Upper Eocene and Oligocene Larger F oraminiferé From Viti Levu, F 1}] ”4:5 ’G OLQGICAL SURVEY/ EROFESSIONAL PAPER 374-A I VB [- a: 213 :4 :3 CH # d a O '52 v72 3) H O 3-1 D.‘ >3 s» 2 b m" F. .2 hi! C —t C F.) 9'5 i _. H D—4 EH :2“ E’. .14 b: j—d E! —4 L» 2 O o: h. «r: a: Ix: Ea H Z #— 2 <: a: 0 EH a: E a: m «a A H z a G O ’5. D— A ,3 ’2. z .«c a: z E <5 32 ”a E :14 9-: ‘77“ g ,w f5 :43 ——1 e G Shorter Contributions To General Geology 1960 GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 7/21} professional paper was primed a: separate c/zapz‘ers 14—] UNITED STATES D PARTMENT OF THE INTERIOR STEWAR L. UDALL, Secretary GEO OGICAL SURVEY Thom s B. Nolan, Director 0575 W V374 m SCIENCES LIBRARY CONTENTS [The letters In parentheses preceding the titles are those used to designate the separate chapters (A) Upper Eocene and Oligocene larger Foraminifera from Viti Levu, Fiji, by W. Storrs Cole. (B) Joints in Precambrian rocks Central City-Idaho Springs area, Colorado, by J. E. Harrison and R. H. Moench. (C) Jurassic (Bathonian or early Callovian) ammonites from Alaska and Montana, by Ralph W. Implay (published in January 1962). (D) Late Jurassic ammonites from the western Sierra Nevada, California, by Ralph W. Imlay (published in January 1962). (E) Reconnaissance geology between Lake Mead and Davis Dam, Arizona-Nevada, by Chester R. Longwell. (F) Ammonites of Early Cretaceous age (Valanginian and Hauterivian) from the Pacific Coast States, by Ralph W. Imlay (pub- lished in September 1960). (G) Foraminifera from the northern Olympic Peninsula, Washington, by Weldon W. Ran. (H) Stratigraphy of outcropping Permian rocks‘ in parts of northeastern Arizona and adjacent areas, by C. B. Read and A. A. Wanek (I) Yampa Canyon in the Uinta Mountains, Colorado, by Julian D. Sears. (J) The Bannock thrust zone southeastern Idaho, by Frank G. Armstrong and Earle R. Cressman. 126 Upper Eocene and Oligocene Larger Foraminifera From Viti Levu, F 1J1 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—A Il/usz‘rdtz'om affirm Eatene and Oligocene four/s from Fri/'2', and Meir orcurreflce 2'72 surrounding drew~ UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1960 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, D.C. CONTENTS Page Abstract ______________________________________________________________________________________________________ A-l Introduction __________________________________________________________________________________________________ 1 Localities _____________________________________________________________________________________________________ 1 Eocene Fauna __________________________________________________________________________________________________ 1 Oligocene Fauna _______________________________________________________________________________________________ 3 Paleoecology _______________________________________________________________________________________________ '_ _ _ 3 Systematic descriptions _________________________________________________________________________________________ 4 Family Camerinidae _______________________________________________________________________________________ 4 Family Rupertiidae ______________________________________________________________________________________ __ 5 Family Discocyclinidae _____________________________________________________________________________________ 5 Literature cited _______________________________________________________________________________________________ 6 ILLUSTRATIONS [Plates 1—3 follow index] PLATE ]. Spiroclypeus, Pellatispira, Biplanispira, and Asterocyclina. 2. Camerina, Biplanispira, and Discocyclina. 3. Helerostegina, Gypsina, and Camerina. Page FIGURE 1. Locality and index map ______________________________________________________________________________ A—2 TABLES Page TABLE 1. Distribution of larger Foraminifera in the upper Eocene samples from Viti Levu and elsewhere ________________ A—3 III SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY UPPER EOCENE AND OLIGOCENE LARGER FORAMINIFERA FROM VITI LEVU, FIJI By W. STORRS COLE ABSTRACT Eight species of larger Foraminifera from Tertiary 1) (upper Eocene) sediments and three species from Tertiary c (Oligo- cene) limestone of Viti Levu, Fiji, are discussed and nine of the species are illustrated. The Tertiary b fauna is identical with described faunas from Indonesia, Eua, Tonga, Saipan Is- land, and the Eniwetok drill holes. The Tertiary c fauna is similar to ones from Gross Kei, Moluccan Islands, and north- eastern Borneo. As the earliest known deposits of Viti Levu previously had been assigned to Tertiary e (Miocene) these faunas not only establish the presence of older sediments on this island, but also provide important connecting links in the geographic distribution of the upper Eocene and Oligocene faunas of the Indo-Pacific area. INTRODUCTION Recently, I received for examination four samples from Viti Levu, Fiji, collected by R. W. Bartholomew of the Geological Survey Department of Fiji. Six random thin sections were made from each of the three Eocene samples and sixteen thin sections were prepared from the Oligocene sample. The larger Foraminifera in these thin sections are the basis of this report. The chief geologist of the Geological Survey Department of Fiji, N. J. Guest, kindly gave permission to publish the results of this study. Ladd (1934) published an extensive report on Viti Levu, Fiji. Collections of larger Foraminifera which he had made have been studied by \Vhipple (in Ladd, 1934, p. 141). At that time the oldest sedimentary for— mation, characterized by the presence of Lepidocyclma (Eulepidina) ephippioides Jones and Chapman (=12. (E .) formosa Schlumberger of \Vhipple), found in Viti Levu was the Viti formation of Tertiary e (Mio- cene) age. Therefore, the discovery of characteristic and well-known faunas of Tertiary 6 (upper Eocene) age in three of the samples and of Tertiary c (Oligo- cene) age in the fourth sample is significant not only in understanding the geologic history of Fiji, but also in comprehending the geographic extent and distribu- tion of lower Tertiary sediments within the Indo- Pacific area. The specimens illustrated were photographed from the random thin sections cut from the samples sub- mitted. The matrix was painted out on the negatives before the prints were made. The sections are depos- ited in the US. National Museum. LOCALITIES The localities from which the three Tertiary I) (up- per Eocene) samples were collected are shown on figure 1 and described in detail as follows: Loc. 1 (Field no. R. B. 174, P. and S. 049—550) 1%; miles east of Taci Trig, southeast of Nadi. Loc. 2 (Field no. R. B. 176. P. and S. 0—59—551)) 1 mile southeast of Namulomulo. east of Nadi. Loc. 3 (Field no. R. B. 183, P. and S. 0—59—55E) 1/2 mile west of Toke, central reaches of Nadi River. Bartholomew wrote Ladd (letter dated 18 December 1959) as follows: In the field the two small limestone outcrops from which sam- ples R. B. 174 and 176 were collected are surrounded by weath- ered flows of basic andesite which I feel are younger in age although I have no concrete evidence for this supposition * * * the sandy fossiliferous tuff R. B. 183 was from a river boulder found in the middle reaches of the Nadi river (tuffs and ag- glomerates of the Suva series). At first I assumed that the specimen had been derived directly from these Lower-Pliocene tuffs, but now realize that it must have been derived second- arily from boulders in the agglomerates. The locality from which the Tertiary c (Oligocene) sample was collected is shown on figure 1 and described as follows: Loc. 4 (Field no. R. B. 220) On the slope of Mount Picker- ing at an elevation of 3,000 feet; a small limestone outcrop surrounded by basic andesite flOWs. EOCENE FAUNA The distribution of the 8 species identified from the Tertiary b (upper Eocene) is shown in Table 1 to which have been subjoined the known occurrences of these species on Saipan, in the Eniwetok drill holes, on Eua in Tonga, and in Indonesia. A—l A—2 SHORTER CONTRIBFTIONS TO GENERAL GEOLOGY 1 0120“ 135° 150° 165° 180° 0 5 \f 15 V 0 m QI/ogkmmuppme Eniwetok ‘ Is , r, , MARSHALL . . IS 0a 05 w 6 0° 9. ‘35 . g 7 can \ 17/3 NEW 0 5) GUINEA <15} %\SOL0M0N =' [S :24 ’° §\ 3 i Q\\ [7% a MARI‘ANA Is 15° 8 . 15° alpan Viti fl Levu. i FIJI [S ' ‘TONGA Newk V I3 Caledonia; Eua , A u s T R A L z A j 30“ , u 303 120° 135° 1503 165° 180° ‘ Vatukoula Lautoka MOUNT PICKERING 99°“ 10 O 10 20 MILES | FIGURE 1. Locality and index map. UPPER EOCENE AND OLIGOCENE LARGER FORAMINIFERA A—3 TABLE 1,—Distrz'bution of larger Foramim'fem in the upper Eocene samples from Viti Levu, Fiji" and elsewhere [r = rare; 0 = common; a = abundant; X = present] Viti Levu, Fiji Eniwetok Saipan drill Eua, Indonesia holes Tonga Loc. 1 Loc. 2 Loc. 3 Camem’na pengaronensis (Verbeek) ______________________ r ________________ X X x x Operculina saipanensis (Cole) __________________________________________ 1' X X __________________ Spiroclypeus vermicularis Tan __________________________ c a ________ X X ________ X Pellatispira provuleae Yabe _____________________________________ r ________ >< __________________ X Biplam'spira mirabilr’s (Umbgrove) ______________________ 1' ________________ X X ________ X fulgeria (Whipple) ________________________________ c ________________ X X x X Discocyclina (Discocycli'na) omphala (Fritsch) _____________________________ a X __________ X X Asterocyclv’na matanzensis Cole __________________________ c c c X X X x As these species are widespread in Tertiary 5 (upper Eocene) of Indonesia and the islands of the central Pacific, the deposits in which they occur on Viti Levu, Fiji, are assigned to this letter stage. \Vhipple (1932, in Hoffmeister, p. 79) described sev- eral species from the Tertiary 1) (upper Eocene) of Eua, Tonga. Certain of these species were identified incor- rectly and others were inadequately described. A re- vised list of certain of these species follows: Names used by Whipple Camerina pcngaroncnsis (Verbeek) Pellatispira fulgeria Whipple Discocyclina (Dismal/cling) fritschi cuacnxis \Vhipple (Asterocyclina) stellata. (d’Archiac) (H. Douvillé) Van der Vlerk (1929, p. 7) assigned to Tertiary 0 several localities in northeast Borneo at which he found Camem'na fichteli and a heterostegine which he identi- fied as H. reticulum Riitimeyer. Bursch (1947, table 1) reported (7. fichtelz' and Gypsina discus in association at several localities on Gross Kei, Moluccan Islands, in sediments which he assigned to Tertiary c. 0. fichfeh' has been reported from Tertiary 0 beds in Java (Doornink, 1932, p. 285), Borneo (H. Douvillé, Names used in this report 0. pengaroncnsis (Verbeek) Biplarnispira fulgeria (Whipple) D. (D.) omphala (Fritsch) D. (D.) omphala (Fritsch) A. mutanzensis Cole This fauna is similar to the one at locality 1 on Viti Levu, Fiji. Although all the species do not occur together in the three samples from Viti Levu, they do occur together elsewhere. Therefore, their distribution in the samples from Viti Levu may be ascribed either to inadequate size of the samples, or, more probably, to slight ecologi- cal controls. OLIGOCENE FAUNA It. was possible to identify only two species with cer- tainty from the one Tertiary c (Oligocene) locality. These are (.‘(Imerhm fic/z/ch’ (Michelotti) and fig/[Mina discus Gratis. There were numerous small specimens of H eterostegz’na in association with these two species, but unfortunately the sections were not sufficiently centered for specific identification. Tertiary c in Indonesia is characterized by the dis- appearance of the restricted Eocene genera, the pres- ence of the reticulate species Uamem'na fichtelé and the absence of Lepz'docyclz'na ( E ulepz‘dina) which appears first. in this area in Tertiary d. 1905, p. 454), Soemba (Caudri, 1934, p. 72) as well as other localities in Indonesia. Cole (ms. in prepara— tion) found this species in the Tertiary c of Guam. This occurrence on Guam represents the most eastern penetration of this species into the Pacific basin so far recorded. PALEOECOLOGY The specimens from locality 1 are embedded in pyro- clastic material through which they are distributed more or less uniformly, but with the individual speci- mens commonly surrounded by matrix. This material is in marked contrast to that from locality 2 which represents a foraminiferal coquina (pl. 1, fig. 1). The individual specimens are often in contact and where spaces intervene between the specimens they are filled The abundant specimens from locality 3 are Discocyclina with broken fragments of foraminiferal tests. (Discocyclina) omphala (Fritsch) which commonly are arranged parallel to each other and generally sep- arated by a thin zone of matrix composed mainly of A—4 small broken fragments of calcareous algae and other organic debris. The best estimate for depth of accumulation of sedi— ments of this type would be 25—40 fathoms in waters with temperatures between 220 (‘ and 27° C Npirodypeus is structurally similar to H eterostegina. a genus still living. Cushman, Todd and Post (1954. p. 320) in discussing the foraminiferal faunas of the lagoons of Rongerik, Rongelap, Bikini and Eniwetok stated— Next in abundance in the lagoons is Heterostcgina suborbicu‘ laris d'Orbigny. which in a few places is more abundant than Amphistcgina. The fauna from locality 2, dominated by Spiro— clypeus vermiculam's Tan, seemingly existed under conditions somewhat similar to those found at present in the lagoons of atolls. The sediments in which Dismay/Cline (Disoocyclina) omphala (Fritsch) occur at locality 3 seemingly ac- cumulated in water which was sufficiently deep so that the Discocyclina were not disturbed by wave or cur- rent action, but into which gentle currents were able to transport organic debris originating in shallower water. SYSTEMATIC DESCRIPTIONS Family CAMERINIDAE Genus CAMERINA Bruguiére, 1792 Camerina fichteli (Michelotti) Plate 3, figures 5, 9—18 1841. Nummulitcs fichtclz‘ Michelotti, Soc. Ital. Sci, Mem., v. 22, p. 296. pl. 3, fig. 7. 1934. Camerina fichteli (Michelotti). Caudri, Tertiary De— posits of Soemba, Amsterdam, p. 72.81 (references). 1947. Nummulites intermedius—fichteli d'Archiac and Miche- lotti 1846, 1841. Bursch, Schweizerische Palaeont. Gesell., Abhand., v. 65, p. 19—21, pl. 1, figs. 4—6, 26; pl. 2. figs. 6, 7; pl. 5, fig. 5 (references and synonyms). This species is a reticulate camerinid. The reticu- late pattern shows in the external View of slightly weathered specimens and in median sections which are not centered (see: fig. 11, pl. 3). The transverse sec- tions superficially resemble those of Spiroolypeus. Discussion—Numerous specimens of this species were found on Guam. Although these specimens were associated at certain localities on Guam with charac- teristic Tertiary 1) (upper Eocene) genera and species (Cloud and Cole, 1953, p. 323), later detailed mapping and studies of the faunas has demonstrated that the Tertiary b specimens represented reworked material (Cole, ms. in preparation). Therefore, the range of (7. fichtelz' does not extend downward into Tertiary b as Cloud and Cole suggested it might to explain the association they found on Guam. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Camerina pengaronensis (Verbeek) Plate 2, figure 4 1958. Camcrina pcngaroncnrsis (Verbeek). Cole, IRS. Geol. Survey Prof. Paper 260—1", p. 753, 754, pl. 231, figs. 1—17 ‘ [imprint date, 1957; references and synonyms] This species occurred infrequently in the thin sec— tions from locality 1. The best transverse section ob- served is figured. Genus Operculina d’Orbigny, 1826 For a review of the synonyms of ()perculz'na see: Cole, 1959, p. 351. Operculina saipanensis (Cole) 1958. Operculinoides saipanensis Cole. Cole, ILS. Geol. Survey Prof. Paper 260«V, p. 755, pl. 232, figs. 7—14; pl. 233, figs. 31, 32 [imprint date, 1957; references]. The identification of this species which occurred in- frequently in the thin sections from locality 3 is based on several complete and well-oriented transverse sec- tions and one oblique median section. Genus HETEROSTEGIN‘A d’Orbigny, 1826 Heterostegina sp. Plate 3, figures 1, 2, 6, 8 As a well oriented median section was not found, it is impossible to identify this species. Two transverse and two median sections are illustrated for future reference. Discussion—Specimens of H eterostegim in the Ter— tiary c of Borneo found in association with Camefina fichteli have been identified by van der Vlerk (1929, p. 16) as H. reticulata Rfitimeyer, the types of which are from the Eocene of Switzerland. Tan (1932, p. 136) referred other Indonesian specimens of Het— erostegina. to H eterostegém cf. H. depressa d’Orbigny. The details which could be observed suggest that these specimens are close to H. duplicamem Cole, a spe- cies described from lower Tertiary e (Miocene) sedi- ments encountered in the Eniwetok drill holes. Genus SPIROCLYPEUS H. Douvillé, 1905 Spiroclypeus vermicularis Tan Plate 1, figures 10—14 1958. Spiroclypcus vermicularis Tan. Cole, U.S. Geol. Survey Prof. Paper 260—V, p. 764, pl. 238, figs. 1—6, 8—10, 11, 12 [imprint date, 1957]. Discussion—The types are from Tertiary b deposits at Koetai, East Borneo. Typical specimens were 1This report, which carries a 1957 imprint, was widely distributed in February 1958. It was not accepted officially by the Geological Survey until copies with improved collotype plates were received in March 1959. UPPER EOCENE AND OLIGOCENE LARGER FORAIMINIFERA found on Saipan and in Eniwetok drill hole F—l. In this drill hole they occur in core 11 at a depth of 4197— 4222 feet ((‘ole, 1958, p. 749). This typical Indo-I’acific genus is known to occur in the Indo-Pacific region only in Tertiary b and Ter- tiary e sediments. Although several species have been described from Tertiary e localities, the only species re— ported from the Tertiary 3) stage is S. /i)e/r'7n.ic/u]/rris. Genus PELLATISPIRA Boussac. 1906 Pellatispira provaleae Yabe Plate 1, figure 3 1957. Pellatispira proralcae Yabe. Cole, U.S. Geol. Survey Prof. Paper 280—1. p. 333, pl. 96, figs. 1, 2, 6; pl. 98, figs. 1—12. This species was represented by two incomplete sec- tions in the thin sections from locality 2. The best sec- tion is illustrated. Genus BIPLANISPIRA Umbgrove, 1937 Biplanispira fulgeria (Whipple) Plate 1. figure 2; plate 2, figure 3 1958. Biplanispira fulgcria (Whipple). Cole, US. Geol. Sur- vey Prof. Paper 260—V, p. 7(‘5 [imprint date, 1957; ref- erences and synonyms]. This species was represented by numerous partial sec- tions in the thin sections from locality 1. The expanded marginal cord is a distinctive and easily recognized fea— ture of this species. Biplanispira mirabilis (Umbgrove) 1958. Biplanispira mirabilis (Umbgrove). Cole, U.S. Geol. Sur— vey Prof. Paper 260—V, p. 765 [imprint date, 1957; ref- erences and synonyms]. A few specimens were found at locality 1 in associa— tion with Biplam'spim fulgeria. These two species normally occur together. Family RUPERTIIDAE Genus GYPSINA Carter, 1877 Gypsina discus Goés Plate 3, figures 3, 4, 7 1947. Gypsina discus Go'es. Bursch, Schweizerische Palaeont. Gesell., Abhand., v. 65, p. 40—42, pl. 3, figs. 2, 4, 13, 17, 22; pl. 5, figs. 6, 7; text figs. 15, 20 (references). Discussion—T he specimens are identical with those which Bursch described in detail from Gross Kei, Moluccan Islands. He identified this species both in Tertiary 6 (upper Eocene) and Tertiary c (Oligocene) beds. The type of the species is from the Caribbean sea, dredged from a depth of 400 fathoms. The embryonic and equatorial chambers (fig. 4, pl. 3) should be compared with the diagram given by 551721 0-50-2 A—5 Bursch (1947, p. 41, text fig. 20) and the vertical sec- ,- tion (fig. 7, pl. 3) should be compared with his sche— matic diagram (Bursch, 1947, p. 35, text fig. 15(7). Family DISCOCYCLINIDAE Genus DISCOCYCLINA Giimbel, 1870 Subgenus DISCOCYCLINA Giimbel, 1870 Discocyclina (Discocyclina) omphala (Fritsch) Plate 2. figures 1, 2. 5—11 1957. [Mammy/Nina (I)ixc0c!/-clinu) omphulu (lt‘ritsch). Cole. U.S. Geol. Survey Prof. Paper 280—1, p. 347-349, pl. 115. figs. 1—12 [references and synonyms]. 1957. Discocyclz‘na (Discocg/clina) indopacifi‘ca Hanzawa, Geol. Soc. America, Mem. 66, p. 82, 83, pl. 12, figs. 1, 2; pl. 13, figs. 2, 5, 6. The part of the vertical section (pl. 2, fig. 7) should be compared with a similar section (Cole, 1957, pl. 115, fig. 10) of a specimen from Saipan. The internal structures are identical. Specimens identified as this species by H. Douvillé (1905, p. 440, text figs. 1, 2) have a marked depressed area within the central umbo. Certain specimens from Saipan (see Cole, 1957, pl. 115, figs. 3, 4, 10) exhibit this same pattern. Other specimens, however, have an inflated umbo (Cole, 1957, pl. 115, figs. 6, 7). A few specimens from Viti Levu, Fiji (pl. 2, figs. 6, 7) have the depressed area within the central umbo, but the majority of the specimens are similar to the one illus- trated as figure 5, plate 2. As previously mentioned.— External shape is not a criterion upon which a species may be based as this character is variable. Internal structure is con- stant, and the main reliance for the definition of species of larger Foraniinifera should be based on the internal structure (Cole, 1957. p. 349). Discussion.——Although several species of Discos-y- clina have been described from Indonesia, they are imperfectly known because of inadequate descriptions and illustrations. One of the species reported from numerous localities is D. jamma (Verbeek). Caudri (1934, p. 87) wrote— Judging from the number of Discocyclina javana Verbeek re- corded from all parts of the Archipelago, one would be inclined to think that this Discocycl'ina was an easily determinable spe- cies. Nothing is further from the truth. D. y'amma has been reported from numerous locali- ties in Indonesia associated with specimens identified as D. omphaia and D. dispama (Sowerby). Study of the literature as well as certain Indonesian specimens from the Vaughan collection in the US. National Museum suggests that all of these Indonesian speci- mens represent. only one species. D. dispansa was described from specimens obtained in India. Therefore, it is doubtful if the Indonesian A~6 specimens which have been referred to D. diaper/ma, were identified correctly. The reader is referred to the excellent summary given by Caudri (1934, p. 94) on the status and use of this specific name by various workers who have referred Indonesian specimens to the Indian species. Seemingly, D. e-uaemis Whipple (1932, p. 84) from Ella, Tonga, has the same internal structure as D. jaw- rma. Hanzawa (1957, p. 82) in his discussion of D. indoymcifica ( =D. omrphala) stated correctly that— The present form [D. inrdopacifica] is allied to Discocgclina (D.) jut-(ma * * * but is easily distinguished by comparing the dimensions of the two forms * * * Figures 9, 10, plate 2, are parts of the same vertical section of a specimen in the Vaughan collection from Indonesia (no. 8—8030), probably sent and identified by A. Tobler as D. (D. ) javana. The lateral chambers (pl. 2, fig. 10) adjacent to the equatorial layer (left side) are open, whereas those at the periphery (right side) are appressed. Moreover, the lateral chambers (pl. 2, fig. 9) in the part of the section near the outer margin of the test are appressed. Therefore, an in- dividual specimen of this species shows two kinds of lateral chambers. The open chambers are shown in the type illustration of D. (D.) jamma and in the illustrations given by \Wiipple (1932, pl. 22, figs. 2, 4) of D. (D.) euaensis. The appressed chambers are typical of D. (D.) omphala (see: fig. 10, pl. 115, Cole, 1957, and fig. 7, pl. 2, of this report). Seemingly, D. (D.) javana is a synonym of D. (D.) omphala. Moreover, it is probable that most of the Indonesian specimens identified as D. (D.) dispcmsa are not that species, but represent D. (D.) omphala. Genus ASTEROCY‘CLINA Giimbel, 1870 Asterocyclina matanzensis Cole Plate 1, figures 1, 4—9 1957. Astcrocyclina matanzensis Cole, U.S. Geol. Survey Prof. Paper 280—1, p. 350, pl. 117, figs. 6-10; pl. 118, figs. 9—18. 1957. Discacyclina (Astemcyclma) stellaris Hanzawa, Geol. Soc. America Mem. 66, p. 84, pl. 14, figs. 1, 5—7. [Not Orbitolitcs stellaris Brunner, 1850, in Rutimeijer, Soc. Helv. Sci. Nat. nouv. Mem., v. 11, p. 118]. 1958. Asterocyclina matanzcnsis Cole. Cole, U.S. Geol. Survey Prof. Paper 260—V, p. 777, 778, pl. 249, figs. 1—17 [im- print date, 1957]. Discussion—Specimens from Indonesia and the cen- tral Pacific region which seemingly are Asterocyclina matanzensis have been referred previously to European species. Provale (1908, p. 75) identified specimens from Borneo as A. lanceolata Schlumberger (1904, p. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 128), a species which Douvillé (1922, p. 78) placed in the synonomy of A. stellam’s (Brunner). thipple (1932, p. 84) found specimens in Tertiary 7) (upper Eocene) limestone of Eua, Tonga, which he assigned to A. stellam (d’Archiac) and others which he (p. 85) compared with A. stella (Giimbel). It is obvious that only one species should be recognized as Whipple was influenced by difference in size which is not a specific character. Hanzawa (1957, p. 84) referred specimens from the Matansa limestone of Saipan to A. stellam‘s (Brunner). As the types of A. matanzensis are from Saipan, Han- zawa and Cole were describing the same species. Later, Cole (1958, p. 777) described and illustrated specimens referred to A. matanzensis from the Eniwetok drill holes. VVeijden (1940) discussed and illustrated the Euro— pean species of Asteromycléna, and Briinnimann (1940, pl. 2, figs. 1, 5—7, 12, 14—17) has given excellent il- lustrations of specimens from northwest Morocco which he assigned to A. stellam‘s (Brunner). The embryonic chambers of A. matamemz‘s are not only smaller than those of A. stellam’s, but also of a dif- ferent pattern (compare fig. 4, pl. 249, Cole, 1958, with fig. 6, pl. 2, Brdnnimann, 1940). The lateral chambers of A. matanzemis are smaller and less open than those of A. steUaNs (compare fig. 4, pl. 3 of this report with fig. 16, pl. 2, Brdnnimann, 1940). LITERATURE CITED Brtjnnimann, P., 1940. Uber die tertitiren Orbitoididen und die Miogypsiniden von Nordwest-Marokko: Schweizerische Palaeont. Gese11., Abhand., v. 63, p. 1—113, 11 pls., 37 text figs., 2 tables. Bursch, J. G., 1947, Mikropalaontologische Untersuchungen des Tertiars von Gross Kei (Molukken) : Schweizerische Palaeont. Gese11., Abhand., v. 65, p. 1—69, pls. 1—5, 22 text figs, 1 table. Caudri, C. M. B., 1934, Tertiary deposits of Soemba: Amster- dam, H. J. Paris, publisher, p. 1—223, pls. 1—5, 3 maps, 21 text figs. Cloud, P. E., Jr., and Cole, W. S., 1953, Eocene Foraminifera from Guam, and their implications: Science, v. 117, no. 3039, p. 323—324, 1 text fig. Cole, W. S., 1957, Larger Foraminifera: U.S. Geol. Survey Prof. Paper 280—1, p. 321—360, pls. 94—118. 1958, Larger Foraminifera from Eniwetok Atoll drill holes: U.S. Geol. Survey Prof. Paper 260—V, p. 743—784, pls. 230-249, 1 text fig., 6 tables (imprint date, 1957). 1959, Names of and variation in certain Indo-Pacific camerinids: Am. Paleontology Bull., v. 39, no. 181, p. 349— 371, pls. 28—31. Cushman, J. A., Todd, Ruth, and Post, Rita, 1954, Recent Foraminifera of the Marshall Islands: U.S. Geol. Survey Prof. Paper 260—H, ‘p. 319—384, pls. 82—93, 3 text figs., 5 tables. UPPER EOCENE AND OLIGOCENE LARGER FORAMINIFERA Doornink, H. W., 1932, Tertiary Nummulitidae from Java: Geol.-mijnb. genootsch. Nederland en Kolonien, Verh., Geol. sen, v. 9, p. 267—315, 10 pls., 12 text figs. Douvillé. H., 1905, Les Foraminiféres (lans le Tertiare de Borneo: Geol. Soc. France Bull., ser. 4, v. 5, p. 435—464, pl. 14, 2 text figs. 1922, Revision des Orbitoides: Geol. Soc. France Bull., ser. 4, v. 22, p. 55-100, pls. 4—5, 26 text figs. Hanzawa, S., 1957, Cenozoic Foraminifera of Micronesia: Geol. Soc. America, Mem. 66, p. 1—163, pls. 1—41, 12 text figs, 7 tables. Ladd, H. S., 1934, Geology of Vitilevu, Fiji: B. P. Bishop Mus., Bull. 119, p. 1—263, pls. 1—44, 11 text figs. A—7 Provale, Irene, 1908, Di alcune Nummulitine e Orbitoidine dell’ isola di Borneo: Riv. Ital. Paleont., v. 14, pts. 1-2, p. 55—80, pls. 4—6. Tan, S. H., 1932, On the genus Cycloclypeus Carpenter: Neder- landsche Akad. Wetensch. Meded., no. 19, p; 1—194, pls. 1—24, 7 tables. . Vlerk, I. M. van der, 1929, Groote foraminiferen van N. 0. Borneo: Nederlandsche Akad. Wetensch. Meded., no. 9, p. 1—44, 51 figs, 1 table. Weijden, W. J. M. van der, 1940, Het genus Discocyclina in Europa: Doctor’s Diss. Leiden, 115 p., 12 pls. Whipple, G. L. in Hoffmeister, J. E., 1932, Geology of Eua, Tonga: B. P. Bishop Mus., Bull. 96, p. 79-90, pls. 20—22. PLATES 1—3 FIGURE 1. 10—14. PLATE 1 A part of a thin section of the foraminiferal coquina from locality 2 to show the abundance of the tests; specimens on the left side are Spiroclypeus vermicularis Tan and the large specimen on the right side is Asterocyclina matanzensis Cole. USNM 627576. . Biplam'spim fulgeria (Whipple) (p. A—5) Oblique section through the embryonic chambers; locality l. USNM 627577. . Pellatispira provaleae Yabe (p. A—5) Oblique transverse section (see: Cole, 1957, pl. 98, fig. 12); locality 2. USNM 627578. . Asterocylina matanzensis Cole (p. A—6) 4. Vertical section, centered; locality 2. USNM 627579. 5. Vertical section, not centered, along the rays; locality 1. USNM 627580. 6, 7. Vertical sections, not centered; locality 1. USNM 627581. 8. Slightly oblique equatorial section of a megalospheric individual; locality 2. USNM 627582. 9. Oblique equatorial section to show the equatorial chambers; locality 2. USNM 627583. Spiroclypeus vermiculan's Tan (p. A—4) 10, 11. Median sections; locality 2. USNM 627584. 12, 13, 14. Transverse sections; locality 2. USNM 627585. PROFESSIONAL PAPER 374—A PLATE 1 GEOLOGICAL ‘SURVEY AND ASTEROCYCLINA y PELLA TISPI RA , BIPLANISPIRA ! SPIROCL YPEUS PROFESSIONAL PAPER 374—45 PLATE 2 GEOLOGICAL SURVEY U ., N“: in: I I: ‘ 1|... a.“ A -': ‘3' ;- 93"qu '«.V, - ‘ . ; 1 I v" CAMERINA, BIPLANISPIRA AND DISCOCYCLINA GEOLOGICAL SURVEY PROFESSIONAL PAPER 374~A PLATE 2 1,. ‘VL , $5” Ha‘f» I; ".»‘31 .2. x .2, .v‘ «p.» - - ”4*“: 1": , M 4., 1§1‘ 4555593! ' if , X 40 CAMERINA, BIPLANISPIRA AND DISCOCYCLINA PROFESSIONAL PAPER 374#A PLATE 1 GEOLOGICAL ‘SURVEY BIPLANISPIRA, AND ASTEROCYCLINA 7 SP1 R OCL YPE US, PELLA TI SPI RA PLATE 2 FIGURES 1, 2, 5—211. Discocyclina (Discocyclina) omphala (Fritsch) (p. A—5) 1’ your m 9, 10. 11. 2. Parts of vertical sections of megalospheric individuals; locality 3. USNM 627586. . Vertical section, not centered, of an umbonate specimen; locality 3. USNM 627587. . Vertical section, not centered, of a specimen with a depressed central zone; locality 3. USNM 627588. Enlarged part of the central area of the specimen illustrated as fig. 6 to show the details of the internal structures. Oblique equatorial section of a megalospheric individual; locality 3. USNM 627589. Parts of a vertical section of a specimen from the Vaughan Indonesian collection identified as Discocyclina (Discocyclz'na) javana (Verbeek) to show the variable character of the lateral chambers; precise locality in Indonesia unknown. USNM 627590. Enlarged part of the central area of the specimen illustrated as fig. 8. 3. Biplam'spira fulgeria (Whipple) (p. A—5) Part of a transverse sectlon to show the expanded marginal cord; locality 1. USNM 627591. 4. Camerina pengaronensis (Verbeek) (p. A—4) Transverse section, not centered; locality 1. USNM 627592. PLATE 3 FIGURES l, 2, 6, 8. Heterostegina sp. (p. A—4) 1, 2. Median sections; locality 4. USNM 627567. 6, 8. Transverse sections; locality 4. USNM 627568. 3, 4, 7. Gypsina discus Goés (p. A—5) 3. Vertical section, near center; locality 4. USNM 627569. 4. Equatorial section to show the embryonic and equatorial chambers; locality 4. USNM 627570. 7. The same specimen as figure 3, enlarged to show the details of the equatorial layer and the lateral cham- bers. 5, 9—18. Camerina fichteli (Michelotti) (p. A—4) 9, 10, 14, 15, 17, 18. Transverse sections to show variation between specimens; 17, the same speci- men as figure 5, enlarged; locality 4. USNM 627571. 11. Section parallel to, but above, the median plane to illustrate the reticulate pattern; locality 4. USN M 627572. 12. Slightly oblique median section to illustrate the reticulate pattern and shape of the chambers of the median plane; locality 4. USNM 627573. 13. Median section of a small specimen showing the embryonic chambers; locality 4. USNM 627574. 16. Strongly oblique median section which shows the chambers of the median plane only in the upper part; locality 4. USNM 627575. ! GEOLOGICAL ’SURVEY PROFESSIONAL PAPER 374—A PLATE 3 ., 0-.‘ I E.- 15 HETEROSTEGINA, GYPSINA, AND CAMERINA U.S. GOVERNMENT PRINTING OFFICE: I960 O—55I7ZI 1;»? E ”/5” 17!" E: . L. . “,7 :' 2%{, or? Joints 1n Precambrian Rocks ‘v—lwh -w‘lv- u- .L A: Central City- Idaho Springs 3 Area, Colorado xi/Z< 5 i GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-B Prepared on may of tfie U.S. Atomic Energy Commission ana’puolis/zea' wit/z toe permission of Me Commission Joints in Precambrian Rocks Central City— Idaho Springs Area, Colorado By J. E. HARRISON and R. H. MOENCH SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—13 Prepared on oe/za/fofz‘fle U.S. Atomic Energy Commission midpuo/is/zeo’ wit/2 toe permission of z‘fle Commission UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961 UNITED STATES DEPARTMENT OF THE INTERIOR Stewart L. Udall, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, DC. - Price 20 cents (paper cover) CONTENTS Page Page Abstract ___________________________________________ B—l Accumulation and interpretation of the joint data ________ B—4 Introduction _______________________________________ 1 Methods and problems of interpretation ___________ 5 General geology ____________________________________ 2 Precambrian joints in igneous rocks _______________ 5 Precambrian rocks ______________________________ 2 Precambrian joints in metamorphic rocks __________ 7 Tertiary rocks __________________________________ 3 Post—Precambrian joints _________________________ 12 Folds __________________________________________ 3 References cited ____________________________________ 14 Faults _________________________________________ 4 Joints _________________________________________ 4 ILLUSTRATIONS ____________ Page FIGURE 1. Index map of Colorado _______________________________________________________________________________ B—1 2. Generalized geologic map _____________________________________________________________________________ 3 3. Contour diagram of joints in granodiorite _______________________________________________________________ 6 4. Contour diagram of dikes in granodiorite _______________________________________________________________ 6 5. Contour diagram of joints in biotite-muscovite granite ___________________________________________________ 7 6. Contour diagrams of joints in metamorphic rocks ________________________________________________________ 8 7. Diagrams showing highs interpreted from contour diagrams _______________________________________________ 9 8. Theoretical joints ____________________________________________________________________________________ 11 9. Contour diagram of shear joints _______________________________________________________________________ 12 10. Stereographic diagrams _______________________________________________________________________________ 13 TABLE Page TABLE 1. Summary of attitudes of joint sets in metamorphic rocks __________________________________________________ B—lO III 573504—61 r. .1 uy—qn‘gm SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY JOINTS IN PRECAMBRIAN ROCKS, CENTRAL CITY-IDAHO SPRINGS AREA, COLORADO By J. E. HARRISON and R. H. MOENCH ABSTRACT Attitudes of about 9,000 joints in Precambrian intrusive and metasedimentary rocks in the 50-square-mile area studied re- veal that some joints sets are systematically distributed. Each of the principal Precambrian intrusive masses contains pri- mary joints. Joints related to folds have formed during two periods of Precambrian deformation and probably during Laramide (Late Cretaceous and early Tertiary) arching of the Front Range. A time sequence of geologic events and jointing can be worked out as follows: First, granodiorite was intruded during the older Precambrian deformation; primary joints formed in the granodiorite, and joints rela ed to sinuous and doubly plunging folds formed in the metas imentary rocks. Second, biotite- muscovite granite was intruded late in an older period of Precambrian deformation; primary joints formed in the granite. Third, Precambrian metamorphic and igneous rocks were locally deformed during a younger period of Precambrian folding; joints related to this folding formed in all Precambrian rocks, and a unique set of slickensided joints formed predominantly in the more massive granitic rocks. Fourth, a system of four joint sets was formed that locally cuts Precambrian rocks but not the Tertiary rocks that intrude them. Joints of this system were locally followed by Tertiary dikes, and therefore can be dated in outcrop only as post—Precambrian but pre—Tertiary. The conformity of the system with that expected from arching of the Front Range highland leads us to conclude that the post-Precambrian system probably is Laramide in age. INTRODUCTION The Central City-Idaho Springs area is about 30 miles west of Denver and is a small part of the Front Range of Colorado (fig. 1). The area was mapped in detail during the field seasons of 1952—54 as part of the US. Geological Survey’s studies on behalf of the Divi- sion of Raw Materials of the US. Atomic Energy Com- mission. The principal purpose of the study was an exhaustive investigation of the geology of the uranium- bearing veins, and this report presents only a small part of the data gathered during the investigation. 50 O 50 \_._.__._._i___g.__.| 190 MILES FIGURE 1.—Index map of Colorado showing relation of the Central City- Idaho Springs area to the Front Range highland. After Lovering and Goddard (1950, fig. 14). In the course of the general study it became apparent to us that several joint sets are related to Precambrian folds and intrusive bodies and that four joint sets are persistent but apparently independent of these Pre- cambrian structures. We studied the joints for the following reasons: (a) Joints obviously represent a part of the geologic history of any region; (b) multiple joint sets in rocks of complex structural history have, in our opinion, been ignored too often or dismissed as too complicated to interpret; (c) this discussion may encourage other geologists working in the Front Range to test an hypothesis set forth here concerning a regional joint system; and (d) a comprehensive knowledge of this proposed regional joint system may lead to a better understanding of Front Range tectonics. The data presented in this report have been drawn from our work and from that of seven of our colleagues. We sincerely thank A. E. Dearth, A. A. Drake, J r., C. C. B—2 Hawley, F. B. Moore, P. K. Sims, E. W. Tooker, and J. D. Wells for their generous contributions of data and stimulating discussions of the problem. Many details of the geology of the area have been summarized from data compiled by us and by our colleagues. For the interpretations of the data we, however, accept full responsibility. The general geology of the area has been described previously in several reports, the most comprehensive of which are three US. Geological Survey Professional Papers (Spurr and others, 1908; Bastin and Hill, 1917; and Lovering and Goddard, 1950). GENERAL GEOLOGY The Precambrian bedrock in the Central City-Idaho Springs area consists of a generally conformable series of folded metasedimentary gneisses, metaigneous rocks, and igneous rocks. The Precambrian rocks have been faulted and intruded during Tertiary time by a series of calc-alkalic to alkalic porphyry dikes and small plu- tons. As this report concerns only the Precambrian rocks, no extensive discussion of the Tertiary intrusive rocks will be given. A generalized summary of the Precambrian geologic history in the area shows the following events: 1. Precambrian sediments Were deeply buried and re- constituted into high-grade gneisses. 2. The foliated metasedimentary rocks were plastically deformed into major folds with north-northeast— trending axes. The deformation was accompanied by the intrusion of granodiorite, and then minor amounts of quartz diorite and associated horn- blendite. 3. Biotite—muscovite granite was intruded near the end of the period of plastic folding. 4. Uplift and erosion of several thousand feet of cover. 5. The Precambrian rocks were deformed locally. Where deformed, the more massive rocks were crushed and granulated; the more foliated gneissic rocks were formed into small terrace, monoclinal, or chevron folds; also some foliated metasedi- mentary rocks were cataclastically deformed. The major post-Precambrian folding, faulting, and intrusion in the Front Range were strongly influenced by the structural framework established during the Precambrian. The post-Precambrian geologic history, as summarized from Lovering and Goddard (1950, p. 57—63), shows the following principal events: 1. A regional Precambrian anticline was gradually worn down, and sediments accumulated in basins to the east and west. Minor uplift of the arch occurred several times during the Paleozoic, in greatest amount during the Pennsylvanian. Dur- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY ing much of the Late Cretaceous epoch, all the Front Range was submerged. 2. The present Front Range was uplifted and arched, generally along the old Precambrian anticline; the arching began in Late Cretaceous time and culmi- nated during the early Tertiary. The bedrock was folded along the margins, faulted, and intruded by porphyry stocks and dikes during early Tertiary time. Mineralization of the Colorado mineral belt accompanied and followed emplacement of most of the intrusive rocks. 3. Minor renewed movement along some of the early Tertiary faults and continued erosion bring the geologic history up to date. PRECAMBRIAN ROCKS The Precambrian rocks in the Central City—Idaho Springs area are an interlayered and generally con- formable sequence of metasedimentary gneisses, gneissic metaigneous rocks, granite, and pegmatite (fig. 2). The oldest rocks are metasedimentary gneisses, which are principally biotite~quartz-plagioclase ‘ gneiss, sillimanitic biotite-quartz gneiss, and microcline-quartz- plagioclase-biotite gneiss. Minor amounts of lime- silicate gneiss, cordierite-bearing gneiss, quartz-mag— netite gneiss, and amphibolite are also found in the area, and these form lenses or pods in the more abundant biotite-rich gneisses and microcline-bearing gneiss. The mineral assemblages in the metasedimentary gneisses are those described by Turner (1948, p. 7 6—88) for sev- eral subfacies of the amphibolite facies. The granite gneiss and pegmatite unit consists prin— cipally of granite and granite pegmatite that grade into each other and into the metasedimentary gneisses. The unit is virtually conformable and forms large mappable units as well as thin layers in the biotite-rich metasedi- mentary gneisses. This unit is probably of metasomatic origin. The metasedimentary gneisses and the granite gneiss and pegmatite are cut by a series of younger intrusive plutons, sills and dikes. The oldest of this series, a medium— to coarse-grained granodiorite, is correlated with the Boulder Creek granite of Lovering and God— dard (1950, pl. 2). The next younger intrusive rock, quartz diorite and associated hornblendite, is fine grained to coarse grained and forms scattered small bodies and dikes. Much of the granodiorite and quartz diorite has undergone some retrograde metamorphism. The youngest intrusive Precambrian rocks are the bio- tite-muscovite granite and its associated pegmatites. The biotite—muscovite granite is a fine— to medium- grained and seriate biotite-muscovite granite that is probably correlative with the Silver Plume granite, the JOINTS IN PRECAMBRIAN ROCKS, COLORADO 10 °40’ 105|°35' B—3 105l °30' EXPLANATION Contact Alluvium, colluvium, and glacial 6,, deposits ......... e p Fault, showing dip ' Dotted where concealed OUATER NARY Biotite—muscovite granite ............. ‘ Anticline Quartz diorite and associated Dmcd Where concealed hornblendite 7 Overturned anticlme x xx x Dotted where comealed Granodiorite Syneline Dotted where concealed x/\\ PRECAMERlAN [j -\- /—\/\/ Granite gneiss and pegmatite Overturned syncline +—+.....\u Monoclinal fold Dotted where concealed 39°45' ~ mug NORYH Avraoxmnz MEAN DFCLmAHoN. 1960 \\\\ \\,\ \\ \ '\\. ‘ N 1 0 l 2 MILES l_L_LLi Linnnl in.._.__... .l _J Geology by J. E. Harrison, R. H. Moench, P. K. Sims, and others, 1952-54 1 FIGURE 2.———Generalized geologic map of Precambrian rocks, Central City-Idaho Springs area, Colorado. type locality of which is at Silver Plume, 0010., 6 miles southwest of the area shown in figure 2. The sills, dikes, phacoliths, and small irregular plutons of biotite—mus- covite granite and pegmatite exposed in the mapped area (fig. 2) apparently are satellitic t0 the main bathe— lith (Levering and Goddard, 1950, pl. 2). TERTIARY ROCKS A series of calc-alkalic to alkalic porphyritic intru- sive rocks that form small plutons and dikes was em- placed into the Precambrian host rocks during early Tertiary time. A description of the porphyritic rocks and their probable mode of emplacement is presented in a paper by J. D. Wells (1960). One of the striking features of the dikes is their rectangular grid pattern in many parts of the area. (Wells, 1960, pl. 19.) This is particularly true in the Central City area where the dikes clearly are in joints in the microcline-bearing gneiss, and many of the joints in the gneiss are in sets that belong to a regional joint system (near northward- and near westward—striking, steeply dipping fractures). FOLDS Two periods of Precambrian deformation can be rec- ognized in the rocks of the Central City-Idaho Springs area. First was plastic folding, during which the meta- sedimentary rocks were recrystallized, the biotite gneisses migmatized, a series of plutons and sheets were intruded, and the more mafic members of the igneous series Were locally retrograde metamorphosed. These B—4 older folds are now outlined by the lithologic units. The second deformation was largely cataclastic and less per- vasive than the earlier major deformation. It was most intense in a narrow belt that trends northeastward through the town of Idaho Springs (fig. 2). This de- formation produced small folds and zones of granula- tion which were superposed on the previously foliated and folded rocks. Folds of the two stages are distinguished by their trends and type. The older folds are dominantly open, upright, doubly plunging folds, but some are tight folds that are upright to overturned and recumbent. The largest of these folds has a wavelength of about 11/2 miles and can be traced along its axis for about 12 miles. The fold axes are sinuous in both a map and a long-sec- tion view, but on the average they trend about N. 30° E. and commonly plunge gently northeast or southwest. The plunge of the folds is markedly steeper than the average in the area along the southwestern part of Chi- cago Creek (fig. 2). The younger folds are terrace, monoclinal, and chev— ron structures on the older larger folds; the largest of the younger folds has a wavelength of about 300 feet. These folds trend N. 55° E. and are remarkably straight. They plunge at different angles, depending upon their position on the older, larger folds. The younger folds have steep axial planes and consistently show an asym- metry that indicates the northwest side moved up. This second folding was accompanied by granulation which was most severe in the igneous rocks and in the poorly foliated metasedimentary rocks. FAULTS Most of the faults in the area are early Tertiary in age, although a very few may be Precambrian faults along which Tertiary movement has occurred. A thor— ough study of the faults has been prepared by Sims and others (written communication, 1959) and the follow‘ ing statements are based largely on that report. The abundant Tertiary faults, many of which have been mineralized, generally follow preexisting planes of weakness in the Precambrian host rocks. Among these planes of weakness are axial planes of tight folds, contacts between rock units, foliation in the gneissic units, and joints. The predominant movement along the Tertiary faults is a few feet to a few tens of feet of strike slip, though some faults have a small component of dip slip. The subsidiary fractures associated with the faulting are also surfaces of shear, and few if any joints seem to have been formed during this period of deformation, SHORTEVR CONTRIBUTIONS T0 GENERAL GEOLOGY JOINTS Considering the long and complex history of the area, it is to be expected that all the rocks would be jointed intensely. Most outcrops in the area show at least 3 distinct joint sets, and 5 or more joint sets in a single outcrop are common. With few exceptions we have related each of the many joint sets to one of several processes—the flow and cooling of the Precambrian and Tertiary igneous rocks, the two Precambrian fold- ings, or the Laramide deformation of the Front Range. To decipher these relations requires a detailed knowl— edge of the structural geology; only with this knowl- edge is it possible to suggest that some joint sets are related, for example, to the second Precambrian fold system, whereas others are persistent from area to area, show little regard for structural variations, and there- fore constitute a regional joint system. The remainder of this report will concern the methods of gathering and plotting the data on the joints, and the interpreta- tion of the joint patterns disclosed. ACCUMULATION AND INTERPRETATION OF THE JOINT DATA About 9,000 readings of joint attitudes were collected in a 50-square-mile area during this investigation. Joints in the two main Precambrian intrusive bodies (granodiorite and biotite-muscovite granite) were plotted on Schmidt equal—area nets, and joints in the Precambrian metamorphic rocks were plotted on 10 Schmidt nets that represent 10 divisions of the entire area. The 10 areas were selected to correspond with areas for which lineation diagrams showing bearing and plunge of the Precambrian folds were available. The joint plots were then counted and contoured using the standard 1-percent area-counting device (see Bill. ings, 1942, p. 117—122, for a simple explanation of the technique). The interpretations presented are based on the prem- ise that joints should and can be related to major geo— logic events in the area. The genetic relations of joints to geologic events can be recognized only locally in the field; dikes related to an intrusive body may appear in a limited number of joint sets within the intrusive mass, or a joint at rights angles to the plunge of folds may remain at right angles although the bearing and (or) plunge of the folds may vary as much as 30° from area to area. Persistent joint sets are recognized on joint contour diagrams, and their genetic relations are in- ferred from their fit with ideal joint sets that would be related to known folds. At a few places in the field, inferred ages of joints can consistently be checked against their actual age relations in the rocks. In addi- tion, the patterns seem to be widespread, for some per- JOINTS IN PRECAMBRIAN ROCKS, COLORADO sistent patterns emerge on each diagram even though 9 individuals working independently collected the data, and no individual contributed data to more than 2 diagrams. We conclude that each of the principal Precambrian magmatic rocks contains joints formed in response to stress during cooling and that the Precambrian meta- morphic rocks contain joints related to folding of those rocks during the two periods of deformation. Some of the joints formed during each period of Precambrian folding have been superposed on the Precambrian in- trusive rocks. A widely distributed “regiona ” joint system seems to have been superposed on all Precam- brian rocks, possibly during Laramide time. METHODS AND PROBLEMS OF INTERPRETATION Both field and oflice interpretations of joints of sev- eral ages are difficult. Where a younger joint system includes joints that are virtually parallel to older joints it may be difficult or impossible to determine whether a given joint is new, or whether it represents reopening or extension of the older joints. To interpret Schmidt net diagrams we look for in- dividual concentrations of poles (highs) on the con- toured diagrams. If only 1 or 2 joint sets exist in a rock and they are separated by many degrees in both strike and dip, then the recognition of the individual highs is simple and direct—no overlap of poles belong- ing to either joint set occurs. However, in a rock that has six or more joints (as do most rocks in this area), none of which can be identified on the basis of some intrinsic geologic characteristic as clearly belonging to one set or another and some of which are only a few degrees apart in the strike and (or) dip, overlap is likely, and some of the highs become difficult to iden- tify. Under these circumstances the system of taking overlapping averages in a l-percent area used to count the points on a Schmidt net plot necessarily results in points belonging to one set also being counted with those of an adjacent set. If the two sets are about the same strength (have the same number of points), then the area of overlap may contain as many, or even more, points than either of the true highs. The sim- ilarity between this problem and those of bimodal distributions in histograms will be apparent to some readers. The result on the contoured Schmidt net dia- gram is along narrow high if the overlapping area con- tains about as many points as each of the true highs, or a single false high if the two true highs are so closely spaced that the overlapping area contains a higher con- centration of points than either of the true highs. The single false high is near the true highs, and perhaps for purposes of joint interpretation is adequate if used 573504~—61—~-r2 B—5 as a single high. The long narrow high can sometimes be recognized as two highs by making closely spaced contours (thus making slight difl’erences in point con— centration or “relief” more apparent), but some long narrow highs are so nearly level along their crestlines - that separations into two highs can be done only by as- suming that the long high represents an unusual spread of joint directions in the rocks (based on experience) and therefore probably represents two closely spaced joint sets rather than one exceptionally dispersed set. If two adjacent elements differ greatly in strength, the stronger high may distort the weaker high’s true loca— tion or even mask it. The weaker high may show only as a small closed contour or as a deflection of the other- wise smooth contours around the stronger high, but the significance of such a small closed contour or deflection may be doubtful. A single joint set may generate two distinct highs on a contour diagram. For example, a joint set perpendic— ular to fold axes is common in this area. The bearing of the older Precambrian folds is reasonably constant in the area covered by each of the contour diagrams, but in several of the areas the plunge of the folds has a range of as much as 40°. A joint set perpendicular to these fold axes has a nearly constant strike, but it has a 40° spread in dip. Because these folds are commonly double or asymmetrically plunging, a single joint set may show a double high, a more prominent high for the most common plunge and a less prominent high for the less common plunge of the fold system. Joint sets that may represent such dispersions in dip are not abundant in the area; the few examples of such dispersions are noted in the last two columns of table 1 as “spread from” the possible related high. Despite the many problems in interpretation, the con— tour patterns do show many distinct highs as well as several deflections that probably indicate highs. Al- though we cannot explain to our own satisfaction every high on every diagram, we can relate to folds all the highs on many diagrams and most highs on the remainder. PRECAMBRIAN JOINTS IN IGNEOUS ROCKS The joints of Precambrian age include two types, primary joints in intrusive igneous rocks and joints re- lated to two periods of Precambrian folding. Primary joint sets in igneous rocks are identified if dikes re~ lated to the igneous mass are found parallel to (follow- ing) joints in that mass. (See Balk, .1937, p. 27-42.) If the dike rock is not related to the intrusive mass in which it occurs, then joints parallel to it may be pri- mary joints that were reopened at a later time, or joints formed at a later time. B—6 Primary joints in igneous granodiorite and Silver Plume granite commonly contain dikes of pegmatite, or‘ light-colored granodiorite. The attitudes of joints in the granodiorite and of dikes in it are shown in figures 3 and 4. The dikes are of two ages; some are light-colored granodiorite that is related to the grano— EXPLANATION llllllllllllll E 2 2.5 2.5—3 Percent More than 3 1, 2,3 Primary joint sets c by Cross-joint set related to younger Precambrian folds [r ? Possible location of longitudinal joint set of regional (Laramide) joint system Fromm 3.—Contour diagram of joints in granodiorite along Ute Creek, upper hemisphere plot of 751 poles. «After Harrison and Wells (1959, fig. 13). diorite (Harrison and Wells, 1959, p. 1'3), and others are biotite-muscovite granite and its associated pegma- tite. The light-colored granodiorite dikes are confined to the granodiorite, are commonly about 2 inches wide, and at places form a grid pattern in outcrop. The steeply dipping joints (sets labeled 2 and 3 on fig. 3) are parallel to the dike grid pattern of the light-colored granodiorite, although it is apparent in the field and on the contour diagram (fig. 4) that more dikes are parallel to the joint set labeled 2 than to the set labeled SHORTEP. CONTRIBUTIONS TO GENERAL GEOLOGY ‘ EXPLANATION WE 2-3 . 3-4 4-5 More than 5 Percent FIGURE 4.—Contour diagram of attitudes of Precambrian biotite-musco- rite granite and associated pegmatite, and light-colored granodiorite dikes in granodiorite along Ute Creek, upper hemisphere plot or 153 poles. After Harrison and Wells (1959, fig. 14). 3. This set labeled 2 also is parallel to dikes of biotite- muscovite granite and its associated pegmatite. Both of these sets are interpreted as primary joints, some of which were reopened and filled during emplacement of biotite-muScovite granite. Balk (1937, p. 27—42) also describes and defines the primary fracture system in an igneous rock in relation to the flow lines in the rock. The granodiorite has been deformed and recrystallized in part, and the original flow lines cannot be determined with accuracy at most places; therefore, direct compari- sons with Balk’s terminology and conclusions are not possible. However, the two steeply dipping primary joint sets plus the principal flat-lying joint set (1 on fig. 3) form a conjugate system typical of the primary joint systems that have been thoroughly studied and described by Balk. The granodiorite was intruded during the period of older folding, but no joints clearly identifiable as be- longing to that series of folds have been impressed on the granodiorite (compare fig. 7, diagrams 7 and 10). The younger period of folding, however, seems to have left a mark because a joint set (labeled 0,,” ) on figure 3 is almost exactly parallel to a joint set in the folded metamorphic rocks that is related to the younger period of Precambrian deformation. JOINTS IN EXPLANATION Percent More than 4 Primary joint set followed by pegmatite dikes p Primary joint set not followed by pegmatite dikes c by Joint set perpendicular to axes of younger Precambrian folds Ir, Cr, drl' drz Joint sets of regional system including longitudinal, cross, and diagonal sets; overlap with x's inferred to have been caused by reopening or extension of primary joints (Precambrian) during Laramide arching FIGURE 5.—Contour diagram of joints in the Alps Mountain stock of; blotlte-muscovlte granite, upper hemisphere plot or 175 poles. The other principal Precambrian intrusive body is the biotite-muscovite granite, which is most extensively exposed in the Alps Mountain stock (fig. 2') . The granite was intruded late in the period of older folding and was apparently deformed very slightly or not at all by the older stresses at the time of intrusion (Harrison and Wells, 1959, p. 20). The granite in the southern PRECAMBRIAN ROCKS, COLORADO B—7 and southeastern part of the area was cataclastically deformed during the younger period of Precambrian deformation and, at many places, zones of closely spaced slickensided fractures trending N. 55° E. cut across the flow lines in the granite; the fractures commonly show striations identical in direction and type with a linea- tions in the cataclastically deformed metamorphic rocks—cataclasis that occurred during the younger deformation. Mortar texture is present in the granite at outcrops where the slickensided fractures occur. These slickensided fractures form a set that differs from all other joints; they will be discussed in a later part of this report and are not included on the joint diagram for the Alps Mountain stock. The Alps Mountain stock contains a group of pri- mary joints as well as joints that are inferred to be younger than the stock. Figure 5 is a contour diagram of joints in the stock. Those joint sets marked with an X are parallel to dikes of pegmatite related to the biotite-muscovite granite; they are inferred to be pri- mary joints in the granite. The joint sets marked with a P are also inferred to be primary because diagrams of surrounding rocks do not contain these sets («compare diagrams 7, 8, and 10, figs. 6 and 7). The joint set labeled 0,,” on Figure 5 is common to all agneous and metamorphic rocks in the Alps Mountain area, does not parallel dikes of pegmatite related to biotite-muscovite granite either inside or outside of the stock, and is at right angles to the axes of the younger‘Precambrian folds or zones of cataclasis. It is inferred to be a joint related to the younger period of Precambrian deforma- tion. The joints labeled l,, 6,, d,1_ and (1,2 on figure 5 are probably new or reopened joints formed during post-Precambrian time and will be discussed in the sec- tion on post-Precambrian points. PRECAMBRIAN JOINTS IN METAMORPHIC ROCKS Many joints in the metamorphic rocks apparently formed during one or the other of the two periods of Precambrian deformation. Diagrams of joints in the metamorphic rocks are shown on figure 6 where each diagram has been plotted in the approximate center of the geographic area that it represents. Figure 7 shows the same joint diagrams without the contours but with the positions of the highs indicated. The positions of joint sets shown on figure 7 are given in table 1. B—S SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY EXPLANATION N 325 Number of poles 1. 1%, 2. 3 Contours, in percent 105.40. Upper hemisphere of Schmidt equal- area projection 1%. 2, 2%,3 105'35’ 39°45' IDAHO SPRINGS 93 FIGURE 6.-—Contour diagrams of joints in metamorphic rocks. JOINTS IN PRECAMBR‘IAN ROCKS, COLORADO B—9 EXPLANATION N Areas of open and upright 105°30’ older folds I “x/ I \ Areas of closed and upright 105 “35’ Areas of closed. tight. upright to overturned older folds fl ( \ I High for joint set of probable Precambrian age l at High for joint set of probable Areas of youngerterrace folds Laramide age (regional joint Closer spacing on map ind/cares system) grater abundance [I High for sheeting joint set of post-Laramide age . , Circled dot or X indicates point 105 40 locations requiring some to much interpretation by the writers 39°45’ KEY TO LETTER SYMBOLS c bo Cross joint related to older lolds db; Diagonal joint related to older folds I bo Longitudinal joinl related to older folds c by Cross joint related to younger folds ? 10 Reason for joint not clear FIGURE 7.—Diagrams showing highs interpreted from contour diagrams, inferred ages of joint sets, and types of Precambrian folding. $38 529280on .830 3 @832 25o.“ $95 :5 SHORTE-R CONTRIBUTIONS TO GENERAL GEOLOGY .5393 “So“ 32328 B ”So” 228926 :2 . o m 3 s . .ESwhm «Eon 3:822 we 23o.” mmEo Nu mummuvmwfimohwhw ”We Wm MM“ 3“ 83mm»... 25°“ 32232 B 25% EEUSEHS N £85 .M .m can .momgm .H .n .52on . .m .3 8:288 .88 a 6.38 gingoum 20mg?» 8 @328 “E2.“ $98 3.8 .w 222 .5 6 3.59.“ 20 was 2% 2:3 32832.80 . ..22 em» .32 0% .22 amp ..32 as .2825 ..22 as .2825.» “2 can .2 ..3m 0:. ..3m own .2 52 ”mpamnwz 2 9% .2 .3 a: .2 .2 02. .2 .3 .8 .2 .3 ohm .2 .3 0....» .2 228252 .3 0mm .2 .3 05 .2 0.2 .2 .02 :2 S .e r o: . a 3 Bo: Esam .mpmwmmvz .32 02. - .32 as ..3m 0% .22 0% ..3m one ..2 ..3m .8 .2 . 3 0202 .2 .2 n2 .2 ............. .2 02 .2 .3 02 .2 .3 a: .2 .3 can .2 can .2 ea .............. .3 03 .2 a...“ .2 .22 mg a .22 can $253 anmms Hmfihwmz . . .. o . .32 02. .32 2 .3m 2 .3m 3 .3m 8 .2 .m a. .3m as. .2 2.2 3 3m 28 8 22252 .mfimmsa :2 OS .2 .............. :2 0mm. .2 :3 am" .2 :3 0%. .2 :3 0mm .2 own .2 .03 :2 0% .2 :3 own .2 .2 .2 .022. Sn m .33 82.. 322m :3 own .2 .3m 03 . . . . . . . . . . . . .. . 2 8 22 8 32 8 22 2. 3m 0mm 28:25 2 mm 2 3w aw 3m 8 2 3 8 2.332 23263me .%AMWw2 $2 0% .2 :3 amp .2 :2 Guam .2 :3 02.2 .2 :3 OS .2 :3 a...” .2 .Ewsgm :3 one“ .2 :3 amp .2 new .2 {a om: h @328 EB.” 2365252 .2 a: .2 .2m mm .3 3 2322 232 anowfin :2momwn2 gm 0 .. . : . $8 2822 “52 3535 .hmm?2 .32 OR. .22 08 .32 as .22 em“. .2822» .235» ..2 .3 .2 .22 02W M2323. “2 .2 .2 S Sea 238% .3 on .2 2 ca. 2 3 .2 2 2 on” 2 3 02 2 3 an 2 3 on” 2 235282 3 can 2 3 28 2 235232 a: w .22 .8 3 0% .2 3m 03 .3 8 8:28 32 25»an :3 ca. .2 :%m mm? .32 03 .22 03 .32 05 .22 mm .22 9.2 .2223 .2 05 .2 .22 can .2833 .2 03. .2 .2moofi 2 as 2 .3 08 .2 :2 03 .2 .3 .8 .2 :3 com .2 :3 on” .2 235582 :3 03 .2 :3 as .2 @3852 mm». m . 2 as .2 . .3m 08 “322.3. : 2 02 .22 as .32 0.: .22 0mm .22 am .2323 .2 can .2 .2835 Jam :3 .2 08.02 . $23 .Wmcwhz 2 o 2. 2 3 02 .2 .2 OS .2 .3 02 .2 .3 05 .2 .3 own .2 238252 .3 oak .2 02.108 .2 .2 Juice 2.: 2 v 0 23.23 222 2265252 .mHAowmz .32 GE. :22 a2. .32 .3 ..3m .8 .3m as .3m 0: .2 .3m 0% .3m 02. .2 .on :3 .2» .2 2 ow... 2 3 08 2 .2 a2 .2 .3 a»: .2 :3 can .2 :3 on” .2 can .2 .02 :3 oz .2 :3 .3 .2 can .2 .02 82 a .3m a: .mnsaEm :3 08 .2 .2m .2 .3 8 2.352 222 2.835 :2 am: .2 322m? ..32 as ...22 0%. .32 .2. .3m or.» .22 as .2825.» .2 0mm .2 .3m 0% ..3m 0% . .2 7m 0% .2 ca. .2 3 a: 2 .2 at .2 :3 oz .2 :3 22 .2 :3 OS .2 32852 :3 0% .2 .3 0% .2 .2 02. .2 cm 82 u . 3 on». .2 a .22 0% . 3 522 382m .HB o8 .Z @37me2 .32 02. .22 am .32 own .22 .3 .22 as 282:3 .2 as .2 .3m 0% ..3m as . .2 2 03 ..2 can .2 3 can 2 .2 02. .2 .3 02 .2 :3 0% .2 :3 0% .2 €232.52 :3 can .2 .3 Own .2 .2 can .2 .2 mm 2 :3 as .2 2 S a m h o m 2. m a 2 i .2 .5 ¢ Son 922 32.3% s 3 use: a as age “252% s 3 $222 . EV ASE 35% ~38 2. 82389322 353 850 88“ 22o.“ $95 $282 2o :25 222 $80 228 328° 23°: 2 :2 Go: 22828 vans 2828822. was: 33 25532: 282285. me; we 2:: 3.3 8 28.2 33322 £500 8895. “—52.1222?— .5 0353:. afloo 3 .232 $2834 “5°C :5 .53 $2.234 23322 B—lO 338 3 62¢ 3 am: com 6893? no 23322322. .85 332 8238:3222. 2.2 32,. “$5.2 ac ”38:32. so asefifismlé 2222B JOINTS IN PRECAMBRIAN ROCKS, COLORADO A brief review of joints expected on fold structures (fig. 8) seems warranted. In either plastic or virtually Imermediale Minimum Maximum STR ESS SYSTEM A Diagonal joint Cross joint Diagonal joint Longitudinal joint FIGURE 8.——’I‘heoretical joints along a fold formed at depth by hori- zontal compression. After Willis and Willis (1934, fig. 47). nonplastic deformation, a joint set may form parallel to the fold axis and one set perpendicular to it. “Re- lease tension—joints” (DeSitter, 1956, p. 131) or “release joints” (Billings, 1942, p. 125) may form parallel to the axial plane of a fold owing to release of the principal stress. Tension joints may also form parallel to the axial plane in the upper part of the fold owing to stretching of the beds or layers across the top part of the fold. A set of joints at right angles to the fold axis (and at right angles to the release joints) may form during elongation of the fold (“extension joints” of Billings, 1942, p. 125). Similarly, a doubly plunging fold may have tension joints formed perpendicular to the axis of the fold owing to stretching of the beds on the crest of the doubly plunging anticline. Shear joints (here called diagonal joints), in addition to longitu- dinal and cross joints, may form in symmetrical posi- tions about the direction of principal stress. Ander— son’s studies (1951, p. 15) indicate that the angle be- tween the greatest compressive principal stress and the surfaces of shear will be less than 45°. Both directions of shear are not necessarily expressed by strain in the rocks. In theory shear joints should have slickensided surfaces, but the deformation may show as a fracture along which movement was so slight as to be indiscern— able. Hills (1953, p. 100—101) expresses the problem as follows: Shear joints are either shearing planes along which the differ- ential slip has been of microscopical amount, or potential shear- ing planes which have become visible as a result of readjust- ments taking place in the deformed rocks as a result of weather- ing, or of fatigue under alternating stress. B—ll Fractures which have the correct relative position to be shear joints but which show no discernible move- ment along them are called diagonal joints in this re- port. An ideal system of joints related to a fold formed by the stress system shown in figure 8 would consist of a release tension joint parallel to the axial plane of the fold (a longitudinal joint), a release tension joint per- pendicular to the axis of the fold (a cross joint), and two shear joints (diagonal joints) symmetrically dis- posed at less than 45° about the cross joint (which is parallel to the direction of maximum stress). The longitudinal, cross, and diagonal joints should have a common line of intersection, which would be parallel to the intermediate axis of stress. The older Precambrian folds do seem to have a joint system of cross, diagonal, and longitudinal joints. Cross joints are the easiest ones to recognize. The theo- retical position of cross joints can be calculated from the average plunge of the folds in a given area and compared to joint—set positions measured from Schmidt net diagrams of the same area; close agreement can be found, as is shown on table 1, columns 2 and 3. The marked variation in bearing and plunge of axes of the older fold system, particularly in the southern part of the area, can be related to a shift in a joint set shown on the diagrams (table 1 and fig. 7). This shift is noticeable in the field where the gradual change in the plunge of the older folds from outcrop to outcrop is accompanied by a gradual shift in one of the more conspicuous (closely spaced) joint sets; the joint set is consistently almost exactly at right angles to the bear- ing and plunge of the older folds as measured from out- crop to outcrop. When we consider that the bearing and plunge of the fold axis that is used to compute the theoretical cross joints is an average of a variable struc- ture, and the attitude of joint sets as read from a Schmidt net is an average whose position may be modi- fied by any or all of the factors previously discussed, then we are surprised at how good a match can be made. Less easy to recognize are joints inferred to be longi- tudinal or diagonal joints related to the older fold system. No field evidence was found to show a clear relation between these joints and the older fold system. The joint sets given in table 1, column 11 and shown on figure 7 as diagonal (dba) or longitudinal joint sets (lbo) related to the older fold system are so named be- cause they correspond approximately in position with the theoretical positions of joint sets on the older folds that can be calculated with some fair degree of ac- curacy. If these diagonal joints do belong to the stress system prevailing at the time of the older folding, then the intermediate axis of stress at the time of the joint- B—12 ing must have been vertical. The character of the older folds suggests that the intermediate axis of stress was horizontal at the time of the folding. The stress system prevailing in the Central City— Idaho Springs area was apparently the same at the time of the younger Precambrian folding and at the time of the jointing. The character of the younger folds suggests that the intermediate axis of stress was horizontal rather than vertical; diagonal (shear) joints formed in such a stress system should strike parallel to the younger fold axes and dip about 45° (compare fig. 8; Billings, 1942, fig. 108B). Release tension joints parallel to the fold axes (longitudinal joints) and per— pendicular to them (cross joints) would have the same relations as shown in figure 8. Diagonal joints related to the younger folding are clearly shown in biotite—muscovite granite and in granite gneiss and pegmatite. These joints (fig. 9) contain High for ”a" Iineation of younger fold system (lower-hemisphere plot) FIGURE 9.-—-Contour diagram of shear joints in biotite-muscovite gran- ite and in granite gneiss and pegmatite, upper hemisphere plot of 63 poles, in percent. slickenside lineations that are parallel to a of the younger fold system. Only 1 of the 2 possible shear joints has formed in the rocks, and therefore, only 1 quadrant of the Schmidt net is required to show their concentration. Apparently the stress was entirely taken up along 1 of the 2 possible directions of shear. Only very small offsets (generally less than one-tenth of an inch) have been observed on the shear joints. Some of these slickensided joints also appear in the metasedimentary rocks where they commonly are along SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY northwestward-dipping layers (P. K. Sims, oral com- munication, 1958). Joints related to the younger period of folding in- clude cross joints and diagonal joints. The nearly con— stant bearing and plunge of the younger fold axes are reflected in the nearly constant strike and dip of a cross— joint set that appears on all Schmidt net diagrams (figs. 3, 5, and 7). The nearness of this joint set to the strike and dip as calculated from the bearing and plunge of the younger fold axes is shown by comparing column 5 with column 6 on table 1. This joint set occurs in all Precambrian igneous and metamorphic rocks, which suggests that it is either late Precambrian or post-Pre- cambrian in age. Areas of more intense younger Pre- cambrian folding generally show a more intense high on the contour diagram at the location of the theoretical cross joint that would be related to that folding (figs. 3, 5, 6, and 7). This correlation of more intense jointing with more intense folding also supports the idea that the joints and folds are genetically related. POST-PRECAMBRIAN JOINTS Joints that are younger than Precambrian include those formed by shorting and those belonging to a re- gional joint system. Sheeting joints form by release of pressure due to erosion of overlying rocks and are flat- lying joints. (See Chapman and Rioux, 1958, for a recent study of sheeting joints.) Such joints are visible in most parts of the area. Because these joints are both irregular and flat, (commonly dipping less than 10°), their true attitude in the field is difficult to determine accurately. The result on a Schmidt net is that the poles of flat joints are dispersed and do not necessarily show as a concentration on the contour diagram. Only on two of the contour diagrams of the metamorphic rocks (2 and 3 on fig. 6) are they sufficiently concentrated to form a distinct high. If sheeting has formed in the in- trusive rocks, it probably has accented the highs for the flat-dipping primary joints marked 1 on figure 3 and P on figure 5. A group of four joint sets has been superposed on the Precambrian rocks. We propose to demonstrate that this group of four joints is a joint system formed by a single stress system. The age of the joint system prob— ably is Laramide. The group of joint sets appears on all diagrams (figs. 3, 5, 6, and 7). In the granodiorite, all four positions occupied by this group of younger joint sets nearly or exactly coincide with the positions of primary joint sets. Three of the joint sets, where they exist, would appear in the diagram in the area covered by the 2—2.5 percent contour around the high labeled 2; the fourth set (la- beled l, on fig. 3) may be represented by the elongated JOINTS IN PRECAMBR‘IAN ROCKS, COLORADO high around the primary joint labeled 3. Similarly, in the Alps Mountain stock (fig. 5), 2 of the 4 joint sets (cl,l and 0,) locally were followed by pegmatite and are primary directions of weakness that may have opened or become emphasized during a subsequent period of stress. The other two joints (d,2 and l,) were not fol- lowed by pegmatite, and at places they cross contacts between the stock and the enclosing metamorphic rocks. The deflection on the southwest side of d.2 (fig. 5) rep- resents a joint set that is followed by pegmatite. We suggest that if d,2 were primary to the granite as is the joint set indicated by the small deflection on its side, then 03,2 should also be followed by pegmatite, because the strike and dip of planes having this general attitude EXPLANATION Size and shape of area of inter- section of the regional joint planes Average bearing and plunge of older folds 105°35' /Average bearing and plunge Y of younger folds Regional diagonal joint Regional cross ”4' joint Regional diagonal l°im ' Regional longitudinal joint STEREOG RAPHIC PROJECTION. LOWER HEMISPHERE Abo .Aby IIII.» . ' V FIGURE 10.—’Stereographlc diagrams of the regional B—13 obviously were favorable for emplacement of pegma- tite during emplacement of the Silver Plume granite. The group of joint sets appears consistently in all metamorphic rocks regardless of their structure (fig. 7), whereas the joint sets related to the Precambrian folding change in direction and (or) intensity with changes in direction or intensity of the Precambrian folds. To determine whether these joints form a genetically related system, we plotted the four joint sets on stero- graphic diagrams (fig. 10) which were then compared visually with the ideal system described on page 11 and illustrated on figure 8. Each diagram ap- proaches the ideal system reasonably closely; the solid 105°30' 39°45’ by ‘8 will“..- joint system and axes of Precambrian fold systems. B—14 black plane and the vertically lined plane are almost exactly at right angles; the unpatterned planes are nearly symmetrically disposed at less than 45° about the vertically lined plane. In most diagrams the four planes intersect in what we consider to be a relatively small volume of error, which projects onto the diagram as an “area of error,” instead of a straight line as the ideal system shows. If we consider all the possible errors, and thus the limit of exactness in the position of the attitudes obtained from the Schmidt net diagrams, it seems surprising that these joint sets so nearly ap- proach an ideal system. Our conclusion is that these 4 joints do form a system expressed as a longitudinal and a cross joint, and 1 0r 2 diagonal joints. But to what stress system do these joints belong? The joint system apparently has no systematic rela- tion to either of the Precambrian fold systems. Shown on figure 10 in each diagram are the average bearing and plunge for each of the Precambrian fold systems in the areas covered by the diagrams. On diagram 4 of figure 10 the bearing of the older fold system is shown as a range because the diagram covers an area where the older fold system gradually changes bearing from one side of the area to the other, hence for this area the range is more descriptive than the average. If the joint system is related to either Precambrian fold system, then the longitudinal joint sets (black planes on fig. 10) should contain the axis of one of the Precambrian fold systems. It does not; therefore we infer from this lack of concordance with Precambrian folds and from the appearance of the system in the youngest Precambrian intrustive rock (biotite-muscovite granite) that the sys- tem is either very late Precambrian or post-Precam- brian. As the system also postdates the youngest Pre- cambrian folding, we infer that it is most likely post- Precambrian in age. The uplift and arching of the Front Range highland (Lovering and Goddard, 1950, p. 57—63) constitute the only major post-Precambrian geologic episode affecting the area to which this joint system could logically be- long. The highland was arched during Paleozoic time and again during Laramide time. These disturbances formed the arch or regional anticline outlined in figure 1. The Laramide disturbance seems to have been more pronounced than any of the Paleozoic disturbances, and the weight of evidence suggests that the regional joint system is Laramide rather than Paleozoic in age. We suggest that stresses which were strong enough to cause Laramide folding and thrusting along the edge of the Front Range and to help elevate the highland arch SHO‘RTEIR CONTRIBUTIONS TO GENERAL GEOLOGY surely would leave some mark on the crystalline core of the arch. The trend of the arch is about N. 15° W. near the Central City—Idaho Springs area, and this direc- tion is reasonably near the trend of the regional longi- tudinal joint (column 8, table 1). The highland dis— appears to the south near Cripple Creek, 0010., which indicates that the arch plunges gently to the south. A highland arch cross joint in the Central City—Idaho Springs area theoretically should dip steeply to the north-northwest to be at right angles to the axis of the gently plunging arch, and actually it does (column 8, table 1). We infer that the regional joint system was formed during the arching and is Laramide in age. The existence of a regional joint system of Laramide age is an hypothesis based on the study of a small part of a large area, but it can be tested by geologists who are working or plan to work in parts of the Front Range where Paleozoic sedimentary rocks overlap Precam- brian crystalline rocks. If the hypothesis is found to be true, then we have another tool that will aid in the unscrambling of the complex geologic history of the Front Range. REFERENCES CITED Anderson, E. M., 1951, The dynamics of faulting: London, Oliver & Boyd, 206 p. Balk, Robert, 1937, Structural behavior of igneous rocks: Geol. Soc. America Mem. 5, 177 p. Bastin, E. S., and Hill, J. M., 1917, Economic geology of Gilpin County and adjacent parts of Clear Creek and Boulder Counties, 0010.: U.S. Geol. Survey Prof. Paper 94, 379 p. Billings, M. P., 1942, Structural geology: New York, Prentice Hall, 473 p. Chapman, 0. A., and Rioux, R. L., 1958, Statistical study of topography, sheeting, and jointing in granite, Acadia Na- tional Park, Maine: Am. J our. Sci., v. 256, p. 111—127. DeSitter, L. U., 1956, Structural geology: New York, McGraw- Hill Book 00., 552 p. Harrison, J. E., and Wells, J. D., 1959, Geology and ore deposits of the Chicago Creek area, Clear Creek County, 0010.: U.S. Geol. Survey Prof. Paper 319, 92 p. Hills, E. S., 1953, Outlines of structural geology: New York, John Wiley & Sons, 182 p. Levering, T. S., and Goddard, E. N., 1950, Geology and ore de- posits of the Front Range, 0010.: U.S. Geol. Survey Prof. Paper 223, 319 p. Spurr, J. E., Garrey, G. H., and Ball, S. H., 1908, Economic geology of the Georgetown quadrangle, Colorado: U.S. Geol. Survey Prof. Paper 63, 422 p. Turner, F. J ., 1948, Mineralogical and structural evolution of the metamorphic rocks: Geol. Soc. America Mem. 30, 342 p. Wells, J. D., 1960, Petrography of radioactive Tertiary igneous rocks, central part of the Front Range mineral belt, Gilpin and Clear Creek Counties, 0010.: U.S. Geol. Survey Bull 1032—E, p. 223‘272. Willis, Bailey, and Willis, Robin, 1934, Geologic structures: 3d ed., New York, McGraw—Hill Book Co., 544 p. , u *9;- W V w t, v egv-Fwa-r '- «mum “a pg 7 5" ’0 EARTH ",:v H65 LIBRARY K 3 7 "/ ‘C— . . Jurassm (Bathoman or Early Callovian) Ammonites From Alaska and Montana GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-C Jurassic (Bathonian or Early Callovian) Ammonites From , Alaska and Montana By RALPH W. IMLAY SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—C Descriptions and illustrations of cep/mlopocls ofpossiéle late Middle Jurassic (Batflmiafl) age UNITED STATES GOVERNMENT PRINTING OFFICE,WASHINGTON: 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of DOCuments, US. Government Printing Oflice Washington 25, D.C. CONTENTS Page Abstract ___________________________________________ C—l Age of the faunas—Continued Introduction _______________________________________ C~l Callovian versus Bathonian in Greenland __________ Biologic analysis ____________________________________ C—2 Callovian versus Bathonian in Alaska and Montana- Stratigraphic summary ______________________________ C—2 Paleogeographic considerations ___________________ Cook Inlet region, Alaska ________________________ C—2 Summation of the evidence ______________________ Iniskin Peninsula ___________________________ C—2 Comparisons with other faunas _______________________ Peninsula north of Chinitna Bay ______________ C—3 Western interior of Canada ______________________ Talkeetna Mountains ________________________ C—3 Arctic region ___________________________________ Western Montana ______________________________ C~5 other regions ___________________________________ Rocky Mountain front north of the Sun River- C—5 Geographic distribution ______________________________ Drummond area ____________________________ C—10 Summary of results _________________________________ Age of the Evide faunas ___________________________________ 0—10 Systematic descriptions ______________________________ nce from Alaska ___________________________ C—lO Literature cited _____________________________________ Evidence from Montana _________________________ 0—12 Index _____________________________________________ PLATE ooqmmusmw FIGURE 1. TABLE 1. S" ILLUSTRATIONS [Plates 1—8 follow index] . Holcophylloceras, Oecotraustes (Paroecotraustes)?, and Arctocephalites (Cranocephalites). . Arctocephalites?, Siemimdzkia?, and Arctocephalz'tes (Cranocephalites). . Arctocephalites (Cranocephalites). . Arctocephalites (Cranocephalites) and Arcticoceras?. . Arctocephalites?, Cobbam'tes, and Xenocephalites?. . Pararez'neckeia and Cobbam'tes. Cobbam'tes. Index map of the principal areas of Jurassic rocks in the Cook Inlet region, Alaska __________________________ . Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in the Talkeetna Mountains, Alaska ___________________________________________________________________________________________ . Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in the peninsula south of Tuxedni Bay, Alaska _______________________________________________________________________________ . Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in the Iniskin Peninsula, Alaska ___________________________________________________________________________________________ Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in northwestern Montana from the Sun River area northward __________________________________________________________________ Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in the Drummond area in western Montana ___________________________________________________________________________________ Correlation of some Middle and Late Jurassic formations in the Cook Inlet region, Alaska, and in western Montana- TABLES Ammonite genera in the Arctocephalites (Cranocephalites) beds in Alaska and Montana showing biological relation- ships and relative numbers available for study _________________________________________________________ . Occurrences and stratigraphic positions of the Callovian ammonites from the upper part of the Bowser member of the Tuxedni formation, above the beds containing Arctocephalites (Cranocephalites) _________________________ . Localities at which ammonites of Bathonian or early Callovian age have been collected in the Arctocephalites (Crane- cephalites) beds in the Cook Inlet region, Alaska ________________________________________________________ . Localities at which ammonites of Bathonian or early Callovian age have been collected in the upper member of the Sawtooth formation in western Montana ______________________________________________________________ Geographic distribution of fossils from the Arctocephalites (Cranocephalites) beds in the Cook Inlet region, Alaska- Geographic distributicn of fossils from the Sawtooth formation in northwestern Montana ______________________ III Page 0—12 0—13 0—13 0—14 0—14 0—14 0—15 0—15 0—15 0—19 0—22 0—28 0—31 Page 0—4 0—9 0—11 0—16 C~17 C—20 C—21 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY J URASSIC (BATHONIAN OR EARLY CALLOVIAN) AMMONITES FROM ALASKA AND MONTANA By RALPH W. IMLAY ABSTRACT Jurassic ammonites of possible late Middle Jurassic (Bathonian) age occur in western Montana in the upper member of the Saw- tooth formation and in the Cook Inlet area, Alaska, in the middle part of the Bowser member of the Tuxedni formation. They are characterized by Cranocephalites, a subgenus of Arc- tocephalites. They include, also, Holcophylloceras, Parareineck- eia, a new genus of the Reineckeiidae, Cobbam'tes, a new genus of the Perisphinctidae, and some specimens assigned questionably to Oecotraustes, Xenoceph-alites, Arcticoceras, Siemiradzkia, and Arctocephalites. Stratigraphically the beds containing these ammonites occupy the position of the Bathonian stage or the basal part of the Callovian stage of Europe. In the Iniskin Peninsula, Alaska, they lie unconformably on beds containing late Bajocian am- monites and grade upward into beds containing early Callovian ammonites. In the Talkeetna Mountains, Alaska, they lie on beds of Early Jurassic age and are overlain by beds containing typical early Callovian ammonites, but are more restricted in distribution than the Callovian beds. The fact that in many places the Callovian beds rest directly on Bajocian beds could mean either that the Cranocephalites beds were never deposited in those places or that they were eroded before the deposition of the Callovian beds. In Montana the Cranocephalites beds seem to grade down- ward into beds containing middle Bajocian ammonites and are overlain sharply with possible disconformity by beds character- ized by the early Callovian ammonite Arcticoceras. As the Arcticoceras beds are equivalent to at least part of the European zone of Macrocephalus macrocephalites at the base of the Callo- vian, the Cranocephalites beds cannot be younger than the basal part of that zone. A somewhat older age for the Grano- cephalites beds in Montana would be favored if a disconformity exists between the Cranocephalites and Arcticoceras beds. Con- ceivably the Cranocephalites beds could span the entire Batho- nian as well as the basal Callovian, but such a long time span for a single ammonite faunule seems unlikely. Faunally the beds characterized by Cranocephalites cannot be dated exactly. They do not contain any genera typical of the Callovian of Europe and only two ammonites that probably belong to the Bathonian genus Siemimdzkia. A Callovian age is slightly favored by the presence of the family Reineckeiidae, by the fact that the new genera Parareineckeia and Cobbam'tes range upward into beds containing typical Callovian ammonites, and by the probability that Cranocephalites gave rise to the Cal- lovian genera Arcticoceras and Cadoceras. This evidence is not at all conclusive, but it does indicate that the ammonites in the Cranocephalites beds are biologically close to ammonites in the Callovian and are not likely to be older than late Bathonian. Considering both stratigraphic and faunal evidence, the Cm- nocephalites beds are tentatively correlated with the Bathonian rather than the Callovian stage and with the late rather than the early Bathonian. If this correlation is valid, the ammonites of Bathonian time occupied two distinct realms of which one included central and southern Europe and the Tethyan region from Mexico to Indonesia, and the other included the Arctic region and part of the North Pacific Ocean. INTRODUCTION The ammonites described herein have been studied primarily to determine whether the middle Jurassic (Bathonian) stage is represented by sedimentary rocks in Alaska and the western interior of the United States. The study was prompted at this time in order to test recent inferences and statements by W. J. Arkell (1956, p. 609) that a retreat of the Arctic Ocean from bordering lands began after early Bajocian time, that the seas retreated from most of the known land areas of the world about middle Bathonian time, that the Arctic Ocean was probably isolated from the other oceans during the Bajocian—Bathonian regression, and that Bathonian rocks are absent in North America north of southern Mexico with the possible exception of one place in northern Alberta. Evaluation of the fossil evidence bearing on the presence or absence of the Bathonian in the United States and Canada should be interesting to many geologists. The fossils from the Cook Inlet region, Alaska were collected by G. C. Martin in 1913, A. A. Baker in 1921, Helmuth Wedow and L. B. Kellum in 1944, C. E. Kirschner in 1946, D. J. Miller and R. W. Imlay in 1948, Arthur Grantz in 1951—53, R. D. Hoare in 1952, L. F. Fay in 1953, and R. L. Detterman in 1958. The fossils from western Montana were collected by C. F. Deiss in 1940 and 1941, R. M. Garrels in 1940, Josiah Bridge in 1941, R. W. Imlay in 1944—58, J. B. Reeside, Jr. in 1944, W. A. Cobban in 1944—46, William Saalfrank in 1945, H. C. Yingling in 1944, M. R. Mudge in 1958 and 1959, and M. W. Reynolds in 1958 and 1959. C-l C—2 BIOLOGIC ANALYSIS The Jurassic ammonites of Bathonian or earliest Callovian age discussed herein include 84 specimens from Alaska and 46 from western Montana. Their distribution by genera, subfamilies, and families is shown in table 1. The table shows that the Cardioceratidae is the dominant family and is represented mostly by Arctocephalites and Cranocephalttes. Next in impor- tance is the family Perisphinctidae which is represented mainly by the new genus Cobbanites and by two speci- mens probably belonging to Stemtradzkta. The fami- lies Phylloceratidae, Oppeliidae, hlacrocephalitidae, and Reineckeiidae are of minor importance. The biological relationships of Arctoeephalttes and Cranocephalites are not settled. Generally, they have been included in the Macrocephalitidae (Spath, 1932, p. 9, 32; Donovan, 1953, p. 78; Arkell, 1954, p. 117), but recently they have been included in the Cardio— ceratidae by Arkell (1957, p. L301), probably because of the presence of a constricted aperture. Also, they appear to be the ancestors of the Cardioceratidae and to have arisen separately from the Macrocephalitidae, according to Arkell (1956, p. 610; 1958, p. 233, 234). The genus Arctocephalites as defined by Spath (1928, p. 174; 1932, p. 32, 33) includes stout to globose in- volute ammonites in which the ribbing is high and sharp on the inner whorls, becomes blunt on the penultimate whorl, and fades on the body whorl, but on some species may become strong again near the aperture. The aperture is constricted. The genus Cranocephal’ttes was based (Spath, 1932, p. 14—16) on some ammonites from East Greenland that were found only 20 meters stratigraphically below Arctocephalites. They resemble Arctocephalites in shape and in the sharpness of ribbing on their inner whorls. They differ from Arctocephalttes by developing a scaphitoid body chamber, by the ribbing remaining strong or fairly strong on the body chamber, and by a tendency of the suture line to simplify. Spath (1932, p. 14) noted that the two genera are connected by transition species and that ”separation was prompted chiefly by their difference of horizon.” TABLE 1.——Ammonite genera in the Arctocephalites (Cranocepha- lites) beds in Alaska and Montana showing biological relation— ships and relative numbers available for study. Number of Family Subfamz’ly Genus or Sub- specimens in— genus Alaska Montana Phylloceratidae. . , , Calliphylloceratinao. Holcophylloceras.. 7 _________ Oppeliidae .......... Oppelliinae _________ Oecotraustes? _____ 1 ________ Macrocephalitidae _______________________ X enocephalites 9 __________ 1 Cardioceratidae ..... Cadoceratinae _______ Arctocephalitesf. _ _ 6 1 Cranocephalites _. . 47 23 Cranocephalites f. _ 16 _________ Arcticoceras ? ............. 1 Reineckeiidae ___________________________ Pararcinecketau" 3 _________ Perisphinctidac ..... Zigzagiceratinae _____ Cobbanites ________ 2 20 Pseudoperisphinc- Siemiradzkia 7. _ _ 2 _________ tin ae SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Recent studies by Donovan (1953, p. 78, 130, 133) have shown that Arctocephalites and Oranocephalites are closely related, that the differences between them were overstressed by Spath, and that Cranocephalttes is not worthy of more than subgeneric rank under Arctocephalites. These conclusions have been sup- ported by Arkell (1956, p. 541; 1957, p. L301). STRATIGRAPHIC SUMMARY COOK INLET REGION, ALASKA INISKIN PENINSULA The Bowser member of the Tuxedni formation on the Iniskin Peninsula (Kirschner and h/Iinard, 1949) ranges from 1,800 to 2,100 feet in thickness and consists of interbedded claystone, siltstone, sandstone, and con— glomerate. At the base are 600 feet, or less, of inter— bedded dark-gray siltstone, sandy siltstone, and claystone that weathers reddish brown, contains many ash beds, and locally bears small fossiliferous limestone concretions. These beds are absent at the south end of the Iniskin Peninsula, southwest of the pass between Right Arm and Oil Bay. Above them follows abruptly about 430 to 730 feet of gray thick-bedded cliff-forming siltstone and sandstone that are interbedded with some units of gray sandy siltstone, siltstone, claystone, and conglomerate. Above follows from 790 to 1,150 feet of gray thick—bedded sandstone that contains many siltstone interbeds and becomes siltier eastward. In all sections the upper 100 feet consists of thick—bedded sandstone. The Bowser member rests concordantly but abruptly on the massive sandstone of the Cynthia Falls sand- stone member of the Tuxedni formation and grades at its top into shelly beds at the base of the Chinitna formation. Within the Bowser member the abrupt contact between the lowest massive siltstone and sand- stone and the underlying few hundred feet of rusty weathering siltstone and claystone represents an un- conformity (written communication, R. L. Detterman, May 15, 1959). Concretions from the rusty-weathering beds in the lower few hundred feet of the Bowser member have furnished late Bajocian ammonites belonging to the genera Leptosphinctes, Sphaeroceras?, Oppelia (Oxy- certtes), Lissoceras, and Polyplectites. From the 430 to 730 feet of sandstone and siltstone in the middle part of the member have been obtained Arctocephalttes (Cranocephalites), Arctocephalttes?, Parareineckeia n. gen, and a number of pelecypods (table 5). From the 790 to 1,500 feet of cliff—forming sandstone at the top of the member have been obtained a varied pele— cypod fauna and the early Callovian ammonites Gros— souom'a sp., Kheraiceras tntermedium Imlay, Kherat— JURASSIC AMMONITES FROM ALASKA AND MONTANA C—3 ceras parm'forme Imlay, K. sp., Xenocephalites hebetus Imlay, X. cicarius Imlay, X. sp., Kepplerites cf. K. tychonis (Ravn), Kepplerites sp., Phylloceras bakeri Imlay, Calliphylloceras freibroclci Imlay, Macrophyllo- ceras grossicostatum Imlay, and numerous fragments of macrocephalitid ammonites (table 2). PENINSULA NORTH OF CHI'NITNA BAY The Bowser member northward from Chinitna Bay becomes finer grained and consists mostly of massive gray siltstone and sandy siltstone but contains some sandstone and conglomerate in its upper part. Its base is not exposed but its top is marked locally by channel conglomerates. Near Bear Creek the lower 300 feet of the member weathers rusty brown and con— tains many ash beds, and has furnished specimens of Sphaeroceras?, Lissoceras, and Oppelia (Oxyceriies) identical with those in the lower few hundred feet of the Bowser member on the Iniskin Peninsula. The overlying 430 feet of massive gray sandy siltstone has furnished Oranocephatites. Above follows 820 feet of massive brown to gray siltstone that have furnished the early Callovian ammonites Xenocephalites hebetus Imlay and X. oicarius Imlay at places about 350 and 500 feet respectively below the top of the Bowser member (table 2). Near Hickerson Lake, north of Chinitna Bay, the ammonites Cranocephalites, Siemiradzkia?, and Parareineclreia n. gen., were obtained from gray siltstone about 1,000 to 1,100 feet below the top of the Bowser member and about 600 feet above the rusty weathering beds. From 200 to 400 feet below the top of the member were obtained specimens of the early Callovian ammonite Kheraiceras cf. K. intermedinm Imlay. At the very top of the Bowser member at the north end of Chisik Island was obtained the Callovian ammonite Kheraiceras intermedium Imlay (table 2). TALKEETNA M OUNTAIN S In the Talkeetna Mountains the Oranocephatites beds have been found at three places (table 5). A small collection (Mesozoic 100. 8573) was made by Mar- tin (1926, p. 228) near Boulder Creek 3 miles above the mouth of East Boulder Creek in the Anchorage (D—4) quadrangle. Arthur Grantz and associates in 1952 and 1953 made several collections (Mesozoic locs. 24115—24118, 24825) on the north fork of the upper part of the Little Nelchina River and several other collections (Mesozoic locs. 24822—24824) on a small northward—draining tributary of the Little Oshetna River. Another small collection was made by R. A. Lyon near the Little Oshetna River (Mesozoic 100. 27515). TABLE 2.——Occurrences and stratigraphic positions of the Callovian ammonites from the upper part of the Bowser member of the Tuxedni formation above the beds containing Arctocephalites (Cranocephalites) [Data on stratigraphic positions furnished by R. L. Detterman] Mesozoic Fossil Feet below top of Feet above Collector, year of collection, and description of localities localities Bowser member Cranocephalites beds 13014 Kheraiceras intermedium Imlay __________________ At top ________________ 820 ____________________ Stanton, T. W., 1904. North end of Chisik Island, 1.25 miles S. 81° E. of Fossil Point, 1 it below base of Channel . conglomerate. 3038 Grossouvrza sp ................................... Not determinable _____ Not determinable _____ Stanton, W. W., and Martin, G. 0., 1904. Shore of Iniskin Bay at entrance to Right Arm, 5.25 miles N. 74° W. of ‘ Front Mountain. 11042 Kheraiceraa parmforme Imlay ..................... 600—650 ________________ 180—230 ________________ Baker, A. A., 1921. Iniskin Peninsula, on Edelman Creek, 1.4 miles N. 15° W. of Front Mountain. 20748 Xenocephalttes sp. juv ........................... 500—550 ................ 280—320 ________________ Kirschner, C. E., 1946, Iniskin Peninsula. On Edelman Creek, 1.2 miles N. 10° W. of Front Mountain. 1 21272 Kheraiceras intermedium Imlay __________________ At top ________________ 820 ____________________ Miller, D. J., and Imlay, R. W., 1948. North end of, Chisik Island, at same place as Mesozoic loc. 3014. 21311 Macrophylloceras grossicostatum Imlay, Phyl- 550-600 ________________ At least 200—250 _____ _. Imlay, R. W., and Miller, D. J., 1948, Iniskin Peninsula, éocriros bakeri Imlay, Calliphylloceras freibrocki 1.92 miles N. 89° E. of dock at mouth of Fitz Creek. in ay. 21312 Xenocephalitex hebetus Imlay, Kheraiceras inter- Afew feet higher than At least 200—250......_ Imlay, R. W., and Miller, D. J., 1948. Iniskin Peninsula, medium Imlay, Macrophylloceras grossicosta- 100. 21311. 1.9 miles N. 86° E. of dock at mouth of Fitz Creek. tnm Imlay, Colliphyllocems freibrocki Imlay. 1 21319 chplerites cf. K. tychonis Ravn.._. _____________ 360—390 ________________ 770—800 ________________ Imlay, R. W., and Miller, D. J ., 1948. Iniskin Peninsula, . . 0.65 miles S. 35° E. of Tonnie Peak. 21320 Parareineckeia sp ________________________________ 370-420 ________________ 410—460 ________________ Imlay, R. W., and Miller, P. 1., 1948. Iniskin Peninsula, , 4.7 miles S. 15° E. of Tonnie Peak. 22436 Macrophylloceras grossicoatotum Imlay ...... _ 550—600 _____ _ At least 200~250.._ . Hartsock, J. K., 1950, Iniskin Peninsula, about same posi- . tion as Mesozoic 100. 21311. 22536 Kherazceras sp ___________________________________ 200—300 ________________ 800—900 ________________ Hill, D. M., and Juhle, R. W., 1950. Right arm of Iniskin . Bay, about 4.25 miles N. 58° W. of Front Mountain. 22549 Kepplentes sp ................................... 200—300 ________________ 700—800 ________________ Hartsock, J. K., 1950. Iniskin Peninsula, 4.08 miles N. . 41° E. of Front Mountain on tributary to Brown Creek. 22553 Kepplerztes sp ................................... 300—400 ________________ 700—800 ________________ Hill, D. M., 1950. Right arm of Iniskin Bay, about 0.13 ' _ mile south of Mesozoic loc. 22536. 1 22686 Kepplerites sp., Kherazceras sp ___________________ At top.____ ___________ 820 ____________________ Grantz, Arthur, 1951. Northwest part of Chisik Island 1.2 . , , miles southwest of the northern tip. 1 22699 Kheraiceras of. K. intermedzum Imlay ____________ 360-380 ________________ 630—650 ________________ Grantz, Arthur, 1951. Peninsula South Of Tuxedni Bay, on , _ ' ridge 1.62 miles N. 51° E. of head of Lake Hickerson. 1 22700 Kherazceras cf. K. intermedzum Imlay ____________ 200—230 ________________ 780—810 ________________ Grlantz, Arthur, 1951, on ridge 1.7 miles N. 51° E. of head of ake Hickerson. I 22713 Xenocephalites hebetus Imlay _____________________ 500 ____________________ 320 ____________________ Grantz, Arthur, 1951. 0.62 mile above mouth of tributary , . ' entering Bear Creek 2.53 miles from Tuxedni Channel. 1 22714 Xenocephahtes vicanus Imlay .................... 350—370 ________________ 450—470 ________________ Grantz, Arthur, 1951. 0.67 miles above mouth of same tributary described under Mesozoic 100. 22713. l Stratigraphic position is well established. 582600 0—61———2 C—4 s09 N C : ° fl \ 152° Q \ l 1‘ in s «w . we“ 435 . . 0 __. 156. I?o° 100 O 100 g | l 200 300 l : SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY OCEAN OCEAN 400 MILES I FIGURE 1.—Index map of the principal areas of Jurassic rocks in the Cook Inlet region, Alaska. (1. Talkeetana Mountains; 2. Peninsula south of Tuxedni Bay; 3. Iniskln Peninsula.) According to Grantz (written communication, Apr. 8, 1959), the ammonite Cranocephalites was found near the Little Oshetna River in the middle of a sequence about 650 feet thick (Mesozoic 100. 24822). The se— quence consists mostly of gray thick—bedded fine- to coarse-grained sandstone that is locally crossbedded. It includes lenses of conglomerate and some beds of siltstone, claystone, and coal. It rests unconformably on the Lower Jurassic Talkeetna formation and is overlain with apparent disconformity by a conglom— eratic sandstone unit about 100 feet thick that also contains Cranocephalites (Mesozoic 100. 27515). The overlying Chinitna formation is about 800 feet thick and has furnished the early Callovian ammonite Para— cadoceras tonniense Imlay about 100 to 150 feet below its top. There is no evidence for a disconformity at the base of the Chinitna formation. The Oranocephalites beds exposed in the upper part of the Little Nelchina River valley, according to Grantz, are about 1,200 feet thick and consist mostly of units of gray medium- to thick-bedded fine- to coarse-grained sandstone and siltstone, but include lenses of pebble and cobble conglomerate in their upper part. The ammonites Arctocephalites?, Oranocep/balites, and Para— reineckeia n. gen., were found from 400 to 800 feet below the top. The base of the section is not exposed. The Oranocephalites beds are overlain concordantly by 100 feet of sandstone and conglomerate that have been mapped as the basal member of the Chinitna formation but have not furnished fossils. Above follows about 850 feet of beds Whose lower part has furnished the Callovian ammonites Cadoceras, (lmmoceras, Xenoceph— elites, and Kheraiceras. The stratigraphic position of (ll'anocephal'ites near Boulder Creek collected by Martin (1926, p. 228; Capps, 1927, p. 30) has not been determined, although Bajocian and Callovian ammonites have been found in the same area of Jurassic exposures. J U RASSIC AMMONITE S 20/ 148“ FROM ALASKA AND MONTANA 40/ 147°20/ \ 62° Chickaloon T A N U 0 A S M Jr 4 \ l l “V l a‘. iRiver N elchina ‘ (Abandoned) O 5 10 MlLES l_l__.|—J_|_J—.—' FIGURE 2.—Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in the Talkcetna Mountains, Alaska. (Numbers on map refer to those given in tables 3 and 5). The Cranocephalites beds in Cook Inlet region con- tain a great variety of pelecypods most of which have not been studied (table 5). However, the occurrence of Grypkaea impressimarginata (McLearn) (Mesozoic locs. 8573, 24118) is interesting as the species in the western interior of the United States is generally restricted to the upper part of the Sawtooth formation that contains Cranocephalites and to the lower part of the Rierdon formation that contains Arcticocems. WESTERN MONTANA ROCKY MOUNTAIN FRONT NORTH OF THE SUN RIVER An ammonite faunule characterized by Arctoce'phalites (Uranocephalites) has been found in calcareous siltstone in the upper part of the Sawtooth formation within the front ranges of the Rocky Mountains in Montana ex— tending from the headwaters of the Sun River north- ward about 60 miles to Glacier Park. The Sawtooth formation (Cobban, 1945, p. 1270—1277; Imlay and others, 1948) within this area comprises 3 members of which the upper 2 are transitional into each other. The lower member consists mostly of sandstone that is generally cemented with silica, is pyritic, and attains 15 feet in thickness but is locally absent. It contains interbeds of dark-gray to black fissile shale and locally contains more shale than sandstone. Near the Sun River the lower member is capped at many places bya thin con— glomerate consisting mostly of chert, quartzite, and limestone particles but containing some particles de- rived from the lower number. The middle member 0—6 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY 152055, 50/ 45/ 40’ 152,35, / _———’ 1-. 4qu FORMAnoV‘ A“ l ’9 l (3‘ ‘ 6 l x7 /x 60°05’ 0 MIN: .nlm a . — — a Swamp‘fl . , ulle .§W"‘Bfl E, y] M M M "I L’ i 60°00’ 59°55’ £25“: zo'eh’a s; awélm” §®§§®é®m O 4!, 4 WA $2»;- FIGURE 3.—Index map showing occurrences of fossils in the Arctocephalites (Cranocephalites) beds in the peninsula south of Tuxedni Bay, Alaska. (Numbers on map refer to those given in tables 3 and 5. Base of Chinltna formation is indicated by dashed lines.) JURASSIC AMMONITES FROM ALASKA AND MONTANA 0—7 153°25’ 20’ 15’ 10’ 05’ 153°OO’ 59°50’ ~ 44, / 45’ X Front Mtn X Shark Tooth 59°40’ FIGURE 4.-Index map showing occurrences of fossils 1n the Arctocephalz‘tes (Cranocephalites) beds in the Iniskin Peninsula, Alaska. (Numbers on map refer to those given in tables 3 and 5. Base of Chinitna formation is indicated by dashed lines.) C—8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 113°20’ 113°00/ 112°30/ 48"” 7 R. 10 w. f R. 9 w R. e w, __ _ oGlacier Park J} T. 31 N. G T. 30 N. ———i_—_—__ \ T. 29 N. \ \ a > c” ,,,,Lfi” ( . ii a A > Dupuyer T. 28 N. T,27 N. Pendroy . 48°00 T. 26 N. T. 25 N. R I VE R R. 5 W. O N ; T. 24 N. Chomaufi T.23 N. k E 9? ON & T.22 N. film} \‘3 4 ‘ I; T. 21 N. i \_,-\/\ ‘L 777777 \ ‘ Cutrock 47“30’ 1 > ‘ cyeel‘ .Augusta T. 20 N. i Willow FIGURE 5.—Index map showing occurrences of fossils in the Arctoecphnlites (Cranocephalites) beds in northwestern Montana from the Sun River area northward. bers on map refer to those given in tables 4 and 6.) (Num- JURASSIC AMMONITES FROM ALASKA AND consists of dark shale that is pyritic and that thickens northward from 18 feet on the Sun River to nearly 170 feet near Badger Creek. From the Teton River area northward it includes many lenses of black phos— phatic pellets that are generally associated with well- rounded belemnite fragments. The upper member consists mostly of siltstone, becomes finely sandy up— ward, and thickens northward from 25 to 60 feet. Glauconite occurs throughout the formation and some sandstone beds in the middle member are highly glau- conitic. Phosphate pellets and waterworn belemnites are common in the formation as high as the lower part of the upper member in the area north of the Teton River. Waterworn belemnites have been found locally near the top of the formation. The Sawtooth formation does not exhibit any evi- dence of a major unconformity during its deposition except possibly at the top of the lower member in the area near the Sun River. Minor interruptions in sed- imentation probably occurred, however, as its litho— logic and faunal characteristics suggest that it was deposited slowly in shallow water under reducing con— ditions (Imlay, 1957, p. 491—493). Such is indicated in particular by the presence of lenses of phosphatic pellets and worn belemnites. The contact of the Sawtooth formation with the overlying Rierdon formation is sharp but without pos— itive evidence of an unconformity as exposed in the Rocky Mountains north of the Sun River. A minor unconformity is indicated, however, by the presence of pebbly beds at the top of the Sawtooth formation in the Sweetgrass Arch area (Cobban, 1945, p. 1273, 1274), in southern Alberta (Weir, 1949, p. 551), and in the Drummond area, Montana (lmlay and others, 1948). In Alberta the pebbles are associated with broken and worn belemnite guards. An unconformity at such a position would correspond stratigraphieally with a marked unconformity between the Rierdon and Piper formations in south—central Montana (lmlay, 1956a, p. 575) and between the Sundance and Gypsum Spring formations in northern Wyoming (Imlay, 1956a, p. 579—580) and western South Dakota (Mapel and Bergendahl, 1956, p. 88—90). Some of the pelecypods in the lower sandstone mem— ber of the Sawtooth formation (table 6) are identical with or closely similar to species described by Warren (1932) from the Rock Creek member (Warren, 1934) of the Fernie formation in southeastern British Colum- bia and western Alberta. As the Rock Creek member has furnished an ammonite assemblage of middle Bajo- cian age (McLearn 1928, 1932; Warren, 1947), the basal sandstone of the Sawtooth formation is probably likewise of that age. 582600 0—61—3 MONTANA (3-9 The middle shale member of the Sawtooth formation has furnished the middle Bajocian ammonite Chandra— cams 20 feet above the base of the formation and 5 feet above the top of the lower member at Swift Res- ervoir, Pandera County, Mont; (Imlay, 1948, p. 19, pl. 5, figs. 1—5). It has furnished, also, at various localities many species of pelecypods (table 6) which elsewhere in the western interior region range in age from middle Bajocian to early Callovian (Imlay, 1956b, p. 70, 71). A few of the species are identical with species described by McLearn (1924) from the Corbula munda and Gryphaea beds on Grassy Mountain near Blairmore, Alberta; these beds have furnished ammo- nites of early Callovian age (Frebold, 1957a, p. 21, 23— 25, 76). Lithologically the medial shale member is similar to the Rock Creek member of the Fernie for— mation in the broad sense used by Frebold, (1957a, p. 14) and it may be equivalent. The Rock Creek mem— ber, however, has furnished middle Bajocian ammo— nites at various levels from top to bottom, whereas the medial shale member of the Sawtooth formation is dated as middle Bajocian only near its base at one locality. At most other fossil localities, the fossil evidence concerning the age of the middle shale mem— ber is inconclusive. However, the presence of Gryphaea impressimarginata McLearn from the highest beds of the middle shale member at Harman Gulch, Teton County, Mont. (written communication, M. R. Mudge, Nov. 18, 1959) indicates that those beds are only slightly older than the overlying upper siltstone mem- ber in which that species is fairly common. The upper siltsone member of the Sawtooth forma— tion in the area between Sun River and Glacier Park has furnished species of ammonites similar to those in the Arctocephalites (Cranocephalites) beds in Alaska and Greenland (table 6). It has furnished, also, many species of pelecypods most of which in the western interior region range from the middle Bajocian into the lower Callovian. However, one of the species Gryphaea impressimarginam McLearn has not been found below R, 14 W. 113°20’ R. 13 W. i Railroad cut 46°40’ — l do 1 2 3 4 MES L_1_1—1__1 FIGURE 6.—1ndex map showing occurrences of fossils in the Arctocephalites (Crane- cephalites) beds in the Drummond area in western Montana. (Numbers on map refer to that given in the tables 4 and (3.) 0—10 the transitional beds at the top of the middle shale member of the Sawtooth formation, nor above the Arcticocems beds in the lower part of the Rierdon formation (Imlay, 1948, p. 14, 18). In Alberta it has been found near Blairmore associated with ammonites of early Callovian age (Frebold, 1957a, p. 19, 73—79). In Alaska it has been found in the Talkeetna Moun— tains associated with Arctocephalites (Cranocephalites). DRUMM 0ND AREA In the Drummond area, Montana, the basal 15 to 30 feet of the Sawtooth formation consist of calcareous yellowish— to reddish-brown siltstone. This is overlain by 110 to 150 feet of highly calcareous medium—gray shale that in its upper part contains beds of shaly lime— stone at intervals of 4 to 10 feet. Above the calcareous shale are silty to sandy beds identical with the upper member of the formation in the area north of the Sun River. This member, as exposed 1 mile west of Mulkey Gulch just north of the highway, consists mostly of 59 feet of interbedded yellowish-gray siltstone, silty shale, and silty to sandy limestone, but at its top includes 6 feet of hard gray calcareous pebbly sandstone that makes a sharp contact with oolitic limestone at the base of the Rierdon formation. The entire sequence appears to be perfectly conformable except possibly that part at the contact with the Rierdon formation (Imlay and others, 1948). The basal siltstone of the Sawtooth formation in the Drummond area contains the ammonites Stemmatocems aff. S. palliserz' McLearn and Normannites sp. and the pelecypods Pleuromya subcompressa (Meek) and T rigom'a montrmaensis Meek, collected by M. E. Kaufl'man of Princeton University. The overlying calcareous shales contain Pleuromya subcompressa (Meek) and T rigom'a montanaensis Meek. The upper silty member contains Camptonectes platessiformis White, Pleuromya subcompressa (Meek), Alodz'olus sp., Lopha sp., Ostrea sp., Gryphaea impressimarginata McLearn, and Arctocephalites? saypoensis Imlay, n. sp. (table 6). The presence of the last two species furnishes a correlation with the upper member of the Sawtooth formation in the area north of the Sun River. AGE OF THE FAUNAS EVIDENCE FROM ALASKA In the Iniskin Peninsula, Alaska, as discussed under “Stratigraphic summary,” the Cranocephalites beds in the middle part of the Bowser member of the Tuxedni formation appear to grade upward into beds of early Callovian age in the upper part of the Bowser member but rest abruptly and unconformably on beds of late Bajocian age in the lower part of the Bowser member (fig. 7). These relations favor a late Bathonian or very SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY early Callovian age for the Oranocephalites beds, pro- vided that there is really no unconformity between those beds and the overlying beds containing such typical Callovian ammonites as Kepplerites, Khemicems, and Grossouvria. (See table 2.) The possibility of an unconformity being present between the middle and upper parts of the Bowser member, although undetected lithologically, is sug— gested by the fact that not a single example of the ammonite Arcticoceras has been found in the upper part of the Bowser member, whereas the genus is common in the lower part of the Callovian sequences in the western interior of North America and in the Boreal region (Imlay 1953a, p. 5; 1953b, p. 53—55). However, above the Cranocephalites beds in the Bowser member are at least 200 feet of beds that have not furnished any Callovian ammonites (see table 2) and that might correspond to the Arcticoceras beds of other regions. Also, the absence of Arcticocems in collections from the Bowser member might be related to unfavorable ecological conditions or to insufficient collecting. Stratigraphically the upper part of the Bowser member cannot be younger than the lower part of the Sigalocems callovt'ense zone of Europe because it under- lies the Chinitna formation whose lower third may be correlated reasonably with that zone (Imlay, 1953b, p. 51~53). It might, however, be as old as the Macro- cephalites macrocephalus zone. Faunally it has nothing in common with either of those European zones, but the fact that all the Callovian species in the Bowser member range up into the lower third of the Chinitna formation suggests that the upper part of the Bowser member may be equivalent to part of the Sigaloceras callom’ense zone. Against this correlation is the fact that none of the collections from the Bowser member contain such typical early to middle Callovian am- monites as Cadoceras, Paracadoceras, Gowem'cems, Cos- mocems, and Lilloettia, which are common in the lower third of the Chinitna formation. Their absence in the collections is difficult to explain by unfavorable facies, considering the number and variety of other Callovian ammonites that have been found in the upper part of the Bowser member (table 2), but might be explained if they were rare or did not exist during the time that the upper part of the Bowser member was being deposited. Such a time during the early Callovian would correspond to the Macrocephalites macrocephalus zone of Europe, judging by the European ranges of certain Callovian am- monites reported by Callomon (1955, p. 254, 255). This dating of the upper part of the Bowser member of the Tuxedni formation with the Alacrocephalites macrocephalus zone implies that the (Wenocephalites beds in the middle of the Bowser member cannot be younger than the lower part of that zone even if the C—ll JURASSIC AMMONITES FROM ALASKA AND MONTANA 435:0: 532,5 5 can .axmaiw £2.48 .31: x80 2: E 25329:: Emm‘azh Bag 33 @532 3:3. mo :ofifictools 559k 3835 EB mcoemwgw :BEnAMEww» 7.6x wocwwgyh 828m 35 «Emuquiéw we.» .EwNwEQ ESSEAW SSSSQS wESBw‘N S 3mw.