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Brachiopoda and Ostracoda of the
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Cobleskill Limestone (Upper Silurian) of Central New York
GEOLOGICAL SURVEY PROFESSIONAL PAPER 730
DOCUMENTS DEPARTMENT
AUG 2 8 1972
MWNAftr
QUIVERS*** 0C CAl*?0R»>iABrachiopoda and Ostracoda of the Cobleskill Limestone (Upper Silurian) of Central New York
By JEAN M. BERDAN
GEOLOGICAL SURVEY PROFESSIONAL PAPER 730
Descriptions and illustrations of 12 species of brachiopods (including one new species J and 2$ species of ostracodes (including four new genera and I/f. new species j
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY V. E. McKelvey, Director
Library of Congress catalog-card No. 70-189150
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price ?1 (paper cover)
Stock Number 2401—2056CONTENTS
Page
Abstract____________________________________________________ 1
Introduction________________________________________________ 1
Previous work__________________________________________ 1
Acknowledgments________________________________________ 3
Scope of the report____________________________________ 3
List of localities________________________________________   5
Paleoecology________________________________________________ 6
Age and correlation_________________________________________ 8
Systematic paleontology------------------------------------- 9
Phylum Brachiopoda____________________________________ 10
Class Inarticulata______________________________   10
Genus Craniops Hall._____________________ 10
Class Articulata__________________________________ 10
Genus Leptostrophia Hall and Clarke.. 10
Genus Morinorhynchus Havlifiek_______	11
Genus Eccentricosta Berdan_______________ 12
Genus Machaeraria Cooper_________________ 13
Genus Microsphaeridiorhynchus Sar-
tenaer_________________________________ 14
Genus Lanceomyonia Havlifiek_____________ 15
Genus Protathyris Kozlowski______________ 16
Genus Howellella Kozlowski_______________ 18
Phylum Arthropoda_____________________________________ 21
Class Crustacea___________________________________ 21
Subclass Ostracoda____________________________ 21
Genus Leperditia Rouault_________________ 21
Genus Garniella Martinsson_______________ 22
Genus Migmatella n. gen__________________ 22
Genus Dibolbina Ulrich and Bassler.. 23
Page
Systematic paleontology—Continued Phyllum Arthropoda—Continued Class Crustacea—Continued
Subclass Ostracoda—Continued
Genus Hammariella Martinsson_____________ 24
Genus Kloedeniopsis n. gen_______________ 24
Genus Tikiopsis n. gen___________________ 27
Genus Welleriopsis Swartz and Whitmore_____________________________________ 28
Kirkbyellid?, gen. and sp. indet_____	29
Hollinid?, gen. and sp. indet____________ 29
Genus Leiocyamus Martinsson______________ 29
Genus Primitiopsis Jones_________________ 30
Genus Halliella Ulrich___________________ 30
Genus Dizygopleura Ulrich and Bassler. 31 Genus Kloedenella Ulrich and Bassler..	37
Genus Eukloedenella Ulrich and Bassler______________________________________ 37
Genus Marginia Polenova__________________ 38
Genus Bonneprimites Swartz and Whitmore_____________________________________ 38
Genus Thlipsuropsis Swartz and Whitmore_____________________________________ 38
Genus Thlipsurella Swartz________________ 39
Genus Cytherellina Jones and Holl____	39
Genus Nunculina n. gen___________________ 40
References cited___________________________________________ 41
Index______________________________________________________ 45
ILLUSTRATIONS
[Plates follow Index]
Plate 1. 2.
3.
4. 0. 6.
Morinorhynchus?, Craniops, Eccentricosta, and Leptostrophia. Lanceomyonia?, Machaeraria?, Microsphaeridiorhynchus, Protathyris, and Howellella.
“Kloedenia," Kloedeniopsis, Welleriopsis?, Tikiopsis, and Leperditia. Hammariella, Garniella, Migmatella, and Dibolbina.
Dizygopleura.
Thlipsurella, Thlipsuropsis, Nunculina, hollinid?, kirkbyellid?, Halliella?, Marginia?, Cytherellina, Eukloedenella?, Bonneprimites?, Leiocyamus, Kloedenella, and Primitiopsis?.
in.IV
CONTENTS
Page
Figure 1. Index map showing generalized outcrop belt of Cobleskill Limestone and approximately equivalent formations in New York State showing
fossil localities________________________________________________________ 4
2-5. Diagrams showing:
2.	Nine transverse sections of Lanceomyonia? dunbari n. sp_________ 15
3.	Twelve transverse sections of Protathyris sulcata____________:__ 17
4.	Twelve transverse sections of Protathyris nucleolata________________ 19
5.	Inferred cross sections of three groups of North American beyrich-
iaceans____________________________________________________________ 25
6.	Scatter diagram showing length versus height of Dizygopleura hallii----	32
7.	Scatter diagram showing length versus height of Dizygopleura monostigma
n. sp__________________________________________________________________   35
8.	Drawing showing interior of left valve of Cytherellina crepiduloides n. sp_ 40
9.	Drawings showing transverse sections of Nunculina striatopuncta n. sp__	41
TABLE
Table 1. Distribution of brachiopods and ostracodes from the Cobleskill Limestone Page (Upper Silurian) of central New York________________________________________________ 7BRACHIOPODA AND OSTRACODA OF THE COBLESKILL LIMESTONE (UPPER SILURIAN) OF CENTRAL NEW YORK
By Jean M. Berdan
ABSTRACT
The Cobleskill Limestone is a thin unit that extends across New York from the westernmost part of Albany County on the east to Seneca County on the west. It is considered to be not younger than latest Silurian (Pridoli) in age, largely because it contains the coral Cystihalysites. The fauna belong to the Eccentrlcosta Zone of the Appalachians, known elsewhere in West Virginia, Virginia, Maryland, Pennsylvania, New Jersey, eastern New York, and Maine. Twelve brachiopods are described and illustrated, of which one species is new. Twenty-five ostra-codes are also described and illustrated, of which four genera and 14 species are new. Kloedeniopsis n. gen. includes some of the ostracodes formerly called Kloedenia in North America. Three ostracode genera—Garniella, Hammariella, Levocyamus— previously known only from the Baltic province in Europe are reported from North America for the first time.
INTRODUCTION
The Cobleskill Limestone is the youngest f ossiliferous formation of unquestioned Silurian age in central New York, and as such, its fauna, though small, is of exceptional interest. It is a thin unit which extends from West Township in Albany County (Goldring, 1935, p. 78) on the east to Seneca Falls in Seneca County on the west, a distance of about 130 miles. According to Rickard (1962, p. 26), its maximum thickness is about 15 feet, but at the type locality near Cobleskill Creek, along the road between Braymansville and Howes Cave in Schoharie County, it is only 9 feet thick. In the eastern part of the outcrop belt the Cobleskill rests uncon-formably upon the Brayman Shale of Silurian age (Rickard, 1962, p. 26), but west of Deck in Herkimer County the Oxbow Dolomite of Late Silurian age appears beneath it. Throughout its extent the Cobleskill is overlain by the Chrysler Limestone of Silurian and Devonian age.
Lithologically the Cobleskill varies from an impure crinoidal limestone to a fine-grained dark-gray aphanitic limestone to buff-colored or drab dolomite. Limestone is more common in the eastern part of the outcrop belt, although even in Schoharie County it tends to be dolo-mitic. West of Clockville in Madison County the for-
mation is largely dolomite (Rickard, 1962, p. 26) except for an area of limestone at Aurelius Station, Frontenac Island, and Seneca Falls in Cayuga County. Fossils are most abundant in the limestone, and especially in the crinoidal limestone, which is commonly associated with biostromal beds of corals.
PREVIOUS WORK
The stratigraphy of the Cobleskill Limestone has been more thoroughly studied than its fauna, probably in part because the dolomitic nature of the rock makes it difficult to extract satisfactory specimens of fossils, and in part because the more dolomitic parts of the formation have very few fossils. Hall (1852, p. 321-322) called it the “coralline limestone” and described it as “* * * a thin mass of limestone, characterized by an immense number of corals, chiefly favosites * * * which forms a band so distinct from any other limestone that it has been for many years known by this name.” He considered it the eastern extension of the Niagara (Lock-port) Limestone of Middle Silurian age, but recognized that the fauna was not exactly the same and so described and illustrated the fossils separately (Hall, 1852, p. 322-338, pis. 72-78). According to Hartnagel (1903, p. 1113-1114), Clarke (in Merrill, 1902, p. r42) was the first to use the name Cobleskill for the “coralline limestone” of Hall and other geologists, but he did not discuss the formation or designate a type section. The most thorough stratigraphic study of the Cobleskill was made by Hartnagel (1903), who demonstrated for the first time that the Cobleskill was not the equivalent of the Lockport, but considerably younger, and published lists of fossils from the Cobleskill at 12 localities in Schoharie County and three localities in the vicinity of Union Springs in Cayuga County.
Grabau (1906, p. 104-111) redescribed the Cobleskill Limestone in the Schoharie and Cobleskill areas, and illustrated the more common fossils. In addition, local details of the stratigraphy and descriptions of lo-
12
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
calities are given in New York State Museum Bulletins for the following quadrangles: Auburn-Genoa (Luther, 1910), Skaneateles (Smith, 1935), Tully (Clarke and Luther, 1905), Syracuse (Hopkins, 1914), Richfield Springs (Rickard andZenger, 1964), and Berne (Goldring, 1935).
Recently, Rickard (1962, p. 23-27) has redescribed and redefined the type section of the Cobleskill at Howes Cave and described its occurrence and lithology across the State from Schoharie County to Seneca Falls, Seneca County, the westernmost exposure of undoubted Cobleskill. Rickard subdivided the Cobleskill at its type section into two parts, a lower massive unit and an upper, thin-bedded, more fossiliferous unit. In the upper unit, he included fossiliferous beds as high as a break 9 feet above the base of the formation. This redescription increases its thickness over the 6 feet given by Grabau (1906, p. 106) and includes all the markedly fossiliferous beds there in the Cobleskill.
The fauna of the Cobleskill has not been described as a unit since Hall (1852, p. 322-338, pis. 72-78) described and illustrated 30 species, all from Schoharie, N.Y. Of these 30 species, three were corals, two stromatoporoids, nine brachiopods, five pelecypods, six gastropods, three cephalopods, one trilobite, and one ostracode. Hart-nagel (1903, p. 1126-1128) listed, but did not describe, 60 species for Schoharie County as a whole. These were grouped as follows: five corals; two stromatoporoids, one form identified as Chaetetes, which may be either a favositid coral or a bryozoan; four bryozoans; one cri-noid; 12 brachiopods; eight pelecypods; six gastropods; nine cephalopods; two worms not including Tentacu-lites; six trilobites; and four ostracodes, two of which were lumped as “Beyrichia, 2 species.” Grabau (1906, p. 317) added one horn coral to Hartnagel’s list, to make a total of 61 species.
Hartnagel (1903, p. 1132-1133) also listed 30 species from the Cobleskill at Frontenac Island, in Cayuga Lake off Union Springs. Of these 30 species, 16 also appear in the list for Schoharie County. However, four and a possible fifth, are species normally confined to the Manlius Limestone of Eearly Devonian age in other parts of the State; as indicated previously (Berdan, 1964, p. B10-B11), these specimens were probably either from a mixed collection or were misidentified, as they have not been found elsewhere in the Cobleskill nor have they been found in later collections from Frontenac Island. In addition, four of the other 10 species listed by Hartnagel for this locality also occur in the Akron Dolomite (Upper Silurian) of the Buffalo area.
Flower (1947, p. 252; 1948, p. 6-7) described two new species of cephalopods from the Cobleskill at Schoharie, N.Y., listed the cephalopod genera (1947, p. 250) and
indicated (1948, p. 3-4) that the trochoceroids described by Hall (1852) as Trochoceras gebhardii and T. tur-binata should be reassigned to Mitroceras and Foersteoceras, respectively.
The only ostracode described originally as coming from the Cobleskill is Leperditia jonesi Hall, 1859, which is believed to be a junior synonym of L. scdlaris (Jones, 1858a, b). The latter is probably from the Bertie Limestone (Upper Silurian) at Williamsville, N.Y. However, at least one species, Dizygopleura hallii (Jones, 1890), which has been listed by Bassler and Kel-lett (1934, p. 66) and Warthin (1937, card 58) as coming from the Manlius Limestone (Lower Devonian), actually comes from the Cobleskill, as indicated by fossils on the same slab as the holotype (BMNH In 35128) in the British Museum (Natural History) collections. The holotype of Dizygopleura clarkei (Jones, 1892), here considered a junior synonym of D. hallii, also comes from the Cobleskill as discussed on page 33.
Howell (1947) described two new “varieties” of spiriferid brachiopods, Howellella vanuxemi hart-nageli and H. octocostata humilis, from the Cobleskill Limestone of the Schoharie area and Frontenac Island. He also identified several Cobleskill specimens as Howellella keyserensis (Swartz, 1923). The types of Howell’s varieties have not been examined, but his illustrations (Howell, 1947, pi. 2) show them to be more coarsely plicate than any of the specimens studied for the present report.
In addition to papers directly concerned with the Cobleskill on a stratigraphic or paleontologic basis, there are several reports on related formations in which fossils are described which also occur in the Cobleskill. To the west, Grabau (1900, p. 363-373) discussed, described and illustrated the fauna of the “Manlius Limestone,” now the Akron Dolomite (Upper Silurian), of Erie County, N.Y.; he listed 12 species from the Akron—one plant, one coral, six brachiopods, two gastropods, one cephalopod, and one ostracode. Although he noted the similarity of this fauna to that of the “Coralline limestone” in the eastern part of the state (Grabau, 1900, p. 352), he failed to recognize that this suggested an equivalence in age (Berdan, 1964, p. B6-B7), a possibility which was left for Hartnagel (1903, p. 1138-1141) to discuss.
To the southeast, Weller (1903) described the fauna of the Decker Limestone (Upper Silurian) of New Jersey, which contains several species that also occur in the Cobleskill. He listed 48 species from the Decker, from the following groups:	six
corals, three bryozoans, 20 brachiopods, six pelecypods, five trilobites, and eight ostracodes. Weller (1903, p. 74) noted that 32 of the 48 species had not been described except from the Decker; of the remain-INTRODUCTION
3
ing 16 species, six are characteristic of the Cobleskill, and most of the other species are either long ranging or doubtfully identified. Pie therefore concluded that the Decker and Cobleskill should be correlated.
Swartz and Whitmore (1956, p. 1039-1041) described and illustrated 17 species of ostracodes and one brachio-pod from the Decker Limestone in the Nearpass section on Wallpack Ridge, in northern New Jersey.
Recently, Hoar and Bowen (1967) discussed the stratigraphy of the Rondout (Upper Silurian and Lower Devonian) of the Hudson Valley and described from it 14 brachiopods, one coral, and one bryozoan. The Rondout, as revised by Rickard (1962, p. 29-31), includes beds equivalent to the Cobleskill in the Hudson Valley, and many of the brachiopods described by Hoar and Bowen (1967) also occur in the type Cobleskill.
ACKNOWLEDGMENTS
This study was begun under the guidance of Prof. C. O. Dunbar of Yale University, whose advice and assistance is gratefully acknowledged. I am deeply indebted to the following for the loan of type specimens and various other assistance: Dr. Rousseau H. Flower and the late Dr. Winifred Goldring, formerly of the New York State Museum; Drs. John G. Broughton, Donald W. Fisher, and Lawrence V. Rickard, and Mr. Clinton F. Kilfoyle of the New York State Museum and Science Service; Mr. Meredith Johnson, former state geologist of New Jersey; and Dr. G. Arthur Cooper and the late Dr. R. S. Bassler of the U.S. National Museum. Especial thanks are due Prof. F. M. Swartz of Pennsylvania State University, who generously made his ostracode collection available for study. W. A. Oliver, Jr., of the U.S. Geological Survey, kindly provided locality data and samples from localities not visited by me.
The writer is particularly grateful to Mr. R. M. Logie, who not only gave permission for the study of his collections, but also made available his field notebooks, sections, and unpublished manuscript.
In conclusion, I would like to thank my assistants, especially Mrs. Marija Balanc, who patiently tolerated tedious hours of picking and preparing ostracodes.
SCOPE OF THE REPORT
This report is based on part of a dissertation submitted for the degree of Doctor of Philosophy at Yale in 1949. The original manuscript described fossils from the Manlius Limestone as well as from the Cobleskill Limestone ; these fossils were obtained from collections made by R. M. Logie during the summers of 1931-33. Logie, as a graduate student at Yale, had studied the stratigraphy of the “Manlius Group” of Clarke and Luther (1905), which included the Cobleskill, Chrysler, and
Manlius Limestones. His unpublished manuscript, notes, and collections were used in the preparation of the present report. The Chrysler Limestone, which lies between the Cobleskill and the Manlius, is virtually unfossiliferous. The faunal studies of the original dissertation wrere therefore concerned with the latter two limestones. It soon became apparent that whereas some of the collections considered Manlius by Logie strongly resembled the Coeymans Limestone (Lower Devonian) in both lithology and fauna, the Cobleskill fauna differed markedly from both the typical Manlius and the Coeymans (Berdan, 1964, p. B15-B16). Rickard (1962), by detailed stratigraphic tracing, has demonstrated that the Manlius and Coeymans interfinger, and therefore it seems obvious that the Manlius and Coeymans faunas should be studied together. Hence it has seemed desirable to extract the descriptions of the Cobleskill fossils and present them as a separate unit.
Work was concentrated on the brachiopods and ostracodes because these groups are among the more abundant elements of the fauna, both in number of species and in number of individuals. Also, in general, they are the best preserved. The next most important group is probably the corals, which are reasonably well preserved at some localities but tend to be spotty in their distribution. Although the number of coral species is not great, they are being studied by W. A. Oliver, Jr., because the association is quite interesting. Gastropods and pelecypods are rather common, but almost always poorly preserved. Cephalopods and trilobites are scarce, and good specimens are rare. Bryozoa, tentaculites, and stromatoporoids are present but unstudied. Conodonts are also present but undescribed.
In the dissertation as originally submitted, 11 species of brachiopods and 12 of ostracodes were described and illustrated. In this report, the number has risen to 12 species of brachiopods and 25 of ostracodes. Although this change is due in part to the increasing specialization in ostracodes on the part of the author, it is also due to the difficulty of collecting a complete sample of a fauna composed of microfossils. Whereas it is unlikely that many more species of brachiopods will be found in the Cobleskill, it is certain that additional ostracodes will be found in the future. Tantalizing fragments of undescribed species turn up in almost every new collection.
Most of the brachiopods from the Cobleskill have been previously described by Hall (1852, 1859), Vanuxem (1842), Grabau (1900), Weller (1900,1903), and Schu-chert (1903a), but these fossils are currently reassigned to other genera (Berdan, 1964, p. B15; Hoar and Bowen, 1967; Bowen, 1967). The brachiopods described herein do not include Atrypa “reticularis” and Leptaena4
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
“rhomboidalis” both of which were reported by Hart-nagel (1903, p. 1126-1127) from the Cobleskill of Schoharie County, because they were not found in the collections studied for the present report. In contrast, only seven of the 25 taxa of ostracodes included in this paper have been previously described; and of these seven species, five have not been previously reported from the Cobleskill. This discrepancy may reflect the lack of adequate microscopes and specialists in the early years of the century when most of the taxonomic work was done on the fossils from this formation. Hartnagel and others recognized the abundance of ostracodes in the Cobleskill but lacked the equipment and background to describe them.
This report is based on collections from the Cobleskill outcrop belt from 12 localities extending from the Seneca Falls 7-minute quadrangle in the west to the Schoharie 71/£-minute quadrangle in the east. These localities are shown in figure 1. Collections were made at
seven of these localities by R. M. Logie, and these were prepared and studied in the laboratory by me. The most fossiliferous localities as indicated by Logie’s collections were re-collected, and four additional localities were visited and collections made. The westernmost locality, at Seneca Falls, has not been seen by me, but material collected by W. A. Oliver, Jr., has been studied. The places from which collections were made are described in the “List of localities” (p. 5), and collection numbers are given to indicate how many collections were made from each locality. The geographic distribution of described species is shown in table 1. The collections generally were not made with stratigraphic control within the Cobleskill Limestone because the formation is thin, and at most localities the section is not complete. However, to judge from places where most of the formation is exposed, the fauna does not appear to change vertically.
Although the Cobleskill Limestone is fairly fossilif-
Outcrop of approximately equivalent formations; Akron Dolomite in western New York and part of Rondout Limestone in eastern New York
25
L_l
0
j_l_
75 MILES
RICHMOND JjrOSAi ■'CBA '
t/y | Y 'QUEENS
'kings
Figure 1.—Generalized outcrop belt of Cobleskill Limestone and approximately equivalent formations in New York State
showing fossil localities. Modified from Rickard (1969, pi. 10).INTRODUCTION
5
erous, it is difficult to extract good specimens. Much of the limestone is aphanitic and breaks through rather than around the fossils, and in the more dolomitic parts of the formation the fossils are generally poorly preserved. Only one locality (fig. 1, loc. 3, Aurelius Station, USGS 3395-SD) has been found where the brachiopods are partially silicified, and here the ostra-codes are so poorly silicified that they cannot be determined from residues, although excellent specimens may be broken out of the rock. Most of the brachiopods and many of the ostracodes were prepared mechanically with rock nippers, needles, and vibratools. However, one locality, at Spring Street, Schoharie (fig. 1, loc. 11), has yielded free specimens, and most of the illustrated ostracodes have come from this place. Many of these species have been found at other localities, and as those that occur elsewhere usually are the most abundant species in the Schoharie collections, it seems reasonable to assume that the association of ostracodes at Schoharie is representative of the Cobleskill at other localities across the State, even though the less common species may have been found only at Schoharie. Two collections were originally made from Schoharie by Logie, and because of the ease of preparing the ostracodes from this locality five additional collections from here were made by me at later dates.
Because of the number and variety of ostracodes found at the Spring Street locality it seems desirable to discuss it more fully than possible in the “List of localities.” According to R. M. Logie’s field notes, dated September 7, 1932, this locality is the same as Brown’s quarry, described by Hartnagel (1903, p. 1120-1121) and Grabau (1906, p. 106-107, 236-237) as being a quarter of a mile southeast of the Schoharie Post Office, in the hollow between the cemetery and the road leading east from the post office. Hartnagel (1903, p. 1120) listed the fossils from this locality and mentioned that the faunas from the different layers vary somewhat. In 1932, Logie described the collections he made as coming from the north edge of the road and just below it, a quarter of a mile east of the Schoharie Post Office, Cromer’s place. He noted that there was hardly any vestige of quarrying left, and the spot is no longer called “Brown’s quarry,” that name being used for another quarry. By 1946, the post office had been moved to the northern end of the village of Schoharie, so that the earlier locality descriptions are no longer applicable. Collections made by me in 1950 (USGS 3393-SD), 1964 (USGS 7283-SD), 1967 (USGS 8062-SD, USGS 8063-SD), and 1968 (USGS 8439-SD) were all from ledges and the dirt beneath them on the south side of the road; that is, not precisely the same spot as R. M. Logie’s collections. One collection made
in 1967 (USGS 8064—SD) was made from the north side of the road. By 1967 the section was very badly overgrown, and some of the outcrops on the north side of the road had been covered by bulldozing for a small dam. The Brayman Shale (Upper Silurian)—reported by Hartnagel (1903), Grabau (1906), and Logie—is apparently no longer exposed.
Hartnagel (1903, p. 1121) described three units at this locality that he considered to belong to the Coble-skill, as follows: 3 feet, 10 inches of limestone at the base, 1 foot, 4 inches of limestone (marble layer), and 10 inches of thin-bedded, somewhat arenaceous limestone. It is difficult now to recognize here any of these subdivisions. USGS collection 8063-SD may have come from Hartnagel’s “marble layer,” as it was obtained from a highly crinoidal limestone and the dirt just beneath it. On the other hand, Logie’s original collection YPM 5244/146 may have come from the thin sandy layers at the top of the Cobleskill which Hartnagel (1903) stated to have abundant Machaeraria’i. lamel-lata, as that species is abundant in Logie’s collection. These thin sandy layers are apparently no longer exposed, although the overlying Chrysler Limestone is exposed in ledges farther up the road.
Ostracodes from the various collections from this locality were obtained primarily by boiling, washing, and picking the dirt, but a few were extracted mechanically. Specimens in the rock are commonly better preserved than those in the dirt, especially with regard to fine surface ornamentation, and thus they supplement the more abundant but slightly corroded free specimens. It should be noted that the free specimens are commonly somewhat compressed or crushed; thus, although an effort was made to select only uncrushed specimens for measurement, there may be an element of error, especially in the measurements of height.
Examination of specimens in the bedrock is also a useful check against the dirt collections that might have been contaminated by material from higher formations. Dirt from collection USGS 8062-SD was found to contain silicified ostracodes from the overlying Coeymans and Kalkberg Limestones as well as specimens from the Cobleskill. Described specimens from this collection were extracted from rock.
LIST OF LOCALITIES
The following fossil localities are shown in figure 1.
1. Abandoned quarry just north of house at end of private road at and just southwest of the city limits of Seneca Falls, Seneca Falls 7^-minute quadrangle, Seneca County. USGS 6084-SD, W. A. Oliver, Jr., collector. McQuan’s quarry of Hartnagel (1903, p. 1137).
447-769 0-72-2BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
6
2.	Frontenac Island, in Cayuga Lake west of Union
Springs, from southeast end of island, Stroma-topora beds, Union Springs 714-minute quadrangle, Cayuga County. USGS 3389-SD, J. M. Berdan collector. See Hartnagel (1903, p. 1130-1134).
3.	About 0.6 of a mile east of Aurelius Station on New
York Route 326, Cayuga 714-minute quadrangle, Cayuga County. YPM 5244/1.56, R. M. Logie collector; YPM 5244/14, R. M. Logie collector; USGS 3395-SD, north side of Route 326, J. M. Berdan collector.
4.	Prospect Hill, at base of microwave tower, 2.7 miles
airline west of Franklin Springs, Clinton 7i/>-minute quadrangle, Oneida County. USGS 5207-SD, J. M. Berdan collector.
5.	Roadcut about 1 mile north of Oriskany Falls on
Route 12B, Oriskany Falls 7^-minute quadrangle, Oneida County. YPM 5244/88, R. M. Logie collector.
6.	Cut on side road to west and above New York State
Route 315, 0.5 mile south of Forge Hollow, Oriskany Falls 7p2-minute quadrangle, Oneida County. YPM 5244/90, R. M. Logie collector.
7.	In the hillside on the southwest side of highway,
above crossroads 1.1 miles southeast of Jerusalem Hill crossroads, West Winfield 71/>-minute quadrangle, Herkimer County. YPM 5244/108, R. M. Logie collector. This locality is probably near YPM 2594, C. E. Beecher collector, from “Jerusalem Hill, N.Y.” See Hartnagel (1903, p. 1167— 1169).
8.	About 200 feet west of the village of Howes Cave on
north side of road between Howes Cave and Bray-manville, Cobleskill 71/£-minute quadrangle, Schoharie County. Type section of Cobleskill. USGS 8065-SD, J. M. Berdan collector. About 4 feet below top of formation. See Hartnagel (1903, p. 1114-1115, 1124), Grabau (1906, p. 106) and Rickard (1962, p. 23).
9.	At head of the shorter of the two streams between
Central Bridge and Howes Cave, Schoharie 7p^-minute quadrangle, Schoharie County. YPM 5244/143, R. M. Logie collector. See Hartnagel (1903, p. 1124-1125) and Grabau (1906, p. 106).
10.	Ledges in pasture near dirt road branching off to
north from road between Central Bridge and Howes Cave, 1.5 miles west-southwest of Central Bridge, Schoharie 7p£-minute quadrangle, Schoharie County. USGS 7198-SD, J. M. Berdan collector. See Hartnagel (1903, p. 1125).
11.	Spring Street, Schoharie, N.Y.; first terrace going
east up hill before fork in road, about 800 feet
east of intersection with main street, across hollow south of St. Paul’s Cemetery, Schoharie 7y2-minute quadrangle, Schoharie County. YPM 5244/146, on the north edge of the road and just below it, Cromer’s place, R. M. Logie collector; YPM 5244/147, 400-500 feet south of Spring Street, R. M. Logie collector; USGS 3393-SD, south side of Spring Street, J. M. Berdan collector; USGS 7283-SD, dirt under ledges on south side of Spring Street, J. M. Berdan collector; USGS 8062-SD, dirt and thin-bedded limestone, south side of Spring Street, about 15-17 feet above top of small dam north of road, J. M. Berdan collector; USGS 8063-SD and USGS 8439-SD, crinoidal limestone and dirt beneath it, south side of Spring Street about 12 feet above top of dam, J. M. Berdan collector; USGS 8064-SD, about same level, north side of Spring Street, J. M. Berdan collector. See Hartnagel (1903, p. 1120-1121) and Grabau (1906, p. 106, 236-237).
12.	About one-third of a mile southwest of Shutter Corners, Schoharie 714-minute quadrangle, Schoharie County. YPM 5244/150, R. M. Logie collector. Also about 0.4 of a mile south of Shutter Corners, ledges in pasture south of road, Schoharie 714-minute quadrangle. USGS 3390-SD, J. M. Berdan collector. See Hartnagel (1903, p. 1116-1119) and Grabau (1906, p. 107).
PALEOECOLOGY
As this report was designed primarily as a systematic study of two groups of Cobleskill fossils, it is not possible to make firmly based statements about the overall paleoecology of the fauna. However, some observations concerning fossil occurrences may be made and some tentative conclusions drawn from them. As indicated in figure 1, the fossils studied came from three general areas in the Cobleskill outcrop belt: (1) A western area near the north end of Cayuga Lake, (2) a central area south and west of Utica, and (3) an eastern area in Schoharie County. Table 1 shows the occurrences of species at the localities in these areas, arranged from west to east. Table 1 indicates certain differences between the western and eastern assemblages; for example, Prota-thyris sulcata has not been found in any of the eastern collections, apparently being replaced by Protathyris nucleolata, and Machaeraria ? lamellata has not been found in the western collections. On the other hand, Eccentricosta jerseyensis is found in the eastern and central collections, and although not found in recent collections from the western localities, it was reported by Hartnagel (1903, p. 1133) from Frontenac Island. It seems probable that the differences in distribution ofPALEOECOLOGY
7
some of the brachiopods and ostracodes were due to differences in the paleoenvironment, rather than to deposition of the Cobleskill as a time-transgressive formation.
The Cobleskill in the western area contains biostromes that are largely composed of stromatoporoids together with associated horn corals. Nonbiostromal beds are of two types: hard dark-blue-gray aphanitic limestone, which breaks with a conchoidal fracture and softer drab buff-weathering thin-bedded magnesian limestone. At Aurelius Station (fig. 1, loc. 3), Protathyris sulcata and Leperditia scalaris are most abundant in the aphanitic limestone, and Microsphaeridiorhynchus litchfieldensis and Howellella are more common in the drab buffweathering beds. Both ostracodes and brachiopods occur in interstices of the biostromal beds, but are commonly broken and difficult to identify. There is some indication, however, that Protathyris nucleolata tends to replace P. sulcata in the biostromes. The association
of P. sulcata, Leperditia scalaris, and Kloedeniopsis hartnageli in aphanitic limestone is found as far east as Forge Hollow (fig. 1, loc. 6) but has not been found in the easternmost exposures of Cobleskill.
Biostromal beds are apparently lacking in the central group of localities, and the Cobleskill in this area tends to be more dolomitic than it is either to the east or west. The collection from Oriskany Falls (fig. 1, loc. 5) is of interest because although the ubiquitous ostracodes Leperditia scalaris and Kloedeniopsis hartnageli are present, they are associated with small gastropods rather than with brachiopods. Otherwise the faunal associations in this area seem to be intermediate between those to the west and those to the east.
The eastern localities, like the western localities, have biostromal beds but the type of biostrome is different. At Shutter Corners (fig. 1, loc. 12) and west of Central Bridge (fig. 1, loc. 10), the biostromes are largely composed of colonial corals, rather than stromatoporoids.
Table 1.—Distribution of brachiopods and ostracodes from the Cobleskill Limestone (Upper Silurian) of central New York
[Locality numbers refer to those in fig. 1 and in the “List of Localities”]
Locality
Western	Central	Eastern
123456789	10	11	12
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
?
X
X
X
X
X
X
X
X
X
X
Brachiopoda
Craniops ovata (Hall)________________________________________
Leptostrophia bipartita (Hall)_______________________________
M orinorhynchus? interstriatus (Hall)_______________ X	X
Eccentricosta jerseyensis (Weller)___________________________
Machaeraria? lamellata (Hall)________________________________
Machaeraria cf. M. deckerensis (Weller)______________________
M icrosphaeridiorhynchus litchfieldensis (Schu-chert).
Lanceomyonial dunbari n. sp______________________________ X
Howellella corallinensis corallinensis (Grabau)___ X	?
corallinensis eriensis (Grabau)_____________________ X
Protathyris sulcata (Yanuxem)________________________________
nucleolata (Hall)______________________________ X	X
Oatracodes
Leperditia scalaris (Jones)_____________________________ X	X	X	X	X	X
Garniella concenlrica n. sp________________________________________________________________ X
Migmatella martinssoni n. gen., n. sp______________________________________________________ X
Dibolbina reticruminata n. sp_______________________________________________________________________________________
Hammariella warthini n. sp__________________________________________________________________________________________
Kloedeniopsis hartnageli n. gen.,	n. sp__________________ X	X	X	X	X	X	X ______________
barretti (Weller)____________________________________________________________________________ X _______________
Tikiopsis denticulata n. gen., n. sp___________________________________________________________________________ X
Welleriopsisl pustulosa n. sp_______________________________________________________________________________________
Leiocyamus punctatus n. sp_________________________________________________________________ X X ________________ X
sp. A__________________________________________________________________________________________________________
sp. B............................................................ X -------------------------------------------
Halliellal sp_______________________________________________________________________________________________________
Dizygopleura hallii (Jones)_______________________________________X X -------------- X X X --------------------- X
monostigma n. sp_______________________________________________________________________________________________
viafontinalis n. sp____________________________________________________________________________________________
costata Ulrich and Bassler_____________________________________________________________________________________
Kloedenella sp________________________________________________________ X X X _______________________________________
Eukloedenellal weldae n. sp______________________________________________________________________________________  X
Bonneprimitesl breviformis Swartz and Whitmore______________________________________________________________________
Thlipsuropsis inaequalis (Ulrich and Bassler)_______________________________________________________________________
X -------------------------------------------------------     X
------------- X
X
x"
X
X
x’
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Thlipsurella parva n. sp______
Cytherellina crepiduloid.es n. sp___________________________________ X
Nunculina striatopuncta n. gen., n. sp___________________________________________________________ X
X
X
X
X
X
X
X
X
X
X
x"
X
x”
X8
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
and may have been responsible for Hall’s (1852) name of “Coralline limestone” for the Cobleskill. In addition, at these and other localities, especially Spring Street at Schoharie (fig. 1, loc. 11), the Cobleskill contains considerable amounts of pelmatozoan debris, especially pieces of stem which may be 1 cm long or longer. Some beds are largely composed of this material and could be considered “crinoidal” limestone, but in others the pelmatozoan debris is sparsely and randomly distributed in a fine-grained matrix, as at the type section of the Cobleskill at Howes Cave (fig. 1, loc. 8). At first glance, the more “crinoidal” beds might be taken for calcareous sands deposited in a high-energy environment; but the presence of unbroken pieces of pelmatozoan stem, complete brachiopods and complete carapaces of ostracodes, together with fine-grained matrix in the interstices of even the most “crinoidal” rock, suggests that these beds represent plantations of crinoids or cystoids which disintegrated in place and were only slightly winnowed by wave or current action. Hyman (1955, p. 117-118) has discussed the relationship of various small crustaceans with living crinoids, and although none of those she mentioned were ostracodes, it seems possible that some of the large ostracodes found in the Cobleskill, such as Tikiopsis denticulata, may have been associated with the pelmatozoans, as they appear to be restricted to the beds of pelmatozoan debris.
Hoar and Bowen (1967, p. 10-13) and Harper (1968) have described the facies changes and discussed the paleoenvironment of the Kondout Formation of the Hudson Valley, part of which is the temporal equivalent of the Cobleskill Limestone. They have suggested that the thin-bedded dolomitic facies was deposited on subaerially exposed mudflats behind reefs and banks which developed parallel to a north-south-trending shoreline not far to the east. The reefs and banks are now represented by a limestone facies containing corals and stromatoporoids. The amount of limestone in the formation increases to the southwest, away from the shoreline, and is greatest in the vicinity of Accord (Port Jackson). According to Goldring (1935, p. 78), the easternmost exposure of the Cobleskill, east of West Township, contains stromatoporoids. This locality is nearly due north of Accord, and might suggest a facies similar to that of the Glasco Member of the Rondout at Accord, with implied similar depth of water and distance from shore. The localities near Schoharie, on the other hand, contain coral biostromes and beds of pelmatozoan debris and suggest slightly deeper water. The more dolomitic central localities and the western stromatoporoid biostromes may indicate a shoaling toward the west. The general picture, therefore, is of a broad, shallow sea or bay with a slightly asymmetric
bottom profile, being slightly deeper to the east. The presence of pelmatozoans and corals suggests that the salinity on the reefs and banks was nearly that of normal sea water and that circulation was not restricted. It is not certain whether the absence of the Cobleskill east of West Township is due to nondeposition on a shallow bar, or erosion prior to deposition of the Thacher Member of the Manlius Limestone, but the stromatoporoid beds at West Township suggest the latter.
AGE AND CORRELATION
The Cobleskill Limestone of Central New York is generally considered to be the stratigraphic equivalent of the lower part of the Rondout Limestone of eastern New York, the Decker Limestone of New Jersey, and the Eccentricosta Zone of the Iveyser Limestone of Pennsylvania, Maryland, and West Virginia (Rickard, 1962; Berdan, 1964). Weller (1903, p. 74-75) noted that Barrett (1878) was the first to recognize the similarity between fossils in what is now the Decker Limestone at the Nearpass quarries in northern New Jersey and those from the “Coralline limestone” at Schoharie. Schuchert (1903a, p. 417) commented on the resemblance of his “Manlius” formation in Maryland, which would be the lower part of the Keyser, to the “Coralline limestone” in central New York. Hartnagel (1903) discussed the position of the Cobleskill equivalent in the Hudson Valley. Although there is little question about the general equivalence of the Eccentricosta Zone in the Appalachians, details still remain to be worked out. For example, Hartnagel (1903, p. 1141-1152) considered the “Middle ledge” of the cement miners in the Hudson Valley, now the Glasco Member of the Rondout Limestone, to be the Cobleskill equivalent, and so called it Cobleskill in his paper. Hoar and Bowen (1967, p. 14), however, believe the Cobleskill to be the equivalent of the Wilbur, Rosendale, and Glasco Members— not just the Glasco. Whether the Cobleskill represents all or only part of the Eccentricosta Zone will have to be determined by a more detailed study of all groups of fossils within it as related to measured sections.
Recently Hoar and Bowen (1967, p. 15-17) and Bowen (1967, p. 11-16) have summarized the evidence of the brachiopods for general correlations, and have provided range charts for the Rondout and Keyser, respectively. To date, the ranges of ostracodes in the Keyser, Decker, and Rondout are too poorly known to make them useful for any precise correlation. Ulrich and Bassler (1913) described 29 species of the Keyser ostracodes of which 12 are from the Eccentricosta Zone, but ranges within the zone are not well defined, and even random sampling indicates that there are manySYSTEMATIC PALEONTOLOGY
9
more species to be described. Weller (1903, p. 252-257) described eight species (one based on a female of one of his other species) from the Decker at the Nearpass section, New Jersey, most of which came from the top 5 feet of the formation. Swartz and Whitmore (1956) added to the ostracode fauna from the same locality by describing 10 new species, all but three of which also came from the upper part of the formation. The ostra-codes of the Rondout are undescribed. Of the described ostracodes from the Keyser and Decker, only four have been found in the Cobleskill; these are Kloedeniopsis barretti, Dizygopleura, costata, Bonneprimites ? brevi-formis, and Thlipsuropsis inaequalis. In addition, Leperditia sccdaris from the Cobleskill has been reported from the Decker.
The few ostracodes in common between the Cobleskill and the Decker and Keyser might be interpreted as due either to differences in facies, or to lack of exact contemporaneity, or to both. Further detailed collecting through measured sections may help to determine which ostracodes are controlled by facies and which are widespread, short ranging, and therefore useful biostrati-graphically. The need for such collecting is shown by a random sample from the Decker at Shawnee on Delaware, Pa. (USGS collection 6060-SD), which contains Dizygopleura costata, Leiocyarrms sp., and Migmatella sp.—all forms that have not previously been known from the Decker and that are the same as or close to species from the Cobleskill. This collection also contains LimMnaria? muricata (Ulrich and Bassler, 1923), a distinctive ostracode that occurs at the top of the Tonoloway Limestone (Upper Silurian) and in the base of the Keyser in Maryland, in the Wilbur Member of the Rondout in the Hudson Valley, and also in the Hardwood Mountain Formation (Upper Silurian) in Maine, but has not as yet been found in the Cobleskill. The Hardwood Mountain also contains a species of the brachiopod E' ccentricosta and the ostracodes Dibolbina sp. and Dizygopleura sp. aff. D. costata, which suggests that it may be close to the Cobleskill in age, although some of its other ostracodes would indicate that it is slightly older.
Hartnagel (1903, p. 1138-1141) correlated the “Bullhead” limestone (now Akron Dolomite) of the Buffalo region in western New York with the Cobleskill Limestone of central New York on the basis of the fauna described by Grabau (1900). Rickard (1962, p. 25) has reviewed the literature on the Akron, and concluded that the relationship between it and the Cobleskill is as yet uncertain. However, the resemblance between the Akron fauna as described by Grabau (1900) and that of the Cobleskill is so strong that it would seem that the burden of proof would be on those who sug-
gest that the two formations are not equivalent. In particular, the presence of Protathyris sulcata and the cephalopod Mitroceras gebhardii (Hall, 1852) in both formations seems most suggestive. However, the fauna of the Akron should be restudied to confirm the identifications and to determine whether any additional species can be found. Other than Leperditia scalaris, no ostracodes have been reported from the Akron, but because of the dolomitic character of the rock they may not have been preserved.
A. J. Boucot (written commun., 1967) has remarked that the brachiopods of the Eccentricosta Zone are endemic in character and cannot be directly correlated with the standard European section. The presence of Cystihalysites in the Cobleskill and other formations of this zone indicates that the Cobleskill is not younger than Silurian, and it has been considered by Berry and Boucot (1970, p. 33) to be Pridolf in age.
The larger beyrichiid ostracodes, like the brachiopods, seem to be endemic in character and restricted to the Appalachian faunal province, although a related genus, Welleriella Abushik, 1968, occurs in the Lower Devonian (Ivane horizon) of Podolia. However, it is interesting that among the smaller ostracodes there are three genera—Hammariella Martinsson, 1962, Garniella Martinsson, 1962, and Leiocyamus Martinsson, 1956—which have not previously been described from North America but which occur in the Baltic province. Perhaps eventually the ostracodes will be of more use in intercontinental correlation.
SYSTEMATIC PALEONTOLOGY
Suprageneric classification of the brachiopods in the present report is based on the “Treatise on Invertebrate Paleontology, Part H, Brachiopoda 1 and 2” edited by Moore (1965). Suprageneric classification of the ostracodes is based in part on the “Treatise on Invertebrate Paleontology, Part Q, Arthropoda 3” edited by Moore (1961), but the beyrichiid genera are classified according to Martinsson (1962).
The terms used herein for morphologic features of the brachiopods are largely those used in the “Treatise on Invertebrate Paleontology, Part H, Brachiopoda 1.” Morphologic terminology for the ostracodes is based on the “Treatise on Invertebrate Paleontology, Part Q, Arthropoda 3,” with the exception of terms used for the beyrichiids which follow those proposed by Martinsson (1962) and Henningsmoen (1965). The terminology used in Moore (1961) and that of Martinsson (1962) are not in conflict except for expressions referring to the lobation of beyrichiid valves. Note, for example, that the “preadductorial node” of Martinsson (1962, p. 64) corresponds to “L2” of Moore (1961), the “adductorial10
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
sulcus” of Martinsson is “S2” of Moore (1961), and so forth. Because Martinsson’s terms have been widely employed by students of beyrichiids it has seemed desirable to use them here rather than to adhere to Moore’s (1961) terminology for the sake of consistency.
Brachiopods were measured with vernier calipers, and ostracodes were measured with a micrometer ocular in a zoom microscope set at a factor of X 2.
Abbreviations used for institutions from which collection or specimen numbers are cited are as follows: American Museum of Natural History, AMNH; British Museum (Natural History), BMNH; New York State Museum, NYSM; U.S. Geological Survey, USGS; U.S. National Museum, USNM; and Yale Peabody Museum, YPM.
Phylum BRACHIOPODA Class INARTICULATA Order LINGULIDA Waagen, 1885 Superfamily LINGULACEA Menke, 1828 Family CRANIOPSIDAE Williams, 1963 Genus CRANIOPS Hall, 1859
Craniops ovata (Hall)
Plate 1, figures 6, 7
Pholidops ovatus Hall, 1859, p. 490, pi. 103-B, figs. 7a, b; Hall and Clarke, 1892, p. 157, 159, pi. 41, figs. 22, 23; Weller, 1903, p. 226, pi. 20, figs. 27-29, p. 300.
Pholidops ovata Hall. Schuchert in Schuchert and Maynard, 1913, p. 294, pi. 53, figs. 10-12.
Description.—Shell biconvex; outline oval, apices eccentric along long axis of valves. Surface ornamented by as many as eight growth varices eccentric about apices. Pedicle valve more convex than brachial valve, internal pedicle valve has a muscle platform composed of two prominent calluses with a low depression between them, united anteriorly. Brachial valve has similar muscle platform but median depression is deeper and extends anteriorly so that platform may appear bilobate.
A wide valve (pi. 1, fig. 7) is 2.3 mm long and 2.0 mm wide. A narrower valve is 2.4 mm long and 2.0 mm wide.
Discussion.—Howell (in Moore, 1965, p. H273) indicates that Craniops shows a scar of attachment on the pedicle valve. Schuchert (in Schuchert and Maynard, 1913, p. 294) described a “cementation scar” on the pedicle valve of Craniops ovata from the lower part of the Keyser Limestone in Maryland. The specimens from the Cobleskill here described are too poorly preserved to determine the presence or absence of this scar, as in most specimens the apex is eroded.
Craniops ovata was originally described by Hall (1859, p. 490) from the “slialy limestone of the Helder-berg group” (New Scotland Limestone) in Albany County, N.Y. Although no specimens from the New
Scotland of Albany County were available for comparison, the Cobleskill specimens have been compared with specimens from the Kalkberg Limestone beneath the New Scotland at Schoharie, N.Y.; no significant differences were apparent.
Size of sample.—Ten single valves and five complete but crushed shells were available for study.
Occurrence.—All specimens of Craniops ovata studied from the Cobleskill came from collections from Schoharie, N.Y. (YPM 5244/146, USGS 3393-SD, USGS 7283-SD, USGS 8063-SD).
Class ARTICULATA Order STR0PH0MENIDA Opik, 1934 Suborder STROPHOMENIDINA Opik, 1934 Superfamily STR0PH0MENACEA King, 1846 Family STR0PHE0D0NTIDAE Caster, 1939 Subfamily LEPT0STR0PHIINAE Caster, 1939 Genus LEPT0STR0PHIA Hall and Clarke, 1892
Leptostrophia bipartita (Hall)
Plate 1, figures 12-14
Leptaena bipartita Hall, 1852, p. 326, pi. 74, fig. 6.
Strophomena bipartita (Hall). Hall, 1859, p. 82.
Stropheodonta bipartita (Hall). Weller, 1903, p. 226, pi. 20, figs. 1-5.
Stropheodonta (Leptostrophia) bipartita (Hall). Schuchert, 1903b, p. 165; Maynard in Schuchert and Maynard, 1913, p. 316, pi. 57, figs. 17,18.
Leptostrophia bipartita bipartita (Hall). Bowen, 1967, p. 31. Strophodonta textilis Hall, 1852, p. 327, pi. 74, fig. 6. Stropheodonta (Leptostrophia) textilis (Hall). Hall and Clarke, 1892, p. 288.
Leptaena------, Hall, 1852, pi. 74, fig. 3.
Description.—Shell planoconvex; outline semielliptical, slightly wider than long. Hinge produced into blunt auricles; hingeline denticulate to two-thirds length from delthyrium. Cardinal area of pedicle valve relatively high; delthyrium not completely closed; lunate aperture between pseudodeltidium and chilidium.
Ornamentation consists of fine angular lirae crossed by closely spaced filae giving reticulate appearance. Lirae straight, nodose in many specimens, and warped around surface irregularities of shell; increase both by implantation and bifurcation, fasciculate in some specimens.
Pedicle valve has leptostrophiid diductor muscle scars bounded by strong posterolateral callus ridges. Dental lamellae lacking.
Brachial valve has large, erect cardinal process resting on tripartite callus platform. Lateral callus buttresses best developed parallel to hinge line, but fan forward to the adductor scars. Adductor scars feebly impressed and narrow; median buttress narrow and low. Two inconspicuous nodes on either side of and posteriorSYSTEMATIC PALEONTOLOGY
11
to the cardinal process may represent socket plates. Chilidium large and covers base of cardinal process.
A representative specimen is 2.9 cm wide and 2.4 cm long. A smaller specimen is 1.8 cm wide and 1.7 cm long.
Discussion.—Hall (1852, p. 326-327) originally described two species, Leptaena bipartita and Stropho-donta textilis, from the Cobleskill Limestone, the former on the basis of a poorly preserved pedicle interior and the latter from a specimen preserving some of the characteristic surface ornamentation described above. Subsequent work has shown that shells with the internal characters of Hall’s Leptaena bipartita have the surface ornamentation of his Strophodonta textilis. Consequently the two names are considered synonymous, and the first has been used because it has page precedence.
Barrett (1878, p. 372) described Strophodonta near-passi as comparable to the figures on Hall’s (1852) plates and having the surface ornamentation of Strophodonta textilis. Prouty and Swartz (1923, p. 426-427) have used Barrett’s name “nearpassi” as a varietal form of Leptostrophia bipartita for those shells in which the radial ornamentation is curved toward the hinge line, rather than being straight as in the types of Hall’s species. Bowen (1967, p. 30-31) and Hoar and Bowen (1967, p. 19-20) consider Leptostrophia bipartita nearpassi a subspecies of Leptostrophia bipartita.
Unfortunately the material studied is mostly fragmentary and poorly preserved. The description of the interior of the brachial valve is based on a specimen of L. bipartita nearpassi (YPM 23795) from near Glen-erie, in the Hudson Valley, as no well-preserved brachial interiors were available from central New York. One specimen of a pedicle valve from Schoharie was calcined to show the posterolateral ridges bounding the diductor scars. In this specimen, the posterolateral ridges subtend an angle of about 90°, whereas the type specimens in the New York State Museum at Albany indicate that the angle is about 60°. Whether the specimen from Schoharie is aberrant, or whether it represents a distinct species cannot be determined from the material at hand.
Size of sample.—More than 10 fragmentary specimens were available for study.
Occurrence.—Leptostrophia bipartita has been found in collections from Shutter Corners (YPM 5244/150, USGS 3390-SD), Howes Cave (YPM 5244/143), Jerusalem Hill (YPM 2594), Glenerie, N.Y. (YPM 5244/ 3.145), and Aurelius Station (YPM 5244/14), but does not appear to be common. Leptostrophia bipartita nearpassi occurs in beds of Late Silurian age from the Hudson Valley, and has been reported from New Jersey
(Weller, 1903, p. 226), Maryland (Schuchert and Maynard, 1913, p. 316), Pennsylvania (Keeside, 1917, p. 201), and West Virginia and Virginia (Swartz, 1929, p. 35).
Superfamily DAVIDSONIACEA King, 1850 Family CHILIDIOPSIDAE Boueot, 1959 Genus MORINORHYNCHUS Havlicek, 1965
Morinorhynehus? interstriatus (Hall)
Plate 1, figures 1-5
Orthis interstriata Hall, 1852, p. 326, pi. 74, figs. 1, 2. Orthothetes interstriatus (Hall). Schuchert, 1897, p. 297; Weller, 1903, p. 229, pi. 20, figs. 8, 9; Schuchert, 1903, p. 165; Grabau, 1906, p. 109, fig. 8.
Schuchertella interstriata (Hall). Grabau and Shimer, 1909, p. 228, fig. 227; Grabau in Grabau and Sherzer, 1910, p. 121-123, pi. 17, figs. 4, 5, pi. 32, figs. la-c. “Schellicienella” interstriata (Hall). Berdan, 1964, p. B15. Orthothetes hyilraulicus Whitfield. Grabau, 1900, p. 365, pi. 22, figs, la-c; 1901, p. 184, fig. 92.
Description.—Shell planoconvex to weakly biconvex, semielliptical in outline; cardinal angles blunt or rounded; greatest width anterior to hingeline. Ventral inter area small, apsacline; dorsal interarea linear. Del-thyrium nearly closed by convex pseudodeltidium; low perideltidial area extends about one-fourth of length from pseudodeltidium to cardinal angle. Notothyrium plugged by base of cardinal process; no chilidial plates seen. Pedicle beak relatively prominent; brachial beak very subdued.
Ornamentation consists of angular costellae curving toward posterolateral margins of shell and increasing by intercalation. Costellae crossed by fine filae.
Pedicle valve contains moderately prominent teeth supported by short dental lamellae that subtend an arc of about 65°. No muscle scars observed.
Brachial valve has small bilobed cardinal process to which relatively ponderous brachiophores are attached anterolaterally. Brachiophores connected to palintrope by horizontal socket plates (pi. 1, fig. 3). Shell thin; external ornamentation impressed on inner surfaces. No muscle scars observed.
Shell small. Figured specimen (pi. 1, fig. 2) is 0.85 of a cm long and 1.1 cm wide. A fragmentary specimen is 1.5 cm long and 2.0 cm wide.
Discussion.—This small planoconvex to concavocon-vex species resembles Morinorhynehus dalmanellifor-mis Havlicek, 1965—the type species of Morinorhyn-chus—in having a convex pseudodeltidium, dental lamellae, and rounded cardinal angles. However, Havlicek (1965, p. 292) stated that Morinorhynehus has a well-developed dorsal interarea and discrete chilidial plates, and because M. ? interstriata has a linear dorsal interarea and no chilidial plates have been oD-12
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
served, the species is only questionably assigned to Morinorhynchus. Havlicek (1967, p. 192) considered that Morinorhynchus was related to Fardenia Lamont, 1985. Fardenia was originally described as having an open delthyrium (Lamont, 1935, p. 310-311), but Boucot (1959, p. 26) and Havlicek (1965, p. 291) later stated that it has a small apical pseudodeltidium. Havlicek (1967, p. 192) further noted that the character of the brachiophores differs in the two genera. Thus there appears to be a valid distinction between the Late Ordovician-Early Silurian genus Fardenia and the Late Silurian genus Morinorhynchus.
The Keyser species Schuchertella prolifica Schuchert, 1913, superficially resembles Ml interstriata, except for its larger size, but lacks dental lamellae (Bowen, 1967, p. 28) and is not congeneric.
Size of sample.—Eleven specimens, many of which were fragmentary, were available for study.
Occurrence.—Morinorhynchus "l interstriatus has been found in the Cobleskill in collections made from Schoharie (YPM 5244/146), between Central Bridge and Howes Cave (YPM 5244/143), at Jerusalem Hill (YPM 2594), near Forge Hollow (YPM 5244/90), at Prospect Hill (USGS 5207-SD), at Aurelius Station (YPM 5244/14), and at Seneca Falls (USGS 6084-SD). It is also found in the Akron Dolomite in the Buffalo area. It has been reported from New Jersey by Weller (1903, p. 229). Beeside (1917, p. 201) tentatively identified it from the Keyser Limestone of Pennsylvania, but it does not seem to occur farther south.
Suborder CHONETIDINA Muir-Wood, 1955 Superfamily CHONETACEA Brown, 1862 Family CHONETIDAE Brown, 1862 Genus ECCENTRICOSTA Berdan, 1963
Eccentricosta jerseyensis (Weller)
Plate 1, figures 8-11
Chonetes jerseyensis Weller, 1900, p. 8; 1903, p. 230-231, pi. 20, figs. 11-16; Maynard in Schuchert and Maynard, 1913, p. 338, pi. 61, figs. 17-19.
Eccentricosta jerseyensis (Weller). Berdan, 1963, p. 254-256; Hoar and Bowen, 1967, p. 18-19; Bowen, 1967, p. 26-27.
Description.—Shell concavoconvex; depth of curvature about one-eighth length of shell. Outline semielliptical ; maximum width about halfway between anterior and posterior margins, not at hinge. Cardinal angles rounded. Wider than long; length about two-thirds width. Cardinal area relatively high; beaks of both valves low. Six to seven spines on each side of beak of pedicle valve, set perpendicular to hinge line; these increase in size toward posterolateral angles of shell.
Ornamentation consists of coarse subangular costae increasing both by implantation and bifurcation; in some specimens they anastomose. Costae curved toward
anterior margin of shell, originating from point behind beak so that hinge line appears to cut them. Very fine filae cross radial ornament but are easily eroded and not visible on many specimens.
Pedicle valve contains short, thick, low median myo-phragm flanked on either side by two posterolateral ridges that presumably mark the posterior boundaries of the diductor muscle scars. Inner surface of valve costellate; costellae marked by impressions of papillae. Dental lamellae lacking.
Brachial valve contains small sessile bilobed cardinal process, each lobe projecting posteriorly, in contact with inner edge of other lobe, forming a small spoon-shaped structure. Cardinal process rests upon a low tripartite callus platform with short median buttress; lateral buttresses form well-developed ridges that parallel the hinge line and bound the dental sockets anteriorly. Crural bases small, rest upon the lateral callus buttresses, and make an angle of about 30° with the hinge line. Two thin myophragms extend about one-fifth of distance from hinge line to anterior margin. Muscle scars absent or lightly impressed, surface ornamentation visible on interior of valves.
A representative specimen is 1.2 cm long and 1.7 cm wide.
Discussion.—Eccentricosta jerseyensis is very abundant at some localities; and, paradoxically, it is difficult to find well-preserved specimens, for where it is present the species tends to occur in shell beds that contain many individuals, most of which are incomplete. Because of its distinctive ornamentation, however, the species can be recognized from small fragments of shell; this characteristic, combined with its restricted vertical range in the middle Appalachians, makes E. jerseyensis a useful guide fossil. Its presence in central New York, the type area of the Cobleskill Limestone, has been one of the chief reasons for correlating this formation with the Decker Limestone of New Jersey and the lower part of the Keyser Limestone of Maryland. Specimens from central New York seem to have somewhat more irregular costae than the type specimen. Specimens from Shutter Comers (USGS 3390-SD) were calcined, which showed that they have hollow cardinal spines.
Size of sample.—More than 15 specimens were available for study.
Occurrence.—This species has been found in collections from Shutter Corners (YPM 5244/150, USGS 3390-SD), Jerusalem Hill (YPM 2594), and Aurelius Station (YPM 5244/14). In Pennsylvania and New Jersey it occurs through approximately 50 feet of limestone and sandstone (Swartz and Swartz, 1941, pi. 1), but in New York it is restricted to the Cobleskill Limestone, which has a maximum thickness of 15 feet. InSYSTEMATIC PALEONTOLOGY
13
Maryland and Virginia it is a zone fossil for the lower part of the Keyset- Limestone (Bowen, 1967).
Order RHYNCHONELLIDA Kuhn, 1949 Superfamily RHYNCHONELLACEA Gray, 1848 Family RHYNCHOTREMATIDAE Schuchert, 1913 Subfamily ORTHORHYNCHULINAE Cooper, 1956 Genus MACHAERARIA Cooper, 1955
Machaeraria? lamellata (Hall)
Plate 2, figures 9-16
Atrypa lamellata Hall, 1852, p. 329, pi. 74, fig. 11.
Atrypal lamellata Hall. Weller, 1903, p. 237, pi. 21, figs. 23-29. Rhynchonella lamellata (Hall). Hall, 1859, p. 78; Schuchert, 1897, p. 359; 1903, p. 167.
Camarotoechia lamellata (Hall). Grabau, 1906, p. 109, fig. 13; Grabau and Shimer, 1909, p. 286, fig. 349; Maynard in Schuchert and Maynard, 1913, p. 352, pi. 63, figs. 9, 10, Stenoschisma lamellata (Hall). Swartz, 1939, p. 84. Machaeraria1 lamellata (Hall). Hoar and Bowen, 1967, p. 31-32.
Description.—Shell small, subquadrate in adults, sub-trigonal to subcircular in young specimens. In adults, length about four-fifths width. Pedicle beak low, tightly curved over brachial beak, which penetrates delthyrium. Foramen apparently open. Brachial valve slightly more convex than pedicle valve, with prominent fold starting at about one-third of length of shell and greatly elevated anteriorly. Complementary sulcus on pedicle valve; anterior margin of pedicle valve produced as linguiform extension into fold.
Shell surface covered with angular plicae that extend from beak to anterior margin; three on fold, two in sulcus, and six to seven on each lateral slope. Plicae crossed by conspicuous concentric lamellae, present even on juvenile specimens, showing on abraded specimens as nodes on radial ornament.
Pedicle valve with thin dental lamellae enclosing angle of about 60°. Muscle scars too feebly impressed to be distinguishable.
Brachial valve with discrete cardinal plates separated by narrow trough containing thin, bladelike cardinal process. Posterolateral margins of cardinal plates project over deep, narrow dental sockets. Cardinal plates triangular, apparently bearing relatively long, curved crura. Low median ridge presumably divides muscle field, of which there is no other indication.
A representative specimen is 0.8 of a cm long, 0.9 of a cm wide, and 0.5 of a cm thick. Free brachial valve of large specimen (pi. 2, fig. 16) is 0.9 of a cm long and 1.1 cm wide.
Discussion.—This species becomes more transverse as it increases in size, developing from a small flat shell with a subcircular outline (pi. 2, fig. 9) into a subquadrate form in which the width is greater than the length. However, at all stages of growth it is marked by the prominent imbricating lamellae which give it its
name. Machaeraria ? lamellata is close to the type species of Machaeraria, M. formosa (Hall), in its possession of a divided hinge plate and a small linear cardinal process in the brachial valve, also in its transverse form and the structure of the pedicle valve. However, it apparently differs in lacking support plates under the crura.
Size of sample.—More than 25 specimens were available for study.
Occurrence.—Machaeraria? lamellata is common in collections from Schoharie (YPM 5244/146, USGS 3393-SD) and the vicinity of Howes Cave (USGS 8065-SD, YPM 5244/143, USGS 7198-SD) but has not been found in collections from farther west in New York, although it is associated with such species as Microsphaeridiorhynchus litchfieldensis and Howellella corallinensis that do occur in the western part of the State. It has been found in the Rondout Formation of eastern New York (Hoar and Bowen, 1967, p. 31-32) and the Decker Limestone of New Jersey (Weller, 1903, p. 237). M.f lamellata has also been reported from the Keyser Limestone of Pennsylvania, Maryland and Virginia and from the underlying Tonoloway Limestone, although Hoar and Bowen (1967, p. 31) noted that specimens from these formations differ from those in the Decker, Rondout, and Cobleskill in having only one plication in the sulcus and two on the fold.
Machaeraria sp. cf. M. deckerensis (Weller)
Rhynchonella deckerensis Weller, 1903, p. 234.
Stenoschisma deckerensis (Weller), Maynard in Schuchert and Maynard, 1913, p. 349.
Original description.—Shell subtriangular, wider than long, the posterolateral margins sloping from the beak, where they form an angle of from 95 to 115 degrees, in nearly straight lines to a point a little posterior to the middle of the shell; the lateral and front margins regularly rounded. The pedicle valve is usually a little less convex than the opposite one; its beak is prominent, arched, but not strongly incurved; the sinus is rather abrupt, not reaching quite to the beak. The surface of the brachial valve curves gently to the margins, except toward the front, where the mesial fold is rather abruptly elevated. The surface of each valve is marked by from twenty to twenty-four simple, angular plications, of which two or three, somewhat coarser than the remainder, are depressed in the median sinus, with a corresponding number elevated in the fold of the brachial valve.
The dimensions of a rather large specimen are: length, 15 mm; width, 19.5 mm; thickness, 10 mm (Weller, 1903, p. 234).
447-769 0-72-314
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
Discussion.—Several fragmentary and distorted specimens of a large rhynchonellid from Shutter Corners have been referred provisionally to this species because of their large size, transverse outline, and numerous angular plications. Serial sections of one of the less deformed shells shoved that the cardinal plates were discrete and were separated by a trough containing a cardinal process, as in M. lamellata. None of the specimens was sufficiently well preserved to be suitable for illustration or positive identification. Only three specimens were found, all from the same locality, Shutter Corners, N.Y. (YPM 5244/150, USGS 3390-SD).
Family TRIGONIRHYNCHIIDAE McLaren, 1965 Genus MICROSPHAERIDIORHYNCHUS Sartenaer, 1970
Microsphaeridiorhynchus litchfleldensis (Schuchert)
Plate 2, figures 17-29
Rhynclionella? litchfleldensis Schuchert, 1903b, p. 167. Camarotoecliia litchfleldensis (Schuchert). Grabau, 1906, p. 109, fig. 14; Maynard (in Schuchert and Maynard), 1913, p. 353, pi. 63, figs. 11-14; Reeside, 1917, p. 201; Swartz, F. M„ 1929, p. 36.
Cupularostrum? litchfleldensis (Schuchert). Hoar and Bowen, 1967, p. 27-28, pi. 2, figs. 26-31.
Cupularostrum litchfleldensis (Schuchert). Bowen, 1967, p. 55-57, pi. 7, figs. 25, 26, 28-33.
Microsphaeridiorhynchus litchfleldensis (Schuchert). Sartenaer, 1970, p. 27-29.
Atrypa sp. Hall, 1852. p. 330. pi. 74, figs. 11,12. fRhynclionella agglomerata Weller, 1903, p. 234-235, pi. 21, figs. 5-11.
Camarotoecliia neglecta Hall. Hartnagel, 1903, p. 1128, 1150.
Description.—Shell small, subtrigonal to subpentagonal in outline, greatest width halfway between beak and anterior margin. Length and width nearly equal, length about nine-tenths width. Posterolateral slopes almost straight, making an angle of about 95° with each other. Pedicle beak overhangs, and brachial beak penetrates delthyrium. Brachial valve slightly more convex than pedicle valve, with well-defined fold in anterior half of shell. Complementary sulcus in pedicle valve. Angular plicae extend from beaks to anterior and lateral margins of shell, covering entire surface except for very small areas on posterolateral slopes of pedicle valve. Normally four plicae on fold, three in sulcus, and six or seven on each lateral slope.
Brachial valve contains small septalium on median septum which extends about half length of shell. Cardinal plates tend to unite over crural cavity and form subpentagonal plate to inner face of which are attached slender, up-curved crura. Dental sockets small, non-crenulate, partly hidden by posterior sides of cardinal plates (pi. 2, fig. 17). Cardinal plates not completely fused, and are always discrete posteriorly, leaving opening into crural cavity.
Pedicle valve contains thin dental lamellae. Muscle scars too lightly impressed to be visible.
A representative specimen (pi. 2, figs. 22-25) is 0.82 of a cm long, 0.89 of a cm wide and 0.5 of a cm thick. A. larger specimen is 1.1 cm long, 1.1 cm wide, and 0.7 of a cm thick. Fragmentary specimens indicate that the species grows larger, but none have been suitable for measurement.
Discussion.—Sartenaer (1970, p. 27-29) has recently designated Rhynchonella? litchfleldensis Schuchert, 1903, the type species of his new genus Microsphaeridiorhynchus, in which only the type species is included. He has removed this species from Cupularostrum Sartenaer, 1961, because, among other differences, the sockets are simple and not crenulated, and he considers it not to belong in Ancillotoechia Havlicek, 1959, because the ventral beak is less projecting and there is no median longitudinal crest on the anterior part of the plate over the septalium (Sartenaer, 1970, p. 28). M. litchfielclensis has a superficial resemblance to Iherir-hynchia santaluciensis Drot and Westbrook, 1966, but as described by Drot and Westbroek (1966), Iherirhyn-chia has more massive internal structures in both valves. Schuchert (1903b, p. 167) originally described M. litchfleldensis as follows:
This species is one of a group represented in the Rochester shales by R.(1) neglecta and in the Helderbergian by /£.(?) transversa. It differs from the former in having more plications with the fold and sinus narrower and less pronounced. It is more closely related to R.(?) transversa, but never attains the size of this species, nor is the fold and sinus so broad.
A form found with typical M. litchfleldensis in some collections is about half its size, subtrigonal in outline, and lacks a fold and sulcus. This may be the juvenile form of M. litchfleldensis, as the fold and sulcus are present on only the anterior half of mature specimens, and all other shell features of this form are consistent with this interpretation.
Size of sample.—More than eight specimens were available for study.
Occurrence.—Microsphaeridiorhynchus litchfleldensis was first described from the Cobleskill Limestone at Schoharie and has been found in collections YPM 5244/ 146, USGS 3393-SD, and several others. It has also been found in collections from Shutter Corners (YPM 5244/150), Howes Cave (USGS 8065-SD), Central Bridge (YPM 5244/143, USGS 7198-SD), Jerusalem Hill (YPM 2594), and Aurelius Station (YPM 5244/ 14). Hartnagel (1903, p. 1128) identified it as Camaro-toechia neglecta and stated that it occurred in the Wilbur Member (Upper Silurian) of the Kondout in the Hudson Valley. It has also been reported from the Rosendale and Glasco Members of the Kondout in east-SYSTEMATIC PALEONTOLOGY
15
ern New York (Hoar and Bowen, 1967, p. 27-28), the Decker Limestone of New Jersey (Weller, 1903, p. 234), and the lower part of the Keyser Limestone in Pennsylvania (Reeside, 1917, p. 188, 190, 201), Maryland (Schuchert and Maynard, 1913, p. 353; Bowen, 1967, p. 55-57), and Virginia and West Virginia (Swartz, 1929, p. 36). In Pennsylvania it is reported as also occurring in the Tonoloway Limestone.
Family UNCINULIDAE Rzonsnitskaya, 1956 Genus LANCEOMYONIA Havlifiek, 1960
Lanceomyonia? dunbari n. sp.
Plate 2, figures 1-8; figure 2
Description.—Shell small, subpentagonal in outline; width and length about equal; thickness nearly three-quarters of width. Pedicle valve shallow, with low sulcus in anterior third, and with linguiform projection into brachial valve at nearly right angle to posterior part of shell. Brachial valve inflated, with low fold corresponding to sulcus. Pedicle beak erect, exposing triangular delthyrium partly penetrated by brachial beak. Pseudoarea present, formed by break in slope between upper surface of umbonal region and concave ventral cardinal slopes. Anterior third of shell ornamented by low, rounded ribs wTith linear interspaces, three in sulcus, four on fold, and three or four on each lateral slope.
Pedicle valve contains short but well-developed dental lamellae, and low median carina which presumably divides muscle field. No other indications of muscle field observed.
Brachial valve contains small septalium. Posterolateral margins of hinge plates appear to extend as flanges over dental sockets. At anterior margin of septalium hinge plates form narrow bridge over crural cavity.
The holotype (pi. 2, figs. 5-8) is 0.8 of a cm in both length and width, and 0.6 of a cm in thickness.
Holotype.—YPM 23798.
Discussion.—This small species was originally thought to belong in Sphaerirhynchia Cooper and Muir-Wood, 1951, but differs from that genus in having ribs only on the anterior part of the shell. It appears to be closer to Lanceomyonia Havlfcek, 1960, but differs from that genus in its small size, and in apparently possessing a small plate bridging the septalium (fig. 2). However, the only specimen available for sectioning was an immature individual, so the structure of the septalium cannot be stated with complete assurance. Because of the paucity of specimens, the species cannot as yet be assigned to a genus with assurance, and is only provisionally placed in Lanceomyonia.
An extremely inflated specimen (pi. 2, figs. 1—4), which is considerably smaller than the type, shows the two-cycle growth pattern considered diagnostic by Hav-licek (1961, p. 110-111) of the subfamily Hebetoechi-inae. This particular specimen may represent another species, or may be a dwarfed specimen of L.f dunbari; the material at hand is not adequate to determine which.
Size of sample.—This species is not common, the description being based on one complete specimen, the immature specimen, and several fragmentary individuals.
<v><o><& <€>
0.1	0.2	0.4	0.45
0.65
Figure 2.—Nine transverse sections of Lanceomyonia? dunbari n. sp. Sections from beak toward anterior showing small cruralium, crura, and dental lamellae. Specimen from Aurelius Station (YPM colln. 5244/14). Length before sectioning 6.2 mm; measurements in millimeters from pedicle valve beak.16
BRACHIOPODA AND OSTRACODA OF COBLE SKILL LIMESTONE, CENTRAL NEW YORK
Several juvenile specimens have been found which are almost completely flat, lack a fold and sulcus, and have only faint plications on the anterior margins.
Occurrence.—The species is widely distributed and has been found in collections from Frontenac Island (USGS 3389-SD), Aurelius Station (YPM 5244/14), Howes Cave (USGS 8065-SD), and Shutter Corners (YPM 5244/150).
Order SPIRIFERIDA Waagen, 1883 Suborder ATHYRIDIDINA Boucot, Johnson, and Staton, 1964 Superfamily ATHYRIDACEA, M’Coy, 1844 Family ATHYRIDIDAE M’Coy, 1844 Subfamily PROTATHYRIDINAE, Boucot, Johnson, and Staton,
1964
Genus PROTATHYRIS Kozlowski, 1929 Protathyris sulcata (Vanuxem)
Plate 2, figures 30-35; figure 3
Atrypa sulcata Vanuxem, 1842, p. 112, fig. 5.
Mcrista sulcata (Vanuxem). Miller, 1877, p. 115.
Whitfieldella sulcata (Vanuxem). Grabau, 1900, p. 367, pi. 22, figs. 2a-d. Grabau, in Grabau and Sherzer, 1910, p. 156-157, pi. 32, figs. 2a-d.
Merista bisulcata Hall, 1859, p. 253.
Description.—Small, subovate in outline; width one-half to three-quarters of length; both valves inflated. Height of both valves equal to or slightly greater than width, the posterior third being most inflated. Pedicle beak prominent, commonly curving over and concealing delthyrium. Brachial beak low, penetrates the del-thyrium, which appears to be open. Both valves sulcate; pedicle valve with subangular sulcus extending from plane perpendicular to hinge line to anterior margin; brachial valve with linear depression extending from umbo to anterior margin.
Surface smooth except for concentric growth lines.
Pedicle valve contains thin, rather short dental lamellae. Muscle scars too feebly impressed to be recognizable.
Brachial valve contains concave cardinal plate pierced at apex by visceral foramen. Posterior end of cardinal plate bounded by dental sockets is triangular, anterior part of plate apparently extends beyond dental sockets. Crura arise from lateral components of cardinal plate. Median septum lacking (fig. 3), muscle scars too feebly impressed to be seen.
Jugum not observed in specimens studied. Large specimens have five to six volutions in the brachidium.
A figured specimen (pi. 2, figs. 30-33) measures 0.64 of a cm in width, 0.82 of a cm in length, and 0.64 of a cm in height.
Discussion.—Kozlowski (1929, p. 223) based his genus Protathyris primarily on the character of the jugum. Unfortunately, no specimens of P. sulcata or of the following species, P. nucleolata, have been found in which the jugum is preserved. However, the thin dental
lamellae in the pedicle valve, the character of the hinge plate, and the absence of a median septum in the brachial valve all agree with Protathyris as described by Kozlowski.
Grabau (in Grabau and Sherzer, 1910, p. 148) assumed that Hindella had a median septum as described by Hall and Clarke (1894) and he proposed the genus Greenfieldia for shells resembling Whitfieldella exter-temally but lacking a median septum in the brachial valve. The jugum of Greenfieldia whitfieldi, the type species, is not known, however, and the types have not been restudied. It is possible that if the jugum of Greenfieldia were found, it would be similar to that of Protathyris. and Greenfieldia would replace Protathyris because it has priority. Under these circumstances, it might be considered logical to put P. sulcata and P. nucleolata into Greenfieldia rather than Protathyris. However, Grabau (in Grabau and Sherzer, 1910, p. 151-152, 156-157) described specimens which he considered P. sulcata and others which he compared with P. nucleolata, and he placed both species in Whitfieldella. Apparently, therefore, they did not agree with his concept of Greenfieldia.
