatic nodules oeg Quimbys Mill Glass rock _ _ near top, bentonite near base . I Dolomite and limestone, dark-brown, fine- ; Magnolia (0f Bays and l l grained,sugary, medium-bedded, conchoidal: 0—18 3 Raasch, 1935) I I dark-brown shale especially at base 5 Trenton I l 13 a o l Limestone and dolomite, li ht- ra , fine- rained 7 Plattevfl'e 2 Mifflin (of Bays, 1938) i i 1 I g g y g 18 3o 55_ Limestone, light-gray, fine-grained, thin- 12— 75 Pecatonica Quarry beds bedded, nodular, conchoidal 17 Dolomite, brown, medium-grained, sugary, 2044 Glenwood Shale th'CK-bedde‘i Shale, green, sandy 0~3 St- Peter Sand ’OCk Sandstone, quartz, medium- to coarsegrained 40 poorly cemented, crossbedded "* FIGURE 38.78tratigraphic column of Plattcvillc, Decorah, and Galena strata in zinc-lead district. STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT the past several years by members of the Iowa Geolog— ical Survey. West of the mining district the Stewartville and Dubuque members can generally be distinguished by lithologic features in the outcrop; however, in the mining district and to the east the differences are more subtle. Furthermore, in drill cuttings, which constitute a major source of information in the mining district, the separation of the Dubuque and Stewartville is generally difficult. ORIGIN AND APPLICATION OF THE NAMES The origin of most of the stratigraphic terms em— ployed in this report is discussed by VVilmarth (1938); names that have been applied since 1938 or older names that for various reasons merit additional treatment are discussed in the paragraphs that follow. MADISON SANDSTONE The term Madison (Howell, 1944; Raasch, 1935) is not used in the present report, as the writers believe that it is not consistently recognizable in the zinc—lead district. PECATONICA DOLOMITE MEMBER Hershey (1894, p. 175) named the Peeatonica from exposures in the Pecatonica River valley “near the Wisconsin line, and northward,” in southwestern Green County (fig. 35). As originally defined the Pecatonica included the sandy and shaly “insensible gradations” (beds of Glenwood age) downward into the St. Peter sandstone. Although Hershey (1897, p. 67) intended the name to be applied chiefly to the Elk Horn Creek area (fig. 31,), and although Sardeson (1897c, p. 333) and Bays and Raasch (1935, p. 297) objected to its use, the name Pecatonica as restricted by Kay (1935a, p. 286) to exclude the “insensible gradations” at its base has received wide adoption, even by Bays (1938). This unit was called the “Lower Buff” by early writers because of its color when weathered. MCGREGOR LIMESTONE DIEMBER The McGregor limestone member was named by Kay (1935a, p. 286) from beds exposed in a ravine a mile west of McGregor, Clayton Count-y, Iowa (fig. 35, loc. 25). The name was applied to the “limestone succeeding the Peeatonica member of the Platteville formation, and underlying the Spechts Ferry member.” This is unit 3 of Bain’s (1905) type section of the Platte- ville, as described on page 261. The McGregor was divided by Bays and Raasch (1935, p. 298) into the McGregor. sensu stricto, below and the Magnolia above. Later Bays (1938) renamed the lower beds Miffiin from their exposure in “the road- cuts and stream banks of the Pecatonica River, at 269 Mifflin, Iowa County, Wis.” in the NE}; sec. 34, T. 5 N., R. 1 E. (1 mile northeast of loc. 18, fig. 35). The Miffiin (of Bays, 1938) is characterized by thinly bedded nodular limestone that weathers light gray, and is 17 )5 feet thick at Miffiin, Wis. The type exposure of the lVIagnolia (of Bays and Raaseh, 1935) is “on and near Highways 13 and 14,” 1 mile south of the town of Magnolia, Wis., in the NWM sec. 26, T. 3 N., R. 10 E, Rock County (loc. 26). In the type outcrops the Magnolia is reported (Bays and Raasch, 1935, p. 298) to consist of 39 feet of light— buff, moderately thick bedded dolomite, with conspicu— ous fucoidal markings on the bedding planes in the upper part of the member. The type section consists of several roadcuts and a quarry as much as a quarter of a mile apart, each exposing only a small part of the Magnolia (of Bays and Raasch, 1935); thus a measurement of thickness can be only an estimate. Other disadvantages of this selection are the lack of a complete exposure of the typical lithology, and the lack of exposure of the stratigraphic relations with the Mifflin (of Bays, 1938) beds .below. N 0 acceptable section in the vicinity of Magnolia, Wis, could be found during the course of the present study. QUIMBYS MILL MEMBER Agnew and Heyl (1946, p. 1585) named the Quimbys Mill member from its exposure in the quarry at Quim— by’s Mill, 5 miles west of Shullsburg, Wis. (fig. 35, 100. 27), including all the beds between the top of the McGregor (Trenton) and the base of the Spechts Ferry (clay bed) there. The Quimbys Mill strata are the “glass rock” of the miners. Kay (1928) included the “glass rock” beds in his description of the type section of the Spechts Ferry which more or less agreed with Shaw and Trowbridge (1916, p. 4). Later Kay (1929, p. 644) described this assignment as possible, but shortly thereafter he (1931, p. 370) felt it desirable to omit these beds from the Spechts Ferry classification. He retained this point of View in later publications (1935a, p. 287) but at no time defined the exact position and nature of the “glass rock” (fig. 39). Bays and Raasch (1935, p. 298) apparently included the “glass rock” beds in the Spechts Ferry but without describing them._ These authors appear to have re- ferred to the “glass rock” as a lithologic facies, for they stated: The Speehts Ferry varies from one district to another. be a soft calcareous shale, a limestone, or a dolomite. Bays (1938) stated that it “passes laterally from shales to limestones to dolomites to cherty dolomites.” The latter two are facies of the “glass rock” or Quimbys Mill member, as recognized in this report. It may SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 270 .82 ooEmnmozz.’ Efimflmmfia .95: 2: .8 ogondomwwfizmw 9E £3539 .oEESEAH .o m:c_§oc_mmflc[.am ”2:55 vogu 35.3w. 5 BEBE»... .oz * .352: 0.2.- vooicoa .unEuE 0°02,sz .0959: 3035.6 59.3... 3.53. m H d a I . .4 .0952: 3:333“. d u .0 Eu... 3:5 qua H .Ia M e 8.5838 M W * m a . u n. W accumuE: W m w w m m m 2.38%: m m w l H J H. H * H 9.0 m a . 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H 2.2me W J o z 2 a D S 0 H u u m 2.0 m m m m w m m _ m. m a .anwE w 5:252 d M 53258 d u. a m. 2.35266 w. u 2.25% w 2:2.266 m m. .0 FE... * * .0 m:fl:n=o :ozmfiaw was—5:0 coszE. vac—5:0 >mgl_<> >m.§(> _&_mw_mm_s_ 3%: 25208.3 am 252823 26 Enamawi Ema: z_mzoom;> 3w w_oz_.:_ .sz <30. mz <39 m: SHAWN. mg m mmm. mmm. mmm: 82 .08, $2 wom. 0 an“: m 50 >(v_ mmh<>>h< DZ( ><¥ ><¥ >(v. . >._(O STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT STRATIGRAPHY OF THE MINING DISTRICT PRE-PLATTEVILLE ROCKS Because this report deals primarily with rocks re— lated to the ore deposits, pre—Platteville strata will be discussed only cursorily. Furthermore, as a detailed investigation of pre-Platteville strata was not at— tempted, information regarding those rocks is taken partly from the work of others, from rather brief studies of outcrops by the writers, and from recent drilling data. PRE-CAMBRIAN ROCKS Pro-Cambrian rocks were reported (Thwaites, 1923, p. 553) in a well at Platteville, “Us. (City well 2, sec. 15, T. 3 N., R. 1 W.), where the drill penetrated “gran- ite” at a depth of 1,714 feet (fig. 35). Wells at the north margin of the district, in Richland Center, Wis. (sec. 1.6, T. 10 N., R. 1 E.), reached similar pre-Cam— brian material at depths ranging from 665 to 678 feet, and the Borden Whey Plant well 2 at Boscobel, Grant County, “Wis, reportedly struck “granite” at 837 feet (100. 1). Information for these wells is in the files of Wisconsin Geological and Natural History Survey, Madison, Wis. Pre-Cambrian rocks in the subsurface of this general area have been discussed by Thwaites (1931) and Gro— gan (1949). In the Baraboo area just northeast of the zine—lead district, and in northern Wisconsin the pre- Cambrian rocks are separated from the overlying Cam— brian sedimentary rocks by an unconformity of con- siderable relief. CAMBRIAN ROCKS The oldest Paleozoic rocks known in the upper Mis- sissippi Valley (fig. 32) are sandstone, siltstone, and dolomite of Late Cambrian age (Twenhofel, Raasch, Thwaites, 1935; Trowbridge, Atwater, 1934). These rocks are exposed only along the northern edge of the zinc-lead district, and farther south they are found in deep wells drilled for water and as oil tests. An ex- cellent exposure of much of the upper 150 feet of Cam— brian is seen in the bluff at the intersection of State Routes 60 and 61 in Crawford County, 2 miles north of Boscobel, \Vis. (fig. 35, 100. 2). The thickness of the Cambrian increases southward from about 1,000 feet at the north fringe of the district (locs. 1, 2) to 1,284 feet at Platteville. The Mount Simon sandstone, which rests uncon— formably upon the pre-Cambrian rocks, ranges from 440 to 780 feet in thickness in the mining district. It is generally light gray, but locally reddish. In the mining district few wells have intersected this sequence; however, Templeton (1950) has shown that near Rock- 389000—56 4 27] ford, 111., (fig. 31) and to the south, different lithofacies are characteristic of the formation. The Eau Claire shale overlies the Mount Simon sand- stone conformably. In the mining district the Eau Claire is mainly sandstone, and its relations with the underlying and overlying strata are gradational. It ranges from 70 to 330 feet in thickness. The Dresbach sandstone is light gray, and is 60—140 feet thick. The Mount Simon, Eau Claire, and Dres- bach together aggregate 700—1,050 feet in thickness in the mining district. Part of this variation is due to the unconformity at the base of the Mount Simon; part to a southward increase in the thickness of the Mount Simon; and part is due to the gradational lithologic relationships of the three formations. Above the Dresbach is the F ranconia sandstone, 110—140 feet thick. The glauconitc in the Franconia is the principal feature by which these strata can be distinguished from the similar overlying and under- lying sandstone. Recently Berg (1953, 1954) has published the results of a thorough study of the facies of the Franconia; because the Cambrian strata are dis— cussed only briefly in this report, however, no attempt was made by the writers to apply these subdivisions of the Franconia to the rocks in and bordering the mining district. The Trempealeau formation, which overlies the Franconia, is principally sandstone and siltstone al— though commonly the lower strata are dolomite. The uppermost beds of the Trempealeau are called the Jordan sandstone, which is composed of clean well— sortcd coarse quartz grains that are subangular to round. The Trempealeau formation is 120—150 feet thick. Locally within the mining district and along its margins a sandstone unit called the Madison or Sunset Point (Raasch, 1951, p. 150) is said to overlie the Jordan sandstone of the Trempealeau formation. Raasch re— gards the Madison as a separate formation, basing this opinion primarily upon sedimentary and lithologic criteria, which Twenhofel and Thwaites (Twenhofel, Raasch, Thwaites, 1935, p. 1711, footnote 45) consider as having little weight. Raasch states that the Madison is poorly sorted silty or conglomeratic quartz sandstone, as much as 60 feet thick. It is not consistently recog- nized in the mining district. In most places beds transitional in lithology fill the interval between the Jordan sandstone and the over- lying dolomite of the Prairie du Chien group (Schuldt, 1943, p. 404). These transition beds consist of alter— nating dolomitic sandstones and arenaceous dolomites and are as much as 27 feet thick. In areas where the transition beds are lacking the contact of the Jordan and the Prairie de Chien appears conformable. 272 Lead minerals have been found in Cambrian rocks near Lansing, in northeastern Allamakee County, Iowa, sec. 10, T. 99 N., R. 4 W., and 35 miles to the north, at Dresbach, in southeastern Winona County, Minn, sec. 18, T. 105 N., R. 4 W.,' both localities are marginal to the mining district (fig. 35). The galena at the Lansing occurrence is in the uppermost beds of the Cambrian, probably the dolomitic transition beds, whereas in the Minnesota locality the minerals were found in a shale 350—400 feet below the top of the Cam- brian, probably in the Eau Claire sandstone. Zinc minerals were seen (Heyl, Lyons, and Agnew, 1951, p. 9) in cuttings from a prospect hole near Mont— fort, in west—central Iowa County, Wis, sec. 30, T. 6 N., R. 1 E. (one mile south of loc. 43, fig. 35), from 149 to 159 feet below the top of the Cambrian in glau- conitic sandstone called Franconia. Evidences of iron mineralization in Cambrian strata are abundant, especially just north of the zinc-lead district. Iron sulfide estimated at 145 percent iron was found in the prospect hole at Montfort, from 141 to 179 feet below the top of the Cambrian, in the Franconia. Water supplies ample for large industrial plants and municipalities are obtained from the Cambrian strata, especially from the Mount Simon and Dresbach. O RDOVICIAN ROCKS PRAIRIE DU CHIEN GROUP The Prairie du Chien strata, which are commonly known in the upper Mississippi Valley by the old name of Lower Magnesian limestone, are seen above the Cambrian strata along the north fringe of the mining district and crop out in the more dissected areas in the central part of the district. Perhaps the most nearly complete exposure is in the quarry at the north edge of Wyalusing, Grant County, Wis. (fig. 35, ice. 3). Rocks of the Prairie du Chien group are extremely var— iable in lithology. In places the group is divisible into three formations—the Oneota dolomite, which overlies the Cambrian, the New Richmond sandstone, and the Shakopee dolomite; the name Root Valley has been applied to a sandstone at the New Richmond position (Stauffer and Thiel, 1941, p. 59) and the name Willow River is used by many in place of Shakopee (Powers, 1935, p. 390). In other places, however, no recogniz- able sandstone unit is found; no threefold division could therefore be made. Furthermore, rocks that occupy the interval represented by the Prairie du Chien in places are sandstone, red shale, green shale, silicified limestone, and limestone. These strata have been assigned to the basal part of the St. Peter sandstone (Heyl, Lyons, Agnew, 1951, p. 5). Recent detailed SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY study by Flint 3 ,on the other hand, has caused him to place them in the Prairie du Chien. The dolomite of the Prairie du Chien group is light buff to light gray, finely to medium crystalline, in part vuggy, and thin to thick bedded, or irregularly bedded or massive. The dolomite is commonly oolitic, sandy with clear rounded quartz grains, and cherty. Locally, especially where evidences of iron—zinc—lead minerali- zation are abundant, the dolomite has been silieified. Thin green glauconitic shale lentils are found along bedding planes and in the dolomite. Mound—shaped Cryptozoon colonies are common at certain horizons. The sandstone is similar to that in the Cambrian below, and commonly contains stringers and beds of greenish glauconitic shale. The sandstone in most places has dolomitic cement. Because of the variation in lithology the bedding is irregular, and generally poor (fig. 40). FIGI'RE 40.AExposure of typical dolomite of Prairie du Chien group in quarry in NEMN‘WMNWM sec. 32, T. 7 N., R. 1 E., Iowa County, Wis. (4 miles north of 10c. 43, fig. 35). In local outcrops of the lower 40 feet of the Prairie du Chien, that rock can be zoned by lithology into several units, as Starke 4 has shown in the area north of the mining district; to these units Raasch (1952) has applied names in the Stoddard quadrangle (50 miles northwest of Platteville, VVis.), and Raasch has like— wise given names to the succeeding 10—40 feet of strata in the Stoddard area. Because of the brief discussion of the Prairie du Chien in the present report, and be- cause the correlative value of Starke’s and Raasch’s units and the value of Raasch’s names have not been established in the mining district, the names and sub- divisions are not used by the writers. The Prairie du Chien attains a maximum thickness of about 240 feet in the zinc-lead district; it and the 3Flint, A. E., 1053, Stratigraphic relations of the St. Peter sandstone and the Shakopee dolomite in southwestern Wisconsin: unpublished Ph, D. thesis, Chicago DIRISVt'arke, G. W., 1949, Persistent lithologic horizons of the Praiiie llll Chien formation from the type section eastward to the crest of the Wisconsin arch: unpub- lished M. S. thesis, Wis. Univ., Madison. STRATIGRAPI—IY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT overlying St. Peter sandstone, from which it is sepa— rated by an uneonformity, aggregate 280—320 feet. Prairie du Chien strata have been correlated with the Canadian series of Missouri (Ulrich, Foerste, and Bridge, 1930; Twenhofel, and others, 1954). The Prairie du Chien strata constitute one of the po— tential mining zones in the zine-lead district. Although this potential has not been properly evaluated as yet, evidence of former mining of lead in these beds and recent testing by the U. S. Geological Survey, 1949— 1951 (Heyl, Lyons, Agnew, 1951; Agnew, Flint, Alling— ham, 1953, p. 7—11) show that, with favorable eco— nomic conditions, these strata might possibly become a lower producing zone and thus prolong the industry in the district. Lead mining in the Prairie du Chien has been restricted to areas of its exposure along the northern fringe of the district. The drilling by the U. S. Geological Survey confirmed the presence of lead and iron minerals in these beds as far south as Mineral Point, Wis., and the Crow Branch diggings, in Grant County, Wis., (fig. 35, Ice. 4). Although zine minerals have been found in these beds, the only locality known to contain any great abundance is that 10 miles north of VVaukon, Iowa (sec. 13, T. 99 N., R. 6 W.), where both zinc and lead were mined. The permeability of the Prairie du Chien is such that it is a source of an adequate supply of water for farm use, especially where the overlying St. Peter sandstone is exposed and dry. Where the St. Peter sandstone is water bearing, commonly the Prairie du Chien is not a good source of water. Locally, the dolomites of the Prairie du Chien are permeable enough to be a reservoir rock and during drilling operations are able to absorb water rather than contribute it. ST. PETER SANDSTONE The St. Peter sandstone is exposed along the VVis— eonsin River and its tributaries, along the Mississippi River southward alomost to Dubuque, Iowa (fig. 35), and in areas of deep dissection within the zinc-lead district. Good exposures are seen along U. S. Highway 151 a few miles southwest of Platteville, Wis. (locs. 5 and 6). The St. Peter consists of clear, fine to coarse, sub— angular to round quartz grains, as a rule poorly ce— mented; where the rock is indurated the cement is dolomitie, calcareous, or siliceous. Greenish argilla- eeous material is present in the upper few feet of the unit and near its base, particularly where the sandstone is abnormally thick; otherwise, it is relatively clean. The sandstone is thin—bedded to massive; crossbedding is characteristic (fig. 41). In many places, a variety of colors, brown and red being the most common, in 273 FlGURE 41.—Cross-bedded St. Peter sandstone in roadeut along State Route 39, near center of NWl/l sec. 1, T. 4 N., R. 5 E., Iowa County, Wis. (2 miles west of loe. 44, fig. 35). the St. Peter is due to oxidation of iron sulfide in the cement. The St. Peter is normally 40 feet thick. However, sandstone of this type has been found (fig. 35, loo. 7) at least 320 feet below the top of the formation (Heyl, Lyons, and Agnew, 1951, p. 33). Where green and reddish shales are present with the sandstone this association of sediments also is known to be more than 300 feet thick and to rest on strata as old as the Fran— conia, shown in the following wells (also see p. 272): Abnormal thicknesses of the St. Peter sandstone [Data in files of Wisconsin Geological and Natural History Survey, Madison, Wis; illinolis Geological Survey, Urbana, 111.; and Iowa Geological Survey, Iowa City, owa Thick- Wells ness, St. Underlying strata Peter (feet) Dodgeville city well 3, sec. 28, T. 6 N., R 3 E., central 315 Trempealcau. Iowa County, Wis. Linden city well 2, see 8, T. 5 N., R. 2 E., 10 miles 385 Franconia. west of Dodgevillc, Wis. Belmont eity well, see. 14, T. 3 N., R. 1 E., north- 303 ?* western Lafayette County, Wis. Shullsburg city Well 3, see. 10, T. 1 N., R. 2 E., La» 397 ?* fayette County, Wis. (fig. 35). Hanover city well, see. 9, T. 26 N., R. 2 13., Southwest 340 Prairie du Chien. corner Jo Daviess County, Ill. Bellevu)e city well, Jackson County, Iowa (fig. 35, 345 Do. 0c. 8 . *Not reached. At least part of this difference in thickness is due to an unconformity at the base of the St. Peter, which is well shown in a quarry in Clayton County, Iowa (sec. 1, T. 93 N., R. 3 W.), directly across the Mississippi River from locality 3 in Grant County, Wis. (fig. 35). Nearly everywhere the St. Peter is unfossiliferous. However, Sardeson (1896a, p. 79) found fossils in the formation in Minnesota and Wisconsin that showed greater similarity with the overlying Platteville than with the underlying Prairie du Chien. Because of its position, he (1896a, p. 83) correlated the St. Peter with the Chazy (see also Twenhofel, and others, 1954). 274 Lead and zinc minerals are almost unknown in St. Peter rocks. Small amounts have been found where mineralized fractures connect with zones of mineraliza— tion in higher beds, as at )Iineral Point, Wis., and at Crow Branch, Grant County, Wis. (fig. 35, 10c. 4). Iron minerals are characteristic of the St. Peter espe— cially in the uppermost few feet, where pyrite cements the quartz sand grains. This evidence of iron mineral- ization appears to be more abundant in local areas that show zinc—lead deposits in overlying beds, and in larger areas where the iron minerals appear to be related to major structural features as at Red Rock, Wis. (sec. 17, 'l‘. 2 N., R. 4 E.) 10 miles northeast of Shullsburg, Lafayette County (fig. 35). In most places the St. Peter sandstone provides an ample supply of water for small towns, for small industrial plants, and for farms. PLATTEVILLE FORMATION GENERAL FEATURES Platteville strata are known throughout the mining district by exposures at the surface and in mines, and by cuttings from wells and prospect drill holes. Expo— sures are numerous; some of the best outcrops of the beds of Platteville age can be seen in the quarry at Spechts Ferry station, Dubuque County, Iowa (fig. 35, loe. 10); along U. S. Highway 151 southwest of Platte— ville, Wis. (Ice. 6); along U. S. Highway 61 southwest of Platteville (100. 12) ; and in the city quarry at Darling- ton, Wis. (10c. 13). In the mining district the Platteville formation con- sists of the following four members in descending order (fig. 38): Quimbys Mill member, McGregor limestone member, Pecatonica dolomite member, and Glenwood shale member. The Platteville formation ranges in thickness from 55 FIGURE 42,—Pecatoniea (Opp) and McGregor (0pm) members of Platteville forma- tion in roadcut, U. S. Highway 151, 8 miles southwest of Platteville, Grant County, Wis. (fig. 35, 100. 6). SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY feet, in the western part (Heyl, Lyons, Theiler, 1952) of the district, to 75 feet near Shullsburg. It apparently lies conformably on the St. Peter sandstone within the mining district, and is overlain disconformably by the Decorah. There is an excellent exposure of the lower three members of the Platteville in the western part of the mining district about 8 miles southwest of Platteville, Wis. (fig. 35,100. 6). This section, hereafter designated the reference for the Platteville formation, appears as follows (see fig. 42): Roadcut, U. S. Highway 151, NWMNEfl sec. 12, T. 2 N., R. 2 IV, Grant Comm, W'is. [Described by A. F. Agnew and A. V. Hey], Jr., Apr. 1, 1943; revised by Agnew, Oct. 4, 1945] Thickness Decorah formation: (feet) Spechts Ferry shale member (clay bed), in part slumped: Shale, bluish—green ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 0. 5 Bentonite, white; weathering orange brown _______ . 2 Shale, yellowish—green above to bluish-green belows _ 2 Shale, brown and olive, soft ______________________ 1 Platteville formation: Quimbys Mill member (”glass rock”): Limestone, dark-purple, fine-grained, dense, con- choidal fracture; very wavy upper surface, thin, dark-brown to black, fossiliferous platy shale parting at base ___________________________ . 3— . 5 McGregor limestone member (Magnolia of Bays and Raasch, 1935): Limestone, light-gray, very fine grained, very dense, conchoidal fracture like “glass rock” above, fairly massive, very fossiliferous, wavy upper surface“ Limestone as next above but less dense, medium bedded above to thin bedded below, fossiliferous,- wavy upper surface __________________________ . 7 Dolomite, light-olive-drab, fine-grained, “sugary,” argillaceous, very thin bedded; nodular ________ Dolomite as next above but thick-bedded; calcite near middle _________________________________ Limestone, thin—bedded yet stands massively as one unit,- light-greenish—gray—brown, Weathering brown, with a few argillaceous streaks,- sparingly fossiliferous, but with fossils and fucoids on top Surface _____________________________________ Limestone, thin-bedded as next above but the beds are distinct; nodular beds and shalypartings; argil— laceoes in upper 0.3 ft, which is very fossiliferous- Limestone, light-buffish-gray, in medium to thick beds; in places gradational into unit next below, 0.9 2.6 3.4 3.6 Total, upper MeGregor _____________________ 15. 8 McGregor limestone member (Miiflin of Bays, 1938): Limestone, light—greenish- to bluish-gray, in massive beds but composed of thin beds which are not separated; ample shaly material in wavy bands; fairly fossiliferous, argillaceous; a peculiar mot- tled light-gray and darker gray 0.1-ft zone, 1 ft below top __________________________________ 3. 9 STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT Thickness Plattevillc formation—Continued (feet) MCGregor limestone member (Mifflin of Bays)—Con. Limestone, light. m . . d 5 1‘ V; Flint-bearing De -: g g limestone E 0 a: E 8 6'? C L 93 : Drab B < C 4. D ? Lower G ra > bed \ 60 Gray 5 y 0‘6‘6 .c o A 4 00 Blue 2 “ Blue 0: ‘ 0 Decorah L c o 83 g gig Oil rock 3 Guttenberg D. L Blue 3 13 E m L Clay bed Spechts Ferry fossiliferoLfs = W limestone g g g Glass rock Quimbys Mill '0 _ .. Blue g g m ,,, L Magnolia (of limestone m w (‘3 o Bays and Raasch, 1935) E __ -—4 _ DD = E (5 Trenton 9 9-, _ w ._ = o Mifflin PlatteVIlle 5 E g: g (of Bays, 1938) N Buff n. Buff Lower limestone Quarry beds Pecatonica limestone bed ’ Glenwood “ Saccharoid U St P t sandstone pper ‘ e 6’5 Sand rock St‘ Peter Sandstone s/andstone sandstone St' Peter FIGURE 45.—Stratigraphic terminology of early geologists compared with that used by miners and drillers and with the classification used in this paper. STRATIGRAPHY OF MIDDLE 0RDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT bed is not a sedimentary conglomerate; it might be due to secondary dolomitization along a favorable horizon, or might be the corrosion zone noted by Sardeson (1898, p. 318 and pl. 9) at the top of his Buff limestone in the St. Paul—Minneapolis area. The lithologic distinction between the brownish argillaceous dolomite beds of the Pecatonica and the light-gray dense fossiliferous generally calcareous beds of the Miffiin (of Bays 1938) in the mining district is somewhat offset by the similarity in thickness of bedding in the upper part of the Pecatonica (p. 278; fig. 42). The Mifflin (of Bays 1938) of localusage contains a fauna rich in gastropods; in the limestone facies bryozoa and microfossils are particularly abundant, but, except for ostracodes, are nearly always absent in the dolomitic facies. In the lower part of the lVIagnolia (of Bays and Raasch 1935) the surfaces of the beds bear great numbers of the ostracode (Leperditia sp. aff. L. fabulites Conrad and large specimens of Lambeophyllum pro- fundum (Conrad). An abundant molluscan fauna, remarkably similar to that in the Pecatonica, has been obtained from the Beloit region. Bays and Raasch (1935, p. 298) stated that in western Wisconsin the Magnolia is thinner and less conspicuous, and that in the “Lead Region it tends to be more limey and more thinly bedded than in the type area.” Referring to the typical Platteville section (p. 274), the limestone and dolomite of the Magnolia (of Bays and Raasch 1935) are typically light to medium gray, slightly mottled with dark-gray markings, fine to medium grained, and contain some soft dove—gray to olive—brown shale. The strata are thin or of medium thickness, and in the lower part look not unlike the Mifliin (of Bays 1938). In many places the upper 1—2 feet are very fine grained, very dense, light-gray fossiliferous limestone that breaks with a conchoidal fracture and is difficult to distinguish from the “glass rock” beds above, the difference in color being the principal distinctive feature, as the “glass rock” beds are purplish brown on a freshly fractured surface. Further stratigraphic study of this part of the Platte- ville formation to the east and southeast may show these “glassy” McGregor strata to be a distinctly recognizable lithologic unit. Chert is present about 12 feet below the top of the Magnolia (of Bays and Raasch 1935) in the Calumet and Hecla mines in sec. 22, T. 1 N., R. 2 E., 2 miles south of Shullsburg, Wis. (fig. 35), and in exposures to the cast. Bays has recorded two localities in the mining district in which limestone conglomerate occurs at the base of the Magnolia (of Bays and Raasch 1935), one 281 of these being in the small quarry south of the city quarry at Mineral Point. Nowhere was any such conglomerate observed during the studies here re- ported, all observations in the mining district pointing rather to a gradational and obscure contact between the .Mifflin (of Bays 1938) and the Magnolia (of Bays and Raasch 1935). According to Bays (p. 278) the heavy minerals of the Magnolia in order of decreasing abundance are garnet, tourmaline, and zircon. Dake (p. 278) found less insoluble material in the eastern facies of the Magnolia (of Bays and Raasch 1935) than in the Pecatonica. The lower part of the Magnolia has more residue than does the upper; the residue is principally quartz and feldspar. The fauna of the Magnolia has not been adequately described. These strata are far less fossiliferous in the mining district than are those of the h/Iifl'lin (of Bays and Raasch, 1935). It has been noted that the Magnolia is only poorly exposed in the type locality at Magnolia. However, where seen in and near the mining district, the thin dense nodular limestones of the Mifflin (of Bays 1938) are very distinctive, as are the thicker bedded less dense dolomite and limestone strata termed the Magnolia by Bays. But, commonly no definite lithologic break is present between the two units, and the beds just above or below the contact are transitional through a zone of 2—3 feet. Moreover, two adjacent outcrops may show the contact at somewhat diflerent stratigraphic horizons. A These Views regarding the transitional nature of the rocks are supported by the fact that in the mining district the combined thickness of the two sets of beds rarely departs appreciably from the average of 28-31 feet, yet the two lithologic types commonly show complementary thickness variations within these limits. The following table illustrates this relationship: Thickness of [VHfllm (of Bags, 1938), Magnolia (of Bags and Raasch,1935), and IVIcG’regor [Localities shown on fig 35] Thickness, in feet Location of outcrop Magnolia Mifliin (of Bays (of Bays and Total 1938) Raasch 1935) Roadcut Grant County, Wis. (10c. 28) ______________ 19. 5 9 28. 5 Ravine, west side valley, in SE MNEV; sec. 25, T. 3 N., R. 3 W., Grant County, Wis. (3 miles north of 100. 12) ___________________________________________ 16. 5 11 27. 5 Quarry, Spechts Ferry station Dubuque County, Iowa (100. 10) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 15. 7 13. 3 29.0 Roadeuts, U. S. Highway 61, Grant County, Wis. (100. 12) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 15 14. 5 29. 5 Readout, U. S. Highway 151, Grant County, Wis. (loo. 6) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 19 ‘ 12 31. 0 Ciatly quarry, Mineral Point, in SE51; SE14 SE14 see. i T. 5 N. R. 3 E., Iowa County, Wis ___________ ‘ 18 ' 12 30.0 ngrry, Darlington, Lafayette County, “ is. (100. 1 13 15 28 0 282 Thus it would appear that, although both the lVIifliin and Magnolia have distinctive lithologic characteristics, the boundary between them is somewhat arbitrary. The retention in the mining district of the member term McGregor with the two facies, rather than substituting two member terms is therefore preferable for the beds above the Pecatonica member and below the Quimbys lVIill member of the Platteville formation. DISTRIBUTION The beds of the McGregor are not so well exposed as the Pecatonica because of the thin-bedded character, but form bluffs where overlying and underlying strata are present. Quarries supplement outcrops along streams. Representative exposures are at the localities given on page 281. FAUNA AND CORRELATION The Mifflin and Magnolia faunas of the McGregor limestone member are clearly of Black River age, but there is disagreement among authors as to the precise position within the Black River. Kay (1935a, p. 288) stated that the McGregor (and the Spechts Ferry above) is equivalent to the Chaumont (upper Black River), whereas Bays and Raasch (1935, p. 300) im- plied that the McGregor should be placed in the Low— ville (middle Black River). Bays (p. 278) later went even farther, in correlating his Mifflin with the upper Pamelia (lower Black River) and asserting that the Magnolia transgresscs the Pamelia—Lowville time line (fig. 44). In the lVIissouri section a part of the Plattin is the equivalent of the McGregor (Twenhofel, and others, 1954). As for the Tennessee-Kentucky se- quence, according to Bays the nearest equivalent of the Mifflin is found in the Stones River there. The Mc- Grcgor also includes the Vanmcemia bed of Minnesota (fig. 37) as used by Winchell and Ulrich (1897). ECONOMIC PRODUCTS McGregor strata constitute a potential zinc—lead mining zone. Zinc—lead ore has recently (1948—1952) been found in these beds south of Shullsburg, Wis, and south of Galena, Ill. Within 2 miles northwest of Shulls— burg these beds have been mined for zinc and lead at the old Mulcahy and the Lucky Hit mines (Agnew, Flint, Crumpton, 1954). Isolated occurrences of zinc-lead ore have been found at other places—Etna mine, a mile north of locality 27, figure 47 (Agnew, Flint, Crumpton, 1954) and Last Chance mine, 2 miles south of locality 4, (Lincoln, 1947). The ore-bearing potential of the McGregor member appears to be better in the eastern and central parts of the district than in the western part. In mineralized areas beds of the McGregor have been leached to a grayish clayey mass, With an accom- panying reduction in thickness. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY QUIMBYS MILL MEMBER At its type locality (fig. 46) the Quimbys Mill member consists of 6 feet of dolomite above 6 feet of limestone, as follows: Quarry, Ouimby’s mill, southeast corner, sec. 11, T. 1 N., R. 1 E, Lafayette County, lVis. [Described by A. F. Agnew, August 25, 1944; revised November 20, 1945] Decorah formation: ”Effigy,” Speehts Ferry shale member (clay bed): Shale, olive, calcareous _________________________ 0. 3 Limestone as below, weathers very ropy .......... . 8 Limestone, light-grayish-buff, fine-grained, dense, very fossiliferous; phosphatic nodules ___________ 1. 5 Bentonite, a white plastic clay, weathers orange— brown ______________________________________ . l Limestone, light-olive-gray, very dense, very thin bedded ........................................ . 2 Total, Spechts Ferry _______________________ 2. 9 Plattcville formation: Quimbys Mill member (“glass rock”): Dolomite, light-brown, fine grained, “sugary,” dense, thin-bedded ___________________________ (5. 0 Limestone, dark-purplish—brown, very fine grained, very dense, conehoidal fracture; in thin, nodular beds, with dark-brown shale partings; half an inch of platy fossiliferous dark-brown shale at base ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 0. 0 Total, Quimbys Mill_-,_. _,-.._,..,r,.,s;,,_, 12.0 McGregor limestone member (Magnolia beds of Bays and Raasch, 1935; “Trenton”): Limestone, light-gray, pinkish, fine—grained, dense; conchoidal fracture (the “glassy” McGregor)____ 1. 5 Limestone, light-gray, fine-grained, thin-bedded-“ 5+ LITHOLOGIG DESCRIPTION AND STRATIGRAPHIC RELATIONS Typically a dense sublithographic limestone, the Quimbys Mill is the “glass rock” of the miners, a clearly recognizable unit present in the eastern and central parts of the district. Quimbys Mill strata in the western part of the mining district are limestone and subordinate amounts of shale, whereas in the eastern part of the district dolomite and a small amount of shale are characteristic. In a north- eastward—trending area across the central part of the mining district the limestone and dolomite beds inter-- mingle. The name “glass rock” is probably derived from the characteristic fracture. rThe designation is found in the description of the quarry at Quilnby’s mill in early reports on the district (“Lumen 1862, p. 163). Until the geOlogic study (Grant, 1903, 1906; Bain, 1905, 1906) about the beginning of the present century, the term “glass rock” was loosely applied to a lithologic STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT FIGURE 46,—Type section of Quimbys Mill member (Opq) of Platteville formation, with Spechts Ferry (Ods) above and McGregor (0pm) below, in quarry at Quimbys Mill, Lafayette County, Wis. (fig. 35, 10c. 27). facies, sometimes to what is here called the Quimbys Mill member, sometimes to the underlying part of the McGregor called Mifflin (of Bays 1938), and often to the lower limy beds of the overlying Guttenberg. The surveys of Grant and Bain in the early 1900’s applied the term “glass rock” especially to the Quimbys Mill beds but mentioned the fact that the lower beds of the McGregor had been and occasionally still were referred to as “glass rock.” From that time until the present, however, the custom has prevailed among the mining men of the district to designate as “glass rock” only those beds now known as Quimbys Mill. Thus in practice the “glass rock” beds are a generally recognized strati- graphic entity. In the western part of the mining district the Quimbys Mill is less than a foot thick and is overlain by bentonite and~interbedded limestone and shale of the Decorah formation (see section 2, p. 305). East of the mining district, where Spechts Ferry strata are absent, the Quimbys Mill is overlain by dolomite of the Guttenberg member of the Decorah formation. A regional dis- conformity therefore exists at the contact of the Quim— 283 bys‘ Mill (Platteville) and Decorah. The Quimbys Mill rests conformably on the McGregor member. Regional dolomitization eastward is shown by the complete dolomite section at Shullsburg and to the east (Agnew, 1950; Herbert, 1946). The Quimbys Mill thickens locally to more than 18 feet in an area just southeast of Shullsburg, Wis. However, eastward from the central part of the mining district the unit is 13—14 feet thick and becomes some- what cherty (see section 3, p. 305). Locally the mineralizing solutions leached the cal— careous elements from the Quimbys Mill, increased the relative brown shale content—called “oil shale” or “oil rock” by many geologists (Scott, Behre, 1935), although this term should be reserved for the Guttenberg member of the Decorah formation—and noticeably diminished the thickness of the unit (Agnew, 1950). For example, in diamond-drill holes (U. S. Bureau of Mines 20 and 17) only 75 feet apart at the Bautsch mine south of Galena, 111. (fig. 35,10c. 30), thicknesses of 13 feet (near normal) and 4 feet, respectively, were recorded. Dolomitization accompanying the zinc—lead mineral— izing solutions notably affected the Quimbys Mill, resulting in a more granular or sugary texture (Agnew, 1950). In such dolomitized rock other primary litho- logic characteristics still are present. Less commonly, silicification accompanying the zinc—lead-bearing solu- tions caused parts of the beds to be replaced by silica so faithfully that the only megascopic difference is in the hardness (Agnew, 1950). Rarely, secondary chert nodules were formed. Bays (p. 278) stated that the cherty dolomite (eastern) facies contains a suite of heavy minerals with garnet dominant, similar to that in the underlying Magnolia (of Bays and Raasch 1935); this is in contrast to the overlying Speehts Ferry shale member, which is char— acterized by zircon. Dake (p. 278) found that the Quimbys Mill contains less insoluble material than does the lVIagnolia; the residue is silicified fossils and some buff to brownish-gray shale. Aberdeen 58 found almost no residue in Quimbys Mill strata near Platteville. DISTRIBUTION Because of their dense and resistant character the Quimbys Mill commonly crops out; moreover, because these beds are valuable as building stone, quarries in them are common. Several of the better exposures of the Quimbys Mill are listed below, to- gether with the thickness and general lithology: 58 Aberdeen, Esther J ., 1931, The location of the break between the Galena and the Platteville limestones: unpublished M. S. thesis. Northwestern Univ., Evanston, Ill. 284 Thickness and general lithology of Quimbys Mill member Thickness Lithology (feet) Limestone and 12 dolomite Laralion P-lutf, north side valley, in NWMNE‘A sec. 7, T. 1 N., R. 2 E., Lafayette County, Wis. (2 miles east of loo. 2’], fig. 35). Quarry, Darlington, County, Wis. (100. 13). Quarry 1 mile north of Darlington, in SWMSE’A sec. 27, T. 2 N., R. 3 E, Lafayette County, Wis. (2 miles north of loc. 13). Quarry, )6 mile east of Calamine, Lafayette County, Wis. (100. 42). Quarry, Lafayette County, Wis. (10c. 31). Quarry, )3 mile north of York Church, Green County, “is. (10c. 44). Quarry, along Honey Creek, Green County, Wis. (100. 45). City quarry, Mineral Point, in SE}£ SEE/Q sec. 31, T. 5 N., R. 3 E., Iowa County Wis. Small ravine from north, at bend of Fever River, in S\V%NE}£ see. 22, T. 2 N., R. 1 E., Lafayette County, Wis. (1 mile northeast of loc. 7). Ravine from east, east of farm house, in SWMNWfi sec. 26, T. 2 N., R. l 151., Lafayette County, Wis. (1 mile southeast of loo. 7). Steep ravines from east, in SPM sec. 27, T. 2 N., R. 1 E., Lafayette County, Wis. (1 mile south of 100. 7). Quarry, west bluff of valley, near center NE}; sec. 8, T. 3 N., R. 1 W., Grant County, Wis. (2 miles north- west of Platteville). Roadcut, County Trunk E, near center W%E% sec. 18, T. 5 N., R. 1 W., Grant County Wis. (3 miles northwest of 100. 4). Roadcut, County trunk 0, in NWM NEl/i sec. 35, T. 3 N., R. 2 W., Grant County, Wis. (2 miles north- west of 100. 6). Roadcut, U. S. Highway 61, Grant County, Wis. (100. 12). l This dolomite is attributed to the lead~zinc mineralizing solutions. Lafayette Dolomite ______ 10+ ..... do_-_____ 14.2 8.4. ,,,.do _______ 13 13.2 N-,do ,,,,,,, 11 Limestone and 8 :I: dolomite. 1 Limestone-_-_ 8i Limestone and 8 :i: dolomite. 1 Limestone___- 3 _ , _ . do _______ ,-_,do _______ 2 Limestone and 1 dolomite. FAUNA AND CORRELATION Strata of the Quimbys Mill are fossiliferous, particu- larly in the limestone facies; the fauna has not yet been described, although Aberdeen (p. 283), Bays (p. 278), and Kay (1929, p. 657) prepared fossil lists. Bays correlated beds of the Quimbys Mill with the Lowville (middle Black River) of the standard New York section (fig. 44), although Kay (1935a, fig. 11) shows its position to be equivalent to part of the Chaumont. Until further paleontologic work has been SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY completed only tentative correlation of these strata with those in other areas can be accomplished. ECONOMIC PRODUCTS The Quimbys Mill (“glass rock”) constitutes one of the ore-bearing zones and has been prospected and mined particularly since 1940 (Agnew, and Heyl, 1947, p. 228). The limestone of the “glass rock” is suitable for a fac- ing stone and has been used for that purpose in many areas, particularly in the central part of the district. DISTRIBUTION OF FACIES OF PLATTEVILLE AGE AND CON- DITIONS 0F DEPOSITION The Platteville strata are rather uniform in lithology, except for the Glenwood shale member whose facies relationships are not completely known as yet, and were products of a marine environment. The Pecatonica is a dolomite or dolomitic limestone throughout the area of study. On the other hand, the McGregor and the Quimbys Mill are limestone to the west, limestone and dolomite in the central part of the mining district, and dolomite to the east. Both the Magnolia beds of the McGregor member, and the Quimbys Mill become cherty to the east. The chertific- ation and dolomitization are apparently related to the major structural axis, the Wisconsin arch; similar relationships of dolomite and structure have been dis— cussed for north-central Illinois by Willman and Payne (1942, p. 64—65), and in nearby states by Cohee (1948, p. 1432). The elastic quartz sandstone, dolomite, and shale of the Glenwood shale member show evidence of relatively coarse deposition under rather shallow open-water “platform” conditions (Krumbein, 1947). The alter- nation of coarse elastic material with the finer clays and the thin bedding, which is commonly somewhat ob— scure, are both characteristic of shallow-water environ— ment; the tendency toward crossbedding seen in south- eastern Minnesota and the area south of Rockford, 11]., marks deposits formed under conditions prevalent in an environment of very shallow water. Pecatonica strata may have been laid down as a clastic limestone platform deposit (Sloss 1947). although the massive bedding characteristic of the Pecatonica is cited by Rich (1951) as a criterion for deep-water deposition. The general absence of fossils also tends to support Rich’s deeper water origin. Furthermore, although the Pecatonica is now a granular sugary dolomite, the original limestone may have been fine grained; if so, Rich’s relatively deep water origin for the Pecatonica sediments gains credence. Mifflin strata (of Bays 1938) of the McGregor mem- ber were generally of shallow—water platform origin STRATIGRAPHY 0F MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT (Sloss, 1947), as shown by the thin nodular beds of limestone separated by silty and clayey fragments, although deeper water environment is suggested by fineness of grain and the sublithographic type of lime— stone, coupled with the slightly bituminous character of some of the shale partings. The highly fossiliferous nature of the Miffiin strata is characteristic of shallow- “. ater deposits. Magnolia strata (of Bays and Rauseh, 1935) of the hchregor member are similar to the Mifflin strata except that the deep—water characteristics are absent; shallow water environment is therefore indicated. In the Quimbys Mill strata we find the same type of conflicting evidence as that seen in the Mifllin except that in these platform (Sloss, 1947) deposits shallow— water criteria are less abundant and apparently of less importance than the deep-water characteristics. The highly bituminous nature of the shale, the lithographic type of limestone, and the general absence of fossils (except on the shale partings) are dominant character- istics. However, thinness and evenness of bedding, reeflike concentrations of fossils, and interbedded shale strata suggest a shallow-water origin for these sediments. DECORAH FORMATION GENERAL FEATURES An excellent exposure in the central part of the min- ing district of all but the upper few feet of Decorah is seen in a steep ravine from the west into the Galena River (locality 32, fig. 35) as follows: Ravine, west side of Galena River, center of east line, sec. 4, T. 1 N., R. 1 E., Lafayette County, Wis. [Described by A. F. Agnew, Aug. 22, 1949] Galena dolomite: ”at?” Cherty unit (zone D): Dolomite, brownish, medium—crystalline, thin- bedded; mottled with calcareous areas iiiiiiiiii 2. 2 Limestone, bufl" to flesh—colored, thin-bedded ______ 1. 0 Covered interval ___________________________________ 6. 8 Decorah formation: Ion dolomite member (gray beds): Limestone, light-buflish-gray, argillaeeous, thin- bedded _____________________________________ 9. 4 Limestone, grayish-buff, coarsely crystalline, very fossiliferous; a 0.1-ft platy grayish shale at base. 2. 0 Ion dolomite member (blue beds): Limestone, bluish-gra y alternating with grayish- bufl’; thin-bedded in lower 0.5 ft; upper 0.7 ft is 1 bed ________________________________________ 1. 2 Limestone, greenish-gray, shaly, platy _____________ . 7 Limestone, fossiliferous _________________________ . 7 Limestone, grayish-buff and bluish, crystalline, mottled, argillaceous; upper 0.4 ft very fossilifer- ous ________________________________________ 1. 4 Limestone, thin-bedded, lower part bluish—gray upper part flesh-colored _______________________ 1. 0 285 Decorah formation—Continued Thickness (feet) Limestone, bluish-gray, medium- to coarsely crystal- line, fossiliferous _____________________________ 1. 0 Total, Ion ________________________________ 17. 4+ Guttenberg limestone member (“oil rock”): Transition beds—limestone, buffish, medium- crystalline, fossiliferous _______________________ . 9 Limestone, brown, thin-bedded, fine-grained, fos- siliferous, band of chert nodules 3.5-feet below top _________________________________________ 5. 0 Limestone, brown, fine-grained, dense, nodular; interbedded brown platy shale _________________ 6. 3 Total, Guttenberg ........................ 12. 2 Spechts Ferry shale member (clay bed): Shale, olive, calcareous; trace of orange benton- ite (‘2) ______________________________________ . 4 Limestone, light-brown to cream; fossil fragments and phosphate nodules _______________________ . 8 Shale, olive; brown and green mottled fine—grained argillaceors limestone; brown platy shale ,,,,,,, . 1 Limestone, light-brown, fine-grained, dense, nodular ______________________________________ 1. 1 Limestone, light—brown, dense, nodular, wavy- bedded; parting of tan platy shale at top _______ . 1 Limestone and thin platy tan shale _______________ . 1 Bentonite ____________________________________ . 1~. 2 Limestone, greenish-buff, nodular, argillaceous, and light-brown interbedded shale _________________ . 3 Total, Spechts Ferry _______________________ 3. 0 Total, Decorah ____________________________ 32. 6+ Platteville formation: Quimbys Mill member (“glass rock”): Limestone, light-brown to brown, thin- to medium- bedded, Very fine grained and dense, conchoidal fracture; dolomitic shaly zone at base __________ 8. 0 Westward from the mining district the Decorah becomes rather uniformly greenish shale with limestone nodules, as is seen at Decorah, Iowa (fig. 35). Calvin’s (1906, p. 85) “typical exposure of the shale at the foot of the bluff on the left of the ‘Dugway’ ” today shows only the upper 15 feet of what corresponds to the Ion dolomite member, of the Decorah formation. Calvin stated further that “the shales overlie the lime- stones in the west quarry of Mr. H alloran, east- of the Ice Cave bridge.” In this quarry only the lower 5 feet or so of the Decorah, which corresponds in position to the Spechts Ferry shale member, is visible above 3 feet of limestone, here assigned to the unnamed member at the base of the Decorah. A section that exposes the full thickness of the Decorah formation was noted by Kay (1929, p. 651), and because it is only 8 miles from the city of Decorah it may be considered typical (see section 4, p. 306). 286 The Decorah formation changes in lithology across the mining district so that at the east border of the district the formation consists wholly of dolomite. In like manner the thickness decreases easterly, the unnamed member is absent east of Platteville, Wis., and the Spechts Ferry is absent in the eastermost part of the mining district. A typical section of the Decorah formation in this eastern facies is given in section 5, page 306. In the western part of the mining district the lithology of the Decorah is limestone and shale, and the formation is approximately 44 feet thick. In the central part of the zinc-lead district the Spechts Ferry has about the same lithology as to the west; the Guttenberg and lon members, however, contain less shale, and regional dolomitization has affected the upper part of the Ion member (Agnew, 1950). The thickness of the Decorah formation in the central area is approximately 41 feet, owing principally to a decrease in thickness of the Spechts Ferry shale member. Farther east, at Darling— ton (fig. 35, 100. 13) the Spechts Ferry is almost absent, and the Guttenberg and Ion are both dolomite because of regional dolomitization; the Decorah in this area is only about 30 feet thick. Gocd exposures of the Decorah formation can be seen as follows: western area, roadcut along U. S. Highway 52 at north edge of Guttenberg, Clayton County, Iowa (fig. 35, 10c. 33) ; central area, east bank of Galena River, Jo Daviess County, Ill. (loc. 34); eastern area, quarry in south part of Darlington, Lafayette County, Wis. (loc. 13). SPECHTS FERRY SHALE MEMBER LITHOLOGIC DESCRIPTION AND STRATXGRAPHIC RELATIONS Kay (1928) noted that in the “ravine southwest of the C. M. & St. P. railroad station at Spechts Ferry,” Dubuque County, Iowa (loc. 10, fig. 35), the Spechts Ferry consists of * * * the eight and one half feet of shales and interbedded limestones [which] form a lithologic unit lying above the “Platte- Ville” limestone; the “Platteville” of Iowa does not include the uppermost beds of the typical Platteville of southwestern Wisconsin. The Spechts Ferry member includes the “glass rock” and overlying shales at the top of the typical Platteville. Later, Kay (1929, p. 645) stated that in the type outcrop of the Spechts Ferry * * * true “glass rock” beds are not present in the base of the Spechts Ferry member, though there are conspicuous limestones. Further: * * * there is no evidence to prove that these limestones are the same, and it is possible that they are younger than the “glass rock” and that those beds are absent at Spechts Ferry. Although the “glass rock” unit (Quimbys Mill member) is virtually absent at this locality, its presence is SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FIGURE 47.7Type section of Spechts Ferry shale member (Ods) of Decorah formation, overlain by Guttenberg limestone member (Odg overhang); underlain by McGregor limestone member (017m) of Plattevillc formation, in quarry 200 yards southeast of Spechts Ferry station, Dubuque County, Iowa (fig. 35, 100. 10). indicated by a thin dark-brown green-mottled fissile shale. The quarry 200 yeards east of the ravine shows the following section (see fig. 47; section 8, p. 307). This description is a slight revision of Kay’s (1929, p. 646, table Ill) description because he included the dark brown shale—herein called Quimbys Mill mem- ber#in the Spechts Ferry shale member. This shale represents the western edge of the “glass rock” unit. The Spechts Ferry is green or slightly bluish-green shale with subordinate thin beds of light—greenish—buff fine-grained sugary fossiliferous dense limestone. The thickness of the Spechts Ferry at the type locality is 8.8 feet, but this decreases to the east so that a short distance west of Shullsburg, Wis. only 3 feet of Spechts Ferry remain (section 9, p. 307). The green shale pinches out farther east, as noted previously; an interesting section in this respect is that in the quarry at Calamine, Lafayette County, Wis, section 10, page 308 (fig. 35, 100. 42; fig. 48). STRATIGRAPHY FIGURE 48.—Quimbys Mill member (Opq) of Platteville formation over- lain by Guttenberg limestone member (Ode) of Decorah formation, in quarry at Calumine, Lafayette County, Wis. (fig. 35, loc. 42). The Spechts Ferry shale member, referred to in the mining district as the “clay bed,” ranges from 1 to 5 feet thick there. Of this thickness perhaps half is limestone which, in zones of mineralization, has been almost wholly leached away, there being left only the argillaceous residues and the original shale beds. The shale is blocky in the outcrop but becomes quite plastic and claylike in the presence of water, as in the mines. The commonly recognized bentonite layer of the miningdistriet occurs in this member 0.3—0.4 feet above the base. This bentonite is the yellowish “pipe clay” of the miners. In the following section the bentonite layer is present; in addition, effects of the mineralization 011 the Gutten- berg and Quimbys Mill strata are a striking feature of this quarry at Mifflin, Iowa County, “Tia, (2 miles northeast of loo. 18, fig. 35). 0F hIIDDLE ORDOVICIAN ROCKS IN 287 THE ZINC—LEAD DISTRICT Quarry along road 3/1—mile south of IVIifllin in SW’KJVEM sec. 34, T. 5 N., R. 1 E., Iowa County, Wis. [Described by A. F. Agnew and A. V. Heyl, April 21, 1943] Decorah formation: ”Effigy” Guttenberg limestone member (oil rock): Limestone, brownish—gray, mottled brown, sugary, dolomitized ______________________________ 4. 0—6. 0 Gougelike material; brown to chocolate—colored shaly clay _____________________________________ 1. 0—3. 0 Spechts Ferry shale member (clay bed): Shale, greenish-brown; a 0.3-ft limestone at base.“ 9 Shale, grayish-green, blocky ________________________ 4 Bentonite, cream-colored; weathers yellow _________ . 4 Shale, green, blocky _____________________________ 4 Total, Spechts Ferry ________________________ 2. 1 Platteville formation: Quimbys Mill member (“glass rock”): Dolomite, light-buff, fine-grained, granular; contains chert nodules of secondary origin--. ,,,,,,,, 3+ The bentonite layer has been noted in many other outcrops; some of the better ones are the following: Quarry, north end of Ice Cave Bridge, in NEMNVV% sec. 15, T. 98 N., R. 8 W., VVinneshiek County, Iowa. This is one of Calvin’s type sections of the Decorah (fig. 35). Ravine along side road, Allamakee County, Iowa. Ion type locality (100. 36). Ravine from south, Clayton County, Iowa. Gregor type locality (100. 25). Roadcut, west side U. S. Highway 52, Clayton County, Iowa. This is the Guttenberg type locality (100. 33). Ravine from West, SEV; sec. 30, T. 4 N., R. 4 W., Grant County, Wis. (8 miles southeast of 100. 17). Roadcut, County trunk A, north side of road, Grant County, Wis. (100. 28). Ravine from west, in SW91 sec. 4, T. 2 N., R. 3 W., Grant County, Wis. (5 miles west of loc. 12). Roadcut, south side County Trunk O, in NW}£NE% sec. 35, T. 3 N., R. 2 W., Grant County, Wis. (2 miles north of 100. 6). Roadcut, northeast side U. S. Highway 61, Grant County, Wis. (Ice. 12). Roadcut, west side U. S. Highway 151, Grant County, Wis. (Ice. 6). Ravine from east, in NWM sec. 20, T. 3 N., R. 1 W., Grant County, Wis. (1 mile west of Platteville). Roadcut, County Trunk E, just east of center sec. 18, T. 5 N., R. 1 W., Grant County, Wis. (3 miles northwest of 100. 