~um v.2 wwcwwgyfl .~_§m5§;§ 333w§d Gugfiwfi v5§®0¢3®m .S‘ScSS meSgwwuwfiwS $2333 Saswscy. 35::em Esme—a .3:in wzogmwnmm , d mevzao . K. €28 85 mESSaE Sam M? 9 $38 85 «Eggafissz .3351. v2.85 wcoam‘Em wzoumczwm >50 .. \ £3§§w§2§mN m w can i.§a§§¢:§§ :Eoohnm m w SuEeS‘BZ mssugfius m m. watééxcé hwnEoE m=8mv=mm .mssmucéEéb ”msswuezaifim m n £33852§3m Sgfis‘smegansg‘ mgwusggufim gum £556 . N. . W b m b , m. u EEaixgsm maxgcxwém .94 AwamBfiscm m. {BESEQO «En M. Sc 1. r \ . H _ . 3:35: W .58 gm“: iékueswufim mmtfiwESi gaxefiiua gafixagab m @2335 W SEE wwfiorw 2530mm: zwtxga‘nefis m. 292% 520 m. >9: 3:32 S u emu; an M Eemfifiisa agcwififii m zfifihownoomfi W N. 5350 m We LE 3?: max: I. @333 wasnuwaSEN m 3885: Ex m m Edam znhméhmfl ww 5%:qu w m. £3333 mwaofifiafigsu 3.5: 93‘ w W J meEQSESm mSSSS camaofinm w ... h w w macaw K 92:: & mw » a” M _ m. . .:_m 25% occumwgm :u‘ c x :g 33.39 $49322“ .m . _ \ vaeERws SEAS $332333va : 4 mséwfefigsm ,wafiwfiflw 3mm Ea . . «mwgdxamésasby % 9 . 4 \ 58 «En ozfimazm 327; v , m» s a 9:3 as w. m «$E§E%§EQ ummwmwmmmwMH /7/ v.55: m32§a32§< : s . g V m m. mafigagafisw‘ 2S3 wimfigega . J . . , . fl D p l N. r K. n. w 396:5 mace _ ‘ _ 1 u u cqmdcgfimczam £93 rmssmgttxw m n as z 5% h ._ 3%.: I . .Sfiw .ufizmazw cofiactow "Swim a nemeSESSU §xm§3~m8 323:336 M. MESS? :M m»§§§3§8~ SESSm musquwSew . mfigffi mEESASGN ustufiyifi msswuewausuk mgitfi msfsfifiwfi wmgfi§N3 «583:5 VJ wwfixwuso was 0 ”22:33: wwwfisguvw H 552:8 2:55 W 6:ng €§§§ m m 4 H .Smaw «ESSEQN w w m mcxuuogcéx Pam m $3215 M m. §§§§3 waswuisSEnw m w w 9 E. m o m. SEE ii :80 we 2% uwmkfihoz «5352 5883 $22 55:8 ”mm: :35 $52595 amam E wzmmcu ozwrwaofiazo «in?» 52%: #25 :80 m5 5 £me 05383530 Exam: .5135 5833 as» E m=mm8 ufimifluahazo 3mg EoEe—RO $33 ”2314: @955 “835.9. E 8:3 Eaucfim wwwSm :agfizm C—12 middle part of the member is gradational into the upper part as reported by field geologists. Strati- graphically, a correlation of the Ura/nocephalites beds with the upper Bathonian seems just as reasonable. Faunally the evidence from the Urcmocephal’ftes beds is indecisive, but the absence in these beds of any ammonite genera typical of the Callovian of Europe contrasts with the presence of such genera in the upper part of the Bowser member and suggests a somewhat older age. In the Talkeetna Mountains, Alaska, the Crane— cephalétes beds on the Little Oshetna River, as mapped by Arthur Grantz, of the US. Geological Survey, rest unconformably on beds of Early Jurassic age and are directly overlain at that locality and near the Little Nelchina River by beds of early Callovian age. They are much more restricted in distribution than the early Callovian beds which at many places rest directly on beds of late to middle Bajocian age. It is not known whether the absence of the Cranocepha- lites beds at these places is due to erosion or to non— deposition. If due to erosion, a Bathonian age for the Cranocephalites beds would be favored. If due to nondeposition the beds could be either Bathonian, or earliest Callovian, or both. EVIDENCE FROM MONTANA In western Montana, (‘ranocephalites has been found only in yellow calcareous siltstone and fine—grained sandstone comprising the upper member of the Saw— tooth formation. This member passes downward gradationally into gray to black shales, known as the middle member of the Sawtooth formation. These shales have furnished the same pelecypod fauna as the upper member except at Swift Reservoir where the Bajocian ammonite Chondroceras was found about 5 feet above the basal member. Near Drummond these gray shales rest on calcareous buff to reddish-brown siltstone that has furnished the Bajocian ammonites Stemmatocems and Normanmltes. The middle member is underlain at many places north of the Sun River by a thin siliceous sandstone or sandy limestone known as the lower member of the Sawtooth formation. This member contains Jurassic pelecypods identical with or closely similar to those in the Bajocian Rock Creek member of the Fernie formation in Canada. The top of this siliceous lower member is marked in many places near the Sun River by a thin bed of pebble to cobble conglomerate of which some of the fragments are identical with the matrix of the lower member. The presence of such a conglomerate suggests that locally the lower and middle members are separated by a disconformity. No evidence for such a discon- formity has been found north of the Sun River area. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The Cranocephalites beds in western Montana are overlain abruptly and with possible local unconformity by beds (Rierdon formation) that contain early Callovian ammonites such as Arcticoceras and Cadocems and that are equivalent at least in part to the Macro- cephalites macrocephalus zone of Europe. An uncon— formity at such a position beneath several ammonite zones of early Callovian age (Imlay, 1953a, p. 5—8) would favor a Bathonian age for the (‘mnocephalites beds and possibly explain the absence of Arctocephalites in the strict sense from the western interior region. However, an age not much older than the early Callo— vian beds is indicated by the fact that the pelecypod species and the ammonite genus Cobbanites continue upward from the Cranocephalites beds into the early Callovian beds and by the fact that one specimen probably belonging to Arcticocems has been found in the highest part of the (’ranocephalites beds. (See pl. 5, fig. 7.) CALLOVIAN VERSUS BATI-IONIAN IN GREENLAND In East Greenland the beds containing Arctocepha— lites and ("ranocephalites were considered by Spath (1932, p. 138, p. 138—146) as probably uppermost Bathonian. He correlated the Arctocephalites beds with the European zone of Macrocephalites macro— cephalus, which he reclassified as Bathonian; the immediately underlying Uranocephalites beds with the European zone of Clydenicems discus; and the over- lying Arcticoceras beds with the zone of Proplanulites keenigf. He thought that these ammonite genera were closely related to each other faunally and followed each other closely in time. He noted that Grano- cephalites occurred only 20 meters below Arcz‘ocephalites (Spath, 1932, p. 14, 133—135) and that the highest beds containing Arctocephalites also contain immature specimens of Arcticocems (1932, p. 135, 143). His assignment of the Arctocephalites beds to the upper Bathonian was contested by Donovan (1953, p. 133) and Arkell (1956, p. 506) on the basis that the zone of Alacrocephalites macrocephalus is early Callovian according to prevailing usage. Arkell (1954, p. 117) also assigned the (’mnocephalites beds to the Callovian because in Alaska Cranocephalites was reported to occur with the Callovian genus Reineckeia (Imlay, 1952, p. 980). This report is in error, however, as the specimens identified as Reinckeia are herein de— scribed as a new genus Parereineckeia. Nevertheless, the Callovian age assignment may be justified by the fact that the family Reineckeiidae is to date known only from beds of Callovian age. Recent studies in East Greenland by Donovan (1957, p. 129—136) have not furnished any additional evidence concerning the ages of the Arctocephalites JURASSIC AMMONITES FROM ALASKA AND MONTANA and Cranocephalites beds, although Donovan tentatively assigns them to the late Bathonian. He suggests that Cadocems probably evolved from Arcticocems or Arctocephalites in the Boreal region, spread rapidly from there into North America and Europe, and that its lowest occurrence in Greenland at the top of the Arcticoceras beds (Spath, 1932, p. 131) “would fall at about the beginning of the range of Cadoceras in Europe; that is, in the Macrocephalus zone” (Donovan, 1957, p. 131). He speculates further that “if 0mm— cephalites, Arctocephalites, and Arcticocems are closely related and not widely separated in time,” as Spath thought, then the “Cranocephalites and Arctocephalites zones would be expected to be upper Bathonian.” However, he does not rule out the possibility that those zones may span the entire Bathonian (Donovan, 1957, p. 136), and he emphasizes that his assignment of those zones to the upper Bathonian is very uncertain. Still more recent studies in east Greenland have been made by Callomon (1959, p. 505—513) who cor- relates the beds characterized by Kepplem'tes tychom's with the European zone of Macrocephalites macro- cephalus on the basis of the presence of identical species of Kepplerites. He notes that this correlation is confirmed by the presence in the overlying beds of ammonites representing the European zone of Sigu- locems calloviense, such as Pseudocadoceras, Propltmu— lites, Gowem'cems, and Kosmocems. He considers that the underlying beds, characterized by the ammOe nite genera Arcticocems, Arctocephalites, and Crane- cephalites, are pre-Callovian and in greater part Ba- thonian. These correlations supports a Bathonian age for the Arctocephalites-Cranocephalites beds else— where and imply that the Boreal Province during Bathonian time developed a different ammonite assemblage than the European and Tethyan provinces. CALLOVIAN VERSUS BATHONIAN IN ALASKA AND MONTANA The ammonite genera associated with Cranocepha- lites in western Montana and in Alaska do not furnish positive evidence concerning the age of the beds in which they occur. A Callovian age is favored slightly by the following facts: 1. One ammonite fragment from the Sawtooth for— mation of western Montana probably belongs to the genus Xenocephalites, which has been found mainly in Callovian beds in Mexico (Burckhardt, 1927, p. 33), Argentina (Stehn, 1924, p. 86-88, 92), Montana (Imlay, 1953a, p. 18—19), Alaska (Imlay, 1953b, p. 78, 79). 2. One ammonite questionably assigned to Arctico- CerS occurs with Cranocephalites at the top of its range in Montana. (3—13 3. The family Reineckeiidae, represented in the Crane- cephalites beds in Alaska by a new genus, Pam- reineckeia, has not previously been reported below the Callovian. 4. The new genera Pamreineckeia and Cobbam’te's range upward from the Cranocephalites beds into beds containing typical early Callovian ammonites. 5. The Cranocephalites beds do not contain any ammo- nite genera typical of the Bathonian of northwest Europe or of the Tethyan region, except two fragments that probably belong to Siemiradzkia. The age value of this genus is suspected because it greatly resembles the Callovian ammonite Grossoucm'a. Against this faunal evidence favoring a Callovian age may be listed the following: 1. The total ranges of Xenocephalz’tes, Arcticoceras, Pararemeckez'a n. gen., and Cobbam'tes n. gen. are not known. They could have existed during the Bathonian as well as during the early Callovian. In fact, the presence of Xenocephalites and Arc— ticoceras in Greenland below beds containing the typical Callovian ammonites Oadocems and Kep— plerites (Spath, 1932, 45, 133, 135, 143) might be interpreted as evidence that they existed before the Callovian. 2. If the family Reineckeiidac was derived from the Bathonian Morphoceratidae or Parkinsonidae, as Arkell (1955, p. 130; 1957, p. L311) suggests, it may have begun in the Bathonian. 3. Two ammonites from the Omnocephalites beds in Alaska probably belong to the genus Siemimd— 2km of Bathonian age, although their preserva- tion does not permit positive identification. 4. The Cranocephalites beds do not contain any am— monite genera typical of Callovian beds. 5. The Omnocephalites beds in Montana and Alaska underlie a succession of beds that contain am- monite genera of early Callovian age, such as Cadocems Paracadocems, Kepplem’tes (Seymoum'tes), Gowericeras, and Khemiceras. Surely some of these genera would occur in the Cranocephalz'tes beds, if those beds were of early Callovian age. 6. Most of the pelecypods in the Oranocephalites beds in the western interior be'ong to species that range from the middle Bajocian into the early Callovian. This might not hold if the entire Bathonian was represented by an unconformity in the western interior. PALEO GEO GRAPHIC C ONSIDERATIONS The peculiar fauna] characteristics of the Arcto— cephalites and Cranocephalites beds that make correla— tions with the European stages difficult are possibly C—14 related to major epeirogenic movements in the Boreal region during Middle Jurassic time. Such movements, according to Arkell (1956, p. 608, 609), are indicated by an absence in the Arctic region of ammonite faunas of middle to late Bajocian age and of Bathonian age. He notes that the Bathonian is missing, also, in many other parts of the world, or is represented by brackish— Water sediments that lack ammonites. Marine beds containing Bathonian ammonites have been found mostly in northwest Europe and the Tethyan region. (See map in Arkell, 1956, p. 608, fig. 98.) Exceptions include one small area in southern Mexico (Burck- hardt, 1927, p. 19, 20, 25, 80, 94, 95; Arkell, 1956, p. 564) and possibly another area in northern Alberta (Frebold, 1953, p. 1237; 1957a, p. 18, 54, 55). This great contraction of the area of ammonite distribution, as compared with the Bajocian stage, was accompanied, according to Arkell (1956, p. 3, 4), by a great reduction in ammonites, both in numbers and in biological categories, and by evolutionary stagnation. From these facts, Arkell (1956, p. 609, 610, 641) deduces that after early Bajocian time a major regres- sion began in the Boreal region and that about middle Bathonian time the seas retreated from most parts of the world that are now land. He infers that during this Bajocian-Bathonian regression, the Arctic Ocean was isolated from the other oceans and consequently that the faunas that lived in the Arctic Ocean devel— oped special characteristics. He speculates that those faunas are now buried beneath the present Arctic Ocean. Establishment of connections with other oceans early in the Callovian permitted the Boreal faunas to spread outward from the Arctic Ocean over the lands now bordering that ocean, into the western interior of the United States and into Japan. Accord- ing to Arkell (1956, p. 610) the first Boreal ammonites to appear were Oranocephalites and Arctocephalz‘tes. These were soon followed in the early Callovian by Oadocems, Arcticocems, and Kepplerites (Seymourites), which in time gave rise to other genera of the Cardi- oceratidae and Kosmoceratidae. Arkell’s explanation for the origin of the dominantly Boreal ammonite families mentioned above seems reasonable, but it is not clear why the Arctic Ocean need have been completely isolated from the Pacific or Atlantic Ocean during Bathonian time, or why Arc— tocephalites and Oranocephalz'tes are necessarily of Cal- lovian age. Partial isolation, owing to emergence of the continents, coupled with differences in temperatures of the oceans may have been sufficient to bring about the development of endemic ammonite faunas. Also, considering that proof is lacking for the Callovian age of Arctocephalites and Cranocephalites, they could be SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the Boreal and northern Pacific Ocean equivalents of the Bathonian of Europe and the Tethyan region. SUMMATION OF THE EVIDENCE The exact age of the beds characterized by the ammonite Oranocephalites has not been determined. Stratigraphically, they could represent all or part of the Bathonian stage, or the basal part of the Callovian stage, or could extend from the Bathonian into the Callovian. Geologists aware of the problem have found a stratigraphic break in the Cook Inlet region, Alaska, that might account for the absence of typical Bathonian ammonites, but in Montana the evidence is inconclusive and contradictory. Faunally, the beds in question cannot be definitely correlated with either the Bathonian or the Callovian. The ammonites present have little in common on the generic level with the Bathonian ammonites of Europe and of the Tethyan region. (See discussion in Arkell, 1956, p. 608, 609.) They show slightly more resem— blance to ammonites in the Callovian than to those in the Bathonian, but the evidence is weak. If they are Callovian age they cannot be younger than the earliest Callovian zone of Macrocephalites macrocephalus, and that zone is at least partly represented by the Arc— ticoceras beds in Greenland and in the western interior of North America. If they are of Bathonian age, they are probably only slightly older than the Callovian, considering that the new genera Cobbanites and Pam- remeckeia range up into definite Callovian beds. It seems improbable that the Arctocephalites and Grano- cephalites beds of the Arctic region span the entire Bathonian, as pointed out by Donovan (1957, p. 136), unless the Bathonian stage represents much less time than the adjoining stages. Considering all available evidence, the Omnocephaylites beds are herein tentatively correlated with the upper Bathonian of Europe. COMPARISONS WITH OTHER FAUNAS WESTERN INTERIOR OF CANADA Ammonites identical with those in the upper member of the Sawtooth formation of Montana have not yet been found in the Fernie formation in the western interior of Canada. However, some small ammonites resembling immature specimens of Arctocephalites (Uranocephalites) have been found on Grassy Moun— tain, near Blairmore, Alberta. These were described by Buckman (1929) under several new generic names, but Spath (1932, p. 13, 14, 33, 36, 145) decided that the specimens described by Buckman (1929, pl. 1, figs. 4—7, pl. 3, figs. 1411) under the names Metacephalites and Miccocephalites are immature representatives of his genus Arctocephalites (1928, p. 174). Warren (1947, p. 73) suggested that they are closer to Cranocephalites, JURASSIC AMMONITES FROM ALASKA AND MONTANA which is now considered to be a subgenus of Arctoceph- elites (Arkell, 1957, p. L301). Imlay (1948, p. 14, 19, 20) noted their resemblances to species of Arctoceph— elites (Omnocephalz‘tes) in the upper member of the Sawtooth formation. Frebold (1957a, p. 18, 19, 57) decided that the ammonites from Grassy Mountain described by Buckman are not determinable generically but that they are definitely of Callovian age as they are associated with Oadoceras (Frebold, 1957a, p. 76). Such an association suggests, however, that they are not immature specimens of Arctocephalz’tes or C'mnoceph— elites because in Montana Cadocems is not associated with those ammonites. ARCTIC REGION Species of Arctocephalz‘tes and its subgenus Cramoce— phalz’tes similar to those in the Cook Inlet region of Alaska and in western Montana have been found at many places in the lands bordering the Arctic Ocean. Arctocephalz'tes (strict sense) has been recorded from the Richardson Mountains in northern Canada (Fre- bold, 1953, p. 1240; 1957b, p. 28), from East Greenland (Spath, 1932, p. 14—32, pls. 1—19 in part; Donovan, 1953, p. 78—84; Donovan, 1957, p. 32—40, 129—136), from Franz Josef Land (Newton and Teall, 1897, p. 500, pl. XL, figs. 1, 1a; Whitfield, 1906, p. 131, pl. 18, fig. 2; Pompeckj, 1899, p. 70, pl. 2, figs. 12a-c; Spath, 1932, pl. 13, figs. 6a, b), from King Charles Land (Frebold, 1951, p. 79) from gravels in Novaya Zemlya (Salfeld and Frebold, 1924, p. 1; Frebold, 1930, p. 71, pl. 23, figs. 1—3), from the Bureya basin of eastern Siberia (Krimholz, 1939, p. 59, pl. 2, figs. 5—6), and have been reported from the Kharaulakh Mountains of north- eastern Siberia (Nikolaev, 1938, p. 5; Arkell, 1956, p. 514). Oranocephalites has been recorded from Prince Patrick Island, Canada (Frebold, 1957b, p. 8, 9, 25, 26, pl. 7, figs. 1a—c, 2, pl. 8, figs. 1a—c), from East Greenland (Spath, 1932, p. 14—32, pls. 1—13 in part), from Novaya Zemlya (Frebold, 1930, p. 95; 1951, p. 81), and has been reported from islands near the mouth of the Khatanga River in northern Asia (Moor, 1937, p. 232, 284; Arkell, 1956, p. 513). An ammonite from the basin of the Bureya River in northern Asia described as Sphaerocems em Krimholz (1939, p. 29, 59, pl. 2, figs. 1—3) was referred by Arkell (1954, p. 117; 1956, p. 516) to Cranocephalz'tes, but it is not a typical Oran ocephalz'tes because it does not have a scaphitoid body chamber. Very few other ammonite genera have been found with Arctocephalz’tes and Cranocephalites in the Boreal region. The ammonite Xenocephalites (Spath, 1932, p. 44, 133, 134, pl. 14, figs. 4a—d) was found loose on the 582600 0——6 1———4 C—15 slope of Mount Hjornefjaeld in East Greenland at the same altitude as a specimen of Cranocephalites pompeckji (Madsen). It could have been derived from a bed con- taining Oranocephalz'zes at an altitude of 740 meters (2,400 feet), or from a bed containing Arctocephali'tes and Arcticocems at an altitude of 760 meters (2,450 feet) near the top of the mountain, or it could have come from a different bed below either main ammonite bed. The association of Arcticocems with Arctocephalites at the top of Mount Hjornefjaeld was considered by Spath (1932, p. 132, 135, 143) to be in the upper part of the range of Arctocephalz'tes. He did not consider that Arctocephalz'tes rangedrhigher into the beds characterized by abundant Arcticuo'ci'eifis although he mentioned (1932, p. 142, pl. 11, fig. 3) one fragment of Arcticoceras from the Arcticocercs beds that appeared to be transitional between Arctocephalz‘tes and Arcticocems. Recently Donovan (1957, p. 133) interpreted one of Spath’s species, Arcticoceras kochz’ Spath, to be an Arctoceph— elites. If this interpretation is valid, the genus Arcto- cephalites ranges higher than Spath considered and is associated at the top of its range with the lowest oc- currence 0f Cadocems. The subgenus Oranocephalites, however, has not yet been found in Greenland with either Arcticocems or Cadocems. OTHER REGIONS Arctocephalites and Cranocephalites have not been found outside of the Arctic region, the Cook Inlet region, Alaska, and western Montana. This is rather astonish- ing because their ocurrence in the Cook Inlet area bordering the North Pacific Ocean suggests that they had free access to that ocean. Perhaps they will yet be found in British Columbia, or farther south on the Pacific coast. The record from Oregon and California is not encouraging, however. In central Oregon the writer has collected the Callovian ammonites Lilloettz'a, Xenocephalz’tes, and Chofiatz'a in the upper part of the Snowshoe formation (of Lupher, 1941) within 100 feet stratigraphically of middle Bajocian ammonites. Like- wise in the Taylorsville area, California, occur such typical Callovian ammonites as Reineckeia, Choflatia, Pseudocadoceras, but no trace exists of any Bathonian, or late Bajocian ammonites. and Paracadoceras, GEOGRAPHIC DISTRIBUTION The occurrence by area and locality of the fossils described in this report are indicated in tables 5 and 6 The positions of the areas are shown in figures 1—6. Detailed descriptions of the individual localities are shown in tables 3 and 4. C—16 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 3.—-Localities at which ammonites of Bathonz‘an or early Callovian age have been collected in the Arctocephalites (Cranocephalites) beds in the Cook Inlet region, Alaska Locality on figs. 2—4 Geol. Survey Mesozoic locality Collector’s field No. Collector, year of collection, description of locality, and stratigraphic assignment 10 __________________ 10 ,,,,,,,,,,,,,,,,,, 10 ,,,,,,,,,,,,,,,,,, 11 ,,,,,,,,,,,,,,,,,, 11 ,,,,,,,,,,,,,,,,,, 12 ,,,,,,,,,,,,,,,,,, 27515 24822 24115 24116 24117 24118 24825 8573 21284 21283 22711 22712 22698 21308 21309 21310 20005 27100 20011 RAL115 53AGz216 52AGz 152 52AGz154 52AGz154A 52AGz155 53AFyI4 13AMa22 48AI84 48AI82 51AGzl42 51AGz143 51AG2115 48A11 48A12 48A13 44AWW F—72 58ADt3 44AWW78 Lyon, R. A., 1959. Talkeetna Mountains (A—2) quad. Lat 62°10’36” N., long 147°40’09” W. From 35 to 55 ft below base of Chinitna formation equivalent in unit of sandstone and conglomerate 100 ft thick. Upper part of Tuxedni formation. Grantz, Arthur, and Fay, L. F., 1953. Talkeetna Mountains (A—2) quad. Lat 62°10’21” N., long 147°42’25” W. On a small south tributary of the Little Oshetna River. Near middle of a sandstone unit 650 ft thick at top of the Tuxedni formation. Grantz, Arthur, Hoare, R. D., and Imlay, R. W., 1952. Talkeetna Moun- tains (A—2) quad. Lat 62°07’33” N., long 147°40’20” W., north fork of upper part of the Little Nelchina River. Upper part of Tuxedni formation form 400 to 800 ft below base of Chinitna formation. Grantz, Arthur, Hoare, R. D., and Imlay, R. W., 1952. Talkeetna Moun- tains (A—2) quad. Lat 62°07’15” N., long 147°42’02” W., north fork of upper part of the Little Nelchina River. Upper part of Tuxedni formation 400—800 ft below base of Chinitna formation. Grantz, Arthur, Hoare, R. D., and Imlay, R. W., 1952. as Mesozoic 100. 24116, except on south side of stream. Grantz, Arthur, 1952. Talkeetna Mountains (A—2) quad. Same location as Mesozoic loc. 24116, but 0.18 mile farther upstream. Tuxedni forma- tion, upper part. 400-800 ft below top. Fay, L. F., and Grantz, Arthur, 1953. Talkeetna Mountains (A—2) quad. Lat 62°07’15” N., long 147°41’29” W. North fork of the upper Little Nelchina River. Upper part of the Tuxedni formation, 400—800 it below base of the Chinitna formation. Martin, G. C., 1913. Talkeetna Mountains. At altitude of 3,400 ft on north side of knob, 1 mile north of Boulder Creek and about 3 miles above mouth of East Boulder Creek. In Anchorage D-4 quad. Tuxedni formation. Imlay, R. W., and Miller, D. J., 1948. Tuxedni Bay area, near head of first stream entering Tuxedni Bay southeast of Bear Creek, 4.1 miles S. 12° W. of Fossil Point. Gray siltstone just below sandstone beds marking top of Bowser member of Tuxedni formation. Imlay, R. W., and Miller, D. J., 1948. Tuxedni Bay area, from stream entering Bear Creek from the southeast at first outcrop above mouth, 4.2 miles S. 20° W. of Fossil Point. Gray siltstone in upper lower part of Bowser member of Tuxedni formation, about 1,000—1,100 ft below base of Chinitna formation. Grantz, Arthur, 1951. Tuxedni Bay area; 0.38 mile above mouth of tribu- tary entering Bear Creek from the southeast, 2.53 miles from Tuxedni Bay, about 1,200 ft below base of Chinitna formation. Grantz, Arthur, 1951. Tuxedni Bay area; 0.45 mile above mouth of tribu- tary entering Bear Creek from southeast, 2.53 miles from Tuxedni Bay. Upper part of Bowser member of the Tuxedni formation, about 1,100 ft below base of Chinitna formation. Grantz, Arthur, 1951. Peninsula north of Chinitna Bay. 011 ridge 1.5 miles N. 39°50’ E. of head of Lake Hickerson. Upper part of Bowser member of Tuxedni formation, about 1,000-1,100 ft below base of Chinitna formation. Imlay, R. W., and Miller, D. J., 1948. Iniskin Peninsula, gulch draining northward into Gaikema Creek from peak on axis of Tonnie syncline, 2.3 miles S. 84° W. from dock at mouth of Fitz Creek. From siltstone about 800 ft above base of Bowser member of the Tuxedni formation. Imlay, R. W., and Miller, D. J., 1948 Iniskin Peninsula. Float in gulch described under Mesozoic 100. 21308, but about 100 ft lower. Bowser member of the Tuxedni formation. Imlay, R. W., and Miller, D. J., 1948. On same gulch described under Mesozoic 100. 21308. About 500 ft above base of Bowser member of the Tuxedni formation. Kellum, L. B., 1944. Iniskin Peninsula. Northeast side of Tonnie Creek about 700 ft upstream from top of lower cascade and 0.85 mile S. 56%° of Tonnie Peak. 400 ft above base of Bowser member of the Tuxedni formation. Detterman, R. L., 1958. Iniskin Peninsula. On Tonnie Creek 0.94 mile N. 61° W. of I. B. A. No. 1 well. Coordinates 9.02, 12.22. Lat 59°45’31” N., long 153°15’09” W. From 25—50 ft above lowermost conglomerate in greenish-gray siltstone and silty shale. Bowser member of the Tuxedni formation, about 1,750 ft below base of the Chinitna formation. Wedow, Helmuth, and Kellum, L. B., 1944. Iniskin Peninsula. In Tonnie Creek, 1.0 mile upstream from trail at mouth of creek just above crest of third falls and S. 486° E. of Tonnie Peak. Near middle of the Bowser member of the Tuxedni formation, about 1,000 ft below Chinitna formation. Same description JURASSIC AMMONITES FROM ALASKA AND MONTANA C—17 TABLE 3.——L0calities at which ammonites of Bathonian or early Callovian age have been collected in the Arctocephalites (Cranocephalites) beds in the Cook Inlet region, Alaska—Continued Locality on figs. 2—4 Geol. Survey Mesozoic locality Collector’s field No. Collector, year of collection, description of locality, and stratigraphic assignment 13 __________________ 14 __________________ 15 __________________ 16 __________________ 17 __________________ 17 __________________ 18 __________________ 19 __________________ 11038 20746 20745 20754 20751 20752 20743 20744 21AB46 46AKr156 46AKr155 46AKr177 46AKr164 46AKr166 46AKr152 46AKr154 Baker, A. A., 1921. Iniskin Peninsula. Near head waters of Bowser Creek about 1,700 ft southeast of point where creek changes course from northeast to southeast, about 2.2 miles N. 8° E. of Front Mountain. From upper middle part of Bowser member of Tuxedni formation, about 700—800 ft below base of Chinitna formation. Kirschner, C. E., 1946, Iniskin Peninsula, on Edelman Creek, 1.4 miles N. 17° W. of Front Mountain. Upper part of Bowser member of the Tuxedni formation, about 800 ft below Chinitna formation. Kirschner, C. E., 1946, Iniskin Peninsula. On Edelman Creek 1.5 miles N. 22° W. of Front Mountain. Fine—grained sandstone in upper part of Bowser member of the Tuxedni formation, about 900—1,000 ft below Chinitna formation. Kirschner, C. E., 1946, Iniskin Peninsula, 2.0 miles N. 32° W. of Front Mountain, fine-grained sandstone in lower middle part of Bowser member of the Tuxedni formation, about 1,800 ft below base of Chinitna formation. Kirschner, C. E., 1946, Iniskin Peninsula. Tributary of Bowser Creek, 1.5 miles N. 40° W. of Front Mountain. Lower middle part of Bowser member of the Tuxedni formation, about 1,300—1,400 ft below base of Chinitna formation. Kirschner, C. E., 1946. Iniskin Peninsula. Tributary of Bowser Creek, 1.5 miles N. 40° W. of Front Mountain. Lower middle part of Bowser member of the Tuxedni formation, about 1,300—1,400 ft below base of Chinitna formation. Kirschner, C. E., 1946, Iniskin Peninsula, on Bowser Creek 1.8 miles N. 80° W. of Front Mountain. Sandy siltstone in lower middle part of Bowser member of Tuxedni formation, about 1,500—1,600 ft below Chinitna formation. Kirschner, C. E., 1946. Iniskin Peninsula on Bowser Creek 2.6 miles west of Front Mountain. Sandy siltstone in lower middle part of Bowser member of Tuxedni formation at about same stratigraphic position as 100. 20743. TABLE 4.——Localities at which ammonites of Bathonian or early Callovian age have been collected in the upper member of the Sawtooth formation in western Montana Locality on figs. 5 and 6 Geol. Survey Mesozoic locality Collector’s field No. Collector, year of collection, description of locality, and stratigraphic assignment 20 __________________ 20 __________________ 20 __________________ 20 __________________ 21 __________________ 22 __________________ 23 __________________ 23 __________________ 23 __________________ 23 __________________ 19183 19185 19186 19192 19195 19609 18718 19601 19604 20355 I45~8~12B I45—8—11A I45—8—11D 146—7—280 Imlay, R. W., Reeside, J. B., Jr., and Cobban, W. A., 1944. Swift Reservoir, north side, sec. 27, T. 28 N., R. 10 W., Pondera County. From 3 ft of siliceous limestone about 6% ft above base of Sawtooth formation in the lower member. Imlay, R. W., Reeside, J. B., and Cobban, W. A., 1944. Swift Reservoir, north side, sec. 27, T. 28 N., R. 10 W., Pondera County. From sandy limestone near top of Sawtooth formation. Imlay, R. W., and Yingling, H. C., 1944. Same location as Mesozoic 100. 19183. From lower part of the upper siltstone member of the Sawtooth formation. Imlay, R. W., and Yingling, H. C., 1944. Same location as Mesozoic 100. 19183. Near base of middle member of Sawtooth formation and 20 ft above base of formation. Imlay, R. W., and Yingling, H. C., 1944. Same location as Mesozoic loc. 19183, but on south side of Swift Reservoir. From basal 2 ft of sandstone of Sawtooth formation. Imlay, R. W., andSaalfrank, William, 1945. Between Middle Fork and North Fork of Teton River in sec. 21, T. 25 N., R 9 W., Teton County. From upper 2 ft of siltstone member at top of Sawtooth formation. Bridge, Josiah, and Deiss, C. F., 1941. Lonesome Ridge, west side of sec. 34. T. 25 N., R. 9 W., Saypo quad., Teton County. Upper member of Sawtooth formation. (Note: Most of collection 18718 was obtained from the Rierdon formation.) Imlay, R. W., and Saalfrank, William, 1945. Lonesome Ridge on line of sees. 33 and 34, T. 25 N., R. 9 W., Saypo quad., Teton County. Upper 2 ft of upper member of Sawtooth formation. Imlay, R. W., and Saalfrank, William, 1945. sees. 33 and 34, T. 25 N., R. 9 W., Saypo quad., Teton County. lower part of upper member of Sawtooth formation. Cobban, W. A., and Imlay, R. W., 1946. Lonesome Ridge on line of secs. 33 and 34, T. 25 N., R. 9 W., Saypo quad., Teton County. From upper silty member of the Sawtooth formation. Lonesome Ridge on line of From C—18 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 4.—Localities at which ammonites of Bathonian or early Callovian age have been collected in the upper member of the Sawtooth formation in western M ontana—Continued Locality on figs. 2—4 Geol. Survey Mesozoic locality Collector’s field No. Collector, year of collection, description of locality, and stratigraphic assignment 23 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 24 __________________ 25 __________________ 25 __________________ 25 __________________ 26 __________________ 27 __________________ 27 __________________ 27 __________________ 27 __________________ 28 __________________ 29 ,,,,,,,,,,,,,,,,,, 20357 18711 18712 18713 18714 18715 19184 22652 22653 22654 22655 27040 27043 27046 27506 19606 19608 27037 27042 27039 27502 27045 I46—7—28D Deiss 5/ 1 Deiss 5/2 Deiss 5/3 5/4 Deiss 5/5 I51—8—17A I51—8—17B I51—8—17C I51—8—17D F224 F223 F225 F291 I45—8—14B I45—8—14A F55 F57 F231 F278 F228 Imlay, R. W., 1946. Lonesome Ridge on line of sees. 33 and 34, T. 25 N., R. 9 W., Saypo quad, Teton County. From lower foot of upper silty member of the Sawtooth formation. Deiss, C. F., 1941. Head of Rierdon Gulch at altitude of about 7,550 ft, S% sec. 23, T. 24 N., R. 9 W., Saypo quad., Teton County. Zone 1 from lower part of middle shale member of Sawtooth formation, 12 ft above base of formation. Deiss, C. F., 1941. Head of Rierdon Gulch at altitude of 7,560 ft, 5% sec. 23, T. 24 N., R. 9 W., Saypo quad., Teton County. Zone 2 from lower part of middle shale member of the Sawtooth formation, about 17 ft above base of formation. Deiss, C. F., 1941. Same location as Mesozoic 100. 18711. Zone 3, from 36—107 ft above base of Sawtooth formation in middle shale member. Deiss, C. F.,1941. Head of Rierdon Gulch, S34 sec. 23, T. 24 N., R. 9W., Saypo quad., Teton County. Zone 4 from basal 13 ft of upper member of the Sawtooth formation, or 107—120 ft above base of Ellis group. Deiss, C. F., 1941. Same location as Mesozoic 100. 18711. Zone 5 from about 10 ft below the top of the Sawtooth formation in upper siltstone member. Imlay, R. W., and Yingling, H. 0., Jr., 1944. Head of Rierdon Gulch, 8% sec. 23, T. 24 N., R. 9 W., Saypo quad., Teton County. From sandy limestone in upper 20 ft of upper member of Sawtooth formation. Imlay, R. W., 1951. About a quarter of a mile north of head of Rierdon Gulch, north-central part of sec. 23, T. 24 N., R. 9 W., Saypo quad., Teton County. From 6 to 10 ft above base of upper silty member of Sawtooth formation. Imlay, R. W., 1951. One mile north of head of Rierdon Gulch in north- central part of sec. 23, T. 24 N., R. 9 W., Teton County. From 15 to 22 ft above base of upper siltstone member of the Sawtooth formation. Imlay, R. W., 1951. About half a mile north of head of Rierdon Gulch in north-central part of sec. 23, T. 24 N., R. 9 W., Saypo quad., Teton County. From 6 ft below top of upper silty member of Sawtooth formation. Imlay, R. W., 1951. Half a mile north of head of Rierdon Gulch in central part of sec. 23, T. 24 N., R. 9 W., Teton County. From upper foot of upper siltstone member of the Sawtooth formation. Imlay, R. W., 1959. Head of Hannan Gulch, NW}£ sec. 35, T. 23 N., R. 9 W., lat 47°43’ N., long 112°43’ W., Saypo quad, Teton County. 29 ft below top of upper siltstone member of the Sawtooth formation. Mudge, M. R., 1958. From head of Hannan Gulch in NW}; sec. 35, T. 23 N., R. 9 W., Saypo quad, Tenton County. From middle shale member of the Sawtooth formation. Mudge, M. R., 1958. Head of Hannan Gulch, NWM sec. 35, T. 23 N., R. 9 W., Teton County. From upper siltstone member of the Sawtooth formation. Imlay, R. W., 1959. Head of Green Timber Gulch, lat 47°42’05” W., long 112°42’00” W., south-central part of sec. 36, T. 23 N., R. 9 W., Saypo quad., Teton County. Upper siltstone member of the Sawtooth formation. Imlay, R. W., and Saalfrank, William, 1945. Wagner basin, north-central part of sec. 25, T. 21 N., R. 9 W., Saypo quad., Teton County. From lower sandstone member of the Sawtooth formation about 3 ft above base of formation. Imlay, R. W., and Saalfrank, William, 1945. Same location as Mesozoic 100. 19606. Upper siltstone member of the Sawtooth formation. Imlay, R. W., Mudge, M. R., and Reynolds, M. W., 1958. Wagner basin, in draw at contact of Paleozoic limestone and Jurassic beds, north—central part of sec. 25, T. 21 N., R. 9 W., Saypo quad, Teton County. From lower sandstone member of the Sawtooth formation. Imlay, R. W., Mudge, M. R., and Reynolds, M. W., 1958. Wagner basin, north-central part of sec. 25, T. 21 N., R. 9 W., lat 47°38’ N., long 112° 42’20” W., Saypo quad, Teton County. From upper 12 ft of upper silty member of the Sawtooth formation. Imlay, R. W., Mudge, M. R., and Reynolds, M. W., 1958. West side of Mortimer Gulch on north side of Gibson Reservoir, near center of sec. 4, T. 21 N., R. 9 W., lat 47°37’ N., long 112°46’ W., Saypo quad., Teton County. From upper silty member of the Sawtooth formation. Mudge, M. R, and Reynolds, M. W., 1959. West side of Mortimer Gulch on north shore of Gibson Reservoir, near center sec. 4, T. 21 N., R. 9 W., lat 47°36’03” N., long 112°45’ W., Saypo quad. Teton County. From upper member of the Sawtooth formation. Mudge, M. R., 1958. North shore of Gibson Reservoir on east side of Big George Gulch, NEV; sec. 5, T. 21 N., R. 9 W., Teton County. From upper7 siltstone member of the Sawtooth formation 3 ft below Mesozoic loo. 2 04 . JURASSIC AMMONITES FROM ALASKA AND MONTANA (3-19 TABLE 4.—Localities at which ammonites of Bathom'tm or early Callovian age have been collected in the upper member of the Sawtooth formation in western M onlana—Continued Locality on figs. 2—4 Mesozoic, Collector‘s field No. Geol. Survey locality Collector, year of collection, description of locality, and stratigraphic assignment 29 __________________ 27047 F227 29 __________________ 27501 F227 30 __________________ 27044 F221 31 __________________ 27503 F286 31 __________________ 27504 F286 31 __________________ 27505 F287 32 ,,,,,,,,,,,,,,,,,, 18324 2/1 32 __________________ 27041 F237 33 __________________ 19623 I45—7—17B 33 __________________ 19625 I45—7—17C Count-y. County. 100 19623. Mudge, M. R., 1958. East side of Big George Gulch on north side of Gibson Reservoir, NE. cor. of sec. 5, T. 21 N., R. 9 W., lat 47°36’19” N., long 112°47’15” W., Saypo quad., Teton County. From lower part of upper member of the Sawtooth formation. Mudge, M. R., 1959. Same as Mesozoic loc. 27047. Imlay, R. W., Mudge, M. R., and Reynolds, M. W., 1958. Home Gulch, SW. cor. sec. 36, T. 22 N., R. 9 W., lat 47°31’ N., long 112°42’ W., Lewis and Clark County. Middle shale member of the Sawtooth formation. Mudge, M. R., and Reynolds, M. W., 1959. Same location as Mesozoic loc. 27504, but about 15 ft lower in upper siltstone member of the Saw- tooth formation. Mudge, M. R., and Reynolds, M. W., 1959. Saddle at north end of Sheep Sheds basin, lat 47°31’45” N., long 112°47’40” W., Lewis and Clark From upper member of the Sawtooth formation. Mudge, M. R., 1959. Saddle NNW. of north saddle in Sheep Sheds basin, lat 47°32’ N., long 112°47’47” W., Lewis and Clark County. Float in lower part of upper siltstone member of the Sawtooth formation. Deiss, C. F.,and Garrells, R. M., 1940. Head of Lime Gulch, SWMi sec. 1, T. 20 S., R. 9 W., Saypo quad., Lewis and Clark County. From 10 ft of sandy shale and limestone near base of measured section, upper member of Sawtooth formation. Imlay, R. W., 1958. Head of Lime Gulch, SWM of sec. 1, T. 20 S., R. 9 W., Saypo quad., lat 47°31’ N., long 112°41’30” W., Lewis and Clark From upper silty member of the Sawtooth formation. Imlay, R. W., and Saalfrank, William, 1945. About 8 miles northwest of Drummond just north of highway in sec. 12, T. 11 N., R. 14 W., Granite County. From yellowish-gray shale and silty nodular limestone in lower 29 ft of upper siltstone member of the Sawtooth formation. Base of silt- stone member is 166 ft above base of Ellis group. Imlay, R. W., and Saalfrank, William, 1945. Same location as Mesozoic From 44 ft of gray calcareous shale and shaly limestone whose base is about 73 ft above base of Sawtooth formation and whose top is about 113 ft below top of formation. SUMMARY OF RESULTS 1. The ammonites from Alaska and Montana described herein include 10 genera and 18 species. Of these, 2 genera, Parareinecketa and Cobbam'tes, and 5 species are described as new. Arctocephalites (Oranocephalites) comprises 54 percent, Cob— bam’tes 17 percent, and Holcophylloceras 5 percent of the total number of ammonite specimens found. Some specimens are referred questionably to 0e00— traustes, Xenocephalttes, Arctocephalt'tes, and Stemtradzkia. 2. Comparable faunules, represented mostly by Arctocephalt'tes and Oranocephalttes, have been found beneath beds of Callovian age at many places in the Arctic region. They have not been found elsewhere in the world, except in Montana and the Cook Inlet region, Alaska. 3. An ammonite faunule characterized by Arctoceph— alites (Cranocepharlites) occurs on the northwest side of Cook Inlet, Alaska, in the middle part of the Bowser member of the Tuxedni formation. The lower few hundred feet of this member con- tains ammonites of late Bajocian age, and the upper 700 to 1,150 feet contains ammonites of early Callovian age. The Cranocephalites beds grade upward into the early Callovian beds, rest abruptly on the late Bajocian beds, and in the Iniskin Peninsula truncate the late Bajocian beds from north to south. The presence of an un— conformity at such a position suggests that the Cranocephalites beds correspond in position with the late Bathonian, or earliest Callovian, or both. 4. Another Arctocephalt'tes (Cranocephalites) faunule occurs in northern Montana in the upper silty member of the Sawtooth formation. This member grades downward into dark—gray shales that, near their base at the Swift Reservoir, have furnished the middle Bajocian ammonite Chondroceras and that rests near Drummond, with apparent con- formity on buff to red siltstone that contains the middle Bajocian ammonites Stemmatoceras and Normanm'tes. The upper member is overlain rather sharply by the Rierdon formation, which contains a succession of ammonite faunules of early Callovian age. Locally, the top of the Sawtooth formation in northwestern Montana contains pebbles and rounded belemnite fragments suggestive of a minor disconformity. Similarly a sedimentary break is indicated by the abrupt change from the yellowish gray siltstone and C—20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 5,—Geogmphic distribution of fossils from the Arctocephalites (Cranocephalites) beds in the Cook Inlet region, Alaska [Numbers 1—19 refer to numbers on figures 2—4. Higher numbers are Geological Survey locality numbers] Talkeetna Mountains Peninsula south of Iniskin Peninsula Tuxedni Bay Tuxedni formation Unnamed unit Middle part of Bowser member H M 0-7 63 q 00 “3 ._. O 11 12 H ca 14 H O! ,_. CD 17 ._. on H <0 22711 21308 21310 20005 27100 20751 20752 Holcophylloceras sp ____________________________ Oecotraustes (Paroecotraustes)? sp _____________ Arctocephalites? alticostus Imlay, n. sp ........ of. A.? alticostus Imlay, n. sp _____________ sp _________________________________________ _ Arctocephalites (Cranocephalz‘tes) pompeclcji (Madsen) ___________________________________ cf. A. pompeckji (Madsen). costidensus Imlay, n. sp. _ A costidensus Imlay, cf. P. shelikofana Imlay Cobbam'tes talkeetnanus Imlay, n. sp Siemiradzkla? cf. S. aurigera (Oppel)__ Belemnite fragments _______________ Parallelodun cumshewaensis Whiteaves. simillimus (Whiteaves) ____________________ Trigonarca? of. T. tumida Whiteaves. Meleagrinella sp. Orytoma sp __________________ Inoceramus m’mius Elchwald- of. I. porrectus Eichwald._ sp _______________________ Comptonectes sp. ____ regent-6.2.3153: """""""""""""" Tancredia s Isocmm‘na ? ____________________ Pleuromya carlottensis Whiteaves sp _________________________ Pholadomya sp ________________ Thracia semiplanata Whiteaves Cercomya? sp __________________________________ sandstone at the top of the Sawtooth formation to a massive oolitic limestone at the base of the Rierdon formation as exposed near Drummond and generally throughout- southwestern Montana. Such a disconformity would be at the same stra- tigraphic position as a well—marked unconformity in south—central Montana, northern Wyoming, and western South Dakota. As the Arcticocems zone at the base of the Rierdon formation cor- responds at least in part with the earliest Callovian Alacrocephalites macrocephalus zone of Europe, the presence of a disconformity between the Rierdon and Sawtooth formations would favor an age older than Callovian for the upper silty member of the Sawtooth formation. Strati— graphically the upper member could be of any age between late Bajocian and earliest Callovian, but the evidence favors a Bathonian age. 5. Faunally, the exact age of the Arctocephalites (Grano— cephalites) beds has not been determined. How- ever, they cannot be older than the Bathonian stage, or younger than the earliest Callovian zone of Macrocepltalites macrocephalus, and that zone is at least partly represented by the Arcticoceras beds in Greenland and in the western interior of North America. They do not contain any ammonite genera typical of the Callovian of Europe and only two ammonites that probably belong to the Bathonian genus Siemimdzlcia. A Callovian age is favored slightly by the presence of the ammonite family Reineckeiidae, by the fact that the new genera Parareineckeia and Cobbanites range up- ward into beds containing typical Callovia ammo- nites, and by the apparent close biological rela- tions of the dominant ammonite Cranocephalites with such Callovian genera as Arcticoceras and JURASSIC AMMONITES FROM ALASKA AND MONTANA C—21 TABLE 6.——Geographic distribution of fossils from the Sawtooth formation in northwestern Montana [Numbers 20—33 refer to numbers on figures 5 and 6. Higher numbers are Geological Survey Mesozoic locality numbers] Sawtooth formation Lower Middle shale sandstone member Upper siltstone member member 20 21 27 20 24 25 30 33 20 22 23 24 25 26 27 28 29 31 32 33 as assess ass as assess newewsaews~erss~a ss§ssssssésssésééssssségééséséssééssésssés Chondroceras oblatum (Whiteaves) ........................... .. .. . .. X .. ._ .. .. .. .. .. .. .. .. .. .. .. .. ._ .. _. .. .. .. .. .. .. .. _. .. .. .. _. _. ._ .. .. .. .. .. .. Xenocephalites? sp ................. .. _ .. .. .. __ .. .. .. .. .. .. .. .. .. .. .. .. X .. __ .. ._ _. .. ._ .. .. ._ .. ._ .. .. .. .. .. .. ._ .. .- .. Arctocephalites? saypoensia Imlay .............. .. .. . .. .. .. ._ .. .. .. .. .. -. .. .. .. -. - _. .. .. .. -. -_ ._ .. .. _. -. __ .. -. ._ X .. - (Cranacephalitea) sawtoothensis Imlay ........ .. .. .. . __ - .. .. .. . - - X X _. X -. -. .. X .. -. X .. X . - - - ._ .. -. .. -. cf.A.grac1'l1's (Spath) ........................ .. .. . .. .. .. __ .. .. .. .. .. .. .. .. X .. .. ._ .. .. .. .. ._ _. .. .. .. .. .. .. .. .. .. ._ .. .. .. cf.A. maculatus (Spath).. .. .. . .. X X .. .. .. X .. .. .. .. ._ .. .. .. .. .. .. .. of. A. platz/notus Spath. .. .. . .. _. .. .. .. .. .. ._ .. .. .. .. .. .. .. ...................... ._.._ -..---X..X--><.- -.X----...- (Cranocephalites)? sp. ...... .. .. - .. .. .. .. .. .. _. .. .. .. -. .. .. .. _. Articoceras? sp ................. .. .. . .. _. ._ .. X .. .. .. .. .. .. .. .. .. .. Cobbanitea spp __________________ .. .. . _. X X .. X ._ .. .. .. .. .. .. .. X X Belemnite fragments ___________ .. X . _. __ .. __ __ .. .. .. .. X X .. .. .. _. .. .. Gastropods undet .................. .. .. . .. .. .. .. .. .. .. .. .. ._ .. .. .. .. .. .. X .. ._ .. .. .. Procen’thz‘um (Rhabdocolpua) sp. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .- .. .. .. .. .. Dentalium sp Nucula sp. Grammatod Idonearca? of. I. rockymont haguei Stanton _______ Modsiolns rosii McLearn.. Pinna ktngi Meek .............. Ozytopma melearnt Warren ______ Meleagrinella curta (Hall). ...... Gervillia sp _____________________ .. .. . .. .. -. __ .. .. Inoceramus sp.. ______ .. X _ .. .. .. ._ .. .. Chlamys sp _____________________ .. .. _ .. .. .. __ .. .. Camptonectes stygina White. ______ .. .. _ >< .. .. __ _. .. platessiformis White. ........ . .. .. .. .. .. __ _. .. __________________________ _-_X._-.--___-.. Lophasp ....................... - .. - -. .. .. __ -_ .. Ostrea strigilecula White ........ . .. . .. .. .. _. .. .. ......................................... ..>< .X..><-.-_>< Gryphaea impressimargmata McLearn _________ .. .. . _. .. _. _. .. ._ sp. juv. of. G. impressimarginata McLearn. .. .. __ )< .. Placunopsis sp ................................ .. .. .. .. .. Tr1gon1'a montanaensis Meek . ...... .. X _. .. .. of. T. trafalgarensis Warren. ______ .. .. __ .. .. of. T. conradi Mee _____________ Aslarte meeki Stanton” ______ of. A. packardi Meek. (Coelastarte) morion 0 sp.... Lucina sp.- Isocyprina? Protocardz'a schuchertt McLearn.. sp ........................... Pleuromya subcompressa Meek. . of. P. oblongata Warren.... Pholadomya kingi Meek ..... inaequiplicatus Stanton. Cercomya punctata (Stanton).. Ouenstedtia? sp ................ Tancredia cf. T. inornata Meek.. ...... Brachiéhbh‘s'h'riEi'e‘tIIZfIIIIZI..._..IIIII .. ._ . .. .. _. __ .. .. .. ._ _. __ _ ._ _. .. .. .. .. _. __ __ ._ .. .. __ .. __ __ ._ __ __ _. __ __ ._ .. >< .. .. .. Pentacrinus asterisous Meek and Hayden.. . .. .. _ _. .. .. .. .. .. .. .. .. .. . .. .. .. .. .. .. X __ _. .. ._ .. __ .. _. __ .. .. .. .. .. .. .. .. .. .. .. .. Crinoid fragments ....................... _-. .. .. - ._ .. ._ _. .. ._ _. .. .. .. - .. .. .. .. .. .. __ -_ .. .. _ .. -_ _. .. ._ .. .. .. .. .. .. X .. _. .. .. -. Echinoid spines ............................................. .. .. . X .. .. .. .. .. .. .. _. .. . _. .. .. .. .. .. __ __ .. _. __ ._ _. .. .. .. .. .. _. .. .. .. .. .. .. .. .. .. Cadoceras. This evidence is not conclusive, but of Europe and the Tethyan region, (b) the lower it does indicate that the ammonites in the Grano- cephalites beds are biologically closer to those in the Callovian than in the Bajocian and are not likely to be older than late Bathonian. 6. The Arctocephalites (Oranocephalites) beds in Alaska and Montana are herein tentatively correlated with the Bathonian rather than the Callovian stage. This correlation is based on the following: (a) in Montana geologists cannot find evidence of an important unconformity that might acccount for the absence of Bathonian ammonites typical 582600 0—61—5 Callovian is well represented by a succession of ammonites in both Alaska and the western in- terior region, and (c) the ammonites in the Arc— tocephalites (Cranocephalites) beds, although biologically related to those in the overlying Callovian beds, do not include any typical Callo- vian genera. If this correlation is valid, the ammonites of Bathonian time occupied two dis- tinct realms of which one included parts of Europe and the Tethyan region from Mexico to Indonesia and the other included the Arctic 0—22 region and some of the North Pacific Ocean. This concept differs somewhat from that of Arkell (1956, p. 608-610), who correlated the Arcto- cephalites (Uranocephalites) beds with the earliest Callovian and inferred that the Arctic Ocean during Bathonian time was completely isolated from the other oceans and that the Bathonian faunas of the Arctic Ocean are now buried be- neath the present Arctic Ocean. Emergence of the continents during Bathonian time, discussed by Arkell, fits either concept. SYSTEMATIC DESCRIPTIONS Genus HOLCOPHYLLOCERAS Spath, 1927 Holcophylloceras sp. Plate 1, figure 1 Seven internal molds of a single species are present in the Cranocephalites beds. These show the deep strongly sigmoidal constrictions that are characteristic of the genus. Traces of fine ribbing are present on the venter of one specimen. The largest mold is a fragment of a large body chamber belonging to an ammonite that was at least 200 mm in diameter. The suture line has only diphyllic saddles. Figured specimen: USNM 130754. Occurrence: Bowser member of the Tuxedni formation at USGS Mesozoic locs. 22698 and 22712; equivalent beds in the Talkeetna Mountains at Mesozoic 100. 24117. Genus OECOTRAUSTES, Waagen, 1869 Subgenus PAROECOTRAUSTES Spath, 1928 Oecotraustes (Paroecotraustes)? sp. Plate 1, figures 2—4 One small septate compressed ammonite is charac- terized by having a tiny umbilicus, a low vertical um- bilical wall, a median raised spiral groove, and low backwardly arched ribs on the upper parts of the flanks. The venter is so worn that its characteristics cannot be determined. There is a suggestion of low broad for- wardly inclined ribbing on the lower part of the flanks. The suture line cannot be traced accurately. The features of this specimen suggest an assignment to the Oppeliidae, but do not fit those of any described genus. The umbilicus is smaller than in Oecotraustes or Paroecotraustes. The spiral groove is much deeper than in Oppelia or in Oxycerites. The absence of sec- ondary ribs likewise excludes Oppelia. The ribs ap- pear to be broader than on any described species of Oxycerites, but this appearance is due partly to weather- ing. The specimen may represent a new genus, but lack of knowledge of the venter precludes any certain generic assignment. Figured specimen: USNM 130747. Occurrence: Unnamed beds in the Talkeetna Mountains at Mesozoic loc. 24116. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Genus XENOCEPHALITES Spath, 1928 Xenocephalites? sp. Plate 6, figures 4, 5, 9. One small specimen bears ribbing similar to that on the much larger holotype of Arctocephalites? sag/po- ensis Imlay, n. sp. (pl. 6, figs. 1, 2), but its body cham- ber is terminated by a constriction and a rib pattern suggestive of an adult shell. If so, it probably is a different species as it is considerably smaller. Also, the venter of the penultimate whorl bears low broad ribs separated by narrow interspaces, which feature is suggestive of Xenocephalites, but not of Arctocephalites Figured specimen: USNM 130775. Occurrence: Sawtooth formation, upper member, at USGS Mesozoic loc. 18714. Genus ARCTOCEPHALITES Spath, 1928 Arctocephalites? alticostus Imlay, n. sp. Plate 2, figures 1—8 The species is represented by five specimens. The whorls are moderately stout and are wider than high. The umbilicus is small and has a steep umbilical wall that rounds rather abruptly into the flanks. The body chamber on the largest specimen represents three—fourths of a whorl and is terminated by a con— striction that is present only on the lower part of the flanks. The ribbing is very high and sharp. The primary ribs curve backward on the umbilical wall, curve forward on the flanks, and become very high on the lower fourth of the flanks. Most primary ribs pass into slightly weaker secondary ribs between the lower fourth and the lower third of the flanks, but some primary ribs do not branch and others are indistinctly connected with secondary ribs. A few secondary ribs arise freely on the lower part of the flanks. The secondary ribs cross the venter transversely and become slightly higher ventrally. The suture line is not well preserved and cannot be traced. The holotype has been compressed laterally, but at a diameter of 36 mm has a whorl height of 18 mm, a whorl thickness of 18 mm, and an umbilical width of 6.5 mm. On the small paratype, shown on plate 2, figure 3, the same dimensions are 15, 8, 11.5, and 3.5 mm respectively. This species has much higher and sparser ribbing than any of the small specimens from Greenland that have been assigned to Arctocephalites or to the subgenus Cranocephalites, but it shows some resemblances to the immature whorls of Arctocephalites sphaericus Spath (1932, p. 40, pl. 6, fig. 3, pl. 19, fig. 4) and A. (Cranocephalites) of. C'. pompeckji (Madsen) (Spath, JURASSIC AMMONITES FROM ALASKA AND MONTANA 1932, pl. 3, fig. 3). It shows more resemblance to A.? saypoensz's Imlay, n. sp., described here, but has higher and more flexuous primary ribs. The holotype of A? alticostus Imlay, n. sp., shows some resemblance to Xenocephalites m’cam‘us Imlay (1953b, p. 78, pl. 28, figs. 1—8), from the Chinitna formation, Alaska, but differs from this and all other species of that genus by being less narrowly umbilicate, by its adult body whorl not contracting from the inner whorls, by its ribs being much higher and thinner on the inner whorls, by its ribs remaining thin on its outer whorl instead of becoming broad and widely spaced, and by the presence of an apertural constriction. This species is not assigned to Oranocephalites be- cause the body chamber does not contract from the inner whorls. It differs from Arctocephalz'tes by its ribs remaining high and sharp on the body chamber instead of weakening or disappearing. It probably represents a new genus or subgenus, but the preser- vation of the specimens in hand does not justify making such an assignment. Types: Holotype USNM 130757; paratypes USNM 130758— 130760. Occurrence: Bowser member of the Tuxedni formation at USGS Mesozoic locs. 20011, 20752, and 21308; from equivalent beds in the Talkeetna Mountains at Mesozoic 10c. 24116. Arctocephalites? saypoensis Imlay, n. sp. Plate 6, figures 1, 2 Arctocephalites sp. juv. cf. A. sawtoothensis Imlay, 1948, US. Geol. Survey Prof. Paper 214—B, p. 19, pl. 6, figs. 2, 5. The holotype has been crushed laterally, but its whorl section originally was probably wider than high. The umbilicus is moderate in width, and the umbilical wall is low and vertical. The body chamber occupies about three—fourths of a whorl, is probably nearly complete, and is not contracted adorally. The ornamentation of the inner whorls is not known. On the outer whorl of the holotype, the primary ribs are strong and high. They curve backward on the umbilical wall and curve forward on the lower fourth of the flanks. On the septate part of the whorl, all primary ribs bifurcate at the top of the lower fourth of the flank. Toward the aperture the rib branch nearest the aperture becomes indistinctly connected With the primary rib, and on the last fourth of the body whorl, there is regular alternation of long radial primary ribs and shorter secondary ribs. All ribs are high and narrow on the venter on which they arch forward gently. The suture line cannot be traced, and dimensions cannot be measured accurately. The presence of many single ribs near the adoral end of the body chamber suggests that the specimen 0—23 is an adult. If so, it is smaller than any described species of Arctocephalz’tes 0r Oranocephalites from Green— land. It, also, has much stronger ribbing than any species of Arctocephalites or Orcnocephalz'tes at a com- parable size. The most similar species is A? alticostus Imlay, n. sp., described herein, from which it differs by having lower less flexuous primary ribs, by having stouter secondary ribs, and by being larger. Its um- bilicus appears to be wider than in Arctocephalc'fes, but this appearance may be deceptive considering that the inner whorls are not preserved and that the specimen has been deformed. Type: Holotype USNM 104149. Occurrence: Sawtooth formation, upper member at USGS Mesozoic 10c. 18324. A small specimen of this species in the Princeton University collections was obtained 4 miles west of Drummond, Mont., in a railroad cut in the NEM of sec. 21, T. 11 N., R. 13 W. Subgenus CRANOCEPHALITES Spath, 1932 Arctocephalites (Cranocephalites) pompeckji (Madsen) Plate 1, figures 5—13 Macrocephalites pompecka' Madsen, 1904, Meddelelser om Gronland, v. 29, p. 189, pl. 8, figs. 5, 6a, b. Cranocephalites pompeckji (Madsen). Spath, 1932, Meddelelser om Gronland, v. 87, p. 16, pl. 3, fig. 3, pl. 4, figs. 8—10. pl. 5, figs. 3, 6—8, pl. 9, fig. 4, pl. 13, figs. 1a, b. Arctocephalites (Cranocephalites) pompeckji (Madsen) afi. var, costata. Spath. Donovan, 1953, Meddeleslser om Gron- land, v. 11], p. 83, pl. 17, figs. 2a, b. Arctocephalites (Cranocephalites) pompeckji (Madsen) var. in- termedia Spath, Donovan, 1953, Meddelelser om Gronland v. 111, p. 83, pl. 17, figs. 3a, b. Six specimens from Alaska are within the range of variation of 0. pompecka' (Madsen) as described by Spath (1932, p. 16—20). They are characterized by a compressed whorl section, a highly arched venter, and by high sharp widely spaced ribs that cross the venter without reduction in strength. The primary ribs curve backward on the unbilical slope, curve for- ward on the flanks, and pass into pairs of slightly weaker secondary ribs between the lower fourth and the middle of the flanks. Many of the pairs of the secondary ribs are separated by single ribs that begin freely on the lower third of the flanks. The secondary ribs incline forward slightly on the upper part of the flanks but cross the venter nearly transversely. The body chamber includes about three—fifths of a whorl. It is terminated adorally by a constriction that is followed by a swelling and then by a smooth area. The suture line shown on plate 1, figure 9, occurs at the beginning of the body chamber and is considerably worn. Traces of the suture preserved on the opposite side of the same specimen show that it is nearly as complex as the suture on Cranocephalz‘tes vulgaris Spath (1932, pl. 3, fig. 5), differing mainly by having a slightly C—24 longer ventral lobe. The suture is characterized by having broad saddles and fairly short lobes and by its auxiliaries ascending toward the umbilical seam. The largest specimen (pl. 1, figs. 11—13), which is slightly compressed, at a maximum diameter of 96 mm has a whorl height of 42 mm, a whorl thickness of 38(?) mm, and an umbilical Width of 16 mm. On a smaller specimen (pl. 1, fig. 6) the comparable dimensions are 62, 27, 26, and 15 mm. Among the Alaskan specimens, the smallest are similar to a small specimen illustrated by Spath (1932, pl. 3, fig. 3). The specimen shown on plate 1, figure 10, resembles 0. pompecka' var. intermedia Spath (1932, pl. 5, fig. 7). The specimen shown on plate 1, figure 6, resembles other variants illustrated by Spath (1932, pl. 4, figs. 9a, b, pl. 13, figs. 1a, b). The largest speci- men from Alaska (pl. 1, figs. 11—13) differs from the holotype of 0. pompeclcji (Madsen) (1904, pl. 8, figs. 6a, b) mainly by having slightly finer and denser ribbing. The species C. pompecka' (Madsen) is more similar to 0. vulgaris Spath (1932, p. 20, pl. 1, figs. 2—4, 6; pl. 2, figs. 1a, b; pl. 3, fig. 5; pl. 4, figs. 1, 3a, b; pl. 5, figs. 1a, b; pl. 8, figs. 1a, b; pl. 10, figs. 3a, b) than to any other described species. It differs by being more compressed and by having higher sharper more widely spaced ribs that remain fairly strong on the venter of the adult body whorl. Type: Plesiotypes USNM 130751—130753. Occurrence: Bowser member of the Tuxedni formation at 21283, 21284, 22698. The species is pOSsibly represented at Mesozoic locs. 20745 and 22711 in the Bowser member. Arctocephalites (Cranocephalites) costidensus Imlay, n. sp. Plate 2, figures 11—19 The species is represented by 35 specimens. The whorls are ovate in section, slightly wider than high. The flanks are gently convex and round evenly into a moderately broad venter. The body chamber occupies about three-fifths of a whorl. The aperture is termi— nated by a pronounced constriction that is followed by a swelling. The ornamentation consists of fine dense ribbing. The primary ribs curve backward 0n the umbilical wall, curve forward on the flanks, and give rise to 2 or 3 somewhat weaker secondary ribs between the lower third and the middle of the flanks. Many other secondary ribs arise freely on the lower third of the flanks. The secondary ribs cross the venter trans— versely, or with a slight forward arching, and are slightly reduced in strength along the venter on some of the largest body chambers. The suture line is characterized by having fairly broad saddles and by its auxiliaries ascending to the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY umbilical seam. All the specimens are deformed so much that measurements are meaningless. This species has finer denser ribbing than any de- scribed species of Arctocephalites or Cranocephalites from Greenland, but approaches most closely to O. gracilis Spath (1932, p. 22, pl. 2, figs. 6 a, b, pl. 3, figs. 1 a, b) which it resembles also, in stoutness. However, even the most coarsely ribbed variants of the Alaskan species (pl. 2, figs. 19) have finer ribs and more closely spaced secondary ribs. Arctocephalites orientalis Krim- holz (1939, p. 59, pl. 2, figs. 5, 6) from northern Asia has as fine and dense ribbing as A. (Cranocephalites) costi- densus Imlay, n. sp., but is much more inflated and appears to have a smaller umbilicus. Types: Holotype USNM 130745; paratypes USNM 130746, 130748, 130749. Occurrence: Bowser member of the Tuxedni formation at Mesozoic. locs. 20754, 21283, 22698, 22712; equivalent beds in the Talkeetna Mountains at Mesozoic locs. 24115, 24116, and 24117. Arctocephalites (Cranocephalites) sawtoothensis Imlay Plate 3, figures 1—10, plate 4, figures 2, 4, 6 Arctocephalites sawtoothensis Imlay, 1948, U.S. Geol. Survey Prof Paper 214—B, p. 19, pl. 6, fig. 7. Arctocephalites metastatus (Buckman) var. sweetgrassensis Imlay, 1948, US. Geol. Survey Prof. Paper 214—B, p. 20, pl. 6, figs. 1, 3. This species is represented by 14 specimens of various sizes and growth stages. These show that the specimen described as Arctocephalites metastatus (Buckman) var. sweetgrassensis Imlay is merely a finely ribbed variant of A. sawtoothensis Imlay. The holotype of Metacephalites metastatus Buckman (1929, p. 11, pl. 3, figs. 1—4) has much lower blunter primary ribs than immature in- dividuals of A. sawtoothensis Imlay and probably is not generically related. Assignment of A. sawtoothensis Imlay to the subgenus Cranocephalites is based on the presence of a contracted body chamber. One small laterally crushed specimen shown on pl. 3, fig 3, is shown for comparison with the holotype of Macrocephalites laminatus Buckman (1929, p. 14, pl. 1, figs. 4, 4a, 5). Types: Holotype USNM 104148; plesiotypes USNM 104150, 130766—130770. Occurrence: Sawtooth formation, upper member, USGS Mesozoic locs. 18718, 19184, 19601, 20355, 22654, 27040, 27042, and 27502. Arctocephalites (Cranocephalites) of. A. gracilis (Spath) Plate 5, figures 1—3 Three specimens from the Sawtooth formation are distinguished from A. sawtoothensis Imlay by having considerably finer ribbing. They are comparable in ribbing with the holotype of Cranocephalites gracilis JURASSIC AMMONITES FROM ALASKA AND MONTANA Spath (1932, p. 22, pl. 3, figs. 1 a, b) from east Green- land but are possibly a little stouter. Figured specimens: USNM 130771. Occurrence: Sawtooth formation, upper member at USGS Mesozoic locs. 19601, 27501. Arctocephalites (Cranocephalites) of. A. maculatus (Spath) Plate 4, figures 1, 3, 5 The septate specimen, illustrated on plate 4, figure 5, is the best preserved of four, although it has been crushed laterally and the details of its ribbing are not preserved. The specimens are characterized by having a stout whorl section, very coarse, thick ribbing, and a smooth contracted body chamber. They are com- parable in stoutness and in coarseness of ribbing with Cranocephalites maculatus Spath (1932, p. 24, pl. 1, figs. 1 a, b, pl. 2, figs. 3 a, b, pl. 3, figs. 6 a, b, pl. 4, fig. 2), from east Greenland, but differ by developing a smooth body chamber. Immature individuals of the species from Montana have not been identified definitely, but are possibly represented by the specimens shown on plate 4, figures 1, 3. Figured specimens: USNM 130773, 130774. Occurrence: Sawtooth formation, upper member at USGS Mesozoic locs. 19184, 22652, 27039, and 27040. Arctocephalites (Cranocephalites) of. A.? platynotus (Spath) Plate 5, figures 4—6, 8 Two specimens from Montana are as broadly de- pressed as A.? platynotus Spath (1932, p. 43, pl. 11, figs. 6 a, b) from east Greenland but difl’er by having much stronger primary ribs and more distinct rib branching low on the flanks: The larger specimen re- presents the adoral part of a scaphitoid body chamber and is marked by two constrictions. Figured specimens: USNM 130772. Occurrence: Sawtooth formation, upper member at USGS Mesozoic 100. 19601 Genus ARCTICOCERAS Spath, 1924 Arcticoceras? sp. Plate 5, figure 7 One adult body whorl is similar in shape to the adult of Arctiococeras rierdonense Imlay (1953a, p. 19, pl. 2), difl’ering mainly by being much smaller and by having a prolonged ventral lappet. The aperture is terminated bya constrictionnear the dorsum. The umbilicus is extremely small. The body chamber occupies about four-fifths of a whorl. Only traces of the suture line are preserved. This specimen, by comparisons with ammonite specimens from the western interior, probably belongs to the genus Arcticocerds rather than to Arctocephalites. 0—25 However, without knowledge of the ribbing of its internal whorls a definite generic assignment cannot be made. Nevertheless, the resemblance to Arcti- coceras suggests that the upper part of the Sawtooth formation is not much older than the Arcticoceras zone at the base of the Rierdon formation. Figured specimen: USNM 130776. Occurrence: Sawtooth formation, upper member at USGS Mesozoic loc. 22654. Genus PARAREINECKEIA Imlay, n. gen. This genus is distinguished from other genera and subgenera of the Reineckeiidae (Arkell, 1957, p. L311—L313) by having larger primary ribs, a single row of tubercles high on the flanks, and an exceedingly weak ventral sinus that does not interrupt the ribbing. The inner whorls are coronate and bear prominent tubercles at the umbilical seam. During growth the whorls become ovate, the tubercles become weaker, and the ribs become broader and more widely spaced. P. hickersonensis Imlay, n. sp., is designated as the type species. The genus likewise includes Reineckeiu (Kellawaysites) shelilcofana Imlay (1953b, p. 101, pl. 55, figs. 1, 2, 5—8). The tuberculate coronate inner whorls of Para- reineckeia may be distinguished from those of Reineckeiav by the position of the tubercles much higher on the flanks. The weakening of tuberculation during growth contrasts markedly with the condition in Reineckeia. The adult of Parareineckeid shows some resemblance to Kellawaysites, but is readily distinguished by its coronate inner whorls, much longer primary ribs, and absence of rib branching on the flanks below the tubercles. The genus Collotia bears tubercles high on the flanks as in Parareineckeia, but it, also, bears rows of tubercles near the umbili( us and on the venter and it has a well-defined ventral groove. The outer septate whorls of Kellawuysites oxyptychoides Spath (1928, p. 266, pl. 41, figs. 5 a, b; 1933, pl. 126, fig. 1) bear tubercles high on the flanks as in Parareineckeia, but the primary ribs bifurcate below the middle of the flanks as well as higher. The genus Epimorphoceras Spath (1928, p. 252—254) differs from Parareineclceia by developing compressed instead of ovate whorls, by loosing its tubercles at an earlier growth stage, by developing fasiculate ribbing, and by having a well- developed ventral sulcus. Parareineckeia hickersonensis Imlay, n. sp. Plate 7, figures 1—5 Only one specimen of this species is known. It is moderately compressed and evolute. Its whorls are much depressed, but become less depressed during growth. The flanks on the inner whorls are divergent. C—26 but on the outer whorls become evenly rounded. The venter on the inner whorls is very broad and de- pressed and makes a sharp angle with the flanks, but during growth the venter becomes gently convex and rounds less abruptly into the flanks. The umbilicus is very wide; the wall is steep and rounds evenly into flanks. The body chamber is incomplete, but includes at least half a whorl. The primary ribs are high, narrow, fairly widely spaced, incline forward on the flanks and terminate at the top of the flanks in tubercles of variable strength. From most tubercles pass pairs of weaker secondary ribs that arch forward slightly on the venter and may, or may not unite in a single tubercle on the opposite side of the venter. Some tubercles are connected across the venter by single ribs or by three ribs. A weak median sinus is present along the midline of the venter on the outer whorl. There are 3 or 4 con- strictions on each whorl. The suture line has broad saddles. The external lobe is slightly shorter than the first lateral lobe. The second lateral lobe is nearly as large as the first lateral lobe. The auxiliaries ascend toward the umbilical seam. The holotype at a diameter of 43 mm has a whorl height of 14.5 mm, a whorl thickness of 19.5 mm, and an umbilical width of 22 mm. At a diameter of 65 mm the other dimensions are 20, 24, and 29 mm, respectively. This species is distinguished from Pararer’neckeia shelikofana (lmlay) (1953b, p. 101, pl. 55, figs. 1, 2, 5—8) by its much coarser ribbing, stronger tuberculation, and more depressed whorl section. Type: Holotype USNM 130756. Occurrence: Bowser member of the Tuxendi USGS Mesozoic 10c. 22698. formation at Parareineckeia of. P. shelikofana (Imlay) Plate 7, figures 6, 7 Two fragments resemble the inner whorls of P. shelikofana (Imlay) (1953b, p. 101, pl. 55, figs. 1, 8) from the Chinitna formation of Alaska. They differ by having slightly sparser and sharper ribs at a com- arable size. As in that species the zone of tuberculation is situated high on the flanks and a weak median sinus is present on the venter. Figured specimen: USNM 130750. Occurrence: Bowser member of the Tuxedni formation at USGS Mesozoic loc. 20745; equivalent beds in the Talkeetna Mountains at Mesozoic 100. 24117. Genus COBBANITES Imlay, n. gen. Cobbam'tes is characterized by having compressed whorls that become more compressed during growth, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY by bearing prorsiradiate ribbing and deeply impressed forwardly inclined constrictions, by developing a smooth body chamber, and by the venter on its inner whorls bearing strongly arched ribs that in some species are slightly weakened along the midline. The primary ribs on the small innermost whorls are promi- nent, are radial, or inclined slightly forward, most of them bifurcate near the middle of the flanks, and along the zone of furcation they become strongly swollen. Tiny tubercles are present at the furcation points on the innermost whorls of a species from Montana. The suture line has a strongly retracted suspensive lobe. The aperture terminates simply. Cobban’ites talkeetnanus Imlay, n. sp., is designated as the type species. Oobbam'tes shows a general resemblance to some finely ribbed species of Chofiatia, such as figured by Neumayr (1871, pl. 14, figs. 1a, b, 2a, b, pl. 15, figs. la, b, 2a, b), and particularly to the subgenus Homoe- oplanult'tes Buckman (1922, pl. 328; 1924, pl. 515; Westermann, 1958, p. 85; Arkell, 1958,13. 211, 225—227), but its primary ribs become much weaker and more closely spaced on the adult body whorl, and its secondary ribs are inclined forward much more strongly, especially on the inner whorls. Also, its peristone does not bear lateral lappets as in Homoeopltmulites. An assignment of Cobbam'tes to the subfamily Zigzagiceratinae (see Arkell, 1957, p. L314—L316) is favored by such features as its prorsiradiate ribbing, the swollen primary ribs on its inner whorls, the tiny lateral tubercles on one species, and perhaps the reduction of ribbing along the midventral line on immature specimens. Its ribbing in particular suggests a relationship with the genus Procerites. It differs from Procerites, however, by having deeply impressed constrictions on its septate whorls and by being more evolute and compressed than most species that have been assigned to Procerites. The subgenus Gracilis- phinctes Buckman (1920, pl. 193; Arkell, 1958, p. 174), has constrictions, but only on its inner whorls. Further— more it differs from Cobbamjtes by having more evolute inner whorls and more involute outer whorls, and on the adult body whorl the ribbing fades first on the lower part of the flanks instead of on the venter. Cobbam'tes also shows resemblances to Gonolkites Buckman (1925, pl. 546a, b; Arkell, 1956, p. 145, 153—160) from the lower Bathonian—but it is much more evolute; the ribbing on the adult whorl fades earliest on the venter instead of on the flanks; and it does not have a distinct ventral groove. Other species of Cobba/m'tes include the specimens from Montana and Alaska assigned to Procerites spp. by Imlay (1953a, p. 33, pl. 23, figs. 13, 17, pl. 24, figs. 9—11; 1953b, p. 102, pl. 53, figs. 1—3), Procerites engleri JURASSIC AMMONITES FROM ALASKA AND MONTANA Frebold (1957a, p. 65, pl. 39, fig. 1, pl. 40, figs. 1a, b) from Canada and probably Procerites? sp. described by Frebold (1957a, p. 66, pl. 40, figs. 2a, b; pl. 41) from Canada. Another species of Cobbanites occurs in the Sawtooth formation of Montana and is described herein. Cobbanites is named in honor of William A. Cobban, of the US. Geological Survey at Denver, Colo. Cobbanites occurs in the Cook Inlet area, Alaska, in the basal part of the Chinitna formation of early Callovian age and in the directly underlying beds whose age is in question. In Alberta it is associated with other ammonites of early Callovian age (Frebold, 1957a, p. 65, 66, 76, 80) in the Fernie formation. In Montana it occurs in the lower part of the Rierdon formation of early Callovian age and in the directly underlying upper member of the Sawtooth formation. Cobbanites talkeetnanus Imlay, n. sp. Plate 7, figures 8—13, plate 8, figure 1 This species is represented by 1 large adult specimen that includes the body chamber and by 1 fragment that shows 5 septate inner whorls. The shell is com— pressed. The whorls are elliptical in section, much higher than wide, and each whorl embraces about two- fifths of the preceding whorl. The flanks are flattened and rounded evenly into the highly arched venter which becomes narrower during growth. The um- bilicus is very wide and shallow; the umbilical wall is low and steeply inclined. The body chamber oc- cupies about four-fifths of a whorl. The aperture on the internal mold is terminated by a pronounced for- wardly inclined constriction. On the inner whorls the primary ribs are fairly high and sharp, are regularly spaced, and are separated by moderately wide interspaces. They begin near the umbilical seam, incline forward gently on the flanks, and bifurcate regularly near the middle of the flanks. The secondary ribs are a little weaker than the primary ribs, curve forward strongly on the flanks, arch for- ward considerably on the venter, and are slightly weakened along the midventral line. Each whorl bears from 3 to 4 deep constrictions that are inclined forward more strongly than the ribs and are generally bounded by 1 or 2 swollen ribs. During growth the ribs become weaker and less strongly projected. On the penultimate whorl the ribbing is weak, is only slightly arched on the venter, and gradually fades adorally. The body chamber is marked only by faint moderately spaced primary ribs on the lower third of the flanks. The suture line, partly exposed at several places on the largest septate whorl, is fairly complex and has long, slender lobes and a strongly retracted suspensive lobe. 0—27 The holotype at a diameter of 190 mm has a whorl height of 59 mm, a whorl thickness of 39 mm, and an umbilical width of 82 mm. Near the aperture the same dimensions are 260(?), 68, 52, and 124 mm, re— spectively. This species is characterized by its compressed whorl section, its deep strongly inclined constrictions, the moderate spacing of its primary ribs, and strong forward inclination of its secondary ribs. It differs from most species of Chofiatia by not developing widely spaced primary ribs on its outer whorls, and in that respect resembles the subgenus Homoeoplanulites (Buck- man, 1922, pl. 328; 1924, pl. 515) from the Lower Cornbrash formation of England. Homoeoplanulites is characterized, however, by the presence of lateral lappets, and its secondary ribs are not inclined forward. Oobbamltes talkeetmmus Imlay, n. sp., has weaker ribbing than on 0. englem' (Frebold) (1957a, p. 65, pl. 39, pl. 40, figs. 1a, b), its secondary ribs are more strongly projected on the flanks, and it appears to be a much smaller species. Types: Holotype USNM 130743; paratype USNM 130744. Occurrence: Unnamed beds in the Talkeetna Mountains at Mesozoic 100. 24116. Cobbanites spp. Plate 6, figures 3, 6—8, 10—15 The genus is represented in the Sawtooth formation by 20 fragments, of which most belong to a species similar to Cobbtmites talkeetnanus Imlay, n. sp., from Alaska. The inner whorls are depressed ovate in section and probably a little wider than high. During growth the whorl section becomes more compressed and on the adult body chamber is about twice as high as wide. The smallest whorls bear prominent moderately spaced primary ribs that incline forward slightly on the lower parts of the flanks and bifurcate fairly regularly near the middle of the flanks. A few primary ribs re- main simple. The furcation points on the smallest whorls are marked by tiny conical tubercles. The secondary ribs are slightly weaker than the primary ribs, are inclined forward on the flanks, and are arched forward strongly on the venter. During growth the ribbing gradually becomes weaker and less strongly arched, but persists on all septate whorls. The adult body chamber is smooth, or bears only faint traces of ribbing low on the flanks. Strong forwardly inclined constrictions are present on all septate whorls and are most deeply impressed on the inner whorls. The suture line has long, slender lobes and a strongly retracted suspensive lobe. All the specimens are too imperfect for measurements to be made. C—28 The ornamentation of the inner whorls of the speci- mens of Oobbanites from the Sawtooth formation greatly resemble the Middle Jurassic genus Parkin— sonia except for the absence of a ventral groove. They likewise resemble the small specimen from Alberta that Frebold (1957a, p. 65, 66, pl. 40, figs. 2 a, b, pl. 41) referred questionably to Procerites. The larger septate whorls are comparable with the paratype of Cobbanites engleri (Frebold) (1957a, pl. 40, figs. 1 a, b) but appear to have more widely spaced ribbing and a more compressed ovate whorl section. They differ from 0. talkeetnanus Imlay, n. sp., from Alaska by attaining a much larger size, by having stronger ribbing on the larger septate whorls, and by developing a higher whorl section. The suture line, partially exposed on one specimen, has a more strongly retracted suspensive lobe than that on the holotype of Oobbanites engleri (Frebold) (1957a, pl. 39). Figured specimen: USNM 130761—130765. Occurrence: Sawtooth formation upper member at USGS, Mesozonic locs. 18718, 19184, 19185, 19601, 19604, 19623, 20355, 20357, 22652, 22654, 27041, 27047. Genus SIEMIRADZKIA Hyatt, 1900 Siemiradzkia? cf. S. aurigera (Oppel) Plate 2, figures 9, 10 Two laterally crushed ammonites have highly evolute coiling and elliptical whorl sections that become more compressed during growth. The body chamber is represented by half a whorl and is terminated by lateral lappets. Both specimens on their inner whorls have sharp evenly spaced forwardly inclined ribbing, but on one specimen the ribbing is much sharper and more widely spaced than on the other. On the outer two whorls of both specimens, the ribbing is sharp, inclined for- ward, variably spaced, and mostly simple. On the body whorl a few ribs fork high on the flanks or are indistinctly connected With secondary ribs. The suture line, partly exposed on one specimen, is fairly simple. These specimens have the fine sharp irregular ribbing that is characteristic of the genera Siemiradzkia and Grossouiria. They are tentatively assigned to Sierni- radzkia rather than to Grossoucria because single ribs are much more common than forked ribs, the ribs do not recurve backward on the venter, constrictions are not prominent, and the sides of the adult whorl tend to flatten. The more finely ribbed specimen is similar to finely ribbed specimens of S. aurigera (Oppel) from Europe (Grossouvre, 1919, pl. 15, fig. 5; Wester- mann, 1958, pl. 36, fig. 2). The more coarsely ribbed specimen develops ribbing on its body whorl similar to that of the more coarsely ribbed specimen of S. aurigera (Oppel) (D’Orbigny, 1843, pl. 149, fig. 1; SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Grossouvre, 1919, pl. 15, figs. 6, 7). The lappets on the Alaskan specimens are much simpler than in S. aurigera (Oppel) but resemble those of S. matisconensis (Lissajous) (1923, pl. 5, fig. 3) or S. berthae (Lissajous) (1923, pl. 5, fig. 1). The Alaskan specimens were once referred by the writer to Planisphinctes (Imlay, 1952, p. 980), which Arkell (1958, p. 212, 213) considers a subgenus of Siemiradzkia. They differ from Planisphinctes how- ever, by their whorl sections becoming elliptical in- stead of circular or depressed and by the body chamber bearing irregular variably spaced ribbing. Figured specimens: USNM 130755. Occurrence: Bowser member of the Tuxedni formation at USGS Mesozoic loc. 22698. LITERATURE CITED Arkell, W. J ., 1950—58, English Bathonian ammonites: Palaeont. Soc. Pub., 264 p., 33 pls., 83 text figs. 1956, Jurassic Geology of the World: Oliver and Boyd Ltd., London, 806 p., 46 pls., 28 tables, 102 figs. 1957, in Arkell, W. J ., Kummel, Bernhard, and Wright, C. W., Mesozoic Ammonoidea: Treatise on Invertebrate Paleontology, Part L, Mollusca 4, 490 p., illus. Buckman, S. S. , 1909—30, [Yorkshire] Type Ammonites: and Wesley Ltd., London, 7 v. 1929, Jurassic Ammonoidea: Canada Natl. Mus. Bull. 58, p. 1—27, 3 pls., 1 fig. Burckhardt, Carlos, 1927, Cefalopodes del Jurasico medio de Oaxaca y Guerrero: Inst. geol. Mexico Bol., no. 47, 108 p., 34 pls. Callomon, J. H., 1955, The ammonite succession in the Lower Oxford clay and Kellaways beds at Kidlington, Oxfordshire, and the zones of the Callovian stage: Royal Soc. London Philos. Trans, v. 239, p. 215—264, pls. 2, 3, 5 figs., 4 tables. 1959, The ammonite zones of the Middle Jurassic beds of East Greenland: Geol. Mag, v. 96, no. 6, p. 505—513, pls. 17, 18. Capps, S. R., 1927, Geology of the upper Matanuska Valley, Alaska: U.S. Geol. Survey Bull. 791, 92 p., 16 pls., 5 figs. Cobban, W. A., 1945, Marine Jurassic formations of Sweetgrass Arch, Montana: Am. Assoc. Petroleum Geologists Bull., v. 29, p. 1262—1303, 6 figs. Donovan, D. T., 1953, The Jurassic and Cretaceous stratigraphy and paleontology of Traill Q, East Greenland: Meddelelser om Gronland, v. 111, no. 4, 150 p., 25 pls., 14 figs. 1957, The Jurassic and Cretaceous systems in East Greenland: Meddelelser om Gronland, v. 155, no. 4, 214 p., 4 pls., 25 figs. Frebold, Hans, 1930, Verbreitung und Ausbildung des Meso- zoikums in Spitzbergen: Skrifter om Svalbard og Ishavet [Oslo], no. 19, p. 183—201, pls. 1—33. 1951, Geologic des Barentsschelfes: Deutsche Akad. Wiss. Berlin Abh., Kl. Math. 11. allg. Naturw. Jahrg. 1950, no. 5, 151 p., 82 figs. 1953, Correlation of the Jurassic formations of Canada: Geol. Soc. America Bull., v. 64, p. 1229—1246, 1 correlation chart. —— 1957a, The Jurassic Ferniel group in the Canadian Rocky Mountains and foothills: Canada Geol. Survey Mem. 287, 197 p., 44 pls., 5 figs. Weldon JURASSIC AMMONITES FROM ALASKA AND MONTANA 1957b, Fauna, age, and correlation of the Jurassic rocks of Prince Patrick Island: Canada Geol. Survey Bull. 41, 32 p., pls. 1—18 [issued January 1958]. Grossouvre, Albert de, 1919, Bajocien-Bathonien dans la Niévre: Soc. géol. France, Bull., 4 ser., V. 18, p. 337—459, pls. 13—16. Imlay, R. W., 1948, Characteristic marine Jurassic fossils from the western interior of the United States: US. Geol. Survey Prof. Paper 214—B, p. 13—33, pls. 5—9. 1952, Correlation of the Jurassic formations of North America, exclusive of Canada: Geol. Soc. America Bull., v. 63, p. 953—992, 2 correlation charts. 1953a, Callovian (Jurassic) ammonites from the United States and Alaska, Part 1. Western interior United States: U.S. Geol. Survey Prof. Paper 249—A, p. 1—39, 24 pls., figs. 1, 2, 3 tables. 1953b, Callovian (Jurassic) ammonites from the United States and Alaska. Part 2. Alaska Peninsula and Cook Inlet regions: U.S. Geol. Survey Prof. Paper 249—B, p. 41— 108, pls. 25—55, figs. 2—9, 6 tables. 1956a, Marine Jurassic exposed in Bighorn Basin, Pryor Mountains, and northern Bighorn Mountains, Wyoming and Montana: Am. Assoc. Petroleum Geologists Bull., v. 40, p. 562—599, 7 figs. —— 1956b, Interpretations of the marine Jurassic fossil record at Lower Slide Lake, Teton County, Wyoming: Wyoming Geol. Assoc. Guidebook 11th Ann. Field Conf., p. 70—71. 1957, Paleoecology of Jurassic seas in the western interior of the United States: Treatise on Marine Ecology and Paleoc- cology, v. 2, Geol. Soc. America, Mem. 67, p. 469—504. Imlay, R. W., Gardner, L. S., Rogers, C. P., Jr., and Hadley, H. D., 1948, Marine Jurassic formations of Montana: US. Geol. Survey Oil and Gas Inv. (Prelim.) Chart 32. Krimholz, G. Y., 1939, Materials on the geology of the Bureya coal basin, 4; Contribution to the stratigraphy of the Jurassic marine strata on the Bureya river [East Siberia]: United Central Geol. Prosp. Inst. Russia Trans, v. 117, 60 p., 3 pls. Kirschner, C. E. and Minard, D. L., 1949, Geology of the Iniskin Peninsula, Alaska: US. Geol. Survey Oil and Gas Inv. (Pre- lim.) Map 95. Lupher, R. L., 1941, Jurassic stratigraphy of Central Oregon: Geol. Soc. America Bull., v. 52, p. 219-270. McLearn, F. H., 1924, New pelecypods from the Fernie forma- tion of the Alberta Jurassic: Royal Soc. Canada Proc. and Trans, 3d ser., sec. 4, v. 18, p. 39—61, pls. 1—9. —— 1928, New Jurassic ammonoidea from the Fernie forma- tion Alberta: Canada Geol. Survey Bull. 49, Geol. Ser. no. 48, p. 19—22; pls. 4—8. 1929, Stratigraphic paleontology, Blairmore region, Alberta: Canada Natl. Mus. Bull. 58, Geol Ser., no. 50, p. 80—107. 1932, Three Fernie Jurassic ammonoids: Royal Soc. Canada Proc. and Trans, 3d ser., sec. 4, v. 26, p. 111—115, 5 pls. Madsen, V., 1904, On Jurassic fossils from East Greenland: Meddelelser om Grb'nland, v. 29, p. 157—210, pls. 6—10. C—29 Martin, G. C., 1926, The Mesozoic stratigraphy of Alaska: US. Geol. Survey Bull. 776, 493 p., 13 figs. Mapel, W. J., and Bergendahl, M. H., 1956, Gypsum Spring formation, northwestern Black Hills, Wyoming, and South Dakota: Am. Assoc. Petroleum Geologists Bull., v. 40, p. 84—93, 2 figs. Moor, G. G., 1937, Explanatory note geologic map northern USSR: Arctic Inst. Trans, v. 87, p. 207—290. Neumayr, M., 1871, Die Cephalopoden-Fauna der Oolithe von Balin bei Krakau: K. K. Geol. Reichsanstalt Abh., v. 5, p. 19—54, pls. 9—15. Newton, E. T. and Teall, J. J. H., 1897, Notes on a collection of rocks and fossils from Franz Josef land, made by the Jack— son-Harmsworth expedition, 1894—96: Geol. Soc. London Quart. Jour., v. 53, p. 477—519, pls. 37—41. Nikolaev, I. G., 1938, Data on geology and mineral deposits of the Kharaulakh range in Geology and mineral deposits of the Lena-Kolyma district; part 1: Arctic Inst. Trans, v. 99, 193 p., 41 figs, 5 pls. Orbigny, Alcide (1’, 1842—51, Paleontologie francaise: Terrains Jurassiques, v. 1. Pompeckj, J. F., 1899, The Jurassic fauna of Cape Flora, Franz Josef Land, in Nansen, F., The Nbrwegian North Polar Expedition, 1893—96: Sci. Results, v. 1, no. 2, 147 pp., 3 pls. Salfeld, Hans, and Frebold, Hans, 1924, Jura—und Kreidefossilien von Nowaja Semlja: Rep. Sci. Results Norwegian Exped. Novaya Zemlya for 1921 (Kristiania), no. 23, p. 1—12, pls. 1—4. Spath, L. F., 1927—33, Revision of the Jurassic cephalopod fauna of Kachh (Cutch): Palaeontologia Indica, new ser., v. 9, 6 pts., 945 p., 130 pls. 1932, The invertebrate faunas of the Bathonian-Callovian deposits of Jameson Land (East Greenland): Meddelelser om Gronland, v. 87, n0. 7, 158 p., 26 pls., 14 text figs. Stehn, E., 1924, Beitrage zur Kenntnis des Bathonien und Cal— lovien in Sudamerika: Neues Jahrb., Beilage—Band 49 for 1923, p. 52—58, 8 pls. Warren, P. S., 1932, A new pelecypod fauna from the Fernie formation, Alberta: Royal Soc. Canada Proc. and Trans, 3d ser., sec. 4, v. 26, p. 1—36, 5 pls. 1934, Present status of the Fernie shale: Am. Jour. Sci., 5th ser., v. 27, p. 56—70. 1947, Description of Jurassic ammonites from the Fernie formation, Alberta: Research Council, Alberta, Rept. 49, p. 67—76, 7 pls. Weir, J. D., 1949, Marine Jurassic formations of southern Alberta Plains: Am. Assoc. Petroleum Geologists Bull., v. 33, p. 547—563, 3 figs. Westermann, Gerd, 1958, Ammoniten-Fauna und Stratigraphie des Bathonien NW-Deutschlands: Beihefte Geol. Jahrb., no. 32, p. 1—103, pls. 1—49. Whitfield, R. P., 1906, Notes on some Jurassic fossils from Franz Josef Land, brought by a member of the Ziegler Exploring Expedition: Am. Mus. Nat. History Bull., v. 22, p. 131—134, pls. 18, 19. Page A Abstract ______________________________________ C—l Alaska and Montana, Callovian versus Batho- nian in ___________________________ 13 Alaska, Cook Inlet region._ _____________ 2—3 Alaska, evidence from.... _____________ 10—12 alticostus, Arctocephalites ___________ 20, 22, 23; pl. 2 Ammonites __________________________ 1, 2, 3, 10, 12, 14 analysis, biologic. 2 Arctic region.__-_..._._ 15 Arcticoceras ___________ 2, 5, 10, 12, 13,14, 15, 20, 25 kochi ______________________________________ 15 rierdonmse ________________________________ 25 sp ________________ 21, 25,- pl. 5 Arctocephaliles _______ 2, 4, 12, 13, 14, 15, 19,22, 23,24, 25 alticostus _______________ 20, 22, 23; pl. 2 costidensus..__ __________________________ 20 (Cranocephalites) _________________________ 2, 3, 5, 9, 10, 15, 16, 17, 19, 20, 21, 22, 24, costidensus ______________________ 24; pl. 2 gracilis _________________ 21,; pl. 5 maculatus... _______ 25; pl. 4 platynotus_. ________ 26,- pl. 5 pompecka' ______ 20, 22, 23; pl. 1 intermedia ________________________ 23 sawtoothensia ____________________ 21, 24; pl. 3 _______________ 21 gracilis.__. _______________ 21 maculatus _____________________ 21 metastatus sweetgmxsensix _________________ 24 platynatus ________________________________ 21 pompeckji... _____________ 20 sawtoothemis" _________________ 23, 24 saypoensis.___ 10, 21, 22, 23; pl. 6 sphaericus ________________________________ 22 sp ________________________________________ 20, 21 sp. juv _____________________ 23 Astarte carlottmsis.... ___________ 20 (Coelastarte) morion _________ 21 meeki _____________________________________ 21 packardi __________________________________ 21 Sp _________________________ 20, 21 asteriecus, Pentacrinus__ 21 aurigera, Siemiradzkia ___________________ 20, 28,- pl. 2 B bakeri, Phyllocems _____________________________ 3 Bathonian versus Callovian in Alaska and Montana _________________________ 13 Bathonian versus Callovian in Greenland____ 12—13 Belemnites ___________________________________ 20, 21 berthae, Siemiradzkia __________________________ 28 Biologic analysis __________ _ ___________ 2 Bowser member, Tuxedni formation __________ 2, 3, 10, 12, 19, 20, 22, 23, 24, 26, 28 Brachiopods __________________________________ 21 C Cadacems _______________________ 4, 10,12, 13, 14, 15,21 Cadoccratinac ____________ _._. 2 Culliphyllocerasfreibrocki 3 Calliphylloceratinae __________________________ 2 Callovian versus Bathonian in Alaska and Montana _________________________ 13 Callovian versus Bathonian in Greenland.___ 12—13 callovzense, Sigalocems ________________________ 10,13 Comptonectes platessiformz’s. slygz'us ________________ 21 sp ________________________________________ 20 INDEX [Italic numbers indicate descriptions] Page Canada, western interior of ___________________ 14—15 Cardioceratidae _____________ 2, 14 carlottensis, Astarte ______ _ 20 Pleuromya ________________________ _ 20 Cercomya punctata ____________________ 21 sp ________________________________________ 20 Channel conglomerate ________________________ 3 Chinitna Bay, peninsula north of____ ,___ 3 Chinitna formation ______________ 2, 4, 10, 16, 17, 23, 26 Chlamys sp __________________________ 21 Choffatia... __________________________ 15, 26, 27 Chondroceras. _____________________________ 12, 19 oblatum __________ 21 Clydom'ceras discus ____________________________ 12 Cobbam'tes ________________ 2, 12, 13, 14, 19, 20, 26, 27, 28 talkeetnanus. ____________ 20, 26, 27, 28; pls. 7,8 spp _______________________________ 21, 27,- pl. 6 (Coelastarte) morion, Astarte... _.__ 21 Collotia _______________________________________ 25 Comparisons with other faunas _______________ 14-15 Cook Inlet region, Alaska _____________________ 2—5 comadi, Trigom'a ______________________________ 21 Corbula munda. i 9 Cosmoceras ___________________________________ 4, 10 costidensus, Arctocephalites ____________________ 20 Arctocephalites (C‘ranocephalites) _ Cranocephalites __________________ 4,5,10,12,13,14, 15, 19,20, 21,22, 23,24 gracilz‘s ___________________________________ 24 maculatus ________________________________ 25 pompecka'.. ________ _ 15, 22, 23,24 intermedia. _____________ 24 vulgaris ______________________ __ 23,24 (Cranocephalites), Arctocephalites ______________ 2, 3, 5, 9, 10, 15, 16, 17, 19, 20, 21, 22, 24, Arclocephalites sp ________________ costidemus, Arctucephalites.-. gracilis, Arctocephalites ______ 5 maculatus, Arctocephalites ____________ 25; pl. 4 platynotus, Arctocephalites ............ 25; pl. 5 pompeckji, Arctocephalites ________ 20, 22, 28; pl. 1 pompeckji intermedia, Arctocephalites ______ 23 sawtoothensis, Arctocephalites ________ 21, 24; pl. 3 Crinoid fragments ____________________________ 21 cumshewaensis, Parallelodon __________________ 20 curta, Meleagrinella ___________________________ 21 Cynthia Falls sandstone member, Tuxedni formation ______________________ 2 D Dentalium sp _______________________________ 21 descriptions, systematic ______________________ 22—28 discus, Clydoniceras ___________________________ 12 distribution, geographic ___________ Donovan, quoted __________________ Drummond area ______________________________ E Echinoid spines ______________________________ 21 Ellis group ___________________________________ 18, 19 englerz‘, Procerz’tes. ___________________ 26,28 Epimorphoceras.. 25 era, SphaerocemL... 15 Evidence from Alaska ________________________ 10—12 from Montana ____________________________ 12 summation of__ 14 eximius Inoceramus. , , __ 20 Page F Faunas, age of the ____________________________ 10—14 comparisons with other ___________________ 14—15 Fernie formation _____________________ 14, 27 Rock Creek member. _ 9, 12 freibrocki, Calliphylloceras _____________________ 3 G Gastropods ___________________________________ 20 Geographic distribution ______________________ 15—19 Gervillia sp ___________________________________ 21 Gonolkites. . _ Gowericeras._ gracilis, Arctocephalttes ........................ Arctocephalites (Cranoeephalites) ....... 24; pl. 5 Cranocephalites ___________________________ 24 Gracilisphinctes. . _ _ 26 Grammatodon sp... Greenland, Callovian versus Bathonian ins". 12—13 grossicostatum, Macrophyllocems ______________ 3 Grosrouvria ________________________________ 10, 13, 28 sp _______ 2,3 Gryphaea._.. 9 impressimarginata _________________ 5,9,10,20,21 Gypsum Spring formation ____________________ 6 H haguei, Idonearca ______________________________ 21 hebetus, Xenocephalz’tesh hickersonensz’s, Pararemecketa" Holcophylloceras ____________________________ 2, 19, 22 sp __________________________________ 20,22; pl. 1 Homoeoplanulites _____________________________ 26, 27 I iddingsi, Isocyprz‘na ___________________________ 21 Idonearca _______________________________ 21 Miami ____________________________ 21 rockymontana _____________________________ 21 impressimarginata, Gryphaea ___________ 5,9,10,20,21 inaequiplicalus, Pholadomya. 21 Im'skin Peninsula _____________________________ 2-3 Inoceramus ezimz‘us ___________________________ 20 porrectus .................................. 20 sp ________________________________________ 20,21 inornata, Tancredia____ ___________________ 21 intermedia, Arctocephalites (Crunocephalites) pompeckji _________________________ 23 intermedia, Cranocephalites pompeckji _________ 24 intermedium, Kheraiceras _____________________ 2, 3 Isocyprina _________________________ 20,21 iddingsz’ ___________________________________ 21 K Kellawaysz‘tea _________________________________ 25 ozyptychoz’des ______________________________ 25 (Kellawaysites) shelikofana, Reineckez‘a. _ 25 Kepplen‘tes ______________________________ 10, 13 (Seymourz'tes) __________________ 13, 14 tychonis ___________________________________ 3, 13 sp ________________________________________ 3 Kheraz'ceras ______ intermedium___ 2,3 parvz’forme ________________________________ 2, 3 sp ________________________________ 3 kingi, Pholadomya _____________________ 21 Pinna _________________ 21 kochi, Articoceras ______________________________ 15 C-3 1 0—32 Page koem‘gz’, Proplanulites ________________________ 12 Kosmoceras __________________________________ 13 Kosmoceratidae ______________________________ 14 L laminatus, Macroeephalites ___________________ 24 Leptosphinctex _____________ _ 2 Lilloettm.. . 10, 51 Lrssoceras ________ . 2, 3 Literature cited _______________ 28—29 Lopha sp _____________________________________ 10, 21 Lower Cornbrash formation, England ________ 27 Lucina sp ____________________________________ 20, 21 M Macroeephalitidae ___________________________ 2 Macrocephalitea laminatus .................... 24 macrocephalus ____________________ 10, 12, 13, 20 pompecka' _______________________________ 23 Macrocephalus ____________________ 13 macrocephalus, Macrocephalites.... .._ 10, 12, 13, 20 Macrophylloceras grossicostatum ______________ 3 maculutus, Arctocephalites ______________ 21 Arctocephalites (Cranocephalites)... . 25; pl. 4 Cranocephalites ____________________ 25 mutisconensis, Siemiradzkia. . 28 mclearm’, Ozytoma _____ _ 21 meeki, Astarte _______________________________ 21 Meleagrinella curta... 21 sp _______________ 20 Metacephalites ______________________________ 14 metastatus _______ 24 metastatus, Metacephalites _____________________ 24 metastatus sweetgrassensis, Arctocephalites ...... 24 Miccocephalites ........ 14 Modiolus 70817.. ... 21 sp _________________________________ 10, 20, 21 Montana and Alaska, Callovian versus Batho- nian in ___________________________ 13 Montana, evidence from __________ 12 Montana, western ________________ 5—10 montanaensz’s, Trigonia ___________ morion, Astarte (Coelastarte) _____ Morphoeeratidae..._ 13 munda, Corbula ______ 9 N Normanm’tea __________________________________ 12, 19 sp _______________ 10 Nucula sp ........... 21 O oblatum, Chondroceras _________________________ 21 oblongata, Pleuromya ________________________ 21 Oecotraustes __________________________________ 2, 22 (Paroecotmustes) sp _______________ 20, 22; pl. 1 Oppeliidae __________ 2 Oppeliinae. 2 Oppelz'a __________ 22 (0:5ycerites).. 2,3 Ostrea strigilecula sp _________________________ Oxycerites ______________________ (Ozycerites), Oppelia 2,3 oxyptychoides, Kellawaysites ..... 25 Own/tome mclearm‘ _______________ 21 sp ________________________________________ 20, 21 P packardi, Astarte ______________________________ 21 Paleogeographic considerations _______________ 13—14 palliseri, Stemmatoceras ______________________ 10 Paraacdocems ________________________________ 10, 15 INDEX Page tonnieme ________________________________ 4 Parallelodon eumshewaensis _____________ ___. 20 simillimus ________________________________ 20 Parareineckeia .............. 2, 3, 4, 12, 13, 14, 19, 20, 25 hickersonensis ______ shelikofana. sp ________ Paroecotraustes ______________ 22 (Paroecoiraustes) sp., Oecotmustea ....... 20,22; pl. 1 Parkinsonia _______________________________ 28 Parkinsonidae.. 13 parm’forme, Kheraiceras ..... 2,3 Pelecypods _________________________________ 2, 12 Peninsula north of Chinita Bay _____________ 3 Pentacrinus asteriscus ________________________ 21 Perlsphinetidae ______________________________ 2 Pholadomua inaeqm’plicatus _________ . 21 kiwi. _ 21 sp ________ _ 20 Phylloceras bakeri. _ 3 Phylloceratidae _ 2 Pinna kingi ________________ 21 Piper formation ____________________________ 9 Placunopsis sp ________________________________ 21 Planisphinctes _______________________________ 2S Platessz'formis, Cumptonectes ________________ 10,21 platynotus, Arctocephalites _____________________ 21 Arctocephalites (Cranocephalites) ______ 25; pl. 4 Pleuramga carlottensis ______________________ 20 oblongata __________ . 21 subcompressa. _ 10,21 sp .......... _ 20 Polyplectz'tes . . _____________________ 2 pompecka', Arctocephalites _____________________ 20 Arctocephalz’tes (Cranocephalites)-. 20, 22,23; pl. 1 Cranrocephaliles ____________________ 15, 22, 23, 24 Macrocephalites __________________________ 23 pompeckji intermedia, Arctocephalites (Crane- cephalites) ________________________ 23 Cranocephalites ________________________ 24 Porrectus, Inoceramus.... - 20 procerites _____ __._ - 26,28 englm’ _ 26,28 sp ______ 27 spp ________________________________ 26 Procerithium (Rhobdacolpus) sp ______________ 21 Proplanulitex _______________ 13 koem’gi ________ 12 Protocardz'a schucherti _______________________ 21 51;) ______________________________________ 20, 21 Paeudocadoceras ______________________________ 13, 15 Pseudoperisphinctinae. _ 2 punctam, Cercomya __________________________ 21 Q Quensiedtia sp ________________________________ 21 R Reineckeia (Kellawaysites) shelikofana _________ 25 Reinckez’a _______________________________ 12, 15, 25 Reineekeiidae ___________________________ 2, 13,20 Results, summary of ________________________ 19—22 (Rhabdocolpus), Procerithz'um sp. ... 21 Rierdon formation _______ - 9, 10, 12, 17, 20, 25 rierdanense, Arcticoceras.... .......... ___ 25 Rock Creek member, Fernie formation _______ 9,12 rockymontana, Idonearca _______________________ 21 Rocky Mountain front north of the Sun River. 5—10 maiz‘, Modiolus ________________________________ 21 S Sawtooth formation” _ . 5, 9, 10, 12, 13, 15,17, 18, 19,20 21, 22, 23, 24, 25, 27, 28 Page sawtoothensia, Arctocephalites __________________ 23, 24 Arctocephalites (CranocephalitesL. 21, 24; pl. 24 saypoensis, Arctocephalites ________ 10,21,22,23; pl 6 schucherti, Protocardza.. ______ 21 semiplanata, Thracia._ _ 20 (Seymourites), Kepplerztes._ ______ 13,14 shelikofana, Pararez’neckeia _____________ 20, 26; pl. 7 Reineckeia (Kellawaysites) ________________ 25 Siemz'radzkia ______________________ 2, 3, 13, 19, 20, 28 aurigera _______________________ _. 20, 28; pl. 28 berthae ___________________________________ 28 matisconensz’s _________________ Sigalocems callom‘e nse. _ . simillz‘mus, Parallelodon ____________ Snowshoe formation ..... sphaen'cus, Arctocephaliles.. Sphaeroceras ____________ era. . . . Stemmatoceras ________ palliseri ___________ Stratigraphic summary ____________ strigilecula, Ostrea __________________ stygius, Campionectes ______________ subcompressa, Pleuromya __________ Summary, stratigraphic ___________ Sundanee formation _____ Sun River, Rocky Mountain front north of... 5—10 sweetgrassensis, Arctocephalz‘tes metastatus _____ 24 Systematic descriptions _______________________ 22—28 T Talkeetna formation _________________________ 4 Talkeetna Mountains. . _ . _ . talkeetnanus, Cobbaniles inornalm. sp ________________ Thracia semiplanata ______________ 20 sp ____________________________ 20 tonm'ense, Paraeadoceras _____________________ 4 trafalgarensz's, Trigonia _______________________ 21 Trigonarca _________________________________ 20 tumida.. Trigom‘a conradi.... montanaensis. trafalgarensis.._. sp ______________ tumida, Trigonorca.... Tuxedni formation ________________________ 16, 20 Bowser member ________________________ 2, 3, 10, 16, 17, 19, 20, 22, 23, 24, 26, 28 Cynthia Falls sandstone member... . - _ _ . 2 tychom’s, Kepplerites .......................... 3,13 V m'cariua, Xenocephalites ....................... 3, 23 uulgan‘s, Cranocephalz‘tea ...................... 23, 24 W Western interior of Canada. _______ 14-15 Western Montana ........................... 5—10 X Xenocephalites ..................... 2, 4, 13, 15, 19, 22 hebetus ................................... 3 vicarius ................................... 3, 23 sp ................................ 3, 21, 22; pl. 6 Z Zigzagiceratinae .............................. 2, 26 PLATES 1—8 PLATE 1 [All figures natural size] FIGURE 1. Holcophylloceras sp. (p. 0—22). USNM 130754 from USGS Mesozoic 100. 22698. 2—4. Oecotraustes (Paroecotraustes)? sp. (p. 0—22). Lateral and ventral views, USNM 130747 from USGS Mesozoic 100. 24116. 5—13. Arctocephalites (Cranocephalites) pompeckji (Madsen) (p. 0—23). 5—8. Plesiotypes, USNM 130753 from USGS Mesozoic loc. 22698. Fig. 8 shows suture line drawn at beginning of complete body chamber of specimen shown on fig. 6. 9, 11—13. Plesiotype, USNM 130751 from USGS Mesozoic 100. 21284. Fig. 9 shows suture line drawn near beginning of complete body chamber. 10. Plesiotype, USNM 130752 from USGS Mesozoic 100. 21283. Shows nearly complete body chamber. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-C PLATE 1 11 ' 7 12 ‘ 13 HOLCOPHYLLOCERAS, OECOTRA USTES (PAROECOTRA USTES)?, AND ARCTOCEPHALITES (CRANOCEPHALITES) PLATE 2 [All figures natural size] FIGURES 1—8. Arctocephalites? alticostatus Imlay, n. sp. (p. C—22). 1, 2. Paratype, USNM 130758 from USGS Mesozoic loc. 20752. 3. Paratype, USNM 130760 from USGS Mesozoic 100. 21308. 4—6. Paratype, USNM 130759 from USGS Mesozoic 100. 20011. 7, 8. Holotype, USNM 130757 from USGS Mesozoic 100. 20752. 9, 10. Siemiradzkia? cf. S. aurigem (Oppel) (p. C—28). Specimens USNM 130755 from USGS Mesozoic 100. 22698. Note lateral lappets. 11—19. Arctocephalites (Cranocephalites) costidensus Imlay, n. sp. (p. 0—24). 11—13, 19. Paratypes, USNM 130749 from USGS Mesozoic 10c. 24117. Suture line drawn from specimen shown on fig. 19. 14, 15. Holotype, USNM 130745 from USGS Mesozoic 100. 24116. 16. Paratype, USNM 130748 from USGS Mesozoic loc. 22712. 17, 18. Paratype, USNM 130746 from USGS Mesozoic 100. 24116. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—C PLATE 2 ARCTOCEPHALITE87, SIEMIRADZKIA?, AND ARCTOCEPHALITES (CRANOCEPHALITES) PLATE 3 [All figures natural size] FIGURES 1—10. Arctocephalites (Cranocephalites) sawtoothensis Imlay (p. 0—24). 1, 2, 4, 5. Lateral and ventral Views of plesiotypes, USNM 130766 from USGS Mesozoic 100. 18718. 3. Plesiotype, USNM 130769 from USGS Mesozoic 100. 27047 showing sharp ribbing. 6, 9, 10. Plesiotype, USNM 130767 from USGS Mesozoic 100. 27040 showing disappearance of ribbing on the body chamber. 7. Plesiotype, USNM 130768 from USGS Mesozoic 100. 27042. 8. Plesiotype, USNM 130770 from USGS Mesozoic 100. 19601. GEOLOGICAL SURVEY PROFESSIONAL PAPER 3747C PLATE 3 AR CTOCEPH ALI TES ( CRA N O CEPH A L] TES) PLATE 4 [All figures natural size] FIGURES 1, 3, 5. Arctocephalites (Cranocephalites) of. A. maculatus (Spath) (p. C—25). 1, 3. Lateral views of two specimens, USNM 130744 from USGS Mesozoic loc. 22652. 5. Adult specimen, USNM 130733 from USGS Mesozoic loc. 19184 showing half a whorl of body chamber. 2, 4, 6. Arctocephalites (Cranocephalites) sawtoothensz's Imlay (p. 0-24). 2, 4. Plesiotype, USNM 104150 from USGS Mesozoic 100. 19601. This specimen was originally described as Arctocephalites metastatus (Buckman) var. sweetgrassense Imlay 6. Holotype, USNM 104148 from USGS Mesozoic loc. 19184. QWENQVMNRHDOZVWDV MWENQVERNDOEDNQ v BBAVAA 0.3m ”.3?ij QMDm QmDm Q fl§¥8m§ 3:35 . . . figuasuawaa mwfifiigsm $595 :mmow oz can afiigvcg s§§m ll mSSERHE . . $933 3.3:“ «Em 33?: ES:% mfiguwx mmfigxwwm . n 332:: S§§m w a 1 m§v§§ SSBSN Um. . m mmfigigsm .333? mSEflEsaN m. 2%. h. M. u H .mBuSEEdeE?» W. .338. §§§e§$v~ .Sscu mwfiffleussb m .1 E83 52$ 5 W 358:? wxgxgs can mwfiggs can a... 38 SSS m s: u SWoEfiN Swgsmmck .233» Eggamok W. Sing ESSN M. Q . S. as...“ «Ed gfigei waxwfifiik c5 M 8525 E38 oz 338%: can .wgufigggvaé 53:8 m. 853.3 =mm8 oz :nEuBEm £353: asswueswsmqmasm .sw‘SwmaE Sufwifix 3:35 W. . . . . . . 3mg :JMMMNE v :oM20 can :SMEJEB 53$? mac—ME awAmmfloozficwwaw :mEEw :ofiwwmmM—Wozm_fim mw . 3mm: :wEo:wW » V . Sham mefiv .Nmmfi mg # H EEcEmO E minnow Semiouqfigo 15.5: E mime 055322—50 . A :— 0 c _ . m . . a H u 3 .3me Ga: 32 = x < 33 = x < 03me 5 £38 3353225 . . . . . . . . . . «Emmi 2: E 2.38 £31335an as... E m=mm£ ofimtwaofiwgo 395m $035.5: E 8:8 Eavaflm wwwflm =§E=fl D—6 LOGTOWN RIDGE FORMATION The Logtown Ridge formation at its type locality on the Cosumnes River ranges in age from Callovian to late Oxfordian, or early Kimmeridgian. Evidence for a Callovian age consists of the presence of the ammonite Pseudocadoceras in the basal 600 feet of the formation. This genus in Europe ranges from the basal part of the zone of Sigaloceras callom'ense into the zone of Peltoceras athlete (Callomon, 1955, p. 255), and is absent from the highest and lowest parts of the Callovian stage. A similar range is indicated in southwest Alaska where Pseudocadocems occurs only in the upper two-thirds of the Chinitna formation associated with other ammonites that are correlated with the Erymoceras coronatum, Kosmoceras jason, and the upper part of the Sigaloceras calloviense zones of Europe (Imlay, 1953b, p. 48—54). Significantly, Pseu- docadoceras is absent in the lower 1,000 feet of the Chinitna formation (Imlay, 1953b, p. 51—53) and in the upper 800 to 1,500 feet of the underlying Bowser member of the Tuxedni formation, although these parts have furnished early Callovian ammonites. This absence of Pseudocadoceras in the lower part of the Alaskan Callovian is comparable to its absence in the Macrocephalites macrocephalus zone at the base of the European Callovian. It follows, therefore, that the presence of Pseudocadoceras in the lower part of the Logtown Ridge formation in California shows not only that the lower part is Callovian but that it is younger than the earliest Callovian of Europe and Alaska (figs. 1, 2). Further evidence concerning the age of the lower part of the Logtown Ridge formation is furnished by the particular species of Pseudocadoceras that are pres— ent. These include P. grewingki (Pompeckj) and prob— ably, also, P. crassicostatum (Imlay, 1953b, p. 94, pl. 49, figs. 19, 20, 22—24). Of these species, P. grewingki (Pompeckj) in Alaska is the longer ranging, but its lowest occurrence is in beds that are correlated with the upper part of the Sigalocems calloviense zone. P. crassicostatum Imlay has been found only in the upper part of the range of P. grew’mgki (Pompeckj) in beds that are correlated with the Kosmoceras jason and Erymocems coronatum zones of Europe (Imlay, 1953b, p. 51—53). By comparisons with Alaska, therefore, the species of Pseudocadoceras that are present in the lower part of the Logtown Ridge formation suggest a middle rather than an early Callovian age. The upper part of the Logtown Ridge formation is dated as latest Oxfordian or early Kimmeridgian by the presence of the ammonite Idoceras afl’. I. planula (Heyl) in Zeiten. This species belongs to a group of species that in Mexico has been found only in the early SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Kimmeridgian (Burckhardt, 1912, p. 102; 1930, p. 64; Imlay, 1939, p. 21). In Europe, however, the group occurs also in beds of latest Oxfordian age (Wegele, 1929, p. 76—78; Arkell, 1956, p. 114, 115) at the top of the zone of Epipeltoceras bimammatum. A late Oxford- ian age for the upper part of the Logtown Ridge forma- tion is favored by the resemblance of the specimen of Idoceras present to a species in the late Oxfordian of Europe and to the fact that the apparently strati- graphically higher Mariposa formation in Calaveras, Mariposa, and Eldorado Counties has furnished ammo- nites that likewise are as old as late Oxfordian. It is possible, of course, that beds that are mapped as the Mariposa formation in one county are the lateral equivalents of beds mapped as the Logtown Ridge formation in another county. Dating the upper part of the Logtown Ridge forma- tion on the Cosumnes River as latest Oxfordian to early Kimmeridgian, based on the ammonite Idoceras, appears to be contradicted by the presence of a large specimen of Peltoceras of late Callovian age, described herein, from the Mariposa formation on nearby Big Indian Creek. It is questioned, however, whether Peltocems actually was collected from the Mariposa formation or Whether it came from some beds within the Logtown Ridge formation. When the Peltoceras was discovered in 1914, the term Logtown Ridge had not been defined, and it seems probable that any beds from Amador County that furnished Jurassic ammo- nites would have been referred to the Mariposa forma- tion. Furthermore, the Logtown Ridge formation is exposed immediately west of Indian Creek and would seem to be a more likely source for a large ammonite than the relatively softer slates of the overlying Mari- posa formation. A stratigraphic position for Pelto- ceras near the middle of the Logtown Ridge formation appears likely, provided that the specimen of Idoceras was actually obtained from the upper part of that formation, as is indicated by the matrix of the specimen. COLFAX FORMATION OF SMITH, 1910 The Colfax formation of Smith crops out near Colfax in the southwestern part of the Colfax quadrangle, Placer County, and has furnished several ammonites of Callovian age. These include, in particular, Ammonites colfaxi Gabb, which Smith (1910, chart facing p. 217) considered to be of Portlandian age but which is herein identified with the Callovian genus Grossouvm'a. This dating is upheld by the presence of Kepplem'tes lorin— clarki Imlay, n. .sp., and K. (Gower'icems) lindgreni (Hyatt) from other localities near Colfax. In Europe Kepplem'tes and its subgenus Gowericeras range through the lower two-thirds of the early Ca1- lovian zone of Sigaloceras callom'ense (Callomon, 1955, JURASSFC ANLIVIONITES, SIERRA NEVADA p. 255) except for two possible occurrences of Kep- pler'ites in the zone of Macrocephalites macrocephalus (Arkell, 1953, p. 117, 119; 1956, p. 120). The sub- genus Seymourites in the Boreal region and in the western interior of North America has a similar range (Spath, 1932, p. 138, 139, 145, 146; Imlay, 1953a, p. 7, 8, 17, 18). In the Cook Inlet region, Alaska, Seymour- ites occurs rarely in the lower part of the range of Pseudocadoceras in beds that are correlated with the Kosmoceras jason and the upper part of the Sigaloceras callozriense zones of Europe. Gowericeras likewise occurs rarely with Pseudocadoceras in beds that are correlated with the upper part of the Sigaloceras callom'ense zone. Both subgenera are more common, however, below the range of Pseudocadocems (Imlay, 1953b, p. 50, 52) in the basal part of the Chinitna formation which is correlated with the lower part of the Sigaloceras cal— lom'ense zone. By comparisons, the occurrences of Kepplem'tes and Gowem'ceras in the Colfax formation of Smith near Col- fax, Calif., might be as young as the Pseudocadocems beds at the base of the Logtown Ridge formation, but most probably are somewhat older and equivalent to some part of the Cosumnes formation. In particular, the resemblance of Keppler’ites (Gowericeras) lindgren'i (Hyatt) to K. (Gowericeras) sp. from Alaska (Imlay, 1953b, p. 100, pl. 53, figs. 6, 7, 10), favors a correlation with the basal part of the Chinitna formation well below the range of Pseudocadoceras. Similarly, the greater resemblance of Kepplerites lorinclarki Imlay, n. sp., to species of Kepplem'tes from the basal Callovian of Europe (Buckman, 1922, pls. 286, 289a, b; Arkell, 1954, p. 118, and 1956, p. 120) than to any described North American species of Kepplerites suggests a very early Callovian age, perhaps corresponding to the Macro- cephal’ites macrocephalus zone of Europe. MARIPOSA FORMATION The Mariposa formation proper and similar slatey beds, extending from Eldorado County southward to Madera County, have furnished the pelecypod Buckie at many places. The specimens of Buchia present have all been referred by Imlay (1959, p. 157) to B. concentrica (Sowerby), which in Eurasia ranges from the upper Oxfordian zone of Perisphinctes cautisnigme to the lower Kimmeridgian zone of Aulacostephanus pseudomutabilis. A similar age for the Mariposa formation is shown by some of the ammonites that are associated with Buch’ia. These are listed by localities as follows: Taramelliceras? (Proscaphites?) ozoic 10c. 901. Amoeboceras (Amoebites) dubium (Hyatt) Mesozoic 10c. 719. Perisphinctes (Discosphinctes) virgulatiformis Hyatt Mesozoic 100. 901. dentiaulatum (Hyatt) Mes- D—7 P. (Dichotamosphinctes) cf. P. muhlbachi Hyatt Mesozoic 100. 901. Subdz'chotomoceras? aff. S. filiplez (Quenstedt) Mesozoic locs. 902, 903, 904. Other ammonites from the Mariposa formation, not associated with Buchia, are: Perisphinctes (Dichotomosphinctes) muhlbachi Hyatt, Mesozoic 100. 27517. P. (Dishotomosphincles) of. P. muhlbachi Hyatt, Mesozoic 100. 