Externally Protathyris sulcata bears a strong resemblance to Terehratula didyma Dalman, 1828, which Kozlowski (1929, p. 227-230) redescribed and assigned to Protathyris. Recently, however, Rubel and Modzalev-skaya (1967) have restudied this species and made it the type of the new genus Didymothyris on the basis of a distinctive structure, the pedicle fulcrum, in the beak of the pedicle valve. Silicified specimens of Protathyris sulcata have been examined by me to see whether such a structure is present in the Cobleskill material, and because no indications of a pedicle fulcrum have been found, the species remains in Protathyris.
Size of sample.-—More than 10 specimens were available for study.
Occurrence.—This very distinctive brachiopod was originally described by Vanuxem (1842, p. 112) as occurring in the “Waterlime Group of Manlius,” for which reason it was later discussed by Grabau (1900, p. 352) as a “typical Manlius limestone species * * *. It is not represented in the Coralline limestone.” As Schuchert (1903b, p. 169) later pointed out, however, Vanuxem (1842, p. Ill) included in his “Waterlime Group” everything between the base of the Cobleskill Limestone and the top of the Jamesville Member of the Manlius Limestone. Although Vanuxem did not mention the exact bed in which his uAtrypa sulcata” occurs, it is not associated with the fossils from the higher beds. Actually, Protathyris sulcata appears to be confined to the Cobleskill. It has been described from the Akron Dolomite by Grabau (1900, p. 367) and hasSYSTEMATIC PALEONTOLOGY
17
Figure 3—Twelve transverse sections of Protathyris sulcata (Vanuxem) showing character of hinge plate and absence of median septum in brachial valve. Specimen from Aurelius Station (YPM colln. 5244/1.56). Length before sectioning measured from beak of brachial valve, 9.3 mm ; measurements in millimeters from beak of brachial valve.18
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
been reported as far east as Litchfield, N.Y., by Schu-chert (1903b, p. 167). The specimens in the collections studied come from Aurelius Station (YPM 5244/14; YPM 5244/1.56; USGS 3395-SD), Prospect Hill (USGS 5207-SD), and Forge Hollow (YPM 5244/90). In most collections it is associated with Howellella corallinensis eriensis and Morinorhynchus ? interstri-atus but is not very common anywhere.
Protathyris nucleolata (Hall)
Plate 2, figures 36-40; figure 4
Atrypa nucleolata Hall, 1852, p. 328, pi. 74, figs. lOa-m.
Merista nucleolata (Hall). Hall, 1859, p. 78.
IMeristella nucleolata (Hall). Whitfield, 1882, p. 321, pi. 25, fig. 5.
Whitfieldella'! nucleolata (Hall). Schuchert, 1897, p. 461; 1903b,
p. 166.
Whitfieldella cf. rotundata (Whitfield). Grabau, 1900, p. 368, pi. 22, figs. 3a, to.
Whitfieldella cf. nucleolata (Hall)1. Grabau in Grabau and Sher-zer, 1910, p. 151-152, pi. 32, figs. 3a, to.
?Whitfieldella sulcata (Vanuxem). Williams, 1919, p. 89, pi. 27, figs. 4, 5,
Description.—Small, subcircular to subpentagonal in outline; width and length nearly equal, but former slightly greater. Anterior margin semicircular, but beak of pedicle valve extended so that posterolateral slopes are nearly straight, joining at an angle of about 100°. Valves nearly equally convex. Pedicle beak curves over and conceals delthyrium, brachial beak penetrates del-thyrium. No distinct cardinal area. Pedicle valve with shallow, poorly defined sulcus in anterior part; brachial valve smooth or with low depression.
Surface smooth except for growth lines.
Pedicle valve with thin dental lamellae extending about one-fifth length of shell. No muscle scars observed.
Brachial valve with cardinal plate similar to that of P. sulcata except that visceral foramen appears larger and anterior part appears to extend farther forward (fig. 4).
Brachidium not observed in material at hand.
One figured specimen (pi. 2, figs. 36-39) is 0.9 of a cm in width, 0.8 of a cm in length, and 0.6 of a cm in thickness. Fragmentary specimens indicate that the species grew nearly twice as large but none are complete enough to measure.
Discussion.—This species is similar to Protathyris minuta (Maynard, in Schuchert and Maynard, 1913) from the Keyser Limestone, as redescribed by Bowen (1967, p. 36-37). However, P. minuta is smaller and more elongate; P. nucleolata has a subcircular outline even in juvenile specimens. Hindella? (Greenfieldia) congregata Swartz, 1923 from the Tonoloway Lime-
stone resembles P. nucleolata in external appearance, but is reported to have a “low raised median line” (Prouty and Swartz, 1923, p. 460) or a myophragm (Bowen, 1967, p. 37) in the brachial valve.
Protathyris nucleolata apparently has a wider geographic distribution than P. sulcata, but is coextensive with it over the western and central part of New York. As far as relative abundance is concerned, the two species are more or less complementary, P. nucleolata being rare in the western part of the State and P. sulcata being rare in the east.
Size of sample.—More than 10 specimens were available for study.
Occurrence.—This species has been found in collections from Seneca Falls (USGS 6084—SD), Frontenac Island (USGS 3389-SD), Aurelius Station (YPM 5244/14), Jerusalem Hill (YPM 2594; YPM 5244/ 108), Schoharie (YPM 5244/146; USGS 3393-SD), and Shutter Corners (USGS 3390-SD). The species was originally described by Hall (1852, p. 328) from the Cobleskill Limestone at Schoharie. Subsequently it has been reported from equivalent horizons in Maryland (Schuchert and Maynard, 1913, p. 441, pi. 73, figs.
37-	40), New Jersey (Weller, 1903, p. 241, pi. 21, figs.
38-	40), and questionably from Pennsylvania (Beeside, 1917, p. 202). Grabau (in Grabau and Sherzer, 1910, p. 151) recorded its presence in the Akron Dolomite of western New York.
Suborder SPIRIFERIDINA Waagen, 1883 Superfamily SPIRIFERACEA King, 1846 Family DELTHYRIDIDAE Waagen, 1883 Subfamily ACROSPIRIFERINAE Termier and Termier, 1949 Genus HOWELLELLA Kozlowski, 1946
Howellella corallinensis corallinensis (Grabau)
Plate 2, figure 49
Spirifer crispus Hisinger. Hall, 1852, p. 328, pi. 74, figs. 9a-h. Spirifer crispus var. corallinensis Grabau, 1900, p. 352.
Spirifer modestus var. corallinensis Schuchert, 1903b, p. 166. Spirifer corallinensis Grabau, 1903, p. 1042, fig. 6.
Howellella keyserensis (Swartz) [part]. Howell, 1947, pi. 3, fig. 4.
Description.—Shell small; outline subrhombic; cardinal angles rounded. Length between three-fourths and four-fifths of width in adult shells. Pedicle area small; pedicle beak curving quite far over it. Delthyrium large, open, with conspicuous deltidial plates that flare outward from delthyrium, except at apex, which is closed by an arcuate plate. Brachial beak and area low and inconspicuous.
Sulcus broad, shallow, and subangular in cross-section. Fold low, rounded, with slight depression on its crest in many specimens.
Ribs lacking, or indicated only by two faint linear depressions on each lateral slope of pedicle valve.SYSTEMATIC PALEONTOLOGY
19
Figure 4.—Twelve transverse sections of Protathyris mieleolata (Hall) showing character of hinge plate and absence of median septum in brachial valve. Specimen from Schoharie, N.Y. (YPM colln. 5244/146). Length before sectioning, 6.6 mm; measurements in millimeters from beak of pedicle valve.
Surface ornamentation consists of very small spinules on concentric growth varices; exfoliated shells appear completely smooth and varices not shown.
Pedicle valve contains dental lamellae extending about one-fourth of length of valve and, in most specimens, a low sharp median carina extending about half the length. Muscle scars not impressed and not recognizable as such.
Brachial valve contains small bilobed cardinal process. Crura supported by crural lamellae which extend about one-sixth the length and rest on floor of valve between dental sockets. Crural lamellae are perpendicular to floor for about half their height, where they are deflected laterally to connect with socket plates.
The holotype is 1.1 cm wide and 0.9 of a cm long. A large specimen is 1.3 cm wide and 0.9 of a cm long and an average specimen is 1.0 cm wide and 0.8 of a cm long.
Discussion.—The holotype of this species (AMNH 1771/4) is an exfoliated specimen that shows two distinct ribs on either side of the fold of the brachial valve, but the pedicle valve is smooth. Unlike some others of its genus, this small species shows no growth varices on exfoliated specimens.
Internally, H. corallinensis possesses the characters diagnostic of the genus Howellella. Although not observed in any of the specimens examined, the crura are probably attached to the crural lamellae at the junction of the vertical and diagonal components.
This species was described by Grabau (1900, p. 352) as a variety of ilSpirifer>' crispus (Hisinger). In a later paper, Grabau (1903, p. 1042) raised it to species rank and indicated that the type was the specimen figured as “/S'.” crispus by Hall (1852, pi. 74, figs. 9d-f). Schu-chert (1903b, p. 166) referred it to a variety of Howellella modesta (Hall, 1857) of the Maryland “Manlius”20
BRACHIOPODA AND OSTRACODA OF COBLE SKILL LIMESTONE, CENTRAL NEW YORK
(now Keyser) Limestone, a similarity which Grabau had already noted. Most subsequent writers have considered II. corallinensis as a distinct species; but Swartz (1939, p. 385), Bowen (1967, p. 48), and Hoar and Bowen (1967, p. 26) have again suggested that both Howellella corallinensis and II. eriensis should be considered as varieties of the Maryland forms Howellella modesta and II. modesta plica,ta (Maynard, 1913). Though they stated that further study of the types of these varieties is necessary.
The problem of this group of nearly smooth species of Howellella involves not only the study of the types, but also examination of large suites of specimens. There is undoubtedly a very close relationship among all four forms, but comparison of the types shows that H. modesta not only shows less evidence of plication and a more feebly developed fold and sulcus than either of the New York species, but it also is less transverse. The holotype of H. modesta plicata is a far larger shell than either of the New York species and is distinctly plicate, as its name implies; but as the plications are not pronounced on the umbo, it would probably be difficult to distinguish a juvenile specimen of this species from mature H. corallinensis. H. corallinensis differs from H. eriensis only in the degree of plication and the depth and shape of the sulcus. These characters do not appear to be constant in large suites of specimens; consequently, H. eriensis is here considered a subspecies of H. corallinensis. The latter is here considered a distinct species because of the differences between it and the type of H. modesta and because the specimens illustrated by Bowen (1967, pi. 6, figs. 21-28) suggest a relatively longer and thicker shell that has well-developed muscle scars. If these differences should prove to be due to paleoecological causes, it would be necessary to place H. corallinensis in synonymy with II. modesta.
The most obvious distinction among the four species of nearly smooth Howellella, two in New York and two in Maryland, is the degree of ribbing. If it is eventually demonstrated that H. corallinensis and H. modesta are the same, the name H. modesta has priority and must be used for all the nearly completely smooth species. However, if II. modesta plicata and II. eriensis also appear to represent the same form, H. eriensis has priority, and the Maryland forms should be referred to this subspecies.
Size of sample.—More than eight specimens were available for study.
Ocurrence.—Howellella corallinensis corallinensis was described from the Cobleskill Limestone at Schoharie and has been found in collection YPM 5244/146. It also occurs in collections from Shutter Corners (YPM 5244/150), Central Bridge (YPM 5244/143),
Jerusalem Hill (YPM 2594), Aurelius Station (YPM 5244/14), questionably from Frontenac Island (USGS 3389-SD), and from Seneca Falls (USGS 6084-SD).
Howellella corallinensis eriensis (Grabau)
Plate 2, figures 41-48
Spirifer eriensis Grabau, 1900, p. 366, pi. 21, figs. 2a, b; Grabau, 1901, p. 199, fig. 119; Schuchert, 1903b, p. 166; Grabau, 1903, p. 1043, fig. 7; Grabau, 1906, p. 109, fig. 11; Grabau and Sherzer, 1910, p. 133, pi. 31, figs. 2a, b; Grabau and Shimer, 1909, p. 320, fig. 404; Maynard in Schuchert and Maynard, 1913, p. 404, pi. 69, fig. 7; Swartz, F. M., 1939, p. 385.
Howellella keyserensis (Swartz) [part], Howell, 1947, p. 6-7, pi. 3, figs. 3, 5-7.
Description.—Shell subquadrate; cardinal angles rounded. Adult shells wider than long; length about three-quarters of width. Pedicle beak extended over relatively small cardinal area. Delthyrium large, open, bordered by flaring deltidial plates. Brachial beak low.
Sulcus moderately deep, broad, subangular in cross section, expanding rapidly toward anterior. Fold low and rounded. Three to four very subdued but distinct, rounded ribs on each lateral slope, separated by linear interspaces.
Surface ornamentation consists of small spinules in concentric bands. Growth varices may be conspicuous.
Interiors of both valves like typical II. corallinensis.
The type specimen is 1.0 cm wide and 0.8 of a cm long; a larger specimen is 1.3 cm wide and 1.0 cm long.
Discussion.—The principal differences between H. corallinensis and the subspecies eriensis are the deeper, more angular sulcus and more distinct ribs of the latter. It was upon these characters that Grabau (1900, p. 366) based his species, though he noted at the time that a very close relationship must exist between the two forms. At the time that the new species was proposed, Grabau (1900, p. 351) believed that the Cobleskill Limestone at Schoharie and the Akron (Bullhead) Dolomite-at Williamsville were of different ages. When the two formations were later correlated, the two forms were left as distinct species because of the apparent differences between them.
A suite of specimens from Aurelius Station, N.Y., which is near the western limit of the Cobleskill and about halfway between Williamsville and Schoharie, contains forms which are gradational between the forms with a smooth shell and a shallow sulcus, representing II. corallinensis, and forms with ribbed shells and deep sulci, representing H. eriensis. A smooth shell with a deep sulcus is relatively common. As the two forms are identical in all other respects, both in size and shape and internal characters, H. eriensis is here consideredSYSTEMATIC PALEONTOLOGY
21
a subspecies of H. corallinensis. Specimens with the characters of II. eriensis tend to have growth lamellae, unlike H. corallinensis, but this character seems to be subject to considerable individual variation and is probably not diagnostic.
Grabau (1903, p. 1044-1046) recognized the existence of intermediate forms between II. corallinensis and H. eriensis and suggested that the latter developed out of the former by an increasing tendency toward plication. He gave as evidence the fact that juvenile specimens of H. eriensis have the characters of II. corallinensis. This interpretation seems reasonable, and as H. corallinensis has page precedence, II. eriensis is here placed in a subspecific category.
Swartz (1939, p. 385) has suggested that “Spirifer” modestus var. plicatus Maynard should be put into synonymy with H. eriensis, the latter being perhaps a subspecies of H. modestus. Further study of the species from the Keyser Limestone may resolve this problem.
Size of sample.—More than 15 specimens, most of which are from Aurelius Station, were available for study.
Occurrence.—Howellella corallinesis eriensis was described from the Akron Dolomite of western New York and is most common in that area, although it has also been found in collections from the Cobleskill Limestone at Frontenac Island (USGS 3389-SD), Aurelius Station (YPM 5244/14; YPM 5244/1.56; USGS 3395-SD), Prospect Hill (USGS 5207-SD), Forge Hollow (YPM 5244/90), and Jerusalem Hill (YPM 2594).
Phylum AETHEOPODA Class CEUSTACEA Subclass OSTEACODA Order LEPEEDITICOPIDA Scott, 1961 Family LEPEEDITIIDAE Jones, 1856 Genus LEPEEDITIA Eouault, 1851
Leperditia scalaris (Jones)
Plate 3, figures 31-34
Leperditia gibbera scalaris Jones, 1858a, p. 250, pi. 10, figs. 10, 11; Jones, 1858b, p. 834, fig. 698.
Leperditia scalaris Jones. Grabau, 1900, p. 371, pi. 22, figs. 6a-d; 1901, p. 219, fig. 150; 1906, p. Ill; Grabau and Shimer, 1910, p. 340, fig. 1655; Grabau and Sherzer, 1910, p. 59, 202, 213, pi. 32, figs. 6a-d; Williams, 1919, p. 86; Swartz, 1939, pi. 1, figs. 15a-c; Shimer and Shrock, 1944, pi. 280, figs. 5-8; Swartz, 1949, p. 312-313, pi. 65, figs. 3-10. ILeperditia jonesi Hall, 1859, p. 372.
Description.—Lateral outline postplete; hinge line about two-thirds of the total length of the shell. Cardinal angles obtuse; posterior and ventral margins smoothly curved; anterodorsal margin straight. Longitudinal outline of shell a smooth curve, not inflated medially. Maximum thickness nearly median in dorsal view and dorsomedian in end view. Maximum length is along an axis at angle to hinge line, extending from
the junction of the anterodorsal and ventral margins to the midpoint of the posterior margin. Maximum height in posterior third of shell.
Anterior and posterior margins have low, indistinct, flattened border. Ventral surface of the overlapping right valve is smoothly rounded in end view, ventral surface of overlapped left valve has smooth flange bordered by a narrow ridge marking the overlap of the right valve. Hinge taxodont. Rather prominent eye tubercles are in the anterior third of the carapace. The shell surface between the eye tubercle and anterodorsal cardinal angle tends to be uneven. Muscle scars in anterodorsal quarter of shell; adductor large, oval, with its long axis perpendicular to the hinge line, composed of 60-70 individual muscle flecks. Adductor is close to, but below and posterior to, chevron-shaped scar beneath eye tubercle. Chevron scar gently curved on anterior limb; posterior limb extends in a nearly straight line posterodorsally and merges with a line of small accessory scars which extend toward hinge line at a steep angle, where there are other small accessory scars. Pronounced swelling in posterodorsal third of left valve just below hinge line. Shell surface smooth or slightly punctate; in naturally or artifically corroded specimens it may appear slightly pustulose. In such specimens, canals radiating from the adductor scar may be seen on the external surface.
The dimensions of the largest figured specimen are 13.5 mm in length and 7.6 mm in height.
Discussion.—This species is characterized by the flattened anterior and posterior borders. Swartz (1949, p. 313) has suggested that the specimens of L. scalaris he illustrated from the Decker Limestone might possibly represent another species because the angulation of the anterior margin that he observed on his material was not illustrated by Jones. However, to judge from the Cobleskill and Akron specimens, this feature does not seem to be constant, and is not considered to be of specific value. Swartz (1949, pi. 65, figs. 9, 10) illustrated the muscle-scar pattern of L. scalaris on specimens from the Decker, and the Cobleskill specimens agree well with his illustrations except that the posterior limb of the chevron scar is more extended dorsally to merge with the small dorsal scars. In most of the Cobleskill material, the chevron scar is difficult to see in reflected light, although the adductor scar may be seen as a swelling on the surface of the shell. However, the chevron scar is more apt to be visible on internal molds.
Hall (1859, p. 372) described Leperditia jonesi from the Cobleskill of Schoharie County as a pustulose form, and separated it from L. alta (Conrad, 1842) from the Manlius Limestone (Lower Devonian) on the basis of its pustulose ornamentation. However, as corroded speci-
447-769 0-72-422
BRACHIOPODA AND OSTRACODA OF COBLE SKILL LIMESTONE, CENTRAL NEW YORK
mens of L. scalai'is appear pustulose, it seems probable that Hall's material was merely badly weathered L. scalaris. The type of L. jonesi has not been examined, but the species is questionably placed in synonymy with L. scalaris.
Size of sample.—More than 10 valves were available for study, but no complete carapaces have been found.
Occurrence.—Leperditia scalaris has been found in collections from Frontenac Island (USGS 3389-SD), Aurelius Station (YPM 5244/14, USGS 3395-SD), Prospect Hill (USGS 5207-SD), Oriskany Falls (YPM 5244/88), Forge Hollow (YPM 5244/90), and Jerusalem Hill (YPM 2594). Although Hall (1859) described Leperditia jonesi from Schoharie, only one indeterminable leperditiid was found in the collections from that locality.
Order FALAE0C0PIDA Henningsmoen, 19S3 Suborder BEYRICHICOPINA Seott, 1961 Superfamily BEYRICHIACEA Matthew, 1886 Family BEYRICHIIDAE Matthew, 1886 Subfamily TREPOSELLINAE Henningsmoen, 1954 Genus GARNIELLA Martinsson, 1962
Garniella concentrioa n. sp.
Plate 4, figures 9-12
Description.—Lateral outline amplete; dorsal margin straight. Free margin semicircular; greatest height from six-tenths to seven-tenths of length. Anterior cardinal angle obtuse; posterior cardinal angle nearly 90°. Valves essentially unisulcate, sulcus broad and deep, with vertical walls and subrectangular ventral termination. Sulcus nearly median, subvertical; ventral end slightly curved anteriorly. Sulcus extends about two-thirds the height of the valve. Velum flat to slightly concave upward in lateral view, apparently tubulous, extending entirely around free margin.
Valve surfaces coarsely reticulate except for velum and median sulcus. Reticulation arranged roughly concentrically around the sulcus and parallel to the free margin. Although the preadductorial lobe is not developed as a distinct structure, its position is indicated by the pattern of the reticulation. Below the adductorial sulcus, and bounding it ventrally, the reticulations are accentuated to form a slight crista, which is paralleled by another separated by one row of reticulations, which are depressed into a distinct groove.
Heteromorph has anteroventral crumina ornamented by four cristae, which extend from the posterior to the anterior end of the crumina parallel to the free margin.
The dimensions of the figured specimen are 1.10 mm in length and 0.70 of a mm in height. Another tecno-morph is 1.25 mm long and 0.70 of a mm high.
Types.—Holotype, USNM162309; paratypes, USNM 162308, YPM 23820, YPM 23821.
Discussion.—Although the only heteromorphic specimen is badly crushed (pi. 4, fig. 11), the cristate crumina definitely places this species in Garniella Martinsson, 1962. It differs from all described species of Garniella, except G. biseriata Martinsson, 1962, in having the cristae extending to the anterior end of the crumina. From G. biseriata it differs in having a larger number of cristae and a much larger fused anterior and median lobe. This species is not common in the Cobleskill, but is quite distinctive. This is the first occurrence of the genus in the Eastern United States.
Size of sample.—Seven specimens were available for study, of which one was a crushed heteromorphic carapace.
Occurrence.—Garniella concentrica has been found in collections from Schoharie (YPM 5244/146, USGS 3393-SD, USGS 7283-SD, USGS 8063-SD) and Jerusalem Hill (YPM 2594).
Subfamily AMPHITOXOTIDINAE Martinsson, 1962 Genus MIGMATELLA n. gen.
Type species.—Migmatella martinssoni n. sp.
Species included.—Only the type species.
Diagnosis.—Trilobate amphitoxotidine beyrichiids with velum reduced in heteromorphs to velar bend except on left valve, where a velar remnant protrudes as a spur posterior to the crumina. Trace of velum on ventral surface of crumina makes scar which is convex toward the plane of commissure of valves. No torus in either tecnomorphs or heteromorphs. Tecnomorphs have obscurely tubulous velum restricted posteriorly on left valve, more restricted on right valve. Lobes emaciated, cuspate, and cristate in tecnomorphs, not cristate in heteromorphs.
Discussion.—This genus is closely related to Mar-tinsson’s three genera Juviella, Lophoctenella, and Cryptolopholobus—especially the latter, which it resembles in having cristate lobes in the tecnomorph but not in the heteromorph. However, it differs from all three genera in having a more restricted velum and in lacking a torus. The preservation of the specimens studied is not good enough to determine whether a denticulate crest is present on the velum as in Lophoctenella and Cryptolopholobus. The name Migmatella is derived from the Greek word “migma,” mixture, because the genus partakes of some but not all of the characters of Martinsson’s three genera.
Stratigraphic range.—At present, Migmatella is known only from beds of Late Silurian age in eastern North America. The genus is present in the Decker Limestone in Pennsylvania, but as yet not enough well-preserved specimens have been obtained to determine whether they represent M. martinssoni or a new species.SYSTEMATIC PALEONTOLOGY
23
Migmatella martinssoni n. sp.
Plate 4, figures 13-22
Description.—Lateral outline preplete; lobes narrow and sulci wide, giving carapace an emaciated appearance. Adductorial sulcus broad and deep, extending two-thirds of distance from dorsal margin to velum. Preno-dal sulcus broad and deep, extending about one-third of distance from dorsal margin to velum. There is a large and pronounced anteroventral depression beneath the preadductorial lobe of the tecnomorphs. All lobes are cuspate and protrude over the hinge line. In tecnomorphs, the preadductorial lobe is narrow, nearly isolated, and subovate; the anterior lobe is thin, as is the syllobium. All lobes in the tecnomorphs are bordered by cristae, which do not occur on the heteromorphs. The general pattern of lobation looks like a slightly distorted W. The velum on the tecnomorphs is wider on the left valve than on the right valve, but is relatively narrow on both, and although tubulous, the tubules are not readily seen. On heteromorphs, the velum is reduced to a velar bend except for a blunt spur beneath the syllobium of the left valve and a velar trace across the ventral surface of the crumina. The crumina is sub-globular in outline.
The ornamentation on the specimens studied is not will preserved, but the tecnomorphs are apparently reticulate between the cristae on the lobes; the heteromorphs are apparently slightly reticulate.
The dimensions of the holotype heteromorph are 1.30 mm in length and 0.65 of a mm in height. A tecno-morph is 1.10 mm in length and 0.80 of a mm in height.
Types.—Holotype, US NM 162314; paratypes, USNM 162310-162313, YPM 23822-YPM 23824.
Discussion.—Although there are marked differences between the tecnomorphs and heteromorphs, such as the cristate lobes of the former, it is improbable that more than one species is present as no other amphitoxotidines in any of the collections resemble either the tecnomorphs or heteromorphs of M. martinssoni. The species is named in honor of Anders Martinsson, who has clarified the systematics of the Beyrichiidae.
Size of sample.—This species is based upon 23 specimens, of which three are tecnomorphic carapaces and one is a heteromorphic carapace.
Occurrence.—Seventeen of the 23 specimens came from collections from Schoharie, N.Y. (USGS 3393-SD, USGS 7283-SD, USGS 8063-SD and YPM 5244/ 146). One small tecnomorph came from Shutter Corners, N.Y. (USGS 3390-SD). One heteromorph and one tecnomorph have been found in a collection from Howes Cave, N.Y. (USGS 8065-SD), and one heteromorph has been found near Central Bridge, N.Y. (USGS
7198-SD). Two additional specimens came from a collection made by C. E. Beecher from Jerusalem Hill, N.Y. (YPM 2594).
Genus DIBOLBINA Ulrich and Bassler, 1923 Dibolbina reticruminata n. sp.
Plate 4, figures 23-28
Description.—Lateral outline amplete; height from dorsum to velum only about one-third of length. Syllobium broad, inflated and subtriangular in lateral view. Adductorial sulcus deep, narrow, slanted anteriorly. Preadductorial lobe is a small round knob, poorly defined by anterior sulcus, which is very shallow and indistinct. Velum very wide, flaring away from contact margin at a high angle; it is nearly at right angles to the plane of commissure. Velum distinctly tubulous. Crumina large, ovate; velum continues across it as a distinct tubulous crest. Distinct torus below velum does not cross crumina. Surface smooth, except for crumina of heteromorph, which is finely punctate, the punctae being arranged in parallel lines so that they appear as fine striae.
The dimensions of a tecnomorph (incomplete) are 1.15 mm in length and 0.37 of a mm in height. The holotype heteromorph is 1.55 mm in length and 0.5 of a mm in height to velum. The width across the crumina of the holotype is 1.3 mm.
Types.—Holotype, YPM 23826; paratypes, YPM 23825, USNM 162315-162317.
Discussion.—The lobation of this species is so similar to that of Dibolbina cristata Ulrich and Bassler, 1923, and D. producta Ulrich and Bassler, 1923, that there is little doubt about the generic assignment. From D. cristata it differs in lacking the fine crista on the syllobium, and from D. producta in having a deeper adductorial sulcus and a more pronounced preadductorial lobe. It lacks, as does D. producta, the basal crest outlining the velum which is present in D. cnstata. The ventral morphology of the cruminae of D. producta and D. cristata is not as yet known. The syntypes of D. cristata, the type species of Dibolbina, include one heteromorphic valve, figured by Kesling (in Kesling and Wagner 1956, pi. 4, fig. 13), but the crumina is crushed, and it is not possible to prepare it to show the ventral side. Until topotype material of D. cristata is available for study, it is assumed that the crumina of D. reticruminata is representative of the genus. In this connection, note that, unlike the related genus Berolinella Martinsson, 1962, the torus in Dibolbina does not cross the crumina.
Size of sample.—Eight specimens, of which three were complete heteromorphic carapaces, and several fragments were available for study. Because of the long24
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
hinge line and deep median sulcus, this species is difficult to recover unbroken.
Occurrence.—With the exception of one tecnomorph from the collection at Shutter Corners (USGS 3390-SD), all specimens were found in collections from Schoharie (YPM 5244/146, USGS 7283-SD, USGS 8062-SD).
Genus HAMMARIELLA Martinsson, 1962 Hanunariella warthini n. sp.
Plate 4, figures 1-8
Description.—Lateral outline preplete; anterior lobe broad, with low cusp; preadductorial lobe ovate to sub-pyriform, not extending to dorsal margin; syllobium broad, low, without cusps. Prenodal sulcus broad but fairly shallow; adductorial sulcus deep and wide. There is an anteroventral depression beneath the preadductorial lobe of tecnomorphs. Striated velum in tecnomorphs extends in a smooth curve from about midheight on anterior end to about midheight on posterior end. Heter-omorph has ovate crumina that is not crossed by either velum or torus. Velum of heteromorph extends from about midheight to crumina posteriorly and is represented only by a velar bend anteriorly. Surface of valves very finely punctate; crumina finely striate over entire surface. Velum in some specimens with fine concentric striations.
The dimensions of a tecnomorph are 1.25 mm in length and 0.85 of a mm in height including the velum. A heteromorph is 1.35 mm in length and 1.0 mm in height including the crumina.
Types.—Holotype, USNM 162304; paratypes USNM 162302, USNM 162303, USNM 162305-162307, YPM 23819.
Discussion.—This species differs from the type of the genus, Hammariella pulchrivelata Martinsson, 1962, in having a narrower velum that extends closer to the hinge line. Furthermore, Hammariella pulchrivelata has the velum abruptly truncated posteriorly, whereas in H. warthini the velum curves smoothly into the surface of the valve. However, the lack of either torus or velum crossing the crumina and the restricted velum, lacking anterior to the crumina, suggest that this species belongs in Hammariella.
According to Martinsson (1967, p. 360, 369-370), H. pulchrivelata is characteristic of a zone in the lower part of the Ludlow in the Baltic region. It is interesting that H. warthini, the first species of Hammariella to be reported from North America, occurs in beds which are considerably younger.
Size of sample.—Four tecnomorphic left valves and four heteromorphic valves, two right and two left, were
available for study. None are unbroken, but the morphology of the species can be determined from examining all of them.
Occurrence.—Hammariella warthini has been found only in collections from Schoharie (USGS 7283-SD, USGS 8062-SD).
Subfamily BEYRICHIINAE Matthew, 1886 Genus KLOEDENIOPSIS n. gen.
Type species.—Kloedeniopsis hartnageli n. sp.
Species included.—
Beyrichia barretti Weller, 1903.
Kloedenia centricomis Ulrich and Bassler, 1908. Kloedenia crassipunctata Swartz and Whitmore, 1956. Kloedenia duplicipunctata Swartz and Whitmore, 1956. Kloedenia fimbriata Ulrich and Bassler, 1908.
* Kloedeniopsis hartnageli n. sp.
Kloedenia kokomoensis Foerste, 1909.
Kloedenia retifera Ulrich and Bassler, 1908.
Diagnosis.—Distinctly trilobate beyrichiines with lobes set below dorsal margin and merging smoothly into it. Lobes neither cuspate nor faceted, no fissus. Marginal structure clearly distinct from domicilium but forming contact margin of valves, so that in end view the carapace appears keeled. Lateral outline amplete in tecnomorphs of most species. Crumina entirely on domicilium, ovate, anteroventral, clearly defined. Crumina does not interrupt marginal structure but may hang below it in lateral view. Ventral surface of crumina smooth or finely striate. Surface of valves smooth or reticulate.
Discussion.—The genus Kloedeniopsis is here proposed to include a group of North American beyrichi-acean species in which the velar and marginal ridges appear to be fused into a flattened marginal rim. A narrow marginal surface is developed on the left valve, which completely overlaps the right valve; there is no canaliculus (Henningsmoen, 1965, p. 341). Kloedeniopsis differs from the similar genera Lophokloedenia Swartz and Whitmore, 1956 and Zygobeyrichia Ulrich, 1916 in the character of the margin, as both of these genera have a velar ridge which is separated from the contact margin and marginal ridge so that there is a distinct marginal surface on each valve and a canaliculus is developed. In addition, in both of these genera the crumina of the heteromorph interrupts and displaces the velar ridge, whereas in Kloedeniopsis the crumina does not affect the marginal structure. The genus Ariklo-edenia Adamczak (1968, p. 72) resembles Kloedeniopsis in lobation, but lacks the distinct marginal structure. Forms illustrated as Welleriella Abushik (1968, pi. 37, figs. 9,10,18,19) from the Lower Devonian Ivane horizon of Podolia appear to be related to Kloedeniopsis,SYSTEMATIC PALEONTOLOGY
25
but are not as distinctly lobate and do not have as distinct a marginal structure.
Martinsson (1962, p. 347) has suggested that most of the North American beyricliiid species assigned to Kloe-denia Jones and Holl, 1886 do not belong in that genus. As redefined by Martinsson (1963, p. 41), Kloedenia s.s. is characterized by reduced lobation except for a prominent cristate preadductorial lobe which protrudes over the hinge line in lateral view and a crumina which is ornamented ventrally by three striate ridges and is assimilated with the domicilium. In contrast, the North American species assigned to Kloedenia have a rounded or globular noncristate preadductorial lobe which never protrudes above the hinge line in lateral view and a crumina which is distinctly set off from the domicilium. The concept of Kloedenia followed by North American authors is generally that of Ulrich and Bassler (1908, p. 300-303), who listed 21 American species originally, and subsequently (Ulrich and Bassler, 1923, p. 639-641) described six more. Later authors have added additional species and removed some from the genus, but at present there are between 25 and 30 species assigned to Kloedenia which are not congeneric with the type species, Kloedenia wilckensiana Jones, 1855.
Several of these species are here included in Kloe-deniopsis, and others may belong to Lophokloedenia Swartz and Whitmore, 1956 or Welleriopsis Swartz and Whitmore, 1956. For example, specimens of “Kloedenia” granulata Hall, 1859, from the Coeymans Limestone of New York show a dorsal crest and node over the adductorial sulcus suggestive of Lophokloedenia, and the holotype of “Kloedenia” oculina Hall, 1859 (NYSM 4144) appears to be a tecnomorphic specimen of Welleriopsis. However, several species assigned to Kloedenia do not agree well with any of the described genera. If, as is here assumed, the marginal structures have taxonomic significance, at least two groups may be recognized among these unresolved species. One such group is represented by li Kloedenia'1'’ normalis Ulrich and Bassler, 1923 and related species. In these species the velar structure is subdued and is more of a bend than a distinct ridge or flange; it is well separated from the marginal structure by a marginal surface. The crumina of “Kloedenia” normalis is large, anteroventral, distinctly set off from the domicilium and apparently does not displace the velar bend. The ventral surface of the crumina is finely striate. The lectotype (USNM 162287) is here designated for u Kloedenia’’’ normalis as a heteromorphic left valve selected from the original six syntypes bearing the number USNM 82997. It is illustrated on plate 3, figure 1, for comparison with Kloedeniopsis hartnageli.
The second group of unresolved species is represented by “Kloedenia''’ montaguensis (Weller, 1903). This group resembles the genera Lophokloedenia and Zygoheyrichia in having a velar ridge which is separated from the marginal ridge so that a canaliculus is developed, and in having the crumina displacing the velar ridge. However, these unresolved species lack the cristate syllobium and node in the dorsal end of the adductorial sulcus characteristic of Lophokloedenia, and also lack the ventral extension of the prenodal sulcus characteristics of Zygoheyrichia. The relationship of “Kloedenia” montaguensis and allied forms to Lophokloedenia and Zygoheyrichia needs further detailed study.
A diagram of the inferred cross sections of “Kloedenia” normalis, Kloedeniopsis hartnageli, and '■'■Kloedenia1'’ montaguensis showing the velar and marginal structures discussed above is given in figure 5. A complete carapace was available only for Kloedeniopsis hartnageli; however, the contact margins of both valves of the other two species were visible and the reconstructions are believed to be correct.
The relationship of the velar to the marginal structures may prove to have some stratigraphic significance, as present knowledge indicates that species having the kind of margin shown by “Kloedenia” normalis occur lower in the section than those having the kind of margin of either “ Kloedenia’’’ montaguensis or Kloedeniopsis.
Martinsson (1963, p. 19) listed six genera, Bingeria Martinsson, 1962; Lophokloedenia Swartz and Whitmore, 1956; Welleriopsis Swartz and Whitmore, 1956; Pseudoheyrichia Swartz and Whitmore, 1956; Welleria Ulrich and Bassler, 1923; and Zygoheyrichia Ulrich, 1916; which resemble the Kloedeniinae in having a long, ovate crumina more or less assimilated with the
m	m	m
ABC
Figure 5.—Inferred cross sections through the preadductorial lobe showing the relationship of the velar ridge to the marginal ridge in three groups of North American beyriehia-ceans. A, “Kloedenia” normalis Ulrich and Bassler, 1923; B, Kloedeniopsis hartnageli n. sp; C, “Kloedenia” montaguensis (Weller, 1903) ; m, marginal ridge; v, velar ridge.26
BRACHIOPODA AND OSTRACODA OF COBLE SKILL LIMESTONE, CENTRAL NEW YORK
domicilium, but that cannot be placed in that subfamily as currently defined and appear to be more closely related to the Beyric'hiinae. With the exception of Bing-eria, all these genera are North American. Kesling (1969, p. 291) has noted that Welleriopsis, Lophokloe-denia, Zygoheyrichia, and Bingeria have a flangelike velum and with further study these might be separated as a new subfamily. Other genera that need investigation are C omikloedenia Henningsmoen, 1954 and Pin-topsis Copeland, 1964. The new genus Kloedeniopsis appears to be more closely allied to the group of genera discussed above than to the true beyrichiines, but is here placed in the Beyrichiinae pending a revision of the group as a whole.
The name Kloedeniopsis has been given to this genus because of its superficial resemblance to Kloedenia Jones and Holl, 1886.
The range of this genus as currently understood is from the Murderian Stage of Fisher (1960), or late Pridoll, through the Helderbergian Stage, or Gedin-nian and early Siegenian; that is, from latest Silurian through earliest Devonian.
Kloedeniopsis hartnageli n. sp.
Plate 3, figures 2-10
Kloedenia notata (Hall). Jones, 1890, pi. 4, figs. 22, 23.
Description.—Lateral outline amplete, nearly twice as long as high. Lobation subdued; adductorial sulcus relatively shallow and narrow, extending from slightly more than half to slightly less than half the distance between the hinge line and the velar ridge. Prenodal sulcus shallow, short, and straight. Preadductorial lobe subdued, not rising far above level of valve surface in dorsal view, subrectangular to ovate in lateral outline. Syllobium broad, evenly curved, and nearly twice the width of the anterior lobe. Dorsal border surface very narrow. Yelar ridge narrow, wider on left valve than on right valve; perilobal depression poorly developed. Shell surface smooth on well-preserved specimens.
Heteromorphs tend to have more ovate preadductorial lobe. Crumina is large, ovate anteroventral swelling of domicilium which isolates preadductorial lobe and overhangs velar ridge, extending posteriorly of adductorial sulcus. Ventral surface of crumina is smooth or with extremely fine longitudinal striae.
The dimensions of a large tecnomorphic valve are 2.75 mm in length and 1.50 mm in height; of a heter-omorphic valve, 2.50 mm in length and 1.40 mm in height.
Types.—Holotypes, USNM 162285; paratypes, USNM 162286, USNM 162286a, USNM 162286b, USNM 162286c, YPM 23813, YPM 23814.
Discussion.—This species is characterized by its smooth surface and rather elongate subrectangular outline. With the exception of Kloedeniopsis kokomoensis (Foerste, 1909), all other species here assigned to Kloedeniopsis are reticulate or punctate. The holotype (USNM 87133) of K. kokomoensis is a coarsely silici-fied tecnomorphic carapace about 3 mm long, which may have been smooth, although the preservation is so poor that it is impossible to be certain. It differs from K. hartnageli in having a broader, more prominent preadductorial lobe and an inflated syllobium.
The specimens illustrated by Jones (1890, pi. 4, figs. 22, 23) as Kloedenia notata (Hall, 1859) are here assigned to Kloedeniopsis hartnageli. Through the courtesy of Dr. R. H. Bate I have been able to borrow from the British Museum (Natural History) the slab (BMNH In 35128) on which is the holotype of Dizygo-pleura hallii (Jones, 1890), which according to Jones (1890, p. 14, 15) is associated with Kloedenia notata. This slab is considered to be from the Cobleskill Limestone for reasons given under the discussion of Dizygo-pleura hallii later in this paper. The slab has on one surface many specimens of Kloedeniopsis hartnageli, two of which are believed to be the specimens figured by Jones as Kloedenia notata. Jones (1890, p. 14,15) indicated that his specimens came from the Waterlime Group, which in 1890 would have included the Coble-skill Limestone, but Hall (1859, p. 380) had described his “Beyrichia” notata as coming from the “tentaculite limestone, and base of the shaly limestone of the Lower Helderberg group, Herkimer county,” which in current terminology would imply that it came from the Manlius Limestone and the Kalkberg Limestone, respectively (Berdan, 1964, p. B4). Hall did not figure his specimens but described “Beyrichia” notata (Hall, 1859, p. 379) as having a finely granulose surface. It seems unlikely that Jones’ smooth specimens from the Cobleskill are con-specific with Hall’s finely granulose types from the Manlius or Kalkberg. The present location of Hall’s types of “Beyrichia" notata is not known, but his description of the species could apply to any of several species of beyrichiid ostracodes in the Manlius Limestone.
Size of sample.—Kloedeniopsis hartnageli is one of the more common species in the Cobleskill Limestone. More than 25 specimens were available for study.
Occurrence.—This species has been found in collections from Frontenac Island (USGS 3389-SD), Aurelius Station (YPM 5200/14, USGS 3395-SD), Prospect Hill (USGS 5207-SD), Oriskany Falls (YPM 5244/ 88), Forge Hollow (YPM 5244/90), Jerusalem Hill (YPM 2594), Howes Cave (USGS 8065-SD), Scho-SYSTEMATIC PALEONTOLOGY
harie (YPM 5244/146, USGS 3393-SD, and others), and Shutter Corners (YPM 5244/150, USGS 3390-SD).
Kloedeniopsis barretti (Weller)
Plate 3, figures 12-17
Beyrichia barretti Weller, 1903, p. 254, pi. 23, fig. 9.
Kloedenia barretti (Weller). Ulrich and Bassler, 1908, p. 301;
1913, p. 532, pi. 97, fig. 17; Bassler, 1915, p. 684. Zygobeyrichia barretti (Weller). Swartz and Whitmore, 1956, p. 1072-1073, pi. 108, figs. 14r-17.
Zygobeyrichia? barretti (Weller). Berdan, 1964, p. B15.
Description.—Lateral outline amplete, subquadrate. Adductorial sulcus wide and deep, slightly inclined anteriorly, extending between one-half and two-thirds the distance from the hingeline to the velar ridge. Prenodal sulcus narrow, nearly as long as the adductorial sulcus, tends to swing posteriorly isolating the preadductorial lobe. Preadductorial lobe suboval in outline, does not protrude laterally far above valve surface. Velar ridge wide on left valve and fringed with short, widely spaced spinelets, narrow ventrally on right valve. Distinct perilobal groove separates velar ridge from domicilium. Surface of valves ornamented with coarse irregular reticulation except on velar ridge and sulci. Dorsal surface narrow.
Crumina is anteroventral expansion of domicilium which may or may not overhang velar ridge. Crumina coarsely reticulate except on ventral surface, which is finely striate.
Two tecnomorphs are 2.65 mm in length and 1.64 mm in height, and 2.50 mm in length and 1.77 mm in height, respectively. A heteromorph is 2.71 mm in length and 1.70 mm in height.
Discussion.—Swartz and Whitmore (1956, p. 1072-1073) placed this species in Zygobeyrichia and stated that the zygobeyrichiid ventromedian swelling and post-median [sic] subventral furrow are well marked. Their illustrations (Swartz and Whitmore, 1956, pi. 108, figs. 14-17) of the holotype also show these features. However, although the very irregular flat-bottomed reticulation characteristic of Z. barretti is present on the specimens from the Cobleskill, most of them do not show the anteroventral furrow of Zygobeyrichia. The similarity in ornamentation and lobation suggests strongly that the Cobleskill specimens are conspecific with Z. barretti, but the absence of a well-developed zygobeyrichiid furrow raises doubts about the generic assignment of the species. Furthermore, the marginal structures of Z. barretti are those of Kloedeniopsis, not Zygobeyrichia as represented by Z. apicalis Ulrich, 1916, the type species of the genus. Consequently, the species is here referred to Kloedeniopsis, although the
27
sulci of K. barretti are longer and deeper than those of any other species assigned to the genus.
Size of sample.—This species is abundant in the eastern part of the Cobleskill outcrop belt. More than 30 specimens were available for study, including more than 10 complete carapaces.
Occurrence.—This species has been found in the Cobleskill Limestone in collections from Schoharie (USGS 3393-SD, USGS 8063-SD, YPM 5244/146) and Howes Cave (USGS 8065-SD) and in collections from the Decker Limestone of New Jersey and the Keyser Limestone of Maryland.
Genus TIKIOPSIS n. gen.
Type species.—Tihiopsis denticvlata n. sp.
Species included.—Only the type species.
Diagnosis.—Trilobate beyrichiines with deep sulci that tend to isolate preadductorial lobe. Anterior lobe and syllobium bluntly cuspate and may rise above dorsal margin in lateral view; preadductorial lobe set well below dorsal margin. Dorsal and ventral surfaces broad, so that complete carapace is wide and boxlike. Velar ridge narrow but distinct, with adnate flap or thickening on ventral surfaces of both valves. Heteromorph not known.
Discussion.—Although few specimens are available and only the tecnomorph is as yet known, the type species is so distinctive that it cannot be placed in any described genus. The peculiar ventral “flap” or thickening of the ventral surface appears to be unique, as do also the deep sulci isolating the preadductorial lobe. Tihiopsis appears to be most closely related to Welleri-opsis Swartz and Whitmore, 1956, but the latter has short sulci which do not extend more than half the height of the valve, and the prenodal sulcus is shallow. Specimens of Welleriopsis sp. cf. W. jerseyensis (Weller, 1903) from the Wilbur Limestone of the Hudson Valley and W. sp. cf. W. diplocystulis Swartz and Whitmore, 1956 from the Coeymans Limestone of central New York do not show the ventral adnate flap of Tihiopsis.
The generic name is derived from the resemblance of the dorsal aspect of a complete carapace to the Polynesian carved wooden figures called “tikis.”
Tikiopsis denticulata n. sp.
Plate 3, figures 24-30
Description.—Lateral outline amplete, subquadrate to subcircular; cardinal angles obtuse; hinge line less than greatest length of shell. Height approximately four-fifths of length. Adductorial sulcus deep, narrow, extending two-thirds of distance from dorsal margin28
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
to velar ridge; prenodal sulcus deep, narrow, curves around to unite with adductorial sulcus dorsally and ventrally, tending to isolate preadductorial lobe. Pre-adductorial lobe suboval in outline, set well below dorsal margin; anterior lobe and syllobium bluntly cuspate, forming a 'broad dorsal border surface into which hinge line is slightly incised. Velar ridge narrow ventrally, wider at cardinal angles, separated from domicil-ium by narrow furrow. Domicilum inflated; free marginal surfaces broad, so that carapace appears boxlike. Ventral surface of velar ridge has adnate flaplike thickening. Contact margin marked by a row of small interlocking denticles on both valves.
Shell surface smooth. Heteromorph not known.
The holotype is 2.50 mm in length and 1.75 mm in height, and another complete carapace is 2.50 mm in length and 1.80 mm in height. A larger single left valve is 2.75 mm in length and 1.85 mm in height. The smallest specimen found is 2.0 mm in length and 1.25 mm in height.
Types.—Holotype, USNM 162292; paratypes USNM 162292a, USNM 162293, USNM 162293a, YPM 23816-23818.
Discussion.—As yet no specimens have been found which can be considered to be heteromorphs of this species. Although the adnate flap of the velar ridge on the ventral surface suggests cruminal structures of heteromorphs of other beyrichiacean ostracodes, no indications of a crumina have been found in any of the specimens studied, and all the specimens are probably tecnomorphs. Further evidence for this view is that the position of maximum width is posterior for all specimens. The smallest specimen (USNM 162292a), which presumably represents a preadult instar, shows the adnate flap developing as a fold on the velar ridge (pi. 3, fig. 30). The significance of this structure is not clear, but it apparently is not analogous to the velar flap on the crumina of other beyrichiaceans. When hetero-morphic individuals of Tikiopsis denticulata are found, its relationships may be clarified. The specific name is based on the presence of interlocking denticles along the contact margin.
Size of sample.—Fifteen reasonably complete specimens were available for study, of which two are complete carapaces and one is a broken carapace. In addition, many fragmentary specimens were examined.
Occurrence.—In collections from “crinoidal” limestone at Shutter Corners (YPM 5244/150, USGS 3390-SD), Central Bridge (USGS 7198-SD) and Schoharie (YPM 5244/146, USGS 3393-SD, USGS 8063-SD, USGS 8439-SD).
Genus WELLERIOPSIS Swartz and Whitmore, 1956 Welleriopsis? pustulosa n. sp.
Plate 3, figures, 18-23
Description.—Lateral outline amplete, subrectangu-lar; cardinal angles obtuse; hinge line less than greatest length of shell. Dorsal outline lanceolate. Height slightly more than half length of shell. Prenodal sulcus shallow, broad, short, being clearly defined only in dorsal third of valve. Adductorial sulcus deeper, broad, extends half or slightly more than half height of valve. Anterior lobe relatively broad, cuspate dorsally, protruding above hinge line. Preadductorial lobe small, subglobular to subovate, set well below hinge line. Syllobium broad, broadly cuspate dorsally. An indistinct zygal ridge is developed beneath the preadductorial lobe and adductorial sulcus. Velar ridge narrow, separated from domicilium by a shallow groove. Ventral surface channeled on both valves. Small denticles around free margins of both valves.
Surface covered with indistinct pustules on which is superimposed a fine granulation. This ornamentation covers surface of domicilium except for sulci.
Heteromorph similar to tecnomorph except that height is relatively greater; valve is inflated so that preadductorial lobe is isolated and velar ridge is obscured, but not obliterated, by inflation of valve.
The dimensions of a large tecnomorph are 3.1 mm in length and 1.75 mm in height. The heteromorph is 3.3 mm in length and 2.2 mm in height.
Types.—Holotype, USNM 162296; paratypes, USNM 162294, USNM 162294a, USNM 162295, YPM 23844.
Discussion.—This species is questionably assigned to Wellenopsis because of the character of the presumed heteromorph. Only one heteromorphic valve has been found as yet, and this specimen does not show as pronounced a cruminal inflation as is illustrated by Swartz and Whitmore (1956, pi. 105, figs. 10, 11) for W. diplo-cystulis, the type species of the genus. Furthermore, species assigned to Wellenopsis by Swartz and Whitmore do not seem to have as pronounced cusps on the anterior lobe and syllobium. However, specimens of IFellenopsis from the Coeymans Limestone (Lower Devonian) show a reduced velar ridge crossing the cruminal inflation as in IF.? pustulosa, although the cruminal inflation is much more conspicuous in the Early Devonian forms. This species appears to be similar in outline and loba-tion to the form described as Kloedenia ? newbrunswick-ensis by Copeland (1962, p. 35-36, pi. 8, figs. 1-8) from the Lower Devonian upper Dalhousie beds of New Brunswick, although differing markedly in ornamentation. This relation suggests that this type of ostracode continues fairly high into the Early Devonian.SYSTEMATIC PALEONTOLOGY
29
Superficially, W. ? pustulosa resembles Tikiopsis den-ticulata, but no specimens have been found showing the adnate ventral flap characteristic of Tikiopsis, and the sulci are shorter and shallower.
Size of sample.—Seven specimens, including three complete carapaces, were available for study.
Occurrence.—All specimens are from collections at Schoharie (YPM 5244/146, USGS 3393-SD, USGS 8063-SD, USGS 8064-SD). A small tecnomorph with similar ornamentation has been found in the Wilbur Member (Upper Silurian) of the Rondout Limestone of the Hudson Valley (USGS colln. 7999-SD).
Welleriopsis? sp.
Plate 3, figure 11
Discussion.—Three small tecnomorphs with the general lobation of Welleriopsis have been found in a collection from Shutter Comers (USGS 3390-SD). These are smooth and somewhat resemble Welleriopsis jersey-ensis (Weller), but have deeper sulci. The material in hand is not adequate for identification or description. The figured specimen (USNM 162291) is 2.05 mm long and 1.30 mm high.
Superfamily DREPANELLACEA Ulrich and Bassler, 1923 Family KIRKBYELLIDAE Sohn, 1961
Kirkbyellid ?, gen. and sp. indet.
Plate 6, figure 15
Discussion.—A single left valve of a coarsely reticulate ostracode has been found at Schoharie (USGS 8064-SD) . The posterior part of the specimen is broken, but the pattern of the reticulations on the ventral part of the valve suggests that there may have been a backwardpointing projection, as in Kirkbyella. However, unlike that genus the specimen is distinctly bisulcate. The straight hinge line, subquadrate outline, lack of velar structures, and indication of a posterior spur suggest that this specimen is a kirkbyellid, although it cannot be assigned to any described genus. The broken specimen is 0.80 of a mm long and 0.45 of a mm high.
Superfamily H0LLINACEA Swartz, 1936 Family HOLLINIDAE Swartz, 1936
Hollinid?, gen. and sp. indet.
Plate 6, figure 14
Discussion.—One left valve, broken anteriorly, which differs markedly from other Cobleskill ostracodes, has been found in a collection from Schoharie (USGS 8064-SD) . The specimen is velate; the velum is tubulous and extends posteriorly to just behind the median sulcus. The median sulcus is distinct and extends more than half the height of the valve excluding the velum. The median lobe is small and oval; the anterior sulcus is indistinct.
On the dorsoposterior side of the median sulcus there is a small rounded knob. This specimen may represent a hollinid allied to ParaboTbina or Triemilomatella, but there is no indication of loculi on the ventral surface of the valve. As only one specimen has been found, it is impossible to assign it to a genus, or even to be sure that it is a hollinid, as it might possibly be an amphitoxotidine beyrichiacean, although the velum is more restricted than is usual in that group. The specimen is 0.80 of a mm long and 0.50 of a mm high.
Superfamily PRIMITIOPSACEA Swartz, 1936 Family LEIOCYAMIDAE Martinsson, 1956 Genus LEIOCYAMUS Martinsson, 1956
Leiocyamus punctatus n. sp.
Plate 6, figures 34-40
Description.—Lateral outline amplete, subovate; dorsal outline of tecnomorphs lanceolate, of heteromorphs lanceolate with a chevron-shaped reentrant at the posterior end. Hinge straight, incised; dorsum gently curved; ends and ventral margin evenly curved. Position of maximum length median; position of maximum width in posterior third of shell; position of maximum height median. Right valve markedly overlaps left along free margins. No velar structure in tecnomorphs; velar structure confined to dolon of heteromorphs. Small tubercles present around free margins of both valves.
Shell surface, including dolonal flanges, completely covered with small, circular punctae except for a round, smooth area in the center of each valve. The inner surfaces of the dolon are smooth. Dolonal flanges short, stout, not extending forward on ventral margin of valve beyond about one-third of the length.
Both valves have a faint raised round area in the interior beneath the smooth spot on the exterior. The hinge of the right valve has a groove for the reception of the sharp edge of the left valve. Both valves have distinct indentations at either end of the hinge.
The dimensions of a representative heteromorph are 0.98 of a mm in length, 0.71 of a mm in height, and 0.48 of a mm in width.
Types.—Holotype, YPM 23840; paratypes, YPM 23837-23839, YPM 23841, USNM 162365,162366.
Discussion.—This species has been assigned to Leiocyamus because the dolon does not form an enclosed chamber and the lateral surface of the valves is not sulcate. Martinsson (1956, p. 30), in his diagnosis of the genus, stated that the dolon was extended forward along the ventral side of the valve. This feature is poorly developed in L. punctatus, the dolon being largely confined to the posterior end of the shell and
447-769 0 - 72 -530
BRACHIOPODA AND OSTRACODA OF COBLE SKILL LIMESTONE, CENTRAL NEW YORK
not extending beyond the midpoint even on the right valve, where it is best developed. This species also differs from the type species, L. apicatus Martinsson, 1956, in having a less prominent dorsal ridge which does not rise to a point, so that superficially the two species appear quite different. However, the absence of sulcation and the open dolon are considered sufficient for the generic assignment.
The primitiopsids are abundant in the Silurian of Europe; but, to date, only one genus, Limbinaria Swartz and Whitmore, 1956, has been reported from the Silurian of North America. The occurrence of this additional European genus in the North American Silurian is therefore of considerable interest.
Size of sample.—More than 50 specimens were available for study.
Occurrence.—Moderately abundant in collections from Schoharie, N.Y. (YPM 5244/146, USGS 3393-SD, USGS 7283-SD) and has also been found in collections from Jerusalem Hill (YPM 2594), Howes Cave (USGS 8065-SD), near Central Bridge (USGS 7198-SD), and Shutter Corners (USGS 3390-SD). A very similar form, perhaps nonspecific, occurs in a collection from the Decker Limestone of Pennsylvania at Shawnee on Delaware (USGS 5839-SD).
Leiocyamus sp. A
Plate 6, figures 47, 48
Discussion.—One heteromorphic carapace from Shutter Corners (YPM colln. 5244/150) is nearly twice as large as specimens of L. punctatus from Schoharie and Jerusalem Hill, measuring 1.83 mm in length, 1.15 mm in height, and 1.01 mm in width. It also differs from typical specimens of L. punctatus in having a large inflated area in the central part of each valve and in having a rounded rather than subangular dorsal ridge. This probably represents a different species, but as only one specimen is available for study, it does not seem desirable to propose a name for it at the present time.
Leiocyamus sp. B
Plate 6, figures 45, 46
Discussion.—A crushed heteromorphic carapace and one right and one left valve have been found that differ from Leiocyamus punctatus. These specimens have a wider dolon that is distinctly set off from the domi-cilium and extends farther forward than that of L. punctatus. Furthermore, in these specimens the dorsum is narrow and the hinge line is not deeply incised. The ornamentation is punctate, but the punctate appear
to be finer on the dolon. These specimens may represent yet another species of Leiocyamus, or may be a variant of L. punctatus. The material at hand is inadequate for determination at this time.
The specimens are from Schoharie, N.Y. (USGS colln. 3393-SD, USGS colln. 7283-SD). A broken specimen from Prospect Hill (USGS colln. 5207-SD) has the same characters as the specimens from Schoharie. A left valve is 1.20 mm in length and 0.70 of a mm in height. A crushed carapace is 1.20 mm in length and 0.75 of a mm in height.
Family PRIMITIOPSIDAE Swartz, 1936 Genus PRIMITIOPSIS Jones, 1887
Primitiopsis? sp.
Plate 6, figure 44
Discussion.—A single tecnomorphic carapace of a sul-cate primitiopsid has been found at Schoharie, N.Y., (USGS colln. 8062-SD). The specimen is fairly coarsely reticulated except for the ventral surfaces of both valves, which form smooth lips. No denticles have been seen along the contact margins, but their absence may be due to the type of preservation. The median sulcus extends slightly less than half the height of the valves, and although its ventral end is wider it does not end in a distinct pit as in Primitiopsis s.s. This specimen is tentatively assigned to Primitiopsis, although until heteromorphic specimens are found it will not be possible to determine whether true Primitiopsis is present in the Cobleskill fauna. The specimen is 1.15 mm long and 0.65 of a mm high.
Family uncertain Genus HALLIELLA Ulrich, 1891
Halliella? sp.
Plate 6, figure 16
Discussion.—A single incomplete valve of a reticulated unisulcate ostracode has been found in USGS collection 7283-SD from Schoharie, N.Y. Slightly more than half the valve is preserved, which is enough to show that the specimen was relatively long in proportion to its height; it has a subrectangular outline and a deep median sulcus which is broad ventrally, like an inverted keyhole. The reticulations extend to the edge of the valve, which overhangs the contact margin, but there is apparently no velate structure. The specimen is here tentatively listed as Halliella?, but it may be an early kirkbyacean. It is illustrated to call attention to this type of ostracode in the Cobleskill fauna. The broken specimen is 0.60 of a mm long and 0.40 of a mm high.SYSTEMATIC PALEONTOLOGY
31
Order KLOEDENELLICOPIDA Seott, 1961
Superfamily KLOEDENELLACEA Ulrich and Bassler, 1908 Family KLOEDENELLIDAE Ulrich and Bassler, 1908
Genus DIZYGOPLEURA Ulrich and Bassler, 1923
Diagnosis.—Trisulcate kloedenellids with left valve overlapping right valve, and bearing a narrow stragular process above Si which fits into a deep narrow notch in right valve.
Discussion.—The above diagnosis differs from that given by Sohn (in Moore, 1961, p. Q182) in including reference to the type of stragular process. This structure, named and discussed by Guber and Jaanusson (1964, p. 2-5), appears to be quite different in the otherwise similar genera Dizygopleura, and Poloniella. In Dizygopleura, the stragular process is narrow, lingui-form, and fits into a distinct notch in the right valve. In Poloniella, the stragular process is wide, as much as one-fourth of the length of the hinge line, and is not clearly set off from the hinge line. Adamczak (1961, p. 295) recognized the differences in hingement between Dizygopleura and Poloniella, as represented by Poloniella devonica Giirich, 1896, but he did not consider them significant. He considered (Adamczak, 1961, p. 295) Dizygopleura to be a junior synonym of Poloniella.
Adamczak (1961) based this conclusion on the similarities of hingement and Jobation in the two genera, and on the ontogenetic development of Poloniella devonica and several other species which he assigned to Poloniella. As discussed above, the hingement of P. devonica differs from that of Dizygopleura swartzi Ulrich and Bassler, 1923, the type species of Dizygopleura, in the character of the stragular process. Dizygopleura characteristically is trilobate, with Si and S3 long, extending more than two-thirds the height of the shell and S2 relatively short. Poloniella is also trilobate, but SI and S3 join beneath S2. There is little difficulty distinguishing typical Dizygopleura from Poloniella on the basis of lobation, but in several species, here considered Dizygopleura, S3 curves anteriorly under S2 and is represented by one or more ventral pits. Two species that have two ventral pits are D. costata Ulrich and Bassler, 1923, and D. hieroglyphica (Krause, 1891); the latter is much discussed in controversies over the relationship of Dizygopleura and Poloniella. Two species that have one ventral pit are D. unipunctata (Ulrich and Bassler, 1923) and D. monostigma, n. sp. These species and others—such as D. angustisulcata Swartz and Whitmore, 1956, in which S3 is almost obsolete so that the species verges on Kloedenella— suggest that sulcation is gradational in kloedenellids and may be a difficult character to use for generic distinctions.
Adamczak (1961, p. 287-289, pi. 1) discussed and illustrated two species, Poloniella tertia Krommelbein, 1953 and P. diversa Adamczak, 1961, which have juveniles as large as adult -2 with Poloniella-like sulcation and adults with sulcation like that of Dizygopleura. This relation would seem to give support to the synonymy of Dizygopleura with Poloniella, and would suggest that the Poloniella type of sulcation is the more primitive. However, typical Dizygopleura appears in the Middle Silurian, whereas Poloniella s.s. is, as far as known, restricted to the Devonian. Furthermore, Lun-din (1965, pi. 10, figs. 3a-q) has illustrated immature instars of Dizygopleura landesi as young as adult -4, which have typical sulcation of the Dizygopleura type; the same is true of immature specimens of D. hallii illustrated in this paper (pi. 5, figs. 21-23). Possibly the adults illustrated by Adamczak represent convergent evolution in Poloniella, or perhaps they do not belong with the immature tecnomorphs as figured.
Although Adamczak has demonstrated that Dizygopleura and Poloniella are closely related, it is questionable whether they are more closely related than Dizygopleura and Kloedenella are. Dizygopleura and Poloniella differ more in the character of the stragular process than do Dizygopleura and Kloedenella. Recently, Weyant (1968, p. 100-101) has suggested that Dizygopleura should be considered a subgenus of Poloniella., and has also described a new subgenus, Framelia, of Poloniella. The stragular process of Framella Weyant, 1968, pi. 2, figs. 8, 9) appeal's to be close to that of Poloniella, which suggests that Framella may be correctly assigned as a subgenus of Poloniella. However, the narrow stragular process and deep stragular notch of Dizygopleura are here considered sufficiently distinctive to warrant retaining Dizygopleura as a separate genus, pending further study of the North American Silurian species as recommended by Weyant (1968, p. 101). This retention seems especially desirable in view of the different geographic and stratigraphic occurrences of Dizygopleura and Poloniella.
Dizygopleura hallii (Jones)
Plate 5, figures 20-45
Beyrichia Hallii Jones, 1890, p. 15, pi. 4, fig. 21.
Beyrichia lialli Jones. Ulrich, 1894, p. 669. (listed under Bollia.) Beyrichia Halli Jones. Giirich, 1896, p. 390.
Kloedenella halli (Jones). Ulrich and Bassler, 1908, p. 319, fig. 62, pi. 43, fig. 4; Clarke, 1909, p. 13, 21; Grabau and Shimer, 1910, p. 359, text fig. 1663g; Bonnema, 1914, p. 1107, pi. fig. 6; Bassler, 1915, p. 683; Kummerow, 1931, p. 158-159.
Poloniella Hallii Jones (sic). Van Veen, 1921, p. 891, fig. 12; 1922, p. 995, fig. 12.
Dizygopleura halli (Jones). Ulrich and Bassler, 1923, p. 696, pi. 62, figs. 24, 25; Swartz, 1933, p. 234.32
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
Dizygopleura hallii (Jones). Bassler and Kellett, 1934, p. 290;
Warthin, 1937, card 58.
Beyrichia Clarkei Jones, 1890, p. 17, text fig. 2.
BeyricMa clarki Jones. Ulrich, 1894, p. 669.
Kloedenella clarkei (Jones). Ulrich and Bassler, 1908, p. 319, 320; 1913, p. 533, pi. 97, fig. 21; Bassler, 1915, p. 683. Dizygopleura clarkei (Jones). Ulrich and Bassler, 1923, p. 698, pi. 62, figs. 31, 32; Swartz, 1933, p. 233-234; Bassler and Kellett, 1934, p. 289; Warthin, 1937, card 58. Dizygopleura cf. D. clarkei (Jones). Swartz and Whitmore, 1956, p. 1086-1087, pi. 109, figs. 26, 27.
Description.—Lateral outline preplete to amplete, subelliptical to subrhomboidal; dorsal outline indented subfusiform. Anterior margin smoothly rounded; ventral margin sinuate, rarely convex; posterior margin curved, meeting sinuate dorsal margin at an obtuse angle. Stragular process narrow, prominently humped. Hinge line slightly incised behind stragular process so that narrow, triangular dorsal border surfaces are
formed on the posterior part of each valve. Stragular process and corresponding notch at dorsal end of Si. Si long, straight to slightly concave posteriorly, relatively deep. S2 wider, deeper, extends about one-half height of valve, curves slightly toward anterior. S3 about same height and width as Si; ventral end curved anteriorly. Lobes about twice width of sulci. Posterior margin of L4 convex toward posterior, separated from posterior margin by indented triangular area in tecnomorphs. Posteroventral keel present on some specimens. Heteromorph differs from tecnomorph in wider L4, slight inflation of posterior triangular area, and narrower S3. Shell surface smooth.
According to my measurements the holotype of Dizygopleura haUii is 1.30 mm in length and 0.75 of a mm in height. The holotype of D. clarkei is also 1.30 mm in length and 0.75 of a mm in height. Measurements of specimens from Schoharie, N.Y., are shown in figure 6.
Figure 6.—Scatter diagram of maximum length versus maximum height for 129 carapaces of Dizygopleura hallii (Jones) from Schoharie, N.Y. (USGS 3393-SI>). Measurements made on left valve. Bach circle concentric about a point indicates an additional specimen with the same measurements, five or more specimens being indicated by a slash through the circles. *, indicates measurements of holotype.SYSTEMATIC PALEONTOLOGY
33
Types.—Holotype of Dizygopleura halli is BMNH In 35128; holotype of D. clarkei is NYSM 4141; plesio-types of D. hallii are USNM 162330-162345, YPM 23827.
Discussion.—Jones (1890, p. 15) described Dizygopleura hallii from a specimen on a small slab of rock which was sent to him by John M. Clarke, who presumably wrote Jones that it came from the “Waterlime Group,” from near Utica, N.Y. Jones (1890, p. 15) stated that the limestone was “Largely composed of small organisms, especially Kloedenia not at a. with small Brachiopods, etc.” This slab, BMNH In 35128, was kindly loaned to me by Dr. R. H. Bate of the British Museum (Natural History). As noted under the discussion of Kloedeniopsis hartnageli n. sp., the ostra-codes identified by Jones as “Kloedenia notata” are here assigned to K. hartnageli, and the associated brachiopods include Morinorhynchus? interstriatus, Howellella corallinensis eriensis, and Protathyris sulcata, all species characteristic of the Cobleskill Limestone. None of these species occurs in the younger Manlius Limestone, and consequently it seems reasonable to conclude that the slab from which Jones described D. hallii came from the Cobleskill rather than from the Manlius as stated by Ulrich and Bassler (1923, p. 697), Bassler and Kel-lett (1934, p. 290), and Warthin (1937, card 58). As noted under the discussion of Protathyris sulcata, the “Waterlime Group” of Vanuxem (1842) included both the Cobleskill and Manlius Limestones.
In the same paper in which he described D. hallii Jones (1890, p. 17) described Dizygopleura clarkei from a drawing sent to him by J. M. Clarke, which he illustrated as a woodcut (Jones, 1890, p. 17, fig. 2). He probably never saw the actual specimen. Dr. Bruce Bell has kindly loaned me a specimen (NYSM 4141) from the New York State Museum which is labeled llBey-richia clarkei Jones, type” and which is presumably the original from which the drawing was made. This specimen is also on a slab of dolomitic limestone, like that on which is the type of D. hallii; and the associated fauna includes the Cobleskill forms Morinorhynchus? inter striatus, Howellella corallinensis subsp. indet., Kloedeniopsis hartnageli, and Leiocyamus sp. A. The slab from the British Museum (BMNH In 35128) has been compared with the slab from the New York State Museum, and although similar in lithology and fauna they were not originally parts of the same piece of rock. However, the slab from the New York State Museum, like that from the British Museum, undoubtedly also came from the Cobleskill Limestone.
Jones (1890, p. 17), presumably quoting information provided by Clarke, stated that Dizygopleura clarkei was “associated with Beyriehia oculina and B. notata-
ventricosa in the Lower-Helderberg Group of Herkimer Co., N.Y.” Although it is not known when Clarke sent the drawing of D. clarkei to Jones, it seems probable that it was before he excluded the Waterlime Group from the Lower Helderberg Group in 1889 (Berdan, 1964, p. B4-B5). Ulrich and Bassler (1913, p. 533, 534) mentioned D. clarkei as occurring in the Keyser Limestone at Cumberland, Md., and stated that the type is from Herkimer County, N.Y. Later, however, Ulrich and Bassler (1923, p. 698, 699, pi. 62, fig. 32) redescribed and reillustrated the type and stated that it occurs in “the Lower (typical) Manlius of Schoharie County, New York.” They noted that D. hallii, Zygo-heyrichia regina Ulrich and Bassler, 1923, and a new species occur with it. At the time Ulrich and Bassler were writing, the Cobleskill was considered the basal member of the Manlius, but their statement that D. clarkei occurs in the “typical” Manlius excludes the Cobleskill. Ulrich must have examined the type of D. clarkei, for a note with the type specimen in the New York State Museum appears to be in his handwriting and lists the associated fauna as given in Ulrich and Bassler (1923). Unfortunately, their remarks of 1923 concerning the horizon and locality from which the type came have led all subsequent workers to conclude erroneously that Dizygopleura clarkei belongs in the Manlius, not the Cobleskill.
Swartz (1933, p. 233, 234) suggested that D. clarkei might be the female dimorph of D. hallii, and this suggestion was accepted by Warthin (1937, card 58), who refigured Jones’ original illustrations of both species in his discussion of D. hallii. The holotype specimens of both species (pi. 5, figs. 44, 45) are lieteromorphic left valves which appear to be conspecific. Consequently, D. clarkei is here considered to be a junior synonym of D. hallii.
More than 500 specimens believed to be conspecific with the holotype of D. hallii have been found in the collections from Schoharie, N.Y.; these have a narrow L4, are slightly smaller than the type, and are considered to be tecnomorphs. To date, only one corroded carapace has been found in these collections which may represent a heteromorph. A possible explanation for this anomalous situation is that the adults did not oc-cupy precisely the same habitat as the juveniles.
As interpreted in this paper, Dizygopleura hallii is a highly variable species, especially as regards the width and depth of the sulci. In particular, S3 may be shallow and narrow (pi. 5, figs. 30-32) or wide and deep (pi. 5, figs. 33-35, 37, 38). Specimens from Schoharie, N.Y., represent both extremes, and could be assigned to two different species; however, the presence of intermediate forms, including the holotype, makes it difficult to recog-34
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
nize any consistent distinctions between the end members of the series. Possibly future studies on additional material will demonstrate the presence of more than one species in the group of specimens here considered as Dizygopleura halli; if so, some of these specimens might be assigned to D. angustisulcata Swartz and Whitmore, 1956, but this assignment will depend upon restudy of the type of this species together with the accumulation of an ontogenetic series to determine whether the species are distinct. Dizygopleura angmtisculcata appears to have a more narrow S3 than any of the forms here included in D. hallii, and as it occurs in the upper part of the Decker Limestone of New Jersey, it may be slightly younger than typical D. hallii.
The syntypes of Dizygopleura hallii ohscura Ulrich and Bassler, 1923 (USNM 63654), have a short, shallow, and narrow S3, and appear to represent a separate species. D. hallii ohscura is from the lower Tonoloway Limestone at Keyser, W. Va., and is presumably older than D. hallii.
The holotype of Dizygopleura clarkei paupera Ulrich and Bassler, 1908 (USNM 53280) from the Keyser Limestone in Maryland, has been refigured on plate 5, figure 17. The specimen is a broken carapace, probably of an immature instar, with S2 wide and deep and little indication of a posterior flange. SI and S3 are filled with matrix on both valves, which may account for the mention of papillae in the sulci in the original description (Ulrich and Bassler, 1908, p. 320). Although the interior and posterior sulci are filled, their course can be distinguished, and they are more vertical than shown in the original illustration (Ulrich and Bassler, 1908, pi. 43, fig. 5). Until additional topotype material can be found and studied, this taxon should be considered a nomen dubium.
Size of sample.—More than 500 carapaces of Dizygopleura hallii were available for study, of which 120 have been measured (fig. 5).
Occurrence.—This species has been found in collections from Shutter Corners (USGS 3390-SD), Schoharie (USGS 3393-SD, USGS 7283-SD, USGS 8063-SD, YPM 5244/146), near Central Bridge (USGS 7198-SD), Howes Cave (USGS 8065-SD), Jerusalem Hill (YPM 2594), Forge Hollow (YPM 5244/90B), Prospect Hill (USGS 5207-SD), and Aurelius Station (YPM 5244/14). The type specimen is identified only as coming from Herkimer County, N.Y.
Dizygopleura monostigma n. sp.
Plate 5, figures 1-12; figure 7
Description.—Lateral outline amplete to preplete, subrhomboidal; dorsal outline indented fusiform. Anterior margin rounded; ventral margin slightly sinuate;
posterior margin curved upward, meeting sinuate dorsal margin at an obtuse angle. Dorsal margin straighter in small instars. Stragular process narrow, humped, fits into deep notch in right valve. Hinge line slightly entrenched posteriorly so that narrow triangular border surfaces occur on the posterior part of both valves. SI deep, long, curved posteriorly, situated beneath stragular process, extends nearly the entire height of valves. S2 wider, shorter, curved strongly anteriorly, extends only about half the height of valves. S3 about same width and depth as SI, curves strongly anteriorly and either extends beneath S2 or is represented by a distinct laterally elongated pit beneath S2. Lobes subequal in width; L2 distinctly bulbous in lateral outline although not extending above surface of valves. Posterior edge of L4 convex toward posterior, separated from posterior margin of valve by indented flange about equal to it in width. This flange is somewhat inflated in heteromorphs, so that in dorsal view the outline is straight from posterior edge of L4 to posterior margin, whereas in tecnomorphs the outline is indented. Shell surface smooth.