4). Outerop, west bank Fever River, in SVV}£S\V% sec. 14, T. 2 N., R. 1 E., Lafayette County, Wis. (2 miles northeast of loo. 7.) Montfort quarry, north side of road, Iowa County, Wis. (100. 43). This is the This is the Mc- The heavy mineral suite of the Spechts Ferry is characterized by zircon (Bays, see footnote p. 278). Insoluble residues from limestones of the Spechts Ferry show brownish silt that differs from the honey-colored resinous silt of the overlying Guttenberg limestone member. Quimbys Mill strata show almost no residue (Aberdeen, see footnote p. 283), and its heavy minerals are characterized by garnet. 288 Near the top of the Spechts Ferry member are minute phosphatic pebbles, nodules, and fossils. Aberdeen attempted to estimate their stratigraphic value, both laterally and vertically. She stated that in the vicinity of Platteville on the basis of fossils two breaks of diastem proportions were recognizable, one at the base of a blue shale bed and another at its top; this bed she referred to the uppermost Spechts Ferry. She found phosphatic nodules in the limestone bed immediately overlying this blue shale bed and the presence of these nodules seemed to justify drawing the line between the Spechts Ferry and Guttenberg at the base of this lime- stone. Kay and Atwater (1935, p. 10]) noted the presence of the phosphatic nodules in this limestone but assigned the limestone to the Spechts Ferry, as Kay had done in his description of the type section in 1929. The field work associated with the present study has shown that the phosphatic nodules are not restricted to this limestone bed, which in the Platteville area is referred by the writers to the basal Guttenberg. In places (as at the Spechts Ferry type locality) phos- phatic nodules are found in one or two limestone beds of the Spechts Ferry member below the upper bed, but separated from it by an interval of shale. Thus it can be said only that the phosphatic nodules occur in a zone near the contact of the two members. The phosphatic pebbles are significant not because they depict a sedimentational break at their horizon, but because they are second only to glauconite in abundance at horizons “within a few feet above strati- graphic breaks” (Goldman, 1921, p. 4); the Platteville- Decorah disconformity occurs 5—10 feet below the phosphatic zone being discussed, and the less obvious Glenwood—St. Peter unconformity occurs 1e8 feet below a similar phosphatic zone with glauconite, at the con- tact of the Glenwood and Pecatonica. Trowbridge and Shaw (1916, p. 39) found in the Spechts Ferry shale member “Dalmanella subaequcta which show evidences of having been rolled or worn” and concluded that, as this species occurs abundantly in the upper part of the Platteville, an unconformity at the contact of the Galena and Platteville (marked by the clay bed) is suggested. Broken fossil shells are common in the coquina lenses of the Spechts Ferry, but are here interpreted as being one of the results of fairly shallow-water environment rather than being reworked from earlier deposits. The Spechts Ferry member west of the mining dis- trict lies conformably on the unnamed limestone member of the Decorah. In the central and eastern parts of the mining district it rests disconformably on the cor- rosion surface at the top of the Quimbys Mill member of he Platteville formation. Farther east the Spechts SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Ferry is absent, and Guttenberg strata rest discon- formably on Quimbys Mill. Bays (1938) stated that the Spechts Ferry and Quimbys Mill are facies. Evidence bearing on this problem is as follows: (1) The bentonitc layer near the base of the Spechts Ferry is consistently present, despite the inverse con— vergences of the Spechts Ferry and the underlying Quimbys Mill strata. This feature was also noted by Kay and Atwater (1935, p. 101), who stated, “it has been believed that the thinning of the member is due to convergence rather than to disconformity [at the top].” (2) The Spechts Ferry and Guttenberg thin to the east; on the other hand, to the east and southeast the Quimbys Mill increases in thickness. (3) In all cases where the two units are exposed to- gether, the Spechts Ferry overlies the Quimbys Mill. (4) There is no known interbedding or inter-fingering of the two types of lithology typified by the green shale and limestone of the Spechts Ferry, and the purplish— brown limestone and brown shale of the Quimbys Mill. (5) In the pitted upper surface of the Quimbys Mill the irregularities contain phosphatic pebbles and fillings of greenish argillaceous dolomite similar to that of the Spechts Ferry. However, features that might be interpreted as arguing for contemporaneity and thus lateral facies are: (1) Faunal contrasts between strata of the Quimbys Mill and the Spechts Ferry may be due solely to dif~ ferent environments and not to different ages. (2) Bays’ (footnote, p. 278) facies changes of the Spechts Ferry from green shale in the west to brown limestone (Quimbys Mill) to buff dolomite (Quimbys Mill) in the east have their parallel in the facies changes of the Guttenberg from green shale in the west to light— brown limestone to buff dolomite in the east, and in those of the Ion from green shales in the west to light- greenish—gray limestones and shales, to greenish buff dolomite in the east. Nevertheless, the zone of phos— phatic nodules at the contact of the Spechts Ferry and Guttenberg carries across these changes in facies. The bentonite layer is therefore of the utmost im— portance because other evidence might be termed not entirely conclusive. This bed of plastic clay was dis— cussed as follows by C. S. Ross (written communication, June 14, 1945): Victor Allen * * * has examined the material and says that it resembles bentonitc of that age [Middle Ordovician] which he has studied. Preservation of ash structures is very rare in both the eastern and the Mississippi Valley regions and so their absence in your material is not surprising. I * * * find abun— dant orthoclase which strongly suggests bentonite * * * also zircon, which Allen says is very characteristic. Therefore, it seems very probable that this material is bentonitc. STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT This bentonite, originally correlated with the Houns— field (Kay, 1931) and later shown (Kay, 1935b, p. 229) to be younger in age, has been reported from the Ordovician of New York; Ontario; from the Minnesota, Iowa, and Wisconsin region; and from Missouri. Allen’s (1932) study of the bentonites in the Missis— sippi Valley provided several conclusive arguments for the truly bentonitic nature of the bed under dis- cussion. Allen found crescent—shaped shards and sanidine feldspar as well as euhedral apatite and zircon grains. The occasional rounded grains of minerals such as garnet, which are foreign to volcanic deposits, he explained as having been “added by wave action during or shortly following the deposition of the volcanic ma- terial.” This and other evidences suggested to him “active agitation and some reworking of the volcanic material before ordinary Decorah sedimentation was resumed.” Within the mining district, the contact of the Spechts Ferry and Guttenberg members is easily discernible, as it shows greenish shale and limestone overlain by brownish limestone and shale. To the east the Spechts Ferry is absent; to the northwest, however, as near Decorah, Iowa, and farther northwest, the basal green shale (Spechts Ferry) member of the Decorah thickens at the expense of the overlying limestone (Guttenberg) member. DISTRIBUTION Because of their shaly character the Spechts Ferry strata are commonly not well exposed. The good ex- posures are usually in quarries or roadcuts that include the limestone or dolomite beds above and below (p. 287). FAUNA AND CORRELATION Microfossils and megafossils are abundant. Kay (1929, p. 658) listed lower and upper Spechts Ferry faunas. His lower fauna came from * * * gray fine-textured, soft, vertically-jointed limestone beds from 1 to 4 feet from the bottom of the member. It has been recognized in Winneshiek County [Iowa] and as far to the southeast as Patch Grove township, Grant County, Wis. [fig. 35, 100. 37]. This collection is apparently from the unnamed lime— stone member, previously described (p. 264). His upper fauna came from the upper foot of “dark blue hard, pyritic shale.” Spechts Ferry strata have been correlated with the Stictoporella bed (fig. 37) of Minnesota (Bays and Raasch, 1935, p. 300; Kay 1940, p. 235), although earlier Kay (1935a, p. 287) had believed the Spechts Ferry to be the equivalent of the Rhinidictya bed above. Kay (1929, p. 666) thought that strata of the Spechts Ferry (together with the lower Guttenberg strata) could be correlated with the Glenburnie member of the 289 Chaumont (upper Black River) of New York (fig. 44) because of the bryozoa. Furthermore, he (1934, p. 330) believed that the bentonite near the base of the Spechts Ferry is “identical with the Hounsfield bento— nite in the Glenburnie.” Bays and Raasch (1935, p. 301) correlated the Spechts Ferry faunas with both the Tyrone of Ten- nessee and the Leray of Ontario (see also Twenhofel, and others, 1954). Kay (1935a, p. 288) noted that the “so-called ‘Decorah shale’ of * * * Missouri is synchronous with the Spechts Ferry member,” and Bays and Raaseh agreed. ECONOMIC PRODUCTS Disseminated zinc and lead minerals are common in. the Spechts Ferry shale member, especially in places where ore minerals occur in the overlying beds. Because the unit is thin, however, and because it is difficult to mine and mill for the zinc and lead content, the Speehts Ferry is not normally considered an ore zone. Dissem- inated pyrite crystals are even more widespread than zinc and lead minerals. The Spechts Ferry in former years was almost without exception the lowest zone penetrated in prospecting and mining, as the miners believed that such a body of shale (which they called the clay bed) was impervious to the descending (ac- cording to views then current) solutions that deposited the zinc and lead minerals; furthermore, as the under- lying Quimbys Mill is an aquifer, the miners were apprehensive about tapping this source of additional water because it might pose new problems of mine drainage. The bentonite in the Spechts Ferry is said to have been used in a few places in the middle 1800’s as a pipe clay. GUTTENBERG LIMESTONE MEMBER Kay’s (1928) original description stated that the Guttenberg “consists of about fifteen and one half feet of brownish fine-textured limestone,” and he (1929, p. 648) subsequently published the type section as seen in a “ravine a mile north of Guttenberg, Iowa.” This ravine is now obscured by U. S. Highway 52 ,' the road- cut, however, may be said to preserve the type section. (See section 11, p. 308; fig. 49.) LITHOLOGIC DESCRIPTION AND STRATIGRAPHIC RELATIONS A typical section of the Guttenberg in the mining distr'ct is that along the west bank of the Galena River, in sec. 4, T. 1 N., R. 1 E, Lafayette County, “Us, given on page 285. Throughout most of the district the thickness of the unaltered Guttenberg is 12—14 feet. On the other hand, east of Mineral Point and Shullsburg the unit 290 FIGURE 49.~—Type section of Guttenberg limestone member (Ody) of Decorah formation; overlain by Ion dolomite member (0di), under- lain by Spechts Ferry shale member (Ods), in roadeut, U. S. High- way 52, 1 mile north of Guttenberg, Clayton County, Iowa (fig. 35, loc. 33). begins to thin and at Blanchardville (fig. 35, 100. 29) it is only 6.5 feet thick. Slightly less than 2 feet remain near Rockford, Ill. The Guttenberg becomes dolomitie east of Shullsburg and Mineral Point (see section 12, p. 308; fig. 35,100.44; fig. 50). Herbert 9 found in some exposures a thin bentonite layer along a shale seam 2—3 feet above the base of the Guttenberg. The limestone below the bentonite layer is grayish brown, that above is tan or light brown. This bentonite layer was found at Spechts Ferry, Dubuque County, Iowa (fig. 35, 10c. 10), northeast of Galena, Ill. (100. 34), and midway between these two localities, in U. S. Bureau of Mines diamond-drill holes at Fairplay, Grant County, Wis. (sees. 25, 26, T. 1 N., R. 2 VV.). Insoluble residues of the Guttenberg show (Dake, footnote p. 278) an increase in quantity over those from the Quimbys Mill; the residue is mainly brownish chert with some quartz sand. Herbert related that the lower BHerbert, Paul, Jr., 1949, Stratigraphy of the Decorah formation in western Illinois: unpublished I’h. l). thesis, Chicago Univ., Chicago, Ill. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FIGURE 50,—Decorah formation, consisting of Ion dolomite member (0112') and Guttenberg limestone member (Ody), overlain by Galena dolomite (Og), underlain by Quimbys Mill member (Opq) of Platte- ville formation, in quarry at York Church, Green County, Wis. (fig. 35, loc. 44). 2 to 3 feet of the Guttenberg has grayish argillaceous residues, Whereas the rest of the member has tan argil— laceous material with red and orange specks. The Guttenberg contains silicified fossils and quartz silt. The Guttenberg unit contains carbonaceous shale partings (fig. 51). Locally the mineralizing solutions leached the limestone from this member as well as from the Spechts Ferry and Quimbys Mill members below, leaving a reduced thickness of beds that consist mostly of shale and argillaceous residuum. The chocolate- colored shaly residues of the Guttenberg found in min- eralized areas are known as the oil rock. The following section illustrates markedly this feature, for it shows less than 5% feet of Guttenberg (fig. 35, loe. 11): Eagle Point Quarrt, U. S. Highway 151, near southeast corner sec. 7, T. 89 N., R. 3 E, Dubuque County, Iowa [Described by A. F. Agnew, spring, 1943] Thickness Decorah formation: (feet) Ion dolomite member (blue beds): Limestone, blue, coarsely crystalline, recrystallized ________________ Guttenberg limestone member (”oil rock”): Limestone, pink, crystalline, mottled; dark-brown shale laminae ________________________________ 1. 2 Shale, dark-brown, with thin lenses of pink lime- stone; nodules of chertified limestone in lower 0.2 ft ______________________________________ . 9 Limestone, light-brownish-pink, nodular, chertified; chocolate shale seams _________________________ 4.0 3.0 STRATIGRAPHY or MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT 291 Eagle Point Quarry, U. S. Highway 151, eta—Con. ' Deeorah formation—Continued T333883 Guttenberg and Spechts Ferry members undifferen— tiated: Shale, chocolate-covered above, grading downward into greenish and yellowish-brown; phosphate nodules in lower 0.2 ft ______________ 0. 3—0. 5 Spechts Ferry shale member (clay bed): Shale, gray-green ________________________________ . 9 Shale, bluish—green __________________________________ . 9 Locally the oil rock is termed “rich” in the zones of mineralization because there its shaly residue phase is most abundant and the calcareous elements have been leached away, thus making the hydrocarbon content more conspicuous. Fairly well leached Guttenberg is called “medium oil rock” by the miners, and that which has been only slightly leached is designated “poor oil rock.” Where no leaching has taken place and the original limestone and shale relations have been preserved, the rock is called “bastard oil rock” or “limy oil rock.” (Fig. 52). The above discussion suggests how an incorrect interpretation of the structure and of the relations between thickness of oil rock and localization of ore deposition came to be the accepted one. Geologists had found that the hydrocarbon-rich facies of the oil rock was thicker in the basins and near ore bodies, and thus they postulated irregularities in deposition to account for this feature; such views were held as late as 1934, when Scott10 said that lateral variations such as 6 inches of oil shale terminating against lime— stone are due to sedimentary environment. Actually, the stratigraphic unit as a whole had thinned greatly 111 such places bGCflUSO mOI‘C 0f the Fromm 51.ACarb0naceous shale partings between wavy dolomite beds —— of Guttenberg limestone member (Orly) of Decorah formation, which 10 Scott, E. R., 1934, Structural eentrolofore deposition: Unpublished M.S.thesis, rests on Quimbys Mill member (0pc) cf Platteville formation, in Northwestern Univ., Evanston, Ill. quarry on Honey Creek, Green County. Wis. (fig. 35, loc. 45). FIGURE 52,7Elfeet of mineralizing solutions on Guttenherg limestone member of Decorah formation. Dark material is brown oil roekwargillaceous and Shaly residuum derived mainly from leaching of material simil tl‘ to the adjoining calcareous rock. Liberty mine NEMNE 1/4 see 16, ’l‘. 2 N., R. 1 E., Lafayette County, \Vis. (1 mile north ofloe. 7, fig. 35). 292 calcareous beds had been removed. The thinning caused by such leaching not uncommonly reduced the Guttenberg locally to 6—8 feet in thickness; indeed, in an extreme case in the Ginte Mine in Illinois (fig. 35, loc. 46), a reduction in thickness was found from the normal 13 feet to a minimum of 2 feet; the 2 feet consisted wholly of oil—rock shale. As another example, two adjacent drill holes (U. S. Bureau of Mines 58 and 59) in the Bautsch ore body (100. 30) gave thicknesses of 13 feet and 7 feet, respectively. The oil rock was called the “chocolate brown rock” and “brown rock” in the early reports (Strong, 1877, p. 695), and these names are still used by older miners near KIontfort, Highland, and Dodgeville, in the northern part of the district. The unit was first described in detail as oil rock by Grant (1903, p. 34), as follows: “[It] is a compact, very finely laminated, soft shale which varies in color from a very light-yellowish gray to a dark choco- late brown color, and even becomes perfectly black in places * * * It contains considerable percentage of carbonaceous matter * * * [and] when dry, particles of this rock will usually burn with a thick smoky flame.” Later Grant (1906, p. 40) stated that “when burning it gives off the peculiar petroleum odor and conse- quently has received the name ‘oil rock.’ ” Partial analyses of three samples of oil rock were reported by Strong (1877, p. 680). A sample taken from the Oakland level, in SW% sec. 5, T. 1 N., R. 2 E. (2 miles northwest of Shullsburg, Lafayette County, VVis.), gave 40.60 percent of “carbonaceous” matter; two samples from the Silverthorn mine, in NEM see. 31, ’l‘. 2 N., R. 2 E. (2 miles farther northwest), showed 18.31 percent and 15.76 percent. Tests made by F. F. Grout on samples from the Dugdale prospect west of Platteville (Bain, 1906, p. 25) showed 20.85 percent of volatile matter and 7.96 percent of true carbonaceous material in thoroughly air—dried shale. Leaching the shale with ether gave a thick, heavy oil * * * [containing] an appreciable amount of sulfur. The more detailed analysis by R. T. Chamberlin (Bain, 1906, p. 26) gave 39.98 percent hydrocarbon, largely methane, and 6.79 percent hydrogen sulfide. One volume of the rock gave 57.46 volumes of gas. David White (Bain, 1906, p. 26) made a micro- scopic examination of slides of the same material, concluding that there were present bodies * * * corresponding to the contours of collapsed and flattened unicellular plants, * * * interpreted as the fossil remains of microscopic, unicellular, gelosic algae * * * The soft brown shales of the oil rock, commonly convoluted with the yellowish bentonitc of the under— lying “clay bed” (Spechts Ferry), were locally termed “bull dum” by the miners. In part of the district (T. 1 N., R. 1—2 E., south— SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY western Lafayette County, Wis.) the Guttenberg con- tains a bed of discrete chert nodules, 1.5—2 feet below its top. Dolomitization accompanying the zinc-lead mineral— izing solutions has caused confusion in the correct identification of the Guttenberg. In some places this dolomitization resulted in bleaching, as in the Trego mine (NEM sec. 10, T. 3 N., R. 1 W., at north edge of Platteville, Wis.), where the otherwise brownish rock is a light-cream color. In most dolomitized areas, however, the Guttenberg retained its original color, but became granular and sugary upon dolomitization, as in the Hoskins mine, Lafayette County, Wis. (SWM sec. 18, T. 1 N., R. 2 E., 2 miles southeast of loc. 27, fig. 35). Silicification likewise was caused by the mineralizing solutions and notably affected the Guttenberg, where the replacement preserved the characteristics of the limestone and shales so faithfully that until the hard— ness is tested the rock appears normal; it is this rock that was named “bastard oil rock” originally, although more recently that term has been applied also to the hard unleached limestone phase of the Guttenberg. In many places the silicification progressed far enough that brown chert nodules were formed from limestone nodules, or grew between the shale laminae, seeming to force them apart. As previously mentioned (p. 288, 289), the contact between Guttenberg and Spechts Ferry members is well—marked in the mining district. To the southeast the Spechts Ferry is absent and the Guttenberg lies with apparently slight regional disconformity on the pitted surface of the uppermost bed of the Quimbys Mill below, whereas northwest of the district the Guttenberg passes into a greenish shale and argillaeeous limestone facies, and in Allamakee and Winneshiek Counties, Iowa, is poorly distinguished, or indistinguishable from the overlying Ion. In the mining district the upper boundary of the Guttenberg is almost as distinct as the lower; light— brown dense limestone and less-abundant chocolate- brown shale beds are overlain by gray—blue more coarsely crystalline limestone and greenish—gray fossil— iferous shale. This change in lithology is even more striking in the areas of zinc-lead mineralization, where an abrupt change from chocolate-brown shale upward into bluish—green shale is seen. Southeast of the mining district the light—gray dolo— mite of the Ion conformably overlies the light—brown dolomite of the Guttenberg, and the contact is distinct. DISTRIBUTION Despite the thin-bedded and nodular character of the Guttenberg, it usually is exposed as ledges and STRATIGRAPHY 0F MIDDLE 0RDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT small cutbanks in streams and also in quarries where the lower or higher beds have been taken as quarry stone. Some good exposures are listed on page 287. FAUNA AND CORRELATION Kay (1929, p. 659) listed species of brachiopods, mollusks, and trilobites from Gut-tenberg strata along the Galena River 2 miles north of Galena, Ill. The fauna gains a bryozoan element in the shaly facies to the northwest, as shown by Kay’s list of bryozoa from an exposure south of IVaukon, Iowa. Kay (1935a, p. 290) stated that many of the species are common to the Rockland limestone (lowest Trenton) of Ontario (fig. 44). In a later publication Kay (1940, p. 235) stated that the “Guttenberg member is believed to be repre— sented in the Rhinidictya and Ctenodonta zones of Minnesota” (fig. 37), and he repeated his 1934 correla— tion of the Guttenberg with the Rockland (lower Tren- ton) of Ontario (see also Twenhofel, and others, 1954). ECONOMIC PRODUCTS The Guttenberg or oil rock contains zinc and lead ore in many places. In areas of rich oil rock the min- erals are normally disseminated, as they are also in the underlying Spechts Ferry. However, in contrast to the Spechts Ferry (p. 289), mining and milling problems in the Guttenberg are not a deterrent. Furthermore, zinc-lead veins are present in many places and are mineable particularly where the over— lying strata are mineralized. ION DOLOMITE MEMBER Kay (1929, p. 650) described the type section of the Ion, but field work by Paul Herbert, Jr., in 1944 made it appear advisable to redescribe the type section. The following section (fig. 35, loc. 36), is presented as a result of this study of outcrops and of a field conference, held August 18, 1945, in which the participants were Paul Herbert, Jr., H. B. Willman, and L. E. Workman of the Illinois State Geological Survey; A. F. Agnew, C. H. Behre, Jr., and A. V. Hey], Jr. of the U. S. Geological Survey. o Outcrop in ravine along road in NW% sec. 35, T. .96 N., R. 4 W., Allamakee County, Iowa [Described by Paul Herbert, Jr., November 8, 1944] Galena dolomite: Thickness Cherty unit (zone D): U”) Limestone, light-grayish—butf, slightly mottled grayish in lower part, finely to medium-crystal- line, dense, fossiliferous _______________________ 6+ 293 Outcrop in ravine along road in NWMi sec. 35, eta—Continued Decorah formation: Thickness Ion dolomite member: (feet) Shale, olive-brown _____________________________ . 3 Limestone, grayish, coarsely crystalline, fossilifer— ous, numerous Prasopora ______________________ 1. 0 Shale, green, Prasopora __________________________ . 5 Shale, greenish, calcareous, and thin grayish-green shaly limestone beds; the ledges 2~3 ft above base contain Glyptorthis and Dinorthis in abundance“ 15. 5 Limestone, thin-bedded, argillaeeous; interbedded greenish shaly partings; ledge containing Glyptor- this 0.5 ft below top __________________________ 3. 2 Limestone, gray or greenish-gray, gray-mottled, thin-be dded ; weathers buff to brown, wavy-bedded, fossiliferous __________________________________ 1. 3 Total, Ion _________________________________ 22 Guttenberg limestone member: Limestone, light- brownish-bufT, finely crystalline, dense, fossiliferous; partings of brown to chocolate-colored shale ______ 8. 3 Rocks of the Spechts Ferry and the McGregor are also exposed at the type section of the Ion. The section crops out in a shallow ravine and is accurately meas— ured only with difficulty. The dips of the beds and the low gradient of the stream make the thickness measurements, especially of the Ion, not very precise. The differences between this described section and the description of Kay is that the upper 4.5 feet of Gutten- berg (as described by Kay 1929) are here placed in the on. This interpretation is favored because this 4.5— foot zone is more similar lithologically to the local Ion, as well as to the Ion in the mining district to the southeast. LITHOLOGIC DESCRIPTION AND STRATIGRAPHIC RELATIONS Sections (see sections 11, 13, p. 308) showing Ion very similar to that at its type locality are exposed at Gutten— berg, Iowa, and a short distance northwest of Potosi, Grant County, Wis. (fig. 35, 100. 47). In contrast, about 10 miles southeast of the above locality the Ion is dolomitic, and this lithology is characteristic of the central and eastern part of the mining district, as follows: (fig. 35, loc. 12). Roadcut, U. S. Highway 61, in NIVfi sec. 7, T. 2 N., R. 2 W., Grant County, Wis. [Described by A, F. Agnew, Apr. 22, 1945] Galena dolomite: Thickness Cherty unit (zone D): (I’m) Dolomite, buff with slight greenish mottling, medium- crystalline to coarsely granular; thick-bedded__ __ 9. 5 Decorah formation: Ion dolomite member (gray beds): Shale, dolomitic, olive-green; with casts of Praso- pora(?) ______________________________________ . 1 294 Readout, U. S. Highway 6'1, etc.~Continued Decorah formation—Continued Ion dolomite member#~Continued Dolomite, olive-gray, mottled, medium- to thick- bedded; grayish-green shale stringers and part— ings ________________________________________ 14. 0 Thickness (feet) Total, gray beds ___________________________ Ion dolomite member (blue beds): Shale, dolomitic, olive—gray, somewhat fossiliferous- . 3 Shale, olive-gray; lenses of coquinalike limestone____ 1. 0 Limestone, olive-gray, medium—crystalline, medium- bedded; in wavy beds with olive shale partings__ 3+ In the eastern part of the mining district the Ion, still a dolomite, has lost the distinctive characteristics of its upper part so that it is inseparable from the basal strata of the overlying Galena formation (see section 14, p. 309, fig. 35, 100. 13). The lithology of the Ion as seen from these sections consists of two facies: western facies of light— to dark— bluish—gray finely to coarsely crystalline fossiliferous limestone beds, with abundant greenish—gray shale beds; and eastern facies of light- to medium—grayish-blue, crystalline to granular, vuggy medium— to massive- bedded less fossiliferous dolomites, with subordinate amounts of olive—gray argillaceous patches and dolomitic shale beds. The thickness of the Ion is consistently 20—22 feet in outcrops and in many drill holes. In places minute phosphatic nodules (smaller and more sparse than those in the upper part of the Spechts Ferry) are present near the base of the Ion. The Ion contains scattered rounded grains of clear quartz sand that are relatively abundant near the base; such grains are likewise present, but are less common, in the Guttenberg below, and in the overlying beds of the cherty unit of the Galena formation. The divisions of the Ion, which are known in the miners’ terminology as the blue and the overlying gray, can be differentiated in most parts of the district. The blue beds consist of about 7 feet of gray dolomitic limestone whereas the gray beds contain approximately 14 feet of lighter gray dolomitic limestone. The blue beds have relatively more of the clear rounded grains of ' quartz sand, are more mottled, and in most places are more argillaceous and shaly than the gray beds. Minute phosphate granules are common near the base of the blue. Outside the district these separate units are not distinct, and in different parts of the district they show some variation. It is therefore best, as with the Mifflin (of Bays, 1938) and Magnolia (of Bays and Raasch 1935) subdivisions of the h/IcGregor member, to use these terms only locally. In the northern part SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY of the mining district the lower, or blue beds of the Ion are referred to as green rock (Strong, 1877, p. 695). Herbert reported the insoluble residues from the Ion to be greenish clay. He also noted at the top of the blue beds, southward from the mining district, an erosion surface that was not seen by the writers. A bentonite bed was observed at the base of the Ion at a quarry in SEX sec. 27, T. 3 N., R. 3 E., Lafayette County, Wis. (2 miles north of 100. 13, fig. 35), where it is the basal 0.2 foot of the Ion and rests on dolomite of the Guttenberg that is 8 feet thick. As was already mentioned (p. 292), the contact of the Guttenberg and Ion is conformable and, although in most of the mining district the differentiation of the beds is relatively simple, to the northwest where the green shale and limestone facies of the Guttenberg occurs it is not so obvious. Likewise, southeast of the district where both the Guttenberg and the Ion are dolomite the boundary between these two units is drawn with some difficulty. The upper contact of the Ion is conformable with the base of the Galena. In most places the contact is easily distinguishable although locally it is indistinct, especially in the eastern area of the outcrop, where strata near the contact are a grayish dolomite mottled with green areas that are argillaceous in part, but include no definite shale beds (see section 14, p. 309). Studies of many outcrops in the region from Rock— ford, Ill., on the southeast to Decorah, Iowa, on the northwest, amply supplemented with the examination of cuttings from wells have shown the contact between the Decorah and Galena to be a conformable one regionally; and detailed, studies of closely spaced outcrops in certain areas of the mining district indicate that these relations remain constant. Thus the writers do not agree with Kay (1932) and Atwater (Kay and Atwater, 1935, p. 109—110), that * * * in the I’pper Mississippi Valley Lead and Zinc District, there is a distinct disconfonnity at base of the Galena dolomite, bringing that formation in contact with beds of the 1011 and of the Guttenberg (“Oil rock member”) members of the Decorah formation. The same authors continued that * * * this is in contrast to the stratigraphic relations in sections northwest of the district, where the Presser limestone of the Galena group lies conformably on the Ion; this conformity continues into Minnesota. Kay later (1939, p. 27) repeated the former statement even more emphatically. It is the considered opinion of the writers that the sections of Kay and Atwater were incorrectly described and that the “elastic beds” which are said to mark this disconformity are actually altered strata in mineralized STRATIGRAPHY OF MIDDLE 0RDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT outcrops or weathered exposures heavily covered with loess and other surficial material. For example, the two cases cited by Kay and Atwater (1935, table I, p. 103 and table II, p. 104) one— eighth of a mile apart at- Speehts Ferry, Iowa, which they give as a major illustration of the so-called dis— conformity, are actually not at all dissimilar. They state (1935, p. 104) correctly that in the quarry the “Ion limestone has been so metasomatized as to become a dolomite.” The effects of this “metasomatism” have been not only to alter the lithology of the affected strata in both exposures, but in addition it reduced materially their thicknesses, as is illustrated by similar changes in limestones of the Quimbys hlill and Guttenberg, described previously (p. 283, 292). The table below lists the observed thicknesses of the various units at the two Spechts Ferry localities, together with the normal thicknesses: Efletts of alteration on thickness at two exposures only 600 feet apart at Spechts Ferry, Dubuque County, Iowa Thickness, in feet Rock units Quarry Ravine Normal Galena: Cherty unit (zone D) ______________________ : 6.0 5. 8 10 Decorah: ‘ Ion dolomite member. __________________________ 16. 3 13. 0 21 Guttenberg limestone member.___ ___ 14. 8 13. (i 15 Spechts Ferry shale member ____________________ 8. 1 8.0 8-8. 1 Platteville: Quimbys Mill member _________________ .3 .2 0. 2—0 3 This alteration of lithology and thickness is a common feature in the mines to the east, and has been noted as far west as the vicinity of Beetown, VVis., (10 miles northwest of the Spechts Ferry localities), where it was accompanied by significant zinc ore mineralization. Kay and Atwater described another exposure (1935, table IV, p. 105), which shows ocher-yellow silty clay with a “poorly defined” 3-inch bed of dolomite. This is nothing more than a weathered exposure in a stream bank. A similar condition is presented in their figure 4; the left part of the figure evidently shows a weathered and rubbly upper part of an outcrop. A detailed study of the outcrop by the present writers clearly established this conclusion. It is thought that the facies changes of the Ion have helped cause this misinterpretation, as the Ion strata are irregularly dolomitic in the area where Kay and Atwater noted the so-called disconformable relations. The misinterpretation was aided by the secondary effect of the alteration by mineralization as previously described. The Ion grades upward into the basal Galena. The rocks in the basal part of the Galena, however, contain slightly less greenish argillaceous material than the Ion 295 does in its dolomite facies in the mining district and to the southeast. Similarly, the basal Galena strata in the limestone facies northwest of the mining district contain less green fossiliferous shales than the Ion beds do in that area. DISTRIBUTION Similar to the Guttenberg member, the Ion is exposed mainly as ledges in streams and in quarries (see p. 287). FAUNA AND CORRELATION At the top of the Ion is a zone of Prasopora insularis Ulrich. These bryozoa are abundant in the north- western part of the area of outcrop, but become less common to the southeast so that only along the western edge of the mining district specimens of Prasopora are observed. This fossil is usually found in the upper foot and a half of the Ion. A zone containing abundant Glyptorthis bellarugosa (Conrad) occurs in the Ion 2—6 feet above its base. Kay (1935a, p. 290) stated that the Ion contains typical Trenton forms (see Twenhofel, and others 1954) and the ostracodes, Kay (1934, p. 331) found, have a “striking similarity” to those of the lower Hull (of Raymond 1914) of Ontario (fig. 44); (Kay, 1940, p. 235) correlated the Ion with the Phylloporina (Chasmatopora) and F ucoid zones of Minnesota (fig. 37). ECONOMIC PRODUCTS The Ion beds are ore-bearing and, together with the overlying Galena dolomite, comprise the host rock of most of the zinc—lead vein (“pitch and flat”) and breccia deposits of the mining district. The “pitch” of local miners refers to an inclined ore—filled fracture, and the “flat” is a vein along bedding; the two types of fracture are closely associated structurally, as the “flats” terminate against the “pitches.” DISTRIBUTION OF FACIES OF THE DECORAH AND CONDI- TIONS OF DEPOSITION The Decorah strata are mainly shale with thin lime- stone bands and nodules west of the mining district; at Decorah, except for the lower, unnamed limestone member, it is difficult to distinguish subdivisions. In the mining district, however, the main part of the Decorah is limestone with relatively little shale, and only the Spechts Ferry shale member contains more shale than limestone. East of the mining district shale in the Decorah is very rare; the rocks are dolomite. Not only is there a change in facies from dominantly shale in the west to dominantly carbonate rock in the east, but in addition the lower, unnamed limestone member and the Spechts Ferry shale member pinch out toward the east—the former in the western part of the 296 mining district, the latter in the eastern part; further- more, the Guttenberg member thins to the east of the district. This is generally in contrast with Platteville strata, as the Quimbys Mill and upper McGregor strata thin toward the west. Coupled with the evidence for a hiatus between the Plattcville and Decorah afforded by the bentonite layers in the lower Decorah strata, this indicates an incursion of the Decorah sea from the west over the corroded surface of the uppermost Platte— ville beds, in contrast to the eastward retreat of the sea at the end of the Platteville. The shale and exceedingly shaly limestone beds of the Decorah were deposited under generally shallow-water conditions of a platform environment (Sloss, 1947). The shale beds are unfossiliferous; however, fossils are found as floods in coquinalike layers, commonly broken and washed, and are found in extremely fossilif— erous fine-grained limestone beds. Thus, although the environment of the shale was generally hostile to life, the shells were contributed during the deposition of clay at times stormy conditions, and the 1- to 2-inch coquinoid layers therefore represent only instants in geologic time (see also Bucher, 1919). The limestone beds and interbedded shale partings of the Decorah in the mining district were deposited under conditions generally similar to those prevailing when McGregor and Quimbys Mill strata were accumu— latingflthat is, generally shallow—water environment. The more coarse—grained dolomitic rock east of the mining district is due to subsequent dolomitization apparently related to the Wisconsin arch (see p. 284). The bentonite beds, the result of volcanic activity probably in the southern Appalachian area (Nelson, 1922), may have caused disruption of animal and plant life development, although not so great as Sardeson (1926b) believed. GALENA DOLOMI’I‘E The beds called the upper magnesian limestone or cliff limestone by Owen (1840, p. 19, 24) were designated “Galena” by Hall (1851, p. 146) from their exposures in the vicinity of the town of Galena, J o Daviess County 111., (fig. 35). The strata making up the Galena in its type area were described by Hall as “gray, or drab- colored limestone, and very friable.” As exposed in the vicinity of Galena, Ill., they consist of light-grayish or drab to light—brownish or buff medium- to thick— bedded medium crystalline to coarse-grained, “sugary,” extremely vuggy dolomite. Many chert bands are present in the lower half of the formation, and the beds normally show a honeycomb type of weathering. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GrENERAL FEATURES Regionally it has been found useful to divide the Galena into two lithologic units, a cherty, and a non— cherty one (Agnew, 1950). The total thickness of the Galena in the mining district generally ranges between 215 and 230 feet. The following table shows the thickness of the Decorah formation, and the Galena dolomite and its subdivisions in wells irregularly distributed in and near the mining district: Thickness of the Decorah formation, Galena dolomite, and its sub- divisions in wells irregularly distributed in and near the mining district [Localities shown on fig. 35] Galena Deenah ______________ Cherty Nencherty Total County Home Well, Clayton County, Iowa (100. 16) ___________________________ 47 125 87 212 Colesburg city well 1, Delaware County, Iowa (100. 21) ........................... 46 107 113 220 Wiest Brothers farm well, sec. 12, T. 3 N., R. 5 W., Grant County, Wis. (2 miles south of 100.9) .......................... 39+ 119 102+ 221+ USBM Pikes Peak DD 7, sec. 33, T. 89 N., R. 2 E., Dubuque County, Iowa (5 miles west ofluc. 22) .................... 49 113 118+ 231+ Swanson farm, sec. 26, ’I‘. 1 N., R. 2 E., Lafayette County, Wis. (2 miles south of Shullshurg) .......................... 25 103 113 216 CHERTY UNIT Workable subdivisions of the cherty unit, arranged (Paul Herbert, Jr., Illinois Geological Survey, oral communications, 1944) in subsurface studies at the Bautsch mine, Illinois (fig. 35, 100. 30), were modified and applied to outcrops both locally and regionally in the course of the studies for the present report. Because these units are not stratigraphic entities large enough or definite enough regionally to require formal names, letter designations similar to those applied by Fowler and Lyden (1932) in the Tri—Qtate zinc district are used. The following points regarding the above classifica- tion are significant: (1) Zone D is lithologically transitional between the Ion beneath and zone 0. (2) Zone 0 contains the lowest widespread chert of the Galena formation; this chert is abundant both as beds and nodular bands, and as separate nodules. (3) Zone B is the lower Receptaeulites zone; it contains Receptacalites oweni Hall abundantly, although not uniformly; chert bands and nodules are not nearly so common as in zone 0, below. (4) In exposures in the area bounded by the towns of Galena, Platteville, Guttenberg, and Dubuque, zone A (see p. 267) can be divided generally as follows, in descending order: STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN Subdivisions of zone A of cherty unit of Galena dolomite Thickness (feet) Unit 1. Dolomite, light-buff, massive above to thin- bedded below; many chert bands; thin shale or shaly zone, locally with bentonite, at base,,-, 32 Unit 2. Dolomite, thin—bedded, as above; chert rare, Receptaculites and Ischadites sparse __________ 6 Unit 3. Dolomite as above, chert common _____________ 6 Unit 4. Dolomite, light—gray to drab, thick—bedded, sparsely cherty near top but chert common near base; Receptaculites and Ischadites present sparsely in a thin zone near middle __________ 26 Total, zone A __________________________ 70 From subsequent field work in the correlation of these subdivisions of the cherty unit, several facts are evident, namely: The shale parting at the base of zone A, unit 1 is in places more or less obscure; in some localities it is only a wafer-thin parting of dolomitic shale, whereas in others it is bentonite and shale; The less—cherty zones differ somewhat in the abund- ance of chert present; the value of this feature is com- plicated in well cuttings by caving from overlying cherty beds; The occurrence of Receptaculites and Ischadites in units 1 and 3 is helpful in outcrop studies, and the gray to drab color of unit 4, while not uniformly noteworthy in the outcrops, is nevertheless of value in the sub— surface studies; Strata in all the above units are commonly marked by extremely honeycomblike weathering (fig. 53); yet in some areas the same beds present a fairly massive appearance. Fucoidal surfaces are generally present and are especially characteristic of zone A, unit 4 and zone B. The four major zones (A—D) described above can be distinguished in outcrops, diamond—drill cores, and churn—drill samples mainly on the basis of the relative abundance of chert, because in churn drill cuttings Receptaculites can not be recognized. As all four of the zones generally have only one type of weathering—and thus the color and texture of the weathered rock are not usefulvthe relative amount of chert present and subtle differences in bedding are the distinctive features in exposures. In the western part of the district bentonite has been noted at a horizon normally represented by a shale parting near the base of unit 1, zone A. Localities showing this bentonite include the roadcut along U. S. Highway 61 in SEMNEM sec. 26, T. 3 N., R. 3 W., Grant County, Wis. (3 miles northwest of loc. 12, fig. 35), and the roadcut along U. S. Highway 52, at the north edge of Guttenberg, Clayton County, Iowa (fig. 35, 100. 33). 297 THE ZINC-LEAD DISTRICT FIGURE 53.—Honeycomblike weathering of zone P of noncherty unit, and zone A of cherty unit of Galena dolomite in roadcut, State Route 11, Grant County, Wis. (fig. 35, 100. 35). The thickness of the cherty unit remains fairly con- stant at 100—105 feet, although in the western part of the mining district isolated chert nodules and a thin band of nodular chert are found as much as 8 feet above the top of the very cherty sequence that marks the top of zone A of that unit. The cherty unit is dolomite in the mining district and to the southeast. Some distance northwest of the district, however, be— yond the mouth of the Wisconsin River the facies consists almost wholly of limestone, and in the same area green shale is also present in the lower three zones. The cherty unit includes units 2 through 8 of Staufier and Thiel’s section west of Wykoff, Minn. (p. 266). NONCHERTY UNIT The noncherty unit includes the upper, noncherty part of the Prosser cherty member, the Stewartville massive member, and the Dubuque shaly member. The first two of these three are similar in lithology and 298 are thus difficult to differentiate, although the base of the Stewartville is supposedly marked by the base of the upper Receptaculites zone. Unfortunately, Re- ceptaculites individuals are found sporadically at least 25 feet below the base of the zone; in poorly exposed strata their pro er stratigraphic assignment is therefore exceedingly di cult. Furthermore, in drill cuttings the Receptaculi es fossils have been destroyed, so the criterion is nonexistent. On the other hand, in areas of excellent exposures a bedding plane at the base of a zone of abundant Re— ceptaculiles can be taken as a datum for mapping geo— logic structure locally. This is the boundary selected between the Stewartville and zone P of the noncherty unit. The lower two subdivisions of the noncherty unit are light-yellowish-buff medium— to coarse-grained crystal— line to granular dolomite in medium to thick beds; the strata weather brownish, and with honeycomblike sur— faces that mask the bedding, making the rock appear massive. Minute yellowish to cinnamon-colored specks are characteristic of parts of the Stewartville. Bentonite is found locally along a bedding plane that normally contains only shale, about 18 feet above the base of the noncherty unit, as in the roadcut along U. S. Highway 20 at the east edge of Galena, Ill. (sec. 20, T. 28 N., R. 1 E). Zone P is 35—40 feet thick, and the rocks of the over- lying Stewartville total 37447 feet. The Dubuque member in the mining district is a light-gray to buff fine grained sugary and silty dolo- mitic limestone that weathers to a yellowish—buff color. This rock is medium- to thin—bedded and contains thin interbeds of platy dolomitic shale; as a result, it was called “shingle rock” by the early miners (Phillips, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1854, p. 129). The dolomitic limestone beds become thinner and more calcareous and shale is more abundant, in the upper part of the member. The contact of the Stewartville and Dubuque is gradational from massive honeycombed dolomite below to medium—bedded dolo- mite and interbedded dolomitic shale above. The Dubuque as a whole is more calcareous than the under- lying Stewartville. The brachiopod Lingala (Pseu— dolingala) iowensis Owen is common, the shell standing vertically in the dolomite. The contact between the Dubuque and the overlying Maquoketa is regionally disconformable (DuBois, 1945, p. 15), and locally a corrosion zone shows pits in the Galena dolomite that are filled with the rocks of basal Maquokcta.11 The thickness of the Dubuque is fairly constant, ranging from 35 to 45 feet in the outcrop. The noncherty unit is dolomite in the mining district and to the cast. Toward the west, however, the lower one—third and upper one-third become limestone, as is seen in Stauffer and Thiel’s section west of VVykofl’, lVfinn. DISTRIBUTION The Galena strata generally form bluffs; the rock is commonly quarried for road material and agricultural limestone. The location and thicknesses in good ex— posures of parts of the Galena and adjacent strata are shown in the following table. Because of its more thinly bedded and shaly char- acter, the Dubuque does not form bluffs as does the more massive rock below. Nevertheless the unit is resistant enough to stand fairly well, and it is locally 11 Rail, R. W., 1951, Ostracods from the depauperate zone of the Maquoketa shale: unpublished M. S. thesis, Ill. Univ., Urban-a, 111. Location and thicknesses (in feet) in good exposures of parts of the Galena and adjacent strata [Localities shown on fig. 35] Location Quarry and roadcut, U. S. Highway 151, Iowa County. Wis. (lee. 49) _______________ Quarry, south side of road NWMSEM sec. 20, T. 3 N., R. 1 W., 2 miles southwest of Platteville, Wis .................................................................. Readout, U. S. Highway 61, SWMSEIANEyé sec. 26, 'I‘. 3 N R. 3 W Grant County, Wis. (3 miles northwest of Ice. 12) Quarry, 500 feet south of County Trunk U, Grant County, V Roadcut, U. S. Highway 1.51, Grant County, Wis. (100. 6) _____ ,. Roadcuts, U. S. Highway 61, Grant County, Wis. (loc. 12) ______ _ East portal, old R. R. tunnel, Lafayette County, Wis. (100. 50) _____________________ Readout, near center cast line NWIANEM sec. 24, T. 1 N., R. 1 E., Lafayette County, Wis. (3 miles east of 100. 50) ............................................. Readout, State Route 11, Grant County, Wis. (10c. 48) ...................... West. portal Illinois Central R. R. tunnel, Jo Daviess County, Ill. (loc. 22) ......... - O Eagle Point Quarry, west side I". _S. Highway 151, Dubuque County, Iowa (100 11) ._ Readout, I.‘ . S. Highway 52, Clayton County, Iowa (106. 33) ________________________ 'Decorah Galena Cherty unit Noncherty unit Ion ‘- Zone D Zone C Zone B Stewart- \‘ille 13+ 10 10 ____________ """""" 8'4 """"" if; STRATIGRAPHY OF MIDDLE 0RDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT well exposed in road cuts and quarries. Some of the better exposures of the Dubuque strata are listed below: Roadcuts along new U. S. Highway 20, in sections 27 and 28, T. 89 N., R. 2 E., Dubuque County, Iowa. (6 miles southwest of loc. 11, fig. 35). Quarry at Loras College, in SEM sec. 23, T. 89 N., R. 2 E., Dubuque County, Iowa. This is the Dubuque type locality (3 miles southwest of 10c. 11). Ravine from east, in SW1 MNE sec. 33, T 27 N. R. 1 E. Jo Daviess County, Ill. (4 miles south of loc. 30). Roadcuts along State Route 11, in sec. 30, T. 1 N., R. 1 W., and in sec. 33, T. 1 N., R. 2 W., Grant County, Wis. (3 miles east, and 1 mile west, respectively, of loc. 48). Roadcut along U. S. Highway 151 at Chicago and Northwestern Ry. underpass, near center of east line see. 18, T. 3 N., R. 1 E., 3% miles east of Platteville, Wis. Wells that intersected representative thicknesses of the Galena are: Cherty Noncherty unit Locality unit (See fig. 35) Zone A Zone P Stewart- Dubuque (feet) (feet) ville (feet) . (feet) W ell, Swanson farm, SEVSWV sec. 26. T. 1N., R E. Lafayette County, Wisl. (2 miles 2south of Shullsburg) ..... 65+ 45 35 33 U. S. Bureau of Mines D, D. holes 15—24, 29, Bautseh lease Jo Daviess County, 111. (100. 30) ............................ 66~71 71—77. 5 42—46 Roadcut, State Route 11, Grant County, Wis. (Ice. 48) ........................... 69. 5 38 8+ __________ . S. Bureau of Mines D. D. hole 6, Pikes Peak lease, SE34 sec, 33, T. 89 N., R. 2 E., Dubuque County, Iowa (5 miles west of 100 22) ___________________ 67 34 49 14+ Woodward farm well near southeast corner NWV sec. 35, T. 89N., R. lE., Dubuque County, Iowa (9 miles west of 100. 22) .............................. 12+ 43 32 33 U S Bureau or Mines churn drill holes 1, 5, Piquette 3lewase, SEVNEV sec 35, T. 3 N., R. ,Grant County, V1 is. (2 miles northwest of Ice. 12) ........... 75:1: 36 19+ __________ Well, Wiest Brothers farm, SEVSWV sec. 12, T. 3N., R. 5W. Grant County, Wis. (2 miles south of Ice. 9) ___________ 73:1: 80 22+ Colesburg city well 1, Delaware County, Iowa (10c. 21) __________________________ 62¢ 43 35 35 VS ell, County Home, Clayton County, Iowa (10c. 16) __________________________ 85d: 7P 17 DISTRIBUTION OF FACIES OF THE GALENA AND CONDITIONS OF DEPOSITION The Galena in the mining district is mainly dolomite, with bands of chert nodules in the lower half. The upper part contains interbedded dolomitic shale. The dolomite (see p. 284) and possibly the chert were formed subsequent to the deposition of the strata and are related to the Wisconsin arch, although in a more general manner than the chert of the Platteville for— mation. The contact of the dolomite and limestone generally ascends in the cherty unit toward the west so that along the western fringe of the district the lower part of the cherty unit is limestone (see also Calvin and Bain, 1900, p. 406—411); limestone islands, such as the limestone lithology of zones 0 and D in the center of the mining district (near 10c. 32, fig. 35) are present, how— ever. Beds of the Dubuque are limestone north- 299 west of Elkader, Clayton County, Iowa (loe. according to Kay (1935c, fig. 8). The Galena strata were deposited as platform lime- stone (Sloss, 1947) in a fossiliferous environment of relatively shallow water. The limestone and shale sediments of the upper subdivision of the noncherty unit, and west of the mining district the lower strata of the noncherty unit were deposited under somewhat deeper water conditions, and 81055 would assign this facies also to the platform type of deposit. The two discontinuous bentonitic seams near the contact of the cherty and the noncherty units denote volcanic activity similar to that which supplied the bentonitic material of the Decorah (see p. 296). 16), FAUNA AND CORRELATION In Minnesota the Prosser member has been divided into the following three zones in ascending order (Ulrich, 1911b, p. 488): Vellamo (Olitambonites) zone, Nematopom zone, and Fusispira zone (fig. 37). Kay (1935a, p. 291) stated that the Vellamo zone is equivalent to the upper Hull (of Raymond 1914) (basal Trenton) in New York, and that the overlying Nema- topora zone has bryozoa that are common in the over- lying Sherman Fall formation in New York (see also Twenhofel, and others, 1954), although Sardeson (1897b, p. 190) had warned that these are facies faunas. Kay (1935a, p. 291) continued, The Lower Receptaculites zone, in which Receptaculitcs owem‘ Hall is abundant, persists southward [from Minnesota] at about the horizon of the Nematopora zone. This is true only for southeastern Minnesota and north- eastern Iowa; there it represents zone 0 as well as B of the cherty unit. To the south the base of the lower Receptaculites zone migrates upward stratigraphically; as a consequence, in the mining district zone 0 con- tains no Receptaculites individuals, whereas zone B above bears that fossil in abundance and is the lower Recepteculites zone there. Toward the north, as is well shown near Guttenberg, Iowa (fig. 35, 100. 33), the fossils are present four feet above the base of zone 0 and upward through all of zone B. Zone A can probably be correlated with the Sherman Fall (fig. 44) of northern Michigan (Kay, 1935a, p. 292). The Kimmswick limestone of lVIissouri is said to be the equivalent of the Prosser. The Stewartville has been correlated with the upper Cobourg (of Raymond, 1921) because of fauna, and with the McCune limestone (of Keyes, 1898) of eastern Missouri (Kay, 1935a, p. 292; Twenhofel, and others, 1954). Sardeson (1907, p. 193) correlated the Dubuque with the Oxoplecia (Triplecia) beds of Minnesota which, however, he placed in the Maquoketa shale. Kay 300 (19350, p. 583) correlated the Dubuque with the Collingwood formation of northern hdichigan both by fauna and because of stratigraphic position (see also Twenhofel, and others, 1954), and Stauffer and Thiel (1941, p. 90) hold that the Dubuque fauna of Minne- sota “seems to lack most of the diagnostic Galena fossils.” This is undoubtedly a facies fauna from the shale and limestone facies of the Dubuque, and thus difficulty may be expected in attempts to correlate it with the dolomite-limestone facies. It has been mentioned by several other stratigraphers that the Dubuque member is Utica or even Richmond in age. On the other hand, Kay (1935c, p. 579; also oral communication, December 27, 1945) has stated that he now considers both the Stewartville and the Dubuque to be of Trenton age, as does Fettke (1948, fig. 2). The existence of a hiatus between the Stewartville and the Dubuque, postulated by Kay and others apparently because of the dissimilarity between the Stewartville and Dubuque faunas, is doubted by the present writers, as no physical evidence of this feature can be found. Furthermore, the writers believe that this dissimilarity is due to facies. As the Dubuque fauna has not been carefully studied throughout all of its facies, the evidence is incon— clusive (see Twenhofel, and others, 1954, p. 270 and chart; Lattman, 1954). ECONOMIC PRODUCTS The Galena, called by the miners the yellow sandy (noneherty unit) and the drab (cherty unit), is the principal host rock for zinc and lead minerals. In the northern part of the district (15 miles northwest of Mineral Point) miners call the upper part of the Ion and the lower part of the cherty unit the wool rock. The main vein (pitch and flat) and breccia deposits are in the lower part of the Galena (zones B, O, and D of the cherty unit. In the upper part of the Galena dolomite (noncherty unit and zone A of the cherty unit are the “openings” along vertical joints (“crev— ices”) from which lead and zinc minerals were mined in the early days. An “opening" (Whitney, 1858, p. 4394140) is a zone of weathered sandy dolomite at a favorable stratigraphic horizon, and was the locus for lead mineralization. Several openings commonly are superimposed along a crevice. An opening normally varies between 5 or 6 feet wide and a fraction of an inch. Above the water table galena is the principal mineral of economic importance, and below it sphaler— ite is in most places predominant; in the zone near the water table smithsonite and galena are most common. The Galena dolomite is the principal source of water for most of the farms in the mining district. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY POST-GALENA ROCKS Because this report deals primarily with rocks related to the ore deposits, post-Galena rocks will be discussed only briefly. Information regarding these strata is derived mainly from studies by Agnew before 1947. More detailed discussions of the Maquoketa will be forthcoming in the publication dealing with the state of Iowa (Agnew, 1955), further work is contemplated for the Silurian rocks, and additional study of the post-Silurian deposits is currently under way. ORDOVICIAN ROCKS—MAQUOKETA SHALE The name Maquoketa was applied by White (1870, p. 181) to the shales exposed along the Little Maquo— keta River about 12 miles west of Dubuque, Iowa (fig. 31). In the mining district the Maquoketa occurs below and at the base of erosional remnants called “mounds;” in Wisconsin these are 4 and 7 miles east of Platteville, 16 miles south of Platteville, and 25 miles northeast of Mineral Point. Elsewhere in Wis— consin the Maquoketa shale is in the uplands south of Shullsburg and along the Grant-Lafayette County line south of Platteville, and in Illinois and Iowa it is exposed next to the escarpment of southward-dipping Silurian strata, which passes easterly and northwesterly from Galena, Ill. The Maquoketa is principally blue or gray dolomitic silty shale and some grayish—buff medium-grained sugary argillaceous thin—bedded dolomite; the lower 30-40 feet of the formation, however, is commonly brown in color. In the basal few feet phosphatic pebbles and minute fossils are present. This is the depauperate zone (Ladd, 1929, p. 371—375), a zone of ”universal smallness” that contains forms which, because of the unfavorable environment, do not attain the size of other species of these genera; they are dis— tinct from forms that are dwarfed, which under favor— able environmental conditions attain larger size. Away from the mining district the Maquoketa varies greatly in lithology; to the west, south, and east dolomite is more abundant than shale. Furthermore, the thickness is not constant. A few miles south of Galena, 111., in U. S. Bureau of Mines Mougin diamond-drill hole (fig. 35, loc. 30), the Maquoketa is only 108 feet thick; 8 miles south of Shullsburg, Wis, in the T. T. Redfern well (fig. 35,10c. 51), it is at least 170 feet thick; (data in files of Illinois Geological Survey, Urbana, III.) at Blue Mounds, Iowa County, Wis, NWX sec. 1, T. 6 N., R. 5 E. (3 miles east of Ice. 49, fig. 35), it is 240 feet thick; (data in files of Wisconsin Geological and Natural History Survey, Madison, Wis.) and in Fayette County, Iowa, it is about 260 feet thick (Savage, 1905, p. 486). STRATIGRAPHY OF MIDDLE ORDOVICIAN At the top of the hIaquoketa where it is thickest, a reddish hematitic clay and pebble zone has been re- ported (Agnew, 1955; Workman, 1950) outside the mining district. This zone (the Neda formation of Savage and Ross, 1916), probably represents a soil zone that marks the unconformity between the Maquoketa and the overlying Silurian. A good exposure of the upper part of the Maquoketa can be seen along U. S. Highway 67 at the south edge of Bellevue, Jackson County, Iowa (fig. 35, 100. 8; fig. 54); the lowermost beds, including the depauperate zone, can be seen in the railroad cut just west of Scales Mound, Jo Daviess County, Ill., SVV}£ sec. 26, T. 29 N., R. 2 E. (1 mile northeast of loo. 51, fig. 35). The Maquoketa strata are a poor host rock for zinc and lead minerals. In the Glanville prospect at Scales Mound, Jo Daviess County, Ill., NVV}£ sec. 24, T. 29 N., R. 2 E. (3 miles northeast of 100. 51, fig. 35), a short drift was driven for sphalerite and barite in dolomite at about the middle of the Maquoketa; the minerals did not occur in paying quantity. In some of the more dolomitic beds pyrite is not uncommon, and in many places it is abundant in the phosphatic depauperate zone. Fror'RE 54.—Maquoketa shale (0m) overlain by dolomite of early Silurian age (Sd), in roadcut and quarry, U. S. Highway 67, half a mile south of Bellevue, Jackson County, Iowa, (fig. 35, loo. 8). ROCKS IN THE ZINC—LEAD DISTRICT 301 The basal part of the Maquoketa contains abundant organic material and in many places gives an oily scum to the water bailed during the drilling of wells and prospect holes. SILURIAN ROCKS Silurian rocks, locally referred to as Niagaran al— though they are older than Niagaran, are found only in the “mounds” and at the southern edge of the min- ing district, where erosion of the southward dipping beds has created an escarpment (p. 300). Excellent ex- posures of the upper beds are seen in quarries at Platte Mound, locality 52, Lafayette County, Wis. (fig. 35) and Belmont Mound, Lafayette County, Wis, NW corner, sec. 2, T. 3 N., R. 1 E. (3 miles east of loc. 52); the lower beds are well exposed at Bellevue, Jackson County, Iowa (loc. 8). The Silurian rocks in the zinc-lead district are mainly yellowish—bufi medium- to coarse-grained “sugary” dolomite, in part vuggy. Near Galena, Ill., the thick- ness totals as much as 200 feet (Willman and Rey- nolds, 1947, p. 7). Near Galena the uppermost 90 feet of rock contains chert and is marked at the top by Pentamerus; next below occurs approximately 20 feet of noncherty strata; below that lies about 65 feet of cherty beds. The basal 20 feet of strata is argillace— ous dolomite. In general the Silurian rocks differ from the Galena dolomite in being less vuggy and more yellowish; furthermore, the Galena dolomite of the mining district possesses no beds comparable to the laminated silty and argillaceous dolomite of the lower part of the Silurian. Rocks of Silurian age overlie the Maquoketa uncon- formably; the basal argillaceous silty zone appears to thicken and thin inversely with the thickness of the underlying Maquoketa. An interesting effect of rock alteration is seen at the Blue Mounds (3 miles east of 100. 49, fig. 35), where the complete sequence of dolomite of Silurian age has been silicified (Whitney, 1862, p. 190. See also well for radio station WIBA—F M transmitter, N W}( sec. 1, T. 6 N., R. 5 E., Iowa County, Wis.; data in files of Wisconsin Geological and Natural History Survey, Madison, Wis.). This is thought to be due to leach- ing and weathering of a limestone that contained siliceous fossil shells (Hubbard, 1900). The dolomite of the Silurian, because of its similarity to that of the Galena, should be a potential host rock for zinc and lead minerals. However, because it is present mainly along the southern margin of the min- ing district and to the south, away from the center of mining activity, and as it is covered throughout most of its extent near the district by glacial deposits, its ore-bearing possibilities have not been appraised. Isolated crystals of sphalerite and galena have been 302 found in many places, and mining attempts have fol- lowed the discoveries of small amounts of galena at Sherrill Mound, 10 miles northwest of Dubuque, and near Clinton and Anamosa (Calvin, 1896, p. 110), Iowa, which are 30—40 miles southeast and southwest of Dubuque, respectively (fig. 31). South and west of the mining district the dolomite of Silurian age is an adequate source of water for farm wells. POST-SILURIAN DEPOSITS Several types of deposits of post-Silurian age have been found locally in the mining district. These include: 1. Boulders of quartz sandstone in anomalous strati— graphic positions, mostly in the Galena and Decorah. These may be related to sandstone “dikes” injected into joints from below, or as sedimentary filling from above. They occur at many localities in the central part of the mining district. 2. Boulders of hematite—near heads of ravines south— east of Hazel Green, Wis. (southwest corner of Lafayette County). 3. Boulders of quartzite and greenstone~near head of ravine in Wisconsin, 7 miles northwest of Spechts Ferry, Iowa (fig. 35, loc. 10). 4. Conglomerate at McCartneywpoorly cemented ag- gregate of local and exotic pebbles, at crest of ridge, near N0. 3, above. . These four types of deposits may have been laid down at one or more times since the end of the Silurian period. During Pennsylvanian time sandstone may have been deposited in what is now the mining district; the present northernmost exposure of sandstone of Pennsylvanian age in this general area is only 35 miles south of Dubuque. During Cretaceous time iron— cemented gravels or conglomerates were emplaced in this general region; the nearest such deposit is at Waukon, Iowa (fig. 35). During Pleistocene time it is possible that some of these deposits were laid down by any of several processes, including ice rafting. Further study of these interesting stratigraphic features is under way. LITERATURE CITED Agnew, A. F., 1950, Detailed stratigraphy of Galena-Decorah- Platteville sequence in Upper Mississippi Valley [abs]: Geol. Soc. America Bull., V. 61, no. 12, pt. 2, p. 1439. 1955, Facies of Middle and Upper Ordovician strata in Iowa: Am. Assoc. Petroleum Geologists Bull. V. 39, no. 9, p. 1703—1752. Agnew, A. F., Flint, A. E., and Allingham, J. W., 1953, Explora- tory drilling program of U. S. Geological Survey for evi— dences of zinc-lead mineralization in Iowa and Wisconsin, 1950~1951: U. S. Geol. Survey Circ. 231. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Agnew, A. F., Flint, A. E., and Crumpton, R. P., 1954, Geology and zinc-lead-barite deposits of area east of Cuba City, Wis.: U. S. Geol. Survey Mineral Inv. Ser. Field Studies Map MF 15. Agnew, A. F., and Hey], A. V., Jr., 1946, Quimbys Mill, new member of Platteville formation, Upper Mississippi Valley: Am. Assoc. Petroleum Geologists Bull., V. 30, p. 15854587. Agnew, A. F., and Hey], A. V., Jr., 1947, Recent developments in the Wisconsin-Illinois-Iowa lead-zinc district: Iowa Acad. Sci. Proc., v. 57, p. 225—231 [1946]. Allan, R. S., 1948, Geological correlation and paleontology: Geol. Soc. America Bull., V. 59, no. 1, p. 1—10. Allen, V. T., 1932, Ordovician altered volcanic material in Iowa, Wisconsin, and Missouri: Jour. Geology, V. 40, p. 259—269. Bain, H. F., 1905, Zinc and lead deposits of northwestern Illinois: U. S. Geol. Survey Bull. 246. 1906, Zinc and lead deposits of the upper Mississippi Valley: U. S. Geol. Survey Bull. 294. Bays, C. A., 1938, Stratigraphy of the Platteville formation [abs]: Geol. Soc. America Proc. 1937, p. 269. Bays, C. A., and Raasch, G. O., 1935, Mohawkian relations in Wisconsin: Kans. Geol. Soc. Guidebook, 9th Ann. Field Conf., p. 296—301. Bell, W. C., 1950, Stratigraphy: a factor in paleontologic taxon- omy: Jour. Paleontology, V. 24, no. 4, p. 492—496. Bell, W. C., Feniak, O. W., and Kurtz, V. E., 1952, Trilobites of the Franconia formation, southeast Minnesota: Jour. Paleontology, V. 26, no. 2, p. 175—198. Berg, R. R., 1953, Franconian trilobites from Minnesota and Wisconsin: Jour. Paleontology, V. 27, no. 4, p. 553—568. 1954, Franconia formation of Minnesota and Wisconsin: Geol. Soc. America Bull., V. 65, p. 857—882. Bevan, Arthur, 1926, The Glenwood beds as a horizon marker at the base of the Platteville formation: Ill. Geol. Survey, Rept. Inv. 9. Boericke, W. F., and Garnett, T. H., 1919, The Wisconsin zinc district: Am. Inst. Min. Engineers Bull. 152, p. 12134235; Trans, V. 63, p. 2134243, 1920. Bucher, W. H., 1919, On ripples and related sedimentary surface forms and their paleogeographic interpretation: Am. J our. Sci., 4th ser., V. 47, p. 149—210, 241—269. 1953, Fossils in metamorphic rocks: A review: Geol. Soc. America Bull., v. 64, p. 275~300. Calvin, Samuel, 1896, The geology of Jone County, Iowa: Iowa Geol. Survey, v. 5, p. 33—112. 1906, Geology of Winneshiek County, Iowa: Iowa Geol. Survey, V. 16, p. 37—146. Calvin, Samuel, and Bain, H. F., 1900, Geology of Dubuque County: Iowa Geol. Survey, v. 10, p. 379—622. Chamberlin, T. C., 1877, Geology of eastern Wisconsin: Geology of Wisconsin, v. 2, p. 914105. 1882, Ore deposits of southwestern Wisconsin: Geology of Wisconsin, V. 4, p. 365~57L Cohee, G. V., 1948, Cambrian and Ordovician rocks in Michigan basin and adjoining areas: Am. Assoc. Petroleum Geologists Bull, v. 32, n0. 8, p. 1417—1448. Cox, G. H., 1911, The origin of the lead and zinc ores of the upper Mississippi Valley district: Econ. Geology, v. 6, no. 5, p. 427—448, 582—603. Davis, R. E., 1906, Mississippi Valley lead and zinc district: Mining World, V. 24, p. 548-549. DuBois, E. P., 1945, Subsurface relations of the Maquoketa and HTrenton” formations in Illinois: Ill. Geol. Survey Rept. Inv. 105. STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC—LEAD DISTRICT Elder, S. G., 1936, The contact between the Glenwood and Platte- Ville formations: Ill. Acad. Sci. Trans, v. 29, no. 2, p. 164—166. Ellis, E. E., 1905, Zinc and lead mines near Dodgeville, Wis: U. S. Geol. Survey Bull. 260, p. 311—315. Fettke, C. R., 1948, Subsurface Trenton and sub-Trenton rocks in Ohio, New York, Pennsylvania, and West Virginia: Am. Assoc. Petroleum Geologists Bull., V. 32, p. 1457,1492, Flint, A. E., and Brown, C. E. 1955, Geology and zinc—lead deposits in the Durango area, Dubuque County, Iowa: U. S. Geol. Survey, Min. Inv. Ser. Field Studies Map MF 33. Fowler, G. M., and Lyden, J. P., 1932, The ore deposits of the Tri-State district: Am. Inst. Min. Engineers Tech. Pub. 446; Trans, v. 102, p. 206—251. Goldman, M. I., 1921, Lithologic subsurface correlation in the “Bend Series” of north-central Texas: U. S. Geol. Survey Prof. Paper 129—A. Grant, U. S., 1903, Preliminary report on the lead and zinc de- posits of southwestern Wisconsin: Wis. Geol. and Nat. History Survey, Bull. 9. 1906, Report on the lead and zinc deposits of Wisconsin: Wis. Geol. and Nat. History Survey, Bull. 14. Grant, U. S., and Burchard, E. F., 1907, Description of the Lancaster and Mineral Point quadrangles: U. S. Geol. Survey Geol. Atlas, folio 145. Grogan, R. M., 1949, Present state of knowlege regarding the pre-Cambrian crystallines of Illinois: 111. Acad. Sci. Trans, v. 42, p. 97—102. Grohskopf, J. G., 1948, Zones of Plattin-Joachim of eastern Missouri: Bull. Am. Assoc. Petroleum Geologists, v. 32, p. 351-365. Hall, C. W., and Sardeson, F. W., 1892, Paleozoic formations of southeastern Minnesota: Geol. Soc. America Bull., v. 3, p. 331—368. Hall, James, 1851, Lower Silurian system, in Foster, J. W., and others, Geology of Lake Superior land district: Congres- sional Documents, 32d Cong, Special sess, S. EX. Doc. 4, p. 140—166; Am. Jour. Science, ser. 2, v. 17, p. 181—194, 1854. Hall, James, 1862, Physical geography and general geology [of Wisconsin] in Hall, James, and Whitney, J. D., Report of the geological survey of the State of Wisconsin, v. 1, p. 1—72. Herbert, Paul, Jr., 1946, Distribution of the limestone and dolomite phases of the Oil rock and Glass rock, in Willman, H. B., Reynolds, R. R., and Herbert, Paul, Jr., Geological aspects of prospecting and areas for prospecting in the zinc-lead district of northwestern Illinois: 111. Geol. Survey Rept. Inv. 116. Hershey, O. H., 1894, The Elk Horn Creek area of St. Peter sandstone in northwestern Illinois: Am. Geologist, v. 14, p. 169—179. -——— 1897, The term Pecatonica limestone: Am. Geologist, v. 20, p. 66—67. Heyl, A. V., Jr., Agnew, A. F., Lyons, E. J., Behre, C. H., Jr. (in preparation), The geology of the upper Mississippi Valley zinc-lead district: U. S. Geol. Survey Prof. Paper. Heyl, A. V., Jr., Lyons, E. J., and Agnew, A. F., 1951, Explora- tory drilling in the Prairie du Chien group of the Wisconsin zinc-lead district by the U. S. Geological Survey in 1949—- 1950: U. S. Geol. Survey Circ. 131. Heyl, A. V., [Jr.], Lyons, E. J., Agnew, A. F., Behre, C. H., Jr., 1955, Zinc-lead—copper resources and general geology of the Upper Mississippi Valley district: U. S. Geol. Survey Bull. 1015—G, p. 227-245. 303 Heyl, A. V., Jr., Lyons, E. J., and Theiler, J. L., 1952, Geologic structure of the Beetown lead—zinc area, Grant County, Wis.: U. S. Geol. Survey Min. Inv. Ser., Field Studies Map MF 3. Howell, B. F., and others, 1944, Correlation of the Cambrian formations of North America: Geol. Soc. America, Bull., v. 55, p. 993—1003, chart. Hubbard, G. D., 1900, The Blue Mound quartzite: Am. Geolo- gist, v. 25, p. 163—168. Ireland, H. A., and others, 1947, Terminology for insoluble residues: Am. Assoc. Petroleum Geologists Bull., v. 31, p. 1479—1490. Kay, G. M., 1928, Divisions of the Decorah formation: Science, new ser., v. 67, pt. 1, p. 16. 1929, Stratigraphy of the Decorah formation: Jour. Geology, v. 37, no. 7, p. 639—671. —-—— 1930, Formations subjacent to the Black River-Trenton line [abs]: Geol. Soc. America Bull., v. 41, p. 201—202. 1931, Stratigraphy of the Ordovician Hounsfield meta— bentonite: Jour. Geology, v. 39, p. 361—376. 1932, Base of Ordovician Galena formation [abs]: Geol. Soc. America Bull., v. 43, p. 268. ——— 1934, Mohawkian Ostracoda, species common to Trenton faunules from the Hull and Decorah formations: Jour. Paleontology, v. 8, p. 328—343. 1935a, Ordovician system in the upper Mississippi Valley: Kans. Geol. Soc. Guidebook 9th Ann. Field Conf., p. 281—295. 1935b, Distribution of Ordovician altered volcanic mate— rials and related clays: Geol. Soc. America Bull., V. 46, p. 225—244. 1935c, Ordovician Stewartville-Dubuque problems: Jour. Geology, v. 43, p. 561*590. 1939, Stratigraphic setting, Wisconsin-Illinois district, in Bastin, E. S., and others, Contributions to a knowledge of the lead-zinc deposits of the Mississippi Valley region: Geol. Soc. America Special Paper 24, p. 25v28. 1940, Ordovician Mohawkian Ostracoda: Lower Trenton Decorah fauna: Jour. Paleontology, v. 14, p. 234—269. Kay, G. M., and Atwater, G. I., 1935, Basal relations of the Galena dolomite in the upper Mississippi Valley lead and zinc district: Am. Jour. Science, 5th ser., v. 29, no. 170, p. 98—111. Kay, Marshall, 1948, Summary of Middle Ordovician bordering Allegheny synclinorium: Am. Assoc. Petroleum Geologists Bull., v. 32, no. 8, p. 1397—1416. Keyes, C. R., 1898, Some geological formations of the Cap-au- Gres uplift [111.]: Iowa Acad. Sci. Proc., v. 5, p. 58—63. Krumbein, W. C., 1947, Shales and their environmental signifi- cance: Jour. Sed. Petrology, v. 17, no. 3, p. 101—108. Ladd, H. S., 1929, The stratigraphy and paleontology of the Maquoketa shale of Iowa: Iowa Geol. Survey, v. 34, p. 305—448. Lattman, L. H., 1954, The sub-Eden beds of the Ohio Valley around Cincinnati: Am. Jour. Sci., vol. 252, no. 5, p. 257—276. Lincoln, F. C., 1947, Last Chance zinc mine, Grant County, Wis: U. S. Bur. Mines Rept. Inv. 4028. McFarlan, A. C., and White, W. H., 1948, Trenton and pre- Trenton of Kentucky: Am. Assoc. Petroleum Geologist Bull., V. 32, no. 8, p. 1627—1646. Nelson, W. A., 1922, Volcanic ash bed in the Ordovician of Tennessee, Kentucky, and Alabama: Geol. Soc. America Bull., v. 33, p. 605~615. 304 Owen, D. D., 1840, Report of a geological exploration of part of Iowa, Wisconsin, and Illinois, 1839: Congressional Docu- ments, 26th Cong, 1st sess., H. Ex. Doc. 239. Percival, J. G., 1855, Annual report on the geological survey of the State of Wisconsin (1854), Madison. 1856, Annual report of the geological survey of the State of Wisconsin (1855), Madison. Pettijohn, F. J., 1926, Intraformational phosphate pebbles of the Twin City Ordovician: Jour. Geology, V. 34, p. 361—374. Phillips, J. V., 1854, The geology of the Upper Mississippi Lead region: Mining Mag, V. 2, p. 129—138. Powers, E. H., 1935, Stratigraphy of the Prairie du Chien (upper Mississippi Valley): Kans. Geol. Soc. Guidebook 9th Ann. Field Conf., p. 350 (fig. 224), 390—394. Raasch, G. O., 1935', Stratigraphy of the Cambrian system of the upper Mississippi Valley: Kans. Geol. Soc. Guidebook 9th Ann. Field :Conf., p. 302—315. 1951, Revision of Croixian Dikellocephalids: Ill. Acad. Sci., Trans. V. 44, p. 137—151. , 1952, Oneota formation, Stoddard quadrangle, Wiscon- sin: Ill. Acad. Sci. Trans, V. 45, p. 85—95. Raymond, P. E., 1914, The Trenton group in Ontario and Quebec: Canada Geol. Survey Summary Rept. 1912, p. 342—350. , 1921, A contribution to the description of the fauna of the Trenton group: Canada Geol. Survey Mus. Bull. 31. Rich, J. L., 1951, Three critical environments of deposition, and criteria for recognition of rocks deposited in each of them: Geol. Soc. America Bull., V. 62, no. 1, p. 1—20. Sardeson, F. W., 1896a, The St. Peter sandstone: Minn. Acad. Nat. Sci. Bull., V. 4, p. 64—88. 1896b, The Galena and Maquoketa series, Pt. 1.: Am. Geologist, V. 18, pt. 2, p. 356—368. 1897a, The Galena and Maquoketa series, Pt. II: Am. Geologist, V. 19, pt. 1, p. 21—35. -—— 1897b, The Galena and Maquoketa series, Pt. IV: Am. Geologist, V. 19, p. 180—190. . *fi 1897c, Nomenclature of the Galena and Maquoketa series: Am. Geologist, V. 19, p. 330—336. — 1898, Intraformational conglomerates in the Galena series: Am. Geologist, v. 22, p. 315—323. -——— 1907, Galena series: Geol. Soc. America Bull., V. 18, p. 179—194. 1926a, Beloit formation and bentonite (1): Pan Am. Geologist, V. 45, p. 383—392. -—— 1926b, Pioneer re—population of devastated sea bottoms: Pan Am. Geologist, V. 46, p. 273—288. —— 1933, Stratigraphic affinities of Glenwood shales: Pan Am. Geologist, V. 60, p. 81—90. Savage, T. E., 1905, Geology of Fayette County: Iowa Geol. Survey, V. 15, p. 433—546. Savage, T. E., and Ross, C. S., 1916, The age of the iron ore in eastern Wisconsin: Am. Jour. Science, 4th scr., v. 41, p. 187—193. Schuldt, W. C., 1943, Cambrian strata of northeastern Iowa: Iowa Geol. Survey, V. 38, p. 379—422. Scott, E. R., and Behre, C. H., Jr., 1935, Structural control of ore deposition in the VVisconsin—Illinois lead-zinc district [abs]: Ill. State Acad. Sci. Trans, V. 27, p. 117. Shaw, E. S., and Trowbridge, A. C., 1916, Galena—Elizabeth quadrangles: U. S. Geol. Survey Geol. Atlas, folio 200. Sloss, L. L., 1947, Environments of limestone deposition: Jour. Sed. Petrology, V. 17, no. 3, p. 109—113. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Stautfer, C. R., 1925, Mineralization of the Platteville—Decorah contact zone in the Twin City region: Geol. Soc. America Bull., v. 36, p. 615—622. , 1935, Conodonts of the Glenwood beds: Geol. Soc. America Bull., v. 46, p. 125—168. Stautfer, C. R., and Thiel, G. A., 1941, The Paleozoic and related rocks of southeastern Minnesota: Minn. Geol. Survey Bull. 29. Strong, Moses, 1877, Geology and topography of the lead region: Geology of \Visconsin [Wisconsin Geol. Survey], v. 2, pt. 4, p. 643—752. Templeton, J. S., 1948, Members of the Glenwood formation in northern Illinois and southern Wisconsin [abs]: Geol. Soc. America Bull., v. 59, no. 12, pt. 2, p. 1357. ——, 1950, The Mt. Simon sandstone in northern Illinois: Ill. Acad. Sci. Trans, v. 43, p. 151—159. Templeton, J. S., and Willman, H. B., 1952, Guidebook 16th Ann. Field Conf. Tri—State Geol. Soc. (central—northern Illinois): Ill. Geol. Survey. Thiel, G. A., 1937, Petrographic analysis of the Glenwood beds of southeastern Minnesota: Geol. Soc. America Bull., v. 48, no. 1, p. 113—122. Thwaites, F. T., 1923, The Paleozoic rocks found in deep wells in Wisconsin and northern Illinois: Jour. Geology, v. 31, no. 7, p. 529—555. , 1931, Buried pre-Cambrian of Wisconsin: Geol. Soc. America Bull., v. 42, no. 3, p. 719—750. Trowbridge, A. 0., and Atwater, G. I., 1934, Stratigraphic prob— lems in the upper Mississippi Valley: Geol. Soc. America Bull., v. 45, no. 1, p. 21—80. Trowbridge, A. C., and Shaw, E. W., 1916, Geology and geogra- phy of the Galena and Elizabeth quadrangles: Ill. Geol. Survey, Bull. 26. Twenhofel, W. H., and others, 1954, Correlation of the Ordovi- cian formations of North America: Geol. Soc. America Bull., v. 65, p. 247—298, chart. Twenhofel, W. H., Raasch, G. 0., and Thwaites, F. T., 1935, Cambrian strata of Wisconsin: Geol. Soc. America Bull., V. 46, no. 11, p. 1687—1744. Ulrich, E. 0., 1911a, Bearing of the Paleozoic Bryozoa on paleo- geography: Geol. Soc. America Bull., v. 22, p. 252—257. ——, 1911b, Revision of the Paleozoic systems: Geol. Soc. America Bull., V. 22, p. 281—680. , 1924, Notes on new names in table of formations and on physical evidence of breaks between Paleozoic systems in Wisconsin: Wis. Acad. Sci., Arts, Letters Trans, V. 21, p. 71—107. Ulrich, E. 0., Foerste, A. F., and Bridge, Josiah, 1930, systematic paleontology [of late Cambrian and early Ordovician forma- tions of Ozark region, Missouri]: Mo. Bur. Geology and Mines, 2d scr., v. 24, p. 188—212. White, C. A., 1870, Report on the geological survey of the State of Iowa: Iowa Geol. Survey, V. 1. Whitney, J. D., 1858, Chemistry and economical geology [of Iowa] in Hall, James and Whitney, J. D., Report on the geological survey of the State of Iowa, v. 1, p. 324— 472. , 1862, Stratigraphical geology, in Hall, James and Whit- ney, J. D., Report of the geological survey of the State of Wisconsin, V. l, p. 140—193. Williams, James Steele, 1952, Discussion in Symposium of evolu- tionary explosions in geologic time: Jour. Paleontology, V. 26, no. 3, p. 387—388. Willman, H. B., and Payne, J. N., 1942, Geology and mineral resources of the Marseilles, Ottawa and Strcator quad- rangles: Ill. Geol. Survey Bull. 66. STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT Willman, H. B., and Reynolds, R. R., 1947, Geological structure of the zinc-lead district of northwestern Illinois: Ill. Geol. Survey Rept. Inv. 124. Wilmarth, M. G., 1938, Lexicon of geologic names of the United States: U. S. Geol. Survey, Bull. 896, pts. 1, 2. Winchell, N. H., and Ulrich, E. 0., 1897, The Lower Silurian de— posits of the upper Mississippi provmce: Minn. Geo]. Survey, V. 3, pt. 2, p. lxxxiii—cxxviii. Workman, L. E., 1950, The Neda formation in northeastern Illinois: 111. Acad. Sci. Trans, v. 43, p. 176—182. STRATIGRAPHIC SECTIONS Section 1.—Type section of McGregor limestone member. Ravine from south, one mile west of McGregor, Clayton County, Iowa, NEV4 sec. 28, T. 95 N., R. 3 W. (fig. 35, too. 25) [Described by Paul Herbert, J r., and A. F. Agnew, Nov. 7, 1944; revised by Agnew, Aug. 18, 1945] Thickness Decorah formation: (feet) Spechts Ferry shale member: Shale, bluish-green, very fossiliferous; many lenses of greenish-buff fine—grained earthy limestone (partly covered) ______________________________ 6. 0 Shale, gray _____________________________________ 1. 6 Bentonite, with platy chocolate shale on top _______ . 1 Shale, brown and green, mottled __________________ . 3 Total, Spechts Ferry ________________________ 8. 0 Unnamed member: Limestone, dark-brownish-gray, medium crystalline__ . 7 Shale, dark-brown, platy, and light-gray, orange- weathering bentonite; bentonite grades laterally into orange siltstone ___________________________ . 4 Total, unnamed member _____________________ 1. 1 Platteville formation: McGregor limestone member: Limestone, light—grayish-bufi‘ with buff mottled areas, fine-grained, somewhat fossiliferous ________ 4. 8 Limestone, light-grayish-pink, very fine grained, very dense, in thin nodular beds, very fossiliferous (mainly brachiopods and bryozoans) ; many grayish- brown thin wavy shale partings _________________ 18. 0 Total, McGregor ___________________________ 22. 8 Pecatonica dolomite member: Limestone, somewhat dolomitic and silty, light- brown, fine- to medium—grained, sugary, in medium to thick beds; basal bed contains phos- phatic nodules ________________________________ 18. 3 305 Section 2.—Roadcut, County Trunk A, center 19% sec. 1, T. 4 N., R. 3 W., Grant County, Wis. (fig. 35, too. 28) [Described by A. F. Agnew, spring 1943; revised Aug. 11, 1953] Decorah formation: 721/3223“ Spechts Ferry shale member: Shale, green to olive, blocky; thin lenses of coquina _________________________________ 4. 5 Limestone, coarsely crystalline, coquinoid, wavy base; argillaceous coquina lens plastered against base ______________________________ 0. 3—0 5 Limestone, light-gray, fine-grained, dense ______ 0. 5—0. 7 Total, Spechts Ferry ____________________ 5. 5 Unnamed member: Limestone, dark-pink, coarsely crystalline ______ 0. 1 Shale, brownish-green, mottled _______________ . 2 Limestone, buff, fine-grained, dense ___________ . 5 Siltstone, dolomitic, brownish-yellow; brown soft bentonite at base, 0.1 ft thick __________ . 7 Total, unnamed member _________________ 1. 5 Platteville formation: Quimbys Mill member: Limestone, purplish-brown, fine- to medium- grained, dense; hard dark-brown shale at top--- . 3 Total, Quimbys Mill ____________________ 0. 3 McGregor limestone member (Magnolia of Bays and Raasch 1935): Limestone, light-gray, fine-grained, dense, con- choidal fracture ___________________________ 2. 0 Limestone as above, thin- to medium-bedded, fracture not conchoidal ____________________ 7. 0+ Section 3.——Quarry just west of Blanchardville, near center sec. 23, T. 4 N., R. 5 E. Lafayette County, Wis., (fig. 35, too. 29). [Described by A. F. Agnew, spring, 1943] Thickness Deeorah formation: (feet) Guttenberg limestone member: _ Dolomite, buff to light-brown, thin-bedded, medium- to coarse-grained, fossiliferous; some reddish- brown shale; a 0.2 ft bed of light gray, fine, dense dolomite at base ____________________________ 6. 5 Platteville formation: Quimbys Mill member: Dolomite, buff, fine-grained, sugary; conchoidal fracture; very fossiliferous, especially in upper 3.5 ft; band of chert nodules 0.5 ft below top; thin limonitic fossiliferous parting at base _______ 13. 0 McGregor limestone member (Magnolia of Bays and Raasch 1935): Dolomite, slightly grayish-buff, medium- to thick- bedded _____________________________________ 12+ 306 Section 4.—Coon Creek section, the second ravine north of road along south line SWM sec. 13, T. 98 N., R. 7 W., Winneshiek County, Iowa, (6 miles east of loc. 14, fig. 35). [Described by A. F. Agnew, Paul Herbert, In, H. B. Willman, October 1, 1944; revised by Herbert, November 7, 1944] Thickness Galena dolomite: (feet) Cherty unit (zone D): Limestone, buff to light-brownish, fine—grained, thin- bedded, fossiliferous; local greenish argillaceous areas and paper-thin green shale partings _______ 15. 0d: Decorah formation: Ion dolomite member: Shale, greenish, calcareous, fossiliferous; Prasopora_- . 4 Limestone, grayish-brown and gray, mottled, coarsely crystalline, dense, fossiliferous; local green shale partings __________________________ 2. 1 Shale, essentially green to gray-green; thin lenses of nodular limestone; Prasopora at top ____________ Limestone, brownish-gray, coarsely crystalline, dense, fossiliferous; some greenish argillaceous 10. 9 areas; interbedded green shale _________________ 1. 4 Shales, green to gray-green ______________________ 7. 9 Total, Ion ________________________________ 22. 7 Guttenberg limestone member: Limestone, gray, with dark—gray spots, medium- crystalline, fairly argillaceous __________________ 1. 0 Limestone, greenish-bufl', dense, nodular, fossilifer- ous; green and partly brown shale ; brown shale at base ________________________________________ 4. 0 Limestone, greenish-gray with dark-gray mottlings, dense, nearly lithographic, fossiliferous; some green calcareous shale ________________________ 1. 5 Total, Guttenberg _________________________ 6. 5 Spechts Ferry shale member: Shale, green to blue—green, with interbedded lenses of greenish fossiliferous coquina-like limestone; thin orange-weathering bentonite 2.4 ft above base--- 14. 5 Total, Spechts Ferry _______________________ 14. 5 Unnamed member: Limestone, dark-gray, dense, glassy ; thin brownish shale at top and base ------------------------- . 7 Limestone, light-brown, mottled gray, dense ------ 1. 1 Bentonite, orange—weathering -------------------- . 2 Shale, dark-brown ----------------------------- . 1 Total, unnamed member -------------------- 2. 1 Total, Decorah ---------------------------- 45. 8 Platteville formation: McGregor limestone member: Limestone, medium-gray, mottled, glassy, thin- bedded _________________________________________ 1. 5 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Section 5. Quarry, 1 mile north of Darlington, in S W}£SE}£ sec. 27, T. 3 N., R. 3 E. Lafayette County, Wis. (2 miles north of Zoo. 13, fig- 35) [Described by A. F. Agnew, August 11, 1945; revised April 7, 1946] Thickness Decorah formation: (feet) Ion dolomite member: Dolomite, light-grayish—blue, coarsely crystalline, sugary, thin-bedded; very fossiliferous near base_ 9+ Shale, white to light—brown; weathers yellowish- orange like bentonite but is hard and gritty because of dolomite grains -------------------- . 2 Guttenberg limestone member: Dolomite, light—brownish-buff, otherwise like Ion above; in thin nodular beds, but weathers massive; fossiliferous --------------------------------- 3. 0 Dolomite as above, but weathers to thin beds ----- 5. 0 Total, Guttenberg ------------------------- 8. 0 Spechts Ferry shale member: Limestone, like Quimbys Mill below, but greenish- gray; dolomitic shale parting at base ___________ . 2 Total, Spechts Ferry ----------------------- 0. 2 Platteville formation: Quimbys Mill member: Limestone, buff, fine-grained, greenish-gray mottled dolomitic shale parting at top; fucoidal openings containing phosphatic pebbles and green shale fragments in upper 0.2 ft _____________________ . 5 Dolomite, light—grayish-buff, slightly pinkish, fine- grained, dense, medium-thick bedded, nodular; conchoidal fracture --------------------------- 13. 5 Section 6.—Quarry Ice Cave Bridge, NE}£NW% see. 15, T. 98 N., R. 8 W., Decorah, Winneshiek County, Iowa (fig. 35) [Described by Paul Herbert, Jr., Nov. 9, 1944; revised by Herbert and Agnew, Sept. 1, 1945] Decorah formation: Spechts Ferry shale member: Rubble of green shale and limestone blocks; thin Thickness (feet) bentonite 0.3 ft above base _____________________ 5 + Shale, dark-green to olive, blocky; 0.2 ft grayish-buff argillaceous limestone beds at top and base ------ 1. 3 Shale, green above, dark brownish-gray mottled green and olive at base ________________________ . 9 Thickness, Spechts Ferry -------------------- 7. 2+ Unnamed member: Limestone, light-brown, fine-grained, very dense, medium—bedded; thin yellowish shale parting at top; undulatory lower surface -------------- 2. 4~2. 7 Shale and siltstone, buff to orange, bentonitic; grades laterally into bentonite; brown platy shale at base ------------------------------------- 0. 2—0. 5 Thickness, unnamed member _________________ 2. 9 Platteville formation: McGregor limestone member: Limestone, gray, weathers light-brown, mottled grayish ______________________________________ 10 + STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT Section 7.—Raoine, west of State Route 51, near center W}éNEV4 sec. 32, T. 97 N., R. 5 W., Atlamakee County, Iowa (fig. 35, « too. 35). [Described by A. F. Agnew, June 29, 1953] Decorah formation: T’E’Ifce'égm Guttenberg limestone member: Limestone, grayish—buff, fine-grained, dense, fossil- iferous; bufi‘ platy interbedded shale ____________ 10. 0 Covered __________________________________________ 10. 0 Unnamed member: Limestone, flesh-colored, fine-grained, dense, fossil- iferous _______________________________________ . 8 Limestone in 2 beds, the upper like that above; the lower bluish to flesh—colored ____________________ 5 Bentonite, orange, soft ______________________ 0. 1~ 0. 2 Thickness, unnamed member _____________ 1. 4~1. 5+ Platteville formation: McGregor limestone member: Limestone, buff to flesh— colored, mottled brown, fine-grained, dense ____________________________ .5 Limestone, buff, thin— bedded ____________________ 22. 0:1: Section 8.——Quarry at Spechts Ferry, Iowa, near center sec. 4, T .90 N., R. 2 E., Dubuque County, Iowa (fig. 35, Zoo. 10) [Described by A. F. Agnew, November 1942; revised October 1945.] Decorah formation: Guttenberg limestone member (”oil rock”) : Limestone, tan to light-pinkish—brown, fine-grained, dense, conchoidal fracture, nodular; interbedded Thickness (feet) brown shaly partings __________________________ 12. 4 Spechts Ferry shale member (clay bed): Limestone, light- to medium-brown, fine grained, crystalline, dense, nodular; phosphatic pebbles rare near top; olive-brown shale parting at top- _ _ . 7 Shale, greenish and brownish, weathers brown; blocky _______________________________________ . 3 Limestone, light-brown to buff, slightly mottled greenish, finely crystalline, dense, fossiliferous; phosphatic nodules rare at base; basal contact wavy ________________________________________ 1. O Shales, greenish-blue and purplish—gray, blocky, thin-bedded; with thin coquinas and dark—brown weathered zones ______________________________ 1. Limestone, light—greenish-gray, fine-grained, dense___0. 1—. Shale, greenish-blue, blocky, very fossiliferous ______ Limestone as above, with coquina at top ___________ Shale, greenish-blue, blocky ______________________ Coquina _______________________________________ Limestone as above _____________________________ Shale, greenish—blue, blocky ______________________ Limestone as above _____________________________ Shale, yellowish-olive, soft, clayey ________________ Shale, purplish-gray, thin-bedded, calcareous, fossil- iferous ______________________________________ Shale, soft, olive, weathers orange (fossil remains?)_~ . 0—. Shale, dark-grayish—green, blocky _________________ Limestone, dark-greenish—gray, fine-grained, dense, conchoidal fracture ____________________________ . 3 r—tmwoai—‘oowwww gov-tn; 307 Section 8.—Quarry at Spechts Ferry, Iowa, eta—Continued Decorah formation—Continued ”$567,?“ Guttenberg limestone member—Continued Shale, dark-grayish-olive, hard. calcareous, fossil— iferous ______________________________________ . 1 Limestone, as next above ________________________ . 5 Shale, dark-brownish-gray _______________________ . 1 Bentonite, weathering yellowish-orange ____________ . 1 Shale, dark-brownish-gray, blocky ________________ . 3 Limestone, as next above; brownish in lower 0.1 ft__ . 3 Total, Spechts Ferry __________________________ 8. 8 Platteville formation: Quimbys Mill member (”glass rock”): Shale, dark-brown, mottled with greenish areas, hard, thin-bedded __________________________________ 0. 1 Shale, dark-brown, platy, and brown dense lime- stone ________________________________________ . 2 Total, Quimbys Mill ________________________ 0. 3 McGregor limestone member (Magnolia [of Bays and Raasch 1935] Trenton): Limestone, light—grayish-buff near top, merging into light-greenish—gray below, finely crystalline, dense, fossiliferous, conchoidal fracture ________________ 3. 1 Section 9.~—Blufl, southeast bank Galena River, in NW}£NE}4 see. 15 T. 1 N., R. 1 E., Lafayette County, Wis. (one mile south of too. 27, fig. 35) [Described by A. F. Agnew, September 18, 1944] Decorah formation: “(1%ng Guttenberg limestone member (”011 rock”): Limestone, light pinkish—buff, fine-grained, dense, conchoidal fracture, nodular, fossiliferous; light- brown, chocolate—colored shale _________________ 13 i Spechts Ferry shale member (clay bed): Shale, brown and greenish-olive, blocky ___________ . 3 Limestone, light—gray, very thin bedded, nodular, fine-grained, dense, fossiliferous ________________ . 9 Limestone, mottled pink and greenish, fine—grained, dense, fossiliferous; phosphatic nodules abundant- . 4 Shales, greenish and brownish, calcareous; limestone nodules; greenish and pink coarsely crystalline coquina ___________________________________ 0. 1—. 2 Limestone, light-greenish—gray, very fine grained, very dense, sublithographic, nodular ___________ 1. 0 Bentonite, white; weathers orange—brown _______ 0. 1—. 2 Limestone, nodular, as above but unfossiliferous- _ 0. 1—. 2 Total, Spechts Ferry ____________________ 3. 0—3. 1 Platteville formation: Quimbys Mill member (”glass rock”): Limestone, dark-pink, more coarsely crystalline than above, nodular, fossiliferous ___________________ 0. 1 Limestone, purplish, medium-grained, dense, con- choidal fracture ______________________________ 6+ 308 Section lO.—0uarry half a mile east of Calamine, Wis, just north of the bend in the road, near the southwest corner sec. 9, T. 3 N., R. 3 E., Lafayette County, Wis. (fig. 35, loc. 42) [Described by A. F. Agnew, August 11, 1945] Decorah formation: 7762,2388 Guttenberg limestone member: Dolomite, light—brown to buff, weathers light- yellow-buff ; fine— to medium-grained; fossiliferous ; in thin, wavy beds with light-brown argillaceous and thin platy shale partings; very shaly and fossiliferous in lower 0.5 ft ____________________ 5+ Dolomite, light-brown to buff, fine-grained, fossili- ferous; very sandy with dolomite granules ______ 2 Dolomite, light-grayish—bufl', finely granular, dense_ . 1 Spechts Ferry shale member: Dolomite, greenish and buff-spotted, argillaceous, containing phosphatic nodules; otherwise not fossiliferous _______________________________ 0. 0—. 1 Platteville formation: Quimbys Mill member: Dolomite, light-grayish—buff, slightly pinkish, fine- grained, medium—bedded, nodular; light—brownish- bufl argillaceous and platy shale partings rare, fossiliferous; zone of involutions at top contains phosphatic pebbles and green argillaceous dolo- mite inclusions ______________________________ 11. 5 Section 11.——Roadcut, U. S. Highway 52, about 1 mile north of Guttenberg, Iowa, in SW% sec. 5, T. 92 N., R. 2 W., Clayton County, Iowa (fig. 35, loc. 33) Described by A. F. Agnew, Paul Herbert, Jr., H. B. Willman, October 1, 1944; revised by Herbert and Agnew, September 3, 1945] Decorah formation: Ion dolomite member: Limestone, dark-gray to pinkish, crystalline, densey Thickness (feet) thinly bedded ______________________________ __ 2. 7 Shale, gray-green, platy, calcareous ,,,,,,,,,,,,, __ . 3 Limestone, as above, but more bluish and fossiliferous- - 8 Shale, as above _________________________________ . 8 Guttenberg limestone member: Limestone, slightly more pink than above, becoming darker pinkish brown downward, nodular; reddish— brown shale common __________________________ 6. 9 Shale, brown, wavy-bedded, some reddish cast _____ . 3 Limestone as above _____________________________ 7. 6 Shale, light-brown ______________________________ . 1 Limestone as above, but very dense, glassy, with conchoidal fracture ____________________________ . 6 Total, Guttenberg __________________________ 15. 5 Spechts Ferry shale member: Shale, greenish-olive, weathering brownish, platy, fossiliferous ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, . 4 Limestone, light-grayish—brown to grayish-green; argillaceous phosphatic nodules common ,,,,,,,,, . 7 Shale, green, blocky; thin coquina beds _____________ 1. 5 Limestone, blue-green; in thin beds, very fossil- iferous _______________________________________ 1. 1 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Section 12.—Quarry %—mile north of York Church, Wis., near center sec. 5, T. 4 N., R. 6 E, Green County, Wis. (fig. 35, Zoo. 44) [Described by A. F. Agnew, spring, 1943] Decorah formation: Ion dolomite member: Thickness (feet) Shale, gray-green, gritty, somewhat fossiliferous, thin-bedded argillaceous greenish-gray dolomite__ 4. 0 Dolomite, in thicker beds but otherwise similar to that above ___________________________________ 5. 5 Guttenberg limestone member: Dolomite, light-gray to buff, pinkish, medium- to fine-grained, somewhat vuggy, thin— to medium- bedded, nodular; a few very thin stringers of reddish-brown platy shale; at base a 0.1-ft zone of red shale and pinkish dolomite _______________ 6. 5 Platteville formation: Quimbys Mill member: Dolomite, light-cream to buff, fine-grained, very dense, semiconchoidal fracture; layer of chert 1.5 ft below top; at base a thin reddish-brown in— distinct shale parting __________________________ 13. 0 Section 13,—Quarry, 500 feet south of County Trunk U, near center of SEIA sec. 18, T. 3 N., R. 3 W., Grant County, Wis. (fig. 85, Ice. 47) [Described by A. F. Agnew, July 1, 1945] Galena dolomite: Twig?” Cherty unit (zone D): Dolomite, buff, vuggy, coarse-grained ____________ 8. 5 Decorah formation: Ion dolomite member (gray beds): Shale parting, olive-gray, dolomitic ______________ . 1 Limestone, dolomitic, bufi to gray, coarsely crystal- line, vuggy __________________________________ 1. 4 Shale, greenish-gray, argillaceous; greenish-gray shaly dolomite _______________________________ . 7 Limestone as above ____________________________ 9. 3 Limestone, light-gray, coarsely crystalline _________ 2. 5 Total, gray beds ___________________________ 14. 0 Ion dolomite member (blue beds): Shale, olive-gray, very fossiliferous; thin coquina beds _______________________________________ 1. Limestone, dark-gray, medium-crystalline, dense- _ _ Shale, greenish-gray ____________________________ Limestone as above _____________________________ Shale as above ________________________________ Limestone as above ____________________________ 1. Shale as above ________________________________ Limestone, grayish—green, coarsely crystalline; rounded medium-sized quartz sand grains _______ Shale parting, greenish-gray _____________________ . l Limestone, light-gray to bulf, coarsely crystalline, NfiWQHCflCD ‘1 transitional with Guttenberg limestone below____ 1. 5 Total. blue beds ___________________________ 7. 5 Total, Ion ________________________________ 21. 5 Guttenberg limestone member (”oil rock”): Limestone, light brownish-pink, medium—crystal— line, dense, fossiliferous; brownish wavy thin shale beds _______________________________________ 5+ STRATIGRAPHY OF MIDDLE ORDOVICIAN ROCKS IN THE ZINC-LEAD DISTRICT Section 14.v~0uarry, southwest edge of Darlington, Wis, in SEL/i sec. 3, T. 9 N., R. 3 E., Lafayette County, Wis. (fig. 85, Zoo. 13) [Described by A. F. Agnew, summer 1943] Galena dolomite: ”Mm“ Cherty unit (zone C): (feet) Dolomite, grayish—buff, coarse-grained, mottled; bands of chert nodules common ________________ 2. 0 Galena and Decorah formations: Cherty unit- (zone D)—Ion member (gray beds): Dolomite, light creamy-gray to light-olive, coarsely granular, mottled ____________________________ 15. 0 Decorah formation: Ion dolomite member (gray beds): Dolomite, lighter colored than above; a very few olive-buff shale beds, including a 0.1-foot shale 2 feet from top, and a 0.2—ft shaly zone 2.5 ft above base ________________________________________ 10. 5 Ion dolomite member (blue beds): Dolomite, dark-bluish—gray to light-blue, fine- to medium—grained, with much interbedded shale—— the upper 0.5 ft is very shaly, fossiliferous ______ 6. O Guttenberg limestone member (”oil rock”): Dolomite, reddish, very coarse—grained, vuggy ————— 3+ 309 38 ‘ ‘ i : Ffafiflxd. .1312; :31“, A! 3 L , m‘., “4,3“ 4 u an: m 2,,“ INDEX A Page G Page Abstract ____________________________________________________________________ 251—252 Galena deposits _______________________________________________________________ 300 Acknowledgments ____________________________________________________________ 254 Galena dolomite, chcrty unit, facies of. ________________________________ 257, 297 Allan, R. S,, quoted. . 260—261 cherty unit, fossils in ............................................ 297 Apatite _______________________________________________________________________ 289 subdivisions ________________________________________________________ 296—297 Aquifer, Quimbys Mill as an _________________________________________________ 289 thickness _____________________________________________________ . ..... 297, 298 Atwater, G. I., and Kay, G. M., quoted ____________________________________ 294,295 conditions of deposition. 299 B correlation ________________________________________________________________ 299 Bain, H. F., quoted ____________________________________________________ 261,262,292 , ‘Ylthfmlts m Mlnnesma’ Chart """"""""""""""""""""" 264 distribution _________________________________________ 298—299 Bays, 0. A., quoted .............. 269, 279 economic roducts 300 Bays, 0. A., and Raascli, G. 0., quoted ______________________________________ 269 . p """""""""""""" facies ................................... 299 Bell, W. C., quoted __________________________________________________________ 261 . . . . . fossfls _______________________________________________________________ 266—267, 299 Beloxt dolomite, claSSification of ___________________________________ 262—264 1i tholo i0 descri tion 255 259 207 Bentonite layer._.. 263, 264—265, 283, 287, 288—289, 290, 292, 294, 296, 297, 298, 299 g . p .- i '7: """"""""""""""""""""""""" ’ ' noncherty unit, bentonite m Bull dum ..................................................................... 292 . . description _________ C fossils ........ Calvin, Samuel, quoted ____________________________________________________ 275, 285 thickness ........................................................ Cambrian age, rocks of _____________________________________________ 254-256, 271-272 stratigraphic column _________________________________________________ Chert __________________________________________________________ 259, 267, 281, 290, 301 stratigraphic relations. ........... 256, 257 Cherty unit. See Galena dolomite. stratigraphic sections ___________________________________________ 285, 293, 306—309 Conglomerate, at McCartney ________________________________________________ 302 subdivisions of __________________________________________________________ 265, 269 Cox, G. H. quoted ____________________________________________________________ 262 thickness __________________________________________________________ 296, 298 D See also Dubuquc member and Stewartville member. Garnet _________________________________________________ 276, 277, 278, 281, 283, 287, 289 Decorah formation, boundary of, with Platteville formation ________________ 261—262 Geographic setting..." 252 condition of deposition _______________________________ 296 Glass rock. See Quimbys Mill member of Platteville formation. correlation with units in Minnesota, chart ________________________________ 264 Glenwood shale member of Platteville formation, conditions of deposition... 284 cross section of ____________________________________________________________ 263 correlation __________________________________________________________ 264,277,278 description ........... 255,259, 285—286 distribution of ........................................................... 277 disconformity with Platteville formation ____________________________ 256,259, 288 economic products ................................................. _ 277 distribution of facies ____________________________________________________ 295—296 fossils _____________________________________________________________________ 277 stratigraphic column.. . .. 268 Iithologic description . . ......... 268, 275—276 stratigraphic relations... _ 256,257 stratigraphic grouping of .................................................. 256 in Missouri ..... ___ 257 stratigraphic relations of ____________________________________________ 257, 276—277 stratigraphic section ____________________________________ 285, 287, 293—294, 305—309 stratigraphic sections. . _ _______________________ 275 thickness _________________________________________________________________ 296 thickness of different facies - _________________________ 276 unnamed limestone member .......................................... 264—265 Grant, U. S., quoted .............................. 276,292 See also S pechts Ferry shale member, Guttenberg limestone member, and Greenstone boulders ............................ 302 Ion dolomite member. Guttenberg limestone member of Decorah formation, correlation ............ 264, 293 Dolomitization, effect of ____________________________________________________ 283,292 cross section showing stratigraphic relations .................... 263 Drcsbach sandstone .................................. 254, 255, 271, 272 distribution ............................................................ 292—293 Driftless Area ____________________________________ 252 effect of dolomitization of _________________________________________________ 292 Dubuquc member of Galena dolomite, contact of, with Maquokcta shale ..... 298 effect of silicification on .................................... 292 contact of, with Stewartville member ___________________________________ 265, 298 facies relations of ................................ 257,286, 288,292 correlation ..................................... 259, 264, 299—300 fossils ................................. 293 stratigraphic column showing _____________________________________________ 268 lithologic description ___________________________________________________ 268, 289 thickness ................................................................. 298 minerals in ............................................................... 293 E stratigraphic grouping of._ 256 Eau Claire sandstone ............................................... 254,255, 271,272 31221152251110 sections... """"" 285,287,290—291,:gg—:3: Ellis. E. E., quoted ........................................................... 262 """"""""""""""""""""""""""""""""""""" ’ F H Hematite boulders ____________________________________________________________ 302 Facics relationships, diagrammatic cross section ______________________________ 257 I Fleld work-... """""""""""""""""""""""""""""""""" 252 .254 Introduction _______________________________________________________________ 252—254 Flat, definition of term ....................................................... 295 . . . , . Ion dolomite member of Decorah formation, correlation . 264, 295 I ossds, Bellerophim bed. __ 264, 265 . . . . . . cross section showmg stratigraphic relations . . _ ................. 263 Clztambomles beds ...................................................... 264, 266 . d ‘ an H t one 300 economic products _________________________________________ 295 ED. 9 a e Z """""""""""""""""""""""""""""" facies relations __________________________________________________ 257, 286, 288, 294 Ivimspira beds... _. 264, 266, 278 fossils 295 Madm“ mnem' 264' 265—266 lithologic description _____________ 268, 293—294 need for study of ... 260—261, 265 . . . _ stratigraphic grouping of .................................................. 256 Nematopom beds ................................................... 264, 266. 248 . . . . _ stratigraphic relations .................................................. 294—295 Receptaculttes zone ............................ 262—263, 267, 268, 296, 294—298, 299 . . . . stratigraphic section .................. _. _ 285, 290, 293—294, 306—309 zone of 011th subaequata ................................... 262—263 . . thickness ........................... _ 259,294, 295,298 Vanuxemuz bed """"""""""""""""""""""""""" ‘ 264’ 282 Iron mineralization 2‘2 273 274 See also Stratigraphic sections and individual formations and members of """""""""""""""""""""""""" ' ’ ’ formations. J Franconia sandstone ................................................. 254, 255, 271, 272 Jordan sandstone ............................................................. 27 1 311 312 INDEX K Page Q Page Kay, G, M., quoted ........................................ 267, 279, 286, 289, 293, 299 Quartzite boulders ____________________________________________________________ 302 Kay, G. Mo and Atwater, 0- 1-. quoted ------------------------------------ 294, 29-5 Quimbys Mill member of Platteville formation, conditions of deposition ______ 285 L correlation ............................................................ 284 Lead minerals ______________________________________ 272, 273, 277, 282,289, 293, 294, 300 322::12f511535h0“1ng: _____________________________________________ 233—32: Literature cited _______________________________________________ ___. . 302—305 economic products... _ 284 Location of zinc-lead district _________________________________ 252,253 effect of dolomitization on. ________ 283 Lower Magncs1an limestone. See Prairie du Chien group. facies relationships iiiiiiiii 257' 284, 288 M lithologic description ________________________________________ 259, 268, 282—283 origin and application of name __________________________________________ 269 McGregor limestone member of Platteville formation, conditions of deposi— stratigraphic grouping of ________________________________________________ 256 tion ——————————————————————————————————————————————————————— 284-285 stratigraphic relations ______________________________________________ 259, 283, 288 correlation. 264, 270, 278, 280, 282 stratigraphic sections ...................................... 274, 282, 285, 305—308 distribution ............. .. 282 thickness _______________________________________________________________ 284, 295 facies relationships. fossils _______________ R 1331:1352?fiiii‘fitff’?ii::i:i:1::: .::::::::::: :1:::::::::::::::::::::::f“""’323 Ram, G- 0-, with Bays, 0. 1., quoted ------------------------- 29 Origin and application of name... 269 ROSS‘ 0' S" quoted """"""""""""""""""""""""""""""""" 288 stratigraphic grouping of ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 256,268 stratigraphic relations _______________________________________________ 281-282 S Stratigraphic sections. 274475, 282, 305_307 St. Peter sandstone, description .................................... 255, 256, 273—274 Madison sandstone", _____ __ 269, 271 stratigraphic sections ............... 275 Magnolia beds ,,,,,,,,,, 269, 274—275, 279—282, 284—285 Sandswne boulders ------- -- 302 See also McGregorlimcstone member of Platteville formation. Sardeson, F- W '1 (111°th ----- 263: 266 Map, showing localities cited in text _________________________________________ 258 Shaw E. W., with Trowbridgc, A. C., quoted ________________________________ 288 Maquoketa shale, contact of, with Dubuque member of Decorah formation... 298 Silicification, effect or --------------------------------------------------------- 292 description ___________________________________ 255, 259, 268, 300.301 Silurian age, TOCkS 01" --------------------------------------------------- 255, 301-302 minerals in ___________ , 301 Smithsonite .................................................................. 300 Mitfiin beds ____________________________________________ 269, 274—275, 279—282, 284—285 Spechts shale member of Decorah formation, condition of deposition .......... 296 See also McGregor limestone member of Platteville formation. correlation ------------------------------------------------------------- 264, 289 Mounds, in VVisconsin.. _______________________________________________ 300 facies relationships. 257, 286, 288, 295—296 Mount Simon sandstone. __________________________ 254, 255,271,272 “155115 ----------------------------- » 289 economic products... _ ...... 289 . N lithologic description ............................................. 268, 286—287 N oncherty unit. S“ Galena dolomite. significance of phosphatic pebbles in ________________________ ‘ 288 stratigraphic grouping of ____________________________________ 256 Oil rock 0 262 283 290 292 stratigraphic relations .................................................. 288, 289 -------------- f""""""“"'““"“““"'"“j""“ I r “ cross sectionshowing.._...___.______.___...__.___________.___.__.._._ 263 ordf::c‘;;:’a::‘:::::‘§“mam“ member 0f Decmah formatzlgg-zfifi 272—274 300—301 stratigraphic sections. __ 274, 282, 285, 287, 291, 305—308 ’ """"""""""""""""""" ’ ’ , thickness _______________________ 259, 286—287, 295 P Sphalerite ________________________________________________________________ 306 Staufler, C. R., and Thie], G. A., quoted _____________________________________ 266 Pecatonica dolomite member 0f Platteville formation, building stone ------- 278) 279 Stewartvillc member of Galena dolomite, contact of, with Dubuque member. 