27460. P. (Dichotomosphinctes?) spp. Mesozoic locs. 490, 24317. Concerning the Eurasian ranges of these ammonites, Tammelliceras ranges through the Oxfordian and Kimmeridgian, and the subgenus Proscaphites is typically Oxfordian (Arkell, 1957, p. L 280—281). Amoeboceras ranges through the upper Oxfordian and the lower Kimmeridgian. The subgenus Amoeb’ites is known only from the lower Kimmeridgian (Arkell, 1957, p. L 306—307; Spath, 1935, p. 30—36). Dichoto— mosphinctes ranges through the Oxfordian (Arkell, 1957, p. L 322) and occurs rarely in the lower Kim- meridgian (Arkell, 1937, p. 61). Discosphinctes in central and southern Europe ranges through the zones of Gregorycems transversarium and Epipeltocems bimam- matum of the upper Oxfordian (Arkell, 1937, p. XLVII, p. 61) and appears to be transitional to Lithacoceras of the lower and middle Kimmeridgian (Arkell, 1937, p. LII). Subdichotomoceras ranges through the Kim— meridgian (Arkell, 1957, p. L 328), but is most char- acteristic of the lower and middle Kimmeridgian. Judging from the ranges of these ammonite genera, the Mariposa formation might be equivalent to the entire Oxfordian and Kimmeridgian stages of Europe. However, the association of certain ammonites with other ammonites, or with Buckie concentrica (Sowerby) indicates that only the late Oxfordian and the early Kimmeridgian are represented by fossils in the Mariposa formation. Thus the late Oxfordian is represented by the faunule at USGS Mesozoic locality 901, which contains Per- isphz'nctes (Discosphz'nctes) virgulatz'formis Hyatt, P. (Dichotomosphmctes) cf. P. muhlbachi Hyatt, Tara,- mellicems? (Proscaphites?) denticulatum (Hyatt), and Buchia concentrica (Sowerby). Of these, the presence of Buchia, is evidence of an age not older than late Oxfordian, both Dichotomosphz'nctes and Proscaphites are much more likely to be Oxfordian than Kimmer— idgian in age, and Discosphz'nctes is typical of the late Oxfordian. Furthermore, the perisphinctid am— monites present are closely similar to species in the late Oxfordian of Cuba and Mexico. P. (Discos- phinctes) virgulatiformz's (Hyatt) is nearly identical with Perisphz'nctes (Discosphmctes) carribeanus J aworski from the late Oxfordian of Cuba (Jaworski, 1940, p. 109, pl. 3, figs. 1, 2; pl. 4, fig. 5 ; pl. 7, fig. 6) and Mexico D—8 (Burckhardt, 1912, p. 35, pl. 7, figs. 4—14). P. (Di- ckotomospkinctes) muklbecki Hyatt greatly resembles P. (Dickotomospkinctes) durengensis Burckhardt (1912, p. 16, pl. 3, figs. 1, 2) from Mexico. The early Kimmeridgian is equally strongly repre> sented by the subgenus Amocbites at USGS Mesozoic locality 719 judging by the range of that ammonite in Eurasia and Greenland. It is probably represented also by the ammonites referred to the Kimmeridgian genus Subdickotomoceres from USGS Mesozoic localities 902, 903, and 904 as those ammonites are associated with Buckie concentrice (Sowerby) of late Oxfordian to early Kimmeridgian age. None of the fossil collections from the l\/Iariposa formation afford any evidence of an age younger than the early Kimmeridgian. An age as old as early Ox- fordian is possible for those collections containing Perispkinctes (Dickotomospkinctes) muklbechi Hyatt at USGS Mesozoic locality 27517 and comparable am- monites at USGS Mesozoic localities 490, 24317, and 27460 that are not associated with Buckie. Such an age seems unlikely, however, considering that the ammonites in question are closely similar to P. (Di- ckotomospkinctes) durengensis Burckhardt from the upper Oxfordian of Mexico. Fossils other than Buckie and the ammonites listed above are scarce in the Mariposa formation. They are poorly preserved and have not been studied carefully and probably would not be useful in dating the for- mation. Such fossils include “Belemnites” pecificus Gabb (USGS Mesozoic locs. 490, 901, 903, 904, 1982, 25638), Avicule? sp. (USGS Mesozoic loc. 901; see Hyatt, 1894, p. 429), Entolium? eurerium (Meek) (USGS Mesozoic locs. 904, 1983), Entolium? sp. (USGS Mesozoic loc. 18937), Nucule? sp. (USGS Mesozoic 100. 18937), Lime? sp. (USGS Mesozoic locs. 27398, 27459), Ceritkium? sp. (USGS Mesozoic loc. 901), and Turbo? sp. (USGS Mesozoic 100. 901). In summation, the Mariposa formation, if dated on the basis of ammonites and the pelecypod Buckie, is of late Oxfordian and early Kimmeridgian age. The evidence shows that some of the beds are locally as old or perhaps slightly older than the upper part of the Logtown Ridge formation on the Cosumnes River. Conceivably some of the Mariposa formation that has not furnished fossils could be younger than early Kimmeridgian. This seems unlikely, however, consid— ering that the Geological Survey geologists have found Buckie concentrice (Sowerby) at 16 localities and that the collections in the museums in California contain this species from many other localities, but nowhere in the western part of the Sierra Nevada has a specimen of the younger Buckie rugose (Fischer) been discovered. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Similarly in the Galice formation in southwestern Oregon, which formation is lithologically and faunally similar to the Mariposa formation, Buckie concentrice (Fischer) has been found at 18 localities, but not a single specimen of Buckie rugose (Fischer) has been found. This contrasts With the abundance of Buckie rugose (Fischer) from northwestern Washington north- ward into northern Alaska. Furthermore, in south— western Oregon, the Galice formation is overlain with angular unconformity by the Riddle formation that con— tains ammonites and Buckie piockii (Gabb) of Port- landian—late Tithonian ages (Imlay and others, 1959, p. 2780). The time represented by the unconformity seems to correspond with the middle and upper Kim— meridgian and perhaps the early Portlandian, which is the time represented in Alaska and the Arctic region by Buckie rugose (Fischer). It seems, therefore, that failure to find this species of Buckie in southwestern Oregon and in Claifornia is related to diastrophism and not to an unfavorable environment or to insufficient collecting. MONTE DE 030 FORMATION The Monte de Oro formation (Turner, 1896, p. 548, 549) contains mollusks of late Oxfordian age to early Kimmeridgian age (figs. 1, 2). The evidence consists mostly of one fairly well preserved specimen of the am- monite Perispkinctes (Dickotomospkinctes) (see pl. 4, figs. 4, 7) that is similar to P. (Dickotomospkinctes) elisebetkeeformis Burckhardt (1912, p. 31, pl. 6, figs. 1—5) from the late Oxfordian of Mexico and of two crushed specimens of Buckie (see pl. 5, figs. 7, 8) that bear very fine radial striae and probably belong to Buckie concentrice (Sowerby). The specimens of Buckie were obtained along the western side of some plant—bearing beds on the north bank of the Feather River from 3 to 4 miles northeast of Oroville (USGS Mesozoic loc. 4801). With them occur the pelecypods Ostree, Modiolus, Trigonie, Meleegrinelle, Lime, Chlamys?, Tencredie, a gastropod, belemnites, and plant fossils. Most of the molluscan genera are represented by only a few specimens, but Meleegrinelle occurs in abundance. The association of Buckie with Meleegrinelle is interesting as Meleegrinelle became scarce after the appearance of Buckie (Imlay, 1959, p. 156) in the late Oxfordian. The fact that Meleegrinelle is repre- sented by many specimens and that Buckie is repre— sented by only two specimens suggests, therefore, that the beds containing these genera represent the time during which Buckie first appeared as a distinct genus. It is possible, however, that the relative abundance of the two genera is related to environ- mental conditions. , JURASSI'C AMMONITES, SIERRA NEVADA In contrast to the evidence afforded by the mollusks, the flora in the Monte de Oro formation has furnished a correlation with the Bajocian of Europe (Ward, 1900, p. 340-377; Fontaine, 1905, p. 48—145; Knowlton, 1910, p. 39, 43, 44). Furthermore, some plant-bearing beds in Douglas County, Oreg. that contain the same plant species have been referred also to the Bajocian (Knowlton, 1910, p. 33—64). These beds in Douglas County, Oreg., all occur, however, within sequences that contain Buchia piochii (Gabb) (Diller, 1908a, p. 376—383; Imlay and others, 1959, p. 2781), a fossil that is characteristic of the latest Jurassic (Portlandian- Tithonian) (Imlay, 1959, p. 159). Because of this association in Oregon, the comparable plant-bearing beds in the Monte de Oro formation near Oroville were at one time referred also to the Portlandian (McKee and others, 1956, p. 3). However, the dis- covery of Buchia cf. B. concentrica (Sowerby) within the same beds as the plants near Oroville and of Dicho- tomospkinctes in associated beds shows that the Monte de Oro formation is considerably older; that is, late Oxfordian to early Kimmeridgian. Therefore, on the basis of the mollusks, the plant species in question range from late Oxfordian to Portlandian, inclusive, and are much younger than the Bajocian. A middle Late Jurassic age for the Monte de Oro formation is not out of harmony with the plant evidence because many species of plants have long ranges. Also, such an age means that the Monte de Oro formation is correl‘ative, at least in part, with the Mariposa slate farther south, which correlation fits very well with present knowledge concerning the Jurassic paleo- geography of California. A Portlandian age for the Monte de Oro formation does not fit because beds of that age are not known anywhere on the east sides of the Sacramento and San Joaquin Valleys. COMPARISONS WITH OTHER FAUNAS TAYLORSVILLE AREA, CALIFORNIA Beds of Callovian age are represented near Taylors- ville by the Hinchman tuff, Bicknell sandstone, and Foreman formations of Diller (1892, p. 370—394) on Mount Jura; by the North Ridge formation of Crick- may (1933b, p. 896, 901) on Mount Jura; and by the Kettle formation of Diller (1908b, p. 84) near Hosselkus Creek east of Mount Jura. In the Hinchman tufi and Bicknell sandstone occur corals and mollusks that Hyatt (in Diller, 1908b, p. 49—52) and Crickmay (1933b, p. 901) considered to be of Callovian age. In the North Ridge formation of Crickmay, which overlies the Hinchman tuff, was found the ammonite Ohoflatz'a hyattz’ (Crickmay) (1933b, p. 901, 913, 914, pl. 32, fig. 3, 583565 0—61—2 D—9 pl. 33) that Arkell (1956, p. 554) said resembled Euro- pean species from the Zl/Iacrocephalites macrocephalus zone. From the lower part of the overlying Foreman formation, was obtained Reineckez'a (Reineclceites) dillem' (Crickmay) (1933b, p. 902, 914, pl. 32, fig. 2, pl. 34, figs. 1—5). Fragments of the same subgenus occur likewise in a collection from the Foreman formation made by Diller (1908b, p. 56, USGS Mesozoic 100. 3143). From talus near the middle of the Foreman formation, Vernon McMath, University of Oregon, collected speci- mens of Pseudocadoceras (identified .by Imlay). These ammonites show that the lower and middle parts of the Foreman formation are of Callovian age not older than the European zone of Sigalocems callom'ense or younger than the zone of Peltoceras athlete. From the Kettle meta-andesite near Hosselkus Creek, Vernon McMath and the writer obtained specimens of Pseudocadoceras schmz'dti (Pompeckj), P. cf. P. grew- ingki (Pompeckj), and Choflatz‘a sp. (USGS Mesozoic loc. 26784). Some hundreds of feet higher strati- graphically were obtained Cadocems sp. juv., Xenoceph- elites? sp., Paracadoceras? sp., and Pseudocadoceras cf. P. grewz’nglci (Pompeckj) (USGS Mesozoic locs. 26785, 26786). These ammonites indicate an early middle Callovian age comparable with that of the loWer part of the middle third of the Chinitna formation in the Cook Inlet region, Alaska (Imlay, 1953b, p. 53). If Paracadoceras and Xenocephalites are correctly identi— fied, the age of the beds is probably not younger than the Sigaloceras calloviense zone of Europe. On the basis of these ammonites, the lower and mid- dle parts of the Foreman formation and a considerable thickness of the Kettle meta-andesite of the Taylors- ville area may be correlated with the lower part of the Logtown Ridge formation and probably the adjoining transitional upper part of the Cosumnes formation on the Cosumnes River. Stratigraphically, the North Ridge formation of Crickmay, the Hinchman sand- stone, and the Bicknell sandstone, all of Callovian age, could be correlative with part of the Cosumnes forma- tion beneath the beds containing Pseudocadoceras. Faunal evidence is lacking for the existence of Ox— fordian or younger Jurassic beds in the Taylorsville area. Crickmay (1933b, p. 902, 903) described some new formations above the Foreman formation and assigned them a middle Late Jurassic to Tithonian age, but he did not publish any evidence. Taliaferro (1942, p. 100) considered that the Foreman formation was equivalent to the Mariposa formation but that could be true only for the upper part that has not fur- nished fossils. The fact that the Foreman formation includes slates similar to those in the Mariposa forma- tion is not a sound basis for correlation because similar D—lO slates occur in the beds of Callovian age near Colfax and locally in the Cosumnes formation, which are both appreciably older than the Mariposa formation. CENTRAL OREGON Lower Callovian ammonites have been found in the Izee—Suplee area of central Oregon throughout about 9,000 feet of beds ranging from the upper part of the Snowshoe formation of Lupher (1941) to within 300 feet of the eroded top of the Lonesome formation of Lupher (1941), which is the youngest Jurassic formation exposed. The collections from the basal part of Lupher’s Trowbridge shale have been mentioned by Lupher (1941, p. 264, 265). They include Lilloettia buckmamj (Crickmay) and Kepplerites (Gowerz'ceras) cf. K. spinosum (Imlay). Ammonites from the upper part of the Snowshoe formation, as mapped by William Dickenson of Stanford University, include Choflatz'a. sp., Xenocephalites vicarius Imlay, Lilloettz'a sp., and Gow- ericeras cf. 61'. spinosum Imlay (USGS Mesozoic locs. 26778—26780). Ammonites from the Lonesome forma— tion, obtained at various levels from near the base to within 1,000 feet of the top, belong mostly to the genus Xenocephalites, and some are identical with X. vicarius Imlay (USGS Mesozoic locs. 26781, 26782, 27372, 27373). One small ammonite obtained 300 feet below the top of the Lonesome formation is probably an im- mature specimen of Xenocephalites (USGS Mesozoic loc. 27383). The ammonite Pseudocadoceras is prob- ably represented in the Lonesome formation in a collection from the southeast corner of sec. 25, T. 19 S., R. 28 E. Judging from these collections, most of the Callovian in central Oregon represents only the lower part of the Callovian stage and is comparable to the lower half of the Chinitna formation and to the upper part of the Bowser member of the Tuxedni formation in the Cook Inlet region, Alaska (Imlay, 1953b, p. 51—53). The presence of Pseudocadocems? in the Lonesome forma- tion of Lupher (1941) suggests that some part of that formation is as young as the Foreman formation of the Taylorsville area and the lower part of the Logtown Ridge formation of the Cosumnes River area in Cali- fornia. SOUTHWESTERN OREGON The Callovian has not been identified faunally in southwestern Oregon. If present, it is possibly rep- resented by the Dothan formation (Diller, 1907, p. 407—411) and the overlying Rogue formation (Wells and Walker, 1953) that lithologically bear considerable re— semblance to the California Cosumnes formation and Logtown Ridge formation, respectively. In contrast, the late Oxfordian to early Kimmeridgian has been SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY identified faunally in the Galice formation (Diller, 1907, p. 403—407), which consists mostly of slates similar to those of the Mariposa formation of California. The faunal evidence consists of the presence of the pelecypod Buchia concentrica (Sowerby) at 18 localities and of perisphinctid ammonites at 4 localities. Most of these ammonites are fragmentary, but one laterally crushed specimen (see pl. 4, fig. 2) from the Almeda mine on the Rogue River, 3 miles below the mouth of Galice Creek (USGS Mesozoic loc. 3326), is a typical rep- resentative of the subgenus Dichotomosphinctes and is similar in appearance to Perisphinctes (Dichoto— mosphz‘nctes) wartaejormz's Burckhardt (1912, p. 25, pl. 5, figs. 1—4, 6) and to P. (Dichotomosphinctes) aff. P. (D.) plicatz’lis d’Orbigny in Burckhardt (1912, pl. 4, figs. 2—4) from the upper Oxfordian beds of northern Mexico. This ammonite constitutes excellent evidence that part of the Galice formation is of late Oxfordian a e. g WESTERN BRITISH COLUMBIA In the Harrison Lake area the ammonites Cadoceras catostoma Pompeckj, Paracadocems harveyi Crickmay, and Pseudocadocems schmidti (Pompeckj) are listed from the middle of the Mysterious Creek formation of Crickmay (1930, p. 55—57). This association of spe- cies and genera in Alaska (Imlay, 1953b, p. 50-53) occurs in beds that are correlated With the Sigaloceras callom'ense zone of Europe. It is probably about the same age as the faunule found in the Kettle meta- andesite on Hosselkus Creek in the Taylorsville area, previously discussed herein. It could be of the same age as the basal part of the Logtown Ridge formation on the Cosumnes River, but the presence there of coarsely ribbed specimens of Pseudocadocems compa- rable to P. crassicostatum Imlay (1953b, p. 50, 94) sug- gests a slightly younger age probably equivalent to the middle Callovian. In the Queen Charlotte Islands an ammonite faunule from the upper part of the Yakoun formation consists of species of Keppler’ites (Seymoun'tes) (McLearn, 1929, p. 4—12) identical with species in the lower and middle thirds of the Chinitna formation in the Cook Inlet region, Alaska (Imlay, 1953b, p. 50—53, 95-99). The fact that Kepplem'tes on the Queen Charlotte Islands is not associated with Oadocems or Pseudocadocems suggests correlation with only the lower third of the Chinitna formation. These occurrences are mentioned because Arkell (1956, p. 554) suggested that Keppler- ites (Gowem‘cems) lindgreni (Hyatt) from near Colfax, Calif, is similar to species of Kepplerites from the Queen Charlotte Islands. The present studies show, however, that the species is quite different, and resem- bles species in Alaska from the very base of the Chi- JURASSIC AMMONITES, SIERRA NEVADA nitna formation (Imlay, 1953b, p. 31, pl. 22, figs. 10—13) and in the western interior from the zone of Goweri- cams costidensum (Imlay, 1953a, p. 6, 7, 31, pl. 22, figs. 10—13) which zone lies below the lowest known occurrence of Kepplem'tes (Seymourites). Also, the fact that the new species of Kepplem'tes, described here- in, from near Colfax differs considerably from any described species of K. (Seymourites) from British Co- lumbia suggests that the beds near Colfax are probably of slightly different age. ALASKA PENINSULA AND COOK INLET REGIONS, ALASKA The lower and middle Callovian are well represented by a varied succession of ammonites in the Alaska Peninsula and in the Cook Inlet region except possibly for the lowest European zone of Macrocephalites macrocephalus (Imlay, 1953b, p. 51—55). That zone may be represented by the upper part of the Bowser member of the Tuxedni formation, which includes such typical Callovian ammonites as Grossomm'a, Kherai- ceras, Xenocephalites, and Kepplerites along with the long-ranging ammonites Phyllocems, Macrophylloceras, and Calliphylloceras. The species that are present all range up into the lower part of the Chinitna formation, so that the upper part of the Bowser member cannot be much older. In fact the presence of one specimen of Kepplerites similar to K. tychonis Ravn suggests that at least part of the Bowser member is equivalent to the lower part of the Sigaloceras callom'ense zone of Europe (Imlay, 1953b, p. 53). Nevertheless, the ab- sence of such ammonites as Lilloettia, Oadoceras, Para- cadocems, Pseudocadoceras, Gowericems, and Cosmoceras from the upper part of the Bowser member implies a position low in the Callovian. The succession of Callovian ammonites that has been established for Alaska cannot yet be demonstrated for California and Oregon because of meager collections and complicated structure. It is implied, however, by the fact that many of the Callovian ammonites that have been found in California and Oregon are identical specifically with the Callovian ammonites of Alaska. Assuming that the succession is approximately the same in all three States, certain correlations may be made, as discussed in the section dealing with “Ages and cor- relations.” Thus the beds near Colfax, Calif, that con- tain Kepplerites and Gowericeras are correlated with the basal part of the Chinitna formation and the high- est part of the Tuxedni formation of Alaska and hence with the European Sigaloceras callov'iense zone and pos- sibly the llzlacrocephalites macrocephalus zone. The beds containing Pseudocadoceres at the base of the Log— town Ridge formation contains species identical with those in the middle to upper thirds of the Chinitna for- D—l 1 mation and are correlated with the middle Callovian of Europe. In contrast, the ammonite Peltoceras from the Logtown Ridge(?) formation on Big Indian Creek in Amador County, Calif, has no counterpart in Alas- ka where the upper Callovian is missing—as it is gen- erally throughout the Arctic region. The Oxfordian and Kimmeridgian stages in Alaska are represented mostly by a succession of species of the pelecypod Buchia, (Imlay, 1955, p. 83—86). However, the lower Oxfordian, present locally in the Naknek for- mation of the Cook Inlet region and the Alaska Penin- sula, is represented by the ammonite Cardioceras (Reeside, 1919, p. 9, 18, 24, 25, 27) that is not associ- ated with Buckie. The overlying beds in the lower part of the Naknek formation contain an abundance of Buchia concentrica (Sowerby) that is associated with the typical late Oxfordian ammonites Amoebocems (Prionodoceras) (Reeside, 1919, p. 30) and Perisphinctes (Dichotomosphinctes). (See pl. 4, fig. 6.) Near the middle of the Naknek formation, Buchia, concentrica (Sowerby) is associated for several hundred feet with B. rugosa (Fischer) and B. mosquensis (von Buch). The last two species continue upward for many hun- dreds of feet to the top of the Naknek formation. Their range in Alaska cannot be dated accurately be- cause of lack of associated ammonites other than Phylloceras and Lytoceras, but by comparisons with their ranges in Eurasia and Mexico, they do not occur lower than the lower Kimmeridgian zone of Aulacoste- phanus pseudomutabilis or higher than the lower Port- landian (Imlay, 1955, p. 74, 75, 85; 1959, p. 165). The lower part of the Naknek formation in Alaska shows faunal relations to the Mariposa formation in northeastern California and to the Galice formation in southwestern Oregon and northwestern California. As in those formations, Buchia concentrica (Sowerby) is the most common fossil. Associated with this species in all three formations is the ammonite Perisphinctes (Dishotomosphinctes). The species of this subgenus present in the Naknek formation (USGS Mesozoic 100. 10796) may be identical with Perisphinctes (Dichoto- mosphinctes) milhlbacht' Hyatt from the Mariposa for— mation. The genus Amoebocems occurs rarely both in the lower part of the Naknek formation and in the Mariposa formation but is represented by different sub- genera of slightly different ages. The species of Phyl- loceras that ranges throughout most of the Naknek formation, but is particularly common in its lower part, is identical specifically with the Phyllocems in the Galice formation (USGS Mesozoic locs. 3322, 3335) and pos— sibly includes some fragmentary specimens of Phyllo- ceras in the Mariposa formation (USGS Mesozoic 100. 27318). D—12 In contrast, the upper part of the N aknek formation has nothing in common faunally with the Mariposa formation and the Galice formation except for the ammonite Phylloceras. The pelecypod Buchz'a rugosa (Fischer), which is common in the upper part of the N aknek formation, has not been found in the Pacific coast south of northwestern Washington. Its absence in Oregon and California is in harmony, however, with the absence in those States of any ammonites of middle Kimmeridgian to early Portlandian age. MEXIC O The only Callovian ammonities from Mexico that have been described are from the southern part of the country in the states of Oaxaca and Guerrero (Burck- hardt, 1927; 1930, p. 26, 32, 35, 36, 43; Arkell, 1956, p. 564). Most of them are different from any ammonites that have been found in the Callovian of California. There are relationships, however, on the generic level. Thus the species of Reineckez'a (Reineckez'tes) described by Burckhardt (1927, pl. 16, pl. 17, pl. 18, figs. 1, 2, 7) from Mexico resemble R. (Reineckeites) dillerz' (Crick- may) (1933b, pl. 32, fig. 2, pl. 34) from the Taylorsville area, in California. Choflatia waitzz' Burckhardt (1927, p. 75, pl. 30, figs. 2—5) is too small for comparison with Chofiatia hyattz‘ (Crickmay) (1933b, pl. 33) from the Taylorsville area. Xenocephalites nikitz'ni (Burckhardt) (1927, pl. 16, figs. 4—9) recalls the presence of a ques— tionable example of the genus in the Kettle meta— andesite of the Taylorsville area. The species of Peltoceras described by Burckhardt (1927, pl. 32, pl. 33, figs. 4—7, pl. 34) differ considerably from the speci- men of Peltoceras from Indian Creek, Amador County, Calif ., but possibly have significance paleogeographically as no other occurrence of Peltocems, or of late Callovian fossils, are known in North America. The Mexican Callovian has no representatives of such ammonites as Cadoceras, Paracadocems, Pseudo- cadoceras, Kepplerz'tes, and Gowerz'cems that occur in the Callovian from California to Alaska along withReinec/c- eia (Reineckeites), Chofiatia, and Xenocephalites. It appears, therefore, that except for the presence of Peltoceras, the Callovian of California is much more similar faunally to that of Alaska than to that of Mexico. This does not imply, of course, that there was any physical barrier between the seas in California and those in Mexico. The Oxfordian ammonites of Mexico that have been described mostly from the area of San Pedro del Gallo, Durango (Burckhardt, 1912, p. 1—40, 203, 204, 209—213, pls. 1—7). At this place the upper 100 meters of Ox— fordian strata have furnished the ammonites Ocheto- ceras, Taramellz‘ceras (Proscaphz'tes), Perisphz'nctes (Dis- cosphz'nctes), and Euaspidoceras, which probably rep— SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY resent the Epipeltoceras bimmamatum zone of central and southern Europe (Burckhardt, 1912, p. 213; Arkell, 1956, p. 563). From the underlying 150 meters of strata have been obtained ammonites belonging to Orem'cems, Tammelliceras, and Perisphinctes (Dicke- tomosphinctes). This faunule is correlated with the Perisphinctes plicatz'lz's zone of northwest Europe (Arkell, 1956, p. 563) and with the Gregoryceras trans- versam'um zone of central and southern Europe (Burck— hardt, 1930, p. 64; Arkell, 1956, p. 114). From these Oxfordian strata the ammonite Amoe- boceras of. A. alternans (von Buch) has also been recorded, from about 4 kilometers north of San Pedro del Gallo north of Potrero de las Tunas (Burckhardt, 1930, p. 66). This occurrence is the southernmost record of the genus in North American and perhaps in the ‘world, being much further south than the Amoebocems from northern Italy recorded by Arkell (1956, p. 175). The faunal sequence at San Pedro del Gallo is of considerable interest in determining the age of the Mariposa formation and of equivalent formations on the Pacific coast. One of the ammonites, Peri- sphmctes (Discosphz'nctes) carribeanus (J aworski) (Burck- hardt, 1912, p. 35, pl. 7, figs. 4—14) from the upper 100 meters of the Oxfordian sequence at San Pedro del Gallo may be identical with P. (Discosphz'nctes) virgu- latiformz's Hyatt (1894, p. 422) from the Mariposa formation. Another ammonite, Perisphinctes (Dickot- omosphinctes) durangensis Burckhardt (1912, p. 16, pl. 3, figs. 1, 2), from the lower 150 meters of the Oxfordian at San Pedro del Gallo is apparently identical with P. (Dichotomosphz'nctes) mfihlbachi Hyatt (1894, p. 426) from the Mariposa formation and with a specimen of P. (Dichowmosphinctes) (pl. 4, fig. 6) from the lower part of the Naknek formation, Alaska. P. (Dichoto- mosphz'nctes) elisabethaeformis Burckhardt (1912, p. 31, pl. 6, figs. 1—5) from the same lower beds at San Pedro del Gallo resembles a specimen of Dichotomosphinctes from the Monte de Oro formation near Oroville, Calif. (pl. 4, figs. 4, 7). Finally, P. (Dichotomo- sphinctes) wartaeformz's Burckhardt (1912, p. 25, pl. 5, figs. 1—4, 6) resembles a specimen of P. (Dichotomo- sphinctes) (pl. 4, fig. 2) from the Galice formation of southwestern Oregon. The Kimmeridgian ammonite faunas of Mexico are varied, well described (Burckhardt, 1906, 1912, 1919, 1921; Imlay, 1939, p. 21, 22, tables 4—7), and obviously have little in common with the fossils from the Mariposa formation in California. They do not contain a single representative of the genus Amoeboceras. They do contain a few representatives of Subdichotomceras (Burckhardt, 1906, pl. 31, figs. 14; Imlay 1939, pl. 10, figs. 1—3, 13) that are similar to Subdichotomoceras? J'URASSI‘C AMMONITES, SIERRA NEVADA aff. S. filiplex (Quenstedt) from the Mariposa for- mation. They do contain Buchia concentrica (Sowerby) which was found by Burckhardt (1930, p. 67, 80) near Mazapil, Zacatecas, in a thin bed lying above beds characterized by species of Idoceras similar to I. balderum (Oppel) and below beds containing Glochi- ceras fialar (Oppel). This occurrence was confirmed by collections made by C. L. Rogers and others (1956, p. 23) in his unit B. Associated with this species of Buckie is another species that Burckhardt (1930, p. 67) compares to Aucella pallasi var. plicata Lahusen but which probably belongs to B. rugosa (Fischer). (See Imlay, 1955, p. 84; 1959, p. 158~159.) The stratigraphic occurrence of these species of Buchia is interesting because the overlying beds con- taining Glochiceras fialar (Oppel) are correlated with the European zone of Aulacostephanus pseudomutabilis (Burckhardt, 1930, p. 64; Imlay, 1952, pl. 2) and the underlying beds containing Idoceras balderum are correlated with the European zone of Rasenia. muta- bilis. By comparison with the Jurassic of California, the absence of Buck/La rugosa (Fischer) from the Mariposa formation would suggest that that formation is older than the beds in Mexico that contain Glochi- cams fialar (Oppel). This is supported also by the absence of Buck/i0, mosquensis (von Buch) from the Mariposa formation, as that species is present in the Glochiceras fialar beds near San Pedro del Gallo, Durango (Burckhardt, 1912, p. 216, 217). GEOGRAPHIC DISTRIBUTION The occurrence by county and locality of the species described in this report is indicated in table 2. The general position of each locality is shown on figure 3. Detailed descriptions of the individual localities are shown in table 3. SUMMARY OF RESULTS 1. The Jurassic ammonites from the western part of the Sierra Nevada include 12 genera and sub- genera and 21 species. Only one species is described as new. Seymourites and Gowericeras are considered subgenera of Kepplem'tes. Dis- cosphinctes and Dichotomosphinctes are considered subgenera of Perisphinctes. 2. These ammonites are all of Late Jurassic age and in terms of European stages, represent the early to late Callovian, the late Oxfordian, and the early Kimmeridgian. 3. The exact strati ra hic osi ' fossils relative to formatiOnal boundaries is Wart field descriptions. However, the faunal evidence is sufficient to show theexact D-13 a es of the formations at certain spots and the 4. The Jurassic beds near Colfax, Placer County, have furnished the Callovian ammonites Gros- souvm’a colfam' (Gabb), Kepplem'tes lorinclarki Imlay, n. sp., and K. (Gower’icems) lindgreni (Hyatt). An early Callovian age is indicated by the presence of Kepplerites and by the close resemblance of K. lindgrem' (Hyatt) to a species in Alaska that occurs considerably below beds of middle Callovian age. 5. The Cosumnes formation at its type locality on the Cosumnes River is at least in part of Callovian age as it has furnished an ammonite, Pseudoca- doceras?, about 500 feet below its top, and its highest beds are-transitional into the Logtown Ridge formation. 6. The Logtown Ridge formation on the Cosumnes River has furnished the Callovian ammonite Pseudocadocems grewingki (Pompeckj) in its lower part about 600 to 675 feet above its base. With this species is associated a coarsely ribbed species that is probably identical with P. crassi- costatum Imlay. By comparisons with Alaska, these ammonites indicate a correlation with the upper third of the Chinitna formation and thence with the middle part of the Callovian stage. The presence of Pseudocadoceras itself is evidence of an age not older than the late early Callovian zone of Sigaloceras calloviense. The Logtown Ridge formation is probably repre- sented also by the ammonite Peltoceras that was ob- tained at, or near, Indian Creek. This ammonite is excellent evidence of a late Callovian age. The upper part of the Logtown Ridge formation on the Cosumnes River has furnished the ammonite I docems of latest Oxfordian to early Kimmeridgian age. 7. The Mariposa formation and similar slatey units containing Buchia concentrica (Sowerby) have furnished a number of ammonites of la’te_Q,xf_Qn; dian arl Kimmerid ian a e. The late Oxfordian is represented by Perisph’inctes (Di— chotomosphinctes) mahlbachi Hyatt and by P. (Discosphinctes) virgulatiformis Hyatt, which are essentially identical with species in Mexico and Cuba. The early Kimmeridgian is rep- resented by Amoebocems (Amoebites) dubium (Hyatt) and probably by Subdichotomocems? aff. S. filiplex (Quenstedt). This age range is confirmed by the presence of Buckie concentrica, (Sowerby) at a number of places in the Mariposa formation from near its base to at least several thousand feet above its base. The late Ox— fordian ammonites from the Mariposa formation D—14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 2.—Geogmphic distribution of Late Jurassic megafossils in the western Sierra Nevada, Calif. [Numbers 1-31 refer to numbers on fig. 3. Most of the larger numbers refer to Mesozoic collections in the U.S. Geological Survey. Collection numbers from the University of California at Berkeley are preceded by the letters UC; from Leland Stanford Junior University by the letters SU; and from the Museum of Comparative Zoology at Harvard University by the letters MCZ] Butte County Placer Eldorado County Amador County Calaveras Tuolumne County Mariposa County County County “Mari- Logtown Log- “Mari- Mari- Monte de Oro Colfax posa” Ridge Cosum- town posa” Forma- Mariposa posa(?) formation formation forma- forma- nes for- Ridge(?) forma~ tion un- formation forma- Mariposa formation of Smith tion tion mation forma- tion known tion tion 1 2 3 4 5 6 7 S 910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 2627281693031 S U9063 M C Z5287 UC. 14—4996 18937 27387 2431 7 27397 27459 27398 902 2731 2 53 1 982 243 27460 1 983 1 6625 3990 3991 3992 4801 4802 2751 6 2751 7 490 25638 24710 2731 7 221 75 27566 903 27395 27396 27315 27394 20554 2731 1 719 904 l SU9064 I 27318 Phylloceras sp __________ _ Taramelliceras? (Proscaphites?) denticulatum (Hyatt) ............ ....__...... -....._-...... ...-.. ._ ..____.. ................................ .-.-.......... ...... ....X.. ... ...... .... .... Kepplerites lorinclarki may, n. Sp ...... ...._......... X "...-.. ......._ .. -- -- -. ________________________________ ................-........ ...... -..................... (Gowericeras) lind- greui(I{yatt)..... _. ......" ..__.. .-.. X ...-..___.-___ ._ ________________________________ __........__..._.. .....-__ .. ... ...... ...... .. .. Pseudccudoceras grew- ingkI' (Pompeckj)... .. ._ .. .. .. .. .. .... ____ _... .. .. .. __ ._ __ x x ________________________________ ._ __ .. .. .. .... .... .. .. .. _. .. .. .. .. .. .. .. ._ .. .. .. .. .. cf. P. grewingki (Pompeckj).... .. .. __ .. .. _. .. cf. P. craasicostatum X I I I I I I I I I I I I I I I I I .9 (Amaebites) dubium (Hyatt) ____________ ...... ....__.. ...- ...._.._.-...- ...... .... ________________________________ ..X.......... .............. ...... .......... .... .. _. Grossauoria calfari (Gabb) _____________ .. .. .. .. .. .. .. .... x .... .... .. .. .. __ .. _. ________________________________ ._ .. .. .. .. .... .... .. .. .. .. .. .. .. .. .. .. .. .. .. .. Perisphinctes? sp ....... ...... ....__.. __._..._.___.. ...-__x__.. __ ________________________________ __ ._ .........._... ......___......... .... ...... ...... Perisphmctes (Dis- cosphinctes) virgulatiformis Hyatt .......... ............................_.....____.... ................................ ...........-............x.................._....... (Dichotomosphinc— tes) mfihlbachi Hyatt __________ .. .. __ __ .- ._ __ .... .... _-__)<.. .. ._ 0 __ ._ __ ________________________________ ... .__._ .... .. .. .- __ .. .. __ .. _. .. _. ._ __ _. of. P. mdhlbachi H att __________ .. .. .. .. .. .. .. .... .... __.. .. .. .. __ __ __ .. __ ________________________________ .... __ ... .... .. .. ..X.. ... ... .. .- .. ..X.. y cf. P. elisabethae- form's Burck- hardt __________ .. .. ...... ..X...._.___.__.- ......___,._ _. ________________________________ ______.... ...- ...- ......_... .-........ .............. (Dichotomosphinc- tes?) spp ........ .. .. _. .. .. .. .. ...- ...- .... .. X .. .. _. .. .. Idaceras of. I. planula (Heyl) in Zeiten.... .. .. .. Idocems? sp ____________ .. .. _. Subdichotomoceras? afi. .... __ _. .. __ ._ __ U .. 0 h .. .. .. .. h ._ S.filiplez (Quenstedt) ........ ...........................-........._.. ... ..............X.............. Peltoceras (Metapelto- ceras?) sp ,,,,,,,,,, “Belemnites” pacificur Gabb .............. “Belemm’tes” sp ........ Turbo? sp ______________ -- III -_ .I II " " 'Z Cerithium? sp __________ .. .. . .. . Gastropods undet ...... .. .. .. . . .. .. _. .. Pinna SD _______________ Modiolus sp. Mytilus sp. . Avicula? sp __________ Meleagrinella sp ..... Meleagrinella? sp ....... Buchia concentrica (Sowerby) _________ .. .. -- __ .. _. __ cf. B. concentrim (Sowerby) ..... .. .. .. .. >< .. .. Chlamys? sp ............ .. ._ __ _. X Entclium? eururium (Meek) ._ 51).. __ Lima sp.. Lima? sp Carbix? sp ______________ ..-... ........ X Rhynccllionellid brachio- ................ _- -. .. .. ._ .- __ X -.-. ...- .. .. -. __ .. .. .. .. --.-____ __---___ .-...-.. .-.----_ ._ -- __ .. _- ..-. ..-. - po Echinoid fragments.... .. .. ._ ._ _. .. ._ __._ V... .... .. .. .. _. .. ._ _. __ ________________________________ __ __ __ ._ __ ..__ __.- __ >< .. ._ _. .. __ _. __ ._ __ ._ .. .. .. .. .. 122° JURASSIC ANLMONITES, SIERRA NEVADA D—15 121° Downieville O C O L U S A 39° 54 ’4 \ ~ 0 Placerville Y O L O 9 E SACRAMENTO 11 /10 /—~-_,— 12 r \\/’ —\l R'We'r \ §'\/’):(X I '4 6 Plymouth S A C R A M E N T 0 A I “g \ ,_ | A ,r i OJackson /\~\ oSanAndreas C A L A V E R A S 16 X Angels Camp 0 \ \ 29—1/ TUOLUMNE \ Copperopoliso 17Mx20 O Sonora . I Stockton ! 21X§ '18 2 CONTRA COSTA SA JOAQUIN I. A X2 MW” 4/ Chmese X23 R“b I CampO X24 I Jacksonville QJ , 25 ['\_ N ’/ U: I l \\ \ ’/ 1 9 (\z \ ‘ /’/ l 3 l l‘/ \“Nd‘ \D,/’ I ('N OCoulterville \ | A N I s L A U s J 26 I Modesto X I D X27 ALAMEDA I I ,/’ \ ”xxx | / ,/ \ M A R I P o s A \ /’ ,/ \ X30 W _______ er /z/ \ MtBullionO OMmposa -- hey/— ‘_'_( M E R c E D ‘ x31 . ) 10 o 10 20 30 4'0 MILES FIGURE 3,—Index map of Jurassic localities in the western Sierra Nevada, Calif. D-16 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 3.—Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif. Locality on fig. 3 Geological Survey Mesozoic localities Collector’s fleld Nos. Localities of other institutions Collector, year of collection, description of locality, and stratigraphic assignment 11 __________ 16625 3990 3991 3992 4801 4802 27313 27516 27517 490 25638 24710 5—1 ______________ 5—2 ............... 5—3 ______________ 5—17 ............. 5—16 _____________ LC—53—282 _______ LC—53—283 _______ Stanford Univ. Mus. Pa- leontology 9063. MCZ—5287 Harvard ..... Stanford Univ. Mus. Paleontology 9065. Univ. Calif. Berkeley A—4996. V. T. Allen, 1927. From hydraulic mine north of Oroville and about 3 miles southwest of fossil locality near Banner Mine, Oroville quad., Butte County, Monte de Oro formation. James Storrs, 1906. North bank of Feather River a quarter of a mile below mouth of Morris Ravine and 3 miles above Oroville, SE. cor. sec. 32, T. 20 N., R. 4 E., Oroville quad., Butte County, Monte de Oro formation. James Storrs, 1906. North bank of Feather River, about 4 miles above Oroville, at mouth of ravine west of Banner Mine, probably NW. cor. sec. 3, T. 19 N., R. 4 E., Oroville quad., Butte County, Monte de. Oro formation. James Storrs, 1906. Along stage road a quarter of a mile southwest of Banner mine, probably east central part of sec. 33, T. 20 N., R. 4 E., Oroville quad., Butte County, Monte de Oro formation. James Storrs, 1907. Western part of the plant-bearing beds and north side of the Feather River from 3—4 miles above Oroville, probably SEl/Q sec. 33, T. 20 N., R. 4 E., Oroville quad., Butte County, Monte de Oro formation. James Storrs, 1907. Near eastern part of plant beds on north side of the Feather River from 3—4 miles above Oroville, probably SEM sec. 33, T. 20 N., R. 4 E., Oroville quad., Butte County, Monte de Oro formation. R. S. Creely, 1956. From north bank of Feather River just north of Sycamore Hill, about 3 miles northeast of Oroville, 450 ft south of NE. cor. sec. 4 near its east edge in T. 19 N., R. 4 E., Oroville quad., Butte County, Monte de Oro formation. L. D. Clark, 1953. Road cut on west side of US. Highway 40, 0.1 mile north of Midget Auto Court and 0.85 mile northeast of road turnofl" to Grass Valley, NWM sec. 26, T. 15 N., R. 9 E., Colfax qlgad, Placer County, Colfax formation of J. P. Smith. J. . Whitney. “From railroad cut at station 2777, see. 53, 1 mile West of Colfax, 14 ft below surface of ground.” Colfax quad., Placer County, Colfax formation of J. P. Smith. Collector and year unknown. Half a mile south of Colfax and a quarter of a mile west of railroad station, Colfax quad., Placer County, Colfax formation of J. P. Smith. Collector and year unknown. Near Greenwood, George- town quad., Eldorado County, “Mariposa” formation. G. W. Kimble and H. W. Turner, probably 1884. Slates Big Canyon about 2 miles north of Placerville, SW54 sec. 36, T. 11 N., R. 11 E., Georgetown quad., Eldorado County, “Mariposa” formation. L. D. Clark and N. K. Huber, 1955. South bank of Cosumnes River 0.1 mile east of the Michigan Bar bridge in the SE% sec. 36, T. 8 N., R. 8 E., Folsom quad., Sacramento County, “Mariposa” formation. R. W. Imlay, 1958, same as Mesozoic 10c. 25638. J. C. Heald. Nashville, Placerville quad., Eldorado County, probably from Logtown Ridge formation. Collector and year unknown. From metamorphosed andesitic tufl". “Presumably from a building stone quarry near the Huse bridge over the Cosumnes River about 6 miles north of Plymouth.” Placer- ville quad., either southern Eldorado County, or northern Amador County, Logtown Ridge forma- tion, near top. L. D. Clark and E. H. Pampeyan, 1953. North bank of Cosumnes River, 4,550 ft S. 55° W. of Huse bridge, at point where river bends sharply southward for half a mile, south central part of sec. 15, T. 8 N., R. 10 E., Fiddletown 7}é-min quad. Eldorado County, Logtown Ridge formation, about 600—675 ft above base. JURASSIC AMIVIONITES, SIERRA NEVADA 13-17 TABLE 3.-—Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif.—Continued Locality on fig. 3 Geological Survey Mesozoic localities Collector’s field Nos. Localities of other institutions Collector, year oi collection, description of locality, and stratigraphic assignment 11 __________ 12 __________ 13 __________ 14 __________ 15 __________ 16 __________ 17__-_-_;___ 17 __________ 17 __________ 18 ______ ____ 19 __________ 19 ______ ____ 20 __________ 20 __________ 20 __________ 21 __________ 21 __________ 27317 22175 18937 27387 24317 719 904 27566 903 27395 27396 27315 27394 27397 901 27568 I-58—9—28A _______ 292 ______________ 293 ______________ 263 ______________ 294 ______________ LC—59—101 _______ Stanford Univ. Mus. Paleontology 9062. R. W. Imlay, 1958. Fossils obtained 100-300 ft above Cosumnes River at same place as Mesozoic loc. 24710 in thin-bedded tuffs from 600-640 ft above base of Logtown Ridge formation. . H. Eric and A. A. Stromquist, 1949. About 600 ft west of base of Logtown Ridge formation on right bank of Cosumnes River about 2 miles below the Huse Bridge and 1,850 ft east of west edge of Fiddle- town 71/4 min quad., lat 38°31’50” N., long 120°51’00” W., NW}{1 sec. 22, T. 8 N., R. 10 E., Eldorado County, Consumnes formation, upper part, about 500 ft below top. F. M. N. Hamilton, 1914. Big Indian Creek, southwest corner of Placerville 30-min quad., Amador County. Probably from Logtown Ridge formation. G. R. Heyl, 1944. mall gulley three-fourths of a mile NNW of Plymouth, Sutter Creek 15-min quad., Amador County “Mariposa” formation. Collector and year of collection unknown. Mokolumne River downstream from Middle Bar Bridge, T. 5 N., R. 11 E., Sutter Creek quad., Amador or Calaveras County, formation unknown. L. D. Clark and D. B. Tatlock, 1952. Cherokee Creek, sec. 22, T. 3 N., R. 12 E., San Andreas quad., Cala- veras County loose boulder in stream bed along a major fault zone. “Mariposa” formation. G. F. Becker, probably 1890. Texas Ranch, in valley of Angels Creek near north edge of sec. 28 or 29, T. 2 N., R. 13 E., Copperopolis quad., Calaveras County, Mariposa formation. Cooper Curtice, 1891. Six miles from Copperopolis on road to Sonora and on grade to Angels Creek near center of sec. 33, T. 2 N., R. 13 E., Copperopolis quad., Calaveras County, Mariposa formation. Cooper Curtice, probably 1891. Wagon road 2 miles west of Reynolds Ferry and 1 mile West of Motherlode, Copperopolis quad., Calaveras County, Calif ., Mariposa formation. Cooper Curtice, 1891. West bank of Stanislaus River opposite mouth of Bear Creek near center sec. 11, T. 1 N., R. 13 E., Copperopolis quad., Calaveras tCounty, Mariposa formation, about 1,000 ft above ase. A. A. Stromquist, 1940—50. About 0.7 mile north of Mormon Creek and 0.5 mile east of Stanislaus River in NEMSEM sec. 25, T. 2 N., R. 13 E., Sonora quad., Tuolumne County, Mariposa(?) formation. A. A. Stromquist, 1940—50. Soldiers Gulch north of Mormon Creek, SEViNEM sec. 25, T. 2 N., R. 13 E., Sonora quad., Tuolumne County, Mariposa(?) forma- tion. A. A. Stromquist, 1940—50. Mormon Creek, probably near east boundary of sec. 36, T. 2 N., R. 13 E., Sonora 15-min quad., Tuolumne County, Mariposa formation. A. A. Stromquist, 1940—50. About 0.4 mile south of Mormon Creek in SWEQSWM sec.31, T.2 N., R. 14 E. Sonor 15-min quad., Tuolumne County, Mariposa forma ion. A. A. Stromquist, 1940«SO. On fault cutting meta- volcanic rock north of Mormon Creek, SE}iSW}i sec. 30, T. 2 N., R. 14 E., Sonora 15-min quad., Tuolumne County, Mariposa(?) formation. 1 Cooper Curtice, 1891. On trail opposite Bosticks Bar near Reynold’s Ferry across the Stanislaus River, SEV; sec. 34, T. 2 N., R. 13 E., Copperoplois quad., Tuolumne County, Mariposa formation. L. D. Clark, D. L. Jones, and N. J. Silberling, 1959. From placer sluiceway trench on north bank of Stanislaus River about 15 ft above low-water mark of Melones Reservoir in the NWMNWV; sec. 3, T. 1 N., R. 13‘ E., Copperopolis quad., Tuolumne County, Emit, Mariposa formation, about 1,000 feet above ase. D—18 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 3,—Descriptitms of the Late Jurassic fossil localities in the western Sierra Nevada, Calif.-—Continued Geological Locality on Survey Collector’s field Nos. Localities of other institutions Collector, year of collection, description of locality, and stratigraphic fig. 3 pieslozoic assignment oca ities 22 ______________________________________ Stanford Univ. MUS. Pa- Vander Hoof. From Wood Canyon(‘?) near Sonora, leontology 9064. Sonora quad., Tuolumne County, Mariposa formation. 23 __________ 20554 Heyl 255 _________________________________ George Heyl, 1947. Woods Creek Canyon, 3 miles northwest of Jacksonville, sec. 2 or 3, T. 1 S., R. 14 E., Sonora 15-min quad., Tuolumne County, Mariposa formation. G. F. Becker, probably 1884. Woods Creek, northwest of Jacksonville, Sonora 15—min quad., Tuolumne County, Mariposa formation. G. R. Heyl, 1946. Crest of Woods Creek Ridge 1 mile northwest of Jacksonville, sec. 12, T. 1 S., R. 14 E., Sonora 15-min quad., Tuolumne County, Mariposa formation, 2,000—3,000 ft above base. Cooper Curtice, 1891. South bank of Tuolumne River at Mofiat Bridge, SW. cor. sec. 18, T. 1 S., R. 15 E., Sonora quad., Tuolumne County, Mariposa formation. L. D. Clark and R. Pack, 1953. MOffat Bridge site near Jacksonville. Railroad cut on south side Of Tuolumne River, 200—225 ft east of contact between Mariposa formation and mafic volcanic breccia. SW. cor. sec. 18, T. 1 S., R. 15 E., Sonora 15-min quad., Tuolumne County, Mariposa formation, 200 ft above base. L. D. Clark, 1953. North bank of Merced River, NW. cor. sec. 26, T. 3 S., R. 16 E., Coulterville quad” hdafiposa County,hdafiposafomnafion,about 1,000 ft above base. H. W. Turner, G. F. Becker, and C. A. White, 1884. Left bank of Merced River a quarter of a mile below Bagby (formerly called Bentons Mills), sec. 6?, T. 4 S., R. 17 E., Coulterville 15-min quad., Mariposa County, Mariposa formation. H. W. Turner, 1892. Hell Hollow, north of Bear Valley in northwest part of T. 4 S., R. 17 E., Coulterville quad., Mariposa County, Mariposa formation. H. W. Turner, 1884. Mariposa estate near Pine Tree Mines, about half a mile east of head of Hell Hollow, T. 4 S., R. 17 E., lat 37°36’ N., long 120°07’ W., Coulterville quad., Mariposa County, Mariposa formation, probably 3,000—4,000 ft above base. W. D. McLearn, received at Natl. Mus. May 3, 1922. Bullion Mountain. Coulterville quad., Mariposa County, Mariposa formation. James Storrs, 1895. Five miles southeast of Princeton (Bullion Mountain post Office), probably Mariposa quad., Mariposa County, Mariposa formation. 23 __________ 27459 __________________ 24 __________ 27398 1 83- 1 ____________ 25 .......... 902 25 __________ 27311 LC—53—42A _______ 26 __________ 27312 LC—53—280 _______ 27 __________ 253 __________________ 28 __________ 1982 __________________ 29 ______ L--- 243 30 __________ 27460 __________________ 31 __________ 1983 __________________ indicate that its lower part locally is Of approxi- mately the same age as the upper part of the Logtown Ridge formation on the Cosumnes River where a specimen of Idocems was Obtained. 8. The Monte de Oro formation is of late Oxfordian to early Kimmeridgian age. The evidence con- sists of 1 ammonite similar to Perisphinctes (Diabotomosphinctes) elisabethaeformis (Burck- hardt) from the late Oxfordian of Mexico and Of 2 crushed specimens of Buckie that probably belong to Buckie concentrica (Sowerby). 9. The affinities of the Callovian ammonites in the western part Of the Sierra Nevada are mainly with those of British Columbia and Alaska as indicated. by the presence of such ammonites as Cadoceras, Paracadoceras, Pseudocadoceras, Kepplerites, and Gowericems. Ammonites in common with both Alaska and southern Mexico include Reineckeia, Chofl'atia, and Xenoce— phalites. Peltoceras occurs in common with Mexico but not with Alaska. In Alaska, how- ever, late Callovian beds that might contain Peltoceras have never been found and in the Cook Inlet region, the late Callovian is represented by an unconformity. 10. The affinities of the late Oxfordian ammonites from California are mostly with Mexico and Cuba, but astonishingly one Of the ammonites, Per- isphinctes (Dichotomosphinctes) mfihlbachi Hyatt is essentially identical both with P. durtmgensis Burckhardt from Mexico and with a specimen from the Alaska Peninsula. 11. Among the early Kimmeridgian ammonites from California, the presence of Amoeboceras in— JURASSI‘C AMMONITES, SIERRA NEVADA dicates affinities with Alaska and the Boreal region. The ammonite Subdichotomoceras has not been found in Alaska but has been found in lVIexico and in many other parts of the world. 12. The ammonite faunas that existed in California from early Callovian to early Kimmeridgian times appear to have had free marine connections northward to Alaska and southward to southern Mexico, but during Callovian time the Alaskan influence was dominant. SYSTEMATIC DESCRIPTIONS Class CEPHALOPODA Genus PHYLLOCERAS Suess, 1865 Phylloceras sp. The genus is represented by fragmentary external and internal molds of a single specimen that has been crushed laterally. The external mold shows that the species has a very small umbilicus and very fine dense flexuous ribs that are grouped in low broad folds on the lower part of the flanks. There is no trace of sigmoidal constrictions. The folds on the lower part of the flanks appear to be much less pronounced than in a species of Phylloceras from the Galice formation of southwestern Oregon (USGS Mesozoic locs. 3322, 3335) or from the Naknek formation of Alaska, but the poor preservation of the specimens makes specific identification impossible. Nonfigured specimen: USNM 130784. Occurrence: ”Mariposa” formation at USGS Mesozoic loc. 27318. Genus TARAMELLICERAS Del Campana, 1904 Subgenus PROSCAPHITES Rollier, 1909 Taramelliceras‘i (Proscaphites?) denticulatum (Hyatt) Plate 1, figures 9—11 Oecotraustes denticulata Hyatt, 1894, Geol. Soc. America Bull., v. 5, p. 427. “Oecotraustes” denticulata Hyatt. Crickmay, 1933a, U.S. Geol. Survey Prof. Paper 175—B, p. 58, pl. 17, figs. 11—13. This species is characterized by a compressed shell, a narrow venter, a very narrow umbilicus, a row of mid- ventral serrations, and by weak gently flexuous ribs that become stronger ventrally on the flanks but weaken on the venter and do not extend to the median ventral serrations. The suture line is poorly exposed. It has been de- scribed and illustrated adequately by Crickmay (1933a, pl. 17, figs. 12, 13). This species was compared by Hyatt with Ammonites lochensis Oppel (1863, p. 207, pl. 54, figs. la—d) from the late Oxfordian of Germany. It appears to be similar in most respects, but has somewhat sparser ribbing. It also shows some resemblance to Ammonites pickleri D—19 Oppel (1863, p. 212, pl. 51, figs. 4a—c). That species differs by having fine ribs and many intercalated ribs of which all extend to the midventral serrations (Jean- net, 1951, pl. 29, figs. 7a, b; pl. 30, figs. 2a, b). These species from Europe have been placed by Jeannet (1951, p. 95, 96) in a new genus Richeiceras, which Arkell (1957, p. L281) considers to be a synonym of Prosca— phites, a subgenus of Taramelliceras. Similar appearing species of Taramelliceras from the late Oxfordian of Mexico (Burckhardt, 1912, p. 12—14, pl. 2, figs. 5—12) all have somewhat finer ribbing than the California species. Interestingly the Mexican species are associated with species of Discosphinctes and Dishotomosphinctes similar to those associated with Taramelliceras? denticulatum (Hyatt). Types: Cotypes USNM 30206. Occurrence: Mariposa formation at USGS Mesozoic 100. 901. Genus KEPPLERITES Neumayr and Uhlig, 1892 Kepplerites lorinclarki Imlay, n. sp. Plate 1, figures 1-8 Twelve fragmentary molds represent a species that is characterized by being fairly small and by having unusually prjominent ribbing for the genus. It has stout ovate whorls and evenly rounded flanks. Its venter is poo ly exposed but is probably evenly rounded. The umbilic s is fairly narrow on the inner whorls but Widens considerably on the body whorl. The body chamber is represented by about half a whorl. The aperture is marked on the internal mold by a broad forwardly inclined constriction that is nearly smooth. The external mold shows that the aperture is marked by an abrupt constriction that is followed by a flat- tened area bearing weak riblets. The ribs on the body whorl are high, triangular in section, and sharp topped. They trend backward on the umbilical wall and curve forward strongly on the flanks. The primary ribs are thicker and higher than the secondary ribs and terminate at about one-third of the height of the flanks in prominent tubercles. From the tubercles pass pairs of secondary ribs that are sep- arated from adjoining pairs by single ribs that begin at or above the zone of furcation. The nearly complete whorl shown on plate 1, figure 7, has about 23 primary ribs. The s ture line cannot be' traced. This species has sharper, sparser, and coarser ribbing than any species of Kepplerites at a comparable size that has been described from North America. It shows a little resemblance to Kepplerz’tes (Seymourites) kuzuryuensis Kobayashi (1947, p. 29, pl. 7, fig. 3) from Japan, but that species has much finer ribbing, more secondary ribs, and attains a much larger size. Among European species it shows considerable resem- D—20 blance in ribbing, whorl shape, and coiling to the inner whorls of Kepplerz'tes kepplerz' (Oppel) as figured by Buckman (1922, pl. 289a, b) and somewhat less resem— blance to K. cereale (Buckman) (1922, pl. 286; Arkell, 1954, fig. 42 on p. 118). It differs from these species by having fewer secondary ribs, by having prominent ribs and tubercles on its body chamber, and by its much smaller size. This species is named in honor of Lorin Clark of the Geological Survey who collected the type specimens. Types: Holotype USNM 130777; paratypes USNM 130778. Occurrence: Colfax formation of Smith at USGS Mesozoic 100. 27313. Subgenus GOWERICERAS Buckman, 1921 Kepplerites (Gowericeras) lindgreni (Hyatt) Plate 1, figures 12, 14 Olcostephanus lindgrem’ Hyatt, 1894, Geol. Soc. America Bull., V. 5, p. 427. ”Galilaeiceras” lindgreni (Hyatt). Crickmay, 1933a, U.S. Geol. Survey Prof. Paper 175—B, p. 57, pl. 17, figs. 9, 10. This species is known only from one specimen that has been somewhat elongated and crushed. Allowing for deformation, the whorl appears to be ovate in section and probably higher than wide. The flanks and venter are evenly rounded. The coiling is evolute, the umbilicus fairly wide, and the outer whorl does not retract appreciably from the remainder of the shell. The body chamber includes at least half a whorl. The ribs curve backward on the umbilical wall, curve forward on the flanks, and apparently cross the venter transversely. The primary ribs are sharp and moderately spaced. At about two-fifths of the height of the flanks they pass into fascicles of weaker second- ary ribs that outnumber the primary ribs 4 or 5 to 1. Most of the furcation prints are swollen and were prob— ably originally tuberculate. Some of the secondary ribs appear to rise freely near the middle of the flanks. The suture line cannot be traced accurately. Details of the dimensions have been published by Crickmay (1933a, p. 57). “Olcostephanus” lindgrem' Hyatt was considered by Crickmay (1933a, p. 57) to be close to Galilaeiceras Buckman (1922, pls. 290, 291), which Arkell (1957, p. L298) regards as a synonym of Gowem'ceras in the family Kosmoceratidae. This general assignment seems reasonable as the species bears many resem- blances to Gowerz'ceras costidensum Imlay from the western interior region (Imlay, 1953a, p. 31, pl. 22, figs. 10—13) and to Gowericeras snugharborensis Imlay from Alaska (Imlay, 1953b, p. 99, pl. 53, fig. 9). It shows even closer resemblances to a specimen of Gow— ericeras from the Talkeetna Mountains (see pl. 1, fig. 13), and is possibly identical specifically. Specific SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY identification will be difficult, however, until other specimens of 0. lindgreni Hyatt are found in California that show the characteristics of the species better than the holotype. “Olcostephanus” lindgreni Hyatt was identified as Kepplem'tes (Gowericeras? or Seymourz’tes)(?) lindgrem' Hyatt by Arkell (1956, p. 554) who said the species seems “to be much like Seymourz'tes figured from Canada by McLearn (1929, pls. 1—8).” The writer considers, however, that “Olcostephanus” lindgrem' Hyatt has more evolute coiling and a wider umbilicus than any of the species of Seg/moum‘tes in— cluding Y akounoeeras and Yakounites) described by McLearn and that it greatly resembles certain species from Alaska and the western interior region described under the generic name Gowem’cems in the sense used by Spath (1932, p. 81, 94). In this sense Gowerz'ceras Buckman (1921, p. 54, pl. 254; 1922,1pls. 287, 288, 404) includes Galilaeiceras Buckman (1922, pls. 290, 291), Galileanus Buckman (1922, pl. 293, and Galilaeites Buckman (1922, pl. 309). Recently Arkell (1957, p. L289) placed Gowerz'ceras in synonymy with Kepplerz'tes without explanation and this assignment apparently is supported by Callomon (1955, p. 235). Nevertheless, the group of species that have been included under Gowericeras as defined by Spath differ from typical Kepplerz'tes and its subgenus Seymourites by having more evolute coiling and by the body chamber not retracting appreciably from the septate whorls. In addition it differs from typical Kepplem'tes by earlier loss of ventral flattening and by the persistence of tubercles on the flanks of the body chamber. In conformity with the scaled-down classi- fication used by Arkell (1940, p. LXVI; 1950, p. 354, 355), Gowerz'ceras probably would rank as a subgenus under Kepplem'tes at least as different from typical Kepplerites as the subgenus Seymoum‘tes. A number of features by which the European species of Gowerz'ceras may differ from the American species assigned to that genus have been mentioned by Dono— van (1953, p. 132; 1957, p. 135). These include bitu— berculate primary ribs, strongly curved primary ribs, an abrupt backward bend of the secondary ribs near their jpnction with the primary ribs, and the presence of a tabulate venter on the inner whorls. An examina- tion of various illustrations of European species of Gowericeras suggests, however, that these are not con— stant features on all the species and are, therefore, probably not of generic or subgeneric importance (com- pare J. de C. Sowerby, 1827, pl. 549; Buckman, 192], pl. 254; 1922, pls. 288, 290, 291, 293, 294, 309; 1923, pl. 404; Corroy, 1932, pl. 24, figs. 3, 4; Douville, 1915, p. 29, pl. 8, figs. 1, 4, pl. 9, figs. 1, 5). Even a flattened venter on the inner whorls is not known to be present JURASSIC AMMONITES, SIERRA NEVADA in all European species that have been assigned to Gowerr'ceras. Similarly in all the species of Gowericeras from Alaska and in most of those from the western interior of the United States, the characteristics of the inner whorls are unknown. Some of the species may have tabulate venters on their inner whorls as do some of the Euro— pean species. As far as the outer whorls are concerned the assignment of certain species from North America to Gowerz'ceras seems reasonable and has been con— firmed by Arkell (1956, p. 550). Types: Holotype USNM 30205. Occurrence: USGS Mesozoic 100. 27516 from the Colfax for- mation of Smith half a mile south of Colfax and a quarter of a mile west of the railroad, Placer County, Calif. Genus PSEUDOCADOCERAS Buckman, 1918 Pseudocadoceras grewingki (Pompeckj) Plate 2, figures 1—8, 11—13 For synonomy see Imlay, 1953b, U.S. Geol. Survey Prof. Paper 249—B, p. 93. Nearly 80 molds of Pseudocadoceras have been collected from thin beds of tufi in the lower part of the Logtown Ridge formatibn on the north bank of the Cosumnes River. Mostvof these are from a strati- graphic interval of about 40 feet, but one of the largest specimens (see pl. 2, fig. 7) was obtained about 75 feet above the others. Most of the specimens are so crushed and deformed that they cannot be identified specifically, but at least 12 specimens may be identified on the basis of ornamentation and coiling with P. grewingki (Pompeckj) from Alaska (Imlay, 1953b, p. 93, pl. 49, figs. 1—12). (See pl. 2, figs. 11—13.) This species is characterized by its narrowly rounded venter, fairly wide umbilicus, and strong sharp ribs that coarsen anteriorly and incline forward on the venter. Bifurcation occurs fairly regularly a little below the middle of the flanks, but on the body whorl the branches tend to be loosely united with the primary ribs. Some ribs remain unbranched. Pseudocadoceras grewingki (Pompeckj) in Alaska is much more common than the other species of the genus and has a longer range. It ranges through most of the upper two—thirds of the Chinitna formation (Imlay 1953b, table 2 on p. 50) and through the middle part of the Shelikof formation. In the upper part of its range it is associated locally with other species of Pseudocadocems of which 2 have much finer and denser ribbing and 1, P. crassicostatum Imlay (1953b, p. 94, pl. 49, figs. 19, 20, 22—24), has coarser and sparser ribbing. The beds containing P. grewingki (Pompeckj) in Alaska are correlated with the European zones of Erymnoceras coronatum, Cosmoceras jason, and the D-21 upper part of the Sigaloceras callov’iense zone. (Imlay, 1953b, p. 53). Types: Plesiotypes USNM 130779, 130781. Occurrence: Logtown Ridge formation at USGS Mesozoic locs. 24710 and 27317. Pseudocadoceras cf. P. grewingki (Pompeckj) Plate 2, figure 22 Five crushed ammonite fragments from the Moku- lumne River show all the characteristics of the genus Pseudocadoceras. In particular the largest and least crushed fragment, herein illustrated, greatly resembles the adult body chamber of P. grewingki (Pompeckj). It bears sharp fairly widely spaced primary ribs that bifurcate a little below the middle of the flanks. The secondary ribs are sharp, a little broader than the primary ribs, and arch forward on the venter. Figured specicmen: USNM 130783. Occurrence: From unknown stratigraphic position at USGS Mesozoic 10c. 27387. Pseudocadoceras cf. 1’. crassicostatum Imlay Plate 2, figures 14—21 Associated with Pseudocadoceras grewinglci (Porn- peckj in the basal part of the Logtown Ridge formation on the Cosumnes River are 15 specimens of the genus that have much coarser and more widely spaced rib- bing and probably belong to P. crassicostatum Imlay (1953b, p. 94, pl. 49, figs. 19, 20, 22—24) from Alaska (See pl. 2, figs. 9, 10). The specimens are so deformed and fragmentary, however, that the identification is not positive. They could be a coarse variant of P. grewingki (Pompeckj). Figured specimen: USNM 130780. Occurrence: Logtown Ridge formation, lower part, at USGS Mesozoic 10c. 27317. Pseudocadoceras? sp. Plate 2, figure 23 One ammonite from the upper part of the Cosumnes formation on the Cosumnes River probably belongs to Pseudocadoceras although it is too corroded for positive identification. It has moderately evolute coiling and strong closely spaced primary ribs most of which bifur- cate at or below the middle of the flanks. At one place the secondary ribs curve backward on the upper part of the flanks, but at other places they curve for- ward. Because of this backward curvature the ammo- nite was once compared by Imlay (1952, p. 975) with the perisphinctid genus Grossoumn'a of Callovian age. However, its coiling is not nearly evolute enough for it to belong to Grossoutria and it does resemble the genus Pseudocadoceras in both coiling and rib pattern. D—22 The local backward curvature of the secondary ribs 011 the flanks could be a result of deformation. This ammonite is significant because it is the only ammonite known from the upper part of the type sec- tion of the Cosumnes formation and is the only evi- dence that that part is of Callovian age. Figured specimen: USNM 130782. Occurrence: Cosumnes formation, upper part, at USGS Meso- zoic 10c. 22175. Genus AMOEBOCERAS Hyatt, 1900 Subgenus AMOEBITES Buckman, 1925 Amoeboceras (Amoebites) dubium (Hyatt) Plate 2, figures 24—28 Cardioceras dubium Hyatt, 1894; Geol. Soc. America Bull., v. 5, p. 420—422. ?Cardioceras whitneyi Smith, 1894, Geol. Soc. America Bull., v. 5, p. 253, 254. Amoeboceras dubium (Hyatt). Reeside, 1919, U.S. Geol. Sur- vey Prof. Paper 118, p. 38, pl. 24, figs. 5—8. (Hyatt). Crickmay, 19339., US. Geol. Survey Prof. Paper 175—B, p. 56. Amoeboceras (Amoebites) dubium (Hyatt). Spath, 1935, Med- delelser om Gronland, v. 99, no. 2, p. 34. Amoeboceras dubius (Hyatt). Hanna and Hertlein, 1941, Cali- fornia Dept. Nat. Res, Div. Mines Bull. 118, pt. 2, p. 166, fig. 60(23). The original type lot contains 15 molds/of which all have been crushed laterally. The species is charac- terized by fairly straight sharp mostly simple moder- ately to widely spaced ribs that incline slightly forward on the flanks and terminate on the ventrolateral margin in prominent clavate tubercules. On several speci- mens two adjoining ribs terminate in a single tubercle. A few ribs fade out on the upper part of the flanks below the zone of tubercles. The tubercles curve strongly forward and terminate at shallow grooves. The midline of the venter bears a stout low serrated keel whose serrations outnumber the tubercles nearly 2 to 1. This species was referred to Amoebites by Spath (1935, p. 34) because some of its ribs disappeared on the flanks below the tubercles. He compared three specimens from Greenland (see Spath, 1935, pl. 3, fig. 1, pl. 5, figs. 1, 6) with both A. dubium (Hyatt) and A. (Amoebites) elegans Spath (1935, p. 33, pl. 4, figs. 1—3) and noted that the holotype of A. elegans Spath differs from A. dubium (Hyatt) by having denser more regularly spaced ribbing near the umbilicus. It ap- pears, also, that A. dubium (Hyatt) may be distin- guished by having fewer secondary ribs and by devel- oping stronger tubercles on the larger whorls. Types: cotypes USNM 30201. Occurrence: Mariposa formation at USGS Mesozoic loc. 719. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Genus GROSSOUVRIA Sieminadzki. 1898 Grossouvria colfaxi (Gabb) Plate 2, figure 29; plate 3, figures 13-17 Ammonites colfaxi Gabb, 1869, Am. Jour. Conch., v. 5, pt. 1, p. 7, 8, pl. 4, fig. 2 [and v. 4, pl. 16]. Perisphinctes colfam' (Gabb). Hyatt, 1894, Geol. Soc. America Bull., v. 5, p. 424, 425. The species is represented by a nearly complete in- ternal mold and by part of an external mold of a single specimen. Both molds have been stretched con- siderably, but before stretching the whorls were prob- ably nearly circular in section. The coiling is evolute and the whorls embrace each other about one-fifth. The umbilicus is.very wide and shallow. The body chamber is represented by slightly more than half a whorl and is probably nearly complete. Its adoral end is slightly flexuous and is curved forward near the middle of the flank, but is not sufficiently well preserved to show if the specimen had a lateral lappet. The ornamentation on the inner whorls consists of variably strong variably spaced forwardly inclined ribs and constrictions. On the adoral half of the penulti- mate whorl the ribs are alternately single and forked. On the earlier formed whorls single ribs outnumber forked ribs. Most of the forked ribs are coarser and higher than single ribs. Bifurcation of the ribs occurs at various heights below the middle of the flanks. The ornamentation of the body whorl is similar to that on the penultimate whorl, but single ribs become more common toward the aperture. Bifurcation occurs at various heights, but mostly below the middle of the flanks. The bifurcation points are particularly prom- inent but probably were not tuberculate. The ribs on the internal mold are high and sharp. On the external mold they are high and round. Blost ribs are curved backward on the upper part of the flanks and on the venter and appear to weaken somewhat on the venter. On the body chamber some of the secondary ribs arise freely high on the flanks and others are indistinctly con- nected with primary ribs. Parts of a simple suture line are preserved near the adoral end of the last septate whorl. The ventral lobe is not exposed. The first lateral lobe is slender and trifid. The second lateral lobe is much shorter than the first. The auxilliaries are weakly developed and are somewhat distorted owing to deformation. This species is assigned to Grossouvria. because of the highly irregular and variable ribbing on its inner whorls, the presence of many constrictions and single ribs, the backward curvature of the secondary ribs on the body whorl, its rounded whorl section, and the char- acteristics of the suture line. Except for the irregular ornamentation on the inner whorls, the presence of JURASSI‘C AMMONITES, SIERRA NEVADA many deep constrictions, and its round whorl section, it could be assigned to Siemeradzkia. Arkell (1957, p. L 319; 1958, p. 212) notes, however, that the Bathonian Siemeradzkia is replaced by the Callovian Grossouvria and that the two are difficult to separate generically “except on stratigraphic grounds.” Grossouvm'a colfam' (Gabb) differs from most species of Grossouvria and Siemeradzkiu by having stronger ribbing and by attaining a larger size. G. anomala (Loczy) (1915, p. 386, pl. 8, figs. 8—11, pl. 14, fig. 5; Neumayr, 1871, pl. 12, figs. 2a, b; Spath, 1931, p. 364, pl. 60, fig. 8) is probably the most similar but has some- what weaker ribbing. G. pseudocobra Spath ( 1931, p. 371, pl. 48, figs. 7a, b) has finer ribbing on its inner whorls. G. leptus Gemmellaro figured by Corroy (1932, pl. 23, figs. 1, 2) is as large as G. colfaxi (Gabb), but has more secondary ribs and fewer unbranched ribs. Siemeradzkic de-mam'ae Parona and Bonarelli (1895, p. 147; Neumayr, 1871, pl. 12, figs. 4a, b, 5) is similar in size and appearance but is more involute, has fewer simple ribs, fewer constrictions, and the ribbing on its inner whorls is more regular. Most species of Ghoflatia and Subgrossouvr’ia differ from G. colfaxi (Gabb) by having more regular ribbing on their inner whorls, by developing more distant pri- mary ribs on their outer whorls, and by not having backwardly curved secondary ribs. A possible excep- tion is Chofiatia (Grossoumia?) (write Spath (1931, p. 362, pl. 40, figs. (6a, b) from India. G. colfam' (Gabb) shows some resemblance to the genus Rursicems Buckman (1919, pl. 145), but its ribbing is more irregular in strength and spacing, single ribs are more common, and its secondary ribs do not curve backward on the venter nearly as strongly. It may be compared, also, to Parapeltoceras annulosum (Quenstedt) (1886—87, pl. 88, fig. 22; Jeannet, 1951, p. 164, pl. 75, figs. 3a, b) but is readily distinguished by its deep constrictions, by its variable ribbing, and by some of its ribs bifurcating low on the flanks. Type: Holotype 5287, Mus. Comparative Zoology, Harvard College. Occurrence: Colfax formation of Smith “From railroad cut at sta. 2777, sec. 53, 1 mile west of Colfax, 14 ft. below surface of ground,” Placer County, Calif. Genus PERISPHINCTES Waagen, 1869 Perisphinctes? sp. Plate 5, figure 4 One small ammonite bears sharp, nearly straight primary ribs that incline forward on the flanks. Most of them bifurcate at or below the middle of the flanks into slightly weaker secondary ribs that cross the ven- ter transversely. Several short ribs are intercalated D-23 on the upper part of the flanks. Two constrictions are present. The preservation of this specimen does not permit positive generic or even family identification. It ap— pears to be a perisphinctid ammonite, although its ribs branch lower than in most genera of the Perisphinctidae. Its rib pattern shows some resemblance to that in Reineckeites of the family Reineckeiidae, but the ven- tral ends of the primary ribs are not swollen or tuber- culate. Figured specimen: Stanford Univ. Mus. Paleontology 9065. Occurrence: The label accompanying the specimen states “Mariposa formation, Nashville, Eldorado County.” The litho- logic features of the specimen suggest that it was obtained from the Logtown Ridge formation instead of from the Mariposa formation. Subgenus DISCOSPHINCTES Dacque, 1914 Perisphinctes (Diseosphinctes) virgulatiformis Hyatt Plate 3, figures 1—10 Perisphz'nctes virgulaliformis Hyatt, 1894, Geol. Soc. America Bu11., v. 5, p. 422, 423. Virgatosphinctoides virgulatiformis (Hyatt). Crickmay, 1933a, U.S. Geol. Survey Prof. Paper 175—B, p. 56, 57, pl. 16, figs. 24—25, pl. 17, figs. 1—8. ?Perisphinctes virgulatus Quenstedt. Burckhardt, 1912, Inst. geol. Mexico B01. no. 29, p. 35-38, pl. 7, figs. 4-14. ?Perisphinctes (Planites) virgulatus Quenstedt var. carribeana Jaworski, 1940. Neues Jahrb., Beilage-Band, Abt. B, p. 109—114, pl. 3, figs. 1—2, pl. 4, fig. 5, pl. 7, fig. 6. ?Discosphinctes cf. D. virgulatus (Quenstedt) of Burckhardt, Imlay, 1945, Jour. Paleontology, v. 19, p. 274, pl. 41, figs. 9—11. ?Discosphinctes carribeanus (Jaworski). Arkell, 1956, Jurassic Geology of the World, p. 573, London. The shell is compressed, discoidal. The whorls are flattened, higher than wide, and embrace the pre— ceding whorls considerably. The umbilicus is fairly narrow for a perisphinctid ammonite. The ornamentation consists of narrow closely spaced forwardly inclined ribs and of weak forwardly inclined constrictions. The primary ribs curve backward on the umbilical margin and curve forward gently on the flanks. Many of them remain simple but many others bifurcate between the middle and the upper third of the flanks. Trifurcating ribs are present locally near constrictions. (See pl. 3, fig. 3.) The secondary ribs are not interrupted on the venter. The suture line is similar to that of Perisphinctes (Discosph'inctes) carribeanus (Jaworski) figured by Burckhardt (1912, pl. 7, fig. 8). The first lateral lobe is long and trifid. The second lateral lobe is much shorter. There are three small auxilliary lobes. The second lateral saddle is as high as the first. This species is placed in the subgenus Discosphinctes Dacque as defined by Arkell (1937, p. XLVIlI—XLIX) D—24 because of its high whorls, involute coiling, dense forwardly inclined ribs, and weak constrictions. It shows no tendency to develop bundles of ribs as in Lithacocems. Virgatosphinctoides, which Arkell (1957, p. L 329) considers a synonym of Subpltmites, has more evolute coiling and the primary ribs become coarse and widely spaced. Die/totomosphinctes has more evolute coiling, deeper constrictions, and nearly radially trending ribs of which most bifurcate regularly on the ventral margin. Perisphinctes (Discosphinctes) virgulatiformis Hyatt appears to be identical with P. (Discosp/tinctes) car- ribeavnus Jaworski (see pl. 3, figs. 11, 12) from the late Oxfordian of Cuba (Jaworski, 1940, p. 109, pl. 3, figs. 1, 2; pl. 4, fig. 5, pl. 7, fig. 6) and Mexico (Burckhardt, 1912, p. 35, pl. 7, figs. 4~14) as far as the fragmentary condition of the type specimens of the California species permits comparison. Until better preserved, or more complete specimens of P. circulattformis are found, the exact specific relationship cannot be de— termined. Types: USNM 30204. Occurrence: USGS Mesozoic loc. formation. 901 from the Mariposa Subgenus DICHOTOMOSPHINCTES Buckman, 1926 Perisphinctes (Dichotomosphinctes) miihlbachi Hyatt Plate 4, figure 8 Perisphinctes mdhlbachi Hyatt, 1894, Geol. Soc. America Bu11., V. 5, p. 426. Dichotomoceras? mzzhlbachz’ (Hyatt). Crickmay, 1933a, US. Geol. Survey Prof. Paper 175—B, p. 57, pl. 18, figs. 1, 2. ?Per'£sphz'nctes durangensis Burckhardt, 1912, Inst. geol. Mexico B01. 29, p. 16, pl. 3, figs. 1, 2, pl. 4, fig. 6. The holotype, represented mostly by an external mold, is characterized by evolute coiling, by moderately spaced high narrow ribs that bifurcate above the line of involution, and by deep constrictions. The primary ribs curve backward at the edge of the umbilicus, and incline forward gently on the flanks. The secondary ribs, exposed at one place on the penultimate whorl where the suture line is preserved (see Crickmay, 1933, pl. 18, fig. 1), arise in pairs from the primary ribs and curve gently backward on the flanks. The dorsal ends of the secondary ribs are likewise exposed on part of the outermost whorl. Some of these arise in pairs from the primary ribs and others arise indistinctly from or al- ternate with the primary ribs. A few of these second— ary ribs curve backward at their junction with the primary ribs. One external mold of an ammonite (pl. 4, fig. 3) from the Stanislaus River opposite Bosticks bar (Mesozoic loc. 901) shows the ribbing typical of Dichotomo- sphinctes and matches very well with the inner whorls SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY of P. (Dichotomosphinctes) mu'hlbachi (Hyatt) at a com- parable size. The specimen was referred to Peri- sphinctes sp.? by Hyatt (1894, p. 423) who notes that The whorl is broader at the same age than is any other species mentioned in this paper; there are consequently fewer whorls at the same age. The lateral costae are single and very long, the bifurcations occurring well up on the abdomen. The immature growth stage of P. mfihlbachi Hyatt is possibly represented also, by one small specimen (pl. 4, fig. 5) from Mount Boullion (Mes. 100. 27460). It bears ribs and constrictions a little coarser and sparser than those on the inner whorls of the holotype. The venter is somewhat worn, but is clearly marked by deep forwardly arched constrictions and by faint continua- tions of the flank ribs. Some of the, primary ribs ap— pear to bifurcate at the margin of the venter, but others appear to remain simple. P. mfihlbachi Hyatt was assigned by Crickmay (1933a, p. 57) tentatively to Dichotomoceras on the basis of its suture line. That genus as defined, how- ever, does not have constrictions and its ribs generally bifurcate at or below the line of involution. Except for these features P. miihlbachi Hyatt greatly resembles the genotype of Dichotomoceras (Buckman, 1919, v. 3, pl. 139A). In shape and ornamentation P. mahlbachi Hyatt likewise greatly resembles Orthosphinctes, but it differs by having a higher point of rib branching and by lacking trichotomous ribs. Considering all its features P. milhlbachi Hyatt shows more resemblances to Dickotomosphinctes than to the other genera mentioned and it greatly resembles several described species of Dichotomosphinctes. For example, P. durangenis Burckhardt (1912, p. 16, pl. 3, figs. 1, 2), from Durango, Mexico, is nearly identical in appearance. P. plicatiloides O’Connell from Cuba (O’Connell, 1920, p. 670, pl. 36, figs. 1, 2; Jaworski, 1940, pl. 4, fig. 4, pl. 5, figs. 5 a, b, pl. 6, figs. 1 a, b) and Mexico (Burckhardt, 1912, pl. 3, figs. 3—6) has somewhat sparser ribbing. P. antecedens Salfeld (in Arkell, 1938, p. 83, pl. 15) and P. rotoides Ronchadze (in Arkell, 1938, p. 90, pl. 16, figs. 1—7) from Europe appear to differ only in minor details of ribbing. The assignment of P. milklbaché Hyatt to the sub- genus Dichotomosphinctes is strengthened also by its apparent identity with a well—preserved specimen of Dichotomosphinctes from the Naknek formation of Alaska shown on plate 4, figure 6. Unfortunately the holotype of I). mithlbachi Hyatt is not sufficiently preserved to show all the features necessary for a positive specific identification. Types: Holotype USNM 30203; comparable specimen from Mount Boullion, USNM 130786; comparable specimen from Rey- nolds Ferry, USNM 103460; comparable specimen from Alaska, USNM 130789. JURASSI‘C AMMONITES, SIERRA NEVADA Occurrence: “Mariposa” formation at USGS Mesozoic 100. 27517. Possibly present in the Mariposa formation at Mesozoic locs. 901 and 27460. Perisphinctes (Dichotomosphinctes) cf. P. elisabethaeformis Burckhardt Plate 4, figures 4, 7 One external mold shows parts of three evolute whorls that bear fine ribbing similar to that on the inner whorls of P. elisabethaeformis Burchkardt (1912, p. 31, pl. 6, figs. 1—5) from the upper Oxfordian of Mexico. The primary ribs begin at the line of in— volution, are nearly straight on the flanks, incline slightly forward, and generally bifurcate on the upper fourth of the flanks. A few primary ribs remain simple and some of the secondary ribs are indistinctly connected with the primary ribs. SeVeral weak'con— strictions are present. This species has much denser ribbing than the speci— men of P. (Dichotomosphinctes) from the G-alice for- mation of southwestern Oregon. (See pl. 4, fig. 2.) Figured specimen: Stanford Univ. Mus. Palentology 9063. Occurrence: Monte de Oro formation. North Bank of Feather River just north of Sycamore Hill, about 3 miles northeast of Oroville, and from 450 ft south of NE. cor. of sec. 4, T. 19 N., R. 4 E., Butte County, Calif. Perisphinctes (Dichotomosphinctes?) spp. Plate 4, figure 1; plate 5, figures 5, 6 Several ammonites are so crushed and stretched that their correct subgeneric position cannot be determined. The coarseness of the ribs and the positions at which the ribs divide into secondary ribs seem to vary as a consequence of stretching. Nevertheless the ammo— nites exhibit evolute coiling and moderate to coarse ribbing. Nearly all the ribs bifurcate along a zone somewhat above the middle of the flanks and the sec— ondary ribs incline forward. A few ribs remain simple and none of the ribs trifurcate. Weak constrictions are present. The bifurcation points appear to be much lower on the flanks than is typical of Dichotomosphinctes, but that may be a result of deformation. If it is normal, however, an assignment of the specimens to T arguatis- phinctes would seem more probable as that genus dif- fers from Dichotomosphinctes by having more simple ribs and somewhat lower points of rib furcation. The specimen shown on plate 5, figure 5, was men- tioned by Hyatt (1894, p. 426) as being closely related to Perisphinctes m'u‘hlbachi Hyatt. It appears, how— ever, to have much finer ribbing and lower points of rib furcation. Figured specimens: USNM 103461, 103787, 103788. Occurrence: Mariposa formation at USGS Mesozoic locs. 490, 27566, and 24317. D—25 Genus IDOCERAS Burckhardt, 1906 Idoceras MI. I. planula (Heyl) in Zeiten Plate 5, figures 12—16 The genus Idoceras in California is represented by one specimen that has been crushed laterally. It in- cludes an external mold of the inner whorls and an in- ternal mold of the outer whorls. On the inner whorls the amount of involution is about two-fifths. On the body whorl it is about one- third. The whorls are subquadrate in section and a little higher than wide. The flanks and venter are nearly flat. The umbilicus is fairly wide. The um— bilical wall is low, vertical, and rounds evenly into the flanks. The body chamber is incomplete, but is repre— sented by three—fifths of a whorl. On the inner whorls the ribs are high, fairly sharp, closely spaced, and incline strongly forward on the up- per part of the flanks. The primary ribs bifurcate just above the middle of the flanks into slightly weaker secondary ribs and are slightly swollen along the zone of furcation. The secondary ribs become thicker but slightly lower ventrally. Most forked ribs are separ- ated by short ribs that begin at the line of furcation. The characteristics of the ribbing along the midline of the venter are not well preserved. One deep constric- tion is present. On the penultimate whorl the primary ribs are sharp and moderately spaced. Most of them bifurcate at about two—thirds of the height of the flanks, but some remain simple and there are a few short ribs on the upper part of the flanks. The secondary ribs broaden ventrally, incline gently forward, and terminate at a nearly smooth zone along the midline of the venter. Several constrictions are present. On the body chamber the primary ribs become more widely spaced and curve forward strongly on the flanks. Most ribs bifurcate fairly high on the flanks and virga- toid branching occurs at two places. The secondary ribs are somewhat higher and broader than the primary ribs. The midline of the venter, exposed at only one place, appears to be nearly smooth. The body whorl has about 37 primary ribs. ‘ This species is assigned to the genus I docems because it has perisphinctid ribbing that is projected forward on the upper parts of the flanks and on the venter and is interrupted along the midline of the venter. It belongs to the group of Idoceras characterized by I. planula (Heyl) in Zeiten and I. balderum (Oppel) as defined by Burckhardt (1912, p. 102). This group is generally very evolute, has simple perisphinctid ribbing at all growth stages and commonly has generally pro- nounced constrictions. It may have some simple ribs D—26 but rarely trichotomous ribs. It attains its greatest development in Mexico where it is confined to beds of early Kimmeridgian age (Burckhardt, 1930, p. 64, tables 4—6; Imlay, 1939, p. 21, table 4). In Europe, however, it occurs both in beds of early Kimmeridgian and of late Oxfordian age (Arkell, 1957, p. L 323). In Mexico it is succeeded in slightly younger early Kim— meridgian beds by a group characterized by I. du- mngense Burckhardt. That group is generally less evolute, commonly has trichotomous and bidichotomous ribbing, and the ribs in the adult become swollen near the umbilicus and on the venter but become feeble or indistinct on the middle of the flanks (Burckhardt, 1912, p. 102). The California specimen of Idocems is similar to the Mexican species I. soteloi Burckhardt (1906, p. 52, pl. 9, figs. 9—12), I. laxecolu-tum Fontannes in Burckhardt (1906, p. 48, pl. 10, figs. 1—3), and I. neogaeum Burck- hardt (1906, p. 51, pl. 11, figs. 5—8) from Zacatecas, Mexico. Of these, I. soteloi Burckhardt has somewhat stronger ribbing on its inner whorls and ventral weaken— ing occurs only on the adoral end of the body whorl. I. lancevolutum Fontanncs in Burckhardt has more closely spaced ribs that are less inclined on the flanks and that become trichotomous near the adoral part of the body chamber. Many of its secondary ribs are indistinctly united with the primary ribs. 1. neogaeum Burckhardt appears to have weaker secondary ribs on its outer whorls and coarser ribbing on its inner whorls. The density of the ribbing on the inner whorls of the California specimen resembles that on the inner whorls of [figueroae Burckhardt (1906, p. 60, pl. 10, figs. 4—7) but the ribbing on the outer whorls is sparser and ap- parently sharper. The ribbing on the California speci- men would appear less sharp, however, if some shell layers were present as on most of the illustrated Mexican specimens. Compared with Idoceras planula (Heyl) in Zeiten from the late Oxfordian of Europe (Quenstedt, 1888, p. 974, pl. 108, figs. 1—5; Wegele, 1929, p. 76, pl. 9, fig. 3) the California specimen is less evolute and has fewer simple and intercalated ribs on its body whorl, but the spacing and sharpness of the ribs are closely similar. 1. schroederi VVegele (1929, p. 77, pl. 9, fig. 6) has denser ribbing and more simple ribs. 1. balderum (Oppel) (1863, p. 242, pl. 67, fig. 2; Loriol, 1877, p. 95, pl. 15, fig. 7; Wegele, 1929, p. 78, pl. 9, fig. 7) is more involute and has weaker and broader primary ribs. The specimen figured as I. laxevolutum (Fontannes) by Ziegler (1959, p. 28, pl. 1, fig. 6) appears to have coarser and straighter primary ribs. Figured specimen: Univ. of California [Berkeley] Mus. Pa- leontology 32724. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Occurrence: Logtown Ridge formation at Univ. of California (Berkeley) loc. A—4996. The field description is as follows: ”from a building stone quarry on Logtown Ridge, near the Huse Bridge over the Cosumnes River about six miles north of Plymouth. Ammonite occurs in a metamorphosed andesitic turf.” Idoceras? sp. Plate 5, figures 10, 11 One small specimen consists of an external mold of three inner whorls and a fragment of an internal mold of the next larger whorl. The three inner whorls are depressed ovate in section. They are marked by prominent forwardly inclined primary ribs and con- strictions. Most of the primary ribs bifurcate slightly above the middle of the flanks, but some remain simple. The secondary ribs arch forward on the vcnter. On the next larger whorl the vcnter bears a strong constriction that is preceded by a swollen rib. The ventral ribs arch forward strongly in a chevronlike manner as in the genus Idoceras. Figured specimen: Stanford Univ. Mus. Paleontology 9064. Occurrence: The field label states “Mariposa formation, Wood Canyon? near Sonora.” Genus SUBDICHOTOMOCERAS Spath, 1925 Subdichotomoceras? afl‘. S. filiplex (Quenstedt) Plate 5, figures 173, 9 Perisphinctes filiplex Quenstedt?. Hyatt, 1894, p. 423, 424. This species is characterized by evolute coiling and by high sharp fairly widely spaced primary ribs of which most bifurcate at about three-fifths of the height of the flanks. A few primary ribs remain simple. The secondary ribs are nearly as prominent as the primary ribs and incline forward slightly. Some of the secondary ribs are indistinctly connected with the primary ribs or arise freely high on the flanks. Several deep constrictions are present on the inner whorls of one fragmentary specimen, but constrictions are not present on any of the outer whorls. Hyatt’s comparison of the California species with “Ammonites” filiplex Quenstedt (1888, p. 1090, pl. 126, fig. 3) from the middle Kimmeridgian of Europe was apt, but the presence of several simple ribs suggests an even greater resemblance with Subdichotomocems inversum Spath (1931, p. 521, 522, pl. 84, figs. 7a, b, pl. 85, fig. 4) from the middle Kimmeridgian of India. Another species with ribbing nearly identical with that of the California species occurs in the upper Kimmeridgian near Mazapil, Zacatacas, Mexico (Burck- hardt, 1906, p. 114, pl. 31, figs. 1—4; Arkell, 1956, p. 562). Also, similar appearing specimens of Subdi- chotomocems are known from the Kimmeridgian of JURASSPC AMMONITES, SIERRA NEVADA southern Coahuila, Mexico (Imlay, 1939, p. 35, pl. 10, figs. 1—3, 13). The California species is placed in Subdichotomoceras rather than in Dichotomosphinctes because of the coarse ribbing on its inner whorls and its rather low point of rib l'urcation. Compared with Perisphinctes (Dichot- omosphinctes) mr‘lhlbachi Hyatt, its ribs are coarser and more widely spaced at comparable sizes and bifurcation occurs much lower on the flanks. Figured specimen: USNM 30203, 130785. Occurrence: Mariposa formation, USGS Mesozoic locs. 902, 903, and 904. Genus PELTOCERAS Waagen, 1871 Subgenus METAPELTOCERAS Spath, 1931 Peltoceras (Metapeltoceras?) sp. Plate 6, figure 1 The Stanford University collections contain a plaster cast of a large ammonite that is characterized by evolute coiling, perisphinctid ribbing on its inner whorls, and bituberculation 0n the outer whorls. The inner whorls are not well preserved, but at one place at a diameter of 25 mm they show two blunt tubercles from which arise pairs of strong ribs that trend transversely on the venter. At diameters greater than 50 Inm, two rows of tubercles are present and both become very prominent adorally. Apparently the inner tubercles develop first and are stronger than the outer tubercles 0n the largest whorls, but this appearance may be deceptive because the cast is poorly preserved, the original mold was crushed and distorted, and the venter of the largest whorl is not preserved. No trace of the suture line is visible. This specimen is assigned to Peltoceras because it has two rows of massive lateral tubercles on its outer whorls, perisphinctid ribbing on its inner whorls, and evolute coiling. As the inner rows of tubercles appear to have developed before the outer, the speci- men is provisionally assigned to the subgenus ZWet— apeltoceras Spath (1931, p. 552. 559, 560, 574—578; Arkell, 1940, p. LXX; Jeannet, 1951, p. 170). How- ever, blunt lateral tubercles appear on the inner whorls at a smaller diameter than in any of the species of Metapeltoceras from India figured by Spath (1931, pl. 110, figs. 4a, b, 8a, b; pl. 114, figs. 1a, b; pl. 105, figs. 8a, b; pl. 110, figs. 53., b; pl. 90, figs. 6a, b; pl. 118, figs. 6a, b; pl. 105, figs. 2a, b; pl. 106, figs. 4a—c), or from Switzerland figured by Jeannet (1951, pl. 72, fig. 5; pl. 73, figs. 5—6, 8; pl. 74, fig. 1; pl. 89, fig. 1;pl. 90, fig. 1, 2; pl. 91, fig. 1, 2). Figured specimen: Stanford Univ. Mus. Palentology 9062. Occurrence: The back of the plaster cast bears the statement, ”Ammonite from Mariposa slate in Big Indian Creek, Amador County south of Nashville, Eldorado County, Calif. Mold collected by F. M. N. Hamilton, State Mineralogist, May, 1941.” D-27 LITERATURE CITED Arkell, W. J., 1935-48, Monograph on the ammonites of the English Corallian beds: Palaeont. Soc. Pub., 420 p., 78 pls. 1950, A classification of the Jurassic ammonites: Jour. Paleontology, v. 24, p. 354—364, 2 figs. 1950~58, Monograph of the English Bathonian ammonites: Palaeont. Soc. Pub., 246 p., 33 pls., 83 text figs. 1956, Jurassic Geology of the World: London, Oliver and Boyd, Ltd., 806 p., 46 pls., 28 tables, 102 figs. 1957 in Arkell, W. J., Kummel, Bernhard, and Wright, C. W., Mesozoic Ammonoidea: Treatise on Invertebrate Paleontology, part L, Mollusca 4, 490 p., illus. Becker, G. F., 1885, Notes on the stratigraphy of California: US. Geol. Survey Bull. 19, 28 p. Buckman, S. S., 1909~30, [Yorkshire] Type Ammonites: 7 v. London, Wm. Wesley and Son. Burckhardt, Carlos, 1906, La faune jurassique de Mazapil avec un appendice sur les fossiles du crétacique inférieur: Inst. geol. Mexico B01. 23, 216 p., 43 pls. 1912, Faunes jurassiques et crétaciques de San Pedro del Gallo: Inst. geol. Mexico B01. 29, 246 p., 46 pls. 1919, 1921, Faunas jurésieas de Symon (Zacatecas): Inst. geol Mexico B01. 33, 135 p. (1919), 32 pls. (1921). 1927, Cefalépodos del Jurasico de Oaxaca y Guerrero: Inst. geol. Mexico B01. 47, 108 p., 34 pls. 1930, Etude synthétique sur le mésozoique méxicain: Schweizer. palaeont. Gesell. Abh., V. 49—50, 280 p., 11 tables, 32 figs. Callomon, J. H., 1955, The ammonite succession in the Lower Oxford Clay and Kellaways Beds at Kidlington, Oxford- shire and the zones of the Callovian stage: Royal Soc. London Philos. Trans, ser. B, Biol. Sci., no. 664, v. 239, p. 215—264, pls. 2, 3, 4 tables, 5 test figs. Corroy, G., 1932, Le Callovien de la Bordure Orientale du Bassin de Paris: Carte géol. France Mém., 337 p., 29 pls., 62 figs. Crickmay, C. H., 1930, Fossils from the Harrison Lake area, British Columbia: Canada Natl. Mus. Bull. 63, p. 33—112, pls. 8—23, 7 figs. 1931, Jurassic history of North America: its bearing on the development of continental structure: Am. Philos. Soc. Proc., V. 70, no. 1, p. 15—102, 2 figs, 14 maps. 1933a, Some of Alpheus Hyatt’s unfigured types from the Jurassic of California: U.S. Geol. Survey Prof. Paper 1754B, p. 51—58, pls. 14—18. —~— 1933b, Mount Jura Investigation: Geol. Soc. America Bull., v. 44, p. 895—926, 11 pls. Diller, J. S., 1892, Geology of the Taylorville region: Geol. Soc- America Bull., v. 3, p. 369—394. 1907, The Mesozoic sediments of southwestern Oregon: Am. Jour. Sci., v. 23, p. 401—421. 1908a, Strata containing the Jurassic flora of Oregon: Geol. Soc. America Bull., v. 19, p. 367—402, map. 1908b, Geology of the Taylorsville region, California: IRS. Geol. Survey Bull. 353, 128 p., map. Donovan, I). T., 1953, The Jurassic and Cretaceous stratigraphy and paleontology of Trail Q, east Greenland: Meddelelser 0m Grcnland, v. 111, no. 4, 150 p., 25 pls., 14 figs. Douville, Robert, 1915, Etudes sur les Cosmocératidés, etc., Mém. Expl. Carte Géol. France, 75 p., pls. 1—24. (Paris). Fontaine, W. M., 1905, The Jurassic flora of Douglas County, Oregon, in Ward, L. F., and others, Status of the Mesozoic floras of the United States: US. Geol Survey Mon. 48, p. 48—185 D—28 Gabb, W. M., 1869, Descriptions of some secondary fossils from the Pacific States: Am. Jour. Conchology, v. 5, pt. 1, p. 5—18, illus. Hanna, D. G., and Hertlein, L. G., 1941, Characteristic fossils of California: California Dept. Nat. Res, Div. Mines Bull. 118, pt. 2, p. 165—182, illus.; with descriptions of Foratninif- era by C. C. Church. Heyl, G. R.,»1948, Foothill copper-zinc belt of the Sierra Nevada, California in Copper in California: California Dept. Nat. Res, Div. Mines Bull. 144, p. 11—29, 1 pl. Hyatt, Alpheus, 1894, Trias and Jura in the western states: Geol. Soc. America Bull., v. 5, p. 395—434. Imlay, R. W., 1939, Upper Jurassic am'nonites from Mexico: Geol. Soc. America, Bull., v. 50, p. 1—78, pls. 1—18. 1945, Jurassic fossils from the southern states, no. 2: Jour. Paleontology, v. 19, p. 253—276, pls. 39—41, 1 text fig. 1952, Correlation of the Jurassic formations of North America, exclusive of Canada: Geol. Soc. America Bull., v. 63, p. 953—992, 2 correlation charts. 1953a, Callovian (Jurassic) ammonites from the United States and Alaska, Part 1. Western Interior United States: US. Geol. Survey Prof. Paper 249—A, p. 1—39, 24 pls., 2 figs, 3 tables. 1953b, Callovian (Jurasssic) ammonites from the United States and Alaska, Part 2. Alaska Peninsula and Cook Inlet regions: U.S. Geol. Survey Prof. Paper 249—B, p. 41— 108, pls. 25—55, figs. 2—9, 6 tables. 1955, Characteristic Jurassic mollusks from northern Alaska: US. Geol. Survey Prof. Paper 274—D, p. 69—96, pls. 8—13, 1 fig., 4 tables ——— 1959, Succession and speciation of the pelecypod Au- cella: U.S. Geol. Survey Prof. Paper 314—G, p. 155—169, pls. 16—19, 1 fig, 1 table. Imlay, R. W., Dole, H. M., Wells, F. G., and Peck, Dallas, 1959, Relations of certain Upper Jurassic and Lou er Cretaceous formations in southwestern Oregon: Am. Assoc. Petroleum Geologists Bull., v. 43, no. 12, p. 2770—2785, 3 figs. Jaw or— ski, Erich, 1940, Oxford-Ammoniten von Cuba: Neues Jahrb., Beilage-Band 83, Abt. B, no. 1, p. 87—137, pls. 3—7. Jeannet, Alphonse, 1951, Stratigraphie und Palaontologie des oolithischen Eisenerzlagers von Herznach und seiner Umge- bung: Beitr. geol. Schweiz, Geotechnische ser., v. 5, lief. 13, 240 p., 107 pls. Knowlton, F. H., 1910, Jurassic age of the “Jurassic flora of Oregon”: Am. Jour. Sci., 4th ser, v. 30, p. 33—64. Kobayashi, Teiichi, 1947, On the occurrence of Seymourites in Nippon and its bearing on the Jurassic paleogeography: Japanese Jour. Geol. and Geog, v. 20, p. 19—31, pls. 7. Lindgren, Waldemar, 1900, Description of the Colfax quad- rangle: U.S. Geol. Survey Geol. Atlas Colfax folio., no. 66, 10 p. Loczy, Ludwig, 1915, Monographie der Villanyer Callovien— Ammoniten: Geologica Hungarica, v. 1, pts. 3—4, p. 255— 509, pls. 13—26. Loriol, P. de, 1876—78, Monographie Paleontologique des cou- ches de la zone a Ammonites tenuilobatus de Badin (Argovie): Schweizer. palaeont. Gesell. Abh., v. 3—5, 200 p., pls. 1—22. Lupher, R. L., 1941, Jurassic stratigraphy of central Oregon: Geol. Soc. America Bull., v. 52, p. 219—270, 4 pls., 3 figs. McKee, E. D. and others, 1956, Paleotectonic maps of the Jurassic system: US. Geol. Survey Misc. Geol. Inv. Map I—175, 6 p., illus. incl. geol. map; with a separate section on paleogeography by R. W. Imlay. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY McLearn, F. H., 1929, Contributions to the stratigraphy and paleontology of Skidgate Inlet, Queen Charlotte Islands, British Columbia: Canada Nat. Mus. Bull. 54, Geol. ser., no. 49, p. 1—27, 16 pls. Neumayr, Melchior, 1871, Die Cephalopoden—fauna der Oolithe von Balin bei Krakau: K. K. Geol. Reichsanstalt Abh., v. 5, p. 19—54, pls. 9—15. O’Connell, Marjorie, 1920, The Jurassic ammonite fauna of Cuba: Am. Mus. Nat. History Bull., v. 42, art. 16, p. 643— 692, pls. 34-38. Oppel, Albert, 1862—63, Ueber jurassische Cephalopoden: Palaeont. Mitt. Mus. Bayer.-Staats, pt. 3, p. 127—162, pls. 40—50 (1862); p. 163—266, pls. 51—74 (1863). Parona, C. F. and Bonarelli, Guido, 1895, Sur la faune du Callovien inférieur (Chanasien) de Savoie: Acad. Sci. Savoie Mém., 4 ser., v. 6, 179 p., pls. 1—11. Quenstedt, F. A. 1883—88, Die Ammoniten des Schwabischen Jura, 3 v.: Stuttgart, 1140 p., 126 pls. Reeside, J. B., Jr., 1919, Some American Jurassic Ammonites of the genera Quenstedticeras, Cardioceras, and Amoeboceras, family Cardioceratidae: U.S. Geol. Survey Prof. Paper 118, 64 p., 24 pls. Rogers, C. L. Zoltan de Cserna, Tavera, Eugenio and Ulloa, Salvador, 1956, General geology and phosphate deposits of Concepcion del Oro district, Zacatecas, Mexico: U.S. Geol. Survey Bull., 1037—A, 102 p., 2 pls. 27 figs, 8 tables. Smith, J. P., 1894, Age of the auriferous slates of the Sierra Nevada: Geol. Soc. America Bull., v. 5, p. 243—258. 1910, The geologic record of California: Jour. Geology, v. 18, no. 3, p. 216—227. Sowerby, J., and J. de 0., 1812—46, Mineral Conchology, 7 v. [For dates see Arkell, 1935, p. 8.] Spath, L. F., 1927—33, Revision of the Jurassic cephalopod fauna of Kachh (Cutch): Palaeontologia India, new ser., v. 9, 6 pts., 945 p., 130 pls. 1932, The invertebrate faunas of the Bathonian-Callo- vian deposits of Jameson Land (East Greenland): Medde- lelser om Gronland, v. 87, no. 7, 158 p., 26 pls., 14 text figs. 1935, The Upper Jurassic invertebrate faunas of Cape Leslie, Milne Land. I. Oxfordian and lower Kimmeridgian: Meddelelser om Griinland, v. 99, no. 2, 82 p., 15 pls. Taliaferro, N. L., 1933, Bedrock complex of the Sierra Nevada, west of the southern end of the Mother Lode [abs]: Geol. Soc. America Bull., v. 44, p. 149—150. 1942, Geologic history and correlation of the Jurassic of southwestern Oregon and California: Geol. Soc. America Bull., v. 53, p. 71—112, 3 figs. 1943, Manganese deposits of the Sierra Nevada, their genesis and metamorphism: California Dept. Nat. Res, Div. Mines Bull. 125, p. 277—332, 10 figs. Turner, H. W., 1896, Further contributions to the geology of the Sierra Nevada: US. Geol. Survey 17th Ann. Rept., pt. 1, p. 521—762. Ward, L. F., 1900, Status of the Mesozoic floras of the United States: US. Geol. Survey 20th Ann. Rept., pt. 2, p. 340—377. Wegele, Ludwig, 1929, Stratigraphische und faunistische Un- tersuchungen im Oberoxford und Unterkimmeridge Mittel- frankens: Palaeontographica, v. 71, p. 117—210, pls. 25—28 (1—4), v. 72, p. 1—94, pls. 1—9 (5—15). Wells, F. G., and Walker, G. W., 1953, Geology of the Galice quadrangle: U.S. Geol. Survey Quadrangle Map (GQ 25) with sections and text. Ziegler, Bernhard, 1959, Idoceras und verwandte Ammoniten- Gattungen im Oberjura Schwabens: Eclogae geol. Hel- vetiae, v. 52, no. 1, p. 19—56, 1 pl., 4 figs. A Page Ages and correlations of formation ___________ D—3—9 Agua Fria slate _______________________________ 3 Alaska Peninsula and Cook Inlet regions, Alaska ___________________________ 11 alternam, A mmumites 12 A moeboceras _________________________ 12 Amador group ___________________________ _ 2 .Ammom'tea colfazi ____________________________ 2, 6, 22 filipler ____________________________________ 26 lochmaia.. 19 pichleri ___________________________________ 19 A moebites ____________________________________ 7, 8, 22 (A moebites), A moebaceras _____________________ 2 dubium A moeboceraa ______________ 13, 14, 22, pl. 2 elegans, Amoeboceras,_ 22 A moeboceras __________________________ 7, 11, 12, 18, 22 ultemans _________________________________ 12 dubium _________ 2, 22 dubius ________ 22 (A moebites) ..... 2 (A moebites) dubium _______________ 13, 14, 22, pl. 2 (A moebites) elegans _______________________ 22 (Prionodoceras) _ . ________________________ 11 annulowm, Parapdtoceras ____________________ 23 anomala, Grossouvria ______ 23 antecedem, Perisphinctcs_.__ 24 Aspidoceratidae _____________ 2 athletu, Peltoceras. _________ 6, 9 A ucella ________________________ 2 pallasi plicata ________________ 13 A ulacostephanus pseudomutabilis ____________ 7, 11, 13 aurarium, Entolium __________________________ 8, 14 aurita, C’hoffiztia (Grossouvria) _________________ 23 A vicula sp ____________________________________ 8, 14 B bulderum, Idoceraa _________________________ 13, 25, 26 Belemnites pacificus _________ _ 8, 14 sp ______________________ _ 14 Bicknell sandstone ___________________________ 9 Big Indian Creek _____________________________ 6, 11 bimammatum, Epipeltoceraa 6, 7, 12 Biologic analysis _________________ _ 2 Bowser member, Tuxedni formation. .__ 6.10 Buchia ______________________________ 2, 7, 8, 11, 13, 18 cwcentrica ____________ 7,8,9, 10,11, 13, 14, 18, pl. 5 moaquensis piochii ________ rugasa __________ buckmani, Lilloettia ___________________________ C Cadaceraa _______________________________ 10,11,12, 18 catastoma. 10 sp. juv _ _ 9 Cadoceratinae . _ _ 2 Calaveras formation __________________________ 3 Calaveras group .............................. 2 Calliphylloceraa_.__ ______________ 11 calloviense, Siaaloceraa. .. 6, 7, 9, 10, 11, 13, 21 Cardioceras ______________________ 11 dubium ___________________________________ 22 whimeyi __________________________________ 22 Cardioceratidae ______________________________ 2 INDEX [Italic numbers indicate descriptions] Page Cardioceratinae ....... 2 carribeanus, Discosphinctes... __________ 23 Perisphinctes (Discosphincles) , _ _ 7, 12, 23, 24, pl. 3 catostoma, Cadoceras __________________________ 10 cautimigrae, Perisphinctes. ____________ 7 Central Oregon __________________ 10 Cephalopoda ______ _ _ _ - 19 cereale, Kepplen‘tes ____________________________ 20 Cerithium sp __________________________________ 8,14 Chinitna formation, 6, 7, 9, 10, 11, 13,21 Chlamys. ___________________ 8,14 Choflatia. ........ .__ 12, 18, 23 hyatti _____________________________________ 9,11 waitzi ____________________________________ 12 (Grossouvria) aurita., sp ................... Colfax formation of Smith. col faxi, A mmo'nites ___________________________ 2, 6, 22 Grossouvria _________________ 13, 14, 22, 23, pls. 2, 3 Perisphinctes _____________________________ 22 Comparisons with other faunas _______________ 9-13 concentrica, Buchia. __,,._ 7,8, 9, 10, 11, 13. 14, 18,pl. 5 Corbis sp _____________________________________ 14 coronatum, Erymoceras _______________________ 6, 21 Cosmoseras. _ coslidensum, Gowerz’ceras _________ Cosumnes formation ________ 2, 3—6, 9, 10, 13, 17, 21,22 Cosumnes River ________ 3, 8, 9, 10, 13, 16, 17, 18, 21, 26 crassicostatum, Pseudocadoceras.. 6, 10, 13. 14, 21, pl. 2 Crem‘ceras ____________________________________ 12 D de-mariae, Siemeradzkia _______________________ 23 denticulata, Oecotraustes _______________________ 19 denticulatum, Taramelliceras __________________ 19 Taramelliceras (Proscaphites)._ 7, 14, 19, pl. 1 Dichotomoceras _______________________________ 24 mdhlbachi ________________________________ 24 Dichotomosphinctes ........... 7. 9, 10, 13, 19, 24, 25, 27 (Dichotomasphinctes) durangensis, Perisphz'nc- tes ____________________________ 8,12,18 eliwbethaeformis, Perisphinctes,. 8, 12, 18, 25, pl. 4 mfihlhachi, Perisphinctes __________________ 7 8,11,12,13,14,18,2A,27,p1. 4 Perisphinctcs _____________________ 2, 8, 11, 12. 25 plicatilis, Perisphinctes _______________ _._ 10,12 wartaeformis, Perisphinctes ................ 10,12 spp., Perisphinctes ................. 7, 25, pls. 4, 5 dillen', Reinrckeia (Reineckeites) __._..._L 9,12 Discosphinctes. - ........ 7. 13, 19, 23 carribeanus. _____________ 23 mrgulatus ................................. 23 (Discosphinctes) cambeanua, Periaphinctes ..... 7, 12,23,24, pl. 3 Perisphinctes ............................. 2 virgulatiformis, Periaphinctes ______________ 7 12, 13, 14, £3, 24, pl. 3 Dothan formation..-..._._1.._._._,________-, 10 dubium, Amorbocerus _________________________ 2, 22 Amoeboceraa (Amoebitea) _________ 13, 14,22, pl. 2 Cardioceraa ............................... 22 dubius, Amoeboceraa .......................... 22 durangeme, Idaceraa __________________________ 26 Page durangemis, Perisphinctea _____________________ 24 Perisphinctes (Dichotomosphinctea) ...... 8,12,18 E 616901”, Amoebaceraa (Amoebitzs) .............. 22 eltsabrthaeformis, Perisphmctes ...... _ 14,25 Perisphinctes (Dichatomasphincm) ........ 8, 12, 18, 25, pl. 4 Entolium aurarium ___________________________ 8, 14 sp _______ 8,14 Epipeltoceras b2mammatum. _ . 6, 7, 12 Erymoceras coranatum ________________________ 6, 21 Euaspidocrras ________________________________ 12 F fialar, Glochiceras _____________________________ 13 figueroae, Idocerae _____________________________ 26 filiplez, Ammonites ___________________________ 26 Perisphinctes _____ _.. 26 Subdichotomoceraa... _. 7,13, 14,26,111. 5 Foreman formation of Diller __________________ 9—10 G Galice formation __________________ 8, 10, 11, 12, 19, 25 Galilaeiceras. _ 20 lind7rem’ - 20 Galilueites .................................... 20 Galileanus ____________________________________ 20 Geographic distribution ______ . 13 Glochz‘cems fialar. _. ______ _ 13 Go wericeras ..... 7, 11, 12,13, 18,20 costidensum _______________________________ 11, 20 snugharborenais ........................... 20 spinosum ..... 10 Kepplerites... 10 (Gowericems) Kepplerites ..................... 2,20 lindgreni, Kepplerz'tes ...... 6,7, 10,13, 14,20,111. 1 sp., Kepplerites __________________________ 7, pl. 1 (Gowericeras or Seymourites) lindgreni, Kep- plmtes ___________________________ 20 G1 egoryceras transnersarium ___________________ 7, 12 grewingki, Pseudocadoceras ______ 3, 6, 9, 13, 14, 8!, pl, 2 Grossouvria __________________________ 2, 3, 6, ll, 21, 22 anomalo. 23 colfazi ____________________ 13, 14, 2t, 23, pls. 2, 3 leptus ________________________ 23 pseudocobra __________ 23 (Grossouvria) mm'ta, Chofi’atia _________________ 23 H harveyi, Paracadocrras ......................... 10 IIinchman tufi ________ 9 Hosselkus Creek _______ 9, 10 Hunter Valley chert..- 3 hyatti, Chofl'atia _______________________________ 9,11 Idoceras ............................. 2, 6, 13, 18,25, 26 balderum_. - 13,25, 26 durangeme ............. _ 26 figueroae _______________ _ 26 laxevolutum _______________________________ 26 neogaeum _________________________________ 26 planula... ________ 3, 6, 14, £5, 26, pl. 5 schraederi. ....................... 26 soteloi" ___________________ 26 sp ________________________________ 14, 26, pl 5 D—30 Page Idoceratinae _____________________________ _ 2 Indian Gulch agglomerates. _ 2 inversum. Subdichotomoceras __________________ 26 J jasan, Cosmoceras ________________________ - 21 Kosmocems __________________________ _ 6, 7 K keppleri, Kepplerites __________________________ 20 Kepplerites _____________________ 7, 11, 12, 13, 18, 19, 20 cereals” ._ 20 keppleri... __ 20 lorinclarki __________________ 6, 7, 13, 14, 19, pl. 1 tychom‘s ___________________________________ 11 (Go wericeras) _____________________________ 2, 20 lindgrem' ____________ 6, 7, 10, 13, 14, 20, pl. 1 spinosmn __________ _ sp ________ Kepplerites (Gozwriceras or Seymourites) lind- grem‘ _____________ Ke'pplerites (Seymourites).-_. (Seymomz'tes) kuzmyuensis ______________ 19 Kettle formation of Diller ___________________ 9 Kettle meta-andesite ______________________ 9, 10. 12 Kosmacrras jason ___________________________ 6, 7 Kosmoceratidae ,,,,,,,,,,,,,,,,,,,,,,,, 2 kuzuryz/ensis, Kepplerites (Seymourites). 19 L laxevolutum, Idoceras ________________________ 26 leptus, Grossouvria __________________________ 23 Lilloettia ______________________________ 11 buckmani _________________________ 10 . 10 _ 8 . 8, 14 lindgrem, Galilaeicems. . __. _ 20 Kepplerites (Gowerzceras) ________________ 6, 7, 10,13,14,?0, pl. 1 (Gamerz‘ceras or Seymourztes) __________ 20 Olcostephanus ___________________________ 20 Literature cited _____________________________ 27428 Lilhacoceras ______________ 7, 24 lochmsz’s, Ammonites _____ 19 Logtown Ridge agglomerates _________________ 2, 3 Logtown Ridge formation ________ 3, 6, 7, 8, 10, 11, 13, 16, 17, 18, 21, 23, 26 Lonesome formation of Lupher _______________ 10 lorinclarki, Ixepplerz’tes __________ 6, 7, 13, 14, 13, pl. 1 Lytoceras _____________________________________ 11 M Macrocephalites macrocephalus _________________ 6, 7 Macrocephalztes macracephalus zone of Europe. 7, 9,11 macrocephalus. Macrocephalites ________________ 6, 7 Jl/[acrophylloceras ____________________________ 11 Mariposa formation ______________ . 2, 6, 78,9, 10, 12, 13718, 23, 24, 25, 27 Mariposa slate ____________________________ 2, 3, 9 Meleayrinella _ 8 sp _________ 14 Metapeltoceras ___________________ 27 (Mempeltoceras), Peltoceras _______ 2 sp., Peltoceras _____________________ 14, 27, pl. 6 Mexico ____________________________________ 12—13 Modiolus ____________ 8 sp ______________________________________ 14 Mokulumne River. . _______ 21 Monte de Oro formation.. 2, 8—9, 16, 18,25 mosqumsis, Buchia ______________ 11, 13 mzihtbachz', Dichatomoceras. __.._ 24 Perisphinctes ____________________________ 24, 25 (Dichotomosphz'nctes)... _______ 7, S, 11, 12, 13, 14, 18, 24, 27, pl. 4 mutabilis, Rasenia ____________________________ 13 Mysterious Creek formation of Crickmay _____ 10 Mytilus sp ____________________________________ 14 N Naknek formation _____________________ 11, 12, 19, 24 mogaeum, Idoceras ___________________________ 26 INDEX m’kitini, Xenocephalztes _________________ North Ridge formation of Crickmay... Nucula sp ____________________________________ S 0 Ochetoceras __________________________________ 12 Oecotraustes denticulata. 19 Olcostephanus lindgreni _____________________ 20 Oppeliidae __________________________________ 2 Ostrea. ._._ s 51)... 14 pacificus, Belemnites._._ 8,14 pallasi plicata, Aucella.. .... 13 Paracadoceras ____________________________ 11, 12, 18 harveyz‘... 10 so ..................................... 9 Parapvltoceras annulosum ____________________ 23 Il’eltoceras __________________________ 6,11,12, 13, 18,27 athleta __________________________________ 6, 9 ( Meta peltoceras) ................ 2 5p ______________ Peltoceratinae ________ I’enon Blaneo agglomerate. ...... 3 Pefion Blanco volcanics. _ ______ 3 Perisphinctes ______________________________ 2, 13, 23 antecedens ______________________________ 24 cantisnigrae _____________________________ 7 colfarri _________________________ 22 dumngensis ______________________________ 24 elisatethaeformis _________________________ 14,25 filz’pler _________________________ 26 mfihlbachi ___________________ plicatiloides..- _ 24 rotoides ....... . 24 virgulatiformis __ 23,24 liirnulatus ______ 23 (Dichotomosphinctes) ......... .._ 2, 8, 11,12. 25 durangensis ______________________ 8, 12, 18 elisabethaeformz's ____________ 8,12, 18, :95, pl. 4 mu lbachi _____ 7, 8, 11, 12, 13, 14, 18, 2.4, 27, pl. 4 olzcatilis __________________________ 10, 12 wartar/ormis ____________ spp ____________________________ 7, 25, pls. 4, 5 (Discosphinctes) __________ 2 carribeanus.... _ 7, 12, 23, 24, p1.3 virgulatiformis. . 7, 12, 13, 14, £3, 24, pl. 3 (Plam‘tes) ziz‘rgulams ______________________ 23 sp ............. 14,23,24,pl.5 Perisphinctidae. .. Perisphinetinae... _______________________ 2 Phylloceras __________________________ 2, 11, 12, 19 Sp ________________________ 14,19 Phylloeeratidae... _ 2 Phylloceratinae ________________ _ 2 ,Iichleri, Ammonites _ 19 Piano Sp _______ 14 piochii, l-Iuchz‘a .............. 8,9 (Planites) Irirgulatus, Pensphinctes ___________ 23 planuvla, Idoceras ________________ 3, 6, 14, 1.5, 26, pl, 5 1,lz'cata, Aucella pallasi ....................... 13 plicatz’lis, Perisphinrtes (Dichotamosphinctes)._ 10,12 plicatiloides, Perisphinctfsuu; _______________ 24 (Prionodoceras), A mocbocems _________________ 11 Proscaphites ................... _ 7, 19 (Proscaphites) denticuvlatum, Taramelliceras_._ 7, 14, 19, pl. 1 Tammellz‘ieras ____________________________ 2, 12 Pseudocadoceras.. _ 2, 3, 6, 7, 9, 10, 11, 12, 13, 18, 21 crassicostatum ...... 6, 10, 13, 14, 21, pl. 2 grewingki... _ 3, 6, 9, 13, 14, 21, pl. 2 schmidti. . - _ 9, 10 sp .............................. 3,14, 21,131.? pseudocabra, Grossouvria ..... 23 pseudomutabilis, A ulacostephanus __________ 7, 11, 13 Pseudoperisphinctinae _______________________ 2 R Rasmia mutabilis ........ _ 13 Reimckeia _______________ _ 18 (Reineckeites) ________ . 12 dilleri _______________________________ 9, 12 Reineckeiidae ___________ Reineckeites ..... (Reineckeites) dilleri, Reineckeiu .............. 9, 12 Reineekeia .............................. 12 Richeiceras _________________________ 19 Riddle formation ___________________________ 8 Rogue formation .................. 10 rotoides, Perisphinctesu _____ 24 rugosa, Ruchia. Rursiceras ............. schmidti, Pseudacadoceras _________ schraederz‘, Idoceras _____ Seymourz'tes. . ....... (Seymourites), Kepplmtes. - . _ kuzuryuensis, Kepplerites ________________ 19 Shelikof formation .......................... 21 Siemeradzlcia ......... 23 de-mariae _________________________________ 23 Sigaloceras callot‘imse ............. 6, 7, 9, 10, 11, 13, 21 Snowshoe formation of Lupher ............... 10 snuaharboremis, aowericeras __________________ 20 soteloi, Idoceras _______________________________ 26 Southwestern Oregon ......... 10 spinosum, aowen’cems ........ _ 10 Kepplerites (”owericeras). 10 Stratigraphic summary ______________________ 2—3 S11 bdichotomoceras. ,. . .. ...... 2, 7, 8, 12, 19, 26, 27 filiplez ...................... 7, 13, 14, 26‘, pl. 5 inversum..... _ 26 Subgrossouliria. _ _ 23 Subplam‘tes ................................. 24 Summary of results ......................... 13 Systematic descriptions ....................... 19—27 ’1‘ Tancredia .................................... 8 sp ........... 14 Taramelliceras ___________________________ 7, 12, 19 denticulatum _____________________________ 19 (I’roscaphites) __________ _ _ _ _ 2, 12 demiculatum ........ 7, 14, 19, pl. 1 'l‘ararnelliooratinan _______ . 1 _ _ 2 Taylorsville area, Galifornia_ _______________ 9—10, 12 Torquetisphinctes- ........................... 25 transversarium, ”regeryceras.. Trigonia._._._.._ sp ...................................... 14 ’l‘rowhridge shale of Lupher ................. 10 Turbo sp ____________________________ 8, 14 tychom’s, Kepplerites __________________________ 11 V vicarius, Xenocephaliter _______________________ 10 1" irgatosphinctoides virgulatiformis ............ 23 virgulatz‘formz’s, Perisphinctes ....... .. 23, 24 Perisphinctbs (DiacosphinctesL. _____ 7, 12, 13,14, 25, 24, pl. 3 l’irgatosphinctaides.. ________________ 23 virgulatus, Discasphinctes. _____________ 23 Perisphinctcs. . . . . __ 23 (Planites) .. 23 Virgatosphinctinae _________________________ 2 Ir’irgatosphz'nctoides ____________________________ 24 W waitzi, Clio/fetid ______________________________ 12 wartaeformis, Perisphinctes (Dichotomosphinc- tes) _______________________________ 10, 12 Western British Columbia ______ whitneyi, Cardiocems _____________ X Xenocephalites __________________________ 10, 11, 12,18 m'kitim‘ _________________________________ 12 vicarius _______________________ 10 9 10 Yakounites _____________________ 20 Yakaunoceras _______________________________ 20 U. S. GOVERNMENT PRINTING OFFICE: 1961 O ~583565 PLATES 1— 6 PLATE 1 [All figures natural size] FIGURES 1—8. Kepplerites lorinclarki Imlay, n. sp. (p. 19). 1—3, 8. Holotype, USNM 130777 from USGS Mesozoic loc. 27313. Figs. 1—3 are from rubber casts of an external mold of the body chamber. Figs. 2 and 3 together represent the same View as fig. 1 but are lighted to emphasize ribbing and tubercles. Fig. 8 is an internal mold of the body chamber of holotype. 4—7. Paratypes, USNM 130778 from USGS Mesozoic loc. 27313. Figs. 4—6 are from rubber casts of external molds. Fig. 4 represents part of an penultimate whorl. Fig. 5 shows the apertural constric- tion. Fig. 6 shows the strong primary ribs and tubercles on the penultimate whorl. Fig. 7 is an internal mold. 9—11. Taramelliceras?(Proscaphz’tes?) denticulatum (Hyatt) (p. 19). Cotypes, USNM 30206 from USGS Mesozoic 100. 901. Note ventral serrations of figs. 9 and 10. Fig. 11 shows gentle ribs on the flanks. Compare with same view published by Crickman, 1933, Prof. Paper 175—B, pl. 17, figs. 12, 13. 12, 14. Kepplerites (Gowericeras) lindgreni (Hyatt) (p. 20). Holotype, USNM 30205 from USGS Mesozoic 100. 27516. 13. Kepplerites (Gowericeras) sp. Specimen, USNM 130791 from USGS Mesozoic 10c. 24793 in the Talkeetna Mountains, Alaska. This specimen is illustrated for comparison with Kepplerites (Gowericeras) lindgrem' (Hyatt). GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 1 KEPPLERITES, G0 WERICERAS. AND TARA MELLICERAS ? FIGURES 1—8, 11—13. 22. 23. 24—28. 29. PLATE 2 [All figures natural size] Pseudocadoceras grewingki (Pompeckj) (p. 21). 1—7. Rubber casts of plesiotypcs, USNM 130779 from USGS Mesozoic 100. 