A typical adult specimen, the holotype, is 1.35 mm in length and 0.70 of a mm in height. For range of dimensions in immature instars see figure 7.
Types.—Holotype, USNM 162323; paratypes, USNM 162320, USNM 162324.
Discussion.—This species is associated with Dizygopleura hallii at Schoharie, N.Y., and was at first considered to be a variant of D. hallii. However, the presence of small specimens showing the characteristic pit beneath S2 suggests that Dizygopleura monostigma should be recognized as a separate species. D. monostigma has also been found in the Keyser Limestone about 5-10 feet above a ledge that contains Gypidula prognostica Maynard, 1913, in an old quarry just west of La Vale, Md. (USGS 8125-SD), which is included in the old Cash Valley section of the Maryland Survey Lower Devonian volume. (See Ulrich and Bassler, 1913.) The Maryland specimens attain a greater size than do those from Schoharie, and the large specimens are dimorphic; apparently none of the Schoharie specimens are adults. Accordingly, the holotype and paratypes have been selected from USGS 8125-SD) from Maryland. The specimens from Schoharie show more variability in S3 than do those from Maryland, as in some specimens the subcentral pit appears to connect directly with this sulcus and be an extension of it. Also, the Schoharie specimens tend to be somewhat longer in proportion to their height, as shown in figure 7. Probably not more than three instars are present in theSYSTEMATIC PALEONTOLOGY
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Figure 7.—Scatter diagram of maximum length versus maximum height for Dizygopleura monostigma n. sp.; 60 carapaces from Schoharie, N.Y., and 40 specimens from the Keyser Limestone just above the Gypidula prognostica Zone, Cash Valley Road, La Vale, Md. (USGS 8125-SD). Specimens from Schoharie shown by points or concentric circles, each circle concentric about a point representing an additional specimen with identical measurements; specimens from La Vale shown by triangles; a slash through concentric circles indicates live or more specimens. *, indicates measurements of holotype.
Schoharie collections, as compared to four (including the adults) in the Maryland collection. Perhaps, as suggested for Dizygopleura haHii, the adults of D. monostigma may have lived in a different habitat in the Schoharie area.
Dizygopleura monostigma differs from D. unipu/nc-tata Ulrich and Bassler, 1923, in having the ventro-median pit elongated horizontally rather than vertically as in the latter species.
Size of sample.—More than 200 specimens were available for study, of which 100 were measured.
Occurrence.—D. monostigma has been found in collections from Schoharie, N.Y. (USGS 3393-SD, USGS 7283-SD, USGS 8063-SD, YPM 5244/146), and just west of La Vale, Md. (USGS 8125-SD).
Dizygopleura eostata Ulrich and Bassler
Plate 5, figures 13-16
Dizygopleura eostata Ulrich and Bassler, 1923, p. 700, pi. 60, figs. 23, 24.
Description.—Lateral outline kloedenelliform; dorsal outline indented subtrapezoidal. Anterior margin rounded; ventral margin sinuate; posterior margin obtusely angulate; dorsal margin nearly straight. Stragu-lar process narrow, on left valve dorsal to Ll and Si, on right valve dorsal to Si; hump not prominent. Hinge line slightly incised; narrow, triangular dorsal border surfaces on each valve. Sulci wide, deep; lobes narrow, giving carapace an emaciated appearance. Si and S3 extend entire height of shell; S2 extends about two-thirds of distance from dorsal to ventral margin.36
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
Beneath S2 is a pit, and between S2 and S3 is another pit. Lobes narrow, not much wider than sulci, cristate. L4 narrow, separated from posterior end of shell by depressed flange in tecnomorphs. Heteromorph with only slightly more thick posterior flange. Shell surface smooth in sulci and on posterior flange, appears slightly punctate on lobes.
A representative adult specimen measures 0.92 of a mm in length and 0.47 of a mm in height.
Types.—Lectotype, TTSNM 162325, the original of figure 23, plate 60 of Ulrich and Bassler (1923). The paralectotype is USNM 63677, the original of figure 24, plate 60 of Ulrich and Bassler (1923).
Discussion.—This distinctive species may be recognized by the two ventral pits beneath S2 and the cristate lobes which give the specific name.
Ulrich and Bassler (1923, p. 699-701) included D. costata in their “Group of Dizygopleura hieroglyphica (Krause)” and commented on its resemblance to that species. They also included in this group their new species D. perrugosa, D. virginica, and D. unipunctata— the characteristic of the group being that the lobes are narrower than the sulci. The illustration of D. perrugosa (Ulrich and Bassler, 1923, pi. 60, fig. 26) is somewhat misleading; the holotype (USNM 63678) is a broken right valve of a heteromorph. The anterodorsal angle has apparently broken in front of the stragular notch, so that the humped dorsal outline of the illustration is probably not as extreme as shown. However, the species seems to be distinctive in that S2 is as long as the other sulci and extends to the ventral margin of the valve. It does not, however, greatly resemble either D. hieroglyphica or D. costata. Dizygoplewa virginica is represented by four cotypes (USNM 63689) which are internal molds. The lobes seem to be thin relative to the sulci, but because of the type of preservation it is difficult to be sure. Dizygopleura unipunctata also appears to differ somewhat from its description and figures; the holotype (USNM 63685) is a left valve with L2 broken, SI long and apparently narrow, S2 narrow and extending about halfway to the ventral margin, and S3 fairly broad. The pit beneath S2 is slightly impressed and vertically elongated. The species seems to be closer to D. monostigma than to D. costata.
In summary, of the five species originally assigned to the group of Dizygopleura hieroglyphica (Krause), probably only two, D. hieroglyphica (Krause) and D. costata Ulrich and Bassler, are very closely related. Both these species have deep pits beneath S2, narrow stragular processes, deep narrow stragular notches, and a subrectangular outline. The principal difference is that D. costata has carinate lobes and D. hieroglyphica does not. A third form, identified as Dizygopleura sp.
cf. D. costata (Boucot, 1961, p. 181), occurs in the Hardwood Mountain Formation of west-central Maine. This form has carinate lobes like D. costata but has three pits rather than two beneath S2. Possibly it, together with D. hieroglyphica and D. costata, should eventually be placed in a new genus.
Size of sample.—Twenty-one specimens were available for study.
Occurrence.—Dizygopleura costata was originally described as occurring in the upper Tonoloway at Key-ser, W. Va. In New York, it has been found only in collections from Schoharie (USGS 3393-SD, USGS 7283-SD, USGS 8063-SD, YPM 5244/146).
Dizygopleura viafontinalis n. sp.
Plate 5, figures 18, 19
Description.—Lateral outline amplete, subelliptical. Anterior margin rounded; ventral margin sinuate; posterior margin rounded, meeting sinuate dorsal margin at obtuse angle. Stragular process narrow, small, only slightly humped. Si narrow, deep, sinuate, with pronounced anterior curve in ventral part. S2 wide, short, not more than half height of valve, curved anteriorly. S3 relatively short, shallow, and narrow, curved anteriorly, begins nearly one-third height of valve below dorsal margin. Ll fairly broad; L2 small, bulbous in lateral outline; L3 broad; L4 not distinctly marked off from posterior border surface. Heteromorph with bulbous inflation of L4. Surface of valves finely punctate, except on bulbous posterior of heteromorph.
The dimensions of the holotype, a heteromorphic left valve, are 1.30 mm in length and 0.70 of a mm in height; a crushed tecnomorphic carapace is 1.17 mm in length and 0.57 of a mm in height.
The name is derived from the locality on Spring Street, Schoharie, N.Y., where the only specimens have been found.
Types.—Holotype, USNM 162329; paratype, USNM 162328.
Discussion.—This species is so distinctive that a new name for it appears desirable, even though only one crushed tecnomorphic carapace and one heteromorphic left valve have been found. The punctate surface and sigmoidal Si distinguish it at once from any of the other species of Dizygopleura in the Cobleskill. Other distinctly punctate species of Dizygopleura, such as D. punctella Hoskins, 1961, D. ventrisulcata Hoskins, 1961, and DA pulchella (Ulrich and Bassler, 1923) have punctae in the sulci (Hoskins, 1961, p. 92-96), not on the lobes as in D. viafontinalis.
Size of sample.—One carapace and one left valve.
Occurrence.—Only in collections from Schoharie, N.Y. (USGS 3393-SD, USGS 8062-SD).SYSTEMATIC PALEONTOLOGY
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Genus KLOEDENELLA Ulrich and Bassler, 1908 Eloedenella sp.
Plate 6, figures 4H3
Disoussion.—'The genus Kloedenella is apparently poorly represented in the Cobleskill Limestone. Nine specimens were available for study, of which four are either crushed or broken. All have a narrow SI extending below the midheight of the valve, a wider and shorter S2 that extends to about the midheight of the valve, and a sinuous ventral outline. The stragular process is narrow and not humped, so that the dorsal outline in lateral view is straight to gently convex. A figured specimen (pi. 6, figs. 41, 42) is 1.15 mm in length and 0.65 of a mm in height.
One specimen from Forge Hollow (YPM 5244/90B) differs from the above description in having a markedly humped stragular process and a relatively greater height in proportion to width. This specimen may not be conspecific with the others. In general appearance it is very close to Kloedenella rectangularis Ulrich and Bassler, 1923, from the lower part of the Tonoloway Limestone at Cumberland, Md., but differs from it in having a sinuous ventral outline. Kloedenella rectangularis, which may be the heteromorph of K. obliqua Ulrich and Bassler, 1923, has a round ventral outline and shorter sulci. The specimen from Forge Hollow is even closer to Kloedenella turgida Ulrich and Bassler, 1908, from the Keyser Limestone at Cumberland, but K. turgida has a short, poorly defined SI. No other species of Kloedenella seem to be comparable to the specimens from the Cobleskill, but the material available is not considered adequate for description.
Occurrence.—In collections from Schoharie (YPM 5244/146, USGS 3393-SD), Oriskany Falls (YPM 5244/88A), Forge Hollow (YPM 5244/90B) and Prospect Hill )USGS 5207-SD).
Genus EUKLOEDENELLA Ulrich and Bassler, 1923 Eukloedenella? weldae n. sp.
Plate 6, figures 25-29
Description.—Lateral outline subovate; dorsal outline cuneate. Greatest width commonly in posterior quarter of carapace. Small vertically elongated median pit situated slightly anterior to the midpoint in length, slightly dorsal to the midpoint in height. Stragular process elongated parallel to length of shell, extending about one-third to one-half length of hinge, not raised into prominent hump. Left valve overlaps right along ventral margin and bears stragular process. Right valve without stragular notch. Ventral margin slightly sinuate. Posterior end of both valves of tecnomorph sharply indented so that there appears to be a vertical
ridge about one-fifth the length of the shell from the posterior margin in lateral view; in dorsal view the posterior appears compressed. Heteromorphs wider posteriorly so that ridge is not as conspicuous in lateral view, and in dorsal view posterior appears inflated. Shell surface smooth except for median pit.
Interior of left valve shows ridge beneath stragular process, forming groove into which right valve fits. Median pit represented internally by a low, indistinct ridge. Posterior of heteromorph may also have low internal ridge (limen) in some specimens. No stragular notch in right valve.
The dimensions of the holotype are 1.00 mm in length and 0.55 of a mm in height.
Types.-—Holotype,	USNM 162361; paratypes
USNM 162359, 162360, 162362,162363.
Discussion.—Eukloedenella? weldae superficially appears very similar to the illustrations of Sulcocavel-lina? altschedatensis Polenova (1960, pi. 4, figs. 3a, b; 4a, b), and also resembles various forms assigned to Sulcella Coryell and Sample, 1932, such as Sulcella (Sulcella) kloedenellides Adamczak, 1968. However, it differs from these species in having the left valve overlapping the right and in apparently having kloedenel-lid rather than a cavellinid hinge structure. Unfortunately, most specimens broke during preparation of the hinge because the species has a rather thin shell, so that the internal features are illustrated only by one left valve (pi. 6, fig. 29). E.f weldae differs from Nynham-ella musculimonstrans Adamczak, 1966, which Adamczak (1966, p. 14, 15) considered a Kloedenellid, in the overlap of the left valve over the right and in the presence of a pitlike S2 in E.f weldae.
This species is placed questionably in Eukloedenella because it differs from most other species in the genus by the nearly central location and pitlike character of S2 and the presence of the posterior ridgelike angulation. The closest form to E. ? weldae is E. abrupta Ulrich and Bassler, 1923, from the Drepanellina clarki Zone at McKees Farm, 7 miles west of Lewiston, Pa. The holotype of E. abrupta (USNM 63638) is a tecnomorphic right valve represented by the part and counterpart in shale. The posterior angulation is much more pronounced in this specimen than in E.f weldae, and the area posterior to the angulation is larger.
The 19 species and subspecies assigned to Eukloedenella by Ulrich and Bassler (1923, p. 666) need restudy in the light of modern concepts. For example, Ulrich and Bassler (1923, p. 668-676) divided Eukloedenella into five species groups, but Swartz (1933, p. 258-259) has indicated that two of the species in their group V are probably heteromorphs of a species in their group IV, which includes E. abrupta. The group of E.38
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
sinuata Ulrich and Bassler, 1923 (group III) includes species with a narrower and more prominent stragular process than those in the other groups, one of which is group II, the group of E. umbilicata Ulrich and Bassler, 1923, the type species of the genus. Possibly more than one genus is present in the species now assigned to Eukloedenella, and further study may show that E. abrupta and E.f weldae should be assigned to a new genus. However, it seems inadvisable to do this without further study of all the species, which is beyond the scope of this paper.
The species is named for Miss E. A. Weld, who assisted in collecting the material described.
Size of sample.—Seventy-eight complete carapaces and 25 single valves from Schoharie, N.Y., were available for study.
Occurrence.—All specimens studied are from collections made at Schoharie, N.Y. (USGS 3393-SD, USGS 7283-SD, YPM 5244/146), except for three poorly preserved specimens from near Central Bridge, N.Y. (USGS 7198-SD).
Family BEYRICHIOPSIDAE Henningsmoen, 1953 Genus MARGINIA Polenova, 1952
Marginia? sp.
Plate 6, figure 17
Discussion.—One right valve of a weakly bisulcate ostracode has been found in USGS collection 8062-SI) from Schoharie. The specimen has a straight hinge line and lacks a stragular process. The surface is covered with fine longitudinal riblets, which tend to anastomose and are approximately parallel to the hinge. The ventral margin has obscure traces of a thin, narrow marginal flange, which is mostly broken. This specimen is very questionably assigned to Marginia because of the character of the ornamentation and ventral margin. The specimen is 1.0 mm long and 0.5 of a mm high.
Family LEPERDITELLIDAE Ulrich and Bassler, 1906 Genus BONNEPRIMITES Swartz and Whitmore, 1956
Bonneprimites? breviformis Swartz and Whitmore Plate 6, figures 30-33
Bonneprimites'! breviformis Swartz and Whitmore, 1956, p. 1053-
1054, pi. 110, figs. 20-22.
Description.—Lateral outline amplete, hemielliptical to hemicircular; dorsal outline broadly lanceolate. Bisulcate, anterior sulcus very weak and shallow, essentially obsolete; median sulcus short, narrow, extends only about one-fifth distance from dorsal to ventral margin. Obscure muscle (?) spot present at ventral end of median sulcus. Surface of valves very convex; greatest width in posterior third of carapace. Obscure velar (?) bend around entire free margin; hinge line
slightly incised. Valves nearly equal, but left valve slightly overlaps right around free margin. Lateral surface of both valves smooth, but ventral surface of domi-cilium on both valves has very fine striae parallel to the free margin.
The dimensions of a complete carapace are 0.95 of a mm in length and 0.67 of a mm in height.
Discussion.—Two complete carapaces and a left valve have been found in the Cobleskill which agree with_fche description and illustrations of Swartz and Whitmore and are consequently assigned to their species. However, as indicated by Swartz and Whitmore (1956, p. 1053-1054), B. ? breviformis is probably not congeneric with the type of the genus, Bonneprimites bonnemai. Unfortunately there is still not enough material to determine the generic or even the familial affinities of this species. Superficially it resembles the primitiopsid genus Scipionis Gailite, 1966, but the ventral marginal structures do not appear to be those of a typical primitiopsid, and no heteromorphs have as yet been found.
Size of sample.—Three specimens were available for study.
Occurrence.—Found only at Shutter Corners (USGS 3390-SD).
Order P0D0C0PIDA Sars, 1866 Suborder METACOPINA Sylvester-Bradley, 1961 Superfamily THLIFSURACEA Ulrich, 1894 Family THLIPSURIDAE Ulrich, 1894 Genus THLIPSUROPSIS Swartz and Whitmore, 1956
Thlipsuropsis inaequalis (Ulrich and Bassler)
Plate 6, figures 4-7
Octonaria inaequalis Ulrich and Bassler, 1913, p. 538, pi. 98, figs 12-18.
Thlipsuropsis inaequalis (Ulrich and Bassler). Lundin, 1965, p. 78-79, pi. 18, figs, la-j, text fig. 45.
IThlipsuropsis longisulcata Swartz and Whitmore, 1956, p. 1088, pi. 110, figs. 14, 15.
Description.—Lateral outline subovate; dorsal margin of larger left valve strongly arched; anterior margin sharply curved; ventral margin nearly straight; posterior margin broadly curved. Lateral outline of smaller right valve subovate to reniform. Dorsal outline subovate to subrectangular, acuminate on both ends. Valves markedly unequal, left valve overlapping right around free margins and overreaching along hinge. Axes of maximum height and length pass about through midpoint of valve; maximum width in posterior half of carapace.
Left valve ornamented by three distinct, conspicuous grooves, which tend to merge in posterior part of shell: one running parallel to the anterodorsal margin which bifurcates dorsally, leaving a thin ridge between its two branches; one ventral to it in central part of valve, short and broad; and one longer below this i larallel toSYSTEMATIC PALEONTOLOGY
39
ventral margin. An indistinct groove below this separates lowest ridge from edge of valve.
Right valve ornamented by three grooves: one subparallel to anterodorsal margin; one shorter groove parallel to posterodorsal margin; and one longer groove ventral to this and diverging from it at an angle.
The dimensions of an average carapace are 0.70 of a mm in length, 0.50 of a mm in height, and 0.35 of a mm in width.
Dismission.—There do not appear to be any significant differences between the specimens from the Coble-skill and the syntypes of Octonaria inaequalis Ulrich andBassler (USNM 53284) from the Keyser Limestone at Cumberland, Md. This is apparently a fairly long ranging and widely distributed species, for Lundin (1965, p. 78-79) has described and illustrated specimens from the Henryhouse Formation (lower Ludlow) of Oklahoma. As Lundin (1965, p. 79) has noted, Thlipsuropsis longisulcata Swartz and Whitmore is probably conspecific with T. inaequalis; but because T. longisulcata is based only on right valves, its relationship cannot be determined until additional material is obtained. To date, no specimens of Thlipsuropsis have been found in our collections of the Decker, so the point remains unsettled.
Size of sample.—Twenty-six carapaces and three single valves were available for study.
Occurrence.—All specimens came from collections from Schoharie, N.Y. (YPM 5244/146, USGS 3393-SD, USGS 7283-SD).
Genus THLIPSURELLA Swartz, 1932 Thlipsurella parva n. sp.
Plate 6, figures 1-3
Description.—Lateral outline suboval, elongate; dorsal outline cuneate. Left valve overlaps right around free margins and overreaches right along hinge. Surface of both valves marked with three small pits; one nearly central, slightly elongated vertically, slightly dorsal to the midpoint of the valves; the other two in posterior third of valves, tending to be slightly elongated horizontally, but nearly round. Posterior of both valves compressed or truncated so that there is a narrow marginal shelf. Anterior of both valves also compressed, but not as sharply, forming an indistinct marginal flange. Axis of maximum height passes through midpoint of shell; axis of maximum length passes through or slightly below midpoint; axis of maximum width is in posterior fifth of shell.
Material inadequate for examination of hinge and interior of shell, but one left valve shows a boss internally as a reflection of the external median pit.
The dimensions of an average specimen are 0.60 of a mm in length, 0.35 of a mm in height, and 0.25 of a mm in width. All specimens appear to be adults.
Types.—Holotype,	USNM 162346; paratypes,
USNM 162347, USNM 162347a.
Discussion.—This small species most closely resembles Thlipsurella ellipsoclefta Swartz, 1932, the type species of the genus, but lacks the small pit anterior to the median pit, and also differs in having the pits nearly circular rather than noticeably elongated. The specific name refers to the small size of the species.
Size of sample.—Twenty-nine carapaces and one left valve were available for study.
Occurrence.—All specimens are from collections from Schoharie, N.Y. (YPM 5244/146, USGS 3393-SD, USGS 7283-SD).
Superfamily HEALDIACEA Harlton, 1933 Family BAIRDIOCYPRIDIDAE Shaver, 1961 Genus CYTHERELLINA Jones and Holl, 1869
Cytherellina crepiduloides n. sp.
Plate 6, figures 18-24; figure 8
Description.—Carapace subovate in lateral and dorsal outline, subcircular in end view. Dorsal margin evenly curved; anterior margin sharply curved; ventral margin nearly straight to slightly concave; posterior margin curved less sharply than anterior margin. Height about one-lialf length. Axes of maximum height and maximum length pass through midpoint of carapace; maximum width in posterior third. Left valve overlaps right valve markedly on ventral margin, slightly overreaches right dorsally. Left valve has indistinct ventral lappet or tongue which wraps over right valve. Right valve lower than left and appears relatively longer. Shell surface evenly curved, smooth. Shell thick.
Interior of left valve has two low swellings or ridges slanted anteriorly from about the midheight of the valve toward the dorsal margin. These ridges divide the valve into three depressions: one poorly defined in posterior half of valve; one median pit, clearly defined, oval, deeper than others; and one in anterior quarter, not as deep as median depression. Anterodorsal half of left valve has thickened margin forming a shelf grooved parallel to margin. On well-preserved specimens shelf tapers posteriorly and is overhung by rim of valve. Trace of marginal groove posteroventrally. Interior of right valve has depressions like left, but no marginal structures.
The dimensions of an average carapace are 1.05 mm in length, 0.55 of a mm in height, and 0.45 of a mm in width.40
BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
Types.—Holotype, USNM 162357; paratypes USNM 162358, YPM 23832-23836.
Discussion.—This species is assigned to the genus Cytherellina Jones and Holl, 1869, because of its thick shell, which is smooth externally but which has two low oblique ridges defining the adductor muscle scar internally. When Jones and Holl (1869, p. 216-217, pi. 14, figs. 1-6) redescribed and reillustrated the type species of Cytherellina, C. siliqua (Jones, 1855), they showed the oblique ridges impressed as grooves on stein-kerns but did not mention the hinge or other marginal structures. Bonnema (1909, p. 72-75) discussed Cytherellina and assigned to it four Late Ordovician species from Estonia, but also did not mention the hinge. Most recently, Becker (1965, p. 384-385) has rediagnosed Cytherellina and has stated that the hinge is simple, with a ridge and groove in each valve. In contrast, C. crepididoides has a ridge and groove hinge structure in the left valve only. Further study of the types and topotype material of C. siliqua is necessary to resolve this discrepancy, but such a study is beyond the scope of this paper.
The hinge structure and marginal structure of C. crepididoides is most similar to those illustrated by Adamczak (1967, figs. 2, 11) for Kuresaaria gotlandica Adamczak, 1967, but C. crepididoides lacks a contact groove in the anterior part of the left valve and, of course, the anterior sulci on the exterior of both valves which are characteristic of K. gotlandica, the type species of Kuresaaria Adamczak, 1967. The anterior position of the hinge of C. crepiduloides is established by its position relative to the adductor muscle scar and the axis of maximum thickness. Adamczak (1967, p. 464), in describing stop ridges in Silenis bassleri (Sohn, 1961) mentions analogous elements in Cytherelina from the Ordovician of Estonia. Bonnema (1909, p. 75, pi. 8, fig. 7) described and figured such structures in Cytherellina, but they appear to be the ends of the contact groove. In C. crepididoides the posterior end of the contact groove is deepened and might be considered an analogous structure, but as the contact groove is missing in the anterior part of the left valve, there is no structure that could be considered an anterior stop ridge.
Becker (1965, p. 384) included a healdiid muscle scar in hi9 diagnosis of Cytherellina. The adductor muscle scar of C. crepididoides is well defined around the margins in some specimens and is oval to round in outline. The individual scars of the muscle bundles cannot be seen clearly in most individuals because of the type of preservation; it is not clear whether the pits shown in figure 8 are actually part of the scar or are adventitious.
Figure 8.—Interior of left valve of Cytherellina erepiduloides
n. sp., showing muscle pit, approximately X 100. Specimen
YPM 23835 from Schoharie, N.Y. Drawing by Elinor
Stromberg.
Cytherellina crepiduloides is readily distinguished from the four Late Ordovician species, C. ulrichi, C. jonesii, C. krausei, and C. ruedemanni described by Bonnema (1909, p. 75-76), as all of these have incised hinge lines and C. crepiduloides does not. This feature also serves to distinguish it from the Middle Devonian C. brassicalis Becker, 1965. C. crepiduloides differs from the Middle Devonian species C.f obliqua Kummerow, 1953 and C. dubia Kummerow, 1953 in outline, and from C. perlonga Kummerow, 1953 in having a thicker shell. Cytherellina crepiduloides appears to be closest to the specimens described by Jones and Holl (1869, p. 216) as C. siliqua from the Aymestry and upper Ludlow beds (Silurian) of England, but C. crepiduloides appears to have a greater dorsal overreach of the left valve.
The specific name is derived from the Latin crepi-dula, a small shoe, and the suffix -oides, because of the resemblance of single valves to little slippers.
Size of sample.—More than 175 carapaces and more than 25 single valves were available for study.
Occurrence.—All specimens studied in detail came from collections from Schoharie, N.Y. (YPM 5244/146, USGS 3393-SD, USGS 7283-SD). The species also occurs at Aurelius Station, N.Y. (USGS 3395-SD), west of Central Bridge, N.Y. (USGS 7198-SD), and at Shutter Comers, N.Y. (USGS 3390-SD).
Genus NUNCULINA n. gen.
Type species.—Nunculina striatopuncta n. sp.
Species included.—Only the type species.
Diagnosis.—Lateral outline subelliptical, dorsum curved; left valve overlaps right around free margins and overreaches right along posterodorsal hinge. Both valves have vertical median sulcus that extends from near dorsum to about midheight of valves. Anterior and posterior ends of both valves slightly flattened. HingeREFERENCES CITED
41
simple. Internally, both valves have a low ridge corresponding to the median sulcus. Free margin of left valve with shallow groove into which the free margin of right valve fits.
Discussion.—This genus superficially resembles Sul-cocavellina Egorov, 1950, or Sulcella Coryell and Sample, 1932. However, considering the widest end of the shell as posterior, the overlap in Nunculina is left over right, rather than right over left as in the two cavellinid genera. The hinge is short and straight, and neither thin sections nor free valves show any indication of tongue and groove structure. Dimorphism has not been observed in this genus; however, because of the weak hingement, the right valve is commonly driven into the left valve in complete carapaces, and it is difficult to be sure that the observed width of the posterior part of the shell actually represents the true width.
The generic name is a diminutive of the Latin Nun-culus, a kind of nut cake.
Nunculina striatopuncta n. sp.
Plate 6, figures 8-13
Description.—Lateral outline elliptical; dorsal outline subfusiform, bluntly acuminate at anterior and posterior ends, constricted medially. Left valve larger than right, overlapping it around free margins and overreaching it along hinge. Dorsal margin evenly rounded; anterior margin sharply rounded; ventral margin slightly rounded to nearly straight; posterior margin rounded. Axis of maximum height about at midpoint; axis of maximum length passes through or slightly below midpoint; axis of maximum width in posterior third of carapace. Median sulcus extends from near dorsal margin to slightly below midpoint of both valves, passes through midpoint or may be slightly anterior to it, not clearly delimited. Hinge short, straight, posterodorsal in position. Shell surface ornamented by very fine reticulation, which appears to form lines parallel to the ventral margin and to extend into sulcus.
Interior of both valves has broad, low ridge corresponding to external median sulcus. Left valve has indistinct groove, strongest anterodorsally, around free margins into which edge of right valve fits. Left valve also has ventral lappet which overlaps right valve. Hinge without grooves or pits on either valve.
A representative specimen measures 0.8 of a mm in length, 0.45 of a mm in height, and 0.35 of a mm in width.
Types.—Holotype, YPM 23830; paratypes, YPM 23829, YPM 23831, YPM 23831a, USNM 162349-162352.
Discussion.-—The hinge of this species has been studied both from single valves and by means of thin
Figure 9.—Transverse sections of Nunculina striatopuncta n. sp. from Schoharie, N.Y., showing contact relationship of valves. A, section through anterior part of shell showing anterodorsal groove in left valve into which edge of right valve fits. Exterior of carapace badly corroded. Paratype, YPM 23831a, YPM eolln. 5244/146. B, section through posterior part of shell showing simple hinge. Paratype, USNM 162352, USGS colln. 7283-SD. Approximately X 90.
sections and appears to be simple. The edges of single valves are subject to abrasion, and fine details of structure may be lost. However, thin sections prepared from apparently uncrushed carapaces also show the two valves meeting with no interlocking structures (fig. 9).
Illustrations of Sulcella volgograda Shishkinskaya (1964, p. 119-120, pi. IV, figs. 1-9) somewhat resemble this species, but as indicated under the generic discussion, the overlap is not the same.
Although a large number of specimens were available for study, all are nearly the same size, and it is possible that only adults are present in the collections, although a few smaller specimens may represent instar A-l.
The species is characterized by the peculiar fine chainlike reticulation, on which the specific name is based.
Size of sample.—More than 400 carapaces and more than 50 single valves were available for study.
Occurrence.—This species has been found at Schoharie, N.Y. (YPM 5244/146, USGS 3393-SD, USGS 7283-SD), and at Jerusalem Hill, N.Y. (YPM 2594).
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Kozlowski, Roman, 1929, Brachiopodes Gothlandiens de la Podolie Polonaise: Palaeontologia Polonica, v. 1, 254 p., 12 pis.
------1946, Howellella, a new name for Crispella Kozlowski,
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BRACHIOPODA AND OSTRACODA OF COBLESKILL LIMESTONE, CENTRAL NEW YORK
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Whitfield, R. P., 1882, Paleontology: [Wisconsin Geol. Survey], Geology of Wisconsin, v. 4, p. 161-363.INDEX
A
Acknowledgments............
Acrospiriferinae...........
Age and correlation........
agglomeraia, Rhynchonella...
Akron Dolomite_____________
alta, Leperditia...........
Amphitoxotid inae__________
Ancillotoechia_____________
angustisulcata, Dizygopleura.
apicalis, Zygobeyrichia____
apicatus, Leiocyamus_______
Arikloedenia...............
Arthropoda.................
Articulata.................
Athyridacea________________
Athyrididae................
Athyrididina...............
Atrypa lamellata...........
nucleolata_____________
reticularis............
sulcata................
sp...................
B
Bairdiocyprididae...........
barretti, Beyrichia---------
Kloedenia...............
Kloedeniopsis___________
Zygobeyrichia...........
bassleri, Silenis___________
Berolinella.................
Bertie Limestone............
Beyrichia________________
barretti................
Clarkei................
clarki__________________
HaUi____________________
halli...................
Hallii.................
notata__________________
notata-ventricosa_______
oculina.................
Beyrichiacea..............
Beyrichicopina..............
Beyrichiidae..............
Beyrichiinae................
Beyrichiopsidae_____________
Bibliography................
Bingeria....................
bipartita, Leptaena.........
Leptostrophia...........
bipartita...........
bipartita, Leptostrophia.. nearpassi, Leptostrophia.
Stropheodonta..........
{Leptostrophia)....
Strophomena............
biseriata, Oarniella........
bisulcata, Merista..........
bonnemai, Bonneprimites_____
Bonneprimites...............
bonnemai................
breviformis.............
Brachiopoda.................
brassicalis, Cytherellina...
Brayman Shale...............
breviformis, Bonneprimites... Bullhead limestone..........
[Italic page numbers indicate both major references and descriptions]
Page
.......... 3
....... 18
_______ 8
_______	14
2,9,12,16, 20
_______ 21
....... 22
_______	14
.......31,34
_______	27
_______	30
_______	24
_______ 21
....... 10
_______ 16
_______ 16
....... 16
_______	13
_______ 18
_______	3
_______ 16
_______	14
_____________ 39
........ 24,27
27
7,9,27) pi. 3
............ 27
_____________ 40
............  23
......... 2
__________ 2
___________24,27
..........32,33
............  32
_____________ 31
_____________ 31
............. 31
__________ 26
_____________ 33
_____________ 33
__________ 22
......... 22
___________22,23
___________24,26
_____________ 38
............. 41
...........25,26
..........10,11
.....7,10; pi. 1
10
.......... 10
__________ 11
.......... 10
....... 10
__________ 10
......... 22
__________ 16
_____________ 38
............  38
_____________ 38
___7,9,38; pi. 6
.......... 10
_____________ 40
............ 1,5
....7,9,38; pi. 6 ........... 9,20
C
Camarotoechia lamellata...........
litchfieldensis..............
neglecta.....................
centricornis, Kloedenia...........
Chaetetes.........................
Chilidiopsidae____________________
Chonetacea________________________
Chonetes jersey ensis_____________
Chonetidae________________________
Chonetidina.......................
Chrysler Limestone________________
Clarkei, Beyrichia................
clarkei, Dizygopleura_____________
Kloedenella..................
pauper a, Dizygopleura.......
clarki, Beyrichia.................
Coeymans Limestone................
concentrica, Garniella............
congregata, Hindella {Greenfieldia).
Coralline limestone...............
corallinensis, Howellella_________
Howellella corallinensis_____
corallinensis, Howellella.......
eriensis, Howellella.........
Spirifer.....................
Cornikloedenia....................
Correlation and age...............
costata, Dizygopleura_____________
Craniops..........................
ovata............................
Craniopsidae______________________
crassipunctata, Kloedenia_________
crepiduloides, Cytherellina.......
crispus, Spirifer.................
cristata, Dibolbina_______________
Crustacea.........................
Cryptolopholobus..................
Cupular ostrum....................
litchfieldensis..............
Cystihaly sites...................
Cytherellina______________________
brassicalis..................
crepiduloides................
dubia------------------------
jonesii______________________
krausei......................
obliqua......................
perlonga.....................
ruedemanni-------------------
siliqua______________________
ulrichi......................
Page
............... 13
............... 14
_______________ 14
............... 24
2
........... 11
........... 12
........... 12
12
12
.............. 1,3
...........  32,33
_____________ 2,33
............... 32
34
............... 32
.... 3,5,25,27,28
______7, 22) pi. 4
____________ 18
..........2,8,16
13,18,19,20,21,33
.......7,18) pi. 2
______7,18) pi. 2
. 7,18,20,33; pi. 2
........... 18
___________ 26
8
. 7,9,31,35) pi. 5
.......... 10
_____ 7,10) pi. 1
___________ 10
..............  24
_____ 7,39) pi. 6
____________ 18,19
_______________ 23
____________ 21
............ 22
_______________ 14
............... 14
________________ 9
.............39,40
..............  40
______ 7,39) pi. 6
..............  40
_______________ 40
............... 40
..............  40
............... 40
_______________ 40
_______________ 40
_______________ 40
Page
didyma, Terebralula.............................   16
Didymothyris....................................   16
diplocystulis, Welleriopsis....................27,28
diversa, Poloniella............................    31
Dizygopleura.....................................  31
angustisulcata.---------------------------31,34
clarkei___________________________________ 2,33
pauper a--------------------------------  34
costata_________________________7,9,31,35)	pi.	5
halli....................................     31
hallii........1............... 2,7,26,31,35) pl.5
obscura.................................  34
hieroglyphica_____________________________- - 31,36
landesi.................... -------------- 31
monostigma.................... 7,31,34;	pi.	5
perrugosa_________________________________-	36
pulchella.................................    36
punctella____________________________________ 36
swartzi..................................     31
unipunctata.............................31,35,36
ventrisulcata..............................   36
viafontinalis......................   7,36;	pi.	5
virginica................................     36
sp..........................................   9
D repanellacea..................................   29
Drepanellina clarki Zone........................   37
dubia, Cytherellina............................... 40
dunbari, Lanceomyonia..................... 7,15;	pi.	2
duplicipunctata, Kloedenia______________________   24
E
Eccentricosta.................................. 9,12
jersey ensis........................ 6,7,12; p\. 1
Zone......................................    8,9
eriensis, Howellella.........................    20,21
Howellella corallinensis....... 7,18, £0,33: pi. 2
Spirifer...................................... 20
Eukloedenella....................................   37
abrupla...................................  37,38
sinuata..................................      38
umbilicata......................- - -..... 38
weldae.............................. 7,37; pi. 6
F
Fardenia.......................................... 12
fimbriata, Kloedenia....................-..... 24
Foersteoceras...................................... 2
formosa, Machaeraria.............................  13
Fr amelia......................................... 31
D
dalmanelliformis, Morinorhynchus_________________ 11
Davidsoniacea----------------------------------   11
Decker Limestone.... 3,8,9,12,13,15, 21, 27,30,34,39
decker ensis, Machaeraria...................... 7,13
Rhynchonella...............................  13
Stenoschisma...............................  13
Delthyrididae............-.......-............ 18
denticulata, Tikiopsis........... 7,8,27,29; pi. 3
devonica, Poloniella...........................   31
Dibolbina--------------------------------------   23
cristata............--------------------- 23
producta.................................    23
reticruminata...-.................- 7,23: pi. 4
sp..................-.............-...... 9
G
Oarniella.....................................   9,22
biseriata.................................... 22
concentrica......................... 7,22; pi. 4
gebhardii, Mitroceras..........................- - -	9
Trochoceras................................... 2
gibbera scalaris, Leperditia...................... 21
Glasco Member of Rondout Formation------------- 8,14
gotlandica, Kuresaaria................
granulata, Kloedenia..................
Greenfieldia..........................
whitfieldi.......................
{Greenfieldia) congregata, Hindella. Qypidula prognostica..................
4546
INDEX
H
Page
31
31
31
31
30
Halli, Beyrichia.............................
halli, Beyrichia..........._ _.........
Dizygopleura...........................
Kloedenella............................
Halliella....................................
sp..................................... 7, 30; pi. 6
Hallii, Beyrichia................................. 31
Poloniella.................................. 31
hallii, Dizygopleura..........2,7,26,SI,35;	pi.	5
obscura, Dizygopleura....................... 34
Hammariella.................................. 9,24
pulchrivelata...........................     24
warthini........................... 7,24;	pi.	4
Hardwood Mountain Formation______________________  36
hartnageli, Howellella vanuxemi.................... 2
Kloedeniopsis........... 7,24,25,26, S3; pi. 3
Healdiacea.............................■..... 39
Helderberg Group..............................  10,33
Henryhouse Formation............................   39
hieroglyphica, Dizygopleura___________________  31,36
Hindella.......................................... 16
(Oreenfieldia) congregata..................  18
Hollinacea......................................   29
Hollinid....................................29;	pi.	6
Hollinidae.......................................  29
Howellella...............................  7,18,19,20
corallinensis................... 13,19,20,21,33
corallinensis ...................... 7,18; pi. 2
eriensis.....................7,18,20,33; pi. 2
eriensis..............................    20,21
keyserensis............................2,18,20
modesta.................................. 19,20
plicata................
modestus...................
octocostata humilis..........
vanuxemi hartnageli............
humilis, Howellella octocostata. hydraulicus, Orthothetes.....__
20
21
2
2
2
11
I
Iberirhynchia....................................    14
santaluciensis..............................   14
inaequalis, Thlipsuropsis_______________7,9,88; pi. 6
Inarticulata......................................   10
interstriata, Morinorhynchus..................... 11,12
Orthis.................................. . 11
Schellwienella.............................    11
Schuchertella...............................   11
interstriatus, Morinorhynchus_______7,11,18,33; pi. 1
Orthothetes................................    11
Jamesville Member of Manlius Limestone........	16
jerseyensis, Chonetes.............................. 12
Eccentricosta....................6,7,12; pi. 1
Weller iopsis..............................   27
jonesi, Leperditia.............................2,21,22
jonesii, Cytherellina.............................  40
Juviella........................................... 22
K
Kalkberg Limestone........................... 5,10
Keyser Limestone__________________________________  8,
9,10,12,13,15,18,20,21,27,33,34,37,39
keyserensis, Howellella......................  2,18,20
Kirkbyella......................................... 29
Kirkbyellid..................................29; pi. 6
Kirkbyellidae................................... 29
Kloedenella....................................7,31,37
clarkei....................................   32
halli......................................   31
obliqua...................................    37
rectangularis................................ 37
turgida....................................   37
sp..................................... 7,87; pi. 6
Kloedenellacea................................   31
Kloedenellicopida..............................  31
Kloedenellidae.................................. 31
kloedenellides, Sulcella (Sulcella)............. 37
Page
Kloedenia....................................   25,26
barretti...................................   27
centricornis................................. 24
crassipunctata.............................   24
duplicipunctata...........................    24
fimbriata.................................... 24
granulata..................................   25
kokomoensis.................................. 24
montaguensis................................. 25
newbrunswickensis............................ 28
normalis..................................... 25
notata..................................   26,33
oculina....................................   25
retifera....................................  24
wilckensiana................................. 25
Kloedeniinae...................................... 25
Kloedeniopsis........................... 24,25,26,27
barretti........................... 7,9,27; pi. 3
hartnageli................... 7,24,25,26,33; pi. 3
................ 26
................... 24
................ 26
................... 40
................... 40
kokomoensis..........
kokomoensis, Kloedenia.
Kloedeniopsis________
krausei, Cytherellina___
Kuresaaria gotlandica...
lamellata, Atrypa........................... 13
Camarotoechia............................... 13
Machaeraria.................5,6,7,73,14; pi.	2
Rhynchonella................................ 13
Stenoschisma................................ 13
Lanceomyonia..................................    15
dunbari.............................. 7,15; pi.	2
landesi, Dizygopleura....................... 31
Leiocyamidae..................................... 29
Leiocyamus..................................9,29,30
apicatus...................................  30
punctatus___________________________ 7, £0,30; pi. 6
sp. A............................. 7,30,33;	pi.	6
sp. B.............................    7,30;	p.	6
sp.........................................   9
Leperditellidae................................   38
Leper ditia...................................... 21
alta_______________________________________  21
gibbera scalaris..........................   21
jonesi................................  2,21,22
scalaris....................-- 2,7,9,21, pi. 3
Leperditiidae..................................   21
Leptaena....................................-	10
bipartita.................................10,11
rhomboidalis..............................  3,4
Leptostrophia..................................   10
bipartita..........................   7,10;	pi.	1
bipartita............................   10
nearpassi.............................   H
(.Leptostrophia) bipartita, Stropheodonta...	10
textilis, Stropheodonta..................... 10
Leptostrophiinae................................. 10
Limbinaria..................................-	30
muricata....................................  9
Lingulacea....................................... 10
Lingulida........................................ 10
litchfieldensis, Camarotoechia................... 14
Cupular ostrum...........................    14
Microsphaeridiorhynchus............7,13,14; pi.	2
Rhynchonella.............................    14
Localities........................................ 5
Lophoctenella..................................   22
Lophokloedenia...........................   24,25,26
M
Machaeraria...................................... 13
deckerensis............................... 7,13
formosa....................................  13
lamellata....................5,6,7,13,14; pi. 2
Manlius Formation................................. 8
Manlius Limestone......................2,3,21,33
Marginia......................................    38
sp_____________________________________88; pi. 6
Page
martinssoni, Migmatella............... 7,22,23;	pi.	4
Merista bisulcata.............................. 16
nudeolata................................ 18
sulcata.................................. 16
Meristella nudeolata........................... 18
Metacopina..................................... 38
Microsphaeridiorhynchus........................ 14
litchfieldensis..................7,13,14;	pi.	2
Migmatella..................................... 22
martinssoni....................... 7,22,23;	pi.	4
sp........................................... 9
minuta, Protathyris............................... 18
Mitroceras......................................... 2
gebhardii...................................  9
modesta, Howellella............................ 19,20
plicata, Howellella......................    20
modestus, Howellella.............................. 21
Spirifer..................................   18
plicatus, Spirifer.......................... 21
monostigma, Dizygopleura...............7,31,34/ pi* 6
montaguensis, Kloedenia........................    25
Morinorhynchus................................. 11,12
dalmanelliformis...........................  11
interstriata............................  11,12
interstriatus.................7,11,18,33; pi. 1
muricata, Limbinaria............................... 9
N
nearpassi, Leptostrophia bipartita................ 11
Strophodonta................................ 11
neglecta, Camarotoechia..........................  14
Rhynchonella...............................  14
New Scotland Limestone............................ 10
newbrunswickensis, Kloedenia.....................  28
normalis, Kloedenia...........................-	25
notata, Beyrichia................................. 26
Kloedenia...............................  26,33
notata-ventricosa, Beyrichia.....................  33
nudeolata, Atrypa................................. 18
Merista..................................... 18
Meristella.................................. 18
Protathyris....................6,7,16,18;	pi.	2
Whitfieldella............................... 18
Nunculina.....................................  40,41
striatopunda......................7,40,41;	pi-	6
Nynhamella musculimonstrans....................... 37
O
obliqua, Cytherellina...................- - -	40
Kloedenella................................  37
obscura, Dizygopleura hallii...................... 34
octocostata humilis, Howellella.................... 2
Octonaria inaequalis...........................38,39
oculina, Beyrichia..........................  -	33
Kloedenia.................................   25
Orthis interstriata...........................-	11
Orthorhynchulinae................................. 13
Orthothetes hydraulicus..............-...... H
interstriatus................................ H
Ostracoda......................-............... 21
ovata, Craniops.........................7,10; pi. 1
Pholidops.................................. 10
ovatus, Pholidops.............................-	10
Oxbow Dolomite...............................    1
P
Palaeocopida.................................   22
Paleoecology.................................... 6
Parabolbina.................................... 29
parva, Thlipsurella............................. 7
paupera, Dizygopleura clarkei.................. 34
perlonga, Cytherellina......................... 40
perrugosa, Dizygopleura........................ 36
Pholidops ovata............................-	1°
ovatus..................................... 10
Pintopsis............................-...... 26
plicata, Howellella modesta.................... 20
plicatus, Spirifer modestus.................... 21INDEX
47
	Page
	38
Poloniella						 31
devonica					 31
diversa					 31
Haim 				 31
tertia			 31
Primitiopsacea				 29
		 30
Primitiopsis					 30
sp					so; pi. 6
		 23
prognostica, Oypidula			34
	12
	16
Protathyris..				 16
minuta						 18
		 6,7,16,18; pi. 2
	.. 6,7,9,16,18,33; pi. 2
			 25
	36
pulchrivelata, Hammariella			 24
punctatus, Leiocyamus				7,29,30
	36
pustulosa, Welleriopsis..		7
R	
		 24
			 37
reticruminata, Dibolbina					 7, S3, pi. 4
	3
		 3,4
	14
	13
lamellata				13
		 14
neglecta						 14
	14
		 13
		 13
		 13
		 14
Rondout Formation			3,8,13,14,29
	.... 8,14
		 18
ruedemanni, Cytherellina		40
S
santaluciensis, Iberirhynchia........................ 14
scalaris, Leperditia....................2,7,9, 21; pi. 3
Leperditia gibbera.......................... 21
Schellivienella interstriata.......................   11
Schuchertella interstriata....................... 11
prolifica...................-............... 12
Scipionis............................................ 38
Page
Scope of the report................................ 3
Silenis bassleri............................... 40
siliqua, Cytherellina............................. 40
sinuata, Eukloedenella............................ 38
Sphaerirhynchia..................................  15
Spirifer corallinensis............................ 18
crispus................................... 18,19
corallinensis............................ 18
eriensis..................................... 20
modestus.................................. 18
corallinensis............................ 18
plicatus................................. 21
Spiriferacea...................................... 18
Spiriferida.....................................   16
Spiriferidina....................................  18
Spring Street locality, Schoharie..............5,6,8
Stenoschisma deckerensis........................	13
lamellata................................. 13
striatopuncta, Nunculina........................... 7
Stromatopora beds................................   6
Stropheodonta bipartita........................... 10
(Leptostrophia) bipartita.................... 10
textilis...............................   10
Stropheodontidae............................... 10
Strophodonta nearpassi.......................... 11
textilis__________________________________ 10,11
Strophomena bipartita...______________________     10
Strophomenacea__________________________________   10
S trophomenida................................     10
S trophomenidina...............................    10
sulcata, Atrypa................................    16
Merista.....................................  16
Protathyris................6,7,9,16,18,33; pi. 2
Whitfieldella............................. 16,18
Sulcella........................................37,41
volgograda................................    41
(Sulcella) kloedenellides.................... 37
(Sulcella) kloedenellides, Suicella............... 37
Sulcocavellina..................................   41
altschedatensis............................   37
swartzi, Dizygopleura............................. 31
Systematic paleontology.........................    9
T
Tentaculites.....................................   2
Terebratula didyma................................ 16
tertia, Poloniella...............................  31
textilis, Stropheodonta (Leptostrophia)........... 10
Strophodonta..............................10,11
Thacher Member of Manlius Limestone____________	8
Thlipsuracea...................................... 38
Thlipsurella...................................... 39
ellipsoclefta______________________________   39
parva.................................7, 39; pi. 6
Page
Thlipsuridae...................................... 38
Thlipsuropsis....................................  38
inaequalis.........................7, 9,38’, pi. 6
longisulcata.............................  38,39
Tikiopsis.....................................  37,29
denticulata........................ 7,8,27, 29; pi. 3
Tonoloway Limestone............. 9,13,15,18,34,36,37
transversa, Rhynchonella.......................... 14
Treposellinae....................................  22
Triemilomatella.................„................ 29
Trigonirhynchiidae................................ 14
Trochoceras gebhardii.............................. 2
turbinata..................................... 2
turbinata, Trochoceras............................  2
turgida, Kloedenella............................   37
U
ulrichi, Cytherellina...........................   40
umbilicata, Eukloedenella........................  38
Uncinulidae......................................  15
unipunctata, Dizygopleura...................31,35,36
V
vanuxemi hartnageli, Howellella___________________  2
ventrisulcata, Dizygopleura......................  36
viafontinalis, Dizygopleura.............7, 36; pi. 5
virginica, Dizygopleura........................    36
volgograda, Sulcella.............................. 41
W
warthini, Hammariella...................... 7, 24; pi. 4
Waterlime Group of Manlius....................  16,33
weldae, Eukloedenella...................7, 37; pi. 6
Welleria.......................................... 25
Weller iella.................................... 9,24
Welleriopsis............................ 25,26,27,28,29
diplocystulis..............................27,28
jersey ensis...............................27,29
pustulosa..............................7, 28; pi. 3
sp.....................................29; pi. 3
Whitfieldella..................................    16
nucleolata................................... 18
rotundata.................................... 18
sulcata..................................  16,18
whitfieldi, Oreenfieldia.........................  16
Wilbur Limestone.................................  27
Wilbur Member..............................    8,9,29
wilckensiana, Kloedenia........................... 25
Z
Zygobeyrichia........................... 24,25,26,27
apicalis..................................... 27
barretti...................................   27
regina....................................... 33PLATES 1-6
Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey Library, Federal Center, Denver, Colorado 80225.PLATE 1
[Figs. 6, 7, X 5; all others X 3]
Figures
1-5. Morinorhynchus? interstriatus (Hall) (p. 11).
1.	Brachial view of crushed fragmentary shell, YPM 23789; Forge Hollow, N.Y., YPM collection 5244/90B.
2.	Pedicle valve of an average specimen, YPM 23790; Aurelius Station, N.Y., YPM collection 5244/14.
3.	Interior of brachial valve showing brachiophores, YPM 23791; Aurelius Station, N.Y., YPM collection 5244/14.
4.	Interior of larger brachial valve showing cardinal process, brachiophores broken, YPM 23792; Aurelius Station, N.Y., YPM collection 5244/14.
5.	Interior of beak area of broken pedicle valve, showing pseudodeltidium and interarea, YPM 23793; Forge Hollow, N.Y., YPM collection 5244/90B.
6,	7. Craniops ovata (Hall) (p. 10).
6.	Exterior and interior of brachial valve, USNM 162277, 162278; Schoharie, N.Y., USGS collection 3393-SD.
7.	Interior of brachial valve, USNM 162278; Schoharie, N.Y., USGS collection 3393-SD.
8-11. Eccentricosta jerseyensis (Weller) (p. 12).
8.	Exterior of pedicle valve showing curving irregular costae, YPM 16070; Jerusalem Hill, N.Y., YPM collection 2594.
9.	Interior of brachial valve showing cardinalia, YPM 16069; Jerusalem Hill, N.Y., YPM collection 2594.
10.	Interior of pedicle valve showing callus platform, USNM 162279; Shutter Corners, N.Y., collection USGS
3390-SD.
11.	Exterior of pedicle valve showing spines, YPM 23794; Jerusalem Hill, N.Y., YPM collection 2594.
12-14. Leptostrophia bipartita (Hall) (p. 10).
12.	Interior of brachial valve showing cardinalia, YPM 23795; near Glenerie, N.Y., YPM collection 5244/3.14S.
13.	Impression of exterior and part of interior of brachial valve showing ornamentation, USNM 162280; Shutter
Corners, N.Y., USGS collection 3390-SD.
14.	Squeeze of calcined specimen showing interior of pedicle valve, YPM 23796; Shutter Corners, N.Y., YPM
collection 5244/150.GEOLOGICAL SURVEY
PROFESSIONAL PAPER 730 PLATE 1
MORINORHYNCHUS ?, CRANIOPS, ECCENTRICOSTA, AND LEPTOSTROPHIAPLATE 2
[All figures X 3]
Figures 1-8. Lanceomyonia'! dunbari n. sp. (p. 15).
1-4. Pedicle, lateral, anterior, and brachial views of small specimen, YPM 23797; Shutter Corners, N.Y., YPM collection 5244/150.
5-8. Pedicle, brachial, anterior, and lateral views of holotype, YPM 23798; Aurelius Station, N.Y., YPM collection 5244/14.
9-16. Machaeraria’l lamellata (Hall) (p. 13).
9-11. Pedicle, anterior, and lateral views of an immature specimen, USNM 162281; Schoharie, N. Y., USGS collection 3393-SD.
12-15. Pedicle, brachial, anterior, and lateral views of a larger specimen, USNM 162282, Schoharie, N.Y., USGS collection 3393-SD.
16. Interior of brachial valve showing divided hinge plate, YPM 23799; Schoharie, N.Y., YPM collection 5244/ 146.
17-29. Microsphaeridiorhynchus litchfieldensis (Schuchert) (p. 14).
17. Interior of brachial valve showing hinge plate and median septum, YPM 23800; Aurelius Station, N.Y., YPM collection 5244/14.
18-21. Pedicle, brachial, lateral, and anterior views of an immature specimen, YPM 23801; Schoharie, N.Y., YPM collection 5244/146.
22-25. Pedicle, brachial, lateral, and anterior views of a large specimen, YPM 23802; Schoharie, N.Y., YPM Collection 5244/146.
26-29. Pedicle, brachial, lateral, and anterior views of a smaller specimen, YPM 23803; Schoharie, N.Y., YPM collection 5244/146.
30-35. Protathyris sulcata (Vanuxem) (p. 16).
30-33. Pedicle, brachial, posterior, and lateral views of an average specimen, YPM 23804; Aurelius Station, N.Y., YPM collection 5244/1.56.
34.	Lateral view of weathered specimen showing spire, YPM 23805. Specimen sectioned after photography. Aurelius Station, N.Y., YPM collection 5244/1.56.
35.	Interior of posterior end of silicified shell showing dental lamellae and hinge plate, USNM 162283; Aurelius Station, N.Y., USGS collection 3395-SD.
36-40. Protathyris nucleolata (Hall) (p. 18).
36-39. Pedicle, lateral, anterior, and brachial views of an average specimen, YPM 23806; Schoharie, N.Y., YPM collection 5244/146.
40. Pedicle view of a larger specimen, YPM 23807; Jerusalem Hill, N.Y., YPM collection 5244/108.
41-48. Howellella corallinensis eriensis (Grabau) (p. 20).
41-44. Pedicle, brachial, anterior, and lateral views of a specimen showing weak lateral costae, YPM 23808; Aurelius Station, N.Y., YPM collection 5244/1.56.
45.	Interior of silicified brachial valve showing crural bases and small cardinal process, USNM 162284; Aurelius Station, N.Y., USGS collection 3395-SD.
46.	Pedicle valve of specimen showing angular sulcus and growth varices, YPM 23809; Forge Hollow, N.Y., YPM collection 5244/90B.
47.	Interior of pedicle valve showing flaring deltidial plates and thin median earina, YPM 23810; Aurelius Station, N.Y., YPM collection 5244/14.
48.	Interior of pedicle valve with cardinal area slightly broken, showing dental lamellae and low median earina, YPM 23811; Aurelius Station, N.Y., YPM collection 5244/14.
49.	Howellella corallinensis corallinensis (Grabau) (p. 18).
Pedicle valve showing lack of lateral costae, YPM 23812; Shutter Corners, N.Y., YPM collection 5244/150.GEOLOGICAL SURVEY
PROFESSIONAL PAPER 730 PLATE 2
LANCEOMYONIA ?, MACHAERAR1A ?, MICROSPHAERIDIORHYNCHUS, PROTATHYRIS , AND HOWELLELLAPLATE 3
[Figs. 31-34, X 5; all others X 15]
Figure 1.	“Kloedenia” normalis Ulrich and Bassler (p. 25).
Lectotype, USNM 162287, one of syntypes numbered USNM 82997, from 182 feet above the base of the Wills Creek Shale, Flintstone, Md., according to original label with specimens. Presumably the same as specimen illustrated by Ulrich and Bassler, 1923, pi. 61, fig. 15.
2-10. Kloedeniopsis hartnageli n. gen., n. sp. (p. 26).
2.	Small tecnomorphic right valve, paratype, YPM 23813; Shutter Corners, N.Y., YPM collection 5244/150.
3,	4, 8. Right lateral, left lateral, and dorsal views of the holotype a tecnomorphic carapace, USNM 162285; Schoharie, N.Y., USGS collection 8063-SD.
5.	Interior of a heteromorphic right valve, paratype, USNM 162286a, showing character of margins. Valve broken at posteroventral margin and with matrix in interior; Schoharie, N.Y., USGS collection 3393-SD.
6,	7. Left lateral and ventral views of a heteromorphic carapace, paratype, USNM 162286; Schoharie, N.Y., USGS collection 3393-SD.
9.	Posterior view of a broken carapace, paratype, USNM 162286b, showing flangelike velar ridge; Shutter Corners, N.Y., USGS collection 3390-SD.
10.	Right lateral view of heteromorphic valve, paratype, USNM 162286c; Schoharie, N.Y., USGS collection 8062-SD.
11.	Welleriopsis? sp. (p. 29).
USNM 162291; Shutter Corners, N.Y., USGS collection 3390-SD.
12-17. Kloedeniopsis barretti (Weller) (p. 27).
12.	Interior of tecnomorphic left valve, USNM 162289, showing marginal structures; Schoharie, N.Y., USGS collection 3393-SD.
13.	16. Ventral and oblique right lateral views of a heteromorphic carapace, USNM 162290, showing marginal spinules; Schoharie, N.Y., USGS collection 3393-SD.
14.	Left lateral view of tecnomorphic carapace, YPM 23815; Schoharie, N.Y., YPM collection 5244/146.
15.	Interior of heteromorphic right valve, USNM 162290a, showing hinge; Schoharie, N.Y., USGS collection 3393-SD.
17.	Right lateral view of tecnomorphic carapace, USNM 162288, showing irregular reticulation; Schoharie, N.Y. USGS collection 8063-SD.
18-23. Welleriopsis? pustulosa n. sp. (p. 28).
18.	Small tecnomorphic right valve, paratype, USNM 162294; Schoharie, N.Y., USGS collection 8063-SD.
19-21. Ventral, left lateral, and right lateral views of tecnomorphic carapace, holotype, USNM 162296; Schoharie,
N.Y., USGS collection 3393-SD.
22, 23. Lateral and ventral views of heteromorphic left valve, paratype, USNM 162295; Schoharie, N. Y., USGS collection 8064-SD.
24-30. Tikiopsis denticulata n. gen., n. sp. (p. 27).
24.	Dorsal view of complete carapace, paratype, YPM 23816, showing resemblance to Polynesian tiki; Schoharie, N.Y., YPM collection 5244/146.
25,	26. Ventral and right lateral views of complete carapace, holotype, USNM 162292; Schoharie, N.Y., USGS collection 3393-SD.
27. Lateral view of large right valve, paratype, YPM 23818; Shutter Corners, N.Y., YPM collection 5244/150.
28. Ventral view of broken carapace, paratype, YPM 23817, showing ventral flaps on both valves; Schoharie, N.Y., YPM collection 5244/146.
29.	Ventral view of right valve showing flap, paratype, USNM 162293; Shutter Corners, N.Y., USGS collection 3390-SD.
30.	Lateral view of small tecnomorphic left valve, paratype USNM 162292a; Schoharie, N.Y., USGS collection 8439-SD.
31-34. Leperditia scalaris (Jones) (p. 21).
31.	Small left valve, USNM 162298, showing well-developed posterodorsal swelling; Aurelius Station, N.Y., USGS collection 3395-SD.
32.	Left valve, USNM 162297, showing eye tubercle; Aurelius Station, N.Y., USGS collection 3395-SD.
33.	Large right valve, USNM 162300, slightly corroded with acid, showing development of pustulose surface like that reported for Leperditia jonesi Hall and traces of adductor and chevron-shaped muscle scars; Aurelius Station, N.Y., USGS collection 3395-SD.
34.	Large broken left valve, USNM 162301; Aurelius Station, N.Y., USGS collection 3395-SD.GEOLOGICAL SURVEY
PROFESSIONAL PAPER 730 PLATE 3
'KLOEDENIA” KLOEDENIOPSIS, WELLERIOPSIS ?, TIKIOPSIS, AND LEPERDITIAPLATE 4
[All figures X 30]
Figures 1-8. Hammariella warthini n. sp. (p. 24).
1.	Immature broken tecnomorphic left valve, paratype, USNM 162302; Schoharie, N. Y., USGS collection 7283-SD. ■
2.	Tecnomorphic left valve showing cuspate anterior lobe, velum broken, paratype USNM 162303; Schoharie, N.Y., USGS collection 8062-SD.
3.	4. Lateral and ventral views of heteromorphic left valve, velum broken behind crumina, holotype, USNM 162304; Schoharie, N.Y., USGS collection 8062-SD.
5.	Heteromorphic left valve showing character of velum behind crumina, anterior broken, paratype, USNM 162305; Schoharie, N.Y., USGS collection 8062-SD.
6.	Tecnomorphic left valve, broken dorsally, showing velum, paratype, YPM 23819; Schoharie, N. Y., YPM collection 5244/146.
7.	Heteromorphic right valve, broken, paratype, USNM 162306; Schoharie, N.Y., USGS collection 8062-SD.
8.	Tecnomorphic left valve showing velum and broken anterior cusp, paratype, USNM 162307; Schoharie, N.Y.-USGS collection 8062-SD.
9-12. Garniella concentrica n. sp. (p. 22).
9.	Tecnomorphic right valve, paratype, YPM 23820; Schoharie, N. Y., YPM collection 5244/146.
10.	Tecnomorphic left valve, paratype, YPM 23821; Jerusalem Hill, N.Y., YPM collection 2594.
11.	Crushed heteromorphic carapace showing cristae on crumina, paratype, USNM 162308; Schoharie, N.Y., USGS
collection 7283-SD.
12.	Tecnomorphic left valve showing crista outlining median lobe, holotype, USNM 162309; Schoharie, N.Y., USGS
collection 3393-SD.
13-22. Migmatella martinssoni n. gen., n. sp. (p. 22).
13.	Right lateral view of crushed tecnomorphic carapace showing cristate lobes and narrow velar bend, paratype YPM 23822; Schoharie, N.Y., YPM collection 5244/146.
14.	Tecnomorphic left valve showing velum reduced to velar bend posteriorly, paratype, YPM 23823; Jerusalem Hill, N.Y., YPM collection 2594.
15.	Right lateral view of small tecnomorphic carapace showing velar bend, paratype, USNM 162310; Shutter Corners, N.Y., USGS collection 3390-SD.
16.	Oblique ventral view of broken heteromorphic left valve showing velar spur and trace of velum across crumina, paratype, USNM 162311; Schoharie, N.Y., USGS collection, 3393-SD.
17.	Lateral view of heteromorphic right valve showing absence of velar spur, paratype, USNM 162312; Schoharie, N.Y., USGS collection 3393-SD.
18.	Lateral view of tecnomorphic right valve,paratype, USNM 162313; Schoharie, N. Y., USGS collection 3393-SD.
19-21. Dorsal, left lateral, and ventral views of a complete carapace, holotype, USNM 162314; Schoharie,
N.Y., USGS collection 8063-SD.
22.	Heteromorphic left valve, paratype, YPM 23824; Schoharie, N.Y., YPM collection 5244/146.
23-28. Dibolbina reticruminata n. sp. (p. 23).
23.	Tecnomorphic right valve, velum and both cardinal angles broken, paratype, USNM 162315; Shutter Corners, N.Y., USGS collection 3390-SD.
24.	Tecnomorphic left valve, velum and part of syllobium broken, paratype, USNM 162316; Schoharie, N.Y., USGS collection 8062-SD.
25.	26. Ventral and lateral views of heteromorphic left valve, velum partly broken, showing torus, paratype, USNM 162317; Schoharie, N.Y., USGS collection 7283-SD.
27.	Ventral view of a complete heteromorphic carapace showing velum extending around crumina and torus not crossing crumina, paratype, YPM 23825; Schoharie, N.Y., YPM collection 5244/146.
28.	Dorsal view of complete heteromorphic carapace, velum slightly broken posteriorly, holotype, YPM 23826; Schoharie, N.Y., YPM collection 5244/146.GEOLOGICAL SURVEY
PROFESSIONAL PAPER 730 PLATE 4
HAMMARIELLA , GARNIELLA , MIGMATELLA , AND DIBOLBINAFigures
PLATE 5
[All figures X 30)
1-12. Dizygopleura monostigma n. sp. (p. 34).
1, 2. Right lateral and left lateral views of small tecnomorphic carapace, about A-3, USNM 162318; Schoharie, N.Y., USGS collection 3393-SD.
3.	Left lateral view of small tecnomorphic carapace showing tendency for ventral pit to connect with S3, USNM 162319; Schoharie, N.Y., USGS collection 3393-SD.
4.	Left lateral view of small carapace, about A-3, paratype, USNM 162320; Keyser Limestone, just above Gypidula prognostica Zone, La Vale, Md., USGS collection 8125-SD.
5.	6. Right and left lateral views of tecnomorphic carapace, A-2, USNM 162321; Schoharie, N.Y., USGS collection 3393-SD.
7, 8. Right lateral and dorsal views of tecnomorphic carapace showing stragular process, about A-2, USNM 162322; Schoharie, N.Y., USGS collection 3393-SD.
9-11. Dorsal, left lateral and right lateral views of adult tecnomorph, holotype, USNM 162323; Keyser Limestone, just above Gypidula prognostica, Zone, La Vale, Md., USGS collection 8125-SD.
12.	Heteromorphic left valve showing broader L4, paratype, USNM 162324; Keyser Limestone, just above Gypidula prognostica Zone, La Vale, Md., USGS collection 8125-SD.
13-16. Dizygopleura costata Ulrich and Bassler (p. 35).
13.	Left lateral view of lectotype, USNM 162325; Tonoloway Limestone (upper), Keyser, W. Va., from cotype lot USNM 63677.
14.	15. Left and right lateral views of a carapace, USNM 162326; Schoharie, N.Y., USGS collection 3393-SD.
16.	Dorsal view of another carapace, USNM 162327; Schoharie, N.Y., USGS collection 3393-SD.
17.	Dizygopleura clarkei paupera (Ulrich and Bassler) (p. 34).
Right lateral view of carapace, holotype, USNM 53280; Keyser Limestone, Cumberland, Md.
18,	19. Dizygopleura viafontinalis n. sp. (p. 36).
18.	Right lateral view of slightly crushed tecnomorphic carapace, paratype, USNM 162328; Schoharie, N.Y., USGS collection 3393-SD.
19.	Lateral view of heteromorphic left valve, holotype, showing sigmoidal SI and punctate surface, USNM 162329; Schoharie, N.Y., USGS collection 8062-SD.
20-45. Dizygopleura hallii (Jones) (p. 31).
20.	Interior of right valve showing stragular notch, USNM 162330; Schoharie, N.Y., USGS collection 8063-SD.
21.	22. Right and left lateral views of small tecnomorphic carapace, A-4 or A-3, USNM 162331; Schoharie, N.Y., USGS collection 3393-SD.
23.	Right lateral view of small tecnomorphic carapace, A-3 or A-4, USNM 162332; Schoharie, N.Y., USGS collection 3393-SD.
24,	25. Right and left lateral views of a slightly crushed tecnomorphic carapace, A-3, USNM 162333; Schoharie, N.Y., USGS collection 3393-SD.
26, 27. Right and left lateral views of a carapace with narrow but deep S3, A-3, USNM 162334; Schoharie, N.Y., USGS collection 3393-SD.
28, 29. Right and left lateral views of a tecnomorphic carapace with wider S3, A-3, USNM 162335; Schoharie, N.Y., USGS collection 3393-SD.
30.	Left lateral view of tecnomorphic carapace with narrow, shallow S3, A-3, USNM 162336; Schoharie, N.Y., USGS collection 3393-SD.
31.	Left lateral view of tecnomorphic carapace with narrow S3, A-2, USNM 162337; Schoharie, N.Y., USGS collection 3393-SD.
32.	Right lateral view of tecnomorphic carapace with narrow S3, A-2 or A-l, USNM 162338; Schoharie, N.Y. USGS collection 3393-SD.
33.	Right lateral view of tecnomorphic carapace with wide S3, A-l, USNM 162339; Schoharie, N.Y., USGS collection 3393-SD.
34.	35. Right and left lateral views of tecnomorphic carapace, A-l, USNM 162340; Schoharie, N.Y., USGS collection 3393-SD.
36.	Left lateral view of tecnomorphic carapace, A-l, YPM 23827; Schoharie, N.Y., YPM collection 5244/146.
37,	38. Right and left lateral views of tecnomorphic carapace with wide and deep S3, adult, USNM 162341; Schoharie, N.Y., USGS collection 3393-SD.
39.	Dorsal view of adult tecnomorphic carapace showing stragular process, USNM 162342; Schoharie, N.Y., USGS collection 3393-SD.
40.	Dorsal view of adult heteromorphic carapace showing posterior inflation, USNM 162343; Schoharie, N.Y., USGS collection 3393-SD.
41.	Left lateral view of adult tecnomorphic carapace with deep sulci, USNM 162344; Schoharie, N.Y., USGS collection 3393-SD.
42.	Left lateral view of adult heteromorphic carapace, USNM 162345; Schoharie, N.Y., USGS collection 3393-SD.
43.	Right lateral view of slightly crushed heteromorphic carapace, NYSM 12718; from slab with holotype of Dizygopleura clarkei, from Herkimer County, N.Y.
44.	Lateral view of heteromorphic left valve, holotype of Dizygopleura clarkei, NYSM 4141; Herkimer County, N.Y.
45.	Lateral view of heteromorphic left valve, holotype of Dizygopleura hallii, BMNH In 35128; near Utica, N.Y.GEOLOGICAL SURVEY
PROFESSIONAL PAPER 730 PLATE 5
DIZYGOPLEURAPLATE 6
Figtjbes
[All figures X 30]
1-3. Thlipsurella parva n. sp. (p. 39).
I,	2. Right lateral and dorsal views of the holotype, USNM 162346; Schoharie, N. Y., USGS collection 7283- SD.
3.	Left lateral view of paratype carapace, USNM 162347; Schoharie, N.Y. USGS collection 7283-SD.
4-7. Thlipsuropsis inaequalis (Ulrich and Bassler) (p. 38).
4,	o. Dorsal and right lateral views of a complete carapace, YPM 23828; Schoharie, N.Y., YPM collection 0244/ 146.
6, 7. Left lateral and dorsal views of another complete carapace, USNM 162348; Schoharie, N.Y., USGS collection 3393-SD.
8-13. Nunculina striatopunda n. gen., n. sp. (p. 41).
8.	Interior of left valve, paratype, USNM 162349, showing slight marginal groove; Schoharie, N.Y., USGS collection 7283-SD.
9.	Dorsal view of complete carapace, paratype, USNM 1623o0; Schoharie, N.Y., USGS collection 3393-SD.
10.	Left lateral view of carapace, slightly broken posteriorly, showing small punctae, paratype, USNM 162351; Schoharie, N.Y., USGS collection 7283-SD.
II.	Interior of left valve showing internal ridge reflecting external sulcus, paratype, YPM 23829; Schoharie, N.Y., YPM collection 5244/146.
12.	Right lateral view of carapace showing overlap, holotype, YPM 23830; Schoharie, N.Y., YPM collection 5244/146.
13.	Left lateral view of large carapace, paratype, YPM 23831; Schoharie, N.Y., YPM collection 5244/146.
14.	Hollinid?, gen. and sp. indet. (p. 29). USNM 162353; Schoharie, N.Y., USGS collection 8064-SD.
15.	Kirkbyellid?, gen. and sp. indet. (p. 29). USNM 162354; Schoharie, N.Y., USGS collection 8064-SD.
16.	Halliella? sp. (p. 30). USNM 162355; Schoharie, N.Y., USGS collection 7283-SD.
17.	Marginia? sp. (p. 38). USNM 162356; Schoharie, N.Y., USGS collection 8062-SD.
18-24. Cytherellina crepiduloides n. sp. (p. 39).
18.	Right lateral view of complete carapace, holotype, USNM 162357; Schoharie, N.Y., USGS collection 3393-SD.
19.	Interior of left valve showing anterodorsal shelf and round depression below it, presumably adductor muscle pit, paratype YPM 23832; Schoharie, N.Y., YPM collection 5244/146.
20.	Interior of right valve showing lack of marginal structures, paratype, YPM 23833; Schoharie, N.Y., YPM collection 5244/146.
21.	Interior of right valve showing adductor muscle pit, paratype, USNM 162358; Schoharie, N. Y., USGS collection 3393-SD.
22.	Dorsal view of complete carapace, paratype, YPM 23834; Schoharie, N.Y., YPM collection 5244/146.
23.	Interior of left valve showing marginal structures, paratype, YPM 23835; Schoharie, N.Y., YPM collection 5244/146.
24.	Right lateral view of crushed carapace, paratype, YPM 23836; Schoharie, N.Y., YPM collection 5244/146.
25-29. Eukloedenella? weldae n. sp. (p. 37).
25.	Left lateral view of complete tecnomorphic carapace, paratype, USNM 162359; Schoharie, N.Y., USGS collection 7283-SD.
26.	Dorsal view of complete tecnomorphic carapace showing indented posterior, paratype, USNM 162360; Schoharie, N.Y., USGS collection 7283-SD.
27.	Right lateral view of heteromorphic carapace, holotype, USNM 162361; Schoharie, N.Y., USGS collection 3393-SD.
28.	Dorsal view of complete heteromorphic carapace showing wide stragular process and inflated posterior, paratype USNM 162362; Schoharie, N.Y., USGS collection 7283-SD.
29.	Interior of large heteromorphic left valve showing groove beneath stragular process and possible adductor muscle pit, paratype, USNM 162363; Schoharie, N.Y., USGS collection 3393-SD.
30-33. Bonneprimites? breviformis Swartz and Whitmore (p. 38).
Dorsal, left lateral, ventral, and right lateral views of a complete carapace, USNM 162364; Shutter Corners, N.Y., USGS collection 3390-SD.
34-40. Leiocyamus pundatus n. sp. (p. 29).
34.	Interior of heteromorphic left valve, paratype, YPM 23837; Schoharie, N.Y., YPM collection 5244/146.
35.	Interior of heteromorphic right valve, showing hinge, paratype, YPM 23838; Schoharie, N. Y., YPM collection 5244/146.
36.	Dorsal view of tecnomorphic carapace, paratype, USNM 162365; Schoharie, N. Y., USGS collection 3393-SD.
37.	Right lateral view of tecnomorphic carapace, paratype, YPM 23839; Schoharie, N.Y., YPM collection 5244/146.
38.	Posterior view of heteromorphic carapace, paratype, USNM 162366; Schoharie, N.Y., USGS collection 3393-SD.
39.	Left lateral view of heteromorphic carapace, holotype, YPM 23840; Schoharie, N.Y., YPM collection 5244/146.
40.	Dorsal view of heteromorphic carapace, paratype, YPM 23841; Schoharie, N.Y., YPM collection 5244/146.Plate 6—Continued
41-43. Kloedenella sp. (p. 37).