265, 298 condiltions of deposition ——————————————————————— .. 284 correiation __________________________________________________ 264, 265-266, 299 corre ation ____________ 264, 278,279 fossils _________________________________________________________________ 265~266 Sistaibution -------------------------------------------------------- 273—279 stratigraphic column showing .......... 268 055i 5 --------------------------------------------------------------------- 279 stratigraphic section, quoted... 266 lithologic description ----------------------------------------- 259, 268, 277-278 Stratigraphic charts ____________________________________ 255, 264, 268, 270, 278, 280 origin and application or name... 269 Stratigraphic column, of Platteville, Decorah, and galena strata ..... _.._ 26S stratigraphic $0119ng 0f—-—- ----- 256 Stratigraphic cross section _____________________________________________ _.. 257, 263 Stratigraphic relations ---------------------------------------------------- 278 Stratigraphic grouping of the rocks _____________________ 256 stratigraphic sections. —- -- 275. 305 Stratigraphic names, origin and application of ______________________________ 269 thickness --------------------------------------------- 257: 259, 278 Stratigraphic principles _____________________________________________________ 260—261 gfiospfiaiic Degbiest m 1;,48'130k9tadshlale-lb ------------------------- 300 Stratigraphic sections ..... _. 261, 262, 266, 267, 274—275, 232, 285, 293—294, 305—309 cm a ic p0 u es, in eca onion 0 mi a mem er ........................ 278 suati ra h or the minin district ______________________________________ 271—302 Phosphatic pebbles, in Quimbys Mill member ................................ 288 Structgur: y______ _____g_ ________________________________________________ 254 Phosphatic nodules, significance of, in Spechts Ferry shale member ___________ 288 Pitch, definition of term _____________________________________________________ 295 T Platteville. formation, boundary of, with Decorah formation. 261—262 Terminology, local, for rocks ______________________________________________ 268, 280 conditions of deposmon ................... _ 284 . ,- . . . . . Thicl, G. A., “1th Stauflcr, C. R., quoted .................................... 266 correlation With units in Minnesota, chart ______ 264 . . . . . Tourmaline ________________________________________________________ 277, 278, 281 disconformity with Decorah formation _____________________________ 256, 259, 288 . distribution of fades of ___________ 284 Trempealeau formation—V” . . 254, 255, 271 . . Trenton beds. See McGregor limestone member of Plattevdle formation. general description ..................................... 255, 257, 268, 274-275 mebfidge ,_ C and Shaw E W quoted . _ 288 stratigraphic relations .................................................. 256, 257 ’ A ' " ’ ' " """"""""""""""""" stratigraphic section ...................................... 274~275, 282, 305—308 W See also Quimbys Mill member, McGregor limestone member, Pccatonica dolomite member, and Glenwood shale member. W001 “301‘ -------------------------------------------------------------------- 300 Prairie dc Chicn group. 255, 256, 271, 272—273 Pro-Cambrian rocks ___________________________________ 254, 271 Z Presser member of Galena dolomite ___________________ 259, 264, 266, 267, 268, 297—298 Zinc minerals ............................... 272, 273, 277, 282, 289, 293, 294, 295, 300 Purpose of the investigation .................................................. 252 Zircon ............................................ 276, 277, 278, 279, 281, 283, 287, 289 mvfiuruyfig. . , wiry . islalagfix i {.3th1: r 4 .mm. wk wan, ., v zjélx Volcanic Rocks of the E1 Modeno Area Orange County California AGEOLOGICAL SURVEY‘PROFESSIONAL PAPER 274—L Volcanic Rocks of the E1 Modeno Area Orange County California By ROBERT F. YERKES SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274—L Descrzptz'm of extrmz've pyroclaytz'c and/70w rocés ofE/ Modem mlcam'cy of middle to late Miocene age UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :1957 UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price $1.00 (paper cover) CONTENTS Fag? Descriptive geolo y-—Continued Abstract-.. """""""""""""""""""""""""""" 3’15 Igneous rockS—Continued Intr‘fduc'fimn- ‘ j ‘ 'j """""""""""""""""""" 313 Associated igneous rocks—Continued Pr (“”998 mvest1gat10ns- ‘ " ‘ ‘ ' ' ’ ‘ ‘ ' ’ ’ “ ".— """""""" 314 Tuffaceous material in La Vida member of Localltles from which samples were obtalned ,,,,,,,,,,, 314 Puente formation _____________________ Descriptive geology ————————————————————————————————— 316 Summary of petrography ____________________ Igneous rocks """""""""" . """"""""""" 316 Sedimentary rocks, Cenozoic system _______________ Tuffs of the Topanga formation ______________ 316 Silverado formation _________________________ E1 Modeno volcanics ________________________ 316 Santiago formation __________________________ Basalt flow member “““““““ , """"""" 3 16 Vaqueros and Sespe formations, undifferentiated- Palagonlte tuff and tuff brecma member- - _ 319 Topanga formation __________________________ General description _________________ 319 Puente formation ___________________________ Palagonlte tuff brecmas """"""""" (319 Quaternary terrace deposits __________________ Bedded palagonite tufl’_._ “““““““““ (319 Stratigraphic position and correlation of the volcanic Andes1te flow and flow brecma member: _ -3 320 rocks ____________________________________________ General description _________________ 320 Structure __________________________________________ Flow breccias _______________________ 320 Folds _________________________________________ Lava flows _________________________ 320 Faults _________________________________________ Hydrothermal alteration ————————————— 321 Disconformities in the volcanic sequence _____________ Limy volcanic breccia ——————————————— 321 Mode of deposition of the volcanic rocks _______________ Undifl‘erentiated volcanic rocks ___________ 321 Subsurface data ____________________________________ Andesite dikes __________________________ 321 Distinction between extrusive and intrusive rocks--- Associated igneous rocks _____________________ 322 Distribution of the volcanic rocks _________________ Breccia ________________________________ 322 References cited ____________________________________ Basalt dikes ____________________________ 322 Index _____________________________________________ ILLU STRATION S [Plates 46 and 47 in pocket] Index map of southern California showing location of areas underlain by El Modeno and Glendora volcanics--- PLATE 46. Geologic map of El Modeno area. 47. Structure sections, E1 Modeno area. FIGURE 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. Index map of eastern Los Angeles basin showing wells drilled into Miocene volcanic rocks ___________________ Pillow structures in basalt flow member, Panorama Heights ______________________________________________ Photomicrograph, basalt flow member _________________________________________________________________ Tuff breccia in palagonite tuff and tuff breccia member, Panorama Heights ________________________________ Bedded palagonite tufl‘ in palagonite tufl" and tuff breccia member, Panorama Heights _______________________ Photomicrograph, bedded palagonite tufl', in palagonite tufl" and tufl’ breccia member _______________________ Lava block with radial and concentric cooling cracks, in andesite flow and flow breccia member, east-northeast of El Modeno _______________________________________________________________________________________ Photomicrograph, vesicular andesite in andesite flow and flow breccia member _____________________________ Andesite dike cutting palagonite tufl“ and tulf breccia member, east-northeast of E1 Modeno ____________________ Photomicrograph, porphyritic augite andesite in andesite flow and flow breccia member _____________________ Photomicrograph, tuff in La Vida member of Puente formation ___________________________________________ [I] Page 322 323 324 324 325 325 326 326 326 326 327 327 327 327 327 328 328 328 331 333 Page 314 315 317 317 319 319 320 320 321 322 322 323 CONTENTS TABLES IV TABLE 1. Petrography of tuffs of Topanga formation ______________________________________________________________ 2. Petrography of basalt flow member _____________________________________________________________________ 3. Petrography of tuffaceous sediments, La. Vida member of Puente formation __________________________________ 4. Log of wells drilled into volcanic rocks __________________________________________________________________ Page 317 318 323 329 A SHORTER CONTRIBUTION TO GENERAL GEOLOGY VOLCANIC ROCKS OF THE EL MODENO AREA, ORANGE COUNTY, CALIFORNIA By ROBERT F. YERKES AB STRACT The El Modeno volcanics form a series of extrusive pyroclastic and flow rocks which crop out near El Modeno, Orange County, Calif. The volcanics have been divided into three members. The basal unit is a basalt flow, which is overlain successively by a palagonite tufl’ and tuff breccia member and an andesite flow and flow breccia member. The volcanics are products of both sub- aerial and submarine extrusion Of materials of intermediate com- position. They are middle Miocene to early late Miocene in age and are tentatively correlated with the Glendora volcanics 25 miles to the northwest. The maximum outcrop thickness of the volcanics is 850 feet. The extrUsive volcanic rocks may be distinguished from the middle Miocene intrusive rocks in this region by their vesicular texture and characteristic alteration to crumbly, earthy masses. The intrusive rocks are cOmmOnly coarser grained, hard and dense, commonly contain biotite, have an ophitic texture, and alter to chlorite-epidote-feldspar rocks. INTRODUCTION The El Modeno volcanics are extrusive, largely pyro- clastic rocks, in part marine, that crop out in an eight- square-mile area east Of El Modeno, Orange County, California, on the west flank Of the Santa Ana Moun- tains. The volcanic rocks rest conformably upon the strata of the Topanga formation, which include at least two thin tuff beds (tul on the geologic map, pl. 46). The El Modeno volcanics are made up Of three members. The lowest member is the basalt flow member (Temb), which rests upon sandstone beds Of the Topanga forma- tion (middle Miocene) and includes at the top a thin stratum of marine siltstone not differentiated 0n the map. This member has a maximum thickness Of 200 feet. Overlying the basalt flow member is the palag— onite tuff and tuff breccia member (T emt), which ranges from 125 to 450 feet in thickness. This tufl'aceous member is overlain by the andesite flow and flow breccia member (Tema), which has an average thick- ness of 200 feet. Locally overlying the andesite flow and flow breccia member is the La Vida member of the Puente formation (T 1212)). The El Modeno volcanics are of middle to late Miocene age and are tentatively correlated with the Glendora volcanics (fig. 55). The detailed mapping of the volcanic rocks was undertaken as part Of the geologic mapping Of the west flank Of the Santa Ana Mountains (Schoell- hamer and others, 1954). In order to show details Of the volcanic sequence, the geologic map which accom- panies this report (pl. 46) has been prepared at a scale of 1 to 12,000. As shown on its index map, the geology of adjacent areas was mapped by D. M. Kinney and J. G. Vedder. John S. Shelton of Pomona College loaned a collection of thin sections Of rocks from well 7 cores from which some of the data Of table 4 was taken. Cores from wells drilled for oil show that volcanic rocks similar to those Of the El Modeno volcanics underlie the Oil-bearing sedimentary rocks of the Puente formation Of late Miocene age beneath a large part Of the eastern Los Angeles basin (fig. 56). In addition, they show that the lowest part Of the Puente formation and the pre-Puente sedimentary rocks are cut by in— trusive rocks Of similar composition. A petrographic study Of the El Modeno volcanics has been included in this investigation, partly to facilitate distinction b3- tween the extrusive and intrusive igneous rocks en- countered in wells. The terminology of the pyroclastic rocks, including the term palagonite, is the one proposed by Wentworth and Williams (1932, p. 45—53). Chlorophaeite, a widely used but ambiguous term, refers herein to a green tO brown alteration product Of ferromagnesian minerals and glass in basaltic rocks. The composition Of the feldspar has been determined in some rocks by extinction-angle methods but in most cases by immer- sion Of fragments in Oils of known refractive index. Special studies were made with the universal stage as needed. The relative volumes of the constituents“ phenocrysts, groundmass, cavity fillings, and clastic grains—were obtained by the point-counter method Of Chayes (1949), except where otherwise noted, and are given as volume percentages of the whole rock. 313 314 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 118°30/ 118°15/ 118°00’ : 117°45/ an, / 0,,”0, @9690: 4£ ”Hun/OI / : 0590 a, SAN GABRIEL. MTS /‘ 0" - \Ul,’ E ’l, " ’5; O - I ”Hm w j \w, 2% E: Haj ”Wu“ 4 V; S = \‘I ’I ‘\‘ r _ \ = \ In” 1‘ \ i , “lg: \\\ - \ In ““0““ "//\I LOS Aflgelesf‘ 911471" gill/I E: 'l 74,, “"‘\‘\\‘ \“ll\“"“\ 5 §‘ I“? S I]! lull/l 1, // S 2 x \\ “mun/,0 Nil-1,“ “w 2% 3.0, 7‘»; r. // '1’!" /I/,,“\“ ‘F\\\~\\‘“\\ 219 .14; "um“ 4mm: ’7" SANTA MON‘CAW«hum/’11,:->"2 w '.~// ”"“‘ GLENDORA AREA $‘yl’fimmm‘ g. "r: ’b’ (’It“ E bo-,J \o‘ul‘ (Shelton, 1946) r ‘ (‘- I ‘ t 5 ’r,’ ’“h S o"\ m‘ ‘51“““”: ..“\\\\II“‘ —,, 3 'I’, = 6/ _- 3 \g\\\\ “\mux‘ / ’l/"o‘ o SR8”! n’ yam-nun CPomona ._/ : 7,,”323229"! SA’IZ‘T’J we \I\" |. Q\§W_: \“uu, ‘ . \ — K I “Les ANGELE \ ‘0- 7? ”"“y“ sin?- / ,-\_ {Haw “(he QM" , , : ”HUI/n14 5 ' "‘s‘s‘ 5- mm”, ' 7 \ 1 ”I“ it“ E 34° : \I | \ “ r :1, g (lame g ‘0‘“ u : it: .. 00 1\\ t ‘ ' 7111M ”4 \I/ 7/10“ ’00 / 4;} q.- ‘ é “In” 5‘0; $3 m5 5 ‘6 '2 8.5, r I ”/3 ”k 42° ”II/Hm, ': ._ / ”0, mm"; y/ u . \J 711‘" "’0u\"’/n‘/ gilmu, v'” ’7\- uu \\ ’6 0T /' \ ‘1 I,” "(\o H I, 40° w: mm“ m I," u I“ \‘ ”‘1” 0, EL MODENO Q,1/3. 0» AREA §Efl1~°§j/Jl, E, .. 844/ V =2 ’4‘\ a; 0 2’4“: . ,4 38 .1: , "‘\ W4 A, , \ . 1 7,3 E ' ’3‘ 2g; ; §/ USanta Ana. ’3’"; \n' a 3/ / 3.69 a). "Inw‘ \ xv / *{kb‘m‘ a OUTLINE MAP ‘w/ E‘II‘NIII $1,] él‘hw ‘ :v‘ 34 “ WITH LOCATION :1» I‘\ '1‘ 7 g “\n‘ OFO INDEX MAP S 71““ 50 150 Miles |_L__I_J—l 1 l I 1 V 122° 120° 118° 116° 118°15’ 1,0 “4““ San Joaquin Hills 118°OO’ ' i V 117°45/ FIGURE 55. Index map of southern California showing location of areas underlain by El Modeno and Glendora volcanics. PREVIOUS INVESTIGATIONS English (1926) included the volcanic rocks of the El Modeno area under the designation intrusive and ex- trusive rocks of Tertiary age. Larsen (1948, p. 108) briefly described the El Modeno volcanics as a series of andesitic lava flows, elastic beds, and intrusives, which he mapped as a unit Of Tertiary age. No detailed study of the volcanic rocks has been published. LOCALITIES FROM WHICH SAMPLES WERE OBTAINED In this report rock samples that have been studied in detail are numbered in the order in which they are described. The following list is a key to their corre- sponding field numbers, the symbols by which the con- taining formation members are represented on plates 46 and 47, and the precise descriptions Of the localities from which the samples were Obtained. R.“ W. VOLCANIC ROCKS, I‘EL MODENO AREA, ORANGE COUNTY, CALIF. 315 118‘ R. 10 w. :17'52'3m R.9 W. I 14 Hahn "7 “NW; ‘ I ‘ ”I/mmlm \\\ g L-—-L_ _J ////nmIIIr/m/,m\\\ § "' E A s T E R N #7 77755‘5 W § P u 'E N -'r E / = gm (MI/4% \ \_‘ WIIK‘"”10% "We 0 ’%,, H I L L s [44% \\ 1 ”a4 1' 05 c 0 Y o T E @e "1 r ”'Irr'rvvvrmm,,,,/ 3 ‘ ' 5 // T. l L L 5 § ”11;, S. 3 °' ., 1 , m 5‘ ummwM/nuwMm,.mw'Wmmmn\\“““' ””0!“ \\ ' ””00, i o 0’ \\ 2 / \ , ’2 \\ /’ 5 \ \ § s r________ \ :3. I 1 I ‘l .27 s “w, 33. 52 ~_ ii‘ I ll 3M ”’2, u my I Fullermn L x 1 ’65. 7/1/mmuufl“ uuw, “mu/mn\\u§5 ngmmnmm "WM H \S\ ‘ i 7 [ ”Wm 0; W7 ‘ A ”/1011 1 / ‘ o 1 1 MINI/””0”, ‘ ' / = ’5 (”/4 my T" E‘ #5 ‘ ’l/mnuunm ”2 T 4 °‘ ‘2 022 § ‘ ‘ \\ s i‘ E" ‘ S\\\ 4 ‘ :. 1,: w E S. m /2 f E ’— 3 ‘ “N5 i ./5 ‘ §\\\\ /' ‘ a? ‘ == 2 ‘ > I ‘ ’2. , \5 J [ \V\\\\\§ V { 1 Z .1 U) Vii“7 ‘55 "*7‘5‘ L7 7>_ 5%!qu L.. 2 ‘ T. » . ‘ 5 1’ ‘ ‘ . T. 5- l ‘V [94 I 5 . ‘ 5. 0‘” \ (f I ‘ , EXPLANATION c 1 I) a \ ‘ Dry hole 7 9 \ . ‘9» 13 ‘ ‘ O o Producmg well (1951) 017 1 0 2 Miles J R, ll w. "8‘ R. lo 117°52'3v' R. 9 w_ ‘A" 5" FIGURE 56.—~Index map of eastern Los Angeles basin showing wells that were drilled into Miocene volcanic rocks. 316 Locality descriptions Field no. No. in this report Rock unit, Description of localities (measurements in plates 46, 47 feet) 5b _______ 1 2300 E. and 225 S. of northwest corner projected sec. 36. T. 4 S., R. 9 W., Elev. 800. Highway cut, 2250 N. and 200 W. of southeast corner sec. 26, T. 4 S., R. 9 W., Elev. 600. Road cut, 2050 W. and 325 N. of easterly corner Irvine Block 15. Elev. 730. 1450 W. and 925 S. of easterly corner Irvine Block 16, Elev. 590. 2325 N. and 1725 W. of southeast corner sec. 15, T. 4 S., R. 9 W., Elev. 470. 2925 S. and 75 W. of northeast corner projected sec. 35, T. 4 S., R. 9 W., Elev. 630. 3775 E. and 1540 S. of northeast corner sec. 13, T. 4 S., R. 9 W., Elev. 1110. 2050 E. and 575 S. of northwest corner sec. 13, T. 4 S., R. 9 W., Elev. 990. 1600 S. and 425 W. of northeast corner projected sec. 35, T. 4 S., R. 9 W., Elev. 610. Road cut, 1200 E. and 2000 N. of BM 277. near southeast corner sec. 34, T. 4 S., R. 9 W., Elev. 415. 2250 N. and 2150 W. of southeast corner sec. 26, T. 4 S., R. 9 W., Elev. 460. Highway out, 2075 N. and 400 W. of southeast corner sec. 26, T. 4 S, R. 9 W., Elev. 590. 1200 N. and 875 W. of southeast corner sec. 23, T. 4 S., R. 9 W., Elev. 600. Road, 900 S. and 3550 E. of northeast corner sec. 13, T. 4 S., R. 9 W., Elev. 1105. 1025 S. and 2300 E. of southwest corner sec. 26, T. 4 S., R. 9 W., Elev. 540. 2230 N. and 1300 W. of southeast corner sec. 26, T. 4 S., R. 9 W., Elev. 660. 1025 N. and 250 W. of southeast corner sec. 26, T. 4 S., R. 9 W., Elev. 800. 350 southwest and 3150 north- west from easterly corner of Irvine subdiv. Blk. 68, Black Stair Canyon quadrangle; Elev. 94 1950 southwest and 1000 north- west from easterly corner Irvine subdiv. Blk. 68, Black Star Canyon quadrangle; Elev. 900. tu, _____ 6e _______ 2 6e _______ 7 Tomb- _ 6d _______ 8 Tomb" 7a _______ 9 Tenth” 7e _______ 10 Temb- _ 4e _______ 11 202 ...... 12 1b2 ______ 13 6b _______ 14 11b ______ 15 13c ______ 16 14i__-.__ 17 31d ______ 18 31c ______ 19 tu2_____ DESCRIPTIVE GEOLOGY IGNEOUS ROCKS TUFFS OF THE TOPANGA FORMATION Two or more thin beds of white vitrie tufl" 5 to 10 feet thick (tul) are interbedded in sandstone of the Topanga formation; one is about 150 feet below the top, and another is about 325 feet above the base of SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY the formation. These tufl’s afford evidence of the earliest volcanic activity during Tertiary time. The tuffs are massive and well sorted, and many specimens are crowded with 0.5- to 2—millimeter opaque white glass bubbles. Fragments average 0.05 millimeter in maximum diameter, are angular, and include clear, colorless glass, plagioclase, micas, iron ore minerals, and, rarely, detrital quartz. The matrix is composed of fragmental and partly altered glass. Sparse fish scales and molds of small mollusks indicate marine deposition. Glass fragments make up as much as 58 percent of the rocks but average about 40 percent. The index of refraction of the glass in four samples ranges from 1.494 to 1.504, with a mean of 1.498, all :l:0.002. These values suggest that silica is present in amounts greater than 70 percent (George, 1924, p. 365). Plagi- oclase crystals and fragments make up no more than 5 percent of the rock, and the composition of the plagioclase ranges between Ange and An50; the average value for the rock is about An35. The incongruity between the intermediate composition of the plagi— oclase and the silica—rich glass fragments suggests a composite source for the material. No massive vol— canic rocks of silicic composition are known from out— crops or well cores in this region. Data pertaining to four samples of the tufls are shown in table 1. Samples 1 and 2 are from the tuff bed that crops out in Section 25 near the center of the map, 150 feet below the top of the Topanga for— mation, and samples 3 and 4 are from the bed 325 feet above the base of the formation, which crops out on both sides of Peters Canyon. EL MODENO VOLCANICS BASALT FLOW MEMBER A vesicular, porphyritic olivine basalt (T cmb) rests conformably on sandstone of the Topanga formation. The basalt is light gray to olive green or brown. A fresh specimen has not been obtained. The rock characteristically weathers to spheroidal masses. Com- monly the rock is somewhat fresher and darker near the surfaces of spheroids or joints and is most deeply altered in the centers of the joint blocks. This anomalous characteristic is ascribed by Fuller (1938) to alteration due to entrapment of volatile materials. Where the volatile materials escaped, as near joints and fissures, alteration is less pronounced. The texture of the rock is everywhere porphyritic and subophitic. Variation occurs mainly in the size of plagioclase phenocrysts and preservation of olivine. The principal minerals are plagioclase’, olivine, chloro- ph‘aeite,. and magnetite. Plagioclase phenocrysts av- erage 0.5 millimeter in maximum diameter, but some VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. 317 Table 1.—Petrography of tufis of the Topanga formation l l ‘ Sample 1 i Sample 2 J Sample 3 i Sample 4 l l .‘ Glass fragments __________________________________________ estimated percent“,l 58 l 20 i 30 I 60 Do _________________________________________________ index of refraction ‘__f l 494 ‘l 1. 504 : l. 447 J 1 499 Plagioclase _______________________________________________ estimated percentwl 1 j 5 l l l 4 Do ______________________________________________________ alpha value 11-} 1. 557 l 1. 545 l 1. 554 l 1 548 Do ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, estimated percent An,_' 53 i 35+? 47 1 42+ Micas ____________________________________________ , ________ estimated percentwi 4 : 10 l 2 l ? Ore minerals _________________________________________________________ down: 2 l 20 J 1 , 1 Matrix _______________________________________________________________ do _____ i 35 ‘ 45 l 60 l 30 Other minerals 2 _______________________________________________________ do, , "J __________ l __________ l 6 g 5 i i l l 1 Accurate to 3:0.002. 2 Includes detrital quartz, tourmaline, augite, and hornblende. are as large as 8 millimeters. The plagioclase microlites alteration of the rock. The vesicles are commonly of the groundmass average 0.05 millimeter in maximum diameter. Olivine crystals are well preserved only in rocks whose groundmass is made up of grains whose average diameter is less than 0.03 millimeter. The unaltered olivine phenocrysts are stubby anhedral grains. The rock is everywhere massive and apparently consists of a single extensive flow; good exposures show pillow structures with siltstone seams (fig. 57). Flow structure is rare. Only sample 5, from a weathered outcrop in Cerro Villa Heights north of Santiago Creek (northwest corner of map area), shows flow structure of trachytic type. Vesicles are usually abundant and not oriented. They range from 0.01 to 16 millimeters and average about 1 millimeter in maximum diameter. The ready access to permeating fluids afforded by this vesicularity probably accounts in part for the deep FIGURE 57.77Basalt new member, Panorama Heights, showing vesicular basalt in pillows with siltstone seams. Pencil in center of photograph is five inches in length. 397755v—57#2 filled or lined with chlorophaeite or zeolites, or, rarely, with calcite. V The basalt flow member is generally between 10 and 200 feet thick, but it is locally absent. In the only unfaulted sequence (structure section C—C’, pl. 47) it is 200 feet thick. The upper surface of the flow shows no sign of penecontemporaneous erosion. Associated with the basalt at its upper contact is a limy siltstone bed that averages 4 feet in thickness, which weathers white 01' grayish white. The siltstone contains fish scales of probable middle Miocene or early late Miocene age (determination by W. Thomas Rothwell). On Burruel Ridge north of Santiago Creek, a bed of light- grayish—white claystone 20 inches thick locally occupies a similar stratigraphic position. The claystone bed FIGURE 58.—Photomicrograph, basalt flow member, sample 9. Shows large (0.45- millimeter) pseudomorph of chlorophaeite and magnetite after olivine, with smaller pseudomorphs in lower half of View. Groundmass is composed of plagioclase microlites, granular augite, olivine, magnetite, and chlorophaeite. Plane polarized light. 318 crops out for a very short distance and rests on a rem— nant of the basalt flow member (near north end of structure section A-A’, pl. 47). The claystone con— tains an abundant fauna of silicified Foraminifera that are considered to be middle Miocene in age (see p. 326). Petrography.——Samples 5 to 10 of the basalt flow member have been studied microscopically. These differ mainly in the amount and size of plagioclase phenocrysts; the groundmass is almost the same in all the samples, as shown in table 2. Each specimen contains large amounts of chlorophaeite, which is commonly present as pseudomorphs after olivine or pyroxene (fig. 58). Very little fresh olivine or pyroxene is found. It is estimated that olivine originally made up between 5 and 15 per- cent of the rock, while pyroxene formed from 5 to 10 percent. Wherever determined, olivine was optically negative, with 2V close to 85°. Pyroxene is of uniform character, apparently of a magnesian or diopsidic variety with positive elongation and range in Z to c from 37° to 40°. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The average composition of the plagioclase—close to An55, the intermediate silica percentage of the essentially unaltered glass—(52 percent), and the moderate amount of olivine indicate that the rock is probably an olivine basalt, though it may be a basaltic andesite. Chlorophaeite replaces olivine and pyroxene indis- criminately, as well as most of the glass formerly present in the groundmass, and fills or lines all cavities. It is nearly opaque and has a dark olive-green to yellow- brown color. It commonly occurs as isotropic or nearly isotropic structureless or spherulitic fibrous patches. The weakly birefringent fibers have parallel extinction and positive elongation and an index of refraction that is variable but close to 1.530. The weak birefringence is attributed to incipient formation of chlorite, which TABLE 2.—Petrography of the basalt flow member [The term chlorophaeite is used as defined on p. 313.] No. of Sample Megaseopic texture Groundmass texture Composition Phenocrysts (sizes are maximum diameter) Groundmass 5 Holocrystalline: Porphyritic: Trachytic. Subophitic. 6 Holocrystalline(?): Porphyritic: Subophitic. 7 Holocrystalline: Porphyritic: Subophitic. 8 Holocrystalline: Porphyritic: Subophitic. 9 Holocrystalline: Porphyritic: Subophitic. 10 Holocrystalline: Coarsely porphy- ritic. l l l l i Indeterminate, badly altered. Generally inter- granular; av- erage grain size 0.01 to 0.05 mm; commonly near 0.03 mm. Plagioclase 20.2 percent, maximum 10 mm, average 3 mm, albite and Carlsbad twins, An55ge2; chlorophaeite 24.2 per- cent, in fan-shaped aggregates of radiating needles filling cavities and as pseudo- morphs after olivine and pyroxene. Plagioclase 25.7 percent, fresh albite— twinned crystals up to 4 mm, average .67 mm, Ansel—58; chlorophaeite 33.3 per- cent, in aggregates of spherulitic fibers with weak birefringence, parallel ex- tinction, positive elongation, isotropic when fresh, index of refraction close to 1.520, about one-fourth in pseudomorphs after olivine and pyroxene, the rest filling cavities averaging 0.5 mm in maximum diameter. Plagioclase 42.7 percent, AIISOAfiZ: augite 4.7 percent; olivine 0.4 percent; chlorophaeite 33.2 percent; tridymite(?) trace, with alpha: 1.480, biaxial positive, 2V: 70°. Plagioclase 28 percent, averages 0.25 mm, Ania—60; chlorophaeite 30 percent as pseudomorphs after olivine and pyroxene; less devitrified glass 5 percent. filling cavities averaging 0.3 mm, index of refraction=1.580, pale olive-buff, clear, isotropic. Plagioclase 23 percent, as fresh albite twins, average 0.75 mm, An47_5,; chlorophaeite, 34 percent, as pseudomorphs after olivine and pyroxene. Plagioclase 41 percent, in large pro- gressively zoned albite-twinned euhedrons averaging 0.5 mm by 2.1 mm, Amy“; chlorophaeite 37 percent, in pale straw- colored fibrous pseudomorphs after olivine and pyroxene, parallel extinction, positive elongation, index of refraction just above that of Canada balsam, birefringence about .015. Plagioclase microlites, in a basis of chlorophaeite and clay min- erals, 48.8 percent: magnetite, well dispersed 0.01—mm grains, 5 percent. Magnetite 11 percent in rod- shaped grains 0.005 mm by 0.05 mm; plagioclase micro- lites 15 percent, Aliza—Bu; chloro- phaeite basis 15 percent. Magnetite 6 percent; calcite 1.8 percent; apatite 1.2 percent; chlorophaeite and clay min- erals 10 percent. Plagioclase 23 percent, as micro- lites averaging 0.03 mm, An33_65; unresolvable basis of chlorophaeite, clay minerals and magnetite, 14 percent. Plagioclase 22 percent, as micro- lites averaging 0.03 mm, Angg_6o; olivine 7 percent, grains averaging 0.03 mm, 2V=90°; pyroxene 9 percent, in grains averaging .01 mm, Z to c=31°; magnetite 5 percent. Plagioclase 11 percent in micro- lites averaging 0.007 mm by 0.05 mm, An57-65; magnetite 1 percent; chlorophaeite 10 per cent, in finely divided fibers; tridymite present in small 0.03 mm crystal. VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. also seems to cause a slight increase in the index of refraction. ' The rare appearance of tridymite as vesicle lining is attributed to dcuteric processes. Shelton (oral communication) reports similar occurrences in the Glendora volcanics. Other minor secondary minerals are calcite and zeolites. PALAGONITE TUFF AND TUFF BRECCIA MEMBER GENERAL DESCRIPTION Resting conformably upon the thin limy siltstone bed associated with the basalt flow member are pyro- clastic rocks (T amt) averaging 200 to 300 feet in thick— ness. The thinnest unfaulted sequence measures 125 feet and the thickest more than 450 feet. The color of this rock, either fresh or weathered, is light grayish buff or tan, in some occurrences with a greenish cast. The rocks in some exposures show lateral and vertical alternations of unsorted fragmental breccias with well- sorted and bedded tuffs. PALAGONITE TUFF BRECCIAS Angular blocks of light-gray vesicular augite andesite are abundant in the tuff breccias. They are as large as 8 to 10 inches in maximum diameter, but average 1 to 2 inches. These blocks, together with lapilli of similar composition, make up about 20 percent of the rock. The tuifaceous matrix of the breccias is in general vesicular, and the cavities are commonly filled or lined with palagonite and clay. The haphazard, unsys- tematic arrangement of the fragments in these deposits, as shown in figure 59, precludes the possibility that FI'TITRE 59.~Palagonite tufl’ and tufl breccia member, Panorama Heights. l’alago- nite tufi’ breecia with blocks and lapilli of vesicular augite andcsite. An irregular contact between two such deposits appears in lower left corner. Handle of pick is about twelve inches in length. 319 they are the product of reworking. The matrix of this rock has not been examined microscopically. BEDDED PALAG ONITE TUFF Interbedded with the fragmental rocks are much thicker and more extensive sequences of thinly bedded, well—sorted, and completely palagonitized tufl’s (fig. 60). These are most prominent in the central and southern parts of the mapped area. Beds in these sequences range from lie to 16 inches in thickness but average lé inch. Fragments of volcanic rocks are common and are of granule size or smaller. Locally, small-scale cross bedding is seen. Some medium to coarse sub— rounded grains of quartz are present and calcite cement is common. Petrogmphy.~Sample 11 was selected as representa- tive of the bedded tuff. This sample is composed of medium, fairly well sorted grains; its texture is uniformly elastic (fig. 61). Clasts have sharp, angular boundaries and maximum diameter of 0.3 millimeter; some glass shards show the effects of flattening. The matrix is minutely vesicular palagonite; its sparse vesicles have a mean diameter of 0.05 millimeter. The estimated composition is 35 percent plagioclase frag- ments (A1130_.60): albite and carlsbad twins sharply defined, in- tensely zoned in both oscillatory and progressive fashion, with single crystals ranging from A1170 at the cores to A1130 at the rims; 1 percent augite and hypersthene(?); 5 percent rounded to sub- angular adventitious quartz grains; 4 percent partly digested glassy basalt in fragments 0.3 millimeter in mean diameter; 55 percent matrix: somewhat vesicular, rarely spherulitic and fibrous light-amber to deep brownish-black palagonite and some patches of calcite, the whole moderately charged with finely disseminated clay or dust particles. Some of the palagonite shows incipient crystallization by fairly definite extinction, but most of it is changed very little between crossed nicols, retaining its amber color throughout. The resolvable anisotropic detail FIGURE 60.~Palagonitc tuff and tufl breccia member, Panorama Heights. Bedded palagonite tufi. Heavy bed near center is eleven inches in thickness. 320 FIGURE Gl.—»Photomlcrograph, bedded palagonite tufi and tuft breccia member. Adventitious quartz, plagioclase, augite, and altered olivine in a matrix of pala- gonitized tuff with calcite and clay minerals. Note angularity of grains. Crossed nieels. takes the form of chloritelike plates with apparently higher indices of refraction. The mean index of refraction of the palago- nite is 1.47. ANDESITE FLOW AND FLOW BRECCIA MEMBER GENERAL DESCRIPTION A series of randomly interbedded light- to dark-gray and reddish vesicular calcic andcsite flow breccias, lavas, and minor tuff breccias (T ema) rests conformably on the tuffaceous rocks and caps almost all the hills in the volcanic area. The lower contact of this unit is slightly irregular and rough but is essentially parallel to the bedding in the underlying tufl's. This series of flows and flow breccias is the most resistant rock in the sequence, as well as the youngest. Its thickness is commonly about 200 feet. FLOW BRECCIAS The andcsite flow breccias are composed of coarsely vesicular angular blocks of light—gray porphyritic calcic andcsite in a matrix of greatly altered fine-grained ande— site (fig. 65.) The blocks are as large as 6 feet in diameter, but average 3 to 4 inches. They are charac— teristically quite fresh but some blocks present a vari— colored appearance due to partial alteration. Blocks make up about 80 percent of the rock. At places altered glass or tuff is included in the matrix. Gravity sorting or other evidence of stratification was not detected. Radial and concentric cooling cracks are commonly present but rarely pronounced in the larger SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY blocks (fig. 62). matrix are common. Microvesicles in the tufl'aceous LAVA FLOWS The lavas are commonly hard, fresh, and light gray. In many places they are jointed and fractured. The rock is a vesicular porphyritic calcic andcsite with the Vesicles drawn out parallel to the lower contacts. Some of the vesicles reach a length of several inches. Chilling and baking of the lower contacts are nowhere pro- nounced. At one locality in the north-central part of the mapped area, just south of Santiago Creek, a red- dish scoriaceous lava is overlain by a dense, blocky flow with prominent joints, which is overlain in turn by a second scoriaceous flow. These three flows are trun- cated at a low angle by a younger dense flow. The scoriaceous flows are commonly intensely altered and are reddish or yellow, whereas the denser rocks are gray and fresher. A few exposures are made up chiefly of ellipsoidal pillows with thin seams of baked siltstone or altered glass and tufl' separating the pillows. The andesitc of the lavas is not distinguishable from that of the blocks in the flow breccias. Petrogmphy.——Sample 12 is representative of the lavas. This rock is light gray, hard, fresh-appearing and moderately vesicular (fig. 63). The vesicles are as large as l centimeter and average 2 millimeters in maximum diameter. The texture is porphyritic with phenocrysts that are as large as 0.38 millimeter and average 0.2 millimeter in maximum diameter. The texture of the groundmass is intergranular. Composition is 37.6 percent plagioclase, including many progressively zoned and albite- twinned crystals, in part andesine and labradorite phenocrysts FIGURE 62.~Andesite flow and flow breccia member, gravel pit approximately one mile east—northeast of El Modeno. Large vesicular andcsite block with radial and concentric cooling cracks in flow breccia. Pick handle about 12 inches in length. VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. Figure 63,—I’hotomicrograph, vesicular andesite from andesite flow and flow breccia member, sample 12. Augite, plagioclase, and vesicles lined with devitrified glass. The glassy groundmass is solidly charged with magnetite grains. Crossed nicols. and in part andesine microlitcs; 36.3 percent augite; 16.3 percent chlorophaeite as alteration product of ferromagnesian minerals that may have included some olivine; 9.7 percent magnetite in well disseminated grains and rod-shaped aggregates; 0.1 percent apatite(?), as submicroscopic inclusions in plagioclase crystals. Tridymite and zeolites are commonly present in small amounts; secondary calcite is common. A zeolite from sample 14 was determined as a variety of phillipsite similar to wellsite. It had the following properties: Angle 3:126}é°; indistinct cleavage parallel to (010) ; twinning present with composition plane paral— lel (010) and perpendicular to b; optic plane and Z(=b) per- pendicular to (010); X to 0:520, Y to c=38°; optically positive; 2V ranges from 26° to 50°, with a mean of 42°; (121.4971, 3:1.4978, 721.5021, all i0.0004; birefringence 0.0050. The mineral is colorless and has strong negative relief in canada balsam. The composition of the unzoned plagioclase phenocrysts ranges from Aim to Aneg, and the mean composition of the microlites is probably close to A1145. The phenocryst zones range from A1170 to An35. The classification of the rock as a calcic andesite is thus somewhat arbitrary and is based primarily on the mean compo— sition of the feldspar of several samples. Plagioclase constitutes as much as 60 percent of other samples. HYDROTHERMAL ALTERATION In the central and northern parts of the area, near the mouth of Santiago Creek, the rocks of the andesite flow and flow breccia member are more deeply altered than in the south. The ferromagnesian minerals are altered to chlorophaeite and chlorite, which gives the rock an overall deep—reddish to yellow or greenish color. Calcite and zeolites fill many cavities. Tridymite, 321 specular hematite, and limonite are present in small amounts. The feldspar commonly remains quite fresh, whereas the tuffaceous matrix shows pronounced palagonitization and random addition of calcite. LIMY VOLCANIC BBECCIA Interbedded in the andesite flow and flow breccia member in the west central part of the mapped area is a 6— to 10—foot bed of deep red—brown limy volcanic breccia (bar). The rock is composed of vesicular and porphyritic augite andesite, in clasts of granule to block size, closely packed in a matrix of calcite grains Whose maximum diameter is 0.1 millimeter. A few plagioclase crystals occur as elastic grains that average 0.3 millimeter in maximum diameter; the patchy, glassy matrix has an index of refraction of 1.555 i 0.002. UNDIFFERENTIATED VOLCANIC ROCKS About 750 feet of undifferentiated volcanic rocks (Temu) crop out in a small area near the east margin of the map, just south of Santiago Creek. These are very poorly exposed but are known to include both the basalt flow and the andesite flow and flow breccia members of the El Modeno volcanics. The palagonite tuff and tuff breccia member also is believed to be present. The undifferentiated volcanic sequence was probably con- tinuous with the differentiated volcanic sequence im- mediately to the west, but these sequences are now separated by faulting (see structure section A—A’, pl. 47). ANDESITE DIKES Steep or vertical, Vesicular and porphyritic andesite dikes (Td2) intrude both the palagonite tuff and andesite flow members as well as sandstone of the Topanga formation (fig. 64). Of the 16 andesite dikes mapped, twelve intrude the palagonite tuff member. The dikes are generally less than 10 feet thick and commonly less than 5 feet thick. Some of the dikes follow fault zones, especially those forming the contact between the palagonite tuff and andesite flow members. The dike rocks are commonly deeply altered and haVe a strong clayey odor. The rock at places shows a decrease in vesicularity and grain size toward the contacts, but it does not show notable chilling or development of glass. At some places the vesicles are elongated parallel to the walls of the dikes, but no prominent flow structure has been noted. The cavities are commonly filled or lined with zeolites and calcite. The dikes are all composed of porphyritic augite andesite identical with that described under the andesite flow and flow breccia member. The similarities in composition and field relations suggest that the dikes are nearly equivalent in age with the andesite flow and flow breccia member. 322 FIGURE tit-Small vesicular augite andesite dike cutting palagonite tuff and turf breccia member. Contact is at lower left. Locality is on north slope of small hill south of gravel pit, one mile east-northeast of El Modeno. Head of pick is about seven inches in length. ASSOCIATED IGNEOUS ROCKS Several minor occurrences of igneous rocks are asso- ciated with the El Modeno volcanics but are not considered a part of the main volcanic sequence. These include a volcanic breccia (Temx) that rests on sand— stone beds of the Topanga formation, two widely separated basalt dikes (Tall), and also a tufl in the La Vida member of the Puente formation, which overlies the El Modeno volcanics. BRECCIA Two poorly exposed outcrops of faulted and deformed breccia were mapped at the northeastern extremity of the central outcrop area, just south of Santiago Creek. The base of this breccia is apparently conformable upon sandstone of the Topanga formation. Where weath- ered, the rock is brownish gray. It has a rubbly appearance, owing to the presence of sharply angular lithic fragments ranging from 2 inches to 10 inches in diameter. The clasts are chiefly vesicular gray ande— site similar to that of the andesite flow and flow breccia member of the El Modeno volcanics, but they also include tan coarse-grained sandstone. The matrix is a coarse—grained sandstone with some lithic granules, typical of the sandstone of the Topanga formation. The upper contact is not exposed. The thickness of the breccia is not accurately determinable but may be as much as 200 feet. The relation of this rock unit to the El l\/lodeno volcanics is not clear. BASALT DIKES Two dense black basalt (likes (Tall) cut the sedi- mentary rocks of the Topanga ()Iiocene) and Santiago SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY (Eocene) formations. One of these is in Weir Canyon in the east—central part of the mapped area, and the other is in SEX Sec. 23, T. 4 S., R. 9 W. These dikes are 2 to 3 feet thick and have indistinct chilled margins. The two dikes are petrographically similar, and both are rather finely porphyritic with phenocrysts up to 0.7 millimeter in maximum diameter. The dikes are younger than the Topanga formation; they may be contemporaneous with the El Modeno volcanics, or they may be younger. Petrogmphg.—Samplc 13 is representative of the dike that cuts sandstone of the Topanga formation. This dike rock is dense, black, nonvesicular, and hyalocrystalline, with a finely porphyritic texture. The groundmass texture is intersertal to intergranular. Its composition is 36 percent unaltered plagioclase (A1155_70), in prominently twinned and pro~ gressively zoned crystals; 24 percent olivine, in phenocrysts up to 0.73 millimeter in maximum diameter, but 0.15 millimeter in mean diameter, commonly altered to antigorite: 10 percent rather poorly preserved augite; 14.5 percent magnetite, in well- disseminatcd grains; 13.5 percent antigorite and chlorophaeitc, pseudomorphous after olivine and pyroxene and as alteration products of the glassy groundmass; and l to 2 percent deep-olive to light-brown basaltic glass. TUFFACEOUS MATERIAL IN LA VIDA MEMBER OF PUENTE FORMATION In the El Modeno area the base of the La Vida member of the Puente formation is characterized by a thin bed of light—yellow to bufi or tan, somewhat sandy tufi’ or volcanic sandstone (TU2). The grains in this rock are between 0.5 and 1 millimeter in maxi- mum diameter. The tuff consists mainly of colorless FIGURE 65.,i’liotomicrograph, andesite flow and flow breccia member, sample 12. Porphyritic augite andesite, illustrating oscillatory twinning and selective altera- tion of plagicclase phenocrysts. Crossed niCols. VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. glass and plagioclase fragmehts with some quartz and lithic fragments in a matrix of strongly altered glass, usually an isotropic claylikd material. The colorless glass commonly has an index of refraction between 1.477 and 1.523i0.002, indicating hydration; the average index of refraction is approximately 1.492. The average composition of the plagioclase is close to A1150. Table 3 summarizes the petrography of six samples from this unit. 323 A similar tuff occurs elsewhere on the contact be- tween sedimentary rocks of the Topanga and Puente formations. On Burruel Ridge north of Santiago Creek this tuff is apparently interbedded in the basal part of the La Vida member of the Puente formation, and it is therefore mapped as a part of that member. The volcanic constituents of the tufl' were probably derived from the El Modeno rocks and deposited locally as an older unit of the La Vida member. TABLE 3.4Petrography of tuflaceous sediments in La Vida member of Puente formation t Sample 14 l Sample 15 l Sample 16 1 Sample 17 ‘ Sample 18 l Sample 19 Matrix _____________________________ type“ Clay ‘ _______ l Glass ,,,,,,, i Glass ,,,,,, 1 Clay 1 or i Clay 1 ______ l Clay.1 ‘ l sericite. ,1 Do ________________ estimated percent- 55 _________ l 45 ,,,,,,,,, ; 65 ,,,,,,,, I 4 _________ i 83 _________ 3 60. Do _______________ index of refraction 2". 1. 535i---_‘ 1. 450d:__,_ 1. 450i--- l 1.555:l:--_, 1.550i__--1 1550:. Glass fragments _________ estimated percentflg 10 _________ 5 __________ few ,,,,,,, . 35 _________ 5 __________ , 10. Do ________________ index of refraction_-' 1. 523 ______ l 1. 477 ______ (?)__-_,-__ 1. 490 ______ 1. 500 ______ l 1. 520. Plagioclase fragments--..,,estimated percent__ 5 __________ l5 ________ ‘ 10 _________ l 25 _________ 5 __________ i 10. Do ____________________ alpha value 2.; 1. 557 ______ l l 558 ........ 1. 558 ______ , 1. 557 ,,,,, ‘ 1 556 ______ 1 1. 555. Other fragments ____________________ typenl Quartz, ____________ ‘ Quartz ...... volcanic quartz, cal- j 20 percent ‘ . siltstone. ‘ l rock frag- cite, mus- i quartz, l l ments. ‘ covite. l musco— ‘ l ‘ Vite. l l 1 The clay matrix of these rocks is semicrystaliine with average grain size less than 0.004 millimeter in maximum diameter. i l : It is isotropic or nearly so, with refractive imlices commonly less than that of canada balsam. Halloysite is apparently the only mineral which satisfies the optical characteristics of this clay matrix. 2 Accurate to $0.002. The alteration of the groundmass glass to “palago- nite” and then to a clay (halloysite?) is illustrated in a thin section of sample 14 (fig. 66) and is attributed to hydrothermal processes (Ross and Hendricks, 1945, p. 67, 71). Although most of these samples are be- Color- less glass bubbles and fragments in a matrix of palagnnitized glass and mont- FIGURE 65.’Photornicrograph, tut? in La Vida member of Pucnte formation. morillonite. Plane polarized light. lieved to be pyroclastic in origin, perhaps deposited in water, the alteration of the matrix has commonly been so complete that the original nature of the rock is not clear. The substantial percentage of detrital quartz and foreign lithic fragments in some occurrences shows that the tuff may grade laterally into tuifaceous siltstone or sandstone. SU'MMARY OF PEI‘ROGRAPHY Although the El Modeno volcanics include olivine basalts (or basaltic andesites), they are dominantly andcsitic in composition. The basalt, the earliest rock in the sequence, is only slightly more ferromagnesian in composition than later extrusive rocks. Mineralogically, these rocks are marked by the com— plete absence of the late reaction products biotite and hornblende. Hypersthene is also apparently absent in the crystal- line rocks, though possibly present in small amounts in pyroclastic rocks. Fresh monoclinic pyroxene is usually present, at least as groundmass grains. It is generally colorless and without pleochroism, with positive elongation and an optic angle ranging from 50° to 60°. The extinction angle, Z to c, ranges from 37° to 40°¥rather low for augite. The mineral appears to be an iron-poor diopsidic augite. Alteration of the augite phenocrysts as well as the olivine and glass to chlorophaeite is commonly complete. This type of alteration has been 324 ascribed to the deuteric activity of entrapped volatile materials (Peacock and Fuller, 1928). Substantiating this interpretation is the deeply altered condition of the volcanic rocks penetrated by wells drilled for oil in this part of the Los Angeles basin. Even in occurrences where the volcanic works are rather definitely un- weathered they present the same complete state of alteration. Olivine is commonly present in most of the crystalline rocks. In the basaltic rocks it originally made up per- haps 5 to 15 percent of the volume, and in the andesitic rocks 5 percent or less. It generally occurs as ovoid grains in the groundmass, although larger pseudo- morphs in nearly every sample have its characteristic orthorhombic shape. The optical properties are: a=1.660:l:0.002, y=1.702:l:0.002; (negative) 2V=84°, about 80 percent forsterite and 20 percent fayalite in composition. The former phenocrysts of olivine are nearly always altered to antigorite and chlorophaeite with some magnetite. In some thin sections this altera— tion is incomplete and a crystal consists of a fresh core and altered rim. Zeolites, which are attributed to hydrothermal solu— tions, occur widespread in all the volcanic rocks. Plagioclase is the most abundant and the least altered mineral in every sample and ranges in composition from Anao to An65. The average composition of the plagio- clase fragments of the Topanga formation tufl's is An35; it is An50 in the tuffs of the La Vida member of the Puente formation. In both the basaltic and andesitic crystalline rocks the plagioclase phenocrysts range in composition from Ann to Anfig. The average composi- tion in the basalt is An55; in the andesite it is An45. In the lavas of the andesite flow and flow breccia member many of the plagioclase phenocrysts show prominent progressive zoning. The groundmass feldspars in the crystalline rocks have either the same or more sodic composition than the rims of the phenocrysts. Glass is abundant only in the tuffs interbedded near the top of the Topanga formation and at the base of the La Vida member of the Puente formation. SeVeral samples of each of these tuff beds have been examined in an attempt to detect the course of differentiation of the source magmas. The values in the following sum— mary were derived from the data of tables 1, 2, and 3, and from the text descriptions. Average per- Average cent $102 of percentAn glass of plagio- Rock Unit clase Tuffs of the Topanga formation__ 70 plus__ 35. Basalt flow member ____________ 52 ______ 55. Andesite flow member __________ none- 1 _ _ 45. Andesite flow member, limy brec— 57 ______ None. cia bed. Tuffs of the La Vida member _____ 70 plus" 50. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY These data may indicate only minor changes in the general course of differentiation. Tuffs are poor guides to the character of their parent magmas, as sorting by wind may segregate the more siliceous material because of its lower specific gravity. Also, in the mapped area there is little evidence concerning the position of the vent or vents. Subsurface data show that the volcanics thicken westward, suggesting that the vents were some distance west of the El Modeno area. An opaque mineral tentatively identified as magne- tite is always present. It occurs in the zoned plagio- clase phenocrysts as inclusions and in olivine grains as minute specks. In the groundmass of every sample it occurs as dendritic clusters or rod-shaped aggregates, as well as disseminated grains. Apatite occurs occasionally as minute inclusions in plagioclase phenocrysts. SEDIMENTARY BOOKS OF THE CENOZOIC SYSTEM SILVERADO FORMATION The strata of Paleocene age in the Santa Ana Moun- tains were named the Silverado formation by Woodring and Popenoe (1945). The westernmost outcrop of this formation in the mountains appears on the east margin of the mapped area, on the limbs and nose of a large westward—plunging anticline that makes up the core of the northern Santa Ana Mountains. The Silverado formation is unconformable on the Upper Cretaceous sedimentary rocks. About 500 feet of Upper Creta- ceous strata are missing beneath this discordance on the crest of the mountains, about six miles east of the mapped area (Schoellhamer and others, 1954). In this area the Silverado formation consists of five lithologic units recognized by Vedder (1950). In stratigraphic order, from bottom to top, these are: (1) a basal conglomerate bed; (2) a lower arkosic sand- stone unit; (3) the Claymont clay bed; (4) a second arkosic sandstone unit; and (5) a marine sandstone bed. The basal conglomerate bed averages from 20 to 40 feet in thickness and consists of subrounded pebbles, cobbles, and boulders derived from the metasedimentary and crystalline rocks of the basement complex to the east. The matrix of the conglomerate is a red to buff coarse-grained micaceous and arkosic sandstone. At most exposures in the northern Santa Ana Mountains a thin bed of reddish sandy clay overlies the basal con— glomerate and tends to stain the conglomerate out- crops a reddish color. The lower arkosic sandstone unit is poorly sorted and cemented, and is predominantly massive or coarsely cross—bedded; it averages 100 feet in thickness in this area. The color of the sandstone is gray to buff; the angular grains of quartz and feldspar are medium- sized to coarse. Some beds up to 4 feet thick have the VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. appearance of a rotten mica schist as they are com- posed almost entirely of biotite flakes. Thin beds of gray or brown sandy clay and siltstone are locally inter- bedded in the sandstone. At the top of this sandstone unit is a thick sequence of beds characterized by the alteration of biotite to the clay mineral anauxite. A yellowish brown to reddish or black pisolitic clay of commercial importance, the Claymont clay bed, occurs about 120 to 150 feet above the base of the for- mation. The clay is a resistant bed, 2 feet in average thickness, which has an almost continuous outcrop. It is hard, massive, and brittle, with a conchoidal frac— ture. Quartz is usually abundant in the lower part of the bed as angular grains. The clay commonly con— tains abundant 3- to 8—millimeter pisolitic aggregates of quartz and clay, particularly in the upper part of the bed. The thickest member of the Silverado formation is a coarse-grained arkosic sandstone unit, which rests on the Claymont clay bed and contains much biotite and anauxite. Locally, this member contains a hard white quartz sandstone bed about 20 feet thick, as well as thinner beds of varicolored sandy clays, siltstones, carbonaceous shales, and lignite. A meager fresh-water fauna occurs locally in the unit. The sandstone mem- ber is about 700 feet thick in the westernmost outcrops of the formation. The marine member of the Silverado formation is about 300 feet in thickness, and consists of soft, gray, well—bedded fine- and medium—grained sandstone. A poorly preserved fauna of Paleocene age includes T ur- M'tella pachecoensis and Glycymeris cf. major (Vedder, 1950, p. 33). SANTIAGO FORMATION The sedimentary rocks of Eocene age in the Santa Ana Mountains were named the Santiago formation by Woodring and Popenoe (1945). Strata of the Santiago formation rest with apparent conformity on rocks of the Silverado formation, although fossil evidence indi— cates a disconformity or a hiatus between the two formations (Vedder, 1950, p. 35). The approximate thickness of the Santiago formation in this area is 700 feet. The basal unit of the formation is a pebble-cobble conglomerate that interfingers irregularly with massive buff sandstone. The conglomerate is made up chiefly of well-rounded pebbles and cobbles of gray quartzite and reddish rhyolite, with less common clasts of light- colored plutonic rocks, set in a matrix of yellowish— brown coarse-grained sandstone. Locally this basal unit grades laterally into a massive, occasionally cross- bedded, coarse-grained arkosic and micaceous marine sandstone. 