27317; 8. rubber cast of plesio- type, USNM 130781 from USGS Mesozoic loc. 24710; 11—13.plesiotypes, USNM 108114, 108116, 108115 respectively, from Alaska included for comparisons with specimens from California shown on figs. 1—8. . Pseudocadoceras crassicostatum Imlay (p. 21). Plesiotypes, USNM 108118 and 108119 from Alaska included for comparisons with specimens from California shown in figs. 14—21. . Pseudocadoceras cf. P. crassicostatum Imlay (p.21). Rubber casts of specimens, USNM 130780 from USGS Mesozoic 10c. 27317. Ventral view shown on fig. 20 shows forward curvature of ribs. Pseudocadoceras cf. P. grewingki (Pompeckj) (p. 21). Specimen USNM 130783 from Mesozoic 10c. 27387. Note low point of rib branching and forward curvature of ribs on venter. Pseudocadoceras? sp. (p. 21). Specimen USNM 130782 from USGS Mesozoic loc. 22175. Amoeboceras (Amoebites) dubium (Hyatt) (p. 22). Cotypes, USNM 30201 from USGS Mesozoic loc. 719. Grossouvria colfaxi (Gabb) (p. 22). Holotype, Harvard University Museum of Comparative Zoology 5287 from near Colfax, Placer County, Calif. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 2 PSEUDOCADOCERAS, AMOEBOCERAS (AMOEBITES), AND GROSSOUVRIA PLATE 3 [Figures natural size unless otherwise indicated] FIGURES 1—10. Perisphinctes (Discosphinctes) virgulatiformis Hyatt (p. 23). Cotypes, USNM 30204 from USGS Mesozoic loc. 901. Fig. 6 shows venter with its adoral end pointed downward. Fig. 9 shows suture lines (X 3) drawn from internal mold of specimen represented by fig. 7. Figs. 1, 2, 4, 5, 7, 8, and 10 are from rubber casts of external molds. 11, 12. Perisphinctes (Discosphinctes) carribeanus Jaworski. Plesiotypes, USNM 130792 from USGS Mesozoic 100/ 26382 at Pan de Azucar, Pinar del Rio Province, Cuba. Illustrated for comparison with P. (Discosphinctes) virqulatiformis Hyatt. 13‘17. Grossouvria colfazi (Gabb) (p. 22). Holotype, Harvard Mus. Comp. Zoology 5287, from railroad cut 1 mile west of Colfax, Calif. 13. Suture lines (X 2) drawn near adoral end of last septate whorl; 14, 17. Ventral and lateral views of internal mold; 15, 16. Rubber cast of external mold showing ribbing under different lighting. Arrows on fig. 15 and 16 show position of same forked rib as that illustrated at the bottom of fig. 17. Compare fig. 17 with fig. 29 on pl. 2 to note differences in appearance under different conditions of lighting. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 3 PERISPHINCTES (DISCOSPHINCTES) AND GROSSOUVRIA .5th .83 20882 mOmD 80.8w Nomom EZmD 589320: :0 308 88.888 .8 88 8995M .Qm .3 fidhfl $3538: AnguggaweSSefiva 88:3&mf»& .w .w .w: 80 8528 383% £3533: .& 3 88838me 888 wqu 6888?: 8:82 .8A 8802 .«o 885:8 8:8 Rm 80:88.88 88de 23 89c ammo: .93 30882 mUmD 89c awnomfi EZmD .8882; «0 828888 anon @2858 E88883 Ava .5 €8th $3338: £3 .& .8 Awsufifigegsgufid meguggamfuk .o .wfipaw: “0 80:58.8 8885: .888 :88 88% 88.8 mo 883 958 :80 $8500 38m n8:395 .8 888.88 8:8 m 83m 858m mo 8:3 £88 8°C mwom kwofiuaoflam .82 388383 88:85 .3m .5 avufiiousm fiEquefuaawE» .& .8 AmfiufianoEScwav mvuoggamwsk .n J. .ocvnm .82 30882 wOmD 89c wwnomfi EZmD h308 88.895 .25 .02 88882 meD 80.: ocwmo: EZMD 638 38.888 Mo 88 8.38m .QN .5 38mm 3933?: .Q .R .8 Awwguggawegsgflqv ”Sofifiawfiwm .m nm .880 $8800 888383. @8880 8:80 3083 8:8 m 83m owsofl 85 :o 888 8882 85 8 8288.88 8:80 83 80.8,: .ommm .82 23082 mOmD 80b 039m: EZmD .Amw .5 .8 AwfiufifiumefigcafiQv wwwugdafiswm .N .Emvm .82 23082 mUmD 89c wwnomfi EZwD 888895 .SN .5 dam Smmwoficnwefingofiva 88:38.:ul A 885:: 85 1:38 885: =E w HE Taoeats sandstone Gneiss, schist. PRECAMBRIAN and granite ' Unconformity ,; , v v v v v v V v v v v v V \ ~ - 10.000’ Alluvium Cemented local basalt flows Fortification basalt member Muddy Creek formation Mount Davis volcanics Basalt, andesite, some rhyolite glass and tuli: coarse sediments at many horizons 0 to 4000+ feet Golden Door volcanics Rhyolite to latite; abundant glass and tuff O to 5000+ feet glass, containing spherulites Patsy Mine volcanics Chiefly andesite and basalt flows; some explosion breccias 0 to 5000+ feet PRECAMBRIAN Gneiss, schist, granite, in- closmg younger igneous bodies pluton E7 EXPLANATION Shale Sand stone Crossbedded sandstone o EEé Conglomeratic sandstone 9 3 eli i O gull 8 @ Dolomite - m Breccia Basalt and andesite flows and tuff % Andesite and basalt flow iii? .ll Rhylolite to latite flows and tuff Spherulitic rhyolite g ass E- Pluton fill Sills and dike FIGURE 2.—Columnar sections north and south of Lake Mead: A, Section in Frenchman Mountain block, 13—20 miles northwest of Hoover Dam; 8, Composite section between Lake Mead and Davis Dam. E8 the overlying sands, silts, and clays of the Plio- cene(?) Muddy Creek formation, which extend be- neath the western basin of Lake Mead. Parts of the Thumb and Horse Spring formations reach a short distance south of Las Vegas IVash, in the northwestern part of the map area, where they end against younger volcanic and intrusive rocks. In gen? eral, however, the entire Frenchman Mountain sec— tion which, from Cambrian to Tertiary(?) units in- clusive, has a total thickness of about 17,000 feet, is absent from most of the area of this report and from a much larger contiguous area on the east, south, and west. There is some evidence that at least part of the Paleozoic section once extended farther south. In the Black Mountains directly south of Boulder Canyon, a large fault block made up of Cambrian shale and limestone is intruded and virtually en- gulfed by igneous rock (Longwell, 1936, pl. 2). N11- merous blocks of limestone and dolomite, lithologi— cally like that in several Paleozoic formations, occur as xenoliths in plutonic bodies in the southeastern part of the River Mountains, near the head of Hem— enway Wash. Barite in and around some of these xenoliths has been prospected extensively. A distinctive section of sedimentary rocks exposed north of Boulder Canyon, between the Ransome fault and Boulder Wash, consists of yellowish dolomite, extremely coarse breccia, and thin beds of sandstone, shale, and limestOne. The higher part of the section encloses sheets of andesitic lava, which become domi- nant upward (Longwell, 1936, p. 1407—1409). This isolated unit of unknown age is included on plate 1 with the group of igneous rocks labelled Tiv. Indirect but strongly suggestive evidence bearing on the former extent of some formations is supplied by the Cretaceous( ?) redbeds section east of French- man Mountain, in which northward-tapering wedges of coarse debris indicate a highland source directly to the south. The basal conglomerate, which bevels across the Triassic and Jurassic(?) formations from south to north, is made up largely of limestone frag- ments, many of boulder and cobble size; lithologic peculiarities and included fossils indicate their deri- vation from several Paleozoic and Mesozoic forma- tions. Scattered pebbles from Precambrian bedrock also are included. Higher in the section great lenses of breccia, probably of landslide origin, contain frag- ments of Precambrian rocks only (Longwell, 1951, p. 352). It is inferred, therefore, that a broad area south of Las Vegas W’ash and Lake Mead was strongly uplifted in late Mesozoic time and denuded of its Mesozoic and Paleozoic sedimentary formations. The area of uplift was later a theater of prolonged ig— SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY neous activity, and resulting lava accumulations con- ceal the older bedrock which supplied the debris of the breccia lenses. The ridge that forms Saddle Island, which possibly marks a high part of the old land surface, has been exhumed by erosion following localized deformation (Longwell, 1936, pl. 2). Because the Horse Spring formation and older sedimentary units occupy only a small fraction of the map area considered here, they are represented in somewhat generalized fashion on plate 1. PLIOCENE(?) BASIN DEPOSITS MUDDY CREEK FORMATION Along the river south of Lake Mead, the oldest sedimentary beds, other than local accumulations of coarse detritus interbedded with volcanic rocks, were deposited in small enclosed basins. These deposits are strikingly like those of the Muddy Creek forma— tion, which are widely exposed east of the F rench- man Mountain block and were well displayed in the wide basin directly north of Black Canyon before the formation of Lake Mead (Longwell, 1936). A thick section of these characteristic beds underlying the basal cap of Fortification Hill (fig. 3) doubtless was once continuous with similar beds that emerge locally from the alluvial cover southeast of Hoover Dam. East of Willow Beach the alluvium has been effectively eroded, exposing the Muddy Creek forma- tion continuously over an area of several square miles. There the section near a fault contact with Precam- brian rocks of the Black Mountains is made up of FIGURE 3.——-View westward on north side of Fortification Hill. capping of superposed basaltic lavas is more than 400 feet thick. Deposits of the Muddy Creek formation, bouldery and poorly bed- ded in foreground (near Fortification fault) are finer grained and better stratified near middle of view. Visible RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA coarse gravels containing angular fragments of gneiss, schist, and granite. Within a few hundreds of feet to the west, these gravels intertongue with and grade into layers of sand, silt, and clay that locally contain considerable gypsum. On the west side of the out- crop area, the section again coarsens and includes angular pieces of gneissic and volcanic rocks. Small remnants of basalt on layers of fine-grained sediments near the Willow Beach road apparently correlate with the basalt cap of Malpais Mesa, about 4 miles to the southwest. All known evidence suggests deposition within ‘a basin that contained a lake during at least a part of the sedimentary history; standing water seems a re- quirement to rationalize the rapid lateral gradation from coarse marginal to fine-grained interior deposits, the regular thin bedding of the fine sediments, and the recurrence of bedded gypsum, gypsiferous clay, and sporadic limestone. These characteristics are shared with the Muddy Creek formation farther north (Longwell, 1928, p. 90; 1936, p. 1419). Three of the limestone beds, 8 inches to 2 feet thick, carry a low percentage of manganese in exposures half a mile in extent (McKelvey and others, 1949, p. 99). , On the east side of Malpais Mesa, the cover of basalt lies on very coarse debris, which in part grades or intertongues westward into regular layers of gray siltstone and yellowish clay like that in the section east of Willow Beach. These fine—grained layers are well displayed in walls of a small valley that heads near the northwest corner of Malpais Mesa. The arrangement of coarse and fine sediments in this sec- tion suggests that a basin of deposition extended westward from the position of the mesa, and presum- ably the greater part of the deposit was eroded after strong uplift near and west Vof the position now occu- pied by the river. The basal part of the section around Malpais Mesa has particular interest. It lies on a rugged surface fashioned on Precambrian rocks east of the mesa, on volcanic rocks to the west. This basal deposit is a very coarse conglomerate and brec- cia in which the laregst blocks range in length from 1 to 4 feet. East of the mesa, fragments that make up the conglomerate in its lower part are almost ex- clusively of Precambrian rock types; west of the mesa, fragments of volcanic rock predominate in the de-i posit, but Precambrian types are important. The coarse well-cemented debris, of a pronounced brown-i ish color, fills an old steep-walled valley hundreds of feet deep, reaching below the present level of the river and heading south-southwest. Overlapping of angular cobbles and small slabs indicates that a swift E9 stream flowed southward in this valley. The Muddy Creek deposition clearly began on very rugged topog- raphy, which became much modified as sediments accumulated. A third area underlain by typical deposits of the Muddy Creek formation lies from 2 to 3 miles east of Boulder City. The best exposures are in the up- per part of Rifle Range Wash where, as noted by C. B. Hunt (written communication), the formation “is represented by about 75 feet of gypsiferous and manganiferous tufl', clay, silt, and sand.” These beds, dissected into subdued badland topography, cover a considerable area and disappear toward the south and west beneath unconsolidated gravel. A shaft and two drill holes put down by the US. Bu— reau of Mines revealed that a silty gypsum bed, 60 to 65 feet thick, contains 3 to 5 percent manganese (McKelvey and others, 1949, p. 99). The manganif- erous beds are dark gray to nearly black; other beds have the tan color that is dominant in fine-grained deposits of the Muddy Creek formation. North of Rifle Range Wash, the sediments coarsen, by grada- tion and intertonguing, and are in sedimentary con- tact with older bedrock. Along the east side of the outcrop area, the section includes at least one flow of basalt and is faulted down against older rocks. Directly south of Boulder City, beds of sedimentary breccia that include tuff are faulted down against Precambrian rocks and quartz monzonite in Boulder Hill. These beds are probably in the Muddy Creek sequence, but alluvial cover conceals their relation to outcrops farther east. The Muddy Creek formation in the vicinity of Las Vegas Wash has been described and mapped by Hunt and others (1942) and McKelvey and others (1949), who report that the section contains three distinct members, separated at least locally by angular un- conformities. The lowest member, conglomeratic and of irregular thickness, locally contains some flows of basalt and andesite. A thick section of similar vol- canic rocks underlies the lowest of the sedimentary units, generally with strong angular unconformity. These older volcanic rocks, which Hunt and McKelvey included with the basal member of the Muddy Creek formation, are now recognized as part of the Mount Davis volcanics and are so represented on plate 1. Apparently the deposition of some sediments in the lower part of the Muddy Creek formation began dur- ing late stages of the Mount Davis volcanism. Move- ments on faults, which initiated basins of deposition, are reflected widely in angular unconformity. As the E10 movements and the volcanic activity doubtless were irregular in space and time, the base of the Muddy Creek formation is not everywhere sharply defined. Widespread eruption of basaltic lavas was renewed later in Muddy Creek time. The Fortification basalt member, locally found in the upper part of the for- mation, is mapped as a distinct unit because of its SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY wide distribution in contact with rocks older than the Muddy Creek formation. . The following stratigraphic table, modified from Hunt and others (1942, p. 301) and McKelvey and others (1949, p. 87), represents the formation at the Three Kids mine and near Boulder Basin of Lake Mead. TABLE 1.—Sequence of Tertiary rocks near Lake Mead Age Formation and Member Description Thickness (feet) Marginal conglomerate and sandstone, grading basinward into siltstone, clay, tuif, and gypsum. Includes thick sheets of 4 Member 3 basalt; these form cap of Fortification Hill, and their 0—2,000 probable equivalents to cast and south are mapped separately as the Fortification basalt member of the Muddy Creek. Muddy Creek Unconformity Pliocene(?) formation Member 2 Conglomerate, sandstone, shale, and gypsum 0—300 Unconforrnity (c) Gypsum (locally manganiferous), limestone, clay, silt- 0—1,500 stone, and sandstone. (b) Tuffaceous sandstone and siltstone, generally man- 0—150 Member 1 ganiferous, some beds with high content of manganese. (a) Bedded conglomerate, with some locally interlayered 0-500 basalt flows. —————*—— Unconformity Miocene(?) Mount Davis Basalt and andesite flOWs and agglomerate. Coarse sedi— 0—2,000+ volcanics mentary debris included locally. Unconformity Oligocene or Golden Door Complex of volcanic rocks, latites to rhyolites, with much Thousands Eocene(?) volcanics glass and tuft. Cut by dikes, stocks, and irregular intrusive of feet bodies. Cumulative evidence in a wide region indicates that sediments of the Muddy Creek formation were de- posited in several adjacent basins under conditions of interior drainage (Longwell, 1928, p. 95; 1936, p. 1422). Coarse sediments near upland sources graded into and intertongued with fine-grained clas- tics and chemical precipitates in basin interiors. Evi- dently the Muddy Creek sedimentation began on a surface made rugged by faulting, and there were re- current movements and volcanic activity while the deposition was in progress. Although the several areas of outcrop south of the lake may represent sep- arate basins, possibly all these coalesced as the sections built upward and spread laterally. As the formation east of the Black Mountains includes evaporites, chiefly halite and gypsum, hundreds of feet thick (Longwell, 1936, p. 1423), and at a maximum the total section measures thousands of feet, perhaps the Muddy Creek interval was of long duration. During that time the Colorado River, as a through—flowing stream, could not have existed in its present location (Longwell, 1946, p. 831). _ High in the formation, Stock (1921, p. 260) found some fragmentary vertebrate fossils which he con- sidered suggestive of Miocene age. Later study in- dicates that these remains have no diagnostic value (M. C. McKenna, written communication, 1956). No additional fossils have been reported, and no evidence for definite correlation is available for sections south of Hoover Dam, which are referred to the Muddy Creek formation tentatively on the basis of physical characteristics and relations. The formation as it is widely exposed in areas bordering the Muddy Moun- tains is strikingly like the Panaca formation, about 100 miles farther north, which is well dated as Plio- cene (Stock, 1921, p. 257). LANDSLIDE BRECCIA Coarse breccia that consists typically of broken fresh rock, with little or no matrix of weathered ma- terial, covers an area of several square miles south— east of Hoover Dam. This material, discussed in de— tail elsewhere (Longwell, 1951), had its source in the Precambrian bedrock of the Black Mountains and is most logically explained as a landslide mass that moved westward over basin deposits. The mass is an 'erosion remnant with a maximum thickness of sev- eral hundred feet. Much of it rests on the Muddy Creek formation; and since locally, near its southern limit, some of the breccia also lies below beds of this formation, the mass seems to be an exceptional unit of the Muddy Creek formation. RECONNAISSANCE GEOLOGY, LAKE The base of the breccia is well exposed in deep washes. In its lower part the breccia is finely com- minuted; and the basal surface of the mass, polished by abrasion in movement, has a low westward dip. Striae marking this surface, in the direction of ‘in- clination, increase its similarity to a fault surface. Upward in the section the rock fragments increase in size to maximum lengths of several hundred feet. The larger fragments retain the banding character- istic of Precambrian bedrock, though in detail most of the rock is minutely shattered. Blocks of basalt, locally mixed with the broken gneiss and granite, probably came from a flow like the one still partly preserved on the flank of the range 3 miles east of Willow Beach (pl. 1), or from local dikes. ‘ Near the southern limit of outcrop, the breccia con- sists of two distinct units; a lower part, brown and softened by chemical weathering, is separated by stream-laid gravels from fresh breccia above. The gravels, 25 to 40 feet thick, have in the lower beds some reworked material from the weathered breccia beneath. Since the two units of breccia are similar fractions of the same formation, the contrast in de- gree of weathering suggests a radical change in local environment. Presumably the older mass, after its emplacement, was exposed for a considerable time to attack by the weather under a climate more humid than that of the present. Some change brought on rapid aggradation, and the younger landslide mass, deeply buried under basin deposits, was sealed frbm weathering until it was exposed by erosion in the Colorado River drainage area. Chemical decay un- der the present aridity is extremely slow. Similar breccia, locally 200 to 300 feet thick, oc- curs at several places between flows in a volcanic assemblage older than the Muddy Creek formation. The most striking of these breccias were seen north- west of Malpais Mesa, and in sections of volcanic rocks exposed on the slope east of the Eldorado Mountains and northwest of Mount. Davis. Probably landslide masses of this kind came from steep fronts of upthrown blocks along active faults (Longwell, 1951, p. 349). ‘ The oldest breccia of this type recognized within the report area is within the Thumb formation, dis- cussed above (p. E8) as probably of Cretaceous age. OLDER ALLUVIUM The older part of the deposits mapped as alluvium is complex in origin, and probably various parts .of it differ widely in age. At several localities beds of well-indurated gravel are tilted as much as 20° to 25°, and possibly some of these beds are older than Quater- nary. A cover of later alluvium conceals older de- E11 MEAD—DAVIS DAM, ARIZONA—NEVADA posits over wide areas, and there is no practical way of correlating isolated outcrops of similar clastic beds that yield no fossils. In the wide valley of the Colorado River southward from Black Canyon, widely distributed well-cemented gravels are exposed in steep cliffs facing the river and along many large washes (fig. 4). These gravels closely resemble the unconsolidated gravels now on the floors of active washes and on slopes between the intermittent stream channels. The rock fragments, most of which were derived from lavas or from Pre— cambrian bedrock, range from sand size to large boul- ders “and are either angular or subangular. Sections of the cemented gravels exhibit differences in arrangement, coarseness, and lithology of the rock fragments. In the lower part of Eldorado Wash (fig. 4), the basal part of each clifl' contains many angular boulders as much as 2 feet long, derived from lavas of several lithologic types. Beds extend below the river level. An erosional unconformity separates this unit from overlying beds that are more regular, less coarse in average texture, and made up chiefly of fragments derived from Precambrian rocks. At the top of the section is a massive layer, about 20 feet thick, in which fragments are of moderate size, with isolated blocks as much as a foot long. In large part the arrangement is disordered; suggestion of layering and size sorting is faint and localized. Crude bed- ding indicates that the two lower units were de- posited by swiftly running water, whereas disorder in the upper layer suggests that it accumulated on a slope removed from active stream channels, under influence of slope wash at times of exceptional runoff, supplemented by slow creep and perhaps by mudflow. FIGURE 4.—Clitf of cemented gravels on south side of Eldorado Wash. Channel of Colorado River is short distance to the left of View. Gravels in three distinct units: (1, fragments derived from vol- canic rocks; b, fragments chiefly of Precambrian rocks; 0, unstrati- fled unit. Cliif is about 40 feet high. E12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Events in the history of the Colorado River are recorded in these deposits, and possibly a thorough study would reveal important details of the story. Does the unconformity above the lower unit in El- dorado Wash record lowering of the river bed, with consequent erosion of widespread alluvium? Abrupt passage from the middle to the upper member in the section also suggests an important change in regimen, for which more than one hypothesis may be offered. Assuredly large shifts in the river level occurred, as evidenced by the highest remnants of cemented river gravel. In the wide basin east of the river and north- east of the Newberry Mountains, and particularly on slopes a few miles southwest of the Portland Mine, such remnants outline a surface which, 3 miles from the river, has an altitude near 1,300 feet and a westward slope of approximately 100 feet per mile (fig. 5). Since the surface presumably leveled off in the mid- dle of the basin, alluvium must have filled the valley to a height more than 500 feet above the modern riverbed. Perhaps fluctuations, both upward and downward through hundreds of feet, occurred during development of the river valley. Evidence of cutting to a level more than a hundred feet below the mod? ern bed was found at the Hoover Dam site (Long- well, 1936, pl. 17) and during earlier investigations by test boring (La Rue, 1925, pl. X). Cemented Colorado River gravels are exposed at several localities, most of them along washes where concealing slope gravels have been removed. One of the best exposures is beside the road about midway between the Portland and Katherine mines, on the east side of the valley opposite the Newberry Mountains, where the sediments consist of crossbedded sand and gravel, the latter containing well-rounded pebbles of lava, gneiss, granite, quartz, chert, and limestone. Only the river could have brought together such an assemblage and developed the forms of resistant peb- bles that are evidence of long transport. This out- crop, which is nearly 3 miles from the modern chan— nel and more than 600 feet above it, records one location of the stream during its long and varied his- W River gravel Beds of Chemehuevi \ Lake Colorado River “Lake Mohave . channel Modern channel of Former river < i: l v Beds of Chemehuevi Lake J; Precambrian bedrock tory of lateral migration and vertical fluctuation. The cemented slope gravels, which support remnants of a widespread high-level surface (fig. 5), were de- posited across the beds of river gravel after these beds were tilted locally, probably by faulting, to dips as high as 30°. It is to the credit of Newberry that he saw these cemented gravels about 100 years ago, and difl’eren- tiated those laid down by the river from the local slope deposits. Relations among the several kinds of alluvium along the Colorado in the wide valley above Davis Dam are shown in figure 5. The river trenched coarse deposits of local origin and laid down thick beds made of far-traveled gravel and sand. After the channel shifted, the abandoned stream deposits were cemented, locally deformed, and in many places buried under local gravels which in turn became consoli- dated. Development of the wide and thick cap of caliche indicates an episode of stability. We have no evidence to suggest the exact geologic date repre- sented by the widespread caliche; but it was clearly formed while the Colorado River was in operation, and therefore long after the Muddy Creek sediments were laid down in interior basins. The caliche cap is older than the lake beds of the Chemehuevi forma- tion of Pleistocene age. CHEMEHUEVI FORMATION Evidence for a deep lake that occupied a vast area in the lower part of the Colorado River valley has been discussed elsewhere (Longwell, 1946, p. 827). Remnants of sediments that now are recognized as lacustrine were reported by Lee (1908, p. 41), who called the assemblage the Chemehuevis gravel and interpreted the entire sedimentary unit as a deposit made by the Colorado River. Lee, in his reconnais- sance over a wide region, was impressed by the abun— dant loose river gravel that covers many remnants of the fine—grained sediment to a depth of several feet. Actually the gravel was deposited at various levels as the river cut down toward its old course at Mixed slope and river Calich ' E gravels, unconsolidated / e cappingx .. . /- eCEmenled river Local gravels weakly i, gravel cemented Beds locally deformed Local gravels firmly cemented SEA LEVEL VERTiCAL EXAGGERATION 2 X l O l MiLE L l l l I l l FIGURE 5.—General relations among sedimentary units designated alluvium on the geologic map, as seen on long slope east of Newberry Mountains. RECONNAISSANCE GEOLOGY, LAKE the end of the lake episode. Gravels in basal beds of the few Chemehuevi remnants preserved near the present river level were no doubt deposited in the in- cipient stage of filling, while the lake was growing headward from the obstruction that blocked the ear- lier river. Many dozens of the remnants of lake deposits, some of large size, are distributed in a belt on either side of the river; they are best preserved in areas free from large washes, particularly where hills of bed- MEAD~DAVIS DAM, ARIZONA—NEVADA E13 rock shield the weak material from erosion. Few remnants remain in the wide section of the valley between Black Canyon and the Newberry Mountains. Large quantities of the lake sediment have survived in pockets among the hills northeast of Davis Dam (fig. 6), and clay from that vicinity was used to make the impervious core of this earthfill dam. Characteristic lake deposits, consisting chiefly of clay in thin laminae, lie at various altitudes because the lake was deep and its floor was on rugged topography. «a FIGURE 6.—View generally eastward, north of Davis Dam site, to Black Mountains. Precambrian rocks exposed in lower and middle parts of View, volcanic rocks in distant range. Lightrolored clay and silt 0f the Chemehuevi formation fill former channel of river and lie in remnants at higher levels. Tailings from old Katherine mill in wash, upper left. Skyline at right is about 10 miles from foreground. (U.S. Bureau of Reclamation photograph.) 661325 0— 63—3 E14 Near Davis Dam the laminated clays extend to a height about 300 feet above the river, where there is an abrupt change to crossbedded fine sand, remark— ably uniform in grain size except in local wedges containing coarser, angular fragments that were brought in by tributary washes. Howard R. Gould, of the US. Geological Survey, kindly analyzed sam- ples of the Chemehuevi sediments from the Davis Dam vicinity, and others from a large remnant of the sediments west of Boulder Canyon. At each 10- cality the median particle diameter of the clay is less than 3 microns. Gould found the samples mark- edly similar to each other and also to clay in the bottomset beds of the present delta of Lake Mead, where the average median is about 2 microns. Sand in the upper member of the Chemehuevi has a me- dian diameter of about 300 microns, and Gould found that the sand has about the same texture as the sand of the topset and foreset beds in the present delta (written communication, 1949). The sum of evidence from the area of the pres- ent study supports the conclusion regarding the former lake on the basis of the sediments upstream from Hoover Dam (Longwell, 1946, p. 827). The fine- grained sedimentary unit represents conditions on the bottom of a deep lake far from the mouth of any large permanent stream. Local wedges of angular fragments are interpreted as delta fans contributed by intermittent streams from bordering highlands (Longwell, 1936, pl. 15). The abrupt change to the overlying sand marks arrival of the foreset beds as filling proceeded and the delta front advanced south~ ward. No doubt the extreme reach of these foreset sands was many miles in advance of topset beds, as is true of the Lake Mead delta; therefore, the basal foreset sands of the Chemehuevi lake may well have been deposited in deep water, in accord with evidence that the upper deltaic member, predominantly of sand, was hundreds of feet thick in the deeper parts of the lake. As the area of total fill advanced down the lake, the river played laterally over the area, cutting and redepositing; as a result, over much of the delta the topmost member was a coarse stream deposit. In contrast with the Lake Mead delta, to which the Colorado River in flood contributes nothing coarser than sand, the stream in Chemehuevi time spread vast quantities of coarse gravel. Most of it was far- traveled, as is indicated by the advanced rounding Of pebbles, cobbles, and boulders of peculiar lithologic composition, many of which were moved tens or even hundreds of miles from parent bedrock. The contrast in stream loads noted above suggests that the river of Chemeheuvi time was more powerful SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY than the present Colorado. As the terraces floored with the coarse gravel have downstream slopes closely comparable to the modern stream gradient, presum- ably a decline in the volume of flow since the terraces were formed is responsible for the decrease in carrying power. Probably, then, the regional climate during Chemehuevi time was more humid than now, at least in the headwaters areas of the river. Many surface features are related to the lake his— tory. Remnants of terraces capped by characteristic river gravels are at many altitudes, and wherever the gravels lie directly on the lake deposits, they record some stage in downcutting from the highest lake level. The lake sediments, especially the topset sands, are inherently weak, and it is not likely any of these have survived at the highest level. Coarse river gravels, on the other hand, are highly persistent if they are on a firm base. The shifting stream on the advancing topset beds must have impinged against bedrock at many points on the valley sides and at the margins of high island masses. At several places large rem- nants of gravel are on bedrock at altitudes somewhat above 1,500 feet; one of these is on Delmar Butte, on the south slope of the South Virgin Mountains (Long- well, 1936, p. 1454). Another is at Sugarloaf Moun- tain, a rounded peak of volcanic rock and a conspicu- ous landmark on the Arizona side south of Hoover Dam. A broad shoulder along the east and south base of the steep knob carries an extensive deposit of typical Colorado River gravels. This conspicuous bench, fashioned on bedrock and veneered with gravel, may actually be a fragment of shoreline of the former lake. Its inner margin is at about 1,530 feet altitude. or nearly 900 feet above the stream bed in Black Canyon before the dam was built. About a mile northeast of and a little lower than the Sugarloaf bench is a group of large potholes con- taining river gravel (Ransome, 1923b). Presumably these features mark a temporary channel of the river at some stage of adjustment on the Chemehuevi sedi- ments. . If the bench at Sugarloaf represents the highest level the river reached on the Chemehuevi fill, the lake at maximum extent was nearly 1,000 feet deep in the vicinity of Davis Dam, and 9 to 10 miles wide in the broad part of the valley south of Mount Davis. Farther south, in the basin north of the Mohave Mountains, the extreme width of the lake must have exceeded 15 miles. The basin still farther south, between the Mohave and “Vliipple Mountains, is known as Chemehuevi Valley and properly gives its name to the deposits, which are exceptionally displayed there. South of this basin, part of which is now occupied RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—~NEVADA by Havasu Lake behind Parker Dam, many remnants of Chemehuevi sediments lie in protected recesses along the canyon cut through the Whipple Mountains. The lowland south of these mountains is extensive both east and west of the river, and although slopes are well graded and generally veneered with recent alluvium, scattered exposures indicate that the lake covered an immense area within which some mountain masses stood as islands. , J. S. Newberry (1861, p. 38), apparently the first to study these sediments, found near the river, in gravels that lie beneath clay of the Chemehuevi forma- tion “a very large and perfect tooth of Elepha‘s pri- migenius.” The gravel bed accords with the beds above (fig. 7) and probably is a stream deposit near the temporary head of the growing lake. Newberry’s account mentioned the clay overlying the grave], but he supposed all the sediments were laid down by the river. Mammal bones and numerous mollusk shells have been found more recently, not directly in the Colo- rado River valley but in tributary valleys and in deposits that seem to be closely related to the Cheme- huevi formation (Longwell, 1946, p. 828). A Pleisto— cene age was assigned to the bones by Simpson (1933), and to the shells by F. C. Baker (written communica- tion, 1932) . A map of the Chemehuevi formation would have value if it represented nearly all the remnants on a highly accurate topographic base, and preferably with differentiation of the significant kinds of sediment. Since most of the remnants are small and scattered over an enormous area, such a map would be very expensive in time and labor. In the present report the deposits are included among those mapped to- gether as alluvium. They are highly distinctive de- - n 7 _ ..",»n ‘5 ,1; ‘ ’ ahfiMW'w 9 '1 O — «w...- W ‘ Way: “3 “£7.13 “1 L ' “'a-ipfj‘m"? w b c a Trap hills rising eastward to the Black mountains b Bluffs of stratified Quaternary gravel and sand 0 Elephant Hill d Alluvial bottom land e Bed of river 0 f E15 posits, and fortunately many remnants lie well above the level of Lake Mohave, though only a few es- caped submergence or wave erosion by Lake Mead. YOUNGER ALLUVIUM Although the larger washes are only intermittent, many are fairly well graded, particularly in the wide segment of the valley between the Newberry Mountains and Black Canyon. The washes are floored with rock debris that ranges in size from silt to boulders. Coarse fragments are predominantly angular or sub- rounded, but some well-rounded pebbles are inter- spersed, probably contributed by old river bars left at high levels. As suggested by the topographic map, large interwash areas in the wide part of the valley ,have fairly uniform and gentle slopes. East of Search- light, the slopes on either side of the valley range between 200 and 250 feet per mile through distances of 8 to 10 miles. These slopes are floored with gravelly debris, made up chiefly of coarse fragments but con- taining also much silt and sand that. probably was contributed, at least in part, by the Chemehuevi fill. Locally, recent gullying has exposed remnants of the old lake clay veneered with slope gravel. The propor- tion of coarse gravel increases generally upslope and toward hills of bedrock. Before the closing of Davis Dam, much of the river south of Black Canyon was margined by alluvial flats that varied in width and in height above low-water stage. The most impressive of these flats, now cov- ered by the widest part of Lake Mohave, lay on both sides of the stream, from the latitude of Searchlight southward beyond Cottonwood Island (pl. 1). In this area the nearly level surfaces, underlain chiefly by stream-laid silt and sand, extended a maximum of more than a mile back from the river. The surface f Tertiary conglomerates, inclined and covered with horizontal beds of gravel FIGURE 7.—Newberry’s section through Elephant Hlll, near mouth of Eldorado Wash (copied from report of 1861). tooth came from basal unit of Chemehuevi formation. above 0. shown in figure 4 of present report. Elephant His Tertiary conglomerates are the cemented gravels E16 of this old flood plain was on the average about 20 feet above low-water mark, and in many places steep banks adjacent to the stream indicated active lateral cutting. The larger tributary washes kept their chan- nels incised below the level of the plain and formed small delta fans that forced the river toward the oppo- site bank. These terminal deposits of tributaries con- tained debris much coarser than that beneath the alluvial flat. Large remnants of terraces on old river gravels were numerous on both sides of the stream course, at altitudes of 60 to 100 feet above low water stage. One of the most extensive of these lay northeast of the Old Ferry at the outer edge of the wide flood plain east of the river. The terrace front sloped up from the flat at the angle of repose of the coarse gravel, made up largely of cobbles with diameters as much as 8 inches, nearly all well rounded and many smoothly polished. The top of the terrace, 60 to 70 feet above low river stage, sloped gradually upward through a width of several hundreds of feet to its outer margin. A similar terrace west of the river and south of Aztec Wash was nearly 100 feet above stream grade. The coarseness of these gravels and the large original volume indicated by the remnants are evidence of great power of the river down to a late stage of its return to the pre—Chemehuevi grade. Pebbles and cobbles in the gravel represent many lithic origins, some of which are common in the Precambrian bed— rock and in younger igneous rocks of the immediate region, whereas others, particularly quartzites, fossili- ferous limestones, and cherts, are not known in any outcrops nearer than the Virgin Mountains. In the broad part of the valley, remnants of river terraces at high levels are exceptional and small. On the resistant bedrock along Black Canyon numerous gravel bars. some of large size, record changing levels of the stream. Above the cliffs a mile upstream from lVillow Beach, on each side of the present lake, exten- sive terrace remnants lie as much as 140 feet above the river bed of 1949. A mile directly west of Willow Beach, a wide saddle in the high ridge north of the river is floored with the river gravels at altitude 1,225 feet; and directly east of the saddle,.pockets of the gravel extend to 1,320 feet, or about 700 feet above the channel of 1949. More than a mile farther downstream and on the south wall of the valley, rem- nants of terrace gravels lie near 1,300 feet altitude. Of many other occurrences in or near Black Canyon, the exceptional remnant at Sugarloaf is the only one thus far recorded as high as the 1,500-foot contour. West of the river valley the alluvial cover is in two basins of interior drainage, separated by a low divide just north of Searchlight. Each basin is margined SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY with an irregular assemblage of fans, which pass out— ward into a well-graded bajada slope furrowed by shallow washes. On many areas between washes, the slope gravels have settled into the smooth mosaic pat- tern of desert pavements. A long arm of the northern basin drains northward to the flat floor, where gravelly slope debris merges with clay and silt in the floor of an extensive playa. East of the Black Mountains the long flat-floored Detrital Valley, draining northward to Lake Mead, is veneered with alluvial deposits that in kind and general. arrangement resemble those of interior basins, although no playa is present in Detrital Valley. Detri- tal Wash has a clearly defined channel, with a low gradient to the north, although a stream carries through only in times of exceptional runoff, and dur- ing dry periods windblown deposits locally obstruct the streambed. Fine sediments in considerable quan— tity lie on the valley floor, not in continuous accumu— lation but undergoing slow, halting transportation down the valley. The advent of Lake Mead has of course created a new control, and doubtless there will be a growing deposit of sediment, dominantly/fine grained, near the mouth of the wash, and steady de- crease in a carrying power that was .feeble before the lake was formed. CRETACEOUS(?) AND CENOZ‘OIC IGNEOUS ROCKS Igneous rocks, both extrusive and intrusive, are of major importance in the bedrock of the area. The larger intrusive bodies are holocrystalline, and at least some of them are appreciably older than any of the volcanic rocks. On the other hand, many of the smaller injected bodies cut thick sections of lavas and tuffs, and some of these bodies occupy positions of vents through which volcanic products issued. Of these products lavas are predominant, but tufts and explo- sion breccias are widespread, and some extensive sheets of perlitic glass may represent fusion of ash dis— tributed in nuées ardentes. The diverse igneous units are considered in a group separate from the sedimentary formations, because the position of these igneous rocks in the geologic column is uncertain. But all are geologically young in comparison with the Precambrian bedrock, and probably most of them originated in association with uplift and orogeny that affected the region in a rela- tively late stage of its history. INTRUSIVE BODIES LARGE PLUTONS The geologic map (pl. 1) shows only part of the intrusive masses that have been recognized in the field; doubtless many others cut the Precambrian RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA rocks in parts of the area not examined closely. For example, a large body of coarse-grained granite and another of quartz diorite are mapped as a single plu- ton near the head of Boulder Canyon, and a definite southern boundary of these plutonic rocks is not in- dicated because it is not known. Most of the bound- aries shown on the map are inexact. The outline of a large mass of granite forming the highest part of the Newberry Mountains is estimated from hasty ex- amination. Representation of a large granitic pluton in the upper part of Aztec Wash is much generalized. A special pattern is used where plutonic rocks make irregular contacts with gneiss in the northern part of the Black Mountains. Many bodies have highly com- plex borders that ramify the Precambrian basement. The present discussion, based on a preliminary sam— pling only, may have some value as a guide for later workers. The larger bodies range in composition from diorite through quartz monzonite to granite. Outcrop areas of these bodies range from about a mile to more than 4 miles in largest dimension. Contacts with older adjacent rocks are for the most part steeply trans— gressive; but the mass exposed at Boulder City and extending more than 4 miles eastward is an unroofed Sill or laccolith, whose base is generally conformable on lavas. Rocks that formed the roof have been wholly eroded from the pluton as exposed. About a mile east of Boulder City erosion has cut through the pluton along an anticlinal axis, from which the under- lying lavas dip to the northeast and southwest. Far— ther east these lavas are essentially horizontal, and the contact with the pluton recedes and advances along walls of crosscutting canyons. Through 20 to 40 feet near the contact the lavas are conspicuously stained with iron oxide; this staining extends irregularly into the pluton also. Locally, the volcanic rocks have been recrystallized and have some resemblance to the adjoining plutonic rock, which near the contact is fine grained because of chilling. In much of its exposed area, the Boulder City plu- ton stands above its surroundings, and in its eastern part the border of the mass forms steep slopes and precipitous cliffs. The ragged outline of its border along transgressive valleys suggests that the original lateral extent of the mass has been considerably re- duced by erosion. In and south of Boulder City, alluvium conceals the mass except for scattered ex— posures, and the southern limit of outcrop is uncer- tain. At its western limit the outcrop is narrow, and apparently the body is covered by volcanic rocks of the River Mountains, though exposures in the critical area do not reveal an actual contact. E17 In specimens collected from the eastern part of the Boulder City pluton, the rock is granodiorite, with quartz. highly poikilitic. Samples from the vicinity of Boulder City are quartz monzonite of medium to coarse grain size, with plagioclase zoned from Anso to A1120. Some of this rock, collected in 1956 by Earl Pampeyan and analyzed in the US. Geological Sur- vey Laboratory by the zircon (lead-alpha) method (Larsen and others, 1952), gave an age of about 50 million years. This suggests that the pluton was em- placed in Eocene time.3 Implications regarding date of the associated lavas are discussed on later pages. The isolated Boulder Hill south of the city contains quartz monzonite similar to that exposed in Boulder City but coarser grained. In the southern part of the hill, the plutonic rock encloses masses of gneiss, pre- sumably Precambrian, some of which merge imper- ceptibly with the quartz monzonite. In this area the igneous rock is less uniform in appearance and in size of grain than the rock in the northern part of the hill. Possibly the quartz monzonite in Boulder Hill repre— sents part of a boss that served as feeder for the sheetlike body exposed in and east of Boulder City. Granodiorite similar to that east of Boulder City underlies a large area east and northeast of F ortifica— tion Hill. Alteration along joints, perhaps in con— nection with later igneous activity, has developed bluish amphiboles, probably crossite and crocidolite (R. G. Coleman, written communication), that make conspicuous patches and streaks in the gray rock. South and west of Fortification Hill the lower slopes are on altered rock, much of it soft and claylike, char— acterized by bright colors which have earned for this area the name “Paint Pots.” Local masses that show ‘little or no. alteration consist chiefly of gray and brownish monzonite porphyry. Ransome (US. Bur. Reclamation, 1950, p. 88) concluded that the wide- spread alteration was caused by introduction of finely disseminated pyrite, and subsequent oxidation with formation of sulfuric acid. The original minerals in the rock were changed to clay minerals, iron oxide, and other secondary products. An assemblage of diverse intrusive bodies occupies much of the area "extending southeast from F ortifica— tion Hill to the junction of the Horsethief and Indian Canyon faults. In the upper part of Kingman Wash, the bedrock is a complex of Precambrian gneiss and younger intrusive rocks of several kinds. South of Kingman Wash the intrusive rock, much of it rich in biotite, is dispersed irregularly through Precambrian gneiss east of the Fortification fault; in the block between this fault and the Horsethief fault, the in- trusive rock surrounds large masses of siliceous lava. “A potassium-argon analysis made in 1962 gave an age of about 23 million years. This indicates a Miocene age. E18 A similar network of intrusive bodies that engulf masses of volcanic rock lies west of the river and is transected by Rifle Range Wash. Some of the intru— sive rock in the latter area is dark diorite. Along the upper part of Eldorado \Vash intrusive masses, shown on plate 1 as a continuous body, form discontinuous outcrops that make highly irregular contacts with Precambrian and volcanic rocks. East and west of Nelson the northern boundary of this intrusive complex transects a thick, tilted section of lavas, with contacts partly intrusive, partly faulted. Apparently this boundary is a complicated example of what Ransome (1904, p. 11) called an “intrusion fault,” whereby the intruding body displaced upward great masses of the older volcanic rock. Ore deposits once extensively mined along and near Eldorado Can— yon occurred in veins along crush zones in the intru— sive rocks (Ransome, 1907, p. 76). Directly south and southwest of Nelson, large masses of volcanic rock are surrounded by and partly engulfed in mon- zonite porphyry that has conspicuous phenocrysts of feldspar in a dark—gray aphanitic groundmass. North of the old Techatticup mine, the thick sec- tion of lavas dips steeply eastward and strikes almost at right angles to the nearly straight contact with a pluton of quartz monzonite. Dioritic rock along the north border may be part of a separate intrusive body. South of the mine, near an irregular boundary with Precambrian rocks, masses of gneiss and schist are engulfed in the pluton. South and southwest of Nelson the contacts between intrusive and Precambrian rocks are highly irregular. Farther south, in the upper part of Aztec Wash. a large intrusive body has a composition at the border- line ,. between quartz monzonite and granodiorite. Orthoclase in what appear to be phenocrysts actually is late porphyroblastic, replacing plagioclase. Biotite and hornblende make up to 15 percent of the ground— mass. Analysis, in the US. Geological Survey Labo— ratory, of samples from this body by the zircon (lead- alplia) method gave an age of 35 million years.“ Many prospects of metallic minerals have been explored in a wide area around this pluton. The rock of lightest color seen in any of the large intrusive bodies is a granite that forms a prominent outcrop in the highest part of the Newberry Moun- tains. This rock has coarse texture, is rich in quartz, contains some oligoclase with the predominant ortho- clase, small amounts of muscovite and biotite, and scattered grains of magnetite and zircon. Study of all large intrusive bodies in the area would show a wide range in composition. 0f the 4A potassium-argon analysis made in 1962 reduces this age to 27 million years. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY rocks that have medium to coarse grain the dominant kinds are quartz monzonite and grauodiorite. DIKES, SILLS, AND PLUGS Small intrusive bodies are numerous and widely distributed; no attempt was made to map them. Dikes and sills range in thickness from a few inches to 100 feet or more and range in composition from basalt to rhyolite. In large part they are associated with volcanic rocks, and they occur in largest number near recognized centers of eruption. Many sills were in— jected between lava flows in thick volcanic sequences; some of the injected sheets are distinguished from flows only by generally coarser grain, by chilled upper margins, and by local crosscutting relations. Swarms of dikes that cut Precambrian rocks in wide expo- sures are assigned to a late geologic age because the dike rocks generally have not been sheared or crushed, and are similar, both in composition and in texture. to rocks in the volcanic sequences. Several agglomerate plugs mark vents. and other irregular bodies perhaps had this origin. Two of the best examples are in the midst of a glass-and-pumice complex directly south of Square Butte, a prominent landmark 6 miles northeast of Nelson. Each plug has a nearly circular plan and nearly vertical walls; one is 300 feet in diameter, the other 150 feet. These and other similar bodies are more fully described in connection with the associated volcanic rocks. VOLCANIC ROCKS Five distinct episodes of volcanism are recognized along the river south of Lake Mead. Four of the resulting assemblages of rocks are widely distributed, and three of these, Eocene( ?) to Miocene(?) in age, are here designated by formation names, from oldest upward, as follows: Patsy Mine volcanics, Golden Door volcanics, and Mount Davis volcanics. Volcanic rocks of the Muddy Creek formation make up the fourth assemblage. The fifth and latest episode‘is represented by local flows of basalt included in slope. gravels that probably are of Pleistocene age. (‘ontident correlation of volcanic sequences over distances exceeding 60 miles may be greeted with some skepticism: but each of the named assemblages has distinctive lithologic characteristics, and the strat— igraphic order of occurrence, wherever two or more of the units are recognized, is wholly consistent. Good evidence indicates more than one eruptive center for each assemblage, and there is of course no assurance that eruptions from several centers supplying simi- lar products were exactly synchronous. Neverthe— less, the striking consistency in order according to RECONNATSSANCE GEOLOGY, LAKE MEAD-DAVIS DAM, ARIZONA—NEVADA average lithologic composition, together with evi- dence for considerable crustal movement and erosion between successive units, clearly marks five chapters in the history of eruption. As noted in the several descriptions below, each of the three older assem- blages has varied lithology, but the overall composi- tion of each major unit is characteristic. A common kind of lava that recurs in two or more of the units presents problems of correlation wherever it forms isolated outcrops. Locally, in several parts of the map area, compli- cations caused by intrusive bodies and by widespread chemical alteration make identification of the volcanic rocks difficult or impossible. PATSY MINE VOLCANICS The oldest of the volcanic assemblages is widely exposed in a belt north of Nelson, in two areas along Black Canyon, and on both sides of Pope Wash. Smaller exposures lie along the road between Epper- sons corral and the Portland mine, and remnants too small to map lie on the Precambrian rocks west of Union Pass. A thick and representative section that extends west to east through the vicinity of the Patsy mine, about 3 miles northwest of Nelson, is chosen as the type section, although the base is not there exposed. The section consists dominantly of lavas, with some thick units of explosion breccia. Tufl’aceous layers are local and of minor importance. The characteris- tic brown to gray brown of the rock, in varied shades but dominantly dark, is an important aid in recog- nizing the unit. Flows vary in thickness from a few feet to more than a hundred feet, but are common 20 to 40 feet thick. Many are vesicular or amygdaloidal in their upper parts, and some that contain large angular fragments in an aphanitic matrix probably were brecciated during flow. A few thick layers made up largely of angular fragments, both small and mod- erate in size, seem to be products of explosive erup— tion. The rock is predominantly aphanitic or has only scattered and rather obscure phenocrysts, chiefly of plagioclase; however, some of the layers are con- spicuously porphyritic. Some flows of basalt in the upper part of the section are studded with reddish grains of iddingsite. Under the microscope many specimens show both augite and pigeonite, with plagioclase zoned from AnGO to A1130. Some are olivine—labradorite basalts, but more are pyroxene andesites. The latter predomi- nate in the lower part of the section, basalts in the upper. In the area north of Nelson, the thick succession of dark-colored lavas is sharply interrupted by a E19 light-colored glassy unit, as much as 100 feet thick, in which yellowish welded tufl’ at the base is suc- ceeded by gray to pinkish-brown aphanitic rhyolite containing lenses and small, spheroidal aggregates of brown and greenish glass. At several horizons are numerous whitish spherulites, 2 to 18 inches in di— ameter, which weather free; many, especially the largest, are covered with smooth, warty excrescences. Some spherulites have concentric zoning and also con- spicuous meridional markings. Chemical analysis of brown glass from this unit gave the result shown in table 2, p. E28 (sample 307). The glassy unit forms a ridge that parallels the road north of Nelson. Oflsetting and duplication of this highly distinc- tive horizon marker indicate the locations of several faults with large displacement. Above the glassy unit the flows are largely dark-brown basalt having a total thickness of perhaps as much as 1,000 feet, though some duplication by faulting may be present. Be- low the glass many strike faults break the section; nevertheless, the estimated thickness of this lower part exceeds 2,000 feet and may be more than 3,000 feet; thus, the total thickness of the Patsy Mine sec- tion appears to be at least 3,000 or 4,000 feet east of the large fault on which the basal part is dropped against Precambrian rocks and concealed. On the south, both west and east of Nelson, the continuous outcrop of lavas ends rather abruptly against bodies of intrusive rock that have surrounded and appar- ently engulfed large masses of the lavas. Two major eruptive centers for the Patsy Mine volcanics are recognized. One of these, about 5 miles northeast of Nelson, is marked by a maze of intru- sive bodies over an area covering more than a square mile. Near the Center of the area great numbers of dikes radiate from large irregular plugs; many of these dikes cut across sections of lava and merge into either flows or sills. All the rock in this complex has the lithologic character and the brown color pre— dominant in the Patsy Mine volcanics. To the south and northeast the complex passes into thick sections of the lavas resting on Precambrian basement. The second conspicuous eruptive center is along Pope Wash, about 3 miles east of the river, where lavas of the Patsy Mine volcanics dip outward from a large plug of gray-brown andesite porphyry. A complex of dikes, small plugs, and irregular bodies that cut the lavas forms a network outside the central body of porphyry. The total thickness of lavas in the section along Pope WVash appears to be well over 5,000 feet. Another possible locus of eruption for the Patsy Mine volcanics is near Hoover Dam. About half a mile downstream from the dam, the characteristic E20 brown lavas, inclined steeply eastward, emerge at stream level from a cover of younger rocks (fig. 8). The base of the volcanic mass is concealed west of the river, where blocks of the next younger series are lowered by faulting. The Patsy Mine lavas at the river, however, are crowded with fragments, large and small, of coarse-grained quartz monzonite; there- fore, a plutonic mass was part of the bedrock through which the old volcanic material issued. Farther downstream the section is much confused by intru- sive bodies of brown porphyry. The exact bound- aries of these bodies were not mapped, and they are included as part of the Patsy Mine volcanics, with which they seem closely related lithologically. About 4 miles downstream from the dam, the lavas dip southward; and the strike swings in a wide arc north- eastward, marginal to a massive body of the brown porphyry. Large dikes extend from this body into the lavas. Younger rocks at the eastern edge of Glass Plateau are faulted down against a mass of the brown porphyry, which there contains numerous large xenoliths of Precambrian gneiss, schist, and pegmatite. Thin sections of the porphyry reveal zoned andesine and oligoclase, with biotite, pyroxene, and much sanidine. The base of the Patsy Mine volcanics, resting on Precambrian rocks, is well exposed at several locali- ties in and near Black Canyon; also at many points farther southwest, and east of the river near the head of Gold Bug Wash. Although at some places the volcanic rocks are in direct contact with the old base- ment rocks, commonly a layer of coarse conglomerate or sedimentary breccia, a few feet to 40 or 50 feet thick, separates the two units. Cobbles and boulders in this deposit are made of the several types of Pre- cambrian bedrock, of volcanic rocks presumably older than the Patsy Mine volcanics, or exceptionally of quartz monzonite probably derived from bodies in- trusive into the Precambrian. At many places, par- ticularly along Black Canyon, the basal unit of the volcanic series is a layer, 100 or more feet thick, of resistant explosion breccia. Many sheer clifl's adja- cent to the river are on this resistant unit, Relations at the exposed upper limit of the Patsy Mine assemblage are highly varied. In the wide belt of exposure northeast of Nelson, including the type section, there is an abrupt change in lithology to the next higher volcanic unit, with no apparent unconformity. In much of the map area, however,- considerable disturbance and erosion occurred between eruption of the Patsy Mine and later volcanic rocks. Downstream from Hoover Dam a thick sedimentary breccia is essentially concordant on the Patsy Mine volcanics, which dip to the east much more steeply SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FIGURE 8,—Unconformity between Patsy Mine and Golden Door vol- Older lavas dip 40° E., younger series nearly horizontal View southward, about 1 mile canics. (note remnant at upper right). south of Hoover Dam. than the overlying Golden Door volcanics (fig. 8). The breccia is conspicuously exposed at the base of the canyon walls at and below the dam, and Ransome (U.S. Bur. Reclamation, 1950, p. 91), in his study of the damsite, reported the thickness of the coarse detrital deposit as 350 to 400 feet. Logically, and in keeping with his sardonic humor, Ransome called this unit the Dam breccia. Since it thins and disappears within half a mile downstream, evidently the breccia represents a local accumulation on a surface with considerable relief. The fragments, as long as 1 foot, consist of porphyry and brown volcanic rock. West of Union Pass the brown Patsy Mine vol- canics are exposed only in small isolated remnants, and the younger Golden Door volcanics in general rest directly on the Precambrian basement. The Patsy Mine volcanics may be present northwest of Eppersons Corral, but if so they have been dropped below the present erosion surface by the Epperson fault. South of Square Butte and also in the upper part of Pope Wash, the Mount Davis volcanics rest directly on the Patsy Mine volcanics, with angular unconformity in varying degree. GOLDEN noon voncamcs The second major unit in the succession of volcanic rocks in the map area consists of lavas, breccias, tufts, and glasses that average considerably higher in silica content than the next older and younger units. This distinctive lithOlogy is expressed in color terms: the Golden Door volcanics are generally light colored, in contrast to the somber brown tones of the Patsy Mine volcanics and the dark gray, brown, and black of the Mount Davis volcanics. A thick section of the sec- ond volcanic assemblage is particularly well displayed RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA in a large area on the flank of the Black Mountains west and southwest of Mount Perkins. In a limited part of this area near the road to Old Searchlight Ferry, the contact between the Golden Door and the younger Mount Davis volcanics is clearly exposed. The volcanic rocks are in fault contact with Precam- brian rocks for several miles north of the road, and this relation continues southward to a point about a mile southwest of Eppersons Corral, where typical lavas of the Patsy Mine volcanics in the footwall block dip southward in normal contact with Golden Door volcanics. The type section near the Golden Door mine, about 3 miles southwest of Mount Perkins, is essentially complete for the general locality, though the top and base are not exposed. Thickness of the Golden Door volcanics at the type locality appears to be at least 5,000 feet, though there may be some duplication by obscure faults. Absence of these rocks from a large area near the head of Pope “lash may be the result of uplift and erosion before the next younger assemblage was erupted. Near Hoover Dam the thickness of Golden Door vol- canics is somewhat more than 1,500 feet; but outcrops are absent in a large area south of the dam, where strong uplift attended by extensive erosion is indi— cated by prominent exposures of the Precambrian basement in the river belt. Locally in this area the Mount Davis volcanics lie directly either on the Patsy Mine volcanics or on Precambrian rocks; probably considerable movement occurred after the Golden Door volcanism and before or during eruption of the next younger assemblage. This history is indicated particularly by relations north and northeast of Eldo- rado Wash. In a belt northeast of Nelson the Golden Door volcanics, stepped down by a succession of faults west of the Eldorado fault, have a thickness as great as 1,200 feet, thinning eastward in each footwall block. East of the Eldorado fault these rocks are absent, and a thick section of Mount Davis volcanics lies with strong unconformity on Patsy Mine volcanics (pl. 1, sec. D—D’). Rhyolites form an important part of the Golden Door volcanics; but there is a wide range in composi- tion between rhyolite and andesite, and the average composition of the sequence varies from one locality to another. Generally the abundance of lavas high in silica appears to increase southward in the belt along the river. Rhyolite and its close relatives make up half or more of the section east of Davis Dam, and at least a third of the type section near the Golden Door mine. By contrast, no rhyolite has been recog- nized near Hoover Dam, where latites predominate; but rhyolite is an important constituent higher in the 1 661—325 0 > 63 - 4 E21 section, near Boulder City. Andesites and latites are the abundant types in the lower part of the type sec- tion, whereas rhyolite becomes more abundant upward. In View of the evidence for cxtcnsive erosion of these rocks in the northern part of the area, the Hoover Dam and Nelson sections may represent only a lower frac— tion that escaped destruction before the Mount Davis eruptions began. This would not imply, of course, that the basal parts of sections at any two localities are essentially identical. Aside from the probability that products erupted at several centers differed among themselves, crustal movements attended by Vigorous local erosion may have been active during the vol- canism, and the part of the assemblage preserved at one locality may be the time equivalent of any frac- tion, high or low, in the thick type section. Detailed measurement. and analysis of the thick type section have not been attempted. The lower half con- sists of flows and breccias, light brown to gray, apha- nitic with subordinate porphyritic texture. Mega- scopically the predominant lithologic type is andesite, but a considerable part of the rock may be latite. Dikes and sills, some of rhyolitic composition, intrude the volcanic rocks locally, and sills may form an ap- preciable part of the total thickness. Above the middle of the section, dacite and rhyolite are increas- ingly abundant, and the upper 1,000 feet consists chiefly of rhyolite, rhyolite tuff, and rhyolite glass. Some units that appear to be flows are on microscopic examination revealed as welded tufi's. Much of the glass is perlitic, and discontinuous layers of light-gray flow-banded aphanitic rock included in thick yellowish tuff is found by thin—section study to be perlitic rhyo- lite. Thin—section study of two flows in the lower part of the type section shows one to be pyroxene andesite, the other quartz latite. A third specimen, probably from a sill, is rhyolite porphyry. Flows in the upper part of the section are identified as perlitic rhyolite, dacite porphyry, rhyolite porphyry, and welded tufl'; the latter is full of glassy and spherulitic rock frag- ments and contorted shards. Layers of dark-gray per- litic glass, also near the top of the type section, have the compositions shown in table 2, specimens 111 and 185. Glass (specimen 148) from a similar section in Gold Bug Wash is remarkably like specimen 185 in chemical composition but has no phenocrysts. An exceptional section of the Golden Door volcanics, in the area east of Davis Dam, has considerable rhyo— lite in the lower part. One flow of spherulitic rhyolite vitrophyre contains sanidine, embayed quartz, and frondlike groups of crystallites, with some sphene and biotite. Several mines and prospects are in rhyolite at horizons not far above the Precambrian basement E22 rocks, which in the large outcrop area west of Union Pass are cut by numerous rhyolite dikes. One of these, a striking rhyolite porphyry, includes pheno- crysts of oligoclase jacketed by albite, sanidine, and quartz. Near the summit of Union Pass, a thick whit- ish tufi' contains masses of yellow translucent opal. A block of volcanic rocks faulted down against Precambrian gneiss several miles west of Davis Dam is indicated on the map as part of the Golden Door sequence, though some Mount Davis volcanics may be included. The lower part of the exposed section con— tains rhyolite breccia and tutf, which are cut by doleritic sills and irregular bodies that at a higher level seem to merge with basaltic lavas. Similar in- trusive bodies of dolerite are common also in a wide belt east of Davis Dam. Directly west of Union Pass along the highway, an extensive mass of this dark rock appears to be intrusive into Precambrian rocks below the Golden Door volcanics. Between this loca- tion and the river, numerous smaller masses of dolerite out both the Precambrian and the volcanic rocks. Probably some of these intrusive bodies represent channelways through which the Mount Davis volcanics were erupted. ’ The rocks exposed in the vicinity of Hoover Dam (fig. 9) were studied by F. L. Ransome for the Bureau of Reclamation, before the dam was built; and his report (U.S. Bur. Reclamation, 1950), of which only a part was printed in modified form has been available to the present writer. Ransome recognized an “older volcanic series”—the gray—brown assemblage down- stream from the damsite, here called the Patsy Mine volcanics—and a “younger volcanic series,” including all higher units in the sequence of volcanic rocks in the vicinity of the damsite. As Ransome noted, the coarse-grained and locally thick sedimentary unit that he called the Dam breccia shows an eastward tilt com- parable to that of the underlying brown lavas, where— as the younger units have been less disturbed. Ran— some’s “younger series” is here correlated in part with the Golden Door volcanics, in part with the younger Mount Davis volcanics. This separation is based chiefly on lithology; the lower units of the series are definitely more siliceous than higher units, which con— sist largely of basalt or trachydolerite._ Structural definition between the two sequences is not as distinct as in other parts of the area; evidence of some grada- tional overlap is discussed in later paragraphs. The lowest and the thickest litliologic unit in the Golden Door section near the damsite is a latite flow breccia, light brown to light red brown on fresh surfaces, littered with fragments, both angular and somewhat rounded, of rock identical with that forming the matrix. This mass, making a large part of the SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY steep canyon walls at and near the dam, ranges in thickness from 300 to more than 600 feet. Apparently its top was much eroded, and depressions so formed were filled with coarse sedimentary rubble, containing fragments as much as 6 feet long. This rubble, firmly cemented to form what Ransome called the Spillway breccia (US. Bur. of Reclamation, 1950, fig. 34), was in part contemporaneous with a thick flow which con- tributed many of the fragments. This flow, resting on the basal volcanic unit or locally on the Spillway breccia, consists of brownish aphanitic rock, with small phenocrysts sparsely distributed. Ransome commented that this rock has the appearance of andesite, but he called it “basic latite” because it has a high content of potassium. Near the head of Black Canyon, this rock interfingers with the Spillway breccia in a way that suggests a local intrusive relation. Although the latite, with thickness locally exceed- ing 300 feet, is extensively distributed on both sides of Black Canyon, it is conspicuously absent over con- siderable areas. These discontinuities may have re- sulted from extrusion on a highly irregular hill-and- valley topography, with continued vigorous erosion during and after emplacement of the latite sheet. The Spillway breccia of Ransome supports this suggested history by its highly irregular thickness and also by local variations in its content from fragments repre- senting wholly bedrock units older than the latite to a dominance of latite fragments. A discontinuous deposit of tufl’, locally as much as 200 feet thick, rests on the basic latite along the north flank of Sugarloaf Mountain. On the southwest slope, where the tufi' is best displayed, the latite flow is absent, and the tuff lies on the older flow breccia. East of the dam the tufl' is broken by faults, and a segment exposed beside the highway includes a layer of dark—gray perlitic glass (table 2, specimen 414). The next unit in the section is a widespread lava sheet, 200 to 400 feet thick, diagnosed by Ransome (U.S. Bur. Reclamation, 1950, fig. 34) as “biotite latite.” The fresh rock is light red to gray brown and contains conspicuous phenocrysts of biotite set in a groundmass in part aphanitic, in part glassy. The feldspar is andesine. Some oxyhornblende accom- panies the more abundant biotite, and calcite pseudo- morphs after the ferromagnesian minerals are present locally. At a few localities two or more flows can be distinguished, but elsewhere the sheet appears to be undivided. I Partial chemical analyses of five specimens show a range in silica content of 66 to 70 percent; yet these specimens have no visible free quartz. The analyses resemble strongly that of the underlying glass, and probably this glass and accompanying tuff renrb RECONNAISSANCE GEOLOGY, LAKE sent the initial eruption leading to formation of the lava sheet. The entire Golden Door section in the vicinity of Hoover Dam is complicated by irregular intrusive bodies, large and small, of a dark rock with the mega- scopic appearance of basalt but with chemical compo- sition like that of trachydolerite. Some of the intru- sive bodies, well exposed in the canyon walls, are ordinary dikes; others have nondescript form, with overall dimensions as much as half a mile long and MEAD—DAVIS DAM, ARIZONA—NEVADA E23 several hundred feet wide. This rock contains scat- tered reddish specks described by Ransome as “fer- ruginous pseudomorphs after olivine.” The trachy- dolerite in this Vicinity resembles, in general appear- ance and in mode of occurrence, irregular bodies in- trusive into Golden Door volcanics near Davis Dam (p. P127) and in many other parts of the map area. The boundary between the Golden Door and Mount Davis assemblages east of Hoover Dam is not sharply defined. A coarse sedimentary deposit, named by FIGURE 9.~Airvivw southeastward across Hoover Dam and eastward-dipping volcanic rocks. The Dry Camp hreccia of Ransome (U.S. Bureau of Reclamation, 1950) is locally the basal member of Mount Davis volcanics. Dissected gravel deposits (top of View) accumu- lated in great thickness on subsiding: hlock southwest of Ilorsothinf fault Golden Door volcanics exposed in canyon wall. Bench at left of Sugarloaf Mountain is mantled with Colorado River gran-ls, at altitude above 1,500 feet. (U.S. Bureau of Reclamation photograph) E24 Ransome (US. Bur. Reclamation, 1950, fig. 34) the Dry Camp breccia (fig. 9), lies on the biotite latite and on local lenses of waterlaid tuft. The breccia, with thickness of as much as 200 feet, contains frag- ments chiefly of monzonite vporphyry locally admixed with numerous fragments of basaltic rock. Thus, al- though some of the intrusive bodies of trachydolerite cut the Dry Camp breccia, and the section directly above is made up dominantly of basaltic flows, clearly a considerable quantity of these dark rocks was ex- posed at the surface while deposition of the Dry Camp breccia was in progress. In fact, a flow of the basalt lies on the biotite latite and beneath the sedi- mentary breccia less than a mile southeast from the east portal to the Hoover Dam area. Confused con- tacts among several lithologic units in a belt east of the dam probably reflect simultaneous volcanism and crustal disturbance, attended by locally rapid erosion and sedimentation. Later faulting and erosion fur- ther complicated the pattern. It seems best to include in the Mount Davis sequence Ransome’s Dry Camp breccia, and also basaltic flows that locally underlie this breccia. West and southwest of Hoover Dam, beyond the limited area studied by Ransome, the highest lavas exposed in the Golden Door section include several thick flows of rhyolite. Apparently the thickness of the section increases westward into the River Moun- tains, where a complex of volcanic rocks and intrusive bodies presumably represents an important eruptive. center. The Boulder City pluton (p. E17), which is similar in chemical composition to the underlying lavas, probably had its origin at this general center during an advanced stage of the Golden Door igneous activity. Most of the rocks in the River Mountains block are similar to the Golden Door volcanics. Two miles north of Boulder City, a small stock of quartz monzonite has a nearly circular outcrop within a wide frame made of steeply upturned lavas that are cut by a network of dikes and irregular intrusive bodies. North and east of Nelson the Golden Door volcanics consist chiefly of explosion breccias and tufts in thick layers. No petrographic or chemical analyses of these pyroclastic units have been made. In that part of the area, the appearance of the light-colored pyro— clastics marks an abrupt lithologic change from the underlying dark lavas in the Patsy Mine volcanics, but no structural discordance is apparent. MOUNT DAVIS VOLCANICS A third thick assemblage of volcanic rocks, which in many places lies with angular unconformity on the Golden Door volcanics or on older rocks, is well ex— SI-IORTER CONTRIBUTIONS TO GENERAL GEOLOGY posed at its type locality on and near Mount Davis, in western Mohave County, Arizona, and is here called the Mount Davis volcanics. This assemblage consists largely of lavas, commonly intercalated with coarse gravels. Although basalt and dark andesite are the most abundant kinds of volcanic rock in the formation, at some horizons sheets of glass and pumiceous tufl with compositions corresponding to latite and rhyolite are widespread. White tufls in particular make a striking contrast with the large thicknesses of basaltic flows below and above (fig. 10). These interruptions in the section are similar to the occurrence of rhyolitic glass in the Patsy Mine sequence north .of Nelson. The following features and relations of the Mount Davis volcanics suggest crustal unrest before, during and after the period of eruptions: (1) In some places the sequence rests on Golden Door volcanics conform- ably, elsewhere with strong unconformity. (2) Over large areas the Mount Davis rocks lie on Patsy Mine volcanics, usually with strong unconformity. Com- monly, a fault or fault zone with large throw sepa— rates blocks, in one of which the Mount Davis sequence rests on Golden Door volcanics, in the other on Patsy Mine volcanics. (3) At several localities the Mount Davis volcanics lie on Precambrian rocks, only a short distance from normal contacts of these lavas on Patsy Mine or on Golden Door volcanics. (4) In many places great quantities of extremely coarse rubble. derived largely from Precambrian bedrock, are in- terspersed with the Mount Davis volcanics. Several of the larger sedimentary units, exposed along impor- tant faults, have a chaotic arrangement suggesting landslides from steep scarps. (5) The exposed sec— tions of Mount Davis rocks are tilted, commonly to dips of 30° or more; and many faults with large dis- placement transect these sections together with older rocks. Where the Mount Davis rests on Golden Door vol- canics, the change in lithology above the contact is abrupt, and the dark lavas in the younger unit gen- erally continue without interruption through a large thickness. In this respect the outcrops directly north of Searchlight Ferry road and about 7 miles east of the old ferry location are somewhat exceptional. There a thick flow of rhyolite with abundant quartz pheno- crysts is enclosed in dark basaltic lavas about 300 feet above the top of the Golden Door section. Above the solitary flow of rhyolite the exposed section con- sists wholly of dark basalt. Marked differences among sections, both in thickness and in general composition. doubtless reflect differ- ences in topography at times of eruption and also varying distance from eruptive centers. Thus at RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DANI, ARIZONA—NEVADA Mount Davis the lower part of the section, overlying Golden Door volcanics with slight angular discord- ance, consists of dark basalt flows hundreds of feet thick. Both units dip steeply westward (pl. 1). This general relation continues along the strike through several miles northward, though in Gold Bug lVash the angular discordance is more pronounced and a layer of coarse conglomerate 10 to 12 feet thick un— derlies the basal flow of the Mount Davis. Five miles farther northeast, along Pope Wash, the Golden Door section is absent; and the Mount Davis volcanics lie directly above Patsy Mine volcanics, both major units dipping steeply eastward though with noticeable an- gular discordance. The following section is exposed: Mount Dan‘s volcanics and Brown Patsy Mine volcanics in upfhrozcn block east of large north-south fault Mount Davis volcanics (partial thickness) in downthrown block; lavas and beds (lip 30" E. Nine units recognized as follows: Feet Basalt flows, brownish ___________________________ 100 Gravel, bedded, very coarse, weakly cemented. Pebbles of Precambrian and volcanic rocks ______ 60 Andesite and basalt, dark-gray, in flows 15 to 40 ft thick _________________________________________ 250 Gravel, bedded, coarse, with pebbles and angular blocks of Precambrian and volcanic rocks ________ 75 Basalt flow, brownish ____________________________ 25 Coarse sedimentary debris in crude beds, weakly cemented. Blocks, as much as 5 ft long, of Pre- cambrian and volcanic rocks ___________________ 300 Andesite flows, gray-brown, alternating with beds -of coarse gravel _______________________________ 100 Andesite and basalt flows, gray-brown, many weath- . ering to rubble of blocks and sand-size particles 650 Basalt and andesite flows, 15 to 40 ft thick, alter- nating with beds of gravel and gray silt ________ 250 Unconformable contact. Brown Patsy Mine volcanics, dipping 25° to 40° E. Large thickness. The total of the above measurements, 1,810 feet, probably is much too small for the tilted section, which is 11/; miles in width of outcrop. Correction was made for duplication by strike faults; but there are no confident key horizons for use in tracing faults and matching accurately between blocks. At any rate, this section is incomplete; its base probably is above the base of the sequence at. Mount Davis as explained below; and the upper part, with unknown thickness, has been eroded from the hanging wall of the large fault on the east. Other belts of outcrop in the gen- eral area present similar difficulties; nearly all are broken by faults, and the top of the Mount Davis assemblage in its typical development was nowhere certainly identified. But several partial sections ap- pear to be fully 3,000 feet thick, and maximum thick- nesses may well exceed 4,000 feet. E25 View looking northeast. Light-colored breccia and tuft, left foreground, is in upper member of Golden Door volcanics. Thick section of overlying Mount Davis volcanics is largely basaltic but includes layers of whitish tufl’. Horizontal Fortification basalt member of Muddy Creek formation forms mesa cap in middle background about 2 miles from camera. FIGURE 10.-—Three units of volcanic rocks north of Nelson. Some of the best exposures of the Mount Davis vol- canics are in the rugged hill country about 5 miles north of Nelson, where valleys with steep walls run nearly at right angles to the strike (fig. 10). There the basal flows of dark basalt are nearly conformable to the yellow-white tuff and breccia of the Golden Door volcanics. As at Mount Davis the lower part of the younger unit consists chiefly of basalt and dark andesite flows. Dikes that cut the section of flows represent feeding channels that supplied magma for numerous sills of dark porphyry, and probably also for flows at higher levels. Above the middle of the section, layers of white pumiceous tufl' contrast sharply with the dark lavas. One of these old ash beds is the basal member of a tripartite unit, highly distinctive, which recurs in widely separated localities; the most extensive outcrop is under Glass Plateau, a few miles south of Hoover Dam. The section north of Nelson (fig. 10) is very thick, though large strike faults and the lack of key horizons make an exact measurement impossible. An estimate of the thickness, from the base to the large fault cut— ting ofl” the outcrop ontthe east, is 3,200 feet. of which the lower 2,200 feet consists almost wholly of volcanic rocks and related sills, whereas in the upper 1,000 feet large quantities of coarse sedimentary debris are in— terspersed with lavas. This higher part of the section is generally like the complete sequence measured near Pope “lash; the lower part, made almost strictly of volcanic rocks. is like the sequence from Mount Davis northward. But the higher part of the section west of Mount Davis also includes many thick beds of E26 coarse-grained sediment. The isolated ridges west of the river at. that latitude are tilted fault blocks in which the bedrock consists of typical basalt and ande- site flows of theMount Davis volcanics, interspersed with beds of coarse conglomerate and breccia. Some of the sedimentary debris exhibits the disordered ar- rangement characteristic of landslide masses, and the fragments were derived almost entirely from Precam- brian bedrock. Presumably the source was the Eldo- rado Mountain block, against which the Mount Davis volcanics are downfaulted. The abundant rubble in- tercalated with the lavas suggests that the fault was active in Mount Davis time. Along Pope Wash and at several other localities, the coarse-grained sediments in the Mount Davis se- quence extend from the base upward; such sections perhaps correspond mainly to the higher member in the general assemblage. In Pope Wash the layers of sedimentary breccia thicken and coarsen northward toward an area of Precambrian bedrock north of the Pope fault. Rock types represented in the conglom- erate are largely Precambrian, in part volcanic rocks including basaltic lavas like those in the Mount Davis sequence. This evidence regarding pr0venance, found in several similar sections, suggests that the Mount Davis volcanism occurred while faulting was active. The thickest sections of lavas accumulated on blocks that were relatively sinking. Rising blocks were sub- ject to rapid erosion, and the resulting debris, derived partly from lavas, partly from older bedrock, was deposited in maximum thicknesses near the borders of the positive blocks. During recurrent volcanism some of the lavas buried slope gravels, and in favored locations the alternating sedimentary and volcanic record has been preserved. Abrupt appearance of coarse sediments in a distinct upper member, as in ' the section north of Nelson, may signify the resump- tion of active faulting near the border of a subsiding block on which a large thickness of volcanic rocks previously had accumulated. The widest belt covered with Mount Davis volcanics is west of the river and extends several miles south— ward from Glass Plateau. Within this belt the pre- vailing dips are eastward, in inany places at a steep angle, through a distance of 5 or 6 miles. The im- pression of great thickness is strong, though strike faults with large throw have caused much duplica- tion. Lavas make up the greater part of the section, and lack of key horizons defeats efforts to map most of the faults continuously or to reckon accurate thick- nesses anddisplacements. Another outcrop area, as much as 4 miles across the average strike, lies west SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY of the river and north of Eldorado Wash. There the dip is generally eastward, above a base that along its outcrop bevels strongly across the Patsy Mine vol— canics onto the Precambrian basement. This relation suggests accumulation on or bordering a rising up- land; and this suggestion is reinforced by the quan— tities of coarse sedimentary breccia interspersed through the section of lavas. Probably this area is crossed by strike faults not shown on the map, and no estimate of the thickness is now possible. Directly northeast of the area, several faults of larger throw are conspicuous because of the contrast between the dark Mount Davis volcanics and underlying whitish tuffs and breccias in the Golden Door section. A short distance farther north, directly west of Malpais Mesa, the Mount Davis volcanics again rest directly on the brown Patsy Mine volcanics, both units dipping steeply to the east. In that vicinity the Mount Davis section has particular interest for two reasons: from a composition dominantly of ba- saltic lavas near the southwest corner of the mesa there is gradation northward into a section with quantities of very coarse sedimentary debris; and the section grades upward, without detectable break, into tan siltstones that appear to be part of the Muddy Creek formation. A steep-walled valley leading to the river from the western slope of the mesa shows the following succession: Thickness (feet) Siltstone, cream-yellow, with some thin-bedded clay, apparently part of Muddy Creek formation; grades downward into layers that have many pebbles and scattered angular cobbles; dip 12° to 15° E __________ 100+ Conglomerate beds, coarse; many of the pebbles angu- lar; Precambrian and volcanic rock types represented; (lip increases downward in section to about 30° E____ 110 Limestone, gray, single layer, aphanitic _______________ 1 Conglomerate beds, coarse; dip increases downward to about 45° E _______________________________________ 75 Breccia, extremely coarse sedimentary; bedding crude or in part lacking; contains many blocks of gneiss 100 to 200 ft long, shattered but intact; probably of landslide origin _____________________________________ 480 Basalt flows with iddingsite, dark; abrupt contact with sedimentary layers above and below; dip 50° E ______ 300 Breccia, very coarse sedimentary, in part crudely bed- ded. Much of it, with no perceptible bedding, con- tains blocks of gneiss 10, 20, and 30 ft long __________ 800-_+- Breccia, volcanic, lavender-gray _______________________ 45 Breccia, sedimentary; fragments largely of volcanic rocks but some of gneiss __________________________ 300 Breccia, massive, sedimentary; blocks chiefly of Pre- cambrian gneiss __ ____ _ 100 Breccia, bedded, sedimentary; fragments largely of vol- canic rocks ________________________________________ 225 Breccia, massive, sedimentary; blocks chiefly of Pre cambrian gneiss ___________________________________ 150 RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA Breccia, bedded, sedimentary; fragments of volcanic rock with several thin layers of tuff interspersed _____ 100 Basalt flows with iddingsite, brown; interlayered with coarse sedimentary breccia containing fragments of gneiss and of volcanic rocks; dip 55° E _____________ 200 Slight unconformity. Patsy Mine volcanics, dipping steeply eastward. The northward increase in coarse sediment, much of it unassorted breccia containing blocks of Precam— brian rock tens of feet long, suggests that the faults bounding the Precambrian block west and south of Willow Beach were active while Mount Davis vol- canism was in progress. Flows that accumulated in large thickness in the area southwest. of Malpais Mesa thinned and wedged out northward against an ag- grading slope adjacent to the rising block of basement rocks. The abundant coarse rubble that recurs through a thick section testifies to a south-facing scarp that was renewed time after time by faulting. Southeast of Hoover Dam ‘a peculiar glassy mem- ber that elsewhere is recognized high in the Mount Davis volcanics lies only a few hundred feet above the base; therefore, the total thickness is compara- tively small in that vicinity. In the southern part of the map area, the section of dark lavas is very thick, though it was not studied in detail. A few miles north of Union Pass these lavas, resting on Golden Door volcanics, dip steeply northeastward, and the belt of outcrop extends east of the area mapped. Northeast of the Portland Mine and west of a large fault, glassy rocks that belong high in the Mount Davis assemblage lie on brown Patsy Mine volcanics. In view of the thick Golden Door section a short dis- tance northeast of and dipping toward this fault, presumably there was important displacement during as well as after the Mount Davis volcanism. Two miles northwest of Davis Dam, a block of dark lavas interlayered with coarse conglomerate, appar- ently part of the Mount Davis, is faulted against Precambrian and Golden Door bedrock. Dikes, sills, and irregular intrusive bodies of basalt and andesite in that vicinity probably are related to the Mount Davis volcanics. Although the lavas of the Mount Davis volcanics are predominantly dark and are properly described as basaltic, flows of dark—gray andesite make up con- siderable thicknesses, and an exhaustive study would be required to determine the relative proportions of basalt and andesite. A random specimen from the lower part of the type section near Mount Davis shows in thin section the following features: E27 No. 146. Glassy basalt. Dark groundmass, in large part glassy. Many minute grains of py- roxene. Abundant olivine, altered mar- ginally to iddingsite. Similar rock, dark brown in many flows, is abundant in the wide area of outcrop 8 to 9 miles south—south- east from Boulder City. A sample thin section is the following: No. 168. Brown amygdaloidal basalt. Dark, glassy groundmass. Labradorite has outer zones crowded with glass inclusions. Much olivine, in part altered to iddingsite and serpentine. Some grains of pigeonite. Amygdales consist largely of zeolites. Many of the dark flows are glassy in such degree that little or no feldspar can be identified in thin section. Two specimens from the vicinity of Square Butte, one of them a. flow directly overlying a layer of pumiceous tuff, can be diagnosed simply as glassy olivine basalts, with iddingsite and minor pigeonite and biotite. These aphanitic dark-gray to nearly black specimens are common in large thicknesses 'of the Mount Davis assemblage. On the other hand, some gray flows are identified as andesites, even on megascopic examination. A specimen collected northwest of Davis Dam has the following thin-section description: No. 374. Groundmass of fine grain, rich in andesine. Some grains of pigeonite, augite, and magnetite masking biotite. Gray rock similar to this makes up many of the flows that are interlayered with conglomerate, along Pope Wash and also in the area of outcrop 2 to 3 miles south of Square Butte. Flows with this lithology are not resistant to arid-climate weathering; many out— crops are partly masked by heaps of disintegrated rock, much of it in sand-size particles. Glassy rocks with high content of silica make a subordinate but conspicuous part of the Mount Davis sequence. Two eruptive centers for this glassy mate- rial are conspicuous: one nearly 5 miles north of Nelson and the other directly south of Square Butte. At each of these localities, plugs made of glassy agglomerate cut across the underlying lavas, which are steeply upturned and disrupted through a radius of a quarter of a mile or more. Layers of pumiceous tuff and dark glass are particularly thick around the centers of eruption. At both localities much of the glassy section was strongly upturned and broken be- fore it was covered discordantly by flows of dark basalt. These relations may suggest successive erup- tions from a source of highly siliceous magma, fol- lowed by resumption of effusions low in silica. But E28 more probably the glassy materials were erupted in— cidentally at a few isolated centers, while the more mafic lavas continued to be poured out in the general area. The plugs of glassy agglomerate were moved appre- ciably as solid units. Their outer surfaces are strongly slickensided and show vertical striae and flutings, and the agglomerate is much fractured. No doubt the siliceous magma stiffened rapidly on nearing the sur— face, at least when activity was waning, and each congealing plug was driven upward by pressure from the magma chamber. The two plugs at the Square Butte center were punched up through whitish por- celaneous glass. Three or four hundred feet south of these plugs, a mass of brecciated glass 250 feet long and more than 1.00 feet wide was driven up through thick layers of glass which locally are vertical or dip steeply westward, in overturned attitude. At a distance from eruption centers, where a glassy section may be seen in normal order, generally the basal part consists of nearly white pumiceous brec- cia and tulf, including some f ‘agments of basalt, the layer totaling 10 to 100 feet in thickness. Above this is compact glass, in part brecciated, much of it dark gray or nearly black in bulk, though transparent and almost white on thin edges. Some sections have suc- cessive irregular layers with colors ranging through brown, red, orange, yellow, and other colors. Many of the glasses have phenocrysts, but some are glassy throughout. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY A. high content of silica appears to be characteristic of the glasses in. the Mount Davis volcanics. Of seven specimens analyzed (table 2) the lowest in silica came from the section 5 miles north of Nelson, high in the thick member of lavas but below the member con— taining coarse sediments. One glassy unit high in the sequence of Mount Davis volcanics is remarkably widespread and is characterized by a persistent combination of features. The upper member of the unit forms the cap of Glass Plateau, and clifl's at the south rim of that plateau show the full makeup of the unit, as follows: Feet Felsite or “stony glass,” chocolate-brown_____ 60—100 Perlitic glass, black _________________________ 20-40 Coarse breccia, fragments of black glass and gray pumice ______________________________ 10—15 Tuff and breccia, white, pumiceous __________ 20—60 Flows of basalt and andesite, thick section. Exposures along a wash 3 miles southeast of Hoover Dam and east of the highway show: Cemented gravels of Muddy Creek(?) formation. Unconformity. Feet Basalt with iddingsite, vesicular _____________ 25 Felsite, chocolate-brown _____________________ 50 Perlitic glass, dark-gray to black, locally re- plete with brownish spherical bodies 2 to 3 in. in diameter ___________________________ 10-40 '1‘qu and breccia, gray, containing large angu- lar blocks of pumice _____________________ 50—200 Irregular contact. Basalt flows, brown to blackish. TABLE 2.——Chemical analyses of 13 volcanic glasses [Rock Analysis Laboratory, University of Minnesota. Eileen Oslund, Analyst] Lab. specimen ____________________ R1542 R1543 R1536 R1537 R1538 R1546 R1539 R1540 R1541 R1544 R1545 R1547 R1548 Original N0 ______________________ 307 311 111 148 185 414 207 297 298 345 350 421 424 76. 19 72. 21 69. 40 73. 93 73. 93 65. 86 66. 85 71. 55 70. 94 72. 91 73. 65 72. 40 79. 46 12.62 12.34 13. 62 12.09 12. 46 l5. 18 15. 25 13. 50 13.41 12. 53 12. 78 12. 94 10. 57 .68 .59 .99 .52 .55 1.99 1.26 .80 1.12 .43 .78 .73 .64 .14 .18 .63 .26 .30 .80 .57 .28 .03 .30 .09 .16 .09 .13 .12 .46 .18 .16 1.12 .46 .24 .34 .13 .19 .34 .17 .79 .97 1.31 .81 . 75 2. 86 1. 38 1. 02 1.42 .69 . 79 . 79 .68 4. 23 3. 33 2. 94 3. 23 3. 21 3. 52 3. 90 3.58 3. 44 3. 67 3. 49 3. 27 2. 92 3. 32 4. 16 5. 33 4. 46 4. 74 3. 83 5. 7 5.02 5. 00 4. 52 4. 58 4. 99 4.16 1.04 4. 75 4.50 3. 77 3. 34 3. 19 3. 53 3. 06 3. 08 3. 99 2. 96 3. 35 .45 .54 1.00 .21 .32 .16 .49 .18 .26 .31 .24 .20 .40 .20 11 . 12 . 30 .12 .15 .42 41 . 18 . 18 . 13 .11 . 13 . 12 .01 .01 .07 .01 .01 .18 .07 .03 .03 .01 .01 .01 .02 .03 .05 .04 .04 .04 .06 .06 .06 .06 .04 .05 .05 .04 99. 83 99. 83 99 80 99. 74 99. 80 99. 50 99. 66 99. 58 99. 36 99. 59 99. 68 99. 56 99. 52 Specimen Description and locality Specimen Description and locality 307. Uniform glass with no phenocrysts, from glassy member in Patsy Mine voi- canics, in ridge east of Welcome fault and 1 mile northwest of Techatticup mine, Eldorado district, Nevada. Specimen is one of many brownish sphe- roids, with diameters 1—3 in., more resistant than enclosing glassy matrix. Uniform glass, no phenocrysts, from glassy matrix enclosing specimen 307. Glass, dark-green to black, forming layer 25 ft thick in Golden Door volcanics, about 500 it below base of Mount Davis volcanics, directly north of Search- light Ferry road, Arizona, about 7 miles east of Colorado River. Small phenocrysts in sample. Nonporphyritic glass, light-gray, from thick glassy unit in Golden Door vol- canics at Gold Bug Wash, about 2 miles east of Colorado River. Glass, dark-gray, with whitish phenocrysts, from Golden Door volcanics in wash 11,4 miles west of Golden Door mine, Arizona. Perlitic glass in Golden Door volcanics, half a mile northeast 01' Sugarloaf Moun- tain, at east side or large loop to south in road leading east from Hoover Dam. Glass, dark-gray to black, from layer high in Mount Davis volcanics, on west side of Welcome fault near north end of the fault as exposed. 311. 111. 148. 185. 414. 207. 297. Porphyritic glass, dark-gray, in upper part of Mount Davis volcanics, east of highway and 2 miles (straight map distance) southeast of Hoover Darn. Glass layer is below thick section of brownish ielsite and above thick pumiceous tufi—breccia. . Glass, reddish-brown, from block in tufi breccia below glass layer of specimen 97 . Glass, dark-gray, from eruptive center in Mount Davis volcanics south of Square Butte, from layer steeply tilted away from plug of agglomerate, has no pheno- crysts. . Glass, light-brown, from layer directly below basaltic lavas of the Mount Davis volcanics, at east side of eru tive center south of Square Butte. . Glass, dark-gray, from layer irectly below brown felsite, half a mile southeast of Three Kids mine. Glass overlies pumieeous tufi. . Brown felsite above glass layer, locality of specimen 421. The assemblage resembles that in upper part of Mount Davis volcanics. RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA South of Las Vegas Wash, near the Three Kids manganese mine, the following sequence is at the top of a thick section of volcanic rocks: Muddy Creek formation. Angular unconformity. Felsite, chocolate-brown, porphyritic; in thick flows ______ _ 2001- Perlitic glass, black; in part thin banded ______ 50 Tutf and breccia, with large blocks of pumice__ 100+ Thick lavas and volcanic breccias. Many other exposures of these distinctive glassy rocks range at least as far south as the latitude of the Portland Mine. Hunt (written communication, 1941) reported a similar glassy unit east of the Black Mountains and north of the Colorado River, at a loca- tion more than 60 miles from the Portland Mine. Presumably, therefore, this unit of the Mount Davis volcanic records a volcanic episode that affected a very large area. Although the unit is in general con- formable Within the Mount Davis, there are several local departures from this relation. Three miles south- east of Hoover Dam, the irregular contact between the glassy unit and underlying basalt appears to be an erosional unconformity. Along the north edge of Glass Plateau, the glassy unit lies on intrusive rocks apparently older than any part of the Mount Davis assemblage. Near the Three Kids Mine, the lavas directly beneath the glassy unit consist of latite and more siliceous rock types and apparently belong to the Golden Door sequence. This varied relation merely strengthens the conclusion, based on other evidence cited above, that crustal movements and local erosion were pronounced while the Mount Davis volcanism was in progress. Comparison of three specimens (297, 298, 421) by chemical analyses given in table 2, shows the high con— tent of silica in these similar units of glass. Specimen 424, the felsite directly above specimen 421, is ab- normally high in silica, some of which may be sec- ondary. A study of nine glass specimens containing pheno- crysts for thin-section examination gave the results summarized in figure 11. Six of the glasses (207, 297, 298, 350, 421, 424) are from the Mount Davis volcanics and are closely comparable to the Golden Door glass (185) that is highest in silica. A perlitic glass (414) from latite in the Golden Door volcanics near Hoover Dam has a rather distinctive composition. VOLCANIC BOOKS OF MUDDY CREEK FORMATION Although the volcanic rocks in this assemblage are part of the Muddy Creek formation, they merit sep- arate treatment as a fourth major division in the rec- ord of volcanism within the map area. Basalt flows E29 locally interlayered with clastic sediments in the basal member of the formation, as at the Three Kids mine (p. E10), probably represent closing stages of the vol- canism that produced the Mount Davis volcanics. Widespread sheets of basaltic lavas in the upper part of the Muddy Creek formation indicate renewal of volcanic activity after a considerable interval of time. A remnant of these lavas forms the cap of Fortifica- tion Hill, which has an area of nearly 2 square miles. In the thickest part of this prominent residual, about 50 superposed flows of olivine basalt have a combined thickness of 500 feet. . Other large remnants of similar basalt in the map area appear to represent a widespread cover that once was continuous over hundreds of square miles. Some remnants are conformable on sedimentary beds that probably belong in the Muddy Creek formation; other remnants lie unconformably on older rocks. The larg- est known remnant, covering more than 10 square miles, lies east of the Black mountain divide. Because of its prominence and distinctive lithology, this upper unit in the Muddy Creek formation is mapped separately as the Fortification basalt member (table 1). Vigorous local erosion in early Muddy Creek time, as indicated by coarse sediments of highly varied thickness, suggests active faulting in the closing phases of Mount Davis volcanism. Basalt flows in these basal deposits of the formation are succeeded by layers of andesite tufi' and tufl'aceous sand, which in- dicate that the Mount Davis volcanism closed with explosive eruptions from reservoirs in which the mag- mas had become less mafic. There followed a lull in volcanic activity, as indicated by nearly 2,000 feet of sandstone, siltstone, clay, and saline materials in which no volcanic rocks have been observed. The thick and uninterrupted succession of basalt flows resting on an equally thick sedimentary se- quence, both in Fortification Hill and in Malpais Mesa, suggests that the flood of lavas in late Muddy Creek time began abruptly and continued rapidly. Although no Muddy Creek deposits now cover the cap of Fortification Hill, the base of the lava sequence is conformable on the beds below. Northwest of the hill the lavas have been downfaulted and tilted north- ward; and north of Boulder Basin a closely similar but thinner section of basaltic flows, tilted gently southward, is included in the Muddy Creek sedimen- tary sequence. Study of this basin before Lake Mead was formed led to correlation of the basalts of the Fortification Hill area with the uppermost of those exposed north of the lake (Longwwell, 1936, p. 1421). In the vicinity of Lake Mead, therefore, the Forti- fication basalt member, as here defined, is part of the E30 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Mg0+ FeO EXPLANAT|ON © Bulk composition Values for specimens 35,0 and 424 are identical 0 Grou ndmass composition 0 Superposition of above For specimen 421 09 190 percent MgO + FeO 50 percent 50 percent K20 +Na20 .9 (‘9 100 100 percent percent 50 percent 0210 185 . 7 Q’s—Gag?” 298 Gya§ég©424 é? VVVVVVVVVVVV/VVVVVVCao s .9 FIGURE 11‘.—(K20+Na20), (Fe0+MgO), CaO ratios in nine porphyritic volcanic glasses, plotted from; data in table 3. Muddy Creek formation. At Malpais Mesa the thick cap of basaltic flows is conformable on beds that resemble Muddy Creek deposits; but no sedimentary layers now cover any .part of the cap. Remnants of basalt forming tops of small buttes in the area mapped as Muddy Creek formation east of Willow Beach are logically correlated with the lavas on Malpais Mesa and Fortification Hill. Other residuals south of Lake Mead rest on varied types of older rock and in them- selves give no hint of any relationship to the Muddy Creek. Several of the larger remnants, lying with strong angular unconformity on tilted Mount Davis TABLE 3.—Bulk composition versus groundmass composition1 in nine volcanic glasses, in percent. [Philip Orville, analyst] SiOz A1203 FeO MgO CaO Na20 K20 Volcanic Specimen unit 2 Bulk Ground- Bulk Ground- Bulk Ground- Bulk Ground- Bulk Ground- Bulk Ground- mass mass mass mass mass mass 69. 40 70.57 13. 62 12.61 1. 09 0.75 1. 31 0. 96 2. 94 2. 40 5. 33 5. 69 0.1) 73.93 74. 63 12. 46 11.85 . 46 . 47 .75 .75 3. 21 3.14 4. 74 4. 26 G.D 65.86 69. 19 15. 18 12. 99 1. 92 46 2.86 2. 13 3. 52 2. 85 3. 83 4. 50 G.D 66. 85 67. 70 15. 25 13. 87 1. 03 92 1. 38 .92 3. 90 3. 51 5. 74 5. 97 M.D 71. 55 72. 85 13. 50 12.40 . 52 44 1. 02 .63 3. 58 2. 98 5. 02 5. 58 M .D 70. 94 71.69 13.41 12. 69 .37 27 1. 42 1.37 3. 44 3.14 5. 00 4. 96 M.D 73. 65 74. 46 12. 78 12.05 .28 24 .79 . 55 3. 49 3. 28 4. 58 4.87 M.D 72.40 73. 12 12.94 12. 32 .50 49 .79 75 3. 27 3. 12 4. 99 4. 67 M.D 79. 46 80.07 11. 57 ll. 29 . 26 21 . 68 62 2.92 2.82 4. 16 4. 14 M.D 1 Groundmass composition is the difference between the bulk chemical composition and the chemical composition calculated for the phenocrysts. 2 G. D., Golden Door volcanics, M. D., Mount Davis volcanics. RECONNAISSANCE GEOLOGY, LAKE volcanics, form prominent mesas in a. wide area-be— tween Nelson and Glass Plateau (fig. 10). A smaller but equally conspicuous residual makes the cap of Square Butte. East. of “lillow Beach an elongate remnant of basaltic lava rests on Precambrian rocks and extends from the summit of the Black Mountain block to US. Highway 93 (pl. 1). The largest re- sidual, several miles south of Boulder Canyon, is closely associated with large basaltic dikes. There is no positive proof that all these remnants represent one and the same sequence of lavas, but inference of this relation is very strong. All consist of vesicular or amygdaloidal olivine basalt, in indi- vidual flows that are thin or of moderate thickness. In all remnants the flows are, nearly horizontal, or dip gently; the steepest dip, about 10°, is in the large residual mass east of “(illow Beach and is readily explained by some tilting of the Black Mountains block in post-Pliocene faulting. Altitudes at the bases of some remnants differ as much as a few hundreds of feet; but topographic relief in Muddy Creek time must have been considerable, and there has been later deformation by faulting and warping (p. F110). In a logical reconstruction the flows of the Fortification basalt member, as they appeared west of the Black Mountains before their dissection by the Colorado River drainage, would form a thick and continuous sheet extending at least 30 miles from north to south, 10 to 15 milesfrom east to west, overlapping both rims of the present river valley and with the top of the sheet at an average height at least 2,500 feet above the present river channel. Wide extension of the flows across older rocks bordering the basins of sedi- mentary deposition indicates that upland sources of sediments had been reduced to moderate relief. The lavas of the Fortification member range in color from nearly black through gray brown to dark brown. Some flows have numerous small vesicles, irregular in form; others have rounded vesicles with diameters as much as three-quarters of an inch, many filled with white amygdales made of zeolites. Most of the rock is glassy olivine basalt, in which the olivine is con- siderably altered to serpentine and iddingsite. Some hand specimens show conspicuous aggregates, as much as half an inch long, made up wholly of olivine; others have large grains of plagioclase crowded with glass inclusions. In Fortification Hill a few layers of dark-brown slaggy tuff are included between flows. The only layers of sedimentary material seen in any section of the lavas are local lenses of conglomerate near the base of the section at the southeast corner of Fortification Hill. Probably the lavas of the Fortification member were erupted in large part from fissures. Many dikes of MEAD—DAVIS DAM, ARIZONA—NEVADA E31 d rk basalt transect the Mount Davis and older rocks, aid such dikes are conspicuous in a considerable area adjacent to Kingman Wash. But one central vent is marked by a plug, about 300 feet in diameter, etched into relief by erosion near the highest part of F orti- fication Hill. Near this plug are numerous brown slaggy bombs, which, with enclosing scoriaceous tuff, indicate some localized explosive activity in addition to widespread eruption of lavas. COMPARISON WITH ADJACENT AREAS Ransome (1907), Lee (1908), and Schrader (1909) gave brief and generalized descriptions of volcanic rocks in parts of the area here considered. All were limited to hasty and scattered field observations in rapid reconnaissance. In an area covering more than 6,000 square miles, Schrader recognized three general assembages which he designated from oldest to young- est: (1) chloritic andesite; (2) undifferentiated ande- sites trachytes, rhyolites, and latites; (3) basalt. Ran- some (1923a) later studied in some detail the geology of the Oatman mining district, Arizona, in the Black Mountains about 10 miles south of Union Pass. His classification of volcanic rocks exposed within an area of about 75 square miles is shown in table 4. Lausen (1931), in a later study of the district, adopted Ran— some’s volcanic sequence with little change. The geologic map of the limited area centering at Oatman is more detailed than any part of the map in the present report. Ransome (1923a) and Lausen (1931) recognized more lithologic units than does the present report, and they applied to each unit a pre- cise petrologic designation. But Ransome noted that attempts to distinguish among andesite, trachyte, and latite present difficulties because these kinds of rock grade almost insensibly one into another. Moreover, widespread alteration, perhaps caused by ore-bearing solutions, has obscured the original nature of many flows in the Oatman section, making exact classifica- cation impossible. Finally, Ransome’s succession at Oatman is incomplete; the upper part of the east- ward-dipping section lies beyond the eastern boundary of his map. For several reasons, then, correlation of the volcanic rocks near Oatman with the sequences only a moderate distance to the north is more difficult than might be expected. Probably the Oatman andesite and the two under- lying units of trachyte correspond in a general way to the Patsy Mine volcanics. Largely on the basis of megascopic examination, brown andesite seems predominant in the latter unit, but detailed petro- graphic study may show that much of the rock is trachyte. Ransome’s descriptions (1923a) indicate a wider variety of colors in his three lower units than E32 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 4.—~Volcanic rocks of Oatman district, Ariz. [Summarized from F. L. Ransome (19238)] Unit General character Thickness (feet) Probable equivalence Basalt ______________ Cotton rhyolite ______ Sitgreaves tulf _______ Meadow Creek and Flag Creek trachyte. Gold Road latite _____ Complex assemblage of lavas and tuffs. grains of biotitc and feldspar. Oatman andesite _____ Esperanza trachyte_ _ _ Alcyone trachyte _____ Bedded breccia _______ Flows of gray lava, in part porphyritic. some gray shale in upper part. of shale and sandstone. Unconformity Basaltic lavas, rich in olivine ____________ Angular discordance 0—1, 000 Fortification basalt member of the Muddy Creek Glassy lavas, in part spherulitic _________ Pumiceous tuff, cream _________________ Lavas, reddish-brown with local development ___________________ Conformable contact , Lavas, greenish-gray, in part porphyritic; considerably altered- _ _ _ Lavas, reddish—brown, with local distribution ___________________ Fragments derived from Precambrian and volcanic rocks. formation. ______________________ 500—600 ______________________ 200—300 250:1: Golden Door , volcanics. Lavas have abundant 3, 000—4, 000 Considerable rhyolite included. 800—2, 700 0—1, 000 Patsy Mine volcanics. Locally altered, greenish; 1, 000—2, 800 Has 100—200 Precambrian complex_ Gneiss, schist, and granite. is evident in the Patsy Mine volcanics, but this dif- ference may reflect more extensive chemical alteration in the Oatman district than farther north. In favor of the suggested correlation are (1) similar average composition of the two assemblages, near or identical with that of andesite; (2) location in the lower part of each section; (3) similar maximum thickness—- 5,000 to 6,500 feet. Neither Ransome nor Lausen mentioned, as occur— ring below the top of the Oatman andesite, any lavas with high content of silica such as the spherulite- bearing rhyolite within the Patsy Mine section near Nelson (p. 19). A distinctive unit of this kind, if it were Widely distributed, would be useful in attempts at correlation. Ransome’s (1923a) Gold Road latite, marking an abrupt and enduring change in composition of lavas, is similar in many ways to the latite section in the Golden Door sequence at Hoover Dam. At the lat- ter locality the latite is strongly unconformable on the older andesite; but this is not the invariable rela- tion between the Golden Door and Patsy Mine units (p. E20). Lausen (1931) described the colors of the latite near Oatman as dark to light gray, lavender, and light brown; he stated that the typical rock has well—developed phenocrysts of feldspar, sparkling flakes of biotite, and some pyroxene, and that in thin section the predominant feldspar is recognized as andesine, and orthoclase is conspicuous. These de- scriptions apply well to the Black Canyon latites. Although no complete chemical analyses of the typical latite near Hoover Dam are available, perlitic glass in the section east of the dam is strikingly like some of the latite near Oatman, as shown in the following table: ' TABLE 5.—Comparison of chemical compositions of two volcanic rocks (1) (2) Sl02 ____________________________ 65. 86 62. 96 A1203 ___________________________ l5. 18 15. 36 Fe203 ___________________________ l. 99 2. 57 FeO ____________________________ . 80 2. 09 MgO ___________________________ 1. l2 2. 50 Cat) ____________________________ 2. 86 4. 26 NagO ___________________________ 3. 52 3. 84 K20 ____________________________ 3. 83 3. 96 H20+ __________________________ 3. 19 1. 37 H20— __________________________ . 49 . 23 Ti()2 ____________________________ . 42 . 72 P205 ___________________________ . 18 . 28 MnO ___________________________ . 06 . 04 Total _____________________ 99. 50 100. 18 1. Perlitic glass beside highway, a quarter of a mile (in straight line) southeast of Hoover Dam. Analysis by Univ. of Minnesota Rock Analysis L boratory. 