41, 42. Right and left views of a tecnomorphic carapace, USNM 162367; Schoharie, N.Y., USGS collection 3393-SD.
43.	Right lateral view of another tecnomorphic carapace, YPM 23842; Schoharie, N.Y., YPM collection 5244/146.
44.	Primitiopsis? sp. (p. 30).
Left lateral view of slightly broken tecnomorphic carapace, USNM 162368; Schoharie, N.Y., USGS collection 8062-SD.
45,	46. Leiocyamus sp. B (p. 30).
45.	Right lateral view of crushed heteromorphic carapace, USNM 162369; Schoharie, N.Y., USGS collection 3393-SD.
46.	Left valve of heteromorph, USNM 162370; Schoharie, N.Y., USGS collection 3393-SD.
47,	48. Leiocyamus sp. A (p. 30).
Oblique dorsal and left lateral views of heteromorphic carapace, YPM 23843; Shutter Corners, N.Y., YPM collection 5244/150.GEOLOGICAL SURVEY	PROFESSIONAL PAPER 730 PLATE 6
THLIPSURELLA , THLIPSUROPSIS, NUNCULINA , HOLLINID?, KIRKBYELLID?, HALLIELA ?, MARGIN IA ?, CYTHERELLINA, EUKLOEDENELLA ?, RONNEPRIMITES ?,
LEIOC YAM US, KLOEDENELLA, AND PRIMITIOPSIS1
U. S. GOVERNMENT PRINTING OFFICE; 1972 O - 447-7697 DAY USE
RETURN TOGeology of the Pulga and Bucks Lake Quadrangles, Butte and Plumas Counties, California
GEOLOGICAL SURVEY
9^75-SeJ $-
r-73/
PROFESSIONAL PAPER 731Geology of the Pulga and Bucks Lake Quadrangles, Butte and Plumas Counties, California
By ANNA HIETANEN
GEOLOGICAL SURVEY PROFESSIONAL PAPER 731
A petrologic and structural study of metamorphic and plutonic rocks
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :	1973UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY V. E. McKelvey, Director
Library of Congress catalog card No. 73-600063
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price S3.45CONTENTS
Abstract ........................................
Introduction ....................................
Previous work ................................
Purpose and scope ...........................
Structural setting ..........................
Rocks of the area ...........................
Metasedimentary formations ......................
Shoo Fly Formation ..........................
Rock units ....................._........
Petrographic description ................
Phyllite and interbedded quartzite...
Orthoquartzite .......................
Limestone ...........................
Structure ...............................
Calaveras Formation .........................
Distribution and thickness...............
Petrographic description ................
Metachert ............................
Phyllite .............................
Marble ...............................
Structure ...............................
Major features.......................
Bedding ..............................
Folds ................................
Foliation ............................
Lineation .....................j.....
Metavolcanic sequence............................
Franklin Canyon Formation....................
Distribution ............................
Primary volcanic structures ...._........
Petrographic description ................
Meta-andesite .......................
Metadacite ..........................
Metamorphosed sodarhyolite .........
Metatuff and tuffaceous metasediment.
Duffey Dome Formation........................
Distribution ............................
Petrographic description ................
Metabasalt ..........................
Metarhyolite ........................
Metatuff ............................
Quartzite and marble interbedded with
metavolcanic rocks ................
Horseshoe Bend Formation....................
Structures due to deformation................
Distribution and major structures........
Description of the rocks.................
Phyllite ............................
Marble ..............................
Quartzite ...........................
Conglomerate ........................
Metavolcanic layers .................
Page
Tentative correlation of metamorphic rocks southwest
of the Melones fault ................................ 22
Cedar Formation......................................   23
Metamorphosed intrusive rocks.......................... 23
Ultramafic rocks.................................   23
Rocks associated with serpentines.................. 28
Metagabbro and hornblendite......................   29
Metadiorite .....................................   30
Metatrondhjemite .................................. 31
Metamorphosed hypabyssal rocks..................... 31
Metamorphism .......................................... 33
Plutonic rocks ........................................ 35
Distribution and division.......................... 35
Bucks Lake pluton ...............................   36
Pyroxene diorite and hornblende-pyroxene
diorite.................................. 36
Structural relations....................... 36
Petrography ............................... 37
Hornblende diorite...........................   39
Hornblende-biotite quartz diorite.............. 40
Hornblende gabbro ............................. 43
Satellitic bodies of pyroxene diorite and
hornblende diorite.............................   43
Grizzly pluton  ....................._............ 44
Oliver Lake pluton...............................   47
Granite Basin pluton .............................  47
Merrimac pluton.................................... 47
Concow pluton....................................   48
Hartman Bar pluton and related bodies of
epidote tonalite ................................ 48
Dikes associated with plutonic rocks.................   49
Magma differentiation based on composition
and age of plutonic rocks............................ 50
Trace elements in plutonic and metamorphic rocks....... 53
Gold-quartz veins .................................     56
Auriferous stream deposits..............._............ 57
Tertiary volcanic rocks .............................. 57
Correlation and age .............................   57
Petrography ...................................     58
Lovejoy Basalt................................. 58
Pyroclastic andesite ........................   58
“Late basalt” of Turner (1898) ..............   59
Olivine basalt ............................ 59
Two-pyroxene andesite ..................... 59
Plagioclase basalts in the Pulga quadrangle... 59
Tertiary unconsolidated materials...................... 60
Summary and conclusions .............................   60
References cited ...................................... 61
Index ................................................. 65
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IIIIV
CONTENTS
ILLUSTRATIONS
[Plates are in pocket]
Plate	1. Geologic map of the Pulga quadrangle and part of the Jonesville quadrangle, Plumas and
Butte Counties, California.
2.	Geologic map of the Bucks Lake quadrangle and part of the Almanor quadrangle, Plumas
County, California.
3.	Map showing pre-Tertiary geology of the Feather River area, Sierra Nevada.
Page
Figure 1. Location of area studied, northern California................................................................ 2
2. Photomicrograph of helicitic inclusions of epidote in late biotite and albite.......................... 5
3. Photomicrograph of orthoquartzite from the Shoo Fly Formation ......................................... 6
4.	Photographs of glaciated outcrops showing structures and compositional variations in metachert
of the Calaveras Formation......................................................................... 7
5.	Photograph of porphyroblasts of cordierite in biotite-anthophyllite schist of the Calaveras Formation
near the northwestern contact of Grizzly pluton ................................................... 8
6.	Photomicrograph of cordierite-biotite-anthophyllite schist from the Calaveras Formation............... 8
7.	Photograph of small cordierite porphyroblasts in a dark biotite phyllite that shows irregular wrinkling
with axes that parallel the major northwest fold axis.............................................. 9
8.	Photomicrograph of cordierite, andalusite, and sillimanite in biotite schist.......................... 9
9-14. Photographs of:
9.	Small folds with steep axes in metachert of the Calaveras Formation............................ 11
10.	Fan-shaped arrangement of cleavage (s=) at the hinges of folds on glaciated horizontal
surface of metachert of the Calaveras Formation............................................. 12
11.	Stretched lapilli in metatuff from the Franklin Canyon Formation .............................. 13
12.	Round spherulites in the outer rim of a pillow in meta-andesite of the Franklin Canyon Formation ..	14
13.	Phenocrysts of albite and amygdules of quartz in metadacite of the Franklin Canyon Formation...	14
14.	Strong stretching parallel to a nearly vertical lineation and fold axis in metabasalt of the
Duffey Dome Formation....................................................................... 19
15.	Photomicrograph of andalusite and staurolite in biotite schist of the Horseshoe Bend Formation........ 20
16.	Photograph of marble from the Horseshoe Bend Formation ............................................... 21
17.	Photomicrographs of altered peridotite................................................................ 24
18.	Graph showing distribution of [Mg/Fe] between enstatite, olivine, and hornblende in olivinite No. 134. 26
19.	Photomicrograph of seams of talc in antigorite serpentine at the east border of the ultramafic
mass south of Bucks Lake .......................................................................... 26
20.	Sketch of lenses and dikelike bodies of metadiorite and metagabbro in metadacite and metasodarhyolite ....	31
21.	Diagrams showing possible pressure-temperature conditions during recrystallization ................... 34
22.	A-C-F diagram for metamorphic rocks...................................................-............... 35
23.	Photograph of round inclusions of fine-grained pyroxene diorite in coarser grained pyroxene-
hornblende diorite ....................:........................................................... 36
24.	Sketch of flattened inclusions of pyroxene diorite in pyroxene-hornblende diorite, Bucks Lake pluton..	36
25.	Photograph of segregations of hornblende and plagioclase in pyroxene diorite, Bucks Lake pluton....... 37
26.	Photomicrograph of pyroxene diorite from Bucks Lake pluton ........................................... 37
27.	Photograph of hornblende-biotite quartz diorite from the Bucks Lake pluton ........................... 40
28.	Photograph of foliated border zone of hornblende-biotite quartz diorite of the Bucks Lake pluton ..... 41
29.	Photomicrograph of tabular plagioclase crystals oriented parallel to the foliation in hornblende-biotite
quartz diorite of the Bucks Lake pluton........................................-................... 41
30.	Photomicrograph of large plagioclase grains with round ends enveloped by trains of biotite and small
interstitial grains of quartz ip the foliated border zone of the Bucks Lake pluton................. 42
31.	Photomicrograph of biotite-hornblende gneiss just north of the northern contact of the Bucks Lake pluton ..	42
32.	Photograph of hornblende-biotite quartz diorite from the border zone of the Grizzly pluton............ 44
33.	Photograph of coarse-grained inner border zone of the Grizzly pluton at Reese Flat......:..........    44
34.	Photograph of light-colored monzotonalite from the central part of the Grizzly pluton................. 44
35.	Photomicrograph of remnant of augite and tiny inclusions of quartz in hornblende in the hornblende
quartz diorite of the Grizzly pluton............................................................... 46
36.	Photomicrograph of stubby euhedral to subhedral plagioclase crystals in monzotonalite of the
Grizzly pluton...........,...“........................................................,............ 46CONTENTS
V
Page
Figures 37-40. Ternary diagrams showing normative amounts of:
37.	Quartz, albite, and orthoclase in the plutonic, metavolcanic, and metamorphosed intrusive rocks
in the Bucks Lake and Pulga quadrangles ................................................. 50
38.	Quartz, plagioclase, and orthoclase in the plutonic, metavolcanic, and metamorphosed intrusive
rocks in the Bucks Lake and Pulga quadrangles ........................................... 50
39.	Quartz, mafic constituents as orthosilicates, and feldspars for the plutonic, metavolcanic, and
metamorphosed intrusive rocks in the Bucks Lake and Pulga quadrangles.................... 51
40.	Albite, orthoclase, and anorthite of the plutonic metavolcanic, and metamorphosed intrusive
rocks in the Bucks Lake and Pulga quadrangles ........................................... 51
41-45. Graphs showing:
41.	Average trace-element concentration in plutonic, metaigneous, and metasedimentary rocks
in the Bucks Lake quadrangle............................................................. 54
42.	Distribution	of	potassium-strontium ratios as function of potassium.......................... 55
43.	Distribution	of	potassium-barium ratios as function of potassium............................. 55
44.	Distribution	of	strontium-barium ratios as function of potassium............................. 55
45.	Distribution	of	calcium-strontium ratios as function of potassium ........................... 56
TABLES
Page
Table	1. Chemical composition and molecular norms of metamorphosed igneous and sedimentary rocks from
the Bucks Lake quadrangle.......................................................................... 15
2.	Chemical composition, calculated formulas, and trace elements of blue-green hornblende from
metagabbro and colorless hornblende, enstatite, and olivine from peridotite, Bucks Lake quadrangle.	25
3.	Chemical composition, molecular norms, and calculated modes of plutonic rocks in the Bucks Lake
and Pulga quadrangles.............................................................................. 38
4.	Percentage of the major constituents measured in stained specimens of plutonic rocks............... 45
5.	Trace elements in plutonic rocks in the Bucks Lake and Pulga quadrangles........................... 53
6.	Trace elements in metamorphosed igneous and sedimentary rocks in the Bucks Lake	quadrangle......... 53
7.	Pebble count of gold-bearing Eocene gravel on Beans Creek, Bucks Lake quadrangle................... 57GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, BUTTE AND PLUMAS COUNTIES, CALIFORNIA
By Anna Hietanen
ABSTRACT
The area studied is at the north end of the western meta-morphic belt of the Sierra Nevada. Structurally it is in the inner belt of the Nevadan arcuate segment, in which northerly trends of the central Sierra Nevada turn to the northwest and locally even to the west. The northeast part of the area is traversed by a major northwest-trending fault zone, the Melones fault, and an adjoining serpentine belt. Orthoquartzite and interbedded phyllite northeast of this belt are continuous with the Shoo Fly Formation of probable Silurian age in the neighboring areas to the north and east. Correlation of the metasedimentary and metavolcanic rocks southwest of the Melones fault is uncertain because strong deformation and recrystallization have destroyed the fossils beyond positive identification. On lithologic grounds and assuming a widespread volcanic activity, the pyroclastic sequence is tentatively correlated with Paleozoic pyroclastic formations in the south and with those dated on the basis of fossil evidence as Devonian and Permian in the neighboring Taylorsville area in the east. Fault contacts occur between the metasedimentary and the pyroclastic rocks in most of the area, but in the central part, where trends turn to the west, and also in the northwestern part, some contacts are not faulted but folded.
Two sets of folds are apparent on good outcrops of distinctly bedded parts of the metamorphic rocks. The major folds trend northwest; the axial plane foliation is either vertical or dips 70°-85° NE. (more rarely to the southwest). The early structures were modified by Late Jurassic and Early Cretaceous plutons that shouldered the wallrocks aside during emplacement and caused a second episode of deformation and recrystallization of the wallrocks to the epidote-amphibolite facies. The second deformation appears as a strong steeply plunging lineation that in places is the axis of folding.
Two groups of intrusive rocks have invaded the metamorphic sequences. The older of these ranges from hornblendite and hornblende gabbro to hornblende quartz diorite and trondhjemite in composition. It represents deep-seated and hypabyssal equivalents of the metavolcanic rocks and is about the same age or only a little younger than the metavolcanic rocks. The younger intrusive group forms round plutons, 3-13 miles in diameter, that range from pyroxene diorite to mon-zotonalite in composition. Potassium-argon ratios in hornblendes and biotites in these rocks have yielded ages ranging from 143 to 128 million years.
Most of the plutons are normally zoned: their border zones consist of hornblende-biotite quartz diorite, and the central parts consist of monzotonalite. The Bucks Lake pluton, however, has an older central mass of pyroxene diorite that is partly brecciated and altered to hornblende-bearing rock along
its borders. Chemical composition and trace-element content, together with the structural relations, suggest that the pyroxene diorite is an early differentiate of the same magma from which the hornblende quartz diorite crystallized. Biotite-epidote tonalite forms one large and several small bodies in the southern part of the Bucks Lake quadrangle. Chemically these are similar to the quartz diorite-monzotonalite plutons; the differences in mineralogy result from a higher water content in the magma. The most silicic differentiates associated with the biotite-rich tonalites have trondhjemitic affinities.
Tertiary volcanic rocks are widespread in the eastern and northwestern parts of the area. The lowermost flows are black basalt that is tentatively correlated with Durrell’s Lovejoy Formation. The overlying pyroclastic andesite is probably equivalent to Durrell’s Penman Formation of Pliocene age. Augite basalt on top of Mount Ararat and small pluglike bodies of olivine basalt in the southern part of the Bucks Lake quadrangle may be equivalent to similar basalt in the Blairs-den quadrangle, which basalt was correlated with Russell’s Warner Basalt of Pliocene age by Durrell.
INTRODUCTION
The Bucks Lake quadrangle and the adjoining Pulga quadrangle are at the north end of the Sierra Nevada gold belt. They cover an area of 458 square miles bounded by lat 39°45' and 40°00' N. and long 121°00' and 121°30' W. (fig. 1). A narrow strip along the north boundary of these quadrangles was also mapped in order to trace the contacts of the granitic plutons. The area is deeply dissected by canyons of the North Fork and the Middle Fork of the Feather River and their tributaries. The highest mountains near Bucks Lake rise 5,000 feet above the canyon of the North Fork, to an elevation of 7,000 feet above sea level. The high plateau to the southeast and northwest is 3,000 feet above the river canyons, at an elevation of 5,000-6,000 feet above sea level.
The area is timbered by pines, fir, incense cedar, and oak. Many slopes are covered by thick growth of man-zanita and mountain laurel. In addition to the roads shown on the maps (pis. 1, 2), many logging roads and trails traverse the area. Exposures are excellent along the rivers and large creeks as well as on the highest elevation near Bucks Lake and in the northernmost part
12
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
123°	122°	121°	120°
Figure 1.—Location of area studied, northern California.
of the Pulga quadrangle, but they are few and small on many slopes and on level ridges of the high plateau.
PREVIOUS WORK
The Bucks Lake and Pulga quadrangles make up the north half of the old Bidwell Bar quadrangle mapped by Turner (1898). The metavolcanic rocks were shown as amphibolite on that map. Turner included the meta-sedimentary rocks in the Calaveras Formation, which he considered to be Carboniferous on the basis of stratigraphic continuity in adjacent areas and on the fossil evidence. Fossils that were considered to indicate a Carboniferous age were found in limestone near Spanish Creek in the eastern part of the Bucks Lake quadrangle,
and on the slope west of Onion Valley Creek, 3 % miles southeast of the mouth of this creek in the southeast corner of the Bucks Lake quadrangle. Rounded crinoid stems and tests of Foraminifera were found in the Diadem lode at Edmanton on the south side of Eagle Gulch (sec. 28, T. 24 N., R. 8 E.). A small area of metasedi-mentary rocks in the northeastern part of the Bucks Lake quadrangle was shown as the Cedar Formation of “Jura-Trias” age.
The southern part of the Pulga quadrangle was included in the description of the Merrimac area by Hietanen (1951). On the geologic map accompanying that report, the subdivision of the metamorphic rocksINTRODUCTION
3
was partly genetic and partly based on the mineral assemblages found in the rocks.
The geologic map of California by Burnett and Jennings (1962) shows metasedimentary rocks of Paleozoic age and metavolcanic rocks of Jurassic and Triassic age, both undivided. Serpentine and other ultramafic intrusive rocks are shown as Mesozoic in age, and the granitic plutons as younger Mesozoic. The small area of Turner’s (1898) “Jura-Trias” Cedar Formation is shown as Triassic marine. The Triassic age of these rocks in the area north of the Bucks Lake quadrangle has been verified by McMath (1958) on the basis of fossils that he found.
The metasedimentary rocks in the extreme northeast corner of the Bucks Lake quadrangle were included in the Shoo Fly Formation of probable Silurian age by Clark, Imlay, McMath, and Silberling (1962) and by McMath (1966). The Silurian age for at least part of the rocks included in the Shoo Fly Formation by these authors was suggested by correlating the rocks with the fossiliferous Silurian Taylorsville Formation farther northeast. Paleozoic stratigraphy in the Taylorsville area was set up by Diller (1908). Later work, however, showed that a part of the sequence that he considered normal is overturned. The first irrefutable proof of this was given by Durrell and Proctor (1948, p. 171), who found that a metarhyolite sequence, the Sierra Buttes Formation of McMath (1966), overlies the Shoo Fly Formation with angular unconformity south of Taylorsville. Revision of stratigraphy in the Taylorsville area is given by McMath (1966, p. 176-178). In this area the Taylorsville thrust separates the overturned sequence of the upper plate from the normal sequence of the lower plate, and both plates include the Shoo Fly and Sierra Buttes Formations (McMath, 1958, 1966).
Creely (1965) found tetracorals of late Paleozoic age, probably Permian, in the limestone interbedded with supposed Calaveras slates in the northwestern part of the Oroville quadrangle, which joins the Pulga quadrangle in the southwest. The fossil locality is in the western continuation of the metasedimentary formation exposed in the southwest corner of plate 3 of this report, just north of lat 39°40' N. and 4 miles to the west.
PURPOSE AND SCOPE
The short summary of previous work shows that very little is known about the stratigraphy, age, and metamorphism of the pre-Cretaceous rocks of the area. The earlier stratigraphy (Turner, 1898) combined all metasedimentary rocks under the name Calaveras, to which a Carboniferous age was assigned on the basis of fossil evidence that is not considered to be conclusive by modern standards. Because no new identifiable fossils were found during this work, an attempt has been made to work out a stratigraphic sequence and correlate the
mappable rock units with the known formations in the neighboring areas. This tentative correlation is based on lithology and on the stratigraphic position of the units.
The stratigraphy and lithologic correlation are complicated by profound deformation and recrystallization that have destroyed most of the primary structures, such as possibe crossbedding, ripple marks, and channeling, that would help in determining whether the strata are right-side-up or overturned. The bedding is preserved in some of the metasedimentary rocks, such as metachert, but in most of the phyllite the only measurable structural element is foliation. The stratigraphy can then be worked out only by mapping the distribution of the rock units.
The stratigraphy is further complicated by faults that divide the area into northwest-trending belts. Each belt seems to have a different lithology, making the correlation across the faults uncertain if not impossible. Comparison of metamorphic and structural history of the individual belts may throw some light on the problem of a possible large age difference between them, such as was suggested on the earlier geologic maps.
The Late Jurassic and Early Cretaceous plutons have modified or destroyed the earlier structures around them, so that these structures can be studied only in rather small parts of the area.
The occurrence of metamorphosed sodarhyolite as the silicic end member of the meta-andesite-metadacite sequence in the eastern part of the area is an intriguing problem in itself. Potassium-rich metarhyolite, probably not much different in age, is associated with metabasalt in the western part of the same belt. Petrologic study of all these rocks should help in solving the problem of this difference in the potassium content of the metarhylolites.
Another problem in the area is the “reversed” zoning in one of the plutons. Most of the plutons are normally zoned, the basic border zones grading to silicic centers, but in the Bucks Lake pluton the most basic differentiate occurs in the central part and seems to grade to silicic hornblende quartz diorite at the borders. Petrologic study of the plutonic rocks helps solve this problem.
This work also contributes to the knowledge of the ultramafic rocks and their serpentinization in the Sierra Nevada and of the pressure and temperature conditions during the metamorphism and plutonism.
STRUCTURAL SETTING
The area lies in the inner zone of an arcuate segment of a tightly folded Nevadan orogenic belt (pi. 3). The regional trends south of the area are southward, and in the central part of the Pulga quadrangle they are westward. Faults divide the area into four belts; rocks of one or two formations are exposed in each belt. Structural relations suggest that generally the younger for-4
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
mations are in the successive belts to the southwest (fig. 1). The rocks are isoclinally folded, and in most parts of the area folds are overturned to the southwest. The faults seem to be high-angle faults, but overthrusting to the southwest—or rather underthrusting in a sub-duction zone, to the northeast—cannot be ruled out. Late Jurassic and Early Cretaceous plutons modified the structures by shouldering the wallrocks aside and causing a second episode of deformation and recrystallization. On the maps (pis. 1, 2) this is clearly demonstrated as the curvature of the trends of the metamorphic wallrocks around the plutons.
A major belt of ultramafic rocks bordered by the Melones and Rich Bar faults crosses the northeastern part of the area. In the south, elongate bodies of ultra-mafic rocks, partly altered to serpentine and talc schist, occur along the fault contacts between the formations. In the central part of the arcuate segment they thicken in places of tectonic low pressure. The ultramafic bodies were deformed and recrystallized during the major period of deformation and recrystallization, indicating that the faults they intruded started to form early. Breccia zones as much as several meters wide along the major faults are evidence of continued movement after the recrystallization. Thus, each fault block forms a unit, making the correlation across the faults uncertain.
ROCKS OF THE AREA
The Melones fault, accompanied by a belt of serpentine, divides the area into two parts that have different lithologies. The rocks northeast of the Melones fault are continuous with the Shoo Fly Formation of Clark, Imlay, McMath, and Silberling (1962) and of McMath (1966) in the adjoining areas. The rocks southwest of the Melones fault are divisible into four mappable units that differ strikingly in their lithology. These are called the Calaveras, Franklin Canyon, Duffey Dome, and Horseshoe Bend Formations.
The name Calaveras Formation was applied by Turner (1898) to all metasedimentary rocks in the Bidwell Bar quadrangle. In this report the name Calaveras is restricted to the belt of metasedimentary rocks that in the Bucks Lake quadrangle lies immediately southwest of the Rich Bar fault and continues westward to the northern part of the Pulga quadrangle. This formation is believed to be the oldest of the four units southwest of the Melones fault. No new evidence indicating the age was found.
The name Franklin Canyon Formation is coined for a sequence of potassium-poor metavolcanic rocks that range in composition from meta-andesite through meta-dacite to metasodarhyolite and contain interbedded layers of metatuff of the same compositions. The main belt of these rocks is in the Bucks Lake quadrangle southwest of the Calaveras Formation. Similar rocks, probably also belonging to the Franklin Canyon Forma-
tion, lie unconformably on the Calaveras Formation in the northern part of the Bucks Lake quadrangle; this relation suggests that the Franklin Canyon Formation is the younger of the two. A continuous section through this formation is exposed in the deep gorge called Franklin Canyon on the Middle Fork of the Feather River (pi. 2).
In the central part of the Pulga quadrangle, the metavolcanic sequence that overlies the Calaveras Formation consists of metabasalt and of metarhyolite rich in potassium feldspar. This sequence is well exposed near Duffey Dome, after which it is named. Its age relation to the Franklin Canyon Formation is uncertain because igneous rocks and Quaternary deposits separate the exposures of the two formations. Together they form the major part of the metavolcanic sequence.
A succession of metamorphic rocks along Marble Creek and to the southeast in the vicinity of Deer Park in the Horseshoe Bend of the Little North Fork of the Feather River is very heterogeneous. It is composed of thin layers and lenticular bodies of quartzite, mica schist and phyllite, limestone, metabasalt, metaandesite, metadacite, metarhyolite, and metatuff, all interbedded and isoclinally folded. This succession is called the Horseshoe Bend Formation. The metamorphic rocks west of the Merrimac pluton are most likely a part of this formation.
Two groups of igneous rocks are distinguished: (1) the older metamorphosed series in small to large bodies and ranging in composition from serpentine and pyroxe-nite through gabbro and quartz diorite to tonalite and trondhjemite and (2) the younger series that forms large plutons consisting of pyroxene diorite, hornblende quartz diorite, tonalite, and monzotonalite. These plutons are the northernmost exposed plutons in the western metamorphic belt of the Sierra Nevada and are comparable in their age and composition to the older plutons in the western part of the central Sierra Nevada (Bateman and Eaton, 1967, p. 1409).
Parts of the Bucks Lake quadrangle and of the northern Pulga quadrangle are covered by Tertiary basalt and pyroclastic andesite. Gravel deposits under these volcanic rocks have been mined for gold, as have some of the Quaternary lake deposits.
METASEDIMENTARY FORMATIONS SHOO FLY FORMATION
ROCK UNITS
The rocks shown as a part of the Silurian (?) Shoo Fly Formation by Clark, Imlay, McMath, and Silberling (1962) and by McMath (1966) are exposed near Snake Lake and on both sides of Spanish Creek in the northeastern part of the Bucks Lake quadrangle. These two exposed parts of the Shoo Fly Formation are separated by Quaternary gravel deposits. The major rockMETASEDIMENTARY FORMATIONS
5
type northwest of Snake Lake is a blastoclastic muscovite quartzite, orthoquartzite, that is weakly deformed. On the west this quartzite lies conformably on muscovite-chlorite phyllite. The outcrops south of the gravel near Spanish Creek consist of isoclinally folded mica schist that includes some thin layers of quartzite, metagraywacke, and interbedded limestone in which Turner (1898) reported fossils of Carboniferous age. Shearing stronger than that in the orthoquartzite is evident in the schist on Spanish Creek. A small isolated outcrop of orthoquartzite on Whitlock ravine (loc. 693) is the only occurrence of orthoquartzite south of the gravel. The strike and dip of bedding in this outcrop suggest that it may be interlayered and folded with the schist.
The contact between the orthoquartzite and the phyllite exposed under it is gradational over a few meters. The gradational rock is micaceous foliated quartzite in which the number and size of the quartz grains decrease toward lower beds. A layer of orthoquartzite is interbedded with the phyllite at locality 292 on Pineleaf Road. Layers of white granular quartzite overlie the orthoquartzite and are interbedded with it.
Two layers of limestone, interbedded with the phyllite, extend from Spanish Creek to Rock Creek and a short distance beyond. Both layers are 30-50 meters thick and contain micaceous material in addition to rather pure carbonate beds. Discontinuous thin layers and lenses of carbonate occur in the underlying shaly beds.
Metatuff, metarhyolite, and metadacite occur in two small synclinal areas within the schist south of Spanish Creek. These metavolcanic rocks probably are a part of the Shoo Fly Formation since the phyllite exposed under them is a lower part of the Shoo Fly Formation. Mineralogy of these metavolcanic rocks is similar to that of the corresponding rock types in the Franklin Canyon Formation.
PETROGRAPHIC DESCRIPTION PHYLLITE AND INTERBEDDED QUARTZITE
The phyllite of the Shoo Fly Formation is fine grained and varies from light beige to brownish gray or dark gray, depending on the micaceous minerals present and on the amount of magnetite and hematite. Dark-gray to black slaty layers on the East Branch of Rock Creek at the east border of the Bucks Lake quadrangle are rich in carbon. In the northernmost part of the quadrangle, very fine grained light-tan muscovite phyllite is interbedded with muscovite-chlorite phyllite. In addition to muscovite and chlorite, biotite is common near Spanish Creek and to the south. Dark- to medium-gray layers rich in quartz are interbedded with phyllite. The thickness of these quartzitic layers ranges from a few
centimeters to several meters; the thicker layers contain micaceous laminae. Some layers along Spanish Creek near the mouth of Whitlock Creek contain large round grains of albite that may constitute as much as 10 percent of the rock.
Thin sections of the phyllite show that chlorite is interleaved with muscovite, and both are parallel to the foliation. Chlorite is very pale green with bluish-gray interference colors. Biotite is reddish brown and strongly pleochroic. In many layers, flakes of biotite transect the wrinkled foliation, which is paralleled by muscovite and chlorite. Biotite is thus clearly younger than the other micaceous minerals. In some specimens helicitic inclusions of magnetite, sphene, and epidote mark the plane of foliation within the biotite flakes (for example, loc. 695, fig. 2).
Stilpnomelane (identified by X-ray pattern) occurs instead of biotite in some layers east of the mouth of Slate Creek (loc. 16). This mineral is found in reddish-brown slender flakes that either parallel the foliation or form radial clusters. The index of refraction, y, is 1.686+0.002.
Albite grains are 1-2 millimeters in diameter and contain rows of inclusions of epidote and sphene. In most grains these inclusions are helicitic, continuing from the albite to the surrounding micaceous minerals (fig. 2). This indicates that albite is not a relict clastic grain but that it was crystallized late during the same episode as the biotite.
Sphene, ilmenite-magnetite, magnetite, and hematite are common accessory minerals. Sphene occurs in tiny euhedral crystals and larger anhedral grains. Much of the magnetite is altered to hematite.
lmm
Figure 2-Photomicrograph of helicitic inclusions of epidote (ep) in late biotite (bi) and albite (ab). The rows of inclusions are parallel to the external foliation. Biotite phyllite of the Shoo Fly Formation from the mouth of Whitlock Creek (loc. 695). Crossed nicols.6
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Garnet was found only in one specimen studied (loc. 16). Crystals are euhedral and only about 0.005 mm in diameter. Some are clearly zoned; the centers have n=1.783±0.002, and the rims n=1.782±:0.002.
Quartzitic layers, foliated and wrinkled, consist of 70-95 percent quartz, 5-20 percent muscovite, and some biotite, magnetite, hematite, and sphene. In the foliated layers, the quartz grains (0.05-0.5 mm long) are elongated parallel to the foliation. In the wrinkled layers, the quartz grains are rounded or polygonal with sutured borders. Undulatory extinction is common in all quartz. Most of the muscovite is between the quartz grains, but some flakes transect the grain boundaries or are included in quartz. A few grains of albite and potassium feldspar occur in some layers.
ORTHOQUARTZITE
The orthoquartzite is light gray, rarely brownish gray, and thick bedded; blastoclastic coarse-grained layers, from 20 centimeters to several meters thick, are separated by thin (5-50 cm) schistose layers that contain more muscovite.
The coarse-grained layers consist of bluish-gray clear round grains of quartz embedded in a finegrained matrix of muscovite and quartz. Most grains of quartz are 1-3 mm in diameter; some larger grains are scattered in light-gray sandstone west of Snake Lake. A few of the large grains of quartz are sub-hedral, but most are well rounded and nearly spherical; very few are elongate. Their color and translucency resemble phenocrysts in quartz porphyry or coarsegrained metarhyolite.
Thin sections show that the rounded grains of quartz make up about 90 percent of the orthoquartzite. Muscovite in tiny flakes and some small quartz grains are interstitial (fig. 3). Quartz grains show only very weak strain shadows and include tiny grains of magnetite, most of which are parallel to healed fractures. In the micaceous layers interbedded with the orthoquartzite, quartz grains are elongate and less than 1 mm long. They constitute about 30 percent of the rock, whereas the sericite-rich matrix makes up 70 percent. The matrix also contains tiny grains of quartz and albite, as well as some magnetite and hematite.
Very fine grained muscovite slate and fine-grained white granular quartzite overlie the orthoquartzite on the ridge north of Snake Lake. Micaceous laminae separate the individual beds of quartzite, which are 2-20 cm thick. The muscovite slate contains thin laminae of strongly deformed granoblastic grains of quartz. The magnitude of elongation and deformation of quartz seems to depend on the amount of muscovite: the layers rich in moscovite are more strongly sheared than the quartz-rich layers.
lmm
I__________________I
Figure 3.—Photomicrograph of orthoquartzite from the Shoo Fly Formation. Smith Lake (loc. 373). Matrix between the round grains of quartz (qu) consists of muscovite and quartz.
LIMESTONE
Most of the limestone is medium grained and light to medium gray; individual beds range from a few centimeters to a meter or more in thickness. A part of the southern unit on Rock Creek, however, consists of thin-bedded brown and white limestone in which white carbonate layers, 2-4 cm thick, alternate with brown micaceous layers of the same thickness. Carbonate-rich phyllite occurs as a gradational rock between the limestone and muscovite-biotite phyllite.
Recrystallization of limestone has destroyed the fossils beyond positive identification. Textures suggestive of fossil remains were observed in some thin sections of gray limestone on the north side of Spanish Creek.
STRUCTURE
Only a few structural features seen on the outcrops are described here because the Shoo Fly Formation covers too small an area for an extensive structural analysis. A complex isoclinal anticlinorium is exposed north of the Bucks Lake quadrangle (Moores, 1970).
Bedding (s,) is well preserved in orthoquartzite where fine-grained micaceous layers are interbedded with coarser grained quartz-rich rock. Bedding can be observed in the phyllite only where thin quartzitic layers alternate with micaceous layers. In most of the homogeneous phyllite, bedding cannot be distinguished, and the foliation (s2) is then the only measurable structure. In a few outcrops of phyllite, however, the bedding is evident because of variations in color, grain size, or the amount of micaceous minerals. Strong folding was observed in some outcrops. In these the foliation is parallel to the axial planes; it transects the bedding at the crests of folds and parallels the bedding on the flanks.META VOLCANIC SEQUENCE
7
The major fold axes trend northwestward, and the rock units are strongly elongated in the same direction, as shown on plate 2. Northeast-dipping bedding, axial plane foliation, and northeast-plunging lineation are common and suggest overturning to the southwest. Indeed, folds overturned to the southwest are exposed on the roadcuts north of the quadrangle. Small second folds with northeast-plunging axes that parallel lineation are common in the phyllite south of Slate Creek.
CALAVERAS FORMATION DISTRIBUTION AND THICKNESS
The major belt of metasedimentary rocks of the Calaveras Formation—interbedded metachert, phyllite, and some discontinuous limestone beds—traverses the mapped area in a northwesterly direction. The Bucks Lake and Oliver Lake plutons were emplaced into this belt and divide it into two branches. The southwest branch extends continuously from the southeast corner of the Bucks Lake quadrangle to the south side of Bucks Lake, where it borders the Bucks Lake pluton and then thins out between this and the Grizzly pluton. The northeast branch extends from the east border of the Bucks Lake quadrangle toward the northwest, forming the wallrocks of the Bucks Lake pluton in the north and enveloping the Oliver Lake pluton. From there this branch continues westward. It is partly covered by Tertiary basalts north of Grizzly pluton, but is well exposed again on the west side of the pluton. The west branch is only 1/2-1 mile wide and is terminated by a fault and metaigneous rocks near Rag Dump. The relation between the bedding and the cleavage together with the southward plunge of the fold axes in this western part of the belt suggest that the beds are younger toward the south, where some volcanic material is interbedded.
The thickness of the rock units vary. In the northern part of the Bucks Lake quadrangle layers of metachert about 100 m thick are interbedded with layers of phyllite of about the same thickness. In the southeastern part of the major layer of metachert is 200-500 m thick; several other layers that are only 5-20 m thick are not shown on the map (pi. 2). The thickness of most of the phyllite is difficult if not impossible*to estimate because of isoclinal folding and well-developed 'vaxial plane foliation that has obscured the bedding. The total exposed thickness of the formation in the northern part of the Bucks Lake quadrangle is 1,500-2,000 m. The total thickness on the Middle Fork of the Feather River may be greater because phyllite is the major rock type there.
PETROGRAPHIC DESCRIPTION METACHERT
The best exposures of metachert are in the northern part of the area. The glaciated outcrops near Campbell
Lake and east of Long Lake (fig. 4) in the Pulga quadrangle and the ridges in the northwest corner of the Bucks Lake quadrangle provide many continuous sec-
B
Figure 4.—Structures and compositional variations in metachert of the Calaveras Formation. A, Glaciated outcrops east of Long Lake in the northern part of the Pulga quadrangle. Thin laminae of micaceous quartzite separate the beds consisting of 95-100 percent quartz. B, Detail of outcrop shown in A. The light-colored layers consist of quartz and are separated by thin micaceous layers.8
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
tions of typical parts of the Calaveras Formation.
The metachert is thin bedded. Light- to medium-gray, rarely dark-gray, beds (3-8 cm thick) consisting of 95-100 percent quartz are separated by dark-brownish-gray micaceous layers (2-3 cm thick) and laminae (1-3 mm thick) in which muscovite and biotite are the common micaceous minerals. Locally chlorite instead of biotite occurs with muscovite; tremolite was seen in a few thin sections. Magnetite is a common accessory mineral.
The layers consisting almost exclusively of quartz are crisscrossed by thin veinlets of quartz. The grains in these veinlets are 0.05-0.5 mm in size, whereas those in the host rock are 0.01-0.03 mm in size. The grain size generally increases toward the plutons by recrystallization. Locally along the contacts part of the micaceous minerals, muscovite and biotite, are segregated into discontinuous laminae parallel to the cleavage that intersects the bedding. The color of the quartzitic layers changes from dark bluish gray through medium gray to very light gray with more thorough recrystallization. In the dark-bluish-gray metachert the magnetite is disseminated, whereas in the more thoroughly recrystallized layers, larger grains of magnetite are common. In a zone 200-500 m wide next to the plutons, the metachert is recrystallized to medium-grained white- to light-gray granular quartzite still preserving its thin-bedded structure. The common grain size in this quartzite is 0.1-0.3 mm for quartz and 0.1-1.5 mm for micaceous minerals.
PHYLLITE
The phyllite of the Calaveras Formation is well to moderately foliated, medium to dark gray, fine grained, and consists mainly of quartz (40-90 percent), muscovite, biotite and (or) chlorite. Albite (1-5 percent) occurs with quartz in some thin layers. Numerous garnet crystals 3-4 mm long occur in biotite phyllite east of the Oliver Lake pluton; elsewhere garnet is rare. Magnetite, hematite, pyrite, sphene, rutile, and tourmaline are the common accessory minerals; abundant graphite and (or) magnetite are disseminated through some layers. In many localities near the plutons, cor-dierite, andalusite, and staurolite crystallized as por-phyroblasts that are larger than the other mineral grains. Cordierite is the most common of these; it occurs either with biotite and andalusite—as in the southern part of the Bucks Lake quadrangle—or with anthophyllite. Sillimanite crystallized with andalusite and cordierite in biotite phyllite just south of the Bucks Lake pluton. Large porphyroblasts of cordierite (%-2 cm long, figs. 5, 6) and prisms of anthophyllite abound in many layers of phyllite north and northeast of Grizzly pluton near the northern border of the Pulga quadrangle. Cordierite also occurs in many micaceous
Figure 5.—Porphyroblasts of cordierite in biotite-anthophyllite schist of the Calaveras Formation near the northwestern contact of Grizzly pluton (loc. 930).
1mm
Figure 6.—Photomicrograph of the rock shown in figure 5. Anthophyllite (a) prisms are clustered around cordierite (c) porphyroblasts. Ordinary light.
layers of metachert at Chambers Peak and elsewhere near the contacts of the plutons. Pseudomorphs of micaceous minerals after staurolite occur in muscovite-biotite phyllite exposed in the west-central part of the area south of the Bucks Lake pluton.
Quartz grains are polygonal or elongate and 0.01-1 mm long. The common size in the lepidoblastic micaceous layers is 0.01-0.03 mm, and in the interbedded quartz-rich layers and laminae, 0.03-0.3 mm. In small clusters and veinlike bodies the quartz grains are somewhat larger, usually 0.3-1 mm long. Toward the plutons and locally elsewhere, grain size grows larger with higher degree of recrystallization.
Muscovite is the major micaceous mineral in most of the phyllite. It occurs in minute interstitial flakesMETASEDIMENTARY FORMATIONS
9
(0.01-0.5 mm long) or is segregated as larger flakes in thin laminae parallel to the foliation.
Biotite is interleaved with muscovite, or it forms larger flakes that intersect the plane of foliation and thus postdate it. In many layers near the plutons, and particularly in the andalusite-staurolite schist, biotite is the sole micaceous mineral. The flakes are 0.2-0.5 mm long and well oriented parallel to the foliation. Most of the biotite is reddish brown, but in some thin sections it is greenish brown. Alteration to chlorite was noted in several thin sections. Incipient alteration is indicated by pale brown or green color, low or bright interference colors, and inclusions of brown rutile, leucoxene, hematite, and magnetite along the cleavage planes.
Chlorite shows more irregularity in its distribution and mode of occurrence than the other micaceous minerals. There are two generations of chlorite: the early small flakes that occur with muscovite and biotite, and the late large flakes that are at angles to the plane of foliation. The early flakes are pleochroic in green and pale green and show brownish-gray to bluish interference colors. Much of this chlorite is next to the minute veinlets of quartz that are common in most of the phyllite. The late chlorite is very pale green to colorless and has dark-bluish-gray interference colors. It commonly contains helicitic inclusions of quartz, graphite, and magnetite.
Albite when present is in small grains that are usually untwinned.
Cordierite porphyroblasts are common in many layers of dark-gray biotite phyllite exposed in the canyon of Bear Creek and along Big Creek in the southern part of the Bucks Lake quadrangle. On the foliation surface these porphyroblasts form tiny knots 1 mm long that are enveloped by biotite (fig. 7). Thin sec-
0	5mm
1	___i____i___i____i____i
Figure 7.—Small cordierite porphyroblasts in a dark biotite phyllite that shows irregular wrinkling with axes that parallel the major northwest fold axis. Calaveras Formation, location 104 on Bear Creek.
tions show two generations of cordierite. The earlier one, cordierite I, contains rows of helicitic inclusions of quartz, biotite, and magnetite. The rows are at an angle to the foliation that envelops the cordierite (fig. 8). The later one, cordierite II, either grew around
lmm
Figure 8.—Photomicrograph of cordierite (c), andalusite (a), and sillimanite (s) in biotite schist on Bear Creek (loc. 85). In the early cordierite, the internal s plane, shown by rows of inclusions, is at an angle to the external foliation. Ordinary light.
cordierite I and included the foliation that enveloped cordierite I or formed new grains in which rows of inclusions form S-shaped curvature joining the external foliation at the crystal borders. Alteration to muscovite and chlorite and also to pinite is common.
Numerous large porphyroblasts of cordierite occur in the phyllite in the northwest corner of the Pulga quadrangle northeast of Jones Meadow (fig. 5). These porphyroblasts and those at Chambers Peak are late. They contain helicitic inclusions of quartz, biotite, and magnetite that are well alined parallel to the foliation of the host phyllite, even in the centers of the crystals. The quartz inclusions are usually small and round. In some quartz-rich layers, however, quartz inclusions are large enough to make cordierite poikiloblasic, or it may even seem interstitial. The biotite flakes in cordierite are smaller than those in the host phyllite. Cracks and border zones of cordierite are altered to pinite, more rarely to sericite. Tiny grains of magnetite are in rows parallel to the foliation. They are more numerous in the central parts than in the border zones of the cordierite metacrysts.
Metacrysts of cordierite near the contact of the Grizzly pluton south of Rag Dump (loc. 954) contain rows of helicitic inclusions of biotite and magnetite. These rows are at an angle to the plane of foliation and prove that this cordierite crystallized early.10
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Anthophyllite in long prisms occurs with cordierite northeast of Jones Meadow (fig. 6). The prisms (1-3 mm long) either are included in cordierite or are among biotite and quartz in the cordierite-bearing layers.
Cummingtonite in needles and slender prisms with Z/\c=15°-16° occurs instead of anthophyllite in many cordierite-bearing layers.
Andalusite in the cordierite-andalusite-sillimanite schist (fig. 8) includes rows of inclusions of ilmenite and quartz that are parallel to the plane of foliation. This andalusite crystallized late, most likely contemporaneously with cordierite II.
Sillimanite was found in a few thin sections of the cordierite-bearing phyllite along Bear Creek. It forms small wisps around and near the cordierite and andalusite (fig. 8). The sillimanite-bearing rock contains very little muscovite and no chlorite or potassium feldspar.
Garnet occurs only in a few localities. Red anhedral to subhedral grains, 5-12 mm long, crystallized in biotite phyllite east of the Oliver Lake pluton (loc. 1161). These grains are in coarse-grained laminae that consist mainly of quartz with some large flakes of biotite. Numerous tiny garnets occur in the fine-grained dark-gray muscovite-biotite phyllite exposed on the north slope of Hartman Bar Ridge in the south-central part of the Bucks Lake quadrangle (loc. 421). Small garnets are included in some of the cordierite at Chambers Peak in the Pulga quadrangle.
Magnetite is ubiquitous. It occurs in grains of various sizes (0.01-0.5 mm) or is disseminated. Alteration to hematite is common.
Pyrite in small cubes and in anhedral grains occurs locally. Also this mineral alters to hematite.
Tourmaline in tiny euhedral prisms is common in all phyllite, but not abundant.
Sphene and rutile are included in chlorite that was derived from biotite. Sphene is in euhedral to anhedral small grains; alteration to leucoxene is common.
Two samples of phyllite from the canyon of Bear Creek (Nos. 85, 104) were analyzed chemically (table 1). Sample 85 contains cordierite and some andalusite and sillimanite. Biotite in 0.03-0.05-mm long flakes is the major dark constituent. Sample 104 is a dark layer in phyllite; it contains abundant biotite, graphite, and magnetite. Some late chlorite transects the earlier minerals. The analyses show that both layers are poor in calcium and contain iron and magnesium in about equal amounts.
MARBLE
Two layers of gray to white marble are exposed along the Middle Fork of the Feather River about 0.2 miles west of the mouth of Bear Creek. Each layer is about 20 m thick (shown as one layer on pi. 2) and consists of thin-bedded gray to white marble that grades to car-
bonate-bearing black phyllite above and below. These layers are discontinuous and grade parallel to the strike into an epidote-rich phyllite.
A very similar gray to white layered marble is exposed just north of the Pulga quadrangle 1 mile west-northwest of Campbell Lake (loc. 1234). This marble is coarse grained because of contact metamorphism by the Grizzly pluton. It is underlain by a metabasalt and metachert and overlain by black phyllite that contains numerous lenses of epidote, many as much as 15 cm long. The phyllite exposed on Big Creek in the central part of the Bucks Lake quadrangle includes several carbonate-bearing layers. These marble layers were not analyzed chemically. They probably consist mainly of calcium carbonate, as do the two analyzed layers in this area.
STRUCTURE MAJOR FEATURES
The striking structural feature in the area, the curvature of the trends of metamorphic wallrocks around granitic plutons, is best shown by the structures in the two branches of the Calaveras Formation that wrap around the plutons. The second folding on steeply plunging axes is especially well demonstrated by intricately folded metachert that is in the triangular areas between the plutons. The change in the trend of the major axes from the northwesterly direction first to westerly then to southerly follows closely the direction of the northern and western walls of the nearby plutons and is clearly a result of the shouldering effect of the invading magma. This is especially well demonstrated in the western part of the Pulga quadrangle, where folds are squeezed perpendicular to the contact of the Grizzly pluton and the trends of the major fold axes parallel the curving contact. In the northwestern part of the Pulga quadrangle, the major fold axes plunge steeply to the southwest, and in the western part they plunge to the south. Thus the beds become younger from the north to the south, provided that right side is up as determined from the relation between bedding and cleavage. This relation indicates that the metasedi-mentary rocks exposed near Rag Dump represent the upper part of the Calaveras Formation.
BEDDING
Bedding is well preserved in the metachert in which thin micaceous layers are interbedded with layers consisting of 95-100 percent quartz (figs. 4, 9). Bedding is difficult to observe in much of the phyllite, and in many outcrops foliation is the only measurable structure. Where quartz-rich or carbonate-bearing layers are interbedded, as along Big Creek, the bedding is discernible because of differences in color, grain size, or amount of micaceous minerals and quartz. Bedding isMETASEDIMENTARY FORMATIONS
11
well preserved in some of the phyllite exposed in the northernmost part of the area, where layers of metachert are interbedded. Phyllite there contains thin layers of metachert not shown on plates 1 and 2 and also layers, 1-5 m thick, in which thin quartz-rich beds alternate with micaceous beds. The thickness of individual beds in these layers is 0.5 cm, whereas thicker beds are common in the normal phyllite.
FOLDS
Three major folds on a regional scale are evident in the Calaveras Formation (pis. 1, 2): (1) An anticline on an axis that plunges steeply to the east is well exposed in the canyon of the North Fork of the Feather River in the northeastern part of the Pulga quadrangle. The south flank of this fold wraps around the southern part of the Oliver Lake pluton, and the north flank encircles it in the north. (2) A large gentle anticline whose axis plunges east-southeast is indicated by curving of the bedding in phyllite and by distribution of interbedded metachert on Big Creek in the central part of the Bucks Lake quadrangle. This anticline is interrupted in the west and in the south by intrusive quartz diorite and covered in the east by Tertiary pyroclastic andesite. (3) A synclinal structure of similar phyllite and metachert south of these plutonic and volcanic rocks is revealed by attitudes of beds on the steep slopes of the canyon of Bear Creek. Small folds whose axes plunge west and northwest are exposed southeast of Red Ridge and north of the Middle Fork on the northeast flank of this syncline.
Evidence of two sets of folds in the Calaveras Formation outside the contact aureoles of the plutons is provided by good exposures along the Middle Fork of the Feather River. East of Sherman Bar small folds on northwest-plunging axes are common. Axes of these folds parallel the lineation shown on plate 2. Near Cleg-horn Bar, where beds dip to the east, small folds have axes that plunge steeply northeastward. In some outcrops between these two locations, two sets of folds are evident. The axis of the major set trends northwest; the axis of the second set trends east or northeast and plunges either southwest or northeast. The large anticline in the central part of the Bucks Lake quadrangle is on this second axis. The axis of small folds on its northeast flank trends northwest, and lineation on its south flank plunges southwest. This indicates that the first (major) folds on the northwest axis were refolded on the easterly (second) axis.
Small folds on the northwesterly axis are common in metachert on the East Fork of Big Creek in the central part of the Bucks Lake quadrangle and on the logging road following the north slope of the Bear Creek canyon. In the latter locality, small isoclinal folds on this
major axis are common also in phyllite and are then accompanied by a well-developed steep axial plane cleavage.
Folds around the steeply plunging second axis and the lineation are well exposed in the northern part of the Pulga quadrangle near Long Lake (fig. 9) and
Figure 9.—Small folds with steep axes in metachert of the Calaveras Formation east of Long Lake. Hammer handle is parallel to fold axes. View is eastward. Axial plunge is 70° NW.
Campbell Lake and on Chambers Peak. Several plunges were measured (pi. 1), and it seems that the folding in these places was intensified and the plunge of the axis may have changed during the emplacement of the plutons. The plunge of the second fold axes elsewhere is less steep, and the trends are more regular.
Near Jones Meadows, at the northwest corner of the Pulga quadrangle, the interbedded phyllite-metachert sequence is tightly folded on an axis that plunges steeply to the south-southwest. The direction of the second fold axes that can be measured in the outcrops varies, and in some outcrops, as on Big Kimshew Creek, two sets of minor fold axes can be measured, one trending subparallel to the contact of the pluton and the other plunging away from it. There the younger beds are to the south, where layers of hornblende gneiss and metabasalt are interbedded with quartzite.
FOLIATION
In much of the phyllite, foliation is the only measurable^ plane. It parallels the axial planes of small folds. On the flanks of large folds, it is either parallel to the bedding or makes a small angle with it.
In the folded metachert and in the interbedded phyllite, foliation is commonly parallel to the axial plane. In a few outcrops near the plutonic rocks, a fan-shaped arrangement of cleavage indicates tightening of the folds after the development of the axial plane cleavage. This is particularly clear in the outcrops 1 mile south of
499-964 0 - 73 -312
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Spanish Peak and in the intensely folded metachert that fills the triangular areas between the plutons in the northern part of the Pulga quadrangle (fig. 10) where
Figure 10.—Fan-shaped arrangement of cleavage (S2) at the hinges of folds on glaciated horizontal surface of metachert of the Calaveras Formation east of Long Lake. Minor faults and breakage are common at the hinges of tight folds.
this feature as well as the irregularity in the orientation of the fold axes can be logically attributed to a later squeezing by the invading plutons.
L1NEATION
The strongest linear element that can be observed in the outcrops is parallel to the axes of the folds—either first or second generation. The lineation is usually an intersection of beddding and foliation and is a direction of strong stretching, as shown, for example, by strongly elongated lenses of quartz in the phyllite. It is well developed in all rocks and can be readily measured. The second linear element appears as an axis of minor folds in the metachert and locally also in the phyllite. Many outcrops of phyllite in the southern part of the Bucks Lake quadrangle show a fine wrinkling of the plane of foliation in outcrops where this plane is parallel to the bedding.
META VOLCANIC SEQUENCE
Metavolcanic rocks southwest of the Melones fault are divisible into three lithologic units that were named the Franklin Canyon, Duffey Dome, and Horseshoe Bend Formations as described under the heading “Rocks of the Area.”
FRANKLIN CANYON FORMATION DISTRIBUTION
A thick heterogeneous sequence of meta-andesite, metadacite, metasodarhyolite, and associated metatuffs traversing the south-central part of the Bucks Lake quadrangle (pis. 2, 3) is here named the Franklin Canyon Formation. The type section in Franklin Canyon
on the Middle Fork of the Feather River (secs. 3, 4, 5, T. 22 N.,R. 8 E.) consists of meta-andesite, metadacite, and metatuff about in equal amounts and includes only thin discontinuous layers of metasodarhyolite, whereas the “a” section, a reference section along Willow Creek west of Mount Ararat, contains abundant metasodarhyolite and less metatuff. A questionable Paleozoic age is assigned to the Franklin Canyon Formation because of its continuity with the Paleozoic section of Ferguson and Gannett (1932) to the south (Hietanen, unpub. data).
On the Middle Fork of the Feather River, the trace of the contact between meta-andesite of the Franklin Canyon Formation and the phyllite of the Calaveras Formation is at an angle to the strike of bedding in the Calaveras. A rather straight, steeply dipping contact and an angular unconformity near Dogwood Peak (pi. 2) and to the northwest indicate a fault. This fault, the Dogwood Peak fault on plate 2, extends from the east slope of Dogwood Peak to Faggs Ranch, where it terminates in an ultramafic body. A thinner unit consisting of meta-andesite, metadacite, and metatuff is exposed on the southwest side of the Rich Bar fault. A section through this unit is well exposed along Big Creek. The structural relations between these rocks and the underlying Calaveras Formation north of Silver Lake and along the Middle Fork at the east border of the Bucks Lake quadrangle indicate an angular unconformity. North of Silver Lake the meta-andesite rests on successively older beds of the metachert and phyllite of the Calaveras Formation toward the northwest.
The southwest boundary of the Franklin Canyon Formation is marked by thin bodies of serpentine and talc schist that extend westward from the vicinity of the Little California mine and probably conceal another fault. This fault, the Camel Peak fault on plates 2 and 3, continues southward to the American House quadrangle, where it passes the east side of Camel Peak and is marked by juxtaposition of structures and by elongate bodies of serpentine. The west end of this fault south of the Granite Basin pluton is concealed by meta-gabbro and metadiorite.
The lowest unit in the Franklin Canyon Formation near Dogwood Peak consists of several massive flows of meta-andesite separated by thin layers of dark phyl-litic metatuff. Toward the west and northwest, metadacite is intercalated with meta-andesite, and farther to the northwest it becomes the major rock type with less meta-andesite and more metamorphosed sodarhyolite. Most of this metamorphosed sodarhyolite is in the central part of the southern metavolcanic belt, northwest of Mount Ararat. Layers of metatuff, pyroclastic rocks, and tuffaceous metasediments are interbedded with all metavolcanic rocks. Only the largest continuous occur-META VOLCANIC SEQUENCE
13
rences of metatuff are shown on the map (pi. 2). Others ranging from a few centimeters to several meters in thickness are common.
Metadacite and associated metamorphosed soda-rhyolite, similar to those in the Bucks Lake quadrangle, are exposed in the western part of the Pulga quadrangle. Structural relations west and southwest of Jones Meadow suggest that these metavolcanic rocks overlie the metasedimentary rocks of the Calaveras Formation. The contact is conformable in some places, unconformable in others. Faults separate two small occurrences of metadacite and metarhyolite from the metasedimentary rocks of the Calaveras Formation in the vicinity of Five Corners at the west border of the Pulga quadrangle. On the west side these occurrences are bordered by a large body of metamorphosed hornblende quartz diorite.
A few thin discontinuous layers of metachert, quartzite, phyllite, and marble are interbedded with the metavolcanic rocks. Most of the quartzite and metachert is at the west end of the southern belt.
PRIMARY VOLCANIC STRUCTURES
Pyroclastic structures, such as volcanic breccia, bombs, lapilli, and rare pillows, are easily recognizable —even when deformed—in all the metavolcanic rocks. Bombs and lapilli are(especially common in metadacite and meta-andesite. Good exposures on the Middle Fork of the Feather River offer the best material for a study of these structures. Most of the meta-andesite and metadacite east of the mouth of Dejonah Creek consists of agglomerate in which volcanic bombs, 5-80 cm long, are embedded in a fine-grained matrix. Interbedded tuffaceous layers contain pebbles of lapilli size (%-5 cm long). Similar structures are striking in many tuffaceous layers on the Middle Fork of the Feather River east of Cleghorn Bar (fig. 11). These layers are intercalated with others that contain large plagioclase crystals. Farther to the east, at the east border of the Bucks Lake quadrangle, pillow structures are well preserved in meta-andesite.
Most of the meta-andesite exposed in roadcuts on Big Creek in the central part of the Bucks Lake quadrangle is agglomerate and contains interbedded layers of lapilli tuff. The meta-andesite on the east slope of Dogwood Peak and that northeast of Silver Lake contain, in addition to pyroclastic material, several thick flows of porphyritic lava. The individual flows, 20-100 m thick, are separated by thin (about lm thick) layers of fine-grained metatuff.
PETROGRAPHIC DESCRIPTION META-ANDESITE
Most of the meta-andesite is fine grained and greenish gray with scattered small phenocrysts of plagioclase.
Figure 11.—Metatuff containing stretched lapilli. Franklin Canyon Formation, Cleghorn Bar on the Middle Fork of the Feather River (loc. 331).
Coarse-grained porphyritic varieties occur in thick flows on Dogwood Peak, on Schneider Creek, and north of Silver Lake. At these localities large phenocrysts (x/<i~2 cm long) of plagioclase and pyroxene are oriented at random, giving the rock the appearance of undeformed and unaltered recent lava. The thin sections show, however, that these rocks are completely recrystallized and consist of albite, epidote, actinolite, and chlorite with only occasional remnants of primary minerals such as augite. Accessory minerals (pyrrhotite, pyrite, magnetite, and ilmenite) are partly altered to hematite; sphene is partly altered to leucoxene. In most meta-andesite numerous tiny grains of sphene—most altered to leucoxene—are included in epidote, chlorite, and actinolite.
The amounts of major constituents in common metaandesite vary. The ranges in percent are albite 10-30 .(rarely 40), epidote 25-60, actinolite 15-30, chlorite 0-20, quartz 0-10. Sphene or leucoxene constitutes as much as 3 percent of the rock. Some layers contain as much as 98 percent actinolite, and other layers are exceptionally rich in epidote. Albite includes numerous small grains of epidote and some sericite. In several thin sections aggregates of chlorite and actinolite have outlines of augite, but remnants of augite are rare elsewhere, except on Dogwood Peak.
Actinolite is in small (0.01-1 mm long) prisms that are oriented at random or subparallel to the foliation. Small grains of epidote either are in large groups or fill14
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
the interstices between the actinolite prisms. Radial or fan-shaped arrangement of long thin aggregates of albite and epidote or of epidote and actinolite, such as is seen in localities 193 and 335, is clearly a relict texture inherited from the orientation of slender plagioclase crystals in spherulitic lava.
In the porphyritic varieties of meta-andesite, large phenocrysts of albite include abundant epidote and muscovite. The included epidote is in subhedral to anhedral grains of medium size, whereas muscovite is in rows of tiny laths. The rows are parallel to the cleavage of albite, and flakes are oriented perpendicular to it or have a radial arrangement. The groundmass consists of small laths of albite, grains of epidote, and prisms of actinolite. The albite laths have numerous tiny inclusions of epidote. On Dogwood Peak, phenocrysts of augite are only partly altered to chlorite, and phenocrysts of plagioclase, containing much less albite than elsewhere, consist mainly of epidote and muscovite.
Amygdules are scarce; they consist of epidote and chlorite. Numerous round light-green aggregates, 1-2 cm long, consisting of a mixture of fine-grained albite and epidote with some actinolite and chlorite, occur in a few localities, as northeast of Silver Lake (loc. 396). East of Cleghorn Bar (loc. 334) similar round light-green aggregates are embedded in dark-green actinolite-rich matrix between the pillows (fig. 12). The outermost layer of the pillows consists of epidote and albite in radial arrangement that is reminiscent of the original spherulitic texture.
Chemical analysis of meta-andesite (No. 463, table 1) shows a high percentage of calcium, iron, and aluminum and a low content of silicon and alkalies. Epidote in this specimen has «=1.719±0.001, /3=1.731±0.002, y=1.740±0.002 indicating 12 mol percent of iron end member (Winchell and Winchell, 1951, p. 449). Some
Figure 12.—Part of the outer rim of a pillow in meta-andesite of the Franklin Canyon Formation east of Cleghorn Bar (loc. 334). Light-colored round spherulites consist of epidote, albite, actinolite, and sphene. The dark matrix is epidote, chlorite, actinolite, and sphene.
of the amphibole is colorless tremolite with a= 1.624 ±0.001; most is light-green hornblende with y=1.663 ±0.001 and a specific gravity of 3.14.
METADACITE
Metadacite is similar to meta-andesite in appearance except for a somewhat lighter color. The main minera-logic difference is that the metadacite contains quartz phenocrysts and amygdules (fig. 13). Averages of esti-
Figure 13.—Phenocrysts of albite (white) and amygdules of quartz (round dark spots) in metadacite of the Franklin Canyon Formation on Taylor Creek south of Meadow Valley (loc. 443).
mated percentages of the major constituents are albite (An5_10) 30, quartz 25, epidote 20, actinolite 15, chlorite 7, muscovite 1, biotite 1, accessory minerals 1. Common accessory minerals are magnetite, ilmenite, pyrrhotite, pyrite, and sphene that is partly altered to leucoxene. Abundant pyrite occurs in places, as for instance at Willow Creek near the Hose mine. Tourmaline is rare.
Phenocrysts of albite include epidote and tiny flakes of muscovite. Many are granulated as are also the quartz phenocrysts. The groundmass is a fine-grained granoblastic mixture of albite, quartz, epidote, actinolite, and chlorite. Secondary veinlets of quartz are common, and some of the rocks mapped as metadacite could be classed as meta-andesite containing veinlets of quartz. Most of the veinlets are folded. They probably were originally cracks that were filled by quartz before or at the beginning of deformation, as were also the vesicles.
Comparison of the chemical analysis of metadacite (No. 464, table 1) with that of meta-andesite (No. 463, table 1) shows that the metadacite contains much less calcium, aluminum, and iron and more silicon and sodium.META VOLCANIC SEQUENCE
15
Table 1.—Chemical composition and molecular norms of metamorphosed igneous and sedimentary rocks from the Bucks Lake
quadrangle
[Analysts: E. F. Munson for sample 134; C. L. Parker for samples 796, 532: V. C. Smith for samples 465, 551, 85, 484; G. 0. Riddle for samples 463, 464, 461, 104]
Specimen			 134	796	532	465	551	463	464	461	85	104	484
Rock type	.... Peridotite partly serpen-tin i zed	Meta- gabbro	Meta- diorite	Meta- diorite	Meta- basalt	Meta- andesite	Meta- dacite	Meta- rhyolite	Andalusite sillimanite cordierite schist	Biotite phyllite	Marble
Locality		V alley Creek	% mile south of Robinson mine	South of Coldwater Creek	China Gulch	1 mile west of Grizzly Mountain	China Gulch		Hose mine	Bear Creek northeast of Lookout Rock	Bear Creek east of Lookout Rock	Marble cone Middle Fork of Feather River
Chemical composition, in weight percent
SiOa			 42.32	48.30	52.18	53.36	50.99	41.32	54.32	66.39	73.48	78.27	0.08
Ti02 			06	.11	.43	.54	2.03	.75	.49	.40	.64	.53	0
A1203 		2.44	20.52	16.93	15.20	13.47	19.90	16.99	15.28	11.94	10.26	.03
Fe203 		2.60	1.81	3.80	2.56	1.48	5.07	2.50	1.97	.94	.32	.01
		39										0
FeO 		5.42	3.62	4.93	4.95	10.96	6.10	4.34	2.61	3.76	2.86	.01
MnO 			13	.11	.16	.17	.22	.17	.11	.11	.09	.05	0
NiO 			27										0
MgO 			 39.03	8.47	5.80	7.58	5.95	6.96	6.58	2.05	2.11	1.83	.56
Cat) 			2.28	13.42	10.25	10.36	8.04	14.85	8.94	5.03	.28	.42	55.34
Na,0 			24	1.95	2.30	1.80	4.07	.94	1.93	4.08	1.23	1.00	0
K.O 			03	.12	.05	.03	.21	.03	.05	.14	2.51	2.29	.01
I>:() 				01	.07	.13	.16	.18	.17	.10	.10	.05	.08	.01
C02 			18	0	.01	.03	.02	.02	.01	.02	0	.03	43.94
Cl 				01	0	.01	0.01	0	0	0	0	0	0	0
F 			01	.01	.03	.03	.03	.04	.02	.03	.08	.06	.01
11.0' 		4.57	1.51	2.85	2.89	1.75	3.74	3.18	1.73	1.73	1.57	0
H.O 			27	.04	.10	.08	.16	.02	.01	.01	.34	.02	0
Subtotal 			 100.26	100.06	99.96	99.75	99.56	100.08	99.57	99.95	99.18	99.59	100.00
Less 0 			00	.00	.01	.01	.01	.02	.01	.01	.03	.03	
Total 			 100.06	100.06	99.95	99.74	99.55	100.06	99.56	99.94	99.15	99.56	
Chemical composition, in ionic percent											
Si02 			 37.21	44.70	50.25	51.31	48.71	40.23	52.43	63.17	72.73	77.05	0.06
Ti02 			04	.08	.31	.39	1.46	.55	.36	.29	.48	.39	0
Alt) 2 			 2.53	22.38	19.21	17.23	15.17	22.83	19.33	17.13	13.93	11.90	.03
Cr+303/2 			27										0
Fe Os 2 			 1.72	1.26	2.75	1.85	1.06	3.71	1.82	1.41	.70	.24	.01
Fe+sO 			 3.98	2.80	3.97	3.98	8.76	4.97	3.50	2.08	3.11	2.35	.005
MnO 				10	.09	.13	.14	.18	.14	.09	.09	.08	.04	0
NiO	.19										0
MgO 			 51.14	11.68	8.32	10.86	8.47	10.10	9.47	2.91	3.11	2.69	.69
CaO 			 2.15	13.31	10.58	10.67	8.23	15.49	9.25	5.13	.30	.44	49.30
NaOi,2 			41	3.50	4.29	3.36	7.54	1.77	3.61	7.53	2.36	1.91	0
ko1/2			03	.14	.06	.04	.26	.04	.06	.17	3.17	2.88	.01
		01	.05	.11	.13	.15	.14	.08	.08	.04	.07	.01
co2 			22		.01	.04	.03	.03	.01	.03		.04	49.88
Cl		 (.02)		(.02)	(.02)							0
F 			 (.03)	(.03)	(.09)	(09)	(.09)	(.12)	(.06)	(.09)	(-25)	(.19)	(.02)
OH 				 (26.81)	(9.32)	(18.31)	(18.54)	(11.15)	(24.29)	(20.47)	(10.98)	(11.42)	(10.31)	0
Total 		. 100.00	99.99	99.99 100.00 100.02	100.00	100.01	100.02	100.01	100.00	100.00
Total anions		. 152.99	159.55	168.80 169.16 160.30	165.65	171.95	174.60	183.78	186.60	149.97
Catanorm, in molecular percent									
0			8.70	10.20			12.71	26.34	50.45	57.71	
Or 			 0.15	0.71	.31	.18	1.28	.19	.31	.85	15.85	14.38	0
Lc											.04
Ah 			 1.95	17.50	21.39	16.70	37.69	8.87	18.06	37.63	11.80	9.54	
An 			 5.27	46.86	37.19	34.62	18.43	52.55	39.13	23.59	.54	1.05	
Co									8.18	6.70	.02
Wo 			 1.70	7.68	5.84	6.94	8.51	9.36	2.50	.43			
En 			 21.80	14.38	16.65	21.73	13.18	8.49	18.93	5.81	6.23	5.37	
Fs 			 1.40	2.68	4.82	5.60	10.80	2.27	4.66	2.35	4.72	3.77	
Fo		 60.36	6.74			2.83	8.78					.13
Fa		 3.81	1.26			2.32	2 35					
Mt 			 2.58	1.89	4.13	2.78	1.60	5.57	2.72	2.12	1.05	.36	.01
11 			08	.15	.62	.78	2.92	1.10	.71	.57	.95	.78	
		40										
Ap 			03	.15	.28	.35	.39	.37	.22	.21	.11	.18	.02
Co 			41		.03	.08	.05	.05	.03	.05		.08	98.58
HI 			04		.03	.03							
Fr 			04	.02	.08	.07	.06	.11	.05	.10	.35	.25	.03
MgS 												1.18
100.05	100.01	100.07	100.06	100.04	100.08	100.03	100.06	100.24	100.16	100.01
Total16
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Table 1.—Chemical composition and molecular norms of metamorphosed igneous and sedimentary rocks from the Bucks Lake
quadrangle—Continued
Specimen			 134	796	532	465	551	463	464	461	85	104	484
Rock type			 Peridotite	Meta-	Meta-	Meta-	Meta-	Meta-	Meta-	Meta-	Andalusite	Biotite	Marble
	partly	gabbro	diorite	diorite	basalt	andesite	dacite	rhyolite	sillimanite	phyllite	
	serpen-								cordierite		
	tinized								schist		
Locality			 Meadow	% mile	South	China	1 mile	China Gulch		Hose	Bear	Bear	Marble cone
	Valley	south of	of	Gulch	west of			mine	Creek	Creek	Middle Fork
	Creek	Robinson	Coldwater		Grizzly				northeast	east of	of
		mine	Creek		Mountain				of Lookout	Lookout	Feather
									Rock	Rock	River
			Mesonorm, i		in molecular percent						
Quartz 				7.27	8.38			12.09	26.56	53.14	60.21	
Andalusite 									.21	8.67	6.83	
Albite 			12.25	21.39	16.70	32.94	l.n	18.06	37.63	11.80	9.54	
Anorthite 			46.86	37.19	34.62	18.43	52.55	39.13	23.25			
Muscovite 										9.16	8.98	
Biotite 			1.13	.49	.29	2.05	.30	.49	1.36	14.89	12.75	0.10
Hypersthene 			8.22	8.68	12.50	18.24	5.82	19.45	7.72			
Enstatite												.10
Actinolite 			12.47	19.57	23.09	6.71	7.69	6.72				
Edenite 			16.80			15.21	24.85					
Sphene 			.23	.93	1.17	4.38	1.65	1.07	.86	.33	.63	
Magnetite 			1.89	4.13	2.78	1.60	5.57	2.72	2.12	1.05	.36	.01
Ilmenite 										73	.37	
Apatite 			.15	.28	.35	.39	.37	.22	.21	.11	.18	.02
Fluorite 			.02	.08	.07	.06	.11	- .05	.10	.35	.25	.03
Calcite 				.03	.08	.05	.05	03	.05		.08	98.58
Halite 				.03	.03							
Magnesite 												1.18
Total 			100.1	100.7	100.6	100.4	100.8	100.03	100.06	100.24	100.16	100.02
METAMORPHOSED SODARHYOLITE
Metamorphosed sodarhyolite is very light gray to white and fine grained. Euhedral to subhedral pheno-crysts of quartz and feldspar are common in some places; others show fragmental stuctures. Staining of the specimens shows very little if any potassium feldspar.
Thin sections confirm the almost complete absence of potassium feldspar. Estimated percentages of the major constituents are quartz plus albite 65-75, muscovite 5-15, chlorite 0-20, biotite 0-15, epidote 2-10, cal-cite 0-5. Magnetite, partly altered to hematite, and sphene are common accessory minerals. Some layers contain numerous cubic crystals of pyrite. Quartz phenocrysts are euhedral to subhedral and ^-1 mm long; many are granulated. Albite phenocrysts are twinned and include small grains of epidote and seri-cite. The groundmass is either granoblastic or lepido-blastic with albite in small laths. Sericite and chlorite or biotite are in laminae and in scattered tiny flakes. In some thin sections pseudomorphs after a ferromagne-sian mineral, probably biotite or hornblende, consist of chlorite that includes small grains of epidote and magnetite. All chlorite is pale green and has a very low birefringence.
Abundant calcite occurs in light-gray metamorphosed sodarhyolite at Carpenter Bar on the Middle Fork of the Feather River (loc. 372) and on Little Bear Creek (loc. 623) 1% miles northwest of Carpenter Bar. The main micaceous mineral in these rocks is chlorite, which occurs as individual flakes, clusters, and laminae. Some of the quartz and albite phenocrysts are frac-
tured and granulated; calcite and small grains of quartz fill the fractures. Chemical analysis (No. 461, table 1) shows less calcium, iron, magnesium, and aluminum and more silicon and sodium than in metadacite.
METATUFF AND TUFFACEOUS METASEDIMENT
Tuffaceous layers interbedded with metavolcanic rocks are fine grained and foliated. The color ranges from dark greenish or bluish gray to light brownish gray. Their mineralogy is similar to the interlayered lavas. Andesitic metatuff consists mainly of epidote, actinolite, and some albite, magnetite, and sphene. Dacitic metatuff has, in addition to these minerals, quartz as small blebs and veins, and it contains more albite. Sodarhyolitic metatuff is rich in quartz and contains 15-25 percent each of albite and muscovite. Biotite or chlorite and epidote are commonly present, and magnetite and sphene occur as accessory minerals. Many layers of sodarhyolitic metatuff are laminated; the quartz-rich laminae are separated by laminae rich in muscovite or chlorite and epidote. Some layers of sodarhyolitic metatuff are exceptionally rich in quartz and grade to fine-grained gray to white granular sericite quartzite, which may represent weathering products of rhyolitic tuff layers.