325 Buff to gray-brown fine— to medium-grained eon— cretionary sandstone, containing a molluscan fauna of middle to late Eocene age, overlies the basal conglom- erate unit. This concretionary sandstone unit has an average thickness of 125 feet. The upper unit of the Santiago formation is conglom- eratic sandstone of possible nonmarine origin that averages 450 to 500 feet in thickness. This sandstone is buff to brown, poorly cemented fand massive, coarse-grained, poorly sorted, and of arkosic composi- tion. Stringers of volcanic and quartzite pebbles form six-inch to one-foot discontinuous lenses in the sand- stone. Large fragments of silicified logs are common and serve to distinguish this unit. VAQUEROS AND SESPE FORMATIONS, UNDIFFERENTIATED Nonfossiliferous sedimentary rocks of the Sespe formation of late Eocene to early Miocene age rest with apparent conformity on strata of the Santiago forma- tion and grade upward and laterally into the fossiliferous marine strata of the Vaqueros formation. Interstratified beds of variable maroon and white or buff conglomeratic sandstone are characteristic of the lower part of the Sespe formation; occasional thin bands of greenish-gray to red clay and mudstone appear higher in the section. Well—rounded pebbles and cobbles of varicolored volcanic rocks and gray quartzite, averag- ing about 3 inches in maximum diameter, are character- istic of the conglomeratic portions of the sequence. The matrix of these rocks is composed of angular quartz, weathered feldspar, and biotite in a semi- consolidated clay cement. In the Santa Ana lVIountains it has not been possible to differentiate the Sespe formation described above from the overlying marine strata of the Vaqueros for— mation. Mollusks characteristic of the Vaqueros forma- tion are present locally in maroon and green beds that are typical of the Sespe formation. The Vaqueros formation of early Miocene age (Loel and Corey, 1932) overlies the Sespe formation and also intertongues with it. The Vaqueros formation con- sists of medium- to coarse—grained gray to buff sand- stone and conglomeratic sandstone with local greenish- gray sandy siltstone. Strata of the Vaqueros formation contain an abundant molluscan fauna which in— cludes Turm'tella inezana santana, Rapcna cf. vaguero- semis, Olivella santana, “Terebm” santana, and Anadam (Larkima) santtma, all of early Miocene age. In the mapped area the combined thickness of these formations averages about 1,400 feet; elsewhere in the Santa Ana Mountains the thickness is as great as 3,000 feet. 326 TOPANGA FORMATION The middle Miocene rocks of the Santa Ana Moun- tains were assigned to the Topanga formation by English (1926, p. 24). The strata of the Topanga formation rest with apparent conformity on beds of the Vaqueros formation. The thickness of the Topanga formation in this area is about 1,100 feet. Buff-colored massive and thickly bedded medium- to coarse-grained gritty sandstones that are scmiconsoli— dated and poorly sorted make up, with minor sandy siltstone and pebbly sandstone, almost the entire formation. Abundant molluscan fossils of middle Miocene age commonly occur near the base of the for— mation but are also found at higher horizons. In the El Modeno area two or more thin beds of white vitric tuff are interbedded in the sandstone of the Topanga formation. These tufl’ beds are not found east of the mapped area. PUENTE FORMATION The sedimentary rocks of upper Miocene age in the Santa Ana Mountains have been called the Puente formation by English (1926, p. 26), using the name assigned by Eldridge and Arnold (1907) to similar strata in the Puente Hills north and west of the El hIodeno area. In the El Modeno area, strata of the Puente forma— tion rest with apparent conformity upon the El Modeno volcanics. North of Santiago Creek and elsewhere strata of the Puente formation overlap rocks of the El NIodeno volcanics, and the Topanga, Vaqueros, and Sespe formations. In one locality, about 2 miles east of the mapped area, about 700 feet of strata of the Puente, Topanga, and, perhaps, of the Vaqueros for- mations are missing below the base of the Soquel mem— ber of the Puente formation. Schoellhamer and others (1954) have divided the Puente formation into four members in the Santa Ana Mountains. In ascending order these are: (1) the La Vida member, consisting of gray to black laminated siltstone which locally contains phosphatic nodules, and interbedded lenticular feldspathie sandstone and con- glomerate beds; (2) the Soquel member, consisting of massive to moderately well bedded coarse—grained to granular poorly sorted buff sandstone with interbedded siltstone and local conglomerate beds; (3) the Yorba member, consisting of thin—bedded haekly chocolate- brown to pinkish gypsiferous and diatomaceous silt— stone and local strata of sandstone and conglomerate; and (4) the Sycamore Canyon member (which does not appear on the geologic map, pl. 46), consisting of inter- bedded conglomerate, medium- to coarse-grained bufl' arkosic sandstone, and siltstone. The La Vida member commonly contains a forami- niferal fauna of early late Miocene age that includes SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Bulimina uvigerinagformis, Epom'des rosaformis, Valvu- lineria grandis, Uvigerina subperegrina, Buliminella curta, Bolivina vaugham', and Epistominella capitanesis»— all referred to the lower part of the Mohnian stage of Kleinpell (1938, p. 121—131). The average thickness of the Puente formation in this area is about 1,800 feet. In the type area in the Puente Hills, to the northwest of El Modeno, the formation reaches a thickness of about 11,000 feet. QUATERNARY TERRACE DEPOSITS Terrace deposits consisting of poorly sorted sand, gravel, and rubble are well developed within the mapped area, which includes the mouth of Santiago Creek. These deposits range in color from light gray to reddish brown. The six levels of deposits along Santiago Creek are found at the following approximate elevations above the stream bed: 10 to 15 feet, 40 feet, 60 feet, 150 feet, 210 feet, and 300 feet. This group of terrace deposits was mapped downstream from the head of Santiago Creek by Schoellhamer and others (1954). Along the south side of Burruel Ridge occur several isolated terrace deposits (Qtu) at elevations from 350 to 550 feet above the stream bed. Sedimentary rocks of the Puente formation have been thrust over high isolated remnants of terraces (Qtd) north of Santiago Creek. STRATIGRAPHIC POSITION AND CORRELATION OF THE VOLCANIC ROCKS The stratigraphic position of the El Modeno volcanics in the standard California section is known within close limits. The underlying Topanga formation con— tains a large molluscan fauna which includes Turritella ocoyana and other guides to Pacific coast middle Miocene strata. Interbedded near the base of the volcanic series is a marine siltstone bed that contains fish scales which are probably characteristic of the middle Miocene or lowest part of the upper Miocene. On Burruel Ridge, north of Santiago Creek near the north end of structure section A—A’ (pl. 47), the basalt flow member is overlain by a silicified claystone bed that contains a rich foraminiferal fauna including Bulimma montereyanu, Epistominella gyroidinaformis, Bagging rebut-ta, Valvulineria- californica obese, and Nom'on costiferum. R. M. Kleinpell has recently eX- amined this collection and considers it to represent the Siphogenerina reedi zone of his Luisian (middle Miocene) stage (oral communication). Resting conformably on the andesite flow and flow breccia member of the El Modeno volcanics is the La Vida member of the Puente formation, which contains Foraminifera diagnostic of the lower part of Kleinpell’s Mohnian stage. The El VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. Modeno volcanics thus appear to be middle to early late Miocene in age. Tentative correlation is made with the Glendora volcanics of Shelton (1946). The Glendora volcanics crop out about 25 miles north of the El Modeno area (fig. 55). They are predominantly andesitic massive flows and tuff breccias, but they are stratigraphically and lithologically more complex than the El Modeno volcanics. The Glendora volcanics are probably some— what older than the El Modeno, as fossiliferous sedi- mentary rocks of the Topanga formation (middle Miocene) are interbedded with and locally overlie the volcanic rocks (Shelton, 1955, p. 79—80). STRUCTURE The structure of the El Modeno area is characterized by faulting rather than folding. The great displace- ment of some of the faults and the relatively small size of most of the fault blocks render structural interpre- tation hazardous. FOLDS The volcanics near the east edge of the mapped area are involved in a faulted syncline which lies between the large westward-plunging anticline that was pene- trated by the National Securities Irvine 1 well and a horst block of rocks of the Sespe and Vaqueros forma- tions which trends northward from Peters Canyon Reservoir, as shown in structure section A—A’ plate 47. The main mass of El Modeno volcanics shown on structure section B—B’ is on the west side of a second but smaller anticlinal fold that is faulted on both limbs. Evidence in the mapped area indicates that folding occurred after the formation of Miocene strata but prior to the formation of the Quaternary terraces. Sedimentary rocks of Pliocene age which crop out north and west of the mapped area are folded but the terrace deposits are undeformed. This evidence indi— cates that most of the diastrophism occurred during late Pliocene or early Pleistocene time. FAULTS Several large faults traverse the area from southeast to north-northwest. These are all steep normal faults downdropped to the west and reflect the north- west-trending regional structural pattern of the Santa Ana Mountains. The large fault that trends north- northwest through the mapped area has a displacement of 1,600 to 2,000 feet. Subsurface data indicate that this fault continues west—northwest of El Modeno for a distance of 12 to 15 miles beneath the alluvial cover of the Los Angeles basin, where it is called the Norwalk fault by oil company geologists. The smaller faults have similar trends and relative displacements. The faults truncate the fold structures and are probably 327 Pleistocene in age. Low-angle reverse faulting thrusts sedimentary rocks of the Puente formation over Quaternary terrace deposits on the south side of Burruel Ridge, near the north edge of the mapped area. DISCONFORMITIES IN THE VOLCANIC SEQUENCE Two disconformities of local nature occur in the volcanic sequence in the east-central part of the mapped area. One occurs near the center of structure section B—B’ where the palagonite tufi' and tufl' breccia member rests on a siltstone of the Topanga formation, with the basalt flow member missing. Just to the south, near the northeast end of structure section 0—0’, the andesite flow and flow breccia member rests upon a similar siltstone (not mapped), with the basalt flow and palagonite tuff and tuff breccia members missing. These two members reappear in the complete sequence east of Peters Canyon. MODE OF DEPOSITION OF THE VOLCANIC ROCKS Submarine accumulation of at least a part of the basalt flow member is indicated by pillows with siltstone seams (fig. 57) and by the OVerlying fossiliferous marine siltstone. The alteration characteristic of the rock strongly suggests deposition in a hydrating environment. Most of the palagonitic tufl's were deposited in water deep enough to effect fairly uniform sorting over a re— latively large area; winnowing by winds probably facili— tated the sorting to some extent. The angularity of the fragments precludes thorough reworking of former sub- aerial deposits. Alteration of glass to palagonite, which is characteristic of these tuffs, is considered by Peacock and Fuller (1928) and MacDonald (1949, p. 59) to be postdepositional, owing to ordinary weathering. Erup- tion of hot tufl’aceous material directly into water or water-saturated sediments would accelerate this dehy- dration. Peacock and Fuller consider the formation of chlorophaeite to be a deuteric process, initiated at the time of deposition. In the northern part of the central volcanic area sev- eral large blocks with distinct cooling cracks (fig. 62), occur in the andesite flow and flow breccia member, each block lying in a matrix of vesicular lava or palagonitic tuff. This is strong evidence for deposition of hot avalanche deposits characteristic of some volcanic explosions. At the same stratigraphic horizons in the southern part of the area, these features are missing and in their place are dense flows with occasional poorly developed pillow structure. - It is concluded from their lithologic and petrographic characteristics that the El Modeno volcanics were formed by both submarine and subaerial deposits of igneous material of intermediate composition. No evidence is at hand concerning the source of these 328 volcanic rocks. The uniformity of the sequence and distribution of individual lithologic units throughout the series indicates a source capable of extruding large quantities of material over a wide area. Subsurface data suggest that the present area of outcrop lies at the eastern margin of the area of deposition and therefore probably at some distance from the position of the source vents. SUBSURFACE DATA Twenty-eight wells drilled for oil in the Los Angeles basin south of the Whittier fault and east of the San Gabriel River have penetrated volcanic rocks similar to those represented at El Modeno (see table 4 and fig. 56). Samples from these wells are commonly amygdaloidal, usually deeply altered and often pyritized. Generally they consist of fragmental or brecciated ex- trusive deposits of intermediate composition. The stratigraphic relations and lithologic character of the volcanic rocks penetrated by wells are apparently similar to those of the outcrops in the El Modeno area. DISTINCTION BETWEEN EXTRUSIVE AND INTRUSIVE ROCKS Several characteristics of the extrusive rocks of Mio- cene age of the eastern Los Angeles basin may serve to distinguish them from the dike and sill rocks that are often observed in the subsurface, intruding sedimentary rocks of Miocene age and older. The stratigraphic position of the extrusive rocks seems to be sharply limited upwards, as they are not known to occur above the base of the La Vida member of the Puente formation. Dikes and sills do not crop out south of the Whittier fault zone, between the El Modeno area and the, San Gabriel River, 10 miles to the west. The stratigraphic position of these intrusive rocks is somewhat uncertain, but they apparently intrude no rocks younger than the lower member of the Puente for— mation. Lithologic distinctions between extrusive and intru- sive rocks are limited mainly to the state and type of alteration; textural distinctions are reliable only in the case of tuffaceous or bedded pyroclastic deposits. The intrusive rocks are commonly hard and dense although the ferromagnesian minerals are often replaced, whereas the extrusive rocks are commonly vesicular and severely SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY altered to crumbly palagonitic masses, interpreted as evidence of submarine accumulation. Petrographically, the intrusive rocks are characterized by chloritized ferromagnesian minerals. These minerals are commonly represented by pyroxene and olivine, occasionally by accessory biotite, and rarely by horn- blende. Albitized feldspars are also seen. The rocks usually exhibit a diabasic, often coarsely ophitic texture. The extrusive rocks are characterized by such alteration products as chlorophaeitc and palagonite; chlorite is rare. The presence of more than 10 percent of glass is generally reliable evidence of extrusive origin, as pointed out by Durrell (1953). The composition of the extrusive and intrusive reeks of the eastern Los Angeles basin south of the Whittier fault may be quite similar. In most of the samples of each rock examined, the plagioclase was found to range between andesine and sodic labradorite in composition, except in the albitized intrusive rocks. Augite, or its alteration products, were present in all the crystalline samples; olivine, in perhaps half the samples of each type. As mentioned above, minor amounts of horn- blende and biotite occur in the intrusive rocks but apparently never total Inorc than 5 percent. However, these minerals have been seen only in rocks believed to be intrusive. The intrusive rocks may be somewhat more alkalic in composition and slightly younger than the extrusive rocks. While there is no structural evi- dence indicating a common source, it is conceivable that the few distinctive characteristics of each type are attributable entirely to their mode of emplacement, and that they are consanguineous and contemporaneous or nearly so. DISTRIBUTION OF THE VOLCANIC ROCKS The distribution of the volcanic rocks indicates that they were deposited over an area of about 770 square miles south of the Whittier fault (see fig. 56 and table 4). Only a few wells are known to have been drilled through the volcanic rocks into older sedimentary rocks. In these few wells the average thickness of the volcanic rocks suggests that they may thicken basinward (west— ward) from El Modeno at a rate near 100 feet per mile. There is no clear evidence in the subsurface data of an unconformity beneath the volcanic rocks, and well cores are not numerous enough to indicate which units of the sequence thicken westward. 329 VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. .585 28853 88 8885258 88: Sam .mHav 3 ES. 888 38:08:53 2883: 23:8 ”on? 5 “38:. 888 38888 :58 8822 888 ””188. 3 a 888 885888 882:5 .888 85:88: .3 3 .N ..m w .a. .ma 5% 888 “we? 8302 .283 2:38 88qu ....... 888 288:5 .vam 282:2 28:8 +aaoH 2.8-52. hmmH 3% HanH .585 8 .m oaa 85: .m 8a ......... H 25.52.: €65.60 :0 5ko «H .3 HH .MH .8: as .888 8858888 .888 35888: rm m. .a. .3 .88 .888 $8 .00 888 8858888 0580:: .8 aom. 985822 28:2 .58 85822 Saab mm 38-83 NEH 83 ”1% .558 8 .3 «S H88 .Z 82 ........ H 85.8885 85288nH 888m «H .3 8 .m .38 89m .888 885888 .888 8a rm w .8 .ma 6% .888 $8 .82. as 888 2888.» Hawwwmuwgm £85822 23:2 58.888 8825 ”mom 6 $3189. 8 32. ”En .585 .8 .3 82 :88“. .m mama ......... 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SEQSE 2: Re S38 :5 Ex 8:.2: £2: Re 95114. Hamid. VOLCANIC ROCKS, EL MODENO AREA, ORANGE COUNTY, CALIF. REFERENCES CITED Chayes, Felix, 1949, A simple point counter for thin section analysis: Am. Mineralogist, v. 34, p. 1—11. Durrell, Cordell, 1953, Tertiary igneous rocks of the Santa Monica Mountains: Pacific Petroleum Geologist, v. 7, no. 12, p. 2—3. Eldridge, G. H., and Arnold, Ralph, 1907, The Santa Clara Valley, Puente Hills, and Los Angeles oil districts, southern California: U. S. Geol. Survey Bull. 309. English, W'. A., 1926, Geology and oil resources of the Puente Hills region, southern California: U. S. Geol. Survey Bull. 768. Fuller, R. E., 1938, Deuteric alteration controlled by the jointing of lavas: Am. Jour. Science, v. 35, p. 161—171. George, V1'. 0., 1924. The relation of the physical properties of natural glasses to their chemical composition: Jour. Geol- ogy, v. 32, p. 353—372. Kleinpell, R. M., 1938, Miocene stratigraphy of California: Tulsa, Okla., Am. Assoc. Petroleum Geologists. Larsen, E. S., 1948, Batholith and associated rocks of Corona, Elsinore and San Luis Rey quadrangles, southern California: Geol. Soc. America Mem. 29. Loel, Wayne, and Corey, W. H., 1932, The Vaqueros formation, lower Miocene of California; Pt. l—Paleontology: Univ. Calif. Pub., Dept. Geol. Sci. Bull., v. 22, p. 31—410. MacDonald, G. A., 1949, Petrography of the Island of Hawaii: U. S. Geol. Survey Prof. Paper 214—D. Peacock, M. A., and Fuller, R. E.,1928, Chlorophaeite, sider- omelane, and palagonite from the Columbia River plateau: Am. Mineralogist, V. 13, p. 360—383. 331 Ross, C. S., and Hendricks, S. B., 1945, Minerals of the mont- morillonite group: U. S. Geol. Survey Prof. Paper 205—B, p. 23—79. Schoellhamer, J. E., and W'oodford, A. 0., 1951, The floor of the Los Angeles basin, Los Angeles, Orange, and San Ber- nardino Counties, Calif: U. S. Geol. Survey Oil and Gas Inv. Map OM 117. Schoellhamer, J. E., Kinney, D. M., Yerkes, R. F., and Vedder, J. G., 1954, Geology of the Northwest Santa Ana Moun- tains, Orange, Riverside, and San Bernardino Counties, Calif: U. S. Geol. Survey Oil and Gas Inv. Map OM 154. Shelton, J. S., 1946, Geology of northeast margin of San Gabriel basin, Los Angeles County, Calif: U. S. Geol. Survey Oil and Gas Inv. Prelim. Map 63. 1954, Miocene volcanism in coastal southern California, in Jahns, R. H. ed., Geology of southern California: Calif. Div. Mines Bull. 170, chap. 7, p. 31—36. 1955, Glendora volcanic rocks, Los Angeles basin, Cali- fornia: Geol. Soc. America Bu11., v. 66, p. 45—89. Vedder, J. G., 1950, The Eocene and Paleocene of the Northwest Santa Ana Mountains: M. A. Thesis, Claremont Graduate School. chtworth, C. K., and Williams, Howe], 1932, The classification and terminology of the pyroclastic rocks: Natl. Research Council Bull. 89, p. 19—53. Woodring, W. P., and Popenoe, \V. P., 1945, Paleocene and Eocene stratigraphy of northwestern Santa Ana Mountains, Orange County, Calif: U. S. Geol. Survey Oil and Gas Inv. Prelim. Chart 12. INDEX Page Acknowledgments. 313 Alteration, augite... 318, 323 Alteration, glass ____________________ 318, 319, 323, 327 hydrothermal ______________________________________ 321 olivine ____________________________________________________________ 323, 324 olivine basalt ____________________________________________________ 316,317,324 Amerada Petroleum Corp., subsurface data _________________________________ 329 Anauxite ___________________________ 325 Andesite, basaltic. ,,,,,,,,,, 318, 323 calcic_. 320 Andesite dikes . . 321 Andesite flow and flow breccia member, character and distribution. 313, 320—321,321 plagioclase in __________________________________________________________ 324 stratigraphic position _________________________________________________ 313,326 Apatite..____ ___________________________________________________________ 324 Augite _________________________________ 318, 319, 321, 323 Bandini Petroleum Co., subsurface data ____________________________________ 329 Basalt, plagioclase in _______________________________________________________ 324 Basalt dikes __________________________________________________________________ 322 Basalt flow member of El Modeno volcanics, character and distribution ______ 313, 316—319, 321 stratigraphic position ______________ 326 Bedded palagonite tuff ________________ __ 319 Burruel Ridge, claystone bed ___________________ 317—318 reverse faulting _________________________________ 327 terrace deposits ________________________________________________________ 326 tuff in La Vida member _______________________ 323 Cerro Villa Heights, outcrop ___________________________________ 317 Chlorite _________________________________ 321 Chlorophaeite, definition ___________________________________________________ 313 occurrence and description. . 316, 318,321, 322,323, 324,327 Clay minerals ............................ 323,324,325 Claymont, clay bed ........................ 325 Claystone bed, basalt flow member ................... .... 317—318 Composition, extrusive and intrusive rocks 313,316,328 Continental Oil Co., subsurface data ................. Cooling cracks ................ Correlation, volcanic rocks __________________________ Descriptive geology ...................................................... 316—326 Deuteric processes .................................................. 319,324,327 Diastrophism, age ......................................................... 327 Differentiation . . 324 Bikes and Sills.... _________________________ 321,322, 328 Disconformities, volcanic sequence .......................................... 327 El Modeno volcanics, age and correlation... ........... 313, 326—327 character and distribution ___________ 316—321, 326 Eocene age, Santiago formation .............................................. 325 Sespe formation .......................................................... 325 Faults ...................................................................... 321, 327 Feldspar, determination ................................. 313 Ferromagnesian minerals, alteration ................................. 313,321,324 Fish scales ......................................................... .. 317,326 Flow breccias.. ._. 313,320 Folds _______________ 327 Foraminiferal fauna. .. 313,326 Fossils ............................................................... 325, 326, 329 Gale, Hoyt S., subsurface data ................................................ 329 General Petroleum Corp. subsurface data .................................... 329 Girard, P. M., subsurface data .......................................... 329 Glass ............................... 324 alteration to paiagonite ....... 327 Glass fragments, La Vida formation. _ 323 Topanga formation ............. 316 Glendora volcanics, comparison with ________________________ 319,327 Halloysite ............................................ Hot avalanche deposits. Hypersthcne ............................................... 319, 323 Intrusive and extrusive rocks, distinction and stratigraphic position .......... 328 La Vida member of Puente formation, character and distribution .......... 313, 326 glass fragments in ................................................ 323 plagioclase in. _ 324 tuff in _________ 322—323, 324 Lava flows, andesite flow and flow breccia member. _. .. 320 Lithologic distinction, intrusive and extrusive rocks ........................ 328 Los Angeles basin, eastern, underlying igneous rocks... _____ _ 313, 329—330 wells drilled into Miocene volcanic rocks ......................... 315, 328—330 McKee Oil Co., subsurface data ............................... _. 329 Magnetite ....................................... . . 324 Methods of study. 313 Miocene age, El Modeno volcanics .................... 326 Glendora volcanics ................................ 327 La Vida member ..................................................... 326 Sespe formation. . _ . ...................................... 325 Topanga formation. .. ...................................... 326 Vaqueros formation ......... . _ . . 325 Molluscan fauna, Santiago formation ...... 325 S ilverado formation ..................... 325 'l‘opanga formation ..................... 326 Vaqueros formation ................................. 325 Morton dz Sons, subsurface data ........................ 329 Norwalk fault ................................................................ 327 Oil wells, subsurface data ............................................... 328, 329—330 Olivine, occurrence and composition ............................ 316, 318, 322, 324 Olivine basalt ...................................................... 316, 323,328 Palagonite .......................................................... 313,319, 323,327 Palagonite tuff and tuf’f breccia member, character and distribution. . . . 313,319,321 Palagonitization ......................................... 321,323,327 Paleocene age, Silverado formation. ................................... 325 Panorama Heights... ................................ 317.319 Peters Canyon, rock samples 316 sequence ...................... 327 Petrographie characteristics, extrusive and intrusive rocks.. 328 Petrographic description, basalt dikes ...................................... 322 basalt flow member .................................... 318 bedded palagonite tuff ................................................. 319—320 La Vida member ................................... . .................. 323 lava flows ....... Topanga tufis ................... Pctrography of El Modeno volcanics. _ . 323 Phillipsite .................................... .. 321 Pillow structure in lava flows....... 317,320, 327 Plagicclase, average c0mposition.... 324 Previous investigations ..................................................... 314 Puente formation, character and distribution ............................... 326 Puente Hills ................................................................. 326 Pyroclastic rocks, terminology.. _. 313 Pyroxene ................................................... 318, 319, 321, 322, 323 Rock samples studied, keys ................................................ 314-316 Santa Ana Mountains, geology ........................................ 324, 325,326 Santiago Creek area, geology. - _ ..... . 317, 320, 322, 325, 326 Santiago formation, character and distribution. . 325 basalt dikes ............................. .. 322 Sedimentary rocks, geology ...................... 324—326 Seguro Petroleum Co., subsurface data ...................................... 329 Sespe formation. See Vaqueros formation. ShelI Oil Co., Inc., subsurface data ......................................... ..- 329 334 INDEX Page Page Silica content of glass, andesite flow member __________________________________ 324 ’I‘opanga formation, dikes-Continued basalt flow member __________________________________________________ . 318, 324 volcanic rocks, character and distribution _________________________________ 313 tufls of La Vida member ______________________________ . ,,,,,,,,,,,,,, 324 petrography ........................................................... 323 tufts of Topanga flow ____________________ . _ ._ . _ 316, 324 stratigraphic position and correlation. . Silverado formation, character and distribution. __________ . 324—325 Sequel member, Puente formation_._.. . __._. ........ 326 Source of volcanic rocks _________________________________________________ 327—328 Standard Oil Company of California, subsurface data ,,,,,,,,,,,,,,,,,,,,,,,, 330 Stratigraphic position, volcanic rocks ................. .. 326 Structure ________________________________________________________________ 327 basalt flow member ...................................................... 317 Subsurface data, rocks penetrated in wells. ...................... 328, 329—330 Superior Oil Co., subsurface data ________________ . 330 Sycamore Canyon member of Puente formation, description __________________ 326 Terminology, pyroclastic rocks ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 313 Terrace deposits _________________________________________________________ 326 Texture, andesite dikes ______________________ andesite flow and flow breccia member.. basalt dikes .......................... basalt flow member ______________________________________________ . palagonite tuff and tuf‘f breccia member ___________________________________ 319 The Texas 00., subsurface data _______________________ . _ .- 330 Thickness of formations in area... .. . .. __._ 317, 319, 320, 322, 324, 325, 326 Tidewater Associated Oil Co., subsurface data ______________________ 330 Topanga formation, dikes ________________________________________________ 322 sedimentary rocks ..................... 326 structural relations. 327 tufts .............................................................. 316—317, 324 Tridymite .............. .._. Trustees Development Association. subsurface data. Tufl's, E1 Modeno volcanics ________________________________________________ 319 Puente formation ................................................. 316. 322—323 Topanga formation ___________________________________________________ 322—323 Union Oil Company of California, subsurface data ........................... 330 Vaqueros and Scspe formations undifferentiated, character and distribution. 325, 326 Volcanic breccia .................................... . ______________________ 321,322 Volcanic rocks, mode of deposition _________________________________________ 327 source .................................... 327—328 stratigraphic position and correlation. .. .. . . subsurface data .............................. undifferentiated, character and distribution ......................... 321,325, 326 Volcanic sequence, disconformities ........................................... 327 Weir Canyon, basalt dikes .................................................. 322 Wells drilled into Miocene volcanic rocks, eastern Los Angeles basin... 315, 324, 328, 329-330 Wellsite ..................................................................... 321 Whittier fault zone ......................................................... 328 Yorba member of Puente formation, description .............................. 326 Zeolite ......................... . .......................................... 321, 324 .wfr, r.5.}i;$«§c.;il;11‘. 732i {vii : PROFESSIONAL PAPER274 PLATE 46 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 4 $333ka 3%?“me smfiab J $805 335: Contact 28933 $32 0:393 S ufiwuofl Saab 3383 Dashed where approximately located >m<_ ._. E for the ma] or ox1des Percent Si02 _______________ 43—48 MgO ______________ 8—15 A12 03 ______________ 8-11 08.0 _______________ 10-12 F82 03 _______________ 4-6 N320 + K20 ________ 2. 5—3. ‘5 F60 _______________ 9—16 The plagioclase in most of the hornblende gneiss is calcic andesine (Ame—45), but the composition ranges between sodic andesine (Anao) and sodic labradorite (An55). The more calcic plagioclase is generally in hornblende-rich gneiss, but some rocks with about equal proportions of hornblende and plagioclase also contain labradorite. Most plagioclase is in clear, irregular to almost equidimensional crystals that range 3 Tweto, 0. L., 1947, Pre-Cambrian and Laramide geology of the Vasquez Moun tains, Colorado: Unpublished thesis, University of Michigan. 340 from 0.5 to 2 millimeters in diameter (pl. 50, A—C). Most of the plagioclase determinations were made by measuring extinction angles on grains of known orien- tation. Grains cut normal to the a crystal axis were . found particularly useful. The abundance and random orientation of plagioclase in most rocks permit close determination of at least several crystals in each thin section by this method. A few determinations were made by measuring indices of refraction. Augite forms small, irregular, essentially colorless grains, generally less than ] millimeter in diameter, that are closely associated with hornblende (pl. 50 0). Some augite grains are irregularly rimmed by pale actinolitic amphibole, but these rims are not common. The augite is optically positive, with a 2V estimated to be near 60°. The maximum extinction angle Z/\c is between 45° and 50°. Rounded blebs of quartz embay hornblende and plagioclase and in places form abundant small poiki- loblastic inclusions in hornblende (pl. 50 B). Locally, small cuspate grains of quartz associated with minor amounts of microcline partly replace the older, larger crystals. Some quartz may be an original constituent of the gneiss, but most of the quartz appears to have been introduced after the hornblende and plagioclase crystallized. Where present, biotite generally is associated with hornblende. In places it forms imperfect pseudomorphs after the hornblende, but more commonly it occurs as flakes and sheaves along cleavage planes or crystal margins of the hornblende. N0 biotite was found in augite—bearing hornblende gneiss. Some of the biotite may have been original in the gneiss, but most ap- parently formed during the period of metasomatic alteration and shearing that followed dynamothermal metamorphism. Some biotite grains are about as large as the associated hornblende (1—3 millimeters), but most are somewhat smaller, less than 0.5 millimeter in diameter. Apatite,in small stubby prisms, is scattered through almost all hornblende gneiss, but nowhere does it exceed a fraction of a percent of the rock. Magnetite and sphene are even less abundant and in places appear to be secondary. Secondary epidote in small irregular grains and aggregates is scattered through the rock. Although many of the chloritic pods in the hornblende gneiss retain little evidence of their origin, some clearly were formed from hornblende-rich masses of rock, and all stages in the alteration can be seen. Horn— blende was altered to chlorite, magnetite, and epidote- clinozoisite; the subordinate plagioclase was highly sauSSuritized and sericitized, and commonly was al- most completely altered. The massive chlorite com- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY monly contains small amounts of epidote, green spinel, and magnetite, most of which is titaniferous as shown by a dense, white “leucoxene” type of alteration product. The serpentine bodies are made up in large part of very fine grained fibrous chrysotile containing abundant dusty to granular magnetite and hematite. Irregular and partly serpentinized aggregates of tremolite and olivine with abundant accessory magnetite and spinel are scattered throughout the serpentine, and scattered flakes of chlorite with associated magnetite cut both the serpentine and the tremolite-olivine relicts. Pris- matic tremolite and rounded to irregular olivine grains occur in crystalloblastic aggregates that are clearly older than the serpentine. Olivine was more easily altered than tremolite, and in many of the partly altered rocks olivine was largely replaced by pseudo- morphs of chrysotile. In the more completely altered rocks tremolite also was serpentinized, spinel disap- peared during serpentinization, and magnetite was largely recrystallized. i STRUCTURE Although the hornblende gneiss is distinctly layered, it lacks key beds or distinctive horizon markers, It was greatly deformed during dynamothermal nieta— morphism and was so changed in later shearingland metasomatic transformations that much of the evidence for determining the detailed structure of the rocks has been lost. Foliation and layering trend easterlyiand northeasterly and generally dip steeply northward. Axial parts of folds were observed throughout the areas underlain by hornblende gneiss; these structures ranged from small drag folds to large isoclinal folds with amplitudes much greater than the areas of ‘out- crop and probably in terms of several thousands of feet. Foliation is parallel to the layering over most of the area, but in some places the foliation apparently transects the axial parts of folds. ‘ All fold axes in the hornblende gneiss plunge steeply, generally about down the dip of the foliation. The orientations of 31 random fold axes plotted on the 1 wer hemisphere of a Schmidt equiarea net (fig. 68) fall Within a relatively small area, and it is significant that no measurement deviates far from the regional trend. Lineation shown by oriented prismatic hornbl nde crystals conforms to the same pattern, and the orie . ta- tion of 18 random measurements also is shown on figure 68. ' Thus the mineral lineation is parallel to the tectonic axis defined by the fold axes, and according to interpretations widely but not universally accepted the direction of tectonic movement may have been largely horizontal. Lineations developed during the subsequent dynamic metamorphism and rheomorphism i METAMORPHISM AND THE ORIGIN OF GRANITIC.ROCKS, NORTHGATE DISTRICT, COLORADO \\\ \\\§ \\\\ \\ \\\§ \\\\ i N *0 Lineation shown by 18 random measure- ments of oriented hornblende crystals Lineation shown by 31 random measurements of minor fold axes FIGURE 68,—Llneation In hornblende gneiss. Contours on 5, 10, and 20 percent concentrations per 1 percent of the area. Plotted on the lower hemisphere of a Schmidt eqniarea net. 341 are parallel to lineation in the regionally metamorphosed hornblende gneiss; apparently the same stress field persisted after the close folding and dynamothermal metamorphism ceased. ORIGIN’ Similar hornblende-rich rocks from many other places in the pre-Cambrian of Colorado and southern Wyoming have been described by many geologists. According to Blackwelder (in Darton and others, 1910), the most abundant metamorphic rocks in the Laramie and Sherman quadrangles are dark greenish hornblende schist; they are abundant on J elm Mountain along the west edge of the Laramie quadrangle and 12 to 15 miles northeast of the Northgate district. From Blackwelder’s description, these rocks appear identical with the hornblende gneiss in the Northgate district. By analogy with similar rocks in other dis- tricts, Blackwelder suggested that they are meta- morphosed basic dikes and lava flows. Ball (1906, p. 376; and in Spurr and others, 1908, p. 45—46) first described hornblende gneiss in the central part of the Front Range, Colorado. He noted that the rock occurred as sheets and dikes and believed it to be metamorphosed mafic igneous rocks. Lovering (1935, p. 10—11) described a similar hornblende gneiss in the Montezuma quadrangle, Colorado, where the hornblende gneiss is essentially conformable with the underlying Idaho Springs formation. Levering sug- gested that it originated through the metamorphism of andesitic flows. Tweto ‘ made a detailed study of the hornblende gneiss in the Vasquez Mountains, north of the Montezuma area. Here bands of hornblende gneiss alternate with gneiss and schist of the meta— sedimentary Idaho Springs formation. After carefully considering the field relations, the variations and limits of composition, and the common association with lime- silicate rocks, Tweto concluded that the hornblende gneiss resulted from the metamorphism of impure dolomite. Hornblende-plagioclase rocks in other metamorphic terranes have been derived, from both igneous and sedimentary rocks. The well-known amphibolites in the Grenville series in New York, Ontario, and Quebec have been attributed (Adams and Barlow, 1910; Buddington, 1939, p. 11—12; Osborne, 1936, p. 197—227) to the metamorphism of impure calcareous sediments, gabbros and diorites, and volcanic flows and tuffs. Hornblende gneiss in the N orthgate district is so highly metamorphosed and was so greatly changed by later transformations that any discussion of origin largely would be conjecture. The present structure ‘ Tweto, O. L., op. cit. 342 and mineralogy are due to intense deformation and metamorphism of what appears to have been originally a layered rock. The composition shows wide variation similar to that observed by Tweto, but no unequivocal metasedimentary rocks were found associated with it. Some dense clinozoisite—epidote-quartz rocks that may have been lime-silicate rocks of sedimentary origin occur in the belt of recrystallized mylonites along Pinkham Creek Canyon, but the relations now are greatly obscured by cataclasis and granitzation. The residual tremolite-olivine—spinel aggregates in the ser- pentine bodies have been completely recrystallized, and no relict texture survives. On the basis of composi- tion, however, these bodies could well represent meta- morphosed ultramafic igneous rocks. Although the composition of the different layers in the hornblende gneiss shows more variation than might be expected in a series of lava flows, it is perhaps even more difficult to envisage a sequence of impure calcareous rocks as thick as required in the Northgate district without some interbedded elastic sediments of distinctive character. The occurrence of serpentine bodies of possible ultramafic igneous origin suggests that the associated hornblende-plagioclase rocks also may have been of igneous origin. A mixed accumula- tion of pyroclastic deposits and lava flows might approximate fairly closely the varied yet related compositions now displayed by the different layers of hornblende gneiss. QUARTZ MONZONITE GNEISS GENERAL FEATURES AND DISTRIBUTION Much of the hornblende gneiss in the Northgate district was converted by metasomatism to a granitoid gneiss of quartz monzonitic composition, and many bodies have a distinctly pegmatitic facies. Abundant pegmatite, also believed to be metasomatic in origin, is closely associated with the quartz monzonite gneiss. The intricate shapes of the quartz monzonite gneiss bodies shown on the geologic map (pl. 48) actually are generalizations, as it was impossible during field work to show all the details on aerial photographs with the approximate scale of 1 inch equals 1,000 feet. ’ According to interpretations outlined later in this report, some of the quartz monzonite gneiss near the northwestern and southeastern corners of the North- gate district became mobile (or rheomorphic) late in the period of metasomatism and invaded the surround- ing rocks. The rheomorphism was irregular, and the areas of once-mobile rocks are very poorly defined. These rocks, therefore, have not been differentiated on the geologic map (pl. 48) but are included within the areas shown as quartz monzonite gneiss. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY occur in the northern part of the district, and part f an irregular body occurs in the southeast corne . Reconnaissance in adjacent areas showed that these bodies are parts of much larger masses of quartz monzonite gneiss. There are numerous small bodies of quartz monzonite gneiss in the central part of the Northgate district, between the larger masses, but they are subordinate to the abundant pegmatite. The quartz monzonite gneiss was formed without deformation of the surrounding rocks except near masses that became mobile after transformation. Remnants of hornblende gneiss abound in the trans- formed rocks, and relict textures can be recognized even in the interiors of some of the larger bodies. The transitions between quartz monzonite gneiss and the other metamorphic rocks on one hand and pegmatite on the other are commonly so gradational that many of the mapped contacts are arbitrary. This gradation is common along the strike of folitation of the quartz monzonite gneiss bodies; across the strike many of tlie contacts are fairly sharp. Most of the larger bodi‘s of quartz monzonite gneiss are relatively massive and “granitic” appearing, whereas many of the smaller bodies mapped are incompletely transformed rocks that in the field resembled quartz monzonite gneiss more than the original metamorphic rock. The pervasive solutions responsible for the transformation altered the original minerals and introduced new minerals along the margins of the older grains; little or no lit-par-lit gneiss or veined gneiss is associated with the large bodies of quartz monzonite gneiss. After transformation from hornblende gneiss to quartz monzonite gneiss, the rock in the large mass near the northwest corner of the district became mobile and invaded the surrounding rocks (see “Rheomorphic quartz monzonite gneiss”). Similar mobilization took place near the southeastern part of the district, but apparently on a much smaller scale. ’ Large tabular bodies of quartz monzonite gnei? LITHOIJOGY Quartz monzonite gneiss includes a diversified gro 1p of medium-grained pink rocks composed dominantly pf feldspar and quartz with minor amounts of biotite br chlorite. The incompletely transformed rocks differ most in appearance, but even thoroughly granitized rocks range widely in texture, grain size, and mineral composition. Most of the rock is layered or gneissose, and three general textural varieties were recognized in the field. The most distinctive variety shows a faint relict texture that resembles that of the original horn- blende gneiss, but this generally is subordinate to gneissose and alaskitic varieties which have entirely new textures. METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO All stages of transition between quartz monzonite gneiss and hornblende gneiss were traced in the field. The relationship is most apparent in those rocks that retained a relict texture through the transformations; the original hornblende was progressively altered to biotite or chlorite and the total content of mafic minerals diminished sharply, some quartz and microcline were introduced, but the rocks as a whole retained a marked textural resemblance to the original hornblende gneiss. The similarity seems dependent largely upon the plagio- clase grains which became more albitic during trans- formation but retained their crystal form and served as a relict skeleton upon which the newly formed minerals were formed. The rock with relict texture is made up of an ag— gregate of nearly equidimensional grains of quartz and feldspar (chiefly plagioclase), as much as 2 milli- meters in diameter and small quantities of biotite or chlorite. The gneissic texture is due chiefly to a faint layering owing to variations in grain size and mineral composition, and to the elongation of some quartz grains and aggregates in the direction of folia- tion. Biotite and chlorite generally are too sparse to affect the foliation, but the few grains present tend to be oriented parallel to the layering shown by the other minerals. Pegmatite layers as much as 2 inches thick are common and generally follow the foliation. Relict textures are absent in the other two closely related textural varieties, which are distinguished by their degree of foliation which in turn is controlled largely by the relative abundance of biotite. Where biotite makes up more than 5 percent of the rock, most of the flakes are oriented nearly parallel to the original layering of the metamorphic rocks and the foliation is fair to good; where biotite is minor or absent, the rock is distinctly alaskitic. The biotite present generally is rather evenly distributed through the rock, but in a few rocks it tends to be aggregated into biotite-rich layers. Quartz and feldspar grains in both the gneissose and alaskitic rocks are in even—grained ag« gregates and show little directional orientation. Some quartz grains are elongate in the direction of foliation, but most tend to be equidimensional. As in the rock which shows relict textures, thin layers of coarser gneiss and pegmatite are abundant and generally follow foliation. These rocks appear fairly uniform in hand specimens, but most outcrops show slight textural variations that give the rock a layered appearance. The several textural varieties are closely associated, and gradations are common. The variety characterized by faint relict textures is absent near quartz monzonite gneiss that became mobile; but where the rocks were relatively undisturbed, different varieties occur in 343 adjacent layers, even in the interior of large masses of quartz monzonite gneiss. Plate 51A shows typical quartz monzonite gneiss exposed in a fresh road cut. In addition to the somewhat coarser bands of quartz monzonite gneiss, many bodies contain abundant irregular masses of pegmatite, and some smaller bodies pass laterally into pegmatite. In field mapping the different bodies were arbitrarily assigned to either quartz monzonite gneiss or pegmatite, depending on the dominant rock type. PETROGRAPHY The textural varieties of quartz monzonite gneiss differ considerably in mineral content. The gneiss with relict textures has significantly less microcline than plagioclase, and biotite or chlorite generally are subordinate. Albite or oligoclase is largely in cor- roded pseudomorphs after the plagioclase of the original hornblende gneiss; locally such plagioclase grains still make up 30 to 35 percent of the rock. Gneiss with new textures, on the other hand, generally has microcline-plagioclase ratios of 1:1 or greater and the gneissose and alaskitic varieties differ chiefly in biotite content. Plagioclase occurs as corroded relicts in these rocks too, but more complete replacement has destroyed the original textures of the rock. Quartz varies widely in abundance but makes up 30 to 45 percent of most quartz monzonite gneiss. Other differences in composition of quartz monzonite gneiss apparently are related to variatiOns in soda and potash concentration in the alkali- and silica- bearing solutions which caused its transformation. Where potash was predominant, the resulting rock characteristically consists of microcline, sodic Oligo— clase, quartz, and biotite; where soda was relatively more abundant the rock is made up of microcline, sodic albite, quartz, and chlorite. Most quartz mon- zonite gneiss formed under potash-rich conditions shows new textures but some has retained relict textures; most gneiss altered by soda—rich solutions has retained relict textures and only some show new textures. The mineralogic transformations transitional between hornblende gneiss and quartz monzonite gneiss differed greatly between potassic and sodic conditions of origin. Spatial relations of the different textural and com- positional types and the succession of mineralogic transformations, discussed in the following paragraphs, indicate that sodic conditions may have been peripheral to potassic conditions and that the inner and pre— sumably higher temperature zones tended to encroach on the outer zones as the transformations progressed. Potash was the predominant alkali in the formation of most quartz monzonite gneiss. In early stages of 344 the transformation, hornblende was converted to bio- tite, plagioclase was altered to a somewhat more sodic feldspar crowded with saussuritic and sericitic inclu- sions, and considerable quartz was introduced. With continued alteration, microcline was introduced along the margins of the older grains, and biotite was progres— sively destroyed. Plagioclase was progressively replaced by microcline and some additional quartz and was con- verted to sodic oligoclase or calcic albite having relatively abundant myrmekite (pl. 513, 0). Typical thoroughly transformed gneiss of this origin consists of 25 to 50 percent microcline, 10 to 35 percent sodic oligoclase, 30 to 45 percent quartz, and as much as 15 percent bio- tite. Muscovite and garnet locally make up several percent of some quartz monzonite gneiss but generally are very subordinate or absent. Soda—bearing solutions were most effective early in the period of transformation and were followed by pro- gressively more potash—rich solutions. In early stages of alteration (pl. 50D), hornblende was converted largely to chlorite, in places through intermediate actin- olite, plagioclase was altered to sodic albite crowded with saussuritic and sericitic inclusions, some quartz generally was introduced, and in places minor quantities of microcline were introduced. Some albite recrystal- lized during this state and albite-rich stringers with pegmatitic texture are relatively common, but most of the intermediate rock shows excellent relict hornblende gneiss texture. Scattered granules and veinlets of epidote are abun- dant. With continued alteration, microcline and more quartz were introduced, and the quantity of chlorite diminished markedly with an increase in microcline content. Saussuritic inclusions in plagioclase in the more altered rocks are very irregularly distributed, and clear to partly clear plagioclase grains are common. Microcline generally makes up only 20 to 30 percent of the quartz monzonite gneiss of this origin, and relict textures are common. The rest of the rock typically is made up of 25 to 35 percent sodic albite, 35 to 45 percent quartz, and as much as 5 percent chlorite and epidote. Plagioclase in all varieties of quartz monzonite gneiss forms irregular grains that characteristically are em— bayed by microcline and quartz (pl. 513, 0). Some crystals are 2 millimeters in diameter, but most are between 0.5 and 1.5 millimeters in diameter. The plagioclase in rocks that formed under predominantly potassic conditions ranges in composition from Ans to Ana} the plagioclase grains in rocks where early soda metasomatism was widespread generally are more sodic than An5. Saussuritic and sericitic inclusions in plagio- clase generally decrease in abundance with an increase in the degree of albitization. This is particularly true SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY in the more sodic plagioclase, but some relatively calcic oligoclase is clear also. Myrmekite is widespread through quartz monzonite gneiss and generally is along the margins of plagioclase grains adjacent to microcline (pl. 510). It is therefore most abundant where micro- cline is most abundant, and is relatively rare in albite- bearing rocks. All plagioclase crystals are highly cor- roded, and evidence from transitional rocks indicates that most grains are sodic pseudomorphs of the inter— mediate plagioclase in the original hornblende gneiss. Irregular grains of microcline range from minor intergranular wisps to relatively large pegmatitic poikiloblasts an inch or more in diameter that commonly contain abundant residual inclusions of unreplaced plagioclase and biotite. Many contacts indicate re- placement relations toward plagioclase and biotite (pl. 513, 0) and gradations in the progressive replacement have been observed. Most of the textural banding noted in outcrops and in hand specimens of quartz monzonite gneiss is due to greater concentration of microcline by metasomatic replacement of primary minerals along certain layers parallel to foliation. Injec- tion apparently had little influence on the formation of these layered rocks. The relative abundance of the different minerals in incompletely transformed rocks indicates that most quartz was introduced early in the transformation, before significant quantities of microcline were intro— duced. The later stages of metasomatic alteration generally show only a slight increase in quartz, but considerable recrystallization apparently took place as it is difficult to determine any consistent age relationship for quartz and microcline in thoroughly transformed rocks. Quartz typically is in lobate to rounded blebs and grains and as elongated crystals and aggregates strung out along the foliation. It definitely corrodes and replaces plagioclase and biotite, and some crystal- lized late in the transformation and cuts microcline as well. Small ragged flakes and grains of biotite are scattered through the quartz monzonite gneiss. The biotite is corroded by microcline and quartz and commonly is associated with abundant dusty to granular magnetite and hematite. In places muscovite is interleaved with biotite or forms discrete flakes. Many of the rocks contain secondary chlorite and magnetite associated with biotite. Chlorite is most common in the rocks in which early albitization was intense. It is especially abundant in partly transformed rocks, where it forms pseudomorphs after hornblende; but where transformation was more complete, chlorite rarely makes up more than a few percent of the rock and generally is in ragged shreds With abundant dusty to granular magnetite and METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO hematite. Sphene and epidote are associated with some of the chlorite and are most abundant in incom- pletely transformed rocks (pl. 50 D). Irregular small grains and aggregates of magnetite and hematite are distributed through most quartz monzonite gneiss. They are commonly associated with corroded biotite and chlorite grains and appear to be most abundant where replacement was most complete; it is likely that most of the scattered grains are residual from the replacement of original ferromagnesian minerals in the rock. Pink garnet is relatively abundant in some of the smaller‘bodies of quartz monzonite gneiss. It has the same appearance and index of refraction as garnet found in partly altered metamorphic rock and pegma— tite; in all probability it is a residual mineral that survived transformation. Zircon and apatite occur as very minor accessory minerals. ORIGIN Quartz monzonite gneiss in the N orthgate district formed through reaction between hornblende gneiss and silica- and alkali-bearing solutions which permeated the rock after dynamothermal metamorphism. Quartz monzonite gneiss is in extremely irregular bodies that do not conform to the highly folded structure of the hornblende gneiss. Although some local control on replacement was exerted by folds in the host rock, almost all medium- to large-sized masses transgress the older structures. In spite of the occurrence of the quartz monzonite gneiss in crosscutting bodies the adjacent rocks show no deformation, and the orientation of foliation in numerous inclusions of hornblende gneiss within quartz monzonite gneiss is parallel to that of the enclosing rock and of the adjacent hornblende gneiss. Even in local areas where bodies of quartz monzonite gneiss conform in part to folds in the hornblende gneiss, the quartz monzonite gneiss shows the same textural evidence for a replacement origin as was noted else- where, and the relations are those of incompletely replaced folded rocks rather than of folded granitoid rocks or phacolithic intrusion. Intermediate stages in the transformation of horn- blende gneiss to quartz monzonite gneiss are found throughout the district. Gradational contacts are common along their strike of foliation, and many small bodies of quartz monzonite gneiss show all stages of the transformation. Although marginal transition zones are not conclusive evidence as to the origin of the in- teriors of such bodies, the presence of relict textures and masses of incompletely replaced rock within large bodies of quartz monzonite gneiss indicates that all of the quartz monzonite gneiss is of replacement origin. 