2. Latite 1 mile southwest of Sunnyside mine, Oatman District, Arizona. Analysis by R. C. Wells, U.S. Geol. Survey. Because of these similarities, Ransome’s Gold Road latite may be correlated with the lower part of the Golden Door volcanics, which in the type section has a considerable thickness of flows resembling the latite of Black Canyon. The trachyte, tuff, and rhyo— lite above the Gold Road unit also are correlated with the Golden Door volcanics, and perhaps con- siderably more rhyolite higher in the section lies east of Ransome’s (1923a) map area. Therefore the Oatman section as described by Ransome (1923a) and Lausen (1931) may omit much of a sequence RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA equivalent to the Golden Door volcanics, and all the Mount Davis volcanics. The highest volcanic unit recognized by Schrader, Ransome, and Lausen consists of olivine basalt in flows that are nearly horizontal and unconformable to older volcanic rocks. Schrader (1909), in his gen- eralized map covering much more than a square de- gree, included in one category flows probably equiva- lent to the Fortification basalt member of the Muddy Creek formation and others, much younger, enclosed by Quaternary( ?) gravels. The basalt mapped near Oatman occurs in remnants at a high altitude, and both in composition and in mode of occurrence it is strongly suggestive of the Fortification basalt member. PLEISTOCENE ( Z) IGNEOUS ROCKS Flows of basalt and several mafic dikes are asso- ciated with weakly cemented gravels in a limited area 6 to 8 miles southeast of Hoover Dam. The out- crops of basalt are erosion remnants of sheets, origi- nally of small or moderate extent, that were erupted on the alluvial slope west of the Black Mountains and at least in part buried as the coarse fan debris continued to build up. In more recent dissection by washes tributary to the Colorado River, the sheets have been more or less laid bare and cut away. Steep cliffs at the edges of some remnants show well-devel- oped columnar structure. The sheets, about 20 feet in greatest thickness, consist of slaggy rock at the top, vesicular rock extending downward through 3 or 4 feet, and a varied thickness of compact basalt grad- ing into vesicular rock at the base. On fresh surfaces the rock is nearly black. Thin sections show a ground- mass aphanitic to glassy, small laths of labradorite, and scattered grains of olivine, pyroxene, and mag- netite. Composition is virtually uniform in all the flows. Near the flows of basalt several camptonite dikes cut the deposits of weakly cemented slope gravels. Campbell and Schenk (1950, p. 672) mapped three general lines of the dike outcrops, all discontinuous and with some abrupt offsets in strike. The area in- cluding these outcrops extends about 2 miles from north to south and has maximum width of about 1,500 feet. The dikes have a northward trend, with a range in strike from N. 20° W. to N. 25° E.; the easternmost of the three lines has an average direc- tion slightly east of north. Thickness of the dikes ranges from 2 to 6 feet; in dip the average is near vertical, with extreme variations from 65° E. to 75° W. Probably the best single exposure is in the east wall of a deep artificial cut along US. Highway 93, 8 miles southeast of the dam in a straight line or nearly 9 miles as measured along the road. The dike E33 is essentially vertical, has a nearly uniform thickness of about 4 feet, and cuts rather evenly across the coarse fan deposit in which there is little sugges- tion of bedding. Numerous phenocrysts of black amphibole in the middle of the dike are 2 to 4 inches long, but the size decreases outward to small fractions of an inch, and no phenocrysts are present in the chilled margins. Many vesicles in the marginal parts of the dike, elongate parallel to the walls, suggest light overburden at the time of emplacement. The groundmass of the dike is largely micro- aphanitic and encloses crystals of somewhat altered olivine, as much as half an inch in diameter, together with scattered small grains of calcic andesine, mag- netite, and apatite. Sporadic grains of quartz are probably xenocrysts derived from the fan deposits or other rocks cut by the dike. According to Camp- bell and Schenk (1950, p. 683), the crystals of am- phibole, which on fractured surfaces resemble obsidian, appear to be kaersutite or a near relative. One chem- ical analysis of the dike rock shows 42.26 percent Si02, slightly higher than the average of 40.70 per- cent for camptonites listed by Hatch, Wells, and Wells (1949, p. 353). Near the southern limit of these dike exposures an old vent, irregularly circular in plan and about 400 feet in diameter, is filled with brown tuff—breccia and some extrusive camptonite. The breadcrust bombs 1 to 2 feet long and angular frag- ments of basalt as large as 2 feet in diameter. This material, indicating eruptive activity, is closely ad- jacent to and probably connected with one of the camptonite dikes and supplies additional strong evi- dence that the dikes as now exposed were emplaced at very shallow depth. Campbell and Schenk (1950, p. 688) were im- pressed by the decrease in size of phenocrysts from the middle of the dike outward, and they concluded that the crystals formed between emplacement and solidification of the magma. They recognized the evidence for very shallow emplacement and estimated that the crystals of amphibole must have formed in a period no longer than 25 days. S. lVarren Carey (oral communication, 1959), in an alternative hy— pothesis, supposed that a magma chamber at con- siderable depth was stationary long enough for growth of the large phenocrysts. Crystals that started forming in the upper part of the chamber slowly sank, and eventually there was gradation in' size from incipient crystals near the upper boundary to large crystals at some depth. When magma was forced upward to form the dikes, the upper part of the fluid, wedging the walls aside, became the margi- nal parts of a dike; fluid containing crystals of small breccia encloses , E34 and medium size followed; and material from a deeper part of the chamber carried the large crys- tals to the middle of the growing dike. Under this concept the large phenocrysts present no special problem. The location and orientation of the dikes suggest strongly that intrusion occurred along fractures re- lated to the north-south fault at the west base of the Black Mountains. All exposures of the main frac- ture in the Vicinity of the dikes indicate that it is a reverse fault dipping steeply eastward. The three nearly parallel lines of dikes in a belt more than a quarter of a mile wide suggest a fault zone of con- siderable width, in large part hidden under fan de- bris. Perhaps repeated movements along several ma- jor fractures in this belt, in part after the slope gravels were weakly cemented, extended the fractures upward across the fan debris and so prepared the way for emplacement of the dikes. STRUCTURE A principal objective of the present study is the deciphering and mapping of major structural fea- tures south of Lake Mead, for comparison with those directly north and west of the lake. Ranges within the latter belt are characterized by thick sections of sedimentary formations that have large areal extent; such bedrock is ideal for effective display and accu- rate mapping of faults and folds. South of the lake much of the bedrock is far less favorable for struc— tural studies. The complex of Precambrian meta— morphic rocks and later plutons has no effective hori- zon markers that outline structural forms or give any satisfactory measure of displacements. Fortunately those needs are in some degree served by the volcanic rocks that cover large areas on both sides of the Colorado River. Recognition of four distinctive assemblages within the thick volcanic accumulation provides, over con- siderable parts of the river belt, a crude substitute for extensive sedimentary formations. Displacement of major volcanic units makes many faults clearly evident; and at exceptional localities it is possible to measure displacements precisely through use of dis- tinctive markers such as layers of peculiar glass or tufi'. Generally, however, quantitative measurements are impossible, because the volcanic formations are lithologically monotonous over wide areas and along the strike are subject to abrupt changes in character and in thickness. Such variations, inherent in de- posits built up around scattered eruptive centers, are intensified in the present case because faulting move— ments during the volcanism provided local basins for SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY thick accumulations, with bordering ridges from which all volcanic products were quickly eroded. Great thrust faults, conspicuous in many ranges of southern Nevada, are not known in the area of the present report. Failure to find such faults in the belt south of Lake Mead is not surprising, because Within that area we must rely chiefly on volcanic rocks for evidence of deformation, and probably all such rocks that have been preserved were formed after the re— gional thrusting ended. Moreover the large thrusts of southern Nevada, so far as they have been reported, are confined to the section of Paleozoic and Mesozoic sedimentary formations. Perhaps some~ of these faults “root” in the Precambrian complex, and this possibility was kept in mind while the field study was in progress. But any thrusts cutting the metamor- phic and plutonic rocks south of Lake Mead probably would be obscure at best and might be wholly con- cealed by the widespread cover of volcanic rocks and later alluvium. One fault zone revealed by excava- tions during construction of Davis Dam has low dip and possibly represents local thrusting; this excep- tional fault (fig. 15) is described elsewhere in the report. The principal structural features between Lake Mead and Davis Dam are steep faults, many with large displacement. Most of these faults are normal, but at least two of the largest have reverse displace- ment along much of their exposed lengths. Blocks between faults generally are tilted, and in the tilting movements several large normal faults were rotated to low angles of dip. Strikes of faults range widely; but northerly components prevail, and in general the displacements seem to be related to relative uplift of the Black Mountains block east of the river, and of the EldoradovNewberry Mountains block west of the river. Through most of its length in this map area, the river valley follows a structural depression between the two major units of uplift. Although much of the de- pressed area is masked by alluvium, excavation by the river has exposed large masses of bedrock and many structural features. Therefore the exhibit of basin-range structure offered by this area is in some respects more satisfactory than any to be found in the Great Basin, where interior drainage is covering most of the downthrown blocks with increasing thick- nesses of debris. In an overall view the structural pattern southward from the Boulder Basin of Lake Mead falls into three well-defined units. (1) In a northern division, ex- tending south to the latitude of Eldorado Wash, blocks are tilted consistently eastward toward a major fault zone along the west base of the Black Mountains. RECONNAISSANCE GEOLOGY, LAKE (2) In a middle division, between Eldorado W'ash and the Dead Mountains, the tilt of fault blocks is conspicuously westward, away from the Black Moun— tains block. (3) In the southern part of the area, tilting generally to the east is pronounced on the Arizona side, and apparently this general attitude continues to the south through the Oatman mining district (Ransome, 1923a; Lausen, 1931). Faulting has been intensive in nearly all parts of the area, and numerous faults visible in the field are not shown on the map. The aim has been to repre- sent faults and fault zones that seem most significant in the structural picture and to omit many related fractures that are grouped too closely to be shown clearly on a map of small scale. Of the faults repre- sented on plate 1, some are very clear field exhibits that can be traced mile after mile without question; others are well exposed in some stretches but else— where are obscure because of monotonous bedrock, igneous intrusions, or alluvial cover. Some fault zones that are complicated by multiple fractures or en echelon displacements are represented as single faults, usually with broken-line symbol. No doubt many faults that merit places on the map were not seen in the time available for study of so large an area. The following detailed discussion considers first the dominant Black Mountains block, and proceeds to the several structural divisions west of this range, taking them in order from north to south. STRUCTURE 01“ BLACK MOUNTAINS SECTION ALONG BOULDER CANYON Faults mark the western edge of the Black Moun- tains structural unit through much of’its extent within the area of this report. Near Boulder Canyon, where stream erosion has provided exceptional exposures, the mountain mass is revealed as a horst, bounded by large faults along both eastern and western margins. Other important faults, with northerly trends and varied displacements, subdivide the mass into several distinct blocks. The overall width of the compound horst is about 8 miles. The Boulder Wash and Ransome faults are paired in bounding a high horst, which is transected by the narrowest and deepest part of Boulder Canyon. Di— rectly south of the canyon and west of the horst, beds of Cambrian limestone and shale dip toward the Ransome fault. Before Lake Mead was filled, the lower part of the Cambrian exposure was at river level, at an altitude near 700 feet. In the ridge east of the fault, Precambrian rocks are at an altitude of over 3,700 feet. Hence, the minimum throw on the fault is about 3,000 feet, and perhaps the full meas- MEAD—DAVIS DAM, ARIZONA—NEVADA E35 ure is much more, as prolonged erosion may have reduced the top of the ridge far below the basal Cambrian horizon. Probably the total throw on the Boulder Wash fault is still greater, as the footwall block contains the thick Muddy Creek section, whereas all rocks in the downthrown block of the Ransome fault are older than Muddy Creek. The block west of the Ransome fault is a graben about 3 miles wide, bounded on the west by the Emery fault. This downthrown block and the bounding faults have clear topographic expression because of differential erosion (pl. 1). Complex faulting marks the west border of the Black Mountains. Directly north of the lake the Pre- cambrian rocks are in fault contact with cemented Colorado River gravels and older deposits. Probably the fault dips steeply eastward,” and compression at- tending the reverse displacement deformed the gravel beds in a wide belt (Longwell, 1946, p. 827: pl. 5). South of the lake two east-dipping faults that strike nearly north cut the complex of Precambrian gneiss and younger plutonic rocks. Along one of these breaks, here called the Indian Canyon fault, deformed bands of gneiss indicate reverse movement but tell nothing about the measure of displacement. This fault shows clearly on aerial photographs and can be traced southward nearly 10 miles to its intersection with the Kingman Road fault. The fault a short dis- tance west. of Indian Canyon joins the larger fault north of present exposures (Longwell, 1936, pl. 2). The reverse ‘fault north of the lake that displaces Colorado River-gravels appears to be continued south- ward as the Fortification 6 fault, on which, however, there is large normal displacement. Directly south of the river the fault surface was well exposed before Lake Mead was formed; the dip is 65° to 75°W., and. dragged up on the side of downthrow are fan de— posits of the Muddy Creek formation and also old Colorado River gravels (Longwell, 1936, fig. 10). As these gravels are either Pleistocene or late Pliocene (Longwell, 1946, p. 828), movement on this part of the Fortification fault continued until late. geologic time. The scarp is bold (fig. 12), but probably it was in large part buried and later exposed by erosion of weak deposits in the hanging wall. In Fortification Hill, 4 miles south of the lake, coarse Muddy Creek deposits near the fault suggest derivation from the steep front of the footwall block (fig. 3). As the 5This fault has been represented as normal (Longwell, 1936, pl. 2, section 11—h"). hut reconsideration of the field evidence has changed this earlier verdict (Longwell. 1946. fig. 2). “Earlier named the Callville fault (Longwell, 1936, fig. 10), but it seems best to use the name of the adjacent ridge as printed on the Hoover Dam topographic map. E36 a*~, SHORTER'CONTRIBUTIONS T0 GENERAL GEOLOGY FIGURE 12. AScarp of Fortification fault, in view southeastward across Colorado River and ruins of old Fort Callville before Lake Mead was formed. Mountain mass is composed of granitic rocks intrusive into Precambrian gneiss. Muddy Creek formation and overlying cemented river gravuls, here shoun along the former stream, are in fault contact with rocks in the scarp. cap of the Fortification basalt member continues across the fault trace without perceptible dislocation, prob- ably most of the displacement on this fault occurred before the end of Muddy Creek time; and the later movement involving Colorado River gravels was con- fined to the part of the fault north of Fortification Hill. A considerable part of the Mead Slope fault is con— cealed by Lake Mead; along this part, once well ex- posed (Longwell, 1936, pl. 2), beds of coarse breccia in the Muddy Creek formation were brought up by reverse movement against old Colorado River gravels. At present the best exposures of this fault are about a mile northwest of Fortification Hill, where Muddy Creek deposits and included basalt are downthrown against altered igneous rocks. Farther northeast, much of the trace is obscured by gravel cover on the dissected slope. STRUCTURE NEAR FORTIFICATION HILL A group of faults with diverse trends outlines sev— eral blocks in a roughly triangular area around Forti- fication Hill. In this group the Indian Canyon and Fortification faults strike nearly north, the Mead Slope fault strikes northeast, and the Horsethief fault strikes northwest. At the north end of the tri- angular area, the Fortification fault is the logical boundary of the Black Mountains. In the southern part of the triangle, relations are less definite. The Fortification fault ends abruptly against the Horse- thief fault, and neither of these has the strong topo- graphic expression that marks the Fortification fault near Lake Mead (fig. 12). Directly south and west of Fortification Hill, all bedrock older than the Muddy Creek formation has been chemically altered, locally with such intensity that the rock has become a weak, claylike mass retaining little evidence of its origin (p. E17). Because of this change the rock varies in resistance to erosion, and positions of faults are in part obscured. South of the basalt-capped mesa, the Fortification fault divides to form a complicated zone of fractures in varied bedrock. A complex of plutonic bodies in- truded into Precambrian gneiss forms the footwall, and porphyritic intrusive rocks enclosing large xeno- liths of Golden Door volcanics make up the hanging wall, in which several prospects of metallic minerals have been opened. RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA The Horsethief fault is best exposed along White Rock Wash, where a clearly defined fracture dipping 70° NE. separates plutonic rocks and gneiss in the hanging wall from brown andesitic lavas in the foot- wall. The lavas, dragged up to dip steeply south— west, are mapped on the basis of color and lithologic character as part of the Patsy Mine volcanics. Beds of the Muddy Creek formation that lie on the lavas with strong angular unconformity also are dragged up to moderate southwest dips. Presumably much of the displacement occurred before these beds were laid down, though possibly in the earlier part of Muddy Creek time. No evidence has been found for dating the latest movements on this fault. In large part the footwall block of the Horsethief fault is hidden by alluvium, but the nearly straight edge of the hanging-wall block clearly suggests a con— tinuous fault trace (pl. 1), along a line that leads to confirmatory outcrops near the lake. These outcrops show the altered igneous rocks .south of Fortification Hill faulted upward against Golden Door and Mount Davis volcanics, and beds of the Muddy Creek forma- tion. Although nothing in the visible evidence gives a trustworthy measure of throw on the fault, compari- son of bedrock on opposite sides indicates large ver- tical displacement. Volcanic rocks identified locally in the belt of altered bedrock south of Fortification Hill are very like the Golden Door volcanics. If this correlation is correct, a short distance south of the lake the fault displacement at a minimum must ap- proximate the combined thicknesses of the Golden Door and Mount Davis sequences, which near Hoover Dam is 2,000 feet or more. A much smaller throw is suggested by'beds of the Muddy Creek; but these beds were deposited on an uneven surface, probably through various stages of the faulting. Beds on one side of the fault may differ considerably in date of deposition from those on the opposite side. More- over, as noted above, the beds of the Muddy Creek exposed in White Rock Wash must have been laid down after a large part of the displacement on the fault had occurred. Convergence of the traces of the Horesthief and Mead Slope faults, and reverse movement on both, may suggest that a wedge—shaped block including Fortification Hill was forced to move westward and upward under compressive stress, but it is not known that these faults were in operation at the same time. The Horsethief fault was active after some part of Muddy Creek deposition but is not known to have involved Colorado River gravel. So far as the evi- dence is known, the Mead Slope fault may have orig— inated after the older river gravels were laid down. E37 FAULTED WESTERN BORDER South of the Horsethief fault the border of the range has four nearly straight segments that alternate in direction between southeast and south through a distance of 14: miles. Faulting along this part of the range border is strongly implied, though actual ex- posures of the fault are few. Conceivably this fault, here called the Kingman Road fault, is continuous with either the Horsethief or the Indian Canyon fault. But the three features are distinctive in them— selves, and discussion is simplified if each has a dis- tinguishing name. In its northern segment the Kingman Road fault is closely parallel to conspicuous layering in the ad- joining Precambrian rocks, but the succeeding north- south segment cuts across the layering at a small angle. Through the two segments, evidence for faulting is of two kinds: (1) general straightness of the contact between bedrock and alluvium and (2) numerous fractures in the bedrock that are nearly parallel to the border. These fractures are seen to best advan- tage in and near workings of a mineral prospect at the north side of West Petroglyph Wash. Presuma- bly these fractures are genetically related to the bor- der fault. Most of the observed fractures dip steeply eastward and suggest reverse displacement on the border fault. This suggestion is supported by obser- vations south of U.S. Highway 93, where the Muddy Creek formation is in contact with the fault. Al- though few actual exposures of a fault surface were seen, the beds of the Muddy Creek are turned up to or past the vertical near the fault and are much deformed in a belt more than 1,000 feet wide. In the adjacent Precambrian rocks the gneissic layers, which near the range crest dip westward at a moder- ate angle, steepen progressively down the slope and near the fault are vertical or even overturned to a steep dip eastward. The sum of evidence strongly indicates reverse movement on the fault. South of the Willow Beach road, the Muddy Creek overlaps fault blocks that consist largely of dark basaltic lavas, apparently part of the Mount Davis sequence. In some of the tilted blocks, the basalt lies directly on Precambrian gneiss. Presumably the whole assemblage of blocks is faulted against the high block forming the range, though the actual trace of the principal fault is concealed by waste. In this segment of the Kingman Road fault, therefore, the dip of the fault surface is not known. Near the Pope Mine the western border of the Black Mountains Precambrian block is offset by an important northwesterly fault. If the Kingman Road fault extends to this locality, its position is effectively E38 hidden, but a fault with about the same strike is conspicuous from the Pope fault southward. A fault extending eastward along the upper course of Pope Wash is logically the extension of the Pope fault off- set by the north-trending fault. Possibly the latter fault continues northward, and this possibility is suggested on plate 1; but as no evidence of the con- tinuation was found, the border fault from Pope . Wash southward is considered as a separate struc- tural unit. It is represented on the map as running continuously southward about 22 miles to the vicin- ity of Eppersons Corral, but it has not been fully walked out; the map representation is the result of extrapolating fault segments studied in a number of separate localities, and the line as mapped may rep- resent a zone of related fractures. The name Epper- son fault is chosen because evidence of large displace- ment is well displayed near Eppersons Corral. In the 3-mile stretch between Pope and Gold Bug Washes, the fault is clearly marked and has large throw. Resistant andesite flows of the Patsy Mine volcanics maintain a prominent scarp on the side of upthrow; weaker basalts and gravel beds in the Mount Davis sequence underlie a lower surface on the down— thrown block. The fault surface was not seen, but it is assumed to dip steeply westward, as do three paral- lel faults that cut the downthrown block. These faults cause repetition in the Mount Davis section, and much coarse alluvium further hides relations; but thick- ness of the younger volcanic sequence exposed here is computed as‘ more than 1,800 feet (p. E25) ; in estimat- ing throw on the Epperson fault, to this figure must be added an unknown but probably large thickness of Patsy Mine volcanics eroded from the footwall. Near and for some distance south of Gold Bug Wash the structure is obscure, especially at the supposed location of the northwestward trending Gold Bug fault. Because of poor exposures this location is uncertain; but no indication was seen that this fault continues east of the Epperson fault. Farther south the Golden Door volcanics, dipping consistently west- ward, are normally downfaulted against Precambrian gneiss in the range. The fault is revealed in particu- larly clear exposures directly east of the Golden Door mine and on both sides of the Searchlight Ferry road. The westerly dip of the fault, at angles rang— ing from 45° to 65°, is seen in outcrops and is ex- pressed in retreat of the Precambrian—Golden Door contact in the valley followed by the road. Near the road there is a marked change in topographic expres— sion of the main bedrock units. Northward for about 17 miles the volcanic rocks in the hanging-wall block SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY form a hilly belt, locally rugged but distinctly lower than the mountain ridge on Precambrian gneiss. South of the road the fault crosses diagonally to the east side of the ridge, which through several miles is on Golden Door volcanics, whereas the Precambrian footwall block is low on the eastern slope. South of Eppersons Corral the structure is com- plex and at some points not entirely clear. Along the road the Precambrian rocks disappear southward under brown andesite identified as part of the Patsy Mine volcanics. These andesites in turn dip south- ward beneath Golden Door volcanics and are cut off to the west by the Epperson fault, which apparently dies out southward in a zone marked by sharp change of strike from southeast to east. A normal fault east of the road drops Golden Door volcanics with steep westward dip against the footwall block of Patsy Mine volcanics and Precambrian gneiss; this fault has a sinuous trace because it dips to the east no more than 20°. A later fault, inclined more steeply east- ward and with large throw, transects the highly de- formed Golden Door rocks and drops against them, on the east, Mount Davis volcanics that dip westward. Probably these faults are related to sharp downwarp— ing along an axis trending north of west, which is responsible for the broad outcrop of Mount Davis rocks athwart the range between Eppersons Corral and Union Pass. .This downwarp is in line with the low, alluviated pass west of the river, between the Eldorado and Newberry Mountains. Probably the structural depression is reflected near Searchlight in wide outcrops of volcanic rocks (not mapped), which 10- cally extend eastward into the broad pass. Several miles southwest of Eppersons Corral, the Mount Davis volcanics, dipping southwestward, are faulted down against brown andesites of the Patsy Mine sequence. In the upthrown block, glass and tufi' that normally are found high in the Mount Davis section rest directly on the andesite of the Patsy Mine volcanics. Absence here of the Golden Door rocks, which form a thick section less than 2 miles to the northeast, and representation of Mount Davis time by only the upper part of the normal section suggest local uplift and much erosion in the vicinity of the present wash, during and perhaps before the Mount Davis episode of volcanism. Many faults and small intrusive bodies, not shown on plate 1, cut the Mount Davis rocks, especially near the old Portland Mine. The downwarp south of Eppersons Corral breaks the continuity of the Black Mountains topograph- ically, lithologically, and structurally. Precambrian basement rocks are again dominant farther south, near RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA Union Pass; but the structure of that area, closely related to the section near Davis Dam, is discussed with that section on later pages. STRUCTURE NORTH AND WEST OF BOULDER BASIN Directly north of Boulder Basin, where the bed- rock consists chiefly of weak deposits in the Muddy Creek formation with included and older basaltic lavas, the structure is not of critical value in the pres- ent discussion. The extreme northwestern part of the map area presents a sample of the Frenchman Moun— tain block, where the geology contrasts sharply with that southward from Lake Mead; the structure sec— tion (fig. 13) illustrates some of the differences. On the. other hand, the Frenchman block lacks the large- scale thrust faults common in neighboring ranges di- rectly to the north and west; its structure of fault blocks tilted steeply eastward is generally similar to the structure near Hoover Dam. South of Las Vegas Wash, limestone of the Horse Spring formation lies unconformably below volcanic - rocks that probably are part of the Golden Door se- quence; but the relation of these limestone beds to older volcanic rocks is not visible. In and around the Three Kids mining district, the Muddy Creek forma- tion is strongly faulted and tilted. Nothing in the pattern of this deformation suggests a close relation to the structural pattern south of the lake. Deforma- tion in the Three Kids neighborhood is marginal to the River Mountains mass, which has a complex pat— tern of faults and tilted blocks that can be deciphered only after a systematic study of the volcanic and plu- tonic bedrock. The isolated outcrop of Precambrian schist in Sad- dle Island may seem anomalous, but sediments in the Thumb formation serve as evidence that in late Meso- zoic time the old basement rocks formed an upland extending westward beyond the present River Moun- Kaibab limestone Moenkopi formation! ermian red beds Moenkopi and Chinle formations Kaibab limestone 5 Moenkopi formation Thumb formation E39 tains (p. E8). No doubt the old rocks now exposed in Saddle Island and in areas south of the lake were mantled with volcanic and sedimentary deposits un- til they were laid bare by erosion in late Cenozoic time. STRUCTURE WEST OF THE BLACK MOUNTAINS BOULDER BASIN TO ELDORADO WASH In a large area south of Boulder Basin, many rock units are distributed in irregular fashion and broken by faults that have diverse trends. There is, how— ever, considerable order in the apparent chaos. The large outcrops of Precambrian rocks along Black Canyon, with overlying Patsy Mine volcanics, repre- sent a northeastward trend of the Eldorado Moun- tain block; near Willow Beach the interval between that block and the Black Mountains is reduced to a minimum. Exposures of Precambrian rocks father west, including Saddle Island, part of the hill south of Boulder City, and the large area 5 miles west of Nelson, seem to mark high parts of a complex struc- tural block west of and tilted toward the main Eldo- rado block. This western structural unit, here called the Nelson block, is bounded on the east and sub- divided by a set of large normal faults, nearly all with the downthrow on the west, which strike more northerly than the Eldorado axis, toward which they die out southward to form a crude en echelon pattern. The two divisions of the area north of Eldorado Wash, as defined above, are now described and dis— cussed as distinct structural units. NOBTHERN ELDOBADO MOUNTAINS BLOCK This unit, from Eldorado Wash northward, is tilted generally to the east and faulted down against the Black Mountains. The abrupt eastern boundary of this block consists of the Kingman Road and Horse- thief faults which, in contrast to all the large faults H / Muddy Creek formation Horse Spring formation 1 I2 MILES DATUM IS SEA LEVEL FIGURE 13,—Geologic section along the line H—H’ on geologic map (pl. 1). E40 west of them, have reverse displacement. Measure of the throw along this fault boundary can only be con- jectured, as no stratigraphic markers are available for comparison on hanging-wall and footwall sides; but the total vertical displacement must ”be thousands of feet. East of Hoover Dam a minimum figure is given by the combined thicknesses of the volcanic sequences, Patsy Mine through Mount Davis, which in the down- thrown block dip toward the fault boundary. A point of interest is the appearance in White Rock Wash of brown andesite of the Patsy Mine volcanics, turned up steeply against the Horsethief fault. Ab- sence of younger volcanic rocks in the outcrop there may be attributed to concealment beneath the Muddy Creek formation. Deformation in the footwall per- haps affects a zone of considerable width; and vol— canic rocks younger than the brown andesites may lie under cover at some distance from the fault. This possibility is in accord with the strong disturbance of the Muddy Creek formation along the Kingman Road fault east of Willow Beach (pl. 1, section 0—0’). Presumably the displacement on the two large re- verse faults was cumulative through a long time in- terval. The Muddy Creek, unconformable on lavas that dip more steeply, contains coarse rubble prob- ably shed from a growing scarp to the east; and these beds in their turn have been deformed in later stages of the movement. Deformation within the major structural blocks is expressed in groups of faults with varied patterns, and in warping effects. Near Hoover Dam, where exposures in the walls of Black Canyon are almost continuous, a set of faults nearly parallel to the edge of the main block occupies a belt about 2 miles wide. Nearly all these faults are normal, with downthrow on the west; some surfaces with horizontal striae sug- gest important strike-slip movements, and a few re- verse faults have local development. With mapping in detail, no doubt the larger faults in this group can be traced farther southeast than they are shown on plate 1. General parallelism of the set to the Horse- thief fault suggests a genetic relation. Another set, cutting the volcanic rocks south of the Willow Beach road junction, closely parallels the Kingman Road fault. Two faults in this set are exceptional, so far as movements have been deciphered, in having down— throw toward the Black Mountains block. This type of displacement may reflect adjustment to the weight of the overriding hanging-wall block of the main fault. Warping is especially pronounced around the two large outcrops of Precambrian rocks west and south- west of Willow Beach. Structure in these areas sug- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY FIGURE 14.—View northeastward across the east-west fault north of Malpais Mesa. Dark lavas (a) of the Patsy Mine volcanics, .dip- ping away from Precambrian rocks in foreground, are faulted down against Precambrian rocks (b) forming high ridge. Mount Davis volcanics (c), beneath low ground in right middle distance, overlie Patsy Mine volcanics in tilted section. gests effects of strong local doming complicated by faulting. Around the Precambrian outcrop north of Square Butte the lavas dip strongly outward in nearly all directions. The set of faults striking northwest- erly into this dome, all with downthrow on the south— west, may reflect torsional strain; a strong vertical couple is suggested by the east-west portion of the Jeep Pass fault, with upthrow on the south, and the large east-west fault with opposite throw directly north of Malpais Mesa (fig. 14). Complex local strains are indicated also by the faults northeast and east of the mesa, which in combination have large dis- placement. Two of these, largely in Precambrian rocks, are clearly recognized only where remnants of volcanic rocks are preserved on the downthrown side. NELSON BLOCK The Nelson structural unit is broken by many faults, some with large displacement. In the northern part of the block, the eastern margin is marked by the Jeep Pass fault, in whose hanging wall a thick sec- tion of Mount Davis volcanics dips steeply toward the footwall of Precambrian gneiss and Patsy Mine vol- canics. Northward the fault divides both directly and en echelon, and displacement appears to die out south of Hoover Dam. The Rifle Range fault borders the west side of a horst which, with the fault at its east- ern border, disappears southward under glassy vol- canic rocks that floor Glass Plateau. South of this plateau the section of Mount Davis volcanics is du- plicated by many local faults and by at least four normal faults of considerable magnitude, the eastern- most of which extends northward from the east-west extension of the Jeep Pass fault. More than a mile, , RECONNAISSANCE GEOLOGY, LAKE MEAD—DAVIS DAM, ARIZONA—NEVADA 19 , farther west in the Hidden Valley fault, also with northerly strike, clearly visible where Precambrian gneiss is in the footwall but obscure farther north in the section of basaltic lavas. is cut off by another, striking northwest, which hinges out to the southeast in Patsy Mine volcanics. The Fuller Road fault has caused large displacement of the Mount Davis volcanics, but the trace has not been followed to an assured limit, either north or south. West of it is the Eldorado fault, which has excep- tionally clear expression through several miles be— cause of contrasting rocks on opposite sides. This fault, on which the throw is among the largest in the map area, may extend considerably father than shown on the map; it is obscured at the south in plutonic rocks and Precambrian gneiss, at the north in basaltic lavas. Through 5 miles or more from Eldorado Wash northward, the vertical displacement presumably is measured in thousands of feet, even if allowance is made for possible eastward thinning of the 3 vol- canic assemblages west of the fault. Farther north the throw may decrease, though the Mount Davis sec- tion is very thick and the measure of duplication by faulting seems indeterminate. Faults in a set west of the Eldorado fault are clearly expressed because of the distinctive pattern made by offsetting of the three volcanic units, Patsy Mine through Mount Davis. The tufls and breccias of the Golden Door volcanics, lighter colored and more resistant to weathering than the lavas above and below, mark locations of faults unmistakably. All faults in the set dip to the west and have normal displacement. The easternmost member of this set makes oblique junction northward with the Eldorado fault; at the south this member, and the one next . west of it, end abruptly near the old Techatticup mine. Although waste hides the critical relations, clearly the thick volcanic sequences also end along a nearly straight line, trending somewhat north of west, at the boundary of a coarse-grained intrusive body. This boundary is interpreted as an intrusion fault (Ran- some, 1904, p. 11), south of which the volcanic rocks were lifted by the rising pluton and eroded. The Welcome fault offsets the pluton; possibly part of the displacement on this fault also occurred while the in— trusion was in progress. West of the Welcome fault, relations between vol- canic and intrusive rocks are obscure. South and west of Nelson, masses of the old lavas are surrounded by plutonic rock and boundaries are indistinct. The thick section of Patsy Mine volcanics on the north, repeated by faults and tilted to the east, strikes south- ward directly into a wide zone occupied in large part At the south this fault E41 by irregular intrusive bodies. The northern bound- ary of this zone is vaguely marked. Possibly many intrusion faults, trending generally east, traverse the belt of intrusive bodies, and masses of the volcanic rocks that were lifted by intrusive action have been eroded, though many engulfed blocks remain. North of the old Wall Street mine a large mass of clay de- veloped by hydrothermal action has been used in brickmaking. Several miles northwest of Nelson, a large fault with downthrow on the east separates the Patsy Mine volcanics from Precambrian gneiss. The north and south limits of this fault are not determined. Broad anticlinal structure involves the Patsy Mine section at the north end of the Precambrian outcrop. Along the structure section D—D’, plate 1, the outcrop of Patsy Mine volcanics is nearly 4 miles across the strike, and prevailing dips to the east are particu- larly steep in the eastern half of this distance. A number of large strike faults repeat the section; but it seems impossible to follow some of the traces through the brown lavas, and even where a distinc- tive horizon of glass provides a guide, only general- ized traces have been mapped, as shown on plate 1. Dips of the faults thus represented are low, locally no more than 20°. Vagueness of the structural de- tails defeats attempts to make a reliable estimate of thickness in this section. West of the Colorado River the structure character— ized by east—dipping fault blocks ends abruptly on the south near the latitude of Eldorado Wash. East of the river the structural boundary is more irregular. In the hanging-wall block of the Ives fault, westward dips prevail as far north as the lower end of Black Canyon; but east of this fault the belt of eastward dips extends to and irregularly south of Pope Wash. In the wide outcrop area of Patsy Mine volcanics tra- versed by this wash, dips are roughly quaquaversal around an igneous plug. The large northwesterly faults bordering this large block are of considerable interest. Three of these—the Pope fault, the fault paired with it to bound a northwest-trending graben, and the Gold Bug fault—are closely parallel, and they are similar in strike to the set of northwesterly faults between Square Butte and the river. The Ives fault, on the west border of the Pope Wash block, becomes an important member of that set in its extension west of the river. ELDORADO WASH T0 NEWBERRY MOUNTAINS South of the Gold Bug fault, dips to the west are general; abruptness of the change in structure along this fault is shown in the structure section E—E’, plate 1. Southward from the lower end of Black E42 Canyon, widening sheets of alluvium hide much of the bedrock; but through a distance of 15 miles, out— crops in scattered ridges reveal that between the Black and Eldorado Mountains the Golden Door and Mount Davis volcanics make up several fault blocks that are tilted consistently to the west. Section F—F’, plate 1, illustrates this structure, some elements of which must be inferred. The Epperson fault dips west; the Big Blackstop fault dipseast; and close similarity of ex- posed structure from Mount Davis westward suggests that the other faults also dip to the east. Outcrops of Golden Door volcanics along the river indicate an important fault east of them. Evidence supporting the two faults next in order to the west is obscured by alluvium; but they are suggested by changes in dip, probably caused by drag. The fault nearest the west end of the section is established by the dip of volcanic rocks toward the nearly straight ‘border of the range. The plug of andesite porphyry at the main border fault along the east side of the Eldorado Mountains, and several bodies of similar rocks alined to the south, indicate that intrusion was controlled in some degree by the fault zone. Northward branching of the fault and irregularity of the range front farther north im- ply that fa'ulting at this border is complex, perhaps on a set of en echelon fractures. Large thicknesses of the exposed volcanics indicate very large displacement in the vicinity of the section F —F ’. In the large alluviated area south of Mount Davis, there are no outcrops of the older bedrock; but in the Black Mountains belt the westward dips persist, ex- cept in the zone of sharp flexure south of Eppersons Corral. The axis of downwarp south of the Portland mine, in line with the north end of the Newberry Moun— tains, is the logical southern limit of the structural unit with prevailing dips westward. Though outcrops Service Buy Line FIGURE 15.—Fault zone in Precambrian rocks at Davis Dam, exposed by excavation east of river. SE. (modified from W. K. Lundgren. TKS. Bure SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY are limited in this unit as a whole, apparently the structure is much simpler than in the wide belt north of Eldorado Wash. STRUCTURE EAST OF NEWBERRY MOUNTAINS The Newberry Mountains afford the widest continu- ous outcrop of Precambrian rocks within the map area. Generally the banding in these rocks trends west of north, and west of the river the average dip of the banding is steep toward the east. Persistence of Precambrian outcrops across the broad valley and eastward to Union Pass marks a broad belt of uplift along an axis trending somewhat north of west, paral— lel to the Portland mine downwarp. ’ Most of the faults in this part of the area are re- vealed by their efi’ects on volcanic rocks, but excava- tions during the building of Davis Dam gave infor- mation on an exceptional fault zone that involves Precambrian bedrock exclusively (Lundgren, written communication, 1949). The only surface indication of this feature was a saddle floored with crushed rock and clay. Exploration by trenching and core drilling showed a continuous though irregular zone with aver- age strike N. 60° to 65° E., dipping 15° to 25° SE; it is continuous at least 1,000 feet along the strike, and extends underground at least 800 feet southeast of the power plant, which is east of the river channel (fig. 15). The full zone includes in its upper part an irregular layer of crushed gneiss, as thick as 30 feet, crossed by seams of clay 1 inch to 2 feet thick. Ten to 100 feet vertically below this layer is another with similar content. In many parts of the fault zone, the power shovels could excavate without blasting. Nothing in available descriptions of this zone sug— gests the nature and measure of displacement. The low average dip and the extent of thorough crushing suggest thrust faulting. Because of the limited 0b— 200 FEET I00 I 4 units of powerplant Zone strikes N. 60°—65° E., dips 15°—25° tten communication. 1949). 2111 of Reclamation Wl‘l RECONNAISSANCE GEOLOGY, LAKE servations the fault is not shoWn on the map, plate 1, but its position is indicated in section G—G’. About 2 miles west and northwest of Davis Dam, volcanic rocks are downthrown on faults that make an irregular pattern. In one block with steep eastward tilt, basaltic lavas interspersed with beds of gravel appear to be part of the Mount Davis volcanics. An adjoining block tilted to the west has typical Golden Door volcanics, including basaltic sills and dikes. Sev- eral miles east of the dam, a set of normal faults with northwest strike repeats a section of Golden Door volcanics. The large outcrop of Precambrian rocks west of Union Pass appears to represent a much- faulted arch whose axis trends northwest. Some of the faults are clearly marked by remnants of lava and tuff, as at the old Frisco mine. The large fault at the Arabian mine, exceptional in direction of strike, has exposed in the hanging wall south of the mine a very coarse breccia that includes quantities of gray limestone. Conceivably the source was in Paleozoic beds that have been eroded from the footwall block. DATING 0F FAULTS In the area south of Boulder Basin, none of the many faults can be assigned definitely to geologic epochs, and few can be bracketed closely in relation to lithologic units. For example, two faults about a mile west of Willow Beach out only Precambrian rocks and Patsy Mine volcanics, but as no younger bedrock has survived erosion there, an upper limit for the date of faulting is indeterminate. Northeast of Nelson, the Welcome fault cuts a thick Mount Davis section that is strongly tilted; but flows of the Forti- fication basalt member of the Muddy Creek formation, covering a nearly even surface of erosion, cross the fault unbroken. The Rifle Range fault, and another 2 miles west of it, have lowered beds of the Muddy Creek with strong drag effects. Movements on many faults may have continued to a date as late as on the Mead Slope fault, which is favorably located to show involvement of the early Colorado River gravels. No faulting of recent alluvium was detected with certainty anywhere in the area, although topographic features southwest of Railroad Pass suggest possible breaks in the fan slope that are not yet obliterated by erosion and deposition. MINERAL DEPOSITS The region south of Lake Mead has long been a prospectors’ paradise, as evidenced by claim notices bearing a wide range in dates and by widely distrib« uted prospecting pits. Some old mines whose records Show large production lie within the area represented E43 on plate 1. The Eldorado Canyon district, with its center near Nelson, boasted the Techatticup and Wall Street mines, credited with total yield of gold and silver valued at several millions of dollars (Ransome, 1907). Production was begun at the Techatticup in 1863 and continued with interruptions until 1942. Development of some properties within or near this district has been started or renewed recently, as at Knob Hill. The Searchlight district, once very active, has been the scene of only small operations in recent years. On the Arizona side of the river, the Kather— ine mine ended a varied record about 1930. Among other properties that prospered for a time were the Gold Bug and Mocking Bird (Schrader, 1909), and the Arabian and Frisco (Lausen, 1931). Gold and silver were the chief objectives in the older operations, though more recently some other metals, including lead, zinc, and copper, have received attention. In the present study no attempt was made to locate and catalog the active prospects and mines within the area; but a few mines, most of them now inactive, are shown on plate 1 to serve as reference points. Nearly all mineral deposits exploited within the area have been in igneous rocks, either plutonic or vol- canic, or in closely associated metamorphic rocks. Ex- ceptions are the manganese ore mined in the Three Kids district from sedimentary beds of the Muddy Creek formation, and gypsum quarried from several bedded formations northwest of Lake Mead. MEAD—DAVIS DAM, ARIZONA—NEVADA GEOLOGIC HISTORY OF THE AREA Evidence now in hand from a large area south of Lake Mead outlines a sequence of events but gives little basis for fixing definite dates. A large part of the history must be deduced indirectly from evidence in the thick stratigraphic sequence directly north and northwest of Lake Mead. Unfortunately the forma- tions of most critical interest, representing the Cre- taceous period and much of Tertiary time, have thus far yielded few diagnostic fossils. But at least the physical evidence given by the sediments has large value, and eventually we may have a more satisfac- tory basis for dating features and events. Conceiv- ably some local deposits, particularly waterlaid ash- beds, that are interlayered with volcanic rocks south of the lake may hold fossils of value. PALEOZOIC ERA The section of Paleozoic formations totals about 8,000 feet in Frenchman Mountain, and somewhat less in the Muddy Mountains, only a few miles from Lake Mead. Ranges farther north and northwest E44 show a much larger total thickness, and regional strat— igraphic evidence indicates clearly a thinning of the Paleozoic toward the southeast. This evidence has been summarized and shown graphically by McKee (1951). His isopach maps indicate for each Paleozoic system a marked decrease in thickness southward through the area of the present report, though accord ing to his logical extrapolations the full Paleozoic section may have measured more than 4,000 feet in the vicinity of the Davis Dam site. At Frenchman Mountain the continuous section from Middle Cambrian through Mississippian is made up almost wholly of marine carbonate rocks. Only the Pennsylvanian and lowermost Permian beds show a considerable increase in content of sand and silt as compared with the same part of the section in the Spring Mountains to the northwest. In general, there— fore, the evidence suggests gradual overlap through a considerable distance toward the southeast, as repre- sented by McKee (1951, pl. 1, 2). MESOZOIC ERA Marine limestone in the Lower Triassic Moenkopi formation is much thinner near Frenchman Mountain than in the Spring Mountains, whereas a much greater abundance of gypsum suggests lagunal conditions near shore. Probably the shoreline of that time was not far south of the present position of Lake Mead, and through all later Triassic and Jurassic time continen- tal conditions extended much farther north. Fine- grained clastic deposits of the Moenkopi and Chinle formations, and the Jurassic crossbedded sandstones, probably covered the area of this report; McKee’s (1951, pl. 2) estimate of about 1,500 feet for each sys- tem seems reasonable. We may suppose, then, that at the close of Jurassic sedimentation the thickness of sedimentary rocks. in the area was several thousand feet. Widespread deformation occurred before deposition of the Thumb formation, which lies with angular un- conformity on the Triassic and Jurassic rocks. The old erosion surface cuts across successively older for- mations from north to south; this cross-cutting indi— cates that uplift increased toward the south. A wide- spread conglomerate at the. base of the Thumb contains pebbles and cobbles that represent several Paleozoic formations and the Precambrian complex. Higher in the Thumb formation are numerous great lenses of shattered Precambrian bedrock; probably these breccias moved northward by landsliding from a fault scarp at the border of a rising land mass from SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY which nearly all rocks younger than Precambrian had been eroded (Longwell, 1951, p. 352). The Thumb formation is provisionally correlated with the Willow Tank and Baseline formations of the Muddy Mountain area, which are orogenic deposits of Cretaceous age (Longwell, 1949, p. 931). If this correlation is correct, the deformation in the area of the present report probably began as early as mid- Cretaceous time, in connection with the development of thrust sheets in southern Nevada and related to the orogeny farther north (Spieker, 1946, p. 150). Pre- sumably the emplacement of plutons in the Black and Eldorado Mountains accompanied this orogeny, and some of the bodies invaded the cover of sedimentary formations before these were stripped away, as evi— denced by xenoliths or roof pendants consisting of Cambrian beds. Extensive layers of tufi’ in the Wil— low Tank formation of the northern Muddy Moun- tains (Longwell, 1949, p. 931), and in the Thumb formation near Lake Mead, mark eruptive activity probably related to the rise of plutons now exposed in the Black and Eldorado Mountain blocks. Provi- sional dating of the older plutons there as Cretaceous is based on this supposed relationship. The generally acidic composition of the Cretaceous tufl's and of the older intrusive bodies is consistent with this corre- lation. The Patsy Mine volcanics were erupted through plutonic bodies, and basal layers of the sequence con- tain fragments of older volcanic rocks. Moreover the base of the Patsy Mine volcanics, wherever exposed, rests on a surface that transects Precambrian rocks and younger intrusive bodies that presumably are Cretaceous in age. A considerable interval marked by wide uplift and erosion must have preceded the Patsy Mine episode, and the Thumb rocks bear wit- ness to at least a part of this interval. The basaltic flows in the upper part of the Thumb formation (fig. 2) can hardly represent any part of the Patsy Mine volcanism, which from some of its nearby vents would have flooded with distinctive andesitic lavas the Thumb basin if in active subsidence. Probably the Patsy Mine volcanics were erupted after the Cre- taceous beds were laid down and deformed. The land surface that received the lavas may have extended northward across Cretaceous and younger bedrock; any Patsy Mine volcanics deposited there must have been removed by later erosion. Presumably, therefore, the only volcanic rocks of Cretaceous age preserved within the area of this report are the basaltic lavas and tuffaceous beds included in the sedimentary sec- tion north of Las Vegas Wash. RECONNAISSANCE GEOLOGY, LAKE CENOZOIC ERA The Horse Spring formation is separated from the Thumb formation by an erosional surface only; there is no perceptible angular divergence between the two units, which were deformed together in. equal degree. Possibly the Horse Spring was deposited in latest Cretaceous or in Paleocene time; the Eocene date now assigned is tentative and uncertain. Many features common to the two formations indicate deposition in subsiding basins, with frequent interruptions. Fresh— water limestone, which forms an important fraction of the Horse Spring section, occurs also, with similar lithology but smaller thickness, in a unit of the Thumb formation. Abrupt wedges of very coarse debris are present in the Horse Spring, though less conspicuous than in the Thumb. Similar basaltic and tuflaceous rocks occur in the two formations, in comparatively small amounts. No lavas resembling the brown ande- sites of the Patsy Mine volcanics are present in Horse Spring sections; surely these great effusions would have filled any subsiding basins near the present lo- cation of Lake Mead. Therefore the reasoning on which the Patsy Mine eruptive history is dated as post-Thumb is equally valid in assigning that history to a date later than the Horse Spring sedimentation. Volcanic activity, intermittent and moderate in this immediate area until the end of Horse Spring sedi- mentation, later became more pronounced. Evidence that this activity was accompanied by large—scale movements on fault blocks has been cited on earlier pages, in descriptions of the volcanic formations. These formations establish an order of events, and the absolute-age value of 50 million years for the Boulder City pluton (p. E17) gives a clue in the search for geologic dates. This value indicates a middle Eocene date for the pluton, and the relation of this body to adjoining lavas suggests a closely similar date for the Golden Door volcanics. The Patsy Mine vol— canics are older; but the early part of the Eocene epoch was long, and this volcanic episode may have occupied only a small fraction of that time. As all available evidence indicates that the Horse Spring formation was laid down before the Patsy Mine epi- sode. that formation is dated logically as Eocene or older. Additional radiogenic age values are needed to check the few now available.’ The Mount Davis volcanics can now be dated only within wide limits. South of Rifle Range Wash lavas and tuffs in the upper part of the Mount Davis se— quence overlie a surface of erosion that transects part of the Golden Door volcanics. At the northwest cor- ner of Malpais Mesa, sedimentary deposits in the up- per part of the Mount Davis sequence grade upward, ”See footnote. p. E17. MEAD—DAVIS DAM , ARIZONA—NEVADA E45 without perceptible break, into a section mapped as part of the Muddy Creek formation. If this correla- tion and the tentative date for the Muddy Creek are accepted, the Mount Davis history is bracketed be- tween middle Eocene and Pliocene dates. Sediments of the Muddy Creek formation reflect relief maintained by continued movements on faults (figs. 3, 12). Coarse deposits at the margins of basins grade into or intertongue with fine sediments laid down on playas or in open lakes. Several large basins of this kind, with sediments reflecting centripetal drainage and containing great quantities of saline de- posits, lie athwart the present course of the Colorado River. Therefore the river, as a through-flowing stream, was not in its present location in Muddy Creek time (Longwell, 1946, p. 821). Great thicknesses of gypsum and anhydrite in the lower part of the Muddy Creek formation east of Boulder Canyon pose a prob- lem of origin. Estuarine beds in southwestern Ari- zona record a northward encroachment of the sea in Pliocene or Miocene time (Wilson, 1933, p. 31). Con- ceivably the arm of the sea extended 200 miles north of these known deposits to the present site of Lake Mead; but this speculation has no support in known evidence. Perhaps the saline deposits of the Muddy Creek were derived from older formations and con- centrated in interior basins. Widespread lavas in the lower and upper parts of the Muddy Creek are almost entirely basaltic. Pro- gressive changes in average composition of volcanic rocks in the general region are of considerable inter- est. The Patsy Mine volcanics, which were erupted through more silicic plutons that probably gave off volcanic products, are predominantly andesitic; but the upper part of the Patsy Mine volcanics includes a unit of rhyolite glass, overlain by considerable basalt. The Golden Door sequence starts with latites and in general becomes more siliceous upward to a predominance of rhyolites. Mount Davis rocks are predominantly basalts and dark andesites, interrupted sharply at several horizons by tufts and glasses that range in composition from latite to rhyolite. The rule of basalt begun in Muddy Creek time continued into the Pleistocene. Thus there has been more than one pronounced swing in predominance from high to low silica content in the volcanic products, and sev- eral brief but pronounced changes in composition dur- ing each major episode. Any outline of structural development within the area can be in general terms only until more specific information may become available. Large-scale thrust faulting, widespread in the region on the north and west, did not directly involve the Frenchman Moun- E46 tain block which was tilted strongly and broken by normal faults (fig. 13). But probably this tilting occurred in connection with movement on large strike- slip faults that were active in late stages of the re- gional thrusting. Since the Horse Spring formation is tilted as steeply as older formations, deformation under regional compression may have continued from Cretaceous into Cenozoic time. 7 Vertical displacements on steep faults have been recurrent through several long epochs. Landslide brec- cias in the Thumb formation suggest that an east- west fault or fault zone, with upthrow on the south, was active near the latitude of Boulder Basin in late Cretaceous time. Presumably the large normal faults that break the Frenchman Mountain block were de- veloped and rotated to their present attitudes during the tilting movement that began early in the Ceno— zoic era. Important faulting in the several episodes of volcanism is attested by abrupt terminations of thick volcanic sequences, and by localized occurrences within these sequences of very coarse sedimentary de- bris, presumably shed from growing scarps. As this kind of evidence is especially pronounced in the Mount Davis sections, perhaps the faulting activity was at a maximum during that volcanic episode, which on the basis of the present tentative chronology con- tinued into the Pliocene epoch. Some faults, occur- ring singly or in sets, are localized near plutonic bodies and probably reflect stresses during intrusion. But the larger faults that were active at the time of Mount Davis volcanism and later have the northerly orientation that is characteristic in neighboring parts of the Basin and Range province. This regional pat— tern was well established through Muddy Creek time. The earliest known Colorado River deposits in the area are unconformable on beds of the Muddy Creek, and are of Pliocene or Pleistocene age (Longwell, 1946, p. 828). Presumably the course of the stream in deep gorges such as Boulder Canyon and Black Canyon, a course that appears illogical in relation to present topography, has resulted from superposition as the river cut down from a higher horizon where it had its initial course on the weak Muddy Creek formation. Local remnants of these weak beds, capped by the Fortification basalt member (fig. 3), testify that the formation once obliterated much of the rug- ged relief now supported by resistant bedrock. Pos- sibly the important movements on faults that have occurred at least locally since the stream course was established have increased relief in the vicinity of Boulder Canyon. Apparently no major changes in the course of the river have occurred between Boulder Canyon and SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Davis Dam. One may suspect that a former course extended southward from the lower part of Kingman Wash; a depression filled with old slope debris from the Black Mountains has some resemblance to a large abandoned stream valley (fig. 9). But no Colorado River gravels are found there, and the depression probably owes its origin to progressive eastward tilt- ing of the block southwest of the Horsethief fault. Minor changes in the course occurred as the river cut down through the lake deposits of the Chemehuevi formation. At Davis Dam the modern valley runs obliquely across the earlier trench which is filled with the lake sediments (fig. 6). Many temporary loca- tions of the stream channel at various levels on the lake beds were abandoned in later adjustments; the high-level potholes and terrace remnants near Hoover Dam mark one such location. Origin of the Pleistocene Lake Chemehuevi pre- sents a problem of much interest. Through hundreds of miles downstream from the Grand Canyon, many remnants of the basal lake deposits lie close to the river channel (fig. 6); therefore, the stream returned almost exactly to its earlier profile, once the obstruc- tion that caused ponding was removed. A natural dam in a narrow canyon, formed by lavas or a land- slide, seems the most likely cause. South of Davis Dam the only restricted part of the valley with walls high enough to meet requirements is Aubrey Canyon in the Whipple Mountains, where Parker Dam is lo— cated. No evidence of a breached natural dam has been found there; moreover, many remnants of lake beds lie downstream from Aubrey Canyon. Solution of the problem will require careful study in a large part of the lower Colorado River valley. REFERENCES CITED Campbell, Ian, and Schenk, E. T., 1950, Camptonite dikes near Boulder Dam, Arizona: Am. Mineralogist, v. 35, nos. 9—10, p. 671—692. Darton, N. H., and others, 1924, Geologic map of the State of Arizona: Arizona Bur. Mines, in cooperation with U.S. Geol. Survey. Gilbert, G. K., 1875, Report on the geology of portions of Nevada, Utah, California, and Arizona: U.S. Geog. and Geol. Surveys W. 100th Meridian Rept. (Wheeler), v. 3, p. 17—187. Hatch, F. H., Wells, A. K., and Wells, M. K., 1949, The petrol- ogy of the igneous rocks: 10th ed., London, Thomas Murby and Co. Hunt, C. B., McKelvey. V. E., and Wiese, J. H., 1942, The Three Kids manganese district, Clark County, Nev.: U.S. Geol. Survey Bull. 936—L, p. 297—319. . Ives, J. C., 1861, Report upon the Colorado River of the West: Washington, U.S. Govt. Printing Office. ' Larsen, E. 8., Jr., and others, 1952, Method for determining the age of igneous rocks using the accessory minerals: Geol. Soc. America Bull., v. 63, no. 10, p. 1045—1052. A‘ RECONNAISSANCE GEOLOGY, LAKE LaRue, E. C., 1925, Water power and flood control of Colo- rado River below. Green River, Utah: US Geol. Survey Water Supply Paper 556, 176 p. Lausen, Carl, 1931, Geology and ore deposits of the Oatman and Katherine districts, Arizona: Arizona Bur. Mines Bull. 131, Geol. ser. 6, (Univ. Bull, v. 2, no. 2), 126 p., 30 figs. Lee, W. T., 1908, Geologic reconnaissanceof a part of western Arizona: U.S. Geol. Survey Bull. 352, 96 p. Longwell, C. R., 1928, Geology of the Muddy Mountains, Nev.: U.S. Geol. Survey Bull. 798, 152 p. 1936, Geology of the Boulder Reservoir floor, Arizona- Nevada: Geol. Soc. America Bull., v. 47, no. 9, p. 1393— 1476. 1946, How old is the Colorado River?: v. 244, no. 12, p. 817—835. 1949, Structure of the northern Muddy Mountain area, Nevada: Geol. Soc. America Bull., v. 60, no. 5, p. 923— 968. ' 1951, Megabreccia developed downslope from large faults: Am. Jour. Sci., v. 249, no. 5, p. 343—355. McKee, E. D., 1951, Sedimentary basins of Arizona and ad- joining states: Geol. Soc. America Bull., v. 62, no. 5, p. 481—506. McKelvey, V. E., Wiese, J. H., and Johnson, V. H., 1949, Pre- liminary report on the bedded manganese of the Lake Mead region, Nevada and Arizona: US Geol. Survey Bull. 948—D, p. 83—101 [1952]. Marcou, Jules, 1858, Geology of North America, etc., 144 p., map: Zurich, Switzerland. Review in Am. Jour. Sci., v. 26, p. 323—333. Am. Jour. Sci., E47 Newberry, J. S., 1861, Geological report, in Ives, J. 0., Report upon the Colorado River of the West: US 36th Cong, lst sess, House Executive Doc. 90, pt. 3, 154 p. Ransome, F. L., 1904, Description of the Globe quadrangle [Ariz.]: U.S. Geol. Survey Geol. Atlas, Folio 111. 1907, Preliminary account of Goldfield, Bullfrog, and other mining districts in southern Nevada: US. Geol. Survey Bull. 303, 98 p. 1923a, Geology of the Oatman gold district, Ariz., a pre- liminary report: U.S. Geol. Survey Bull. 743, 58 p. 1923b, Ancient high-level potholes near the Colorado River [abs]: Science, New ser., v. 57, p. 593. Schrader, F. C., 1909, Mineral deposits of the Cerbat Range, Black Mountains, and Grand Wash Cliffs, Mohave County, Ariz.: U.S. Geol. Survey Bull. 397, 226 p. Simpson, G. G., 1933, A Nevada fauna of Pleistocene type and its probable association with man: Am. Mus. Novitates. v. 667, p. 1—10. Spieker, E. M., 1946, Late Mesozoic and Early Cenozoic his- tory of central Utah: US Geol. Survey Prof. Paper 205—D, p. 117—161. Stock, Chester, 1921, Later Cenozoic mammalian remains from the Meadow Valley region, southeastern Nevada: Am. Jour. Sci., 5th ser., v. 2, p. 250—264. US. Bureau of Reclamation, 1950, Geological investigations in US. Bur. Reclamation, Boulder Canyon Project final reports: pt. 3, Bull. 1, 231 p. Wilson, E. D., 1933, Geology and mineral deposits of south- ern Yuma County, Arizona: Arizona Bur. Mines Bull. 134, Geol. ser. 7, 236 p. MEAD—DAVIS DAM, ARIZONA—NEVADA A Page Absolute age determinations, potassium-argon and zircon methods ............. E17, 18 Access ........................................ 3 Acknowledgments. Alluvium, older _____ _ _ _ younger ................................... 15—16 Alluvial flats, below Black Canyon ___________ 15—16 Andesite, Golden Door volcanics ............. 21 Mount Davis volcanics“ ........ 24, 27 Anhydrite, origin ................ 45 Arabian mine, fault ............ 43 Aubrey Canyon, Pleistocene damsite ......... 46 Aztec sandstone .............................. 6 Aztec Wash area, high level terraces __________ 16 B Basalt 1n Mount Dav1s volcanics ......... 24 25,27 in Patsy Mine volcanics 19 Basalt flows .................................. 18 Basalt-capped buttes strat1graph1c relat1ons._ 29—31 Base maps ................................... 3 Basin deposits, Pliocene ..... _ 8—11 Basin-range structure, exhibit of. _ 34 Bictite latite of Ransome Patsy Mine volcanics ........... 19 Black Canyon, physiography- . .-_.. 4 structure ................................. 40, 41 Black Mountains area, Cambrian rocks ______ 8 emplacement of plutons ___________ 44 Epperson fault ___________________________ 38 fault zone ................................ 34—35 physiography plutonic rocks. .. Precambrian rocks. . structural relations ....................... 35—37 structure west of ......................... 39—43 Black Mountains block, uplift 34 faults ..... Boulder Basin, structure northward and west- ward ............................. 39 structure westward ....................... 43 Boulder Basin area, Muddy Creek basaltic flows _____ 29 physiographic descr1ption. . _ , ............ 4 Boulder Basin-Eldorado Wash area, structure. 39—41 Boulder Canyon, section along ............... 35—36 Boulder Canyon area, basalt dikes. _______ 31 history ................................ 46 plutonic rocks ........................ _ 17 Boulder City area, Mount Davis volcanics. . _ _ 27 Muddy Creek formation ................. rhyolite of Golden Door volcanics ________ structural relations ....................... Boulder City pluton, absolute age ............ composition and age determination ' relation to Golden Door activity .......... Breccia, explosion Golden Door ......... sedimentary ........................... 23—24, 26 C Camptonite dikes ________ Cenozoic history of area INDEX Page Chemihuevi formation, conditions of deposi- tion ______________________________ E14 fossils _______________ lake deposits ....... particle size ............................... 14 Chemihuevi lake, history ..................... 14, 46 Chinle formation ......... .. 6,44 -.. 3—4 10, 35, 46 Chemihuevi time ........ 14 Colorado River valley, older alluvium ......... 11—12 physiographic description ...... .. 4 Precambrian rocks ..... .. 5 Columnar sections ............................ 7 D Dacite, Golden Door ......................... 21 Dam breccia, of Ransome.._. . 22 Davis Dam ............................. 3 Davis Dam area, Chemihuevi lake deposits.- 14— 15 Colorado River history ................... 46 fault zone ................. 34, 42—43 Golden Door volcanics ..... . 21—22 Mount Davis andesite ...... _ 27 older alluvium ............................ 12 Paleozoic history ......................... 44 rhyolite ............... . 21 Deformation. _________ . 44 Detrital Valley, alluvial deposits. . ._- . 16 Dikes and sills, Golden Door volcanics ....... 21 Dry Camp breccia, of Ransome .............. 23—24 E Earlier work in area .......................... 4 Eldorado Canyon, ore deposits ............... 18 Eldorado Canyon mining district ............. 43 Eldorado Mountains, emplacement of plutons. 44 landslide breccia _____________________ _ 11 northern block. . . 39—40 physiography ............................. 4, 38 Precambrian rocks ....................... 5, 40 Eldorado-Newberry Mountains block, uplift. 34, 35 Eldorado Wash area, gravel in ________________ 11 intrusive masses ...................... 18 Mount Davis volcanics ................... 26 older alluvium ............................ 11 structural features ........................ 41 Eldorado Wash to Newberry Mountains, structural features ................ 41—42 Eruptive centers ............................. 34 F Faulting, age ................................. 46 displacement _____________________________ 46 history of ......................... 35, 43, 45—46 Muddy Creek time._ __________________ 10, 29,31 recent ....................... 43 regional pattern .......................... 46 Faults, Boulder Wash ........................ 35 Callville. See Fortification fault _________ 35 Faults, dating of. . ...... 43 Eldorado._.. .___ 21, 41 Emery ................................... 35 Epperson ................................. 20, 38 Fortification... _ 35,36, 37 Fuller Road ___________ 41 Gold Bug ............. 41 Hidden Valley___________. 41 llorsethicf .................... 17, 23, 36, 37, 39, 40 Page Faults —Continued in Patsy Mine volcanics .................. E19 Indian Canyon ..................... 17, 35, 36, 37 Ives ....................... ..._ 41 Jeep Pass .................. _._- 40 Kingman Road ____________ 35,37, 39,40 mapping of ............................... 34 Mead Slope fault ______________________ 36, 37, 43 Pope .................... __ 38, 41 Ransome ................... . 35 Rifle Range ................. . 40 rotation and displacements ............... 34 Welcome..- Fieldwork ....... Flows, Golden Door volcanics ......... Folds, mapping of ............................ 34 Fortification basalt member of Muddy Creek formation, basal basalt unit ...... 29 composition of ..................... 31 correlation in Lake Mead area ............ 29-30 equivalence in Oatman district ........... 32,33 erosion remnants......._.. ............... 30—31 eruption of ............................... 31 Muddy Creek formation ________ original extent ............................ 31 Fortification fault, intrusive bodies near ...... 17 Fortification Hill area, Muddy Creek basaltic flows ......................... 29, 30 Muddy Creek formation. 8 olivine basalt .............................. 29, 31 “Paint pots” ............................. 17 physiography structure... tufi ...................... Fossils, Chemihuevi formation ............... 15 Frenchman Mountain area, Cretaceous red- beds .............................. 8 Lower Cambrian rocks 5 Mesozoic history ...... 44 Muddy Creek formation ................. 8 Paleozoic history ......................... 43—44 Precambrian rocks. 5 sedimentary rocks ........................ 6 Frenchman Mountain block, structural his- tory ........................... 39, 4546 Frisco mine, faults ............................ 43 G Garnet _______________________________________ 5 Geologic history of the area ................... 43—46 Geological Society of America, Penrose grant.. 3 Geology of area, general ______________________ 5 Golden Door volcanics. ......... 21 Mount Davis volcanics... 24 chemical and thin—section analysis. _. 28-29 Patsy Mine volcanics, chemical analysis... 28 faulting ............................... 20 horizon marker _____ 19 Glass Plateau area, basalt-capped buttes ...... 31 faulting in Patsy Mine volcanics .......... 20 Mount Davis volcanics ................... 26, 28 Gold Bug mine ..................... . 43 Gold Bug Wash, Golden Door volcanics ...... 21 fault near ................................. 38 Golden Door mine, structural relations near. . 38 Golden Door volcanics. . 18 age ................................. 45 bulk and groundmass compositions ....... 30 compositional change _____________________ 4 5 E49 E50 Page Golden Door volcanics—Continued character and distribution ________________ E20 equivalence in Oatman district ___________ 32 intrusive bodies in ........................ 23, 27 rocks of ............... __- 21—24 stratigraphic relations. . _____ 20, 21 structural relations. . 37 41,42, 43 xenoliths _________________________________ 36 Gneiss ________________________________________ 5 Grand Wash Cliffs, Precambrian rocks ....... 5 Granite ____________________________ 5 Granitic rocks, younger _________ 6 Gypsum ...................................... 43. 44 in Muddy Creek formation ............... 9, 10 origin ..................................... 45 H Hoo“er Dam area, eruptive complex _________ 19—20 glassy unit ________________________ 27 Golden Door section... _______________ 23 Golden Door volcanics. ............... 21—24 landslide breccia .......................... 10—11 latite ..................................... 21 Mount Davis volcanics ........ 28 Muddy Creek formation ................. 8 older alluvium ............................ 12 Patsy Mine volcanics ..................... 20 Pleistocene basalt sheets and dikes ....... 33 sedimentary breccia ............. 20, 23—24 volcanic rocks ................... 22 Horse Spring formation, age __________________ 6, 45 I Igneous plug, structure ....................... 41 Igneous rocks, Cretaceous and Cenozoic ______ 16 Pleistocene ............................... 33-34 sediments in ______________________________ 29. 31 Intrusion, structural control of 42 Intrusive bodies ______________________________ 16—18 K Kingman Wash area, igneous complex ________ 17 Knob Hill, mining activity ___________________ 43 L Lake Mead, access for fieldwork ______________ 3 Lake deposits, Chemihuevi formation ........ 12—14 Lake Mohave, alluvial flats beneath __________ 15 fieldwork ............................. ._ 3 Lake Mohave project _________________________ 3 Landslide breccia, Muddy Creek formation . _ 10 Las Vegas Wash area, Cretaceous volcanic rocks _____________________________ 44 Mesozoic uplift _____________________ 8 Mount Davis volcanics, glassy rocks . 29 Muddy Creek formation ___________ 9 sedimentary rocks ________________________ 6,8 Latite, Golden Door volcanics ________________ 21, 22 Mount Davis volcanics; .......... 24 Lava sheet, in Golden Door volcanics ________ 22 M Malpais Mesa, basalt-capped buttes __________ 30 landslide breccia .......................... 11 Mount Davis volcanics, measured section. 26—27 Muddy Creek basaltic flows ______________ 29, 30 Muddy Creek formation _. _______ 8,9 physiographlc description . _________ 4 structural relations ______________ 40 Manganese ___________________________________ 9 Marine carbonate rocks, Frenchman Moun- tain .............................. 44 INDEX Page Marker beds ................................. E34 Mesozoic history of area ...................... 44 Mineral deposits .................... 43 Mocking Bird mine ............... 43 Moenkopi formation ..................... _ 6 marine limestone-gypsum proportions. _ .. 44 Mount Davis, type locality of Mount Davis volcanics ......................... 24 Mount Davis area, landslide breccia_ ._ 11 Mount Davis volcanics ............ 18, 24—29 age ....................................... 45 associated unrest ......................... 24, 26 bulk and groundmass composition of volcanic glasses ........ 30 displacement ............ 41 eruptive centers .......................... 27, 28 faulting during volcanism ................ 46 glassy units, high-silica ............... 27, 28 petrographic description .............. 27 lithologic description ...... measured section ...... sedimentary breccia. sedimentary debris _______________________ 25, 26 sediments in .............................. 29, 31 stratigraphic relations. ____________ 20, 21 structural relations ........... 25, 27, 37, 38, 42, 42 type locality .............................. 24 Mount Davis volcanism, associated faulting. 29, 38 Mount Davis—Golden Door contacts __________ 24—25 Mount Perkins area, Golden Door volcanics._ 21 Muddy Creek formation ..................... at Boulder Wash fault .................... 35 basin deposition .......................... 9, 10 compositional change-.. 45 Horse Spring formation ................... 6 manganese ore ............................ 43 Paleozoic history _________________________ 43-44 structural relations .................... 35, 37, 40 Muddy Creek time, displacement during ___ 37 topographic relief ......................... 31 N National Park Service, cooperation ........... 3 National Science Foundation, grant .......... 3 Nelson area, basalt-capped buttes. _ . 30-31 eruptive complex ............... _ 19 Golden Door volcanics. . 24 27 intrusive contacts. _ . 18 monzonite porphyry ..... 18 Mount Davis volcanics. ........... 25,26 Patsy Mine volcanics. _ ........... 19 structural relations .................... 39, 41, 43 Nelson block, structural features ............. 40—41 Newberry Mountains area, granite ...... 18 older alluvium. _ .. physiography. _ plutonic rocks ............................ 17 Precambrian rocks _______________________ 5 structure east of .......................... 42—43 Newberry Mountains—Eldorado Wash, struc- ture .............................. 41—42 0 Oatman district, Arizona, volcanic rock clas- sification ....................... . 31-33 Opal ....................................... . 22 P Paleozoic history of area ...................... 43—44 Patsy Mine volcanics ............... 18,19—20.37,40 age ....................................... 44, 45 Page Patsy mine volcanics, comparison with Oat- man rocks... compositional change .......... distribution and description .............. 19 Patsy Mine volcanics, eruption of ............ 19, 44 stratigraphic relations .......... . 20, 21, 25 structural relations. ........ .. 1’8, 41 type section ................ 19 Pleistocene igneous rocks ..................... 33, 45 Pleistocene Lake Chemihuevi, origin ......... 46 Plutonic rocks, relations to volcanic rocks. . _ 17 Plutons ....... composition. dating of ................................. 44 erosion of ................................. 17 Pope mine, fault near ............ . 37 Pope Wash area, eruptive complex ........... 19, 41 Mount Davis volcanics ................... 26,27 Mount Davis-Patsy Mine contact, meas- ured section ............ .._ 25,41 Patsy mine volcanics- . 19 structural relations ....................... 38 Portland mine, faulting and folding near ..... 38,42 Precambrian rocks ........ 5-6, 36, 38, 39, 40, 41,42-43 R Railroad Pass, recent faulting ................ 43 Ransome, F. L., classification of rocks, Hoover Dam ..................... 22—23 classification of rocks, Oatman mining district ........................... 31-33 ’ References cited- . ..................... 46—47 Relief ............................... 4 Rhyolite, in Golden Door volcanics.. 21, 22, 24 in Mount Davis volcanics ......... . 24 Rifle Range Wash area, igneous complex ..... 18 River Mountains, rhyolite .................... 24 zenoliths ................ 8 structural relations .......... 39 S Saddle Island, schist ......................... 6, 8, 39 5, 6 16 Mount Davis—Golden Door contact ..... 24 structural relations ....................... 38 Searchlight mining district _ 43 Sedimentary deposits .................. ._. . 5 Sedimentary formations, northwest of Lake Mead ............................ 6-8 Spherulites, Patsy Mine volcanics ............ 19 Spillway breccia, of Ransome... 22 Square Butte, basalt cap. . . 31 doming ............ 40 eruptive centers ...................... .. 27-28 high-silica glass ....................... _ 27 Mount Davis andesite .............. 27 Structural blocks, deformation within ........ 40 tilting .................................... 34—35 Structural development .............. 45—46 south of Lake Mead ............ Structural pattern ............................ 34—35 Sugarloaf Mountain area, Golden Door volcanics ......................... 22, 23 high-level terraces .......... . 14,16 Surface features ..................... . . . 4 T Techatticup mine, gold and silver ........ 43 intrusive rocks ............... 18 41 Terraces, high -1evel.; ......................... 16 Tertiary rocks of region, sequence of .......... 10 Page Three Kids Mine area, glassy rock ............ E29 structural relations .......... 39 Tertiary sequence ........... _ _ . .. 10 Thumb formation, age of basaltic flows and tufis ______________________________ 44 basal conglomerate .......... 44 correlations _________ 44 landslide breccia ________________________ 8, 10,46 stratigraphic section ______________________ 6 Topography __________________________________ 4 Trachydolerite bodies, in Golden Door vol- canics _____________________________ 23, 27 Tufis, in Golden Door volcanics ______________ 24, 25 Mount Davis volcanics ___________________ 24 U Union Pass area, Golden Door volcanics ______ 22, 43 Mount Davis volcanics ___________________ 27 Precambrian rocks ............. 39, 42 structure .................. v ______________ 42 U.S. Bureau of Reclamation, Lake Mohave project ___________________________ 3 INDEX PBKe U.S. Forest Service, aerial photography _______ E3 Uplift ________________________________________ 44 V Vegetation ____________________________________ 3 Virgin Mountains, Precambrian Mountains.. 5 Volcanic glasses, bulk and groundmass com- position .................... ._ 30 chemical analysis and petrographic de- scription. ........................ 27—28 Volcanic rocks ________________________________ 18—34 age ....................................... 18, 44 assemblages ______________________________ 34 correlation ................................ 18 progressive compositional changes.-. . _ __ _ 45 Volcanic rocks of Muddy Creek formation__.. 29—31 comparison with adjacent areas ___________ 31—33 comparison with Ransome’s classification. 31—32 Volcanism, faulting movements during ....... 34 of Muddy Creek time. .................. 29 0 E51 W Page Wall Street mine, gold and silver ............. E43 Wall Street mine area, hydrothermal clay..._ 41 Washes, younger alluvium in ................. 15 West Petroglyph Wash, Kingman Road fault- 37 Whipple Mountains area, Chemihuevi lake deposits .......................... 15 White Rock Wash, Horsethief fault .......... 37, 40 Willow Beach area, basalt-capped buttes ..... 30, 31 higl -1eve1 terraces ........................ 16 Muddy Creek formation. ....... 8 physiography ___________________ 4 structural relations .................... 39, 40, 43 unassorted breccia ........................ 27 Y Yale University, cooperation ................. 3 Z Zircon method, age determinations ........... 17, 18 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 574—E GEOLOGICAL SURVEY PLATE 1 114°50’ 40' EXPLANATION BEWIO’ 36° 10’ Qal Alluvium and lake deposits t Gravel, sand, and silt (Recent); lake deposits of Chemehuevi formation (Pleistocene); early deposits of Colorado River; and cemented slope _ gravels, locally cut by dikes and overlain by basaltic lavas (Pleistocene?) , Pleistocene and Recent O U AT E R N A R Y 1\ VI'I Muddy Creek formation Conglomerate, sandstone, silt, clay gypsum, and basalt flows; local breccia I of landslide origin. South and east of Lake Mead.- Tm f, Fortification basalt member, at top, underlain by lower part offor- mation, or by older rocks beyond limits of deposition of lower part of Muddy Creek Tml, lower part of Muddy Creek formation Tmb,breccia of landslide origin, locally present Within lower part of ‘ Muddy Creek. Pliocene(?) ‘ Volcanic and intrusive rocks In part hydrothermally altered; ranging in age from Patsy Mine to Mount Davis. Sedimentary rocks north of Boulder Canyon are included Intrusive rocks Intrusive bodies cutting Mount Davis or older volcanic rocks; locally including maSses of invaded rocks TERTIARY Mount Davis volcanics Basalt and dark andesite predominant; widespread tujf and glass; abundant sedimentary breccia Eocenefl) to Miocenefl) - 36°OO’ Golden Door volcanics Latite to rhyolite; abundant explosion breccia, tuff, and rhyolite glass Patsy Mine volcanics Brown andesite, with much basalt’in upper part; one sheet of rhyolite J . glass containing'spherulites Ths Horse Spring formation Fresh—water limestone, siltstone, sedimentary breccia, volcanic tufl”, J and basaltic lava Eocene(?) CRETACEOUS(?) TERTIARYI?) l1 LIJ O \ I. I , Z Intruswe rocks 3 Granitic rocks and porphyry, visibly in contact with prevolcanic rocks or S isolated by alluvium, gp. No known intrusive contacts with Tertiary D volcanic rocks. May be in part eqivalent to Tig unit. Similar rocks Z with interspersed masses of invaded Precambrian complex, gpi; bound- 4; aries vague . (C < v 3 . as -. Thumb formation 0: 8 'v Reddish—brown sandstone and siltstone,fresh-water limestone, gypsum, U U conglomerate, coarse breccia, and basaltic lava - > // Chinle and Moenkopi formations 93:” Shale, sandstone, conglomerate, limestone, and gypsum J «0/ Kaibab and Toroweap formations 5Q / - TT 5” Includes Permian red beds locally J Sedimentary rocks Limestone and shale, in part thermally altered CAMBRIAN PERMIAN TRIASSIC Metamorphic and igneous rocks Complex of gneiss, schist, and granitic rocks. Many included igneous bodies of Cretaceous or later age, not mapped separately J PRECAM— BRIAN Contact Dashed where approximately located, dotted where concealed 4U —-—---. 0 Fault, showing dip \ Dashed where approximately located, dotted where concealed. \ U, upthrown side; D, downthrown side \L I \ Anticline \ Showing position and plunge of crestline \ 25 \ J— Strike and dip of sedimentary and volcanic rocks 90 + Strike of near-vertical beds 6 Horizontal beds / o \ Strike and dip of schistosity \ + \ Strike of vertical schistosity ).\ X / ‘ Mme ~BIRD MINE Volcanic anzd‘jPrecarn‘brian rocks. (riot mapped; \ l ,“\,w .7/V "\ I .I" ()1 "- "-1" j // / \‘ (“fig . ' ‘ / N0f> K // \\ *‘mmapbed “ " I Not mapped - ' .. Aa‘ 4“ A__‘_\vv,,«/7L\>f ‘” Tl EE/V / /_/, /// #4” 'M__W// / TRUE NORTH APPROXIMAYE MEAN IIFCLINATION, I962 ‘ ' . ,, 5 ' ' ' a ...... . , ' .. ,/ J / _ 40' I I?) INTERIOR—GEOLOGICAL SURVEY. WASHINGTON, D. C —61052 ‘ . :I'V Geology mapped by C. R. LongwelI .53) ' IV)’ I? i I l I I I I g L For sources of base, see Introduction A 4000' per 4000’ Tvasv va ’ 2000' SEA LEVEL pluton 2000’ SEA LEVEL : o > c , to Boulder City 0 X o 2 DD 2000’ 4000' 4000' 2000’ 2000' SEA LEVEL SEA LEVEL 4000’ 2000’ SEA LEVEL 4000/ Section H—H’ shown on Figure 13 2000’ SEA LEVEL GEOLOGIC MAP AND SECTIONS OF AREA ALONG COLORADO RIVER BETWEEN , LAKE MEAD AND DAVIS DAM, ARIZONA AND NEVADA SCALE 1:125 000 5 O SMILES l l————l l———l .' . CONTOUR INTERVAL 200 FEET DATUM IS MEAN SEI LEVEL *- $5 75 77’7 ‘ P4 #0 . 377‘ 7 « G/ypiggmsms and . .AssOciated Trilobites ‘in the United States r — ‘1 GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—F \ Go Ass ciated Trilobites in the United States By ALLISON R. PALMER tagnostas and SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—F Tae systematics, faana/ associations, ana’ strati— grapnic significance of American species of Glyptagnostus are a’iscassea’, anaI associateaI z‘ri/o— oiz‘es representing 2] genera anaI 31 species are a’escrioeaI andfigarea’ UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing ORiCe Washington 25, DC. CONTENTS Page Page Abstract ___________________________________________ F—l Systematic paleontology—Continued Introduction _______________________________________ 1 Crepicephalidae ________________________________ F—27 Acknowledgments ___________________________________ 3 Kingstoniidae __________________________________ 29 Trilobites associated with Glyptagnostus _______________ 3 Leiostegiidae? __________________________________ 29 Stratigraphic significance of Glyptagnostus ______________ 6 Menomoniidae _________________________________ 30 Ecologic observations _______________________________ 10 Pterocephaliidae ________________________________ 31 Conclusion _________________________________________ 11 Aphelaspidinae _____________________________ 32 Systematic paleontology _____________________________ 11 Pterocephaliinae ____________________________ 40 Agnostidae ————————————————————————————————————— 11 Locality information and faunal lists __________________ 41 Clavagnostidae _________________________________ 14 Alabama _______________________________________ 42 Glyptagnostidae ________________________________ 15 Nevada ________________________________________ 42 Pseudagnostidae ________________________________ 18 Tennessee ______________________________________ 43 Asaphiscidae ___________________________________ 22 Texas _________________________________________ 43 82333.3332?11f1??::::::::::::::::::::::::::::::: 33 Selectedreferences ---------------------------------- 44 Cheilocephalidae ________________________________ 27 Index _____________________________________________ 47 ILLUSTRATIONS [Plates follow index] PLATE 1. Agnostidae and Clavagnostidae. 2. Glyptagnostidae and Pseudagnostidae. 3. Cedariidae, Crepicephalidae, Cheilocephalidae, Catillicephalidae, and Asaphiscidae. 4. Aphelaspidinae. 5. Aphelaspidinae. 6. Menomoniidae, Pterocephaliinae, Leiostegiidae?, Kingstoniidae, and rostral plates. Page FIGURE 1. Global occurrences of species of Glyptagnostus __________________________________________________________ F—2 2. Occurrences of species of Glyptagnostus in Nevada ______________________________________________________ 3 3. Occurrences of species of Glyptagnostus in Alabama _____________________________________________________ 3 4. Ranges of identified species of trilobites in Glyptagnostus-bearing beds at Woodstock, Ala ____________________ 4 5. Ranges of identified species of trilobites in Glyptagnostus-bearing beds at Cedar Bluff, Ala ____________________ 4 6. Ranges of identified species of trilobites in Glyptagnostus-bearing beds at Cherry Creek, Nev _________________ 5 7. Ranges of identified species of trilobites in Glyptagnostus-bearing beds at McGill, Nev _______________________ 6 8. Correlation of faunal sequences in parts of early Upper Cambrian sections at McGill and the Snake Range, Nev _____________________________________________________________________________________________ 8 9. Correlation of lower parts of Upper Cambrian faunal successions between North America and Sweden _________ 10 10. Stratigraphic relations of the Dunderberg and Hamburg formations between McGill and Cherry Creek, Nev--- 10 11. Evolutionary development of the pydidium of Glyptagnostus _____________________________________________ 17 12. Partial reconstruction of Carinamala longispma n. sp ____________________________________________________ 23 13. Comparison of length of frontal area to length of glabella for the type lots of Aphelaspis walcam’ Resser and A. brachyphasis n. sp __________________________________________________________________________________ 34 14. Partial reconstruction of Listroa toxoura n. sp __________________________________________________________ 41 TABLE Page TABLE 1. Summary of morphology, faunal associations, stratigraphic range, and correlation of Glyptagnostus species in the United States ____________________________________________________________________________________ F—7 III SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES IN THE UNITED STATES By ALLISON R. PALMER ABSTRACT Glyptagnostus is represented in the United States by two species, G. reticulatus (Angelin) and G. stolidotus Cpik. The former is further represented by two subspecies, G. reticulatus reticulatus (Angelin) and G. reticulatus angelini (Resser). The oldest species, G. stolidotus, has been found only in association with species of Cedan'a. The youngest subspecies, G. reticulatus reticulatus, is known only in association with Aphelaspis and the acrotretid brachiopod Angulotreta. G. reticulatus angelini occu— pies an intermediate stratigraphic position in association with aphelaspinid trilobites and the acrotretid brachiopod Opisthotreta. Comparison of faunal successions in the Snake Range and at McGill, Nev., provides strong evidence to show that the beds with G. reticulatus angelini and aphelaspinid trilobites are contemporaneous with beds assigned to the Crepicephalus zone in central United States. Two biofacies, designated as the Crepicephalid and Pterocephaliid biofacies, are recognized. The contact between beds with trilobites of the Crepicephalid biofacies and younger beds with trilobites of the Pterocephaliid biofacies, previously thought to be the same age over all of the United States, is shown to be measureably older in parts of Nevada and Alabama than it is in central United States. Trans- gressive replacement of the Crepicephalid biofacies by the Pterocephaliid biofacies is thus indicated during the early Late Cambrian. Accurate placement of Glyptagnostus in the American Cam— brian section provides new evidence for correlating these beds, at least down through the Crepicephalus zone, with beds no older than the Olenus zone of the standard Upper Cambrian section of Sweden. Trilobites representing 21 genera and 31 speciesfound in association with Glyptagnostus, principally in eastern Nevada and central Alabama, are described. New taxa include: Homagnos- tus comptus n. sp., Aspidagnostus laem's n. sp., Aspidagnostus rugosus n. sp., Pseudagnostina contracta n. gen. n. sp., Carinamala longispina n. gen. n. sp., Cedaria brevifrons n. sp., Coosia longocula n. sp., Komaspidella occidentalis n. sp., Deiracephalus um’comis n. sp., Aphelaspis brachyphasis n. sp., Aphelaspis subditus n. sp., Olenaspella regularis n. sp., Olenaspella separata n. sp., Listroa toxoura n. gen., n. sp. INTRODUCTION Glyptagnostus is a bizarre genus of Upper Cambrian agnostid trilobites with a striking radial and generally also reticulate ornament on the cephalic cheeks and the pleural regions of the pygidium (pl. 2, fig. 1—8, 11). It has been recorded from North America at the following places (fig. 1): British Columbia (Kobayashi, 1938), southwest Texas (Wilson, 1954), western Ten- nessee (Grohskopf, 1955), central Alabama (Butts, 1926; Resser, 1938), and Newfoundland (Kindle and Whittington, 1959). During the past decade, and particularly during the field seasons of 1958 and 1959, Glyptagnostus was collected from the following areas in Nevada (fig. 2): (a) Hot Springs Range; (b) Tybo; (c) Hamilton district; (d) Cherry Creek; (e) McGill. Near McGill and Cherry Creek, fossiliferous sequences including Glyptagnostus, from the lower part of the Dunderberg formation, were intensively collected. Data obtained from these collections and from re- collection of previously known localities in the Cona- sauga formation at Woodstock and Cedar Bluff, Ala. (fig. 3) form the principal basis for the conclusions reached in this paper. Outside North America, Glyptagnostus has been re- ported from the northeastern Siberian platform (Savizky and Lazarenko, 1959) northwestern Siberian platform (Miroshbikov and others, 1959) ; south Korea (Kobayashi, 1949); southeastern China (Lu, 1956); northeastern Australia (Whitehouse, 1939; Cpik, 1956, 1958, 1961) ; Tasmania (Banks, 1956); southern Sweden (Angelin, 1854; Westergard, 1922, 1947); southeastern Norway (Brogger, 1882; Strand, 1929; Henningsmoen, 1958); Bornholm (Poulsen, 1923); and Great Britain (Belt, 1867; Lake, 1906). Kobayashi (1949) was im- pressed by the wide distribution of Glyptagnostus and considered all the forms then known to him to represent a single species, G. reticulatus (Angelin). He conceived of a “Glyptagnostus hemera, the oldest world instant,” believing that “because morphic complexity (of G. reticulatus) suggests high specialization, homotaxial dif- ference of time may be expected to be slight * * *,” and that all occurrences of Glyptagnostus reticulatus could therefore be considered contemporaneous. Recently, Opik, working with the Glyptagnostus faunas of Australia, and the writer, working with American material, have found evidence that seems to require modification of Kobayashi’s thesis. Opik (1958, 1961) has already published some of his observations F—1 SHORTER OONTRIBUTION S TO GENERAL GEOLOGY F—2 .§§§3§§b Ho 38me no macflahflooo EQSUIA @59lo oowfl aomfi _ . GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES —-—’—.._.._l _________________ I HOT SPRINGS = i I RANGE I I L- I i Golconda I : i | UTAH \, I \ / I .‘ | 046 \, N EVA DA ; Q, ~\ I" """"" — q? x I (I? \\ I"J ., \ , ARIZONA “f HAMILTON DISTRICT Glyptagmstus occurrences 40 MKES FIGURE 2,—Oocurrences of species of Glyptagnostus in Nevada. on the range of Glyptagnostus. The purpose of this paper is to examine the systematics and stratigraphic significance of Glyptagnostus as developed from all known occurrences of the genus in the United States. ACKNOWLEDGMENTS This study includes all collections with Glyptagnostus belonging to the US. Geological Survey and US. National Museum. In addition, Dr. W. C. Bell, University of Texas, loaned all the material of the Glyptagnostus-bearing exotic boulder BM—4 (Wilson, 1954) from the Woods Hollow shale, Marathon region, Texas. Dr. Hans Frebold, Geological Survey of Can— ada, loaned collections of Glyptagnostus and associated trilobites described by Kobayashi (1938) from the Brisco—Dogtooth area, British Columbia. Guidance to the Glyptagnostus-bearing beds near Cherry Creek and McGill, Nev., was provided in 1958 by J. C. Young, then a graduate student at Princeton University. Cor— respondence with Dr. A. A. Cpik, Bureau of Mineral Resources, Canberra, Australia, who is working on the Glyptagnostus-bearing strata of Australia, has been extremely helpful in the development of some of the systematic and stratigraphic ideas presented in this F—3 paper. Most of the photographs on the accompanying plates were prepared by N .W. Shupe and R. H. McKin- ney, of the US. Geological Survey, and photographs of the unusual Deimcephalus unicornis n. sp. were made by Jack Scott, of the US. National Museum. TRILOBITES ASSOCIATED WITH GLYPTAGNOSTUS The test of the validity of Kobayashi’s thesis of a Glyptagnostus hemera lies in the determination of the stratigraphic range and species content of Glyptagnostus. All published records indicated to Kobayashi that Glyptagnostus was a rare trilobite found in only one fauna in each major area of occurrence (that is, north- western Europe). All the described specimens, in the absence of large enough assemblages to permit biometric analysis, seemed to represent the same bizarre species. Thus he concluded that Glyptagnostus was a monotypic genus with a negligible stratigraphic range—a reason— able conclusion from the available evidence. Glyptagnostus is found associated with three different nonagnostid trilobite faunas in the United States. Generally, it is associated with only one of these faunas at any particular locality. Two or more Glyptagnostus- bearing nonagnostid trilobite faunas are known to occur I - \ \ GEORGIA ‘ I ALABAMA /' MISSISSIPPI Birmingham Glyptagmstus occurrences 40 MILES FIGURE 3.—Occurrences of species of Glyptagnostus in Alabama. E O o x.— X X X 2887—00. x 2886—CO° x >'< x x X X X Covered '- e‘ :5 3 EXPLANATION E =‘ :8 E :3 FEES s E 3 § 78, Shaleand . 3 v: 9‘ d. . d. siltstone g a 3 § g g g g. § § 3 E E s Q g g E BEE :§ . . g s . L»... 5 -:§.§§§§.s§ mes e 8 52 3 8 d“. :52 :3 <3 FIGURE 4.—Ranges of identified species of trilobites in Glyptaynostus-bearing beds at Woodstock, Ala. in stratigraphic succession only at McGill, Nev. cessions of fossiliferous beds including part or all of the range of Glyptagnostus, however, are known only at Woodstock and Cedar Bluff, Ala., and McGill and Cherry Creek, Nev. The trilobite assemblages and the Glyptagnostus population morphology at each of these localities are in the following discussion. Woodstock, Ala. (fig. 4).——Thirteen feet of dark- brown weathered shale and siltstone of the Conasauga formation, including several thin beds of gray silty fine-grained laminated limestone are exposed in an old railroad cut at the southeast edge of Woodstock. Glyptagnostus has been observed in most of the lime- stone beds although it is common only in colln. 2886—00, Where it is associated with rare specimens of Deira- cephalus unicorm's n. sp. and Pemphigaspis sp. The only identifiable trilobites in colln. 2887—00 are speci- mens of Glyptagnostus. Colln. 2888—00 is from a limestone bed about 2 inches thick. The lower, light- colored part contains moderately common specimens of Cedam'a prolifica (Walcott) and Pseudagnostina con- tracta n. sp. and rare specimens of Glyptagnostus. The upper, dark-colored part contains moderately common specimens of Glyptagnostus and Proagnostus sp. asso- ciated with rare specimens of C. prolifica and P. con- Suc- ’ SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY tracta. A small collection by Charles Butts in 1904 from this railroad cut contains D. unicorm's and Glyptagnostus associated with Kingstomla appalachia Resser and anunidentifiable species of Carinamala n. gen. In all the collections, Glyptagnostas is represented by cephala and pygidia having a prominent radial ornament but no significant reticulation of the checks or pleural fields. The pygidia, in addition, have a broad longi- tudinally undivided penultimate segment of the poste- rior part of the axis that is about three times longer than the small triangular terminal segment (fig. 11). Cedar Blufi, Ala. (fig. 5) .———About 40 feet of brown weathered shale of the Conasauga formation containing rare limestone beds 1 inch or less in thickness are exposed in a drainage ditch along the west edge of the Covered 2875—CO 0 ’ 2876-00- X—X X—X 2877-00 (USNM - 10c. 89d) 2878—00 - 2879—00 0 f 1: Q) E 0 € E EXPLANATION § 15 g I: , :6 in 41‘ D. >3 FEET a g d a z 3; m 3’9 § 3 *5 o ‘0 § ___. r73 .3 s #3 5 ° 6 ---—- § ‘5 c. s s '5 E” s a .E a: :3 g 3 fit :5 ‘S s E § Limestone, g: E a; g g '5 -° :3 § ~33 bed and lens '8 "° 3 m ‘w § IS 3 10 9- 8 § g a) 9‘ S. ”5 2% 9: 3° - a Q s E‘ E S“ N S w 3° g 7, 3 . ”9 % $5 s E s s s s i s <1 9: c: m 5 <1 w v: <:: 5’3 FIGURE 5.—Ranges of identified species of trilobites in GIyptagnostus—bearing beds at Cedar Bluff, Ala. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES high-school playground 3 blocks east of the old town square in Cedar Bluff. Fossils were recovered from the shale and from layers of silt and clay between layers of calcite fibers perpendicular to the bedding in the rare limestone beds. An extremely fossiliferous lens of medium-crystalline gray limestone was present in the vicinity of colln. 2877—CO. Only one small scrap of this lens was found on the visit to this locality in 1959, but Charles Butts and E. O. Ulrich made a large collection from a lens at this spot in 1920. The speci- mens of Glyptagnostus in their collection Were used in the biometric study summarized on figure 11. In most of the collections from Cedar Bluff, Glypta- gnostus is associated with Aphelasp’is buttsi (Kobayashi). In colln. 2879—CO, Blountia bristolensis (Resser) and an indeterminate species of Aphelaspis are present. The collection made by Butts and Ulrich in the vicinity of 2877—00 contains many specimens of Olenaspella separate n. sp., in addition to common specimens of Glyptagnostus. Aspidagnostus rugosus n. sp., Agnostus inexpectans Kobayashi, and Pseudagnostus communis? (Hall and Whitfield) are present in collns. 2875—00 and 2876—CO. Glyptagnostus is represented in all the collections at Cedar Bluff by cephala and pygidia having a prominent reticulate ornament of the cheeks and pleural fields and having the terminal segment of the pygidial axis rela- tively longer than that of the pygidia at Woodstock, Ala. (fig. 11). Cherry Creek, Nev. (fig. 6) .—About 250 feet of silt- stone with interbeds and lenses of gray fine-grained silty generally laminated limestone, mostly less than 3 inches thick characterizes the lower part of the Dunderberg formation along the east side of the Cherry Creek Range about 4 miles north of the town of Cherry Creek. Most of the limestone beds are unfossiliferous. Three limestone beds in the lower 12 feet of the Dunder- berg formation contain Glyptagnostus and associated trilobites. The trilobite assemblages of all 3 beds are virtually the same and include 8 species of trilobites besides the species of Glyptagnostus: Aspédagnostus rugosus n. sp., Agnostus inexpectans Kobayashi, Acmar- hachis acutus (Kobayashi), Aphelaspis subditus n. sp., Oheilocephalus sp., Listroa toxoura n. gen., n. sp., Olenaspella regularis n. sp., and an undetermined aphelaspinid species. The specimens of Glyptagnostus in these three collections are essentially identical in ornament with the specimens at Cedar Bluff, Ala., but have a relatively longer terminal segment on the posterior part of the pygidial axis (fig. 11). Two collections in the upper 2 feet of a massive limestone unit beneath the Dunderberg formation, here assigned to the Hamburg limestone, contain a totally different trilobite assemblage: Carinamala 2535-00. x7xxxxxx E Pterocephaliid ‘5 biofacies E E4 i'é %’ E (:1 2534—00' Txxxxxx x . Illlll g 24M” Di_se_01£9:m_itr___§,:,i,i:fLL“ c: plcephahd Egggfig: X X X X X X biofacies .D g A :2: FEET0 E Q) 2 g E . 45’ §La€ m =d .9 Q 5 a. ss§$§§§g 2 EXPLANATION_§%d§§m=§M5:-. g ._ Egsg‘gségg S'.,- §22§§ss§§§§§§§% itstone §§335§§ gascéag .-_—_-. 3g sumssés. gems §§E§§s§§§§wa§§ Limestone SE 33 § “ 5 g S a ,_ g o §§§.s.,§ N bedandlens §§3 mgsggvagg S 000Mm& fix 4x . X—X X- X—‘X* 4X X 4X4 X—Xv— Xfl<——X—X X—'X TTXXXXXX X X Crepicephalid biofacies E3 Eé‘é a 's. 9;. '3 $5,. . 2 a ; sis dad s as mnézdve=9 u dévfa §£BQ:50= Ewes“!!! s§g=§§§ g 9:,s'§€ .§3v~§‘ag° §§§§§gesa§§§s§ '3 §i§s§5§§§§3§§§ §s§E§§3§§sss§c§ gr.ss as§§§§§§§ §§g§-°§§§§ §' 3388sw §~~ua£°a§ aooo<<}é spella regularis or Tybo,Hamil— region. length bz— ptero— Angulotreta sp. ton district, cephalid. Hot Springs Henderson Range. Markham N 0.1 well, Lake ———————————————— angelini With Olena- County. Crepicephalus spella separata or McGill _____________________ Cedar Bluff- zone. Opisthotreta sp. G. stolidotus, primarily ____________________ McGill? __________________________________ __ Woodstock- radial; length b3<}é ________________ length bz—crephi- Cedaria cephalid with zone. Cedaria spp. F~8 populations from about the middle of the American range of the genus, and collns. 2471—00 and 2534—CO from Cherry Creek, Nev., representing the youngest populations of the genus. The results are shown on figure 11. They indicate a progressive lengthening of b3 from the oldest to the youngest populations. The oldest populations are ornamented almost entirely by radial furrows (pl. 2, figs. 2, 5); populations of inter- mediate age have considerable intrapopulation variation in development of a reticulate ornament (pl. 2, fig. 4); specimens in the youngest populations are always strongly reticulated (pl. 2, figs. 1, 3). The systematic significance of these observations is discussed on page F—18. One species and two subspecies of Glyptagnostus are recognized here: the oldest populations are assigned to 0. stolz'dotus Opik; the intermediate and youngest populations are assigned to G. reticulatus angelim‘ (Resser) and G. reticulatus reticulatus (Angelin), respect- ively. By using the ratio of b2 to b3 and the degree of development of the ornament on specimens of Glyptag— nostus from stratigraphically unplaced collections, together with the composition of the associated trilobite and brachiopod faunas, each of the Glyptagnostus sam— ples from the United States has been assigned a position Within the range of the genus on table 1. An important development of the study of Glyptag- nostus has been evidence for a much more complex bio— facies problem in the Cambrian than was previously thought to exist. This has a direct bearing on the stratigraphic range of Glyptagnostus and on general con- cepts of faunal zonation within the Cambrian. At first glance, the range of the genus would appear to be from the Cedam'a zone to the Aphelaspis zone of the standard early Upper Cambrian faunal succession (Howell and others, 1944) because the oldest population of Glyptagnostus is associated with the type species of Oedam'a at Woodstock, Ala., and the youngest popula— tion is associated with Aphelaspz's and Angulotreta at Cherry Creek, Nev. However, the section at McGill, Nev., provides evidence to indicate that such appear- ances might be misleading. A major faunal break involving nearly complete change of trilobites at the family level has been recog— nized for years between the early Upper Cambrian Crepz'cephalus zone and the overlying Aphelaspz's zone (Lochman and Wilson, 1958, p. 332). In contrast, the work of Lochman and Duncan (1944) and the writer (Palmer, 1954) has shown that there is only a gradual evolutionary change from the faunas generally assigned to the older Cedarz'a zone to those generally assigned to the overlying Orepicephalus zone. At McGill, Nev., a bed with Oedam'a and Carinamalar is present immediately below a bed with Aphelaspz‘s and SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Snake McGill Range O O O . . : Aphelasms g e. : Angulotreta -——- . C 5 ; Oleaaspella Crep’icephalus E _. in Opzsthotrcw Tm'crem'cephalus : . Aplwlaspzs Kingsttmia . Coosina cedm‘a ___ Carinamala FEEB EXPLANATION Limestone 100 :='5=.'_.'i Interbed—destone and siltstone FIGURE 8.—Corre]ation of fauna] sequences in parts of early Upper Cambrian sections at McGill and the Snake Range, Nev. Glyptagnostus (fig. 8). The first reaction to this relation would be to suspect the presence of a disconformity because there is no interval for trilobites assignable to the Orepicephalus zone. This reaction would be strengthened by a casual examination of the section in the Snake Range, Nev., 50 miles to the southeast (fig. 2), where collections made in 1959 show that Cedam'a and Carinamala, are found in beds about 350 feet below the contact between the Orepz'cephalus and Aphelaspz’s zone faunas. This contact is approximately at the top of unit 16 of the Lincoln Peak formation (Drewes and Palmer, 1957, p. 118). The upper beds of unit 16 con— tain a fauna consisting of Urepicephalus sp., T ricrepi— cephalus, and Crepicephalus? perplexus Palmer. In the immediately overlying beds, the fauna is completely changed and includes Aphelaspis haguei (Hall and Whit— field), Chez'locephalus sp., Glaphyraspz’s sp., and Angu- lotreta sp. Comparison of the basal Aphelaspis zone assemblage from the Snake Range with the section at McGill, however, shows that this assemblage correlates not with the lowest Aphelaspis-bearing beds but with an assemblage in beds above those with Aphelaspis brachyphasis n. sp., Aphelaspis buttsi (Kobayashi), Glyptagnostus reticulatus angelim' Resser, Olenaspella separate n. sp., and Opisthotreta. Thus, the older Aphelaspis—bearing beds at McGill must correlate in part with beds bearing a totally different trilobite fauna GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES assignable to the Crepicephalus zone (s. l.) in the Snake Range. The only alternative would be to require disconformities at McGill and in the Snake Range, for which there is no positive faunal or physical evidence. With regard to the Snake Range, faunal relationships between the Aphelaspis and Crepicephalus zones are essentially identical to those in central Texas (Palmer, 1954, p. 715), where this abrupt change in faunas is clearly unrelated to significant changes in sedimentation. The indicated correlation between McGill and the Snake Range is supported by the brachiopod sequence at McGill. The contact between beds with Optstho— treta and overlying beds with Angulotreta'in the mid— continent region corresponds approximately to the contact between the Crepicephalus and Aphelaspis zones (Palmer, 1954), whereas at McGill the contact between the Opisthotreta and Angulotreta-bearing beds lies between the Aphelaspz's-Glyptagnostus sequence and younger beds with aphelaspinid trilobites. The necessary conclusion is that the major trilobite ‘faunal break present in all known early Upper Cambrian sections below the lowest Aphelaspis-bearing beds is not everywhere of the same age and represents in most areas a biofacies change in response to still unknown changes in ecology. Because the beds below the change in biofacies generally have representatives of the Crepicephalidae and because all the beds immediately above the biofacies change have representatives of the Pterocephaliidae, these two primary biofacies are here designated as the Crepicephalid and Pterocephaliid biofacies. The oldest presently known beds containing the Pterocephaliid biofacies are found at McGill, Nev., and Cedar Bluff, Ala., in early Late Cambrian deposits far from the continental core. The youngest beds con— taining the Crepicephalid biofacies are found in the interior region. This fact indicates that the change from Crepicephalid to Pterocephaliid biofacies began near the continental margins and moved shoreward. Older beds containing trilobites of the Pterocephaliid biofacies may thus be found when early Late Cambrian beds still farther from the continental core are examined. The age of the youngest assemblage of the Crepi— cephalid biofacies at McGill, Nev., presents another problem. Besides species of Cedaria and Carinamala, it contains Coosia longocula n. sp. and Kamaspide/la occidentalis n. sp.—species closely related to Coosia connata (Walcott) and Komaspidella Ihea (Walcott) from the lower beds of the Orepicephalus zone at its type area in Wisconsin. At Woodstock, Ala., Cedaria and Carinamala are associated with Pemphigaspis, a genus generally found only in beds correlative with the Crepicephalus zone (s. l.) in the upper Mississippi Valley and Texas (Palmer, 1951, 1954). A Cedam'a 618549 0 - 62 7 2 F—9 species was reported from Murphy Creek, Quebec, on the same bedding surface as a Crepicephalus species by Kindle (1948, p. 449). Through the kindness of Dr. Kindle, the writer had the opportunity to examine collections from boulders in the Cow Head conglomerate of Newfoundland containing Cedaria gaspensis Rasetti in association with a species of Crepicephalus. Because Cedaria gaspensis is closely related to C. prolifica Walcott from Woodstock, Ala., and to 0’. brevifrons n. sp. from the highest beds of the Crepicephalid biofacies at McGill and Cherry Creek, Nev., evidence is accumu- lating which indicates that members of the C'. prolifica species group (p. F—26) occur in beds that correlate with the Crepicephalus zone rather than the Cedam'a zone as these zones are recognized in the midcontinent region of the United States. Thus, the unit occupied by Glyptagnostus in the American Cambrian section would seem to correspond principally to the Crepice- phalus zone (s. l.) of the standard early Upper Cambrian faunal succession, with possible extension upward into beds that correlate with the lower part of the Aphelaspis zone (table 1). The range of Glyptagnostus shown on figure 12 of Lochman and Wilson (1958) is based on a misidentifi- cation by the writer (Palmer) of a fragment of a wrinkled agnostid in the Elvim'a zone of the Eureka district, Nevada, and the writer’s belief, in 1957, that the structurally and stratigraphically isolated Glyptag- nostus-bearing beds in the Hot Springs Range, Nev.— the only western Glyptagnostus locality then known— were younger than the Aphelaspis zone. Determination of the proper position of Glyptagnostus in the American early Upper Cambrian now provides a more precise correlation of beds of this age with beds in the standard section of Sweden (fig. 9). Glyptag— nostus reticulatus reticulatus, the youngest subspecies of the genus in the American section, occurs in beds equivalent in age to the Aphelaspis zone. In Sweden (Westergard, 1947, p. 22), G. reticulatus reticulatus occurs in the lowest two subzones of the Olenus zone, indicating that the base of the Olenus zone corresponds approximately to the Aphelaspis zone. The older American subspecies, G. reticulatus angelim' is associated with Agnostus inerpectans and Homagnostus comptus in beds equivalent in age to the Urepicephalus zone. This assemblage of agnostid genera is certainly of Late Cambrian age in terms of the standard section, and it is probable that American beds with these trilobites correlate approximately with the Agnostus pisiformis zone in Sweden. The precise correlation of American beds equivalent to the Cedar'ia zone with beds in the Swedish section cannot yet be satisfactorily determined. Clavagnostus, found in the late Middle Cambrian of Sweden, has been F—lO NORTH AMERICA SWEDEN 2: s abol' a: . . Par ma g Elmma spinubsa s Irvingella (Pamirm'ngella) ———> m z Dunde b ' '4 r ergw Homagnostus obesus Olenus Aphelasp’is Glyptagnostus retv'culatus reticulum—9 Crepicephalus Agmstus (s. s.) Agmstus inst" "tennis ? Ceda'ria Cla’vagnostus ___-?