Phyllitic layers intercalated with meta-andesite and metadacite in the southern part of the Bucks Lake quadrangle contain more albite and epidote and less muscovite and chlorite (or biotite) than the regular metasedimentary phyllite. Large crystals of albite occur occasionally, and pebbly layers are common (fig. 11). These layers were originally tuffaceous sediments.META VOLCANIC SEQUENCE
17
Some layers interbedded with metatuffs and tuffaceous metasediments contain carbonate as individual grains, clusters of grains, and small lens-shaped or layerlike bodies. Lenses of white marble, 5-20 cm long, are common in many layers exposed on the Middle Fork of the Feather River. Some of this carbonate is probably sedimentary. In the tuffaceous layers, however, albite and calcium carbonate crystallized from the anorthite component of the plagioclase at low temperatures, either during volcanism (spilite reaction) or later during regional metamorphism. Addition of C02 is necessary in either case. In a spilite reaction the C02 could have had a volcanic source; during metamorphism, CO, may have been added from a release elsewhere, as for instance, from a source where dolomite reacted with silica to form tremolite.
DUFFEY DOME FORMATION
DISTRIBUTION
Metabasalt is the major rock type of the Duffey Dome Formation, which forms an east-west-trending belt south of the Bucks Lake and Grizzly plutons. In the south this belt is bordered by serpentine exposed northwest of the Merrimac pluton. In the east it wraps around the Granite Basin pluton, grading over to meta-gabbro near the contacts of this pluton. A type section through the northern part of this formation is well exposed near Duffey Dome in sec. 16, T. 23 N., R. 6 E., in Pulga quadrangle. A reference section through the southern part of the formation is exposed along the road to Bear Ranch Hill in secs. 19 and 30, T. 23 N., R. 6 E. Steep outcrops on Bear Ranch Hill (see fig. 14) are a part of this metabasalt. In the canyon of the North Fork of the Feather River, a layer of metabasalt 400 m thick is exposed about half a mile north of Pulga, where it is exposed above a metatuff and metachert.
The Duffey Dome Formation is believed to be probably Paleozoic and possibly somewhat younger than the Franklin Canyon Formation on the basis of structural relations east of the Granite Basin pluton. Fold axes in this vicinity plunge northwest, indicating that the younger beds are to the west. The eastward plunge of fold axes along the contact with the Horseshoe Bend Formation west of the Granite Basin pluton suggests that Horseshoe Bend is younger. Elsewhere metaigne-ous rocks or faults separate these three formations.
Some discontinuous layers of metarhyolite rich in potassium feldspar, metatuff with layers rich in quartz, and thin-bedded quartzite and metachert are intercalated with the metabasalt. A few layers and dikelike bodies of light-gray hornblende-albite rock with considerable quartz also are interbedded (not shown on pi. 1). Small bodies of white marble are exposed in a roadcut just south of Grizzly Creek.
PETROGRAPHIC DESCRIPTION METABASALT
The metabasalt is dark greenish gray to black and commonly foliated; hornblende prisms are subparallel to the foliation. Most of the metabasalt could be classified as amphibolite. Near Grizzly Summit parts of it grade into a massive lighter colored hornblende-plagio-clase-quartz rock in which hornblende prisms are oriented at random.
Thin sections show that green hornblende («= 1.639 ±0.001, y=1.666±0.001 in specimen 551) is a major constituent of all the metabasalt in amounts ranging from 45 to 65 percent. Albitic plagioclase (10-50 percent), epidote (2-20 percent), and magnetite (1-10 percent) are always present. The light-colored parts of metabasalt near Grizzly Summit contain as much as 15 percent quartz. Some of the quartz occurs in clusters and small lens-shaped aggregates. This quartz may have originated in recrystallized fragments of older quartzite or metachert that were incorporated into lava during the eruption. Some of the light-colored rock is a result of segregation of quartz and albitic plagioclase into small masses and dikelike bodies. The amphibole crystals in all light-colored masses are larger and lighter green than they are elsewhere in the same rock. Next to the quartz veins and lenses, they are similar to the actinolite in the metadacite.
Chemically the metabasalt (No. 551, table 1) differs from the meta-andesite in its higher content of silicon, ferrous iron, and sodium and lower content of aluminum, ferric iron, and calcium.
Medium-grained metabasalt that is much less deformed than the common type is exposed half a mile south of Duffey Dome. This metabasalt contains bio-tite, quartz, and abundant epidote in addition to the common major constituents, hornblende and plagioclase. Part of the hornblende is in large crystals that have ragged ends, are randomly oriented, and show pleochroism Z=blue green, Y= green, X=pale green. Biotite is in clusters of small greenish-brown grains. Most of the epidote is in large subhedral grains among hornblende, plagioclase (An13), and quartz, but some of it forms small inclusions in hornblende. Ilmenite, partly altered to leucoxene, or surrounded by sphene, is a common accessory mineral. Some of the plagioclase is in large subhedral crystals that include small epidote and hornblende crystals.
METARHYOLITE
Small bodies of light-bluish-gray fine-grained metarhyolite are interlayered with metabasalt north of the Merrimac pluton. The texture in most outcrops is por-phyritic, but in some is trachytic and equigranular. Fragmental textures are common. Phenocrysts of quartz and feldspar are embedded in a fine-grained18
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
slightly schistose groundmass. Staining of cut surfaces shows that these rocks are rich in potassium feldspar, in contrast with the soda-rich end members of the Franklin Canyon Formation.
The potassium feldspar either is untwinned or shows a weak microcline twinning under the microscope. Some of the individual phenocrysts consist partly of albite and partly of microcline. Large holoblasts of muscovite are common near many phenocrysts. Biotite is the most common dark constituent and occurs in tiny flakes subparallel to the foliation. Large flakes of grayish-green chlorite with ultrablue interference colors are either in clusters or rim some of the quartz veins. Chlorite includes a sphenelike mineral and is most likely a secondary mineral formed by introduction of a hydrous molecule after the major period of recrystallization. Epidote is in scattered small grains or in clusters. Some large grains of epidote occur next to quartz vein-lets, which transect most of the metarhyolite at irregular intervals. Magnetite, ilmenite, apatite, and sphene are the common accessory minerals.
METATUFF
Greenish-gray fine-grained schistose layers consisting mainly of amphibole and chlorite, with some albite, epidote, quartz, magnetite, and rutile or sphene, are interbedded with metabasalt and probably represent metamorphosed tuff layers. The amphibole is commonly actinolite and rarely green hornblende. Most of these layers are only a few meters thick and are therefore not shown on plate 1.
Metatuff of rhyolitic composition is interbedded with metarhyolite near Palmetto and on the road to Bear Ranch Hill southeast of Kister. These metatuffs are very light bluish gray and rich in quartz. Many layers are laminated and all are strongly deformed. Phenocrysts of quartz and albite (Anr>) are common. Muscovite is the major micaceous mineral. Potassium feldspar, biotite or chlorite, some epidote, and magnetite are the other constituents.
A few layers of metatuff recrystallized to amphibole schist are interbedded with metabasalt south of Duffey Dome. The major constituent in these layers is actinolite or actinolitic hornblende (40-70 percent). Chlorite and (or) biotite (5-20 percent) occur with it or form thin laminae that include epidote. The light-colored constituents are albite (AnM0) and quartz. Magnetite, sphene, and brown rutile are the accessory minerals. The large amount of actinolitic hornblende indicates that these metatuffs are of basaltic composition.
A unit of thin-bedded hornblende-biotite-quartz-plagioclase gneiss is well exposed on roadcuts and on railroad cuts 0.7-1 mile north of Pulga. The beds are 1-4 cm thick and have alternating assemblages of horn-
blende-quartz, hornblende-biotite-quartz, hornblende-albite-quartz, and biotite-quartz. The range in amount of dark constituents in individual thin layers from 5 to 60 percent results in strong color contrasts. Layers of biotite quartzite are interbedded on the northern (lower?) part of this unit. On the south side it is bordered by a body of serpentine. The composition of the layers indicates that this unit contains alternating layers of tuffaceous material (hornblende-albite-quartz layers) and sedimentary material rich in quartz.
Interbedded hornblende and biotite-plagioclase gneiss with a discontinuous layer of biotite quartzite is exposed north of the thin-bedded hornblende-biotite gneiss. The quartzite is light gray and thin bedded and resembles the metachert of the Calaveras Formation exposed on the south side of Bucks Lake.
Metahasalt interbedded with the metasedimentary and tuffaceous layers is dark and fine grained. It consists of hornblende, albite, epidote, and chlorite and is mineralogically and texturally similar to the metabasalt of the Duffey Dome Formation.
QUARTZITE AND MARBLE INTERBEDDED WITH META VOLCANIC ROCKS
The quartzite interbedded with the metavolcanic rocks is light gray to white and thin bedded. Micaceous laminae separate thin (1-3 cm thick) layers of quartz. Some layers, such as those just south of Grizzly Mountain and another half a mile north of Kister, have textures typical of metachert. The quartzite layers south of Grizzly Mountain are very fine grained and are irregularly traversed by tiny veinlets of more coarsegrained quartz. More thorough recrystallization elsewhere has produced equigranular granoblastic white quartzite in which only the bedding typical of less altered metachert indicates the origin. For example, in the quartzite half a mile north of Kister, individual layers 2-3 cm thick consisting of white medium-grained quartzite are separated by micaceous layers that are only 2-6 mm thick.
The marble exposed at Carpenter Bar on the Middle Fork of the Feather River consists of white to gray medium-grained calcium carbonate. It grades to micaceous and actinolite-bearing calcareous phyllite, presumably a metatuff, that contains lenses, 10-15 cm long, of similar white marble.
Abundant contact minerals such as epidote and grossularite have crystallized in the marble south of Grizzly Creek. The epidote is dark green to black, with shiny crystal faces. Euhedral crystals occur in the cavities from which calcium carbonate has weathered out. Grossularite is in large brown euhedral crystals that show anomalous gray interference colors and strong zoning under the microscope.META VOLCANIC SEQUENCE
19
STRUCTURES DUE TO DEFORMATION
Metavolcanic rocks were folded and deformed with the metasedimentary rocks and thus show similar structural features. The compact flows are much less deformed than the softer tuffaceous layers. Central parts of some thick flows seem undeformed, whereas the tuffaceous layers are strongly schistose, with lapilli drawn out to spindles 10 times longer than their shortest dimension. (See Hietanen, 1951, p. 589-590.) All gradations between these two extremes occur.
Some of the pyroclastic andesite on Big Creek shows very little deformation, if any, and thus acted as a thick compact unit similar to that of the flows. These layers may have been welded during the eruption. Part of the meta-andesite on the east slope of Dogwood Peak shows slightly deformed fragmentary structures.
Foliation can be measured in 80 percent of the outcrops, and lineation in about 50 percent. Micaceous minerals are well oriented parallel to the foliation and lineation. Actinolite in the meta-andesite and metada-cite is commonly subparallel to these structures and is rarely oriented at random. Parallel orientation of green hornblende in the metabasalt lends a foliated structure and fairly good lineation to most of these rocks. On Bear Ranch Hill metabasalt is strongly sheared and stretched; it breaks into pencil-shaped fragments parallel to an almost vertical lineation (fig. 14) that also parallels fold axes.
Figure 14.—Strong stretching parallel to a nearly vertical lineation (arrow) and fold axis in metabasalt of the Duffey Dome Formation at Bear Ranch Hill.
HORSESHOE BEND FORMATION
DISTRIBUTION AND MAJOR STRUCTURES The sequence of interbedded metasedimentary and metavolcanic rocks exposed in the southwestern part of the Bucks Lake quadrangle and in the southern part of
the Pulga quadrangle is lithologically different from the formations described earlier and, therefore, could not be included in any of them. This sequence is here named the Horseshoe Bend Formation after Horseshoe Bend of the Little North Fork, most of which is at the southeast corner of the Pulga quadrangle (pi. 1). Its type section, a continuous section through a part of this sequence, is well exposed on roadcuts along the Little North Fork of the Middle Fork of the Feather River (secs. 1, 12, 13, T. 22 N., R. 6 E.). The metamorphic rocks around the Merrimac pluton, which were described earlier (Hietanen, 1951), are included in this formation. The details of their petrography and structure are in the earlier report.
The Horseshoe Bend Formation is separated by faults and metaigneous rocks from the Franklin Canyon and Duffey Dome Formations except on the west side of Granite Basin pluton, where the eastward plunge of the fold axes suggests that it rests on the Duffey Dome Formation. It is thus the youngest formation in the Paleozoic(?) metavolcanic sequence.
The Horseshoe Bend Formation includes layers that are petrologically similar to various layers in the Calaveras Formation, others that are similar to the Franklin Canyon Formation, and still others similar to the Duffey Dome Formation. In addition, there are interbedded layers of metaconglomerate with pebbles of metachert, and layers of bluish-gray quartzite that is different from metachert. Many lens-shaped bodies of marble are included in biotite phyllite. Moreover, there are layers of metalatite very rich in biotite, a rock type not found in the Franklin Canyon Formation.
Several angular fragments of metadiorite, similar to that associated with the metavolcanic rocks of the Franklin Canyon Formation, are included in metada-cite exposed in roadcuts at Horseshoe Bend. These inclusions, as well as the conglomerates, suggest that the Horseshoe Bend Formation is probably younger than the Calaveras Formation and younger than the Franklin Canyon Formation. The southeasterly plunges of the fold axes at the headwaters of Marble Creek suggest that the rocks of the Horseshoe Bend Formation rest on the metavolcanic rocks of the Duffey Dome Formation (if beds are right-side up, as indicated on a few outcrops by the relation between cleavage and bedding).
West of Four Trees, however, a fault accompanied by a long body of serpentine separates these two formations. This fault is probably the western extension of the Camel Peak fault, which in the Bucks Lake quadrangle separates the rocks of the Horseshoe Bend Formation from the Franklin Canyon Formation. The metamorphic rocks south of this fault are divided by the Merrimac pluton into two parts that probably belong to the same formation. In each part the older20
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
rocks are phyllite with discontinuous layers of quartzite, metachert, and marble. The volume of intermediate metavolcanic rocks is greater in the eastern part of the belt, perhaps owing to a greater part of the strata exposed. In the western part, west of the Merrimac pluton, metabasalt overlies the metasedimentary rocks that near Poe railroad station include discontinuous layers of meta-andesite, metadacite, metarhyolite, and metatuff. A thick layer of conglomerate (or agglomerate?) with meta-andesite pebbles marks the contact between the metasedimentary rocks and overlying metabasalt. Similar metabasalt overlies the interbedded sequence of metasedimentary and intermediate metavolcanic rocks in the easternmost part near Camel Peak (pi. 3).
South of the Pulga quadrangle the Horseshoe Bend Formation is bordered by another fault—the Big Bend fault on plate 3—that extends through Big Bend toward the east and curves around the Bald Rock pluton toward the south. Thus the Horseshoe Bend Formation occupies the innermost southwesterly belt of the Nevadan arcuate segment in which the northerly trends of the Sierra Nevada turn westward.
Distribution of the rock types (particularly the limestone) , overturning of folds toward the southwest on the west and southwest sides of the Hartman Bar pluton, and steep dips on the northeast side of this pluton suggest that the major structure in the eastern part of the belt occupied by the rocks of the Horseshoe Bend Formation is a synclinorium into which the Hartman Bar pluton was emplaced. The syncline near Big Bar Mountain and an anticline south of it are the major structures in the western part (see B-B' on pi. 1). Juxtaposition of structures, such as foliation and linea-tion, south of Mill Creek is suggestive of a fault between the metabasalt and the metasedimentary rocks to the north, along the Flea Valley Creek near Pulga. This fault seems to continue eastward and could well be concealed by long bodies of talc schist and metagabbro west of the Hartman Bar pluton. Minor displacements were observed on the south side of these bodies.
DESCRIPTION OF THE ROCKS PHYLLITE
A thick unit consisting of biotite-muscovite phyllite and interbedded quartzite, metachert, and marble borders the Hartman Bar pluton in the northeast and southwest and is in the middle part of the section of the Horseshoe Bend Formation just south of the quadrangle. The phyllite is fine grained and gray to black and consists mainly of quartz, biotite, and muscovite with some magnetite and hematite. A few small crystals of garnet and tiny porphyroblasts of cordierite occur in places; chlorite and some epidote are common along shear zones. The interbedded quartzite layers (1-2 m
thick) consist of white to gray micaceous or granular quartzite, in which individual beds are 1-2 cm thick.
Biotite-muscovite phyllite and interbedded metachert exposed on the northwest side of the Merrimac pluton are probably equivalent to this unit. The phyllite here includes layers rich in andalusite and staurolite. Anda-lusite is in small (1-4 mm long) anhedral light-bluish-
Figure 15.—Andalusite (a) and staurolite (st) in biotite (bi) schist of the Horseshoe Bend Formation 1.3 miles east of Big Bar Mountain (loc. 1019). Ordinary light.
gray porphyroblasts that are enveloped by biotite. Thin sections show that anadalusite includes many grains of quartz, biotite, and magnetite (fig. 15). In some porphyroblasts the rows of small inclusions are at an angle to the external foliation, which bends around the porphyroblasts. In a few porphyroblasts the rows of inclusions have an S-shaped curvature, and the outermost part coincides with the external foliation. In some layers several grains include the present foliation. These relations suggest that andalusite started to crystallize early and continued forming during and after the deformation.
Staurolite is in small anhedral to subhedral crystals, 0.2-0.3 mm long, among quartz and biotite or included in andalusite (fig. 15). Foliation bending slightly around the crystals indicates that they are early. (See also Hietanen, 1951, p. 575.) Small euhedral crystals of garnet (0.1-0.2 mm) occur in some layers of biotite phyllite southwest of Coyote Gap (for instance, Iocs. 989,1022).
A sequence of metasedimentary rocks that is exposed on either side of Flea Valley Creek near Pulga consists mainly of biotite-muscovite phyllite and chlorite phyllite with interbedded quartzitic and conglomeratic layers and discontinuous layers of limestone and marble. Layers of tuffaceous material metamorphosed to actinolite-epidote-chlorite phyllite and layers of metabasalt are also interbedded. A section through this sequence near Pulga has been described (Hietanen,META VOLCANIC SEQUENCE
21
1951, fig. 5). A metasedimentary sequence consisting of black phyllite, metachert, and some limestone is well exposed on the railroad cuts near the Poe railroad station and on the road to Bardees Bar in the southwest corner of the Pulga quadrangle and in an area joining it in the south (Hietanen, 1951). Thick beds of agglomerate with some interbedded black phyllite overlie this sequence on the north canyon wall north of Poe and on railroad cuts near Poe. These beds form the lowermost part of the overlying metavolcanic sequence that consists mainly of metabasalt.
Much of the phyllite along Marble Creek is rich in biotite and contains pistachio-green epidote in clusters, small lenses (2-4 cm by 3-15 cm), and veinlike segregations. Layers of biotite phyllite and layers rich in calcite and containing lens-shaped segregations (5-10 cm long) of white calcite are interbedded with epidote phyllite. A sequence of conglomerate, quartzite (1-2 m thick), black phyllite (0.5-1 m), tremolite-biotite quartzite (1-5 m), and phyllite with calcite lenses is repeated several times within a distance of half a mile. This is probably due to the folding on the axis that plunges 55°-60° SE. No folds were observed, but there is a wrinkling around this axis.
MARBLE
The largest exposure of marble is along the Middle Fork of the Feather River. This layer is about 300 m thick and extends from Marble Cone on the north side of the river southward to Hartman Bar Ridge, where it terminates against intrusive tonalite. It is bordered on the west side by this same tonalite and on the east side by dark-gray muscovite-biotite phyllite that contains small garnets. The marble is white and coarse to medium grained and consists almost exclusively of calcite. Numerous large rounded boulders of this marble of ornamental quality occur for half a mile along the river bottom east of Marble Cone. Chemical analysis (table 1) shows that the marble is mainly calcium carbonate, with only half a percent MgO. Magnetite, in very small amounts, is an accessory mineral.
On the eastern part of the occurrence, light-gray oval rings, 1 cm thick and 5 by 10-15 cm in size, are scattered through the snow-white sugary marble. Thin sections show that the gray part contains abundant disseminated magnetite. The regular shape and even thickness of the rings suggest that they are remains of ovoid to kidneyshaped bodies, presumably fossils.
Two thin marble layers separated by phyllite and shown on plate 1 as one layer extend across the river about 1 mile east of Marble Cone. Some beds consist of white marble, but most contain abundant micaceous minerals and grade into calcareous phyllite that contains epidote-rich layers.
Lens-shaped bodies of white to light-gray marble are
interbedded with phyllite and quartzite in a northwesttrending zone that extends from the south border of the Bucks Lake quadrangle through Deer Park to Marble Creek in the Pulga quadrangle. Some of these lenses extend for more than 1 mile, but most are only 100-200 m long and a few meters thick. They consist of white calcite with an irregular greenish-gray design of dark minerals—epidote, phlogopite, and pyrite (fig. 16). Biotite phyllite near the marble contains abundant
0	1 2 3cm
1 --1___I____I
Figure 16.—Marble from the Horseshoe Bend Formation on the Little North Fork of the Middle Fork of the Feather River 0.2 mile northwest of the mouth of Glazer Creek. The white parts are calcite; dark material is epidote, phlogopite, and pyrite.
calcite, albite, epidote, and pyrite. Calcite and albite are segregated into small lenslike and layerlike masses that are embedded in biotite-epidote-quartz-albite phyllite.
Several thin layers of marble are interbedded with phyllite, quartzite, and hornblende gneiss (metatuff) north of Pulga. About 300 and 400 m north of Pulga, small lenses of white calcite are embedded in light-gray micaceous and calcareous phyllite. A layer half a mile to the north is 1 m thick and consists of white marble. The layer exposed just north of Flea Valley Creek continues about 0.6 miles to the west and consists of very light gray calcium carbonate with some pyrite and muscovite, occasional diopside, and actinolitic hornblende. This layer is underlain by thin-bedded gray quartzite and overlain by hornblende gneiss (metatuff).
QUARTZITE
Most of the quartzite in the Horseshoe Bend Formation is light gray to white and granular. Some of it is thin bedded and resembles metachert, but bedding typical of clastic sediments (sands and tuffs) can be22
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
detected in many other places. Several layers of white granular quartzite are interbedded with phyllite on Rock Island Ridge. Phyllite near these layers contains lenses of similar quartzite. On the south side of Bear Gulch, a thick layer of white granular quartzite is exposed just north of metadacite and metarhyolite (pi. 2). This quartzite extends to the quadrangle border in the southeast and to Marble Creek in the northwest. It is in part thin bedded and rich in muscovite; in some thicker layers micaceous minerals are scarce. On the higher slope on the south side of Bear Gulch, some layers of thin-bedded (3-5 cm) white quartzite have irregular bedding that gives a lenticular appearance to the quartzite. In these layers small lenses of granular quartzite are enveloped by muscovite laminae.
At the road junction to the Bear Ranch Hill, a layer of bluish-gray quartzite crops out just south of bluish-gray metarhyolite. The quartzite is granular and lacks the type of bedding characteristic of metacherts. This quartzite continues to the southwest and is well exposed north of the Silver Crescent mine. It is in part thin bedded (1-10 mm), but also includes thick beds (20 cm-1 m) and grades to metarhyolite in the northwest. Discontinuous layers of similar gray to white granular quartzite are interbedded with metavolcanic rocks of the Horseshoe Bend Formation in many other places. This quartzite is most likely a metamorphosed weathering product of silicic volcanic rocks, particularly of rhyolitic tuff.
CONGLOMERATE
Conglomerate and pebbly layers are common in quartzite exposed in the upper drainage of Marble Creek and for a distance 1 % miles westward from Four Trees. The pebbles consist of light-gray to white granular quartzite, presumably metachert. They are embedded in a fine-grained medium-gray dense matrix and are flattened in the plane of foliation. Similar pebbles are embedded in some layers of phyllite. The matrix in most layers is micaceous, but in some it contains actino-lite and epidote.
METAVOLCANIC LAYERS
The meta-andesite and metadacite of the Horseshoe Bend Formation are petrographically similar to the corresponding rocks in the Franklin Canyon Formation. Metabasalt is well foliated and mineralogically similar to the metabasalt in the Duffey Dome Formation. Blue-green hornblende in typical dark metabasalt, such as that exposed on the road to Sky High in the southwest corner of the Bucks Lake quadrangle (loc. 241), shows y=1.693±0.002, /?=1.668±0.002, and Z/\c=18°. In some lighter colored layers hornblende is very pale green and has y=1.681±0.002 (loc. 243).
Metalatite exposed on the Little North Fork of the Middle Fork of Feather River (loc. 856) is brownish gray and crudely foliated and contains biotite that can
be readily identified in the field. Thin sections show that biotite occurs in large flakes and clusters that represent former phenocrysts. Phenocrysts of quartz are granulated, and phenocrysts of albite include many small flakes of muscovite, chlorite, and epidote. The groundmass consists of quartz, albite, epidote, chlorite, muscovite, biotite, and magnetite.
Metatuff of latitic composition occurs as thin layers along the Little North Fork. These layers consist of quartz, albite, muscovite, and biotite with some chlorite, ilmenite-magnetite, sphene, and pyrite. Small phenocrysts of quartz and albite are common. Metatuff occurring with meta-andesite and metadacite contains abundant actinolite and at most only a small amount of biotite and muscovite.
The thin discontinuous layers of metarhyolite occurring with metadacite along the Little North Fork of the Middle Fork of the Feather River contain very little if any potassium feldspar and are most likely silica-rich differentiates of dacitic magma. In contrast to these, the thin layer of metarhyolite exposed on Marble Creek (loc. 1256) is rich in potassium feldspar. The possibility that this body is a dike cannot be ruled out.
TENTATIVE CORRELATION OF METAMORPHIC ROCKS SOUTHWEST OF MELONES FAULT
The continuity of the outcrops of the metamorphic rocks south of the area is interrupted by Cenozoic volcanic rocks that cover higher elevations on ridges south of the Bucks Lake quadrangle. The older rocks are, however, exposed at lower elevations in the deep canyons of the South Fork of the Feather River and its tributaries and seem to continue southward parallel to the regional trend. On the geologic map of the Chico sheet (Burnett and Jennings, 1962), a part of the metavolcanic rocks south of the Cenozoic cover is shown as Mesozoic and the other part as Paleozoic. All these rocks are probably of Paleozoic age because the succession of lithologic units in the Bucks Lake quadrangle is in a general way similar to the Paleozoic section along the North Fork of the Yuba River as described by Ferguson and Gannett (1932).
Farther south, just north of the 39th parallel, Chandra (1961) described in detail a Paleozoic section west of the Melones fault and correlated the pyroclastic rocks with the Mississippian Tightner Formation of Ferguson and Gannett (1932). This formation includes meta-andesite and metadacite, whereas metabasalt is included by Chandra in the overlying Cape Horn Slate, which is in turn overlain by a heterogeneous succession of metasedimentary rocks including conglomerate, phyllite, metachert, quartzite, and limestone. In general this succession is similar to the pyroclastic sequence—the Franklin Canyon and Duffey Dome Formations and the overlying Horseshoe Bend Forma-CEDAR FORMATION
23
tion in the Pulga and Bucks Lake quadrangles.
Correlation across the serpentine belt to the Paleozoic formations on the east side of the Melones fault is even more uncertain. Nevertheless, the sections through the Calaveras Formation around the 38th parallel (Clark, 1964) include a pyroclastic unit that could be broadly equivalent to the pyroclastic sequence of this report.
Comparison of the succession of lithologic units in the Pulga and Bucks Lake quadrangles with that in the neighboring Taylorsville area as described by McMath (1966) indicates that the following correlations are possible:
1.	The blastoclastic quartzite and interbedded muscovite phyllite around Snake Lake in the northeast corner of the Bucks Lake quadrangle are probably equivalent to the middle part of the Shoo Fly Formation.
2.	The interbedded metachert and phyllite southwest of the Rich Bar fault—the Calaveras Formation of this report—may be equivalent to parts of the Shoo Fly Formation elsewhere.
3.	The metavolcanic sequence, which overlies the rocks of the Calaveras Formation, may include units equivalent to petrologically similar units in the pyroclastic sequence of the Taylorsville area. Specifically, the metadacite and metamorphosed sodarhyolite of the Franklin Canyon Formation may be broadly equivalent to the Sierra Buttes Formation of McMath (1966) in the Taylorsville area. The meta-andesite on the Dogwood Peak and that northeast of Silver Lake could be equivalent to the Taylor Metaandesite.
4.	Assuming widespread volcanism of the same type, the metarhyolite and metabasalt of the Duffey Dome Formation could have been laid down contemporaneously with the Mississippian Peale and Goodhue Formations of McMath (1966) in Taylorsville area. The Horseshoe Bend Formation, which overlies the
Duffey Dome Formation at the headwaters of Marble Creek and is separated from the Franklin Canyon Formation by a belt of ultrabasic rocks in the southern part of the Bucks Lake quadrangle and in the area to the south (in the American House quadrangle), includes units lithologically similar to the Permian Reeve and Robinson Formations. The Reeve Meta-andesite of the Tayorsville area consists of keratophyre breccia and tuff, fusulinid limestone, and chert-pebble conglomerate. The sequence of metadacite, metarhyolite, metatuff, phyllite, quartzite, metachert-pebble conglomerate, and marble exposed along Marble Creek and along the Middle Fork and the South Branch of the Middle Fork of the Feather River south of the Bucks Lake quadrangle could be equivalent to this formation. No positive identification of fossil remains could be
made because of profound deformation and recrystallization. Textures reminiscent of fossils were observed in some thin sections of carbonate-rich layers. Tiny waterworn cavities form spirals on the surfaces of some small calcite-quartz aggregates embedded in black phyllite in the streambed of the South Branch of the Middle Fork of the Feather River about 0.7 mile south of the Bucks Lake quadrangle. These aggregates, 1-3 cm long and l/%-2 cm thick, are flattened in the plane of foliation and recrystallized to the extent that identification of the original fossils is impossible.
CEDAR FORMATION
Muscovite slate in a small wedge-shaped area on the north border of the Bucks Lake quadrangle just east of the Melones fault is shown as the Cedar Formation on the Bidwell Bar map (Turner, 1898). This formation has been dated as Triassic by McMath (1958) in the area north of the quadrangle, where it includes fos-siliferous limestone beds, and Permo(?) -Triassic by Moores (1970). The east boundary in the Bucks Lake quadrangle is marked by a juxtaposition of structures along a shear zone and thus may be a fault.
The slate is light beige and fine grained. Only the plane of foliation can be measured in most outcrops; some show isoclinal folding and axial plane cleavage. Farther to the north, on the East Branch of the North Fork of the Feather River, this formation consists of muscovite-chlorite phyllite with interbedded layers of black limestone.
METAMORPHOSED INTRUSIVE ROCKS
Two large and several small bodies of ultramafic rocks — peridotite, olivinite and pyroxenite — partly altered to serpentine, soapstone, and talc schist were emplaced at an early date and were deformed with the metamorphic rocks. Small bodies of pyroxenite (mostly altered to hornblendite), metagabbro, metamorphosed quartz diorite, and metatrondhjemite were intruded into the volcanic rocks and were recrystallized with them. These metamorphosed intrusive rocks probably are deep-seated equivalents of the chemically similar metavolcanic rocks. Dikelike bodies of meta-andesite and metamorphosed quartz porphyry cut the metasedi-mentary and metavolcanic rocks.
ULTRAMAFIC ROCKS
The continuous belt of ultramafic rocks in the northeastern part of the area is bordered by high-angle faults on either side—the Melones fault on the northeast and the Rich Bar fault on the southwest. Smaller masses elsewhere resemble sills or dikes, many of which were emplaced in tectonically suitable places as along faults or in tectonic low-pressure areas, such as fold apices (south of Big Bar Mountain and east of Rocky Ridge in the Pulga quadrangle; Coyote Gap and northwest of24
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Hartman Bar in the Bucks Lake quadrangle). A mass on Oak Ridge fills the triangular area between the plu-tons and was probably deformed by them.
Most of the ultramafic rocks are dense dark-green rocks that either weather to a rusty color or break into blocks with shiny green slickensides. All degrees of ser-pentinization of the primary constituents — olivine, pyroxene, and amphibole—occur within large masses, as well as further alteration to antigorite-carbonate rock, talc-carbonate rock, and talc schist. The outermost layer commonly consists of talc schist and is separated from the surrounding metasedimentary or metavolcanic rock by a layer of tremolite rock. Most of the small masses are talc schist.
Thin sections show that the primary minerals are well preserved in the central parts of the two largest masses in the Bucks Lake quadrangle. The estimated percentages of the major constituents—olivine 50-70, pyroxene 10-30, amphibole 10-20, magnetite and chromite 1-2—indicate according to Johannsen’s classification (1951) that they are hornblende-pyroxene olivinite and peridotite. Both clinopyroxene and orthopyroxene are common. Amphibole is very weakly pleo-chroic (y=very light beige, «=/?=colorless) to colorless; its Z/\c=17°-21°, and —2V is large. Very thin (0.005-0.002 mm) seams of serpentine minerals, mainly chrysotile, occur along fractures in the grains and around grain boundaries (fig. 17). Many seams transect the grain boundaries and occur equally in olivine, pyroxene, and amphibole. This, together with the texture, proves that the amphibole is primary. Where serpentinization has advanced farther, the seams are wider and consist of a fine-grained mesh of serpentine minerals that give chrysotile and lizardite X-ray powder patterns. (See Whittaker and Zussman, 1956.)
Chemical analyses of the hornblende-pyroxene olivinite exposed on Meadow Valley Creek (loc. 134) are shown in table 1. The primary minerals, olivine, pyroxene, and amphibole, were separated from this rock and also analyzed. The calculated formulas and percentage of end members are shown with the analyses and the trace element contents in table 2. Olivine is forsterite with only 10 percent fayalite. Pyroxene is entatite that contains 9 percent ferrosilite and very little calcium and aluminum, which were calculated as Tschermak’s molecule, CaAl.SiO„. The calculation of the formula of the primary amphibole indicates that it is a magnesium-rich hornblende with 1.2 A1 substituting for Si. It differs from common igneous hornblende mainly because of exceptionally high magnesium and low iron and calcium contents.
The distribution of [Mg/Fe] between olivine and enstatite is about equal (fig. 18), but because of much larger [Mg/Fe] in hornblende, the distribution coeffi-
cient, Kd [Mg/Fe], for En/Ho=0.694 and for Ol/Ho =0.712.
I____lmm
B
Figure 17.—Photomicrographs of altered peridotite. A. Chrysotile along minute fractures and grain boundaries in olivine (ol), pyroxene (px), and amphibole (a). Hornblende-pyroxene olvinite at Meadow Valley Creek (loc. 134). Crossed nicols. B, Early irregular small fractures in olivine (ol) are filled by chrysotile; the wide fractures parallel to the cross joints are filled by magnesite (m) and antigorite (a). Peridotite 1 mile southeast of Frenchman Hill (loc. 783). Crossed nicols.
Comparison with experimental work and with other Alpine-type peridotites (Medaris, 1969) shows that the distribution of [Fe/Mg] between olivine and enstatite in sample 134 is similar to that in the experimental work at 900 °C and to that in the Alpine peridotites. Medaris also pointed out that distribution does not change between 900° and 1,300°C and cannot be used as a geologic thermometer. Rather the only conclusion thatMETAMORPHOSED INTRUSIVE ROCKS
25
Table 2.—Chemical composition, calculated formulas, and trace elements of blue-green hornblende from metagabbro (specimen 796) and magnesian hornblende, enstatite, and olivine from peridotite (specimen 134), Bucks Lake quadrangle
[Data for chemical composition by C. O. Ingamells, project leader; N. H. Suhr, Penn. State Univ., determined by emission spectrometry in samples from peridotite (specimen 134) the following: SiC>2, AtOri, MgO, CrO, TiCh, MnO, CrcCh, NiO, BaO, SrO. Trace elements determined from spectographic analyses by R. E. Mays, except Ba, Y, and Yb which were analyzed by Chris Heropoulos]
	796	-h	134	: h	134	—e	134	—O
	Blue-green	hornblende	Magnesian	hornblende	Enstatite		Olivine	
	Weight percent	Molecular equivalent	Weight percent	Molecular equivalent	Weight percent	Molecular equivalent	Weight percent	Molecular equivalent
Chemical composition								
SiO. 			 43.63	7263	49.0	8153	53.0	8819	41.0	6822
ALO: 			 14.47	1419	7.4	726	1.52	149	.10	10
Cr:(V 			 .05	3	.67	44	.24	16		
Fe2On 			 3.70	232	.9	56	.20	13	1.7	107
FeO 			 7.69	1070	2.91	405	6.31	878	8.25	1148
MnO 			 .15	21	.10	14	.17	24	.16	23
NiO 				.08	10	.07	9	.30	40
MgO			 13.04	3234	23.8	5903	35.8	8879	48.6	12054
TiO.. 			 .21	26	.22	27	.05	6		
I *:()•■ 				<.01		<.01		<.01	
V,052 			 .04	3						
CaO 			 12.23	2180	11.3	2015	1.14	203	.13	23
BaO 				<.01		<.01		<.01	
SrO				<.01		<.01		<.01	
Na.O 		1.90	307	1.10	177	.13	21	.00	
K;0 			 .23	24	.09	10	.02	2	.002	
F 			 .02	11						
II.O 			 1.8	999	2.9	1610	1.5	833	.25	139
IFO 									
Total 			 99.16		100.5					
Si ...................
A1 ...................
Cr ...................
Tetrahedral.2	=
A1 ...................
Cr ...................
Fe3+ .................
Ti ................
V.....................
Ni .............
Mg ...................
IV ................
Mn ...................
M(l)-M(3)...2	=
Feu ..................
Mn ...................
ca................;...
M (4) .......2	=
Ca....................
Na ...................
K ....................
A-site ......2
nil ..................
F.....................
6.36
1.64
8.00
0.85
.01
.41
.02
.01
2.83
.87
5.00
0.07
.02
1,91
2.00
0.54
,04
0.58
1.75
,01
1.76
Mg/Fe = 3.01 Al/Mg = 0.88 a = 1.651 P = 1.662 y = 1.671
Number of ions in a unit cell
	6.75	1.88	1.00
	1.20	.06	
	.05	.01	
	8.00	1.95	1.00
	0.02		
	.09		0.03
	.02		
	.01		.01
	4.89	1.89	1.77
		.19	.17
	5.03		
	0.34		
	.01		
	1.65	.04	
	2.00	2.12	1.98
	0.02	Percentage of end members	
	.29	Enstatite 	89.15	Forsterite 	
	.02	Ferrosilite 	 8.96	Fayalite 	
	0.33	Tschermak’s mol... 1.89	
	2.67		
	2.67		
Mg/Fe	= 14.38	Mg/Fe 9.95	Mg/Fe = 10.4
Al/Mg	T 0.25		
a	= 1.622	a = 1.662	a = 1.653
p	= 1.630	P = 1.666	P = 1.670
y	= 1.641	y = 1.671	y = 1.688
Trace elements, in parts per million
Ba			 5	16	<4	<4
Be 			 0	<2	<2	<2
Co 			 38	24	60	160
Cr 			 350	6,000	1,600	50
Cu 			 22	44	13	9
Ga			 20	<7	<7	<7
Ni 			 70	600	600	2,100
Se 			 90	60	<10	<10
Sr 			 8	28	<4	<4
V			 210	290	60	<4
Y				 10	20	<20	<20
Yb 	 			 1	2	<2	<2
Zr 			 7	20	<20	<2026
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Figure 18.—Distribution of [Mg/Fe] between enstatite, olivine,
and hornblende in olivinite No. 134 (table 1).
can be made on the basis of similarity of distribution in the natural occurrences and in the experimental work is that these minerals crystallized in equilibrium also in the natural occurrence.
Comparison of the trace element content of the analyzed olivine, enstatite, and hornblende with that of their host rock (table 5, No. 134) shows that most of the chromium and vanadium are in the amphibole, whereas nickel and cobalt are concentrated in olivinev. The concentration of copper in the host rock is higher than in the analyzed minerals, indicating that the opaque minerals contain copper.
The large ultramafic mass south of Bucks Lake shows every stage of serpentinization and steatitization from olivinite that is only about 20 percent serpentinized through serpentine-talc-carbonate rock to soapstone with appreciable carbonate content or to talc schist. The rock around Frenchman Hill consists of olivinite and dunite that weathers rusty red. The dunite has two sets of fractures. The earlier ones that are seen in thin sections as irregular or subparallel fractures, 0.01-0.02 mm wide, may lend a very slight irregular foliation to the rock in outcrop. These tiny fractures are filled by fibrous serpentine minerals, probably chrysotile. Fibers are elongate perpendicular to the walls of the fractures. Another set of fractures is throughgoing and measurable in the field. These fractures are 0.5-1 mm wide and transect the rock at 0.5-3-cm intervals. They are approximately perpendicular to the regional fold axes and thus are most likely tension fractures. These tectonic fractures are filled by magnesite and antigorite; the magnesite is in the center, and laths of antigorite radiate from it or are perpendicular to it (fig. 17). The laths of antigorite penetrate deep into olivine crystals,
and in places clusters of antigorite replace olivine a short distance outside the cross joint fracture.
In the advanced stages of serpentinization and steatitization toward the borders of the masses, the alterations have advanced from wide throughgoing fractures (1-4 cm wide) into the host rock in an irregular manner, producing patches that consist of antigorite and carbonate or of talc, antigorite, and carbonate. Pyroxene is the first mineral to be replaced by carbonate and antigorite. Relict outlines and cleavage of former pyroxene are seen as segregations of tiny grains of magnetite deposited along these planes during the first stage of serpentinization. At the second stage only a part of the olivine is replaced by antigorite. In places, as in location 171 (pi. 2), chrysotile and lizardite persist after a considerable amount of antigorite and carbonate are formed. At these places, serpentinization had proceeded farther before the formation of carbonate and antigorite began.
Near Grizzly Mountain and to the southeast, talc appears first along fractures and then as clusters with carbonate (fig. 19). Toward the south and southeast border zones of the mass, talc is a major constituent. A part of the border zones consists of talc schist or of talc-carbonate and antigorite-carbonate rock, and another part of antigorite-talc-carbonate and talc-antigorite rock. Specular hematite and chromite are common accessory minerals in the antigorite-talc-carbonate rock.
All the ultramafic rock on Soapstone Hill has altered to soapstone that consists of talc, carbonate, and antigorite in varying amounts. Relict textures seen in thin section are similar to those in partly steatitized rocks on Grizzly Mountain; thus perhaps the origin and his-
Figure 19.—Seams of talc (t) in antigorite serpentine at the east border of the ultramafic mass south of Bucks Lake (loc. 73). Crossed nicols.METAMORPHOSED INTRUSIVE ROCKS
27
tory of alteration are also similar. Magnetite in the soapstone is crystallized as anhedral to subhedral grains and clusters. Carbonate fills fractures and occurs in many places as rhombic crystals.
Many contact zones between the ultramafic rocks and the metasedimentary or metavolcanic rocks consist of tremolite or of talc-tremolite rock, indicating outward migration of calcium and magnesium from the serpentinized peridotite. Abundant tremolite-actinolite also occurs in the wallrock next to the contact. The thickness of the tremolite-rich layer ranges from about 10 cm to several meters. The tremolite needles are light to medium green, commonly larger than the other minerals, talc and antigorite, and are subparallel to the contact or oriented at random.
Chemical reactions leading to these various stages of serpentinization and steatitization of the hornblende-pyroxene olivinites can be summarized as follows:
1.	The primary minerals—olivine, pyroxene, and am-phibole — underwent minor serpentinization along irregular fractures. The small amount of H20 needed may have been in a magmatic rest solution in the intergranular cavities of the ultramafic rock during the latest phase of intrusion. The serpentine minerals formed were chrysotile and lizardite. The qualitative reactions can be expressed as
3MgSiOs + 2H20	-*Mg3(0H),Si205 + Si02
3 enstatite + 2 water -* serpentine + silica,
3Mg,(OH)2Si»022 + llftO —► 7Mg;,(0H)1Si205 + 10SiO2 3 cummingtonite +11 water —► 7 serpentine	+ 10 silica,
3Mg2Si04 + Si02 + 4H20	-> 2Mgi(OH),Si2Os
3 olivine + silica + 4 water -» 2 serpentine.
The silica released in the first and second reactions was subsequently used in the third reaction. Some magnetite was precipitated with the serpentine minerals along the fractures. Where amphibole is primary, as in the analyzed specimen (No. 134, table 2), hydrogrossular may have crystallized from the calcium and aluminum contained in the amphibole.
2.	Magnesite and antigorite crystallized along later, wide fractures as a result of introduction of C02 and H20, presumably from the surrounding sedimentary rocks, which would have released C02 and H20 during the first episode of metamorphism. The structural control of the fracture system near Frenchman Hill suggests that these fractures were formed during deformation. Since the regional metamorphism was syntectonic, the crystallization of antigorite and magnesite occurred during this first period of metamorphism. The silica needed for formation of antigorite from olivine was released according to the reaction
Mg2SiO, + 2C02	—> 2MgC03 + Si02
olivine + 2 carbon dioxide —► 2 magnesite + silica.
3.	Crystallization of talc in addition to antigorite and magnesite required an addition of silica from outside. This reaction is far more common in thin bodies that were strongly deformed by tectonic movements than in large masses. In the thin layers of talc schist, the foliation and lineation are parallel to the corresponding structures in the enveloping metamorphic rocks, indicating that the talc was crystallized during the deformation. Talc was formed in outer zones of the masses essentially during the same phase as antigorite and carbonate in the inner zones, but the front of introduced silica lagged behind that of C02 and H20. Not all olivine was first serpentinized and then altered to talc. Thin sections show a considerable amount of olivine in the rocks in which talc replaces primary minerals. Thus the reaction occurred only where enough silica was available and is expressed as
3Mg2SiOi + 5Si02 + 2 H:0 -> 2Mg2(OH)2Si,Ow olivine + 5 silica + 2 water —► 2 talc
or
3MgSiO:i + Si02 + H20 - Mg3(OH)2Si4O10 enstatite + silica + water -*■ talc.
4.	Crystallization of abundant tremolite along the contact zones of the ultramafic masses indicates that calcium, which was released during the serpentinization and steatitization of amphibole and pyroxene, migrated outward and was combined with outward-migrating magnesium and with silica of the wallrock to form tremolite as
2 CaO + 5MgO + 8Si02+H20	-*■ Ca2Mg5 (OH) 2Si»022
(from peridotite) (from wallrock) -+ tremolite.
Some of the tremolite in the ultramafic mass, which was earlier altered to talc-carbonate rock, was formed during the second episode of metamorphism as
Mg3 (OH) 2Si,O,0 + 2 CaMg(COj)2 + 4Si02 -> Ca2Mg5(OH)2
Si8022 + 4C02
Talc	+ 2 dolomite	+ 4 silica —► tremolite.
This reaction occurred at the temperatures of the epidote-amphibolite facies.
Exchange of elements during the serpentinization is thus essentially similar to that described from many other areas (Thayer, 1966; Page, 1967; Cerny, 1968); that is, water migrated into the ultramafic mass, and calcium and magnesium moved out. The volume increased, but this was due mainly to tectonism, as shown by the fact that serpentinization started along the expansion cracks that parallel the cross joints. Thus the shearing, crushing, and other tectonic effects may
499-964 0 - 73 -528
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
have greatly facilitated serpentinization by making the ultramafic mass accessible to H20 and C02, which were expelled from the surrounding rocks during this same phase of regional metamorphism.
The mineralogy of the serpentinized peridotite in the northern part of the Bucks Lake quadrangle differs somewhat from that just described; chrysotile and lizardite make up most of the rock, in which relict olivine is surrounded by a corona of fibrous pyroxene. Similar pyroxene with Z /\ c=36°-40° surrounds spots of serpentine minerals with secondary magnetite, which originally precipitated along fractures in former olivine. Large grains of primary pyroxene in this rock have altered to a mixture consisting of cummingtonitic amphibole (Z/\c=13°) and hydrogrossular. Several large grains of hydrogrossular replacing olivine occur in locality 395. Most of the long amphibole (antho-phyllite?) prisms, which in locality 385 transect the serpentine, are altered to chrysotile and lizardite still preserving the parallel extinction. This amphibole is later than the first stage of serpentinization. The sequence of events was as follows:
1.	Partial serpentinization of olivine, primary pyroxene, and primary amphibole accompanied by precipitation of magnetite along the fractures.
2.	Continued serpentinization accompanied by crystallization of secondary amphibole, hydrogrossular, and chlorite.
3.	In places serpentinization of secondary amphibole and crystallization of chlorite.
Formation of chlorite is especially common near fault zones.
Most of the small ultramafic bodies consisted originally of peridotite with a higher percentage of pyroxene than is present in the two largest masses just described. In some small bodies, peridotite is altered to amphibole-serpentine rock, as seen for example in small ultramafic bodies exposed in localities 466 and 62. In locality 466, pyroxene was originally the major rock constituent (70-90 percent) and occurred in large crystals that included small olivine crystals. Pyroxene, some still showing subhedral outlines, is altered to light-green to colorless amphibole and olivine to serpentine, talc, and colorless amphibole. Chrysotile and magnetite occur along the relict cracks of former olivine.
A serpentinized part of a long thin ultramafic body along the north border of T. 22 N., R. 7 E., consisted originally of about 70 percent pyroxene and 30 percent olivine. The relict cleavage of pyroxene and relict cracks of olivine are indicated by magnetite that precipitated along these surfaces at an early stage of serpentinization. Olivine was first altered to chrysotile along cracks, and the rest of this mineral was later altered to talc and serpentine minerals, mainly antigorite. Pyroxene was
altered first to amphibole, and aggregates of antigorite then developed within the large amphibole crystals, replacing about 50 percent of the original volume of the amphibole. Wide seams of chrysotile-type serpentine with magnetite in their central parts transect this rock, which now consists of about 30 percent amphibole, 60 percent serpentine minerals, and 10 percent talc.
A small body of altered pyroxenite extends for more than 1 mile from the south slope of Frazer Hill (loc. 550) toward the southeast. Thin sections show relict prophyritic texture. The large (1-3 mm long) pheno-crysts of pyroxene now consist of several smaller clino-pyroxene crystals that show Z/\c~35° and + 2V~ 60° and are partly altered to tremolite. The fine-grained groundmass contains numerous medium-size (0.1-0.2 mm) crystals of pyroxene, many of which are euhedral and partly altered to amphibole. Alteration to amphibole is highly irregular, proceeding along fractures and forming patches in the groundmass and within larger pyroxene crystals. The fine-grained granoblastic groundmass consists of about 40 percent pyroxene and 60 percent amphibole. Tiny grains of magnetite are included in pyroxene, primarily along its cleavage. Where amphibole is the major constituent, magnetite forms somewhat larger, scattered grains.
A part of the long thin ultramafic body along the north border of T. 22 N., R. 7 E., consists of pyroxenite that has been partly altered to amphibole rock, with further partial alteration to antigorite and very little talc and carbonate. The pyroxenite is coarse grained and consists of about 70 percent clinopyroxene. Alteration to amphibole is mainly along the cracks and grain boundaries, whereas antigorite and talc form small patches and occur along fractures and shear zones.
Thus the original composition of ultramafic rocks ranged from dunite and olivinite to peridotite and pyroxenite. Chemical analysis of a representative sample of olivinite (No. 134, table 1) shows that these rocks are rich in magnesium, and thereby they differ strikingly from the members of the other igneous rocks series in this region. (See fig. 39.) They are typical representatives of Alpine-type peridotite-serpentine masses that were emplaced along fault zones in a cool and mainly solid state. The high-temperature contact aureoles are absent, and microbrecciation is ubiquitous. The early serpentine minerals that fill the interstices and the tiny cracks formed by microbrecciation probably represent the only liquid contained in the ultramafic crystal accumulate during its ascent from a deep-seated magma chamber or from the mantle.
ROCKS ASSOCIATED WITH SERPENTINES
Several small masses consisting of albite or albitic oligoclase with some actinolitic hornblende, muscovite, and rarely corundum occur within the serpentines.METAMORPHOSED INTRUSIVE ROCKS
29
Some of these are dikes with fine-grained borders; the others are coarse-grained masses similar to albitites. A dike consisting of oligoclase and corundum was described by Lawson (1903) under the name of plumasite. Crystals of axinite, small masses of vesuvianite, and a dikelike body consisting of rodingitelike rock occur near Pulga.
Four small masses of coarse-grained albitite cut the serpentine. Two of these—both hornblende bearing— are along the Melones fault (Iocs. 290, 400); the third one, a muscovite albitite, is a north-trending dike on the north slope of Grizzly Mountain (loc. 172); and the fourth mass is north of Pulga (loc. 1263).
The albitite at locality 290 is dark bluish gray and consists mainly of albite with some quartz, hornblende, chlorite, calcite, zoisite, and epidote. Albite (An3) constitutes 95 percent of the light-colored parts of the outcrops. It occurs in anhedral grains that are 1-3 mm in diameter and have irregular outlines. Actinolitic hornblende is segregated in layerlike bodies.
Albitite at locality 400 has elongate clusters of large (0.5 mm) grains of quartz, subhedral crystals of albite, and trains of bluish-green hornblende in a mosaic of small (0.1 mm) grains of quartz and albite. Crystals of hornblende are rimmed by needles of actinolite. Ilmenite-magnetite surrounded by sphene occurs as an accessory mineral.
The muscovite albitite at Grizzly Mountain is light tan and coarse grained. Albite is in anhedral grains 1-2 mm in diameter. Most of the quartz is in anhedral grains; some grains are bounded by crystal faces. Large flakes (1-2 mm long) of muscovite are in radiating clusters, and numerous tiny flakes are included in albite. There are small grains of accessory magnetite.
A fine-grained quartz porphyry dike cuts serpentine on a low ridge 1.7 miles east of Spanish Peak (loc. 1044) northeast of the locality in which Lawson (1903) described a dike of coarse-grained oligoclase-corundum rock (plumasite) with fine-grained or porphyritic borders. Phenocrysts in the fine-grained dike are quartz and albitic plagioclase; the groundmass consists of quartz, albitic plagioclase, and biotite. Tiny crystals of corundum and magnetite occur as accessory minerals. Blocks of coarse-grained white rock found in an old digging just south of the dike consist of 98 percent oligoclase (An15) with very little actinolite, muscovite, chlorite, and a few small grains of quartz. These blocks probably were left after corundum-bearing rock was quarried out.
Brown crystals of axinite occur with quartz in veinlike masses cutting the meta-andesite just west of the serpentine near locality 1044 in secs. 16 and 21, T. 24 N., R. 8 E. The meta-andesite contains tiny phenocrysts of albite in a groundmass of actinolite, epidote, and albite;
round vesicles are filled by quartz and epidote.
A specimen showing the contact of the meta-andesite and quartz-axinite vein was received from A. Pabst, University of California at Berkeley. Microscopic examination of this specimen shows that small angular inclusions of meta-andesite, some partly digested, occur in this vein near its walls and that hairlike tremolite extends from the wallrock into the vein quartz and is partly included also in the axinite. Axinite occurs in subhedral large crystals that show <*=1.671+0.001, /?=1.676+0.001, y=1.682±0.001, and —2V=82°.
Vesuvianite that occurs as small masses in serpentine and talc schist is fine grained, apple green, and translucent. A layerlike body of gray-green massive rock consisting of fine-grained gray-green vesuvianite, with epidote, oligoclase, tremolite, grossularite and calcite, is exposed at the 2,200-foot elevation north of Pulga. This mass is similar in its mineralogy and mode of occurrence to rodingite and may have a similar origin, representing segregation of calcium released from pyroxene of the ultramafic rock during its serpentinization.
Small masses of fibrous tremolite (nephrite) with an extinction angle Z /\ c=20° occur at the contact of serpentine and metasedimentary rocks on Mill Creek near Pulga. Thin sections show that the tiny prisms are bent and interlaced, resembling massive talc in the soapstones. The nephrite in this contact zone seems to have crystallized from talc according to the reaction talc + 2 dolomite + 4 silica tremolite. Thjis reaction was found to be common in the contact zones between the ultramafic bodies and their siliceous wallrocks, as described in the section “Ultramafic Rocks.” METAGABBRO AND HORNBLENDITE
Four large (1-2 square miles) and several small bodies of metagabbro are exposed in the southwestern part of the Bucks Lake quadrangle and in the southern part of the Pulga quadrangle (pis. 1, 2). The two largest ones occur next to the younger plutons, the Hartman Bar pluton and the Granite Basin pluton. The third largest body is in the vicinity of Big Bar Mountain and extends westward across the North Fork of the Feather River. The fourth largest body of metagabbro is exposed just north of the Pulga quadrangle in the southernmost part of the Jonesville quadrangle. All occurrences are inhomogeneous, including masses exceptionally rich in amphibole, in places hornblendite, and grading to parts rich in plagioclase. Gradation to metamorphosed hornblende quartz diorite is common. Some of the border zones of ultramafic bodies consist of hornblendite and metagabbro (for instance, loc. 467).
Metagabbro is gray green to dark green or black and medium to medium coarse grained. The major constituents, green to black hornblende and white to light-greenish-beige plagioclase, can be identified in hand30
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
specimens. Thin sections show that epidote is the third major constituent and that quartz and chlorite are present in some metagabbro. Ilmenite and sphene partly altered to leucoxene, magnetite, and apatite are the common accessory minerals. Small flakes of muscovite are included in plagioclase. The percentages of the major constituents and the anorthite content of plagioclase vary considerably. The dark coarse-grained part of the metagabbro, such as the outcrops on the northwestern part of the two largest bodies in the Bucks Lake quadrangle and much of the metagabbro west of the Granite Basin pluton, consists of 70-80 percent hornblende and grades in places to hornblendite. In a common variety the percentages of the major constituents are hornblende 50-70, plagioclase 10-30, and epidote minerals 10-35. Hornblende is either bluish green to green or pale green to almost colorless under the microscope; the darker varieties are strongly pleochroic. Some occurs in large anhedral to subhedral crystals that may include round plagioclase grains, and some is in small prisms, many of them incuded in plagioclase. Clinopyroxene, partly altered to bluish-green hornblende, occurs in a few localities (as Iocs. 666, 1095). The anorthite content of plagioclase is commonly low (An10-i5); however, in parts of the coarse-grained gab-bro, plagioclase is andesine (An35.45), and near plutons it is bytownite or anorthite. In these rocks epidote is scarce, and hornblende is darker green, indicating that these parts were probably recrystallized at higher temperatures. In contrast, some other parts of these metagabbro bodies contain chlorite, pale-green to colorless amphibole, and abundant epidote minerals.
The distribution and structure of the well-preserved and highly altered parts in the same mass indicate that the high activity of H20 near and in the shear zones along the contacts and locally elsewhere was responsible for crystallization of abundant low-grade minerals such as chlorite and epidote. On the other hand, the metagabbro around the Granite Basin pluton is coarsegrained hornblende-plagioclase rock that underwent a second episode of recrystallization during the emplacement of the pluton. In this rock blue-green hornblende occurs in large poikiloblastic crystals or in clusters of prisms having parallel orientation. In locality 796, south of Robinson mine, large pale-green amphibole crystals are rimmed b;> blue-green amphibole. Small prisms of similar blue-green amphibole are included in plagioclase. The indices of refraction of the blue-green amphibole are between 1.651±0.001 and 1.671±0.001, and specific gravity is 3.17-3.20. A chemical analysis of mainly blue-green material separated from this rock (No. 796, table 2) shows a considerably higher aluminum and alkali contents and a little lower iron content than is common in hornblende from unaltered igneous rocks.
Plagioclase is in anhedral grains that show traces of annealing recrystallization. They show shadowy traces of having been clusters of tiny anhedral grains. The borders of the twin lamellae are jagged or wavy, preserving in part the outlines of the former tiny grains (for example, loc. 546). This is a feature resembling that illustrated earlier (Hietanen, 1951, fig. 21) from a metasomatic gabbro in the Pulga quadrangle. Light-green zoisite with a=1.699±0.001, /?=1.703±0.001, y=1.714±0.001 occurs as an alteration product in plagioclase, fills fractures, and forms segregations.
Metagabbro included in altered tonalite at Hartman Bar on the north side of the Middle Fork of the Feather River (loc. 205) consists of euhedral stubby hornblende crystals (60-65 percent) and interstitial plagioclase. Thin sections show that green hornblende has altered partly to colorless amphibole that includes small grains of epidote. Plagioclase (An30) contains epidote and sericite as alteration products. Chlorite, muscovite, and magnetite are the minor constituents.
Comparison of the chemical composition of metagabbro (No. 796, table 1) with that of metavolcanic rocks shows the closest similarity to be with the metaandesite. The percentages of magnesium, sodium, and silicon are only a little higher in the metagabbro, and the percentage of iron is lower.
MET A DIORITE
Metagabbro grades in places to a lighter colored rock that contains more plagioclase and quartz and less hornblende. The composition of this rock is hornblende quartz diorite. It forms a part of the large mass mapped as metagabbro on the east side of the Granite Basin pluton and the border zones of metagabbro west of Hartman Bar and along Coldwater Creek. Small bodies consisting of similar metadiorite occur with metadacite in the southern part of the area.
In several places, metadacite grades into metadiorite, and some of the rock mapped as metadacite is fine- to medium-grained metadiorite. These two rock types seem to be genetically related. Their mineralogy and chemistry are identical, but their textures reflect different rates of cooling. The intrusive relation between the metavolcanic rocks and metamorphosed intrusive rocks (fig. 20) is exposed on the ridge south of Catrell Creek at an elevation of 4,800 feet (east of loc. 850). Here lens-shaped and dikelike bodies of metadiorite and metagabbro cut the metadacite and metamorphosed sodarhyolite.
The metadiorite consists of plagioclase, quartz, light-green hornblende, epidote, sphene, and magnetite. It is thus mineralogically similar to the metadacite in this area. The differences between the two are mainly textural. In the metadiorite, plagioclase and hornblende grains are large enough to be recognized with the unaided eye, and the rock seems equigranular. Horn-METAMORPHOSED INTRUSIVE ROCKS
31
1 METER
Figure 20.-Lenses and dikelike bodies of metadiorite (mdi) and metagabbro (mgb) in metadacite (md) and meta-sodarhyolite (mr). Dark clots of hornblende (ho) also occur. Ridge south of Catrell Creek; elevation 4,800 feet.
blende is pleochroic in greens (y=light bluish green, /3=light green, «=very light yellowish green, y /\ 20°). Albitic plagioclase (An2-8) includes abundant fairly large anhedral grains of epidote. Ilmenite, sphene partly altered to leucoxene, and chlorite are visible in some thin sections. Quartz is in small grains or groups of grains that probably represent granulated large grains.
A large sill-like body of metadiorite in the westernmost part of the Pulga quadrangle is mineralogically similar to the metadiorite in the Bucks Lake quadrangle. Variation in grain size and in the ratio of dark and light minerals makes it rather inhomogeneous. Much of this sill is coarse grained, but border zones and many outcrops in the central part are fine to medium grained and resemble metadacite. In some places, hornblende is in long slender prisms that are oriented at random.
The two analyzed specimens of metadiorite (NoS. 465, 532, table 1) are very similar to metadacite. There is only a little more calcium in the metadiorite. This chemical similarity supports the field observation that the two rock types are genetically related.
MET ATRONDHJE MITE
The northern border zone of a small body of very light gray medium-grained equigranular metatrondhje-mite occurs along the south boundary of the Bucks Lake quadrangle. The central part of this body is well exposed south of the quadrangle on the South Branch of the Middle Fork of the Feather River (current study area in fig. 1) where it consists of albite, quartz, biotite,
actinolite, and some epidote, muscovite, chlorite and magnetite. Mineral content indicates that it is chemically similar to the metasodarhyolite (table 1, No. 466) and the altered trondhjemite (Hietanen, 1951, table 1, specimen 328).
METAMORPHOSED HYPABYSSAL ROCKS
Metamorphosed hypabyssal rocks are genetically related to metavolcanic rocks and to metamorphosed intrusive rocks. Dikes of andesitic and dacitic composition are mineralogically similar to the meta-andesite and metadacite consisting mainly of albite, epidote, and actinolite. Relict textures of typical hypabyssal rocks are rarely preserved, and only the field occurrence shows that the rock is a dike and not a flow. Metamorphosed dikes of andesitic composition occur at localities 34, 414, and 417, and those of dacitic composition at localities 111, 117,198, and 673.
Ultramafic dikes consisting mainly of very light green hornblende and interstitial chlorite are exposed along Bear Creek (loc. 108). A small amount of epidote is included in the hornblende. Ilmenite and sphene are partly altered to leucoxene. A greenish-gray dike consisting of a fine-grained feltlike mesh of chlorite and a few small grains of magnetite cuts the soapstone on Soapstone Hill (loc. 762).
Most of the gabbroic dikes consist of altered horn-blende-plagioclase rock, and a few contain pyroxene instead of hornblende or in addition to it (loc. 397). Hornblende is commonly in small euhedral prisms, more rarely interstital to plagioclase. The composition of plagioclase ranges from albite to andesine, depending on the degree of alteration of the anorthite component to epidote. Aggregates consisting of chlorite and colorless amphibole and having outlines of olivine occur in the dike that is exposed along the east contact of the small tonalite body on the east slope of Dogwood Creek (loc. 598). Plagioclase (An:is_40) in this rock includes small grains of epidote and tiny flakes of muscovite. Magnetite, sphene, and apatite occur as accessory minerals.
In a hornblende gabbro dike about 1 mile south of Grizzly Mountain (loc. 663), euhedral hornblende crystals are included in large plagioclase grains. A dike exposed in the southwestern part of sec. 6, T. 23 N., R. 9 E., (loc. 639) consists of long plagioclase laths oriented at random and of interstitial hornblende in equal amounts. A dike in sec. 4, T. 23 N., R. 8 E., (loc. 730) is a typical example of dark fine-grained lamprophyres that are common in the area. It consists of 70 percent green hornblende, 20 percent plagioclase, and 10 percent epidote.
In an altered diabase dike that is exposed in sec. 21, T. 24 N., R. 8 E., (loc. 95), the major constituents are altered plagioclase and interstitial augite. Epidote, chlorite, and leucoxene occur as alteration products;32
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
most of the small epidote grains are in plagioclase. Chlorite fills shear fractures and envelops many magnetite grains. Sphene is altered to leucoxene.
Gabbroic dikes along Slate Creek (loc. 153) and in the northern part of the Bucks Lake quadrangle (loc. 384) are medium grained and dark greenish gray and consist mainly of altered plagioclase and hornblende. Some interstitial chlorite and quartz and a few grains of magnetite and sphene are the other constituents. Plagioclase has altered to aggregates of epidote minerals and albite that have preserved outlines of the original euhedral crystals. Some of the large hornblende crystals are rimmed by needlelike amphibole and contain remnants of augite. Aggregates consisting of magnetite and chlorite (sp. 153) have outlines suggesting that they were originally olivine. Some of the opaque mineral is ilmenite-magnetite that shows lamellar texture.
Three types of altered dikes of intermediate composition are common: (1) medium-gray fine- to mediumgrained dioritic dikes with euhedral hornblende needles oriented at random, (2) dark-greenish-gray dioritic dikes in which augite is partly altered to hornblende and the anorthite component of plagioclase to epidote, and (3) quartz monzonitic dikes.
Examples of the first type are exposed at localities 293 and 412. Hornblende prisms in these dikes are 1-3 mm long; thin sections show that they are the common green variety and make up about 20 percent of the rock. Light-colored minerals are plagioclase and quartz. Epidote occurs as an alteration product in the plagioclase. Magnetite is a common accessory mineral.
Dikes at the mouth of Slate Creek (loc. 694, 711) contain augite phenocrysts that are partly altered to hornblende and rimmed by small radiating needlelike flakes of reddish-brown biotite. Calcic plagioclase has been replaced by a fine-grained mixture of albite and epidote minerals. Quartz occurs as subhedral to anhedral grains and as interstitial granophyre. Magnetite and ilmenite, partly altered to leucoxene, are the accessory minerals.
Quartz monzonitic dikes are medium-gray finegrained rocks in which needlelike phenocrysts of hornblende, 0.5-1 mm long, are oriented at random. Thin sections show that hornblende is weakly pleochroic («=pale green, /?=green, y=green) and Z/\c=21°. Small subhedral crystals (0.1 mm long) of muscovite, epidote, and chlorite form a considerable portion of the rock. The groundmass is fine grained and consists of quartz and albite. Quartz monzonitic dikes are common in the southern part of the area, where they cut meta-morphic rocks (loc. 253) and older plutonic rocks (loc. 208).
The altered plagioclase porphyry that cuts meta-gabbro at Coldwater Creek (loc. 643) resembles the
altered quartz monzonitic dikes, but it is more silicic and has no hornblende. It consists of quartz, albite, muscovite, epidote, chlorite, and some magnetite. Phenocrysts are albite; they are 1-3 mm in diameter and include epidote crystals. Fine-grained porphyritic dikes northwest of Granite Basin (loc. 772) consist mainly of quartz and albite with some biotite and muscovite and very little potassium feldspar.
The most silicic types among the metamorphosed hypabyssal rocks, the quartz porphyries, contain large euhedral to subhedral phenocrysts of quartz. Some of these dikes also contain small phenocrysts of hornblende, and some others, phenocrysts of plagioclase (as at loc. 451). A hornblende-bearing variety cuts serpentine in a roadcut along Bean Creek (loc. 289). Quartz phenocrysts in this rock are about 1 cm in diameter and are granulated. Hornblende phenocrysts are much smaller (0.2-2 mm long), and a few still-smaller euhedral apatite prisms and chlorite flakes (0.1 mm in size) are also embedded in a fine-grained groundmass that consists of quartz, plagioclase, and needlelike amphibole prisms.
The textures of the granulated quartz phenocrysts suggest two phases of growth. The central part is a very fine grained granoblastic aggregate that has outlines of euhedral crystals; it is covered by a shell of somewhat coarser grained quartz. The c axis of most grains in the shell radiate out from the central aggregate. The shell includes small euhedral hornblende crystals, some needles of hornblende, and ( in a few phenocrysts, epidote. The fine-grained core apparently represents the original phenocryst. The coarser shell formed later, most likely during metamorphism. Hornblende phenocrysts also are zoned; the central part consists of common green hornblende and is rimmed by a thin layer of colorless amphibole, which in turn is covered by a blue-green amphibole similar to that in the groundmass.
A porphyritic dike with quartz and albite phenocrysts cuts phyllite at locality 451. The groundmass of this dike is fine grained and rich in biotite and also contains muscovite, quartz, albite, and some magnetite and hematite.
Dikelike bodies of medium- to coarse-grained silicic rock occur with metadacite and metamorphosed soda-rhyolite along Willow Creek (Iocs. 76,814), atthe mouth of Onion Valley Creek (loc. 343), and south of Granite Basin (loc. 804). These rocks contain euhedral to subhedral phenocrysts of quartz, set in a medium-grained groundmass of quartz, albitic plagioclase, epidote, and either chlorite (Iocs. 76, 814) or actinolite (loc. 804). Plagioclase includes numerous tiny flakes of muscovite; sphene, partly altered to leucoxene, and magnetite are the common accessory minerals. Mineralogically, these rocks resemble metamorphosed tonalites, but their texture is porphyritic and indicates hypabyssal cooling.METAMORPHISM
33
METAMORPHISM
The common mineral assemblages in the metasedi-mentary and metavolcanic rocks outside the immediate contact aureoles of the Cretaceous plutons are musco-vite-biotite-chlorite-albite and epidote-actinolite-albite, indicating metamorphism to the border zone between the greenschist and the epidote-amphibolite facies. Higher grade assemblages occur only in fairly narrow contact aureoles around the plutons. The common indication of the higher grade is coarsening of the grain size toward the pluton over a zone about 1 mile wide. In this zone, assemblages of andalusite-staurolite, andalu-site-cordierite, and cordierite-anthophyllite, all with biotite and muscovite, occur in aluminum-rich layers in phyllite. Assemblages of epidote-actinolite-oligoclase (An10_i2) and hornblende-oligoclase are common in the metavolcanic rocks; these mineral assemblages are typical of the higher part of the epidote-amphibolite facies. Sillimanite was found only in one locality, in the southern contact aureole of the Bucks Lake pluton, where it occurs with andalusite and cordierite. Pseudo-morphs of yellow mica after staurolite occur elsewhere near this southern contact, indicating (together with the assemblage andalusite-sillimanite) that the upper stability limit of staurolite was exceeded here. Plagio-clase (An40), green hornblende, quartz, and epidote are common in metabasalt south of the Grizzly pluton and northwest of the Merrimac pluton. This mineral assemblage indicates that there the pressure-temperature conditions of the amphibolite facies were reached in the innermost parts of the contact aureoles.
The upper stability limit of staurolite was also exceeded in the inner contact aureole of the Merrimac pluton east of Chino Creek. There, staurolite occurs with andalusite in the outer contact aureole (loc. 1019) but not in the inner one (loc. 1020), where large por-phyroblasts of andalusite crystallized with biotite and muscovite.
Textures in the cordierite- and andalusite-bearing rocks suggest that there have been at least two episodes of metamorphism. In many cordierite and andalusite porphyroblasts, the internal s plane, as shown by rows of inclusions, is at an agle to the external foliation that wraps around these early porphyroblasts. In places near the contacts of the plutons, some of the porphyroblasts include the present foliation, indicating postkinematic recrystallization. Staurolite crystallized during and towards the end of the deformation, as shown by a slight bending of external s plane around some crystals and by the fact that some of the staurolite includes the external foliation or is included in late crystals of andalusite.
The occurrence of sillimanite with cordierite and andalusite in the quartzite and phyllite just south of the Bucks Lake pluton indicates that during the second
episode of recrystallization temperatures in this part of the contact zone were higher than elsewhere. No kyanite crystallized anywhere in the area. The pressure during the recrystallization must have been lower than that at the triple point of the three aluminum silicates. Crystallization of andalusite first with staurolite then with cordierite and sillimanite shows that the metamorphism is of Pyrenean type, as was concluded earlier (Hieta-nen, 1967). These relations allow an estimation of metamorphic pressures and temperatures. The fact that staurolite occurs with andalusite but was not stable with sillimanite plus cordierite indicates that pressure during the recrystallization was lower than that at the intersection of the andalusite-sillimanite boundary with the upper stability boundary of staurolite. On the basis of the latest experimental work on the stability of staurolite (Hoscheck, 1967, 1968; Ganguly and Newton, 1968; Richardson, 1968) and on the stability of the aluminum silicates (Newton, 1966; Weill, 1966; Alt-haus, 1967; Richardson and others, 1969), andalusite-sillimanite-cordierite phyllite is estimated to have recrystallized at about 4 kb (kilobars) and at temperatures higher than the upper stability limit of staurolite, thus between 650° and 690°C (fig. 21A). Since muscovite and not potassium feldspar occurs with sillimanite, the upper temperature limit must have been below 650°C (Evans, 1965). In the Pulga quadrangle, where staurolite is included in late andalusite, the early andalusite crystallized first, then staurolite with more andalusite, both being late kinematic. Finally, the latest andalusite crystallized postkinematically. The temperature during this latest phase was higher than during the earlier episode because the upper stability limit of staurolite was exceeded. The lower stability limit of staurolite was determined experimentally by Ganguly and Newton (1968) at about 530°C at 4 kb. The upper limit is 650°C, according to Hoschek (1968). These experimental values are shown graphically in figure 21 A. In relation to the kyanite-sillimanite transition, this upper stability limit of staurolite seems to be at too high a temperature, because in many regionally metamorphosed areas a kyanite-almandite-muscovite zone succeeds the staurolite-kyanite zone, at pressure not much higher than that of the triple point, thus at about 3-7 kb (Hietanen, 1967,1968). The total lack of potassium feldspar and absence of any signs of beginning of melting of granitic material in the cordierite-andalusite-sillimanite-two mica phyllite indicate that the peak of the metamorphic temperature in the southern part of the Bucks Lake quadrangle must have been below 640°C (Yoder and Eugster, 1955; Tuttle and Bowen, 1958). These rocks were metamorphosed below the melting temperature of pegmatitic material, thus below 610°C at about 4 kb (Piwinskii, 1968). The shaded area in figure 2 IB shows the stability range of staurolite34
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
as deduced from these relations; the heavy line A-A' is the possible geothermal gradient during metamorphism in this area.
The metavolcanic rocks were recrystallized under the same physical conditions as the interlayered metasedi-mentary rocks. Thus, the assemblage epidote-actinolitic hornblende-plagioclase (An8_i2) was stable at the peak temperatures 600°-650°C at about 4 kb. Since the early crystallized minerals in the pelitic layers remained
A
TEMPERATURE, IN DEGREES CENTIGRADE 200	300	400	500	600	700	800	900
stable during the deformation and second episode of recrystallization, the recrystallization in the metavolcanic rocks could have also occurred over a period of time, starting before the latest episode of deformation (which was contemporaneous with the emplacement of the plutons) and reaching its peak after it. The temperature during the postkinematic phase was higher than that during the synkinematic phase. The crystallization of bluish-green rims around colorless and pale-green actinolite prisms reflects these two phases.