345 Petrographic study of intermediate stages in the formation of quartz monzonite gneiss indicates that most plagioclase is pseudomorphous after the plagio- clase in the original hornblende gneiss, and that replace- ment by quartz and microcline began along grain boundaries and gradually engulfed the adjacent crys- tals. Hornblende was converted to biotite or chlorite, and the ferromagnesian content decreased as the transformation progressed. Even though most horn— blende gneiss is poorly foliated, the foliation apparently exercised considerable control on the flow of the hydro- thermal solutions and thus in turn controlled the layered character of quartz monzonite gneiss. Contacts of quartz monzonite gneiss bodies are commonly sharp across the t1 end of foliation. Thus field and petrographic evidence indicates that transformation was accomplished by tenuous solutions that were capable of penetrating large masses of rock without disturbing the structural continuity of that rock. Lime, magnesia, and iron were largely replaced by potash, soda, and silica. Early conversion of horn- blende to biotite and the introduction of quartz, followed by the formation of microcline and more quartz in most of the quartz monzonite gneiss, indicate that potash and silica were important constituents of the solutions. Albitization was not intense in most of these rocks, and the plagioclase most commonly is sodic oligoclase. This fact suggests that the soda concentra- tion of most of the solutions was relatively low. Local transformation of hornblende gneiss to albite- chlorite-quartz rocks without a significant decrease in plagioclase content followed by later formation of microcline and more quartz, indicates that locally the early solutions were soda rich but that they became more potassic as transformation progressed. These albitic rocks occur throughout the gneiss complex, even in the interiors of large bodies of quartz monzonite gneiss. No control for this type of alteration was discerned in the field; such alteration, however, is par- ticularly abundant in many relatively small bodies of quartz monzonite gneiss. It is suggested that the sodic alteration may have been a local marginal effect of solutions enriched in soda by potash metasomatism of plagioclase feldspars at depth. As granitization pro~ gressed, sodic alteration was followed by potash metasomatism. BIOTITE-GARNE'I‘ GNEISS GENERAL FEATURES AND DISTRIBUTION Irregular bodies of biotite—garnet gneiss (biotite- garnet—quartz-plagioclase gneiss) occur in the central part of the N orthgate district, Where they are associated with abundant pegmatite, and in the southeastern part, 346 associated with quartz monzonite gneiss and minor amounts of pegmatite. The largest bodies of biotite- garnet gneiss are near the lower reaches of Camp Creek and the North Platte River, where several connected masses 1,000 to 6,000 feet long and 500 to 1,500 feet wide crop out (pl. 48). Many smaller bodies are found here and elsewhere throughout the area where pegma- tite is abundant; many are too small to be shown on the geologic map (pl. 48). The scattered masses of biotite-garnet gneiss are closely associated with pegmatite, and show all grada- tions from hornblende gneiss to pegmatite. The grada- tion into pegmatite is through transitional zones either of lit-par—lit gneiss or by a general coarsening of grain and decrease in biotite content. The bodies of biotite- garnet gneiss are so discontinuous and haphazardly distributed, and the contacts are so indistinct and irregular, that it seems very probable that the rock originated through transformation of hornblende gneiss. This interpretation is supported by the many un— transformed or partly transformed relicts of hornblende gneiss commonly found within bodies of biotite-garnet gneiss. LITHOLOGY Biotite-garnet gneiss ranges from slightly garnetized hornblende gneiss to coarsely porphyroblastic augen— gneiss, banded lit-par—lit gneiss, and even pegmatite. Variable grain size and uneven texture characterize the interior of most bodies of biotite-garnet gneiss. In most biotite-garnet gneiss the different minerals tend to be distributed unevenly, and the degree of mineral segregation increases with increase in garnet, quartz, and biotite. Layering is conspicuous in some rocks, and quartz and feldspar form discontinuous thin layers and lenses interleaved with layers rich in biotite. Red garnet is irregularly distributed through most of the rock. It is most abundant in or near quartz-feldspar layers; elsewhere the garnet aggregates are commonly surrounded by light—colored halos that are poor in biotite. Where layering is not conspicuous, quartz and plagioclase with minor amounts of biotite form ir- regular or lenticular aggregates in biotite-rich gneiss. Such biotite-rich and biotite-poor masses of rock intergrade completely and commonly form masses a few inches to a few feet in diameter. The transition zones between hornblende gneiss and biotite-garnet gneiss are commonly narrow and are marked by the appearance and progressive increase in abundance of biotite and quartz. Red garnet may occur in some of the transition zones, but generally it is more abundant in the more altered rock. With increasing quantities of biotite, the foliation becomes more marked, but in general the rock in the transitional zones strongly resembles hornblende gneiss. Within SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY a few inches in from the margins, hornblende becomes rare, and biotite, quartz, and plagioclase crystals generally are coarser than the grains in the original rock. In local facies some even-grained aggregates of plagioclase, quartz, and biotite with minor amounts of garnet and scattered relicts of hornblende make up fairly large bodies, but more commonly such aggregates form only small bodies near the margins of more typical biotite-garnet gneiss. ' Near the large pegmatite bodies, the gneiss is ex- tremely variable and the quartz-feldspar layers pass into small pods and stringers of relatively fine-grained quartz-plagioclase-garnet pegmatite. Feldspar augen or small pegmatitic knots of quartz, plagioclase, and garnet occur singly or in beadlike strings along the foliation; in places these knots coalesce into fairly persistent bands several inches thick, or into irregular masses a few inches to a few feet in diameter. With increasing numbers of pegmatitic pods and stringers, the gneiss attains a typical lit-par-lit structure; many have a distinctly knotted appearance in outcrop. As the quantity of associated pegmatite increases, the biotite—rich bands become thinner and more discon- tinuous; and microcline, hitherto a minor constituent, becomes progressively more abundant. All gradations exist between the lit-par-lit variety of biotite-garnet gneiss and many of the larger, microcline-rich pegma- tite bodies. PETROGRAPHY The texture of the biotite—garnet gneiss along its margins greatly resembles that in the surrounding horn— blende gneiss (pl. 52A). Hornblende and plagioclase grains closely resemble in size, shape, and composition such grains in hornblende gneiss and apparently are relict. Biotite occurs along the cleavage and grain margins of hornblende and as separate flakes. Where not strung out along later shear zones, biotite tends to be distributed evenly through the gneiss and is oriented nearly parallel to the layering; the rock is distinctly better foliated‘ than the original hornblende gneiss. Irregular to lobate quartz grains have replacement relations toward the other minerals. A representative specimen of this rock is made up of about 40 percent plagioclase (An28_35), 30 percent quartz, 15 percent hornblende, and 15 percent biotite. As much as 5 percent microcline is found in some rocks near the margin. Hornblende is absent or is very subordinate to biotite a short distance from the contact, and the quartz here is somewhat coarser and more abundant than along the margins. The minerals in most of the biotite-garnet gneiss are unevenly distributed, and the texture shows wide variation. In banded varieties the quartz-plagioclase layers are discontinuous and have very indistinct METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO margins. Commonly they coalesce into / irregular masses with pegmatitic texture. The darker biotite- rich layers generally are somewhat finer grained than the light-colored layers and are thickest and most abundant where associated pegmatite is sparse. Gar- net, with associated quartz, biotite, and blue amphibole, forms irregular to rounded aggregates many of which are as much as half an inch, and more rarely several inches, in diameter. Most garnet aggregates are in the quartz-feldspar layers or are surrounded by light- colored halos poor in biotite, but locally garnet occurs in nests of coarse biotite. The mineral composition of these different “typical” biotite-garnet rocks varies greatly, but most of these rocks consist of about 40 to 45 percent plagioclase, 25 to 35 percent quartz, 15 to 20 percent biotite, and as much as 15 percent garnet. Relict hornblende in minor amounts is widespread, and several percent of microcline occurs in some specimens. Some quartz-plagioclase-garnet stringers have a typical pegmatitic texture in which some quartz and feldspar crystals are an inch or more in diameter and associated biotite and garnet are only a little less coarse. The texture of the rock adjoining the pegma- titic stringers is locally very similar to the more normal biotite-garnet gneiss, but commonly it is even more irregular. Much of the biotite-garnet gneiss and related rocks underwent minor granulation during the period of shearing that elsewhere formed hornblende-biotite gneiss and mylonite gneiss. Quartz stringers and rela— tively coarse, undeformed biotite follow some granu- lated zones through these rocks, and both quartz and biotite, as well as plagioclase, are ground up and spread out along others. Thus the shearing appears to have taken place at about the same time as the trans- formation. The composition of plagioclase in biotite-garnet gneiss is remarkably uniform and is generally between A1128 and An35. A striking feature is that within any given body, the plagioclase has the same composition whether it occurs as relict crystals in the narrow, horn- blende-bearing marginal zones, as relict or recrystallized grains in the main part of the body, or as coarse and completely recrystallized grains in the quartz-plagi— oclase-garnet pegmatite stringers. In several suites of specimens from different biotite-garnet gneiss bodies the range in composition of plagioclase was only 3 or 4 per- cent of anorthite (close to the limit of accuracy of de- termination), and the range in individual specimens was nearly as great. The only general variation noted in plagioclase composition is in those pegmatitic rocks containing 10 percent or more of microcline; in these the plagioclase composition generally is near An25. One local and significant deviation in plagioclase 402890—57 3 347 composition was noted in a specimen of slightly altered hornblende gneissfrom the margin of a relatively small body of biotite-garnet gneiss. Most of the specimen is made up of about 45 percent hornblende, 40 percent plagioclase, 10 percent quartz, and 5 percent biotite. Plagioclase and hornblende have the same textural relationship of these minerals in normal hornblende gneiss, quartz corrodes the plagioclase and hornblende, and biotite occurs along cleavage planes and margins of hornblende. An irregular stringer of about one-eighth inch thick of biotite-garnet-plagioclase rock follows along the foliation of this slightly altered hornblende gneiss. This stringer of typical biotite-garnet gneiss, which contains a few ragged hornblende relicts only partly altered to biotite, grades into the adjacent horn- blende gneiss. The composition of 15 plagioclase grains was determined by measuring extinction angles on grains of known orientation; five grains from the relatively unaltered hornblende gneiss have an average compo- sition of Anao, five grains from the margins of the biotite—garnet gneiss stringer range from An35 to An37, and five grains from the central part of the stringer range from An“, to An“. The alteration here produced a distinctly more calcic plagioclase than that in the original rock. Plagioclase grains have the same general size and shape in the marginal transition zones and in the even- grained varieties of biotite-garnet gneiss as in the sur- rounding hornblende gneiss. In more uneven—textured biotite-garnet gneiss, however, the plagioclase ranges widely in grain size and was largely recrystallized. The large recrystallized grains in the quartz-plagioclase- . garnet pegmatite stringers generally embay smaller plagioclase grains. As most of the crystals are clear, the change in composition was not due to a saussuritic breakdown of the original plagioclase. Plagioclase makes up 40 to 50 percent of most biotite-garnet gneiss, regardless of grain size or texture. This is only slightly less than the average amount in hornblende gneiss. Only in pegmatitic varieties of biotite-garnet gneiss does the quantity of plagioclase vary significantly; plagioclase commonly makes up 50 to 70 percent of the quartz-plagioclase-garnet stringers and pods, and it is relatively minor where abundant microcline is present. Hornblende is most abundant in the transition zones between hornblende gneiss and biotite-garnet gneiss, where it occurs in irregular grains that commonly are partly altered to biotite (pl. 52 A). Where biotite is subordinate, the hornblende is similar to that in ad- jacent, unaltered hornblende gneiss; as the quantity of biotite increases, the hornblende relicts become smaller, less abundant, and much more irregular. Hornblende in the typical biotite—garnet gneiss is in scattered, ragged 348 grains, which are generally associated with abundant biotite. Hornblende generally is absent in the biotite- garnet gneiss near pegmatite and quartz monzonite gneiss. Some of the pegmatitic pods, however, contain hornblende crystals one—half inch or more long, and ap- parently the adjacent rock was considerably enriched in hornblende. Biotite is closely associated with abundant horn- blende in the marginal transition zones and in partly transformed hornblende-rich inclusions within biotite- garnet gneiss bodies. Biotite is regularly distributed through the relatively even grained biotite-garnet gneiss. The relationship with scattered hornblende relicts indicates that the biotite here is in part at least an alteration product of hornblende. Where trans— formation was more complete, most biotite is in separate grains that show no trace of their origin, but all relict hornblende crystals have some closely associated biotite. In the uneven-textured, thoroughly recrystal- lized rocks, biotite forms irregular concentrations and stringers that vary widely in grain size. Biotite is coarsest where it is most abundant, and in some rocks it forms local concentrations with grains one-half inch or more in diameter. More commonly it is mixed with variable amounts of plagioclase and quartz or is closely associated with garnet aggregates. Coarse-grained biotite is a minor constituent of many pegmatite pods and stringers. The biotite in all these occurrences has essentially the same optical properties, and presumably has essentially the same chemical composition. The pleo- chroic colors are yellow and dark brown,‘ and the 2V is small, in many thin sections being sensibly zero. The higher index of refraction (B essentially equals 7) was measured for 6 specimens representative of all degrees of transformation; 4 of these measurements were between 1.65 and 1.66, 1 was between 1.64 and 1.65, and another was slightly above 1.66. These properties are characteristic of ordinary biotite, and no evidence was seen for either markedly magnesian or markedly ferriferous biotite. The total hornblende and biotite content generally decreases from the marginal transition gneiss to the lit-par-lit gneiss and pegmatitic gneiss. Hornblende comprises 35 percent or more of most hornblende gneiss, and in the marginal parts of biotite-garnet gneiss bodies combined hornblende and biotite make up 25 to 35 percent of the rock. Biotite generally makes up only 15 to 25 percent of those rocks where hornblende is minor or absent, and as little as 5 percent of much lit-par—lit gneiss and rock out by abundant pegmatite. Red garnet is widely but irregularly distributed through biotite-garnet gneiss and associated pegmatite, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY and locally it also occurs in the adjacent hornblende gneiss near a contact with pegmatite 0r biotite-garnet gneiss. Garnet is coarsest and most abundant near pegmatite bodies and in many places is found only in thin peripheral zones around pegmatite. In other places, garnets are distributed throughout relatively large masses of biotite—garnet gneiss. Rock with abundant garnet generally has less biotite than similar rock with less garnet. The garnets are completely isotropic and probably belong to the almandine- pyrope group. The index of refraction of garnets in 26 specimens from all occurrences was determined. In 24 specimens the index was between 1.79 and 1.80, and in 2 specimens the index was significantly above 1.80. Thus the composition of most garnets in biotite- garnet gneiss and related rocks probably is near Aim-Pym. The garnet typically occurs as granular, poikiloblastic aggregates with abundant rounded quartz inclusions and variable amounts of closely associated blue amphibole and biotite. All stages in the formation of garnet were seen, and it apparently formed from materials derived from the breakdown of both hornblende and biotite. In the earliest stages, garnet formed in scattered, irregular to rounded spots as much as one-half inch in diameter consisting of small grains of blue amphibole and biotite with a few small garnet granules set in a fine mosaic of quartz and sericitized plagioclase (pl. 52 B). Adjacent. hornblende and biotite generally are somewhat cor- roded. As the quantity of garnet increases, the quan- tity of blue amphibole, biotite, and plagioclase de- creases, and the quartz aggregates into rounded blebs surrounded by or closely associated with granular garnet (pl. 52 0). The larger garnets are in rounded to very irregular aggregates with abundant lobate to rounded quartz inclusions and variable quantities of closely associated biotite (pl. 52 0). The biotite occurs in peripheral concentrations, scattered inclusions, and fracture fillings; some relatively large crystals project haphazardly into or through the garnet. Small grains of blue amphibole are associated with many garnet aggregates but generally are absent where biotite is abundant. The garnets within biotite concentrations are surrounded by thin rims of fine quartz, sericitized plagioclase, and biotite, and the larger adjacent biotite crystals are strongly corroded (pl. 52 D, E'). The blue amphibole associated with many garnet aggregates is most abundant where the surrounding rock is rich in hornblende, but it is relatively common even where the hornblende in the adjacent gneiss is insignificant in amount (pl. 52 3,13, F). Most of the blue amphibole is in small, irregular to idioblastic grains that formed as an intermediate step in the development of garnet, but in some hornblende- METAMOFPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO rich rocks the original hornblende crystals adjacent to the garnet aggregates were partly or entirely con- verted to blue amphibole. The pleochroic colors of the blue amphibole are yellow, blue green, and green blue in contrast with the yellow, grass green, and dark green of unaltered hornblende in hornblende gneiss. Although biotite is a common associate of garnet, the rock around the larger garnet aggregates commonly is relatively poor in biotite and hornblende, and in places the minerals in these light—colored halos are distinctly coarser grained than those in the rest of the rock. The biotite-poor halos that surround garnet aggregates and the relatively low percentage of biotite and hornblende in those rocks where garnet is abundant indicate that most of the garnet-forming material was locally derived from the biotite and hornblende. Total biotite and garnet, however, rarely exceeds 25 percent of typical biotite-garnet gneiss and generally is less than 20 percent; consequently these totals represent a significant decrease in the iron and magnesia held in the original hornblende gneiss. The quantity of quartz in biotite-garnet gneiss varies widely, but generally it makes up 20 to 40 percent of the rock. Even in marginal zones it comprises as much as 30 percent of some biotite—garnet gneiss. It forms small lobate grains in slightly altered rocks; with increasing alteration the quartz became coarser, more irregular, and somewhat more abundant. Microcline in wisps and small grains constitutes as much as 5 percent of some typical biotite-garnet gneiss (pl. 52 0'), but in much of the rock it is absent. Some biotite-garnet gneiss, particularly near large microcline- bearing pegmatite bodies, contains 30 percent or more of microcline in grains that range from very small wisps to almost rectangular augen an inch or more in length. Myrmekite is widespread in these rocks, and many microcline cyrstals are crowded With unre- placed inclusions of plagioclase, biotite, and quartz. Some of these inclusions are aggregates that show the normal relationship of biotite-garnet gneiss; micro- cline, therefore, was evidently the last mineral formed in the biotite-garnet gneiss. Accessory minerals in original hornblende gneiss make up only a fraction of a percent of the rock; apatite is the most abundant of these, but sphene is also widespread. Both apatite and sphene, as well as variable amounts of Secondary epidote, are much more abundant in the biotite-garnet gneiss, and appear to become more abundant with an increase of garnet and microcline. Zircon and magnetite also are fairly common in biotite—garnet gneiss, but they are greatly subordinate to apatite, sphene, and epidote. ‘ 349 ORIGHNT Abundant evidence indicates that biotite-garnet gneiss originated by transformation of hornblende gneiss. Contacts between these tWo rock types are gradational and irregular; many untransformed or incompletely transformed remnants of hornblende gneiss occur throughout the biotite-garnet gneiss; and many details of the transformation can be ob- served under the microscope. The close association with pegmatite and minor amounts of related quartz monzonite gneiss and the evidence for recurrent shearing during transformation indicate that the trans- formation was a phase of the general dynamic and metasomatic metamorphism that affected the gneiss complex during the later stages of regional meta- morphism. Except for the relatively late introduction of micro— cline (changes more closely related to the origin of microcline-rich pegmatite discussed in the following section), the transformations produced chiefly minerals containing considerable lime, magnesia, and iron, and introduced abundant silica. Normal hornblende gneiss, having roughly equal proportions of intermediate plagioclase (Ange—55) and hornblende, was converted to a rock composed of biotite, garnet, quartz, and plagioclase (An23-35). Total ferromagnesian content shows a slight but progressive decrease with increased alteration. To accomplish these changes, silica for the quartz was needed in excess of the few percent which may have been derived from the breakdown of hornblende to biotite and garnet, as the quantity of quartz inmost biotite—garnet gneiss exceeds that of the combined biotite and garnet and is about the same as that of hornblende in the original rock. Some potash, in addition to that already present in the amphibole, may have been required to permit the formation of biotite . from hornblende. Potash concentration in the early stages was apparently low, however, for little microcline was formed then. The other alterations required removal of small amounts of lime, magnesia, and iron. These changes contrast notably with those in the adjacent zones where quartz monzonite gneiss was formed. Large quantities of lime, magnesia, and iron were replaced by alkalies and silica as the intermediate plagioclase of the hornblende gneiss was converted to sodic oligoclase or albite and the ferromagnesian min- erals were largely destroyed. Although under classical theories of metamorphism the minerals of the biotite-garnet gneiss are generally considered to originate at higher temperatures than those in quartz monzonite gneiss, geologic evidence here 350 indicates that this was not the case. Biotite-garnet gneiss occurs with abundant pegmatite in a zone ap- proximately peripheral to the large quartz monzonite gneiss bodies, a zone where the temperature should have been somewhat lower. More probably the differences in reaction were related to differences in concentration of the materials in solution. Yoder (1952, p. 615—617) has shown that the same mineral assemblages can form under widely different temperature and pressure conditions, de- pending on the bulk composition of a system. Evi- dently most alkalies in the solutions were precipitated in the formation of quartz monzonite gneiss, a precipita- tion Wegmann (1935, p. 326) postulates as taking place within a narrow zone or “front.” As the solu- tions migrated outward and were impoverished in alkalies they undoubtedly were enriched in displaced lime, magnesia, and iron. Thus the alteration of the rock above the granitization “front” would take place in an environment relatively low in alkalies and rich in lime, magnesia, and iron. There was no precipitation of these materials in the biotite-garnet gneiss to form a “basic front” (Reynolds, 1944, p. 235—238; Read, 1948, p. 11—12); rather there is evidence for slight removal. However, the uniformity of composition of plagibclase and garnet indicates that these minerals formed. by reaction with solutions considerably richer in lime, magnesia, and iron than those in deeper zones. Although progressive mineralogic and textural changes clearly indicate the replacement origin of most biotite-garnet gneiss, the origin of quartz—plagioclase- garnet pegmatite is not so obvious. Bodies of this rock range from small knots a few inches in diameter through thin discontinuous stringers in lit—par-lit gneiss to relatively persistent, veinlike bodies a few inches thick and as much as several tens of feet long and irregular masses up to several feet or more in diameter. Because of their coarse grain and low biotite content these rocks are distinctive; but the bodies do not displace their walls, and the contacts characteristically are gradational. Although present in different proportions, the minerals are the same as those in the wall rocks; and neither plagioclase nor garnet shows any change in composition across the contacts of the pegmatitic bodies. Evidently the quartz-plagioclase-garnet pegmatite resulted from the same alteration that produced the adjacent biotite— garnet gneiss. PEGMATITE GENERAL FEATURES AND DISTRIBUTION Quartz-microcline-plagioclase pegmatite is abundant in a zone in the central part of the Northgate district, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY between the large masses of quartz monzonite gneiss in the northern and southeastern parts of the district. Associated with the abundant pegmatite are small bodies of quartz monzonite gneiss, but they are largest and most abundant to the north, where the pegmatite and quartz monzonite gneiss zones overlap. The largest pegmatite bodies are in the west—central part of the district where some very irregular masses are more than 2 miles long and 2,000 feet wide. Biotite- garnet gneiss is associated with the abundant pegmatite through the central part of the pegmatite zone, where quartz monzonite gneiss is subordinate. In the south- ern part of the pegmatite zone where relations have been greatly obscured by later igneous intrusion, Laramide faulting, and Tertiary alluviation, pegmatite appears to be much less abundant than farther north. It forms many small bodies on Pinkham Mountain and eastward where shearing appears to have been active during the period of metasomatism that followed dynamothermal metamorphism (see “Lithology” fol- lowing). The southern margin of the pegmatite zone coincides with an irregular belt of mylonite gneiss near Pinkham Creek. Some pegmatite is associated with the large masses of quartz monzonite gneiss both north and south of the pegmatite zone, but is less abundant here than in the central part of the district. Although some of the smaller pegmatite lenses bulge the foliation and layering in their wall rocks and apparently represent injected material, most of the larger bodies show replacement relations toward the host rock. Rocks surrounding the ramifying pegmatite masses are not displaced or deformed, and the foliation in the wall rock and in numerous undigested inclusions of country rock in pegmatite shows the same orienta- tion. In some places contacts of pegmatite bodies are sharp, but elsewhere pegmatite grades into such diverse rocks as hornblende gneiss, hornblende—biotite gneiss, biotite-garnet gneiss, and quartz monzonite gneiss. Locally many smaller bodies range from quartz mon— zonite gneiss in one part to pegmatite in another. Pegmatite and quartz monzonite gneiss generally appear contemporaneous, but where an age sequence can be determined pegmatite is always the younger. LITHOLOGY With few exceptions, pegmatite in the Northgate district shows little mineralogic zoning, but is a simple aggregate of quartz and feldspar with subordinate muscovite, biotite, garnet, and magnetite or hematite. The texture characteristically is uneven, and some grains are as much as several inches in diameter. Very coarse pegmatite is rare. Many pegmatite bodies have a distinct megascopic foliation shown by abundant METAMORPHISM AND THE ORIGIN OF GRANITIC BOOKS, NORTHGATE DISTRICT, COLORADO elongate quartz aggregates, or, more rarely, by musco- Vite-covered folia. The pegmatite ranges widely in composition from plagioclase rich, microcline poor through all gradations to those in which nearly all the feldspar is microcline. Where plagioclase is abundant the rock generally is white to gray and is relatively fine grained for pegmatite. Microcline occurs in scattered pink crystals, and garnet and biotite are most abundant in these rocks. Where microcline is more abundant, the rock is distinctly pink and generally coarser grained. In microcline- rich pegmatite, plagioclase is in scattered grains and in irregular granular aggregates. In places quartz and the associated feldspar show the same range in grain size, but more commonly the quartz is in irregular aggregates between larger feldspar grains. Muscovite is abundant in a few bodies, but is very scarce or absent in most. Magnetite, or hematitic and limonitic pseu- domorphs after magnetite, is widespread in the peg- matite, and in places makes up several percent of the rock. Most contacts of pegmatite with quartz monzonite gneiss and biotite-garnet gneiss are completely grada- tional. In quartz monzonite gneiss the pegmatite occurs either as narrow bands parallel to foliation or as irregular masses of various shapes and sizes. Biotite— garnet gneiss grades into microcline-rich pegmatite through an abrupt increase in microcline, a decrease in biotite, and a general increase in grain size. The change is most abrupt in the medium-grained even- textured biotite-garnet gneiss, whereas in the lit-par-lit variety, where much of the adjacent rock has a pegma— titic or near pegmatitic texture, the transition more commonly is gradational. The relations between pegmatite and hornblende gneiss are considerably more varied. Some contacts are sharp but more commonly a narrow, epidote—rich transition zone exists between the two rocks. Chlorite, pink plagioclase (albite), garnet, and specularite are common associates of epidote in the transition zone; microcline is progressively more abundant toward the center of the pegmatite. The transition zone is highly variable in texture and ranges from pseudo- morphic hornblende gneiss through structureless ag- gregates to distinctly pegmatitic textures. Quartz was widely leached from some pegmatite bodies and locally some quartz monzonite gneiss bodies as well. The leached rock comprises a cellular feldspar skeleton of the original rock. Many of the cavities contain scattered to numerous flakes of specular hematite and a few of the holes are lined with small, euhedral quartz crystals. Most of the masses of leached rock are only a few feet or tens of feet in diameter and make up only a small part of the affected 351 bodies. The leaching was erratically distributed, and except for a slight tendency toward localization near the bulbous ends of pegmatite bodies, no structural control was discerned. In some places numerous partly leached relicts occur through the more cellular rock. PETROGRAPHY The relative abundance of the different minerals in the pegmatite varies widely from quartz-plagioclase- garnet pegmatite with subordinate microcline to quartz- microcline pegmatite with little or no plagioclase or garnet. Quartz makes up 20 to 30 percent of almost all the pegmatite, and in most of the rock microcline is significantly more abundant than plagioclase. Garnet, generally with some associated biotite, is relatively abundant in those rocks where plagioclase is abundant, but it is rare and irregularly distributed in microcline- quartz pegmatite. Muscovite is abundant in a few places but generally is rare. Minor quantities of magnetite are widespread. Plagioclase generally occurs in irregularly shaped aggregates with quartz, and rocks where plagioclase is the most abundant feldspar are finer grained than the more common, microcline-rich pegmatite. Plagioclase was one of the earliest minerals in the pegmatite to crystallize, and most of it is corroded and partly replaced by microcline and quartz. In those bodies where plagioclase makes up more than a few percent of the rock its composition generally ranges from Anzo to Anao. Where plagioclase is a minor constituent of the pegmatite, it tends to be distinctly more sodic and ranges from Anm to An”. Some grains are clear but most are somewhat saussur- itized; a few grains are heavily crowded with saussuritic and sericitic inclusions. Little correlation exists be- tween composition and degree of alteration. Myrme- kitic borders are common on plagioclase grains where con- siderable replacement by microcline has taken place. Microcline ranges from small crystals between the plagioclase grains to large, irregular to almost rectangu- lar crystals, many of which contain abundant corroded inclusions of plagioclase. Commonly several adjacent inclusions have the same optical orientation. In plagioclase—rich pegmatite, the microcline apparently formed in a previously existing rock, and all degrees of replacement can be seen from these early rocks to rocks in which the feldspar is largely microcline. Quartz occurs in irregular to lobate grains and aggre- gates that are unevenly distributed through the rock. Where plagioclase is abundant the associated quartz appears to be about contemporaneous, but where micro- cline is the predominant feldspar much of the quartz is corrosive toward the plagioclase and appears to be of about the same age as the microcline. As quartz in 352 the plagioclase-rich pegmatite and in the microcline- rich pegmatite is about equally abundant, the apparent difference in relative age may be due in large part to recrystallization of quartz already present. This re- crystallization is further indicated by a general increase in grain size of quartz with an increase in microcline content. In those pegmatite bodies that show a megascopic foliation’, the elongated quartz aggregates appear under the microscope as stringers and veinlets along recrys- tallized cataclastic zones. Granulated feldspar and quartz along these zones have recrystallized to a fine interlocking aggregate of irregular grains, and are cut by the larger quartz stringers which definitely occur later than the shearing. Where present, muscovite forms small grains in the recrystallized cataclastic aggregate and larger flakes and layers associated with the late quartz stringers. Both varieties crystallized after shearing. Garnet has about the same index of refraction in pegmatite as it has in the adjacent biotite-garnet gneiss. The irregular to rounded grains and aggregates have a typical sieve texture, with abundant blebby quartz inclusions and variable quantities of closely associated biotite. ' Garnet is most abundant and the associated biotite is most common in pegmatite that is rich in plagioclase; garnet is relatively minor and biotite is absent in pegmatite where replacement by microcline was more complete. The garnet grains appear to have been inherited in large part from an earlier stage in the transformation and replacement of hornblende gneiss. The contacts between pegmatite and hornblende gneiss are marked in many places by abundant epidote and lesser quantities of chlorite and albite. Some of these rocks show good relict texture of the original hornblende gneiss, with chlorite pseudomorphs of horn— blende set in a dense matrix of epidote. More com— monly the alteration product is a dense green rock composed of predominant granular to prismatic epidote with variable quantities of pink albite (An2-5). Sphene, chlorite, and hematite are common accessory minerals. In places the epidote-albite rock is coarse grained and has a pegmatitic texture. Garnet is fairly common in hornblende gneiss near pegmatite and in the transition zones, and in one place a dense garnet-clinozoisite— scapolite—albitessphene rock occurs along a pegmatite- hornblende gneiss contact. ORIGIN Pegmatite and quartz monzonite gneiss are commonly closely associated in the Northgate district and field and petrographic data suggest that they both origi- nated through metasomatism. The large pegmatite bodies are extremely irregular and contain numerous SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY inclusions of metamorphic rocks. With few exceptions the wall rocks and inclusions show no evidence of de- formation, and the foliation in the inclusions and the wall rocks generally has the same orientation. Many of the contacts are gradational. Some of the smaller pegmatite bodies clearly displace their walls, but most of the pegmatite in the larger masses evidently replaced rather than intruded the metamorphic rocks. This conclusion is further suggested by the progressive re- placement of plagioclase by microcline as well as the occurrence of apparently relict plagioclase with rela- tively calcic composition (Aflzo—so) and garnet even where microcline is relatively abundant. ‘ Microcline in all the pegmatite, even in the central part of large pegmatite bodies is corrosive toward plagioclase, and in marginal zones between pegmatite and biotite-garnet gneiss, microcline clearly formed after the biotite-garnet gneiss was formed. These same relations are found in the gradational contacts of bio- tite-garnet gneiss inclusions within pegmatite as well. The composition of most plagioclase in the pegmatite in the Northgate district is more calcic (An20_30) than is common in quartz-feldspar pegmatite, and garnet in the pegmatite has about the same composition as garnet in adjacent biotite-garnet gneiss. Apparently both the plagioclase and garnet are relict. Although a distinct sequence in time between biotite- garnet gneiss and pegmatite is implied by the late intro- duction of microcline, it seems likely that the two rocks were formed about contemporaneously, but that the biotite-garnet gneiss formed ahead of an advancing pegmatite “front.” This hypothesis is consistent with the common close association of pegmatite with the more thoroughly transformed biotite-garnet gneiss and the apparently Continuous local sequence in time be- tween the two rocks. Although commonly closely associated, biotite-garnet gneiss and pegmatite bear no constant relation to each other in space. Biotite-garnet gneiss generally is most completely transformed near large pegmatite bodies, but many thoroughly trans- formed masses of biotite-garnet gneiss have relatively little closely associated pegmatite, and many pegmatite bodies have no associated biotite-garnet gneiss. No unequivocal example of concentric zoning of biotite- garnet gneiss around a large mass of pegmatite was observed, and in many places a pegmatite body grades into highly altered biotite-garnet gneiss on one side and into hornblende gneiss on the other. ‘ Trans- forming solutions at a given locality apparently changed with the advance of the pegmatite “front” from those that caused the formation of biotite-garnet gneiss (rela- tively rich in lime, magnesia, and iron) to those that Caused the formation of pegmatite (rich in potash). Where the later solutions followed the same general METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLOI1‘ADO channels as the earlier solutions, biotite—garnet gneiss and pegmatite are closely associated; where new chan- nels formed or old channels shifted during transforma- tion, the alteration products occur either alone or with minor intermixing. HORNBLENDE-BIOTITE GNEISS GENERAL FEATURES AND DISTRIBUTION Hornblende-biotite gneiss includes a group of well- foliated rocks made up of varying proportions of horn- blende, biotite, quartz, and plagioclase. Small amounts of microcline are widespread, but erratically distributed. The rocks form a complexly interlayered series that range from unaltered hornblende gneiss to fine-grained mylonite gneiss, and petrographic evidence indicates that the present textures and mineral composition are related to the degree of shearing and recrystallization the different rocks were subjected to subsequent to dynamothermal metamorphism. Foliation in the horn- blende-biotite gneiss is parallel to the layering in adjacent hornblende gneiss, and the different rocks appear to be interbedded. The mixed rocks do not persist along the strike; the layers feather out and grade into hornblende gneiss. The hornblende-biotite gneiss is erratically distributed, and it is not separated from hornblende gneiss on the geologic map (pl. 48). These rocks are most abundant on the southern part of Pinkham Mountain and along Pinkham Creek, Where they are associated with mylonite gneiss. Some horn- blende-biotite gneiss occurs south of the belt of mylonite gneiss, but relations are obscured by large masses of quartz monzonite gneiss and by Laramide faulting. Farther north, hornblende-biotite gneiss alternates with larger and larger masses of normal hornblende gneiss. No hornblende-biotite gneiss was seen in the northern and northwestern parts of the district. LITHOLO GY Hornblende-biotite gneiss varies widely in mineral composition and texture from place to place as it is made up of a completely gradational series of rocks. The foliation generally is more distinct than in horn- blende gneiss. Where hornblende is abundant the rock has a grain size about comparable with that in the associated hornblende gneiss. With increasing biotite and quartz, the rock becomes finer grained and more closely foliated. Although some hornblende and plagi- oclase grains are commonly slightly larger than the other mineral grains, the rock loses the distinctive salt-and-pepper aspect of hornblende gneiss and ac- quires a more even, dark-gray color. Although closely foliated, the rock does not split evenly along a single plane; the fracture is hackly, and foliation appears to be a compromise direction between several planes of larger crystals. 353 mineral orientation. As the grain size becomes smaller, the gneiss grades into dense, uniform to banded, gray rock characteristic of mylonite gneiss. Feldspar augen and irregular quartz-feldspar stringers are abundant in miny places, particularly near bodies of quartz monzonite gneiss or pegmatite. The quartz and feldspar stringers and augen are generally parallel to the foliation, although in places they form irregular, cloudy masses. The contacts of these masses are characteristically indistinct, and the stringers and masses apparently result from replacement or trans- formati01 rather than injection. PETROGRAPHY Hornblende-biotite gneisses are somewhat granulated rocks intermediate in texture between hornblende gneiss and mylonite gneiss. Fine-grained quartz and biotite and abundant accessory minerals occur along shear zones and in recrystallized, cataclastic aggregates that surround the larger, relict grains of plagioclase and hornblende (pl. 53 A); the quantity of quartz and biotite is directly related to the degree of granulation of the rock. Biotite tends to be oriented along several sets of shear planes, and the foliation is more distinct than that in typical hornblende gneiss. In places a single set of shear planes is dominant and in such rocks even relatively biotite—poor gneiss has good megascopic foliation. Most of the hornblende—biotite gneiss, how- ever, shows several sets of shear planes in the direction of megascopic foliation that intersect at low angles. Minerals are also considerably granulated between the In these rocks the degree of foliation depends on the quantity of oriented biotite and on the angles of intersection of the shear planes. In some rocks cataclasis took place only between the grains; these rocks have almost no foliation. No generaliza- tion can be made concerning the relationship of degree of foliation with degree of comminution. Hornblende and plagioclase occur as ragged relict grains set in finer, granulated rock. Broken grains of plagioclase are also abundant in the surrounding granu- lated rock, but fine-grained hornblende is uncommon. The grain size of the larger crystals is comparable with that in normal hornblende gneiss. Hornblende relicts generally are not as abundant as plagioclase relicts, and they are commonly altered in part to biotite. Where there was significant granulation, the plagioclase is distinctly more sodic than that in the associated horn— blende gneiss, and generally is either sodic andesine or calcic oligoclase. Most grains are considerably seri- citized and saussuritized, but relatively clear grains also are abundant. Plagioclase generally is about as abun- dant in the resulting rock as it was in the original hornblende gneiss. 354 Although a small quantity of biotite is commonly associated with the relict hornblende grains, most of it occurs with quartz and plagioclase in fine-grained crystalloblastic aggregates along the shear zones and between the larger plagioclase and hornblende crystals. Biotite forms irregular to well-formed platy crystals that range in size from very small grains to grains nearly as coarse as some of the hornblende crystals. Many of the biotite plates are oriented along the shear planes, but many also show random orientation in the granulated rock between the relict crystals. Depending largely on the degree of shearing, biotite ranges in abundance from a trace to about 20 percent of the rock. Quartz forms small, about equidimensional grains associated with the recrystallized biotite and plagioclase and somewhat larger grains in elongated aggregates along shear zones. Quartz makes up as much as 30 percent of some rocks {it is generally most abundant where biotite is most abundant. Small quantities of microcline are widespread, but it is most abundant in the vicinity of quartz monzonite gneiss and pegmatite bodies where aggregates make up the augen and granitic-appearing stringers. Microcline occurs in small wisps and irregular grains in the recrys— tallized cataclastic zones of the gneiss. Microcline replaces relict hornblende and plagioclase grains, as well as biotite and plagioclase in the cataclastic mortar. Several poikiloblastic microcline grains were observed that cut across granulated zones and contained biotite inclusions oriented in the direction of the shear plane; these microcline grains obviously crystallized after shearing. The transition from hornblende-biotite gneiss to the associated quartz monzonite gneiss takes place chiefly by an abrupt increase in the quantity of intro— duced microcline. Although microcline definitely was introduced along some granulated zones, in many places it was broken by later shearing. Apatite, sphene, and magnetite are much more abun- dant in hornblende-biotite gneiss than in unsheared hornblende gneiss. They commonly make up several percent of the biotite- and quartz-rich gneiss, and in some specimens they constitute about 5 percent of the rock. Irregular grains of epidote are scattered through most of the rock. They are erratically distributed, generally in minor amounts, although in places epidote forms as much as 15 percent of the gneiss. ORIGIN The transition from hornblende gneiss through inter- mediate hornblende-biotite gneiss and schist to mylonite gneiss is marked by progressively more intense shearing and granulation. In all these rocks, only hornblende and plagioclase occur in the relatively large relict SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY crystals; the groundmass consists essentially of a fine aggregate of crystalloblastic biotite, quartz, and feld- spar. The transformation involved granulation of the original hornblende gneiss by penetrative movement and shearing. Plagioclase was broken and altered to a somewhat more sodic feldspar, but the quantity of plagioclase in the rock did not change appreciably. Hornblende, on the other hand, was broken down and the constituent materials recrystallized as a mixture of biotite, quartz, and the lime—bearing accessory minerals apatite, sphene, and epidote. These new minerals did not form pseudomorphs after hornblende but occur scattered through the granulated part of the rock. As indicated by the relations of microcline along granulated zones in the rock, the shearing was accom- panied by local feldspathization. The cataclasis, there- fore, appears to have taken place during the same general period of time in which regional metasomatism produced the quartz monzonite gneiss and pegmatite elsewhere in the district. Some of the potash required by biotite could have been derived from external sources, and perhaps some quartz also may have been introduced, but the increase in abundance of biotite and quartz with increase in degree of'granulation and decrease in abundance of hornblende makes a local source more probable. How- ever, most biotite in the granulated zones shows no relation to broken hornblende remnants and quartz is unevenly distributed so the recrystallization of mate— rials derived from sheared hornblende involved some movement in solution. Possibly this accounts for the variable quartz—biotite ratio and the erratic distribution of the lime-bearing accessory minerals. MYLONITE GNEISS GENERAL FEATURES AND DISTRIBUTION The mylonite gneiss is made up of very fine grained crystalloblastic rocks that originated through intense shearing and granulation, followed by moderate re— crystallization, of the different rocks in the gneiss complex. These rocks vary widely in mineral composi- tion, depending on the composition of the original ,I gneiss, on the intensity of shearing, and on the degree of recrystallization. Many of the rocks are streaked with discontinuous layers of contrasting color and composition, and rounded to lozenge-shaped augen are common. Following the nomenclature compiled by Waters and Campbell (1935, p. 478, 481), these rocks are called mylonite gneiss; locally, rocks have been so intensely sheared that all original textures were destroyed and these are classed as ultramylonites. Mylonite gneiss is most abundant along the walls of Kings and Pinkham Creek Canyons; smaller areas of METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO this rock are exposed in the core of Sentinal Mountain and along the front of the Medicine Bow Mountains northeast of Sentinal Mountain (pl. 48). Mylonite gneiss is most abundant where the original rock was dominantly hornblende gneiss; it dies out to the east and south in large masses of quartz monzonite gneiss. The margins of some large quartz monzonite gneiss bodies were reduced to mylonite, but short distances in from the contacts only a minor amount of intergranular cataclasis took place. LITHOLOGY Most mylonite 'gneiss derived from hornblende gneiss is a very fine grained medium- to dark-gray micaceous rock that is closely foliated and in part streaked. The streaks are due to alternating biotite— rich and feldspar-rich layers that are commonly folded and crenulated on a small scale. Hornblende crystals occur in bands along the folia of some of these rocks. The foliation is uneven, and fractures commonly sparkle with reflections from abundant fine biotite. Rounded feldspar augen are relatively common, and in places they are strung out along layers like series of beads. A dense, white to greenish-gray, slightly greasy- appearing rock that may have been either a lime- silicate rock or a normal hornblende gneiss occurs along the walls of Pinkham Creek Canyon. This rock is made up of a very fine aggregate of epidote and clino- zoisite and minor amounts of quartz. Much of it is megascopically structureless, but quartz-rich varieties show faint streaks parallel to the foliation of the adjacent gneiss. Quartz monzonite gneiss was more resistant to shearing than hornblende gneiss, hence only the marginal parts of larger bodies even in the zones of greatest movement were reduced to mylonite. Many of the smaller bodies, however, were ground up to a very fine-grained pinkish-gray rock with a distinct quartzitic appearance. These siliceous-appearing rocks commonly show color banding parallel to the foliation of adjacent rocks. Where granulation was not So complete, remnants of abundant rounded to ovoid pink feldspar grains are set in a thin-layered, vitreous- appearing groundmass. The crinkled layers bend around the augen much as flow bands in lava bend around phenocrysts. Moderately sheared quartz mon- zonite gneiss is distinctly finer grained and better foliated than normal quartz monzonite gneiss, but the cataclastic texture is not generally obvious. Most mylonite gneiss derived from pegmatite has a distinctive appearance. Abundant rounded to lozenge- shaped augen of pink feldspar as much as several inches in diameter are surrounded by a fine groundmass with a streaked, pseudofluidal texture. The contrasting 402890—57—4 355 - colors of the pink to gray “flow bands” that branch and bend around the pegmatite relicts and augen are due largely to the tendency of quartz and feldspar to segregate into separate layers. Minor amounts of biotite and muscovite occur along some of the foiia and accentuate the banding. Where the original rock was completely ground it is difficult to determine if the light-gray to pink ultramylonite was derived from quartz monzonite gneiss or from pegmatite. PETROGRAPHY The common dark-gray mylonite gneiss derived from hornblende gneiss shows an excellent recrystallized cataclastic texture under the micrOscope. Rounded and broken plagioclase augen, generally calcic oligo- clase, are set in a fine, crystalloblastic groundmass of feldspar, quartz, and biotite (pl. 53 B). Hornblende crystals are few or absent in most specimens, but locally they are abundant and are concentrated along relatively hornblende-rich layers. Some hornblende occurs in recrystallized, poikiloblastic grains (pl. 53 0). Curving streaks, or “flow bands” marked by abundant biotite flakes, branch and bend around the rounded feldspar augen. Those rocks that were reduced to a fine-grained cataclastic aggregate with very few larger grains, later recrystallized to fairly even textured, dense rocks composed of biotite, feldspar, and quartz grains that are generally 0.2 millimeter or less in di- ameter. The megascopic banding is commonly in- distinct under the microscope. Much quartz occurs in the recrystallized cataclastic rock, but some ag- gregates and microscopic veinlets string out along the curving bands. Epidote, apatite, and sphene are com- mon accessory minerals. This rock is the end member of the transitional series called hornblende-biotite gneiss that grades from slightly sheared hornblende gneiss to mylonite gneiss. The fine-grained, white to greenish-gray rock of uncertain origin that occurs along Pinkham Creek Canyon is composed largely of clinozoisite and epidote with lesser quantities of quartz. Some epidote and clinozoisite crystals are 1 millimeter long; most grains are less than 0.5 millimeter in diameter. Quartz makes up only 10 to 20 percent of most of the rock, but locally it is much more abundant and tends to occur in bands or streaks. Sphene is a common minor accessory mineral. All gradations exist between slightly sheared quartz monzonite gneiss and ultramylonite. Some rocks that appear in hand specimen to be relatively fine grained quartz monzonite gneiss show marked intergranular cataclastic texture in thin section. Where shearing was not intense, granulation was confined to relatively thin zones along grain margins. With an increase in 356 degree of shearing, the zones of intergranular brec- ciation became wider, and integrated shear zones cut through the rock (pl. 53 D). These shear zones generally intersect at relatively low angles in the direction of megascopic foliation. Where the ultra- mylonite stage was reached, most of the original grains are milled Out to a fine cataclastic aggregate, and one of the several intersecting shear planes generally is dominant. The relict feldspar augen that survived are rounded and fractured, in places giving the ap- pearance of having been rolled. Some of the larger grains show the external form of augen, but under crossed nicols they appear almost as thoroughly brec- ciated as the groundmass (pl. 53 E, F). With extreme granulation almost all the original grains were pulver— ized, and shearing separated the different minerals in the groundmass into quartz—rich and feldspar-rich bands that bend around the ovoid feldspar augen. Most of the recrystallized grains in these rocks are less than 0.3 millimeter in diameter. The composition of plagioclase apparently was not greatly altered during the granulation of quartz monzonite gneiss. Although plagioclase in the ground- mass is too fine grained to determine its composition accurately, it appears to have about the same index of refraction as the associated augen, which are either calcic albite or sodic Oligoclase. Biotite was broken down into chlorite and sericite, which occur as scattered wisps and shreds through the rock. Although the cataclastic origin of the rocks is obvious, the present texture is crystalloblastic. Quartz apparently re— crystallized most easily and is distinctly coarser than the feldspar. All grains have irregular, interlocking contacts. - Pegmatite underwent the same general changes as quartz monzonite gneiss. The augen