__—_ T21 . Lejopwe a 5 Lejopyge laevigata g g Bolaspidella 35 o FIGURE 9.~Corre1ation of lower parts of Upper Cambrian faunal successions between North America and Sweden. observed in association with Oedam'a in both Eastern and Western United States. However, recent discovery of Lejopyge in quantity in association with American late Middle Cambrian species of Bolaspidella, and Modocz'a, indicates that perhaps the generally accepted Middle-Upper Cambrian boundaries of Sweden and North America are approximately equivalent. Lochman (1956, p. 447) placed the entire American sequence of beds of Dresbach age in the Middle Cam- brian and correlated it with beds older than Agnostus pisiformis in the Scandinavian section. No direct evidence was given to support this correlation, and it is now apparent that it was in error. Lochman and Wilson (1958) placed all beds of Dresbach age in the Upper Cambrian, and no mention was made of the earlier correlation. Lochman and Wilson (1958, p. 333) also lowered the top of the Dresbachian stage and placed it at the “pronounced faunal break at the base of the Aphelaspis faunizone * * * ” Because this pronounced faunal break has been shown here to be of measurably different ages at different places, it is not suitable for a boundary between temporally defined units, and revi- sion of the Dresbach stage from its generally accepted usage on this basis does not seem to be warranted. ECOLOGIC OBSERVATIONS Comparison of the McGill and Cherry Creek sections (fig. 10) indicates the definite presence of an uncon- formity between the Dunderberg and Hamburg for- SHORTER CONTRIBUTION S TO GENERAL GEOLOGY mations in the Cherry Creek section. In both areas the contact between ,beds bearing trilobites of the Crepicephalid and Pterocephaliid biofacies is also the contact between the relatively thickbedded clean limestone of the Hamburg limestone, and the silty limestone and siltstone of the overlying Dunderberg formation. Pterocephaliid trilobite species and acro- tretid brachiopods like those found in the basal beds of the Dunderberg formation at Cherry Creek, however, occur about 80 feet above the base of the Dunderberg formation at McGill, and the Pterocephaliid trilobite species found in the lower part of the Dunderberg formation at McGill are missing at Cherry Creek. . There is no clear evidence for a significant unconformity at the base of the Dunderberg formation at McGill, although its absence cannot be entirely ruled out. The faunal characteristics of the upper beds of the Hamburg limestone at McGill and Cherry Creek indi- cate that the unconformity at Cherry Creek may have resulted from local nondeposition rather than from any significant pre-Aphelaspis erosion. The topmost beds in both areas contain Oedam'a brem'frons, Carinamala longispina, Coosia longocula, Komaspidella occidentalis, and Pseudagnostina convergens. A few feet below these beds is another fauna characterized by a species closely related to Kingstom'a spicata Lochman. If there had been any significant erosion prior to the deposition of the Aphelaspis-bearing beds, the identity of the species assemblages in the uppermost beds of the Hamburg limestone would seem to be a remarkable coincidence. Regional stratigraphic evidence indicates that a belt of relatively clean carbonate sedimentation represented Cherry Creek McGill Aphelasp'is subditus, Olenaspella regularis, I/istroa toxoum, Angulotreta sp., _{ Glyptagnostus reticulatus reticulatus FEET O HIATUS Aphelaszns‘ brachyphasis, Olenaspella separate, Opisthotreta sp., Glyptamwstus reticulatus \ 50 angelim' Cedan'u brevifrons, Cam'namala longispimz, Coosia longocula, Komaspidella occidentalis, ( Opisthotreta sp., Pseudagrwstina convergens EXPLANATION I- -' Interbedded limestone and siltstone Limestone FIGURE 10.—Stratigraphic relations of the Dunderberg and Hamburg formations between McGill and Cherry Creek, Nev. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES by the Hamburg was replaced by a belt of predomi- nantly silty sedimentation which moved generally east- ward across the carbonate belt for a brief period during the early Upper Cambrian (Palmer, 1960b, p. 53). 1f cessation of carbonate sedimentation resulted from external changes in a continuing marine enviroment, then subsequent significant erosion of the upper surface of the carbonate deposits would not be expected. The differences in age of the initial deposits of the succeed- ing environment of silt sedimentation could thus be related to difference in time of burial of topographic irregularities on the upper surface of the carbonate sediments. The fact that Glyptagnostus reticulatus, represented by different subspecies, is abundant only in the lowermost silty limestone beds of the Dunderberg at both McGill and Cherry Creek indicates that its habitat may have been controlled by some ecologic factor related to the silty substrate adjacent to the seaward edge of the belt of clean carbonate sedimentation. CONCLUSION Glyptagnostus has been shown on the preceding pages to be represented in the United States by two species, G. stolidotus Opik and G. reticulatus (Angelin), with the latter species divided into two subspecies, G. reticulatus angeliml Resser and G. reticulatus reticulatus (Angelin). G. stolidotus is the oldest, known only in association with trllobites of the Crepicephalid biofacies. G. re- ticulatus angelim' is the next younger, occurring in association with trilobites of the Pterocephaliid bio- facies and the acrotretid brachiopod Opisthotreta in beds that are contemporaneous with those bearing the Crepicephalus fauna of the interior United States. G. reticulatus reticulatus is the youngest, occurring in asso- ciation with different pterocephalid trilobites than G. reticulatus angelini and with the acrotretid brachiopod Angulotreta in beds that are correlated with the Aphe- laspz's zone of the standard early Upper Cambrian faunal succession. Glyptagnostus seems to have re- quired a more restricted environment, or a different environment for optimum development than the asso- ciated nonagnostid trilobites because it occurs in silty sediments bearing other trilobites of either the Crepi- cephalid or Pterocephaliid biofacies and is most common in silty rocks near their contact with relatively clean carbonate rocks. The same two species of Glyptag- nostus appear in the same stratigraphic order asso- ciated with trilobites of the Crepicephalid and Ptero- cephaliid biofacies in Australia (Opik, written com- munication, 1959) and perhaps also in northern Siberia (Savizky and Lazarenko, 1959, p. 189—192). Although the “Glyptagnostus—hemera” of Kobayashi may have been an oversimplification, as Glyptagnostus is rstidae (p. F—18). F—ll now shown to have a significant stratigraphic range and is no longer monotypic, the genus and its species still constitute the most precise tools presently available for intercontinental correlation of early Upper Cambrian deposits. SYSTEMATIC PALEONTOLOGY The descriptive terms used here are defined or illus- trated on pages 42, 44, 46, and 47 of Part 0 “Arthro- poda 1” in Treatiseon Invertebrate Paleontology, (Harrington and others, 1959) or in the glossary on pages 117 to 126 of the same volume. Diagnoses and descriptions are given here for all taxa that are revised or described as new, or for which only incomplete published information is available. Assignments to family or subfamily without comment indicate acceptance of the assignments given in the Treatise. Order AGNOSTIDA McCoy Suborder AGNOSTINA McCoy Family AGNOSTIDAE McCoy Diagnosis.—Agnostid trilobites with cephalon having glabella tapered forward, frontal lobe generally dif- ferentiated; median node present, generally poorly de- fined. Basal lobes simple. Preglabellar median fur- row present or absent. Border generally well defined. Pygidium with axis subparallel sided, strongly round- ed posteriorly, generally greater than one-half length of pygidium; divided into two generally well defined anterior segments and an unsegmented posterior part. Postaxial median furrow absent. Median axial node continuous across first and second axial segments on many species. One pair of marginal spines generally present. Discussion—Two distinct types of agnostids are commonly found in assemblages of Upper Cambrian trilobites. One type, with axis of the pygidium bearing an expanded pseudolobe represents the Pseudagno- The second type, with the axis of the pygidium subparallel sided, rounded at the rear, and generally not reaching the border furrow is considered here to represent the Agnostidae. Three genera of this family, Agnostus, Homagnostus, and Proagnostus are associated with Glyptagnostus. Homagnostus was at one time considered by the writer as a synonym of Geragnostus (Palmer, 1954, 1955), but it was later reinstated and included in a subfamily Geragnostinae (Palmer, 1960a). Although Geragnostus seems to be the Ordovician descendant of Homagnostus, it is also apparent from examination of species of Homagnostus and Agnostus that these genera are closely related. Both stratigraphic and morpho- logic factors favor a closer relationship of Homagnostus F—12 to Agnostus than to Gemgnostus, and such a classifi— cation is followed here. There is a great need for critical reevaluat on of the constitution of the families of agnostid trilobites as can be shown by comparison of the family groupings used in this paper and those presented in the most recent . classification of agnostids (Howell, 1959). The Agnostidae as defined by Howell (1959, p. 172), although including Agnostus and Homagnostus, in- cludes at least two genera, Acmarhachis and Asp/Mag- nostus, that are shown here to be morphologically dissimilar and probably unrelated to Agnostus. Genus AGNOSTUS Brongniart Agnostus Brongniart, 1822, p. 38. Kobayashi, 1939, p. 159. Westergard, 1946, p. 68, 84. Type species.—-Entomolithus paradoxus pisiformis Linneaus, 1757 (p. 122). Diagnosis.——Agnostidae with frontal lobe of glabella bluntly rounded anteriorly. Preglabellar median fur— row complete. Axis of pygidium slightly tapered to slightly expanded posteriorly; posterior end always sharply rounded. Pleural fields confluent behind axis. Discussion—This genus is restricted to agnostids conforming to the diagnosis given above, which is principally the meaning given to it by Kobayashi (1939). Westergard (1947, p. 4) included Homagnostus as a subgenus in Agnostus. However, species of Homagnostus consistently have an incomplete preglabel— lar median furrow on the cephalon, and a more bluntly rounded and generally broader axis on the pygidium. These differences are considered to be of generic value (Palmer, 1960a, p. 62). Agnostus inexpectans Kobayashi Plate 1, figures 1—11 Agnostus inexpectans Kobayashi, 1938, p. 172, pl. 16, figs. 30—33. Diagnosis.—Members of Agnostus with cephalon having anterior third of posterior glabellar lobe bearing deep notches in sides. Pygidium with first two axial segments well defined. Axis constricted at second segment. First axial segment trilobed. Second axial segment crossed lengthwise by axial node that con- tinues posteriorly onto posterior part of axis. Discussion.——The Nevada specimens of A. inescpectcms have been compared with Kobayashi’s illustrated specimens from British Columbia and are identical in all observable features. This species is most similar to Agnostus neglectus Westergard (1946, p. 85, pl. 13, figs. 7—9) from the late Middle Cambrianof Sweden in having a constricted second segment on the axis of the pygidium, and relatively strong development of the lateral furrows on the posterior lobe of the glabella. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY It differs from A. neglectus by the notched character of the lateral furrows of the posterior glabellar lobe, and by the more strongly defined axial node on the axis of the pygidium. Occasional specimens with a particularly bluntly rounded anterior glabellar lobe have a suggestion of a median notch in the front margin of this lobe. Occurrence: Conasauga formation: USGS collns. 2875—00 (5 cephala), 2876—00 (4 cephala, 4 pygidia), Cedar Bluff, Ala. Lower part of Dunderberg formation: USGS collns. 2466—00 (12 cephala, 16 pygidia), 2476—CO (1 cephalon, 3 pygidia), 2477—CO (1 cephalon, 1 pygidium), 3040—00 (1 cephalon, 1 pygidium), 3041~CO (2 cephala, 6 pygidia), 3046—00 (2 pygidia), 3049— CO (1 cephalon, 1 pygidium), McGill, Nev.; USGS collns. 2471— CO (3 cephala, 3 pygidia), 2534—00 (4 cephala, 5 pygidia), 2535—00 (?1 cephalon), Cherry Creek, Nev. Unnamed for- mation, USGS colln. 1370—00 (2 cephala, 1 pygidium), Hot Springs Range, Nev. Woods Hollow shale: Boulder BM—4 (2 cephala), Marathon region, Texas. Figured specimens: USNM no. USGS colln. Part 143122a ____________ 2534—CO ______ Cephalon. 143122b ____________ 2534—00 ______ Pygidium. 143123 ............. 2875—00 ______ Cephalon. 143124 _____________ 2876—00 ______ Pygidium. 143125a, b __________ 2466—00 ______ Cephala. 143125c—e ___________ 2466—00 ______ Pygidia. Genus HOMAGNOSTUS Howell Kobayashi, 1939, p. 162. Shimer and Shrock, 1944, p. Shaw, 1951, Homagnostus Howell, 1935, p. 15. Whitehouse, 1939, p. 261. 600. Lochman and Duncan, 1944, p. 139. p. 110. Palmer, 1960a, p. 62. Oncagnostus Whitehouse, 1936, p. 84. Geragnostus Palmer, 1954, p. 719; 1955, p. 88 (G. tumidosus only). T ype species.—Agnostus pisiformis obesus Belt, 1867 (p. 295, pl. 12, fig. 4). Diagnosis.—Cephalon with well-defined bilobed gla- bella and distinct border. Preglabellar median furrow, if present, incomplete, generally deepest near glabella and fading out before reaching border furrow. Pygidium with prominent well—defined axis generally broader than pleural regions. Posterior part of axis generally parallel sided or expanded slightly, well de- fined posteriorly, reaches nearly to border furrow. Discussion—Relations of tnis genus to Agnostus and Gemgnostus are discussed in the recent paper on the Dunderberg fauna (Palmer, 1960a, p. 62). Homagnostus comptus n. sp. Plate 1, figures 12—15 Diagnosis.—Members of Homagnostus with pregla- bellar median furrow short, present only adjacent to frontal lobe of glabella. Pygidium with first pair of lateral furrows straight, not connected across axis; first segment not trilobate. Axial node prominent, extended from second axial segment onto anterior part of pos- terior part of axis. Combined length of first two axial GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES segments less than length of posterior part of axis. Surfaces of all parts of exoskeleton covered with fine granules or roughened. Discussion—The distinctive fine granular ornament, which can only be observed after coating specimens lightly with magnesium oxide or ammonium chloride, and a somewhat. better developed preglabellar median furrow are the only features that distinguish this species from H. tumidosus (Hall and Whitfield). The lack of a trilobate first axial segment on the pygidium and the distinctive ornament distinguish this species from all known foreign species. Occurrence: Lower part of Dunderberg formation: USGS collns. 2466—00 (>20 cephala and pygidia), 2477—00 (3 cephala), 2478—CO (1 pygidium), 2480—CO (1 pygidium), 3020—00 (1 cephalon, 2 pygidia), 3054—00 (1 cephalon, 1 pygidium); 3055—00 (2 cephala), McGill, Nev. Figured specimens: USNM USGS colln. Part 143126 __________ 2466—00 _____ Holotype cephalon. 143127a, c _______ 2466—00 _____ Pygidia. 143127b _________ 2466—00 _____ Cephalon. Homagnostus sp. Plate 1, figure 16 Discussion—Rare specimens of a species of Homag- nostus are associated with abundant specimens of Glyptagnostus reticulatus and Aphelaspis buttsi in shale in USGS colln. 2878—00, Cedar Blufl’, Ala. The cephalon has the preglabellar median furrow developed for about half the distance from the front of the glabella to the border furrow. The pygidium has the distance from the end of the axis to the border furrow only slightly less than the breadth of the border. Because of the small size of the specimens and imperfect shale preservation, accurate specific identification of these specimens cannot be made. Occurrence: Conasauga formation, USGS colln. 2878—00 (1 complete individual, 1 cephalon), Cedar Bluff, Ala. Figured specimen: USNM 143128, USGS colln. 2878—CO, complete individual. Genus PROAGNOSTUS Butts Proagnostus, Shimer and Shrock, 1944, p. 601. Type species.—Proagnostus bulbus Butts, 1926, pl. 9, fig. 12. Diagnosis.—Agnostidae with glabella bilobed, pre- glabellar median furrow present, median glabellar node on anterior part of posterior glabellar lobe. Pygidium with axis subparallel sided, broadly rounded at rear, reaches to or nearly to border furrow. Median axial node present on second axial segment. Pair of marginal spines present. Description—Agnostidae with cephalon moderately convex transversely, gently to moderately convex longitudinally; border well defined by broad moderately F—13 deep border furrow. Glabella well defined by axial furrows, bilobed; anterior lobe strongly rounded at front; first glabellar furrow complete; posterior lobe with low elongate median node on anterior part. Basal glabellar lobes well defined, triangular, undivided. Cheeks divided in front of glabella by complete moder- ately deep preglabellar median furrow. Pygidium moderately convex transversely, gently to moderately convex longitudinally, border well defined by broad moderately deep border furrow; posterolateral marginal spines present. Axis well defined by axial furrows, subparallel sided, broadly rounded posteriorly, reaches to or nearly to marginal furrow. Median axial node elongate, located on second axial segment, extend- ed slightly posteriorly onto posterior part of axis. Transverse furrow between first and second axial seg- ments generally complete. If present, transverse fur- row between second axial segment and posterior part of axial lobe interrupted by axial node. Discussion—Although the name Proagnostus was first used in a plate description by Butts (1926, pl. 9), the only published description of the genus is in Shimer and Shrock (1944, p. 601). This genus differs from Homagnostus, with which it has been considered a synonym by Kobayashi (1939, p. 163) and Howell (1959, p. 173), by having a complete preglabellar median furrow on the cephalon, the median glabellar node on the anterior rather than posterior part of the posterior glabellar lobe, and the axial node on the pygidium not extended forward onto the first axial segment. Of the five species assigned to Proagnostus by Resser (1938, p. 48) only the type species, P. bulbus Butts is here retained. Lochman and Duncan (1944, p. 138) placed P. centerensis Resser and P. maryvillensis Resser, which lack a preglabellar median furrow, in the new genus Baltagnostus. P. romensis Resser is represented only by a pygidium that lacks transverse furrows on the axis and is probably a species of Kormagnostus. P. major Resser is represented by badly worn internal molds of cephala and pygidia that cannot be satisfac- torily identified, and the name should be restricted to the types. The cephala seem to lack a preglabellar median furrow, and the species is thus not properly referable to Proagnostus. Lochman (1940, p. 24) noted correctly that Kormagnostus speciosus Resser, which has cephala with a well-defined frontal glabellar lobe and complete preglabellar median furrow associated with the figured pygidium, is a species of Proagnostus and not of Kormagnostus. Proagnostus modestus de— scribed by Lochman (1944, p. 77) may belong to this genus, but the pygidia, which have the critical generic features, are all meraspid forms, so that confirmation of the generic assignment must await description of holaspid pygidia. F—14 Proagnostus‘! sp. Plate 1, figure 17—19, 23 Numerous cephala and pygidia associated with Glyptagnostus reticulatus at Woodstock, Ala., represent a species that may belong to Proagnostus. For some undetermined reason the matrix adheres to the cheek areas of both cephala and pygidia, so that presence of a complete preglabellar median furrow, and for most specimens, length of the axis, cannot be certainly determined. Several specimens show a furrow begin- ning to extend forward from the axial furrow in front of the glabella. One specimen (pl. 1, fig. 19) shows that the axis of the pygidium does not quite reach to the border furrow; however, on most specimens the posterior end of the axis is not defined by the axial furrow. The prominent elongate axial nodes on the cephalon and pygidium and the fact that the axis does not reach the border furrow on the pygidium distin- guish these specimens from Proagnostus bulbus Butts. The latter feature also distinguishes the specimens from P. speciosus (Resser). Until better specimens showing presence or absence of a complete preglabellar median furrow are obtained, the generic assignment must remain tentative. Occurrence: Conasauga formation, USGS colln. 2888—00 (8 cephala, 23 pygidia), Woodstock, Ala. Figure specimens: US-‘NM USGS colln. Part 1431292», b __________ 2888—00 ______ Cephala. 1431290, d __________ 2888—00 ______ Pygidia. Agnostid, genus and species undetermined Plate 1, figures 31—33 Pygidia possibly related to those identified here as Proagnostus? sp. are present in USGS collns. 2475—00 and 3056—00 in Nevada. They have the axis defined only at the sides and have a long, slender median axial node. The poor definition of the first two seg- ments of the axis serves to distinguish these pygidia from the Alabama specimens. Except for the presence of posterolateral marginal spines, the Nevada pygidia are similar to those of Ciceragnostus cicer (Tullberg) illustrated by Westergard (1946, pl. 14, figs. 4, 6, 8, 9). Cephala possibly belonging with the Nevada pygidia in USGS colln 3056—00 have a well-defined glabella that lacks a transverse furrow outlining the anterior glabellar lobe. The cheeks are confluent in front of the glabella. If the cephalon-pygidium associ- ation in Nevada is correct, then these agnostids do not have the characteristics presently considered diagnostic of either Proagnostus or Ciceragnostus, and they prob- ably should be placed in a new genus. Inadequacy of the present samples and uncertainty about associa- tion of parts do not warrant doing so at this time. SHORTER OONTRIBUTIONS TO GENERAL GEOLOGY Occurrence: Upper beds of Hamburg limestone: USGS collns. 2475—00 (2 pygidia), McGill, Nev.; 3056—CO (3 cephala, 1 pygidium), Cherry Creek, Nev. Figured specimens: USNM USGS colln. Part 143137a ____________ 3056—00 ______ Cephalon. 14313710 ____________ 3056—00 ______ Pygidium. 143138 _____________ 2475—00 ______ Pygidium. Family CLAVAGNOSTIDAE Howell Diagnosis.—Agnostid trilobites with cephalon having glabella well defined by axial furrows, pointed ante- riorly, reaching about two-thirds length of cephalon. Anterior glabellar lobe not outlined by transverse glabellar furrow. Basal glabellar lobes present, simple. Preglabellar median furrow present, complete. Border narrow, well defined by border furrow. Pygidium with axis long, slender; sides of anterior part subparallel; posterior part tapered to sharp point at border furrow. Posterior third of axis distinctly depressed below anterior part of axis. Pair of pits usually present immediately adjacent to anterior end of depressed part of axis. Border well defined by bor- der furrow, bears pair of posterolateral marginal spines. Median marginal spine present or absent. Discussion—Howell (1959, p. 173) considered the Clavagnostidae to be a monotypic family. Opik (written communication, July 1959), however, noted the association of the cephalon of Aspidagnostus parma- tus Whitehouse, type species of Aspidagnostus, which is like that of Clavagnostus, with a pygidium having an axis also like that of Olavagnostus but bearing a median spine unlike any Clavagnostus species. Similar cephalon-pygidium relationships have been found in both Alabama and Nevada. It now appears probable that these are the correct cephalon and pygidium for Aspidagnostus rather than the association illustrated by Whitehouse (1936, pl. 9, figs. 5, 6) and that the genus belongs in the same family as Clawgnostus, rather than in the Agnostidae where it has been placed previously (Howell, 1959, p. 173). Genus ASPIDAGNOSTUS Whitehouse Aspidagnostus Whitehouse, 1936, p. 104. Howell, 1959, p. 173. (Cephalon only.) T ype species.wAspidagnostus parmatus Whitehouse, 1936, p. 105, pl. 9, fig. 5 only. Diagnosis.—Clavagnostidae with cephalon having slight median point on anterior margin. Pygidium with border interrupted by deep groove extending from end of axis onto prominent median marginal spine. Low knobs on border adjacent to groove. Discussion—This striking agnostid genus with its posteriorly tapered pygidial axis and median marginal spine is unlike any other known agnostid genus. Be- GLYPTAGNOSTUS AND ASSOCIATED T‘RILOBITES cause of its occurrence only in beds of middle Dresbach age and its distribution from Australia to North America, this genus, in association with Glyptagnostus, is particularly critical for accurate intercontinental correlation. Species are discriminated principally on ornament. Two species are recognized in the American collections: A. laem's n. sp., associated with Cedaria; and a younger species, A. rugosus n. sp., associated with aphelaspinid trilobites. Aspidagnostus laevis n. sp. Plate 1, figures 20—22 Diagnosis.—-—Members of Aspidagnostus with cheeks of cephalon and pleural fields of pygidium smooth. Glabella with large basal lobes that nearly touch behind posterior glabellar lobe. Pygidium with median node on axis poorly defined; transverse furrows behind first axial segment curved forward to isolate anterolateral axial lobes. Discussion—This species differs from A. rugosus n. sp. and A. parmatus Whitehouse by lacking either furrows or pits on the cheeks of the cephalon and the pleural fields of the pygidium. It differs further from A. rugosus by having distinct anterolateral axial lobes and a less well defined median axial node on the pygidium. Occurrence: Upper beds of the Hamburg limestone, USGS coll. 2475—00 (3 cephala, 1 pygidium), McGill, Nevada. Figured specimens: USNM USGS colln. Part 143130 __________ 2475— CO _____ Holotype cephalon. 143131a _________ 2475—CO _____ Pygidium. 14313lb _________ 2475—00 _____ Cephalon. Aspidagnostus rugosus n. sp. Plate 1, figures 24—30 Diagnosis.—Members of Aspidagnostus with cheeks of cephalon having several broad, shallow radially directed furrows. Pygidium with median axial node elongate, moderately well defined; pleural fields with several shallow depressions. Discussion—This species differs from A. parmatus Whitehouse by having furrows rather than pits on the cheeks of the cephalon and by having a somewhat shorter and broader glabella. It differs from both A. parmatus and A. laevis n. sp. by lacking distinct antero— lateral lobes on the axis of the pygidium. The median axial node on the pygidium is better defined for a greater distance than the median axial node of A. laevis. Two immature silicified pygidia with slightly irregular pleural fields are present in USGS coll. 2466—CO, McGill, Nev. Although they have a median marginal spine, they lack the groove across the border character- F—15 istic of other Aspidagnostus species (pl. 1, fig. 24). This may be an immature feature, however, and the specimens are tentatively included in A. rugosus. Occurrence: Conasauga formation: USGS coll. 2875~CO (1 cephalon), 2876—00 (7 cephala, 16 pygidia), Cedar Bluff, Ala. Lower 12 ft. of Dunderberg formation: USGS 0011. 2471— CO (1 cephalon, 3 pygidia), 2535—CO (1 pygidium), Cherry Creek, Nev. Lower part of Dunderberg formation: USGS coll. 2466— CO (2 pygidia), 3049—00 (1 pygidium), 3051—00 (1 cephalon), McGill, Nev. Figured specimens: USNM USGS' colln. Part 143132 __________ 2466—CO _____ Pygidium. 143133 __________ 3049—00 _____ Holotype pygidium. 143134a _________ 2471—00 _____ Cephalon. 143134b _________ 2471—00 _____ Pygidium. 143135 __________ 2535—00 _____ Pygidium. 1431368. _________ 2875—00 _____ Cephalon. 143136b _________ 2875—00 _____ Pygidium. Family GLYPTAGNOSTIDAE Kobayashi Genus GLYPTAGNOSTUS Whitehouse Glyptagnostus Whitehouse, 1936, p. 101. Kobayashi, 1939, p. 155. Shimer and Shrock, 1944, p. 600. Kobayashi, 1949, p. 1—6. Opik, 1961, p. 428. Type species.——Glyptagnostus toreuma Whitehouse, (1936, p. 102, pl. 9, figs. 17—20) =Agnostus reticulatus Angelin, 1851 (p. 8, pl. 6, fig. 10). Diagnosi8.—Agnostid trilobites with cephalon having bilobed glabella; frontal lobe subquadrate in outline. Basal lobes elongate, divided. Narrow border present. Pygidium with posteriorly tapered axis connected to border furrow by postaxial median furrow. Posterior part of axis divided into three parts. Narrow border with pair of short marginal spines present. Cheeks and pleural fields of cephalon and pygidium with prom- inent ornament of radial furrows of several ranks, often connected by cross furrows to form reticulate pattern. Description—Cephalon with glabella bilobed; an- terior lobe well defined, subquadrate; posterior lobe generally higher than anterior lobe, without distinct median node. Preglabellar median furrow present, complete, but with irregular course. Basal glabellar lobes elongate, divided by transverse furrow into slender anterior part and triangular posterior part. Border narrow, well defined by border furrow. Pygidium with axis long, tapered to point posteriorly, connected to border furrow by postaxial median furrow. Axial node prominent, elongate, extends entire length of first two axial segments and continues onto anterior part of posterior part of axis. FurrOWS defining first two axial segments deep, extended inward from axial furrows to axial node. Furrows between first and second segment directed slightly forward from axial furrow. Posterior part of axis divided into three parts (b1, b2, b3, fig. 11); b2 outlined anteriorly by shallow F—16 furrows extending posterolaterally from near tip of axial node to axial furrows, and posteriorly by deep transverse furrow; generally longer (sagittal) than either b1 or b3. Sides of posterior part of axis marked by longitudinal row of four or more pits adjacent to axial furrows. Border well defined by border furrow, bears pair of short marginal spines. Cheeks of cephalon and pygidium highly ornamented with furrows. Cephalon with kidney-shaped lobes always present adjacent to anterior glabellar lobe. Other furrows on cheek radiate inward from border furrow. Radiating furrows of several lengths in defi- nite pattern; longest furrows extend inward nearly to axial furrows; generally'between each pair of long fur- rows is shorter furrow extending inward about half breadth of cheek; between this furrow and each long furrow is still shorter furrow; margin of cheek between each of these furrows may be notched. Pygidium ornamented with similar pattern of radia- ting furrows of several ranks extending inward from border furrow. Younger species of genus with cross furrows connect- ing basic pattern of radial furrows thus producing retic- ulate ornament. Details of ornament not perfectly symmetrical on individuals and variable within populations. Discussion—This genus appears to be most closely related to the Middle Cambrian genus Ptychagnostus. Species of both genera have a preglabellar and post- axial median furrow, divided basal glabellar lobes, and a posteriorly tapered pygidial axis. A similar radial ornament is developed on the cephalon of many species in the subgenus Ptychagnostus (Ptychagnostus). (See Westergard, 1946, pl. 11, 12.) The principal distin- guishing features at the genus level are that species of Ptychagnostus nearly always have a subtriangular an- terior glabellar lobe, the radial ornament is not devel- oped on the pygidium, the kidney-shaped areas adjacent to the anterior glabellar lobe are not developed, and the posterior part of the axis of the pygidium is not subdivided. Glyptagnostus has been placed most recently in the Hastagnostidae (Howell, 1959, p. 178). However, the posteriorly tapered pygidial axis of Glyptagnostus and the postaxial median furrow are gross differences from Hastagnostus and a close relationship between the ge— nera seems unlikely. Westergard, using Agnostidae in a more expanded sense than it is used here, placed Glyptagnostus in this family (Westergard, 1947, p. 5). The posteriorly tapered sharp-pointed pygidial axis of Glyptagnostus is structurally distinct from the posteri- orly rounded axis of typical members of the Agnostidae (s. s.) and Glyptagnostus should probably be excluded from this family also. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY A reclassification of the agnostid trilobites is badly needed. Until such a reclassification is forthcoming, there is no satisfactory family to include Glyptagnostus although a monotypic suprageneric taxon, Glyptag- nostinae, was proposed by Kobayashi (1939, p. 154). The genus should probably ultimately be grouped with Ptychagnostus, Triplagnostus, Gom'agnostus, and perhaps Doryagnostus, all of which have a structurally similar pygidial axis. Species are recognized within the genus principally on details of development of the axis of the pygidium and on major variations in ornament. Glyptagnostus stolidotus Gpik Plate 2, figures 2, 5 Glyptagnostus stolz’dotus Cpik, 1961, p. 432, pl. 70, figs. 1-8, text fig. 16. Diagnosis—Member of Glyptagnostus with cephalon and pygidium having primarily radial ornament. Pygidium with length of b3 less than one-half length of b2 (fig. 11). Discussion—The ornament of this species illustrates the basic radial pattern of the ornament of the genus that is often obscured by cross furrows in G. reticulatus (Angelin). G. stolidotus differs consistently from all specimens of G. reticulatus by the characters given in the diagnosis. Although there is variation between individuals in details of ornament, there are no char- acters yet observed that would permit consistent dis- tinction between the American and Australian forms of this species. Occurrence: Conasauga formation: USGS collns. 2886—00 (20 cephala and pygidia), 2887—00 (1 pygidium), 2888-00 (2 cephala, 8 pygidia), 2889—00 (1 cephalon, 1 pygidium); USNM loc. 90b (2 cephala, 2 pygidia), Woodstock, Ala. Figured specimens: USNM USG S colln. Part 143140a ____________ 2886—00 ______ Cephalon. 143140b ____________ 2886—00 ______ Pygidium. Glyptagnostus reticulatus (Angelin) Agnostus reticulatus Angelin, 1851, p. 8, pl. 6, fig. 10. Tullberg, 1880, p. 23, pl. 1, figs. 12 a, b. Brogger, 1882, p. 57, pl. 1, figs. 11a, b. Lake, 1906, p. 8, pl. 1, fig. 11. Wester- gard, 1922, p. 117, 193, pl. 1, figs. 11, 12. Poulsen, 1923, p. 23, pl. 1, fig. 3. Ptychagnostus reticulatus (Angelin) Jaekel, 1909, p. 400, fig. 19. Pseudagnostus reticulatus (Angelin) Butts, 1926, pl. 9, fig. 5. Glyptagnostus reticulatus (Angelin) Kobayashi, 1938, p. 170, pl. 16, fig. 34. Westergard, 1947, p. 5, pl. 1, figs, 1—9. Kobayashi, 1949, p. 1—6, pl. 1, figs. 1—15. Henningsmoen, 1958, p. 184, pl. 5, fig. 17. Opik, 1961, p. 430, pl. 70, figs. 9411, text fig. 15. Agnostus nodosus Belt, 1867, p. 295, pl. 12, figs. 3a, b. Glyptagnostus toreuma Whitehouse 1936, ). 102, pl. 9, figs. 17—20. Glyptagnostus angelini Resser, 1938, p. 49 pl. 10, fig. 23. F—17 GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES ,ngaegfiafie E 33339 23 Ho unwfinoflgwc Enaosfigmlfi H555 mmmhwifidi Z. .3 1&0ng 84 omA 0N4 OH; 004 8.0 8.0 0nd omd omd OYO _ 1 _ _ _ _ _ _ _ fl _ fl _ 60-8% .:__8 mama 2.01m N m3”. Euz woduNflmmdnmfl x30 §w§$8m mgmeggwafiw Aumw do. Ezmzv 2.01m N 8.03 mmnz Sdu§$dn§ we €835 .sgswga ac 3533033 §wm§§w§u~w .\ ow \wg %% «a + «WV 8 «00 0 OIVMmN .OOIHNVN 62:0”v meme 2.0!6 N owdu. Enz mod + Nnfiond ”ma: cfiwmcfl $3338sz «.3333»? gwwgagagw _ _ _ _ _ H _ _ ofio 0N6 omd ovd omd cod 0nd owd omd OHA DNA omé SHBlEWIWIW NI ‘Eq HJ.E)N3'I F—18 Diagnosis.——Members of Glyptagnostus with basic pat- tern of radial furrows connected by irregular pattern of cross furrows, producing reticulate ornament on cephalic cheeks and pleural fields of pygidium. Pygidium with length of b3 greater than one-half length of b2. Lateral parts of b2, and also b1 and b3 on stratigraphically younger specimens, marked off as side lobes by shallow longitudinal furrows. These furrows extend forward on some specimens to outline narrow lateral lobes on second axial segment. Glyptagnostus reticulatus reticulatus (Angelin) Plate 2, figures 1, 3, 8 Diagnosis—Members of Glyptagnostus reticulatus with length of b3 on axis of pygidium averaging more than 0.7 length of b2. Posterior part of axis generally with well-developed longitudinal furrows outlining lateral lobes. Ornament of cephalon and pygidium generally strongly reticulate, but not nodose. Glyptagnostus reticulatus angelini (Resser) Plate 2, figures 4, 6, 7, 11 Diagnosis—Members of Glyptagnostus reticulatus with length of b3 on axis of pygidium averaging less than 0.7 length of b2. Longitudinal furrows outlining lateral lobes on axis of pygidium poorly developed. Degree of reticulation on cephalon and pygidium variable. Discussion—Specimens are included in G. reticulatus that show an apparent progressive phylogenetic change with time. Older forms have pygidia with a relatively short b3, poorly developed longitudinal furrows out- lining lateral lobes on the posterior part of the axis, and variable development of the reticulate ornament on both cephalon and pygidum. Younger forms have pygidia with a relatively long b3 (fig. 11), well-developed longitudinal furrows outlining lateral lobes on each division of the posterior part of the axis, and strongly developed reticulate ornament on all specimens in a population. On specimens with the longest b3, the furrows outlining the lateral lobes converge slightly forward and give it an elongate pentagonal outline. On specimens with shorter b3, the furrows outlining lateral lobes are subparallel. Because of complete stratigraphic gradation between the morphologic extremes,» these extremes are considered here to repre- sent only subspecies of G. reticulatus. Resser (1938, p. 49) proposed the name G. angelini for specimens now included in the older subspecies herein designated as G. reticulatus angelim'. The younger subspecies, which agrees most nearly in details of morphology with the Scandinavian types of G. reticulatus, is G. reticula— tus reticulatus. A third subspecies, G. reticulatus SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY nodulosus Westergard, has been recognized only in Sweden and the island of Bornholm (Westergard, 1947, p. 7). Specimens in the United States referable to G. reticu— latus angelim' are found principally in association with species of the acrotretid brachiopod Opisthotreta Palmer in beds that are correlated (table 1) with the Grepice- phalus zone. Specimens referable to G. reticulatus reticulatus are found principally in association with species of the acrotretid brachiopod Angulotrem Palmer, in beds correlated with the Aphelaspis zone. Occurrence: Lower part of the Dunderberg formation: USGS collns. 2466—00 (2 cephala, 3 pygidia), 2476—00 (6 cephala, 6 pygidia), 2477—CO (2 cephala, 10 pygidia), 2479—00 (1 cephalon), 2480—00 (1 cephalon), 3020—00 (1 cephalon), 3039— CO (1 cephalon), 3043—00 (1 cephalon), 3045—00 (1 cephalon), 3046—00 (1 cephalon), 3049—00 (1 pygidium), 3050—00 (2 cephala, 1 pygidium), 3053~CO (1 cephalon), McGill, Nev.; 2471—00 (11 cephala, 10 pygidia), 2534—00 (9 cephala, 6 pygidia), 2535—00 (1 cephalon, 3 pygidia), Cherry Creek, Nev. Uppermost beds of Swarbrick formation: USGS collns. 3057— CO (1 cephalon), 3058—CO (2 pygidia), 3059400 (10 cephala, 6 pygidia), Tybo, Nev. Unnamed formations: USGS collns. 3106—CO (1 cephalon), Hamilton district, Nevada; 1370—00 (2 cephala), Hot Springs Range, Nev.; Henderson—Markham No. 1 well, depth 2,858 ft (1 cephalon), 2,860 ft (1 pygidium), Lake County, Tenn. Woods Hollow shale: Boulder BM—4 (3 cephala, 1 pygidium), Marathon region, Texas. Conasauga formation: USGS colln. 2875—00 (4 cephala, 2 pygidia), 2876—00 (2 cephala, 2 pygidia), 2878—CO=USNM localities 89d, 91 (>20 cephala and pygidia), 2879—00 (1 cephalon), Cedar Bluff, Ala. Figured specimens: USNM USG'S colln. Part 143139a ____________ 2471—CO ______ Cephalon. 143139b ............ 2471—CO ______ Pygidium. 143141 _____________ 2476—00 ______ Association slab. 143142a ____________ 2466—00 ______ Cephalon. 143142b ____________ 2466~CO ______ Pygidium. 143143 _____________ Wilson boulder Cephalon. BM~4. Family PSEUDAGNOSTIDAE Whitehouse Diagnosis.—Agnostid trilobites with cephalon having glabella slightly tapered forward, frontal lobe generally differentiated from remainder of glabella. Basal lobes simple. Preglabellar median furrow either present or absent. Pygidium with posterior part of axis expanded to form pseudolobe reaching to posterior border furrow. Border always present, with or without marginal spines. Median axial node developed on second segment, may be extended onto pseudolobe. Terminal node present adjacent to border furrow on axial line. Discussion.~—Trilobites with these characters are known only from beds of Late Cambrian and possibly earliest Ordovician age. At least four genera can be assigned to the family: Pseudagnostus J aekel (synonyms Rhaptagnostus Whitehouse and possibly Pseudorhap- GLYPTA GN OS T US AND ASSOCIATED TRILOBITES tagnostus Lermontova), Pseudagnostina n. gen., Mach- aimgnostus Harrington and Leanza, and Acmarhachis Resser (synonyms Oedorhachis Resser, Cyclagnostus Lermontova). The principal distinguishing characters of the genera are in the development of the pseudolobe on the pygidium and the preglabellar median furrow on the cephalon. All species of Pseudagnostus have a com- plete preglabellar median furrow and have only the anterior part of the pseudolobe defined by accessory furrows. Species of Pseudagnostz'na lack a preglabellar median furrow and have the pseudolobe undefined. In Acmarhachis the preglabellar median furrow is present, absent, or only partly developed in front of the glabella, and in all species the pseudolobe is fully defined. These three genera are represented by many species at various stratigraphic levels in Upper Cambrian rocks of all continents. A monographic study of this family is needed to evaluate the species. It is quite possible that such study will show that some species are of particular importance for intercontinental correlation of Upper Cambrian rocks. Machaimgnostus is a monotypic genus that is re- ported to have the anterior part of the axis of the pygid- ium trisegmented rather than bisegmented as in all other genera of the family (Harrington and Leanza, 1957, p. 63). It is possible that the third pair of axial muscle scars which in some specimens are moderately well developed on the anterior part of the pseudolobe (Palmer, 1955, pl. 20, figs. 11, 14) has been interpreted as an extra segment. If this can be confirmed, then there is little difference between Machaimgnostus and Pseudagnostus, and they might be considered synonymous. Genus ACMARHACHIS Resser Acmarhachis Resser, 1938, p. 47. Howell, 1959, p. 173. Oedorhachis Resser, 1938, p. 49. Shimer and Shrock, 1944, p. 601. Howell, 1959, p. 185. Cyclagnostus Lermontova, 1940, p. 126. Howell, 1959. p. 182. Type species.—Acmarhachis typicalis Resser, 1938, p. 47, pl. 10, figs. 4, 5. Diagnosis.—-—Pseudagnostidae with cephalon having well—defined bilobed glabella. Preglabellar median furrow present or absent; generally absent; if present, shallower than axial furrOWS. Border well defined. Basal glabellar lobes simple. Pygidium with axis well defined, constricted at second segment; pseudolobe well defined, expanded and extended to border furrow at axial line. Median axial node on second segment only. Border well defined, with pair of short posterolateral marginal spines. Discussion—This distinctive genus differs from other pseudagnostid genera by having a well-defined bilobed glabella and by generally lacking a preglabellar median F~19 furrow on the cephalon. The pygidium is structurally like Pseudagnostis but has the pseudolobe fully defined and touching the border furrow only near the axial line. Four species, Acmarhachis typicalis Resser, Oedor- hachis ulrichi Resser (=0. typicalis Resser), Cyclag- nostus elegans Lermontova, and Homagnostus acutus Kobayashi, are here assigned to this genus. The first three are the type species of their respective genera; Acmarhachis is retained as the oldest name for the taxon. In the most recent classification of the agnostid trilobites (Howell, 1959), these genera are placed in three families, Agnostidae, Pseudagnostidae, and Spinag- nostidae. However, except for details of the pygidial border, development of some furrows, and ornament, the species are structurally alike. Each has an ex- panded pseudolobe reaching to the border furrow of the pygidium and bearing a terminal node, features here considered characteristic of the Pseudagnostidae. Species of Acmarhachis in common with those of other genera of the Pseudagnostidae can only be cer- tainly identified if pygidia are present. Most cephala are not distinguishable from those of agnostids such as Peronopsis and some species of Homagnostus. Acmarhachis, as here recognized, occurs in beds of early Late Cambrian age in Eastern and Western United States and in Siberia. Oedorhachis ulrichz' Resser differs from A; typicalis principally by lacking any trace of a preglabellar median furrow and by having the median part of the pygidial border thickened and slightly raised. It does not differ in any significant respect from Oedorhachis typicalis Resser. Although 0. typicalis is described in the para- graph preceding the description of 0. ulm'cln' (Resser, 1938, p. 50), ulm'chi is chosen as the name of the species to avoid the problem of homonomy resulting from A. typicalis and 0. typicalis being considered congeneric. The other four species of Oedorhachis described by Resser (1938, p. 50, 51) differ in pygidial and cephalic features from Acmarhachis and are assigned as follows: 0. tennesseensis and 0. greendalensis belong to Pseu; dagnostus; 0. meslem' is tentatively assigned to Proagnos- tus; and 0. boltonensis belongs to Pseudagnostina. (See p. F—21.) Cyclagnostus elegans Lermontova differs from A. typi— calis principally by having a complete, although shallow, preglabellar median furrow and apparently by having a smooth rather than a granular or roughened surface on the pygidium. Homagnostus acutus Kobayashi, recently assigned questionably to Pseudagnostus (Palmer, 1960a, p. 62), is more properly assignable to Acmarhachis in light of review of the Appalachian agnostids. It differs from A. typicalis principally because the axial segments of the pygidium are less well defined and because the fur- F—20 row between the first and second axial segments are incomplete. Acmarhachis acutus (Kobayashi) Plate 2, figures 14, 15 Homagnostus acutus Kobayashi, 1938, p. 172, pl. 16, figs. 18-22. Pseudagnostus? acutus (Kobayashi) Palmer, 160a, p. 62, pl. 4, figs. 10—12. . Diagnosis—Members of Acmarhachis with cephalon having preglabellar median furrow present, absent, or only partly developed; if present, generally shallow. Pygidium with first segment of axis poorly defined on outer surface of exoskeleton, somewhat better defined on exfoliated specimens. Furrow between first and second axial segments not crossing axis. Discussion—This species differs from A. elegans (Lermontova) and A. typicalis Resser by not having the furrow between the first and second axial segments cross the axial lobe. It difiers from A. ulrichi (Resser) by lacking the thickened upturned median part of the pygidial border. Occurrence: Lower part of Dunderberg formation: USGS‘ collns. 2471—CO (3 cephala, 4 pygidia), 2534—00 (6 cephala, 2 pygidia), 2535—CO (1 pygidium), Cherry Creek, Nev. Figured specimens: USNM No. USGS colln. Part 143146a ____________ 2471—CO ______ Cephalon. 143146b ____________ 2471—CO ______ Pygidium. Acmarhachis typicalis Resser Plate 2, figures 12, 13, 17 Acmarhachis typicalis Resser, 1938, p. 47, pl. 10, figs 4-, 5. Diagnosis—Members of Acmarlmchis with cephalon having preglabellar median furrow developed only as short projection forward from anterior end of glabella. Pygidium with first two segments of axis well defined by complete transverse furrows; axis markedly con- stricted at second segment; pseudolobe pointed poste- riorly. Surface of exoskeleton faintly roughened. Discussion—The species differs from A. acutus (Kobayashi) by having the first two segments of the axis well defined. It difi'ers from A. ulrichi Resser and A. elegans (Lermontova) by having the pseudolobe dis— tinctly pointed posteriorly. The median part of the border of the pygidium is also not thickened and upturned as in A. ulrichi. One pygidium is USGS colln. 2475—00 has a prominent pair of longitudinal curved furrows within the pseudo- lobe (pl. 2, fig. 17). These are considered here to represent an exaggerated development of the muscle scar areas seen on many species of the Pseudagnostidae. Occurrence: Upper part of Hamburg limestone, USGS colln. 2475—00 (2 cephala, 4 pygidia), McGill, Nev. Figured specimens: USNM No. USG’S colln. Part 143 145a ____________ 2475—00 ______ Cephalon. 143145b ____________ 2475-00- ____ Pygidia. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Acmarhachis? sp. Plate 2, figures 9, 10 An agnostid possibly assignable to Acmarhachis occurs with Glyptagnostus stolidotus Opik at Woodstock, Ala. It has a slender parallel-sided glabella with a well- defined subquadrate frontal lobe and no preglabellar median furrow. The pygidium has a long well-defined axis, narrowest at the second axial segment and with an expanded pseudolobe(?). A prominent median node is present on the second axial segment. Unfortunately, the median part of the border of both pygidia in the collection is damaged, so that the relation of the end of the axis to the border furrow cannot certainly be deter- mined. On the illustrated specimen there seems to be a shallow depression between the end of the axis and the border furrow. If they are in contact this species is referable without question to Acmarhachis. If they are not in contact the generic placement is not clear, although the species would have most in common with species of Homagnostus. The glabellar shape and long, expanded posterior part of the axis distinguish this species from other described American agnostids. Occurrence: Conasauga formation, USGS colln. 2886—00 (5 cephala, 2 pygidia), Woodstock, Ala. Figured specimens: USNM No. USGS colln. Part 143 144a ____________ 2886—0 0 ______ Cephalon. 143144b ____________ 2886—00 ______ Pygidium. Genus PSEUDAGNOSTINA n. gen. Type species.—~Pseudagnostina contracta n. sp. Diagnosis.4—Pseudagn0stidae With cephalon having well-defined border. Glabella bilobed; frontal lobe well defined. Median axial node situated at about midlength of posterior glabellar lobe. Preglabellar median furrow absent. Pygidium with only anterior third of axis defined by straight axial furrows. Pseudolobe undefined. Trans- verse furrows lacking. Median axial node and median terminal node present. Border well defined, with pair of posterolateral marginal spines. Description.—Cephalon moderately to strongly con— vex transversely, moderately convex longitudinally. Outline subsemicircular; sides straight, expanded slightly forward from straight posterior margin; anterior margin broadly rounded. Border well defined by broad shallow border furrow. Glabella moderately narrow, tapered forward, distinctly bilobed; anterior lobe smaller than posterior lobe, strongly rounded anteriorly; posterior lobe without trace of lateral fur- rows; median node low, elongate, at about midlength of posterior lobe. Basal lobes well defined, subtri- angular, undivided. Cheeks confluent in front of glabella, without trace of preglabellar median furrow. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES Pygidium moderately to strongly convex trans- versely and longitudinally. Outline subsemicircular; sides straight, subparallel; posterior margin broadly rounded; short posterolateral marginal spines present. Border well defined by shallow marginal furrow. Axis defined by straight axial furrows only adjacent to first two segments. Pseudolobe not defined. Transverse furrows not apparent. Median node low, round, located at position of second axial segment. Terminal node present adjacent to border. Discussion—The combination of a Peronopsis-like cephalon and Pseudagnostus-like pygidium is a new combination for the Pseudagnostidae. Isolated cephala cannot be distinguished from cephala of Peronopsis or some species of Homagnostus and Geragnostus. Pygidia may be recognized by lack of transverse furrows and lack of definition of the pseudolobe, combined with the well-defined short dorsal furrows adjacent to the anterior axial segments. The pygidium described as “Agnostus” nordicus Lochman (1940, p. 23) may representanother species of Pseudagnostina. This has been combined, as Pseu- dagnostus? nordicus (Lochman) (Palmer, 1954, p. 721), with a cephalon originally described as “Agnostus” valentinus Lochman, which has an unusually small anterior glabellar lobe and a deep preglabellar median furrow. The association of cephalon and pygidium as parts of the same trilobite is based on rather weak cir- cumstantial evidence and the possibility that it might be erroneous should be kept in mind. Oedorhachis boltonensis Resser from the Cedam'a zone in northwestern Virginia is represented by cephala and pygidia that conform in all respects to Pseu- dagnostina. Pseudagnostina contracts. n. sp. Plate 2, figures 18—20, 22—25 Diagnosis.—Me1nbers 0f Pseudagnostina with axial furrows on pygidium slightly convergent. Discussion—The only described agnostids that are referable to Pseudagnost’ina are Oedorhachis boltonensis Resser and possibly Pseudagnostus? nordicus (Lochman) discussed under genus Pseudagnostina n. gen. Pygidia of both species differ from P. contracta by having the dorsal furrows parallel or slightly divergent posteriorly. One pygidium (pl. 2, fig. 18) of P. contracta has a row of paired pits converging posteriorly on the pseudolobe. This feature has been observed on specimens of several pseudagnostid species, and its value as a criterion for taxonomic difierentiation (as in Rhaptagnostus White- house, 1936, and Pseudorkaptagnostus Lermontova, 1940) is suspect. Occurrence: Conasauga formation: USGS coll. 2888—00 (4 .cephala, 9 pygidia), Woodstock, Ala. Upper part of Hamburg 618549 0 - 62 — 3 F—21 limestone: USGS collns. 2474—C0 (1 cephalon, 2 pygidia), 2475—00 (5 cephala, 2 pygidia), McGill, Nev.; USGS colln. 3056—00 (3 cephala, 2 pygidia), Cherry Creek Nev. Figured specimens : USNM USG S colln. Part 143149a ________ 2888—00-- _ _ Pygidium. 143149b ________ 2888—00 _ _ _ _ Cephalon. 143 150 _________ 2888—00 - _ - _ holotype pygidium. 143151 _________ 2475—00-- _ _ Cephalon. 143152 _________ 2474—00 __ _ _ Pygidium. 143153a ________ 3056—00---- Cephalon. 143153b ________ 3056—CO__ _ _ Pygidium. Genus PSEUDAGNOSTUS Jaekel Pseudagnostus Jaekel, 1909, p. 400. Kobayashi, 1935, p. 107; 1937, p. 451; 1939, p. 157. Shimer and Shrock, 1944, p. 601. Shaw, 1951, p. 112. Palmer, 1954, p. 719; 1955, p. 93; 1960a p. 61. Plethagnostus Clark, 1923, p. 124; 1924, p. 16. Rhaptagnostus Whitehouse, 1936, p. 97. Type species.—Agnostus cyclopyqe Tullberg, 1880 (p. 26). Diagnosis.—Pseudagnostidae with cephalon having bilobed glabella and preglabellar median furrow. Basal glabellar lobes simple. Pygidium with anterior third of axis defined by sub- parallel axial furrows; pseudolobe moderately well to poorly defined by accessory furrows that may disappear posterolaterally so that pseudolobe merges with pleural fields. Marginal spines present or absent. Pseudagnostus spp. Plate 2, figures 16, 21, 26 Specimens assignable to Pseudagnostus have been found in collections with species of Glyptagnostus in Alabama and Nevada. These specimens could be assigned to Pseudagnostus communis (Hall and Whit- field), as that species is presently recognized, but it is apparent from the large collection of undescribed agnostid material available to the writer that present means of determining species of Pseudagnostus are inadequate. Until a review of all Upper Cambrian specimens of Pseudagnostus is undertaken meaningful species identification cannot be given. Occurrence: Conasauga formation: USGS collns. 2875—00 (2 pygidia), 2876—00 (2 pygidia); Cedar Bluff, Ala. Uppermost beds of Swarbrick formation: USGS collns. 3057—00 (23 cephala, 27 pygidia), 3058—00 (5 cephala, 5 pygidia), 3059—00 (6 cephala, 5 pygidia); Tybo, Nev. Unnamed formation: USGS collns. 1370—00 (6 cephala, 2 pygidia); Hot Springs Range, Nev. Figured specimens: USNM Na. USGS colln. Part 143147a ____________ 3058—C0 ______ Cephalon. 143147b ____________ 3058—00 ______ Pygidium. 143148 _____________ 287 5—00 ______ Pygidium. F-22 Order PTYCHOPARIIDA Swinnerton Family ASAPHISCIDAE Raymond Subfamily BLOUNTIINAE Lochman Genus BLOUNTIA Walcott Blountia Walcott, 1916, p. 396. Shimer and Shrock, 1944, p. 619. Palmer, 1954, p. 721. Howell, 1959, p. 292. Homodictya Raymond, 1937, p. 1114. Rasetti, 1946, p. 454. Shaw, 1952, p. 473. Howell, 1959, p. 292. Type species.——Blountia mimula Walcott, 1916 (p. 399, pl. 61, figs. 4—40). Diagnosis.—Asaphiscidae with cranidium moderately to strongly convex transversely and longitudinally, moderately to strongly. rounded anteriorly. Glabella poorly defined on outer surface, well defined on mold by narrow shallow axial furrows, tapered forward, strongly rounded anteriorly; lateral furrows lacking. Occipital ring very short (sagittal), generally not dif- ferentiated from glabella on outer surface. Frontal area with distinct border separated from brim by slight to sharp change in slope; brim generally continues longitudinal convexity of glabella; length (sagittal) of border equal to or slightly more than that of brim. Fixed cheeks downsloping, generally continuing trans- verse convexity of glabella, width about one-half or less basal glabellar width. Palpebral lobes poorly defined, situated anterior to glabellar midlength. Pos- terior limbs broad, sharply pointed. Posterior border furrow broad, shallow, curved forward near tip of limb. Course of anterior section of facial sutures nearly straight forward from palpebral lobes to border. Ad— axial course and ventral sutures not known. Course of posterior section divergent convex behind palpebral lobe. Free check with border broad, moderately well de- fined, width about equal to width of ocular platform. Eye small, not differentiated by infraocular ring from ocular platform. Genal spine broad based, rapidly tapered, short, sharp pointed. Thorax composed of 7 to 9 segments. Each segment with elevated axis and obscure pleural furrow. Tips of segments slender, sharp pointed, laterally directed. Pygidium subsemicircular to subparabolic in outline, gently to moderately convex transversely and longi- tudinally. Axis long, slender, poorly defined on outer surface reaching to or across border furrow; mold shows seven or more well—defined ring furrows of nearly con- stant depth. Border slightly narrower than greatest width of pleural field, moderately to poorly defined, generally downsloping. Pleural fields on mold with numerous shallow pleural and interpleural furrows of comparable depth. Surfaces of all parts smooth. Discussion—This genus differs only slightly from SHORTER OONTRIBUTION S TO GENERAL GEOLOGY Mnym'llia (Rasetti, 1956, p. 1267), principally by hav- ing the cranidium moderately to strongly convex trans- versely, rather than flat or gently convex transversely. Blountia bristolensis Resser Plate 3, figures 33, 34 Blountia bristolensis Resser, 1938, p. 65, pl. 12, fig. 24. Maryvillia bristolensis Resser, 1938, p. 87, pl. 12, fig. 38. Maryvillia hybrida Resser [part], 1942, p. 71, pl. 13, figs. 14, 15. Blountia m'xonensis Lochman, 1944, p. 43, pl. 4, figs. 7—12. Palmer, 1954, p. 722, pl. 79, fig. 4. Diagnosis—Members of Blountia with cranidium having anterior margin evenly rounded. Width of fixed cheek about one-third basal glabellar width. Length of border (sagittal) slightly greater than length of brim. Pygidium subsemicircular in outline, border furrow moderately well defined at anterolateral margin, becoming shallow towards rear, interrupted by end of axis that extends onto border. Discussion—The specimens of Blountia at Cedar Bluff, Ala. although somewhat crushed, do not differ in any significant feature from either B. m'xonensis Lochman, or B. bristolensis Resser, here considered synonyms. Marym'llia bristolensis Resser, represented by cranidia only, was placed in Blountia by Rasetti (1956, p. 1268). It comes from the same collection as Blountz'a bristol- ensis Resser, represented by a pygidium, and they are here considered parts of the same species. Both cranidium and pygidium are indistinguishable from B. nixonensis Lochman. B. bristolensis is perhaps the youngest species of Blountia. The principal difference from older species is the moderately well developed border furrow that is interrupted by the end of the axis on the pygidium. Occurrence: Conasauga formation, USGS colln. 2879—00 (6 cranidia, 11 pygidia), Cedar Bluff, Ala. Figured specimens: USNM USG S calln. Part 143167a _________ 2879—00 _____ Cranidium. 143167b _________ 2879—00 _____ Pygidium. Family CATILLICEPHALIDAE Raymond Genus PEMPHIGASPIS Hall Pemphigaspis Hall, 1863, p. 221. Palmer, 1951, p. 763. 1951, p. 302. Rasetti, 1945, p. 603. Hallaspis Raasch and Lochman, 1943, p. 230. Tasch, Type species.—Pemphigaspis bullata Hall, 1863 (p. 221, pl. 5a, figs. 3—5). Discussion—This genus has been fully described in an earlier paper (Palmer, 1951), and the following specimens discussed provide no new information. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES Pemphigaspis sp. Plate 3, figure 32 Two fragmentary cranidia associated with Glypta- gnostus stolidotus Opik have the anteriorly expanded glabella, Y-shaped posterior glabellar furrows and granular outer surface characteristic of specimens of Pemphigaspis. Neither specimen is well enough pre- served to determine its specific identity. Occurrence: Conasauga formation, USGS colln. 2886—00 (2 cranidia), Woodstock, Ala. Figured specimen: USNM 143166, USGS colln. 2886—00, cranidium. Family CEDARIIDAE Lochman The Cedariidae are here considered as a family rather than reduced to a subfamily as recently done by Lochman (1959, p. 301). If structure of the glabella, is to mean anything in suprageneric classification, as it seems, for example, in the Pterocephaliidae and Parabolinoididae (Lochman, 1959, p. 256, 272), then. the differences between Cedaria and the type genera (Llanoaspis and Raymondina) of the other two sub- families grouped by Lochman with Cedariinae are at least family differences. A revised diagnosis of the Cedariidae would require examination of many genera not otherwise included in this study and is beyond the scope of this paper. Some of the characters that seem to be important for members of the family are the obscurely furrowed, anteriorly tapered glabella that is strongly rounded in front, combined With the divergent anterior sections of the facial sutures, and the broad posterior limbs with the border furrow curving forward distally. Genus CARINAMALA n. gen Type species.—Carinamala longispina, n. sp., text figure 12. Diagnosis—Cedariid? trilobites with cranidium hav- ing prominent well-defined anteriorly tapered unfur— rowed glabella connected to broad concave border by shalIOW median furrow that crosses narrow brim. Border furrow narrow, shallow. Fixed cheek broad, With prominent raised eye ridge and extremely prom- inent raised palpebral lobe. Upper surface of pal- pebral lobe with shallow furrow or several pits. Anterior section of facial suture nearly vertical in front of palpebral lobe; posterior course nearly per- pendicular to axial line immediately behind palpebral lobe. Free cheek with short (exsagittal) ocular platform merged with large eye surface and separated from border by broad shallow border furrow. Inner edge of cheek with concave notch and spur produced by F—23 FIGURE 12.—Partial reconstruction of Carinamala lanaispma n. sp., about X 6. posterior section of' facial suture. Outer edge of cheek curved abruptly in to base of slender genal spine. Rostral plate subtriangular in outline. Hypostome and thorax not known. Pygidium subsemicircular in outline, with prominent narrow axis reaching nearly to posterior margin, bearing shallow ring furrows. Pleural regions with shallow pleural furrows. Border poorly defined, concave. Posterior margin evenly rounded. Description.—Small- to medium-sized opisthoparian trilobites (estimated maximum length 45 mm). Cranidium with all parts well defined. Glabella moder- ately convex transversely, gently convex longitudinally, tapered forward, strongly rounded in front, well defined by broad shallow axial furrow of nearly constant depth; lateral glabellar furrows not apparent. Occipital furrow narrow. Occipital ring with or without median node or spine. Frontal area composed of broad gently concave border with inner margin well defined by shallow narrow border furrow that has slight median posterior inbend and bears single row of pits each With central granule. Brim gently downsloping, with median depression in front of glabella, narrower than border; broadens laterally, becomes vertical adjacent to facial sutures. Fixed cheeks slightly upsloping, gently convex; Width, exclusive of palpebral lobe about two—thirds basal glabellar width. Eye ridge prominent, narrow, gently curved posterolaterally, raised above cheek surface, continuous with palpebral lobe. Palpe- bral lobe extremely elevated, upper surface with groove or several pits. Posterior limbs broad; tip rounded. Posterior border furrow moderately deep, broad. F—24 Anterior section of facial suture nearly vertical from palpebral lobe to marginal furrow, curved strongly across nearly horizontal border and continued along border to cut anterior margin near axial line, then curved strongly backward to cut posterior margin of doublure at nearly right angle. Rostral suture sub- marginal. Posterior section of facial suture nearly perpendicular to axial line behind palpebral lobe, curved broadly backward and inward to cut posterior margin near base of genal spine. Rostral plate subtriangular in outline with concave sides and narrow posterior stem. Free cheek with narrow (exsagittal) ocular platform. Border broad, separated from ocular platform by broad shallow border furrow. Outer margin of border curved abruptly inward to base of genal spine. Inner margin behind eye with concave notch and spur developed from posterior section of facial suture. Genal spine slender, in side View raised above edge of border of cheek. Eye surface faceted only in upper half. Infraocular ring not present. Hypostome and thorax not known. Pygidium subsemicircular in outline with length about four-tenths width. Axis narrower than pleura] lobes, reaching nearly to posterior margin; 3 or 4 shallow ring furrows apparent behind articulating furrow. Pleural regions gently convex with 1 or 2 shallow pleural furrows and poorly defined broad concave border having raised evenly curved margin. Discussion—This genus is tentatively placed in the Cedariidae because of the shape of its glabella, the broad posterior limb on the cranidium, the lack of an infraocular ring and the presence of the curved notch and spur on the free cheek. Its most distinguish- ing characteristics are the prominent ocular ridges and .palpebral lobes on the cranidium, and the constriction of the border of the free cheek at the base of the genal spine. A specifically indeterminate cranidium of Carinamala (pl. 3, fig. 3) is associated with Glyptagnostus stolidotus Opik at Woodstock, Ala. Specimens belonging to Carinamala are also present in collections from the Snake and Schell Creek Ranges and at McGill and Cherry Creek, Nev. Only the type species, 0. longispina n. sp., from a bed 6 inches below the lowest occurrence of Glyptagnos— tus reticulatus at McGill, N ev., and the specimen from Woodstock, Ala., are here described. 0. longispina is also present at Cherry Creek, Nev. The Snake Range specimens, which are associated with Cedaria prolifica Walcott, represent another species, and the specimens from the Schell Creek Range are specifically indeterminate. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Carinamala longispina n. sp. Plate 3, figures 1, 2, 4-7; text figure 12 Diagnosis.—Member of Carinamala with cranidium having ocular ridge and palpebral lobe continuous, undifferentiated, increasing distally in height above surface of fixed cheek, flat on top. Palpebral lobe with 2 or 3 shallow pits in upper surface. Occipital ring with short median spine directed upward from surface and then curved abruptly backward in a nearly hori- zontal plane. Free cheek with long slender genal spine. Pygidium known only for this species, its characters same as for genus. Discussion—This species differs from the unnamed species associated with Cedaria prolifica in the Snake Range by having the palpebral lobe and ocular ridge undifferentiated, pits rather than a groove in the upper surface of the palpebral lobe, an occipital spine, and longer genal spines. The surface of the eye is unusual in that facets are apparent only on the upper part. The number of facets per square millimeter is about 750, the same as in- Cedaria, but the eye surface on a Carinamala cheek has only about half as many facets as the eye surface on a Cedaria cheek of comparable size. Occurrence: Upper beds of the Hamburg limestone: USGS collns. 2474—00 (37 cranidia, 10 free cheeks, 16 pygidia), 2475—CO (cranidia, 15 free cheeks, 41 pygidia), McGill, Nev. 2470—00 (1 cranidium, 3 pygidia), Cherry Creek, Nev. Figured specimens: USNM No. USGS colln. Part 143 154 _________ 2475—00 _ _ _ _ Holotype cranidium. 1431559. ________ 2475—CO__ _ _ Cranidium. 143155b, c ______ 2475—00-- __ Pygidia. 143155d, e ______ 2475—00---- Free checks. Carinamala sp. Plate 3, figure 3 Discussion—A single poorly preserved cranidium at Woodstock, Ala., associated with Kingstonia alabamen- sis Resser and Glyptagnostus stolidotus Opik has the broad border, preglabellar median furrow, nearly ver- tical anterior course of the facial suture, broad fixed cheek and glabellar shape characteristic of Carinamala. Lack of knowledge of the structure of the palpebral lobe, occipital ring, and posterior limb prevents its specific determination. Occurrence: USNM loc. 90b (1 cranidium), Woodstock, Ala. Figured specimen: USNM 143156, USNM loc. 90b, cranidium. Genus CEDARIA Walcott Cedaria Walcott, 1924, p. 55; 1925, p. 78. Shimer and Shrock, 1944. p. 621. Palmer, 1954, p. 726. Type species.—Oedaria prolifica Walcott, 1925 (p. 79, pl. 17, figs. 18—21). GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES Diagnosis.—Subiso‘pygous pseudoproparian trilobites with cranidium having well-defined border, unfurrowed glabella tapered and strongly rounded anteriorly, nar- row fixed cheeks, and generally distally expanded posterior limbs with border furrow curved forward at tip. Free cheek with short (exsagittal) ocular platform and with curved notch and spur on inner margin at base of slender genal spine. Pygidium subsemicircular in outline, nearly as large as cephalon with broad or narrow border of nearly constant width, pleural field crossed by three or more pleural furrows, axis promi— nent, narrow, reaching to inner part of border. Description. Subisopygous trilobites with cephalon subsemicircular in outline, gently to moderately convex transversely and longitudinally; genal spines long, slender. Cranidium with glabella well defined, tapered forward, strongly rounded anteriorly, unfurrowed. Occipital furrow narrow. Occipital ring generally with- out ornament. Frontal area divided into distinct brim and border by shallow border furrow. Border generally of nearly constant breadth, length (sagittal) subequal to or less than that of brim. Fixed cheeks narrow, hori- zontal or slightly upsloping; width, exclusive of palpe- bral lobes between % and % basal glabellar width. Palpebral lobes flaplike, situated opposite or slightly posterior to midlength. Posterior limb generally broad— ened outward, less commonly slightly tapered, distal end strongly rounded; border furrow curved forward near tip to cut anterior margin of limb. Anterior section of facial sutures directed forward and outward from palpebral lobes to marginal furrow, then turned sharply inward across border to smooth juncture with anterior margin before reaching axial line. Connective sutures curved towards axial line. Rostral plate present on all species; shape ranges from broad (transverse) with concave sides to subtriangular. Posterior section of facial suture directed outward at nearly right angles to axial line until across marginal furrow, then curved strongly backward along border to cut posterior margin of cephalon near base of genal spine. Free check with short generally subparallel sided ocular platform. Border generally well defined, with broad curved notch and spur on inner margin at base of slender genal spine. Inner margin of doublure beneath border of cranidium with row of tubercules opposed to pits generally developed in marginal furrow of cra- nidium. Anterior tip of doublure convex towards axial line. Visual surface of eye holochroal, not separated from ocular platform by infraocular ring. Hypostome parallel sided, strongly rounded pos— teriorly, strongly convex transversely, moderately to strongly convex longitudinally. Middle body not F—25 divided. Lateral furrows and lateral border distinct. No posterior border. Thorax composed of 6 or 7 segments. Axis well defined. Pleural region of each segment with broad marginal furrow extended into short slender sharp pleural tip. Pygidium subsemicircular in outline, nearly as large as cephalon. Axis prominent, with four or more ring furrows apparent behind articulating furrow; reaches to inner part of border. Pleural region gently convex, moderately to poorly divided into broad or narrow, flat or slightly concave border of nearly constant width and subtriangular pleural field crossed by three or more pleural furrows of constant depth. Posterior margin smooth. Surface of all parts of exoskeleton generally smooth, rarely granular. Pits not present. Discussion—This genus presently includes eight distinct species: 0. eurycheilos Palmer, 0. gaspensis Rasetti, O. milleri Resser, C. minor (Walcott), C. nironia Lochman and Duncan, 0. prolifica Walcott, O. tennesseensis Walcott, and O. woosteri (Whitfield). Two species, 0. milleri Deland and Shaw (not Resser) and 0. buttsi Resser do not belong to the genus. A third species, C. puelcluma Rusconi is inadequately described and unfigured and cannot be evaluated. Cedaria milleri Deland and Shaw is represented by two cranidia that differ most conspicuously from any species of Oedaria by the presence of a short subequally divided frontal area and a relatively large glabella. The cranidia are more likely referable to an undeter- mined species of the Crepicephalidae. Cedaria buttsi Resser has the gross aspect of a species of Oedaria but lacks a defined cephalic border, has palpebral lobes placed anterior to the glabellar mid- length, and has laterally tapered posterior limbs that do not reach to the lateral cephalic border. None of these are characteristic features of Cedaria and indicate that “O.” buttsi is not referable to Cedaria although it may represent an undescribed genus of the Cedariidae. Cedaria woosteri (Whitfield) is an atypical species with the anterior and posterior branches of the facial sutures fused, so that-the free cheek is in two parts: the eye surface and the border bearing the genal spine. Perhaps this species should also be removed from Cedaria. Except for the granular surface of the cranidium of O. milleri Resser and a nearly identical cranidium assigned to 0. nixonia by Lochman and Duncan (1944, pl. 10, fig. 5), all known Cedaria cranidia are smooth. The rostral plate has been developed for 0. minor (Walcott) and O. prolifica (pl. 6, figs. 13, 14). The considerable range in structure of the rostral plate ‘—26 within the genus indicates that it has potential value as an additional specific character. The hypostome is certainly known only for Cedaria minor (Walcott). Cedaria prolifica Walcott Plate 3, figures 9, 10, 14—16, 20; plate 6, figure 14 Cedaria prolifica Walcott, 1925, p. 79, pl. 17, figs. 18—21. Resser, 1938, p. 67, pl. 11, figs. 1, 2, 6, 7. Shimer and Shrock, 1944, pl. 264, figs. 3—7. Cedaria afl. C. gaspensis Rasetti, Wilson, 1954, p. 269, pl. 24, fig. 20. Diagnosis.———Members of Cedaria with cranidium having moderately to strongly flared frontal area. Border convex, well defined by border furrow bearing many close-spaced pits each with small central granule; length (saggital) on large specimens (greater than 4 mm in cranidial length) about equal to length of brim; length on small specimens generally slightly less than length of brim. Length of frontal area slightly greater than one-half length of glabella. Fixed cheeks up- sloping. Palpebral lobes strongly arcuate, slightly elevated above surface of fixed cheeks, situated at or slightly posterior to midlength of glabella. Posterior limbs slightly expanded outward from base of palpebral lobe to about midlength of limb, then tapered to tip with broadly curved anterior outline. Occipital ring with small median node near anterior edge. Free cheek with anterior and posterior edges of ocular platform subparallel or slightly divergent outward. Rostral plate subtriangular in outline (pl. 6, fig. 14). Pygidium with number of ring furrows on axis pos- terior to articulating furrow ranging from 5 or 6 on specimens about 3 mm in length to 7 or 8 on specimens greater than 10 mm in length. Number of pleural furrows ranges from 4 on specimens 3 mm in length to 5 or 6 on specimens greater than 10 mm in length. Length of border (exsagittal) about is to )4 length of pygidium. Discussion—This species is distinguished from all other species of the genus on the features given above. The most similar species are C. gaspensis Rasetti, 0. minor (Walcott), and O. brevifrons n. sp. that seem to form a species group characterized by a convex cranidial border, only slightly expanded posterior limbs, and a narrow pygidial border. Pygidia of C. gaspensis have at least two more axial and pleural segments than comparable sized specimens of other species in the group. 0. minor has less divergent anterior sections of the facial sutures than 0. prolifica and a transverse subquadrate rostral plate instead of a subtriangular rostral plate (cf. pl. 6, figs. 13, 14). 0. brem'frons has a considerably shorter frontal area than any of the other species in the group. It is perhaps significant SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY from a paleoecological viewpoint that all the species in this group come from the most seaward deposits of the Cedariu zone. 0. guspensis is from the western Gaspé Peninsula; 0. prol'ifica is found in Alabama, the Marathon region, Texas, and the Snake Range, Nev.; 0. minor is from the House Range, Utah; and 0. brevifrons is from McGill, Nev. The specimens from Texas that Wilson (1954, p. 269) compared with O. gaspensis lack the distinctive number of pygidial segments of that species and conform in all features to 0. prolifica. Several free cheeks in USGS colln. 2888—00, from Woodstock, Ala., have the outer surface of the eye preserved showing the facets. The surface curves through an arc of about 180° and has about 750 facets per square millimeter. On a cephalon about 5 mm long, the estimated total number of facets on the eye is about 1,500. Exfoliated cranidia at both Woodstock and Cedar Blufl’, Ala, show that the posterior pair of glabellar muscle scars were quite large. This may be a useful additional feature in the systematics of these trilobites when more specimens showing the muscle scars have been examined. Occurrence: USGS colln. 2888—00 (11 cranidia, 4 free cheeks, 23 pygidia), Woodstock, Ala. Figured specimens: USNM Uses colln. Part 143159a, d, e ________ 2888—00 ______ Cranidia. 143159b, c __________ 2888—00 ______ Pygidia. 143159f _____________ 2888—00 ______ Free cheek. 143 1 96 _____________ 1 208-00 ______ Rostral plate. Cedaria brevifrons n. sp. Plate 3, figures 8, 11—13 Diagnosis.—Members of Cedaria with free cheeks and pygidium not distinguishable from 0. prolific-a. Crani- dium with length of frontal area about one-third length of glabella exclusive of occipital ring; length of border slightly greater than length of brim; fixed cheeks nearly horizontal. All other cranidial features as in 0. pro- lifica. Rostral plate not known. Discussion—The short frontal area is the most dis- tinctive character of this species. Its relations to other species of Cedaria are reviewed in the discussion of 0. prolifica. Occurrence: Uppermost beds of Hamburg limestone: USGS colln. 2475—00 (13 cranidia, 5 free cheeks, 41 pygidia), McGill, Nev.; USGS colln. 3056—00 (8 cranidia, 1 free cheek, 4 pygidia), Cherry Creek, Nev. Figured specimens: USNM No. USGS colln. Part 143 157 _________ 247 5—00 _ _ _ _ Holotype cranidium. 143158a ________ 2475—00 _ _ _ _ Free cheek. 143158b, c ______ 2475—CO____ Pygidia. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES Family CHEILOCEPHALIDAE Shaw Genus CHEILOCEPHALUS Berkey C’heilocephalus Berky, 1898, p. 290. Palmer, 1954, p. 757. Pseudolisam'a Kobayashi, 1935, p. 162. Shimer and Shrock, 1944, p. 621. The fragmentary material associated with Glyptag- nostus does not add any new information to the descrip- tion of the genus already given (Palmer, 1954). Cheilocephalus sp. Plate 3, figures 30, 31 Several incomplete cranidia from one collection and a pygidial fragment from another collection repreSent all the identified parts of Cheilocephalus so far found associated with Glyptagnostus. Two of the cranidia have the exoskeleton preserved. These have a dis- tinctive ornament of scattered small granules on all observed parts except the areas of the glabellar furrows on the glabella. Ornamented specimens of Cheilocephalus have pre- viously been known only from the Dunderberg'ia and Elm'ma zones, where specimens with a granular external surface of the exoskeleton have been reported (Wilson, 1951; Palmer, 1960a). The species of Cheilocephalus from the Aphelaspis zone have a smooth external crani— dial surface (Palmer, 1954). The specimens here illustrated differ from the younger specimens with similar ornament by having the granules smaller and more scattered on the cranidial surface, and by having a relatively broader and flatter cranidial border. The pygidium is only a fragment of the right pleural region showing the broad concave pygidial border crossed by pleural furrows, typical of the genus. Identification of these specimens below the genus level must await more material. Occurrence: Lower part of Dunderberg formation: USGS collns. 2534—00 (1 pygidium), 2535-00 (4 cranidia, 1 pygidium), Cherry Creek, Nev. Figured specimens: USNM 143165a, b, USGS colln. 2535—00 cranidia. Family CREPICEPHALIDAE Kobayashi Crepicephalidae Kobayashi, 1935, p. 275. Coosellidae Palmer, 1954, p. 727. The Crepicephalidae, as used in this paper, is the senior synonym of the Coosellidae as originally proposed and constituted (Palmer, 1954, p. 727). The rejection of Crepicephalidae and the proposal of Coosellidae for a group of related genera including Orepz'cephalus (Palmer, 1954) was intentionally illegal according to the rules of zoological nomenclature. It was done to emphasize the point that the content and concept of the Coosellidae (legally Crepicephalidae) had no re- semblance other than Orepicephalus to Kobayashi’s original content and concept of the Crepicephalidae. 618549 0 - 62 - 4 F—27 This has apparently created more confusion than clar- ity in the field of trilobite systematics as shown by the use of both Coosellidae and Crepicephalidae as distinct families in different superfamilies in the “Treatise on Invertebrate Paleontology” (Lochman, 1959, p. 248, 309). An attempt to formulate a rational approach to the composition of the family in trilobite classification has been made by the writer (Palmer, 1960a, p. 59). This states in essence that stratigraphy and paleogeography should play an- important supplementary role to mor- phology in attempts to determine relationships between trilobites. Related trilobites should not only share morphologic similarity but should also come from faunas where stratigraphy and paleogeography indi- cate a conceivable opportunity for continuous gene flow between the supposedly related forms. Neither stratigraphy nor paleogeography appear to have been considered as factors in the assignment of genera to the Crepicephalidae and Coosellidae in the Treatise. Until the content of these families can be reviewed, which is beyond the scope of this paper, the writer considers them to represent uncritical associations of, in large part, unrelated genera. Genus COOSIA Walcott Coosia Walcott, 1911, p. 94; 1913, p 210. Shimer and Shrock: 1944, p. 623. Palmer, 1954, p. 730. Lochman, 1959, p. 309. Type Species—Comic superba. Walcott, 1911 (p. 94, pl. 16, figs. 1, 1a). Diagnosis.—Crepicephalidae with cranidium having border generally longer than brim, poorly defined by broad shallow border furrow. Occipital furrow straight, narrow, of nearly constant depth. Free cheek with short genal spine, or with genal angle bluntly rounded. Border on anterior part about equal in Width to acular platform. Hypostome and rostral plate not known. Thorax with 12 segments. Pleural furrow of each segment situated close to anterior margin, extended from axial furrow about half length (transverse) of pleural region. Pygidium subsemicircular in outline, axis prominent, with three ring furrows generally apparent behind articulating furrow. Terminal part of axis merged posteriorly with border. Border broad, flat, or con- cave, not clearly differentiated from pleural field. Pleural field crossed by one or more shallow pleural furrows and, or some species, interpleural furrows also. Posterior margin evenly rounded or with slight median indentation. Discussion—This diagnosis is principally that given by the writer earlier (Palmer, 1954, p. 730) with the F—28 addition of information regarding the lack of genal spines in some species and deletion of the statement regarding the shortness of the pygidial axis, which is now known to be longer than half of the pygidial length in some species. Coosia longocula n. sp. Plate 3, figures 17—19, 21—24, 27—29 Diagnosis—Members of Coosia with cranidium hav— ing frontal area short, subequally divided into brim and border; length slightly more than three—eighths length of glabella. Fixed cheeks gently convex, horizontal; width about one—third basal glabellar.width. Palpebral lobes long, narrow, arcuate; midpoint situated slightly an- terior to glabellar midlength; depressed slightly below level of fixed cheek; length averaging slightly less than three-fourths length of glabella. Anterior section of facial suture diverging forward from palpebral lobe t0 border, then curved inward across border to cut anterior margin about midway between anterolateral cranidial corners and axial line; ventral course not known. External surface of exoskeleton roughened on cranidia as much as 7 mm in length, granular on at least some larger cranidia; terrace lines prominent on borders of all holaspid cranidia. Free cheek with broad well-defined border. Lateral and posterior border furrows shallow, of comparable depth, joined at genal angle. Genal spine absent, genal angle nearly a right angle. External surface of ocular platform granular; border with prominent terrace lines. Pygidium subsemicircular in outline; length slightly greater than one-half Width. Axis about one-half length of pygidium, bears three shallow straight ring furrows. Border broad, slightly concave, not clearly differentiated from pleural field. Pleural field crossed by 2 or 3 shallow pleural furrows. First interpleural furrow well developed, forms distinct pair with second pleural furrow. External surface of exoskeleton either smooth, except for terrace lines on outer part of border and poorly defined granules along sides of axis, or covered with moderately to poorly developed terrace lines. Discussion—The long palpebral lobes on the cranid- ium, combined with the short subequally divided frontal area; the lack of a genal spine on the free cheek; and the well-developed first interpleural-second pleural furrow pair on the pygidium distinguish this species from all others presently assigned to the genus. De- scribed species with generally similar cranidial and pygidial outlines are 0008730. connata (Walcott) and Coosia pernamagna Wilson. These species have pal- pebral lobes only about half the length of the glabella and considerably broader (exsagittal) posterior limbs on the cranidium. The pygidia either lack the well- SHORTER CONTRIBUTION S TO GENERAL GEOLOGY developed first interpleural-second pleural furrow pair (0. connata) or have the second interpleural furrow also developed (0. pernamagna). Several immature cranidia of 0. ongocula are present in USGS collns. 2475—00 and 3056—00 (pl. 3, fig. 24). These are characterized by a large low conical swelling on top of the glabella between the palpebral lobes, a depressed area across the brim on the axial line, and 2 or 3 large granules in an arcuate row paralleling the palpebral lobe on the fixed cheek. Although these features may be characteristic of O. longocula n. sp., it is possible that they are characteristic of immature specimens of other species of the Crepicephalidae, and they should be looked for in future collections of species in this family. Occurrence: Upper beds of Hamburg limestone: USGS colln. 2475—00 (6 cranidia, 2 cheeks, 4 pygidia), McGill, Nev.; USGS colln. 3056—00 (13 cranidia, 5 pygidia), Cherry Creek, Nev. Figured specimens: USNM USGS colln. Part 143 160 _________ 2475-00 _ _ _ _ Holotype cranidium. 14316151 ________ 2475—00--- _ Free cheek. 143161b, c, e____ 2475—00---- Pygidia. 143161d, f ______ 2475—00---- Cranidia. 143162a, b ______ 3056—00-- __ Cranidia. 1431620 ________ 3056—00- _ _ _ Pygidium. Coosia sp. Plate 3, figures 25, 26 A second species of Coos-ta is represented by pygidia that are relatively broader and have a longer axis and a narrower border than 0. longocula. A free cheek with a short genal spine and fragmentary cranidia that seem to have a relatively longer border than 0. longo— cula are associated with them. Because samples of both this species and 0. longocula are small and because specimens of both species are present in USGS colln. 2475—00, the possibility that all the specimens repre- sent a single species. cannot be completely eliminated. The free cheeks with genal spines are smaller than the specimens of 0. longocula that lack spines, and they lack a distinct granular ornament as do the smaller 0. longocula cranidia. This could be interpreted as indi- cating a loss of the genal spine during development. However, small pygidia having the characteristics of each species (pl. 3, figs. 25, 27, 28) indicate that the pygidial features are not related to differing ontogenet- ic stages. Furthermore, the diflerences may be popu- lation differences because USGS colln. 2474—00 contains only specimens of Coosia sp., and colln. 3056—00 contains only specimens of 0. longocula. Until more specimens of Coosia sp. are collected to determine the form of the cranidium and of larger free cheeks, the species cannot be adequately described or compared to known species, although the specimens GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES described above are tentatively considered to represent a species distinct from O. longocula. Occurrence: Upper beds of Hamburg limestone: USGS collns. 2474—00 (7 pygidia, 1 free cheek), 2475—00 (1 pygidium, 1 free cheek); McGill, Nev. Figured specimens: USNM USGS colln. Part 143163 _______________ 2474—00 _______ Pygidium. 143164 _______________ 2475—00 _______ Free cheek. Family KINGSTONIIDAE Kobayashi Genus KINGSTONIA Walcott Kingstom'a Walcott, 1924, p. 58; 1925, p. 103. Resser, 1936, p. 24. Shimer and Shrock, 1944, p. 627. Shaw, 1952, p. 471. Tasch, 1952, p. 859. Lochman 1953, p. 886. Palmer, 1954, p. 724. Ucebia Walcott, 1924, p. 60; 1925, p. 118. Type species—Kingstonia apion Walcott, 1925 (p. 103, pl. 16, figs. 27—28a). Discussion—This genus has been discussed in recent years by Shaw (1952), Tasch (1952), Lochman (1953), and Palmer (1954). Although there is difference of opinion about the advisability of recognizing subgenera within Kingstonia, there is general agreement that the small nearly featureless trilobites from rocks of Dres- bach age, with subhemispherical cranidia bearing bluntly rounded or pointed posterior limbs and with or without a narrow border, are congeneric. The speci- mens here discussed provide no new information on the subgeneric problem. Kingstonia alabamensis Resser Plate 6, figures 11, 12 Kingstonia alabamensis Resser, 1938, p. 84, pl. 12, fig. 8. Cranidia of this species are characterized by long pointed posterior limbs and a narrow border bearing terrace lines. A single almost completely exfoliated pygidium is also present in the type lot. It has a distinctly subtriangular outline, at least eight axial segments, and downsloping rather than depressed lateral parts to the pleural regions. Until the content of Kingstom'a can be thoroughly reviewed, which is beyond the scope of this paper, comparison of K. alabamensz's with other species in the genus will have little meaning. Occurrence: Conasauga formation: USNM loc. 90b (7 cranidia, l pygidium), Woodstock, Ala. Figured specimens: Holotype cranidium and associated pygi- dium, USNM 94939, USNM loc. 90b. Family LEIOSTEGIIDAE? Bradley Genus KOMASPIDELLA Kobayashi Komaspidelta Kobayashi, 1938, p. 174. Raasch and Lochman, 1943, p. 226. Lochman, 1959, p. 315 Type species—Agraulos? thea Walcott, 1890 (p. 277). F—29 Diagnosis—Small Leiostegiidae(?) with cranidium subtrapezoidal in outline, gently to moderately convex transversely and longitudinally, gently rounded ante- riorly. Glabella prominent, subparallel sided, bluntly to evenly rounded anteriorly, well defined by narrow axial and preglabellar furrows of constant depth. Glabellar furrows hardly apparent. Occipital furrow narrow, deep, of constant depth. Occipital ring short (sagittal) not noticeably tapered distally; low, poorly defined median node present. Frontal area short (sagittal), strongly convex, undivided; length less than one-tenth length of glabella. Fixed cheeks flat to moderately convex, horizontal or slightly downsloping; width, exclusive of palpebral lobes, less than half basal glabellar width. Palpebral lobes moderately to poorly defined, narrow, depressed slightly below sur- face of cheek, situated slightly posterior to glabellar midlength; length between }é and % length of glabella. Posterior limbs narrow, tapered slightly distally; posterior border furrow deep, narrow. Hypostome, rostral plate, free cheeks, and thoracic segments not known. Pygidium subtriangular in outline, moderately to strongly convex transversely and longitudinally. Axis well defined, prominent, tapered evenly backward, strongly rounded at posterior end, reaching nearly to posterior margin. Axial segments numerous, short, poorly defined except at anterior end of axis. Pleural regions downsloping near axis, depressed at lateral margins. Border, if present, narrow, poorly defined. Pleural fields smooth or crossed by shallow close spaced pleural and interpleural furrows of nearly equal depth. Posterior band of first pleural segment generally con- tinued across poorly defined border as low narrow ridge. Margin smooth. External surface of exoskeleton smooth or pitted. Discussion—The placement of this distinctive genus in the Leiostegiidae (Lochman, 1959) is only provision- ally accepted. Although Komaspidella conforms to the present diagnosis of the family, not enough is known of the morphology of the genus to ascertain adequately its relationship to the Early Ordovician genus Leio- stegium. No known American trilobite of Dresbach age can be confused with Kamasp'idella. The most similar genus is Atcktaspis (Lochman and Duncan, 1944) from the Crepicephalus zone in Montana; Atak- tasp’is, however, has a pygidium with a long terminal axial spine and a cranidium with a bluntly pointed anterior margin. In the redescription of Komaspidella (Raasch and Lochman, 1943, p. 226), the outer surface of the exo- skeleton was stated to be “probably granulated.” Because the external surface of K. occidentalis n. sp. is smooth, it was important to learn if ornament might F—30 be of value in the systematics of species of Komaspi- della. Collections of the two described species, K. thea (Walcott) and K. seeleyi (Walcott) in the US. National Museum, were examined and latex casts were made of cranidia and pygidia of both species, which are known only from sandstone molds. Several specimens of K. seeleyi showed a definite surface ornament of coarse shallow pits, but no granulation was apparent. The sand matrix around all known specimens of K. thea is too coarse to permit determination of the nature of the external surface. Granules on Lonchocephalus ehippewaensis Owen, known from siltstone preservation, are not apparent on specimens of this species associated with K. thea in a sandstone matrix. Thus, there is no present evidence for a granular surface of the exoskeleton for any species of Komaspidella. The principal characteristics for species discrimina— tion within Komaspidella seem to be the development of ring furrows, pleural and interpleural furrows on the pygidium, and presence or absence and degree of definition of a border on the pygidium. Glabellar shape and degree of convexity of the fixed cheeks of the crani- dium are less definitive supplemental characteristics. Komaspidella occidentalis n. sp. Plate 6, figures 6, 7 Diagnosis—Members of Komaspidella with cra- nidium having fixed cheeks nearly flat, slightly down— sloping. Pygidium with only one distinct ring furrow behind articulating furrow. Pleural fields with poorly developed pleural and interpleural furrows. Border present, poorly defined, crossed by narrow ridges of the posterior bands of the first two pleural segments. External surface of exoskeleton smooth. Discussion—This species differs from K. thea, (Walcott) and K. seeleyi (Walcott) by having less convex fixed cheeks and a slightly more slender glabella on the cranidium. The pygidium has 1 distinct ring furrow behind the articulating furrow, rather than 2 or more, and ridges from more than one posterior band of the anterior pleural segments of the pygidium crossing the border. The border is intermediate in definition between K. seeleyi, which has a well-defined border and K. thea which lacks a definite border. K. seeleyi also lacks any trace of pleural and interpleural furrows on the pleural fields. Komaspidella loperi (Resser), described as a species of Kingstom'a by Resser (1942, p. 50) is known only from pygidia. It differs from all of the species dis— cussed above by lacking a border and by lacking ring furrows posterior to the articulating furrow. Occurrence: Upper beds of Hamburg limestone: USGS collns. 2474—00 (1 cranidium, 3 pygidia), 2475—00 (2 cranidia, 6 pygidia), McGill, NeV.; USGS colln. 3056—CO (1 pygidium), Cherry Creek, Nev. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Figured specimens: USNM USGS colln. Part 143194 _________ 247 5—CO__ __ I-Iolotype pygidium. 143195 _________ 24 75—CO__ _ - Cranidium. Family MENOMONIIDAE Walcott Genus DEIRACEPHALUS Resser Deiracephalus Resser, 1935, p. 21. Asteraspis Kobayashi, 1935, p. 224. Description.—Cranidium subtrapezoidal in outline, moderately to strongly arched transversely and longi- tudinally; length as much as about 10 mm. Glabella prominent, tapered forward, bluntly rounded anteri- orly, well defined by axial and preglabellar furrows; length slightly more than half that of cranidium. Occipital ring generally with strong median spine, usually directed upward; however, a long axial glabellar spine may be present in place of the occipital spine. Frontal area divided into distinct brim and border; anterolateral corners depressed. Strong median ridge extends forward from preglabellar furrow, broadening anteriorly and merging with border. Brim wider than border. Fixed cheeks upsloping, breadth three-fourths or less basal glabellar width. Palpebral lobes small, situated opposite or slightly posterior to glabellar midlength, at highest point of fixed cheek. Posterior limbs about equal in length (transverse) to basal glabel- lar width, tapered to point. Posterior marginal furrow deep throughout length of posterior limb. External surface smooth or with 1 or 2 sizes of granules on all parts. Free cheeks, thorax, pygidium, rostral plate and hypostome unknown. Discussion—The discovery of the species described below has required modification of statements in the original generic diagnosis (Resser, 1935, p. 21) con- cerning structure of the occipital ring. Also, a free cheek in the type lot of D. aster (Walcott) cited by Resser (1935) for its faceted eye surface, does not fit the cranidium of this species and is probably not the cheek of a species of Deiracephalus. In the type lot of D. multisegmentus (Walcott), the nearly complete specimen figured by Walcott (1916, pl. 24, fig. 5a) for this species has palpebral lobes situated on elevated fixed cheeks, close to and opposite the anterior end of the glabella. This specimen probably represents a species of Densonella. The cranidium in figure 5 (Walcott, 1916) is properly referable to Deimcephalus. Deiracephalus unicornis n. sp. Plate 6, figures 1—4 Diagnosis.——Members of Deimcephalus with long strong backswept median spine developed from upper surface of glabella just in front of occipital furrow. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES Occipital ring narrow, without median spine. External surface of exoskeleton bears scattered small granules. Discussion—This remarkable species is represented only by imperfect cranidia. Nevertheless, the glabellar shape, upsloping fixed cheeks and indication of a median ridge on the brim of one specimen support the identification of the specimen as a species of Deird- cephalus. N 0 other species of the genus, and in fact, no other American Upper Cambrian trilobite has a strong spine developed from the top of the galbella in front of the occipital furrow. Since this description was prepared, many cranidia of this species have been observed in collections made by C. H. Kindle and H. B. Whittington from boulders in the Cow Head conglomerate, western Newfoundland. Two cranidia with the glabellar spine characteristic of this species but with a narrower glabella are present in USGS colln. 3056—00 associated with Oedcm'a brew]- rons n. sp. (pl. 6, fig. 4). Occurrence: Conasauga formation: USNM loc. 90b (1 cra- nidium), USGS colln. 2886—00 (2 cranidia), Woodstock, Ala. Figured specimen: USNM USGS colln. Part 143189 _________ 2886—CO _ _ _ _ Holotype cranidium. 143190 _________ 3056—CO___- Cranidium. Family PTERO CEPHALIIDAE Kobayashi Diagnosis.—Subisopygous opisthoparian ptycho- parioid trilobites with cephalon generally gently to moderately convex transversely and longitudinally. Glabella straight sided, tapered forward, bluntly rounded or truncate anteriorly. Axial furrows deeper than preglabellar furrow. Shallow fossulas developed on many species. Lateral glabellar furrows generally shallow or absent; when present, either straight or slightly bigeniculate. Occipital furrow generally pres- ent. Occipital ring of most species with median node ; median occipital spine rare. Frontal area generally divided into distinct brim and border. Width of palpe- bral area more than one-fourth basal glabellar width; eye ridges generally poorly developed. Palpebral lobes arcuate, situated opposite middle third of glabella. Posterior limbs slender, sharp pointed; posterior border furrow nearly straight. Anterior section of facial suture straight forward or slightly divergent from front of palpebral lobe to border, then curved inward to cut anterior margin more than one-half distance from anterolateral corners of cranid- ium to axial line. Rostral suture, when present, barely submarginal. Connective sutures convex towards axial line, joined to form median suture only in later members of family. Posterior section of facial suture invariably divergent sinuous, cuts posterior margin of cephalon adaxial to base of genal spine. F—3 1 Hypostome with poorly differentiated median body and posterior lobe. Lateral border generally well de— fined, narrow. Posterior border poorly defined or absent and, when present, narrow. Rostral plate, when present, subtrapezoidal to sub- triangular in outline, with concave sides (pl. 6, figs. 15—19). Free cheek with border generally well developed. Genal spine present, lateral margin continuous with margin of main part of check. Eye surface on all known specimens separated from ocular platform by infra- ocular ring. Thorax of 12 to 13 segments. Axis moderately to strongly convex transversely, generally prominent. Pygidium with prominent posteriorly tapered axis, moderately to strongly convex transversely and raised above pleural regions. Width of axis generally less than width of pleural region. Border generally poorly de- fined, on most specimens narrowed behind axis. Pleural field with pleural furrows, when developed, broader and deeper than interpleural furrows. Discussion—The arrangement of the trilobites grouped here in the Pterocephaliidae is in accordance with principles outlined earlier (Palmer, 1960a, p. 59). Differences in assignment of some genera from those given in Harrington and others (1959) result from restudy of the trilobites concerned and from new information about their morphology and, stratigraphic relationships. American trilobites sharing the char- acteristics given in the diagnosis are: ‘Aphelaspis Resser (synonyms Proaulacopleura Kobayashi, Labiostria Palmer), Blandicephalus Palmer, Oernuolim— bus Palmer, Listroa n. gen., Litocephalus Resser (syn- onym Pterocephalina Resser), Olenaspella Wilson, Pterocephalia Roemer, Pterocephalops Rasetti, Sig— mocheilus Palmer, and Taenora Palmer. Some foreign genera, particularly Eugonocare Whitehouse from Australia, Olentella Ivshin from Kazakhstan, Russia, and Nericz'a Westergard from the late Middle Cambrian of Sweden, seem to belong to this family. Maladioidella Endo from the Upper Cambrian of Manchuria has a cranidium characteristic of the Pterocephaliidae, but a pygidium atypical of the group and is questionably retained in the family. Pedinocephalus Ivshin, from the Upper Cambrian of Kasakhstan, Russia, has peculiar concave sides to the glabella but might also belong to the Pterocephaliidae. Six of the genera included in the Pterocephaliidae by Lochman (1959) are removed or retained in the family uncritically for reasons given below. »D’£kelocephalites Sun and Iranella Hupé could not be restudied and available illustrations and descriptions do not allbw proper evaluation of their characteristics. They appear similar to some Pterocephaliidae and are retained in F—32 the family with the understanding that until they can be critically restudied their family relationships are really uncertain. Kazelia Walcott and Resser is represented by distorted cranidia having a downsloping convex frontal area with a poorly defined border. This is structurally unlike any genera here retained in the Pterocephaliidae. The type species, K. speciosa Walcott and Resser, is too poorly preserved to be critically compared to other trilobites. Its position in a suprageneric classification is not at the moment satisfactorily determinable. Camamspis Ulrich and Resser and Camamspoides Frederickson are represented by nearly smooth cranidia, moderately convex transversely and longitudinally, with downsloping frontal area and fixed cheeks, posteriorly placed poorly defined palpebral lobes, and short posterior limbs. These characteristics are unlike those of any other Pterocephaliid genus, and these genera probably represent another family as yet undetermined. Dytremacephalus Palmer has a narrow convex border and glabellar shape suggestive more of the Elviniidae (Palmer, 1960a, p. 64), where it is tentatively placed, than the Pterocephaliidae. The family of trilobites most closely related to the Pterocephaliidae is the Olenidae. Olenus (s. s.) has many features in common with older genera of the Pterocephaliidae, particularly in the structure of the pygidium—cf. Olenaspella separate n. sp. with Olenus gibbosus (Wahlenberg) and 0. transversus Westergard. However, the totality of characters of the Olenidae, particularly with regard to the development of the glabellar furrows, shape of the glabella and size and position of the palpebral lobes, distinguish the Olenidae, which seem to be dominant in the early Upper Cambrian principally in the North Atlantic region, from the Pterocephaliidae, which dominate partly contempora- neous deposits on the southern and western margins of Cambrian North America. (Compare illustrations of Olenidae in Henningsmoen, 1957, with those of Pter— ocephaliidae, Palmer, 1960a, and this paper.) Subfamlly APHELASPIDINAE Palmer Diagnosis.——Pterocephaliid trilobites with border on cephalon commonly well defined, convex (sagittal); less commonly flat or slightly concave. Pygidium with border subequal in width or narrower than pleural field; always narrowest behind axis. Margin with or without spines. Discussion.—The diagnosis given above is modified slightly from that originally given (Palmer, 1960a, p. 80) to include Olenaspella Wilson from North America, Eugonocare Whitehouse from Australia, and Nericia Westergard from Sweden which have somewhat nar- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY rower pygidial borders than the genera previously included. At some later date it may be preferable to remove these genera to a separate subfamily, but aside from their pygidial features they agree fully with other genera in the Aphelaspidinae. As the subfamily now stands, it includes: Aphelaspis Resser, Eugonocare Whitehouse, Litocephalus Resser, Nericia Westergard, Olenaspella Wilson, and Tamara Palmer. Genus APHELASPIS Resser Shimer and Shrock, 1944, p. 619. Ivshin, 1956, p. 31. Lochman Aphelaspis Resser, 1935, p. 11. Palmer, 1954, p. 643. 1959, p. 256. Proaulacopleura Kobayashi, 1936, p. 93. Clevelandella Resser, 1938, p. 68. Labiostria Palmer, 1954, p. 750. Howell, 1959, p. 269. Lochman, 1959, p. 258. Type species.—Aphela,spis walcotti Resser, 1938 (p. 59, pl. 13, fig. 14). (See Palmer, 1953, p. 157, for discus- sion.) Diagnosis.—~Aphelaspidinae with border furrow on cranidium present or absent. Glabella generally with- out well defined lateral furrows. Free cheek with lateral and posterior border furrows, when present, joined at genal angle, extended short distance onto base of genal spine. Thorax with 13 segments. Pygidium transverse subovate in outline. Axis with 1 to 5 ring furrows posterior to articulating furrow. Pleural regions with pleural furrows hardly apparent on most specimens. Border poorly defined, narrowest at axial line, broadens laterally. Posterior margin smooth, evenly curved or slightly angular at posterolateral corners. Description—Small- to medium-sized aphelaspinid trilobites (greatest length about 40 mm). Cranidium with glabella straight sided, tapered forward, bluntly rounded or truncate anteriorly ; lateral glabellar furrows generally shallow, straight, obscure. Occipital furrow shallow, always present across axial line. Occipital ring with small median node or spine. Frontal area divided into brim and border. Border furrow present or absent. Length of border variable. Fixed cheeks horizontal or slightly upsloping; width about one-half or less basal glabellar width; palpebral lobes moderately to poorly defined by shallow arcuate palpebral furrow, situated about opposite midlength of glabella; eye ridge generally low, poorly defined. Posterior limbs long, narrow, tapered to sharp points; posterior border furrow moderately deep. Free cheek with lateral and posterior border furrows, when present, joined at genal angle and extended onto long, slender genal spine. Anterior section of facial sutures slightly divergent forward from palpebral lobes to border furrow, then curved sharply inward across border to cut anterior mar— GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES gin about two—thirds distance from anterolateral crani- dial corners to axial line. Connective sutures curved towards axial line but cut margin of doublure before reaching axial line, outlining subtriangular to subtrape- zoidal concave-sided rostal plate. Posterior section of facial sutures divergent sinuous. Hypostome without distinctive generic character- istics. Thorax with 12 or 13 segments; axis narrower than pleural lobes; pleural tips of each segment short, sharp. Pygidium transversely subovate in outline with pos- terior margin smoothly curved or slightly angular posterolaterally, with or without median inbend. Axis prominent, tapered posteriorly, reaches to inner edge of poorly defined border that is narrowest on axial line; 1 to 5 ring furrows apparent behind articulating furrow. Pleural regions with shallow, generally obscure pleural furrows. Discussion.——From study of abundant material of early Aphelaspidinae from Nevada, it has become increasingly apparent that the characteristics of Aphe- laspis, Labiostria, and Proaulacopleum overlap suffi- ciently to prevent satisfactory recognition of three distinct taxa. The classification adopted here groups together in Aphelaspis all Aphelaspidinae with simple pygidia that lack either marginal spines or a median notch. Labiostm'a and Proaulacopleum are considered subjective synonyms of Aphelaspis. Species are defin- able on characteristics of the border furrow of the cephalon, structure of the free cheek, development of ring furrows on the axis of the pygidium, and details of length of the cephalic border and pygidial shape. Clevelandella Resser, although represented only by molds of cranidia in shale, is most likely a synonym of Aphelaspis. Not enough is known of the type species, Saratogia ammo Walcott, to define it or to compare it adequately with other species of Aphelaspis. The genus as defined above includes 10 described American species: Aphelaspis walcotti Resser (synonym A. hamblenensis Resser), A. quadrata Resser (syno- nym A. lama, Resser(?)-only cranidia known), A. simu- lans Resser, A. haguei (Hall and Whitfield), A. buttsi (Kobayashi), A. constricta Palmer, A. conveximarginatus (Palmer), A. longifrons Palmer, A. spinosus Palmer, and A. brcchyphasis n. sp. Aphelaspis tumifrons Resser, previously considered a distinct species of Aphelaspis (Palmer, 1954, p. 744), differs from all other aphelaspid trilobites by having anteriorly placed poorly defined palpebral lobes. It probably represents a new genus related to the Housiidae. Aphelaspid cranidia lacking a border furrow are at present found only among species of Aphelaspis. Cra- nidia of species of Aphelaspis that have a border furrow F—33 cannot be consistently distinguished from those of Litocephalus and Olenaspella in the absence of associated pygidia. Aphelaspis brachyphasis n. sp. Plate 4, figures 1—19 Diagnosis—Members of Aphelaspis with cranidium having a length of frontal area about six-tenths length of glabella exclusive of occipital ring. Border slightly downsloping, flat or very gently convex; length (sagit- tal) variable, generally between )6 and )4 length (sagittal) of brim. Border furrow hardly apparent. Palpebral lobe hardly defined by palpebral furrow. Free cheek with broad-based genal spine tapered rapidly to sharp point. Pygidium transversely subovate in outline with sharply rounded lateral margins and slight median indentation behind axis. Axis well defined, bearing 1 0r 2 distinct ring furrows posterior to articulating furrow. A much shallower additional ring furrow apparent on some specimens. Border poorly defined, variable in width from )4 to )6 that of pleural region. Discussion—This species is represented by abundant silicified specimens of all parts in USGS colln. 2466—00, as well as many limestone specimens. One of the most unusual features is the variability in width of the dou- blure of the pygidium (pl. 4, figs. 6—10, 16, 17). Speci- mens with the widest doublure (pl. 4, figs. 9, 10) have a broad slightly concave border. Specimens with the narrowest doublure (pl. 4, figs. 6, 7) have a relatively narrow, slightly downsloping border. In a small sample these differencies might be thought to be specific; how- ever, a complete series of specimens showing gradual changes in the breadth of the doublure between the two extremes is present in the silicified sample. The gra- dational series in one size class rules out the possibility that this is a dimorphic character. The full range of variation among pygidia of all sizes, rules out the pos- sibility that this is an ontogenetic character. The variation seems to be merely a more striking example than usual of intraspecific variability. A. brachyphasis is most similar to A. walcotti Resser from which it differs primarily by having a consistently shorter frontal area. More than 30 cranidia covering all holaspid sizes in the type lot of A. walcotti and in the silicified sample of A. brachyphasis were compared for this character. Regressions for length of frontal area against length of glabella for both species (fig. 13) show the difference to be significant. Although this could be a geographic difference, the Nevada specimens are apparently older than the Virginia specimens (table 1), and the populations are here considered to represent different species. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY F—34 .% d flaggfiin .V BE ammmom $83.3 ”Emgvcavw we $2 33 one he EBSM go 532 8 33 ESE «o flung we nomtaafiool.m~ "392% 95523.5. z_ .8: Sdmfio no 1525 86 8d 03 oo.m or...“ 84V om.m oo.m 8N cod 8; I, lllII ___._«________________‘______—A___~____E_1_‘____d‘__«__ 8.0 u >m mod H; wwn z NN.o+on.lo. 00.69% .c:8 mam: dm .: 3§§§§S wfiwfimfimi mfionxm \ 8.0”. an 2 mmdnwwwduu 30H .92 Ezw: hwmmwm £8333 mfimgmfiaw _.___________~_~____¥__,~_W._F_H_O~__E___V___k._____ I l [Illlll 1 1 l I ill 004 cm; CON OmN oo.m om.m ooé omgv 09m SHEILEIWITIIW NI ‘8) VEHV 'lViNOHj :IO HiSNI-I'l GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES A cranidium, free cheek, and pygidium from the type lot of A. walcotti Resser are illustrated (pl. 4, figs. 23, 28, 33) for comparison with A. brachyphasis. Occurrence: Lower part of Dunderberg formation: USGS collns. 2466—00, 2477—00, 2478—00, 2479—00, 2480—00, 3020—00, 3041—00, 3043—00, 3044—00, 3045—00, 3046—00, 3049—00, 3050—00, 3051—00, 3052—00, 3053—00, 3054—00, 3055—00 (all collections except 2477—00, 3040—00, and 3051—00 have more than 20 specimens), McGill, Nev. USGS colln. 1374—00 (more than 20 specimens), Hot Springs Range, Nev. Figured specimens: USNM USG'S colln. Part 143 168 ________ 2466—00 _ _ _ _ Holotype cranidium. 143169a _______ 2466—00--- _ Cranidium. 143169b _______ 2466—00--- _ Free cheek. 1431690, (1 _____ 2466—00 _ - _ - Thoracic segments. 143169e-i ______ 2466—00 _ _ - _ Pygidia. 143169j, k _____ 2466—00-- -_ Hypostomes. 143170a _______ 2478—00---- Free cheek. 143 170b _______ 2478—00 _ _ _ _ Cranidium. 1431700 _______ 2478-00-- _ _ Pygidium. 143 171 ________ 2479—00 _ _ _ _ Thorax and p ygidium. 143 172a _______ 3055—00 _ _ _ _ Cranidium. 143172b, c _____ 3055—CO____ Pygidia. Aphelaspis buttsi Kobayashi Plate 4, figures 23, 26, 31, 32 Olenus cf. 0. truncatus Butts, 1926, p. 77, pl. 9, figs. 6, 7. Proaulacopleura buttsi Kobayashi, 1936, p. 93, pl. 15, fig. 6. Resser, 1938, p. 95, pl. 16, fig. 18. Diagnosis—Members of Aphelaspis with cephalon bearing long slender genal spines reaching nearly to posterior end of thorax on largest specimens; length from point where posterior section of facial suture cuts cephalic margin to tip of genal spine twice or more length of posterior section of facial suture. Eye ridges directed laterally at right angle to axial line. Posterior pair of lateral glabellar furrows moderately well im- pressed, straight, inclined posteriorly. Border furrow evenly curved. Free cheek with lateral and posterior border furrows barely extended onto genal spine. Thorax with 13 segments, each with short sharp post'erolaterally directed pleural spines. Pygidium with length slightly less than half width. Three ring furrows present on axis posterior to articulat- ing furrow. Pleural fields with 3 or 4 shallow pleural furrows, and shallow pleural grooves between first, second, and sometimes third pleural segments. Fur- rows and grooves do not extend onto border. Border narrow, breadth one-sixth or less breadth of pleural region. Discussion—The short broad pygidium with a nar- row border, the long genal spines, and the moderately well defined cranidial border and glabellar furrows are the most distinctive characters of this species. F—35 It has the narrowest pygidial border of any species assigned to Aphelaspis Several complete individuals from Cedar Bluff, Ala, show the form of the rostral plate for this species (pl. 6, fig. 15), which is mainly like that determined for Aphelaspis by reconstructing the cephalic doublure using well—preserved free cheeks (Palmer, 1960a, fig. 8e, p. 64). Preparation of cranidia and free cheeks of Olenus gibbosus Wahlenberg from Westergotland, Sweden, shows that this species had a rostral plate comparable to that of Aphelaspis buttsi. Occurrence: Lowermost beds of Dunderberg formation: USGS colln. 2476—00 (19 cranidia, 8 free cheeks, 18 pygidia), McGill, Nev. Conasauga formation: USGS collns. 2875—00 (1 complete specimen, 4 cranidia, 1 free cheek, 5 pygidia), 2876—00 (6 cephala, 1 free cheek), USGS colln. 2878—00 *USNM 100. 910 (30 specimens showing all parts), Cedar Bluff Ala. Figured specimens: l USNM USGS colln. l Part 143176a- _ __ 2476—00 ________ Cra idium. 143176b _ _ _ _ 2476—00 ________ Pygi ium. 1431760- _ _ - 2476—00 ________ Free cheek. 143197 _____ USNM 100. 