Additional information on metamorphism and genetic relationships between the various metamorphic rocks can be deduced from the chemistry of the rocks. Atomic ratios of excess aluminum, calcium, and combined iron, manganese, and magnesium calculated from the chemical analyses of the metavolcanic and metasedimentary rocks (table 1) are shown in an A-C-F diagram (fig. 22). For comparison, the analyses of metavolcanic and metamorphosed igneous rocks of the Merrimac area (table 1, Hietanen, 1951) were plotted in the same diagram. The plots for the metabasalt (Nos. 551, M175), metaandesite (463, M156), and metadacite (464, M384, M230), as well as those for the corresponding meta-igneous rocks (796, 532, 465), are within the epidote-actinolite-biotite subtriangle, whereas those for the metarhyolite (M406), metamorphosed sodarhyolite (461, M147), and altered tonalite (M328) are within the epidote-almandite-biotite subtriangle. (The epi-dote-biotite join separates rocks that contain actinolite from those that do not.) The plots for the metadiorite and metagabbro are within the cluster of the plots for the metadacite and meta-andesite; all show a Ca/Fe-t-Mg ratio of about 42:58. The metamorphosed sodarhyolite and trondhjemite have the same Ca/Fe + Mg ratio, but are richer in aluminum than the meta-andesite and metadacite. In contrast, the Ca/Fe + Mg ratio of metarhyolite (M406) is 14:86, reflecting a low calcium content.
The similarity of the chemistry and mineralogy of the meta-andesite, metadacite, metasodarhyolite, metagabbro, and metadiorite, together with the field evi-
Figure 21.—Stability of staurolite during recrystallization. A, Stability boundaries of staurolite (Hoschek, 1967, 1968) and Mg-cordierite (Schreyer and Yoder, 1964; Schreyer, 1967) in relation to stability fields of Al-polymorphs according to Althaus (1967, A), Newton (1966, N), Richardson, Gilbert, and Bell 1969, R), and Pugin and Khitarov (1968, P). Melting of granite after Luth, Jahns, and Tuttle (1964). I, triple point estimated on basis of geologic thermometry and field relations (Hietanen, 1967, 1969). B, Field relations and a possible pressure-temperature gradient (A-A') during the recrystallization in the Pulga and Bucks Lake quadrangles. Shaded area shows stability field of staurolite. Melting of igneous rocks after Piwinskii (1968). Modified from Hietanen (1967).PLUTONIC ROCKS
35
Andalusite
A
Figure 22.—A-C-F diagram for metamorphic rocks. The numbers refer to analyses in table 1; those with prefix M are from Hietanen (1951) with their locations shown on plates 2 and 3. The rock types are as follows: 85, 104 metasedimentary rock, Calaveras Formation; M406 metarhyolite, Horseshoe Bend Formation; 461, M147 metamorphosed sodarhyolite; 464, M384 metadacite; 463, M156 meta-andesite (Nos. 461, 464, 463 from the Franklin Canyon Formation); 551, M175 metabasalt (No. 551 from the Duffey Dome Formation); M230 metatuff; M328 altered tonalite; 465, 532 metadiorite; 796 metagabbro; M117 inclusion of wallrock in quartz diorite; M270 inclusion in monzotonalite; 134, M2, M188 serpen-tinized peridotite.
dence, suggests a close genetic relationship and a common metamorphism for all these rocks. Metarhyolite contains much less calcium and more potassium than metamorphosed sodarhyolite. Metarhyolite similar to M406 occurs with the metabasalt of the Duffey Dome Formation. Compared with the meta-andesite, this metabasalt (No. 551) has a much lower calcium content and higher sodium content. The differentiation of the Franklin Canyon sequence may have produced a sodarhyolitic end member because of a low potassium content and a high calcium content. This is supported by the fact that each extrusive member of this sequence has a deep-seated and hypabyssal equivalent, all showing closely similar chemical characteristics and probably originating in the same magma chamber. In particular, the composition of metagabbro is close to that of meta-andesite; metadiorite is similar to metadacite; and metamorphosed quartz porphyry and trondhjemite are chemically similar to metamorphosed sodarhyolite. These metamorphosed plutonic rocks occur as small masses and sill-like bodies in the meta-volcanic sequence. They were deformed and metamorphosed with the volcanic rocks and thus must have been emplaced soon after the volcanic activity. They
are comparable with intrusive rocks in Mount Rainier National Park (Fiske and others, 1963), where Tertiary volcanic rocks are cut by sills and a pluton of the same composition, representing intrusion of magma into its own volcanic pile. In the Bucks Lake quadrangle the composition of the parent magma was close to that of metadacite. Crystallization and segregation of mafic minerals and calcic plagioclase produced metagabbro and meta-andesite; the rest of the magma was left poor in the constituents of the early crystallized minerals and solidified as sodarhyolite and trondhjemite.
PLUTONIC ROCKS DISTRIBUTION AND DIVISION
The Bucks batholith, a unit on the geologic map of the Bidwell Bar quadrangle (Turner, 1898) and on the Chico Sheet (Burnett and Jennings, 1962), comprises three plutons, each petrologically distinct and separated from the others by a zone of metamorphic rocks. The Grizzly pluton is the largest, underlying about 86 square miles in the central and northern parts of the Pulga quadrangle. The exposed area of the Bucks Lake pluton is about 78 square miles: 55 square miles in the Bucks Lake quadrangle and 23 square miles in the adjoining part of the Pulga quadrangle. The third pluton, the Oliver Lake pluton, is small and kidney shaped and lies north of the other two. It covers 6 square miles in the northernmost part of the Pulga quadrangle and adjoining part of the Jonesville quadrangle.
Other plutons include the Granite Basin pluton, a small round pluton south of the Bucks Lake pluton which has an area of about 6 square miles. The Merri-mac pluton, which was studied earlier (Hietanen, 1951), extends into the southern part of the Pulga quadrangle. The eastern marginal zone of a small pluton exposed around Concow Reservoir in the Paradise quadrangle extends to the southwest corner of the Pulga quadrangle. The five western plutons, Grizzly, Oliver Lake, Granite Basin, Merrimac, and Concow, are petrologically similar, grading from hornblende-quartz diorite at the borders td monzotonalite in the central parts. The eastern plutohs dlffer from these and from each other considerably. The Bucks Lake pluton has a pyroxene-bearing center that grades through hornblende diorite to hornblende-biotite-quartz diorite at the borders. In the southern part of the Bucks Lake quadrangle, part of a large pluton, here called the Hartman Bar pluton, and several small stocklike masses consist of biotite and epidote tonalite.
The plutonic rock names used in this report are based on normative amounts of minerals, particularly on the composition of normative feldspar in the rocks, following thus the subdivision of the granitic rocks by Hieta-
499-964 0-73-436
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
nen (1961). Some of the mineralogically and chemically similar rocks in this area and in the central Sierra Nevada have been given different names (Bateman and others, 1963, 1966, 1967) because those authors used the modal classification.
BUCKS LAKE PLUTON
The Bucks Lake pluton has an exceptional structure and unusual distribution of rock types, indicating a complicated history of intrusion. Its central part consists of massive fine-grained pyroxene diorite and coarser, slightly foliated hornblende-pyroxene diorite; the border zones are strongly foliated hornblende-biotite quartz diorite. A narrow contact zone of hornblende diorite between the pyroxene-bearing center and quartz-rich border zone is texturally similar to the pyroxene-bearing phase and is probably an altered border phase of hornblende-pyroxene diorite. It will be shown that the pyroxene-bearing center is older than the rest of the pluton and can be considered as a huge inclusion in the hornblende-biotite quartz diorite. The evidence is based on the petrology and structure and is supported by absolute age determinations by Gramme, Merrill, and Verhoogen (1967).
PYROXENE DIORITE AND HORNBLENDE-PYROXENE DIORITE
The pyroxene-bearing center of the Bucks Lake pluton is well exposed around Bald Eagle, on Bucks Mountain, and on Camp Rodgers Saddle. Most outcrops consist of two distinct rock types: a fine-grained granoblastic pyroxene diorite and coarser grained hornblende-pyroxene diorite. The fine-grained variety is locally brecciated and occurs as inclusions in the coarse rock, and thus appears to be older. The structural and petrologic relations suggest that fine-grained variety is an early crystallized phase (roof?) of the same magma from which the hornblende-pyroxene diorite crystallized somewhat later. There are distinct differences and similarities in their mineralogy and structure, described in the next two sections.
STRUCTURAL RELATIONS
Swarms of inclusions of fine-grained pyroxene diorite in coarser hornblende-pyroxene diorite are common around Bald Eagle, at Bucks Mountain, and west of Camp Rodgers Saddle. The inclusions are round or ellipsoidal and range from a few centimeters to 1 m or more in diameter (10-20 cm is most common). The inclusions on the east slope of Bald Eagle are round or slightly angular with round corners (fig. 23). On the west slope, where foliation of the host rock is flat lying, the inclusions are flattened parallel to this plane (fig. 24). Flattened and elongated inclusions of finegrained pyroxene diorite also occur southeast of Cape
Figure 23.—Round inclusions of fine-grained pyroxene diorite in coarser grained pyroxene-hornblende diorite. Bucks Lake pluton, 1 mile southeast of Bald Eagle.
Figure 24.—Flattened inclusions of pyroxene diorite in pY roxene-hornblende diorite, north of Bald Eagle (loc. 533).PLUTONIC ROCKS
37
Lake and 1 mile southwest of Three Lakes near the border zone of the pyroxene-hornblende diorite.
The large inclusions and much of the continuous exposure of fine-grained pyroxene diorite north and south of Bald Eagle contain irregular masses and stringers of coarse-grained hornblende, rarely of hornblende and plagioclase (fig. 25). Similar segregations
Figure 25.—Segregations of hornblende (ho) and plagioclase (pla) in pyroxene diorite, Bucks Lake pluton southeast of Bald Eagle. The faint lines that are nearly perpendicular to the top and bottom of the photograph are joints.
occur in places in coarse-grained hornblende-pyroxene diorite next to and between the fine-grained inclusions. There is every gradation from these hornblende-rich segregations to sporadically occurring clusters of hornblende, which are scattered in the coarse-grained hornblende-pyroxene diorite between the inclusions. Many outcrops give the impression that the finegrained pyroxene diorite was fractured in an irregular manner and that hornblende crystallized along these fractures and replaced the other minerals, particularly the pyroxene. A part of the components of plagioclase moved out, and another part precipitated as coarsegrained pegmatitic material with hornblende (fig. 25) along the fractures.
At lower elevations around Bald Eagle and Bucks Mountain the hornblende-pyroxene diorite is medium grained and equigranular and shows a weak foliation because of subparallel orientation of plagioclase and pyroxene. Scattered fine-grained inclusions are far less common in this type, and only a few outcrops have segregations of hornblende. In most outcrops the medium-grained variety is fairly homogeneous.
The plane of foliation can be measured in the medium-grained hornblende-pyroxene diorite, but not in the fine-grained pyroxene diorite, except where inclusions are flattened in the plane of foliation. Dips are 15°-40°, and strikes are subparallel to the contacts or to the major regional trend.
PETROGRAPHY
The fine-grained pyroxene diorite and the inclusions consist mainly of plagioclase (An48.56), augite, hypers-thene, and magnetite. Sporadic clusters of olive-green hornblende and a few grains of quartz occur in some outcrops. Tiny crystals of apatite are few and scattered. Pyroxene is in small subhedral grains (0.2-0.6 mm, rarely larger) that have rounded corners. Plagioclase crystals are much larger (0.5-2.5 mm) and include small rounded pyroxene crystals (fig. 26). Magnetite
lmm
Figure 26.—Photomicrograph of pyroxene diorite. Plagioclase (pi) is subhedral, oriented at random, and includes small pyroxene (px) grains. Bucks Lake pluton, location 125, one-half mile northwest of Lower Bucks Lake.
grains, irregular in shape, occur with pyroxene. Plagioclase is complexly twinned but rarely zoned. The zoning when present is very weak and irregular; nevertheless, it indicates a slightly higher An content in the central parts of the grains.
The indices of refraction of hypersthene measured in specimen 125 are «=1.688±0.001, /?=:1.699±0.001, y=1.702±0.001. Diopside in the same rock has «= 1.684±0.001, /?=1.691±0.001, y=1.714±0.001. Some of the hypersthene shows exsolution lamellae of clino-pyroxene parallel to the prismatic cleavage. Much of the magnetite is included in pyroxene, and some this included magnetite is enveloped by green hornblende. Chemical analysis of pyroxene diorite (No. 125, table 3) shows about equal amounts of oxides of magnesium, total iron, and calcium and more than 50 percent Si02.
In some specimens, pyroxene is partly altered to green hornblende and chlorite. Some of the plagioclase (for instance, in specimen 495) includes fine-grained aggregates of zoisite. In these aggregates, individual grains have subparallel orientation that seems independent of crystallographic planes of plagioclase. These aggregates seem to be remnants of calcium-rich inclusions, perhaps of meta-andesite. Indeed, some of them38
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
Table 3.—Chemical composition, molecular norms and calculated modes of plutonic rocks in the Bucks Lake and Pulga
quadrangles
[Analysts: G. O. Riddle for samples 125, 122, 474, 209, 522, 521; C. L. Parker for samples 707,
844, 837, 699; V. C. Smith for sample 293]
Specimen			 125	707	844	293	837	122	474	209	522	521	699
Rock type			Hornblende Pyroxene-		Hornblende	Hornblende-biotite			Tonalite	Hornblende	Monzotonalite	
	diorite	diorite	hornblende	diorite		quartz diorite			quartz		
			diorite	dike					diorite		
Locality			 V2 mile	Workmans	Bald	South side	1 mile	West shore	V2 mile	1 mile	Robinson	0.8 mile	Big
	northwest	Bar,	Eagle	of Three	south of	of Bucks	south of	east of	Mine	south of	Kimshew
	of lower	North Fork			Three	Lake	Silver	Hartman		Grizzly	Creek
	Bucks	Feather			Lakes		Lake	Bar,		Summit	east of
	Lake	River						Middle			Bald
								Fork			Mountain
								F eather			
								River			
Chemical composition, in weight percent											
SiO: 			 52.95	53.14	53.45	56.89	57.76	58.41	62.18	60.83	63.18	66.85	71.61
TiO, 		1.10	1.04	1.05	.76	.82	.81	.66	.44	.61	.40	.22
ADO. 			 15.75	15.99	17.50	15.98	17.13	16.47	16.28	18.38	17.10	16.58	14.77
Fe,03 		2.61	1.96	2.52	1.94	2.19	1.65	1.50	2.73	1.64	1.23	.73
FeO		5.49	5.26	4.59	4.23	3.67	3.60	3.33	2.26	2.70	1.83	.97
MnO 			13	.12	.11	.10	.10	.09	.09	.13	.08	.07	.04
MgO 		8.85	8.29	6.92	6.37	4.67	4.93	3.51	2.07	2.56	1.74	.92
Cat) 		9.03	8.57	8.82	6.83	7.17	7.15	5.69	5.80	5.43	4.16	2.57
Na,t> 		3.41	3.45	3.78	3.97	4.05	4.43	4.34	3.53	4.17	4.41	3.94
K;() 			22	.58	.35	.91	1.14	1.10	1.20	1.39	1.11	1.83	3.50
P,(>, 			25	.22	.28	.18	.20	.44	.16	.18	.18	.14	.06
CO, 			01	0	.01	.09	.04	.01	.01	.01	.06	.02	.03
Cl 			01	.06	.02	.01	.04	.04	.02				.01
F 			02	.04	.02	.04	.04	.03	.03	.03	.03	.03	.02
H,0* 			19	1.20	.29	1.20	.84	.73	.76	2.04	1.01	.67	.41
ILO 			07	.06	.13	.06	.13	.01	.05	.05	.08	.04	.11
Subtotal 			 100.09	99.98	99.84	99.56	99.99	99.90	99.81	99.87	99.94	100.00	99.91
Less 0			01	.03	.01	.02	.03	.02	.01	.01	.01	.01	.01
Total 			 100.08	99.95	99.83	99.54	99.96	99.88	99.80	99.86	99.93	99.99	99.90
Chemical composition, in ionic percent
SiO,		.. 48.58	49.25	49.27	53.01	53.71	54.01	57.96	57.95	59.20	62.31	66.99
TiO, 		.76	.72	.73	.53	.57	.56	.46	.32	.43	.28	.15
AIO3/2 		17.03	17.47	19.01	17.55	18.77	17.95	17.89	20.64	18.88	18.21	16.28
Fe+303/2 		1.80	1.37	1.75	1.36	1.53	1.15	1.05	1.96	1.16	.86	.51
Fet:0 		4.21	4.08	3.54	3.30	2.85	2.78	2.60	1.80	2.12	1.43	.76
MnO 		.10	.09	.09	.08	.08	.07	.07	.10	.06	.06	.03
MgO 		.. 12.10	11.45	9.51	8.85	6.47	6.79	4.88	2.94	3.58	2.42	1.28
CaO 				8.88	8.51	8.71	6.82	7.14	7.08	5.68	5.92	5.45	4.15	2.58
NaO,, 		6.07	6.20	6.76	7.17	7.30	7.94	7.84	6.52	7.58	7.97	7.15
KO: 2 		.26	.69	.41	1.08	1.35	1.30	1.43	1.69	1.33	2.18	4.18
PO5/2 		.19	.17	.22	.14	.16	.34	.13	.15	.14	.11	.05
CO, 			.01		.01	.11	.05	.01	.01	.01	.08	.03	.04
Cl 		(.02)	(.09)	(.03)	(.02)	(.06)	(.06)	(.03)				(.02)
F 			(.06)	(.12)	(.06)	(-12)	(.12)	(.09)	(.09 j	(.09)	(.09)	(•09)	(.06)
OH 				(1.16)	(7.42)	(1.78)	(7.46)	(5.21)	(4.50)	(4.73)	(12.96)	(6.31)	(4.17)	(2.56)
Total 		99.99	100.00	100.01	100.00	99.98	99.98	100.00	100.00	100.01	100.01	100.00
Total anions .. ..	.. 156.56	160.13	158.12	163.06	163.18	162.43	165.94	172.27	168.74	169.42	171.35
Catanorm, in molecular percent											
Q 		1.00	1.13	2.06	6.20	7.98	7.08	13.93	18.48	17.64	20.85	26.53
Or 		1.29	3.43	2.06	5.41	6.76	6.49	7.13	8.45	6.63	10.88	20.88
Ab 		.. 30.25	30.53	33.62	35.78	36.19	39.40	39.06	32.60	37.88	39.85	35.65
An 		26.81	26.69	29.69	23.28	25.46	21.93	21.62	28.22	24.95	19.60	12.18
Co 									1.14		.23	.10
Wo	6.36	5.71	4.79	3 55	3 41	4.22	2 23		.25		
En 			24.21	22.90	19.02	17.69	12.95	13.59	9.75	5.88	7.15	4.83	2.57
Fs 		5.31	5.53	4.04	4.32	3.19	3.43	3.36	1.22	2.34	1.54	.76
Mt 		2.70	2.05	2.62	2.04	2.30	1.72	1.58	2.94	1.73	1.29	.77
II 	 			1.52	1.45	1.46	1.07	1.15	1.13	.93	.63	.86	.56	.31
Ap 		.52	.46	.58	.38	.42	.92	.34	.39	.38	.29	.13
Cc 		.03		.03	.23	.10	.03	.03	.03	.15	.05	.08
HI .. .	.03	.19	.06	.03	13	.13	.06				.03
FI 			.09		.11	.10		.07	.06'	.06	.08	.07
Total 		.. 100.02	100.15	100.03	100.09	100.13	100.06	100.08	100.04	100.04	100.05	100.06PLUTONIC ROCKS
39
Table 3.—Chemical composition, molecular norms and calculated modes of plutonic rocks in the Bucks Lake and Pulga
quadrangles—Continued
Specimen			 125	707	844	293	837	122	474	209	522	521	699
Rock type			 Pyroxene	Hornblende	Pyroxene-	Hornblende	Horn blende-biotite			Tonalite	Hornblende	Monzotonalite	
	diorite	diorite	hornblende	diorite		quartz diorite			quartz		
			diorite	dike					diorite		
Locality			 V£> mile	Workmans	Bald	South side	1 mile	West shore	y> mile	1 mile	Robinson	0.8 mile	Bift
	northwest	Bar,	Eagle	of Three	south of	of Bucks	south of	east of	Mine	south of	Kimshew
	of lower	North Fork		Lakes	Three	Lake	Silver	Hartman		Grizzly	Creek
	Bucks	Feather			Lakes		Lake	Bar,		Summit	east of
	Lake	River						Middle			Bald
								Fork			Mountain
								Feather			
								River			
Molecular mode											
Quartz 		1.00	8.2	1.7	11.2	11.3	11.9	18.4		21.3	23.3	27.7
Orthoclase 		1.29	2.0	1.6							4.9	17.7
Plagioclase 			 57.06	29.7	58.2	40.5	53.2	51.4	54.5		57.2	57.5	47.1
An 		(47)	(34)	(45)	(25)	(40)	(33)	(34)		(37)	(31)	(24)
Hypersthene 			 23.16	5.0	15.9								
Diopside 			12.73	5.8	4.5								
Hornblende 			46.9	16.9	40.3	22	22.6	11.9		6.6	2.7	1.4
Biotite 					10.8	19	18.7	19.5		17.8	14.5	7.7
Magnetite 		2.70	.4	(l.9				.3		6	.5	.4
Ilmenite 		1.52	.5		) 								
Sphene 						.4	.1	.4		.3	.2	.1
Apatite 			52	.4	.6	.4	.4	.9	.3		.4	.3	.1
Subtotal 			 99.98	98.9	101.3	103.2	106.3	105.6	105.3		104.2	103.9	102.2
aio3/2 			5.0	.1	+ 2.6	-.3		4				
OH 			3.6	.4		- .8	- 8	- 3		+ 2.1		+ .4
CaO								+ .2				
Total			107.5	101.8	105.8	105.2	104.8	104.4		106.3		102.6
also include green amphibole, and some a few flakes of chlorite and muscovite.
The large sporadic grains of hornblende are irregular in shape and include many rounded grains of plagio-clase and some round grains of pyroxene and magnetite forming a poikilitic texture. This hornblende crystallized late and replaced a part of plagioclase, pyroxene, and magnetite.
The coarse-grained pyroxene-hornblende diorite in which the inclusions of fine-grained pyroxene diorite occur consists of plagioclase (An46_48), augite, hypers-thene, hornblende, and magnetite. The main differences between the coarse host rock and the fine-grained inclusions are (1) a somewhat lower anorthite content in the plagioclase of the host, (2) a definite increase in the amount of hornblende (40-70 percent of the dark constituents), and (3) a larger grain size of the host. The difference in grain size is due mainly to the larger size of the plagioclase crystals (1-4 mm) and abundant large poikilitic hornblende. In addition to the poikilitic hornblende, green hornblende surrounds many pyroxene and some magnetite grains and is clearly secondary. The plagioclase crystals are tabular with irregular ends and have subparallel orientation.
In chemical composition, the pyroxene-hornblende diorite (No. 844, table 2) is similar to the pyroxene diorite, except for a higher content of A1203 and a little less FeO and MgO.
The medium-grained homogeneous hornblende-pyroxene diorite has 60-70 percent plagioclase (An46_48), 15 percent hornblende, and 15 percent
pyroxenes. Plagioclase crystals are 1-3 mm long and subparallel to the foliation. Most hypersthene crystals are rounded or have rounded ends. Alteration to chlorite and amphibole is common along the cracks, and many grains are spotted green because of partial alteration to hornblende. Pyroxene grains are commonly %-2 mm long. Magnetite and some apatite occur as accessory minerals. Some hornblende occurs as larger grains similar to the poikilitic hornblende in the coarse variety at Bald Eagle, but most hornblende is in small grains (1-2 mm), many of which have pyroxene cores. The poikilitic grains are usually olive green, whereas the secondary hornblende with pyroxene cores and the hornblende surrounding the magnetite have a bluish tint.
Secondary hornblende becomes more abundant and pyroxene less abundant toward the border zones of the hornblende-pyroxene diorite mass. Remnants of pyroxene in the centers of hornblende crystals can be easily recognized in the field because they are green on a fresh surface and they weather rusty brown.
HORNBLENDE DIORITE
A zone of hornblende diorite—a few meters to several hundred meters wide—occurs between the central pyroxene-bearing diorite and the hornblende-biotite-quartz diorite border zone. At higher elevations the hornblende diorite is medium grained; the dark hornblende crystals contrast with the square crystals of milky white plagioclase. In the canyon of the North Fork of the Feather River, which cuts through 4 miles40
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
of this zone, the hornblende diorite is dark gray, partly because of higher amphibole and magnetite contents and partly because of the dark-gray color of fresh plagioclase. The complete gradation from hornblende-pyroxene diorite to hornblende diorite reflects the decreasing amount of pyroxene toward the border zones of the pyroxene-bearing central mass. The intermediate rock next to the hornblende diorite has remnants of pyroxene at the centers of hornblende crystals. Textur-ally, the hornblende diorite is similar to the pyroxenebearing diorite, and many features in the mineralogy resemble the central mass more than the quartz dioritic border zone.
Plagioclase (usually An37_43) constitutes about 60 percent of the typical hornblende diorite at higher elevations. Darker masses at Bucks Mountain and in the river canyon have only about 40 percent plagioclase (An.!2_45) and are thus gabbroic diorite. The grains are tabular, 1-3 mm long, and oriented at random or subparallel to the contact. Segregations of fine-grained zoisite, in places accompanied by some tiny muscovite flakes, form irregular patches in plagioclase clusters. Some large plagioclase crystals (2-5 mm long), many of them zoned, occur in the rock exposed in the river canyon.
Quartz is scarce or absent; when present it is in interstitial small grains. A few sporadic grains of biotite occur in some thin sections.
Hornblende is pale to bluish green; many grains have colorless centers. Some of these centers consist of cum-mingtonite or of a mixture of cummingtonite and bluish-green hornblende; some include tiny grains of quartz. A few still have remnants of pyroxene surrounded by either colorless or blue-green amphibole. Segregations of dustlike magnetite are common at the outer border of the colorless centers.
At Workman’s Bar (loc. 707), several hypersthene crystals enveloped by a thin layer of blue-green amphibole occur in dark gabbroic hornblende diorite that contains abundant colorless amphibole included in green amphibole. Some amphibole grains have outlines of pyroxene and include tiny remnants of pyroxene. Many amphibole crystals with colorless centers occur in nearby outcrops of the same gabbroic hornblende diorite, but pyroxenes are lacking. Clearly, all pyroxene was altered to amphibole in this rock; this is supported by chemical similarities between this rock (No. 707, table 2) and the pyroxene diorite (No. 125).
In gabbroic hornblende diorite near Tobin, remnants of pyroxenes are surrounded by colorless and blue-green amphiboles and pseudomorphs consisting of a fine-grained mixture of amphiboles and chlorite but still showing outlines and relict cleavage of the former pyroxene. In places, this rock is fine grained and has a
texture typical of pyroxene diorite. Small grains of fer-romagnesian minerals, now pale-green amphibole with bluish rims, have shapes similar to the small grains of pyroxene in the pyroxene diorite. These textures, together with the similarity in chemical composition, show that the hornblende diorite is an altered border zone of the hornblende-pyroxene diorite. In some outcrops (loc. 410), large secondary grains of plagioclase (An32_33), biotite, and hornblende are embedded in the fine-grained partly altered pyroxene diorite, which contains a considerable amount of both pyroxenes, augite, and hypersthene. Similar gabbroic diorite and hornblende gabbro are included in pyroxene diorite near the east border of the Pulga quadrangle south of Bucks Creek.
HORN BLENDE-BIOTITE QUARTZ DIORITE The outer zone of the Bucks Lake pluton consists of light- to medium-gray coarse- to medium-grained hornblende-biotite quartz diorite. Foliation becomes increasingly more pronounced toward the border of the pluton (figs. 27, 28). For descriptive purposes, this zone is divided into three subzones on the basis of slight differences in mineralogy and texture. The innermost subzone, next to the pyroxene-bearing central mass, has more hornblende and less quartz than the middle subzone, and it contains a few inclusions of pyroxene-
012 3cm l__I_I_1
Figure 27.—Hornblende-biotite quartz diorite from the Bucks Lake pluton, 1 mile south of Three Lakes (loc. 837). Dark minerals are hornblende and biotite; light-colored minerals and plagioclase and quartz (table 3).PLUTONIC ROCKS
41
Figure 28.—Foliated border zone of hornblende-biotite quartz diorite of the Bucks Lake pluton, 1 mile south-southwest of Spanish Peak (loc. 195). Dark minerals are hornblende and biotite; light-colored minerals are plagioclase and quartz.
bearing diorite. Dark minerals are commonly oriented at random or show only poorly developed parallel orientation. The outermost subzone is strongly foliated and finer grained than the middle zone. It contains abundant long thin sheetlike inclusions of dark fine-grained hornblende-biotite-quartz-plagioclase gneiss, some of it rich in quartz and biotite. Along the southern contact, this zone grades to dark-gray coarse-grained hornblende-rich diorite and hornblende gabbro.
Thin sections show that the innermost subzone consists of 60-65 percent plagioclase (An37_40), 4-5 percent interstitial quartz, about 25 percent hornblende, 5-8 percent biotite and some magnetite, sphene, and apatite. Plagioclase crystals are tabular and 1-4 mm long; where foliation has developed, plagioclase crystals are subparallel to it. Hornblende and biotite crystals are large (1-3 mm) and irregular in shape. Many hornblende crystals have colorless centers that include small rounded blebs of quartz. These centers are similar to those in the outermost zone of the hornblende-pyroxene diorite and the hornblende diorite, and they have the same origin. They originally consisted of pyroxene, and a few of them still include remnants of pyroxene. When the pyroxene was altered to colorless amphibole, the excess Si02 was included as small blebs of quartz. Calcium and aluminum needed for this reaction were most likely derived from the anorthite component of plagioclase, as, for example, in the following reaction
3(Fe,Mg)Si03 + 2CaAl2Si208 + H20 -3 pyroxene -f anorthite + water
Ca2(Fe,Mg)3Al2(0H)2Si6Al2022 + Si02
hornblende	+ quartz.
The number of colorless centers decreases away from the pyroxene-bearing rocks. In the dark finer grained inclusions, some pyroxene persists, always covered by a shell of colorless to blue-green hornblende. It seems thus that the hornblende-biotite quartz diorite magma digested some of the earlier crystallized pyroxenebearing rocks.
Chemical analysis (No. 837, table 3) shows that the innermost subzone contains less MgO and CaO and more Si02 and K20 than pyroxene-hornblende diorite.
The middle subzone is lightest in color. Most of the rock in this zone contains about 15 percent hornblende, 10 percent biotite, 63 percent plagioclase (An33_35), and 7 percent quartz. The hornblende crystals are smaller (1-2 mm long) than in the inner zone and are subparallel to the foliation. The indices of refraction measured in specimen 122 are a=1.657±0.001, /?=1.672± 0.001, y=1.680±0.001. Biotite flakes, 1-2 mm long and having y=1.650±0.001, are subparallel to the foliation or segregated into laminae. Quartz is in medium-size grains between tabular plagioclase crystals (fig. 29). A few hornblende crystals have colorless centers that include small quartz blebs. Chemical analysis of a specimen (No. 122, table 3) from the west side of Bucks Lake is very similar to that of the inner zone. Pyroxene diorite exposed on a peninsula on the opposite side of
Figure 29.—Tabular plagioclase (pi) crystals oriented parallel to the foliation in hornblende-biotite quartz diorite of the Bucks Lake pluton. Quartz (qu) is in interstitial grains of medium size. Hornblende (ho) and biotite are either in individual grains or clustered in irregular lamellae parallel to the foliation. Location 846, 1 mile northeast of Bucks Lake. Crossed nicols.42
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
the lake may extend underwater, parallel to the foliation, and so location 122 may be closer to the contact of this pyroxene diorite than the map shows (pi. 2).
The outermost subzone is strongly foliated and contains sheetlike inclusions of altered wallrocks, now bio-tite gneiss, biotite-hornblende gneiss, and hornblende gneiss. Thin sections show textures typical of the felds-pathized contact aureoles. The large plagioclase grains have round ends and are embedded in a fine-grained matrix of quartz and biotite (fig. 30). Some hornblende
lmm
Figure 30.—Large plagioclase (pi) grains with round ends enveloped by trains of biotite (bi) and small interstitial grains of quartz (qu). Small hornblende (ho) crystals are clustered with biotite; large ones are rounded and embedded in quartz-biotite matrix. Foliated border zone of the Bucks Lake pluton, location 474, one-half mile south of Silver Lake. Crossed nicols.
is in large crystals that have round ends; smaller grains are clustered with biotite parallel to the foliation. Chemical analysis (No. 474, table 3) shows less MgO and CaO and more Si02 than in the inner zones. The indices of refraction of hornblende and biotite in specimen 474 are the same as those in specimen 122. This zone includes a large lens of pyroxene-bearing diorite at Spanish Peak and a small lens at Miller Fork.
Along the southern contact the foliated hornblende-biotite-quartz diorite grades to dark hornblende-rich diorite and hornblende gabbro. Along the northern and northeastern contacts, where the wallrocks are biotite phyllite and biotite quartzite, the contact is gradational over a few meters. Toward the contact the grain size of the phyllite and quartzite increases, and secondary large rounded or tabular grains of plagioclase and anhe-dral elongate grains of hornblende occur in increasing numbers in these metasediments, which are thus changed to gneissic rocks (fig. 31). The contact between the newly formed, rather fine-grained biotite-hornblende gneiss and the quartz diorite seems sharp in
Figure 31.—Biotite-hornblende gneiss just north of the northern contact of the Bucks Lake pluton (loc. 721). Large subhedral secondary crystals of plagioclase (pi) and hornblende (ho) are embedded in fine-grained metasedimentary matrix consisting of quartz, biotite, and some hornblende. Crossed nicols.
outcrops, but thin sections show that large plagioclase crystals in the foliated quartz diorite near the contact are enveloped by trains of small grains of quartz and biotite. In places, the matrix between the large plagioclase and hornblende crystals is similar to the biotite gneiss; the only difference between the gneiss and the foliated quartz diorite is that large grains of plagioclase and hornblende are more numerous in the quartz diorite.
The ellipsoidal shape of many secondary plagioclase grains in the gneiss contrasts with elongate and tabular shapes in the typically igneous middle subzone. This ellipsoidal shape persists in the foliated hornblende-bio tite quartz diorite 1 mile (see fig. 30) from the contact and thus is restricted to the zone where sheetlike inclusions and other wallrock remnants are common. The rounded ends of plagioclase crystals are bordered by small grains of quartz and not by plagioclase; thus rounding is not the result of postconsolidation granulation of plagioclase. Rounding must be due, instead, either to crystallization in the partly solid, still-mobile matrix or to growth in a solid rock, such as inclusions or walls, that was digested. Differences in other textures, particularly for quartz and biotite, should favor one of these two possibilities.
Firstly, quartz was last to crystallize from the magma and has preserved evidence of relations between the movements and final consolidation in the three subzones. In the innermost subzone, quartz is interstitial, only slightly strained, and not granulated. In the middle zone, quartz is in medium-size strained grains between large tabular plagioclase crystals and has been thus slightly granulated. In the outermost zone, it isPLUTONIC ROCKS
43
in small strained grains, suggesting postconsolidation movement. Thus, the degree of granulation increases toward the border. Such a relationship would result if, for instance, the outermost subzone solidified while magma was still moving in the inner zones. Complete lack of granulation in the innermost zone suggests that quartz there crystallized after the movements had ceased. Thus, consolidation proceeded in a normal way, from the borders toward the center.
Secondly, the following evidence suggests that much of the wallrock (biotite phyllite and quartzite) was digested by the invading magma: (1) Sheetlike inclusions of wallrocks, (2) discontinuous laminae of biotite,
(3)	numerous small remnants of biotite quartzite, and
(4)	increase in quartz content and decrease in hornblende content toward the outer border zone. Expansion of the intrusive body was thus partly a mechanical process and partly chemical. Chemical expansion occurred mainly near the walls, where feldspathization similar to that along the present contacts must have been in operation over a long period of time. Thus, the entire outermost shell, with its common wallrock remnants and ellipsoidal plagioclase crystals embedded in a finegrained quartz and biotite matrix, may have been a gradually migrating contact zone. If so, the pronounced foliation next to the contact is in part inherited from the wallrock, and the oval shapes and sutured borders of the plagioclase crystals result from having grown in generally solid rock.
Both of these explanations differ from the assumption by Gromme, Merrill, and Verhoogen (1967), who considered the foliated texture of the outermost shell to be due to postconsolidation pervasive cataclasis. Thin sections show that some of the tabular plagioclase crystals in the middle zone have been bent and a few broken, probably by movement of a crystal mush that still had some interstitial liquid. Signs of strain in the plagioclase of the outermost shell are no more pronounced than in the middle subzone, and as just discussed, the ellipsoidal shape could not have been produced by cataclasis alone since the crystals are embedded in a mixture of small grains of quartz and biotite. The evolution of this pluton is discussed further after description of the neighboring plutons.
HORNBLENDE GABBRO
The hornblende-rich differentiates that occur as long thin masses along the southern contact of the Bucks Lake pluton consist of plagioclase and hornblende in varying amounts. The darkest varieties contain about 20 percent plagioclase and 80 percent hornblende. These grade to normal hornblende gabbro with about equal amounts of hornblende and plagioclase and further to hornblende quartz diorite with about 30-40 percent
hornblende, 60 percent plagioclase, and small amounts of quartz and biotite. All these dark border phases contain abundant alteration products, such as epidote and sericite included in plagioclase, and chlorite and rutile in amphibole. Amphibole is most likely primary; it is green to pale green or colorless. Magnetite and sphene occur as accessory minerals.
SATELLITIC BODIES OF PYROXENE DIORITE AND HORNBLENDE DIORITE
Four small bodies of pyroxene-bearing diorite or hornblende diorite are exposed in the northwestern part of the Pulga guadrangle. Three of these are west of the Grizzly pluton, and one is on the west side of the Oliver Lake pluton.
A small elongate body of pyroxene diorite on the west side of the Grizzly pluton is well exposed at Oak Point. It extends northward for about 2 miles and is 50-200 m thick. The main part is fine-grained gray rock consisting of pyroxene and plagioclase (An46_48) with magnetite and very little hornblende. Pyroxene is mostly augite, but some is hypersthene. Hornblende is an alteration product after pyroxene.
An olivine-bearing dark pyroxenite is exposed in a roadcut 1 mile north of Oak Point (loc. 917). This rock is coarse grained and consists mainly of clinopyroxene, orthopyroxene, and olivine. Some brown hornblende with inclusions of brown rutile and few grains of plagioclase (An43) are interstitial. Olivine is included in clinopyroxene. Orthopyroxene has exsolution lamellae of clinopyroxene parallel to the cleavage. Numerous tiny magnetite grains are also included in orthopyroxene. Some tremolite occurs as an alteration product. This pyroxenite grades over to hornblende-pyroxene gabbro and further to hornblende diorite on its west side.
The hornblende diorite west of the pyroxene diorite at Oak Point resembles mineralogically and texturally the altered border zone of the pyroxene diorite in the Bucks Lake pluton. It consists of medium-gray fine- to coarse-grained hornblende-plagioclase rock with very little quartz and biotite. Plagioclase in hand specimen is bluish gray, a color that makes the hornblende diorite appear darker than is common in hornblende quartz diorite. Thin sections show that hornblende has bluish-green border zones and pale-green to colorless centers that include small round grains of quartz. Plagioclase contains An45 and is thus similar to the plagioclase common in the altered pyroxene-hornblende diorite. A small body of hornblende diorite on the east slope of Transfer Ridge about 1 mile west of Oak Point consists of medium-gray hornblende diorite similar to that at Oak Point. Another small body of similar hornblende diorite is exposed along Kimshew Creek northwest of Kimshew Point (loc. 1172).44
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
The hornblende diorite west of the Oliver Lake pluton is separated from the hornblende quartz diorite border zone of that pluton by darker dioritic and gabbroic rocks rich in hornblende. Hornblende-rich gabbroic rocks occur also on the west side, where a dike of hornblende quartz diorite, several meters wide, cuts these rocks. The southern part of this hornblende diorite body consists of dark-gray pyroxene-bearing rock that is very similar to the altered hornblende-pyroxene diorite in the Bucks Lake pluton. Thin sections show that many crystals of green hornblende, the major dark constituent in this rock, have colorless centers consisting of pyroxene and (or) of cummingtonite. The pyroxene was first partly altered to green hornblende, the necessary aluminum being derived from the anorthite molecule of the plagioclase. The remaining central part that was sheltered by green hornblende was altered to cummingtonite that shows characteristic polysynthetic twinning. Some augite and orthopyroxene are still included in a few grains.
The petrologic similarity between the rock types in these small satellitic bodies and the pyroxene and hornblende diorite in the Bucks Lake pluton is striking and can only be explained by a common origin.
GRIZZLY PLUTON
The Grizzly pluton is a typical representative of normally zoned plutons, which are common in the Sierra Nevada (Moore, 1963; Bateman and Wahrhaftig, 1966, p. 121). Its border zone consists of gray mediumgrained strongly foliated hornblende-biotite quartz diorite devoid of potassium feldspar (fig. 32). Toward the center, the rock becomes gradually lighter in color and the grain size coarser, and the foliation becomes indis-
012 3cm i-1-1-1
Figure 32.—Hornblende-biotite quartz diorite from the border zone of the Grizzly pluton. Dark constituents, hornblende and biotite, are subparallel to the foliation. Light minerals are plagioclase and quartz. Location 886, upper end of penstock at the mouth of Bucks Creek.
tinguishable (figs. 33, 34). The specimens collected across the border zone show a gradual increase in the amount of potassium feldspar and quartz and a decrease in the amount of dark constituents toward the center (table 4). In the central part the average potassium feldspar content is 5-15 percent, quartz 25 percent, and dark constituents (hornblende and biotite) 10-20 percent. The zoned plagioclase ranges from An25
Figure 33.—Coarse-grained inner border zone of the Grizzly pluton at Reese Flat (loc. 941). Dark minerals, hornblende and biotite, are subparallel to the foliation, which is still measurable.
Figure 34.—Light-colored monzotonalite from the central part of the Grizzly pluton. Dark minerals are biotite and hornblende, gray is quartz, and white is plagioclase and micro-cline.PLUTONIC ROCKS
45
Table 4.—Percentage of the major constituents measured in stained specimens of plutonic rocks [Nos. Mils, M119, M121 are from Hietanen (1951). Locations 145-699 are from central part of Grizzly pluton]
Distance from border Rock type in miles		Location	Specific gravity	Plagioclase		Quartz	Potassium feldspar	Hornblende and biotite
Grizzly pluton								
Hornblende quartz diorite		0.1	894	2.78	An*,	50.0	15.0	0	35.0
Do 		.1	M118		Ari;i4 44	48.9	16.7	2.3	32.1
Do 				.1	938	2.788		58.0	18.0	0	24.0
Do 				.6	887	2.785		54.0	20.0	1.0	25.0
Do 		.7	888	2.775	An,	53.8	17.1	4.5	24.6
Do 				.8	886	2.80	An™	52.1	14.5	2.9	30.5
Do 	 			1.0	885	2.74		57.0	13.2	.3	29.5
Do 				1.2	890	2.783	An™	54.0	20.0	1.0	25.0
Monzotonalite		.3	941	2.736		49.8	22.8	5.2	22.2
Do 			.4	1109	2.725		58.5	24.8	5.4	21.3
Do 		1.4	893	2.713	Attn	54.4	17.4	5.0	23.2
Do 	 			.5	M119			45.9	27.7	8.4	18.0
Tonalite 			... 1145	2.731	All25-37	62.3	20.5	1.0	16.2
Do 			... 1146	2.715		57.7	26.9	3.5	13.9
Do 			 			... 1144	2.72		57.0	23.0	2.0	18.0
Do 			... 1177	2.67		58.4	27.9	2.8	10.9
Monzotonalite 			... 1143	2.70	All31-35	57.4	25.0	6.4	11.2
Do 			... 1178	2.73		50.0	21.6	8.0	20.4
Do 			... M121		A1125-35	44.4	30.8	9.6	15.2
Do 				... 915	2.682	Ann	52.8	25.4	9.8	12.0
Quartz monzonite 			... 699	2.669	All25-35	48.8	27.3	16.9	7.0
Do 				... 1155	2.726		43.0	28.2	13.9	14.9
Granite northwest border facies ...		... 1134	2.642	All25-26	33.3	28.7	31.0	7.0
Granite dike 0.1 mile outside			... 1135	2.637		32.0	33.7	28.6	5.7
Oliver Lake pluton
Hornblende quartz diorite............. 948	2.795	An33.«	57.9	12.7	0	29.4
Do ................................ 1131	2.765	51.4	10.0	2.6	26.8
Do ...............................  1127	2.735	55.4	17.3	3.1	24.2
Do ...............................  1239	2.74	53.1	24.1	4.5	18.2
Monzotonalite ........................ 946	2.72	AnM	46.0	24.2	12.8	17.0
Do ................................ 1132	2.695	47.9	24.2	10.7	17.2
Do ............................... 1133	2.70	Aita	50.7	18.6	14.516.2
Granite Basin pluton
Hornblende quartz diorite................... 522	2.75	An^-ss	60.7	18.3	0	21.0
Do .................................... 799	2.76	61.6	11.9	0	26.5
Do ....................................... 747	2.70	58.3	23.5	.7	17.5
Do ....................................... 798	2.696	57.5	24.9	.8	16.8
Do ....................................... 775	2.71	55.1	29.4	2.2	13.3
Do ...................................... 1094	2.673	56.7	23.9	3.0	16.5
Monzotonalite ................................ 1255	2.73	54.9	26.2	5.8	13.1
Do .................................... 521	2.69	An*. 47	59.0	24.0	6.0_______11.0
Merrimac pluton
Hornblende quartz diorite.................... 1063	2.748	59.1	19.7	0	21.2
Do ..................................... 1077	2.74	62.1	19.2	.1	18.6
Do ..................................... 1076	2.67	61.6	25.4	0	13.0
Do ..................................... 1074	2.86	49.0	8.8	0	42.2
Do ..................................... 1003	2.73	58.7	21.2	2.6	17.5
Monzotonalite ............................. 1002	2.703 An2M4 52.3	27.2	5.5	15.0
Do ................................... M400	.... An^o	52.6	21.0	5.3	21.0
Do ................................... M312	.... An2o-3<>	58.0	26.0	10.5	10.5
Granitic dike ..............................  1009	2.64	47.0	34.3	19.0	5.0
Concow pluton
Hornblende quartz diorite............... 977	2.62	An32_35	56.4	18.7	3.2	21.7
Do ................................. 977a	2.61	52.0	34.3	0	13.7
Hartman Bar pluton
Trondhjemite................................ 1292	2.70	49.7	43.8	0	6.5
Do .................................... 1282	2.673	53.2	39.5	0	7.3
Tonalite.................................... 1281	2.75	57.9	31.5	0	10.6
Do ..................................... 584	2.68	An25.«	61.4	25.9	0	12.7
Hornblende quartz diorite................... 1214	2.77	An!(	61.0	17.7	0	20.4
Aplite dike ................................. 585________2.625	An^,	51.6_______25I8_______209________1.7
Satellites
Quartz diorite ................................... 1032___________2.765________Aita-is_______59.2_________17.9__________0___________22.846
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
at the rims to An:)5 at the centers and is thus more sodic than the plagioclase in the quartz dioritic border zone. (See table 4.) The rocks of the central part are grano-diorite according to Johannsen’s classification (1952).
Subdivision of such rocks by feldspar content has been suggested by Hietanen (1961,1963). According to this subdivision, the rocks of the interior of the pluton are monzotonalite, and those of the border zone are quartz diorite, with applicable mineral modifiers. The thickness of the quartz dioritic border zone varies: in the southeastern lobe it is more than 1 mile, whereas in the north and west sides of the pluton it is less than a quarter of a mile. Within this range, the percentage of dark constituents decreases from 30-35 percent to about 15 percent. In much of the central part, the monzotonalite is very light colored, containing only 7-12 percent dark constituents, 3-4 percent hornblende, and 3-8 percent biotite.
Thin sections of rock from the strongly foliated border zone show that it consists of hornblende-biotite quartz diorite in which plagioclase (Ani7_38), hornblende, and biotite are subparallel to the foliation. Plagioclase is in tabular crystals that are 2-3 mm long and have rounded or irregular ends. Hornblende (20-25 percent) and biotite crystals (10 percent) are rather irregular in shape and include quartz, sphene, and magnetite. Remnants of pyroxene occur in the centers of a few hornblende crystals near Storrie, between the west end of Oak Ridge and Grizzly Dome (fig. 35). At Oak Ridge, the pyroxene has Z A c=43°; it is enclosed in a shell of light-bluish-green hornblende which in turn is enclosed in a green hornblende shell. Patchy alteration of pyroxene to light-green hornblende is common. The primary hornblende in the same rock is olive green.
Vi mm
Figure 35.—Remnant of augite (a) and tiny inclusions of quartz (q) in hornblende (ho). Hornblende quartz dioritic border zone of the Grizzly pluton (loc. 890). Crossed nicols.
Magnetite, sphene, and epidote are clustered with hornblende and biotite. Small euhedral to subhedral crystals of apatite are included in plagioclase.
A few small interstitial potassium feldspar grains appear in the inner part of the foliated border zone. Their size and number increase within 100-400 m from the border toward the center to raise the amount of potassium feldspar along most of the contact from 1 to 4 percent. The rock within this inner border zone is coarser than the rock of the contact zone and slightly less foliated. Its color is lighter, owing to the smaller amount of hornblende (10-20 percent), than in the contact zone. Specimens 885, 886, 887, 888, 890, and 893 (table 4) in the wide border zone of the eastern lobe are representative of this type. Some of the potassium feldspar shows microcline grid structure, and some is un twinned.
A few plagioclase (An32.36) grains have myrmekitic border zones adjacent to the neighboring orthoclase. Grains of epidote are clustered with hornblende. Sphene is principally included in the biotite; some of the opaque iron ore (ilmenite-magnetite?) is rimmed by sphene.
Within the next 200-400 m toward the interior, the potassium feldspar content increases to about 8 percent (Nos. Ml 19, 941, 1109, table 4), and the hornblende content decreases to 10-15 percent. Much of the central part consists of very light gray coarse-grained massive monzotonalite in which potassium feldspar and dark-mineral contents show some local variation. In this rock, plagioclase (An25.j5) is in stubby, zoned, and complexly twinned euhedral to subhedral crystals (fig. 36) that are 1-3 mm long. Smaller crystals are included in large quartz grains. Potassium feldspar is interstitial and shows microcline grid structure or is untwinned.
Figure 36.—Monzotonalite southeast of Kimshew Point, Grizzly pluton (loc. 915). Microcline (mi) and some quartz (qu) are interstitial. Plagioclase (pi) is in stubby euhedral to subhedral crystals that are zoned and complexly twinned. Crossed nicols.PLUTONIC ROCKS
47
Biotite is the major dark constituent; flakes are 2-4 mm long, and many are partly altered to chlorite that includes small grains of sphene. Hornblende is in short prisms and in anhedral grains. Small grains of epidote and muscovite are included in plagioclase crystals. Large grains of epidote are clustered with hornblende and biotite. Sphene, magnetite, and apatite are common accessory minerals. Specimens 699, 915, 1143, 1144, 1145, 1146, 1177, and M121 (table 4) are representative of this central part. Chemical analysis of the lightest colored variety (No. 699, table 3) shows lower iron, magnesium, and calcium contents and higher potassium content than the border zone rocks. (Compare Hietanen, 1951, table 1, loc. Nos. 119, 121.)
Granite with about 30 percent potassium feldspar, 33 percent plagioclase (An25), 29 percent quartz, 6 percent biotite, and very little hornblende is the end member of the crystallization differentiation within this pluton (No. 1134, table 4). Dikes of the same composition (No. 1135, table 4) cut the plutonic rocks as well as country rocks. Chemical analysis of such a dike has been given earlier (Hietanen, 1951, loc. 116, table 1).
OLIVER LAKE PLUTON
The Oliver Lake pluton is normally zoned and resembles the Grizzly pluton except for some mineral-ogic differences in the mafic border zone. The quartz dioritic border zone is more than 1 mile wide on the west side of the southern part of this small pluton; elsewhere it is less than one tenth of this width. The southwestern border zone consists of medium-grained dark-gray slightly foliated rock in which tabular plagioclase crystals are subparallel to the foliation. The plagioclase shows complex twinning and is zoned (from An33 at the rims to An,s at the centers). The dark constituents, biotite and hornblende, make up 35 percent of the rocks (see table 4) and occur as fairly large crystals. Quartz (about 15 percent) is interstitial. Magnetite, epidote, and sphene are common accessory minerals.
Many hornblende crystals in this dark border zone have light-bluish-green to colorless centers that include tiny round grains of quartz. They are similar to the hornblende in hornblende diorite of the Bucks Lake pluton, in which rock this texture was traced to the alteration of pyroxene to hornblende. A few of the hornblende crystals in the Oliver Lake pluton still include augite, proving that here also the light-colored centers with quartz inclusions are relict texture after digested pyroxene. The northern part of this border zone contains more pyroxene, and near Mud Lake the border zone grades over to pyroxene-hornblende diorite.
Toward the east the dark border facies becomes lighter, and the amount of interstitial potassium feld-
spar increases. The rock grades over to a monzotonalite with 10-15 percent potassium feldspar (Nos. 946,1132, 1133, table 4). The rock around Ben Lomond is similar to the light-colored central part of the Grizzly pluton.
GRANITE BASIN PLUTON
The Granite Basin pluton is chemically and mineral-ogically similar to the Grizzly pluton. Its border zone is hornblende-biotite quartz diorite, and its center is monzotonalite (table 4). On the northwest side, the quartz dioritic border zone is only about 100 m wide; on the east side, it is about 1 mile wide. Most of the border-zone rocks are fairly coarse grained and weakly foliated. A fine- to medium-grained border phase with large plagioclase crystals is exposed on the bottom of Buckhorn Creek. Near the Robinson mine some of the biotite is altered to chlorite, and plagioclase (An25-40) contains epidote and sericite as alteration products. Some large grains of epidote are interstitial, whereas others occur next to biotite and hornblende or, more rarely, are included in these dark minerals. Hornblende is a common green variety and has a=1.656±0.001, y=1.678±0.001. Biotite is strongly pleochroic in browns and shows /3=y= 1.651 ±0.001. Chemical analyses and calculated norms of this rock (No. 522) are shown in table 3.
The inner border zone of the pluton contains about 3-10 percent interstitial potassium feldspar, most of which shows a good microcline grid structure. Plagioclase is euhedral to subhedral, strongly zoned, and complexly twinned. Many grains show oscillatory zoning. In others, a narrow rim of An20-25 surrounds a zoned core of An45_47. In a few cores, a small central part is as calcic as An,,0. The central parts of many plagioclase crystals contain small grains of epidote and muscovite as alteration products. Large grains of epidote occur with hornblende and biotite. The indices of refraction of hornblende measured in specimen 521 are a= 1.656 ±0.001, y=1.679±0.001. Biotite in the same specimen has /?=y=1.650±0.001 and thus is virtually the same as that in the quartz dioritic border zone. Quartz is in large- to medium-size grains that include small plagioclase grains or are interstitial. Magnetite, sphene, and apatite are the common accessory minerals.
In chemical composition, this rock (table 3, No. 521) is similar to the monzotonalitic inner border zone of the Grizzly pluton (Hietanen, 1951, table 1, loc. No. 119).
MERRIMAC PLUTON
The Merrimac pluton has already been described in a general way (Hietanen, 1951); some additional information is given here for comparison with the other normally zoned plutons.
The quartz dioritic border zone of this pluton is48
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
fairly narrow in the north and northwest, but wide in the northeast, where a coarse-grained massive hornblende quartz diorite rich in hornblende (No. 1074, table 4) is exposed west of the Tertiary basalt that covers a part of the border zone. Dark-gray foliated hornblende quartz diorite is exposed east of the basalt. The quartz dioritic border zone in this vicinity is about 1 mile wide; its mineralogy is similar to that of the border zone of the Grizzly pluton (Nos. 1063, 1074, 1076, 1077, table 4). The inner part of the border zone consists of light-gray massive monzotonalite that contains 2-7 percent potassium feldspar, about 15 percent dark constituents, and 25 percent quartz. In the central part of the pluton, the potassium feldspar content is higher (4-15 percent), and there is less hornblende and biotite (about 5 percent each). The mineralogy and chemical composition are similar to those of a specimen from the Grizzly pluton (No. 699, table 3).
CONCOW PLUTON
The easternmost part of a small pluton around Con-cow Reservoir is exposed on the southwest border of the Pulga quadrangle. The border zone of this pluton consists of coarse-grained light-gray foliated biotite-hornblende quartz diorite similar to parts of the marginal facies of the Merrimac pluton (table 4). Plagioclase (An32_35) in this rock is subhedral, strongly zoned, and complexly twinned. Biotite in large flakes is the major dark constituent (15 percent). Hornblende (7 percent) is bluish green and occurs in small prisms. Quartz (19 percent) is in large grains that include blocky crystals of plagioclase. Magnetite, sphene, apatite, and epidote occur as accessory minerals.
The contact between this biotite-hornblende quartz diorite and serpentine is exposed along a dirt road north of Pine Cluster Ranch (loc. 976). In the marginal zone of quartz diorite, biotite is altered to chlorite that includes sphene, epidote, and magnetite. Large grains of epidote make up about 10 percent of the rock. Plagioclase (An2G) includes grains of epidote and muscovite. A fine-grained gray dioritic dike separates this altered plutonic rock from the marginal talc-carbonate rock of the serpentine mass.
HARTMAN BAR PLUTON AND RELATED BODIES OF EPIDOTE TONALITE
One large and several small bodies of coarse-grained light-pinkish or greenish-gray massive tonalite are exposed in the southern part of the Bucks Lake quadrangle. The northern part of the largest body, the Hartman Bar pluton, is well exposed on the slopes of Hartman Bar ridge and on the steep lower canyon walls of the Middle Fork of the Feather River at Hartman Bar and to the southwest. Biotite is the only dark con-
stituent in this rock. It occurs as large flakes or as rather thick plates (0.5-1 cm long) that are oriented at random and give the rock a distinctive appearance. Thin sections show that the major constituents are plagioclase (An25-4o) in large subhedral to anhedral twinned and zoned crystals, strained quartz, biotite, epidote, and some muscovite. Hornblende and potassium feldspar are absent in the border zone exposed in the Bucks Lake quadrangle. In the southern part of the pluton, however, in the area currently being studied (fig. 1), a small amount of hornblende is common. Epidote occurs as large grains next to biotite. Magnetite, apatite, sphene, and zircon occur as accessory minerals.
In the northern border zone exposed along the river, biotite is altered to strongly pleochroic chlorite (y= green, a—pale-yellow green) that includes sphene, rutile, and leucoxene parallel to the cleavage. Plagioclase is altered to albite that includes numerous tiny grains of epidote and muscovite. The large grains of epidote, many included in chlorite, are more numerous than they are in the unaltered rock. Quartz is granulated and occurs in clusters of small strained grains between the large subhedral crystals of plagioclase. Chemical analyses show that the composition of the border zone (No. 209, table 3) is similar to that of the border zone of the Granite Basin pluton (No. 522, table 3). The unaltered rock farther from the contact has more potassium, all of which is in biotite, and less calcium, and thus much less epidote. These constituents, together with a higher percentage of quartz, bring the composition of the central part to that of tonalite (No. 584, fig. 40). Abundant hornblende in addition to chlorite crystallized near the contact with marble at Marble Cone. This hornblende is bluish green and occurs in slender euhedral to subhedral prisms included in large quartz and albite grains. Albite includes numerous tiny grains of epidote and muscovite. Calculation of chemical composition from the measured mode for sample 584 (quartz 24.7, plagioclase (An32) 60.7, biotite 12.7, muscovite 2.4, epidote 0.5, and magnetite 0.4 percent) shows that the essential difference between the Hartman Bar pluton and the other plutons is not in the chemical composition but in the mineralogy, which indicates lower temperature assemblages and more water for the Hartman Bar pluton.
Several small bodies of epidote-chlorite tonalite similar to the border zone of the Hartman Bar pluton occur in the southeastern part of the Bucks Lake quadrangle. The largest of these extends southward from Lookout Rock; the western part is covered by Eocene pyroclastic andesite. Hornblende quartz diorite borders this tonalite in the southwest. Two other bodies of similar tonalite are at the mouth of OnionDIKES ASSOCIATED WITH PLUTONIC ROCKS
49
Valley Creek and on the east slope of Dogwood Creek. In all these small bodies, as in the border zone of the Hartman Bar pluton, epidote is one of the major constituents (10-25 percent), and plagioclase, which makes up more than 50 percent of the rock, is albitic. Quartz makes up 20-30 percent, and chlorite 10-15 percent. Sphene and magnetite are the accessory min-erals. Small grains of epidote and muscovite are included in plagioclase.
Mineral assemblages in these masses are similar to those in the “altered trondjemite” at Big Bend (Hiet-anen, 1951, p. 579-580) and may belong to the same age group. Granulation of quartz and crystallization of epidote, muscovite, and chlorite from plagioclase and biotite indicate that these bodies were slightly deformed and partly recrystallized. In the largest body, the Hartman Bar pluton, only the outer zone is strongly altered; the central part remains fairly intact. The intrusive contact relations along the river show that the Hartman Bar pluton is younger than the meta-gabbro, which is considered to be an intrusive equivalent of meta-andesite.
DIKES ASSOCIATED WITH PLUTONIC ROCKS
Dikes of hornblende gabbro, hornblende quartz dio-rite, monzotonalite, granite, and pegmatite fill the fracture systems in the plutonic rocks and also cut the metamorphic rocks. These dikes differ from the plutonic rocks only in texture. Some are porphyritic; others are fine grained and similar to those in the Merrimac area (Hietanen, 1951, p. 584-586).
A gabbroic dike along the east contact of a small epidote tonalite mass in the southeast corner of the Bucks Lake quadrangle (loc. 598) consists mainly of hornblende and plagioclase. Hornblende prisms, 1-2 mm long, make up 40 percent of this rock. Aggregates of fine-grained chlorite have outlines indicating that they were formerly olivine crystals. Plagioclase (An38-4o) is interstitial to hornblende. Magnetite, sphene, epidote, and apatite are the common accessory minerals. In another gabbroic dike, which cuts the metamorphic rocks about 1 mile south of Deanes Valley (loc. 639), the plagioclase is in slender laths (0.5-1 mm long) oriented at random, and hornblende is interstitial.
A light-gray quartz diorite dike cuts the metamorphic rocks along the road to Bear Ranch Hill (loc. 909). In this dike, clusters and slender prisms of green hornblende are oriented at random in a fine-grained groundmass that consists of oligoclase, quartz, hornblende, and sparse biotite. A fine-grained silica mineral (originally chalcedony) fills the cavities in this dike. Magnetite partly altered to hematite and a few grains of epidote occur as accessory minerals. In the quartz diorite dike at Hartman Bar (loc. 208), phenocrysts
are hornblende and plagioclase. Hornblende crystals are euhedral and about 1 mm long; feldspar phenocrysts are studded with alteration products (muscovite and epidote). Groundmass is fine grained and consists of albite, quartz, epidote, and muscovite. Magnetite, sphene, and apatite occur as accessory minerals. A similar dike cuts the metadacite on the Little North Fork of the Middle Fork of the Feather River in the southeast corner of the Pulga quadrangle (loc. 253).
A quartz diorite dike that cuts the hornblende-biotite quartz diorite on the south side of Three Lakes was analyzed chemically (No. 293, table 3). In this dike, large clusters of hornblende and biotite and phenocrysts of hornblende (2-8 mm long) are embedded in a fine-grained groundmass consisting of slender prisms of hornblende (0.5-1 mm long), laths of plagioclase (0.1-0.3 mm long), tiny grains of quartz, small clusters of epidote, and a few grains of magnetite, apatite, and sphene. Clusters of hornblende and biotite have outlines suggesting that they are pseudomorphs after pyroxene.
A fine-grained dark monzotonalite dike in quartzite 1.5 miles north of Deadman Spring (loc. 142) consists of albite, quartz, biotite, and magnetite. Albite in tiny lath-shaped crystals and a few granulated quartz phenocrysts are embedded in a fine-grained ground-mass consisting of biotite, albite, and quartz.
Another porphyritic dike of monzotonalitic composition cuts phyllite 1 mile south of Haskins Valley (loc. 451). In this dike, numerous large (0.5-1 cm long) phenocrysts of albite (An5.10) with inclusions of orthoclase and a few phenocrysts of quartz are embedded in a fine-grained groundmass consisting of albite, quartz, and biotite. Magnetite and hematite occur as accessory minerals. Several porphyritic dikes of monzotonalitic composition north of the Bucks Lake pluton are well exposed along the North Fork of the Feather River (Iocs. 1029, 1039). Large (2-5 mm) phenocrysts of plagioclase (An28_43), in some dikes strongly zoned and containing epidote minerals and muscovite as alteration products, are embedded in porphyritic groundmass consisting of plagioclase, quartz, some orthoclase, hornblende, and biotite partly altered to chlorite. Magnetite, apatite, zircon, and sphene occur as accessory minerals.
A fine- to medium-grained gray granitic dike consisting of about 25 percent potassium feldspar, 35 percent plagioclase, 28 percent quartz, and 12 percent muscovite plus biotite is exposed at the headwaters of Marble Creek (loc. 1086) between metamorphosed sodarhyolite and biotite phyllite. Plagioclase (An12) is in subhedral to anhedral grains that are larger than the other mineral grains and include small round grains of quartz. Granophyric intergrowth of quartz and feld-50
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
spars is common. Magnetite, hematite, calcite, and epidote occur as accessory minerals.
MAGMA DIFFERENTIATION BASED ON COMPOSITION AND AGE OF PLUTONIC ROCKS
Chemical analyses shown in table 2 were plotted in ionic percentages in several ternary diagrams (figs. 37-40). The analyses published earlier (Hietanen, 1951, table 1) and those of the metamorphosed igneous rocks are included for comparison. The differentiation curves for the plutonic rocks were drawn by visual inspection.
Figure 37 shows variations in normative amounts of quartz, albite, and orthoclase, as computed from ionic percentages. Distribution of the points represents a continuous band that extends from the albite corner to the center of the diagram. The points at the albite corner represent the pyroxene diorite and its alteration product, hornblende diorite, of the Bucks Lake pluton. The points for the inner part of the hornblende-quartz dioritic border zone of this pluton form the next cluster toward the center. In this part, remnants of pyroxene occur in centers of some hornblende crystals. The outer
0	EXPLANATION
Figure 37.—Normative amounts of quartz (Q), albite (Ab), and orthoclase (Or) in molecular percent in the plutonic, meta-volcanic, and metamorphosed intrusive rocks in the Bucks Lake and Pulga quadrangles. The numbers refer to the analyses in tables 1 and 3; those with prefix M are from Hietanen (1951). Biotite tonalite (Nos. 584, 1210, 1272) percents are calculated from measured mode.
border zone of the Bucks Lake pluton (No. 474), as well as the quartz dioritic border zones of the normally zoned plutons (M118, 522), falls along the curve at 25 percent quartz and 12 percent orthoclase. The composition of the inner parts of the normally zoned plutons plots along the curve that trends toward the ternary eutectic, which is represented by the composition of aplitic granite dike rock (No. M116). This curve represents the trend of differentiation. In the normally zoned plutons, such as the Grizzly pluton, the composition from the border toward the center moves along this curve toward the ternary eutectic, as shown by M118, M119, M121, 699, and M116.
Variation in the normative amounts of plagioclase, quartz, and orthoclase shows a very similar trend (fig. 38). The points are somewhat more scattered, but are nevertheless clustered at the plagioclase corner and near the plagioclase-quartz sideline, from which the composition moves toward the ternary eutectic. In both figures 37 and 38, the points for the metamorphosed igneous rocks are scattered along the sideline away from the orthoclase corner, and many plot into the negative quartz side (below the baseline of the triangle).
Q	EXPLANATION
Figure 38.—Normative amounts of quartz (Q), plagioclase (PI), and orthoclase (Or) in the plutonic, metavolcanic, and metamorphosed intrusive rocks in the Bucks Lake and Pulga quadrangles. Numbers refer to analyses in tables 1 and 3; those with prefix M are from Hietanen (1951). Biotite tonalite (Nos. 584, 1210, 1272) percents are calculated from measured mode.I
MAGMA DIFFERENTIATION BASED ON COMPOSITION AND AGE OF PLUTONIC ROCKS	51
In a Q-M-F diagram (fig. 39), points for the plutonic rocks are clustered along and near a curve close to the F corner. The basic differentiates plot near the M-F sideline, and the silicic end members along the Q-F sideline of the triangle. The points for the metamorphosed igneous rocks show a wider scatter.
Figure 39.—Normative amounts of quartz (Q), mafic constituents (M) as orthosilicates (see Burri, 1964), and feldspars (F) in molecular percent in the plutonic, metavolcanic, and metamorphosed intrusive rocks in the Bucks Lake and Pulga quadrangles. Numbers refer to analyses in tables 1 and 3; those with prefix M are from Hietanen (1951). Biotite tona-lite (Nos. 584, 1210, 1272) percents are calculated from measured mode.
Variations in the feldspar composition are shown in the albite-orthoclase-anorthite diagram (fig. 40). Tielines for the subdivision of intermediate and silicic calc-alkalic plutonic rocks on the basis of their normative feldspar content (Hietanen, 1961, 1963) are also shown. The pyroxene diorite and the quartz dioritic border-zone rocks plot near the albite-anorthite sideline between An33 and An50, whereas in the inner zone the plagioclase is An2g_35, and orthoclase content is 15-30 percent. These rocks have the feldspar content of monzotonalite. Sample 699, which has the highest percentage of potassium feldspar among specimens from the coarse-grained central part of the Grizzly pluton (see table 4), plots close to the tieline through 30 percent orthoclase (thus, at the borderline between the monzotonalite and quartz monzonite). The light-colored border-zone rock on the northwestern part of the Grizzly pluton (Nos. 1134, 1135, table 4) is mineralogically similar to the pegmatite at locality Ml 16 and thus has the composition of a true granite. The differentiation curve in the Ab-An-Or diagram
An	EXPLANATION
Figure 40.—Normative amounts of albite, orthoclase, and anorthite in molecular percent in the plutonic, metavolcanic, and metamorphosed intrusive rocks in the Bucks Lake and Pulga quadrangles. Numbers refer to tables I and 3; those with prefix M are from Hietanen (1951). Biotite tonalite (Nos. 584, 1210, 1272) percents are calculated from measured mode.
trends from the diorite side of the albite-anorthite sideline through the monzotonalitic composition to granite. The plagioclase is usually An25-3T in the intermediate group with 10-15 percent modal orthoclase (table 4) and thus is less calcic than in the quartz diorite and in its potassium feldspar-bearing equivalent, grano-diorite.
The “altered trondhjemite” in the Big Bend area (Hietanen, 1951, table 1, loc. 328) plots in the tonalite group at the tieline through 15 percent orthoclase (M328). The large amount of epidote in this rock as well as in the border zone of the Hartman Bar pluton (No. 209) raises the normative anorthite content much above the modal content. For comparison, granite-trondhjemite (M204) from the Bald Rock pluton south of the Pulga quadrangle (Hietanen, 1951, table 1, loc. 204) and typical samples of biotite tonalite from the Cascade pluton (loc. 1210, 1272, pi. 3) plot outside the trend line in the albite-orthoclase-anorthite diagram. Compton’s study (1955) of the modal composition in the southern part of the Bald Rock pluton shows that most of its central part is similar to sample M204, and that this rock grades through monzotonalite and tonalite to hornblende-biotite quartz diorite toward the borders, thus closely following the dotted trend line in figure 40.
Clustering of all points along well-defined curves in all ternary diagrams indicates that all plutonic rocks in the Pulga and Bucks Lake quadrangles are differen-
499-964 0-73-252
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
tiates of the same parent magma, the oldest offshoots being most basic and the later ones becoming increasingly enriched in silicon, potassium, and iron, as is common in a normal differentiation series. On the other hand, the clustering of points for the hornblende quartz diorite (Nos. 293, 122, 837) halfway between the points for the pyroxene diorite and those for the horn-blende-biotite quartz diorite supports the conclusion that the hornblende quartz diorite may have digested large amounts of pyroxene diorite. This conclusion was arrived at on the basis of field evidence and study of thin sections as described in the following paragraphs.
In the field, pyroxene diorite was found as sparse inclusions in the hornblende quartz diorite; more commonly, rusty-weathering pyroxene is seen in the centers of some large hornblende crystals, a texture indicating that the hornblende quartz diorite has digested the older pyroxene diorite. The absence of potassium feldspar in the inner border zone of the Bucks Lake pluton can be a result of digestion of basic pyroxene diorite. Mixing of the pyroxene diorite (No. 125, table 3) and monzotonalite (Nos. M119, M121, table 4) in about equal amounts would give the composition of this zone (Nos. 837, 122). In accordance with this, pyroxene diorite may have occupied much wider areas than are now exposed. The presence of a few inclusions of altered pyroxene diorite in the eastern lobe of the Grizzly pluton suggests that pyroxene diorite was among the older rocks there. The exceptionally wide border zone east of Grizzly Dome consists of hornblende quartz diorite, in which some of the hornblende crystals still have pale-green centers and include small round grains of quartz, a feature that elsewhere was found to be a result of digestion of pyroxene-bearing rocks by the invading younger magma. A similar dark-gray wide border zone is in the southwestern lobe of the Oliver Lake pluton and is there bordered by pyroxene-bearing diorite to the north. In thin sections of rock from this border zone, a few grains of hornblende still include some pyroxene, and others have pale-green centers that include small round grains of quartz. The amount of quartz and biotite is less than in the normal hornblende quartz diorite. Also, this border zone may have digested pyroxene diorite that formerly occupied a much wider area than now exposed.
It is noteworthy that the hornblende in the specimen from the center of the eastern lobe of the Grizzly pluton shows the same age as the hornblende in the altered border zone of the pyroxene diorite (Gromme and others, 1967). The rock type at this locality is quartz diorite, according to Gromme, Merrill, and Verhoogen (1967). The surrounding rocks contain 8-9 percent potassium feldspar (table 4) and are monzotonalitic. It is possible that a part of the hornblende in the speci-
men collected by Gromme, Merrill, and Verhoogen (1967) is an alteration product after pyroxene and thus of the same age as the hornblende in the hornblende diorite. No age determinations are available for the pyroxene diorite, but the pyroxene is obviously older than its alteration product. According to Gromme, Merrill, and Verhoogen (1967, p. 5676), the hornblende diorite was magnetized at about the same time as the quartz diorite, but pyroxene diorite was magnetized at a different time.
Field evidence and thin sections show that all the pyroxene diorite is older than the hornblende quartz diorite-monzotonalite series. The alteration of pyroxene diorite to hornblende diorite was contemporaneous with intrusion of the hornblende quartz diorite-monzotonalite series. A part of the pyroxene diorite was subsequently digested by this younger magma. According to Gromme, Merrill, and Verhoogen (1967), the younger magma, the Merrimac pluton, is about 130 m.y. (million years) old. Biotite in the outer quartz dioritic border zone of the Bucks Lake pluton is of the same age (129 m.y.) as the monzotonalite (Gromme and others, 1967). The hornblende in the altered parts and in the products of digestion is 142-143 m.y. old and thus is older than the hornblende and biotite in the monzotonalite. Since alteration actually took place during the intrusion of monzotonalite magma, the age 142-143 m.y. is a mixed age. More argon was retained by this secondary hornblende than by the hornblende crystallized from the younger magma. The pyroxene diorite must have been intruded before the pyroxene was altered to hornblende and thus must be older than the mixed age of 143 m.y. The very different magnetic polarity suggests that it could be considerably older. The oldest potassium argon ages determined for hornblende in the plutonic rocks of the Sierra Nevada are 148 m.y. (Evernden and Kistler, 1970). The pyroxene diorite could have a comparable age.
Deformation and alteration of the small tonalite plutons in the southern part of the Bucks Lake quadrangle suggest that these plutons are older than the monzotonalite. The metamorphic rocks provide evidence of two episodes of recrystallization, the later episode being connected with the intrusion of the young plutons. The earlier episode was probably associated with the intrusion of pyroxene diorite and tonalite. It is noteworthy that the highest temperature mineral assemblages in the metamorphic rocks are in the part of the area where several small bodies of epi-dote tonalite are exposed. The age relations between the tonalite and the pyroxene diorite could not be determined because these rocks are nowhere in contact. The tonalite has a lower temperature mineral assemblage, possibly because the tonalite magma con-TRACE ELEMENTS IN PLUTONIC AND METAMORPHIC ROCKS
53
tained more water. No age determinations of the unaltered biotite tonalite of the Hartman Bar pluton are available at present.