tend to be much larger than those in comparably sheared quartz mon- zonite gneiss, but the streaked groundmass in both rocks has the same aspect. STRUCTURE Foliation in hornblende-biotite gneiss and mylonite gneiss is parallel to that in the associated unsheared rocks, and lineation shown by minor fold axes and mineral elongation conforms closely to that in horn- blende gneiss (fig. 69). Apparently the same general stress field persisted through regional metamorphism and dynamic metamorphism, but the type of deforma- tion changed from isoclinal folding to more localized shearing and granulation. Only the northern margin of the belt of sheared rocks is well exposed in the Northgate district; the rest of the belt is overlain by younger sedimentary rocks, and Laramide reverse faults make the relationship more SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Lineation shown by 23 random measure- ments_of oriented elongate minerals and minor fold axes FIGURE 69,—Lineation in hornblende-biotite gneiss and mylonite gneiss. Contours on 5, 10, 20, and 30 percent concentrations per 1 percent of the area. Plotted on the lower hemisphere of a Schmidt equiarea net. confusing. The northern margin of mylonite gneiss is irregular but fairly sharp, and generally is about parallel to the regional trend of foliation. A small copper prospect adit along Pinkham Creek near the eastern edge of the district crosses part of the zone of mylonite gneiss in a mass of relatively unsheared rock. Surface exposures indicate that the rock is unaltered, but careful inspection of the walls of the adit disclosed that many narrow bands of granulated rock out the otherwise unsheared hornblende gneiss. Presumably the irregularities on the northern margin of the mylonite gneiss were due to local concentration of the movement into narrow zones. The hornblende-biotite gneiss to the north of the zone of most intense shearing resulted from relatively minor, irregularly distributed movement. Mylonite gneiss merges to the east into large masses of quartz monzonite gneiss. The margins of these large bodies generally show intense granulation, but this feature is lost a short distance from the edge of the bodies where the rocks appear similar to the quartz monzonite gneiss in the rest of the district. Evidently the large bodies of quartz monzonite gneiss were massive enough to resist penetrative shearing that reduced the smaller bodies and weaker rocks to mylonite. The apparent offset of the northern margin of the belt of mylonite gneiss across the Independence METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO Mountain fault zone near Kings Canyon (pl. 48) I probably is misleading, as this offset is the reverse of that to be expected along a northward-dipping reverse fault. More probably the broad zone of mylonite gneiss contains relatively large masses of ungranulated rock, or is made up of several distinct bands of mylon— ites, and the actual northern margin may not be exposed south of the Independence Mountain fault. ORIGIN Mylonite gneiss resulted from the intense granulation of all rocks in the gneiss complex during the same period of shearing that produced hornblende-biotite gneiss. As pegmatite and quartz' monzonite gneiss bodies (formed at an earlier stage in the shearing) were reduced to mylonite, the belts of intense granulation apparently formed late in the period of shearing. The relative movement between the rocks in the northern and south- ern parts of the district apparently has become more and more localized along certain zones as the shearing progressed. RHEOMORPHIC QUARTZ MONZONITE GNEISS GENERAL FEATURES AND DISTRIBUTION Some quartz monzonite gneiss in the northwestern and southeastern parts of the Northgate district shows evidence that it became mobile, or rheomorphic, after it was transformed, and intruded the surrounding rocks as diapirlike injections. The banded structure of normal quartz monzonite gneiss was largely de- stroyed, and a more uniform, aplitic texture was formed. Where movement was not great, highly contorted original banding still can be recognized, and this banding is commonly cut by a new, less distinct folia- tion. The foliation of unreplaced hornblende gneiss inclusions shows great departures from the regional east and northeast trend of foliation and layering, and reflects major features of deformation resulting from movement of mobile quartz monzonite gneiss. The name quartz monzonite gneiss as applied to the rheomorphic rock in the Northgate district is not strictly accurate in all places. Much of the rock is alaskitic in composition and has an aplitic rather than gneissic texture. Microcline is commonly more abun- dant than plagioclase, and many rocks are granitic ,rather than quartz monzonitic in composition. Foli- ated and quartz monzonitic rocks are relatively com- mon, however, and the diflerent compositional and textural types are complexly intermixed throughout the areas of rheomorphism. As these variations were not mapped separately during field work (pl. 48), the unsatisfactory genetic name rheomorphic quartz mon- zonite gneiss has been used for convenience and to avoid confusion with a younger quartz monzonite 357 believed to be of intrusive origin (see “Intrusive quartz monzonite”). Evidence for rheomorphism is clearest in the north— west corner of the district, where a funnel-shaped mass of quartz monzonite gneiss about 1% miles long by % mile wide intruded and deformed the rocks in the adjacent gneiss complex (pl. 49). Relict features and the unhomogeneous character of adjacent layers of rheomorphic quartz monzonite gneiss indicate that the movement was not as a true melt. Similarly deformed quartz monzonite gneiss occurs along the southeast edge of the mapped area and may be marginal to a larger mass of formerly mobile rocks. Relationships in that area are so poorly understood that the following discussion will deal largely with the area in the north- west part of the district. STRUCTURAL SETTING The funnel-shaped mass of once mobile quartz monzonite gneiss near the northwest corner of the dis- trict consists of discontinuous layers of quartz mon— zonite gneiss and minor amounts of hornblende gneiss which close completely around it and give it a distinct annular appearance. Layers dip 60° to 70° N. on the south flank, 80° to 85° W. on the east nose, 80° N. through vertical to 85° S. on the north flank, and the ‘ northwest nose plunges 50° to 60° SE. (pl. 49). Where annular layers are parallel or nearly parallel to the foliation or banding in the surrounding gneiss complex, margins of the funnel—shaped mass are completely gradational. They grade into normal rocks of the gneiss complex to the south and into highly deformed rocks to the west and southwest; the northern margin is outside the area mapped and was not observed. The highly deformed layering in the rocks to the west and southwest splits and bends around the north- western nose of the ”funnel,” and rocks in the vicinity of the nose are massive, nearly structureless quartz monzonite. The eastern nose of the funnel-shaped structure is sharply transgressive against adjacent hornblende gneiss and pegmatite, and the annular layers cut almost at right angles across the more normal trend of the country rocks. Massive rock marks the transition between the funnel-shaped mass of quartz monzonite gneiss and the surrounding rocks in the areas where the annular layers swing from nearly normal to parallel to the adjacent banding and foliation. New structures are most prominent along the flanks of the funnel-shaped mass where most movement apparently was concentrated; some relict structures can be recog- nized in the core and toward the outside edges of the “funnel.” The area of highly deformed rocks to the west and southwest of the funnel-shaped mass contains horn- 358 blende gneiss and quartz monzonite gneiss that range from nearly normal rocks of the gneiss complex to massive, recrystallized rocks having no relict textures. In the absence of distinctive horizon markers, it is difficult to determine the details of structure in this area, but the relationship of the deformed hornblende gneiss inclusions indicates the general course of de- formation. The axial plane of a northward—plunging fold adjacent to the funnel-shaped mass trends almost at right angles to the axial planes of folds in regionally metamorphosed rocks away from the area of rheomor- phism. Original small-scale layering in the quartz monzonite gneiss was highly crumpled during this KN k1 Lineation shown by spindle-shaped bodies and minor fold axes; 3 measurements plotted on the lower hemisphere of a Schmidt equiarea net FIGURE 70i—Lineation in rheomorphic quartz monzonite gneiss. deformation, indicating that rheomorphic deformation followed metasomatic transformation. Some thin layers in the original quartz monzonite gneiss were milled out into spindle-shaped masses 1—2 inches in diameter and 1—2 feet long. Lineation shown by these spindles and by the contorted layers conforms to the same pattern of lineation in regionally metamorphosed hornblende gneiss and in the later, dynamically meta— morphosed mylonite gneiss (see fig. 70). Apparently the same stress field persisted through regional meta- morphism, metasomatic and dynamic metamorphism, and mobilization. Deformation of the rock west of the funnel-shaped structure apparently was accompanied by rock flowage, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY particularly of the quartz monzonite gneiss. The larger folds show thickening on limbs and crests, and new structures are best displayed in areas of greatest appar— ent thickening. The southern margin of the large mass of quartz monzonite gneiss that encloses the rock believed to have been mobile follows the normal regional trend of the gneiss complex. Noting the part of the large, northward-trending cross fold within the outer- most discontinuous are of hornblende gneiss inclusions (pl. 49), it can be seen that the fold starts on the west from an interlayered series of quartz monzonite gneiss and hornblende gneiss about 1,500 feet thick. The hornblende gneiss inclusions in the fold show a pro— gressively wider spacing outward from the core, and the interlayered series of rocks where the fold loses its identity to the east is nearly twice as thick as at the western end. Much of the apparently thickened quartz monzonite gneiss in the core and eastern limb of the fold is massive, and only minor relict texture survived deformation. If the outer, discontinuous band of horn- blende gneiss inclusions were straightened out, it would extend nearly to the east end of the mass showing annular flow structure. Thus the intrusion of the funnel—shaped diapir of mobile quartz monzonite gneiss apparently forced the displaced rocks to flowrelatively westward, and the movement is recorded by the folding. Quartz monzonite gneiss shows the greatest thickening, but local bulging of hornblende gneiss inclusions indi— cates that this rock also underwent flowage. N 0 sur— faces of discontinuity other than the layering were dis- covered in this area, and apparently the deformation was wholly by flow and without faulting. The area between the northward-trending fold and the North Platte River underwent deformation as intense as that in the area to the east. The hornblende gneiss inclusions are highly contorted and irregular, and the larger bodies of quartz monzonite gneiss are massive, as though they too were thickened. The relationship is believed to record the movement of relatively mobile quartz monzonite gneiss, but geologic data on adjacent areas are insufficient to permit an evaluation of the structures. - The markedly different behavior of the rocks east and west of the funnel-shaped mass is probably due to differences in the mobility of the surrounding rocks. The large mass of quartz monzonite gneiss feathers out into hornblende gneiss a short distance east of the “funnel”; the rocks here probably were somewhat cooler and more brittle, and the flow structure cuts sharply across them. Quartz monzonite gneiss is abundant west of the funnel—shaped mass, and recon- naisance west of the NOrth Platte River disclosed that it is the dominant rock there also. Apparently toward the interior of this large mass of quartz monzonite METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO gneiss the rock was so soft that itdeformed readily during local movement of more mobile rock. The crumpling, steeply inclined fold axes, and evi— dence for lateral displacement within rocks to the west and southwest of the funnel-shaped intrusion closely correspond to the general description given by Weg— mann (1930, p. 70) for examples of diapir injection in southern Finland. LITHOLO GY Rocks in the area where the quartz monzonite gneiss is believed to have been widely mobilized show all gradations in the destruction of the preexisting layered structure of quartz monzonite gneiss and the formation of a variable, but generally aplitic texture. Although still medium grained, most of the rocks are somewhat coarser than the nonrheomorphic quartz monzonite gneiss and many of the grains are 3 millimeters or more in diameter. Typically, the rock consists of quartz and feldspar and a little biotite which form an even—grained pink aggregate. The biotite is oriented nearly parallel to the larger scale layering, but in most rocks it is sparse and widely scattered and the foliation is weak. Locally biotite is more abundant and forms thin, dis- continuous bands, rendering the rock distinctly gneissose. Although most rocks show little banding or foliation in a hand specimen, they are distinctly layered on a larger scale. The layers recognized in outcrops range from a few feet to a few tens of feet in thickness. lVIany adjacent layers differ only slightly or not at all in tex— ture and composition; elsewhere the rocks of the several layers differ markedly. Hornblende gneiss is abundant in the area of deformed rocks west and southwest of the funnel—shaped mass and, although subordinate, is widespread within the funnel—shaped mass showing annular layers. Inclusions of hornblende gneiss are oriented parallel to the layering in rheomorphic quartz monzonite gneiss, and the contacts of the inclusions are sharp. ' Quartz monzonite gneiss with highly contorted but still recognizable original layerng is the most abundant country rock throughout the area of apparently folded rocks west and southwest of the funnel-shaped mass. In most places a new foliation cuts the deformed layers, and all stages in the disruption of the original texture can be seen. The original layering is still readily recognizable where it is parallel to the new foliation, but it is hazy and indistinct Where it is cut by the new foliation. Relict textures are best displayed in the smaller bodies or near the margins of the larger masses of quartz monzonite gneiss ; they were largely destroyed in areas where significant thickening took place. Irregular pegmatitic masses occur throughout the rheomorphic quartz monzonite gneiss. These masses 359 have gradational margins and apparently formed by local recrystallization that obliterated all previous structures, including the crumpled original layering and the later, indistinct foliation and layering related to rheomorphic movements. Though generally sparse, biotite is the most, common ferromagnesian mineral in the rheomorphic quartz monzonite gneiss. Hornblende, or hornblende and bio- tite, occurs in some layers, and the rock, although still leucocratic, commonly has a slightly different aspect than biotite-bearing quartz monzonite gneiss. In outcrop, hornblende-bearing rocks appear somewhat more closely knit and blocky, the color generally is lighter, and where hornblende makes up more than a few percent of the rock it gives the rock a distinctive foliation. Most of these difierences are so minor that they are difficult to describe, but the rocks can be recognized readily in the field. Hornblende gneiss inclusions appear much the same as normal hornblende gneiss in the rest of the gneiss complex, although locally the plagioelase and hornblende occur in light— and dark—colored clusters. PETROGRAPHY The rheomorphic quartz monzonite gneiss commonly is an aggregate of plagioelase, microcline, and quartz ranging in texture from typically crystalloblastic with mutually interfering grain boundaries to mixtures of crystalloblastic and replacement textures. Accessory minerals are biotite, hornblende, magnetite, and garnet. Except for the minor biotite, minerals in these rocks show little or no dimensional orientation but occur in aggregates of equidimensional, xenoblastic grains. Although most rocks appear equigranular in hand speci- men, they show a wide range of grain size in thin section. Plagioclase in the rheomorphic quartz monzonite gneiss for the most part is clear or only slightly saus- suritized. In the more common, biotite-bearing and alaskitic facies, most plagioelase is between Ans and An15 in composition; in hornblende—bearing quartz monzonite gneiss, most of it is somewhat more calcic. Plagioclase forms nearly equidimensional grains as much as 2.5 millimeters in diameter in rocks with dis— tinct crystalloblastic texture, but most of it is corroded by microcline and quartz and shows all stages of re— placement. )Iany plagioelase grains show the effects of minor deformation that was not shared by the ad— jacent microcline and quartz (pl. 54 A, B). Twin lamellae are distorted, grains show wavy extinction, and some crystals were broken into mosaics of smaller grains with slightly differing orientations. Only a small percentage of the plagioelase grains are distorted or broken, but the minor cataclasis took place throughout 360 the area where rocks were mobile. The grains evi- dently were bent and broken while the rocks were being deformed, and these plagioclase grains, evidently, sur- vived movement Without significant recrystallization. Myrmekite is widespread in the rheomorphic quartz monzonite gneiss and occurs most commonly along the margins of plagioclase adjacent to microcline (pl. 54 0). The myrmekite formed subsequent to the brecciation and deformation shown by some of the plagioclase grains. Microcline crystals range from mere intergranular wisps to relatively large, poikiloblastic grains 3 milli- meters or morelin diameter that enclose relict inclusions of plagioclase. Locally some grains have mutually interfering, crystalloblastic relationships with the adja- cent minerals, but in many places, microcline is inter— stitial to plagioclase and tongues project into broken plagioclase grains along fractures or strained zones clearly showing replacement relations toward plagioclase (pl. 54 A—C). Twinning is Slightly distorted in a few grains of microcline, but adjacent grains show no related cataclastic texture. Although microcline varies greatly in grain size, most crystals are medium grained and are either of about the same size as the associated plagio— clase crystals or a little coarser. Quartz evidently recrystallized during a relatively long period. It occurs with plagioclase and microcline in the crystalloblastic aggregates, and as lobate to irregular grains that cut microcline as well as plagioclase and biotite. When observed under low magnification and with crossed nicols, quartz in many rocks appears as an overprint of lobate to irregular grains impressed on the microcline and plagioclase aggregate. Grain size of the quartz is highly uneven; the grains in the crystalloblastic aggregates are nearly as large as the associated feldspar grains and are coarser and more irregular than the lobate to rounded grains that cut microcline. Quartz also did not share the deformation shown by some plagioclase and in many places pref- erentially replaced the strained parts of plagioclase crystals (pl. 54 B). The irregular masses of pegmatitic rock that cut the crumpled layers of rheomorphic quartz monzonite gneiss formed through the more complete recrystalliza— tion of microcline and quartz following rheomorphic deformation. The relationship is somewhat similar to those observed in most thin sections where microcline and quartz are corrosive toward plagioclase and biotite. Biotite rarely makes up more than a few percent of the rheomorphic quartz monzonite gneiss, and much of the rock carries only a trace as small, corroded shreds and grains with abundant associated magnetite. Mag- netite is generally most abundant where biotite is most highly corroded. A few layers of the rock, however, SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY contain as much as 10 percent of biotite, and it either forms a crystalloblastic aggregate with plagioclase, microcline, and quartz or has mutually interfering con- tacts with plagioclase and is embayed irregularly by microcline and quartz. Where biotite is most abun- dant, the flakes are as much as 1% millimeters long, but most of the corroded shreds are less than 1. Magnetite is more abundant in rheomorphic quartz monzonite gneiss than in normal quartz monzonite gneiss, and in places constitutes as much as 2 percent of the rock. It occurs as small, equant crystals 1 millimeter or more in diameter scattered through the rock and as dusty grains associated with the resorbed biotite. Many of the larger grains tend to be idio- morphic. The relative increase in magnetite and a decrease in biotite content and the close association of magnetite with corroded biotite crystals indicate that much of the disseminated magnetite was produced by recrystallization of material left from the destruction of biotite. Small, rounded to idiomorphic, red garnet crystals as much as 2 millimeters in diameter occur through the rheomorphic quartz monzonite gneiss. They show no evidence of their origin, but it is likely that they are recrystallized relicts that survived mobilization and deformation. Hornblende occurs in some of the discontinuous layers of quartz monzonite gneiss in the funnel—shaped mass and in the deformed rocks to the west and southwest. It ranges from mere traces to 10 percent of some rocks and generally is most abundant where microcline makes up 25 percent or less of the rock. Irregular grains of hornblende generally have mutually interfering con- tacts with plagioclase grains, and, in those rocks that have minor replacement relationships, with microcline and quartz grains as well. Where microcline is abun- dant, the hornblende occurs in small ragged grains irregularly embayed by microcline. Sillimanite, and associated muscovite, was found in two specimens from the rheomorphic quartz mon- zonite gneiss; it makes up nearly 15 percent of a re- sistant, spindle-shaped body about 2 inches thick ' and 1% feet long from the area of deformed rocks, and a little was seen in a specimen from the north flank of the funnel-shaped mass. In this specimen, the sillimanite and muscovite occur along several closely spaced fractures that cut the crystalloblastic texture of the rheomorphic rock. The minor shear zones were largely healed by later recrystallization, and the muscovite and sillimanite are both younger than the shearing. Sillimanite forms single needles and sheaves, and also bundles enclosed in muscovite, microcline, or quartz. Much of the muscovite has a peculiar, myrmekitic texture with irregular, wormy METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO quartz inclusions, and in part is closely associated with biotite and apparently formed from it. Petrographic relationship suggests that biotite along the shear zone altered to muscovite and minor magnetite, and that muscovite in turn altered into sillimanite and perhaps microcline. The materials migrated considerably during recrystallization, and details of the alteration are obscure. Sillimanite and muscovite, however, are confined to the shear zones; muscovite is associated with either biotite or sillimanite. This distribution indicates a progressive alteration. A similar sequence is indicated by relationships to the spindle-shaped body, but greater migration of recrystallizing materials makes interpretation difficult. The biotite-bearing and alaskitic varieties of rheo— morphic quartz monzonite gneiss carry significantly more microcline than the average quartz monzonite gneiss elsewhere in the district. Seventeen specimens from the funnel-shaped mass and the deformed rocks to the west ranged from 30 to 50 percent, and averaged 41 percent microcline. The average microcline content of 22 specimens of typical quartz monzonite gneiss from all parts of the district was only 32 percent, ranging from 10 to 50 percent and with the great majority between 20 to 40 percent. The plagioclase content (An5_15) averages only 25 percent in the 17 specimens of rheomorphic gneiss; of these only 7 can be classed as quartz monzonitic or granodioritic, where- as the remaining 10 are truly granitic in composition. Only traces of biotite are present in 9 of the 17 specimens of rheomorphic rock; 5 specimens have 1 to 5 percent, and 3 have 5 to 10 percent biotite. Mag- netite is an abundant accessory mineral in all the speci- mens and makes up 1 to 2 percent of 10 or more of them. The quartz content ranges from 25 to 50 percent and averages 35 percent in the 17 specimens. Hornblende-bearing rheomorphic quartz monzonite gneiss varies much more in composition than the more common varieties of rheomorphic quartz monzonite gneiss. The quartz content is uniform and ranges from 30 to 35 percent in all specimens studied. Micro- cline ranges from mere traces to 50 percent of the rock and, generally is irregularly distributed. Of eight specimens studied it averages almost 30 percent. Mutual crystalloblastic relationship is more common in these rocks than in the biotite-bearing rocks, but even here most microcline tends to embay the plagio- clase and hornblende (pl. 54 D). Plagioclase ranges from 20 to 60 percent of the eight specimens studied and averages about 35 percent. The composition ranges from Anw to Ange and averages An2o. Plagio- case is generally most calcic where it is most abundant, but in one specimen with only traces of microcline, 361 sodic oligoclase (Ann) makes up nearly 60 percent of the rock, while in another, calcic oligoclase (Ann) makes up only 20 percent and is subordinate to microcline. Deformed plagioclase grains occur in four of the eight specimens studied. The hornblende content also varies greatly; two of the eight specimens studied con- tain only traces, four contain 1 to 5 percent, and the other two 5 to 10 percent. Where it is most abundant the hornblende occurs in a crystalloblastic aggregate with plagioclase, and locally with microcline and quartz. Generally it is somewhat corroded, and where it is only a minor constituent, it forms small ragged wisps and grains. Magnetite constitutes as much as 2 percent of these rocks and is even more abundant here than in the biotite-bearing varieties. Traces of biotite occur in all these rocks. The inclusions of hornblende gneiss in rheomorphic quartz monzonite gneiss resemble normal hornblende gneiss in hand specimen, but in thin section they dis— , play a completely recrystallized texture (pl. 54 E). The hornblende and plagioclase grains are more equant and much less irregular than in regionally metamor- phosed hornblende gneiss. In all specimens studied the plagioclase is highly saussuritized and sericitized and ranges in composition from Anao to A1135. A little quartz is widespread, generally in small, rounded blebs. Some specimens show a tendency toward mineral segre- gation and have irregular clusters of somewhat coarser hornblende and plagioclase set in the more typical hornblende-plagioclase aggregate. ORIGIN The quartz monzonite gneiss in the larger bodies near the northwest and southeast corners of the N orth- gate district show many features that seem best ex- plained by local mobilization of the gneiss following metasomatic transformation. The foliation and layer- ing characteristic of the quartz monzonite gneiss else— where in the district are highly deformed, and are progressively destroyed with an increase in the degree of deformation. Near the northwest corner of the district, a funnel-shaped mass consisting largely of concentric layers of quartz monzonite gneiss appears to have intruded the adjacent rocks. The mass is sharply transgressive at its east end, and grades into highly deformed rocks along its western and south- western margins. The contorted structures in the marginal rocks are most easily explained by plastic deformation of relatively mobile rocks shouldered aside by the invading funnel—shaped mass. The widespread occurrence of relict textures and structures throughout the area of rheomorphism, the marked contrast in composition between many adjacent layers, and the petrographic evidence for intergranular 362 shear suggest plastic rather than fluid movements. The rheomorphic intrusion and deformation apparently resulted from penetrative intergranular movements combined with shear between layers. Crumpled layering and the gradual destruction of normal quartz monzonite gneiss textures and the formation of new textures with an increase in degree of deformation indicate that the mobilization followed the metasomatic transformation. As the lineation shown by spindle-shaped bodies and axes of small crenulations in contorted gneiss is parallel to that in the regionally and dynamically metamorphosed rocks, the mobilization presumably took place under the same stress field. Corrosive relationship of microcline and quartz grains and the irregular pegmatitic masses that obliterate earlier structures indicates that silica— and alkali-bearing solutions similar to those active in meta- somatic transformation persisted through rheomorph- ism. Thus it seems probable that the change from regional metamorphism to dynamic and metasomatic metamorphism and to rheomorphism reflected a pro- gressive change in conditions during a single orogenic episode. CONDITION or nocxs The funnel—shaped mass of quartz monzonite gneiss is the only structure within the area of rheomorphic rocks near the northwest corner of the district that cannot be explained by plastic deformation of rocks that previously occupied nearly the same position they now fill. Although from geometric considerations alone the funnel-shaped structure conceivably could have resulted from rotation of a relatively resistant mass of rocks, several lines of evidence indicate that the “funnel” originated through plastic intrusion of a relatively soft mass of rocks. If the deformed rocks west and southwest of the funnel-shaped mass were straightened out and cor- rected for thickening, they would occupy much of the area now filled by the rocks in the funnel-shaped mass. Thus the funnel—shaped mass appears to be a foreign body that intruded the surrounding rocks, deforming and displacing them relatively westward. The rocks in the funnel-shaped mass are indistin— guishable from many of the more deformed and thick- ened rocks in the adjacent areas. These grade into normal rocks of the gneiss complex with a decrease in the intensity of deformation and recrystallization. The destruction of old textures and formation of new thus provides a crude measure of the extent of defor— mation. As relict textures are almost completely absent on the flanks of the “funnel,” it appears that the rocks here were more mobile than the most plastic rocks in the adjacent, highly deformed masses where relict textures are still widespread. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Had the funnel-shaped structure originated by rotation of a relatively resistant mass of rocks, the annular layers would have originated through differ- ential rotation of the different layers. It is significant that these layers are neither most prominent nor most closely spaced near the periphery, as might be expected if the rocks composing the “funnel” were resistant; instead the layers, though well formed throughout the structure, are somewhat more prominent near the middle of the limbs, indicating that the differential movement was evenly distributed. The amount of differential movement between the layers appears to have been great. For example, inclusions of hornblende gneiss near the northwest and southeast ends of the mass were so dragged that their foliation strikes at right angles to the regional trend. The amount of rotation indicated by the map pattern, however, is so small that the distributive movement between any two layers would be almost unmeasurable and certainly inadequate to account for so great a drag. METHOD OF MOVEMENT The method by which the rheomorphic rock moved was such as to yield relatively homogeneous layers with similar or contrasting composition, separated by sharp discontinuities. The hornblende gneiss inclusions and the quartz monzonite gneiss that still shows such relict features as crumpled original layering, apparently retained structural continuity during deformation and acted as plastic solids. To what extent the rocks with entirely new textures behaved as plastic solids and to what extent as viscous fluids are questions considerably more difficult to answer. Many of the alaskitic rocks are structureless or only slightly gneissose in hand specimen, but they occur in discontinuous layers that close around the funnel—shaped mass. Within each layer the rocks are relatively uniform and may be either very similar to or markedly different from rocks in adjacent layers. Layering is fully as distinct where rocks in adjacent layers are almost indistinguishable from each other as where they contrast sharply; evidently the layering is an essential structure of the rocks. Leucocratic hornblende—bearing quartz monzonite gneiss is a minor but widespread rock in the funnel- shaped mass and in the more deformed parts of the adjacent 'rocks. This rock shows the recrystallized texture of rheomorphic rocks, but is extremely variable in composition. The plagioclase is generally more calcic, and the microcline is less abundant and more irregularly distributed than in the more common varieties of rheomorphic quartz monzonite gneiss. Hence the hornblende-bearing rheomorphic rock is more closely related mineralogically to hornblende METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO gneiss than to quartz monzonite gneiss and probably originated from hornblende gneiss by penetrative shearing while the rocks were mobile. Rocks that show contorted original layers have the same microtextures as the layered rocks without relict textures, and are cut by similar irregular peg- matitic masses. Deformed plagioclase grains are found in all facies of the rocks. Apparently complete fluidity was not attained by any large segment of rocks. The significantly larger percentage of microcline in rheo— morphic quartz monzonite gneiss and the postdeforma— tion crystallization of microcline and quartz, however, indicate that the mobile rocks were at least lubricated by alkalic solutions, and the material surrounding the plagioclase grains may have closely approached a melt. Penetrative intergranular movement in the presence of alkalic solutions, followed by recrystallization, con- verted the originally banded quartz monzonite gneiss into a more uniform, alaskitic rock with more abundant microcline and minor amounts of biotite. Where hornblende gneiss was subjected to penetrative move— ment, much of‘ the hornblende was destroyed, the plagio— clase was converted to a more sodic feldspar, and the rock was irregularly permeated by alkalic and silicic solutions. The hornblende gneiss that was not sheared out but was dragged along passively, recrystallized somewhat but did not change composition greatly. The sharp discontinuities between relatively even textured layers, which range from very similar composi- tions to markedly different compositions, indicate that much of the movement in the mobile rock took place by shear between the layers. Apparently movement was that of a very plastic solid or an extremely viscous fluid in which the layers retained their compositional identities. DIRECTION OF MOVEMENT In determining the direction of flow, much hinges on the question of how the orientation of structures at the present time compares with the orientation at the time of origin. This is difficult to answer as it is impossible even to determine the extent or direction of Laramide deformation within the pre—Cambrian rocks, without considering the long periods for which we have no record. There is no petrographic evidence, however, for a period of metamorphism later than that during which the rocks in the gneiss complex were formed, and the regional trend of foliation and lineation in the gneiss complex are uniform. Most local deviations in the attitude of foliation occur in the vicinity of crests and troughs of folds. Evidence for local de- formation was seen only along large Laramide faults, and involved cataclasis rather than flexure. 363 That large—scale tilting, folding, or inversion took place seems unlikely from a consideration of the zonal distribution of the different rock types. Large masses of quartz monzonite gneiss occur in the northern and southern parts of the district, and each of these masses shows evidence that some of the rock became mobile subsequent to transformation. These two masses reached about the same stage in formation at the time of origin, and presumably might have been at compara- ble depths. Pegmatite and biotite-garnet gneiss bodies are abundant through the central part of the district in a zone peripheral to the large bodies of quartz mon- zonite gneiss, and this zone may have been down— warped. This suggestion, however, is not borne out by any systematic variation in attitude of foliation through the district. Although pegmatite and biotite- ’ garnet gneiss are not uniformly distributed, they both occur throughout the zone, so presumably there has been no strong east-west tilting. Although not con- clusive, these considerations suggest that the present vertical coordinate through the rheomorphic rock was not far from vertical at the time of metamorphism and mobilization. The annular layers of the funnel—shaped mass could arise most easily by differential movement either around or in the direction of the axis of the funnel. Evidence that the rocks in the annular structure were more plastic than the surrounding rocks at the time of deformation (see “Condition of rocks”) makes it difficult to understand how rotational movement could account for the features shown. If the funnel- shaped structure had been a mass of mobile rock that intruded and shoved aside the adjacent rocks by movement in the direction of the axis, the differential movement due to frictional drag on the walls would have been distributed through much more of the mass than if the structure had been a rotating resistant body. In a mobile mass the greatest differential move- ment would have taken place along the flanks where the most prominent layering and best formed new textures now occur, and movement of the mobile rock would be limited only by the physical condition of the intruded rocks. It seems necessary to postulate amount of movement in terms of at least several thousands of feet to account for the discordant relationship of the annular structure and the orientation of hornblende gneiss inclusions parallel to the rheomorphic layering and locally athwart the regional trends. The funnel shape and the general appearance of the mass, indicative of a foreign body that shoved aside the preexistent rocks, implies a rootless body of mobile rock which has the greater part of the body above the levels now exposed. CAUSE OF MOVEM'ET It seems plausible that the mo ement was governed largely by gravity. Quartz monzonite gneiss is much less dense than hornblende gneiss, and if large enough masses of the lighter rock beca e mobile under the influence of high temperature and abundant solutions in the pores, the buoyant for e would exceed the strength of the surrounding rock: and the mobile rock would rise. Movement in the direction of the axis of the annular structure would be ubparallel t0 the tec- tonic axis as shown by the linjation of fold axes in regionally and dynamically metamorphosed rock and thus about at right angles to the direction commonly inferred for regional tectonic trahsport. The regional stress field that persisted through the complex sequence of metamorphism in the district could hardly account for movement of this type. i 364 TABLE 1.—Approximate specific gravities of pre—C’ambrian rocks from the N orthgate distritt, Colorado Rock Specific Specimens ‘ gravity measured Hornblende gneiss---_------__-__--_ 2. 95-3. 00 3 Quartz monzonite gneiss ____________ l 2. 61—2. 63 3 Biotite-garnet gneiss ________________ 2. 80—2. 85 2 Pegmatite __________________________ 2. 58—2. 59 2 Hornblende—biotite gneiss ___________ i- 2. 80—2. 82 2 Mylonite gneiss _____________________ 2. 68—2. 78 2 Rheomorphic quartz monzonite gneiss- 2. 64 2 Intrusive quartz menzonite _________ ‘ 2. 61-2. 63 3 The specific gravity of typical pecimens of most pre- Cambrian rock types in the diEtrict was determined (table 1),.and the average of the rocks in several parts of the district was approximated. The specific gravity of biotite-bearing rheomorphici quartz monzonite is about 2.64, the average for the rocks cropping out in a strip of gneiss complex a mile .wide along the south margin of the large mass of q artz monzonite gneiss that includes the once mobile rocks is about 2.76, and the average for rocks in a large lock of gneiss complex south of this strip is about 2.80. The average specific gravity of rocks in that part of the gneiss complex lying between the large mass of qu rtz monzonite gneiss in the northwest part of the di trict and the stock of intrusive quartz monzonite (pl. 48) is near 2.78. These comparative figures re resent only the order of magnitude of the difference during mobilization. Variations due to elevated temperature and pressure are not considered, and more 'mportantly the effect of solutions in the pores is notil shown. likely, intergranular alkalic solutions were abundant If, as seems SH RTER CONTRIBUTIONS T0 GENERAL GEOLOGY in the mobile rock, they would have lowered the specific gravity of that rock significantly. A comparison of the specific gravity of adjacent blocks of rocks now exposed considers only part of the environment at the time of rheomorphism; the buoyant force of the mobile rocks depended as well on the specific gravity of the overlying rocks. Metasomatism was zonal, and transformation probably decreased upward. The hydrostatic pressure of the cooler and presumably more dense overlying rocks would provide a powerful mechanism to force the lighter, mobile rocks upward. DACITE PORPHYRY GENERAL FEATURES AND DISTRIBUTION A very fine grained, medium- to dark-gray por— phyritic rock occurs in several northward-trending dikes near the lower end of Camp Creek (pl. 48). The rock is extremely hard and resistant to weathering and crops out in many places. The dikes are nearly vertical and as much as 5 feet thick and 3,200 feet long. Most dikes end in hornblende gneiss. No offset of the walls was detected across any of the dikes, and no fractures or groups of fractures were discerned along the strike. Apparently they were injected into tension fissures. The dikes trend nearly at right angles to the strike of foliation of the gneiss complex and in the same general direction as the plunge of fold axes in the metamorphic rocks. Evidently the tension fissures along which the dikes were injected were not related to the original deformation plan of the gneiss complex. Similar small dikes are found in xenoliths in the intrusive quartz monzonite stock south of the lower part of Camp Creek; these are definitely older than the enclosing granitic rock. The dikes are thus intermediate in age between the rocks in the earlier pre-Cambrian gneiss complex and the later intrusive quartz monzonite and may be unrelated to either. PETROGRAPHY The dacite porphyry typically is composed of 40 to 50 percent sodic andesine, 15 to 20 percent green biotite, 20 to 25 percent quartz, 10 to 15 percent orthoclase, and 5 percent epidote. Apatite and mag- netite are relatively abundant minor accessory min- erals. Andesine occurs as idiomorphic phenocrysts as much as 1.5 millimeters long and as small, lathlike crystals in the fine groundmass. Biotite occurs in irregular plates and generally is evenly distributed throughout the rock. A few ragged poikilitic horn- blende phenocrysts as much as 1 millimeter in diameter are found in some dikes. Quartz and orthoclase form a fine mosaic interstitial to the other major con- stituents. Epidote is secondary. The crystals in the METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO groundmass generally are 0.3 millimeter or less in diameter. INTRUSIVE QUARTZ MONZONITE GENERAL FEATURES AND DISTRIBUTION Quartz monzonite forms a stock and associated dikes in the central part of the Northgate district and several related dikes near the northeastern part of the mapped area. Although the relief is not great, the area of the stock is extremely rough. Weathering and erosion of the relatively coarse grained and jointed rock have reduced the surface to a rugged area of rounded pinnacles and boulders, cliffs, and benchlike flat areas. Very little soil or talus is present. The main body of the stock passes eastward into a complex of dikes that cuts the older gneisses 0n Pinkham Mountain. Al- though the broad summit of Pinkham Mountain is relatively flat and is covered by a heavy pine forest and a thick mantle of weathered rock, the quartz monzonite is more resistant to weathering than the surrounding gneiss, so the dikes tend to stand up as low outcrops. , Reconnaissance off the area mapped, near the Colorado-Wyoming State line, showed that a large mass of similar granitic rock extends from a point about a mile east of the N orthgate district for about 6 miles eastward to near the Laramie River, where it is covered by younger sedimentary rocks. The western margin of this body is crosscutting and sharp and shows little evidence of contact metamorphism. A similar large granitic mass occurs in the central part of the Park Range, 20 to 25 miles southwest of the Northgate district. Thin sections of specimens collected along Boswell Creek, about 2 miles east of the Northgate district, and near Rainbow Lake in the Park Range were studied for comparison. Both of these specimens strongly resemble that in the N orthgate district, and the stock in the Northgate district appears to be but one of many similar granitic masses that occur in the pre-Cambrian of northern Colorado and southern Wyoming. This rock closely fits the descriptions given by Blackwelder (1908, p. 787—788; and in Darton and others, 1910, p. 5) for the Sherman granite in the Laramie and Sherman quadrangles 15—30 miles to the northeast, and therefore in the two preliminary reports published on the Northgate district (Steven, 1953; 1954) it was called Sherman granite. However, Harrison,5 working in the type locality of the Sherman granite, described field relations that strongly support 5Harrison, J. E., 1951, Relationship between structure and mineralogy of the Sherman granite, southern part of the Laramie Range, Wyoming-Colorado: Unpub- lished thesis, Univ. Illinois. absent. 365 his contention that the Sherman granite there originated through metasomatism. Thus the earlier correlation of the intrusive quartz monzonite in the Northgate district with the Sherman granite may not have been correct, and it now seems more appropriate not to apply a proper name to the rock until more regional work is done to establish the proper correlations. LITHOLOGY The main body of the stock is made up largely of a medium- to coarse—grained, somewhat porphyritic rock. Rectangular pink microcline phenocrysts half an inch or more long are set in a variable groundmass of pink microcline, white plagioclase, and glassy quartz. Bio- tite varies Widely in abundance; in places it makes up nearly 10 percent of the rock and elsewhere is entirely The texture and grain size of the quartz monzonite vary Widely, not only between the stock and the associated dikes but also within each body, and significant quantities of relatively fine grained, distinctly porphyritic quartz monzonite also occur. On weathered surfaces the rock appears dull gray to brown, but the fresh exposures are mottled pink and gray. The rock in some of the larger dikes and irregular masses on Pinkham Mountain resembles that in the central part of the stock, but most of the rock in the dikes, and some near the margin of the main body is fine to medium grained and appears distinctly aplitic. Biotite is a minor constituent in most of the rock in the peripheral zones, and the quartz and feldspar form an aggregate of anhedral grains containing scattered larger crystals of microcline and quartz. The rock contains a few well-formed microcline phenocrysts; most of the larger grains are irregular in shape. Small masses of fine-grained pegmatite are common in some dikes, and all gradations exist between theSe and the surrounding alplitic rock. Fine-grained porphyritic quartz monzonite occurs in several dikes and small masses northeast of the stock and near the east edge of the district. The dikes range from less than a foot thick and several tens of feet long to nearly 75 feet thick and more than 3,000 feet long. Larger bodies are slightly coarser grained than the small bodies. Many of these dikes are too small to be shown on the geologic map (pl. 48). The phenocrysts in these dikes are plagioclase, whereas those in the stock are microcline, and are set in a very fine grained pinkish-gray groundmass of quartz, feld— spar, and biotite. PETROGRAPHY Two generations of minerals are generally present in the intrusive quartz monzonite. Ragged biotite and lath—shaped plagioclase crystals comprise the 366 older generation, and these grains are widely broken and deformed on a minor scale. The younger genera- tion of minerals consists of irregular plagioclase grains, irregular to rectangular microcline—perthite grains, and irregular to rounded quartz grains and aggregates. The younger mineral grains are not deformed, and they complexly embay the older crystals. MAIN BODY OF THE STOCK Typical rock in the main body of the stock is medium to coarse grained and is composed of about 5 percent biotite, 30 to 35 percent plagioclase, 30 to 35 percent microcline-perthite, and 30 percent quartz. Zircon, apatite, and fluorite comprise the minor accessory minerals. Depending on the quantity of microcline, the stock ranges in composition from the more common quartz monzonite to granodiorite or to granite. Locally rocks vary greatly in composition, and in these rocks either quartz, microcline, or plagioclase may greatly predominate. The plagioclase composition ranges from An, to Ann, but in most of the rock it is sodic oligoclase. It occurs in corroded laths as much as 4 millimeters long, and in irregular, untwinned grains that in part replace the lath-shaped plagioclase crystals. Many of the lath— shaped plagioclase crystals are deformed, and much of the polysynthetic twinning was partly or completely destroyed during the deformation and later alteration. A hazy or “ghost” twinning still can be recognized in many of these crystals. The cores of some of the laths are crowded with fine sericite and very fine grained saussuritic inclusions; the arrangement of these in- clusions in some crystals indicates that the plagioclase originally was appreciably more calcic in composition and may have been zoned. The irregular and untwinned plagioclase grains are not deformed; they evidently formed by recrystallization after cataclasis. These grains generally have about the same composition as the earlier, deformed crystals adjoining them, and the sericite and saussuritic inclusions in the recrystallized plagioclase are in patches rather than zones. Clear borders are common in all plagioclase crystals, and the cores of many grains have in part been cleared of the inclusions. Microcline—perthite forms irregular to nearly rec— tangular phenocrysts and smaller, irregular grains in the groundmass. Much of it embays the deformed plagi- oclase (pls. 54 F, 55 A, B) and biotite and commonly contains abundant inclusions of them. Microcline is not deformed and it definitely crystallized after the brecciation of the early plagioclase and biotite. The age relationship between microcline and recrystallized plagioclase is not so definite, and the two minerals commonly appear about contemporaneous. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Myrmekite is widespread along the contacts between plagioclase and microcline grains. It occurs as rounded growths embaying microcline, as border zones on both relict and recrystallized plagioclase crystals, and as irregular growths within some deformed plagioclase crystals. The plagioclase in myrmekite commonly is slightly more sodic than the associated oligoclase or albite. Irregular grains and aggregates of quartz embay the relict plagioclase and biotite crystals and appear to have been introduced both contemporaneously with and slightly later than the microcline. Some of the quartz aggregates are comparable in size to the microcline phenocrysts, but generally they are smaller. In places abundant irregular to rounded grains of quartz embay all other constituents of the rock. This relatively late quartz is common near the margin of the stock or in the adjacent dikes but is not restricted to these occurrences. All the quartz shows wavy extinction, but this could have been produced much later than the time of introduction. Small, ragged crystals of green biotite scattered throughout the rock in places form as much as 10 per- cent of the rock, but locally they are entirely absent. Many of the grains are deformed and broken and most are embayed and corroded by undeformed microcline and quartz. Biotite commonly contains inclusions of magnetite, and in many places has been altered in part to a mixture of sericite, chlorite, and magnetite. Sec- ondary epidote also is common. One small area near the center of the stock is par— ticularly significant as it contains no microcline. The plagioclase here is sodic albite (An3_5), and is associated with considerable quartz, and some idiomorphic epidote. Albite makes up nearly 70 percent of the rock, and more than half of this quantity has recrystallized as undeformed grains that range from small, irregular crystals to rectangular phenocrysts more than half an inch in length. The remainder of the albite occurs in pseudomorphic laths, most of which show marked effects of deformation. These latter grains are abundant and preserve some of the texture of the rock (pl. 55 0) that existed before recrystallization. The rest of the rock consists of 20 to 25 percent quartz with replacement relations, and 5 to 10 percent irregular to idiomorphic epidote. The relict texture shows that plagioclase was one of the major constituents of the original rock and that quartz and microcline either were lacking or were present in subordinate amounts. The original ferro— magnesian minerals were completely destroyed. MARGINAL_ BIKES The composition of the rocks in the complex of dikes on Pinkham Mountain differs significantly from that METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO in the interior of the stock. Quartz, microcline, and plagioclase are generally present in nearly the same proportions as in the main body of the stock. How- ever, biotite is much less abundant here, and the average plagioclase is calcic albite in contrast to the common sodic oligoclase found in the main body of the stock. , Biotite generally forms only minor wisps and shreds generally associated with different amounts of chlorite, sericite, and magnetite. In places these secondary minerals form crude pseudomorphs after biotite, but elsewhere they are disseminated through the rock. A trace of muscovite occurs in some dikes, but gen— erally it is rare. Here and there several percent of biotite has survived the alteration, and in one specimen studied biotite made up about 8 percent of the rock. In 10 specimens the composition of the plagioclase ranged from Ana to An”. Generally the composition ranges from Ans to Anw. Plagioclase forms corroded and deformed pseudomorphic laths, as well as unde- formed irregular grains that embay the earlier crystals. The broken grains originally had abundant polysyn- thetic twinning, but much of this was destroyed during deformation and subsequent recrystallization. The surviving twinning commonly is patchy or in hazy “ghosts” like that in the interior of the stock. The recrystallized plagioclase is untwinned and definitely replaces the earlier plagioclase; in a given area the composition of the plagioclase in both habits is essen— tially the same. The saussuritic and sericitic inclusions in the relict and recrystallized grains of plagioclase in the marginal dikes cluster into irregular patches sepa- rated by abundant relatively clear plagioclase. Clear rims are common, and some crystals are almost free of inclusions. In general the more sodic the plagioclase, the fewer the inclusions; some almost clear crystals of albite contain only sparse evenly distributed, saussuritic inclusions. As in the central part of the stock, microcline- perthite does not have a cataclastic texture, and it corrodes and replaces the deformed plagioclase laths. The larger microcline grains contain abundant relicts of the earlier minerals, many of which show common optical orientation. The phenocrysts in the marginal dikes are more irregular than those in the main body of the stock, though still nearly rectangular. The smaller grains are very irregular. The texture in the pegmatitic parts of the dikes results largely from coarse microcline crystals, which show the same replacement relations as those in the finer grained parts of the rock; the pegma— tite texture thus was formed at the time when micro— cline was introduced. Quartz apparently was the last important constit- uent to be introduced. Some appears to have formed 367 about contemporaneously with the microcline, but other grains definitely embay the microcline. Some quartz occurs as irregular masses and rounded blebs and rods that apparently replace all the other minerals. In places a pseudographic texture formed, and one specimen from the core of Sentinal Mountain (pl. 55 D) shows that the quartz rods in adjacent microcline and albite grains have a common optical orientation. In places where replacement by microcline was less complete, some relict texture of the original rock can be seen. Bent and broken plagioclase laths of random orientation, now pseudomorphed by albite, show mutually interfering relations characteristic of a normal granitic texture. Commonly recrystallized albite is present, but not enough to mask the original texture. SATELLITIG BIKES The composition of the rock in the satellitic dikes near the east edge of the district is variable. As in the stock and associated marginal dikes, plagioclase and biotite appear to have been the original minerals of the rock. These were replaced in varying amounts by potash feldspar, more sodic plagioclase, and quartz. Generally plagioclase, potash feldspar, and quartz each make up about 25 to 35 percent and biotite 5 to 10 percent of the rock. The groundmass of these rocks is very fine grained; the phenocrysts are as much as 2 millimeters long. In contrast to the rock in the stock, the phenocrysts were original constituents of the rock and are plagioclase rather than microcline. Plagioclase, both phenocrysts and in groundmass, is highly corroded, and much of the original twinning was destroyed. Commonly the crystals are crowded with saussuritic and sericitic inclusions, and the composition is difficult to determine. The original plagioclase crystals were irregularly albitized, and in thin sections compositions range from near mid-oligoclase (An15) to calcic albite (An7). Irregular, recrystallized plagio- clase crystals which replace the early plagioclase laths are common, but they are generally not as abundant as in the stock or marginal dikes. Plagioclase and biotite are corroded and replaced by a very fine grained aggregate of potash feldspar and quartz. Some quartz clearly embays microcline, but in much of the rock no age sequence could be deter- mined for these two minerals. Many corroded plagio- clase laths are surrounded by micrographic intergrowths of potash feldspar and quartz (pl. 55 E), in places with the quartz rods arranged almost radially around the plagioclase cores. The thickness of the micrographic rims is related to the degree of replacement of the plagioclase. Where plagioclase laths still retain their form, the rims are thin; where the laths are highly corroded, the rims are thicker and much more irregular. 