910- - Complete individual. Aphelaspis subditus n. sp. Plate 4, figures 20—22, 25 Diagnosis—Members of Aphelaspis with cranidium having lateral glabellar furrows lacking on outer surface of exoskeleton. Eye ridges directed laterally nearly at right angles to axial line. Border furrow present, evenly curved. Length of border between 1/2 and % length of brim (sagittal). Free cheek with lateral and posterior border furrows well defined, joined at genal angle, hardly extended onto genal spine. Genal spine long, slender, reaching to about fifth thoracic segment. Thorax with 12 segments. Pleural tips curved slightly, pointed, directed posterolaterally. Pygidium with 2 or 3 ring furrows on axis posterior to articulating furrow. Border barely defined, narrow, horizontal or slightly downsloping; breadth % to % that of pleural region. Pleural fields without distinct pleural furrows or with first pair moderately developed. Posterior margin with slight median indentation. Discussion.——This species differs from A. buttsi (Kobayashi) by having both glabellar and pygidial furrows much less well developed, shorter genal spines, and a relatively broader less well defined pygidial border. It differs from A. brachyphasis n. sp. by having a well-defined border furrow on the cranidium and free cheeks, longer and more slender genal spines, and generally one more ring furrow on the axis of the pygidium. Occurrence: Lower part of Dunderberg formation: USGS collns. 2471—00 (8 cranidia, 4 pygidia), 2534-00 (2 cranidia, F—36 2 pygidia), 2535—CO (20 specimens), Cherry Creek, Nev. Up- permost beds of Swarbrick formation: USGS collns. 3057-C0, 3058—CO, 3059—CO (each with > 20 specimens), Tybo, Nev. Figured specimens: USNM USG S colln. Part 143173 _____ 2535—00 ________ Holotype cranidium. 143174a- _ __ 2535—CO ________ Pygidium. 143174b- ___ 2535—00 ________ Cranidium. 143175 _____ Mount Hamilton Complete specimen. district. Aphelaspis sp. undet. Plate 4, figures 27, 29 Cranidia and pygidia associated with Blountia bristo- lensis Resser at Cedar Bluff, Ala., represent a species of Aphelaspis with a border furrow on the cranidium. The specimens are crushed, so that accurate specific determination is not possible. However, the fixed cheeks appear narrower, and the palpebral lobes appear somewhat more posteriorly placed than on A. buttsi. The pygidium appears to have a slightly wider and less well defined border. The cranidia resemble A. subditus n. sp. more closely than A. buttsi in structure of the fixed cheeks, but the pygidia have much better defined axial and pleural furrows than A. subditus. The specimens are illus— trated here for comparison with other Aphelaspis species. Occurrence: Conasauga formation, 2879-00 (12 cranidia, 3 free cheeks, 4 pygidia), Cedar Bluff, Ala. Figured specimens: USNM No. USGS colln. Part 143177a ____________ 2879—00 ______ Cranidium. 143177b ____________ 2879—00 ______ Pygidium. Genus OLENASPELLA Wilson Olenaspella Wilson, 1956, p. 1344. Type species.—Pambolinella? evansi Kobayashi, 1936 (p. 92, pl. 15, figs. 7, 8, 10). Diagnosis.wAphelaspidinae with cephalon having border well defined by narrow border furrow. Free cheek with lateral and posterior marginal furrows joined at genal angle, extended slightly onto base of genal spine. Pygidium transversely subovate to subsemi— circular in outline, with axis prominent, generally bear— ing three or more ring furrows posterior to articulating furrow. Pleural fields flat or gently convex transversely with 3 or 4 broad sha110w pleural furrows apparent. Interpleural grooves may be present between first, second, and third pleural segments. Border narrow, poorly defined; margin bears 1 to 3 pairs of slender posteriorly directed spines, anteriormost pair always present, developed from first pygidial segment. Description—Small- to medium-sized opisthoparian ptychoparioid trilobites (estimated maximum length SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY about 60 mm) with cephalon subsemicircular in outline, bearing distinct slender genal spines. Cranidium gently to moderately convex transversely and longitudinally. Outline, exclusive of posterior limbs, subquadrate, width between facial sutures at palperbral lobes about equal to length. Glabella tapered forward slightly, truncate anteriorly, gently convex longitudinally, moderately convex trans- versely; sides straight or slightly bowed outward. Axial furrow shallow, distinct, of nearly constant depth, or shallowed slightly at contact with eye ridge. Two pairs of shallow nearly straight oblique lateral glabellar furrows present; posterior pair most distinct, deepest towards axial line. Occipital furrow well defined, shal- low across axial line, deepest between axial line and axial furrow, not connected to axial furrow. Occipital ring without ornament or with low median node. Frontal area with well—defined brim and border. Border flat or gently to moderately convex (sagittal). Width (sagittal) about one-half or less that of brim. Border furrow shallow to moderately deep, of constant depth. Brim gently arched (sagittal). Fixed cheeks horizontal or gently upsloping; width (excluding palpebral lobes) between )6 and )4 basal glabellar width. Palpebral lobes prominent, arcuate, moderately well defined by shallow arcuate palpebral furrow; length on mature specimens from a, to about }4 length of glabella. Eye ridge barely apparent on most specimens, extending across cheek at nearly right angle to axial line. Posterior limbs narrow, tapered to sharp point. Pos— terior border furrow well defined, moderately deep. Posterior margin straight near glabella, angled slightly backward beyond point where tip of limb begins to slope downward. Posterior section of facial sutures divergent sinuous; anterior section divergent straight from palpebral lobe to border furrow, then curved abruptly toward axial line and continued straight across border to cut anterior margin at slight angle about four-fifths of distance from lateral corner of cranidium to axial line. Connective sutures converge posteriorly to cut posterior margin of doublure near axial line. Rostral suture straight, nearly marginal. Rostral plate subtrapezoidal in outline, narrowing posteriorly, with concave sides. Hypostome moderately to strongly convex trans— versely and longitudinally. Anterior margin nearly straight near axial line, abruptly curved back to anterior wing. Anterior border concave (sagittal). Middle body not divided into anterior and posterior lobes. Middle furrow apparent only adjacent to lateral furrow. Anterior wings slender, tapered to sharply rounded tips with single prominent wing process shown by dimple GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES in outer surface. Lateral border well defined by lateral furrow. N o posterior marginal furrow or border. Posterior wings prominent, directed nearly vertically, tapered to sharp point. Doublure hardly present at axial line along posterior margin. Free cheek with lateral margin gently to moderately curved, merged imperceptibly with margin of genal spine. Genal spine slender, tapered to sharp point. Lateral and posterior border furrows moderately well defined, connected and extended for short distance onto base of genal spine, nearer to inner than outer margins of spine. Inner spine angle greater than 90°. Anterior projection of cheek long, slender; doublure broadest opposite point where facial suture reaches anterior margin, then tapered to a sharply rounded point along inner margin. Thorax of 12 or 13 segments, length and width about equal; axis narrower than pleural regions. Pleural furrow distinct, not extended onto pleural spine. Pygidium with axis well defined, tapered posteriorly; 'profile flat or slightly upturned at posterior end. Length of axis generally more than eight-tenths length of pygidium. Articulating furrow and 2 to 4 ring furrows generally distinct, extending across axis; 1 or 2 incomplete additional ring furrows sometimes apparent. Outline of articulating half ring generally present on first axial ring. Pleural regions flat or gently arched transversely; width equal to or as much as about 1% times broader than width of axis. Two, or more com- monly 3 or 4, broad, shallow pleural furrows apparent, abruptly curved backward distally. Interpleural fur- rows may be apparent between first, second, and third pleural segments. Border narrow, poorly defined; width one-fourth or less that of pleural region. Margin bears one or more pairs of posteriorly directed spines, outer pair generally longest. Marginal spines always devel- oped from first pygidial segment. Doublure narrow. External surfaces of all parts of exoskeleton smooth finely pitted or finely granular. Discussion—The most distinctive features of the cephalon of trilobites of this genus are the narrow well- defined border, the moderately broad fixed cheeks with moderately long palpebral lobes, and the nearly straight posterior glabellar furrows. The pygidium, which ap- pears to be more distinctive than the cephalon, is characterized by its narrow border bearing 1 to 3 pairs of marginal spines, the presence, generally, of three or more ring furrows behind the articulating furrow on the axis, the general presence of an interpleural groove between the first and second pleural segments, and the axial lobe profile that is either flat or slightly turned up at the end. Two other aphelaspid genera with pygidial spines are known: an unnamed genus (p. F—40) has pygidia with F~37 only a single pair of broad-based flat marginal spines, lacks well-defined pleural furrows, and has a relatively broader and less furrowed axis; Nericia, Westergard (1948, p. 15) has pygidia with short evenly spaced marginal spines and an axis that seems to be structurally similar to that of Olenaspella. The crani- dia, however, have short poorly defined palpebral lobes and broad-based posterior limbs which distinguish them from most American species of the Aphelaspidinae. Wilson (1954, p. 1345) included Parabolinella occi- dentalis (Wilson, 1951, p. 651, pl. 95, figs. 2—5, 11) in Olenaspella. The cranidia are characterized by two pairs of deep slightly curved glabellar furrows and a rounded anterior end to the glabella. The free cheeks have the lateral and posterior border furrows separated. These features indicate a closer affinity of 0. occidental’is with Kindbladia, and the species is not considered here to belong to Olenaspella. Olenaspella evansi (Kobayashi) Plate 5, figures 4, 5, 7 Parabolinella? evansi Kobayashi, 1936, p. 92, pl. 15, figs. 7—10. Parabblinella evansi Kobayashi, 1938, p. 186, pl. 16, figs. 11, 12(?). (Figs. 13-15 are specifically indeterminate; fig. 14 is an olenid.) [Magnesia—Members of Olenaspella with pygidium having length about four-tenths width; axis with 2 or 3 ring furrows present behind articulating furrow; pleural regions without well—defined border, crossed by three shallow pleural furrows. Margin with three pairs of moderately short slender evenly spaced pos- teriorly directed spines. Discussion—Although this species does not occur in association with Glyptagnostus, there has been some confusion about its identiy that has a bearing on the concept of the genus Olenaspella. The types of this species are specimens sent by C. S. Evans, of the Geological Survey of Canada, to C. E. Resser, of the US. National Museum, for identification in preparation of a report on the Brisco-Dogtooth map area of British Columbia (Evans, 1933). These were studied by Kobayashi on his visit to the United States in 1933 and subsequently described and figured (Ko- bayashi, 1936.) The remainder of Evans’ material is in the collection of the Geological Survey of Canada and was studied by Kobayashi and described at a later date (Kobayashi, 1938). In the original description of Parabolinella? evansi (Kobayashi, 1936, p. 92), the only locality listed was “north of Jubilee Mountain, British Columbia.” The illustrations are good and show a pygidium with 3 pairs of marginal spines although the text states that only 4 spines (2 pairs) are present. Several pygidia with 3 pairs of marginal spines are present in the type F—38 lot. Other specimens identified as Parabolinella evansi were illustrated later (Kobayashi, 1938) from collection P 6/5, “north of Jubilee Mountain, west side of the Columbia River, west of Harrogate,” British Columbia. N 0 pygidia were illustrated in this paper. A pygidium from west Texas with two pairs of marginal spines was described, figured, and identified by Wilson (1954, p. 281) as Parabolinella evansi Kobayashi. He apparently placed more emphasis on Kobayashi’s text describing a 4-spined pygidium than on the illustration showing a pygidium with 6 marginal spines. This is borne out by the fact that the 1936 reference to Parabolinella? evansi in Wilson’s synonymy excludes citation of the figure of the six-spined pygidium. In the text, how- ever, he states, “Kobayashi mentions only 4 spines on the posterior margin, but his figure shows 6. The writer’s material shows 4: it is probable that the number of spines increases with size of the pygidium.” No evidence is presented to support this statement. Wilson (1956, p. 1344) reported a small 4-spined pygidium associated with the cranidium of Parabolinella evansi figured by Kobayashi in 1938, plate 16, figure 11. At this time, Wilson also chose a lectotype for Pam- bolinella evansi from among the specimens illustrated in 1938 and described a new genus Olenaspella With 0. evansi as type species. It is thus necessary for proper identification of the type species of Olenaspella to review all evidence concerning the morphology of Para- bolinella? evansi. All the specimens in the US. Na- tional Museum and in the collections of the Geological Survey of Canada that have a bearing on this problem have been reexamined. Kobayashi (1938, p. 154) listed Pseudagnostus latus Kobayashi, Homagnostus acutus Kobayashi, and Dun- derbergt'a canadensis Kobayashi as species associated with the figured specimens of Parabolinella evansi from locality P 6/5. The blocks containing the illus- trated specimens of P. latus and H. acutus also have cranidia and free cheeks of Parabolinella evansz' to- gether with several pygidia bearing three pairs of mar- ginal spines and identical in all respects with the pygidium illustrated by Kobayashi in 1936. Thus it is reasonably certain that the trilobite described as Parabolinella evansi in both 1936 and 1938 is a species with three pairs of marginal pygidial spines and that the original description is in error. Search was made for the 4-spined pygidium reported by Wilson to be associated with the illustrated crani- dium of P. evansi (Kobayashi, 1938, p. 186), but no such pygidum was observed, and there is no evidence to support the statement that the 4-spined pygidium is an early stage of the 6-spined form or that a trilobite with such a pygidium is even associated with P. evanse'. Wilson’s “topotype” material of “P. evansi” (Wilson, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1956, p. 1344) contains only 4-spined pygidia, compar- able in size to the 6-spined pygidia of P. evansi in the Evans collections. The trilobites with the 4-spined pygidium are considered here to represent another species, Olenaspella regularis n. sp. Also, inasmuch as Kobayashi’s 1938 specimens were not part of the type lot of Parabolinella evansi, the choice of a lectotype from among them was invalid. A new lectotype, GSC 15150, the pygidium originally illustrated by Kobayashi (1936, pl. 15, fig. 10), is here designated. Figured specimens: Geological Survey of Canada No. (GSC) 15147 cranidium, 15148 free cheek, 15151 pygidium. From Evans collection P 6/5, north of Jubilee Mountain, British Columbia, Canada. Olenaspella regularis n. sp. Plate 5, figures 1—3 Parabolinella evansi Wilson, 1954 [not Kobayashi, 1936, 1938], p. 281, pl. 25, figs. 10, 15—17. Diagnosis—Members of Olenaspella with pygidium having 3 or 4 ring furrows behind articulating furrow on axis. Pleural regions with 2 or 3 shallow pleural furrows curved abruptly backward near inner edge of poorly defined narrow border, and extended onto bor- der. Shallow interpleural grooves apparentbetween first and second pleural segments near outer edge of pleural field. Margin with 2 or 3 pairs of spines. Most specimens with two pairs of spines, outer pair longest; each pair connected to posterior band of first or second pleural segment by low narrow ridge. Third pair of spines, if present, short, adjacent to inner edge of second pair of spines (pl. 5, fig. 3). Discussion—The pygidium figured by Wilson (1954, pl. 25, fig. 16) as Parabolinella evansi is identical with the pygidia of 0. regularis. It is unlikely that it rep— resents the same species as the pygidium originally il- lustrated as P. evansi by Kobayashi (1936, pl. 15, fig. 10) (see p. F—37, pl. 5, fig. 5), which has 3 pairs of evenly spaced marginal spines and only 2 ring furrows posterior to the articulating furrow. This species is definitely younger than 0. separata n. sp. (table 1), but its age relationship to 0. evansi (K0— bayashi) is not yet certain. Infraspecific variability is also apparent in 0. regularis as it is in 0. separate n. sp. with regard to details of shape of both cranidia and pygidia in samples from different localities. The geo- graphic range of 0. regularis extends throughout the Cordilleran region. It was described from west Texas as Parabolinella? evansi by Wilson (1954, p. 281) and also reported by Wilson (1956, p. 1344) as topotype ma- terial of Parabolinella? evansi from near Jubilee Moun- tain, British Columbia. It has now been found in four GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES areas in Nevada (fig. 2): the Hot Springs Range, Mount Hamilton, Cherry Creek, and McGill. Occurrence: Lower part of Dunderberg formation: USGS colln. 2471—CO (4 cranidia, 1 free cheek, 8 pygidia), 2534—CO (22 cranidia, 1 free cheek, 7 pygidia), Cherry Creek, Nev. Unnamed formation: USGS colln. 1370—00 (2 cranidia, 1 free cheek, 7 pygidia), Hot Springs Range, Nev. Woods Hollow shale: Boulder BM—4 (>20 specimens), Marathon region, Texas. Figured specimens: USNM USGS colln. Part 143179 _________ 2534—CO- _ _ - Holotype pygidium. 143180 _________ 2534—00", , Cranidium. 143199 _________ 2471—001-" Pygidium. Olenaspella separate. :1. sp. Plate 5, figures 6, 8—21, 23—26, 28, 30—32 Diagnosis—Members of Olenaspella with pygidium having length about one—half width. Axis generally with 4 to 5 ring furrows behind articulating furrow. Pleural regions crossed by 3 or 4 shallow pleural fur- rows; narrow interpleural furrow between first and second segments developed on some specimens. Bor- der poorly defined. Posterior margin with 1 to 3 pairs of spines, one pair of long slender spines always devel- oped from first pleural segment; second pair always short, developed either from second pleural segment or from border between first and second pleural segments; third pair, when present, slightly longer than second pair, always developed from second pleural segment. Second and third pairs of spines always placed nearer to first pair of spines than to axial line. Discussion—This species is characterized by the spacing of the marginal pygidial spines. Even when three pairs of spines are present, they are grouped near the lateral margin of the pygidium leaving a long non- spinous medial part of the margin. This character- istic distinguishes 0. separata from 0. regularis n. sp., which has two pairs of approximately evenly spaced prominent marginal spines, and 0. evansi (Kobayashi), which has three pairs of evenly spaced, equally devel- oped marginal spines. If larger collections and more detail about strati— graphic distribution of specimens assigned to this species are obtained, several subspecies may be recognizable, or the species may be considered to be too inclusive. At McGill, Nev. 0. separata ranges through about 35 feet of beds in association with Glyptagnostus reticulatus angelim'. In the lower part of its range, pygidia are slightly shorter and broader than those in the upper part of its range (cf. pl. 5, figs. 6, 15). Some specimens have a short second pair of marginal spines from the second pleural segment. Only one pair of marginal spines has been observed on specimens from the upper part of the range of the species at McGill (cf. pl. 5, figs. F—39 6 and 24 with 15 and 16). Specimens from north- western Nevada and Cedar Bluff, Ala, have the pygidial outline like that of specimens from the lower part of the range of the species at McGill, but they have 1, 2, or 3 pairs of marginal spines without any apparent correla- tion of number of spines with size. All the specimens discussed above are considered here to represent a single species whose populations vary slightly in both space and time. It is definitely older than 0. regularis (table 1) and may be older than 0. evansi. One sample, USGS colln. 2466—00, contains moder- ately abundant silicified parts of 0. separata from the lower part of its range at McGill, Nev. The holaspid pygidia show a distinct morphologic series from smaller specimens with only one pair of pygidial spines to larger specimens with a short second pair of spines (pl. 5, figs. 17—19, 23, 24). In addition to the observed variability in develop- ment of pygidial spines in this species, the cranidial border is also noticeably variable in both length (sagit- tal) and convexity (pl. 5, figs. 12, 13, 26). This varia— tion adds to the problem of determining characteristics of this species and also prohibits certain species identi- fication of isolated cranidia. Occurrence: Lower part of Dunderberg formation: USGS collns. 2466-CO (>30 specimens of all parts), 2477—00 (16 cranidia, 4 free cheeks, 8 pygidia), 2478—00 (4 pygidia), 2479—00 (1 cranidium, 1 free check, 4 pygidia), 2480—CO (2 free cheeks, 2 pygidia), 3020-00 (3 cranidia, 2 free cheeks, 4 pygidia), 3039— CO (1 specimen complete except for free cheeks), 3040—00 (1 cranidium, 3 pygidia), 3045-00 (2 cranidia, 1 pygidium), 3046-CO (4 cranidia, 4 free cheeks, 5 pygidia), 3049—00 (1 pygidium, 1 free cheek), 3050—00 (1 cranidium, 1 free cheek, 2 pygidia), 3051—CO (1 pygidium), 3052—00 (1 pygidium), 3053— CO (2 pygidia), 3054—CO (4 pygidia), 3055—CO (3 cranidia, 3 3 free cheeks, 8 pygidia), McGill, Nev. Conasauga formation: USNM 10c. 89d (22 cranidia, 3 free cheeks, 10 pygidia), Cedar Bluff, Ala. Unnamed formation: USGS colln. 1370—CO (8 cra- nidia, 2 free cheeks, 15 pygidia), Hot Springs Range, Nev.; USGS colln. 3106—CO (3 cranidia, 1 free cheek, 3 pygidia), Mt. Hamilton, Nev. Figured specimens: USNM USG'S colln. Part 1431813, 2477—00 ________ Pygidia. d, e 143181b, f__ 2477—CO ________ Cranidia. 143181c _ _ _ _ 2477—C0 ________ Free cheek. 143182 _____ 3039—CO ________ Holotype, complete individual. 143183 _____ 2480—00 ________ Pygidium. 143184 _____ 3046—CO ________ Pygidium. 143185a—f___ 2466—00 ________ Pygidia. 143185g- _ _ . 2466—CO ......... Free cheek. 143185h, i- 2466—CO ,,,,,,,, Thoracic segment. 143185j __ 2466—00 ........ Thoracic segment. 143187 _____ 1374-00 ________ Pygidium. 143186a, c_. USNM loc. 89d Pygidia. 143186b- _ _ _ USNM loc. 89d. _ Association slab. F—40 Aphelaspidinae gen. and sp. undet. Plate 5, figures 22, 27, 29 A new genus of aphelaspid is represented by rela- tively rare cranidia, free cheeks, and pygidia in USGS colln. 25‘35—CO. The cranidia are characterized by having prominent, well-defined palpebral lobes, a well- defined moderately convex border, and an obscurely furrowed glabella. The free cheek has well-defined lateral and posterior border furrows joined at the genal angle and extended slightly onto the genal spine. The pygidium is subquadrate in outline and has a short prominent axis with two well-defined ring furrows behind the articulating furrow. The pleural regions are broad, without a well-defined border, but are extended into two well-separated broad-based poste- riorly directed marginal spines. All the parts are distinctly pitted. Congeneric and perhaps conspecific specimens are also present in association with G. reticulatus at Tybo, Nev. Similar associations of cranidia, cheeks, and pygidia representing an undescribed genus are'known from slightly younger beds at several localities in Nevada. Because of inadequate samples of the species associated with G. reticulatus, this genus is not named here. The younger species will be described in a subsequent paper in which the generic and specific relationships of the specimens here illustrated can be discussed. Occurrence: Lower part of the Dunderberg formation, USGS colln. 2535—CO (5 cranidia, 1 free cheek, 1 pygidium), Cherry Creek, Nev. Uppermost beds of the Swarbrick formation: USGS colln. 3058—00 (4 cranidia, 2 pygidia), Tybo, Nev. Figured specimens: USNM USGS colln. Part 143188a __________________ 2435—00 ,,,,,, Cranidium. 143l88b __________________ 2535—C0 ______ Pygidium. 1431880 __________________ 2535—CO ______ Free cheek. Aphelaspinid'! sp. Plate 4, figures 30, 34 Several pygidia associated with Glyptagnostus reticu- latus and Olenaspella separate n. sp. in a small collection in limestone from the Conasauga formation are charac- terized by being broad and short and having an evenly rounded margin and a slender axis bearing 3 or 4 ring furrows posterior to the articulating furrow. The pleural fields are crossed by three shallow pleural furrows separated by even shallower interpleural furrows. The border is narrow and hardly tapered toward the axial line. The narrow well-segmented axis and narrow border of nearly constant breadth resemble pygidia of the late Middle Cambrian Scandi- navian genus Andrarina rather than American species of Aphelaspis. N0 Andrarina-like cranidia were ob— served in the small collection exaniined, and the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY generic affinities of the pygidia cannot be certainly determined. Occurrence: Conasauga formation, USNM loc. 89d (3 pygidia), Cedar Bluff Ala. Figured specimens: USNM pygidia. 143178 a, b, USNM loc. 89d, Subfamily PTEROCEPHALIINAE Diagnosis.—“Pterocephaliid trilobites with border of cranidium generally broad, concave, and longer (sagittal) than brim. Border of free cheek generally broad, concave. Pygidium with broad, poorly defined border on most species.” Palmer, 1960a, p. 84. Discussion—The new genus Listroa, which is next described, increases to four the number of genera assigned to this subfamily. This is presently the oldest genus in the subfamily, which now has repre- sentatives in North America ranging throughout all but the lowest part of the stratigraphic interval occupied by the Pterocephaliidae. The three younger genera described or reviewed earlier (Palmer, 1960a, p. 84) are Oernuolimbus Palmer, Sigmocheilus Palmer, and Pterocephalia Roemer. Genus LISTROA n. gen. T ype species.—-Listr0a toxoura n. sp., figure 14. Diagnosis.—Pterocephaliinae (total length generally less than 40 mm) with cranidium having obscurely furrowed well—defined glabella; border moderately broad, flat or slightly concave; fixed cheeks nearly horizontal; eye ridges moderately well defined, directed posterolaterally from junction with dorsal furrow; and anterior sections of facial sutures cutting anterior mar- gin with distinct angle. Free cheek with broad, poorly defined, nearly flat border. Lateral and posterior border furrows joined, extended short distance onto genal spine. Pygidium with short prominent posteriorly tapered axis bearing 2 or 3 ring furrows posterior to articulating furrow; tip somewhat elevated. Pleural regions mod- erately to strongly convex. Broad, poorly defined border strongly depressed. Posterior margin with strong median identation. Description.—Pterocephaliinae (estimated maximum length about 40 mm) with cranidium having glabella obscurely furrowed, straight sided, tapered forward, bluntly rounded anteriorly, well defined by shallow narrow axial furrows. Occipital furrow shallow; occip- ital ring with median node. Frontal area gently to moderately concave, divided into downsloping brim and flat or slightly convex, horizontal or slightly downsloping border by sharp but slight change in slope. Contact between brim and border evenly curved. Length of frontal area between }6 and full length of glabella, longest in larger specimens. Length of border GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES FIGURE 14.—Partlal reconstruction of Listroa toroura n. sp. slightly greater than that of brim. Fixed cheek hori- zontal, nearly flat; width of palpebral area between )4 and )6 basal glabellar width. Palpebral lobe moder- ately to poorly defined by shallow arcuate palpebral furrow, situated about opposite glabellar midlength. Eye ridges moderately to poorly defined, directed posterolaterally from junction with dorsal furrow. Posterior limbs slender, sharp pointed; posterior border furrow shallow. Anterior section of facial suture divergent forward from palpebral lobe to marginal furrow, then turned abruptly inward to cross border and cut anterior margin with distinct angle somewhat more than half distance from anterolateral cranidial corner to axial line. Posterior section divergent, sinuous. Free cheek with poorly defined, broad, nearly flat border separated from ocular platform by shallow lateral border furrow. Posterior border furrow shallow, joined with lateral border furrow at genal angle, eX- tended short distance onto genal spine. Gena] spine broad, flat at base, tapered rapidly posteriorly. Thorax and hypostome not known. Pygidium with prominent posteriorly tapered axis having tip elevated somewhat, reaching to inner edge of border; 2 or 3 shallow ring furrows present posterior to articulating furrow. Pleural regions moderately to strongly convex with poorly defined downsloping or depressed border generally as broad posterolaterally as pleural field. Low postaxial median ridge generally present. Pleural furrows shallow, extending to or onto border. All furrows better defined on exfoliated speci- mens. Posterior margin with median indentation. Surface [of exoskeleton smooth or finely pitted. Some specimens show rare scattered granules. F—4 1 Discussion—This genus diflers from Aphelaspt's by having a broad border and slightly flared frontal area on the cranidium, and by having a downsloping border and distinct posterior median notch on the pygidium. The structure of the cranidial border is more like that of a pterocephalinid trilobite than like typical members of the Aphelaspidinae, and Listroa is tentatively included here in the Pterocephaliinae. Listroa toxoura n. sp. Plate 6, figures 5, 8—10; text figure 14 Diagnosis.~Members of Listroa with cranidial border nearly flat, slightly downsloping, making gentle angle with brim. Sagittal length of frontal area generally not greater than three-fourths length of glabella. Pygidium with 2 or 3 distinct ring furrows posterior to articulating furrow. Discussion.—Aphelaspis longifrons Palmer (1954, p. 745, pl. 84, figs. 9, 12; pl. 85, figs. 2, 3) is a species now more properly assigned to Listroa. It differs from L. toxoum by having a Longer frontal area, a slightly convex border on many specimens, a much more dis- tinct angle between the brim and the border, and generally one less distinct ring furrow on the axis of the pygidium. Occurrence: Lower part of the Dunderberg formation: USGS collns. 2471—00 (7 cranidia, 1 free cheek, 1 pygidium), 2534—00 (9 cranidia, 1 pygidium), 2535—00 (4 cranidia, 2 free cheeks), Cherry Creek, Nev. Uppermost beds of Swarbrick formation: USGS collns. 3057—00 (4 cranidia), 3058—00 (4 cranidia), 3059~CO (6 cranidia), Tybo, Nev. Figured specimens: USNM USG S colln. Part 1431913 _________ 2535—CO _____ Cranidium. 143191b _________ 2535—00 _____ Free cheek. 143192 __________ 2471—00 _____ Holotype cranidium, 143193 __________ 2534—CO ..... Pygidium. LOCALITY INFORMATION AND FAUNAL LISTS The collections referred to in this paper are cataloged under 1 of 2 sets of numbers. Collections listed in the U.S. National Museum catalog bear green-paper circles with handwritten locality numbers. Collections of the U.S. Geological Survey are listed in the Cambrian- Ordovician locality catalog and bear orange-paper circles or rectangles with machine—printed collection numbers. USGS collection numbers referred to in the text bear the suffix (—CO) to differentiate them from a parallel series of numbers in the Silurian-Devonian locality catalog with suflix (—SD). All USGS collections, unless otherwise indicated, were made by the writer in 1958 (Nevada) or 1959 (Alabama, Nevada). Names of collectors and col— F—42 lecting dates of USNM localities are indicated with each collection. Faunal lists are given only for collections not shown on figures 4—7. ALABAMA Cedar Blufi.—Measured section in shales and a fear thin limestones of the Conasauga formation cropping out in a drainage ditch along the west edge of the high school playing field and the continuation of this ditch on the south side of the road at the south edge of the playing field in the town of Cedar Bluff. The distances given are calculated stratigraphic distances above or below the bed at the north end of the culvert beneath the road at the south end of the high school playing field. Although the average dip of the beds is 15° NE, the Conasauga formation in the vicinity of Cedar Bluff is so strongly folded that these beds could be upside down. They are assumed to be in normal sequence, however, in the absence of positive evidence to the contrary. 2875—CO. 35 ft above datum in parting between }é-in. layers of vertical fibers of calcite that make a 1-in. limestone bed in a dominantly shale sequence. 2876‘00. 2 ft below coll. 2875-C0 in similar 1-in. limestone bed. 2877—00. About 5 ft above datum, fossiliferous medium- grained gray limestone concretion, lithically identical with limestone at 'USNM loc. 89d. 2878—C0. At north end of culvert (datum.) Brown shale. 2879—00. 3 ft below datum in ditch on south side of road. Thin limestone similar to coll. 2875~CO. USNM 10c. 89d. Two blocks southeast of hotel at Cedar Bluff. Collected by Charles Butts and E. O. Ulrich, 1920. [This is appioximately the locality of the 1959 measured section] USNM 100. 910. One-third of a mile east of Cedar Bluff on Rome road. Collected by Cooper Curtice, 1875. [The Rome road of 1875 is now the street at the south edge of the high school playing field. The exact position of this col- lecting locality might be in an overgrown roadcut on the abandoned part of the old Rome road at the south edge of a churchyard just east of the high school playing field.] Agnostus inexpectans Kobayashi Aphelaspis buttsi (Kobayashi) Aspidagnostus rugosus n. sp. Glyptagnostus reticulatus angeltm’ (Resser) Olenaspella separata n. sp. Woodstock—A short section of beds of the Conasauga formation is exposed in a partly overgrown railroad cut on the southwest (inner) side of a curved spur track of the Southern Railway about 200 feet southeast of the main street of Woodstock at the west edge of town. Several ledges of nearly flat lying fine grained to very fine grained silty laminated limestone separated by brown-weathering shales crop out for about 15 feet above the level of the railroad track. 2886‘CO. 7 ft above railroad track. fine-grained limestone, 2 in. thick. Dark-gray silty laminated SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 2887—00. 8 ft above railroad track. Brownish-gray very fine grained silty limestone; bottom part of ledge 2 ft thick. 2888—CO. 11 ft above railroad track. Limestone bed, 1V2 in. thick; lower inch light gray, very fine grained; upper 1A in. dark gray, fine grained; contact of dark and light parts irregular. 2889—00. 12 ft above railroad track. as 2886—CO. USNM loc. 90b. Cut 011 Louisville and Nashville Railway north of Woodstock, Ala. Collected by Charles Butts, 1904, 1905. [This is probably the same locality as that collected in 1959. There are no other outcrops of the Conasauga formation along the railroad tracks in the vicinity of Woodstock] Specimens also labeled 90b with Meteor- aspis nuperus (Resser) and Dciracephalus aster (Walcott) (Resser, 1938, pl. 11, figs. 43—45) do not have any associ- ated parts of the trilobites that occur with Glyptagnostus stoltdotus at this locality and probably came from a. bed not located in 1959. Limestone bed, same NEVADA Cherry Creek.——Measured section on east side of Cherry Creek Range, reached by driving 7.1 miles west on paved road from U.S. Highway 93 toward the town of Cherry Creek, then turning north on graded road for 4.0 miles to jeep trail leading up canyon to the West. The Dunderberg formation is exposed in the canyon bottom and on the ridges t0 the north and south about 1 mile up the canyon beyond the end of the Jeep trail. The section was measured in the canyon bottom. 2470—00. 3 ft below base of Dunderberg formation on ridge north of measured section. Gray very fine grained crinkly- bedded limestone. 2471—CO. 1 ft above base of Dunderberg formation on ridge north of measured section. Gray fine-grained silty limestone bed 2 in. thick. 2534—CO. 2 ft above base of Dunderberg formation in measured section. Limestone bed, lithology same as 2471—00. 2535—CO. 11 ft above base of Dunderberg formation in measured section. Limestone bed, lithology same as 2471—CO. 3056—00. 1V2 ft below base of Dunderberg formation in measured section. Limestone, lithology same as 2470—C0. Hamilton district.— 3106—CO. West side of Pogonip ridge, 500 ft east of the Monte Cristo mine, SWM sec. 27, T. 16 N., R. 57 E., Green Springs quadrangle, Nevada. Collected by F. L. Humphrey, 1947. Glyptagnostus reticulatus (Angelin) Olenaspella separata n. sp. Hot Springs Range.— 1374—C0. Limestone lens in structurally disturbed unit of thin—bedded chert and siliceous shale (Roberts and others, 1958, p. 2827). Extreme NEl/iNWM sec. 31, T. 40 N., R. 41 E. (unsurveyed), Hot Springs Peak quadrangle. Glyptagnostus reticulatus angelim’ (Resser) Homagnostus sp. Cheilocephalus sp. Agnostus cf. A. tnexpectans Kobayashi Pseudagnostus sp. Aphelaspts sp. Olenaspella separata Palmer GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES 1370—00. Limestone lens in structurally disturbed unit of thin- bedded chert and siliceous shales (Roberts and others, 1958, p. 2827), on ridge S}/2NE%SE% sec. 28, T. 39 N., R. 40E., Osgood Mountains quadrangle, Nevada. Agnostus inexpectans Kobayashi Glyptagnostus reticulatus reticulatus (Angelin) Olenaspella regularis n. sp. - Pseudagnostus sp. McGill.—Measured section in small canyon on west side of Duck Creek Range, reached by driving 1.35 miles north of McGill Post Office, turning right onto abandoned section of U.S. Highway 93 and continuing 0.6 mile to trail leading up slope to the right, crossing large pipeline and continuing into small canyon. Exposures of basal beds of Dunderberg formation are west of trail about 100 yards before first switchback. 2474—00. 1 ft below base of Dunderberg formation. Gray- brown very fine grained crinkly-bedded limestone, 2 in. thick. 2475—00. Top bed of limestone unit beneath Dunderberg formation. Limestone as in 2474—00, 2% in. thick. 2476—00. 6 in. above base of Dunderberg formation. Gray fine-grained silty laminated-limestone bed 2 in. thick. 2477—00. 16 ft above base of Dunderberg formation. Lime- stone as in 2476—00, 3 in. thick. 2478—00. 27 ft above base of Dunderberg formation. Lime- stone as in 2476—00, 1 ft thick. 2479—00. 33 ft above base of Dunderberg formation Lime- stone as in 2476—00, 2 in. thick. 2480—00. 40 ft above base of Dunderberg formation. Lime- stone as in 2476—00, 2 in. thick. 3039—00. 5 ft above base of Dunderberg formation. Lime— stone lens, lithology as in 2476—00, 2 in. thick. 3040—00. 20 ft above base of Dunderberg formation. Lime- stone lens as in 3039—00. 3041—00. Same bed as 2478—00, 27 ft above base of Dunder- berg formation. 3043—00. 30 ft above base of Dunderberg formation. Lime- stone as in 2476—00., 1 in. thick. 3044—00. 32 ft above base of Dunderberg formation. Lime- stone as in 2476—00, 1 in. thick. 3045—00. 35 ft. above base of Dunderberg formation. Lime- stone as in 2476—00., 2 in. thick. 3046—00. 38 ft. above base of Dunderberg formation. Lime- stone as in 2476—00, 2 in. thick. 3049—00. 31 ft above base of Dunderberg formation. Lime- stone lens as in 3039—00, 1 in. thick. 3050—00. 32.5 ft above base of Dunderberg formation. Lime- stone lens as in 3039—00, 2 in. thick. 3051—00. 34 ft above base of Dunderberg formation. Lime- stone as in 2476—00, 2 in. thick. 3052—00. Same as 3045—00, 35 ft above base of Dunderberg formation. 3053—00. 37 ft above base of Dunderberg formation. stone as in 2476—00, 2 in. thick. Lime- F—43 3054—00. Same as 3046—00, 38 ft above base of Dunderberg formation. 3055—00. 39 ft above base of Dunderberg formation. Lime- stone as in 2476—00, 2 in. thick. Not in measured section— 2466—00. Lower part of Dunderberg formation on ridge crest north of measured section. Gray fine-grained silty lami- nated limestone bed 2 in. thick. Excellent silicified trilobites. 3020—00. 15 ft above base of Dunderberg formation on north facing slope of ridge north of measured section. Limestone as in 2466—00. Tybo.—0011ections from upper 10 feet of east- dipping beds of Swarbrick formation at east end of exposures, on east side of gully entering Tybo canyon and about 350 feet north of Tybo canyon road. 3057—00. Gray medium-grained silty limestone bed 3 in. thick. 3058—00. 1 ft above 3057—00, similar limestone bed. 3059—00. 4 ft above 3057—00, similar limestone bed. Fauna mainly the same in all three collections: Aphelaspis subditus n. sp. Aphelaspidinae, gen. and sp. undet. Glyptagnostus reticulatus reticulatus (Angelin) Listroa toxoura n. sp. Pseudugnostus sp. TENNESSEE Henderson Oil 00., Markham No. 1 well, 3.3 miles S. 50° E. of Tiptonville, Lake County, Tenn. (Grohs- kopf, 1955, p. 127). Paleozoic rocks from 2,230 to 3,242 feet consist “essentially of dark grey dense to medium grained limestone, dark siliceous shales, some of which are definitely slaty, and basic igneous ma- terial.” (Grohskopf, 1955). At depths of 2,858, 2,860, and 2,862 ft are specimens of Glyptagnostus reticulatus (Angelin). TEXAS Limestone boulder, 2 feet in diameter, consisting of “dark gray to brownish black fine-grained limestone, slightly fossiliferous; containing lenses of pebble con- glomerate with abundant fragments of * * * trilobites in both the matrix and in the pebbles.” Wilson, 1954, p. 256. Woods Hollow shale, East Bourland mountain, Marathon region, Texas. Agnostus inexpectans Kobayashi Aphelaspis sp. Glyptagnostus reticulatus (Angelin) Homagnostus obesus (Belt) Listroa sp. undet. Olenaspella regularis n. sp. Pseudagnostus cf. P. communis (Hall and Whitfield) F—44 SELECTED REFERENCES Angelin, N. P., 1851, Paleontologica Scandinavica. Pars I— Holmiae. 1854, Paleontologica Scandinavica. Pars II—Holmiae. Banks, M. R., 1956, The Middle and Upper Cambrian series (Dundas group and its correlates) in Tasmania, in El Sistema Cambrico, su paleogeografia y el problema de su base, Internat. Geol. Cong. 20th, Mexico City 1956, Symposium, v. 2, pt. 2, p. 165—212. Belt, Th., 1867, On some new trilobites from the Upper Cambrian rocks of North Wales: Geol. Mag.. v. 4, p. 294—295. Berkey, C. P., 1898, Geology of the St. Croix Dalles: Am. Geologist, V. 21, p. 270—294. Brbgger, W. C., 1882, Die silurischen Etagen 2 und 3 im Kristian— iagebiet und auf Eker, ihre Gleiderung, Fossilien, Schicht- enstorungen und Kontactmetamorfosen: Univ.-Programm (Christiania), p. 1-376. Brongniart, Alexandre, 1822, Histoire naturelle des crustaces fossiles, sous les rapports zoologiques et geologiques. Savoir: Les Trilobites: 154 p., 11 pl., F. G. Levrault (Paris). Butts, Charles, 1926, The Paleozoic rocks, in Geology of Ala- bama: Alabama Geol. Survey Spec. Rept. 14, 312 p. Clark, T. H., 1923, A group of new species of Agnostus from Levis, Quebec: Canadian Field Naturalist, v. 37, p. 121—125. 1924, The paleontology of the Beekmantown series at Levis, Quebec: Bull. Am. Paleontology, V. 10, no. 41, 134 p. Drewes, Harald, and Palmer, A. R., 1957, Cambrian rocks of southern Snake Range, Nevada: Am. Assoc. Petroleum Geologists Bull., V. 41, no. 1, p. 104—120. Evans, C. E., 1933, Brisco-Dogtooth Map area, British Colum- bia: Canada Geol. Survey Summary Rept., pt. A 2., p. 106-187. Grohskopf, J. G., 1955, Subsurface geology of the Mississippi embayment of southeast Missouri: Missouri Geol. Survey and Water Resources Rept., v. 37, 2d ser., 133 p. Hall, James, 1863, Preliminary notice of the fauna of the Potsdam sandstone: New York State Cabinet Nat. History, 16th Ann. Rept., p. 119—222. Hall, James and Whitfield, R. P., 1877, Paleontology: U.S. Geol. Explor. 40th Parallel Rept., v. 4, p. 199—231. Harrington, H. J., and Leanza, A. F., 1957, Ordovician trilobites of Argentina: Lawrence, Kans., Kansas Univ. Dept. Geol. Spec. Pub. 1, 276 p., 140 fig. Harrington, H. J., and others, 1959, Arthropoda 1, in Treatise on invertebrate paleontology, Part 0: Lawrence, Kans., Geol. Soc. America and Univ. Kansas Press, 560 p., 415 text figs. Henningsmoen, Gunnar, 1957, The trilobite family Olenidae: Norske vidensk.-akad. Olso Skr., no. 1, 303 p. 1958, The Upper Cambrian faunas of Norway with descriptions of non—Olenid invertebrate fossilsz. Norsk geol. tidsskr., v. 38, p. 179—196. Howell, B. F., 1935, Cambrian and Ordovician trilobites from Herault, southern France: Jour. Paleontology, v. 9, p. 222-238. —1959, in Harrington, H. J., and others, 1959. Howell, B. F., and others, 1944, Correlation of the Cambrian formations of North America (chart 1): Geol. Soc. America Bull., v. 55, no. 8, p. 993-1003. Ivshin, N. K., 1956, Verkhnekembriyskiy trilobity Kazakhstana, chast’ I: Akad. Nauk Kazakhskoy SSR, 97 p. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Jaekel, 0., 1909, Uber die Agnostidcn: Deutsche geol. Gesell. Zeitschr., v. 16, p. 380—401. Kindle, C. H., 1948, Crepicephalid trilobites from Murphy Creek, Quebec, and Cow Head, Newfoundland: Am. Jour. Sci., v. 246, no. 7, p. 441-451. Kindle, C. H., and Whittington, H. B., 1959, Some stratigraphic problems of the Cow Head area in western Newfoundland: New York Acad. Sci. Trans, ser. 2, v. 22, no. 1, p. 7—18. Kobayashi, Teiichi, 1935, The Cambro—Ordovician formations and faunas of south Chosen—Paleontology, part 3: Tokyo Imp. Univ., Fac. Sci., Jour., sec. 2, v. 4, p. 49—344. 1936, On the Parabolinella fauna from province Jujuy, Argentina with a note on the Olenidae: Japanese Jour. Geology and Geography, v. 13, no. 1—2, p. 85-102. 1937, The Cambro—Ordovician shelly faunas of South America: Tokyo Imp. Univ., Fac. Sci., Jour., sec. 2, v. 4, p.374—522, 1938, Upper Cambrian fossils from British Columbia with a discussion on the isolated occurrence of the so-called Olenus beds of Mt. Jubilee: Japanese Jour. Geology and Geography, v. 15, no. 3—4, p. 151—192. 1939, On the agnostids (pt. 1): Tokyo Imp. Univ., Fac. Sci. Jour., sec. 2, v. 5, p. 69—198. 1949, The Glyptagnostus hemera, the oldest world- instant: Japanese Jour. Geology and Geography, v. 21, p. 1—6. Lake, Philip, 1906, A Monograph of British Cambrian trilobites, Part 1: London, Palaeont. Soc. Pub., v. 60, p. 1—28. Lermontova, E. V., 1940, in Vologdin, A. G., Atlas of the leading forms of the fossil faunas of the U.S.S.R., v. 1, Cambrian, Moscow. Lochman, Christina, 1940, Fauna of the basal Bonneterre dolo- mite (Upper Cambrian) of southeastern Missouri: Jour. Paleontology, v. 14, p. 1—53. 1953, Notes on Cambrian trilobites—homonyms and synonyms: Jour. Paleontology, v. 27, no. 6, p. 886—889. Lochman, Christina, 1956, The evolution of some Upper Cam- brian and Lower Ordovician trilobite families: Jour. Paleon- tology, v. 30, no. 3, p. 445-462. 1959, in Harrington, H. J., and others, 1959. Lochman, Christina, and Duncan, Donald, 1944, Early Upper Cambrian faunas of central Montana: Geol. Soc. America Spec. Paper 54, 179 p. Lochman, Christina, and Wilson, J. L., 1958, Cambrian biostra— tigraphy in North America: Jour. Paleontology, v. 32, p. 312-350. Lu, Yen-Hao, 1956, On the occurrence of Lopnorites in northern Anhwei: Acta Paleont. Sinica, v. 4, p. 267—284, pl. 1. Miroshnikov, L. D., Kravtsov, A. G., and Shcheglova, O. S., 1959, Skhema stratigrafii nizhnego i srednego Paleozoya severo-zapadnoi okrainy sibirskoi platformy: Akad. Nauk SSSR Doklady, v. 126, no. 2, p. 359—362. Opik, A. A., 1956, Cambrian geology of Queensland, in El Sistema Cambrico, su paleogeografia y el problema de su base, Internat. Geol. Cong. 20th, Mexico City 1956, Sym- posium, v. 2, p. 1-24. 1958, in Les relations entre Precambrian et Cambrien: Centre Natl. de la Recherche Sci. Colloques Internat., v. 76, p. 23. 1961, Alimentary caeca of agnostids and other trilobites: Paleontology, v. 3, pt. 4, p. 410—438, pl. 68-70. GLYPTAGNOSTUS AND ASSOCIATED TRILOBITES Palmer, A. R., 1951, Pemphigaspis, a unique Upper Cambrian trilobite: Jour. Paleontology, V. 25, p. 762—764. 1954, The faunas of the Riley formation in central Texas: Jour. Paleontology, V. 28, no. 6, p. 709—786. 1955, Upper Cambrian agnostidae of the Eureka district, Nevada: Jour. Paleontology, v. 29, no. 1, p. 86—101. 1960a, Trilobites of the Upper Cambrian Dunderberg shale in the Eureka district, Nevada: U.S. Geol. Survey Prof. Paper 334—0, p. 53—109. 1960b, Some aspects of the Early Upper Cambrian stra— tigraphy of White Pine County, Nevada, and vicinity: Intermountain Assoc. of Petroleum Geologists, Guidebook, p. 53—58. Poulsen, Christian, 1923, Bornholms Olenuslag 0g deres Fauna: Danmarks geol. undersog., ser. 2, no. 40, p. 1—83. Raasch, G. 0., and Lochman, Christina, 1943, Revision of three early Upper Cambrian trilobite genera: Jour. Paleontology, V. 17, p. 221—235. Rasetti, Franco, 1946, Early Upper Cambrian trilobites from western Gaspé [Quebec]: Jour. Paleontology, V. 20, p. 442—462. 1954, Phylogeny of the Cambrian trilobite family Catil- licephalidae and the ontogeny of Welleraspz’s: Jour. Paleon- tology, v. 28, p. 599—612. 1956, Revision of the trilobite genus Maryvillia Walcott: Jour. Paleontology, v. 30, no. 5, p. 1266—1269. Raymond, P. E., 1937, Upper Cambrian and Lower Ordovician Trilobita and Ostracoda from Vermont: Geol. Soc. America Bull., v. 48, no. 8, p. 1079—1146. Resser, C. E., 1935, Nomenclature of some Cambrian trilobites: Smithsonian Misc. Colln., v. 93, no. 5, 46 p. 1936, Second contribution to nomenclature of Cambrian trilobites: Smithsonian Misc. Colln., v. 95, no. 4, 29 p. 1937, Third contribution to nomenclature of Cambrian trilobites: Smithsonian Misc. Colln., v. 95, no. 22, 29 p. 1938, Cambrian system (restricted) of the southern Ap- palachians: Geol. Soc. America Spec. Paper 15, 139 p., 16 p1. 1942, New Upper Cambrian trilobites: Misc. Colln., v. 103, no. 5, 136 p., 21 pl. Roberts, R. J. and others, 1958, Paleozoic rocks of north-central Nevada: Am. Assoc. Petroleum Geologists Bull., v. 42, p. 2813—2857. Savizky, V. E., and Lazarenko, N. P., 1959, Korrelyatsiya razrezov i skhema stratigraficheskogo raschleneniya Kem- briyskikh otlozheniy Anabarskoy anteklizy, in Stratigrafiya siniyskikh i kembriyskikh otlozheniy severo—Vostoka sibir- skoy platformy: Trudy Nauch. Inst. Geol. Arktiki Minis- terstva geol. i okhrany nedr SSSR, V. 101, p. 152—192. Shaw, A. B., 1951, The paleontology of northwestern Vermont. I. New Late Cambrian trilobites: J our. Paleontology, V. 25, no. 1, p. 97—114. 1952, Paleontology of northwestern Vermont. II. Fauna of the Upper Cambrian Rockledge conglomerate near St. Albans: Jour. Paleontology, v. 26, no. 3, p. 458—483. Smithsonian F—45 Shimer, H. W., and Shrock, R. R., 1944, Index fossils of North America: New York, Technology Press, Massachusetts Inst. of Technology; John Wiley & Sons, 837 p. Strand, Trygve, 1929, The Cambrian beds of the Mj¢sen district in Norway: Norsk geol. tidsskr., V. 10, p. 307—365. Tasch, Paul. 1951, Fauna and paleoecology of the Upper Cam- brian Warrior formation of central Pennsylvania: Jour. Paleontology, V. 25, p. 275-306. 1952, Notes on the taxonomy of kingstoniid trilobites: Jour. Paleontology, V. 26, p. 859—861. Tullberg, S. A., 1880, Om Agnostus arterna i de Kambriska aflagringarne Vid Andrarum: Sveriges Geol. Undersokning, ser. C, no. 42, 37 p. Walcott, C. D., 1884, Paleontology of the Eureka district: U.S. Geol. Survey Mon. 8, p. 1—64. 1890, Description of new forms of Upper Cambrian fossils: U.S. Natl. Mus. Proc., V. 13, p. 267—279. 1911, Cambrian faunas of China: Smithsonian Misc. Colln., v. 57, no. 4, p. 69—108. 1913, Research in China, V. 3: Carnegie Inst. of Washing- ton, pub. 54, 375 p., 29 p1. 1916, Cambrian trilobites: Smithsonian Misc Colln., V. 64, no. 5, p. 303—456. 1924, Cambrian geology and paleontology, pt. 5, no. 2, Cambrian and Lower Ozarkian trilobites: Smithsonian Misc. Colln., V. 75, no. 2, p. 53—60. 1925, Cambrian geology and paleontology, pt. 5, no. 3, Cambrian and Ozarkian trilobites: Smithsonian Misc. Colln., v. 75, no. 3, p. 61—146. Westergard, A. H., 1922, Sveriges olenidskiffer: Sveriges Geol. Undersokning, ser. Ca, no. 18, p. 1—205. ———1946, Agnostidea of the Middle Cambrian of Sweden: Sveriges Geol. Undersokning, ser. C, no. 477, Arsbok 40, no. 1, p. 1—140. 1947, Supplementary notes on the Upper Cambrian trilobites of Sweden: Sveriges Geol. Undersokning, ser. C, no. 489, p. 1-34. 1948, Non-agnostidean trilobites of the Middle Cambrian of Sweden. I.: Sveriges Geol. Undersokning, ser. C, no. 498, p. 1—32. Whitehouse, F. W., 1936, The Cambrian faunas of northeastern Australia. Parts 1 and 2: Queensland Mus. Mem., V. 11, p. 59—112. 1939, The Cambrian faunas of northeastern Australia. Part 3. The polymerid trilobites: Queensland Mus. Mem., v. 11, pt. 3, p. 179 —282. Wilson, J. L., 1951, Franconian trilobites of the central Appala- chians: Jour. Paleontology, v. 25, no. 5, p. 617—654. 1954, Late Cambrian and Early Ordovician trilobites from the Marathon Uplift, Texas: Jour. Paleontology, v. 28, no. 3, p. 249—285. 1956, Revisions in nomenclature and new species of Cambro-Ordovician trilobites from the Marathon uplift, West Texas: Jour. Paleontology, V. 30, p. 1341—1349. Approved for publication, August 1960. 1 . __________ -. ‘20 typicalis _______________ D Acrotretid brachiopods _______________________ 7, 10, 18 acutus, Acmarhachis ________________________ 5, 20, pl. 2 Homagnostus ________ _.- 19, 20, 38 Pseudagnostus ______________________________ 20 Agnostid gen ___________________________________ 7, 9 gen. and sp. undet.....___._ ________ 14, pl. 1 trilobites. ____________ 1, 6, 11, 12, 14, 15, 16, 18, 19 Agnostida._ 11 Agnostidae _________________________ 11, l2, 13, 14, l6, l9 Agnostina ___________________________ 11 nodosus _____________________________________ 16 nordicus ____________________________________ 21 pwiformis reticulatus- - . Aqraulos thea ___________________________________ 29 Alabama ...... 42 Cedar Blufl. - _ 4, 5, 6, 7, 9, 12, 13,15, 18, 21, 22, 26, 35, 36, 39, 40, 42 Woodstock" .. 4, 5, 7, 8, 9, 14, 16, 20, 23, 24, 26, 29, 31, 42 ' ‘ ', K‘ , ‘ ______ 24,29,p1.6 Andrurina ________________________________ _-_ 40 angclmi, Glyptag‘mostus ___________________ .. 16,18 Glyptaanostus reticulum.-. 7,8,9, 11, 18, 39, 42, pl. 2 ...................... 7, 8, 9, 11 . 7,8 Angulotreta-bearing beds ________________________ 9 Aphelaspid trilobites ___________________________ 33 Aphelaspidinae... _ 32, 33, 36, 37, 40, 41,43, pl.5 trilobites- . . ___________________ 9, 15, 32 Aphelaspimd sp.. 40, pl. 4 sp. undet .................................. 5 Aphelaspis ___________________ 7, 8, 31, 32, 33, 35, 36, 40, 41 brachuphasis- . ____________ 5, 8, 33, 35, p14 buttsi..-. .-_ 5, 8, 13, 33,36, 36, 42, pl. 4 camtricta. _ _ 33 canvezimarginatus ___________________________ 33 fauna _______________________________________ 6 8,33 33 33 33,41 33 33 spinosus ____________________________________ 33 subditus ______________________ 5, 35, 36, 43, pl. 4 tumifrous- _______________ 33 waleotti. _____ 32, 33, 35, pl. 4 zone.-.. .-.- 6, 7, 8, 9, 11, 18, 27 sp .......................................... 42,43 sp. undet ............................... 36, pl. 4 Aphelaspis—bearing beds ....................... 8, 9, 10 INDEX [Italic numbers indicate descriptions] Page Aphelaspis—Glyptaonostus sequence .............. F—9 apion, Kingstom'a ............................... 29 appaluchia, Kingstonia .......................... 4 ammo, Saratogia. . ._ 33 Asaphiscidae ................................... 22 Aspidagnostus ___________________________ 6, 7, 12, 14, 15 laem's ............. 6, 16, pl. 1 parmatus. ........ .-._ 14,15 ruaosus ........... 5, I5, 42, pl. 1 aster, Deiracephalua ............................. 30, 42 Asteraspis ...................................... 30 Ataktaspis ...................................... 29 B Bultagnostus .................................... 13 Blandicephalus- 31 Blountia .......... 29 brixtolensisnu ________ 5, 22, 36, pl. 3 mimula ..................................... 22 nizonensis .................................. 22 Blountiinae- ___ Bolaspidella ______ boltonensis, Oedorhachis. . . brachz/phasis, Aphelaspis ............. 5, 8, 33, 35, pl. 4 brevifrons, Cedaria ............ 5, 6, 7, 9, 10, 26‘, 31, pl. 3 Brisco-Dogtooth area, British Columbia ........ 3,37 bristolensis, Blountz‘a ................... 5, 22, 36, pl. 3 Marym'llia __________________________________ 22 bulbus, Proagnostus. ................. 13,14 bullata, Pemphigaspis. ....................... 22 buttm', Aphelaspis _____ 5, 8, 13, 33, 36, 36, 42, pl. 4 Cedaria ..................................... 25 Proaulacopleura ............................ 35 C Camaraspis ..................................... 32 Camaraspm‘des .................................. 32 canadensis, Dunderbergia-_ ........... 38 Carinamala ............. 4, 7, 8, 9, 23, 24 longispina- - .. - 5, 6, 10, 23, 24, pl. 3 sp ...................................... 24, pl. 3 Catillicephalidae ............................... 22 Cedar Blufl, Ala ........... 4, 5, 6, 7, 9, 12, l3, 15, 18, 21, 22, 26, 35, 36, 39, 40, 42 Cedaria ....................... 7, 8, 9, 10, 15, 23, £4, 25, 26 brevifrons .................. 5,6, 7,9, 10, 26,31, pl. 3 buttsi ....................................... 25 _____ 26 ..... 6 gaspemis ................. ..- 9, 25, 26 millerL. minor... nizonia. prolifica ................. 4, 7, 9, 24, 25, £6, pie. 3, 6 puelchana ................... 25 tennesseemis .......... woosten' ............... zone_. SDD--., —————————————————————————————————— 7 Cedariid trilobites .............................. 23 Cedariidae ............. __ 23 Cedariinae ................... .- 23 centerensis, Proagnosms ....................... 13 Cu " ‘ x ........... -- 31,40 Page Cheilooephalidae ............................... F—27 Cheilocephalus .................................. 97 sp ............................... 5, 8, 27, 42, pl. 3 Cherry Creek, Nev--. 3 4, 5, 6, 7, 8, 10, 12, 14, 15, 18, 20, 24, 26, 27, 28, 30, 36, 39, 40, 41 Cherry Creek Range ........................... 5, 42 chippewaensis, Lonchacephalus .................. 30 cicer, Ciceragnostus .......... 14 Ciceragnostus ............. cicer .................. Clavagnostidae _____ Clavagnostus ........ Clevelandella ____________ communis, Pseudagnostus ....................... 5,43 comptus, Homagnostus ............... 5, 9, 12, pl. 1 Conasauga formation ....... . 1, 4, 12, 13, 14, 15, 16, 18, 20, 21, 22, 23, 29, 31, 35, 36, 39, 40, 42 Conclusion ............... 11 commta, Coosia ................................. 9 constricta, Aphelaspis ........................... 33 contracta, Pseudagnostina. 4, 5, 6, 20, 21, pl. 2 convergens, Pseudagnostina-. ....... 10 convezimarginatus, Aphelaspzs ....... 33 Coosellidae ...................................... 27 Coosia .......................................... 27 cannula... longocula ......... pernamagna ...... mperba ..................................... 27 sp _______________________________________ 28, pl. 3 Cow Head conglomerate.. _____ 9 Crepicephalid biofacies __________________ ._ 9, 10, 11 Crepicephalidae ...................... - 9, 25, 27, 28 Crepicephalus ___________________________________ 27 fauna ....................................... 6 perplerus _ eleguns ______________________________________ 19 D Deiracephalus __________________________________ 7, 30 aster ________________________________________ 30, 42 multisegmentus _____________________________ 30 umcornis ______ _ 3, 4, 80, pl. 6 Densonella ____________________________ _. 30 Dikelocephalites _______________________ . 31 Doryagnostus ___________________________________ 16 Duck Creek Range _____________________________ 5, 43 Dunderberg fauna... ___. l2 Dunderberg formation ___________________ l, 5, 6, 7, 10, 11, 12, 13, 15, 18, 20, 27, 35, 39, 40, 41, 42, 43 Dunderbergia ________ 27 _ 38 Dytremacephalus ________________________________ 32 E Ecologic observations ___________________________ 10 elegans, Acmarhachz‘s ____________________________ 20 Cyclagnostus... l9 Elm'm'a zone ____________________________________ 9, 27 F-47 F—48 Page Elviniidae ______________________________________ F—32 Entomolithus paradoxus pisiformis _______________ 12 Eugonocare _____________________________________ 31, 32 eurychez‘los, Cedarz'a _____________________________ 25 evansi, Olenaspellm. 37, 38, 39, pl. 5 Parabolinella ___________________________ 36, 37, 38 G gaspensis, Cedaria ____________________________ 9, 25, 26 Geragnostinae_. _____ 11 Geragnostusk. 11, 12, 21 gibbosus, Olenus ......... 32, 35 Gluphyraspw ____________________________________ 6 8 15 Glyptagnostinae ________________________________ 16 Glyptagnostus.__. 1, 3, 4, 5, 6, 7, 8, 9, 11, 15, 16, 18, 27, 37 angelim‘ ____________________________________ 16, 18 distribution ________________________________ 1 oldest American population... _ 7 oldest populations of genus. __ _ 8 pygidium of ________________________________ 7 reticulatus _________ 1, 7, 11, 13, 14,16, 18, 24, 40,42, 43 angelini ____________ 7, 8, 9, 11, 18, 39, 42, pl. 2 nodulosus. _ ___________________ 18 reticulatus" ____ 8, 9, 11, 18, 43, pl. 2 stolidotus ____________ 7, 8, 11, 16', 20, 23, 24, 42, pl. 2 stratigraphic significance of _________________ 6 toreuma _____________________________________ 15, 16 youngest population of genus__ 8 sp _________ 6 Glyptagnostus-bearlng beds, Hot Springs Range ______________________________ 9 Glyptagnostus-bearing collection at McGill _____ 7 Glyptagnostus-hemera ___________________ 11 Gom'agnostus ___________________________________ 16 Green Springs quadrangle, Nevada _____________ 42 greendalensis, Oedorhachis _______________________ 11 H haguez‘, Aphelaspis ______________________________ 8,33 Hallaspis _______________________________________ 22 hamblenensis, Aphelaspis _______________ 33 Hamburg limestone ____________________________ 5, 6, 10, 11, 14, 15, 20, 24, 26, 28, 29, 30 Hamilton district, Nevada _____________________ 18, 42 Hastagnostidae _________________________________ 16 Homagnostus. ______ 11,12,13, 19, 20, 21 acutus" ._- 19, 20, 38 comptus.. . 5 9,12, pl 1 obesus ______________________________________ 43 tumidasus __________________________________ 13 _ 13, 42, pl.1 Homodictya __________________________ 22 Hot Springs Peak quadrangle. ........ 42 Hot Springs Range, Nev _________ 9, 12, 18,21,35, 39, 42 House Range, Utah ____________________________ 26 Housiidae _______________ 33 hybrida, Marym‘llia ______________________________ 22 I inexpectans, Agnostus ________________ 5, 9, 12, 42, 43, p1.1 Iranella _________________________________________ 31 J Jubilee Mountain, British Columbia ........... 38 K Kazelia.. 32 speciosa ........ 32 Kinbladia _______________________________________ 37 Kingstom'a ...................................... 29 alabamensis._ _ 24,29,pl.6 upion ______________________________ 29 appalachz’a _______________________ 4 spicata ______________________________________ 10 INDEX Page Kingstoniidae __________________________________ F—29 Komuspz’della ___________________________________ 2.9, 30 loperz‘ ______ 30 occidentalis ___________________ 5, 6, 9, 10, 29, 30, pl. 6 seeleyi __________________________ _ 30 that ___________________________ _ 9, 30 Kormagnostus ____________________ _ 13 speciosus ____________________________________ 13 L Labiostria ___________________________ 31, 32, 33 laevis, Aspidagnostus ________ 6,15, pl. 1 law, Pseudagnostus ____________________________ 38 laza, Apheluspia ________________________________ 33 Leiostegiidae ............. _ . 29 _______ 29 Lejopyge _________________________ 10 Lincoln Peak formation ________________________ 8 Listrou ______________________________________ 31, 40, 41 tozoura...- 5, 7, 1,1, 43, pl. 6 sp. undet. _____________________ 43 Litocephalus ______________________ 31,32, 33 Llanoaspis ______________________ 23 Locality information and faunal lists ___________ 41 Lonchocephalus chippewaensix..__ 30 longifrons, Aphelaspis ___________________________ 33, 41 longispina, Carinamala _____________ 5, 6, 10, 23, 24, pl. 3 longocula, Coosz‘a ................. 5, 6, 9, 10, 28, 29, pl. 3 lopen', Komaspidella ____________________________ 30 M Machairagnostus___. 19 major, Proagnostus" 13 M aladioidella. .- _________________________________ 31 Marathon region, Texas _____________ 3, 12, 18, 26, 39, 43 maryvillensis, Proagnostus _____________ 13 Maryvillia _________________ 22 bristolensis._ ........... 22 hybrida _____________________________________ 22 McGill, Nev ___________________________________ 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 24, 26, 28, 29, 30, 35, 39, 43. Menomoniidae _____ 30 meslm‘, Oedorhachis _____ 19 Meteoraspis nuperus.... 42 milleri, Cedaria ..... 25 mimula, Blomm‘a _______________________________ 22 minor, Cedan'a __________________________________ 25,26 Mississippi Valley.. 6, 9 modestus, Praagnostusa . 13 Modocia _______________ _ 10 Mount Hamilton, Nev _________________________ 39 multisegmentus, Deiracephalus __________________ 30 Murphy Creek, Quebec ________________________ 9 N neglectus, Agnostus _____________________________ 12 Nericia ______________________________________ 31, 32, 37 Nevada ________________________________________ 42 Cherry Creek...- 3, 4, 5, 6, 7, 8, 10, 12, 14, 15, 18, 20, 24, 26, 27, 28, 30, 36, 39, 40, 41 Hamilton district ___________________________ 18, 42 Hot Springs Range ___________ 9, 12, 18,21,35,39, 42 McGill ........ 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13,14, 15, 20, 24, 26, 28, 29, 30, 35, 39, 43 Tybo ___________________________ 18, 21, 36, 40, 41, 43 nixonensz's, Blountia ___________________ 22 m'zom'a, Cedaria _____________ 25 nodosus, Agnostus _______________ 16 nodulosus, Glyptagnostus reticulatus" 18 Nonagnostid trilobite faunas __________________ 3, 6, 11 nordicus, Agnostus ______________________________ 21 Pseudagnostus _________ 21 nuperus, Meteoraspis ...... 42 0 obesus, Agnostus pisz’formis ______________________ 12 Homagnostus _______________________________ 43 Page occidentulis, Komaspidella ........ F—5, 6, 9, 10, 29,30,111. 6 Parabolinella. ._ _ 37 Oedorhachz's __________ 19 boltonensis __________________________________ 19, 21 greendalensis ________________________________ 19 mesleri ...... 19 tennesxemsis _______ 19 typicalis ....... 19 uln'chz' ______________________________________ 19 Olenaspella .................... 7, 31, 32, 33, 36, 37, 38, 39 ______ 37, 38, 39, pl. 5 regularis ........................ 5, 7, 38, 39, 43, pl. 5 separata __________________ 5, 8,32, 38,39, 40, 42, pl. 5 Olenidae _______________________________________ 32 Olentella ____________________________________ 31 Olenus _______ 32 gibbosus .................................... 32, 35 transversus __________________________________ 32 truncatus ______ 35 zone ___________ 9 Oncagnostus __________ 12 Opisthoparian ptychoparioid trilobites _________ 36 Opisthoparian trilobites ________________________ 23 Opisthotreta _________ ___- 7,8, 9, 18 sp _______________________ _ 7 Osgood Mountams quadrangle, Nevada ........ 43 P Parabolinella __________________________ 38 evansi ..... __ 36, 37, 38 occidentalis __________________________________ 37 Parabolinoididae _______________________________ 23 paradozus pisz‘formz's, Entomolithus“ 12 parmatus, Aspidagnostus ________________________ 14, 15 Pedinocephalus _________________________________ 31 Pemphiguspz‘s ............................ ___ 9, 22, 23 bullata ______________________________________ 22 4, 23, pl. 3 pernamagna, Ooosia _____________________________ 28 Peronopsis ______________________________________ 19, 21 perplerus, Crepicephalus.- _ 8 pisiformis, Agnostus ________ . ___ 9,10 Entomolithus paradoxus. _____ 12 obesus, Agnostus ____________________________ 12 Proagnostus _______________________________ 11, I3, 14, 19 bulbus.. ....... 13, 14 centeremz‘s ___________________ 13 major ________________________ 13 maryvillensis ________________________________ 13 modestus .................................... 13 romensz‘s .......... 13 speciosus ___________________________________ 14 Sp ______________________________________ 4, 14, pl. 1 Proaulacopleura ______________ __ 31,32, 33 buttsi _____________________________________ 35 prolifica, Cedan'a. _ 4, 7, 9, 24, 25, 26', pls. 3,6 Pseudagnostidae _________________________ 11, 18, 19,20 Pseudagnostina ____________________________ 7, 19, 20, 21 cantracta _____ _ 4, 5, 6, 20, 21, pl. 2 convergens- _ _____________ 10 Pseudagnostis.., _____________ 19 Pseudagnostus. _ ___________ 18, 19, 42, 43 acutus ______________________________________ 20 communis _____________________________ _ 5, 43 lotus ________________________________________ 38 nordicus ____________________________________ 21 reticulatus __________________________________ 16 spp _______________________________________ 21, pl. 2 Pseudolisaniu__ 27 Pseudorhaptagnostus ____________________________ 19, 21 Pterocephalz‘a ____________________________ _ 31,40 Pterocephaliid biofacies ______________________ 9, 10,11 Pterocephaliid trilobites ________________________ 32, 40 Pterocephaliidae _______________________ 9, 23, 31,32, 40 Pterocephaliinae ________________________________ 40, 41 Pterocephalina __________________________________ 31 Pterocephalops __________________________________ 31 Page Ptychagnostus __________________________________ F-16 (Ptychugnostus) _____________________________ 16 reticulatus ______________ 16 (Ptychagnostus), Ptychagnostus __________________ 16 Ptychopariida __________________________________ 22 puelchana, Cedaria .............................. 25 Q quadrata, Aphelaspis ............................ 33 R Rag/momma ____________________________________ 23 reoularis, Olenaspella ............... 5, 7,38,39,43, pl. 5 reticulatus, Agnostus ____________________________ 15,16 Glyptagnostus ______ 1, 7, 11, 13, 14, 16, 18, 24, 40, 42, 43 reticulatus __________________ 8, 9, 11, 18, 43, pl. 2 angelini Glyptagnostus _____ 7, 8, 9, 11,18, 39, 42, pl. 2 nodulosus, Glyptagnostus ____________________ 18 reticulatus Glyptagnostus ________ 8,9, 11,18,43,p1. 2 Pseudagnostus ___________________ 16 Ptychagnostus. _ ....... 16 Rhaptagnostus _______________ 18, 21 romensis, Proagnostus ........................... 13 rugosus, Aspidagnostus __________________ 5, 15, 42, pl. 1 S Saratogia ammo _________________________________ 33 seelepi, Komaspidella ____________________________ 30 INDEX Page separata, Olenaspella ........ F—5, 8, 32, 38, 39, 40, 42, pl. 5 Shell Creek Range _____________________________ 24 Sigmocheilus .................................... 31,40 simulans, Aphelaspis ___________________________ 33 Snake Range, Nev ......................... 8, 9, 24, 26 specioxa, Kazelia ............ 32 speciosus, Kormagnastus ........................ 13 Proagnostus ________________________________ 14 spicata, Kingstonia ........ _ 10 Spinagnostidae ____________ ___ 19 spinosus, Aphelaspis __________ 33 stolidotus, Glyptagnostus-.. 7,8, 11, 16, 20, 23, 24, 42,pl. 2 Stratigraphic significance of Glyptagnostus ...... 6 subditus, Aphelaspis __________________ 5, 35, 36, 43, pl. 4 Subisopygous opisthoparlan ptychoparioid tri- lobites ______________________________ 31 Subisopygous pseudoproparian trilobites _______ 25 superba, Coosia __________________________________ 27 Swarbrick formation ______ 18, 21, 36, 40, 41, 43 Systematic paleontology.. 11 ’I‘ Taenora ________________________________________ 31, 32 Tennessee. . 43 tennesseensis, Cedaria ___________ _ 25 Oedorhachis _________________________________ 19 Texas __________________________________________ 43 thea, Agraulos" _ _ 29 Komaspidellu _______________________________ 9, 30 F—49 Page toreuma, Glyptagnostus ________________________ F—15, 16 toroum, Listroa ______________________ 5, 7, 41, 43, pl. 6 transversus, Olenus ____________________ 32 Tricrepicephalus ______________________ 8 Trilobites associated with Glyptagnostus ________ 3 Triplagnostus _______________________ 16 truncatus, Olenus _______________________________ 35 tumidosus, Homagnostus ________________________ 13 tumifrons, Aphelaspis.__. ______ 33 Tybo, Nev ............ 18,21,36,40,41,43 typicalis, Acmarhachis" __ 6, 19, 20, pl. 2 Oedorhachis _________________________________ 19 U Ucebia __________________________________________ 29 ulrichz‘, Acmarhuchz‘s ............................ 20 Oedorhachis _________________________________ 19 unicorm’s, Deimcephalus _________________ 3, 4, 30, pl. 6 V valentinus, Agnostus ____________________________ 21 W wulcottz‘, Aphelaspis .................... 32, 33, 35, pl. 4 Woods Hollow shale ____________________ 3, 12, 18, 39, 43 Woodstock, A1a_.4, 5, 7,8,9, 14, 16, 20, 23, 24, 26, 29, 31, 42 woosteri, Cedaria ________________________________ 25 PLATES 1—6 FIGURES 1—11. 12—15. 16. 17—19, 23. 20—22. 24—30. 31—33. PLATE 1 Agnostus inexpectans Kobayashi, X 10 (p. F—12). 1, 6. Cephalon and pygidium from type lot, NMC 12005, Ice. P 6/6, north of Jubilee Mtn., west side of Columbia River, west of Harrogate, British Columbia, Canada. 2, 7. Cephalon and pygidium, USNM 143122 a, b. USGS colln. 2534—00, Cherry Creek, Nev. 3, 8. Cephalon, USNM 143123, from USGS colln. 2875—00; pygidium, USNM 143124, from USGS colln. 2876—CO, Cedar Bluff, Ala. 4, 5, 9—11. Silicified cephala and pygidia showing changes during holaspid development, USNM 143125 a—e, USGS colln. 2466—00, McGill, Nev. Homagnostus comptus n. sp., X 10 (p. F—12). 12. Holotype, silicified cephalon, USNM 143126. 13—15. Silicified paratype pygidium and small holaspid cephalon and pygidium, USNM 143127 a—c. All from USGS colln. 2466—CO, McGill, Nev. Homagnostus sp. X 10 (p. F—13). Latex cast of complete specimen in shale, USNM 143128, USGS colln. 2878—CO, Cedar Blufl’, Ala. Proagnostus? sp., X 10 (p. F—14). Cephala and pygidia, USNM 143129 a—d, USGS colln. 2888—CO, Woodstock, Ala. Aspidagnostus laem’s n. sp., X 10 (p. F-15). 20. Holotype cephalon, USNM 143130. 21, 22. Paratype pygidium and cephalon, USNM 143131 a, b. All from USGS colln. 2475—00, McGill, Nev. Aspidagnostus rugosus n. sp., X 10 (p. F—15). 24. Silicified meraspid 1 pygidium lacking groove in posterior border, USNM 143132, USGS colln. 2466-00, McGill, Nev. 25. Holotype pygidium, USNM 143133, USGS colln. 3049—00, McGill, Nev. 26—28. Cephalon and pygidium, USNM 143134 a, b, USGS colln. 2471—00; Pygidium, USNM 143135, USGS colln. 2535—00, Cherry Creek, Nev. 29-30. Cephalon and pygidium, USNM 143136 a, b, USGS colln. 2875—00, Cedar Bluff, Ala. Agnostid, gen. and sp. undet. X 10 (p. F—14). 31, 32. Cephalon and pygidium, USNM 143137 a, b, USGS colln. 3056—00, Cherry Creek, Nev. 33. Pygidium, USNM 143138, USGS colln. 2475—CO, McGill, Nev. PROFESSIONAL PAPER 374~F PLATE 1 GEOLOGICAL SURVEY GNOSTIDAE GNOSTIDAE AND CLAVA A PLATE 2 FIGURES 1, 3. Glyptagnostus reticulatus reticulatus (Angelin) X 8 (p. F—18). 2,5. Cephalon and pygidium, USNM 143139 a, b, from USGS colln. 2471—00, Cherry Creek, Nev. Glyptagnostus stolidotus Cpik X 6 (p. F—16). 4,6,7,1L Cephalon and pygidium USNM 143140 a, b, from USGS colln. 2886'CO, Woodstock, Ala. Glyptagnostus reticulatus angelim' (Resser) (p. F—18). 4. Slab showing infraspecific variation, compare reticulation on cephala in upper half of picture, X 3, USNM 143141, USGS colln. 2476—C0, McGill, Nev. 6, 11. Cephalon and pygidium, silicified, X 10, USNM 143142 a, b, USGS colln. 2466—00, McGill, Nev. Bluff, Ala. 7. Holotype, nearly complete specimen, X 4, USNM 26314, USNM loc. 89d, chert cobble from Cedar 8. Glyptagnostus reticulatus reticulatus? (Angelin) X 6 (p. F—18). Cephalon from Wilson boulder BM—4, USNM 143143, Marathon region, Texas. 9, 10. Acmarhachis sp., X 10 (p. F—20). Cephalon and pygidium, USNM 143144 a, b, USGS colln. 2886—00, Woodstock, Ala. 12, 13, 17. Acmarhachis typicalis Resser, X 10 (p. F—20). Cephalon and pygidia, note strong development of muscle scar areas on fig. 17, USNM 143145 a—c, USGS colln. 2465—00, McGill, Nev. 14, 15. Acmarhachis acutus (Kobayashi) X 10 (p. F—20). 16,21,26. Cephalon and pygidium, USNM 143146 a, b, USGS colln. 2471—00, Cherry Creek, Nev. Pseudagnostus spp., X 10 (p. F—21). 16, 21. Cephalon and pygidium, USNM 143147 a, b, USGS colln. 3058—00, Tybo, Nev. 18—20, 22—25. 26. Pygidium, USNM 143148, USGS colln. 2875—CO, Cedar Blufi‘, Ala. Pseudagnostina contracta n. sp., X 10 (p. F—21). 18, 22. Pygidium and cephalon, note muscle scar pits on fig. 18, USNM 143149 a, b, USGS colln. 2888—00 Woodstock, Ala. 23. Holotype pygidium, USNM 143150, USGS colln. 2888—00, Woodstock, Ala. 19, 24. Cephalon, USNM 143151, USGS colln. 2475—00; pygidium, USNM 143152, USGS colln. 2474—CO, McGill, Nev. 20, 25. Cephalon and pygidium, USNM 143153 a, b, USGS colln. 3056—CO, Cherry Creek, Nev. GEOLOGICAL SURVEY‘ PROFESSIONAL PAPER 374*F PLATE 2 24 GLYPTAGNOSTIDAE AND PSEUDAGNOSTIDAE FIGURES 1, 2, 4-7. 8, 11—13. 9, 10, 14—16, 20. 17—19, 21—24, 27—29. 25, 26. 30, 31. 32. 33, 34. PLATE 3 Carinamala longispina n. sp. (p. F—24). 1. Stereogram of holotype cranidium, latex cast, X 2, USNM 143154. 2. Cranidium showing posterior limbs, and pits in palpebral lobes, X 3, USNM 1431553.. 4, 5. Pygidia, X 3, USNM 143155b, c. 6, 7. Free cheeks, upper surface of genal spine of fig. 6 damaged by grinding, X 2, USNM 143155d, e. All from USGS colln. 2475—CO, McGill, Nev. . Carinamala sp. (p. F—24). Incomplete cranidium, X 3, USNM 143156, USNM loc. 90b, Woodstock Ala. Cedaria brevifrons n. sp. (p. F—26). 8. Stereogram of holotype cranidium, X 2, USNM 143157. 11. Free cheek, X 2, USNM 143158a. 12, 13. Larger pygidium, X 2; smaller pygidium, X 3, USNM 143158b, c. All from USGS colln. 2475—CO, McGill, Nev. Cedaria prolifica Walcott, X 3 (p. F—26). 9. Stereogram of cranidium, USNM 143159a. 10, 16. Pygidia, USNM 143159b, c. 14, 15. Cranidia, smaller cranidium with unusually long frontal area and narrow fixed cheeks for comparison with more common form shown in fig. 9. Larger cranidium exfoliated. USNM 143159d, e. 20. Free cheek, USNM 143159f. All from USGS colln. 2888—00, Woodstock, Ala. Coosia longocula. n. sp. (p. F-28) 17. Stereogram of holotype cranidium, X 5, USNM 143160. 18. Free cheek showing distinctive genal angle, X 3, USNM 143161a. 19. Larger cranidium, X 4, USNM 143162a. 21, 22. Larger pygidia, X 2 and X 3, note difference in ornament, USNM 143161b, c. 27, 28. Smaller pygidia, X 8, showing change in shape with growth, USNM 143161e, 143162c. 23, 24. Smaller cranidia, X 10, note prominent median glabellar swelling and large granules on fixed cheek of smallest specimen, USNM 143162b, 143161d. 29. Closeup of frontal area of large cranidium, X 4, showing fine granular ornament, USNM 143161f. Figures 17, 18, 21, 22, 24, 27, 29, from USGS colln. 2475—00, McGill, Nev. Figures 19, 23, 28 from USGS colln. 3056—C0, Cherry Creek, Nev. Coosia, sp. (p. F—28). 25. Pygidium, X 5, USNM 143163, USGS colln. 2474—CO, McGill, Nev. 26. Free cheek, X 4, USNM 143164, USGS colln. 2475-CO McGill, Nev. Cheilocephalus sp. (p. F—27). 30. Small cranidium, X 6, USNM 143165a. 31. Larger cranidium, X 4, with granular surface, USNM 143165b. Both from USGS colln. 2535—CO, Cherry Creek, Nev. Pemphigaspis sp., X 5 (p. F—23). Fragmentary cranidium, USNM 143166, USGS colln. 2886—CO, Woodstock, Ala. Blountz’a bristolensis Resser, X 3 (p. F—22). Exfoliated cranidium and pygidium, USNM 143167a, b, USGS colln. 2879—00, Cedar Bluff, Ala. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374AF PLATE 3 32 CEDARIIDAE, CREPICEPHALIDAE, CHEILOCEPHALIDAE, CATILLICEPHALIDAE, AND ASAPHISCIDAE PLATE 4 FIGURES 1—19. Aphelaspis brachyphasis n. sp. (p. F—33). 20—22, 25. 23, 26, 31, 32. 24, 2s, 33. 27, 29. 30, 34. 1. Stereogram of holotype cranidium, X 6, USNM 143168. 2. Small cranidium, X 6, for comparison with small cranidium of Olenaspella separata, pl. 5, fig. 21. USNM 1431698.. 3. Free cheek, X 4. USNM 143169b. 4, 5. Ventral View of anterior and posterior thoracic segments, X 8, USNM 1431690, d. 6-10. Series of pygidia, X 8, showing range of variation of width of doublure and border, USNM 143169e—i. 18, 19. Internal oblique and exterior views of hypostomes belonging to either this species or Olenaspella separata, X 6. USNM 143169j, k. Figures 1—10, 18, 19, silicified specimens from USGS colln. 2466—CO. 11—13. Free cheek, X 4; cranidium, X 3; pygidium, X 4, USNM 143170a—c. USGS colln. 2478—CO. 14. Thorax and pygidium, X 2, USNM 143171. USGS colln. 2479—00. 15—17. Cranidium and pygidia, X 5, illustrating differences of cranidial form between populations and extremes of variation of pygidial form within a population, USNM 143172a—c. USGS colln. 3055—00. All specimens from McGill, Nev. Aphelaspis subditus n. sp. (p. F—35). 20. Stereogram of cranidium, X 4, USNM 143173a. 21, 22. Pygidium, X 3; and exfoliated cranidium, X 5, USNM 143174b, c. All from USGS colln. 2535—CO, Cherry Creek, Nev. 25. Complete specimen, X 3, USNM 143175. Associated with Aphelaspis hvaquei (Hall and Whitfield) and Olenaspella reqularis n. sp. in a 40th parallel Survey collection from the Hamilton district, Nevada. Aphclaspis buttsi (Kobayashi) (p. F—35). 23. Stereogram of characteristic cranidium, X 4, USNM 143176a. 26, 32. Pygidium and free cheek, X 3, USNM 143176b, c. All from USGS colln. 2476—00, McGill, Nev. 31. Holotype, complete exfoliated specimen, X 2, USNM 93048, USNM 100. 910, Cedar Blufl’, Ala. Aphelaspis walcotti Resser (p. F—33). 24. Stereogram of latex cast of internal mold of holotype cranidium, X 3, USNM 94923. 28. Free cheeks on slab with holotype, X 3, USNM 94.923. 33.. Pygidium, X 4, USNM 94923. All from USNM 100. 1011, Tin Bridge, 3 miles southwest of Saltville, Va. Aphelaspis sp. undet. (p. F—36) Cranidium, X 3; pygidium, X 2, both exfoliated, USNM 14317711, b. USGS colln. 2879-CO, Cedar Bluff, Ala. Aphelaspinid? sp. (p. F—40) Pygidia, X 3, for comparison with Aphelaspis and Andrarina, USNM 143178a, b, USNM loc. 89d. Cedar Bluff, Ala. ‘ PROFESSIONAL PAPER 374-F PLATE 4 GEOLOGICAL SURVEY APHELASPIDINAE PLATE 5 FIGURES 1-3. Olenaspella regularis n. sp., X 3 (p. F—38). 1. Cranidium, USNM 143180a, USGS colln. 2534—00. 2. Holotype pygidium, USNM 143170, USGS colln. 2534-CO. 3. Variant pygidium showing development of second pair of inner marginal spines, USNM 143199, USGS colln. 2471—00. All specimens from Cherry Creek, Nev. 4, 5, 7. Olenaspella evansi (Kobayashi) (p. F—37). Cranidium, X 2, GSC 15147, pygidium, X 4, GSC 15151; and free cheek, X 2, GSC 15148, from original type lot of Parabolinella? evansi (Kobayashi, 1936), north of Jubilee Mtn., British Columbia, Canada. 6, 8—21, 23—26, 28, 30—32. Olenaspella separata n. sp. (p. F—39) 6. Pygidium, X 3, with single pair of marginal spines, USNM 143181a. 8. Large cranidium, X 1, USNM 143181b. 9. Free cheek, X 3, USNM 1431810. 10, 11. Pygidia, X 2 and X 3 with two pairs of marginal spines, USNM 143181d, e. 12. Smaller cranidium, X 3, USNM 143181f. Figures 6, 8—12 from USGS colln. 2477—CO, McGill, Nev. 13. Holotype, nearly complete individual, X 2, USNM 143182, USGS coll. 3039—CO, McGill, Nev. 14. Profile of silicified pygidium, X 5, USNM 143185a, USGS colln. 2466—C0, McGill, Nev. 15. Pygidium, X 3, with more elongate form characteristic of specimens in upper part of range of species, USNM 143183, USGS colln. 2480—CO, McGill, Nev. 16. Pygidium, X 4, USNM 143184, USGS colln. 3046—00, McGill, Nev. 17—19, 23, 24. Growth series of silicified pygidia showing development of inner pair of mar- ginal spines in larger specimens. 17, X 10; 18, X 6; 19, 23, 24, X 4. USNM 143185b—f. 20. Silicified free cheek, X 6, for comparison with associated cheek of Aphelaspis brachyphasis (pl. 4, fig. 3), USNM 143185g. 21, 26. Small silicified cranidium, X 6; larger cranidium in limestone, X 4, USNM 143185h, i. 25. Silicified thoracic segment, ventral View, X 8, USNM 143185j. Figures 14, 17—21, 23—26 from USGS colln. 2466-CO, McGill, Nev. 28. Pygidium with tiny second pair of marginal spines on inner side of prominent marginal spine, X 2, USNM 143186a. 30. Cranidia and pygidia with one pair of marginal spines, X 2, USNM 143186b. 31. Pygidium with three close-spaced pairs of marginal spines, X 2, USNM 143186c. Figures 28, 30, 31 from USNM 10c. 89d, Cedar Bluff, Ala. 32. Pygidium with three close-spaced pairs of marginal spines for comparison with fig. 31, X 2, USNM 143187. USGS colln. 1374—00, Hot Springs Range, Nev. 22, 27, 29. .Aphelaspidinae, gen. and sp. undet. (p. F—40). Cranidium, X 4; pygidium, X 3; free cheek, X 4, USNM 143188a—c, USGS colln. 2535—00, Cherry Creek Nev. PROFESSIONAL PAPER 374-F PLATE 5 GEOLOGICAL SURVEY APHELASPIDINAE PLATE 6 FIGURES 1—4. Deimcephalus unicorm's n. sp. (p. F—30). 1—3. Front, top, and side views of holotype, X 2, USNM 143189, USGS colln. 2886—00, Woodstock, Ala. 4. Incomplete cranidium, X 3, USNM 143190, USGS colln. 3056—00, Cherry Creek, Nev. 5, 8—10. Listroa toxoura n. gen., n. sp., X 6 (p. F—41). 5, 10. Cranidium and free cheek, USNM 143191 a, b. USGS colln. 2535—CO. 8. Stereogram of holotype cranidium, USNM 143192, USGS colln. 2471—CO. 9. Stereogram of pygidium, USNM 143193, USGS colln. 2534—00. All from Cherry Creek, Nev. 6, 7. Kamaspidella occidentalis n. sp. (p. F—30). 6. Stereogram of cranidium, X 5, USNM 143194. 7. Stereogram of holotype pygidium, X 4, USNM 143195. Both from USGS colln. 2475—00, McGill, Nev. 11, 12. Kingstonia alabamensis Resser, X 6 (p. F—29). 11. Holotype cranidium, USNM 94939. 12. Exfoliated pygidium from type lot, USNM 94939. Both from USNM loc. 90b, Woodstock, Ala. 13—19. Rostral plates. 13. Cedaria minor (Walcott), X 3, USNM 62779, USNM loc. 30N, Weeks formation, House Range, Utah. 14. Cedam'a prolifica Walcott, X 1, USNM 143196, USGS colln. 1208—C0, Lincoln Peak formation, Snake Range, Nev. 15. Aphelaspis buttsi (Kobayashi), X 4, USNM 143197, USNM 100. 910, Cedar Bluff, Ala. 16—19. External and internal Views of silicified rostral plates, X 20, from either Aphelaspis brachyphasisor Olena- spella separata, USNM 143198 a—d, USGS colln. 3020—00, McGill, Nev. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—F PLATE 6 , .IL. vrrv’WWf‘tf?’ 4w '4 “Jr 19 MENOMONIIDAE, PTEROCEPHALIINAE, LEIOSTEGIIDAE?, KINGSTONIIDAE, AND ROSTRAL PLATES 735 75 Pé V- 37% ’6 ”-59 «,6 F oraminifera from the Northern Olympic Peninsula, Washington .7 GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—G F oraminifera from the Northern Olympic Peninsula, Washington By WELDON W. RAU SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—G Stratz'grapflz’c and paleoecologz'c szgmfccmce of Foramz'mferdfrom a Tertiary segue” ce UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON :1964 ‘\ \ UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Oflice Washington, D.C., 20402 CONTENTS Abstract ___________________________________________ Introduction and acknowledgments ___________________ Geologic summary __________________________________ Stratigraphy ___________________________________ Structure ______________________________________ Planktonic assemblages __________________________ Benthonic assemblages __________________________ Age and correlation _____________________________ Foraminifera from the Aldwell formation ______________ Age and correlation _____________________________ Paleoecology ___________________________________ Foraminifera from the Twin River formation ___________ Age and correlation _____________________________ Lyre River section __________________________ Deep Creek section _________________________ Coast section _______________________________ (DtDOiODCfiOJrhrAI-FWWCOMb—Ir—IH Foraminifera from the Twin River formation—Continued Age and correlation——Continued Isolated outcrops ___________________________ Characteristics of faunal units ________________ Regional correlation _________________________ Paleoecology ___________________________________ Foraminifera from the Clallam formation _______________ Summary of paleoecologic interpretations based on F oraminifera _____________________________________ Identified species ____________________________________ Systematic discussion ____________________________ Additional identified species ______________________ Collecting localities __________________________________ References cited ____________________________________ ILLUSTRATIONS [Plates 1—4 in pocket; others follow index] PLATE 1. Geologic map showing U.S. Geological Survey collection localities. 2. Foraminifera from a part of the Twin River formation on Lyre 1River. 3. Foraminifera from a part of the Twin River formation on Deep Creek. 4. Foraminifera from a part of the Twin River formation between the mouths of East Twin River and Murdock Creek. TABLE 1. Benthonic Foraminifera from the Crescent formation _______________________________ 3. Foraminifera from isolated localities in the Twin River formation ____________________ Page G3 4 PLATES 5—7. Foraminifera from the northern. Olympic Peninsula, Washington. FIGURE 1. Stratigraphy of this report, southwest Wash- ington, and a Pacific Coast standard _______ 2. Frequency of occurrence of species in Twin River formation ________________________ TABLES TABLE 4. Foraminifera from the Clallam formation _____ 5. Additional identified species _________________ 6. Collecting localities ________________________ 13 14 14 24 26 28 31 Page G5 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FORAMINIFERA FROM THE NORTHERN OLYMPIC PENINSULA, WASHINGTON By WELDON W. RAU ABSTRACT Foraminifera from a Tertiary sequence that crops out on the northern part of the Olympic Peninsula, Wash., show strati- graphic and ecologic significance. Forty-two species that are important both to correlations and to ecologic interpretations are. illustrated and systematically discussed. The Foraminifera indicate that some of the rocks may be as old as early Eocene. The oldest rocks are tentatively referred to the Penutian stage of Mallory. Other parts of the sequence are referred to the Ulatisian and Narizian stages of Mallory, the Refugian stage of Schenck and Kleinpell, and the Zemorrian and Saucesian stages of Kleinpell. Several short periods of shallow, sheltered sea conditions are suggested by the Foraminifera from several parts of the strati- graphic sequence, but Foraminifera from most of the rocks suggest relatively deep, open-sea conditions. With the excep- tion of shallow, warm-water conditions in rocks of probable mid- dle Eocene age, the Foraminifera suggest that cool-to-cold water temperatures, regardless of depth, prevailed during the deposi- tion of most of the rocks of Tertiary age in the northern Olym- pic Peninsula. INTRODUCTION AND ACKNOWLEDGMENTS This report deals with the stratigraphic and ecologic significance of F oraminifera contained in a Tertiary sequence that crops out in the northern part of the Olympic Peninsula, Wash. (pl. 1). The work was done as a part of a program of geologic investigations for oil and gas possibilities conducted by the US. Geological Survey. The geology of four 15—minute quadrangles, the Pysht, Lake Crescent, Joyce, and Port Angeles, was mapped and the results published as two separate re- ports (Gower, 1960; Brown and others, 1960). Sam- ples for foraminiferal study were collected during the course of the geologic fieldwork in the summer months from 1952 to 1956. Stratigraphic sections were meas- ured by plane table and telescopic alidade. F oraminifera indicative of Eocene, Oligocene, and Miocene age were recognized in the northern Olympic Peninsula. Assemblages compare with previously known faunas from other parts of the west coast and are referred to the Penutian, Ulatisan and marizian stages of Mallory (1959), the Refugian stage of Schenck and Kleinpell (1936), and the Zemorrian and Saucesian stages of Kleinpell (1938). Detailed studies of the Foraminifera are hampered by their scarcity and poor preservation. Foraminifera are particularly rare in the older part of the sequence but they generally become more plentiful and are bet- ter preserved in the younger strata. Many hundreds of samples were taken, but assemblages that are signifi- cant of age and environment were obtained from 183 localities. Several methods of disaggregating the samples were tried, but the kerosene—water method was the most suc- cessful. When possible, approximately 150 grams of each sample was washed and all residue that was re- tained on a 150—mesh screen was examined. Many members of the US. Geological Survey gave assistance on the report. R. D. Brown, Jr., H. D. Grower, and P. D. Snavely, Jr., collected many of the samples, measured some of the sections, and supplied the geologic data upon which parts of this report are based. All photographs of Foraminifera accompany- ing the report were retouched by Mrs. Mary Wagner. GEOLOGIC SUMMARY STRATIGRAPHY The Soleduck formation of Reagan (1909) is strati- graphically the lowest unit known to crop out in the area and consists primarily of argillite and graywacke with minor amounts of conglomerate, arkosic sand— stone, and reddish calcareous argillite in association with volcanic rocks. Within the mapped area, the for- mation crops out only in the area south of a line ex— tending generally east and west of the south shore of G1 G2 Lake Crescent (pl. 1). The thickness of the formation is unknown, but in the mapped area it is estimated to be about 16,000 feet. However, these rocks are be— lieved to overlie similar rocks to the south, and the formation may therefore be much thicker. Although stratigraphically diagnostic fossils have not been found in the formation, its age is tentatively assigned as early Eocene (Brown and others, 1960). No F oraminifera from this formation were studied in connection with the present report. In some places the Crescent formation conformably overlies, and in other places it interfingers with, Reagan’s Soleduck formation. It consists primarily of pillow basalt, flow breccia, amygdaloidal basalt, and waterlaid tufl' with minor amounts of tuffaceous sedi- mentary rocks and reddish calcareous argillite. In the area mapped by Gower (1960) and by Brown and others (1960) the formation is exposed chiefly in a belt that extends from Round Mountain on the east to Dead— mans Hill on the west. It is also exposed on the north flank of the Clallam syncline between the mouth of Whiskey Creek and the Elwhat River. The formation varies considerably in thickness and generally becomes thinner to the west; its greatest thickness in the southeastern part of the mapped area is estimated to be 25,000 feet, and the thinnest sec- tion, which is in the extreme western part near Bear Creek, is estimated to be 6,500 feet thick. Foramini- fera from 11 localities indicate that the Crescent for- mation is post—Cretaceous in age and may be, in part at least, as young as middle Eocene. The Aldwell formation conformably overlies and interfingers with the Crescent formation. It consists mainly of well-indurated marine siltstone with lesser amounts of standstone and volcanic rocks. Discontinu- ous outcrops of this unit are present south of the Clallam syncline and extend from east to west across the area (pl. 1). The Aldwell formation has a maximum thick— ness of about 3,000 feet in the vicinity of Lake Aldwell, but it is thinner elsewhere and in some places it is over— lapped by younger rocks. The age assignment of the formation is based largely on Foraminifera, and they suggest an early late Eocene age. The Lyre formation as redefined by Brown and others (1956) conformably overlies the Aldwell formation and consists chiefly of conglomerate and sandstone. It crops out in the central part of the mapped area in a belt that extends from about a mile east of the Elwha River to beyond the west border of the mapped area. The thick- ness varies from more than 3,000 feet in the East Twin River area to only a few feet in some places; in other parts of the area the formation is entirely absent. Al- ‘SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY though no Foraminifera were obtained from the Lyre formation, assemblages of late Eocene age were col- lected from the rocks that crop out immediately above and below the formation. The Twin River formation, as redefined (Brown and Gower, 1958) overlies the Lyre formation and older rocks. Its outcrop belt occupies approximately the northern half of the mapped area and extends beyond both the east and west boundaries. The Twin River formation is divided into a lower, a middle, and an upper member. The lower member is chiefly thin- bedded siltstone and sandstone and has a maximum thickness of 7,500 feet and an average thickness of about 2,000 feet. The middle member is primarily massive to thin-bedded siltstone and contains abundant concre— tions. In places it is estimated to be as much as 5,000 feet thick, and it has an average thickness of about 2,000 feet. The upper member is predominantly massive, semi—indurated mudstone and sandy siltstone but in- cludes some beds of calcareous sandstone. Its thickness is about 3,500 feet in the western part of the area, where its upper contact with the Clallam formation is exposed. F oraminifera from the Twin River formation range in age from late Eocene to late Oligocene or early Miocene, The Clallam formation is the youngest known Terti- ary unit in the area. It generally crops out only in the area north of Last Creek and west of Pillar Point. The formation is composed primarily of poorly sorted gray fine— to medium-grained thick—bedded sandstone with minor amounts of conglomerate and sandy siltstone. It is estimated to be more than 2,500 feet thick. A Miocene age has been assigned to the Clallam formation, on the bases of both the mollusks and Foraminifera. STRUCTURE The principal structural feature of the area is the Clallam syncline. Its axis has been mapped from a point near the mouth of Murdock Creek eastward to the east boundary of the area. It is a west—trending asym- metric fold with steeper dips along its south limb. Smaller east—plunging folds are also present, particu- larly in the eastern part of the area. The Soleduck formation of Reagon is intensely deformed but no large continuous folds have been traced. Most of the major faults are parallel to the fold axes and trend generally westward. Some of them show stratigraphic displace- ments of as much as 5,000 feet. A few north—trending faults are also present, particularly in the eastern part of the area. No major faulting is believed to affect the measured sections; therefore, faults are not shown on plate 1. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON FORAMINIFERA FROM THE CRESCENT FORMATION Two distinctly different types of foraminiferal faunas were found in the Crescent formation. One of these consists almost entirely of planktonic Foraminifera and is known only from lenticular bodies of reddish argil— laceous limestone interbedded with volcanic rocks. The other type of fauna consists chiefly of benthonic Fora— minifera, and is known to occur only in basaltic sand- stone and tuffaceous siltstone in the upper part of the Crescent formation. PLANKTONIC ASSEMBLAGES Foraminifera were first reported from the lenticular bodies of reddish argillaceous limestone of the Crescent formation by Pardee (1921, p. 232) and were later mentioned by Park (1946, p. 310). About 50 thin sec- tions of reddish argillaceous limestone from 12 localities were examined in connection with the present study. Five of these localities, f11711 to f11715 (pl. 1), are within the mapped area. Because the fossils could not be separated from the matrix, they were examined only in thin section and were not specifically identified. Most of the F oraminifera are planktonic and are either globigerinids or globorotalids, but none are globotrun- canids (pl. 7, figs. 12, 13). The Foraminifera are abundant locally and are commonly concentrated in thin layers. Such concentrations of planktonic Foramini- fera as are found in the calcareous rocks of the Crescent formation are rarely found in other Tertiary rocks of the Pacific Northwest. The abundance of planktonic foraminiferal remains and the lack of benthonic foraminiferal remains in these red argillaceous limestone beds could be indirectly at- tributed to contemporaneous volcanic activity. The small lenticular bodies of red limestone probably repre- sent periods during which volcanism was locally inac- tive. Nevertheless volcanism probably continued in nearby areas because volcanic debris is incorporated in the red limestone. It is unlikely that any type of For- aminifera can live in or near areas that are undergoing submarine volcanism. Planktonic Foraminifera can be brought into such an environment by ocean currents, but they probably would die in mass and their tests would be deposited in concentrations as part of the accumulating sediments. Benthonic or nonfloating forms are less likely to be transported in large numbers by ocean currents and therefore in general only plank- tonic foraminiferal tests would be deposited. The planktonic assemblages of the Crescent formation are probably post-Cretaceous in age because they con- sist of globigerinids and globorotalids without any globotruncanids, which are indicative of a Cretaceous age. G3 BENTHONIC ASSEMBLAGES In addition to the planktonic fauna, 25 species of benthonic Foraminifera were collected from six other localities, f11716 to f11721, in basaltic sandstone and tuffaceous siltstone of the upper part of the Crescent formation (table 1). Although locality f11721 was mapped as Twin River formation by Brown and others (1960), the foraminiferal fauna from there is typical of the Crescent formation; it is therefore regarded here as fauna of the Crescent formation. Locality f11720 at Observatory Point yielded the most complete assem- blage. Berthiaume (1938) described several species of orbitoid Foraminifera from this locality. Samples collected during the present study also contain a few orbitoid Foraminifera, but Amphistegina caliform'ca Cushman and M. A. Hanna is the most common form in these collections. TABLE 1.—Benthonic Foramintfem from the Crescent formation [><, abundant to common; /, few to rare; ?, question-ably identified] Locality (pl. 1) Species (arranged taxonomically) fll716 {11717 {11718 fll719 {11720 fll72l ? Tritazz'limz sp __________________________________________ ____ _ 7Quinqueloc1llma Sp ________ Robulus spp _________________ Nodasaria latejugata Giimbel ______ 7Lagena sulcata (Walker and Jacob _ _ Elphz‘dtum sp _____________________________ __ Bulimina corrugata Cushman and Siegius ............... ?Bulimina schencki Beck _______________ Discorbia aff. alvea/ta stavemis Bandy. Valvulinerz‘a cl. V. cooperensz‘s Bandy cf. V. indiscriminata Mallory ______ \\\\\\ | . x n Epom'des sp. _ ..__ ?Epom'des sp. _ Rotorbz'nella calliculus Bandy __________________ ._ _ Amphistegz’na califomica Cushman and M. A. Hanna..- / _ Anomalina packardz‘ Bandy _____________________________ __-. _ _ Cibicides celebrua Bandy _____________ hvowelli, Bandy [1944], not Toulm lobatus (d’Orbigny) ______________ mcmastersi Beck ______________ ?Cibicides sp ______________________ Discacyclina psila Woodring ______ (Aktmocyclina) aster (Woodrin .-_ X\ The association of orbitoid Foraminifera with many Amphistegina suggests a marine environment with warm, shallow water. Vaughan (1945,p. 69,70) stated: The Discocyclinidae are warm-, shallow-water organisms. * * * The best temperature conditions [for the Discocycli- nidlae] would be those between 25° and 31°C. The depth of water in which the Discocyclinidae lived ranged from near or slightly below tide level to perhaps 100 meters. Some forms probably lived in tide pools. Cushman (1950, p. 300, 301) stated: This family [Amphistegenidael is largely limited to the Ter- tiary and Recent oceans. Astertgem‘na is often abundant on coral reefs and in warm shallow waters of the West Indian region, but less abundant elsewhere. Am-phistegma is very abundant in similar conditions and often is present in enormous G4 numbers in shoal water, particularly of the Indo—Pacific. It is frequent in such conditions through the late Tertiary. It is very probable that the genus is limited to about 30 fathoms in its living condition as, like other large Foraminifera, it seems to have commensal algae, the limits of which on account of the penetration of Sunlight in the ocean are limited to this same depth. AGE AND CORRELATION On the basis of orbitoid Foraminifera, Berthiaume (1938) correlated the Crescent formation exposed at Observatory Point with the orbitoid-bearing Sierra Blanca limestone of Santa Barbara County, Calif, and referred them both to an early middle Eocene age. Mallory (1953) agreed with this correlation, but also suggested a correlation of the Crescent formation With the “Mabury Reef sandstone” and “basal Spiroglyphus sands” at Media Agua Creek in California. He as- signed all these units to his Penutian stage, which he regarded as early Eocene (Capay) in age (Mallory, 1959). The fauna here described from the Crescent forma— tion substantiates a general age assignment of early to early middle Eocene. However, in terms of Mallory’s stages the present fauna suggests a Ulatisian age rather than a Penutian age because of the common occurrence of Amphistegim califomz'ca. This species was re- corded by Mallory only from his Ulatisian stage (1959, p. 84), which he regarded as middle Eocene and possibly early Eocene in part (Mallory, 1959, p. 77). In addition to the previously suggested correlations the fauna of the Crescent formation may also be corre- lated with that described from rocks of Eocene age at Cape Blanco, Oreg. (Bandy, 1944). Practically all the species in the Crescent fauna are represented by closely related forms in the Cape Blanco fauna and five species are regarded as identical. FORAMINIFERA FROM THE ALDWELL FORMATION Foraminifera are not abundant in the Aldwell forma- tion, but 49 species from nine localities in different parts of the formation were identified (table 2). AGE AND CORRELATION The foraminiferal fauna of the Aldwell formation can best be correlated with Laiming’s A—2 zone of the Eocene of California (1940; see also fig. 1, this report). Approximately one-third of the species known from the Aldwell formation (table 2) were recorded by Laimin g from his A—2 zone, and many others in the Aldwell formation are either comparable with or similar to spe- cies of his A—2 zone. U migem'na churchi Cushman and Siegfus, U. garzaemsis Cushman and Siegfus, Bulimina cormgata Cushman and Siegfus, and B. limta Cush- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 2.—Fommmifera from the Aldwell formation [X, abundant to common; /, few to rare; ?, questionably identified] Locality (Pl. 1) Species (arranged taxonomically) N Q! IO CD I\ (X! C5 O s E a a a a a a :2 v—1 H H H H H H H _. —1 —1 v-1 H v-1 v-l 1-4 v—1 .H M .... .. -... .... .... u. 9-: .. Gaudn/iaa Sp ............................. _._. _._- _..- _._- .... ...- Tritaltlmatolei Cushman and Siegfus ..... _._- ___. _._- / ___- Silicoswmmlina Califormca Cushman and Church ___- _-_- / --.- Robulus holcombensis Ben... I / cf. R. pseudovortea: Col _._- ___- _._- ____ welchi Church ________ / 519D“. ------------ .- -------------------- ~ '2 Vagmulmopsis vacamllensis(G.D.Hanna) . Marginulina cf. M. subbullatu Hantken.__ ?Demalina dusenbmyi Beck..- Dentalina Sp. C [of Rau, 1948]. Nodosaria latejugata Gumbel._ longistagata d’Orhigny ______ .__ _ Pseudoglandulinacf. P. inflate (Broneman) _._- ? ___- ___- -___ / ._.. ..._ _._- Bolivinapsis directa (Cushman and Siegfus) _._. ___- ___- ___. _._- ___. _._- ___- / Plectofrondicularia packardi multilineata Cushman and Simonson ________________ .... ___. _-_. ? _._. / ? _-_. ___. ?Amphimarphina ignota Cushman and Siegfus ________________ ' _________________ _ _._ _..- _._. / _._- _._- / _-_. _._- Amphimorphina caliform‘ca Cushman and McMasters ............................. Bulimina cf. B. bradburyi Martin _________ ccrrugata Cushman and Seigfus _______ X Zirata Cushman and Parker ...... cf. B. avata d’Orbigny ............. Bifarina nuttalli Cushman and Siegfus Uviyerina ehurchi Cushman and Siegfus... garzacnsis Cushman and Siegfus ...... Angulogerina hannai Beck ________________ Pleurostomella Sp _________________________ _._- _._. ___- ._., _.._ / Valvulineria tumeyensia Cushman and Simonson ____________________________ Gyroidina orbiculan‘s planata Cushman Eponidea umbonatus (Reuss) _________ - yeguaensis Weinzierl and Applin. - . .... _._. / Cancris joaquinensis Smith ________________ ? ___. ._-. 7 X ___. / Asterigen’na crusaiformis Cushman and Siegfus ................................. ‘I _._- _._- _._- / / / / / Amphistegina sp ___________ ..- ___. / Alabamina kernensis Smith.._ '7 Cassidulina globoxa Hantken._ Allomorphina maostoma Kan-er“ C'hilostomella cf. 0. oolina Schwaget ....... _._- ___. . _._- _._- Pullem‘a cf. P. salisburyi R. E. and K. C. Stewart _________________________________ _._- __-_ _._- ..._ ___- Globigerina cf. 0. yegmemis Weinzierl and pphn _________ . / ? _._- / / ?Globigerina sp. C _-_. ___. _._. _-_. _._. ?Globorotalia sp.-. _._- _._- ___- _._- Anomalina cf. A. regina Martin. _._- ___- _._- _._- _._- / Cibz'cides celebrus Bandy .......... . elmaensis Rau ______________________ ? _-_. ___. ___. ? hodgei Cushman and Schenck. martinezensis malloryi Smith.. cf. C. venezuelanus N uttall.-._ ?Cibi6ides Sp ...................... ._-_ -_.- ___. / ___. _-_- man and Parker, all of which are in the Aldwell, are regarded as characteristic of the A—2 zone. A low posi- tion in the A—2 zone is suggested for the Aldwell fauna because it contains such species from Laiming’s C zone as Astem'gem’na crassiformis Cushman and Siegfus, BifM-z'na nuttalli Cushman and Siegfus, Bolivinopsis directa (Cushman and Siegfus), and Tritamilz’na colez‘ Cushman and Siegfus. Laiming (1940) showed that these species, which are common in his C zone, also occur in the lower part of his A—2 zone. The fauna of the Ald- well formation is correlated with the A—2 rather than C—zone faunas because it contains only about one-half as many species that are known from the C zone as are known from the A—2 zone or higher. This correlation is supported also by stratigraphic evidence because B- zone assemblages which normally separates C-zone and FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON A-zone assemblages have not been found in the rela— tively complete section above the Aldwell formation. Of the faunas noted in Mallory’s division of rocks of Eocene age in the California Coast Ranges (1959) , the fauna of the Aldwell formation is best compared with that of his Bulimi’na comgata zone of the lower part of his Narizian stage. The Aldwell formation contains G5 Amphimorphina califomz'ca Cushman and McMasters, a form that Mallory indicated is restricted to the upper part of his subjacent Ulatisian stage in California. Therefore a part of the Ulatisian stage may be repre- sented in the Aldwell formation. However, A. califor- him is found frequently in western Washington and Oregon in association with Foraminifera that compare Cenozoic correlation on Pacific coast Southwest Washington , rt (adapted from Weaver and others, 1944) (Rau, 1953) This repo Age Age Stage Zone 0f Zone Formation Formation Laiming Saucesian _ . Astoria(?) formation Clailam 1 (of Kleinpell, 1938) Epistomtmlla puma (lower part) I” formation Miocene QIigo- 4' '7‘ ‘ Mlocene Upper member Zemorrlan Pseudoglandulina (of Kleinpell, 1938) aff. P. inflata Lincoln formation . Oligocene of Weaver,(1912> Middle member Oligocene Epom'des Kleinpelli : Refugian .9 (of Schenk and E Klein ell, 1936 E0- p ) Sigmamorphina § _ __,_ _,_ _ Oligocene schemki a , > ii 7 .5 ' 3 Bulimina schencki Sk k h k ’— oo umc uc formation Lower member A-1 Plectofrondiculam’a .7 cf. P. jenkinsi Northcraft Narizian formation (of Mallory, 1959) A-31 Um'gen’na ‘ Lyre formation cf. U. yazooem‘ls McIntosh formation A-2 Eocene Eocene 7 Aldwell formation Bulimina Ctr B. jacksonensis _“ 7 7 Ulatisian ‘: ' z 2 2 (of Mallory, 1959) B Vaginulirwpsis vacam'llensis . assemblage Crescent(?) formation Crescent formation , (base not exposed) Penutian __ _ _7_ _ _ _7_ _ _ (of Mallory, 1959) C 2 ( f MBi‘i‘Wariesm D ‘ § 7 — o a or , Paleocene Ynez?“ Schmuck formation Paleocene (of Mallory, 1959) E of Reagan,(1909) (?) _ .'_)— _ __7__ Cretaceous Cretaceous(? 1 Position of A-S zone modified by Rau (1958) 2 B zones not differentiated FIGURE 1.——-A comparison of the stratigraphy of this report with that of southwest Washington and a standard of the Pacific Coast. 1678833 0—63—2 G6 best with those of Mallory’s B. cormgata zone and therefore, locally at least, A. caliform'ca may not be necessarily indicative of a pre-Narizian age. Faunas resembling those in the Aldwell formation are also found in the Canoas siltstone member of the Kreyenhagen shale (Cushman and Siegfus, 1942) and in the Alhambra formation (Smith, 1957) of California; similar faunas have also been found by the writer in the upper part of the Yamhill formation and the lower parts of the Nestucca and Toledo formations in Oregon, and in the McIntosh formation of Washington. PALEOECOLOGY The similarity of all known assemblages of the Ald- well formation suggests that they probably lived in similar ecological conditions, but conclusions regard- ing these conditions are necessarily based on consider— able supposition. It is possible to be reasonably certain of only a very generalized concept of the environment in which the Foraminifera of the Aldwell formation lived. Bandy’s work (1953) with Recent Foraminifera from three widely spaced profiles normal to the California coast, off San Diego, Point Arguello, and San Fran- cisco, is the only record of west coast assemblages that are at all similar to the fauna of the Aldwell formation. These assemblages are confined to the deepest and cold- est water that was sampled, and are largely from the Point Arguello profile. Several of the species in these Recent assemblages are similar to species of the Aldwell formation and most of the genera are represented in the fauna of the Aldwell formation. The comparable ferms from off the California coast are recorded chiefly from depths between 3,000 feet and 12,000 feet and at temp- eratures between 15°C and 0°C. The number of indi- viduals with similarities to the Foraminifera of the Aldwell formation generally decreases in shallower and warmer water. From these generalized comparisons with Bandy’s work on Recent Foraminifera it can only be concluded that some of the Foraminifera in the Aldwell formation probably would have thrived in an environment of rela- tively deep and cold water. FORAMINIFERA FROM THE TWIN RIVER FORMATION Foraminifera are more common in the Twin River formation than in any other formation in the mapped area. Assemblages were found in nearly 400 samples and, of these, approximately 160 samples contained sufficient foraminiferal material to be useful in this study. Foraminifera were collected from three meas- ured sections, the Lyre River (pl. 2), Deep Creek (pl. 3), and on the coast between the mouths of the East SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Twin River and Murdock Creek (pl. 4). Many samples were also obtained from isolated outcrops and short sections throughout the mapped extent of the Twin River formation (table 3) . Most samples contain only a few species of Forami- nifera and are only sparsely fossiliferous, but because many samples were studied, a sizeable number of species were identified from the formation. Because they are poorly preserved, many of the Foraminifera are tenta- tively or questionably identified. AGE AND CORRELATION Precise correlations and age determination of foram- iniferal assemblages in the Twin River formation are hampered by the scarcity and poor preservation of F oraminifera. Furthermore, some species that are known to have different stratigraphic ranges in other areas are found together in parts of the Twin River formation. This apparently anomalous association of species may be due to varied local ecology or perhaps to a reworking of fossils from lower parts of the sec- tion; therefore, age determinations of assemblages from isolated outcrops and correlations of faunas from parts of measured sections are based on assemblages or groups of assemblages rather than on individual species. Four faunal divisions are recognized and they are referred to the upper Eocene upper Narizian stage (Mallory, 1959), the Eocene and Oligocene Refugian stage (Schenck and Kleinpell, 1936), and a lower part and an upper part of the Zemorrian stage (Kleinpell, 1938) of Oligocene or Miocene age. F oraminifera were collected from all three members of the formation in a measured section in the Lyre River area (pl. 2) ; this section is used as the basic ref- erence for the study of the foraminiferal sequence in the Twin River formation. LYRE RIVER SECTION Foraminifera are scarce in the lower member of the Twin River formation in the Lyre River section. Those species which are present, however, suggest a late Eo- cene age and for the most part they are recorded from the upper part of the Narizian stage of Mallory (1959). Angulogerina hamai Beck, Cassidulina globosa Hant- ken, and Globigem'na of. G. yeguaensis )Veinzierl and Applin are the most significant species because they are most commonly known from rocks of late Eocene age in other areas. No Foraminifera were obtained from approximately 1,400 feet of sandy strata in the upper part of the lower member, and the age of the upper part of the lower member could not be determined. Foraminifera indica— tive of the Refugian stage make their lowest occurrence in the Lyre River section at the base of the middle G7 FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON I I I I I \ \ I I I I I I I I I I \ I I I I I I I I I I I I I I I I I I I - I I I I I I I I I - I I ...... Exam 9% :mfiamao 3.35: .m as I I I I I - \ I I I I I I I I I I I \ I I - I I I I I I I I I \ I I I I I I I I I I - I I I - I I .......... Exam was «35550 8.32.? - I I I I I I I I I I I I I I I I - I I I I I I I I I I I I I I - - I I I I I I I I I \ \ I - I I ............ Siam Ea 92:550 33.: I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I - I \ I I I - I \ w I I I ........ 33on was 555:0 Eugteo I I I -. - I - I .. I I I I I I I - I ~. \ I I I I I I I .- I I I I I I I I I I I I I I I I I -. I I - I .- I I .- I I - - I IwEEEQ was :aaamno E3323 ESENEQ I I I I I I I I I \ \ I I I I I I I I I I I I I I - I I I I I I I I I I I I I I I I I I I I I I I I I I .- I I I I I - ........ 23:35 3585:..335 ufiuiExgm I I I I - I I I I I I I I I I I I \ I \ I I I I I I -. \ I \ I I I I \ I I I I I I I I I I I I \ I I I \ I I I -. I \ ..................... 55:25 .2233: \ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I \ I I \ \ I \ I I . I ... I I I I \ I I I I ............................. xenopom and :afinmdo “3333 €53an \x--.- \ \ :\ \ \ 7:..\ F :x. 7- \ I; 7.. \ \ \ \ 7.. 7-... 71...-.. \ 7..-. \ 7-: \ .. ............................ 5.55m 6:1. $5550 83533.: «353.9 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I \ I I I I I I-:E::O fiSiSNw .E stagfigfixgewa I I I I I I I I I I I I I I I I I I I I I I I I I I I \ I I I I I I I I I .63»on and 55559 88:3 fiaofiamem X I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ......... @335 53:55 .N do EEEEBN I I I I I I \ N. I X I I I X I X X I I I I I I I \ I I \ I I I I I I I I I I I I I I I232 65... 6.33.5 ”€333an .2 a? X I I I I I I I I I . I I I I I I I I I I I I I I ................ $58539 EitfigEez I X I I I I I I I I I I I I I I I ..................................... am I I I I I I I I I I I I I I I I I I I I I I I \ I I \ I I I I I I \ I I I I I I I I I X I I I I I I I I I I I I I I I ......... 53H Nutfiufimogwa uEeSeEoEEm. I I I I I I I I I I I - I I I I Aug-$35 SSS .nw «o sfiaRSEEeaaugmfl I I I I I I \ I I I I I I I I I I I I I I I I I I I I I I I I I I I I ~. I I I I I I -------------------- >=Hf9c wEwBEQ I I I I I I I I I I I I I I I I v I I I I I I I I I I I I I I I I I I I I I I I I I IESNNO can amfizmscv 3525 d .3 - - w -- .- -- .- \ - -- - .- -. - -- - -- -- -. .- .- -. -- - .- -. .- \ -. - -- -. -- - - .- - .- -- \ -- - - - -. .- -. - - -- - \ -- - -- -. .. ----------------- Sam-55.3 Esif... I I I I I I I I I - I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I \ I I I I I - I I I I I I I I I ......... 5530 can :aEAwso E§E3 I I I I I H I I I I I I I I I I I I I I I I I I ~. I \ I I I I I I \ I I I I I I u. I X I I I I I I I I I I I I I I I Iiaafio was 5:230 fia:e§a§§§¢ I H H H- -. I -- I -- I -- \ -- I - -. - \ I - -- I - - - - -. - I -- .- - .- - -- I I -- -- -- - .- -- - -. \ - - - - I I - - - -- I - .- ............ 283 E; .823: 38:; HI I -H HH I H HH H -\. HH H HH H H. I -H HH HH H H I -. I I I I \ I I I I I I I I I I I I I I I I h I I I I I I I I I I .................. :cwEazFS 33.523... \ \ \ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ................... EomEazFSV £32: I I I - I -. \ I I \ I I I I I .ofikufiwm was 5:530 53.538 2335 - - I I \ \ ............ AnnwEoEomv 85$ N Ea - - I IX \ I\ \ \ \ h II\ \ \ I \ II \ II \ I \ II\ N. -\ \ I \ II \ I... w IIIIII M. II\ \ I N. .................................... 355 .2225 85:: ....~ .3 eésugefiegsnl \ \ \ - \ - -. M. w - I I I - - I - m. I \ - N. - \ - I I I \ \ X - IIIIIIIIIIIIIIIIII znmfiuofi u»§S»E§~ I - M. I - I ....................... 6&an 3&3st I I - .................. :EESM SEE .2 .3 I \ I I I I \ I- \ I .- I I I I I I I I \ I I I I I - I I I I I I IIIIIIIIIIIIIIIIIII H5932 usuflww .2 .Ea . I - . - I . I I \ I I I I ~. I I I I I I I I I I N I I - I I I I I I I I I I ............. wmzom SEES: .2 go 3.225%? M. I -I- IIX -I\ --.I.------. .I \ - I \ I\ \IIIIIIIIIIIIIIII \ IIIIIII M. II \ I N. I ..................................... mam \ -\- \ \ I \ H H H H H H H H H .- I -\. H H -. -H I H .\. H H H H- ... I \- - - I -- I .- N. I .- - I - -. H - -- - I - - H - - I -- \ - - - I I- .................. 3:: 58:3 0 .am I I I I I I -. - I I w.- -\-\ I I H H- I - - I I - I N. K. N. a I I I I a I I \ \ - I I - I I I - - - - - I - ..................... Evfi 5mm r; W .Qm I I I I I - I I I I I I I I I I I I - I I I I - I I -. I I - I I I - I - - I -. I I .................................... 5 .EEA E5 555:0 SSEEEu .Q go - ........................ xumm S5o§¥§ ............. zaflnuofi 35.53.39 .Q do - ...................................... >52 .525 was $5530 ES .Q .6 252.39 H H HH HH HH HH HH H HH H HH HH -\- H HH HH HH I H H HH HH HH HH H I .K... I HH I I I I I I I I I H- I I I H- H. H. I I N. I H. I I I I I I I I I ..... :8:qu SEES»; .3 .3 $3353: I I I I I I I I I I I I I I I I I HH I I I I I I I H I HH I HH H HH H H HH H H HH -H HH HH H -H -H -H H HH H H -H H -.- H “ -\- H H H H I-I-r-n- .................. nohzhww SSEMW I: :u Ed ENE w: M§§ . . .7-. \ --\ \ \ \ \ 7; \ x--7-\ 7. \ .. . --\ :::\:::: 7. \ .