TRACE ELEMENTS IN PLUTONIC AND METAMORPHIC ROCKS
A study of trace-element content yields important additional information about the different magma types and supports the conclusion that the metavolcanic rocks and the early intrusive masses are genetically related. Quantitative spectrographic analyses of trace
elements in the samples that were analyzed chemically are shown in tables 5 and 6. All samples contain appreciable amounts of Ba, Sr, Cu, V, Cr, Ni, and Zr and low concentrations of Co, Ga, Y, and Sc. A small amount of B (80-90 ppm) occurs in the metasedimentary rocks that contain a few small grains of tourmaline.
For comparison, the average concentrations of trace elements in rocks of very similar silica content in each group (plutonic, metamorphosed plutonic, metavolcanic, and metasedimentary) were plotted in figure 41 as functions of Si02, which serves as an index of differ-
Table 5.—Trace elements in plutonic rocks in the Bucks Lake and Pulga quadrangles, in parts per million
[Analyst: Harriet Nieman. Looked for but not found (some found in samples 293) : Ag, As, Au, B, Be, Bi, Cd, La, Mo, Nb, Pb, Pd, Pt, Sb, Sn, Te, U, W, Zn,
Ce, Ge, Hf, In, Li, Re, Ta, Th, Ti, Eu]
	125	707	844	293	837	122	474	209	522	521	699
Ag 	 B 	 Ba 			 210	250	94	<2 <50 360	420	400	500	550	490	650	520
Be 	 Cd 	 Co 			 39	35	16	<10 <200 32	21	22	17	10	13	8	4
Cr			 600	610	210	420	174	250	112	17	39	28	17
Cu 			 200	71	34	71	49	20	28	2	3	10	6
Ga 			 19	19	8	23	18	18	19	21	19	19	15
Ge 	 La 	 Mo 	 Nb 	 Ni 			 159	490	87	<50 <100 <5 <20 180	62	120	56	<5	26	12	6
Pb 	 Sc			 51	40	11	<50 29	22	30	25	17	17	10	<50 5
Sn 	 Sr 			 560	570	183	<50 810	430	680	400	440	490	440	300
V 			 320	220	108	180	250	162	137	137	128	76	38
Y 			 25	35	<20	20	37	26	28	22	22	17	<20
Yb 			 2	3	<2	3	2	2	2	2	2	1	
Zr 			 50	90	<50	110	90	210	300	131	110	150	48
Table 6.—Trace elements in metamorphosed igneous and sedimentary rocks in the Bucks Lake quadrangle, in parts per million
[Analyst: Harriet Nieman. Looked for but not found (some found in samples 85, 465, and 551) : Ag, As, Au, B, Be, Bi, Cd, La, Mo, Nb, Pb, Pd, Pt, Sb, Sn,
Te, U, W, Zn, Ce, Ge, Hf, In, Li, Re, Ta, Th, Tl, Eu]
	134	796	532	465	551	463	464	461	85	104
Ag 	 B 	 Ba 			 4	20	20	<2 <50 10	<2 <50 100	5	25	44	<2 80 1800	800
Be 	 Cd 	 Co 			 95	22	24	<10 <200 28	<10 <200 40	32	30	10	<10 <200 7	9
Cr 			 2200	260	140	290	12	23	204	6	54	87
Cu 			 110	2	54	110	18	298	172	38	110	70
Ga 			13	18	15	20	22	16	15	19	14
Ge 	 La 	 Mo 	 Nb	 Ni 			 2000	37	36	<50 <100 <5 <20 80	<50 <100 <5 <20 46	45	60	<5	<50 <100 <5 <20 50	36
Pb 	 Sc 			 18	58	53	<50 70	<50 67	91	94	26	<50 19	10
Sn 	 Sr 			167	270	<50 340	<50 80	450	127	194	<50 60	61
V 			 50	146	360	200	310	640	280	144	100	72
Y 				26	30	60	35	43	23	20	32
Yb 				2	4	7	4	5	2	4	3
Zr 				<50	70	130		62	112	130	173TRACE-ELEMENT CONCENTRATION, IN PARTS PER MILLION
um	mgb mdi mv
_]___l_____l_____l__l____l_l_l_
40	45	50	55
pxd hd	qd
_J	_____l_______I____l_____I__
60	50	60
Si02 CONTENT, IN WEIGHT PERCENT
mto
_l___i
70
70
ms
i i
75
J
80
Figure 41.—Average trace-element concentration in plutonic, metaigneous, and metasedimentary rocks in the Bucks Lake quadrangle. Pxd, average for pyroxene diorite (Nos. 125, 707, 844, table 5); hd, average for hornblende-quartz diorite (Nos. 293, 837, 122, table 5); qd, average for quartz diorite (Nos. 474, 209, 522; including monzotonalite, 521, table 5); mto, monzotonalite (No. 699, table 5); mv, average for metavolcanic rocks (Nos. 463, 464, 461, table 6); mdi, average for meta-diorite (Nos. 532, 465, table 6); mgb, metagabbro (No. 796, table 6); um, ultramafic rock (No. 134, table 6); and ms, average of metasedimentary rocks (Nos. 85,104, table 6).TRACE ELEMENTS IN PLUTONIC AND METAMORPHIC ROCKS
55
entiation. In the plutonic sequence, the decrease of Cr, Ni, Co, Cu, V, and Sc and increase of Ba with increasing Si02 are well demonstrated. Sr and Zr show the highest concentration in the intermediate members, whereas the averages of Ga and Y stay nearly constant through the plutonic series. Trace-element content in the border zone of the Bucks Lake pluton is similar to that in the metasedimentary rocks (ms in fig. 41), except for considerably more Sr and less Ba and Cu in the plutonic rock. The high concentrations of Sr reflect the large amount of plagioclase in the quartz diorite, whereas Ba is contained in biotite (0.30 percent), most of which is in the metasedimentary rocks.
Comparison of the plutonic sequence with the meta-igneous sequence shows that the average concentrations of Co, Ga, Y, and Zr in the intermediate meta-igneous (metadiorite) and metavolcanic rocks (mdi and mv in fig. 41) are close to those in the pyroxene diorite and hornblende quartz diorite (pxd and hd in fig. 41), whereas the average concentrations of Ba and Ni are much lower, those of Sr and Cr are a little lower, and those of Cu, V, and Sc are higher in the metamorphosed igneous rocks.
The ratios K/Sr, K/Ba, Sr/Ba, and Ca/Sr for plutonic and metaigneous rocks were plotted on a logarithmic scale using weight percentage of K as an index of differentiation (figs. 42, 43, 44, 45). In each of four diagrams (figs. 42-45), the metamorphosed plutonic
Figure 43.—Distribution of potassium-barium ratios as function of potassium. The numbers refer to tables 5 and 6.
Figure 44.—Distribution of strontium-barium ratios as function of potassium. The numbers refer to tables 5 and 6.
Figure 42.—Distribution of potassium-strontium ratios as function of potassium. The numbers refer to tables 5 and 656
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
POTASSIUM CONTENT, IN WEIGHT. PERCENT Figure 45.—Distribution of calcium-strontium ratios as function of potassium. The numbers refer to tables 5 and 6.
rocks plot within the region defined by metavolcanic rocks; thus the two groups of rocks may be genetically related. In contrast, the younger plutonic rocks are much richer in K, and all ratios show definite trends. K/Sr and K/Ba ratios increase with increasing K, whereas Sr/Ba and Ca/Sr ratios decrease with increasing K.
The trends of K/Ba, Ca/Sr, and Sr/Ba ratios for the plutonic sequence are very similar to those for the continental basalt, as shown by Condie, Barsky, and Mueller (1969), whereas the trend of K/Sr ratio is well between those for submarine and continental basalts of these authors. The metaigneous rocks plot in the area occupied by ultramafic rocks and chondrites. Their exceptionally low K content may have been accentuated during metamorphism by removal of some K. The differences in the trace-element content, together with the low K content, suggest a different source for these two magmatic sequences.
GOLD-QUARTZ VEINS
Several low-grade gold-quartz veins are in the area. Some have been mined in the past; others are now being developed. Averill (1937) described two mines: the Robinson mine on the southeast border of the Bucks Lake quadrangle and the Virgilia at the mouth of Rush Creek on the East Branch of the North Fork of the Feather River. In addition to these two, the Shenandoah mine east of Rich Bar, the Silver Star mine 1 mile east of Coyote Gap, and the Little Nell mine east of Deadman Spring have produced in the past. Mines presently being developed are the Ontop mine on Willow Creek in the Bucks Lake quadrangle and the 3-Ravines mine about 2 miles southwest of Coyote Gap in the Pulga quadrangle. At the Robinson mine on the south border of the Granite Basin pluton, the quartz gold-bearing veins fill fissures mainly in the quartz
diorite, but some also occur along the contact between the quartz diorite and the metagabbro. The structures are nearly vertical and strike east-west.
The Silver Star mine is at the northwest contact of the Merrimac pluton. The country rock here is biotite-muscovite phyllite that may have been originally a rhyolitic metatuff. This mine was in operation on a small scale 20 years ago, but has since been abandoned. The gold was washed from claylike material that filled the shear zones and fractures in a quartz vein.
Pabst and Stinson (1960) reported an occurrence of the black uranium-bearing titanium mineral brannerite in the gold-bearing dike at the Little Nell mine at an elevation of 3,300 feet in the southeastern part of sec. 35, T. 23 N., R. 8 E. The dike rock is sericitized, contains albite and quartz phenocrysts, and is cut by vein-lets of clear albite and dolomite. Brannerite occurs along the dike wall, in adjoining fractures, and in some albite vugs. Broken crystals of brannerite are coated by gold, which is thus later. Coating of anatase occurs as an alteration product after brannerite.
At the Virgilia mine, low-grade ore occurs in a dio-ritic dike that is partly silicified. The dike parallels the Melones fault and is only a short distance northeast of this major fracture zone. Averill (1937) reported that parts of this dike are entirely replaced by white quartz and that gold occurs both free and in pyrite. This lode is in the phyllite of the Triassic Cedar Formation and extends parallel to its strike (N. 40° W., dip 70° NE.) about 2 miles to the northwest. It also has been mined about half a mile to the southeast of the river at York Creek. At the north boundary of the Bucks Lake quadrangle, a quartz porphyry dike, part of it strongly sheared, occurs along the strike of this lode.
Another gold-bearing quartz vein is on the southwest side of the serpentine belt, southwest of the Rich Bar fault. Gold has been mined from this vein in the Shenandoah mine at French Creek about half a mile southeast of Rich Bar at the East Branch of the North Fork of the Feather River. At Ontop mine, the gold-bearing quartz vein is along a shear zone that is about 0.1 mile to the northeast of a narrow serpentine belt that probably conceals a fault. The quartz vein follows a sheared and altered quartz porphyry dike that consists of quartz, albite, calcite, muscovite, biotite, and pyrite. This dike continues to the southeast, separating meta-sodarhyolite in the north from metadacite to the south.
The gold-bearing quartz veins in the 3-Ravines mine are only 30-50 cm thick. Two parallel veins 0.2 miles apart, striking N. 60°E and dipping 60°NW., are being prospected for silver and gold. Gold occurs as flakes, rarely as crystals, between the quartz grains. Most of the ore is low grade, but in places abundant free gold can be seen with the naked eye. Silver-bearing galenaAURIFEROUS STREAM DEPOSITS
57
also is unevenly distributed through these veins. These lodes are in biotite-muscovite phyllite and can be followed about half a mile along the strike.
AURIFEROUS STREAM DEPOSITS
Small auriferous stream deposits are exposed under the Tertiary volcanic rocks and on the serpentine north of Meadow Valley. These were mapped by Turner (1898), who considered them as Neocene. Similar gravels from the central Sierra Nevada have been dated paleobotanically as middle Eocene by Potbury (1935) and MacGinitie (1941). Plagioclase in the La Porte Tuff of Evernden and James (1964) overlying auriferous gravel has been dated by them as 32.4 m.y. old.
All these gravels have been mined hydraulically for gold, which occurred in the lowest part of a channel where the gravel coarsens. In the Bucks Lake quadrangle two of the mines, the Pine Leaf and the Little California, have been in operation until recently. Most of the auriferous gravels consist of cobbles (5-20 cm in diameter), pebbles (%-5 cm in diameter), and sand. Pebble counts were made of gravel on Bean Creek (sec. 3, T. 24 N., R. 8 E.) at an elevation of 4,600 feet, northwest of the pyroclastic andesite. The results are shown in table 7. Most of the cobbles and pebbles are vein quartz; the second largest group is Silurian clastic quartizite of the Shoo Fly Formation. The nearest outcrop of Shoo Fly sandstone (blastoclastic muscovite quartzite) is more than 1 mile to the northeast; thus material probably was transported from that direction. Only a few small pebbles of other local rocks were found in this gravel.
Table 7.—Pebble count of gold-bearing Eocene gravel on Beans Creek, Bucks Lake quadrangle, sec. 3, T. 24 N., R. 8 E.
	Size (cm)	Number	Percent
Pebbles			
Vein quartz 		. %-i	972	64.1
	1-2	228	15.0
Total			1,200	79.1
Chert 		y2-i	82	5.4
	1-2	41	2.7
Total			123	8.1
Quartzite, Shoo Fly Formation....	y2-i	115	7.6
	1-2	79	5.2
Total			194	12.8
Grand total			1,517	100
Larger pebbles	and cobbles		
Vein quartz 		2-5	275	48.7
	5-20	61	10.8
Total				336	59.5
Chert		2-5	0	0
	5-20	0	0
Shoo Fly		2-5	205	36.3
	5-20	24	4.2
Total			229	40.5
Grand total			565	100
TERTIARY VOLCANIC ROCKS CORRELATION AND AGE
Tertiary volcanic rocks cap wide areas in the southeastern part of the Bucks Lake quadrangle and in the northern part of the Pulga quadrangle. The oldest flows are shown as older basalt of Neocene age on the map of the Bidwell Bar quadrangle (Turner, 1898) and as Eocene basalt on the Chico sheet (Burnett and Jennings, 1962). This basalt underlies pyroclastic andesite of Pliocene age in the area covered by the Chico sheet. Basalt of Pliocene age occurs as small pluglike bodies in the southern part of the Bucks Lake quadrangle, and its silicic differentiate, basaltic andesite, rests on pyroclastic andesite on Mount Ararat. These three units can now be correlated with the Tertiary volcanic rocks that are widespread in the areas to the east and to the south.
The basalt at Walker Plains and some small occurrences of the older basalt in the Bucks Lake quadrangle are shown as a part of the Lovejoy Formation or Love-joy Basalt by Durrell (1959b). His description of megascopic and microscopic aspects of this basalt in its type section on Red Clover Creek, Blairsden quadrangle (secs. 30, 31, T. 25 N., R. 12 E.) fits well all older basalt in the Bucks Lake and Pulga quadrangles. Durrell (1959b, p. 216) established a late Eocene or possibly earliest Oligocene age for this formation on the basis of stratigraphy in the Blairsden quadrangle, at Table Mountain near Oroville, and in the Sacramento Valley. Dalrymple (1964) determined potassium-argon ages for several specimens of basalt and concluded that the Lovejoy must be more than 13.6 m.y. The overlying rhyolite, however, provided a minimum age of 22.2 m.y. A maximum age of 23.8 m.y. is given by plagioclase in a vitric tuff under the Lovejoy basalt at South Table Mountain near Oroville. Thus, potassium-argon dating yields an early Miocene age for the Lovejoy Basalt.
Pyroclastic andesite overlies Durrell’s (1959b) Lovejoy Basalt in the southern part of the Bucks Lake quadrangle and is probably equivalent to the andesite and mudflow breccias of the Pliocene Penman Formation that Durrell (1959b, 1966) described in the Blairsden quadrangle and in the northern Sierra Nevada in general. Much of this unit consists of mudflow breccia and pyroclastic material in which rounded fragments, 1-50 cm long, of light-gray to medium-gray andesite are embedded in fine-grained very light gray debris. Most of the rock east of Bear Creek is medium-gray andesite with sparse black hornblende crystals. This andesite weathers to a gray soil that contains hornblende.
The andesite north of Meadow Valley is darker, and much of it weathers to rusty-brown soil that contains round boulders (20-60 cm in diameter) of andesite.
Basaltic andesite on Mount Ararat and the small58
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
pluglike bodies of olivine basalt that are younger than the pyroclastic andesite were mapped by Turner (1898) as “late basalt” of probable Pleistocene age. On the Chico sheet (Burnett and Jennings, 1962), these rocks are shown as Pliocene. Durrell (1959a, 1966) correlated similar basalts in the Blairsden quadrangle with Russell’s (1928) Warner Basalt. Comparison of this basalt to Durrell’s description leads to the conclusion that all late basalt may be equivalent to the olivine basalt of Pliocene age, as exposed in the Blairsden quadrangle. The small pluglike bodies in the southern part of the Bucks Lake quadrangle have a well-developed columnar structure, usually vertical, but are concentric at locality 317 forming there a structure typical of fumaroles. Pyroclastic material extends eastward from this cone and fills two fractures, several meters wide, in the meta-morphic rocks. The basaltic andesite that rests on pyroclastic andesite on Mount Ararat has nearly horizontal, closely spaced joints similar to those in the two-pyroxene andesite on Table Mountain.
PETROGRAPHY
LOVEJOY BASALT
The basalt exposed under the pyroclastic andesite is considered to be a part of the Love joy Formation or Lovejoy Basalt of Durrell (1959a, b). The name Love-joy Basalt is adopted here because in this area and to the south very little, if any, gravel occurs between the lava flows. The basalt is dark gray to black, fine grained, and vesicular. In most localities only one flow is exposed. On many slopes, its flat upper surface forms terraces under younger andesitic material, and its sidewalls are vertical cliffs with irregular columnar jointing. Talus fields at the base of these vertical cliffs contain polygonal to rounded blocks, 10-50 cm in diameter, that in many places cover the lower contact. Vesicles, 1-2 cm in diameter, are common but sparse. Abundant magnetite makes some of the basalt intensely black.
The major constituents of the basalt are plagioclase (An50), augite, magnetite, and olivine. Phenocrysts of plagioclase are few and small (0.3-0.5 mm long), except in the well-crystallized basalt, where plagioclase laths are larger and continue into interstitial areas filled by glass in the finer grained basalt. Olivine is scarce; where present it occurs in euhedral crystals that are about twice the size of augite crystals. The texture of the groundmass is ophitic; tiny laths of plagioclase (0.1-0.2 mm long) are oriented at random or show a slight subparallel orientation. Subhedral augite and magnetite grains (0.04-0.07 mm long) are interstitial. Glass with dendritic magnetite fills the interstices between the other minerals. In a few samples interstitial calcite occurs in small patches. Hematite and goethite fill some of the cavities. Slender colorless needles that transect
some of the glass could not be identified for certain. They may be apatite since the chemical analysis shows a high content of P205. The groundmass in the dark basalt is colored black by fine-grained magnetite. In the gray basalt, magnetite is in cubic crystals, and only a few tiny dust-size particles are included in the interstitial glass, which makes up a small fraction of the rock. Plagioclase constitutes as much as 60 percent of this rock, augite 30 percent, and magnetite 10 percent. Chemical analysis (Hietanen, 1972) shows that the composition is similar to that of andesitic basalts.
PYROCLASTIC ANDESITE
The andesitic rocks in the Bucks Lake quadrangle include light- to medium-gray porphyritic lavas, light-gray pyroclastic material, and mudflow breccia with boulders of andesite. Most of the andesite is studded with light-gray to white equant or elongate euhedral to subhedral phenocrysts of plagioclase (1-4 mm long) and sparsely sprinkled with shiny black slender prisms of hornblende, 1-5 mm long. In some boulders, very dark to black vesicular matrix is studded with small white plagioclase phenocrysts.
Microscopic examination shows that the large blocky phenocrysts of plagioclase (An37-50) are weakly to strongly zoned and complexly twinned. Rims and cleavage planes include small grains of augite and dustlike magnetite. Only the centers of some other crystals contain inclusions. Many plagioclase phenocrysts include irregularly bounded lamellar parts that are isotropic, evidently glass. Augite is the main dark constituent; it is in subhedral to euhedral phenocrysts 1-2 mm long. Most of the andesite contains a small number of hornblende crystals, 1-5 mm long, that are enveloped by a thick layer of fine-grained black magnetite as a result of heating. Extinction angles are small or 10°-15°, suggesting, together with the reddish-brown color, that this mineral is oxyhornblende. In some specimens, hornblende was destroyed completely; the relict black magnetite rims envelop a fine-grained mixture of augite, plagioclase, and dustlike magnetite. In many other specimens, brown hornblende is less oxidized; it is pleochroic in tan and light brown and has an extinction angle of 16°-17°, a little larger than that in the reddish-brown oxyhornblende.
Hypersthene with — 2V—-60° is the main dark constituent in a very light gray coarse-grained andesite that occurs as boulders in the pyroclastic material north of Deanes Valley (loc. 136). Hypersthene crystals are subhedral, 0.2-1.5 mm long, and have reddish-brown rims. A weak reddish-brown coloration extends inward toward the center of the crystals, camouflaging the pleochroism. A few crystals of colorless augite occur with hypersthene and include small grains of hypers-TERTIARY VOLCANIC ROCKS
59
thene. Magnetite occurs as large subhedral crystals (0.2-0.5 mm long) and as small round to subhedral grains in the groundmass. Groundmass of the porphy-ritic andesite consists of small blocky crystals of plagio-clase, augite, and magnetite. Interstitial glass is common, but rarely plentiful.
“LATE BASALT” OF TURNER (1898)
The olivine basalt and basaltic andesite that are younger than the pyroclastic andesite differ mineralogi-cally mainly in their olivine content. The basalt in the plugs is rich in olivine, whereas the basaltic andesite has very little or no olivine. Some of the andesite is rich in plagioclase and contains orthopyroxene and clino-pyroxene. Chemical composition of these rocks was discussed earlier (Hietanen, 1972).
OLIVINE BASALT
The olivine basalt is fine- to medium-grained gray rock that is studded with yellowish-green olivine pheno-crysts, 1-4 mm long. Thin sections show that large euhedral to subhedral olivine crystals are embedded in a fine-grained groundmass consisting of tiny laths (0.1 mm long) of plagioclase, crystals of augite, olivine, and magnetite, and interstitial glass. In places (loc. 587), augite also occurs as phenocrysts, but these are smaller (0.2-1 mm long) than the crystals of olivine. The basalt at locality 317 contains more plagioclase and less olivine than most other basalt and is accordingly lighter in color. At locality 510, the grain size of the basalt becomes increasingly coarser toward the center of the circular outcrop. The fine-grained borders of this plug are separated from the surrounding meta-morphic rocks by powdery microbreccia. A small pluglike body half a mile to the south (loc. 513) consists of similar olivine-rich basalt. The indices of refraction of olivine in this rock are a=1.690±0.002, /3=1.710± 0.002, y=1.725±0.002 indicating, according to Win-chell and Winchel (1951), the composition FoT3 Fa27.
TWO-PYROXENE ANDESITE
The basaltic anesite on Mount Ararat and on a hill west of it is light gray, fine to medium grained, and equigranular. Thin sections show a well-developed flow structure that is due to subparallel orientation of slender plagioclase laths and augite prisms. Laths of plagioclase (Anli0_65) are 0.2 mm long and constitute about 60 percent of the rock. Augite prisms are 0.1-0.3 mm long and 0.05-0.1 mm thick and make up about 38 percent of the rock. Magnetite (2 percent) in small euhedral to subhedral crystals is ubiquitous. In structure, texture, color, and mineralogy, this basalt resembles the hypersthene andesite on Table Mountain.
In the fine-grained andesite on Table Mountain in the southeast corner of the Bucks Lake quadrangle, hypersthene and augite occur in about equal amounts. Turner (1898) described and illustrated this rock, commenting that the only other locality where hypersthene was found is 0.6 miles southwest of Mount Ararat. The hypersthene andesite on Table Mountain is a light-gray dense rock that has an almost horizontal closely spaced joint system. In this rock, plagioclase (An3M0) is the major constituent (about 70 percent), orthopyroxene and clinopyroxene constitute about 20 percent, and magnetite is an accessory mineral. Some interstitial glass is common.
PLAGIOCLASE BASALTS IN THE PULGA QUADRANGLE
Basalt in the northwest corner of the Pulga quadrangle is continuous with the Lassen Peak volcanic rocks of Pliocene age (Lydon and others, 1960). Most of this basalt is fine grained and vesicular, with only a few small phenocrysts of augite and olivine. Ground-mass is very fine grained and consists of tiny laths of plagioclase, grains of augite, and magnetite.
Glomeroporphyritic coarse-grained basalt is exposed on Last Chance Creek (loc. 1141) on the east border of the above occurrence. Thin sections show that the large clustered plagioclase (An55-65) phenocrysts are complexly twinned and very weakly zoned. Small inclusions of augite, magnetite, and hematite are common along the rims and cleavage planes. Augite and olivine phenocrysts are few and small. Groundmass has a near-ophitic texture consisting mainly of plagioclase laths and interstitial augite with some magnetite and olivine.
A very similar glomeroporphyritic basalt is exposed east and northeast of Table Mountain in the north-central part of the Pulga quadrangle, in the area shown as Tertiary basalt on the Chico sheet. In this vicinity five to six successive flows are exposed as terraces. The lowest flow extends northward to the vicinity east of Campbell Lake, where it overlies the northern border zone of Grizzly pluton and its metasedimentary wall-rocks. A similar glomeroporphyritic basalt, shown as Pliocene on the Chico sheet, is exposed north of Jones Meadows and to the northeast in the southern part of the Jonesville quadrangle, as shown on the Westwood sheet (Lydon and others, 1960). In all these localities, plagioclase phenocrysts are large and clustered, whereas the augite and olivine phenocrysts are few and small.
The basalt in the vicinity of Murphy Flat and Ben Lomond is fine grained, resembling the groundmass in the glomeroporphyritic basalt. A few tiny phenocrysts of plagioclase, olivine, and augite are embedded in a fine-grained groundmass of tiny laths of plagioclase and small grains of augite and magnetite.60
GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
TERTIARY UNCONSOLIDATED MATERIALS
Glacial deposits. — Glacial moraine material forms several rounded ridges on the northeast slopes of Spanish Peak and Mount Pleasant and in the vicinity of Silver Lake, where numerous round boulders of mainly hornblende-biotite quartz diorite are embedded in unsorted sandy material. Glaciated surfaces of hornblende-biotite quartz diorite and hornblende-pyroxene diorite are well exposed at higher elevations above these ridges. Smaller deposits of glacial debris occur on the north slope of Grizzly Mountain and on the east slope of Dogwood Peak. Morainal material is also widespread at higher elevations in the north-central part of the Pulga quadrangle, especially near Crane Valley and North Valley. Some of these deposits have been washed for gold and have yielded moderate amounts.
Lake deposits.—Meadow Valley is underlain by lake deposits (gravel and sand) that in places carry gold. Gopher Hill gravel on Spanish Creek has been mined intermittently since the last century. Lake beds extend toward Snake Lake in the northeast and toward the southeast to ridges on both sides of Deer Creek. These gravels have been mined hydraulically at many places; they were described by Turner (1898).
Pleistocene river gravels and some undivided gravel deposits. — Old river gravels occur at high elevations along rivers at many places, as for instance at Rich Bar on the East Branch of the North Fork of the Feather River and at Hartman Bar, Butte Bar, and elsewhere on the Middle Fork of the Feather River (not shown on pi. 2). Most of these old gravel bars have been washed for gold. Rich Bar was the most productive. Rusted parts of hydraulic equipment abandoned in the steep canyon of the Middle Fork mark many old mining sites. Some of the gravel deposits are old deposits that have been reworked, as for example much of the gravel along Spanish Creek near Gopher Hill (sec. 12, T. 24 N, R. 8 E.) and to the south.
SUMMARY AND CONCLUSIONS
The Pulga and Bucks Lake quadrangles lie at the north end of the western metamorphic belt of the Sierra Nevada. The Melones fault and accompanying serpentine belt divide the area into two parts with different lithologic sequences on either side. The metamorphic rocks northeast of the serpentine belt are continuous with the Shoo Fly Formation in the adjoining areas. Correlation of the metasedimentary and metavolcanic rocks southwest of the Melones fault is uncertain because of profound deformation and recrystallization that have destroyed the fossil evidence. The major belt of the metasedimentary rocks southwest of the Melones fault, the Calaveras Formation, consists of interbedded
metachert and phyllite indicating a marine environment during the deposition. Lying unconformably on the Calaveras Formation, and faulted against it in the southwest, are metavolcanic rocks consisting of metaandesite, metadacite, and metamorphosed sodarhyolite (the Franklin Canyon Formation) in the eastern part of the area and metabasalt and metarhyolite (the Duffey Dome Formation) in the western part. Pillow structures occur locally in the lower part of the Franklin Canyon Formation, which is believed to be the older of the two formations, but most of the metavolcanic rocks show well-preserved pyroclastic structures, including tuffaceous layers. Southwest of the metavolcanic belt and separated from it by a fault is a sequence of interbedded metavolcanic and metasedimentary rocks called the Horseshoe Bend Formation. This formation occupies a synclinorium between two major faults and includes metavolcanic rocks that are similar to those in the Franklin Canyon and Duffey Dome Formations. Discontinuous layers of phyllite, quartzite, metachert, and limestone are interbedded.
Correlation of these three pyroclastic formations with sections of the metasedimentary and metavolcanic formations farther south and with the Paleozoic section of the Taylorsville area across the Melones fault was attempted on lithologic grounds. Assuming that volcanic activity of similar nature was widespread, the pyroclastic sequences interbedded with the Paleozoic metasedimentary rocks are tentatively correlated with lithologically similar pyroclastic rocks farther south, that is with the Tightner Formation of Ferguson and Gannett (1932) and of Chandra (1961) and with the Devonian to Permian pyroclastic sequence of the Taylorsville area (McMath, 1966).
Two age groups of intrusive rocks are present in the area. The older rocks are closely associated with metavolcanic rocks and represent the deep-seated equivalents of metabasalt, meta-andesite, metadacite and metamorphosed sodarhyolite. They range in composition from hornblendite and metagabbro through meta-diorite to metatrondhjemite. The mineral assemblages in the metaigneous rocks are similar to those in the equivalent metavolcanic rocks; the only difference is in texture. The younger intrusive rocks form plutons that have foliated quartz dioritic border zones and that with but one exception grade to massive monzotonalite at their centers. The exception is the Bucks Lake plu-ton, which includes a large mass of pyroxene diorite in its central part. The chemical composition and the trace-element content of this pyroxene diorite, together with the structural relations, indicate that it is an early differentiate of the same magma from which the quartz dioritic border zone crystallized. The potassium-argon age for the pyroxene diorite is, according to Gromme,REFERENCES CITED
61
Merrill, and Verhoogen (1967), 143 m.y., whereas the quartz dioritic border zones of the Bucks Lake, Grizzly, and Merrimac plutons range from 140 to 130 m.y. in age.
Two episodes of deformation and metamorphism are indicated by structures and sequence of recrystallization in the metamorphic rocks. During the first episode the rocks were isoclinally folded on northwest-trending axes and acquired a strong foliation parallel to the axial planes. A second folding and recrystallization accompanied the emplacement of the Late Jurassic and Early Cretaceous plutons. Steeply plunging lineations and intricate folding around steep second axes are strongest near the plutons and resulted from shouldering of the wallrocks aside by the invading magma.
Generally muscovite, chlorite, and biotite crystallized in the phyllitic layers, and epidote, actinolite, and chlorite crystallized in the metavolcanic rocks during the first episode of metamorphism, indicating a metamorphic grade between the greenschist and epidote-amphibolite facies. The metamorphic grade is higher around the plutons, as shown by coarsening of the grain size and by the mineral assemblages, such as biotite-garnet, staurolite-andalusite, and cordierite-anthophyl-lite, which are typical of the higher part of the epidote-amphibolite facies. Sillimanite was found only in one locality—the canyon of Bear Creek south of the Bucks Lake pluton, where it occurs with andalusite and cor-dierite. Elsewhere andalusite and cordierite crystallized next to the intrusive rocks, and in places there are pseudomorphs of yellow mica after staurolite. Stauro-lite was stable with andalusite farther from the contact. The amount of biotite increases and that of muscovite decreases toward the plutonic rocks. Chlorite is generally absent near the contacts or, if present, is a product of later alteration. These relations indicate that pressure during the second episode of metamorphism was lower than that at which staurolite can coexist with sillimanite. The temperature next to the plutons was higher than that of the upper stability boundary of staurolite.
The ultramafic rocks differ strikingly in composition and trace-element content from the other intrusive rocks and thus must have had a different origin. They have features characteristic of Alpine-type peridotite-serpentine masses most closely resembling those of mantle origin by Wyllie’s (1969) classification. They do not have the high-temperature contact aureoles that emplacement of liquid magma or hot crystal mush would produce. On the basis of their texture and mineralogy, they were probably emplaced as a moderate-to low-temperature crystal accumulate which, in its early stages, had only about 10 percent interstitial hydrous basic liquid. The early serpentine minerals,
which fill interstices and tiny irregular cracks, may have precipitated from this liquid, which could have greatly facilitated the emplacement along and near the fault zones. The tiny early cracks were formed by microbrecciation at an early stage, most likely during the upward movement of the masses. The regional structures, such as crude foliation and cross joints accompanied by second serpentinization, are clearly overprinted on these early features.
The second stage of serpentinization of the ultra-mafic bodies is intimately associated with the metamorphic events. These two phenomena were not only concurrent but also chemically complementary in respect to outflowing and inflowing components: H20 and C02 released by the metasedimentary rocks during metamorphism are the very components that invaded the ultramafic masses during their serpentinization. As a consequence of serpentinization, calcium migrated out, forming calc-silicates at the contact and in the silicic masses within the ultramafic bodies. The excess silica from these masses migrated into the serpentine and reacted to form talc. The system as a whole may have operated isochemically, and the amount of available H20 may have been a controlling factor in the degree of serpentinization.
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GEOLOGY OF THE PULGA AND BUCKS LAKE QUADRANGLES, CALIFORNIA
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Lawson, A. C., 1903, Plumasite, an oligoclase-corundum rock near Spanish Peak, California: California Univ. Pub. Geol. Sci., v. 3, no. 8, p. 219-229.
Luth, W. C., Jahns, R. H., and Tuttle, O. F., 1964, The granite system at pressures 4 to 10 kilobars: Jour. Geophys. Research, v. 69, p. 759-773.
Lydon, P. A., Gay, T. E., and Jennings, C. W., 1960, Geologic map of California, Olaf P. Jenkins edition, Westwood sheet: California Div. Mines, scale 1;250,000.
MacGinitie, H. D., 1941, A middle Eocene flora from the central Sierra Nevada: Carnegie Inst. Wash. Pub. 534, 178 p.
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Medaris, L. G., Jr., 1969, Partitioning of Fe** and Mg++ between coexisting synthetic olivine and orthopyroxene: Am. Jour. Sci., v. 267, no. 8, p. 945-968.
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Moores, E. M., 1970, Pre-batholith structure and stratigraphy of the Lake Almanor and Greenville quadrangles, northern Sierra Nevada—Progress report [abs.]:	Geol. Soc.
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[Italic page numbers indicate major references]
A
Page
Page
H
Page
Actinolite .................. 13, 14,18, 19, 33, 61
Age, plutonic rocks........................ 52
volcanic rocks ........................ 57
Albite ..........
Albitite ......
Amphibole .....
Andalusite ____
Andesite ......
pyroclastic
5, 8, 9, 13, 16, 18, 28,33
..................... 29
.... 24, 27, 28, 32, 39, 40
........ 8, 10, 20, 33, 61
................... 19, 60
.................... 58
Anthophyllite .......................... 10, 61
Anticline .............................. 11, 20
Antigorite ......................... 26, 27, 28
Apatite ...................... 39, 41, 47, 48, 49
Augite ....................... 32, 37, 43, 58, 59
Auriferous stream deposits .............. 57
Axinite ................................. 29
B
Bald Eagle ........
Basalt ............
Basaltic andesite .
Bean Creek .........
Bear Creek ........
Bear Gulch ........
Bear Ranch Hill ....
Bedding ............
Big Bar Mountain ..
Big Bend fault ....
Big Creek ..........
Big Kimshew Creek
Biotite ........ 5,
Bombs .............
Brannerite ........
Buckhorn Creek.....
Bucks Lake ........
Bucks Lake pluton .
Bucks Mountain .....
Butte Bar..........
........................ 36,	37
............................ 59
............................ 57
.......................  32,	57
............. 9, 10, 11, 31, 57
......................... 21
................... 18,	22,	49
......................... 6, 10
........................ 23,	29
......................... 20
..................... 9,	10,	12
........................ 11
8, 9, 14, 17, 20, 33, 40, 46, 61
............................ 13
............................ 56
............................ 47
..........................   41
.......... 3, 7, 33, 35, 86, 61
................... 36,	37,	40
......................... 60
Calaveras Formation ............... 2, 4, 7, 60
Calcite .................................. 16
Camel Peak fault...................... 12,	19
Camp Rodgers Saddle....................... 36
Campbell Lake ................... 7, 10, 11, 59
Cape Horn Slate ......................... 22
Cape Lake ..............................   36
Carpenter Bar ........................ 16,	18
Cascade pluton .......................... 51
Catrell Creek............................. 30
Cedar Formation ...................... 2,	28
Chambers Peak ....................... 8, 9, 11
Chino Creek .............................. 33
Chlorite .. 5, 8, 13, 16, 18, 20, 29, 32, 37, 39, 49, 61
Chromite ................................. 24
Chromium ...............................   26
Chrysotile ........................... 26,	28
Cleghorn Bar ............................. 11
Clinopyroxene ........................ 30,	43
Coldwater Creek ...................... 30,	32
Conclusions .............................. 60
Concow pluton ........................ 35,	48
Conglomerate ............................ 22
Copper .................................. 26
Cordierite ................... 8, 9, 20, 33, 61
Corundum ............................ 28,	29
Coyote Gap .......................... 23,	56
Crane Valley ............................ 60
Cummingtonite ........................... 10
D
Deadman Spring ...................... 49.	56
Deanes Valley ....................... 49,	58
Deer Park ............................ 4,	21
Deformation ....................... 3, 34, 61
metavolcanic rocks .................. 18
Dejonah Creek ........................... 13
Diadem lode............................... 2
Dikes ............................. 29, 31, 32
association with plutonic rocks ..... 49
Diorite ................................. 46
hornblende....................... 89,	48
hornblende-pyroxene.................. 86
pyroxene ........................ 86,	43
Dogwood Creek ....................... 31,	49
Dogwood Peak ................... 12, 13, 23, 60
Duffey Dome Formation .............. 4, 17, 60
Dunite .............................. 26,	28
E
East Branch of Rock Creek ................ 5
East Branch of the North Fork of the
Feather River................ 23
East Fork of Big Creek................... 11
Epidote ........ 13, 16, 18, 20, 29, 32, 47, 49. 61
Epidote tonalite ......................   48
F
Faults ............................... 3,	23
Flea Valley Creek ................... 20,	21
Folds ..................... 4, 7, 10, 11, 18, 61
Foliation ....................... 3, 11, 19, 37
Franklin Canyon Formation .......... 4, 12, 60
Frazer Hill ...........................   28
Frenchman Hill ........................   26
G
Gabbro ............................ 31, 42, 49
hornblende .......................... 48
Garnet ........................ 6, 8, 10, 20, 61
Glacial deposits ........................ 60
Gold ................................ 57,	60
Gold-quartz veins ....................... 56
Goodhue Formation ....................... 23
y Gopher Hill .............................. 60
Granite Basin .........................   32
Granite Basin pluton ................ 35,	47
Gravels ...............................   60
Grizzly Dome ............................ 46
Grizzly Mountain .................... 29,	60
Grizzly pluton .............. 7, 33, 35, 44, 61
Grossularite ............................ 18
Hartman Bar ........................ 23,	60
Hartman Bar pluton...................... 48
Hartman Bar Ridge................... 10,	21
Hematite .......................... 5, 20, 59
Hornblende ................. 28, 30, 32, 37, 46
Hornblende-biotite quartz diorite.... 40, 47, 48, 60
Hornblende diorite ................. 89,	48
Hornblende gabbro ...................... 48
Hornblende-pyroxene	diorite ........ 86,	60
Hornblendite ........................... 29
Horseshoe Bend Formation .......... 4, 19, 60
Hypersthene ................... 37, 39, 43, 58
I, J. K,
Ilmenite .....
Jones Meadow . Kimshew Creek
......... 5,29
9, 10, 11, 13, 59
.......... 43
L
Lake deposits .............................. 60
La Porte Tuff...............;............ 57
Lapilli .................................... 13
Last Chance Creek .........................  59
Limestone ............................... 5, 6
Lineation ........................... 12, 19, 61
Lithology of the area........................ 4
Little Bear Creek ........................   16
Little California mine.................. 12,	57
Little Nell mine ........................... 56
Little North Fork of the Feather River...	4
Little North Fork of the Middle Fork
of the Feather River ... 19, 22, 49
Lizardite ................................   28
Location ...................................  1
Long Lake..............................   7,	11
Lookout Rock ............................... 48
Lovejoy Basalt ......................... 57,	58
M
Magnesite .........................   26,	27
Magnetite .............................. 5,
10, 16, 20, 24, 30,	32, 37, 39, 43, 47, 58
Marble ............................ 10, 18, 21
Marble Cone ......................... 21,	48
Marble Creek ............. 4, 19, 21, 22, 23, 49
Meadow Valley ....................... 57,	60
Meadow Valley Creek .................... 24
Melones fault ........................ 4,	60
rocks southwest ..................... 22
Merrimac pluton ................ 33, 35, 47, 61
Meta-andesite ............ 4, 12, 18, 22, 23, 34
Metabasalt ............... 4, 17, 22, 23, 35, 60
Metachert ............................ 7,	23
Metaconglomerate .......................  19
Metadacite ....... 4, 5, 12, 13, 14, 22, 23, 34, 60
Metadiorite ................... 19, SO, 34, 35
Metagabbro .......................... 29,	34
Metaigneous rocks ................... 55,	60
Metalatite ............................. 22
Metamorphic rocks, correlation.......... 22
6566
INDEX
Page
Page
Page
Metamorphism ...................... 10, 33, 61
Metamorphosed hypabyssal rocks ........... 31
Metamorphosed intrusive rocks ............ 23
Metarhyolite ............ 3, 5, 17, 22, 23, 35, 60
Metasedimentary formations ................ 4
Metasedimentary rocks ..................... 3
recrystallization ................... 34
Metasodarhyolite .................. 4, 12, 34
Metatrondhjemite ......................... 31
Metatuff ...................... 4, 5, 16, IS, 22
Metavolcanic rocks .................... 4,	55
recrystallization ................... 34
Metavolcanic sequence .................. 12,	60
Middle Fork of the Feather River.......... 7,
10, 16, 18, 23, 48, 60
Mill Creek ........................... 20,	29
Miller Fork ............................   42
Monzotonalite .......................... 46,	49
Mount Ararat ........................... 57,	59
Mount Pleasant ........................... 60
Mud Lake ................................. 47
Murphy Flat .............................. 59
Muscovite ......... 5, 8, 14, 16, 20, 28, 33, 47, 61
N
Nevadan orogenic belt ...................... 3
Nickel .................................... 26
North Fork of the Feather River........... 11,
17, 29, 39,	49
North Fork of the Yuba River............... 22
North Valley .............................  60
O
Oak Point ..........
Oak Ridge ..........
Oligoclase .........
Oliver Lake pluton .
Olivine ............
Olivine basalt .....
Olivinite ..........
Onion Valley Creek
Ontop mine .........
Orthopyroxene ......
Orthoquartzite .....
.................. 43
.................. 46
.............. 28, 33
............ 7, 35, 47
24, 27, 28, 43, 58, 59
.................. 59
............... 28
............ 2, 32, 49
56
.................. 43
............... 4, 6
P
Peale Formation ........................... 23
Penman Formation ..........................  57
Peridotite ............................. 27, 28
Petrography, hornblende-pyroxene
diorite .............................. 37
pyroxene diorite ..................... 37
Phyllite ............................ 5, 8, 20, 23
Pillows ................................ 13, 60
Pine Leaf mine ............................. 57
Plagioclase .............................. 13,
17, 29, 31, 37, 39, 43, 46, 49, 58 Plagioclase basalts ....................... 59
Plumasite 				 28
			 35
			 50
Plutons 				 3, 44, 47, 61
Potassium feldspar 				 17
Previous work 				 2
Purpose and scope				 3
Pyrite 				 10
Pyroclastic andesite ...			 57
	.... 13. 24. 27. 28. 39. 40. 43	
Pyroxene andesite 				 59
Pyroxene diorite 				 36, 43, 60
Q
Quartz .......... 8, 13, 18, 20, 29, 32, 37, 40, 47
Quartz diorite ...................... 47, 48, 49, 60
hornblende-biotite ................... 40
Quartzite ........................... 5, 18, 21, 23
R
Rag Dump ..........
Recrystallization .
Red Clover Creek....
Red Ridge .........
Reeve Formation ....
Reeve Meta-andesite
Rich Bar ..........
Rich Bar fault ....
Robinson Formation
Robinson mine .....
Rock Creek ........
Rock Island Ridge ...
Rocky Ridge .......
Rush Creek ........
Rutile ............
........ 7, 8, 10
3, 30, 33, 52, 61
.............. 57
........... 11
............. 23
.............. 23
......... 56, 60
...... 4, 12, 23
.............. 23
..... 30, 47, 56
.......... 5, 6
........... 21
.............. 23
.............. 56
.......... 10
S
Schneider Creek ........................ 13
Serpentines, associated rocks .......... 28
Serpentinization ................. 26, 27, 61
Shenandoah mine .......................... 56
Sherman Bar .............................. 11
Shoo Fly Formation ..................... 3, 4, 6
Sierra Buttes Formation ................ 3, 23
Sillimanite ...................... 8, 10, 33, 61
Silver ..................................  56
Silver Crescent mine...................... 22
Silver Lake ...................... 12, 13, 23, 60
Silver Star mine ......................... 56
Slate ..................................   23
Slate Creek ............................ 5, 7, 32
Snake Lake ....................... 4, 6, 23, 60
Soapstone ................................ 26
Soapstone Hill ......................... 26, 31
Sodarhyolite .................. 3, 13, 16, 23, 60
South Branch of the Middle Fork of the
Feather River ............... 23
South Fork of the Feather River .......... 22
Spanish Creek ...................... 2, 4, 6, 60
Spanish Peak ................... 12, 29, 42, 60
Sphene .............. 5, 10, 29, 30, 32, 41, 47, 48
Staurolite ......................... 20, 33, 61
Steatitization ......................... 26, 27
Stilpnomelane ............................. 5
Stratigraphy .............................. 3
Structural setting ........................ 3
Structure ................................. 6
Calaveras Formation ................  10
hornblende-pyroxene diorite ......... 36
metavolcanic rocks .................. 18
pyroxene diorite ...................  36
Summary .................................. 60
Syncline ............................... 5, 20
T
Table Mountain ....................... 57,	59
Talc ..................................... 28
Talc schist .......................... 24,	26
Taylor Meta-andesite ..................... 23
Taylorsville Formation .................... 3
Three Lakes .......................... 37,	49
3-Ravines mine ........................... 56
Tightner Formation ................... 22,	60
Tourmaline ............................... 10
Trace elements ........................... 53
Transfer Ridge .........................   43
Tremolite ........................ 24, 27, 29, 43
Trondhjemite ............................. 51
Tuffaceous metasediment .................. 16
U
Ultramafic rocks ................... 4, 23, 61
Unconsolidated materials ............... 60
V
Vanadium ................................   26
V egetation ................................ 1
Vesuvianite ............................... 29
Virgilia mine ............................. 56
Volcanic breccia .......................... 13
Volcanic rocks ............................ 57
Volcanic structures ....................... 13
W
Walker Plains ........................ 57
Warner Basalt ........................ 58
Whitlock Creek ........................ 5
Willow Creek ................... 12, 32, 56
Workman’s Bar ........................ 40
Z
Zoisite .................................. 37
Zoning ................................... 3
U. S. GOVERNMENT PRINTING OFFICE : 1973 O - 499-9647 D 'V
/- J ' -.;,c2a '
W Channel Movement of 73aM Meandering Indiana Streams
GEOLOGICAL SURVEY PROFESSIONAL PAPER 732-A
Prepared in cooperation with the State of Indiana Department of Natural ResourcesChannel Movement of Meandering Indiana Streams
By JAMES F. DANIEL
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 732-A
Prepared in cooperation with the State oj Indiana Department oj Natural Resources
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY W. A. Radlinski, Acting Director
Library of Congress catalog-card No. 74-175750
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 35 cents (paper cover)
Stock Number 2401-1221CONTENTS
Page
Abstract ............................................. A1
Introduction .......................................... 1
Concepts .............................................. 2
Movement defined ................................. 2
The sine-generated curve ..................... 2
Moving reference axis ........................ 2
Observed modes of movement ................... 3
Theoretical mechanics of movement................. 5
Impulse momentum ...........................   5
Channel-forming discharge .................... 6
Page
Concepts—Continued
Theoretical mechanics of movement—Continued
Channel-forming discharge redefined ............ A6
Field investigation ...................................   7
Study sites ......................................... 7
Data analysis ....................................... 9
Interpretive discussion ................................ 14
Individual sites ..................................  14
General conclusions ................................ 15
Summary ...............................................  17
Selected references .................................... 17
ILLUSTRATIONS
Page
Figure 1. Graph showing sine curve of the best fit to data for the White River near Worthington site ........... A2
2.	Diagram showing general mechanism of meander loop movement .................................... 3
3.	Diagrams showing effects of stationary and (or) translating end points on general mechanisms of
meander loop movement...................................................................-... 4
4.	Sketch identifying elements of the momentum concept ........................................... 5
5.	Graph showing traveltime for the East Fork White River between U.S. Geological Survey gages at
Columbus and Seymour ....................................................................... 7
6.	Map of Indiana showing location of investigated meander sites and gaging stations ............. 8
7-12. Plan-view channel patterns for:
7.	Paw Paw Creek near Urbana .............................................................. 9
8.	Carpenter Creek near Egypt ...................................................-......... 9
9.	White River near	Martinsville ............................................................ 10
10.	White River near	Worthington .............................................................. 11
11.	East Fork White	River near Vallonia......................................................  12
12.	Muscatatuck River near Austin ............................................-.............. 13
13.	Map showing definition of actual end points from theoretical loop, plotted on 1937 loop, for the White
River near Worthington site ................................................................ 13
14-20. Graphs:
14.	Path-length increase versus flow volume for the White River near Worthington site .......... 13
15.	Path-length increase versus flow volume for the White River near Martinsville site ......... 13
16.	Path-length increase versus flow volume for the East Fork White River near Vallonia site.	13
17.	Accumulated flow	volume versus water	year	for	the	White	River near Worthington site ....... 15
18.	Probable relation	of path-length increase	to	silt-clay	percentage .......................... 15
19.	Dimensionless relation of path-length increase and flow data to silt-clay percentage ....... 16
20.	Dimensionless relation of path-length increase and flow data to width-depth ratio ......... 16
TABLES
Page
1.	Selected site characteristics ...................................................................... A7
2.	Suspended-sediment loads for East Fork White River at Seymour ...................................... 14
Table
IIIPHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
CHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
By James F. Daniel
ABSTRACT
The process of channel movement in a meander system involves rotation and translation of meander loops and an increasing path length. The amount of path-length increase is directly proportional to the impulse supplied by discharge and is inversely proportional to the silt-clay percentage of the material composing the channel perimeter.
Comparable paths have been obtained by standardizing measurements with a sine-generated curve and a moving reference axis. Analysis of previous investigations and time-of-travel data indicates that the discharge effective in channel formation consists of the range beginning just higher than the average and continuing throughout all higher discharges. Of six field sites investigated, three meander systems had path-length increases of sufficient magnitude to correlate with above-average discharge volume, one had no discernible change over a 30-year period, and two had changes which were too small for correlation owing to the short period of time covered by the available data.
Because of the consistency of yearly above-average discharge volumes, it was possible to develop a general relation between path-length increase per thousand cubic-feet-per-second-days per square mile of drainage area above average discharge and the width-depth ratio of the channel. Little progress was made toward defining relationships for rotation and translation.
INTRODUCTION
For many years the planimetric meander form has both intrigued and perplexed geomorphologists. Each investigation has added some facet to the knowledge of meanders. Today, while no one will claim that all the answers are known, the state of knowledge is such that the physical characteristics of meanders can be described in mathematical models with a reasonable degree of accuracy. Laboratory and field investigations, such as the one by Toebes and Sooky
(1966), have provided information about the mechanics of flow within a meander, while theoretical investigations, such as those by Langbein and Leopold (1966) and Scheidegger and Langbein (1966), have delved into statistical concepts related to the development of meanders.
Much information is available about why meanders begin and about meanders in a static situation. However, a meander is not a static entity. It is dynamic in every respect. Valuable farmland in the flood plains of meandering streams is lost or changes ownership, and powerplants next to eroding banks require expensive bank stabilization, as do highway bridges and other structures which are in the path of moving, meandering channels. Investigations are needed regarding how, how much, and at what rate meanders move. Relationships need to be developed with which movement of meanders can be predicted. It is to these factors, which are of practical importance after the initiation of meandering, that this report is addressed.
Many persons have provided assistance to the author during this project, especially Richard F. Hadley, U.S. Geological Survey, Denver, Colo., who performed the field reconnaissance and made many suggestions about data collection. This investigation was conducted with financial cooperation by the Indiana Department of Natural Resources, Division of Water, whose personnel also contributed by supplying the field surveys for two of the sites investigated. Most of the personnel of the Indiana District at one time or another aided in the field surveys, often under adverse climatic conditions.
A1A2
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OP RIVERS
CONCEPTS
It is the thesis of this report that the process of channel movement in a system already in a state of meandering involves rotation and translation of the loops and an increasing path length. Any one or any combination of these forms of movement may occur, depending on the boundary conditions of the loop. Each of the components of movement must be known in order to predict movement. Direction of movement is related to the impulse required to change flow direction, and rate of movement is related to discharge and grain size of the bed and bank material.
MOVEMENT DEFINED The Sine-Generated Curve
Historically, the meander pattern has been described as either a sine curve defined by amplitude and wavelength or a series of semicircles defined by radius and wavelength. Many authors have correlated these parameters with discharge in an attempt to discover regional or universal relationships between them. Upon cursory examination of a topographic map showing meanders, it is apparent that measurements of their amplitudes, wavelengths, and radii would be very subjective. Each investigator would undoubtedly have a slightly different interpretation of each of these parameters. The result is that there are many slightly different but similar equations relating these parameters in existing literature. The work of Carlston (1965) did much to rectify some of the discrepancies between equations.
Langbein and Leopold (1966) provided a method to remove at least some of the subjectivity from the description of meanders. They showed the best description of a meander loop to be a sine-generated curve described by the equation:
g
sin p 2*-	(1)
where 0=the angle of deviation of a tangent at the end of s from the mean downstream direction.
“=the maximum angle of deviation of path from the mean downstream direction (usually in degrees). s=a segment of P (in feet), and P=the path distance through one wavelength (usually in feet).
By inspection of the example (fig. 1) for the White River near Worthington, it can be readily seen that a sine curve is the best fit for the data of this meander loop. Although a complete wavelength does
Figure 1.—Sine curve of the best fit to data for the White River near Worthington site, July 5, 1937.
not exist, the meander is uniquely defined by the parameters « and P. This method has been used to describe the path length of the concave bank for movement comparison of the meanders under investigation in this report.
Moving: Reference Axis
This study was begun using the procedure that cross sections would be surveyed at each site, steel pins would be set within the cross sections, and measurements of erosion and deposition at these pins would be made. After obtaining these movement data, correlations would be made with discharge. This procedure was in fact followed. However, after some insight was gained about the mode of movement, it was found that this type of data had little applicability to the problem under investigation.
For example, figure 2 shows a theoretical meander for two instants in time. At time tu the loop is defined by and P1( while at at time t2, it is defined by “2 (w2 ^ wi) and P, (P■, £ P,). If, between t1 and t2, measurements of erosion were periodically made at section A, the data obtained from each measurement would represent the end point of different fractions of the total path length. Therefore, any correlation of these data would not represent the movement of a point on the meander loop but would represent the time at which different points on the dynamic loop would reach a fixed reference. The data obtained would have little application to prediction of future movement of this meander or comparison to movement of another meander.
Let us consider, however, the result of using the concepts of a sine-generated curve and a dynamicCHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A3
system. At time h the meander loop is defined by “i and P,. Therefore, we can determine the stationing of the maximum deviations of the channel from the mean downstream direction, i/JP, and %Pi. The mean downstream direction is the line connecting those points. We can then set our reference axes along this line (labeled d,) and perpendicular to it (labeled (,) with the origin at i,4P,. At time t2 the same operations are performed, resulting in coordinate axes d2 and l2 and points %P2 and %,P2. We can then define the movement of the meander by measurements of the length and direction of the line from 14P1 to %P2, the rotation of the axes, and the change of « and P. These measurements of equivalent points and parameters of a developing loop would have value in prediction of future movement and comparison with different loops.
We have, in effect, made our measurements with reference axes which translate and rotate with time. This concept leads to a number of methods by which meander development could be described, and the method used in this report will be described in a subsequent section.
Observed Modes of Movement
Implied in the construction of figure 2 is the idea that the meander is evolving by two mechanisms. At time t2, P2 ^ P„ <»2 ^ «1; and d2 ± d,. This is one mode of change which has been observed for the meanders under study for this investigation. Ob-
served movements constitute five general classes of expansion (increasing P) and rotation (d2^di), depending on the boundary conditions of the loop. One class of movement is shown in figure 2 and the other four general classes are illustrated in figure 3. These five modes are applicable to vertically stable (little or no aggradation or degradation), alluvial channels investigated in this study. Channels incised in bedrock would have the meander pattern imposed by the stream when degradation began. Because of the abrasive effect of bedload, their mode of movement is basically vertical rather than lateral.
The concept of increasing path length (AP), a contributing factor to the movements shown in figure 3, was inferred by Langbein and Leopold (1966, p. H2) :
In the context of the whole river system, a meandering segment, often but not always concentrated in downstream rather than upstream portions of the system, tends to provide greater concavity by lengthening the downstream portion of the profile. By increasing the concavity of the profile, the product of discharge and slope, or power per unit length becomes more uniform along a stream that increases in flow downstream. Thus the meander decreases the variance of power per unit length * * *.
The conclusion is reached that meanders provide a greater path length which makes energy dissipation more uniform. It is reasonable to extend this conclusion to say that, unrestricted, the path length would continue to increase until energy dissipation is uniform. In the field, natural cutoffs or chuting (Friedkin, 1945) would occur before uniform energy dissipation was achieved. Therefore, in the dynamic system, increasing path length is a requirement.
Figure 3 illustrates an extension of this concept. In figure 3A, points a, and a/, are essentially fixed. Such a condition exists when dense vegetation or “clay plugs” restrict movement of the banks at these points. In this situation, erosion results simply in a path-length increase. In figure 3B, point Oi is fixed while cq is not, and in figure 3C the reverse is true. In either situation, the two mechanisms, change of downstream direction (rotation) and increasing path length, are more equal in effect. Figure 3D shows a loop whose condition is very near dynamic equilibrium in a uniformly erodible medium. Such a condition is approached in laboratory experiments (Friedkin, 1945) in which the whole meander sys-] tern tends to translate downstream.
Not shown are conditions which might result if the less erodible parts of the loop constituted other segments of the loop. Many possible combinations j are obvious. The significant point is that a meander j system works toward equal energy dissipation byPHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
ai has stationing Vi Pi a'i has stationing zAPi
Figure 3.—Effects of stationary and (or) translating end points on meander loop movement.CHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A5
increasing the path length, and where erosion rates within a loop differ greatly, rotation also occurs.
These mechanisms of movement should have application to all forms of free meanders when they are viewed throughout a period of time. Boundary conditions at the end points of and within each loop can result in the dominance of any single mechanism of increasing path length, rotation, or translation, but the usual condition would be some combination of the three.
THEORETICAL MECHANICS OF MOVEMENT
That meandering is a stochastic process has been established by previous studies. One can reasonably expect, however, that cause-effect relationships govern the movement of an individual meander.
Impulse Momentum
Friedkin (1945, p. 11) wrote, “The rate of bank erosion depends upon the force of the water against the banks as well as the toughness of the banks.” It is a small step from this idea to the concept of impulse-momentum change, which seems to offer the most reasonable basis for an explanation of movement.
Assume a segment of channel with constant curvature as shown in figure 4. The mean velocity vector of the fluid, which has a discharge of q and
Figure 4.—Identification of elements of the momentum
concept.
flows in the channel between points A and B, can be represented by the unit vector v which is parallel to a tangent to AB at any point.
At point A, q has momentum pqvA and at point B, q has momentum pqvB where p is the density of the fluid. The difference in the two values is the change of momentum in the intervening reach and ideally is equal to the force applied by the bank to
the water. Of prime interest, however, is the force applied by the water to the bank—that is, the impulse of the water on the bank.
The mechanism of bank movement can be explained in terms of the applied impulse on the bank and the resulting momentum of dislodged bank material. The following equation expresses this mechanism:
fa
Fqdt=(mvB)b-(mvA)b	(2)
tA
where Fq is the force supplied by the water, tA and tB are the times at which q pases points A and B, (mvA)b is the product of mass and velocity of the bank at tA, and (mvB)b is the same product at tB. The bank material between A and B has no momentum at tA. However, in an erodible material the impulse dislodges individual grains of bank material which are moved by the flow and do have momentum at tB. Equation 2 can then be rewritten for the grains affected by q as: tB
Fqdt=(m„vB)b	(3)
tA
As AB —> 0, equation 3 represents the impulse at a point where the left side of the equation is the force of the fluid on the bank, the time interval of force application has end points tA and tB, and the direction of the force is always tangent to the channel. In the real situation this direction of force tends to increase the path length.
The foregoing expression does not take into account the process occurring on the opposite bank where material is being deposited and hence losing momentum. For the streams investigated and for most streams with similar climatic and physical conditions, the channel characteristics are relatively stable; that is, even though meanders move with some rapidity, widths, depths, and width-depth ratios remain fairly constant so that the amount of material deposited very nearly equals the amount of material removed. Therefore, equation 3 is an adequate, albeit gross, means of representing movement of the concave bank if it can be assumed that the force effective in removing bank material is directly proportional to the total flow in the stream, Q. This assumption has been made, and it is the movement of the concave bank which has been analyzed.
The next steps are to put equation 3 in a form more easily analyzed with available data and make the necessary real-world substitutions. For a constant force, equation 3 can be rewritten as:A6
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
Fv (tB-tA) = (mgVB)b	(4)
Movement is another way of expressing material removed, (mgvB) b. Because the direction of force is always toward increasing path length (AP), the right side of equation 4 is proportional to AP. Force is proportional to Q. Different materials erode at different rates, depending on the cohesiveness of the material. The more cohesive the material the slower it erodes, so AP is inversely proportional to cohesiveness. A convenient measure of cohesiveness is the percentage of silt and clay in a material, M, as defined by Schumm (1960). Substituting in equation 4 results in the relation:
Q(tB-tA)
M
«A P
(5)
This expression lends itself to the use of flow-duration data.
Duration data are compiled in tables listing the number of days for narrow discharge ranges. The product of the number of days for each range (N) and the average discharge of that range can be used as a constant discharge for a definite period of time with little error being introduced by using the average discharge of the range. All such products can then be accumulated so that relation 5 becomes:
A P «
2(QN)
M
(6)
which is the basis for the analysis of data obtained in this investigation.
The development of relation 6 gives a macroscopic view of the mechanics of meander expansion. This explanation does not take into account the many microscopic processes which take place in a meander, such as bed or bank shear, superelevation, eddy currents, or transverse flow. The contribution of these factors is unquestionable, but they do not always have to be considered in determining direction or magnitude of channel movement. The important consideration is the net effect, and the impulse-momentum concept applied to the concave bank supplies just that. It is a measure of the net effect of flow on an erodible material. The work done (or energy expended) in changing momentum from one value to another is the same no matter what process effects that change.
Channel-Forming: Discharge
All discharge within an alluvial channel has some effect on the channel-shape parameters. Because of this it is impossible to relate these parameters to only one discharge. Several investigators have alluded to this premise.
Carlston (1965) found the most significant relationships for meander wavelength to involve average discharge and the mean discharge for the month of maximum discharge. Schumm (1968, 1969) found that when average, bankfull, and mean annual flood discharge are each correlated with the percentage of silt and clay in the channel perimeter and channel properties, the results are, to nearly equal degrees, very significant explanations of meander wavelength and channel cross-sectional properties. Stall and Fok (1968) found that hydraulic geometry was best explained using the discharge at 10-percent flow duration. These relationships show that there is a range of discharge from at least the average to the mean annual flood which controls the dimensions of meanders.
The position of the main-velocity thread in a meander loop at varying discharge has been shown by Friedkin (1945, pi. 9). He indicated that low flow attacks the upstream part of the concave bank, half-bankfull flow attacks the mid-part, and bank-full flow attacks the downstream part. At discharge greater than bankfull, the meandering velocity pattern is not destroyed, and the turbulence effective in erosion may be increased (Toebes and Sooky, 1966).
Channel-Forming: Discharge Redefined
Consideration of all the relationships developed indicates not only that all discharge affects channel dimensions, but that there is a threshold discharge at and above which the major part of channel formation occurs. Channel dimensions should depend upon those flows for which the channel acts as a unit. At low flows (less than average), the pool and riffle sequence within channel limits is effective, resulting in a low-water channel which often meanders within the confines of the bankfull channel. At some discharge the pool and riffle sequence is drowned out, and the channel acts as a unit at all higher discharges. The point is probably reached near average discharge as the relationships discussed have indicated.
Some further evidence can be gained from study of traveltime data. Figure 5 presents the results of several traveltime determinations for the East Fork White River. The break in slope occurs near average discharge and is characteristic of unpublished traveltime curves for most of the streams in Indiana which exhibit a pool and riffle condition at low flows.
Channel formation can be considered, then, to begin at just above average discharge and continueCHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A7
Figure 5.—Traveltime for the East Fork White River between U.S. Geological Survey gages at Columbus and Seymour.
for all higher discharges. This range can also be considered to be directly related to the expansion of a meander loop.
The remainder of this paper is an attempt to test the conclusions reached up to this point—namely, that path-length expansion is directly proportional to the volume of flow for above-average discharge days and inversely proportional to the percentage of silt and clay in the bed and bank material.
FIELD INVESTIGATION
STUDY SITES
The sites investigated for this project are shown in figure 6, and some pertinent physical characteristics are listed in table 1. All sites were within a reasonable distance from a U.S. Geological Survey stream-gaging station (fig. 6) except for Paw Paw Creek which is ungaged. As shown in table 1, a wide range of characteristics is represented.
The surficial geologic characteristics were formed during the Wisconsin Glaciation in the Pleistocene Epoch. At the maximum glacial advance, the northern two-thirds of Indiana was covered by Wisconsin ice. The two sites on the White River and the site on the East Fork White River are south of the maximum Wisconsin glacial advance, but the material filling the present river valleys is outwash from the melting of this last continental glaciation. The Muscatatuck River site is also south of the Wisconsin boundary, but the predominately clay material at the site was deposited in a lake whose basin was formed during the previous Illinoian Glaciation. The lake sediments of the Carpenter Creek site and the morainal features of the Paw Paw Creek site were deposited during glacial retreats of the Wisconsin Glaciation.
The weighted silt-clay percentage (fine fraction) was computed by a method described by Schumm (1960), but a diameter of 0.062 mm (millimeter), instead of 0.074 mm, was used as the dividing point
Table 1.—Selected site characteristics
[Depositional environment: After Wayne (1958)]
Name and location	Drainage area (sq mi)	Period of record (water years)	Average discharge at gaging station (cfs)	Channel slope (ft per ft)	Width- depth ratio	Weighted silt-clay percentage	Depositional environment
Paw Paw Creek near Urbana—	8.60			0.0018	7.2	7.9	Ground moraine.
Carpenter Creek near Egypt ....	48.0	1949, 1951, 1953-67	33.7	.00064	8.0	29	Lake sediments.
White River near Martinsville..	.. 2,520	1930-31, 1946-67	2,258	.00035	27	2.2	Valley-train sediments.
White River near Worthington.. East Fork White River	... 4,390	1929-67	4,459	.00023	20	2.6	Do.
near Vallonia 		.. 2,530	1928-67	2,346	.00024	14	6.9	Do.
Muscatatuck River near Austin		 367	1933-35, 1937-43	387	.00025	5.8	87	Lake sediments.A8
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
87°	86°	85°
Figure 6.—Location, of investigated meander sites and gaging stations.CHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A9
Map No.
1
2
3
4
5
EXPLANATION FOR FIGURE 6
Meander sites
Name and location
Paw Paw Creek near Urbana, Wabash County, sec. 12, T. 28 N., R. 6 E.
Carpenter Creek near Egypt, Jasper County, sec. 22, T. 28 N., R. 7 W.
White River near Martinsville, Morgan County, sec. 7, T. 11 N., R. 1 E.
White River near Worthington, Greene County, sec. 28, T. 8 N., R. 5 W.
East Fork White River near Vallonia, Jackson County, secs. 19, 30, T. 5 N., R. 4 E.
Meander sites—Continued
Map No.	Name and location
6	Muscatatuck River near Austin, Scott County,
secs. 33, 34, T. 4 N., R. 6 E., and sec. 3, T. 3 N., R. 6 E.
Gaging stations
National No.
Name
5-5240
3-3540
3-3605
3-3655
3-3670
Carpenter Creek at Egypt.
White River near Centerton.
White River at Newberry.
East Fork White River at Seymour. Muscatatuck River near Austin.
for fine and coarse fractions. A dividing-point diameter of 0.062 mm conforms to the Wentworth grade scale and results in only a slightly smaller percentage. The difference is not enough to destroy comparability. Material for these analyses was collected at several locations on both banks within each study reach, and the results were averaged for each reach. The variability within each reach was considered sufficiently small that a reach could be treated as having fairly homogeneous lithology throughout.
The field investigations were carried out from the spring of 1966 to the spring of 1969. Channel locations were identified from aerial photographs and, except for those from 1939 and 1958 for the Martinsville site, were obtained from the files of the Indiana Department of Natural Resources. The two exceptions were obtained from the files of the Soil Conservation Service, U.S. Department of Agriculture. Plan-view channel patterns for all sites are shown in figures 7 through 12. The method of analysis will be illustrated with the White River near Worthington site (fig. 10).
N
O 100	200 FEET
No trees on either bank
Figure 7.—Meander system at the Paw Paw Creek near Urbana site. Surveyed by J. F. Daniel and J. W. Tucker, April 3, 1969.
DATA ANALYSIS
Field surveys at the White River near Worthington site were made June 7, 1966, and July 23, 1968, by Indiana Department of Natural Resources personnel. The results of those surveys and the bank locations based on aerial photographs taken July 5, 1937, and April 16, 1962, are shown in figure 10. Any further usefulness of this site was destroyed when a natural cutoff formed in late June 1968.
\
\
Figure 8.—Meander development at the Carpenter Creek near Egypt site. Surveys by J. F. Daniel and others.A10
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
Each path location was analyzed independently as follows:
1.	The direction angles with an assumed mean
downstream direction were measured for equal, short tangents of the cut-bank path length.
2.	The direction angles and the stationings were
plotted, and a sine curve was fitted to the points. (See fig. 1.)
3.	The path length, corrected mean downstream
direction (obtained by adjusting the vertical coordinate scale), and amplitude of the sine wave were determined from the graph.
4.	The theoretical loop was then compared with
the actual loop by plotting the positions of both, beginning at the midpoint stationing of the actual loop.
Barren

Figure 9.—Meander development at the White River near Martinsville site. Surveys by State of Indiana Department
of Natural Resources.CHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
All
5. A line joining the %- and %-wavelength points on the theoretical loop was extended to the actual loop, as in figure 13. This method objectively defines %P and on the actual loop, and the path distance between these two points was measured.
Using duration data which were computer-compiled by class interval, the total flow volume of all
days having discharge greater than the effective discharge was accumulated. It has already been shown that this effective discharge occurs at a discharge slightly greater than the average. Therefore, accumulation was begun with the first class interval greater than the average. Volume for each class interval was computed by taking the product of the
Figure 10.—Meander development at the White River near Worthington site. Surveys by State of Indiana Department
of Natural Resources.A12
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
average of the class and the number of days in the class. While this is not an exact measure, the class intervals are small enough that very little error is introduced.
The effective-discharge volume was then plotted versus the accumulated path-length increase as in
figure 14. It appears that the few points available define a straight line, which was fitted by eye. Using the same technique, the same relations were developed for the White River near Martinsville and the East Fork White River near Vallonia sites (figs. 15,16).
Figure 11.__Meander development at the East Fork White River near Vallonia site. Surveys by J. F. Daniel and others.CHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A13
\	^	N
\ \ \ \
0	100	200 FEET
\ Trees are continuous on both banks
\
Figure 12.—Meander system at the Muscatatuck River near Austin site. Surveys by J. F. Daniel and R. J. Southwood, April 28, 1966.
O	Computed point
®	End point
---------Theoretical loop
---------Actual loop
Figure 13.—Definition of actual end points from theoretical loop, plotted on 1937 loop, for the White River near Worthington site.
FLOW VOLUME FOR DAYS ABOVE AVERAGE DISCHARGE, IN MILLIONS OF CFS-DAYS
Figure 14.—Path-length increase versus flow volume for the White River near Worthington site.
FLOW VOLUME FOR DAYS ABOVE AVERAGE DISCHARGE,
IN MILLIONS OF CFS-DAYS
Figure 15.—Path-length increase versus flow volume for the White River near Martinsville site.
FLOW VOLUME FOR DAYS ABOVE AVERAGE DISCHARGE,
IN MILLIONS OF CFS-DAYS
Figure 16.—Path-length increase versus flow volume for the East Fork White River near Vallonia site.A14
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
INTERPRETIVE DISCUSSION
INDIVIDUAL SITES
The differences between bank locations at different times at the sites on Paw Paw Creek near Urbana, Muscatatuck River near Austin, and Carpenter Creek near Egypt were small; therefore data obtained from studies at these three sites were not adequate for analysis.
Bank locations of Paw Paw Creek for 1941 and 1962, as determined from aerial photographs, are not significantly different from those mapped by surveys in 1967, 1968, and 1969. There is field evidence of erosion and change, as identified by measurements of steel pins set in the channel, but the scale factor of the photographs in combination with such slight changes in bank location makes the data unreliable for developing a mechanism applicable to other sites.
The bank location of the Muscatatuck River near Austin site has not changed during the period 1940-66, as determined from aerial photographs in 1940, 1949, and 1956 and a field survey in 1966. Rotation of steel pins in the channel indicates that bank creep moves earth material toward the bank face where it is loosened by freeze and thaw cycles and carried away by high flows. This indicates that the channel is widening, but at such a slow pace that it is not readily measurable. Another valuable insight learned at this site is that, for this particular relation between silt-clay percentage and discharge volume, the increase of path length is virtually nil.
There was also no significant change at the Carpenter Creek at Egypt site. However, field surveys for a longer period than 1967-69 would probably yield information that would allow analytical results. Aerial photographs for 1939 could not be used to obtain a comparable path because of uncertainty of reference-point location.
The studies at the East Fork White River site yield information which is reliable. The data on expanding path length were collected for a 33-year period when the site was not directly affected by man. The author believes, however, that any further data collection at this site would not be worthwhile
because the loop is moving into a prior channel location. Data obtained will no longer be applicable to a singly defined loop.
In conjunction with the field investigation at this site, measurements of daily suspended-sediment load were made at the gaging station upstream. The suspended loads measured during the field-survey period are presented in table 2. Russell F. Flint (written commun., 1966) estimated the average yearly load on the basis of an indirect method of analyzing periodic samples collected during the period 1963-65. Because the daily load record is short and the estimated yearly load seems disproportionately high, no reasonable relation of sediment load to expansion rate has been found. The data herein are presented for future reference.
Some discussion of the White River near Martinsville site is needed to explain the two curves in figure 15. Between 1958 and 1964, the middle part of the loop was stabilized with riprap and the upper part of the loop was apparently straightened. This channel alteration appears to have resulted in an increased rate of path lengthening owing to increased erosion in the downstream part of the loop. It seems likely that this increased rate will be temporary and that there will be a return to the prealteration rate. For this reason the author believes that the previous rate can be used for comparison with rates of other sites.
General relations can be developed from the studies at the Vallonia and Martinsville sites, which were just discussed, and at the Worthington site,
Table 2.—Suspended-sediment loads for East Fork White River at Seymour
Survey period	Sediment-load period	Sediment load (tons)
4-20-66 to 4- 5-67	7- 1-66 to 4- 5-67	220,705
4- 6-67 to 4-24-68	4- 6-67 to 4-24-68	312,146
4-25-68 to 4- 8-69	4-25-68 to 4- 8-69	971,099
Estimated annual			 721,000
		CHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A15
which was used to illustrate methods in the section on data analysis.