368/ In some places plagioclase is almost completely replaced by irregular, radial masses of micrographic quartz and potash feldspar. The relatively large dike in the eastern part of sec. 36, in undivided T. 12 N., R. 79 W., is unusual in contain- ing no potash feldspar. Relatively clear albite (An3_5) makes up about 60 percent of the rock. Sericite in— clusions are fairly abundant, but zoisite or clinozoisite inclusions are very minor. The albite is in laths with relict granitic texture and in irregular replacement grains of the same composition (pl. 55 F). Some irregular to nearly rectangular albite crystals 2 to 3 millimeters long replace both the early laths and the smaller replacement grains of albite and enclose many residual inclusions. Biotite apparently once made up about 10 percent of the rock, but almost all of it has been altered to ragged aggregates of chlorite and mag- netite. Irregular quartz grains comprise as much as 30 percent of the rock; they embay all the minerals except some late epidote. Epidote is very abundant in places but generally comprises only about 5 percent of the rock; it occurs in veinlets, random crystals, and granular aggregates. Although the plagioclase has been thoroughly albitized and in part recrystallized, much of the original texture of the rock can be seen. Apparently the original rock was a biotite diorite or quartz diorite. , WALL-ROCK ALTERATION Contact alteration along the walls of the stock and the dikes has been slight, and rarely affected more than a few feet of the country rock. Hornblende gneiss was most readily altered, and it commonly is somewhat silicified and epidotized adjacent to the granite. Along many contacts, particularly where the wall rock is quartz monzonite gneiss or quartz- and biotite-bearing gneisses, no evidence of alteration was recognized in the field. Thin sections from a suite of specimens collected across a contact of intrusive quartz monzonite and horn- blende gneiss were studied. Essentially unaltered horn— blende gneiss 10 feet or more from the contact consists of about equal amounts of andesine and hornblende, with as much as 5 percent biotite. Minor amounts of epidote occur as scattered granules. Adjacent to the contact, the rock has a cataclastic texture, and the original minerals have been somewhat altered. Horn- blende was transformed in part to chlorite and epidote, biotite was altered to chlorite, and plagioclase was saussuritized and changed in composition to near A1120. Minor amounts of quartz and potash feldspar were introduced along fractures and cataclastic zones, and abundant epidote occurs in veinlets and scattered grains as well as with chlorite in pseudomorphs after horn— blende. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY ORIGIN The sharp, essentially unaltered contacts, the mark- edly rectilinear pattern of the dikes which can be related in large part to directions of physical weakness in the wall rocks, and the finer grained rock in the peripheral zones of the stock and in outlying dikes all indicate a magmatic origin for the quartz monzonite in the Northgate district. The occurrence of plagioclase phenocrysts in the very fine grained, chilled satellitic dikes near the east margin of the mapped area, which contrast with the late microcline phenocrysts in the main body of the stock, and the remnants of normal granitic texture that can be clearly dated as older than the metasomatic introduction of microcline and quartz are convincing evidence. The variation in texture and composition of the quartz monzonite apparently is related in large part to deuteric alteration. Plagioclase, biotite, and perhaps some quartz were the earliest minerals to crystallize from the magma, and they probably formed a dioritic or quartz dioritic rock. The rock was pervasively deformed after it was consolidated or nearly consoli- dated, and many biotite and plagioclase crystals were bent and broken. Silica- and alkali-bearing solutions permeated the broken rock, and the early minerals were corroded and in part replaced by abundant microcline, quartz, and more sodic plagioclase. The intensity of the alteration varied throughout the stock and associated dikes, and the mineral transformations show a crude zoning. Generally, the plagioclase is more sodic, and the biotite is largely altered to chlorite and sericite in the peripheral zones. REPLACEMENT The ma‘gma from which the rock in the stock origi- nally formed apparently was emplaced chiefly by means of magmatic stoping. The northern contact of the stock, for example, has many angular, steplike irregu- larities (pl. 48); and in one place a narrow dike projects from the main body of the stock parallel to a nearby section of the angular contact. In this place the dike was frozen while prying off a block from the wall of the stock. The extremely complex pattern of dikes on Pinkham Mountain displays all stages in the disruption of the roof over a stock. These dikes have sharp contacts against essentially unaltered wall rocks and show no evidence of a replacement origin. The magma apparently penetrated fairly wide-spaced fractures in advance of most active stoping. These fissures, perhaps opened by the pressure of the rising column of magma, were irregularly enlarged by local stoping, permitting irregular masses of magma to pro- ject into the fractured and veined roof. Continued stoping gradually engulfed the pendants and septa I METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO between these areas of more rapid stoping. Effects of this process are most clearly shown along the southern flank of Pinkham Mountain, where the rocks are well exposed. Narrow dikes with regular walls, perhaps representing fissures formed by local spreading, connect angular masses of granite which are fringed in part by a lacework of small dikes. Many of these small dikes completely surround blocks of, country rock, and were actively intruding the shattered wall rocks and engulfing some blocks when cooling of the stock stopped the process. It is difficult to determine which of the dikes or irregular masses of granite were emplaced along frac- tures opened by actual spreading of the roof of the magma chamber. Once stoping enlarged a single fracture or zone of fractures to any extent above the general top of the magma body, other fissures could open by the movement of blocks of country rock toward the already active zone of stoping, and no further dilation of the roof or walls of the magma chamber would be required. The maximum spreading of a fracture that can reasonably be credited to the hydrostatic pressure of the magma is limited to the narrowest width across the fissure, and in most places this appears to have been relatively small. This is well illustrated by the irregu- lar, generally northward—trending dike in secs. 9 and 16, T. 11 N., R. 79 W., about a half mile east of the Fluor- spar mine (pl. 48). This dike ranges from about 400 to 1,000 feet in thickness. Although the walls of the dike differ in detail, they appear to correspond and super- ficially the block of metamorphic rock to the west ap- pears to have broken from the wall and roof of the magma chamber and to have drifted several hundred feet out into the magma. Near the northern margin of sec. 16, however, a projection of metamorphic rock comes within about 50 feet of bridging across the dike, so any drifting or forceful separation must have been small, and the broad dike more probably resulted from piecemeal stoping along an originally irregular fracture. The block of metamorphic rocks west of this dike dis- plays the most extreme wall-rock fragmentation found near the stock, and has the aspect of a large-scale breccia cemented by dikes of quartz monzonite. The magmatic stoping apparently was controlled by two general groups of fractures. Many of the smaller blocks pried from the roof and walls of the magma chamber broke along fractures, either nearly parallel to the foliation or at right angles to it. Small blocks in particular show this control, although several large masses also are bounded by these fractures. Most of the fissures formed along these directions of weakness are irregular and generally do not persist far. Thus the small-scale fracturing of the country rock and the piece- 369 meal stoping by the magma appear to have been con- trolled largely by directions of weakness inherent in the wall rocks. Another group of fractures trends eastward to south— eastward about parallel to the elongation of the stock. These fractures control parts of the northern wall of the stock and are followed by most of the larger dikes that extend eastward from the main body of the stock to- ward the Baker Pit and the Camp Creek mine (pl. 48). They trend obliquely to the foliation in the gneiss complex, and most have relatively smooth and regular walls. The fissures followed by these dikes are not re- lated to known directions of weakness in the wall rocks, and are much more regular and persistent than those following the foliation or related fractures. They may well have originated in the initial fracturing and spread- ing of the roof of the magma chamber by the hydro- static pressure of the rising column of magma. The more abundant but smaller scale fissuring along foli- ation thus may have resulted from the detailed brec- ciation of a roof already stretched and broken, along eastward- to southeastward-trending master fissures. Despite the highly broken condition of the roof and walls of the stock, and the evidence of magmatic stoping, the main body of the stock is almost free of xenoliths. As wall—rock alteration is slight and the xenoliths that are found are very little altered, this lack of xenoliths cannot be due to assimilation. Rather it must have resulted from the sinking of the blocks to levels below those now exposed. To accomplish this removal of xenoliths below a zone of very active stoping, the sinking must have been rapid as there is no concen- tration of xenoliths near the periphery of the stock. Along the northern margin of the stock, the quartz monzonite is relatively free of xenoliths as far as the contact, and even the irregular, larger bodies of quartz monzonite in the stoping area enclose few blocks of country rock. Many blocks of country rock do occur in the quartz monzonite, however, in the vicinity of the breccialike aggregate of metamorphic blocks and granitic dikes near the Fluorspar mine where stoping was most active, and the mine workings show abundant xenoliths in quartz monzonite: Rapid sinking of the blocks implies a large average size of the blocks, a significant difference in density between the xenoliths and the melt, or a relatively low viscosity for the magma. Abundant evidence for piecemeal stoping indicates that the average stope blocks were relatively small so the fragment size probably was not an important factor in clearing the exposed quartz monzonite of inclusions. The rocks in the gneiss complex include such varied types as quartz monzonite gneiss, pegmatite, hornblende gneiss, hornblende-biotite gneiss, and mylonite gneiss. Of 370 these, the hornblende-bearing metamorphic rocks have relatively high specific gravity, but other rocks, such as quartz monzonite gneiss and pegmatite, are not significantly different from the quartz monzonite now found in the stock (table 1). The specific gravity of the original melt probably was lower than that of the rock now found in the stock, but the difference may not have been as great as might be expected, as petro- graphic evidence indicates that rock that first crystal- lized may have been dioritic in composition. Even so, the few xenoliths that are found show no selective accumulation of the lighter rocks. Thus, by elimina- tion, the magma appears to have had a relatively low Viscosity. Positive evidence for the low viscosity is the ease with which stoping was accomplished along relatively narrow fissures. It is difficult to imagine a viscous melt penetrating the wall rocks in as intricate a manner and in as small dikes as it did on Pinkham Mountain and permitting the blocks so loosened to sink easily to great depths. ORIGINAL ROCK Deformation and cataclasis of the early minerals could have taken place only after complete or nearly complete consolidation of the magma. No unaltered reinnant of the original rock has been found, but several lines of evidence indicate that it probably was dioritic or quartz dioritic. Biotite and lath—shaped plagioclase crystals are the only minerals that clearly show brecciation. Micro- cline, where not broken by later, unrelated movements is not deformed and everywhere is corrosive toward deformed biotite and plagioclase. Irregular, recrystal- lized plagioclase grains of about the same age as the microcline also are not deformed and clearly replace the earlier crystals. Most of the quartz was introduced at about the same time or even a little later than micro- cline. Under the microscope, almost all quartz shows the wavy extinction generally attributed to strain; so evidence of deformation cannot be used to establish the presence or absence of an earlier generation of quartz. A former interstitial habit of early quartz could easily have been masked by quartz introduced later. In the central part of the stock where albitization was least intense, many of the relict plagioclase laths contain zonally arranged saussuritic inclusions of zoisite or clinozoisite and sericite. These probably were inherited from an original zoned and more calcic feldspar. As the inclusions commonly are somewhat disrupted and clear rims of plagioclase grains are common, it is probable that even here albitization L involved some introduced material and was not merely saussuritic alteration. This is further suggested by content of plagioclase. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the progressive disruption and decrease in abundance of saussuritic inclusions with an increase in albite Thus the original plagioclase probably was significantly more calcic than the sodic oligoclase or calcic albite now found. Relict granitic texture still persists in some of the marginal and satellitic dikes and in local areas in the stock where less microcline was introduced. Although considerable albitization and recrystallization of plagio- clase and alteration of biotite took place during altera- tion, enough relict texture is preserved to indicate that biotite probably made up 10 percent for more of the original rock and that plagioclase constituted much of the remainder. DEUTERIC ALTERATION Alteration of the original igneous rock produced a crude zoning of transformation products, which is shown best by the degree of albitization of plagioclase and alteration of biotite. In the main body of the stock, most of the plagioclase is sodic oligoclase which generally contains abundant saussuritic inclusions. Biotite, although considerably corroded, is still fairly well preserved and has only a minor amount of asso- ciated chlorite, sericite, and magnetite; Large rec- tangular phenocrysts of microcline are common. In the marginal dikes the plagioclase generally is more thoroughly albitized and in places is highly sodic albite; the abundance of saussuritic inclusions decreases with an increase in degree of albitization. Very little biotite persists, as most of it was replaced by microcline and quartz or was converted to mixtures of sericite (and muscovite), chlorite, and magnetite. Microcline pheno- crysts are not nearly as abundant here as in the main body of the stock. Although more variable, the rocks in the satellitic dikes to the east generally belong to the same zone as the rocks in the marginal dikes. The zoning does not appear to be due to incomplete reaction. The plagioclase in the pseudomorphic laths and in the recrystallized grains has essentially the same composition in any given specimen, so at least the plagi— oclase apparently approached equilibrium with the altering solutions. Biotite in the main body of the stock and the mixture of sericite, chlorite, and magne— tite in the peripheral zones also probably approached equilibrium, as assemblages of biotite-oligoclase—quartz and chlorite-sericite-albite—quartz are common associa- tions in regionally metamorphosed rocks where approx— imate equilibrium commonly is postulated. More probably the zoning resulted from differences in temperature or concentration of the altering solu- tions in the different parts of the stock and associated dikes. Experimental data indicate that the con- trasting mineral assemblages formed during regional METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO metamorphism can result either from changes in bulk composition or from changes in temperature-pressure conditions (Yoder, 1952). Under otherwise similar conditions, oligoclase and biotite are formed at higher temperatures than are albite, chlorite, and sericite, so the zonal arrangement of these minerals, with the lower temperature assemblages in the peripheral zone, is what might be expected. On the other hand, the concentrations of the materials dissolved in the through- traveling late magmatic solutions undoubtedly changed from place to place, so bulk compositional factors may have been important. Little is known of what happened to the lime, mag— nesia, and iron removed from the replaced minerals. Some of the lime could have been fixed in the minor amounts of epidote which are relatively common in the dikes and near the walls of the stock, but most was removed in solution. Little could be held in saussuritic inclusions in plagioclase, as these inclusions decrease in abundance with an increase in degree of albitization. The chlorite and secondary magnetite occur chiefly in ' minor aggregates left from the dissociation of biotite, and represent only a small percentage of the magnesia and iron in the original rock. No concentrations of calcic or ferromagnesian secondary minerals were noted in the vicinity of the stock, but as the wall rocks carry abundant hornblende and intermediate plagioclase, it is impossible to trace the origin of the widely distributed secondary chlorite and epidote. It is difficult to explain the relatively minor alteration of the wall rock around a body as intensely endomor— phosed as the quartz ~monzonite stock in the N orth— gate district. Perhaps the drop in temperature of the deuteric solutions as they passed from the relatively hot mass of the stock into the cooler wall rock in- hibited further reactions, but this hypothesis encounters difficulties when it is applied to the complex of dikes on Pinkham Mountain, where the dikes could hardly have been at significantly higher temperatures than the surrounding rocks. LATE MAGMATIC SOLUTIONS The solutions that caused alteration of the original rock probably originated at depth within the igneous body. An external source is unlikely as the wall rocks show only minor alteration adjacent to the intrusive contact, and in the stock the endomorphic alteration products are arranged in crude zones, With the higher temperature minerals nearer the center. Residual magmatic solutions of local origin conceivably might account for some of the alteration, but the volume of residual magma remaining after crystallization of the plagioclase could hardly account for the microcline which averages 35 percent of the rock and quartz which 371 averages 30 percent. The zonal arrangement of the alteration products is consistent with the thesis that solutions of late magmatic origin moved upward and outward through the brecciated rock of the stock. Some of the constituents in the solutions can be determined from the minerals introduced or trans— formed by them. Judging from the quantity of microcline and quartz that corrodes and replaces the deformed plagioclase and biotite, potash and silica were important constituents of the solutions. Some quartz may have been original, but much of it was introduced during alteration. The progressive albitization of plagioclase proves that soda was present in the solutions. Some albitization was undoubtedly merely saussuritic, but zoisite and sericite inclusions are most abundant in the main body of the stock, Where the plagioclase is most calcic, and they are almost entirely absent in some sodic albite. In any individual specimen, however, the composition of plagioclase generally is independent of its content of saussuritic inclusions, and both relatively clear and heavily clouded grains have about the same composi- tion. The general decrease in saussurite with increasing albite content is accompanied by a progressive dis- ruption of the original zonal arrangement of the inclusions within individual crystals. Plagioclase crys- tals with zonally arranged inclusions are restricted to the main part of the stock, and even here they are not abundant. Potash apparently was more abundant than soda in the late magmatic solutions that invaded the stock and related dikes. O’Neill (1948, p. 167—180), in a series of experiments on the hydrothermal alteration- of feldspars, showed that the substitution of potash for soda in albite is a revisible reaction controlled by the law of mass action. Thus about a third of the rock could have been replaced by microcline only if the concentration of potassium ions in the solution was significantly higher than that of sodium ions. Replace~ ment of plagioclase by microcline would impoverish the solution in potassium ions; at the same time the sodium ion concentration would increase residually and from the replaced plagioclase. This may account in part for the increased albitization toward the pe- ripheral parts of the stock. The presence of abundant microcline in the dikes and near the margins of the» stock, however, indicates that even here the potassium ion concentration was high relative to sodium ion concentration. It has long been recognized that the- residual liquid from the crystallization of a normal subalkaline magma is rich in alkalies, silica, and water; and Bowen (1928, p. 100) has shown that potash com- monly increases relative to soda in the late differentiates. Experiments by Gruner (1944, p. 578—589) and 372 O’Neill (1948, p. 167—180) indicate that the trans- formation of albite to potash feldspar and the albitiza- tion cf plagioclase take place most readily in basic solutions and that alkali leaching takes place in acid solutions. , SUMMARY AND CONCLUSIONS Rocks buried deep in geosynclinal belts undergoing orogeny are deformed and profoundly metamorphosed, and not uncommonly are transformed to an assemblage of rocks with a general granitic composition. The relative importance of metamorphic processes versus igneous processes in the formation of these granitic bodies is currently one of the most warmly debated subjects in geology. Read (1943, 1944) has summarized the evolution of many of the ideas on the formation of these granite masses, particularly the ideas concerned with meta- morphic origin. His comments on the views evolved during the early part of this century by many European workers, notably the French geologists Michel-Levy, Lacroix, and Termier, and the Fennoscandians Seder- holm and Holmquist, are of interest as it is chiefly on the foundations laid by these men that many of the present-day theories of granitization are built. These geologists all believed that regional metamorphism, granitization, and remelting (anatexis and palingenesis) are integral parts of the same general process. Al— though they held widely different opinions as to the role of granitic magma in this process—chiefly Whether it was the cause or the result of the transformations—— a magma capable of movement and intrusion was a reality to them. To this degree at least they were in. agreement with the more confirmed believers in the efficacy of magmatic differentiation and crystallization to explain the features displayed by granitic rocks. Modern workers on granitic rocks have a bewildering diversity of ideas regarding their origin, and there is a tendency on the part of some toward restrictive “schools of thought.” The chief cleavage concerns the role, or even the necessity, of magma in the origin of granites. The present writer strongly agrees with Read (1948, p. 2; 1951, p. 1) that the answer to this question is to be found in field work, and the descriptions and interpreta- tions in this report are intended to record some basic data that may contribute toward the eventual solution of some of the problems of granitic rocks. N0 extensive review of the literature is made here, and only reports of particular application are cited. The two groups of granitic rocks in the Northgate district—the intrusive quartz monzonite and the quartz monzonite gneiss—differ so widely that they probably are completely unrelated and their association in space is fortuitous. It is possible, however, that the two SHORTER CONTRIBUTIONS TO GEiWERAL GEOLOGY contra ting types represent an early stage and a late stage in the general process through which granitic rocksform. The progressive dynamothermal meta- morph'sm, granitization, and rheomorphism described for the rocks in the gneiss complex may well mark the successive steps in the formation of a granitic magma— a series of events which locally proceeded just beyond the stage of incipient melting. The intrusive quartz monzonite, on the contrary, originated through the consol' ation of a liquid, a magma, which had risen high e ‘ ough in the earth’s crust so that much evidence of its origin was lost. At the levels now exposed it moved} upward chiefly by means of magmatic stoping. Although the intrusive quartz monzonite shows ample evidence of alkali and silica metasomatism, this altera- tion can reasonably be ascribed to the deuteric action of latelalkalic and silicic solutions residual from normal magmatic differentiation. NotLonly are the rocks in the roots of an orogenic belt subjec ed to the extra heat from the work expended during deformation, but also to the elevated temper- ature and pressure of the deeper levels of the earth’s crust to which they are depressed. High-grade meta- morphic and migmatitic rocks attest to the increased chemitial activity of the rocks under these conditions, and itiseems a natural conclusion that either partial or complete melting of sialic rocks can take place should temperatures become high enough for long enough periods. Daly (1933, p. 292—293) cites several ex- amples of melting related to shallow intrusive rocks which ‘had only limited quantities of heat available; such conditions are less favorable for melting than are prese t in the roots of an orogen Where the sialic rocks are allieady hot and apparently there is an ample source of ad itional heat. Eskola (1932, p. 473—474; 1933) has p oposed that the rocks under these conditions are subjefit to differential anatexis, with the low-melting constituents being melted before the rest of the rock and squee ed out to form either a granitic magma or a granit c “ichor” which is capable of Widespread metasbmatism. Gr ‘nitization without the loss of coherence of the affect d rocks must take place at temperatures lower than those required for liquification, and it appears logica that if the heating process is sufficiently slow, migmLtizing reactions within the heated body of rock should precede the formation of any significant quantity of lten rock. Following Eskola (1932, 1933), the low-melting constituents, the alkalies, silica, and volatiles, of the rocks in the roots of the orogen should beco ye chemically active and mobile before the rest of the rock. As long as the quantity of such mobile material at any one place remains small, the rock should retain its physical continuity, and the chemical l ' magmas . . METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NOBTHGATE DISTRICT, COLORADO reactions involving the permeating mobile fraction should be of the “granitizing” variety. As the pro- portion of mobile material increases, however, the rock should at some time lose its coherence and become rheomorphic. These changes should be expected not only in the zone of differential anatexis, but also in the overlying rocks into which the mobile material has migrated—or been squeezed, to use Eskola’s phrase- ology—where relatively high concentrations can be built up by a continuing supply from below. Wegmann (1930, p. 58—75) has postulated that when rocks reach a rheomorphic condition, they move by diapir injection, and includes within this process both magmatic and nonmagmatic movements. Most ex— ponents of granitization apparently agree that a stage of plastic flow can be reached, but some of them seem hesitant to make what seems like the next logical as- sumption—a slightly higher temperature acting for a somewhat longer time should result in significant remelting so that the entire mass ycan act essentially as a liquid. Depending on the local stress conditions, a mass of rock conceivably can move while the quantity of intergranular liquid is still quite small (Sosman, 1948, p. 116) ; conversely, a relatively large percentage of the mass might have to become liquid before sufficient driving force or pressure is attained for it to breach the surrounding rocks. The mechanisms outlined above are not original; they are essentially the same as those summarized by Waters (1948, p. 107—108) who stated, “The picture I have tried to present . . . is a prejudice that is by no means new. It is essentially the same process advocated by Michel-Levy, Eskola, Barrell, Seder- holm, Lawson, and many others.” Turner and Ver- hoogen (1951, p. 305) in summarizing their chapter on the granite—granodiorite plutonic association find, If the extreme hypothesis of granitization by solid diffusion . . . is excluded, we find a suprising unanimity of opinion in recent writings on the general course of origin and evolution of granitic . By all of these writers [Raguin, Eskola, Backlund, Wegmann, Reinhard, Niggli, MacGregor and Wilson, Read, Holmes, Bowen, and others] genesis of granitic magma . . . is attributed to differential fusion of mixed rocks in the continental basements. It is my impression that this “unanimity of opinion” is one of degree only, but nonetheless there appears to be a considerable field of common thought. GRANITIC ROCKS IN THE GNEISS COMPLEX Before any conclusions can be reached on the general significance of the various transformations described for the rocks in the gneiss complex in the N orthgate district, the origin of the transforming solutions must be considered. They may have been derived, as the 373 writer believes, from the differential anatexis of sialic rocks, or they may have originated through crystal- lization of a granitic mass at depth, a mass which is nowhere exposed in or near the Northgate district. No direct evidence is known that would favor a magmatic source for the granitizing solutions. Recon- naissance in parts of the Medicine Bow Mountains adjacent to the Northgate district showed that mig- matitic rocks are widespread, but all of the granitic masses that appeared to be of magmatic origin were clearly younger. Blackwelder (in Darton and others, 1910), in his discussion of the pre-Cambrian rocks in the Laramie and Sherman quadrangles to the northeast, describes a granite gneiss with field relations apparently quite similar to those of the quartz monzonite gneiss in the N orthgate district. Blackwelder considered the granite gneiss to be a mildly metamorphosed granite of mag- matic origin. But whether this granitic gneiss is magmatic or migmatitic in origin, it occurs in relatively small, irregular bodies rather than in large subjacent masses, and thus seems a relatively unlikely source for widespread granitizing solutions. Similar pre-Cambrian rocks were described by Spencer (1904, p. 37—41) from the Encampment district, Wyoming. Spencer reported two groups of granitic rocks—an older, somewhat gneissose quartz diorite which he described as being “metamorphosed,” and. a younger, variable but generally coarse-grained red granite which is essentially unaltered. Both of these rock types are reported as “intrusive” into a hornblende schist formation, and are older than a considerably deformed metasedimentary formation. Correlations involving these kinds of rocks are hazard- ous at best, and it would be diflicult without additional detailed field work to say whether or not one or the other of these granitic rocks might have been the source of granitizing solutions of great regional extent. It is significant, however, that Spencer described no migmatitic rocks in the Encampment area, and if any are present they must have been included with one or the other of his granitic types. The behavior of the masses of quartz monzonite gneiss in the Northgate district which became mobile suggests that the causal forces were local and self- contained and the movement was in the nature of a diapir injection. Movement took place only in the larger masses of quartz monzonite gneiss, where the greatest softening might be expected under either hypothesis, but the annular flow structure in the northwest corner of the area is funnel-shaped down- ward, and seems rootless. Were the granitization related to a magmatic source below, such an apparently isolated mass of mobile rock would not be expected, 374 but rather the rocks should have softened generally downward toward the source of energy. The dynamothermally metamorphosed hornblende gneiss, which before metasomatism was the predom- inant rock type in the district, is relatively deficient alkalies and silica, and even under the differential anatexis hypothesis it is necessary to seek an outside source for the granitizing material. The hornblende gneiss was derived from a layered rock; however, and originally it must have been laid down under surface or near-surface conditions, whether as an accumulation of volcanic material or as impure carbonate sedimentary strata. Being geographically well Within continental limits, such surficial rocks quite likely would have been underlain at some depth by a basement of more typically sialic rocks, which would be considerably more susceptible to partial melting under the conditions present in the roots of an orogen. GRANITIC BOOKS OF MAGMATIC ORIGIN The contrast in physical behavior of the rocks in the gneiss complex at the time of the progressive regional metamorphism, metasomatism, and mobilization as compared to their behavior at the times of the intrusion of the dacite porphyry dikes and the quartz monzonite stock and associated dikes, indicates that considerably different depths in the earth’s crust were involved. ~The earlier sequence of events clearly took place deep in the zone where rocks behave plastically in response to deforming forces. The same rocks, however, responded to the stresses attendant to the later igneous intrusion by fracturing, and behaved strictly as brittle solids. In addition, the rocks were cool enough during these later periods to chill the relatively narrow dacite dikes so that they are made up of a typically dense, fine—grained rock. Although the quartz monzonite in the stock owes much of its present texture to deuteric reaction, it locally shows a significant decrease in grain size toward the margins, and many of the small satel- litic dikes near the east edge of the mapped area are typically fine grained and were originally porphyritic, again pointing toward relatively rapid cooling. Thus the intrusive magma rose high above the levels at which it originated, and invaded a relatively cool environment where the rocks were brittle and easily fractured. Chilling of the magma at these levels apparently was too rapid to permit soaking and migma- tization of the adjacent country rocks by magmatic fluids, which so profoundly endomorphosed the in- trusive mass. Thus the contacts are sharp and the intrusive character of the stock is clear cut. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY l LITERATURE CITED Adams, l“. D., and Barlow, A. E., 1910, Geology of the Haliburton and Bancroft areas, , Province of Ontario: Geol. Survey Ca ‘ada Mem. 6, 419 p. Ball, SEX” 1906, Pre—Cambrian rocks of the Georgetown quad- ran‘ 1e, Colorado: Am. Jour. Sci., 4th ser., v. 21, p. 371- 389. Beekly, A. L., 1915, Geology and coal resources of North Park, Colo: U. S. Geol. Survey Bull. 596. Blackw ‘lder, Eliot, 1908, Pre—Cambrian rocks in southeastern Wy ming: Science, v. 27, p. 787— 788. Bowen, . L., 1928, The evolution of the igneous rocks: 332 p., Princeton, N. J ., Princeton Univ. Press. Buddington, A. F., 1939, Adirondack igneous rocks and their me ‘amorphism: Geol. Soc. America Mem. 7., 354 p. Buddington, A. F., and Leonard, B. F., 1953, Chemical petrology an . mineralogy of hornblendes in northwest Adirondack granitic rocks: Am. Mineralogist, v. 38, nos. 11 and 12, p. 891—902. Burcha , E. F., 1933, Fluorspar deposits in western United Sta es: Am. Inst. Min: Met. Eng. Tech. Pub. 500, 26 p. Cox, D. ,C., 1945, General features of Colorado fluorspar deposits: Colo. Sci. Soc. Proc., v. 14, no. 6, p. 263—285. Daly, R. A., 1933, Igneous rocks and the depths of the earth: 598 p., New York, McGraw-Hill Book Co., Inc. Darton, N. H., Blackwelder, Eliot, and Siebenthal, C. E., 1910, Deécription of the Laramie and Sherman quadrangles, Wyoming: U. S. Geol. Survey Geol. Atlas, folio 173. Eskola, P., 1932, On the origin of granitic magmas: Mineral— ogi che and Petrographische Mitteilungen 42, p. 455—481. 1933, On the differential anatexis of rocks: Bulletin de la Commission Geologique de Finlande no. 103, VII, p. 12—25. Goldring, E. D., 1942, An occurrence of ilscmanite: Am. Mineral- ogist, v. 27, no. 10, p. 717—719. Gruner,lJ. W., 1944, The hydrothermal alteration of feldspars in cid solutions between 300° and 400° C.: Econ. Geology, v. 9, no. 8, p. 578—589. Hague, Arnold, 1877, North Park, Park Range, in Hague, Arnold, and Emmons, S. F., Descriptive geology. U. S. geological ex loration of the fortieth parallel (King): Prof. Papers En . Dept. U. S. Army, no. 18, v. 2, p. 94—!41. Ladoo, R. B., 1923, Fluorspar mining in the western states: U. S. Bur. Mines Rept. Inv. 2480. ,1927, Fluorspar; its mining, milling, and utilization: U. S. Bur. Mines Bull. 244, 185 p. Loveri g, T. S., 1935, Geology and ore deposits of the Monte- zuma quadrangle, U. S. Geol. Survey Prof. Paper 178. Miller, :J. C., 1934, Geology of the north and south McCallum an liclines, Jackson County, 0010., with special reference to pe roleum and carbon dioxide: U. S. Geol. Survey Circ. 5. O’Neill,‘ T. F., 1948, The hydrothermal alteration of feldspars at 250° to 400° C.: Econ. Geology, v. 43, no. 3, p. 167—180. Osborne, F. F., 1936, Petrology of the Shawinigan Falls district: Gebl. Soc. America Bull., v. 47, no. 2, p. 197—227. Read, H. H., 1943, 1944, Meditations on granite: Pt. 1, Geol. AsSoc. London Proceedings, v. 54, pt. 2, p. 64—85. Pt. 2. ibid., v. 55, pt. 2, p. 45—93. ,1948, Granites and granites, in Origin of granite: Geol. Sol. America Mem. 28, p. 1—19. ,1951, Metamorphism and granitization: Geol. Soc. of Sohth Africa, Alex. L. du Toit Memorial Lectures no. 2, 27 p. Colorado: METAMORPHISM AND THE ORIGIN OF GRANITIC ROCKS, NORTHGATE DISTRICT, COLORADO Reynolds, D. L., 1944, The southwestern end of the Newry igneous complex: Geol. Soc. London, Quart. Jour., v. 99 pt. 3—4, p. 205—246. Sosman, R. B., 1948, Discussion, in Origin of granite: Geol. Soc. America Mem. 28, p. 116. Spencer, A. C., 1904, The copper deposits of the Encampment district, Wyoming: U. S. Geol. Survey Prof. Paper 25. Spurr, J. E., Garrey, G. H., and Ball, S. H., 1908, Economic geology of the Georgetown quadrangle, Colorado: U. S. Geol. Survey Prof. Paper 63. Steven, T. A., 1953, Geology of the Northgate fluorspar district, Colorado: Wyo. Geol. Assoc. Guidebook, 8th Annual Field Conference, 1953. 1954, Geology of the Northgate fluorspar district, Colo- rado: U. S. Geol. Survey Mineral Inv. Map MF 13. Turner, F. J., and Verhoogen, Jean, 1951, Igneous and meta- morphic petrology; 602 p., New York, McGraw-Hill Book Co., Inc. ' 375 Warne, J. D., 1947, Northgate fluorspar, Jackson County, 0010.: U. S. Bur. Mines Rept. Inv. 4106. Waters, A. C., 1948, Discussion, in Origin of granite: Geol. Soc. America Mem. 28, p. 106—108. Waters, A. C., and Campbell, C. D., 1935, Mylonites from the San Andreas fault zone: Am. Jour. Sci., 5th sen, v. 29, no. 174, p. 473—503. Wegmann, C. E., 1930, Uber Diapirismus (Besonders im Grundge- birge): Bull. de la Comm. Geologique de Finlande no. 92, III, p. 58-76. 1935, Zur deutung der Migmatite: schau, Band 26, p. 305—350. Yoder, H. 8., Jr., 1952, The MgO—A1203—Si02—H20 system and the related metamorphic facies: Am. Jour. Sci., Bowen volume, p. 569—627. Geologische Rund- Page Adirondack Mountains ....................... 339 Anatexis ...................... ..- 372, 373 Annular layers ............................. 357, 363 Baker pit ..................................... 369 “Basic front”. 350 Bureau of Mines exploratory program ........ 336 Camp Creek ............................... 338,364 . Camp Creek mine ____________________________ 369 Colorado Geological Survey Board ........... 336 Colorado Metal Mining Fund Board ......... 336 Deuteric alteration ......................... 368, 374 Diapir injection ............. - 357,359, 373 Distribution, biotite—garnet gneiss. ....... 345 dacite porphyry .......................... 364 hornblende-biotite gneiss ................. 353 hornblende gneiss ........ 338 intrusive quartz monzonite ............... 365 mylonite gneiss ........................... 354 pegmatite ................. 350 quartz monzonite gneiss... ........... 342 rheomorphic quartz monzonite gneiss ..... 357 Dynamic metamorphism ................... 340, 349 Dynamothermal metamorphism.. .. 338, 340, 345,372 Fluorspar ............ ‘ 337 Fluorspar mine ....... 369 Foliation, hornblende-biotite gnelss ........... 353 hornblende gneiss ........................ 340 mylonite gneiss .......... 356 rheomorphic quartz monzonite gneiss _____ 357, 359, 363 Front Range, Colorado ______________ . ........ 341 Gneiss complex..- 337 Grenville series ............................... 341 Idaho Springs formation ...................... 341 Independence Mountain fault .............. 337, 357 J elm Mountain ............................... 341 ' Kings Canyon .............................. 354, 357 Laramide orogeny ............................ 337 Laramie and Sherman quadrangles ......... '.. 341 Laramie River _______________________________ 365 Lineation, hornblende-biotite gneiss. ..... 356 hornblende gneiss.. .-- 340,341 mylonite gneiss ........... 356 rheomorphic quartz monzonite gneiss _____ 358 INDEX Page Lithology, biotite-gamet gneiss ............... 346 hornblende-biotite gneiss. . . . 353 hornblende gneiss ........... . 338 intrusive quartz monzonite ............... 365 mylonite gneiss ___________________________ 355 pegmatite _________________ 350 quartz monzoni te gneiss ......... ...- 342 rheomorphic quartz monzonite gneiss ..... 359 Lit-par-lit gneiss .............................. 346 McOallum anticlines _________________________ 336 Magmatic stoping ........................... ‘. 368 Medicine Bow Mountains __________ 335, 336,337,355 Metasomatism _________ 342, 344, 345, 349, 352, 364, 372 Minerals, albite ........................ 344, 351 andesine... . 339, 364, 368 apatite. . . . 339, 340, 345, 349, 354, 355, 364, 366 augite. . .. 339, 340 biotite .................................... 340, 344, 349, 351, 353, 354, 355, 360, 361, 364, 366, 367 blue amphibole ___________________________ 348 chlorite ................. 340, 344, 351, 352, 366, 368 chrysotile ...................... clinozoisite ____________________ epidote. 340, 344, 345,349, 351, 354,355, 364, 366,368 fluorite.. ' 366 garnet ...................... 345, 348, 351, 352, 360 hematite ........................... 340, 345, 352 hornblende ..... 339, 344, 353, 355, 360, 361, 368 labradorite. ........... .. 339 magnetite ................... .. .. 340, 344, 345,349, 351,354, 360, 361, 364,366 microcline .............. 344, 349, 351, 354, 360, 361 microcline-perthite ________ .. 366, 367 muscovite .............................. 351, 360 myrmekite ......................... 351, 360, 366 oligoclase .............. .. 344, 355 olivine ................ _ 340 orthoclase _________________ .. 364 plagioclase.. 339, 344, 351, 353, 359, 361, 366,367, 368 quartz .................................... 340, 344, 349, 351, 353, 354, 355, 360, 361, 364, 366, 367 sericite. . 366 serpentine. .540 sillimanite ________________________________ 360 specularite ________________________________ 351 sphene..... 345, 349, 352, 354, 355 spinal ..................................... 340 tremolite _________________________________ 340 zircon ______________________________ 345, 349, 366 Page Montezuma quadrangle ______________________ 341 N orthgate district, location ___________________ 335 North Park ___________ 335 North Park Basin-... _ .. 337 North Platte River ......................... 335, 358 Origin, biotite-garnet gneiss .................. 349 hornblende-biotite gneiss ................. 354 hornblende gneiss ............... 341 intrusive quartz monzonite ............... 368 mylon ite gneiss ........................... 357 pegmatite ........ 352 quartz monzonite gneiss .................. 345 Park Range ................................ 335,364 Petrography, biotite-garnet gneiss ............ 346 dacite porphyry .......................... 364 hornblende-blotite gneiss ....... 353 hornblende gneiss ............... 339 intrusive quartz monzonite ..... 365 mylonlte gneiss ........................... 355 pegmatite ................................ 351 quartz monzonite gneiss .............. 343 rheomorphic quartz monzonite gneiss. 359 Pinkham Creek ............................ 350,353 Pinkham Creek canyon. .......... 342,354, 355 Pinkham Mountain.. . ...... 350, 353, 365, 368 Pliocene deformation ......................... 337 Rheomorphism ................. 340, 342, 357, 361, 372 Rock flowage ................................. 358 Sedimentary rocks, early Tertiary ............ 337 Mesozoic ................................. 337 North Park formation 337 Permian ................................ -.. 337 Quaternary ............................... 337 White River formation. Sentinal Mountain.. Sherman granite ..... Specific gravity, Dre-Cambrian rocks ......... 364 Structural setting, rheomorphic quartz mon- zonite gneiss ................................ 357 Structure, hornblende gneiss .............. 340 mylonite gneiss ........................... 356 Ultramafic masses .......................... 338, 342 Ultramylonite ................... ' ............. , 355 Vasquez Mountains .......................... 341 377 PLATE 50 A. Typical hornblende gneiss, with hornblende, h, and plagia- clase, p. ' B. Typical quartz-bearing hornblende gneiss, with hornblende, h, plagioclase, p, and quartz, q. 0. Typical pyroxene-bearing hornblende gneiss, with hornblende, h, augite, py, and plagioclase, p. D. Slightly altered hornblende gneiss. Plagioclase, p, is crowded with saussuritic inclusions; hornblende, h, is somewhat altered to chlorite, c, and epidote, e; small amounts of microcline, m, and quartz, q, have been introduced. GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 50 PHOTOMICROGRAPHS OF HORNBLENDE GNEISS GEOLOGICAL SURVEY ‘ PROFESSIONAL PAPER 274 PLATE 51 VIEW AND PHOTOMICROGRAPHS OF QUARTZ MONZONITE GNEISS PLATE 51 A. Typical quartz monzonite gneiss exposed in a fresh road out along Lawrence Creek. B. Typical thoroughly transformed quartz monzonite gneiss. Relict plagioclase grains, 7), are corroded and replaced by microcline, m, and quartz, q. 0. Typical thoroughly transformed quartz monzonite gneiss. Relict plagioclase, p, enclosing secondary myrmekite is corroded and replaced by microcline, m, and quartz, q. PLATE 52 . Marginal facies of biotite-garnet gneiss. Hornblende, h, is in part altered to biotite, b, quartz, q, and accessory apatite. a, and sphene (dark granules). Microcline, m, is a very minor constituent. Plagioclase, p, is essentially unaltered. . An early stage in the formation of a garnet from biotite. Scattered granules of garnet, g, and blue amphibole, h, are set in a fine-grained aggregate of quartz, plagioclase, and mica. The original biotite, b, is corroded, and the plagioclase, p, is eliminated from the area around the garnet granules. Epidote, e, is a common accessory. . Typical thoroughly transformed biotite—garnet gneiss. Ir- regular garnet grains, 9, commonly poikilitic with abundant rounded blebs of quartz, q, and blades of biotite, b, are set in an aggregate of quartz, q, plagioclase, p, biotite, b, and generally minor microcline, m. . Garnet, 9, formed at the expense of biotite, b, with the de- velopment of accessory apatite, a, and epidote, e. The dark granules of magnetite in the biotite apparently formed as a result of the transformation. Plagioclase, p, is eliminated from the garnet; quartz, q, commonly forms rounded blebs Within the garnet, although not in this field. The reaction zone between the garnet and biotite generally is a fine aggregate of quartz, sericitized plagioclase, and pale mica. ' . Garnet, g, and secondary blue amphibole, h, formed at the expense of biotite, b. Quartz, q, is a common associated mineral. . Garnets developed directly from hornblende gneiss. Original hornblende, H, and plagioclase, p, are in part replaced by quartz, q, and an aggregate of garnet crystals, 9, and secondary blue amphibole, h. Apatite, a, is a common accessory. GEOLOGICAL SI’RVEY PROFESSIONAL PAPER 274 PLATE 5? w m. X75 PHOTOMICROGRAPHS OF BIOTITE-GARNET GNEISS GEOLOGICAL SI‘RVEY PROFESSIONAL PAPER 274 PLATE 53 .‘Vo‘ ,‘ "ll 4' -t I, ' PW '. PHOTOMICROCRAPHS OF HORNBLENDE-BIOTITE GNEISS AND MYLONITE GNEISS PLATE 53 . Typical hornblende—biotite gneiss, with broken original horn~ blende, h, and plagioclase, 1), crystals and recrystallized biotite, b, quartz, q, and apatite, (1, along shear zones. . Mylonite gneiss derived from hornblende gneiss. Relict plagioclase, p, and hornblende, h, grains are set in a fine— grained groundmass of biotite, b, quartz, q, and plagioclase, p. Apatite, a, and magnetite, m, are common accessory minerals. . Recrystallized hornblende porphyroblast in mylonite gneiss derived from hornblende gneiss. The groundmass is largely a fine-grained aggregate of plagioclase, quartz, and biotite, with a few ragged fragments of the original horn- blende, h. . Intermediate stages in the formation of mylonite gneiss from quartz monzonite gneiss. Relict microcline-perthite, m, plagioclase, p, and quartz, Q, crystals are set in a fine- grained groundmass of quartz and feldspar. Recrystal- lized quartz, q, stringers mark some of the more noticeable shear planes. . Mylonite gneiss derived from quartz monzonite gneiss. In plane-polarized light the apparent augen is surrounded by a fine-grained foliated aggregate of quartz, feldspar, and hematite. . Same as E, under crossed nicols. The augen is shown to be a rounded aggregate of quartz, q, and plagioclase, p, frag- ments which has not been comminuted as finely as the groundmass. PLATE 54 A. Deformed plagioclase, p, corroded and replaced by unde- formed microcline, m. B. Deformed plagioclase, p, corroded and replaced by unde- formed microcline, m, and quartz, q. C. Deformed plagioclase, p, with myrmekitic rims, corroded and replaced by microcline, m, and quartz, q. Note the relict myrmekitic quartz bleb now surrounded by micro- cline, cline. D. Hornblende-bearing rheomorphic quartz monzonite gneiss. Hornblende, h, plagioclase, p, and quartz, q, form a crys- tal loblastic aggregate which is in part replaced by micro— cline, m. E. Hornblende gneiss from an inclusion in rheomorphic quartz monzonite gneiss. Note the almost equant grains of horn- blende, h, and plagioclase, p, and the irregular grains of quartz, q. Apatite, a, is a common accessory. F. Deformed early plagioclase, p, corroded and replaced by microcline-perthite, m, and quartz, q. Note the preferen- tial replacement of deformed zones. GEOLOGICAL SI'RVHY PROFESSIONAL PAPER 274 PLATE 54 M3" ‘ _ ~ .9 .er . PHOTOMICROGRAPHS OF RHEOMORPHIC QUARTZ MONZONITE GNEISS AND INTRUSIVE QUARTZ MONZONITE GEOLOGICAL fil'RVl-ZY PROFESSIONAL PAPER 274 PLATE 55 PIIOTOMICROCRAPHS 0F INTRUSIVE QUARTZ MONZONITE PLATE 55 . Early plagioclase, p, corroded and replaced by microcline— perthite, m. Note the residual in Elusions of plagioclase. . Highly corroded plagioclase, p, relict enclosed in microcline- perthite, m. . Specimen from an area within the sto k Where no microcline was introduced. Deformed early lagioclase, p, showing relict texture is corroded and rep] ced by recrystallized plagioclase, mo, and epidote, e. . Pseudographic quartz, q, enclosed in both plagioclase, p, and microcline-perthite, m, hosts. E. Specimen of a fine-grained porphyritic dike. Original plagio— clase phenocrysts, p, enclosed in a micrographic ground- mass. . Specimen from a dike which had no microcline introduced. Early plagioclase; 12, showing relict texture is corroded and replaced by recrystallized plagioclase, rp, quartz, q, epidote, e, and chlorite, c. Shorter Contributions to General Geology 195 5—57 l GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 Tfiz’s Professional Paper was paélz’saea’ as separate cflapters, fl—M ‘ UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director (A) (B) (C) (D) (E) (F) (G) (H) (I) (J) (K) (L) (M) CONTENTS 1 \ [The letters in parentheses preceding the titles are those used to designate the separate chapters] Volcanic-rich middle and upper Eocene sedimentary rocks northwest of Rattlesnake Hills, central Wyoming, by Franklyn B. Van Houten Dakota group in northern Front Range foothills, Colorado, by Karl Mi Waagé ___________________________________ Basal Eagle Ford fauna (Cenomanian) in Johnson and Tarrant Counties, Tex., by Lloyd William Stephenson Characteristic Jurassic mollusks from northern Alaska, by Ralph W. Imlay _______________________________________ Owl Creek (Upper Cretaceous) fossils from Crowleys Ridge, southeast rn Missouri, by Lloyd William Stephenson Middle Ordovician rocks of the Tellieo-Sevier belt, eastern Tennessee, by Robert B. Neuman Ecology of Foraminifera' 1n northeastern Gulf of Mexico, by Orville L ‘Bandy ____________________________________ Palmlike plants from the Dolores formation (Triassic), southwestern Cdlorado, by Roland W. Brown ________________ Additions to the flora of the Spotted Ridge formation in central OregonL by Sergius H. Mamay and Charles B. Read__ Fossils from the Eutaw formation, Chattahoochee River region, Alabama-Georgia, by Lloyd William Stephenson _____ Stratigraphy of Middle Ordovician rocks in the zinc-lead district of Wisconsin, .Illinois, and Iowa, by Allen F. Agnew, Allen V. Heyl, Jr. C. H. Behre, Jr., and E. J. Lyons _____________________________________________________ Volcanic rocks of the El Modeno area, Orange County, Calif” by Robert F. Yerkes _______________________________ Metamorphism and the origin of granitic rocks, Northgate district, Coldrado, by T. A Steven ____________________ ’__ V 1 Page 15 53 69 141 179 205 211 227 313 335 UNITED STATES DEPARTMENT OF THE INTERIOR R 80 W PROFESSIONAL PAPER 274 PLATE 48 GEOLOGICAL SURVEY . . Outline of area covered by plate 49 WYOMING COLORADO ' Pliocene(?) Oligocene Upper Cretaceous Lower and Upper Cretaceous Lower Cretaceous i Benton shale 9 "c2 El.) :3 s 7‘ g m E b 75\ ' fi . E k/ & e .- MOUNTAIN § 9 7o , a) k; s ' S D: S S be S 6 “a s .e S 8 O A) S at S U E Q / a n u n.‘ .‘. ,- Unmapped sedimentary /\< (/rocks Hi i V x. Map compiled from aerial photographs. R. 80 W. \ 2:::::::::::::::‘ Land grid from U. 8. Bureau of Land . Management township plats, surveyed INTERIOR—GEOLOGICAL SURVEY. WASHINGTON, D C M R4141 in 1938739 I t t 0 Geology by T. A. Steven, R. B. Johnson, GEOLOGIC MAP OF THE NORTHGATE DISTRICT, COLORADO AND WYOMING G- 2000 0 Scale 1 :24, 000 10, 000 Feet i——-il~—l TRUE NORTH EXPLANATION SEDIMENTARY ROCKS Qal Alluvium Qt Talus, landslide, and alluvial-fan deposits st Dune sand, mostly stable th _ Terrace gravels Tnp North Park formation UNCONFORMITY Twr White River formation UNCONFOR’M/TY 2 Pierre shale %% Niobrara formation % Dakiota sandstone UNCONFOPM/TY Morrison formation 7/ // Sundance formation UN CONFORMITY Chugwater formation Forelle limestone, Pi, locally underlain by Satanka(?) shale, PS UN CONFORMITY METAMORPHIC AND lNTRUSIVE ROCKS Intrusive quartz monzonite E Dacite porphyry dikes pCu Undifferentiated metamorphic rocks Pegmatite Biotite-garnet gneiss Mylonite gneiss Quartz monzonite gneiss Includes local bodies of rheomorphic quartz monzouite gueiss pCh Hornblende gneiss i Includes local bodies of hernbleude—biotite grLeiss Contact Dashed where approximately located 50 Fault Showing dip; dashed where approximately located; dotted where concealed; U, upthrown side, D, dowrithrowrt side 90 —1— Vertical fault L10 Strike and dip of beds 90 Strike of vertical beds 70 Strike and dip of foliation + Strike and dip Of vertical foliation 6O 75 1 Strike and dip of foliation and plunge 0f lineation 70 / Bearing and plunge Of lineation ’X‘ Fluor'spar mine CRETACEOUS TERTIARY QUATERNARY JURASSIC PERMIAN AND TRIASSIC PERMIAN FRE—CAMBRIAN UNITED STATES DEPARTMENT OF THE INTERIOR. GEOLOGICAL SURVEY EXPLANATIO TERTIARY PRE~CAMBRIAN ,————~——-fi // /// 4 V 7 v 7 / \ / '4' ‘-,\','/.\'.‘/ H \ ///// // -. . \\ //Twr//// " ‘ pCpL ,\ qum \ pCh4 " \p€L>\ //”'//// > A > r~ / / 20411,"): - \ White River Pegmatite Quartz monzonite Hornblende Undifferentiated gneiss gneiss metamorphic rocks formation // /;/Twr/;;; // /////// ////// ;;;//;///7//;;////;;/ \ //// /// .17 R. 79 W. GEOLOGIC MAP OF THE NORTHWEST PAIR" OF THE NORTHGATE DISTRICT, WYOMING AND COLORADO 5000 Feet I R. 80 W. 1000 Illlll 55 ___ _.A_ + Contact Strike and dip Vertical Dag/led where approx— of foliation foliation mafe/y /ocafed / / \ X / \ .. / /7 ’—/\ \ \ / . .../ / -. ~/fi"_\ \ \ WYOMING \_ I\ / ,’ j OQLORAEO / ‘ PROFESSIONAL PAPER 274 PLATE 49. ~ 70 -‘\ Plunge of Trend lines lineation of layers Taken from aer/a/ pfiofograp/Is TRUE NORTH I Geology by T. A. Steven, 1948 402890 0 - 56 (In pocket)