GENERAL CONCLUSIONS
Data indicate that for each of the three sites for which analysis was possible a well-defined relationship could be developed between time and path length as well as between discharge and path length. The relation between time and path length is not as sharply defined as that between discharge and path length, but for all practical purposes they are equivalent. The explanation for this is indicated in figure 17 where there is a lack of large deviations between the mass curve and the dashed line. This indicates that annual discharge volumes for days above average discharge are relatively constant. Therefore, an increase in path length would be relatively constant from year to year. This condition is more likely to occur in a subhumid climate, such as that in Indiana, than in a semiarid climate, such as that in the Great Plains, where yearly changes in discharge volume for days above average discharge are relatively much greater. Therefore, while a yearly path-increase rate for the sites in Indiana is sufficient for use, the same method probably could not be used for meander loops developing from different climatological conditions. For streams in different climates, the path-length versus discharge-volume relation should yield better results.
Through the study of the annual path-length increase, some insight can be gained into the effect of grain size. In figure 18 the rate of path-length increase has been transformed to a per-square-mile basis and plotted versus the silt-clay percentage. Not shown is the point defined by the Muscatatuck site (no expansion; 87 percent silt and clay), but it was considered in shaping the curve. Again, while not enough data are available for “proof” of a hypothesis, the points do indicate that the expansion rate would have a nonlinear relation to the silt-clay percentage. It seems reasonable that this relation would be asymptotic to the silt-clay axis, indicating that no bank would completely resist erosion. The extension of the curve toward zero silt and clay may be asymptotic to the rate axis also, but it probably
Figure 17.—Accumulated flow volume versus water year for White River near Worthington site.
Figure 18.—Probable relation of path-length increase and silt-clay percentage.
would be discontinuous at some point close to that axis. This would indicate that as the path length increased at an extremely rapid rate the radius of curvature of the channel would become infinite, thereby resulting in a straight reach with little or noA16
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
change in path length. In other words, at some extremely small silt-clay percentage, the path length would not increase. The channel could still move, but the path length would not change except for short periods of time.
In order that comparison with meander migration in other regions can be made in the future, the data have been put into dimensionless form as shown in figure 19. The scatter of the points with regard to silt-clay percentage indicates a lack of
250
o o z Z <
200
150
gSS
c <
* p
l 50
0
O ------Worthington
O --------Martinsville
Vallonia------ O
------------1____________i___________i____________i___________
0	2	4	6	8	10
WEIGHTED SILT-CLAY PERCENTAGE
Figure 19.—Dimensionless relation of path-length increases and flow data to silt-clay percentage.
orderly progression. However, when width-depth ratio is used as the dimensionless parameter for the abscissa, as in figure 20, a logical sequence of points is obtained.
The apparent discrepancy between these two treatments can best be explained by sampling error. Schumm (1960) related width-depth ratio to silt-clay percentage of the bed and banks. His data were derived from cross sections and indicate a definite correlation between the two parameters. For this investigation several points within each reach were sampled for silt-clay percentage, and the results were averaged for the reach. The scatter of data in figure 19 indicates that enough samples to establish a statistically significant average may not have been obtained. Apparently, then, the average width-depth ratio is a more integrated, and hence better, measure of the average silt-clay percentage than the bed and bank samples themselves.
Figure 20.—Dimensionless relation of path-length increase and flow data to width-depth ratio.
The interpretation of figure 20 is similar to that of figure 18. The higher the width-depth ratio, the lower is the silt-clay percentage and the faster is the path-length increase. Conversely, the lower the width-depth ratio, the higher is the silt-clay percentage and the slower is the path-length increase. Again, as in the interpretation of figure 18, one would expect that no channel would completely resist erosion so that any curve should pass through the origin. However, because of the few points available, an extension of the curve to the origin has not been shown.
The inclusion of the drainage area in the ordinate may or may not tend to restrict the validity of figure 20 to climatic or geologic conditions similar to those for which it was developed. If it does and if the concept is correct, one would expect to find a family of curves, each representing a particular environment. To test this relation by studying meanders in other areas would seem to be a logical “next step” to this investigation.
The foregoing interpretation of figure 20 tends to invalidate the relation shown in figure 18. Because of this and because of its more usable dimensionless form, the author feels that figure 20 represents the best treatment of the available data. It could be used to estimate path-length increase of alluvial streams in Indiana having width-depth ratios within the approximate range of 8 to 28 and for most flow volumes. Time intervals for path-length increases can be related to flow volume by doing flood-volume frequency analyses for shortCHANNEL MOVEMENT OF MEANDERING INDIANA STREAMS
A17
time intervals or by considering only long intervals (several years) and using average discharge. It must be remembered, however, that path-length increase is only part of the movement mechanism.
The mechanisms of translation and rotation have been described earlier in this paper (figs. 2 and 3) but not enough data are available for a quantitative analysis of the total process. If the end points of a loop are likely to be stable, such as at the Vallonia site, then rotation and translation cease to have an appreciable effect. A useful estimate of movement might then be made with figure 20. Because this condition seldom exists, further investigation of rotation and translation is also a next step to this investigation.
It has also been impossible to evaluate the effects of vegetation on loop expansion. Qualitative descriptions of vegetative cover proposed by Dansereau (1957) and listed by Strahler (1965) have been given on the site illustrations. The percentage of path length supporting dense vegetation is nearly equal for each of the three sites used to develop the relation shown in figure 18. It seems logical that vegetation would slow down expansion. However, unless vegetation covers 100 percent of the path, the experience at the Martinsville site indicates that the effect may be overcome by expansion in that part of the loop which is not protected. The effect of dense vegetation can be likened to the effect of very different material composition; for example, abandoned clay-filled meanders are often the inhibiting factors that control channel movement on the lower Mississippi River (C. R. Kolb, written com-mun., 1969). Because similar problems in analyzing movement result from either cause, much more data are needed before any quantitative effect of vegetation or very different material zones can be assigned.
SUMMARY
The attempt has been made in this report to review some established principles of channel geomorphology and to use those principles to give some insight to the process and prediction of meander movement.
Meander loop movement has been investigated by using a sine-generated curve to determine the end points of a loop from which the actual path length can be measured. Using the simple physical model of impulse momentum, a relationship of discharge to loop expansion has been deduced and related to grain size of the bank material.
Consideration of traveltime data and the regression analyses of many other investigators has led
to the conclusion that channel-forming discharge begins very near, but just higher than, average discharge and continues throughout all higher discharges. Channel movement is then a function of the time distribution of the higher discharges.
A division of the channel material into fine and coarse fractions has been used in order to relate the rate of expansion to the cohesiveness of the banks. Suspended-sediment discharge records were collected for one site but are not of sufficient length for rigorous analysis.
Several simple models of channel movement by rotation, translation, and expansion have been illustrated on the basis of the experience gained from this investigation. No general relation has been found with which the first two processes could be analyzed. Therefore, the goal of movement prediction has not been achieved. However, if reasonable relationships can be found to relate rotation and translation to common factors, those relationships, along with the expansion relation which has been defined, will give scientists a tool with which it may be possible to predict the movement of meanders.
SELECTED REFERENCES
Bagnold, R. A., 1960, Some aspects of the shape of river meanders: U.S. Geol. Survey Prof. Paper 282-E, p. 135-144.
Carlston, C. W., 1965, The relation of free meander geometry to stream discharge and its geomorphic implications: Am. Jour. Sci., v. 263, p. 864-885.
Dansereau, Pierre, 1957, Biogeography, an ecological perspective: New York, The Ronald Press Co., 394 p. Friedkin, J. F., 1945, A laboratory study of the meandering of alluvial rivers: Vicksburg, Miss., U.S. Waterways Expt. Sta., 40 p.
Guy, H. P., Rathburn, R. E., and Richardson, E. V., 1967, Recirculation and sand-feed type flume experiments: Am. Soc. Civil Eng. Trans., v. 93, p. 97-114.
Langbein, W. B., and Leopold, L. B., 1966, River meanders— theory of minimum variance: U.S. Geol. Survey Prof. Paper 422-H, 15 p.
Leopold, L. B., Bagnold, R. A., Wolman, M. G., and Brush, L. M., 1960, Flow resistance in sinuous or irregular channels: U.S. Geol. Survey Prof. Paper 282-D, p. 111-134.
Leopold, L. B., and Langbein, W. B., 1962, The concept of entropy in landscape evolution:	U.S. Geol. Survey
Prof. Paper 500-A, 20 p.
Leopold, L. B., and Maddock, Thomas, Jr., 1953, The hydraulic geometry of stream channels and some physiographic implications: U.S. Geol. Survey Prof. Paper 252, 27 p.
Leopold, L. B., Wolman, M. G., and Miller, J. P., 1964, Fluvial processes in geomorphology:	San Francisco,
W. H. Freeman & Co., 522 p.A18
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
Popov, I. V., 1965, The use of hydrologic-morphological analysis in water intake planning: Soviet Hydrology, Selected Papers, no. 5, 1965, p. 437-450 (1966).
Scheidegger, A. E., and Langbein, W. B., 1966, Probability concepts in geomorphology: U.S. Geol. Survey Prof. Paper 500-C, 14 p.
Schumm, S. A., 1960, The shape of alluvial channels in relation to sediment type: U.S. Geol. Survey Prof. Paper 352-B, p. 17-31.
------1968, River adjustment to altered hydrologic regimen-—Murrumbidgee River and paleochannels, Australia: U.S. Geol. Survey Prof. Paper 598, 65 p.
------1969, River metamorphosis: Am. Soc. Civil Eng.
Trans., v. 95, p. 255-273.
Stall, J. B., and Fok, Yu-si, 1968, Hydraulic geometry of Illinois streams: Illinois Univ. Water Resources Center Research Rept. 15, 47 p.
Strahler, A. N., 1965, Introduction to physical geography: New York, John Wiley & Sons, Inc., 455 p.
Thornbury, W. D., 1950, Glacial sluiceways and lacustrine plains of southern Indiana: Indiana Dept. Conserv., Div. Geol. Bull. 4, 21 p.
Toebes, G. H., and Sooky, A. A., 1966, Hydraulics of meandering rivers with flood plains: Am. Soc. Civil Engineers Water Resources Eng. Conf., Denver 1966, Preprint 351, 38 p.
Twidale, C. R., 1964, Erosion of an alluvial bank at Bird-wood, South Australia:	Zeitschr. Geomorphologie,
New Ser. v. 8, no. 2, p. 189-209.
Wayne, W. J., 1958, Glacial geology of Indiana: Indiana Dept. Conserv., Geol. Survey Atlas Min. Resources Map 10.
Wolman, M. G., and Leopold, L. B., 1957, River flood plains: some observations on their formation: U.S. Geol. Survey Prof. Paper 282-C, p. 87-109.
Woodyer, K. D., 1968, Bankfull frequency in rivers: Jour. Hydrology, v. 6, p. 114-142.
U. S. GOVERNMENT PRINTING OFFICE : 1971 O - 443-512Scott-SCOUR AND FILL IN TUJUNGA WASH-A FANHEAD VALLEY IN URBAN SOUTHERN CALIFORNIA—Geological Survey Professional Paper 732-B
75

Scour and Fill in Tujunga Wash—
A Fanhead Valley in Urban Southern California—1969
GEOLOGICAL SURVEY PROFESSIONAL
Prepared in cooperation with the California Department of Water Resources
PAPER 732-B
JUL U 1973
A /JScour and Fill in Tujunga Wash-A Fanhead Valley in Urban Southern California—1969
By KEVIN M. SCOTT
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 73 2-B
Prepared in cooperation with the California Department of Water Resources
An analysis of well-documented large and destructive changes of a stream channel in an urbanized area subject to floods
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :	1973UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY V. E. McKelvey, Director
Library of Congress catalog-card No. 72-600245
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 — Price 70c domestic postpaid or 50c GPO Bookstore Stock Number 2401-00322CONTENTS
Page
Abstract___________________________________________________ B1
Introduction and acknowledgments____________________________ 1
The storms__________________________________________________ 2
Precipitation and runoff_______________________________ 3
Recurrence intervals of the 1969 floods________________ 4
The environment_____________________________________________ 4
Characteristics of the drainage basin__________________ 4
Characteristics of Tujunga Wash________________________ 4
Terrace levels of Tujunga Wash_________________________ 6
Bed material of Tujunga Wash___________________________ 6
Scour and fill______________________________________________ 6
Factors that influence scour and fill in fanhead valleys
and on alluvial fans_________________________________ 8
Changes in water discharge and sediment load__	8
Movement of bed forms and debris flows_____________ 8
Lateral shift of channel- _________________________ 8
Change in channel slope____________________________ 9
Change in base level_______________________________ 9
Tectonic effects and long-term aggradation or
degradation______________________________________ 9
Page
Scour and fill—Continued
Factors that influence scour and fill in fanhead valleys and on alluvial fans—Continued
Manmade changes________________________________ BIO
Methods of study—photogrammetric determination of
scour and fill_______________________________________   10
Types and accuracy of photogrammetric mapping_______	10
Construction of cross sections______________________ 11
Scour and fill in Tujunga Wash___________________________ 11
Scour and fill portrayed on cross sections__________ 11
Summary and conclusions__________________________________ 25
Flow diverted to distributary channel_______________ 25
Vertical scour due to local reduction in base level-	25
Lateral scour of terraces_________________________   27
Changes in longitudinal profiles____________________ 27
Photogrammetric methods applied to the determination of scour and fill_______________________________ 28
Application of tesults____________________________   28
References cited_________________________________________ 28
ILLUSTRATIONS
Page
Figure 1.	Index map of study area_____________________________________________________________________________________ B3
2.	Longitudinal profile of Tujunga Creek_____________________________________________________________________________ 4
3.	Map of Tujunga Wash showing limits of urbanization and location	of cross sections_________________ 5
4.	Photograph showing view looking upstream along the south channel of Tujunga Wash__________________________________ 7
5.	Longitudinal profiles of the main channels of Tujunga Wash_______________________________________________________ 12
6.	Sections A-A', B-B\ and C-C', Tujunga Wash_______________________________________________________________________ 13
7.	Sections D-D' and E-E', Tujunga Wash_____________________________________________________________________________ 14
8.	Photograph showing inundation along south channel of Tujunga Wash, February 25,	1969_____________________________ 15
9.	Sections F-F' and G-G', Tujunga Wash___________________________________________________________________________   17
10.	Sections H-H' and Tujunga Wash___________________________________________________________________________________ 18
11.	Sections J-J' and K-K', Tujunga Wash_____________________________________________________________________________ 19
12.	Photograph of south channel of Tujunga Wash showing destruction	of the south-channel Foothill Boulevard bridge. _	21
13.	Sections L-L' and M-M', Tujunga Wash_____________________________________________________________________________ 22
14.	Photograph showing view looking northwest of what remained of the Bengal Street terrace after February 25 flood
peak__________________________________________________________________________________________________________ 23
15.	Section N-N', Tujunga Wash___________________________________________________________________________________     24
16.	Sections O-O' and P-P', Tujunga Wash---------------------------------------------------------------------         26
TABLE
Table
1. Summary of flood discharges at gaging stations in Tujunga Creek drainage
in
Page
B3*PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIFORNIA—1969
By Kevin M. Scott
ABSTRACT
A unique combination of substantial channel change and documentation of the changes by high-order photogrammetry was studied in Tujunga Wash in southern California. Extensive scour and fill occurred during the recordbreaking 1969 floods in this 3-mile-long, partly urbanized fanhead valley. Maxima of 20 ±2 feet of net scour and 35±2 feet of net fill were measured on 31,000 scale-feet of cross sections plotted to illustrate changes in distributary channels of the wash. Net elevation change of the channel thalweg varied from as much as 14 ±2 feet of scour to as much as 16 ±2 feet of fill.
The most dramatic causes of scour and fill in Tujunga Wash were (1) the unexpected yet possibly natural diversion of flood-flow to a major distributary channel of the wash in which urbanization had progressed, (2) local reduction in base level which occurred when floodflow in both of the main distributary channels entered a large gravel pit, and (3) lateral scour of an aggradational surface within the wash because of natural adjustment of a distributary channel to flood discharge. Additional scour and fill were due to locally raised base level and to the natural lateral shift characteristic of channels in the broad, ephemeral washes of arid and semiarid regions.
Scour proceeded upstream from the edge of the gravel pit probably as much as 3,000 feet and was instrumental in the failure of three highway bridges. An entire residential street and seven homes built on an unstabilized cutback of the channel were destroyed by lateral scour. Damage at most, if not all, of the localities could be indirectly ascribed to man’s disregard of natural geomorphic processes on alluvial fans and in fanhead valleys.
The textural similarity of the bed material of the active channels and the deposits exposed within the wash by the 1969 floods suggests that all the deposits were formed under the present, or a similar, hydrologic regime. Thus, rapid lateral shifts of channel position as a result of major floods should not be unexpected anywhere in the wash. During long intervals of dry weather, however, the memories of previous flood disasters become dim, and building sites in the washes and on bordering terraces prove irresistible to developers and home buyers. Urban development on the unstabilized cutbank of a natural flood channel on an alluvial fan or fanhead valley is generally a poor risk.
Comparing preflood and postflood profiles downstream from the point of a fanhead jump, it is apparent that channel diversion locally resulted in scour of one major channel which corresponded in amount with fill in the other major channel. Not only were scour and fill comparable in amount, but the postflood profiles of both
channels became nearly parallel, after smoothing of pronounced preflood irregularities in the channel which were both natural and the result of the works of man. Analogies with mechanisms active in the maintenance of a long-term equilibrium in the formation of alluvial fans are possible.
Analysis of the photogrammetric data indicated that accuracy of design mapping (contour interval, 2 feet; scale, 1: 600) is sufficient to define net changes in scour and fill throughout a flood course, in parts of the channels to the nearest foot of elevation. Detection of minor gullying outside the main distributary channels was possible on low slopes.
INTRODUCTION AND ACKNOWLEDGMENTS
Many urban areas in southern California are bounded by rugged mountain ranges. Streams draining the mountains flow initially through steep bedrock channels, then debouch during floods from the steep fronts of the ranges to rapidly deposit debris on broad, semicircular cones known as alluvial fans.
Streams that drain the frontal watersheds of the San Gabriel and San Bernardino Mountains form alluvial fans directly at the mountain front. Larger streams that drain the interior of the mountain ranges, although confined to deep V-shaped canyons throughout much of their courses, make the final 1-5 miles of their departure from the mountain front through broad, expanding valleys hydrologically similar to the pieshaped segment of a fan. These valleys, here described as fanhead valleys, are the intermountain extensions of fan alluviation. Such upper fan embayments also have been described as fanbay areas which, however, are generally features of a smaller scale.
In their natural state, channels both on the fans and in the fanhead valleys are unstable washes like those of desert regions—ephemeral and capable of shifting rapidly in response to changes in flow.
It was on the fans, particularly in fanhead areas, where stream processes were most active and where the greater part of the damage caused by the record-breaking floods of January and February 1969 was
B1B2
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
concentrated. It was also on the upper parts of the fans where the conflict between urbanization and the natural environment was most dramatically illustrated. Such areas are often the last land available in southern California in a pattern of urbanization moving upward from the level land of the basins toward the mountain front. Individual flood-control facilities for every major fan-forming drainage have not kept pace with urban development. Well-planned flood-control facilities in older developed sections held damage to a minimum in basin areas and on most of those fans where facilities were complete.
Several Indirect factors contribute to the local destructive intensity of floods in southern California. One is the ephemeral nature of stream channels on fans and in fanhead valleys. Little or no surface flow occurs during most of the year, and in many years storm runoff is of small magnitude and short duration. During the long intervals of dry weather, memories of previous flood disasters become dim, and building sites in the washes and on bordering terraces prove irresistible to developers and home buyers. This problem was magnified by a prolonged dry period, lasting from the mid-1940’s to 1965, that coincided with a time when the population of southern California multiplied explosively. In addition, urban planners have not been uniformly cognizant of the geomorphic setting and the nature of floodflows on alluvial fans. At the heart of this aspect of the problem, as noted by Rantz (1970), is the lack of a direct central planning authority to exercise uniform control over the 78 municipalities that exist in Los Angeles County alone.
The problem of flooding on fans generally was not one simply of damage from rising flood waters; rather, it was largely one of rapid lateral shift in channel position, either by erosion of the banks of stream terraces supporting structures seemingly safe from the greatest flood or by the seemingly random jump of the flow to old or completely new channels radiating from the fan apex. Property destruction from this cause occurred on fans throughout southern California in 1969.
This report treats an example of flood effects on both channel morphology and the activities of man in a fanhead valley—Tujunga Wash (fig. 1). The purpose of the study is to (1) provde urban planners with a case history of the changes in channel morphology in a fan environment; (2) analyze these changes in terms of scour and fill; (3) indicate the causes of scour and fill wherever possible; and (4) show how high-order photogrammetry can detect such channel changes. The circumstances connected with scour and fill in Tujunga Wash are examples that apply in principle to
innumerable other fanhead valleys that may become urbanized in a similar manner throughout the Southwestern United States.
The changes in Tujunga Wash were of two general kinds: changes that would have occurred under natural conditions, and changes that were interrelated with human modification of the channel. In the first, if destruction in similar geomorphic settings is to be avoided in the future, planners must appreciate the potential magnitude of the natural changes—the way in which ephemeral fan channels adjust to changing flow conditions—before making zoning decisions. Secondly, with knowledge of the harmful effects of a few of man’s activities in the channels, control of such activities must be exercised, or compensating protective measures planned in the event of economic justification.
The study was made in cooperation with the California Department of Water Resources. Agencies that provided information are acknowledged in the body of the report; individuals who provided assistance are too numerous to mention, but lack of space does not reflect the lack of the author’s gratitude.
THE STORMS PRECIPITATION AND RUNOFF
The storms of late January and late February 1969 caused floods approaching or exceeding the previous flows of record at many localities (Waananen, 1969). Moist tropical air moved strongly out of the Pacific as a series of storms during the periods January 18-22, January 24-27, and February 22-25. The pattern of precipitation for the February storm, which caused the greatest damage in Tujunga Wash, is shown in figure 1.
Distribution of rainfall in the upstream drainage basin of Tujunga Creek generally was similar in the January 18-22 and February 22-25 periods. During the January 24-27 storm, greater quantities of precipitation, 18-20 inches, fell in the central part of the basin near Big Tujunga Reservoir. Totals for the January 18-22 and February 22-25 storms ranged from 12 to 14 inches in the same area. Precipitation during February maintained saturated-soil conditions that permitted the runoff from the storm of February 22-25 to compare with that of the more intense storm of January 24-27.
The January 1969 floods in southern California were comparable to those of March 1938, the greatest since the legendary flooding of 1862. This was not true in the Tujunga Canyon area, however, where peak discharges were less than in 1938 (table 1), in part because the 1938 storm was unusually intense in the TujungaSCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B3
118*15'
Figure 1.—Index map of study area. The stream-gaging stations shown are operated by the Los Angeles County Flood-Control District. Isohyetals compiled by the Los Angeles County Flood-Control District.
Creek watershed. Although renewed flooding in February 1969 produced peak discharges in Tujunga Creek comparable to those of January (table 1), the February flows proved to be more devastating in their effects on urbanization in the area studied because of factors described below.
Values of peak discharges through Tujunga Wash are not well defined. Maximum mean hourly inflow into Hansen Flood-Control Basin (fig. 1) during the February storm period was 26,000 cfs (cubic feet per second) from 0700 to 0800 hours on February 25 (Simpson, 1969b, pi. 86). Inflow from an additional drainage area of 21 square miles is included in this figure. Discharge in the wash is estimated to have reached a maximum of more than 17,000 cfs during the predawn hours of February 25 (Simpson, 1969a, p. 40).
Table 1.—Summary of flood discharges at gaging stations in Tujunga Creek drainage
Stream and Station place of No. determination	Drainage area (square miles)	Period of record	Date	Maximum discharges	
				Cfs	Recurrence interval (ratio to 50-year flood)
11-0940. Tujunga	64.9	1948-69	1-23-43	i 14,800	1.2
Creek be-			12-29-65	6,550	.42
low Mill			1-25-69	12,900	1.02
Creek, near			2-25-69	13,500	1.1
Colby					
Ranch.					
11-0955. Tujunga	106	1916-69	3- 2-38	s.s so,boo	2.6
Creek near			1-25-69	3 2O', 600	1.1
Sunland.			2-25-69	320,000	1.05
1	Exceeded by March 1938 flood. Peak inflow to Big Tujunga Reservoir (drainage area 81.4 sq mi) 35,000 cfs, Mar. 2, 1938.
2	Estimated.
3	Affected by storage in Big Tujunga Reservoir (constructed 1931).B4
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
RECURRENCE INTERVALS OF THE 1969 FLOODS
A perspective of the relative significance of the 1969 floods in the Tujunga Creek basin is indicated by their recurrence intervals—the number of years, on the average, in which a given peak flow will be equaled or exceeded once by the annual peak discharge. A 50-year flood, for example, has one chance in 50 of being equaled or exceeded in any one year. Such a flood need not recur only once every 50 years; because of the irregularity of climatic trends, it could occur several times in a shorter time interval.
The recurrence intervals of peak discharges on both January 25 and February 25 were slightly in excess of 50 years at both the upstream station, Tujunga Creek below Mill Creek, near Colby Ranch, and at the station only 3 miles above the canyon mouth, Tujunga Creek near Sunland (table 1). The back-to-back occurrence of two 50-year floods in the basin does not lengthen the odds against another major flood in the near future, however.
THE ENVIRONMENT CHARACTERISTICS OF THE DRAINAGE BASIN
Tujunga Creek above the mountain front drains 115 square miles of the western San Gabriel Mountains. Big Tujunga Flood-Control Reservoir (fig. 1) acts as catchment for 71 percent of the basin, but its capacity is small (3,819 acre-ft in 1966) in relation to its drainage area (81.4 sq mi). Large flows, such as those of January and February 1969, may pass the spillway only slightly attenuated.
The area is one of normally erosion-resistant rocks which, because of geologically recent faulting and fracturing, supply large quantities of debris to drainage courses through processes of mass movement, as well as normal runoff-erosion mechanisms. Annual debris yields to Big Tujunga Reservoir, in 39 seasons (1930-31 to and including 1968-69), have averaged 2,500 cu yd per sq mi per yr (cubic yards per square mile per year), or 1.56 acre-ft per sq mi per yr. Debris inflow between October 1966 and March 1969 was 7,550 cu yd per sq mi per yr, or 4.68 acre-ft per sq mi per yr. Most of the debris represented by the 1966-69 figure was deposited during the 1969 storms.
Geologically recent uplift of the basin is indicated by steep, dissected slopes, which average 40 percent throughout the watershed, and convexity in parts of the stream profile (fig. 2). Other explanations of a convex profile are possible, but the nearness of a convexity to the range front suggests that change of base level by uplift relative to the San Fernando Valley is the most probable cause. The rift zone of the San Gabriel fault, a major lateral-slip fault with many miles of displacement, controls the stream-channel
O
c
CP
cr
Figure 2.—Longitudinal profile of Tujunga Creek.
alinement in the northwest-southwest reaches upstream from the gaging station, Tujunga Creek near Sunland. Relative uplift of the upper part of the basin may have been accompanied by lateral movement on this fault. The continuing nature of tectonic activity in the watershed was illustrated by the major earthquake of February 9, 1971, during which as much as 4 feet of vertical displacement occurred along a faultline of thrusting at the north side of Tujunga Wash.
Basin relief is more than 5,000 feet, ranging from elevations of 7,124 feet at the summit of Pacifico Mountain to 1,290 feet where Tujunga Creek leaves the mountain front and enters Tujunga Wash. Valleys are V-shaped, except for parts of the main channel in which bedrock constrictions have acted as natural debris dams to form flat areas of alluviation. The average slope of the main channel over most of its 25-mile course is 135 feet per mile.
Hillslopes throughout the basin are covered with a dwarf forest of chaparral, an association of xerophytic shrubs and stunted tree forms that reflect the semiarid, Mediterranean climatic pattern—one of summer drought and winter rains. Such vegetation is highly inflammable during the dry season. Loss of watershed cover by fire can greatly increase runoff and erosion in the basin, but this was not a factor in 1969.
CHARACTERISTICS OF TUJUNGA WASH
Downstream from the mountain canyon Tujunga Creek enters a reach, Tujunga Wash, which can best be described as a fanhead valley (fig. 3). The contrast with the mountain canyon is sharp. When viewed from the air, the wash appears as a sinuous white ribbon of coarse alluvium poured from the mountain front, and is the most striking physiographic feature in San Fernando Valley. The wash forms the floor of Tujunga Valley and is 3 miles long and half a mile wide in the interval before surface flows reach the spillway eleva-Figure 3.—Limits of urbanization and location of cross sections of channels in Tujunga Wash. Cross sections are shown in figures 6, 7, 9, 10, 11, 13, 15, and 16. Topography is from U.S. Geological Survey 1:24,000 quadrangle map (Sunland quadrangle) and is not comparable with elevation data used to plot the cross sections.
%
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B5B6
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
tion of the Hansen Flood-Control Basin. It was in this reach that large quantities of scour and fill occurred, and along which property damage was most severe.
Tujunga Wash is a complex of active and abandoned channels. It resembles an alluvial fan in that it likewise is an alluvial fill formed by deposition from a stream whose competence is suddenly reduced as it leaves the confining reaches of its mountain course. Rather than an abrupt change in slope of the channel where it meets the fan apex, it is the change in hydraulic factors associated with flow through noncohesive materials— an increase in width and a decrease in depth of flow— that generally causes deposition of debris on fans and in fanhead valleys such as Tujunga Wash. Infiltration of flow in permeable valley deposits is an additional factor which causes the concentration of deposition in fanshaped loci at mountain fronts.
The stream channel of Tujunga Wash in an unmodified state is free to migrate laterally through bed material of boulder gravel, but only floodflows have the competence to transport material of that size. The main active channel on the north side of the wash (fig. 3) has a nearly constant slope marked by small irregularities, both natural and man-made. A second, historically less-active, major channel branches from the main channel at the mountain front and runs along the south side of the wash. As on an alluvial fan or delta, the tendency is one of formation of distributaries at the point where flow leaves the mountain front, but in Tujunga Wash this tendency is restricted by the bedrock side slopes of Tujunga Valley.
The channels, though typical of ephemeral desert washes, do not readily fit the systems of channel nomenclature that were developed in humid regions. Channel patterns include a spectrum of types, depending on flow regime. At low flow each sand-floored distributary meanders in a bar-braided pattern with low sinuosity (less than 1.3) within its individual wash. Little lateral cutting of the boulder-gravel banks takes place. Pools and riffles are not well defined by bed relief. Features possibly analogous to riffles appear during periods of no flow as concentrations of boulders spaced at regular intervals along the channel (Leopold, Emmett, and Myrick, 1966, p. 207); similarly, features that may correspond to pools are seen as sand-covered reaches underlain by gravel apparently less coarse than that in the rifflles. At high discharges (fig. 4), flow fills the main drainage courses, and the flow pattern becomes complexly braided with multiple bars. Rapid lateral shift of individual channels is common, although, during the floodflows of 1969, this occurred within the confines of the two large-scale braided channels discussed above.
TERRACE LEVELS OF TUJUNGA WASH
The most widespread of the depositional surfaces in Tujunga Valley is the central floor of Tujunga Wash into which the present natural channels have been entrenched, to a preflood depth of 8-10 feet near the Foothill Boulevard crossing. This surface is similar to that of undissected alluvial fans elsewhere in southern California—undulating, broadly convex upward in lateral profile, covered with mature desert vegetation. It is the most conspicuous surface on each side of the valley and is that upon which urbanization has encroached most extensively. The preflood location of the destroyed Bengal Street (fig. 3) was on this surface.
Other terraces observed were a level sporadically present 7-8 feet above the channel on the south side of the wash, and two higher levels, one 10-15 feet and another 70-90 feet above the natural channel along the north side of Tujunga Valley. The lower o' the latter two levels has been extensively urbanized; the higher is an old surface, also aggradational, grading to a former, higher level of valley fill.
BED MATERIAL OF TUJUNGA WASH
The gravel underlying the most widespread surface of the wash is similar in all sedimentological respects to the bed material of the channels. There was no significant difference in the size distributions of four samples of material underlying the main surface and five samples of bed material from the active channels. All samples were boulder gravel of bimodal distribution with the primary mode in the phi-classes —6.0 to —7.0 (64-128 mm) or —7.0 to —8.0 (128-256 mm).1 Mean size of the samples ranged from phi values of — 5.3 to —6.6 (40-100 mm). Sorting, nearly equivalent to standard deviation of the size distribution, was between 1.8 and 2.5 phi units, ranges commonly characterized as poorly sorted.
It is clear, considering the similarity in size distributions, that all the deposits exposed within the wash were formed under the present, or a similar, hydrologic regime. The significance of this conclusion is that there is no basis for assuming that any part of the main depositional surface of Tujunga Wash, because of greater coarseness of material, is immune to destruction by lateral shift of the channels. As noted above, it was this main depositional surface upon which new urbanization was progressing most rapidly prior to the 1969 flooding.
SCOUR AND FILL
Scour as discussed in this report is the removal of sediment from the channel and overbank areas of a stream by the action of fluid flow, virtually the defi-
1 The phi (<f>) grade scale may be compared with size in millimeters by the relation, mm =Figure 4.—Looking upstream along the south channel of Tujunga Wash to the point where the floodflow of February 25, 1969, branched near the head of the wash. The lined channel from Haines Canyon is visible in the foreground. Wescott Avenue is seen from lower right to upper center where its intersection with Grove Street, upper right, is inundated. Photograph by Harold Morby, Golden West Broadcasters.
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B7B8
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
nition of Culbertson, Young, and Brice (1967, p. 1). Conversely, fill is the deposition of material on bed or banks.
The connotation of scour is related to the method of measurement. For example, scour recorded by scour chains or ribbons buried vertically in a bed is the maximum depth of dilation of the grain bed during a flood. The net amount of scour, determined from preflood and postflood surveys of Tujunga Wash, is not the maximum depth of scour that existed in much of the wash during passage of the 1969 flood peaks. However, the large magnitude of channel changes in Tujunga Wash as well as the extreme coarseness of the bed material precluded study with scour chains. Values of scour and fill as measured by means of preflood and postflood surveys are the net subtraction or addition, respectively, of sediment on the valley floor.
The following summary of the causes of scour and fill is not comprehensive but includes the dominant processes that account for most scour and fill in ephemeral streams. It describes those processes most active in fanhead valleys and on alluvial fans.
FACTORS THAT INFLUENCE SCOUR AND FILL IN FANHEAD VALLEYS AND ON ALLUVIAL FANS
CHANGES IN WATER DISCHARGE AND SEDIMENT LOAD
The flow of water and sediment in alluvial channels is complex and involves the mutual adjustment of a number of variables—water discharge, sediment discharge, size of bed material, the fall velocity of a characteristic sediment particle, width, depth, velocity, slope, and a characteristic of the pattern of streamflow (Maddock, 1969).
The adjustment of channels to changes in flow variables can be partly illustrated by the channel changes that accompany the passage of a flood. Width, mean depth, and mean velocity each increase as power functions with increasing discharge at a cross section, part of the set of relations described as the hydraulic geometry of channels by Leopold and Maddock (1953). Shear stress on the bed increases, and sediment is scoured. If a large debris load is introduced on the rising stage, however, deposition may occur, associated with a decrease in flow resistance, or roughness, a change in bed form, and a reduction in depth. On the falling stage, competence of the flow to transport sediment is reduced, and fill generally occurs, most commonly back to the same or a similar level as that which existed before the flood. Similarly, temporary episodes of scour, also related to changes in debris load, and contrary to the trend toward fill, are possible on the falling stage.
Few studies have been able to define the variation in scour and fill due to change in flow factors longitudinally along a stream. In general, the ephemeral channels of semiarid areas have been found to scour
temporarily during floods (Leopold, Wolman, and Miller, 1964, p. 235). Lane and Borland (1954) concluded, from sediment yield to a reservoir, that the substantial scour in a few cross sections must be balanced by fill elsewhere in the same section of channel. Studies of perennial streams in humid areas suggest that scour and fill alternate in certain reaches.
MOVEMENT OF BED FORMS AND DEBRIS FLOWS
Large-scale gravel waves representing either dune forms or the snouts of debris flows were associated with 1969 flood discharges in other canyons along the front of the San Gabriel Mountains. Cessation in movement of concentrations of gravel formed by either process caused substantial quantities of fill at points along some expanding reaches. In Tujunga Wash and other large drainages the receding stages of water discharge were sufficiently prolonged to destroy dune forms characteristic of a high flow regime.
No gravel dunes or debris-flow snouts were visible during field inspection of all reaches of Tujunga Wash. Dune movement doubtless occurred during the peak flows, however, and caused small, temporary quantities of scour and fill.
LATERAL SHIFT OF CHANNEL
The position of the type of channel found on alluvial fans may change either by sudden redirection, or jump, of the flow, such as when distributaries form at the fan apex, or by the lateral migration of a single channel that will occur under constant flow conditions in most channels formed in noncohesive materials. In truly braided flow, the multiple channels are subject to continuous shift and splitting. Much the same mechanism is responsible for the major changes in direction that occur at the apex of a fan or fanhead valley when the bedrock-confined flow first enters an environment where flow is unconfined and bed material is noncb-hesive. Fahnestock (1959) illustrated the manner in which braided streams flowing through glacial-outwash debris change their channels: As flow increases the channel widens and in some places depth decreases, until competency is not sufficient to transport bed material; a bar is then formed, commonly near the middle of the channel, and flow divides into two channels. This process is repeated as flow increases and the channels anastomose in the constantly changing pattern characteristic of braided flow. Figure 4 shows the major division of flow that occurred near the apex of Tujunga Valley, top-center part of photograph, and the anastomosing of braided flow in the south channel, left of center.
The thalweg of alluvial channels may undergo lateral shift without a similar shift in overall channel position. In humid-region streams, this shift commonly is tem-SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B9
porary during high discharges. In ephemeral washes, the changes are greater and are more likely to survive the runoff event.
CHANGE IN CHANNEL SLOPE
A major channel shift in a fanhead valley or on an alluvial fan is commonly associated with a change in slope. Diversion of the channel at a fan apex is generally to a radial path with a steeper slope, temporarily increasing the ability of the stream to scour. However, over a longer interval, deposition will build on the new segment of the fan until another channel shift occurs along a path of greater slope. It is this occasional shifting of the watercourse and the locus of deposition at the fan apex that gives the alluvial fan its symmetrical, conical form. Such change is a natural, expectable phenomenon.
CHANGE IN BASE LEVEL
The level of the body of water into which a stream flows, its base level, affects the gradient of the stream channel. If the base level of a stream changes, scour or fill is induced in the channel upstream from the new base level.
If a new and higher base level is introduced, by construction of a dam, for example, fill will occur throughout a length of the upstream reach. The distance to which fill will extend in such a case cannot be well defined and varies for different types of streams; Leopold, Wolman, and Miller (1964, table 7-6) reviewed a number of case histories. In general, introduced base levels affect only limited sections of upstream reaches. A similar, unknown degree of fill could be expected to have occurred in Tujunga Wash above the Hansen Flood-Control Basin (fig. 1).
A reduction in base level, on the other hand, will increase the erosive ability of a stream through increase in gradient. A steep headcut formed at the point of lowered base level may move upstream, commonly flattening with time and extending the increase in slope over a greater length of channel. Such a lowered base level occurred in Tujunga Wash when floodflows from both main channels poured into a large gravel pit (fig. 3).
TECTONIC EFFECTS AND LONG-TERM AGGRADATION OR DEGRADATION
If there is a trend toward fill lasting over a period of years, the change represents aggradation; if the change is one of net long-term scour, it is called degradation.
Plainly, the fan or fanhead valley itself is the site of net aggradation over geologic intervals at the same time the channels of the watershed that supply the sediment to the fan are being degraded. Periods of aggradation and degradation can affect channels in both geomorphic settings, however, generally because of climatic and
human effects on the hydrologic regimen of the drainage basin. The trend of the changes at present is helpful in the practical considerations of scour and fill—bridge siting and design, lined-channel construction, allowance for sediment supply in the design of impoundments, to name a few.
In southern California the picture is complicated by tectonic changes—raising or lowering of the mountain masses relative to the depositional areas. Uplift, geologically recent and continuing at present in some areas, has greatly increased the sediment supply and rate of fan construction along the fronts of many ranges, including the San Gabriel Mountains. The effect is that of lowering the base level or locally increasing the slope of the stream channel within the mountains.
Yet another factor to consider in the interpretation of available data is the difference in effects on channels of a large floodflow as opposed to a period of low and moderate flows. A single catastrophic flood in California streams often has resulted in extensive fill in most areas (Stewart and LaMarche, 1967; Scott and Gravlee, 1968), followed by degradation during successive periods of lower flows if discharges remain sufficient to transport bed material deposited by the flood. Unfortunately, it is exceedingly difficult to generalize on this subject because of the other variables that affect scour and fill.
In few places is there more topographic diversity to affect the variables controlling scour and fill than in southern California. Consequently, it is not surprising that an unpublished survey of 1968-69 changes in streambed elevations at gaging stations in the region by R. P. Williams of the Geological Survey showed no significant overall trend toward either scour or fill. Study of Williams’ data with reference to physiographic position of the gaging stations showed a probably significant trend toward aggradation in settings similar to Tujunga Wash.
Differences in long-term trends of scour and fill, that is, aggradation or degradation, on parts of the same river system in southern California are illustrated by the channel of the Santa Ana River prior to the construction of major dams. At the station Santa Ana River near Mentone, in a fanhead reach, fill occurred during, and for years previous to, the major flood of 1938. Downstream, at the station Santa Ana River near Prado, scour occurred progressively over the same period (Troxell and others, 1942, fig. 40). Firm conclusions obviously cannot be based on data from single stations. Every study of scour and fill based on cross sections at gaging station sites must note that such locations are likely to be unrepresentative of the stream as a whole. And, even though a trend toward scour or fill may be recorded at a particular section for years,BIO
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
there is no assurance that the trend will continue, or that it could not be reversed in the future.
More uniform results were presented by Hickey (1969) for gaging-station sites in coastal northern California, an area more humid and less physiographi-cally diverse than southern California. Streambed-elevation changes at 42 of 51 sites represented fill in response to the 1964 flood, the largest of record at most stations in that region. No regional trends toward aggradation or degradation were evident from yearly measurements during the periods of record at the stations.
There can be little doubt, however, that trends toward both aggradation and degradation are occurring in streams in southern California. Regionally, the area shows evidence of what may be the same long-term alluviation noted by Leopold, Emmett, and Myrick (1966, p. 194) in the Southwest. Also, as in the Southwest, deposits of this period of alluviation are now undergoing dissection in southern California.
MANMADE CHANGES
Most of the above causes of scour and fill can be related to the works of man, and, as will be seen below, this was true of many of the channel changes in Tujunga Wash.
Not previously discussed were the effects of manmade obstacles, such as bridge piers and constrictions of the channel. Culbertson, Young, and Brice (1967) summarized the effects of construction of river structures on channels, generally those of humid regions, and the principles clearly extend to the ephemeral channels of semiarid areas.
A specific aspect is the effect of a dam on the downstream channel. One common effect of a reservoir is to reduce flood discharges, increase base flow, and, by trapping most sediment, cause the release of dear-water flows downstream. With the change in discharge and change in sediment load relative to discharge, the downstream channel is scoured and may change its cross-sectional configuration. Or, fill may occur in response to large sediment contributions from tributaries, increased vegetation due to reduction of peak discharges, or approximately uniform releases. The effects of Big Tujunga Flood-Control Reservoir (fig. 1) on the morphology of Tujunga Wash expectably are minor because of the small capacity of the reservoir and the channel distance between the dam and the mountain front that allows the sediment load of flood-flows to readjust to discharge.
METHODS OF STUDY—PHOTOGRAM METRIC DETERMINATION OF SCOUR AND FILL
A study of scour and fill in Tujunga Wash was possible because of the unique combination of large-
magnitude channel changes and the availability of high-order photogrammetry. Preflood and postflood photogrammetry of nearly the entire reach of interest was included in four sets of maps: two derived from aerial photography before both floods and two from photography flown within a short time after the February flood.
The photography was flown on the following dates, and maps were constructed with the following scales and contour intervals:
Contour
Date of	Scale of map interval	Source
photography	of map
(feet)
Preflood
9-13-66__________1	in. = 100	ft	5	City of Los Angeles.
(1:1,200)
6-10-68__________1	in. = 50	ft	2	California Division of
(1:600)	Highways.
Postflood
3- 6-69_________1 in. = 50 ft 2	Do.
(1:600)
3-15-69__________1	in. = 100	ft	5	City of Los Angeles.
(1:1,200)
Dates on the cross-section lines in the following figures indicate the photography from which each was derived. Maps at the smaller scale (1:1,200) and larger contour interval (5 ft) covered the upstream end of the wash where changes from flood-induced scour and fill were relatively minor. Where scour and fill could be defined only by overlap of data at the two differing scales, the smaller scale was expanded computationally two times during the section-plotting process to match the larger scale. Fortunately, however, the area of greatest changes was covered by the larger scale maps. Because flow of sufficient competence to move boulder gravel did not occur between September 1966 and June 1968, it was assumed that the 1966 photography recorded conditions virtually constant through 1968. Both sets of photography define the configuration of Tujunga Wash at the start of the 1968-69 storm season.
TYPES AND ACCURACY OF PHOTOGRAMMETRIC MAPPING
Two types of mapping are common in highwayengineering practice in California- reconnaissance mapping and design mapping (Kulhan and Slavoj, 1969, p. 58-61). Both types may include extensive reaches of important channels, thus lending themselves to study of channel morphology, and both are illustrative of the techniques and accuracy available in photogrammetry which can be specifically applied to studies of channel morphology.
Reconnaissance mapping is primarily for route planning. Terrain factors control the combination ofSCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 Bll
scales and contour intervals, which range from 1:1,200 to 1:4,800 and 5 to 20 feet, respectively.
Design maps commonly are prepared at a scale of 1:600 with a 2-foot contour interval and include spot elevations at locations where interpolation between contours will not give a correct elevation. Such maps are of an accuracy that permits their use in many cases as a substitute for a final location survey and as the basis for calculation of earthwork volumes. Katibah (1968) noted that maps of this scale commonly are plotted by the 5-diameter direct projection plotter and that, with this instrument, as relief increases, the practical mapping width possible with each photograph decreases in proportion to the total relief. If there is no relief, the practical mapping width is 1,500 feet, using a width of 6 inches on the photographs. With as much as 200 feet of relief, for example, a channel survey with photography at the design scale could be included in a single flight line with a practical mapping width of 1,300 feet.
Both types of maps conform to the National Map Accuracy Standards. The standards, among other requirements, state that 90 percent of all contours must be accurate to within one-half of the contour interval and that all shall be within one interval of their true elevation, except where terrain is hidden by brush. No less than 90 percent of the spot elevations should be within one-fourth of the contour interval from true elevation. In addition, present specifications for design maps in California state that the arithmetic mean shall not exceed:
±0.40 foot for 20 points tested,
±0.30 foot for 40 points tested, and ±0.20 foot for 60 or more points tested.
Tolerances for the mean are based on a standard deviation of 0.60 foot and a 99 percent probability. Amounts of scour and fill measured in this report are based on differences in elevations of two maps with the above standards of accuracy. Although, as will be seen below, the accuracy of the maps used surpasses these standards, critical values of scour and fill are described as approximate, with the above error factors understood to apply.
Standards for horizontal control are rigorous to the point that horizontal-control error has less effect on accuracy of the data than does scale-change or sectionplotting error.
CONSTRUCTION OF CROSS SECTIONS
Tujunga Wash was initially studied in the field to select representative sites. Cross sections then were located on the topographic maps, and individual points on cross sections were plotted at the map scale before reduction to publication size.
Emphasis in plotting was placed on accurate determination of slope inflections and thalweg depths; at such points, elevations were determined by graphical interpolation between contours and between spot elevations and contours. Points so located are marked on the sections as questionable. Other points on the cross sections that do not coincide with contour elevations and that are not marked as questionable indicate close proximity (at map scale) of section lines to spot elevations.
Finally, the cross-section locations were reexamined in the field to assess the degree of artificial modification of the channel that occurred in the short interval between the time of the floods and the postflood photography.
SCOUR AND FILL IN TUJUNGA WASH
Cross sections were located to show the most significant changes due to scour and fill, and to be representative of changes within each section of reach. Sites that would overemphasize the magnitude of local changes were avoided. Location of the sections had to conform to the overlap areas of the different sets of maps, and the selected sites utilize the maximum coverage. In the upper half of the wash, section lines are the grid lines of the California coordinate system. Flow in the rest of the wash was oblique to the coordinate system; sections located there were referenced to permanent structures or topographic features whenever possible. Coordinate-section line intersections are shown on the sections for reference in possible future studies.
Profiles showing change in elevation of the channel thalwegs (fig. 5) were constructed from the cross-section data to illustrate the longitudinal variation in scour and fill diagrammatically. Conclusions regarding the general behavior of ephemeral channels on alluvial fans will be based on these profiles following the description of the changes at individual sections.
Specific aspects of each preflood and postflood cross section are discussed in the following section.
SCOUR AND FILL PORTRAYED ON CROSS SECTIONS
SECTION A-A'
Little change that is not artificial is evident in section A-A' (fig. 6), in the confined channel within the mountain front. The fill indicated on the south bank (left bank in the cross sections) is a riprapped highway embankment. Scour or fill that might have occurred in the thalweg as a result of constriction of the natural channel by the highway embankment did not take place. The north bank (right bank in the cross sections) is bedrock. Close correspondence of photo-grammetrically oriented points on this steep slopeB12
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
Figure 5.—Longitudinal profiles of the main channels of Tujunga Wash illustrating scour and fill.
testifies to the accuracy of the mapping from which the sections were constructed.
SECTION B-B'
Fill across the entire channel apparently occurred at site B-B' (fig. 6) and cannot definitely be ascribed to any one cause. The section is at the point Tujunga Creek leaves the mountain front and enters Tujunga Wash.
Downstream from this section, between the January and February storms, a causeway embankment was constructed in place of a private bridge destroyed by the flow of January 25. The bridge previously provided the sole access for about 200 residents living on the north side of Tujunga Valley. Culverts through the causeway were designed to transmit flows substantially larger than those of January, but in the early morning hours of February 25 the causeway acted as a temporary impoundment and failed, releasing a surge of unknown, but probably small, magnitude into the valley. The fill at section B-B' may represent debris trapped behind this temporary impoundment. Again, apparent fill on the left bank is a highway embankment.
SECTION C-C'
No significant change occurred at section C-C' (fig. 6), located just below the point where Tujunga Creek enters Tujunga Wash. Near this point, flood-flows were split into two main channels, one on each side of the valley, and the beginning of the south channel can be seen in this cross section. Splitting of the
main flow near the valley apex can be seen at the top center of figure 4.
Although splitting of the flow may have been influenced by the temporary causeway, the important point is that formation of single or multiple distributaries at the apex of the fanhead valley was a phenomenon to be expected under natural conditions. Preflood topographic maps reveal that the course of the south channel had a thalweg similar in elevation to that of the normal low-water channel adjacent to the north bank, and therefore virtually equivalent in its ability to capture flow under natural flood conditions. It can be seen in this section and downstream sections that the medial part of the wash actually had the highest elevation.
SECTION D-D'
The convex-upward shape of the floor of the wash is well illustrated in sections D-D' and E-E' (fig. 7), supporting the basic analogy of Tujunga Wash to an alluvial fan.
The left 500 feet of cross section D-D' corresponds closely with the rear property line of houses on the west side of Wescott Street (figs. 4, 8). The line of section D-D’ is along the fence separating the houses on Wescott Avenue from the abandoned orchard shown in figure 4 and along the remnants of fence behind the inundated homes shown in the left-center part of figure 8.ELEVATION ABOVE MEAN SEA LEVEL, IN FEET
A
A'
Intersection of	Intersection of
N 4,212,500;	N 4,213,500,
<
Ui
c/>
Z
<
>
o
z
o
<
>
Intersection of B	N 4,212,000;
E 4,193,000
B'
Intersection of N 4,212,500;
E 4, 192,500
1330
1320
1310
1300
1290
1280
1300 r
1290
1280
Intersection of N 4.211,500;
E 4,192,000
C' ,
Same point as D
1270
N
0	250 FEET
1	__I___I___I___I___I
Figure 6.—Sections A-AB-B'} and C-C'. Locations of these and all following sections are shown in figure 3.
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B13ELEVATION ABOVE MEAN SEA LEVEL, IN FEET
D	D'
Line of section is rear property line of houses on west side of Wescott Avenue (projected across channel)
E
E'
N 4,210,000	N 4,211,000	N 4,212,000
Figure 7.—Sections D-D' and E-E'
B14	PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERSFigure 8.—Inundation along south channel of Tujunga Wash, February 25, 1969. Wescott Avenue is visible at left center. Grove Street is inundated along lower right side of photograph. Section D-D' profile is near rear fences of homes on far side of Wescott Avenue. Photograph by Harold Morby.
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B15B16
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
The west end of Grove Street was covered by flood-deposited sediment, shown as fill in section D-D'. At the time of the 1969 floods, urbanization, as represented by Grove Street, was spreading rapidly across the channel on the south side of the valley (figs. 4, 8). Fill shown in the vicinity of Grove Street on section D-D', about 2 to 3 feet, is slightly less than that observed at nearby points in the field by means of buried automobiles and other debris.
Fill occurred in the north channel, but not to any significant degree.
SECTION E-E'
Little change is evident in section E-E' (fig. 7). The broadly convex-upward shape of the valley floor stands out plainly. Flow did not overtop the central part of the valley in this reach, and some of the differences in elevation in the central part of the valley more likely are due to bulldozing than to error in the method or in plotting, although error is a possibility. Poor correspondence of some elevations on this section is due to the fact that postflood control is less accurate, being derived from the 1:1,200-scale mapping.
The left bank in this reach is the outside of the concrete Haines Canyon Flood-Control Channel, which fortuitously diverted the south channel flows away from a highly urbanized part of the wash and stopped lateral scour that might have damaged many more homes.
Fill apparent in the south channel is natural and may reflect normal aggradation near the apex of a fan or fanhead valley.
SECTION F-F'
Fill near the left bank of section F-F' (fig. 9) is similar to that on section E-E' and can be ascribed to the same origin. Concomitant scour and fill, typical of the lateral migration of ephemeral channels, occurred in the north channel. Lateral scour was restricted there by the steep valley-side slope.
Surprisingly close correspondence of the preflood and postflood surveys in the middle section of the wash, which was not inundated, verifies the accuracy of the changes seen in the channels. Again, some of the small apparent differences are due to the difference in scale and level of accuracy between the preflood and postflood maps. Also, the connection of widely spaced control points with straight lines does not necessarily portray the actual shape of the section between control points.
SECTION G-G'
From section G-G' (fig. 9) and those preceding, it is clear that the south channel was a major natural drainage of the wash, having actually a lower thalweg
elevation than the north channel in this section of the wash. It is not surprising, therefore, that a substantial part of the floodflow entered this channel in spite of levees intended to contain flow from Tujunga Creek in the north channel.
As in the upstream sections, there is evidence of fill in the south channel and shift in position of the north channel.
SECTION H-H'
At this point in Tujunga Wash (fig. 10), the pattern of fill in the south channel ceased. Section H-H' may be the possible upstream limit of the effects of locally reduced base level which occurred at a large gravel pit, 2,600-3,000 feet downstream.
Note the beginning of enlargement and an apparent slight deepening of the north channel.
SECTION /-/'
A pronounced increase in the amount of net vertical scour can be seen to have occurred in the north channel at section I-V (fig. 10). The south channel also was deepened, and in both, the scour represented net removal of bed material from the cross section. There is little corresponding fill as was true in the simple lateral shift of a channel seen in sections F-F', G-G', and others upstream. These changes, in both channels, point incontestably to the effects of lowered base level further downstream.
SECTION /-/'
Net vertical scour of the thalweg increased to more than 10 feet in the north channel and to about 4 feet in the south channel at section J-J' (fig. 11). Again, there is little corresponding fill. The above figures probably approach the maximum amounts of scour that occurred at this point during peak flow because, in these oversteepened channels, scour may have continued on the receding stage of the flood. In other words, most of the scour that occurred at this section constituted net removal of bed material from the reach.
Minor gullying from local runoff in the central part of Tujunga Wash is detectable in this cross section. Section J-J' and all sections downstream are direct comparisons of design maps at the highest order of accuracy (contour interval: 2 ft).
SECTION K-K'
The section line of K-K’ is parallel to Foothill Boulevard (fig. 3) and 150 feet upstream (fig. 11). Net scour that occurred at this section is representative, on the conservative side, of the net scour that took place at the two Foothill Boulevard bridges and the single span, downstream from Foothill Boulevard, of Wentworth Place (fig. 3). The large Foothill Boulevard bridge over the north channel did not fail during theELEVATION ABOVE MEAN SEA LEVEL IN FEET
F	F
G
G'
CD
Figure 9.—Sections F-F’ and G-G’.
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B17ELEVATION ABOVE MEAN SEA LEVEL. IN FEET
H
H'
/'
Figure 10.—Sections H-H' and
B18	PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERSELEVATION ABOVE MEAN SEA LEVEL, IN FEET
J	J'
K
Edge of Foothill Boulevard bridge abutment
K'
Figure 11.— Sections J-J' and K-K',
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B19B20
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
January flows, although the Los Angeles Fire Department reported erosion around pier supports and considerable vibration on the span. Failure of the structure, built in 1937, occurred during the peak February flow by scour around the piers.
It was surprising that the bridge stood as long and as well as it did. Net thalweg scour was about 9 feet in the north channel and 5 feet in the south channel at this section; these figures do not approach the maximum net scour that occurred at specific points in the section—about 20 feet in the north channel and 15 feet in the south channel. The large amounts of debris from both lateral and vertical scour were uncompensated by any significant degree of fill in either channel.
Figure 12 shows the south channel upstream from the Foothill Boulevard bridge. The incision of the main part of the south channel is clearly evident in the steep sides of the wash and the knickpoint and plunge pool formed where tributary flow, as shown at the bottom of the photograph, joins the larger channel.
The accuracy of the photogrammetry is such that minor gullying in the central part of the wash also is detectable in section K-K'.
SECTION L-L'
Only the south channel is shown in cross section L-L' (fig. 13) because of a gap in the photogrammetry. The line of section transects the Bengal Street terrace which, before the floods, was the site of middle-class suburban homes with lots extending to the edge of the terrace. Before the floods, the terrace level at this point was 8 feet above the south channel. Postflood, however, the remnant of the terrace is 19 feet above the bottom of the channel. Net vertical scour of about 11 feet took place in the channel thalweg during the 1969 floods at this site.
Of more practical concern was the lateral scour that removed 75 feet of the terrace at this line of section, including all of Bengal Street and seven of the homes that bordered Bengal Street. A comparable amount of scour occurred on the right bank of the south channel-Channel change at this site basically was one of incision and enlargement of the old channel without much tendency of the channel to shift laterally. The cause of the incision was the lowering of local base level which took place when flow entered the gravel pit a short distance downstream combined with adjustment of the channel configuration to the large flood discharge. That the scour at this site was primarily a function of the reduced base level, however, is proved by corresponding scour in the north channel and an increase in scour in both channels in a downstream direction.
Figure 14 shows the incision of the wash into the residential area and the remnant of the Bengal Street terrace early on the morning of February 25, shortly after most of the lateral scour had already taken place.
SECTION M-M'
Section M-M' (fig. 13) crosses the upstream end of the gravel pit into which both north and south channels flowed. Earthen embankments intended to channel flow around the pit were not effective, particularly in the south channel where flow was much greater than expected, primarily due to branching of the flow at at the valley apex.
Sand and gravel were mined sporadically at this site from 1925 until the mid-1960’s when, after failure of the lessee to obtain appropriate zoning on additional acreage, the operation became inactive. Estimates by the landowner of the amount of debris added to the main pit were 200,000-300,000 tons for the January period and 2-3 million tons for the February storm, the latter figure presumably including the earlier total. Mining of the newly added debris began in 1969.
The cross. section shows that about 20 feet of fill occurred uniformly across the bottom of the pit. The north channel, seen at the right end of the section, entered the pit a short distance downstream. About 14 feet of net vertical scour took place in the north-channel thalweg, and as much as 24 feet of scour occurred at a single point. The steepness of the north-channel thalweg, indicated here by its still considerable elevation above the pit bottom, suggests that erosion of channels upstream from the pit would have continued, had large discharges continued for a longer period of time.
SECTION N-N'
A greater quantity of fill, as much as 35 feet, is shown near the downstream end of the gravel pit in section N-N' (fig. 15). At this point, flows from both the north and the south channels had entered the pit and rejoined, the total flow then exiting through an old channel along the south side of the valley where desilt-ing ponds had been constructed.
Visible on the right side of this section is the rip-rapped berm against which the main channel was apparently intended to be confined downstream from Foothill Boulevard. Construction of a small levee to confine the low-water channel against the riprapped berm can be seen near the right end of the section. The berm itself was undamaged by the floodwaters which, unfortunately, were diverted away from the berm through both natural and manmade causes.Figure 12.—South channel of Tujunga Wash showing destruction of the south-channel Foothill Boulevard bridge, upstream on the right, and the smaller Wentworth Place bridge. The left end of section K-K' is the embankment supporting the Foothill Boulevard bridge abutment, left of center. Photograph by Harold Morby.
SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B21ELEVATION ABOVE MEAN SEA LEVEL, IN FEET

L
Point on terrace
L'
Edge of Foothi 11 Boulevard
N
M
1190 1180 -1170 1160 -1150 -1140 -1130
AT
Base of highway f i 11 — Foothill Boulevard
0	250 FEET
1	I I I I I
Figure 13.—Sections L-L' and M-M'.
B22	physiographic and hydraulic studies of riversFigure 14.—View looking northwest of what remained of the Bengal Street terrace shortly after the February 25 flood peak. Bengal Street originally ran east-west (upper left to lower right in photograph) across the area now occupied by the south channel of Tujunga Wash and intersected the street shown at left center. Height of the cutbank at the edge of the terrace is 18 feet. Photograph by Harold Morby.
'SUVWV, kWl V\VU\V\	ASH.—hYKSlffiM) V ALLEY IN VnR.BA.lS5 SOUTHERN CALIF.—1969 B23ELEVATION ABOVE MEAN SEA LEVEL, IN FEET
N	AT
Top of hill
Elevation: preflood, 1160.9 ft;
postflood, 1160.7 ft	Point on terrace above berm
N
Figure 15.—Section N-N'
B24	PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERSSCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B25
SECTION O-O'
That most of the floodflow was in the south channel is readily apparent in cross section 0-0' (fig. 16); little scour and fill occurred in the north channel during the period before flow entered the gravel pit upstream from this section. The scour that proceeded upstream from the pit edge captured all the subsequent floodflow in the north channel.
The most significant change in the south channel was one of fill—net vertical deposition in the thalweg of about 10 feet. The channel widened by some 60 feet to accommodate the unusually high discharge, but no marked net erosion of the main terrace level occurred. It is difficult to assign an exact cause to the thalweg fill that occurred at this point; upstream effects of the Hansen Flood-Control Basin, or deposition in the preflood channel which apparently was deepened to drain the gravel pit, are likely explanations.
Note the extremely close correspondence of the topography outside the flood channels.
SECTION P-P'
A similar quantity of fill—about 12 feet in the south-channel thalweg—occurred at section P-P' (fig. 16). About 3 feet of fill also occurred in the north-channel thalweg, lending support to the idea that channel fill here and at the preceding site was due in part to the backwater effects of the reservoir. The spillway elevation of the reservoir is reached 4,100 feet downstream from this section.
Not evident at this section line and undocumented by the photogrammetric coverage was a severe quantity of lateral erosion that occurred just downstream. There, south-channel flow was directed strongly against the bedrock wall of the canyon and removed a two-block section of Wentworth Street, previously a major, four-lane arterial highway. Similar destruction of Wentworth Street at the same locality occurred during the 1938 flood; this damage went unrepaired and Wentworth Street remained impassable until the early 1960's.
SUMMARY AND CONCLUSIONS
Changes in the channels of Tujunga Wash and the resulting property damage caused by the 1969 floods were great because of both natural and manmade causes. The effects of man were significant, not necessarily because of incomplete flood-control measures, but because of man’s failure to recognize the true character of the natural landscape—in this area, the fact that Tujunga Wash is similar in most respects to an alluvial fan and that its natural ephemeral channels can be expected to change dramatically during floods.
The chief difference between Tujunga Wash and an alluvial fan is that the wash continues to be partly constricted by bedrock valley-side slopes for a considerable distance after surface flow leaves the mountain front. The practical significance of this difference is that flood effects, such as channel changes, are concentrated in a smaller radial segment, centered at the mountain front, than is typical of an alluvial fan.
Scour or fill due to a variety of specific causes occurred in Tujunga Wash. The causes included possible natural channel aggradation, lateral movement of distributaries, local decrease in base level, local increase in base level, and natural adjustment and shift of the channel in response to changes in flow parameters. However, several major changes in the channel and the resultant property damage serve as especially graphic examples of what can be expected to occur under similar conditions—the combination of a major flood and an urbanized alluvial fan. These major changes are summarized in the following sections.
FLOW DIVERTED TO DISTRIBUTARY CHANNEL
Although attempts had been made to contain all expected flow in the north channel of Tujunga Wash, a significant part (about one-half) of the flood discharge entered the south channel (figs. 4, 8; sections C-C', D-D', and E-E'). No judgment can be made as a result of this study as to whether or not the causeway created as an access road to the north side of Tujunga Valley was the cause of this diversion. A significant point, however, is that formation of distributaries at the apex of a fan or fanhead valley was a natural, expectable occurrence. Splitting of the February 1969 floodflow occurred where and when it likely would have done so under entirely natural conditions. The south channel was nearly as probable a natural flood course within Tujunga Wash as was the north channel.
The question as to why urbanization was allowed to proceed within the south channel (fig. 8) before completion of adequate flood-control measures is one that must be left to others. Damage along the south channel farther downstream (between sections D-D' and F-F') would have been high were it not for the fortunate protection afforded by the concrete outlet channel from Haines Canyon.
VERTICAL SCOUR DUE TO LOCAL REDUCTION IN BASE LEVEL
The thalwegs of both north and south channels were scoured from the vicinity of section H-H' to the point where both channels entered the gravel pit west of Foothill Boulevard, a distance of 2,600-3,000 feet. The net vertical scour of the channel thalweg increased progressively downstream to about 14 feet in section M-M’.ELEVATION ABOVE MEAN SEA LEVEL, IN FEET
0	O'
Top of berm on right bank
p	p'
Point behind
Point on terrace	berm on terrace
Figure 16.—Sections O-O' and P-P’.
B26	PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERSSCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B27
The vertical scour in this section of the channel was largely the direct result of the lowering of base level when flow broke through from each channel into the gravel pit. Scour then proceeded upstream and ceased in the oversteepened reaches only when flow was no longer competent to transport the bed material.
The failure of three bridges spanning this reach, two on Foothill Boulevard and one on Wentworth Place, was one result of the scour. This event emphasizes the need for hydrologic considerations in the issuance of future gravel-mining permits in streambeds without effective flood-control channels. Because sand and gravel constitute the most important inorganic mineral resource in southern California, plans for mining must be made in certain channels. Such planning could help forestall a potential shortage of aggregate as well as reduce the harmful effects of channel diversion and scour triggered by mining operations in active channels.
LATERAL SCOUR OF TERRACES
The most dramatic damage (fig. 14, section L-L') was due to lateral scour of the main surface in Tujunga Wash. Bengal Street and seven homes bordering it disappeared shortly after 5:30 a.m. on February 25. Scour along the sides of the south channel removed 75 feet of land surface from the urbanized left bank and 125 feet from the right bank. This lateral scour was concomitant with net thalweg scour of 11 feet, caused basically by the change in base level discussed above. The effects of vertical scour combined with the lateral scour served to remove 18 feet of the land surface (net vertical scour) at the site of Bengal Street in section L-L'.
Basically what occurred in the south channel adjacent to the Bengal Street terrace was dimensional enlargement of the flooded channel cross section by a factor of two; shape and hydraulic parameters of the channel remained the same. The increased flow in the south channel was the result of the distribution of part of the flow from Big Tujunga Canyon at the apex of the wash combined with flow from Haines Canyon. A greater degree of impervious surface due to urbanization in the Haines Canyon drainage acted to increase peak discharge from that source which, however, was minor compared to flow within the wash. Generally, lateral change in the south channel was one of adjustment to the increased discharge. Added to this change was the increased scour due to reduced base level; this effect served to incise the channel and reduce its tendency toward lateral movement.
The equilibrium configuration toward which the stream with its lowered base level was tending is largely a matter of opinion, but it is probable that equilibrium would not have been attained even with continued
high discharges for several days. Channel instability would probably have continued. What channel changes would have occurred with only the increased discharge, had not incision of the channel taken place, can only be surmised. Without the base-level effects of the gravel pit, thalweg scour of a lesser amount would have occurred and would have been in large part temporary during passage of the flood peaks. Lateral erosion locally would have been greater but also more subject to the vagaries of a constantly shifting, alluvial-fan drainage course; erosion of the Bengal Street terrace might have been greater or may not have occurred at all. Natural channel shift probably was the cause of the loss of Wentworth Street, downstream from the cross-section sites.
Once again, however, it is clear that the danger to homes on the terrace was evident before the flood from a consideration of the geomorphic setting of Tujunga Wash. Urbanization on the unstabilized cutbank of a natural flood channel on an alluvial fan or fanhead valley generally is a poor risk.
CHANGES IN LONGITUDINAL PROFILES
Inspection of figure 5 reveals some potentially significant conclusions regarding the general behavior of ephemeral channels on alluvial fans. Comparing preflood and postflood profiles downstream from where much of the flow left the north channel and entered the south channel, the point of fanhead jump, it is apparent that the diversion locally resulted in scour of the north channel that corresponded in amount with fill that occurred in the south channel. The correspondence is most notable in the reach from 1.7 to 1.4 miles above the spillway elevation of Hansen Flood-Controi Basin (fig. 5). Not only was scour in the first channel matched by fill in the channel to which the fanhead jump occurred, but the postflood profiles of both channels became nearly parallel, after smoothing of pronounced preflood irregularities in the channel which were both natural and the result of the gravel pit and other works of man.
By analogy to a natural fan, the smoothing and similarity in gradient of the profiles may be functions in maintenance of a long-term trend toward equilibrium. Small floods or debris-flows and mudflows, both of the latter commonplace on many fans, may over the short term create distributary channels in the fanhead area with irregular profiles representing temporary inequilibrium. The preflood, largely manmade irregularities in Tujunga Wash may be considered analogous to these smaller, natural features. Thus, the jump of a major channel during a major flood, as seen in Tujunga Wash, will involve smoothing as well as steepening and through this action represents an essential median-B28
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
ism by which the maintenance of an equilibrium is accomplished over geologic time.
It is probable that with sustained flow over a long period, this change in accord with long-term equilibrium would have been even more pronounced in Tujunga Wash, but,as noted above, the exact equilibrium profile is a matter of conjecture. In any event, the jump in flow from the north channel to the south channel at the apex of Tujunga Wash was a likely natural adjustment of the alluvial system.
PHOTOGRAMMETRIC METHODS APPLIED TO THE DETERMINATION OF SCOUR AND FILL
Photogrammetry of the order of that used for highway-design maps can be a valuable tool in the quantitative study of channel change. Comparison of four sets of design maps of Tujunga Wash, two compiled before and two after the 1969 floods, clearly allowed significant measurements of scour and fill. Most of the maps used had a contour interval of 2 feet and were plotted at a scale of 1 inch equals 50 feet (1:600). Others with a contour interval of 5 feet at a scale of 1 inch equals 100 feet (1:1,200) were used locally.
Accuracy standards by which such maps are prepared required that contour lines be accurate to within one-half of the contour interval, resulting in confidence limits of ±1 foot for design maps. Specification accuracy of amounts of scour and fill derived from differences between two such maps is ±2 feet. Empirically, however, comparing the elevations on design maps of points not affected by scour or fill, accuracy generally surpassed this figure. Even specification accuracy was acceptable in dealing in this study with scour of as much as 20 feet (section K K') and fill of as much as 35 feet (section N-N').
APPLICATION OF RESULTS
The scour and fill that occurred in Tujunga Wash, although possibly unique in magnitude and diversity of cause, is a concentrated example of many of the changes that may occur under natural or urbanized conditions during floods on alluvial fans and in fanhead valleys. Such changes, before urbanization, went largely unnoticed except when catastrophic, and their widespread effects on urbanization in southern California became substantially more than academic for the first time during the 1969 floods.
An increasingly greater proportion of new urbanization is subject to the processes described in this report. Pressure is relentless for development of increasingly marginal areas in terms of danger from geologic and hydrologic hazards. Fanhead valleys similar to Tujunga Wash represent the last undeveloped areas not subject to slope-stability problems in much of urban southern California.
Solutions need not involve only the construction of engineering works in such areas. The flood-control structures in the Los Angeles County Flood-Control District functioned well during the 1969 floods. However, as programs of a scale to assure safe urbanization are applied to smaller areas, diminishing returns rapidly become evident. It is economically impractical to protect the area downstream from every frontal watershed in the mountains of southern California. The present program of debris-basin construction by the Los Angeles County Flood-Control District, for example, does not attempt to do this and is based on sound economic considerations made by the county, not by developers. What is generally needed is an increased focus on the natural realities of the environment before urbanization in arid and semiarid areas, followed by uniform zoning and planning in accord with those realities. It may even appear in some instances that the greatest eventual benefit-cost ratio will be achieved in fanhead washes through uses other than as additions to an existing sea of homesite congestion.
REFERENCES CITED
Culbertson, D. M., Young, L. E., and Brice, J. C., 1967, Scour and fill in alluvial channels, with particular reference to bridge sites: U.S. Geol. Survey open-file report, 58 p.
Emmett, W. W., and Leopold, L. B., 1965, Downstream pattern of river-bed scour and fill, in Proceedings Federal Inter-Agency Sedimentation Conference, 1963: U.S. Dept. Agriculture, Agr. Research Service Misc. Pub. 970, p. 399-409. Fahnestock, R. K., 1959, Dynamics of stream braiding as shown by means of time lapse photography[abs.]: Geol. Soc. America Bull., v. 70, p. 1599.
Hickey, J. J., 1969, Variations in low-water streambed elevations at selected stream-gaging stations in northwestern California: U.S. Geol. Survey Water-Supply Paper 1879-E, 33 p. Katibah, G., 1968, Photogrammetry in highway practice: California Div. Highways, p. 8-17.
Kulhan, E. F., and Slavoj, D. E., 1969, Photogrammetry: Berkeley, California Univ., Inst. Transp. and Traffic Eng., 70 p.
Lane, E. W., and Borland, W. M., 1954, River-bed scour during floods: Am. Soc. Civil Engineers Trans., v. 119, p. 1069-1089. Leopold, L. B., Emmett, W. W., and Myrick, R. M., 1966, Channel and hillslope processes in a semiarid area, New Mexico: U.S. Geol. Survey Prof. Paper 352-G, p. 193-253.
Leopold, L. B., and Maddock, Thomas, Jr., 1953, The hydraulic geometry of stream channels and some physiographic implications: U.S. Geol. Survey Prof. Paper 252, 57 p.
Leopold, L. B., Wolman, M. G., and Miller, J. P., 1964, Fluvial processes in geomorphology: San Francisco, W. H. Freeman & Co., 522 p.
Maddock, Thomas, Jr., 1969, The behavior of straight open channels with movable beds: U.S. Geol. Survey Prof. Paper 622-A, 70 p.
Rantz, S. E., 1970, Urban sprawl and flooding in southern California: U.S. Geol. Survey Circ. 601-B, 11 p.
Scott, K. M., and Gravlee, G. C., 1968, Flood surge on the Rubicon River, California—hydrology, hydraulics, and boulder transport: U.S. Geol. Survey Prof. Paper 422-M, 40 p.SCOUR AND FILL IN TUJUNGA WASH—A FANHEAD VALLEY IN URBAN SOUTHERN CALIF.—1969 B29
Simpson, L. D., 1969a, Summary report, storms of 1969: Los Angeles County Flood-Control District, 55 p.
------ 1969b, Hydrologic report on storms of 1969: Los Angeles
County Flood-Control District, 286 p.
Stewart, J. H., and LaMarche, V. C., Jr., 1967, Erosion and deposition produced by the flood of December 1964 on Coffee Creek, Trinity County, California: U.S. Geol. Survey Prof. Paper 422-K, 22 p.
Troxell, H. C., and others, 1942, Floods of March 1938 in southern California: U.S. Geol. Survey Water-Supply Paper 844, 399 p.
Waananen, A. O., 1969, Floods of January and February 1969 in central and southern California: U.S. Geol. Survey open-file report, 233 p.
* U.S. GOVERNMENT PRINTING OFFICE: 1973-51 S—658/25