-x\ 7.. \ xx.-.:-----A.-....-.m.m---Ikngm......s....w........ ................ 3:56 S33 E do ”SEEN N. .................................... am ggnN -\. HH I H HH H HH HH HH H HH HH HH HH HH HH HH I HH H HH HH H HH HH H H. I I I I I H H. I I HH HH H H. I H I I I H. I -H I I I I I I I I I Momm ESE .5 do $233.25 I I -\- I I I I I I I I I I I I I I H I I I I I - I I I \ - I \ - I \ N \ - I - I I I I \ I - I I HH-H-III ............... am u§3§~eEE§~ 33.39 ”.3258 agmmoSEm. I I I I I I I . . N. ISmEW 9% 53530 SEES eEEucEtQm. . \ \ \ N. X a - I ............................ :mm .2283 I I I I I I I I I. ............. kiwi-5% ESQ—gut» .0 do m. \ \ X m m. \ N. I \ m. I X m I \ I ........... «ESE 15:23am $3395.. \ \ a. N. N. .................................... 25m 35 dnqmm «383623 a§~§£§§§o N . I ................................... 50:50 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I . ES £3530 35338 e§§essn8§m I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I -\- I I I - I \ I I ....... 95me was $5530 ES a§§s§§ I I I I I I I I I I I I I I .- I I .- I -\- I -\- I -\. -\- I I NA- : .\- I I I I I I - I I I I -\- I I I H- - - I - M. I I - - I -------------------- 3am EngwfigfifieS I I I I I I I I I I I I I I I - - I - \ I I I I I I I .- I I I I I I -\- -\- I I I I I I I I -\- I I I -H - I I H .\- H- H- H- - I -------------- xuom SEES M .E Sfitwtek - I I - - - I I - I I I I - - - - - I I -. I I I I .- - I I I I I - I I - I - I I - -. .H -H .H - I --------------------------------- an gawkwgm I I I I .- .\- -. I I \ I - .- - -\- -\- .\- -\. I .- - I I -\- \- .\I I .- - -. I -\- I I I I .- I .- -\. I -\- I - I - I - I \ -------------------------- aw uSEaSueEEPN -\- -\- I I -\. - I I I I I I -\- - I I -. I I I I I - - I I -\- I I I .\I I I I I I I I I I I I I - \ \ I I -H I I I H. -\- H HH H HH H- ------ 93595 £253.33: .6 do 5.5.355 I I I I I - - I - I I I I I I I I I I I I I I I I I I I I I I I I I I I I - I I I I I I I I I I I I I I I I - .- - - ----------------------------------- m .am I I I I I I I - I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I - I - -\ . - \ III-mamflm 35 $5550 5.58 u§~§§> \ \ - - I I - I I ------------------------- am «gmsefimafifim 01-81 [J V6LIIJ £6LIIJ SgLIIJ 6§LIIJ SILIIJ LfLIIJ 9fL111 QVLII} IILIIJ EVLIIJ 6£L11¥ 8£L111 LSLII! 088111 6L811} BLSIIJ Z1811} 06811} £88111 £88111 188111 9LSIIJ 9L8III ZLSIII 898111 99811! 99811! 89811! 598111 198111 098111 IVLIII EELIIJ ZSLIIJ 188111 38811! OVLIII 98811! 988111 £8811! £5811! VLSII! SL811} $9811! 66L11} ZILIIJ $8LIII 3an “030A AEEEEonoxS wownahav an”: JESSE Ea €298 93: fiaewm an... 523.6 on“: .5532 $.88 am: £355: was“ firhcaoa . 2 .3 .3285 33:52 3932335 c. ”2.2 o..— 58 .\ HoEEoo 8 unacaaaa .X_ :SugfiBek .ESafigwm QE§SO 8:223: 2: § :cfisgicx hue-em SEE.- ufi § 33:38» @2393 Sosa Em®§§EeRIfi $5.8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY .. .. .. .. .. .- .. -. -. -. .. -. -. -. .. .. -. -. .. .- .. .- .. .. .. .- .. .. .- -. .. -. .. .. .. .- n n .H m n n -H ..H .. .. .H -. .. u .. -. .H .. \ -. -. .. \ n .. .. .. .. .......................... Haggis“ .. .1 .. .- .- .I -I -. -. .. .. I- .- .. - -. -I . - .- .. - II .. .. .. - -. \ -- .- -. \ I. .. -I 1. ........... Saga—Z §§Su§uu§ua.0 .«o .. .. -. .. : .. .. .. .. .. .. -. -. .. n H. .. Hzn ”Hun n H mu m H .. n-“ n ..-. -H -. .. H. .. .. ...-. ..-. -.-- \ .. .. .. .. .- \ .. \ -. .. \ .. .. ........... Eam3§§ asoafiss -. .. .. .. .. -.-. -. ..-. .. .. -. -. .. .. .. .. n.-. .. I .. .. .-.. : .. -. n .. H. .. m .-w mm .H n H mm .. .... -.-. -H .. .. \. \ .4 h .. \ .. .. .. .. .H ..H ............... aaéoégfis .. .. .. .. .- .. .. .. -. .. .. .. .. .. -. -- .. -- .. .. .. .. .. .. -. .- .. .. -. .. -. .. .. .. .. u .. -. -. .. \ .. -. H. u n .\. n n H. u n w u n u .. n n v u n n H. u-....muwwmomamfiflmuw«Rafi m.\..\.m.\1\.mnu.\.umnxmsmm inn Ck. \ \ \ \ \ \ \ \x\ \ \ T; T- \ \ \ \ \.....::...: \ ..\ ......................... =§§§§ . . . . .. .. .. .. . .. .. .. .. .. .. .. : 1 : .. .. .. 1 .\. .. .. .. .. «A H v» .\. .\. .. X \ X \ .. .. \ H .................... Exam Ssssasifi .. 1 .. .. .. 1 .. .. 1 .................................. :ownom 95 58:30 a .. \ \ \ .. \ .. ........................... . \ \\\~ ................................ mdw 1111.\.H....-HHHHMHHH.\.HH.\.HHH. ...H.\.1H1...111......-... .................................. <.% 1 1 .. 1 1 1 1 1 .. .. 1 1 .. 1 1 \ w .. .. \1 \ 1 1 .. .. .. .................................. SEA: 1 1 1 1 .. .. 1 .. 1 1 1 can EoEEog €53.39 .c as SEEQSG .\.1111\..1. 1 11H .\.HH1HHHHH1 \11 \ \ 1 .. \1 \ 111111.: .. .11..1.... .. ............... Manamamfitgefiseuéam -. 1 I. 1 .. -..-........-...11-.111....H ..HH-HH...H--.-..1.. N. 11...... \ ..11-.1...- ~. ...-....1....1.-1...-.aEBwum.O.Mcfim.m.mghge3~aw.n~.wo 1 .. .. .\. 1 1 .. 1 .. 1 1 .. .. 1 .. 1 .. 1 1 .. .. .. \ . 1 . .. \ .. .. 1 1 1 1 \ 1 1 .. .. 1 .. 1 \ 1 X .. 1 .. 1 1 .. \ 1 1 .. .. .. ............. finflfiobv 833:3 E§§§ 1 1 .\. 1 1 .. .. 1 1 1 1 .. . .. . .. 1 . . .. .. .. .. 1 \ 1 .. \ .. .. \1 1 .. 1 M. 1 .. .. 1 .. 1... 1 .. \ \ \ 1 1 1 1 1 \ .. \ 1 1 ........ pumaanom 528.0 do SEESuSEO 1 1 1 .. .. 1 1 1 1 1 . .. . . 1 . - .. 1 1 1 1 .. .. 1 .. .. .. .. .. .. 1 .. 1 1 1 .. .. 1 1 .. 1 1 .. 1 1 .. \ 1 1 1 .. \ 1 .. .. 1 .. ........... “9.3M a§8~23§ afififefioav- .. .\. I\. .- .. .. II .- .I -I .. .. X I\. H .H .\IH .. H -H .H \ .- .I .. .- -. II .I I. -. .I .I .. I. .. .. II .. I. -I I. .. .I .. .. .. .. I. I. -I -. II -. -. .. I- .. I. .. .- .- .. .......................... Qm wuumchsfimmmao 1 1 .. 1 1 1 .. 1 1 1 .. .. H .. 1 H. 1 .H H .. H. H. H H H H H H H H .N. \1 .. 1 X 1 X .. 1 \ 1 1 1 1 1 “ .\. 1 w 1 1 -. .. .. 1 1 .. .. .. 1 .. 1 .. ....................... 32m 2332:“ .. 111.. 1 1 ......1.. 11..1.... 1 ~ .. 111 ....................... nemanamgoas \\\ \XX\XX\X\XX\XX\\\11111\XX\X\\a......11..1........1..1......111.............\.1..1 .................................. nomnom 1 1 .. 1 .. .. .. .. .. .. 1 .. .. .. .. . 1 1 1 1 1 .. was 58:30 Setggagfiu uSEEmBU 1 -. .. 1 -. .. .. .. -. 1 .. .. .. .. -. 1 .. .. 1 .. 1 1 H H H H H H H H H H H H H .. H X .. \ X \ .- \ x 1 \ .. .. X .. :\ \.. .. 1 .. \ N \ \1 .. ................ .EEm 332:3. 2:533?- . \ \....-..-......-... \ \1111 ................................. #823 1 1 1 .. 1 .. 1 .. 1 1 1 1 .. .. 1 1 .. 1 .. 1 .. . 95 5353.0 «5322.3 ngwEaSeSD 1 .. 1 .. 1 . 1 1 .. .. . 1 H1 1 .. .. 1 .. .. .. .. H H. H 1 H H H .H H. .. .. .H 1 1 1 .. .. 1 .. 1 1 .. .. 1 1 .. 1 1 .. 1 .. 1 .. 1 1 1 \ 1 1 1 1 1 ........................... am ugssgasw 1 . : .. -. .. 1 .. -. .. .. .. 1 .. 1 .. -. p .. .. \ \1 .. : 1 .. ................................... 333m .. 1 .. 1 .. 1 1 1 1 1 1 1 .. . . . .. 1 .. was aaann—O fiESHSmEo egtuutsufl .. 1 1 1 .. 1 .. .. .. 1 .. 1 -. H. H. -H 1 .. H H .. H H. .. H 1 .- .. .. .. .. .. 1 .. 1 .. .. .. .. .. .. .. 1 1 1 1 1 .. .. .. .. .. 1 .. 1 1 ... .. .. .. .. .. 1 .................... gm 3§ue§§§§em ~. .w...~.\\~....\\ \ 1 .. .. .. .Aagm 9.3 gamma—UV SE38 aEESQEN .. 1 .. .\. ....... 5:54 95 EMEESW» £2$§u3 1 1 .. 1 .. 1 . 1 1 1 1 .. 1 .. .. . . . 1 .. .. 1 ..................... mmsam 23:33.: \ \ X X \ \ . \ \ \ .. . . N. \ . 1 \ a .. 1 .. 1111111.. 1 1..11.. ..1.. 1.1.1.11fiaBBmd.Mwna.m.m can $5530 Suggeufie «33952: 1 1 1 .................. 32an $333... ..N do .. .. 1 .. 1 1 -. .. \ .. 1 1 ................................ nemnoawm EB mafia-:0 $332»: .5533 nufigam \ 1 \ ~. \ ........... aaflnmao SEER 3253895 1 .. 1 1 .. -Egonow was 52:5:an 28:8 aSEeSQ \ . X \ 1 .. 1 ................. nfifim figufiiafi ”.2330 \ .. 1 .. 1 .. 1 1 1 .. 1 .H H 1 .. .H H .H H 1 .. .. 1 \ .. 1 1 1 .. .. .. 1 .. \ 1 1 1 .. .. 1 1 1 1 1 .. .. .. ~. .. 1 .. 1 1 1 1 1 .. 1 1 1 1 ...-newcofi_m was 58:30 flatufig‘a 1.1....- 11 -.. ......11 .. \ ..1...\ 11...- ...... \ 1.111111... ....1... ....................... sammmm§eae§s ......1..HHH..H.\.HHHH...H:1..1 \ \ ......:.1......... .....1 ........................ smmggogs 1 1 \ 1 ................................... 35am 1 1 1 1 1 1 1 I. 1 1 1 1 1 33:53 ”mggeafii 5 Ex ES§~§N~5 1 -. .. 1 1 ........... stmOeA Egg .Q do $333.5 1 1 -. .. -. .................................... 9E5 .559 33:88 .H go etaaggenfimm \ \ .- \ 1 .................. gown SEES EE§£§§N 1 1 1 1 1 ........... dam SENEQ ..8 EE»%§3§® 1 1 .. 1 1 1 1 1 1 1 1 1 1 .. .. 1 1 1 . 1 1 .. 1 \ 1 X X \ 1 1 1 1 \ 1 \ 1 \ \ N. \ 1 1 1 \ 1 \ 1 1 1 1 \ X 1 1 1 1 ....... mEuEm can :aEfiDO 333.2% 1 1 .. .. 1 1 1 1 I- 1 1 1 1 1 .. .- -. .. 1 IN H. 1 1 1 1 1 1 1 1 ~. .- 1 1 1 1 1 -- 1 1 1 .- -. 1 1 1 1 1 1 .. -. 1 1 1 1 1 1 1 -. .. .- 1 1 .................... :aESmDO Saiozg 1 1 1 1 1 .. 1 1 1 1 1 1 1 1 1 1 1 1 .- 1 1 .H H H 1 1 1 1 1 1 1 1 1 1 1 X s. \ w 1 \ \ \ \ 1 1 X X 1 X X 1 1 1 1 1 1 1 1 1 1 1 1 .. .................... 55:30 E§a$8 1 1 .. 1 .- 1 .- 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1H. 1 H. 1 1 .. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 .- 1 I- 1 1 1 w .. 1 1 1 1 M. 1 1 .. .. 1 ..1m3m2w was daanmso E935 eSSEE» X \ -- 1 . .- . -- 1 1 -. -. -. 1 1 -. .. -- -. -. -. 1 1 -- -- -. -- -- -- -. -. .. -. -. -- 1 -- -- -- 1 1 1 ................................. 3:53 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I. 1 1 I. .- was 55:30 2.52:: 33: uEEEEaD \ \ \ X -- -- -. -- -. 1 -- -. 1 -. -. -. 1 -. .. -- -. .- 1 -- 1 -- 1 .- -. -- -- -- -- -. -. 1 .. 1 -. 1 1 1 -. 1 ............................ 2352M 1 1 -. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 .. 1 . 1 was 58:30 $3.23»? SeEEaS - -. .-hI-I.-.-....---.-\....--...-----I---.~15..-..---I-...II-... .................................. EE 1 1 1 1 1 1 1 1 1 1 I. 1 1 1 1 1 1 1 -I 1 1 .. 1 .. 1 .. 1 1 . 1 . . .n< can. Emanmno mwmgugfitfi .m ..8 1 1 1 1 1 1 1 1 1 1 1 I. 1 1 1 -\. .. .\. 1 -\- 1 1 1 1 1 1 1 1 1 . 1 .H H. H. 1 .. 1 1 .. 1 1 1 .. .. 1 1 1 1 1 1 1 1 1 1 1 1 1 .. 1 1 1 1 1 .................. :aEanO 3:23 $.3on 1 I. 1 1 -- 1 1 .- 1 1 1 1 1 1 1 1 1 1 1 1 1 .. I. -- 1 1 1 . . 1 . 1 1 1 1 .. 1 X 1 1 1 .- 1 1 1 1 1 1 1 -. 1 1 .. 1 1 1 1 1 ............................... am 2:335 1 1 1 1 1 1 1 .. 1 1 1 1 1 .\. -\. 1 .\- 1 .. 1 I. 1 .\. -\. 1 .\. 1 1 1 -H 1 1 .\ -H -\ 1 ~. 1 .. 1 1 1 1 1 1 1 1 1 .. 1 1 -I 1 .. 1 1 1 1 1 1 1 1 I. 1 ............................. am 3.253835% . . 1 1 1 1 .. 1 -. 1 \ \ . 1 .. -. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 .............................. Siam 1 1 1 .. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 .. 1 1 1 1 1 1 1 1 1 1 1 \ 1 1 1 1 \ \ 1 1 1 .. 1 1 1 1 1 1 \ I \ - was :afinmao SEES: ”3:33: 1 1 1 1 1 .. .. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 . 1 1 .......................... Moon $3.23. N. \ A. \ XX\ \ >\\ \\\ s\ \1\ X.~.\ --\\ \X-.\I.\\\X\\-. .................. hnwfiuokcsgefifiv 62.5300 Iwiamaq “Ex €230 3&5: aSExsm ILBIU OLSIIJ 69811! £9811! 96LIIJ V6LII! S6LIIJ ZGLIII IBLIIJ 06LIIJ GSLIIJ SSLII} SQLIIJ ZQLIII IQLIIJ OQLIIJ GfLIIJ SVLIII LVLII! QVLIIJ 9?LIIJ VVLIIJ SfLIII 6£LII¥ SSLIIJ l QSLIIJ QSLII} ISLIIJ 688IIJ 088111 SLSIII 8LSIII 51811! LSLIIJ OVLIIJ 068111 SBSIIJ £88111 18811} 9L81II QLSII! ZLSII} 89811} 998111 99811} 298111 Z9811! 19811! 09811} TfLIIJ ESLIIJ ZSLIIJ 988111 988111 VSSIII 88811! 88811} LLBII} VLSIIJ SL811} fQSIII 66LII¥ ZfLIIJ PSLIIJ G8 “wan-D SBo‘H awe .:&52M 25 £558 an: Essex 32: $8236 ad: 5:52 EEEEESS wannabe 3mm: ioqfisvd omfim cflbofioN macaw : .5 >283 cannflqooléguggmexfi .Ezmgwgum 93:33 :.sufse: 2: :.g :Sgfita $9.3m $.35“ 22 § $2333 @2223 Sosa Swh§§§ok1fi ”:58 FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON member, immediately above the sandy strata of the upper part of the lower member. Because the highest assemblage of Narizian age and the lowest assemblage of Refugian age are separated by 1,400 feet of unfossil- iferous section, the boundary between these two stages cannot be placed precisely, and therefore, in this report, is questionably placed in the middle of the unfossilif- erous part of the section. The following, Whose lowest occurrence is above the unfossiliferous sandstone, are the more significant species of the Refugian stage: Quinquelocuh’na weacem' Rau Nonitm cf. N. pompilioides (Fichtel and M011) Bulimin‘a alsatica Cushman and Parker sculpting lac-imam Cushman and Parker Refugian Foraminifera occur throughout all but ap- proximately the upper 300 feet of the middle member of the Twin River formation in the Lyre River section. Such species as Cancrz's joaquc’nemz’s Smith and Cassi- d-ulina globosa Hantken occur in the underlying strata of the Narizian stage as well as in the Refugian stage, but none occur in rocks of the overlying Zemorrian stage; therefore a combination of Narizian and Refu— gian species in an assemblage is used as evidence to differentiate faunas of the Refugian stage from those of the overlying Zemorrian stage. The base of the Zemor- rian stage is indicated by the lowest occurrence of Bulimina cf. B. alsatz’ca Cushman and Parker, Cassi- dulz'na, crassz'punctata Cushman and Hobson, and Sphaeroz'dz'na variabélis Reuss. The known occurrence of these species is limited to rocks no older than those assigned to the Zemorrian stage. Additional species that characterize the Zemorrian stage in the Pacific Northwest and which are also present in the Lyre River section are Entosolem'a sp., Bobulus of. B. calcar (Linné), and Nom'on incisum (Cushman). A lower fauna and an upper fauna of the Zemorrian stage are recognized in the Twin River formation, but these two faunas do not necessarily correspond to the lower and upper faunas of the Zemorrian stage of Kleinpell in California. In the Lyre River section the lowest occurrence of the upper fauna of the Zemorrian stage is best indicated by the lowest occurrence of Nom’on incisum (Cushman), about 100 feet below the top of the measured section. DEEP CREEK SECTION Foraminiferal assemblages from the Deep Creek sec- tion suggest an age no older than that of the Zemor- rian stage (pl. 3). Foraminifera were not found in the lowest part of the formation in the Deep Creek section, but the lowest assemblages obtained resemble those of the lower part of the Zemorrian stage in the 678833 0—63—3 G9 Lyre River section. No Foraminifera characteristic of either the Refugian or the Narizian stage were found in the lower assemblages from the Deep Creek section. The occurrence of Cassidulina crassz'punctata Cushman and Hobson in the lowest assemblages from the Deep Creek section is significant because this species not only is a common species in the Zemorrian stage throughout the Pacific Northwest, but its lowest occurrence is in the Lyre River section above the base of the Zemorrian stage. Bulimina cf. B. alsatica Cushman and Parker, although not a common form in the Twin River forma- tion, is found also in the lower assemblages of the Deep Creek section. Its lowest occurrence in the Lyre River section is in the lowest beds assigned to the Zemorrian stage. The lowest occurrence of Nom’on incisum. (Cush- man) is a few hundred feet below the top of the meas- ured section in Deep Creek and best marks the base of the upper part of the Zemorrian stage in this section. Buliminella subfusiformc’s Cushman, Bolivina, margi- nata adelaidamz Cushman and Kleinpell, and U vigem’na gallowayz' Cushman also make their lowest occurrence in the uppermost part of the measured section in Deep Creek, and E pom'des mamfieldz' oregonensz‘s Cushman and R. E. and K. C. Stewart was found in several sam- ples in the upper half of the measured section. None of these species are abundant, but they are important because they rarely occur in rocks older than those assigned to the Zemorrian stage. Records of U. gallo- wayi Cushman are confined largely to rocks assigned to the Zemorrian stage. COAST SECTION Faunas of the upper part of the Zemorrian stage are well represented in the rocks exposed along the coast between the East Twin River and Murdock Creek, where a thick section of rocks is assigned to the upper part of this stage (pl. 4). Because in the area of this report the coastal section contains the most complete section of rocks assigned to the upper part of the Zemorrian stage, it is regarded as a reference section. Nonion incisum (Cushman) occurs at the base of the coastal section and is found throughout the lower half of this measured section. Elphz'dz'um cf. E. vmrz'mctum (Reuss) is common in several samples from the upper part of the coastal section, and within the mapped area this species is known only from the upper part of the Zemorrian stage. Cassz'dulm wassz'punctata Cushman and Hobson is present in a number of the samples from the coastal section and is regionally indicative of the Zemorrian stage. A high position in the Zemorrian stage is suggested by the presence of Builimina alligata Cushman and Laiming, U vigem’na gallowayi Cushman, G10 and Cassidulinoides sp. because of'their common occur- rence in the upper part of the Zemorrian stage in other regions of the Pacific Northwest. ISOLATED OUTCROPS Studies of foraminiferal assemblages from the Twin River formation are based chiefly on collections from the three measured sections, but faunas from these sections are augmented by many collections from scat- tered localities in other parts of the northern Olympic Peninsula. About 300 samples of Foraminifera were collected at random and 65 of these contain fossils that are useful in dating the containing rocks (table 3). The relative age of assemblages from these samples was determined by comparing them with faunas in the measured sections. The 65 samples from scattered lo- calities contain assemblages that range in age from Narizian to late Zemorrian, Assemblages referred to the Narizian stage are gen- erally of two types. Some are similar to those of the Aldwell formation, but most are similar to assem- blages that are believed to be younger than those of the Aldwell formation. However, the younger ap- pearing assemblages do not always occur in the highest stratigraphic position. This anomalous condition may be due to reworking, or it may indicate that the fauna is more indicative of facies than of age. The following species were not found in the meas- ured sections but are present in assemblages from iso- lated outcrops. They are at least locally indicative of the Narizian stage and are useful in delimiting its up— per extent. Quinqueloculim goodspeedi Beck Robulus welchi Church Bulimina corrugata Cushman and Siegfus Valvulinerta aff. V. jacksonensis persimilis Bandy Asterigem’nw crassiformis Cushman and Siegfus. Oibicides lobatus (d’Orbigny) Refugian, lower Zemorrian, and upper Zemorrian as— semblages from isolated outcrops do not differ signifi- cantly from assemblages from the measured sections. CHARACTERISTICS OF FAUNAL UNITS Faunal divisions in the Twin River formation are based primarily on observations of the Foraminifera in the Lyre River section. Additional and substantiat- ing information was obtained from other sections and from isolated outcrops. Particular use was made of the observed range of species, the recorded range in other areas of species present in the Twin River formation, the association of species, and the frequency of occur- rence of species. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Many species do not characterize any one faunal unit because they are found throughout the formation. Other species occur so rarely that their significance is not known. Species displaying the greatest signifi- cance are listed on figure 2. This figure shows the observed ranges, combination of occurrence, and fre- quency of occurrence of selected species. The fre- quency of occurrence of a species is given as a ratio, in percent, of the number of samples in which a given species occurred with respect to the total number of samples obtained from a given stage or stage subdivi- sion. Because many more samples were available in the younger stages, the evidence concerning the limits of these stages and ranges of the species in them is much more reliable than is that concerning the rela- tively unfossiliferous lower part of the section. There- fore, the calculations shown on figure 2 should be con— sidered only as a broad guide for determining which species are probably the most useful stratigraphically in the Twin River formation. REGIONAL CORRELATION Foraminiferal assemblages of the Twin River for- mation that are comparable to those referred to Mal- lory’s Eocene Narizian stage are known in southwest Washington from an upper part of the McIntosh formation and parts of the Skookumchuck formation. There they are referred to either the Bulimina schencki-Plectofmndicularia cf. P. jenkinsz' zone or the Uvigem'na cf. U. yazooensz's zone (Rau, 1958). In west- ern Oregon similar assemblages are known from the Coaledo formation (Cushman, Stewart, and Stewart, 1947, p. 57—69) and from a lower part of the Toledo for— mation (Cushman, Stewart, and Stewart, 1949), and they have been observed by the writer from parts of the Nestucca formation. In California similar assem- blages are known from the Alhambra formation (Smith, 1957) and the Kreyenhagen shale (Cushman and Siegfus, 1942). Although faunas similar to those in both the lower and upper part of the Kreyenhagen shale are present in the Twin River formation, they do not necessarily occur in the same stratigraphic order as they do in the Kreyenhagen shale. In the Twin River formation these two faunas may represent two different environments or one of them may have been reworked into the Twin River formation from older rocks. All the above-mentioned west coast assemblages have been referred to Laiming’s A—l or his A—2 zone of California. In the standard west coast section (\Veaver and others, 1944) these zones are considered late Eocene in age (fig. 1) . FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON G11 Stages . Refugian Zemorrian (Schenck Narizian Species (Kleinpell,1938) and (Mallory, Kleinpelly 1959) Upper Lower 1936) 53‘ 55 33 17 Noninn incisum (Cushman) .......................................................................... 2y Elphidium cf. E. minutum (Reuss) ................................................................ H Bolivina marginata adelaidana Cushman and Kleinpell ........................................ 8 Buliminella subfusiformis Cushman .............................................................. 6 Cassidulina crassipunctata Cushman and Hobson ............................................... 43 27‘ Eponides mansfieldi aregonensis Cushman and R. E. and K. C. Stewart ................. 12 5__________ Cassidulinoides sp .................................................................................... 12 6 Sphaeraidina variabilis Reuss ..................................................................... 9 H Bulimina cf. 3. alsatica Cushman and Parker .................................................. 7 fl Robulus cf. R. calcar (Linné) ...................................................................... 4 9 Quinqueloculina weaveri Rau ........................................................................ 25 10 8 Anomalina californiensis Cushman and Hobson ................................................... 15 M 7 Bulimina alsatica Cushman and Parker ............................................................ 7 12 2 _________ Entosolenia sp ......................................................................................... 10 8 1- _ _ _ Uuigerina cocoaensis Cushman ....................................................................... M Bulimina sculptilis laciniata Cushman and Parker ........................................... 6 Plectofrondicularia packardi packardi Cushman and Schenck ............................... 13 3 Alabamina kernensis Smith ......................................................................... 13 6 Cancris joaquinensis Smith ........................................................................ 12 9 Bulimina schencki Beck ............................................................................. 4 2 Cassidulina globosa Hantken ...................................................................... 6 5 Cibicides celebrus Bandy ........................................................................ 3 g Angulogerina hannai Beck ........................................................................ 2 n Cibicides martinezensis malloryi Smith ........................................................ 1- ._ _ ._ 3 Globigerina cf. Gr yesuaensis Weinzierl and Applin ........................................ 7 Cibicides lobatus (d’Orbigny) ...................................................................... 5 Quinquelaculina goodspeedi Hanna and Hanna .................................................... 5 Asterigerina crassaformis Cushman and Siegfus .............................................. 3 KEY _ _ _ __ — - - < 5% 5—10% 11~20% 21—30% 31—50% > 50% Width of bar indicates percentage categories based on the ratio of number of samples containing listed specieszto total number of samples examined in each stage or stage subdivisionh x Total number of samples examined in each stage or subdivision. 2 Number of samples in which listed species was found. FIGURE 2,—Frequency of occurrence of selected species of Foraminifera in the Twin River formation. G12 Twin River assemblages that are assigned to the Refugian stage are comparable with Refugian assem- blages from the lower and middle part of the Lincoln formation of Weaver (1912) in southwest Washing— ton, where they are referred to the Sigmovmov'phz'na schencki and E ponides klez'npelli zones (Rau, 1958). In western Oregon similar Refugian assemblages are known from the Keasey formation and Bastendorff shale (Cushman and .Schenck, 1928; Detling, 1946) and they have been observed by the writer from a middle part of the Toledo formation near Waldport, Oreg. Comparable Refugian assemblages of California are known from the Tumey formation (Cushman and Simonson, 1944), the Gaviota formation (Wilson, 1954), and the VVagonwheel formation (Smith, 1956). In terms of the standard west coast section (Weaver and others, 1944), the Refugian stage is “Eo-Oligo- cene” and Oligocene in age. Zemorrian assemblages similar to those of the Twin River formation are known from the upper part of Weaver’s Lincoln formation in southwest Washington, where they are referred to the Pseudoglamdulina aff. P. inflata zone (Rau, 1958), the upper part of the To- ledo formation of western Oregon, and the upper part of the San Lorenzo formation of California (Cush- man and Hobson, 1935). The Zemorrian stage is gen— erally regarded as “Oligo~Miocene” in age. PALEOECOLOGY Only generalized interpretations can be made of the environment in which the Foraminifera of the Twin River formation lived because many of the species are extinct. Conclusions are necessarily based largely on the assumption that fossil species required the same environment as similar living species. Furthermore, data on many living species are incomplete and in some cases controversial. The following generalized inter- pretations are based on depth and temperature records of living species either identical with or similar to species known from the Twin River formation. Data on the depths and temperatures under which certain Foraminifera are known to live come from several inde- pendent records and, in many cases, are too numerous to cite in the discussion. The following references are cited as the major sources of depth and temperature data used in this report: Cushman (1927), Norton (1930), Natland (1933), Kleinpell (1938, p. 11—19, fig. 5), Glaessner (1947, p. 183—194), Parker (1948), Phleger and Parker (1951), Crouch (1952), and Bandy (1953). Particular attention has been given to species that were found in substantial numbers or that occurred persistently throughout thick sections of the forma- tion. Because the occurrence of many species is rare or SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY sporadic, the number of species used in determining paleoecology is limited. The Foraminifera of the Twin River formation gen- erally suggest an environment of deep cold water in an open sea. Gyroidina orbiculam's planata Cushman is the most common and persistently occurring species known in the formation. Records of this species and similar species show that they prefer cold water at bathyal (600 to 6,000 feet) to abyssal (6,000 feet or more) depths. A similar environment is indicated by the commonly occurring species Uvigem’na cocoaensis Cushman, U. garzaensz's Cushman and Siegfus, and Cassidulina crassipunctata Cushman and Hobson. Although it is never found in large numbers, the planktonic form Globigem'm is found in places and suggests that the mapped area may have had reasonably good access to an open sea. Although the evidence is not conclusive, Foraminifera from the lower part of the formation suggest a more shallow environment than do the Foraminifera from the middle and much of the upper part of the formation. Angulagem’m and certain species of Gibicides that are similar to species generally recorded from upper bathyal and neritic depths (approximately 2,000 feet to tidal depth) were found in many of the samples from the lower part of the formation. Deep-water species, such as Gyroidim orbiculam's planata, also are present. The depth at which the combination of species from the lower part of the Twin River formation lived is there- fore estimated as moderate, uppermost bathyal to lower neritic (approximately 1,000 to 300 feet). Several assemblages from isolated localities within the lower part of the formation are comparable to the cold‘, deep-water fauna of the Aldwell formation and may have been reworked into the Twin River forma— tion. However, if they lived during the deposition of the Twin River formation, a depth greater than 1,000 feet may have also existed in local areas during depo- sition of the lower part of the formation. Costate Uvz'gerina, Plectofondz'cularia, and Nom'on pompz'lioides suggest bathyal depths (6,000 to 600 feet), whereas Camcm’s and Alabamma are recorded from cold but shallower water. These Foraminifera occur to- gether in the middle and in much of the upper part of the Twin River formation and suggest bathyal depths, between 6,000 and 1,000 feet. During the deposition of the uppermost part of the upper member of the Twin River formation, depths probably were decreased but water temperatures re- mained at least cool. Gyroidina, together with several other forms characteristic of bathyal to lower neritic depths, persist throughout the middle and upper mem- bers of the formation. However, E lphidz'um of. E. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON mimtum (Reuss) and Nomlon incisum (Cushman) be- come common in the fauna of the uppermost part of the upper member of the formation. Foraminifera of this type suggest shallow-water conditions. N. incisum suggests cool temperatures in a somewhat sheltered en- vironment. Cool conditions are further suggested by the presence of abundant Cassidulz'na of the type that is found in cool water of Recent seas. Although the up— permost part of the formation does contain some deep- water F oraminifera the greater abundance of shallow forms here than in any other part of the formation sug- gests that the water became more shallow but that the temperature remained cool. Probably in the final stages of deposition of the Twin River formation upper neritic depths became dominant, a prelude to distinct neritic conditions that prevailed during the deposition of the overlying Clallam formation. FORAMINIFERA FROM THE CLALLAM FORMATION The known foraminiferal fauna of the Clallam for- mation consists of 11 species (table 4) collected from three localities (f11891, f11892, f11893) in the north— west part of the mapped area. TABLE 4.——Fommmifera from the Clallam formation IX, abundant to common; /, few to rare; ?, questionably identified] Locality (pl. 1) Species (arranged taxonomically) 111891 f11892 £11893 Triloculina sp _____________________________________________________ / ........ Robulus sp ................................................................ / Nonion costiferum (Cushman). ___ inciwm (Cushman) ___________ Elphz‘dium cf. E. mimztum (Reuss Bulimina cf. B. ovate d 0rbigny. _ Bolivina advena Cushman _______________ Vulvulineria cf. V. depressor Cushman_.. Gyroidimz orbicularis plunata Cushman __________ Epgnidea mansfieldi oregonensia Cushman and R. E. and / . 0. Stewart. Anomalina californiensz’s Cushman and Hobson ................... / Although the fauna is small, it nevertheless is indi- cative of age. Nom'on costifemm makes its lowest occurrence within the area at the base of the Clallam formation. According to Kleinpell (1938, p. 116), N. costifemm makes its first occurrence in the Saucesian stage of California. This statement is substantiated by observations of the writer in Oregon and in south- western Washington. In southwestern Washington it makes its lowest occurrence in the E pistominella puma zone (Rau, 1958), which occurs largely in strata mapped as the lower part of the Astoria( ?) formation (Snavely and others, 1958; Pease and Hoover, 1957). In western Oregon its lowest known occurrence is near the base of the Nye mudstone in the Yaquina Bay area. The foraminiferal faunas of both the lower part of the Astoria( ?) formation and the Nye mudstone are con- sidered to be of Saucesian age by the writer. Both G13 Bolivim advemz Cushman and Valvulinem’a of. V. de- pressa Cushman support a Saucesian age even though thev occur in small numbers in the Clallam formation. The upper age limit of the known foraminiferal fauna of the Clallam formation is not as strongly indicated. Anomalina califomz'ensz's makes a rare oc- currence at one locality. This species is little known above the lower part of the Saucesian stage. A Sauce: sian age for at least the lower part of the Clallam for- mation is further suggested by stratigraphic evidence because in places the Clallam formation rests conform- ably on Zemorrian age strata of the Twin River forma- tion (Gower, 1960). Foraminifera were not collected from the uppermost part of the Clallam formation and therefore the age of that part of the formation was not determined on the basis of Foraminifera. The Sauce— sian stage of the standard west coast section (Weaver and others, 1944) is regarded as “Oligo-Miocene” in age. The small foraminiferal fauna of the Clallam forma- tion is also suggestive of the environment in which it lived, probably a shallow, cool, and somewhat sheltered sea. Nom'on costifemm is common in samples from the three localities. Kleinpell (1938, p. 15; and table 1) inferred that this species is common in neritic waters and in areas sheltered from current action. Further- more, Kleinpell (1938, fig. 5) considered the genus Nonion to be a cool-temperate-water form. E thz'dz'um of. E. minutum is also common in the Clallam fauna. Species similar to it are almost always found at shallow depths (Phleger and Parker, 1951, pt. 2, p. 10). E po- m'des mansfleldi oregano/mats occurred at all three Clallam localities. This species is similar to E. hamwz', which Phleger and Parker (1951, pt. 1, p. 51) indicated is confined to depths of less than 100 meters in the north- west part of the Gulf of Mexico. Gyroz'dz'na orbiculam's planata, which occurred at one locality in the Clallam formation, is the only conflicting evidence for a shallow depth, because records of this species are usually from greater depths. However, its known preference for cold water suggests cool-water conditions as suggested by Nom'on. The remaining species from the Clallam formation occur too rarely, or their recorded environ— ments are too varied, to be suggestive of the probable environment. SUMMARY OF PALEOECOLOGIC INTERPRETATIONS BASED ON FORAMINIFERA The abundance of planktonic Foraminifera known from parts of the Crescent formation suggests that sometime following the Cretaceous period and prior to late early Eocene or middle Eocene time, open-sea con- ditions probably prevailed in the area. The absence of benthonic forms in these assemblages suggests that G14 the environment was unfavorable for the existence of bottom—dwelling Foraminifera. The distribution of planktonic Foraminifera is largely dependent upon ocean currents; therefore, their presence in the Crescent formation suggests that they were brought into the area even though conditions were not continuously favorable for their existence. The concentrations of planktonic foraminiferal remains in certain places in the formation - suggest periodic annihilation. Conditions for mass destruction of planktonic Foraminifera could have re— sulted from extensive submarine volcanic activity that is indicated by the numerous pillow basalt flows in the Crescent formation. In late early to middle Eocene time shallow protected bays existed at least during the deposition of the upper part of the Crescent formation, as is indicated by the presence of benthonic Foraminifera that required shal- low, warm, clear water. These conditions may have resulted from the extrusion of volcanic material to the extent that the seas became shallow and in places broken by barrier reefs or islands. In the early part of late Eocene time the area prob- ably underwent considerable subsidence, because all foraminiferal assemblages known from the overlying Aldwell formation indicate a cool, deep-water environ- ment. This postulation is supported by the almost total absence of megafossils and the fine-grained nature of the sediments of the formation. The absence of Foraminifera in the overlying Lyre formation may be due to a rapid deposition of the coarse elastic sediments of this formation. Such sediments most probably were deposited under turbulence which, in turn, would have created muddy seas, a condition un- favorable for most Foraminifera. Following the deposition of the Lyre formation and during late Eocene time, the lower part of the Twin River formation was probably deposited at various depths, but generally in a moderately shallow sea. If the Aldwell-like assemblages, found in a few places in the lower part of the Twin River formation, were not reworked, considerable depths existed locally in the area during that time. However, generally the Foraminifera of the lower part of the Twin River formation suggest moderately shallow depths, upper- most bathyal to lower neritic. By Refugian time (late Eocene or early Oligocene), deepening of the sea continued, although in places, par— ticularly to the west, moderately shallow depths con- tinued to prevail. Maximum depths of deposition for the Twin River formation were probably attained throughout most of the mapped area during the early part. of Zemorrian time (late Oligocene or early Miocene). The Forami- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY nifera suggest that the sea was shallowest in the western part of the area but that it gradually deepened during Zemorrian time. By the close of Zemorrian time the sea rapidly became more shallow. The much greater thickness and generally coarser grained nature of the Twin River formation in the vicinity of Deep Creek, as compared to the formation in the Lyre River area, suggest that a source of sediments may have been closer to the Deep Creek area than to the Lyre River area. Furthermore, combined information on the paleoecology and age inferred by Foraminifera suggests that shallow conditions existed for a longer period of time in the Deep Creek area than they did in the Lyre River area. In the Deep Creek section, foraminiferal information is available only from the middle member, a lithologic unit primarily of bedded siltstone and sandstone. Foraminifera indicate that all but the upper 500 feet of this member is early Zemorrian in age. The upper 500 feet is late Zemorrian in age. In the Lyre River section to the east all the Foraminifera of the middle member, except those from the upper 300 feet of the member, are Refugian in age. Foraminifera from the upper 300 feet of the middle member and those from almost all the upper member in the Lyre River section are of early Zemorrian age. The upper member of the formation is chiefly mudstone. Therefore, the siltstone and sand- stone of the middle member were deposited during the Refugian time in the Lyre River area, whereas in the Deep Creek area their deposition continued throughout much of Zemorrian time to the west. The sediments of the middle member not only were deposited for a longer period of time in the Deep Creek area, but their greater thickness in a unit of time indicates they also accumu- lated more rapidly there than they did to the east in the Lyre River area. These comparisons show that, although the three members of the Twin River formation maintain a strati- graphic sequence, the geologic age as well as the amount of time represented by any one member can vary throughout the mapped area. Limited foraminiferal evidence indicates that during Saucesian time (early Miocene) at least part of the Clallam formation was deposited under shallow, cool- water conditions in a protected environment. Coal beds in the upper part of the Clallam formation indicate that other parts of the formation are continental deposits. IDENTIFIED SPECIES SYSTEMATIC DISCUSSION Discussions and illustrations are restricted to 42 species that display either stratigraphic or paleoeco- logic significance in the northern Olympic Peninsula. A FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON complete synonomy of each species is not attempted, but rather pertinent references are listed, one of which will supply a more complete synonomy. The frequent use of qualifiers such as “of.” and “afi'.” has been necessary because many forms are represented by few specimens and many specimens are poorly preserved. Family VALVULINIDAE Genus TRITAXILINA Cushman, 1911 Tritaxilina colei Cushman and Siegfus Plate 5, figure 2 Tritawilina colei Cushman and Siegfus, 1935, Cushman Lab. Foram. Research Contr., v. 11, pt. 4, p. 92, pl. 14, figs. 5,6. Cushman and Siegfus, 1942, San Diego Soc. Nat. History Trans, v. 9, no. 34, p. 403, pl. 15, figs. 12, 13. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 128, pl. 27, fig. 9. This species is present in a few samples from the Aldwell formation and the lower part of the Twin River formation. It was originally described from the Kreyenhagen shale (Cushman and Siegfu‘s, 1935) and has since been recorded from California through- out rocks of Eocene age. Figured specimen (USNM 626981) from USGS lo- cality f11884. Family MILIOLIDAE Genus QUINQ'UELOCULINA d’Orbigny, 1826 Quinqueloculina goodspeedi Hanna and Hanna Plate 5, figure 1 Qumqueloculina goodspeedt' Hanna and Hanna, 1924, Washing- ton Univ. [Seattle] Pub. Geology, v. 1, no. 4, p. 58, pl. 13, figs. 3, 4. Beck, 1943, Jour. Paleontology, v. 17, no. 6, p. 592, pl. 99, figs. 1, 2. Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 429, pl. 63, figs. 6—8. This species is characterized by its elongate shape, rounded cross section, and a slightly protruding, round aperture with a thin tooth extending from the base. Although it is uncommon in the mapped area, it is useful when present because it indicates a late Eocene age in western Washington. It is known from the Cowlitz formation (Beck, 1943), the Skookumchcuk formation, and the upper part of the McIntosh forma- tion of southwestern Washington (Rau, 1958). It occurs in the lower part of the Twin River formation in the northern Olympic Peninsula. Figured specimen (USNM 626982) from USGS locality f11874. G15 Quinqueloculina weaveri Ran Plate 5, figure 3 Quinqueloculina weavem’ Rau, 1948, Jour. Paleontology, v. 22, no. 2, p. 159, pl. 28, figs. 1—3. . Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 430, pl. 63, fig. 4. Quingueloculina weavem' differs from Q. goodspeedz' in that its cross section is more angular, the apertural face slopes, and the base of the aperture is flattened. This speciesusually occurs in rocks of the Refugian stage, but it is also found in the northern Olympic Pen- insula in rocks assigned to the Zemorrian stage. Figured specimen (USNM 626983) from USGS 10— cality f11793. Family LAGENIDAE Genus ROBUL‘US Montfort, 1808 Robulus cf. R. calcar (Linné) Plate 5, figure 4 Robulus cf. R. calcar (Linné). Rau, 1951, J our. Paleontology, v. 25, no. 4, p. 431, pl. 63, figs. 23, 24. Angular areas are present on the periphery of some specimens of Bobulus where the periphery is joined by the sutures. Blunt spines even are formed at these angular areas on some specimens. All specimens dis- playing these features are tentatively and in a broad sense referred to B. calm?" (Linné). This general form seems to be a good marker fossil for rocks of the Zemor- rian stage in western Washington and Oregon because it is recorded only from rocks of this age in southwest- ern Washington (Rau, 1958) and is known from the rocks of the same age in western Oregon. It occurs in the upper part of the Twin River formation in the northern Olympic Peninsula. Figured specimen (USNM 626984) from USGS 10- cality f11754. Robulus welchi Church Plate 5, figure 6 Robulus welchi Church, 1931, California Dept. Nat. Resources, Div. Mines Rept. State Mineralogist. No. 27, p1. C, figs. 13, 14. Church, 1943, California Dept. Nat. resources, Div. Mines Bull. 118, p. 182. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 143, pl. 7, fig. 8. Because of poor preservation, identification of this species is based on a group of specimens rather than a single individual. The species is not common but is present in a few samples from the Aldwell formation and the lower part of the Twin River formation. In western Washington and Oregon this species is known G16 only from rocks of late Eocene age. California records are also all from strata of late Eocene age (Mallory, 1959, p. 143). Figured specimen (USNM 626985) from USGS 10- cality f117 26. Family NONIONIDAE Genus NONION Montfort, 1808 Nonion costiferum (Cushman) Plate 5, figure 5 Nomio'nella bouecme Chapman (not d’Orbigny), 1900, California Acad. Sci. Proc., ser. 3, Geology, v. 1, p. 225, pl. 30, fig. 14. Nom’on costiferum (Cushman). Kleinpell, 1938, Miocene stra- tigraphy of California: Am. Assoc. Petroleum Geologists, p. 229, pl. 15, fig. 13. Rau, 1948, Jour. Paleontology, v. 22, no. 6, p. 777, pl. 119, figs. 5, 6. Rau, 1951, Jour. Paleontology, v. 25, no. 4, p. 436, pl. 64, fig. 7. This species is common in all samples from the Clallam formation but was not found in any of those below the formation. It is recorded from many locali- ties of Miocene age in California, Oregon, and Wash- ington (Kleinpell, 1938). The lowest occurrence of N om'on c‘ostifemm generally coincides with the base of the Saucesian stage. Therefore its lowest occurrence in the northern Olympic Peninsula at the base of the Clallam formation suggests a Saucesian age for at least the lower part of the formation. Figured specimen (USNM 626986) from USGS locality f11891. Nonion incisum (Cushman) Plate 5, figure 9 Nom’onim incisa Cushman, 1926, Cushman Lab. Foram. Re- search Contr., v. 1, pt. 4, p. 90, pl. 13, fig. 3. Nomion incisa (Cushman). Cushman and Laiming, 1931, Jour. Paleontology, v. 5, no. 2, p. 104, pl. 11, fig. 10. N om'on incisum (Cushman). Cushman and Parker, 1931, Cush- man Lab. Foram. Research Contr., v. 7, pt. 1, p. 7, pl. 1, fig. 26. Cushman and LeRoy, 1938, Jour. Paleontology, v. 12, no. 2, p. 125, pl. 22, figs. 8,9. Many variations are shown among the specimens that are referred to this species. Some of the more con- spicuous variations are in the amount of flaring of the latter chambers, the height relative to breadth, the thickness, and the amount of depression of sutures. Regardless of these variations, all specimens fall with- in the limits of the species sensu Zato. Nonion incisum is a useful fossil in the northern Olympic Peninsula because there it is known to occur only in the upper part of the Zemorrian stage and the Saucesian stage where it is reasonably frequent. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Variations of the species have been recorded from California and Oregon from rocks referred to the upper part of Kleinpell’s Zemorrian stage and to the lower part of his Luisian stage (Kleinpell, 1938, p. 146, 232, 233). Figured specimen (USNM 626987) from USGS locality f117 31. Nonion cf. N. pompilioides (Fichtel and Moll) Plate 5, figure 7 Forms displaying bilateral symmetry and a broad final chamber are tentatively referred to Nonion pom- ,m'Zioz‘des (Fichtel and Moll). (See Cushman, 1939, p. 19, pl. 5, figs. 9412.) Most of the specimens came from rocks of the Zemorrian stage; however, a few specimens were also found in rocks of the Refugian stage. Figured specimen (USNM 626988) from USGS locality f11749. Genus ELPHIDIUM Montfort, 1808 Elphidium cf. E. minutum (Reuss) Plate 5, figure 8 The description of this species given by Cushman (1939, p. 40) agrees closely with that of a number of specimens from the upper part of the rock sequence of the northern Olympic Peninsula. However, his illus- trations (Cushman, 1939, pl. 10, figs. 22—25) all display coarser retral processes than are developed on the speci- mens under question. Inasmuch as Cushman stated that the retral processes are very slightly developed, they may have been overemphasized in his illustrations. Elphidéum of. E. minutm was found only in rocks assigned to the upper part of the Zemorrian stage and the Saucesian stage within the mapped area. It is also recorded from rocks of Zemorrian and Saucesian age in southwestern Washington (Rau, 1951, 1958). Figured specimen (USNM 626989) from USGS local— ity f11891. Family HETEROHELICIDAE Genus PLECTOFRONDICULARIA Liebus, 1903 Plecto‘frondicularia packardi multilineata Cushman and Simonson Plate 5, figure 15 Plectofrondicularia packardi multilineata Cushman and Simon- so, 1944, Jour. Paleontology, v. 18, no. 2, p. 197, pl. 32, figs. 2—4. Detling, 1946, Jour. Paleontology, v. 20, no. 4, p. 355, pl. 49, figs. 3, 5. Rau, 1948, J our. Paleontology, v. 22, no. 2, p. 171, pl. 30, fig. 19. Smith, 1956, California Univ. Dept. Geol. Sci. Bull., v. 32, no. 2, p. 94, pl. 12, fig. 6. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON Plectofrondtcular'ia gram'lis Smith, 1956, California Univ. Dept. Geol. Sci. Bull., v. 32, no. 2, p. 93, pl. 12, figs. 2—5. The Tertiary sequence of Washington, Oregon, and California contains a strain of Plectofrondz'wlam‘a which displays considerable variation in form. The variant most significant stratigraphically was originally described from the Bastendorfi' shale of Oregon and called P. packardi Cushman and Schenck (1928). Sub- sequently a more common and widely distributed vari- ant was described from the Tumey formation of Cali- fornia and referred to P. pow/cardi multilineata Cushman and Simonson (1944). Studies of the faunas of the Tertiary rocks of Oregon and Washington strongly suggest that there, at least, P. packardz’ pack- ardz' does not occur above the Refugian stage and is found only occasionally in the underlying Narizian stage. However, P. packardi multilineata occurs throughout rocks of late Eocene, Oligocene, and possibly early Miocene age. Many variants of the strain dis- playing a complete gradation from one form to another were found in samples from the northern Olympic Peninsula. Those referred to P. packardi packardi have few short and coarse costae which are sometimes curved on the initial chamber. The remaining forms of various shapes with varying number of straight and longer costae are referred to P. packardz' multilz‘neazfia. Certain variances in the latter group have been exam- ined for stratigraphic value and have been found to be of no importance. Therefore, they are all grouped under the single name P. packardz’ mwltz’lz'neata in this study. P. gracilis Smith is within this group and is placed in synonomy with P. packardi multiléneata in the report. Figured specimen (USNM 626990) from USGS locality f11736. Plectofrondicularia packardi packardi Cushman and Schenck Plate 5, figure 13 Plectofrondicularia packardi Cushman and Schenck, 1928, Cali- fornia Univ. Dept. Geol. Sci. Bu11., v. 17, no. 9, p. 311, pl. 43; figs. 14~15. Cushman and Simonson, 1944, Jour. Paleontology, v. 18, no. 2, p. 197, pl. 31, figs. 17, 18, pl. 32, fig. 1. Detling, 1946, Jour. Poleontology, v. 20, no. 4, p. 355, pl. 49, fig. 1. Rau, 1951, Jour. Paleontology V. 25, no. 4, p. 438, pl. 65, fig. 12. Wilson, 1954, California Univ. Pub. Geol. Sci. Bull., v. 30, no. 2, p. 138, pl. 15, fig. 8. Smith, 1956, California Univ. Pub. Geol. Sci. Bull., v. 32, no. 2, p. 94, pl. 12, figs. 1, 7. Discussion of this species is under Plectoforndic- ulam'a packardz' mvultz'lz'neata. Figured specimen (USNM 626991) from USGS 10- cality f11876. G17 Family BULIMINIDAE Genus BULIMINELLA Cushman, 1911 Buliminella subfusiformis Cushman Plate 5, figure 12 Buliminella subfusiformis Cushman, 1925‘, C‘ushman Lab. Foram. Research Contr., v. 1, pt. 2, p. 33, pl. 5, fig. 12. Cushman, Stewart, and Stewart, 1947, Oregon Dept. Geol- ogy and Mineral Industries Bull. 36, pt. 1, p. 17, pl. 2, fig. 7. Rau, 1951, Jour. Paleontology, v. 25, no. 4, p. 439, pl. 65, fig. 5. This species occurs rarely in the rocks of the northern Olympic Peninsula, only in the upper part of the Twin River formation. Records of Buliminella subfusiformis in Washington, Oregon, and California strongly sug- gest that it does not occur in rocks older than those of the Zemorrian stage. In southwest Washington it is recorded from the Pseudoglandulz‘na aff. P. inflata zone and the E pistomz'nella, puma zone (Rau, 1958) of the Zemorrian and Saucesian stages, respectively. It is known in Oregon from the Astoria formation (Cush- man, Stewart, and Stewart, 1947) and the Nye mud- stone. In California, Kleinpell (1938) recorded this species from the lower part of the Zemorrain stage to the lower part of the Delmontain stage. Figured specimen (USNM 626992) from USGS locality f11867. Genus BULIMINA d’Orbigny, 1826 Bulimina corrugata Cushman and Siegfus Plate 5, figure 11 Bulimma corrugata Cushman and Siegfus, 1936, Cushman Lab. Foram. Research Contr., v. 11, pt. 4, p. 92, pl. 14, fig. 7. Graham and Classen, 1955, Cushman Found. Foram. Re- search Contr., v. 6, pt. 1, p. 19, pl. 3, fig. 17. Rau, 1956, Cushman Found. Foram. Research Contr., v. 7. pt. 3, p. 75, pl. 15, fig. 5. The present specimens are small, tend to be triangular in cross section, display the greatest breadth slightly above the middle, and have numerous longitudinal costae extending continuously over all but the last chamber. These features characterize Bulimi’na cor- mgata as described by Cushman and Siegfus. This species was found locally in the Crescent and Aldwell formations and the lower part of the Twin River formation. In southwest Washington it is re- corded from the Bulimina of. B. jacksonensz's zone and the U oigem’na cf. U. yazooemis zone of McIntosh forma- tion (Rau, 1956, 1958). In Oregon it has been observed by the writer in samples from the Umpqua formation, lower part of the Toledo formation, Nestucca formation, Yamhill formation, and the Elkton siltstone member of the Tyee formation. The highest occurrence of B. G18 cormgata in both Oregon and Washington is generally in the lower part of the sequence of late Eocene age. According to Mallory (1959), B. corrugata occurs in California in rocks ranging in age from his Ulatisian stage to his Narizian stage. Figured specimen (USNM 626993) from USGS locality f11886. Bulimina lirata Cushman and Parker Plate 5, figure 17 Bulimma lirata Cushman and Parker, 1936, Cushman Lab. Foram. Research Contr., V. 12, pt. 2, p. 43, pl. 8, fig. 2. Cushman and Simonson, 1944, Jour. Paleontology, v. 18, no. 2, p. 198, pl. 32, fig. 13. Smith, 1957, California Univ. Pub. Geol. Sci., v. 32, no. 3, p. 174, pl. 24, fig. 13. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges, Am. Assoc. Petroleum Geologists, p. 193, pl. 37, fig. 1. Bulimma cf. B. lirata Cushman and Parker. Cushman and Sieg- fus, 1942, San Diego Soc. Nat. History Trans, v. 9, no. 34, p. 413, pl. 17, fig. 3. A few costate specimens of Bulimina are relatively broad with respect to length and taper rapidly to a sharp initial end. They compare well in all respects to B. Zimta Cushman and Parker, which, according to Mallory (1959, p. ‘85), is known from his Penutian, Ulatisian, and Narizian stages of the upper part of the Eocene sequence of California. This species has not been recorded previously from Washington or Oregon but has been observed by the writer in samples from the Umpqua formation and rocks of probable equivalent age in Oregon. In the northern Olympic Peninsula it was found in a few samples from both the Aldwell formation and the lower part of the Twin River formation. ' Figured specimen (USNM 626994) from USGS locality f11873. Bulimina alsatica Cushman and Parker Plate 5, figure 16 Bulimina alsatica Cushman and Parker, 1937, Cushman Lab. Foram. Research Contr., v. 13, pt. 1, p. 39, pl. 4, figs. 6, 7. Cushman and Parker, 1947, U.S. Geol. Survey Prof. Paper 210—D, p. 102, pl. 24, figs. 10, 11. A small, comparatively broad Bulimina with jagged costae over all chambers except those of the last whorl compares well with the illustrations and description of B. alsatz'ca Cushman and Parker. This species is known from rocks of Oligocene age in France and Germany and from rocks of Miocene age in Italy, Spain, and Florida. It has also been tentatively recorded from rocks of Oligocene age in ‘Vashington (Rau, 1958). In the Twin River formation it occurs most frequently in SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY rocks that are assigned to the Zemorrian stage. It also makes a rare occurrence in the Refugian part of the Twin River formation. Figured specimen (USNM 626995) from USGS locality f11749. Bulimina cf. B. alsatica Cushman and Parker Plate 5, figure 14 This form differs from Bulimina alsatioa in that costae do not extend as far up on the test and the costae appear to be pointed projections on the base of the chambers rather than platelike costae over the entire chamber. This form is found together with B. alsatica in the upper part of the Twin River formation. Figured specimen (USNM 626996) from USGS locality f11815. Bulimina schencki Beck Plate 5, figure 10 Bulimma capital/‘11? Cushman and Dusenbury (not Yoko- yama), 1934, Cushman Lab. Foram. Research Contr., v. 10, pt. 3, p. 61, pl. 8, fig. 10. Bulimina schcncm’ Beck, 1943, J our. Paleontology, v. 17, no. 6, p. 605, pl. 107, figs. 28, 33. Mallory, 1959, Lower Tertiary biostratigraphy 0f the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 196, pl. 16, fig. 15. A few specimens were found in the lower part of the Twin River formation that display all the character- istics of Bulimz'na schema/62'. One specimen questionably identified as this species came from the Crescent forma- tion. Bulimina schema/lei Beck (1943) was originally de- scribed from the Cowlitz formation of southwest Wash- ington and has been recorded since from the Skookum- chuck formation of the same area (Ban, 1958). In California Mallory (1959) recorded this species from the upper part of his Ulatisian stage and his Narizian stage. It has been found in the Poway conglomerate, Cozy Dell formation, Point of Rocks formation, and the type Tejon formation (Mallory, 1959). Figured specimen (USNM 626997) from USGS locality f11875. Bulimina sculptilis laciniata Cushman and Parker Plate 6, figure 1 Bulimina sculptm's Cushman. Cushman and Schenck, 1928, California Univ. Dept. Geol. Sci. Bull., V. 17, no. 9, p. 311, pl. 43, fig. 16. Bulimina sculptilis lacim‘ata Cushman and Parker, 1937, Cush- man Lab. Foram. Research Contr., v. 13, pt. 1, p. 38, pl. 4, fig. 4. Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 441, pl. 65, fig. 22. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON This large Bulimina with continuous, jagged, and platelike costae was found only in strata of the Twin River formation that. are referred to the Refugian stage. It was originally described from beds at VValdport, Oreg., which are regarded as Zemorrian in age by the writer. It is also known in Oregon from the Basten— dorif shale and the Keasey formation (Cushman and Schenck, 1928) of Refugian age. The southwestern Washington occurrences are frdm the Sigmomorphina schemeki zone of the Refugian stage and the Bulimi’na schencki-Plectofrondz'cvularia cf. P. jenlcz'nsi zone of latest Eocene age (Rau, 1958). Although the species is found occasionally both above and below the Refugian stage, its occurrence is most frequent in the Refugian stage. Figured specimen (USNM 626998) from USGS 10- cality f11865. Genus ENTOSOLENIA Ehrenberg, 1848 Entosolenia sp. Plate 6, figure 2 Test broadly ovate, slightly compressed, walls smooth, finely perforate; aperture a narrow slitlike opening. Length of figured specimen 0.35 mm; breadth 0.29 mm; thickness 0.23 mm. This form is uncommon in rocks of the northern Olympic Peninsula. Its known occurrence is confined largely to strata of Zemorrian age in the Twin River formation and therefore locally, at least, it has strati- graphic significance. Figured specimen (USNM 626999) from USGS 10- cality f11751. Genus BOLIVINA d’Orbigny, 1839 Bolivina advena Cushman Plate 6, figure 4 Bolivina, advent; Cushman, 1925, Cushman Lab. Foram. Research Contr., v. 1, pt. 2, p. 29, pl. 5, fig. 1. Kleinpell, 1938, Miocene stratigraphy of California: Am. Assoc. Petroleum Geologists, p. 264, pl. 7, fig. 6. Cushman, Stewart, and Stewart, 1947, Oregon Dept. Geology and Mineral Industries Bull. 36, pt. 1, p. 18, pl. 2, fig. 12. Rau, 1951, Jour. Paleontology, v. 25, no. 4, p. 442, pl. 65, fig. 9. This species is rare in the present material. It occurs only in the uppermost part of the Twin River formation and the Clallam formation. It is known in southwest Washington from the Epistomz'nella pared zone (Rau, 1958), and in Oregon it is recorded from the Astoria formation (Cushman, Stewart, and Stewart, 1947). The species is known in California from rocks ranging in age from that of the Saucesian stage to the Mohnian G19 stage (Kleinpell, 1938). In the northern Olympic Peninsula the presence of Bolivina advena in the rocks suggests a relatively high stratigraphic position in the local Tertiary sequence. Figured specimen (USNM 627000) from USGS 10- cality f11749. Bolivina marginata adelaidana ‘Cushman and Kleinpell Plate 6, figure 8 Bolivina marginata adelaidana Cushman and Kleinpell, 1934, Cushman Lab. Foram. Research Contr., v. 10, pt. 1, p. 10, pl. 2, figs. 1, 2. Cushman, Stewart, and Stewart, 1947, Oregon Dept. Geol- ogy and Mineral Industries Bull. 36, pt. 1, p. 18, pl. 2, fig. 13. Rau, 1951, Jour. Paleontology, v. 25, no. 4, p. 443, pl. 65, fig. 14. The spinelike extension of the chambers at the pe- riphery and limbate sutures are well developed on the present specimens. This form occurs in rocks of Zemor- rian age in the Twin River formation. In western )Vashington and Oregon it occurs only in strata that are no older than those of the Zemorrian stage. It is recorded from the Pseudoglanduléna alf. P. inflata zone and Epz'stomdnella gamma zone of southwestern VVash- ington (Rau, 1958). In Oregon it is known from the Astoria formation (Cushman, Stewart, and Stewart, 1947) and it has been observed by the writer from the Nye mudstone, the Yaquina formation, and the upper part of the Toledo formation. Records of this variety in California are largely from beds of Saucesian age (Kleinpell, 1938, p. 277). Figured specimen (USNM 627001) from USGS locality f11869. Genus BIFARINA Parker and Jones, 1872 Bifarina nuttalli Cushman and Siegfus Plate 6, figure 3 Lowostomum applini Plummer. Nuttall, 1930, Jour. Paleon- tology, v. 4, no. 3, p. 285, pl. 24, figs. 4, 5. Bifdrina mtttalli Cushman and Siegfus, 1939, Cushman Lab. Foram. Research Contr., v. 15, pt, pt. 2, p. 28, pl. 6., fig. 6. Cushman and Siegfus, 1942, San Diego Soc. Nat. Hist, v. 9, no. 34, p. 413, pl. 17, fig. 4. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 204, pl. 29, fig. 2. The specimens under consideration compare well with the type Bifam'na nuttalli in that the general shape of the test is similar, the base of the chambers are crenulated, and there are longitudinal costae on the early part of the test. B. nuttalh’ has not been re- corded previously from lVashington, but it has been observed in Oregon in the Umpqua formation by the G20 writer. This species is known in California from beds that are referred to Laiming’s C zone and the lower part of his A—2 zone. Mallory (1959, p. 84, 204) indi— cated that B. nuttallz' occurs in his Ulatisian stage and the lower part of his Narizian stage. Figured specimen (USNM 627002) from USGS locality f11728. Genus UVIGERINA d’Orbigny, 1826 Uvigerina churchi Cushman and Siegfus Plate 6, figure 9 Um-gem‘na churchi Cushman and Siegfus, 1939, Cushman Lab. Foram. Research Contr., v. 15, pt. 2, p. 29, pl. 6, fig. 16. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 206, pl. 17, fig. 6. The irregular longitudinal costae broken between chambers and the blunt initial end are characteristic features of Um'gerimz church/i that are well shown on the specimens from the northern Olympic Peninsula. This species occurs in more than half of the assemblages of the Aldwell formation and is questionably identified from several samples from the lower part of the Twin River formation. U. chm-chi has not been recorded previously from either Washington or Oregon but a similar form referred to as U. of. U. yaizooensz's Cush- man is recorded from the zone of the same name of southwestern Washington (Rau, 1958). The latter form differs from U. churchi in that the test is more elongate and the costae are higher and more distinct. In California, U. churchz' is known from strata that are referred to Laiming’s A—2 zone (Laiming, 1940), and Mallory (1959) showed the occurrence of this form in his Narizian stage. Figured specimen (USNM 627003) from USGS locality f11728. Uvigerina cocoaensis Cushman Plate 6, figure 5 Uvigem‘na cocoaensis Cushman, 1925, Cushman Lab. Foram. Re- search Contr., v. 1, pt. 3, p. 68, pl. 10, fig. 12. Cushman and Schenck, 1928, California Univ. Dept. Geol. Sci. Bull., v. 17, no. 9, p. 312, pl. 43, figs. 17—19. Cushman and Simonson, 1944, Jour. Paleontology, v. 18, no. 2, p. 199, pl. 33, fig. 1. Cushman, 1946, Cushman Lab. Foram. Research, Spec. Pub. 16, p. 28, pl. 5, figs. 15—20. Rau, 1951, Jour. Paleontology, v. 25, no. 4, p. 444, pl. 65, fig. 28. Wilson, 1954, California, Univ. Pub. Geol. Sci., v. 30, no. 2, p. 140, pl. 16, fig. 2. Smith, 1956, California Univ. Pub. Geol. Sci., v. 32, no. 2, p. 96, pl. 12, fig. 11. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY This well-known species occurs in the northern Olympic Peninsula only in strata of Refugian age. Because of its relatively frequent occurrence in the Twin River formation and because of its known re- stricted occurrence in rocks of the Refugian stage in other areas, it is a useful species for identifying rocks of Refugian age in the northern Olympic Peninsula. In southwest \Vashington Um'gem'na cocoaensz's is re- corded from the Sigmomorphina scheme/67$ zone (Rau, 1958), and in Oregon it is known from the Bastendorff shale and the Keasey formation (Cushman and Schenck, 1928; Detling, 1946). Records of the species in California are from the Tumey formation (Cushman and Simonson, 1944), the Gaviota formation (Wilson, 1954), and the Wagonwheel formation (Smith, 1956). In all cases the containing beds have been regarded as Refugian in age. Figured specimen (USNM 627004) from USGS locality f11862. Uvigerina gallowayi Cushman Plate 6, figure 7 Um'germa gallowayi Cushman, 1929, Cushman Lab. Foram. Research Contr., v. 5, pt. 4, p. 94, pl. 13, figs. 33, 34. , Kleinpell, 1938, Miocene stratigraphy of California: Am. Assoc. Petroleum Geologists, p. 294, pl. 5, figs. 1, 2, 5. Cushman and Simonson, 1944, Jour. Paleontology, v. 18, no. 2, p. 200, pl. 32, figs. 18, 19. Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 444, pl. 65, fig. 24. This species is restricted to a few samples from the upper part of the Twin River formation. Although uncommon in the area, its presence high in the local se- quence is in accordance with previous records of Um'gem'na gallowayi which are from beds of the Zemorrian stage only. In southwestern Washington it is known from beds that are assigned to the Zemorrian stage (Rau, 1958). There are no records of the species from Oregon but the writer has observed it in the Bas- tendorif shale. In California it is recorded from beds mapped largely as the Vaqueros formation or Temblor formation (Kleinpell, 1938, p. 294). Figured specimen (USNM 627005) from USGS locality f11748. Uvigerina garzaensis Cushman and Siegfus Plate 6, figure 6 Uvigerina garzaensis Cushman and Siegfus, 1939, Cushman Lab. Foram. Research Contr., v. 15, pt. 2, p. 28, pl. 6, fig. 15. Cushman and Simonson, 1944, Jour Paleontology, v. 18, no. 2, p. 199, pl. 32, figs. 20, 21. Detling, 1946, Jour. Paleontology, v. 20, no. 4, p. 357, pl. 50, fig. 8. Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 445, pl. 65, fig. 19. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON This species is one of the more ,frequently occurring forms in the Tertiary sequence of the northern Olympic Peninsula. It is found throughout the Aldwell and Twin River formations. The shape and size of the test are noticeably varied but these variations are gra- dational and show no stratigraphic significance. Sev- eral described species probably are within the range of variance of the present specimens, but no strati- graphic usefulness is gained by dividing the group and therefore in this report they are all referred to one species, Uvigem'na garzaemz's. U. garzaensis has very little stratigraphic significance but its presence does suggest a general environment of cool water at substan- tial depths. In California U. garzaensz's is recorded largely from rocks of late Eocene age. It is known from the Coaledo and Bastendorff formations of Oregon (Detling, 1946) and has been observed by the writer in many other as— semblages from Oregon of late Eocene age. It is re— corded from southwestern Washington from rocks of the same age (Rau, 1958). Figured specimen (USNM 627006) from USGS locality f11748. Genus ANGULOGERINA Cushman, 1927 Angulogerina hannai Beck Plate 6, figure 11 Angulogerinav hanmzi Beck, 1943, Jour. Paleontology, v. 17, no. 6, p. 607, pl. 108, figs. 26, 28. Cushman, Stewart, and Stewart, 1947, Oregon Dept. Ge- ology and Mineral Industries Bull. 36, pt. 5, p. 102, pl. pl. 12, fig. 16. Specimens from the northern Olympic Peninsula compare in detail with Beck’s description and illustra— tion of Angulogem’na haw/Lei. Although individuals of this species are never found in abundance in any one sample, it occurs frequently in the rocks of Eocene age within the area, particularly in the lower part of the Twin River formation. The species was originally described from the Cow— litz formation (Beck, 1943). It has since been recorded from the Bulimina solatencki-Plectofrondicularia of. P. jealcinsi zone of late Eocene age in southwest Washing- ton (Rau, 1958) and from beds of late Eocene age in the Helmick Hills of western Oregon (Cushman, Stewart and Stewart, 1947). Figured specimen (USNM 627007) from USGS locality f11886. G21 Family ROTALIIIDAE Genus GYROIDINA d’Orbigny, 1826 Gyroidina orbicularis planata Cushman Plate 6, figure 10 Gyroidma orbicularis planata Cushman, 1935, U. S. Geol. Sur- vey Prof. Paper 181, p. 45, pl. 18, fig. 3. Cushman and Siegfus, 1942, San Diego Soc. Nat. History Trans, v. 9, p. 419, pl. 17, fig. 32. Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 447, pl. 66, figs. 4—6. Gyroidz'na orbiculom's plamta is common in much of the Tertiary sequence of the northern Olympic Penin- sula. It occurs in several samples from the Aldwell formation, is well represented in most of the samples from the Twin River formation, and is present in one sample from the Clallam formation. Its long range makes it of little stratigraphic use. However, ecologi- cally it is useful, because it suggests substantial depths in cool to cold water. 0. orbiculam's planata is re- corded from rocks of late Eocene age and rocks that are referred to the Refugian and Zemorrian stages in southwestern Washington (Rau, 1958). Although not recorded from western Oregon, it has been observed by the writer from many parts of the Tertiary sequence there. In California, it is recorded from rocks of late Eocene age (Mallory, 1959). Figured specimen (USNM 627008) from USGS locality f11749. Genus EPONIDES Montfort, 1808 Eponides mansfieldi oregonensis Cushman, Stewart, and Stewart Plate 6, figure 12 Epom‘des mansfieldi Cushman. Cushman and Parker, 1931, Cushman Lab. Foram. Research Contr., v. 7, pt. 1, p. 12, pl. 2, fig. 10. Epom’des mansfieldi oregonensis Cushman, Stewart, and Stewart, 1947, Oregon State Dept. Geology and Mineral Industries Bull. 36, pt. 2, p. 48, pl. 6, fig. 4. Ban, 1951, J our. Paleontology, v. 25, no. 4, p. 447, pl. 66, figs. 14—16. The outstanding features of E pom'des mansfleldz' oregonensis are the papillate umbonal area on the ven- tral surface, the depressed sutures on the same surface, and the slightly scalloped periphery. In the northern Olympic Peninsula its lowest occur- rence is in the lower part of the Zemorrian stage but it occurs most frequently in the upper part of the Zemor— rian stage. The known occurrence of this form in south- western Washington is in the Pseudoglamlulina afl’. P. inflate and E pistomz'nella parva zones, which are as- signed to the Zemorrian and Saucesian stages, respec- G22 tively (Rau, 1958). It is recorded from western Oregon from the Astoria formation (Cushman, Stewart, and Stewart, 1947) and has also been observed by the writer from the Nye mudstone, the Yaquina formation, and the upper part of the Toledo formation. Associated Fora— minifera suggest that the Nye mudstone is Saucesian in age, whereas the Yaquina formation and the upper part of the Toledo formation are of Zemorrian age. The known occurrence of E. mansfieldz' oregonensz's is therefore in rocks no older than the Zemorrian age. Figured specimen (USNM 627009) from USGS locality f11791. Genus CANGRIS Montfort, 1808 Cancris joaquinensis Smith Plate 6, figure 13 Canon's joaquinensis Smith, 1956, California Univ. Pub. Geol. Sci., v. 32, no. 2, p. 98, pl. 15, figs. 5, 6. Specimens from the northern Olympic Peninsula compare in all respects with the illustrations and de- scription of Canon's joaguz’nensz's Smith. The species was originally described by Smith (1956) from the Wagonwheel formation of California, which he assigned to the Refugian stage. Smith indicated that the species also was observed from the Bastendorff and Keasey formations of Oregon. In the northern Olympic Penin- sula area the highest occurrence of 0. joaquinensis is in the Refugian stage, but its lowest occurrence in the area is in rocks of late Eocene age. This upper Eocene occur— rence extends the lower range of the species, but its highest occurrence in the Refugian stage in northern Olympic Peninsula is useful for differentiating faunas of a pre-Zemorrian age from those of Zemorrian age. Figured specimen (USNM 627010) from USGS locality f11862. Family AMPHISTEGINIDAE Genus ASTERIGERINA d’Orbigny, 1839 Asterigerina crassiformis Cushman and Siegfus Plate 6, figure 14 Asterigerina crassiformis Cushman and Siegfus, 1935, Cush- man Lab. Foram. Research Contr., v. 11, pt. 4, p. 94, pl. 14, fig. 10. Cushman and Stone, 1949, Cushman Lab. Foram. Research Contr., v. 25, pt. 4, p. 82, pl. 14, fig. 16. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 242, pl. 37, fig. 13. This species makes its most frequent occurrence in the Aldwell formation but is also present in a few samples from the lower part of the Twin River formation. There are numerous records of this species from Cali- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY fornia (Mallory, 1959), all from rocks of middle and late Eocene age (Ulatisian and Narizian stages of Mal- lory). Cushman and Stone (1949) recorded it from the Verdun formation of Peru. Although there are no records of the species from Oregon, it has been observed by the writer in several samples from the Umpqua formation. Figured specimen (USNM 627011) from USGS locality f11726. Genus AMPI-IISTEGINA d’Orbigny, 1826 Amphistegina californica Cushman and M. A. Hanna Plate 7, figure 6 Amphisteyina californica, Cushman and M. A. Hanna, 1927, San Diego Soc. Nat. History Trans, v. 5, no. 4, p. 56, pl. 6, figs. 3—5. All specimens are from the Crescent formation and there they are the most common benthonic form known in the formation. Although they are all poorly pre- served, a composite of the features that can be observed on various specimens constitutes Amphistegina, cali— form'ca as described by Cushman and Hanna (1927). Amphistegina caliform'ca was originally described from sea cliffs near’La J olla, Calif. Mallory (1959) recorded the species only from his Ulatisian stage. There are no records of this species from either Oregon or Washington, but the writer has observed forms which may be species in the Umpqua formation of west- ern Oregon and in rocks in southwestern Washington tentatively assigned to the Crescent formation by Pease and Hoover (1957). Figured specimen (USNM 627012) from USGS locality f11720. Family CASSIDU’LINIDAE Genus ALABAMINA Toulmin, 1941 Alabamina. kernensis Smith Plate 7, figure 1 Alabami-mz kernensis Smith, 1956, California Univ. Pub. Geol. Sci., v. 32, no. 2, p. 99, pl. 15, figs. 3,4. Smith (1956) described this species from the VVagon- wheel formation of California and also noted its oc- currence in the Bastendorfi shale of Oregon. The Refu- gian stage is represented in both of these formations. In the northern Olympic Peninsula Alabamz'na ker- nensz's is found in rocks of Refugian and pre-Refugian ages in the Twin River formation and in the underlying Aldwell formation of Eocene age. These occurrences extend the records of A. kemensis into rocks of late Eocene age, but the Refugian stage remains the upper limit of its known occurrence. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON Figured specimen (USNM 627013) from USGS locality f11862. Genus CASSIDULINA d’Orbigny, 1826 Cassidulina crassipunctata Cushman and Eobson Plate 7, figure 3 Cassidulz’na crassipunctata Cushman and Hobson, 1935, Cush— man Lab. Foram. Research, Contr., v. 11, pt. 3, p. 63, pl. 9, fig. 10. Considerable variation in form is shown among indi- viduals placed under this species, but they are within the limit of variation of the description of Cuslnnan and Hobson (1935). Cassidulina crassz'punctata is one of the more common species in rocks of Zemorrian age in the Twin River formation. Its lowest occurrence is useful for determining the base of the Zemorrian stage. This species has been tentatively referred to in south- western ‘Vashington (Rau, 1958) where it also occurs in rocks of the Zemorrian stage. The species was described from the type San Lorenzo formation of California (Cushman and Hobson, 1935) and has since been recorded in California from the Vaqueros and Temblor formations. All records of the species are from rocks of the Zemorrian stage. Figured specimen (USNM 627014) from USGS locality f11796. Cassidulina globosa Hantken Plate 7, figure 4 Cassidulina globosa Hantkeu. 1875. Magyr. kir. foldt. int. I§vk6n., v. 4, p. 5-1, pl. 16, fig. 2. Beck, 1943, Jour. Paleontology, v. 17, no. 6, p. 609, pl. 108, figs. 7, 13, 14. Ban, 1951, Jour. Paleontology, v. 25, no. 4, p. 449, pl. 67, fig. 5. Smith, 1956, California, Univ. Pub. Geol. Sci., v. 32, no. 2, p. 100, pl. 14, fig. 2. Mallory, 1959, Lower Tertiary biostratigraphy of the Cali- fornia Coast Ranges: Am. Assoc. Petroleum Geologists, p. 226, pl. 33, fig. 11. This species was found in the Aldwell formation and the lower part of the Twin River formation. It makes its highest occurrence in rocks of Refugian age, but it is more common in older rocks of late Eocene age. Cassiduh'na globosa has a wide geographic distribu— tion in rocks of late Eocene and early Oligocene age. It is recorded from Europe, Peru, Mexico, southeast— ern United States, California, Oregon, and “’ashing— ton. The species is not found in large numbers in the northern Olympic Peninsula, but when present indi— cates a pre-Zemorrian age. Figured specimen (USN M 627015) from USGS locality f11843. G23 Family CHILOSTOMELLIDAE Genus CASSIDULINOIDES Cushman, 1927 Cassidulinoides sp. Plate 7, figure 2 Test elongate, only slightly compressed, close coiled in early development, last few chambers tending to un- coil; chambers distinct, slightly inflated, last few in- creasing rapidly in size; sutures distinct, slightly de- pressed; walls smooth, finely perforate; aperture a broad slit approximately 45 degreesto the axis of great— est breadth at the terminal end. Length, 0.31 mm; breadth, 0.19 mm; thickness, 0.16 mm. This form is known to occur only in the upper part of the Twin River formation or in those rocks assigned to the Zemorrian stage. There it appeared in a num- ber of samples but was never common in any one sample. Figured specimen (USNM 627016) from USGS locality f11869. Genus SPHAEROIDINA d’Orbigny, 1821 Sphaeroidina variabilis Reuss Plate 7, figure 7 Sphaeroidma variabilis Reuss, 1851, Zeitschr. deutsch geol. Ges., v. 3, p. 88, pl. 7, figs. 61—64. Barbat and von Estorfi, 1933, Jour. Paleontology, v. 7, no. 2, p. 173, pl. 23, fig. 19. This species, although never abundant, is in an ap- preciable number of samples from the upper part of the Twin River formation. All specimens are from rocks assigned to the Zemorrian stage. In southwest “lashington it is also known from rocks of Zemorrian age (Rau, 1958) and in Oregon from the Astoria formation and Nye mudstone of Saucesian age. California records of the species are largely from rocks of the Zemorrian and Saucesian stages (Kleinpell, 1938). The many records of Sphaeroz'dina variabilis in Europe are from rocks of Oligocene and Miocene age. ‘Vithin the northern Olympic Peninsula its presence indicates an age no older than that of the Zemorrian stage. Figured specimen (USNM 627017) from USGS locality f11815. Family GLOBIGERINIDAE Genus Globigerina d’Orbigny, 1826 Globigerina of. G. yeguaensis Weinzierl and Applin Plate 7, figure 5 The genus Globz’gem’m is represented by several forms in the Tertiary sequence of the northern Olympic G24 Peninsula, but none are common. A form referred to as G. cf. G. yeguaensis is the only one that appears to be morphologically distinct and to be at least of local stratigraphic significance. This form is confined to rocks of Eocene age in the lower part of the Twin River formation and in the Aldwell formation. It is lobate, the three chambers of the last whorl increase rapidly in size, the walls are coarsely perforate, and the aperture has a lip. Figured specimen (USNM 627018) from USGS locality f11729. Family AN OMALINIDAE Genus ANOMALINA d’Orbigny, 1826 Anomalina californiensis Cushman and Hobson Plate 7, figure 8 Anomalma caliform'ensis Cushman and Hobson, 1935, Cushman Lab. Foram. Research Contr., v. 11, pt. 3, p. 64, pl. 9, fi . 8. Smigth, 1956, California Univ. Pub. Geol. Sci., v. 32, no. 2, p. 100, pl. 16, fig. 3. Considerable variation in form is observed in speci- mens that are referred to An-omalz'na caliform'ensis. Some individuals are decidedly asymmetric, whereas others are nearly bilaterally symmetric and are difficult to differentiate from Nonion pompilioides. In most cases the test of A. califomiensis is thinner than that of N. pompz’lz’oz’des. In both the northern Olympic Peninsula and south- western Washington the occurrence of A. caliform'ensis is confined to the Refugian and Zemorrian stages. California records of this species are from rocks of the Refugian stage (Smith, 1956), Zemorrian stage, and lower part. of the Saucesian stage (Kleinpell, 1938). Figured specimen (USNM 627019) from USGS locality f11876. Genus CI'BICIDES Montfort, 1808 Cibicides celebrus Bandy Plate 7, figure 10 Cibic'ides celebrus Bandy, 1944, Jour. Paleontology, v. 18, no. 4, p. 374, pl. 61, fig. 8. Specimens occurring in the Crescent and Aldwell formations and the lower part of the Twin River for- mation compare in all details with the description and illustrations of Oibicides celebrus Bandy. This species is recorded from southwestern Washington from rocks of late Eocene age and of the overlying Refugian stage SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY (Ban, 1958). It was originally described from beds of Eocene age exposed at Cape Blanco, Oreg. (Bandy, 1944). - Figured specimen (USNM 627020) from USGS locality f11874. Cibicides lobatus (d’Orbigny) Plate 7, figure 9 Cibicides lobatus (d’Orbigny). Bandy, 1944, J our. Paleontology, v. 18, no. 4, p. 374, pl. 62, fig. 1. Planoconvex, highly compressed specimens compare well with Bandy’s description and illustrations of Cibicides Zobatus (d’Orbigny) from beds of Eocene age at Cape Blanco, Oreg. In the northern Olympic Peninsula, 0. lobatus occurs in beds of Eocene age in the lower part of the Twin River formation and in the Crescent formation. Figured specimen (USNM 627021) from USGS locality f11882. Gi‘bicides martinezensis malloryi Smith Plate 7, figure 11 Oibicides martinezensis malloryi Smith, 1957, California Univ. Pub. Geol. Sci., v. 32, no. 3, p. 193, pl. 31, fig. 7. The present specimens display high convexity of the ventral side and low convexity of the dorsal side; they have a coarsely perforate surface, and the early whorls are obscured on the dorsal side. These features are characteristic of Uibz'ce'des martinezensés malloryi. In the northern Olympic Peninsula this form makes one appearance in beds of Refugian age but all other oc- currences are in rocks of late Eocene age in the lower part of the Twin River formation and the Aldwell for- mation. 0. m-artinezensz’s malloryz' was described from the Alhambra formation of California (Smith, 1957). Specimens similar to this form have also been observed by the writer from both the Umpqua and Tyee forma— tions of Oregon. Figured specimen (USNM 627022) from USGS locality f11799. ADDITIONAL IDENTIFIED SPECIES All species identified from the northern Olympic Peninsula but not illustrated in the report are listed in table 5, a reference is given for each species. An illus- tration and description of each listed species can be ob- tained from these references. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON G25 TABLE 5.——Additional identified species from the northern Olympic Peninsula, Washington Species Reference Vulvnlina curta Cushman and Siegfus _________________________ Cushman and Siegfus, 1942, p. 401, pl. 15, figs. 7, 8. Gandrgina cf. G. alaeanensis Cushman ________________________ Rau, 1948a, p. 158, pl. 27, fig. 3, 4. Karreriella cf. K. contorta Beck ______________________________ Beck, 1943, p. 592, pl. 98, figs. 4, 5. Karreriella washingtonensis Rau ______________________________ Rau, 1948a, p. 158, pl. 27, figs. 5, 6. Silicosigmoilina californica Cushman and Church _______________ Smith, 1957, p. 155, pl. 19, figs. 8, 12. ' Quinquelooulina imperiarlis Hanna and Hanna _________________ Beck, 1943, p. 592, pl. 98, figs. 9, 10. cf. Q. triangularis d’Orbigny ______________________________ Mallory, 1959, p. 130, pl. 36, figs. 5, pl. 39, fig. 5. Spiroloonlina teacanus Cushman and Ellisor ____________________ Rau, 1948a, p. 160, pl. 28, figs. 4, 5. Sigmoilina tennis (Ozjzek) ___________________________________ Rau, 1951, p. 430, pl. 63, fig. 2._ Trilocnlina cf. T. gilboei Beck _________________ .. _______________ Beck, 1943, p. 594, pl. 101, figs. 1—3. Robnlus holcombensis Rau ____________________________________ Rau, 1951, p. 431, pl. 63, figs. 14—17. cf. R. pseudovortew Cole __________________________________ Smith, 1957,4p. 158, pl. 20, figs. 12,13. cf. R. teranus (Cushman and Applin) _____________________ Rau, 1948a, p. 163, pl. 29, figs. 16,17. E’Vaginnlinopsis vacavillensis (G. D. Hanna) __________________ Mallory, 1959, p. 157, pl. 11, fig. 8, pl. 40, figs. 1, 7. Marginulina cf. M. subbullata Hantken ________________________ Cushman and Siegfus,1942, pl. 16, fig. 21. Dentalina cf. D. oolei Cushman and Dusenbury _________________ Cushman and Dusenbury, 1934, p. 54, pl. 7, figs. 10—12. cf. D. consobrina d’Orbigny _______________________________ Cushman and Dusenbury, 1934, p. 55, pl. 7, figs. 13—15. dusenbnryi Beck _________________________________________ Beck, 1943, p. 599, pl. 105, figs. 20, 23. cf. D. quadi‘nlata Cushman and Laiming ___________________ Cushman and Laiming, 1931, p. 99, pl. 10, fig. 13. sp. A [of Rau, 1948] _____________________________________ Rau, 1948a, p. 166, pl. 29, fig. 3. sp. C [of Rau, 1948] ____________________ , __________________ Rau, 1948a, p. 167, pl. 29, fig. 7. sp. D [of Rau, 1948] _____________________________________ Rau, 1948a, p. 167, pl. 29, fig. 8. Nodosam‘a cf. N. anomala Reuss _______________________________ Cushman and Parker, 1931, p. 4, pl. 1, figs. 12—14. cf. N. hamilli Kleinpell ___________________________________ Kleinpell, 1938, p. 218, pl. 4, figs. 4, 5. latejugata Gilmbel _______________________________________ Rau, 1956, p. 74, pl. 14, figs. 18—21. longistagata d’Orbigny ___________________________________ Hedberg, 1937, p. 671, pl. 91, figs. 3, 4. Pseudoglandulina cf. P. inflate (Bronemann) ___________________ Rau, 1948a, p. 168, pl. 30, fig. 3. Lagena conscripta Cushman and Barksdale _____________________ Mallory, 1959, p. 175, pl. 14, fig. 4. co‘stata (Williamson) _____________________________________ Mallory, 1959, p. 175, pl. 14, fig. 3 ; pl. 41, fig. 7. heragona scalariformis (Williamson) _____________________ Cushman and Laiming, 1931, p. 101, pl. 11, fig. 4. swbstriata Williamson ____________________________________ Cushman and Laiming, 1931, p. 100, pl. 11, fig. 1. sulcata (Walker and Jacob) ______________________________ Cushman and Parker, 1931, p. 6, pl. 1, fig. 20. Gnttulina frankei Cushman and Ozawa ________________________ Rau, 1948a, p. 170, pl. 30, figs. 17,18. hantkeni Cushman and Ozawa ____________________________ Rau, 1948a, p. 169, pl. 30, figs. 11, 12. irreg-ularis (d’Orbigny) ___________________________________ Rau, 1948a, p. 169, pl. 30, figs. 7, 8. cf. G. pacifica (Cushman and Ozawa) ______________________ Cushman and Ozawa, 1930, p. 50, pl. 37, figs. 3—5. problema d’Orbigny ______________________________________ Cushman and Ozawa, 1930. p. 19, pl. 2, figs. 1—6; pl. 3, fig. 1. Pseudopolymorphina cf. P. ligua (Roemer) _____________________ Cushman and Ozawa, 1930, p. 89, pl. 22, figs. 5, 6. Sigmomo-rphimt pseudoschencki Rau __________________________ Rau, 1951, p. 436, pl. 64, fig. 11. Bolivinopsis directa (Cushman and Siegfus) ___________________ Cushman and Siegfus, 1942, p. 409, pl. 16, figs. 27,28. Plectofrondicularia cf. P. jenkinsi Church ______________________ Church, 1931, pl. A, figs. 5, 7—9. Amphimorphina californica Cushman and McMaste;s ___________ Cushman and McMasters, 1936, p. 513, pl. 75, figs. 21—25. Nadogenerina cf. N. adolphina (d’Orbigny) ____________________ Mallory, 1959, p.216, pl. 41, fig. 10. Bulimina alligata Cushman and Laiming ______________________ Cushman and Parker, 1947, p. 112, pl. 26, fig. 14. cf. B. bradbnryi Martin __________________________________ Cushman and Parker, 1947, p. 96, pl. 30, fig. 9. cf. B. ovata d’O‘rbigny ____________________________________ Cushman and Parker, 1947, p. 106, pl. 25, figs. 8, 9. pnpoides d’Orbigny _______________________________________ Cushman and Parker, 1947, p. 105, pl. 25, figs. 3—7. Globobulimina pacified Cushman ______________________________ Cushman and Parker, 1947, p. 134, pl. 29, fig. 37. Bolivina cf. B. jacksonensis Cushman and Applin_-_-_‘ _________ Cushman, 1937, p. 57, pl. 7, figs. 17, 18. Uvigerinella obsea impolata Cushman and Laiming ____________ Cushman and Laiming, 1931, p. 111, pl. 12, fig. 11. Siphonodosaria friezelli Rau __________________________________ Rau, 1948a, p. 171, pl. 30, fig. 10. Ellipsonodosaria cf. E. cocoaensis (Cushman) __________________ Beck, 1943, p. 608, pl. 108, fig. 10. Discorbis aff. D. alveata stavensis Bandy ______________________ Bandy, 1949, p. 95, pl. 16, fig. 1. cf. D. humilis LeCalvez __________________________________ LeCalvez, 1949, p. 24, pl. 3, figs. 48—50. Valvulineria cf. V. cooperensis Bandy _________________________ Bandy, 1944, p. 371, pl. 61, fig. 3. cf. V. depressa Cushman __________________________________ Kleinpell, 1938, p. 311, pl. 9, fig. 22. aff. V. jacksonensis persimil-is Bandy ______________________ Bandy, 1949, p. 83, pl. 13, fig. 4. cf. V. indi-scriminata Mallory _____________________________ Mallory, 1959, p. 230, pl. 20, fig. 2. menloensis Rau __________________________________________ Rau, 1951, p. 446, pl. 66, figs. 17—22. tumeyensis Cushman and Simonson _______________________ Cushman and Simonson, 1944, p. 201, pl. 33, figs. 13, 14. G26 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 5.—Additional identified species from the northern Olympic Peninsula, Washington—Continued Species Valvalineria—Continued willapaensis Rau Gyroidina condoni (Cushman and Schenck) ____________________ Eponides daprei ciervoensis Cushman and Simonson _____________ cf. E. ellisorae Garrett____ umbonatus (Reuss) ___ yeguaensis Weinzierl and Applin Rotorbinella collicalus Bandy __________________________ Epistomina eocenica (Cushman and Hanna) ___________________ Baggina teninoensis Ran _ Oet‘atobnlimina washbarni Oushman and Schenck ______________ Allomorphina macrostoma Karrer _____________________________ Chilostomella cf. 0. oolina Schwager ___________________________ Pallenia bulloides (d’OrbigDY) _ of. P. saliaburyi R. E. and K. 0. Stewart ___________________ Anomalina packardi Bandy ___________________________________ cf. A regina Martin ______ Oibicides elmaensis Rau _____ haydoni (Cushman and Schenck) _________________________ hodgei Cushman and Schenck ____________________________ howelli Bandy- momastersi Beck _ cf. 0'. venezuelanas Nuttall_, _____________________________ Discocyclina psila Woodring __________________________________ COLLECTING LOCALITIES All foraminiferal collecting localities referred to in the report are listed in table 6. The formation from which each collection was made together with a public land description of each locality is also given. TABLE 6—Collecting localities in the northern Olympic Peninsula, Washington [Public—land descriptions in reference to Willamette meridian; measurements in feet] U.S.G.S. Formation Description locality 111711 ......... Crescent ______ 3100 N. and 1600W. of NE. cor. sec. 26, T. 30N., 111712 _________ ___.do .......... 2000Nl. of SW. cor. sec. 24, T. 30N., R. 10W. 111713 _________ ...-do __________ 55%Ng. $1d 3000 E. of SW. cor. sec. 19, T. 30 N., 111714 _________ ___-do .......... Road cut, Hurricane Ridge road, Olympic Na- tional Park, 5800 N. 80° W. from elevation 3541 on Round Mountain. 111715 _________ .--.do .......... Road cut, Hurricane RidgNe road, Olympic Na- tional Park, 5800 N. 88°W .irom elevation 3541 on Round Mountain. 111716 _________ .-.-do .......... Devils Point, Lake Crescent, 900 S. and 4100 E. ofNW. cor. sec. 23, T. 30N., R W. {11717 _________ .-.-do __________ Northwest part of Crescent Bay, 2500 N. and 1100 W..01SE cor. sec. 20,T..,31N .8W. {11718 ......... .--.do __________ 31%) Nwand 50 E. of SW. cor. sec 22, T. 31 N. 111719 _________ .-.-do __________ East of Tongue Point approximately three—quarters of a mile 2900 N. and 1150 E. of SW. cor. sec. 22, T. 31 ,R. SW. 111720 ......... ____do __________ Observatory Point, 2225 N. and 4350 E. of SW. cor. sec.25, T 31N.. R. 8W. 111721 _________ _do _____________ West Fork Siebert Creek, 500 S. and 700 W. 01 NE. cor. sec. 15, T. 29N.,R. 5W 111722 _________ Aldwell _______ On East Peri-Ply road, 5050 S. and 3400 W. of SE. cor..secl,T..,30N R.010.W 111723 _________ .do _____________ Lyre River, 400 S. and 2400 W. of NE. cor. sec. 15, T. 30N., R. 9W. 111724 ......... -do _____________ Pi’I‘dIIlianlééR 2350 SW and 500 W. of NE. cor sec. 14, R.9 111725 ......... _do ............. Ridge north of Indian3 Creek, 700 S. and 600 W. of NE cor. sec. 19,T N. R.7W. 111726 ......... _do _____________ East side Lake Ald“ ell 700 N. and 200 W. of SE. cor. sec. 21, T. 30N, .7.W 111727 ......... .do ............. Valley Creek, 2300 S. and 400 W. of NE. cor. sec T.30.,N R.6 6W Reference Rau, 1951, p. 447, pl. 441, figs. 23—25. Cushman and Schenck, 1928, p. 313, pl. 44, fig. 6, 7. Cushman and Simonson, 1944, p. 201, pl. 34, figs. 2, 3. Cushman, Stewart, and Stewart, 1947, p. 79, pl. 10, fig. 7. Rau, 1951, p. 448, pl. 66, figs. 1—3. Beck, 1943, p. 608, figs. 1—4. Bandy, 1944, p. 372, pl. 61, fig. 6. Ban, 1948a, p. 172, pl. 31, figs. 1—3. Ran, 1956, p. 76, pl. 15, figs. 24, 25. Cushman and Schenck, 1928, p. 314, pl. 45, fig. 1. Rau, 1948a, p. 173, pl. 31, figs. 4, 5. Ban, 1951, p. 450, pl. 67, fig. 8. Kleinpell, 1938, p. 338, pl. 5, figs. 10, 13. Rau, 1951, p. 450, p1._67, figs. 9, 10. Bandy, 1944, p. 373, pl. 61, fig. 7. Mallory, 1959, p. 261, pl. 38, fig. 6. Rau, 1948a, p. 173, pl. 31, figs. 18—26. Oushman and Schenck, 1928, p. 316, pl. 45, fig. 7. Rau, 1951, p. 451, pl. 67, figs. 28—30. Bandy, 1944, p. 374, pl. 61, fig. 9. Beck, 1943, p. 612, pl. 109, figs. 2, 4, 15. Mallory, 1959, p. 274, pl. 31, fig. 6. Berthiaume, 1938, p. 496, pl. 61, figs. 8—11. (Aktinocyclina) aster (Woodring) ________________________ Berthiaume, 1938, p. 496, pl. 61, figs. 1—7. TABLE 15.—Collecting localities —Continued U. S.G Formation Description locality 111728 ..... Aldwell ___________ Valley Creek, 1800 N. and 850 W. of SE. cor. sec. , T.30 N. R. 6 W. 111729 __________ do _____________ Ennis Creek, 1300 S. and 350 W. 01 NE. cor. sec. 23, T. 30 N. .6 W. 111730 __________ do _____________ Ennis Creek, '1500 S. and 400 W. of NE. cor. sec. 23, T. 30 N., R. 6 W. 111731 _____ Upper member of Pearson Creek, 2100 N. and 2200 E. of SW. cor. Twin River. sec. 27, T. 32N., R. 12W 111732 _____ Lower member of Burnt Mountain Road, 3150 S. and 950 E. 01 NW. Twin River. cor. sec. 35, T. 31N., R. 2W. 111733 __________ do _____________ Burnt Mountain Road, 3600 S. and 1350 E. of NW. cor. sec. 35, T. 31 N., R. 12W. {11734 __________ do ............. Burnt Mountain Road, 1400W S. and 400 E. 01 NW. cor. sec. 2, T. 30N, R.1 111735 _____ Middle member South Fork Pysht River, 21500 S. and 2700 E. of of Twin River. NW. cor. sec. 19, T. 31 N. R. 11 W. 111736 .......... do ............. South Fork Pysht River, 1900 S. and 2600 W. of NE. cor. sec. 19, T. 31N., R.11.W 111737 .......... do ............. South Fork Pysht RiveNr, 214200 S. and 1800 W. 01 NE. cor. sec. 19, T. 31N R.11 W. 111738 .......... do ............. South Fcrk Pysht River, 2200 S. and 1050 W. of NE. cor. sec. 19, T. 31N., R. 1W. 111739 .......... do ............. South Fork Pysht’ RNiver, 550 N. and 400 E. 01 SW. cor..sec20,T.13 N.,R.11W. 111740 .......... do ............. 1850SW and 1550W. ofNE. cor. sec. 31, T. 31N., R. 11 111741 _____ Lower member of Beaver Creek, 800 E. of NW. cor. sec. 18, T. 30N., Twin River. R.11 111742 .......... do ............. Beaver Creek, 1550 S. and 950 W. of NE. cor. sec. 18, T. 30 N, R. 11 W. 111743 ..... Upper member 01 Approximately 1 mile west or Pillar Point, 1200 N. Twin River. and50 E. of SW. cor. sec. 33, T. 32N., R. 111W. {11744 .......... do _____________ Approximately 1 mile west 0! Pillar Point, 700 N. and400E. otSW. cor. sec. 33, T. 32N., R. 11W 111745 __________ do _____________ Approximately 1 mile west 01 Pillar Point 600 N. and 10001“ oiSW. cor. sec. 33, T. 2N 11. 11w. 111746 __________ do _____________ Tributary to Pysht River, 1000 N. and 200 E. of SW. cor. sec. 16, T. 31N., R. W. 111747 ..... Middle member Middle Creek, 1950 S. and 1700 E. of NW. cor. sec. of Twin River. 28, T. 31N., R.11W. 111748 ..... U per member of Pillar Point State Park on beach, 2800 N. and 500 win River. W. of SE. cor. sec. 10, T. 31N., ’R. 11 W. 111749 _______________________ Pillar Point State Recreational area on beach. 1400 NVavndQOOE. ofSW. cor. sec. 11, T. 31N..,R 11 111750 __________ do ............. Between Pillar Point and mouth of Jim Creek, 1100 Nwand 1600 E. of SW. cor. sec. 11, T. 31 N., R. 11 111751 .......... do ........ .._-. Approximawa three-fourths mile northwest of mouth of Jim Creek, 800 W. of NE. our. '1‘.31 N. R. 11 W. 56.0 14, FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, TABLE 6.—Oollecting localities—Continued WASHINGTON G27 TABLE 6.—Oollecting localities—Continued U.S.G.S. Formation Description U.S.G.S. Formation Description locality locality 111752 _____ Upper member r-i’ Jim lCrelg’l'r, 1515.0 Nwand 100 E. 01 SW. cor. sec. 14, 111800 ..... U’piper mRemher of 01111 coast,8$r$-qu§rtgggg aglzefeast 01 Eas4'1'1‘wgi Twir1 River. 3111 w1n iver. iver, 1 .an 3 .o .cor.sec.2 , . 111753 __________ do ............. Jim Creek, 1000N. and 550E. of SW. cor. sec. 13, N., R 1 W. T, 3., R. 11 W. 111801 .......... do ............. On coast, 1% miles east of East Twin River, 600 N. 111754._._. Middle member Deep Creek, 2700 N. and 1600 W. 01 SE. cor. see. 30, and 600 E. 01 SW. cor. sec. 19, T. 31 N., R. 9 W. 01 Twin River. T 3 . ., R. 10 W. 111802 __________ do _____________ On coast, 2E miles east of East Twin River, 800 N. 111755 _____ (__lo _____________ Deep Creek 2500N. and 1600W. 01S1.. cor. sec. 30, and 4600E .01 SW cor. sec. 19, T. 31 R..9W T 31 N. R 10 W. 111803 __________ do _____________ On coast, 2/ miles east 01 East TwinN River, 800 111756. ____ _____ do _____________ Deep'Igrge’qu 1750 N. 0.6:?“ 2000 W. 01 SE. 001. sec. sNivand 6100 E. 01 SW. cor. sec 19, T. 31 N. 1 . 111757 __________ do _____________ DgngCgelellif- 103010119. me 2000 W. 01 SE. cor. Sec. 111804 .......... do ............. 0111I coast, 2% 111:1ilesf SW; of East ’Il‘gvi% I??? 5150 .an 6500 4. o . cor. sec. , . , 111758 __________ do _____________ Deep Creek, 600N. 0and 2100W. 01 SE. cor. sec. 30, 9W. T. 31 N. R. 10 111805 .......... do ............. 0n coast, 1% miles west of Murdock Creek, 500 111759 __________ do _____________ Delep Creek, 300 livand 2100 W. of SE. cor. sec. 30, ngmd 5400 W. 01 SW. cor. sec. 19, T. 31 N., R 111760 __________ do _____________ Deep30reekh10i)0W N. and 2500 W. 01 SE. cor. sec. 30, 111806 .......... do ............. Orfieoasfg, 11% vmvilesx vgvlelst 01 Murdgckr Careeg, 8120 .an 450 .o 1.cor.sec. , .1 . . 111761 _____ Deep Creek 100S Wand 2350 E. 01 NW. cor. sec. 31, 9 W. ' T. 31 R. 10 W. 111807 __________ do _____________ 0n coast, 1% miles west 01 Murdock Creek, 1100 111762 _____ DeTep3gNekR300 Swand 1450E. 01 NW. cor. sec. 31, N v‘fnd 3450 W. 01 SE. cor. sec. 19, T. 31 N., R. 10 111763 _____ Delep3 CNekRSOOOSW and 600 E. of NW. cor. sec. 31, 111808 __________ do _____________ On epast, lwmilelg gvlgst of Muriléicrllg (grelelk,112003‘lg. 1 1 an 1800 n cor. sec . 111764 _____ Dggp’ICrelek,’ 1950 1S1W‘d 1200 W. 01 NE. cor. sec. 111809 .......... do ............. 01(13 coafit three-quaéters 0W3 inilSeEwest 01 Mufgo’crk ree 700 N an 700 o cor. sec 111765 ..... Deep Creek 1900 :81. and 2100 E. of NW. 001‘. sec. 31 N., W. 1, T. 31 N.,R.1111810 __________ do _____________ On coast, half a mile west 01 Murdock Creek, 5400 111766 _____ DeepT Creek 1200,1S. and 400 E. of NW. cor. sec. N and 100E. ofSW. cor. sec. 29, T. 31 N., R. 9W. 36,T 3.1 N. 111811 __________ do ............. Murdock Creek, 950 N. and 800 E. 01 SW. cor. sec. 111767 _____ DeepTCrelek,1900 S. and 1800 W. 01 NE cor. see. 29, T. 31 N., R. 9 W. 36,T 1N. ., R. 11 W. 111812 __________ do _____________ Water well near Gettysburg Ranch, 200 S. and 700 111768 _____ DeepT Craeek, 12R00 181. and 200 W. 01 NE. cor. sec. W. 01 NE. cor. sec. 28, T. 31 N., R. 9W. 36,T .31 N. ., R. 111813 __________ do _____________ Lyre River. 400 N. and 1050 W. of SE. cor. sec. 28, 111769 _____ Deep Creek, 800 S. and 400 E. of NW. eor. sec. T. 31 N., W. 31, T. 31 N., R.10.W 111814 .......... do _____________ Lyre River, 200 N. and 800 W. of SE. cor. sec. 28, 111770 _____ Deep Creek,1800 S. and 1200 W. 01 NE. cor. sec. 3.1 N, R. 9 W. 36, T. 31 N. .11 W. 111815 .......... do ............. Lyre River, 150 N. and 750 W. of SE. cor. sec. 28, 111771 _____ Deep Creek,1900 S. and 1000 W. 01' NE. cor. sec. T.31 N. R. 9 W. 36, T. 31 N. .11 W. 111816 .......... do _____________ Lyre River, 650 W. 01 SE. cor. sec. 28, T. 31 N., 111772 _____ Deep Creek, 2300 S. and 900 W of NE. cor. sec. 36, R. 9 W. T. 31 N., R. 1.W 111817 .......... do ............. Lyre River, 50 SW and 650 W 01 NE. cor. sec. 33, 111773 ..... Deep Creek, 2800 S. and 1050 W. ofNE. cor. sec. 36, 1 N, R. T. 31 N. R. 11 W. 111818 __________ do _____________ Lyre River, 150 S. and 650 W. 01 NE. cor. sec. 33, {11774, Deep Creek, 3000 S. and 1100W. ofNE. cor. sec. 36, T. 31 N. R. 9 W. 111775. T.13 N., R. 11 111819 .......... do ............. Lyre River, 250 S. and 650 W 01 NE. cor. sec. 33, 111776...._ Deep Creek, 31008. and 1100W. ofNE. cor. sec. 36, T3 N, R 9W T.3 N. R.11.W 111820 .......... do ............. Lyre River, 350 S. and 600 W. 01 NE. cor. sec. 33, 111777....- Deep3 Creek, 1700 N. and 1000W. 01 SE. cor. sec. 36, T. 31 N., R. 9 W. T. 31 N. .11 W. 111821 .......... do ............. Lyre River,R 450 S. and 600 W. of NE. cor. sec. 33, 111778. _ .__ Deep Creek. 1650 N. and 1000 W. of SE. cor. sec. 36, T.31 N., R.9 W. T 31 ., R. 11 1W. 111822 .......... do ............. Lyre River, 600 S. and 450 W. of NE. cor. sec. 33, 111779 .......... do _____________ Deep Creek, 1600 N. and 1000W. of SE. cor. sec. 36, T3.1 N., R. 9 T. 31 N, R. 11 W. 111823 .......... do ............. Lyre River, 700 S. and 350 W. 01 NE. cor. sec. 33, 111780 .......... do ............. Deep Creek, 1500N. and 1000 W. ofSE. cor. sec. 36, T 31 N. R.9 W. T. 1 N, R. 11 W. 111824 .......... do ............. Lyre River, 750 S and 200 W. 01 NE. cor. sec. 33, 111781 .......... do _____________ Deep Creek 1400N. and 1000W. 01 SE.cor. sec. 31, T. 31 N, R. 9 W. T 31 N., 11.1 111825 .......... do ............. Lyre River 1250 s. of NE cor sec. 33, T. 31 N., 111782 .......... do ............. Deep Creek, 8001 N. and 1000 W. of SE. cor. sec. 31, 11.9 T.31 N., R. 11 W. 111826 .......... do ............. LyTreoRiver,1700 S. and 300 E. of NW. cor. sec. 34, 111783 .......... do ............. Deep Creek 700 N. and 1000 W. of SE. cor. sec. 31, 1 N, R. 9W T. 311N.. R.11W. 111827 .......... do ............. Lyre River, 1750 S. and 400 E. of NW. cor. sec. 34, 111784 .......... do _____________ Deep Creek. 6510 N. and 100 W. of SE. cor. sec. 31, T. 31 N, 9W T. 31 N., R.11.W 111828 .......... d0 ............. Lyre River, 1800 S. and 450 E. 01 NW. cor. sec. 34, 111785 .......... do ............. Deep Creek, 500 N., 1300 W. of SE. cor. sec. 31, T. 31 N. R. 9 W. T. ,R.11.W 111829 .......... d0 ............. Lyre River, 2150 S. and 400 E. 01 NW. cor. sec. 34, 111786 .......... do _____________ Deep Creek, 45110 N. and 1300 W. of SE. cor. sec. 31, T.31 N., R. 9 W. T 1W. 111830 .......... do ............. Lyre River, 2500 S. and 500 E. 01 NW. cor. sec. 34, 111787 .......... do _____________ 400N.and4001E..01SW cor. sec.,28T.31N., R. T.1.3N, R.9W 0W.111831 .......... do ............. Lyre River, 2600 S. and 550 E. 01 NW. cor. sec. 34, 111788 ..... Upper member 01 On0 coast, 2 miles west 01 West Twin River, 4500 N. T 31 N., R. 9 W. Twin River. and 2700W orSE. cor. sec. 21, T. 31 N. R. 10 W 111832...- Middle member 01 Lyre River, 1900 N. and 850 E. of SW. cor. sec. 34, {11789 ..... On coast, 2 miles west of West Twin River, 3700 N. Twin River. T.131N., R. 9 W. and 2400 W. ofSE. cor. sec. 21, T. 31 N., R. 10 W. 111833 _____ Lyre River, 1850 N. and 850 E. 01 SW. cor. sec. 34, 111790 _____ On coast, 2 miles west 01 West Twin River, 3150 N. T. 31 N, R. 9 W. and 1600 W. of SE. cor. sec. 21, T. 31 N., R. 10 W, 111834 ..... Lyre River, 1700 N. and 800 E. 01 SW. cor. sec. 34, 111791 ..... On coast, 114 miles west 01 West Twin River, 2800' T R W VNV. and 400 E. of SW. cor sec. 22, T. 31 N., R. 10 111835 .......... d0 ............. LylreaRiver, 1650 N. and 750 E. 01 SW. cor. sec. 34, . 1N R. 9W “1792 ----- 01111 coasti 2351 {113 mile SVWSt of West TMT1 River, 2100 111836 .......... d0 ............. LyreaRiver, 115005;. and 650 E. of SW. cor. sec. 34, an o cor. sec. 23 31 R,. 1 N 9 10 W. 111837 __________ do _____________ Lyre River, 1250 N. and 600 E. of SW. cor. see. 34, 111793 ..... On coast, 500 west of West Twin RivNer, 2450 N. T. 31 N. R. 9 W and 2700 E. 01 SW. eor. sec. 23, T. 31N R. 10 W. 111838 .......... do ............. Lyre River, 1050 N. and 550 E. 01 SW. cor. sec. 34, 111794 ........... do ............. On Twin River Road, 1100 S. and 550 W. of NE. T. 31 N, ’I. 9 W. cor. sec 26, T. 31 N. W. 111839 .......... do .............. Lyre River, 750 N. and 550 E. of SW. cor sec. 34, 111795 __________ do ............. On Twin River Road, 700 N0 and 250 E. of SW. cor. 1‘. 31 ., -W9 sec. 24, T. 31 N, R. 10W 111840 .......... do ............. Lyre River, 700 N. and 550 E. 01 SW. cor. sec. 34, 111796 .......... do ............. On coast, a quarter 01 a mile east 01 East Twin T. 31 N, R. 9W zfinger,'210010NV‘.I11nd1200 E. of SW cor. sec. 24, T. 111841 .......... do ............. Lylre River 350 N. and 650 E. of SW. cor. sec. 34, 31 N. YR.9 111797 .......... do ............. On coast, halra mile east of East Twin River, 850 111842 .......... do ............. Lyre River, 250 N. and 750 E. of SW. cor. sec. 34. N.and2200E. otSW. cor.sec. 24,T..31N, R.10 T 31N., 11.9 W. W. 111843 .......... do ............. Lyre River, 100 N and 700 E. of SW. cor. sec. 34. 111798 .......... do ............. On coast, three- -quarters 01a mile east of East Twin T. 1 N, gigangmuNWand 2500E. 01 SW. cor. sec. 24, T. 111844 .......... do ............. Lyfire River, 700 E. 01 SW. cor. sec. 34, T. 34 N., “1799 ----- Lower member of 111845 .......... do ............. Lyre River, 150 s. and 750 E. 01 NW. eor. sec. 3, T. 30 N., R. 9 W. Twin River. 011 road on east side of East Twin River, 1300 N. and600W. OISE. corsec. 1, T, 30N,, R. 10W SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 6.—Oolleoting localities ——Continued U.S.G S Formation Description locality 111846 _____ Middle member of Lyre River, 300 S. and 850 E. of NW. cor. sec. 3, Twin River. T. 0 N., R. 9 W {11847 __________ do _____________ LyTre River, 400 S. and 900 E. of NW. cor. sec. 3, T.30 N, R. 9 W. 111848 __________ do _____________ Lyre River, 450 S. and 1000 E. of NW. oor. sec. 3 T.30 N., R. 9 W. {11849 __________ do _____________ Lyre River, 550 S. and 1100 E. of NW. 001'. sec. 3 T. 30N., R. 9W. 111850 __________ do _____________ Lyre River, 600 S. and 1150 E. of NW. cor. sec. 3, T. 30N., R. 9W. 111851 __________ do _____________ Lyre River, 1200 S. and 1250 E. of NW. cor. sec. 3, T.30 N. R. 9 W. [11852 __________ do _____________ Lyre River, 1350 S. and 1150 E. of NW. cor. sec. 3, T. 30 N. R. 9W 111853 __________ do _____________ Lyre River, 1550 S. and 1000 E. of NW. cor. sec. 3, T30 N. ’R. 9W. 111854 __________ do _____________ Lyre River, 1600 S. and 950 E. 01‘ NW. cor. sec. 3, T. 30 N. W 111855 _____ Lower member of Lyre River, 700 N. and 1000E. of SW. cor. sec. 3 Twin River. T. 30 N. R. 9 W. {11856 __________ do _____________ Lyre River, 600 N and 1100 E. of SW. cor. sec. 3 T. N. R. 9 W. 111857 __________ do ______________ Lyre River, 400 N. and 1200 E. of SW. cor. sec. 3 T.30 ().N, R. 9W. 111358 __________ do _____________ Lyre River, 100 N. and 1450 E. of SW. cor. sec. 3, T. 30N., R 9W. 111859-.." _____ do _____________ Lyre River, 1100 S. and 1600 E. of NW. cor. sec. 10, T. 30 N.,, R. 9 W. 111860. _._. Upper member or On coast, half a mile east of Gettysburg Ranch, 250 Twin River. S‘gnd 2750 E. of NW. cor. sec. 27, T. 31 N 111861 _____ Middle member 011 coast, a quarter 01a mile east of Field Creek, 800 01 Twin River. S. and 700W. oiNE. cor. sec. 27, T. 31N., R!) W. {11862 __________ do _____________ On coast, hall‘amile east of Field Creek 600 S 93nd 700E. oiNW. cor. sec. 26, T. 31N., R. 9W. f11863_____ _____ do _____________ 0n coast, 1 mile west or Whisky Creek, 500 s and 1700E. of NW. cor. sec. 26, T. 31N W. 111864. _ .__ Lower member or On coast, 1 mile east of Whisky Creek, 1400 N. and Twin River. 2000E. 01 SW. cor. sec 19, T. 31 N R 8W 111865 _____ Middle member Salt Creek valley, 1400 S. and 600 W. of NE. cor. of Twin River, sec. 34, T. 31 N., R. 8W. [11866_____ _____ do _____________ Salt Creek valley 400 S. and 500 E. of NW cor sec. 35, T. 31 N, R. 8W. {11867 _____ Upper member of Freshwater Bay, 3300 N. and 1100 W. of NE. cor. Twin River. sec. 31 T. 31N ,, 7_w 111868 __________ do _____________ 09117031112 1(\lrreek,w 400N. and 350W. ofSE. cor. sec. 31, 111869 __________ do _____________ Freshwater Bay,w 3000 N. and 1500 E. of SW. cor. sec. 32, T. 31N., R. 7W 111870 __________ do _____________ Freshwater Bay, 2400 N. and 1400 W. of SE cor. sec. 32. T. 31N., R. 71 111871 __________ do _____________ ZIOOWN. and 150 E. of SW. cor. sec. 33, T. 31N., R {11372 _____ Lower member of Eden Valley, 1200 N. and 1200 W. of SE. cor. sec. Twin River. 7, T- 30 N R. 7W 111873 __________ do _____________ Ridge south of Eden Valley, 1400 s. and 2300 E. of NW. cor. sec. 17, T. 0.,N R. 7. W. (11874 __________ do _____________ On Elwha River north of Olympic Power Plant gag, 20997.8“! and 2000 W. of NE. cor. sec. 15, T. 111875 _____ Middle member Tumwater Creek,1200 S. and 200 W. of NE. cor. of Twin River. sec 17 T 30N., R.6 111876 __________ do _____________ Tumwater Creek 1900 s. and 450 W of NE. cor. sec. 17, T. 30N. ,,R 6W 111877 __________ do _____________ Ennis Creek, 600 S. and 300 W. o1 NE. cor. sec. 23, T. 30N., R. 6 W. 111878 ..... Upper member of Ennis Creek, 1400 S. and 2800 W of NE cor. sec. Twin River. 13 T'30N-1R W. 111879.-.-. _____ do _____________ Ennis Creek 550 S. and 2600 W of NE. cor. sec, 13, T. 30 N., R6 {11880 .......... do _____________ Legs Creek 135% IW and 450 W. of SE. cor. sec 12 111881 _____ Middle member Morse Creek, 800 S. and 1100 E. of NW. cor. sec. of Twin River. 17, T. 30 N. R. 5 W. [11882. .._. _____ do _____________ Headwaters of Bagley Creek, 450 S. and 1350 E. of NW. cor. sec. 3, T. 29N.,R. 5W 111883 ..... Lower member of Headwaters of Bagley Creck,1100 S. and 1100 E. Twin River. of NW. cor. sec. 3, T. 9N., R. 5W f11884 .......... West Fork Siebert Creek, 150 S. and 800 E. of NE. cor. sec. 15, T. 29N., R. 5W. 111885 ..... Middle member West Fork Siebert Creek, 2150 S. and 200E. oi of Twin River. NW. cor. sec. 11, T. 29 N., R. 5W 111886 .......... do__ _ Siebert Creek, 1600 S. and 900 E. of NW. cor. sec. 35, T. 30 N. ., R. 5 W f11887 ..... Siebert Creek tributary, 1150 S. and 1850 W. of NE. cor. see. 26, T. 30N., R. 5W. {11888 ..... Power line east of Siebert Creek, 1100 W. of NE. 001. sec. 26, T. 30N., R. 5W. 111889 ..... 1700 s. and 1150 W of NE cor. sec. 15, T. 30N., Twin River R. 5 W. 111890 ----- Siebert Creek, 650 s. of NW. cor. sec. 13, T. 30 N., R. 5 W. 111891 _____ Pearson Creek, 350 N. and 2000 E. of SW. cor. sec. 26, T. 32N., R.1 t11892 ..... Pearson Creek, 12002N. and 1100 E. of SW. cor. sec. 36, T. 32N., W. 111893 __________ do _____________ 2 0n coast, 1mile west 01 Pillar Point, 300N. and 1750 W. OISE. cor. sec. 33, T 32N,, R. 12W REFERENCES CITED Bandy, O. L., 1944, Eocene Foraminifera from Cape Blanco, Oregon: Jour. Paleontology, v. 18, no. 4, p. 366—377, 3 pls. 1949, Eocene and Oligocene Foraminifera from Little Stave Creek, Clarke County, Alabama: Am. Paleontology Bull., v. 32, no. 131, 210 p., 27 pls. 1953, The frequency distribution of Recent Foraminifera of California, pt. 1 of Ecology and paleoecology of some California Foraminifera: Jour. Paleontology, v. 27, no. 2, p. 161—182, pls. 21—25. Barbat, W. F., and von Estorff, F. E., 1933, Lower Miocene Foraminifera from the southern San Joaquin Valley, Cali- fornia: Jour. Paleontology, v. 7, no. 2, p. 164—174, pl. 23. Beck, R. S., 1943, Eocene Foraminifera from Cowlitz River, Lewis County, Washington: J our. Paleontology, v. 17, no. 6, p. 584—614, pls. 98—109. Berthiaume, S. A., 1938, Orbitoids from the Crescent formation (Eocene) of Washington: Jour. Paleontology, v. 12, no. 5, p. 494—497, 1 p1. Brown, R. D., Jr., and Gower, H. D., 1958, Twin River forma- tion (redefinition), northern Olympic Peninsula, Washing- ton: Am. Assoc. Petroleum Geologists Bull., v. 42, no.-10, p. 2492—2512. Brown, R. D., Jr., Gower, H. D., and Snavely, P. D., Jr., 1960, Geology of the Port Angeles-Lake Crescent area, Clallam County, Washington: US. Geol. Survey Oil and Gas Inv. Map OM—203. Brown, R. D., Jr., Snavely, P. D., Jr., and Gower, H. D., 1956, Lyre formation (redefinition), northern Olympic Peninsula, Washington: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 1, p. 94—107. Church, C. C., 1931, Foraminifera of the Kreyenhagen shale, in Chap. 2, Mining in California: California Jour. Mines and Geology 27th Rept. State Mineralogist, p. 202—213, pls. A—C. 1943, Descriptions of Foraminifera in Part 2 of Geologic formations and economic development of the oil and gas fields of California: California Div. Mines Bull. 118, p. 182. Crouch, R. W., 1952, Significance of temperature on Foraminif— era from deep basins off southern California coast: Am. Assoc. Petroleum Geologists Bull., v. 36, no. 5, p. 807—843. Cushman, J. A., 1927, Recent Foraminifera from off the west coast of America: Scripps Inst. Oceanography Bull., Tech. Ser., v. 1, no. 10, p. 119—188, 6 pls. ———1937, A monograph of the subfamily Virgulininea of the foraminiferal family Buliminidae: Cushman Lab. Foram. Research Contr., Spec. Pub. 9, 228 p., 24 pls. ———1939, A monograph of the foraminiferal family Noni- onidae: U.S. Geol. Survey Prof. Paper 191, 100 p. —— 1950, Foraminifera : their classification and economic use, 4th ed.: Cambridge, MaSS., Harvard Univ. Press, 605 p. Cushman, J. A., and Dusenbury, A. N., Jr., 1934, Eocene Forami- nifera of the Poway conglomerate of California: Cushman Lab. Foram. Research Contr., v. 10, pt. 3, p. 51—65, pls. 7-9. Cushman, J. A., and Hanna, M. A., 1927, Foraminifera from the Eocene near San Diego, California: San Diego Soc. Nat. History Trans, v. 5, no. 4, p. 45—64, pls. 4—6. Cushman, J. A., and Hobson, H. D. 1935, A foraminiferal faun- ule from the type San Lorenzo formation, Santa Cruz County, California: Cushman Lab. Foram. Research Contr., v. 11, pt. 3, p. 53—64, pls. 8, 9. Cushman, J. A., and Laiming, Boris, 1931, Miocene Foraminifera from Las Sauces Creek, Ventura County, California: Jour. Paleontology, v. 5, no. 2, p. 79—120, pls. 9—14. FORAMINIFERA, NORTHERN OLYMPIC PENINSULA, WASHINGTON Cushman, J. A., and McMasters, J. H., 1936, Middle Eocene Foraminifera from the Llajas formation, Ventura County, California: Jour. Paleontology, v. 10, no. 6, p. 497—517, pls. 74—77. Cushman,’ J. A., and Ozawa, Yoshiaki, 1930, A monograph of the foraminiferal family Polymorphinidae recent and fos- sil: U.S. Museum Proc., v. 77, art. 6, 185 p., 40 pls. Cushman, J. A., and Parker, F. L., 1931, Miocene Foraminifera from the Temblor of the east side of the San Joaquin Val- ley, California: Cushman Lab. Foram. Research Contr., v. 7, pt. 1, 16 p., 2 pls. 1947, Bulimina and related foraminiferal genera: U.S. Geol. Survey Prof. Paper 210—D, p. 55—176, pls. 15—30, Cushman, J. A., and Schenck, H. G., 1928, Two foraminiferal faunules from the Oregon Tertiary: California Univ., Dept. Geol. Sci. Bull., V. 17, no. 9, p. 305—324, pls. 42—45. Cushman, J. A., and Siegfus, SS, 1935, New species of Forami- nifera from the Kreyenhagen shale of Fresno County, Cali- fornia: Cushman Lab. Foram. Research Contr., v. 11, pt. 4, p. 90—95, pl. 14. 1942, Foraminifera from the type area of the Kreyen- hagen shale of California: San Diego Soc. Nat. History Trans, v. 9, no. 34, p. 385—426, pls. 14—19. Cushman, J. A., and Simonson, R. R., 1944, Foraminifera from the Tumey formation, Fresno County, California: J our. Pa- leontology, v. 18, no. 2, p. 186—203, pls. 30-34. Cushman, J. A., Stewart, R. E., and Stewart, K. C., 1947, Five papers on Foraminifera from the Tertiary of western Oregon : Oregon Dept. Geology and Mineral Industries Bull. 36, pts. 1—5, 111 p., 13 pls. 1949, Upper Eocene Foraminifera from the Toledo forma- tion, Toledo, Lincoln County, Oregon : Oregon Dept. Geology and Mineral Industries Bull. 36, pt. 6, p. 126—144, pls. 14—16. Cushman, J. A., and Stone, Benton, 1949, Foraminifera from the Eocene Verdun formation of Peru: Cushman Lab. Foram. Research Contr., v. 26, pt. 4, p. 73—83, pls. 13, 14. Detling, M. R., 1946, Foraminifera of the Coos Bay lower Ter- tiary, Coos County, Oregon: J our. Paloentology, v. 20, no. 4, p. 348—361, pls. 46—51. Glaessner, M. F., 1947, Principles of micropaleontology: New York, John Wiley and Sons, Inc., 296 p. Gower, H. D., 1960, Geology of the Pysht quadrangle, Washing- ton : U. S. Geol. Survey Geol. Quad. Map GO—129. Hedberg, H. D., 1937, Foraminifera of the middle Tertiary Carapita formation of northeastern Venezuela: Jour. Pa- leontology, v. 11, no. 8, p. 661—697, pls. 90—92. Kleinpell, R. M., 1938, Miocene stratigraphy of California: Am. Assoc. Petroleum Geologists, 450 p., 14 figs., 22 pls., 18 tables. Laiming, Boris, 1940, Some foraminiferal correlations in the Eocene of San Joaquin Valley, California: Sixth Pacific Sci. Cong. Proc., v. 2, p. 535—568, 9 figs. LeCalvez, Y., 1949, Rotaliidae et familles aflines [pt. 2] of Re- vision des foraminferes lutéiens du Bassin de Paris: France Service Carte Geol. Mem., 54 p., 6 pls. Mallory, V. S., 1953, some lower Eocene correlations of the Pacific Coast [abs]: Geol. Soc. America Bull., v. 64, no. 12, pt. 2, p. 1520. 1959, Lower Tertiary biostratigraphy of the California Coast Ranges: Am. Assoc. Petroleum Geologists, 416 p., 42 pls. G29 Natland, M. L., 1933, the temperature- and depth-distribution of some Recent and fossil Foraminifera in the southern California region: Scripps Inst. Oceanography Bull., Tech. Ser., v. 3, no. 10, p. 225—230. Norton, R. D., 1930, Ecologic relations of some Foraminifera: Scripps Inst. Oceanography Bull., Tech. Ser., v. 2, no. 9, p. 331—388. Pardee, J. T., 1921, Deposits of manganese ore in Montana, Utah, Oregon, and Washington: US. Geol. Survey Bull. 725—0, p. 141—243. Park, C. F., Jr., 1946, The spilite and manganese problems of the Olympic Peninsula, Washington: Am. Jour. Sci., v. 244, no. 5, p. 305—323, 5 figs. Parker, F. L., 1948, Foraminifera of the Continental Shelf from the Gulf of Maine to Maryland: Harvard Coll. Mus. Comp. Zoology Bull., v. 100, no. 2, p. 214—241, 7 pls. Pease, M. H., and Hoover, Linn, 1957, Geology of the Doty-Minot Peak area, Washington: US. Geol. Survey Oil and Gas Inv. Map O‘M—188. Phleger, F. B., and Parker, F. L., 1951, Ecology of Foraminifera, northwest Gulf of Mexico: Geol. Soc. America Mem. 46, pt. 1, 88 p.; pt. 2, 64 p.; 20 pls. Rau, W. W., 1948a, Foraminifera from the Porter shale (Lin- coln formation), Grays Harbor County, Washington: Jour. Paleontology, v.22, no. 2, p. 152—174, pls. 27—31. 1948b, Foraminifera from the Miocene Astoria forma- tion in southwestern Washington: Jour. Paleontology, v. 22, no. 6, p. 774-782, pl. 119. 1951, Tertiary Foraminifera from the Willipa River valley of southwest Washington: Jour. Paleontology, v. 25, no. 4, p. 417—453, pls. 63—67. 1956, Foraminifera from the McIntosh formation (Eocene) at McIntosh Lake, Washington: Cushman Found. Foram. Research Contr., v. 7, pt. 3, p. 69—78, pls. 14, 15. 1958, Stratigraphy and foraminiferal zonation in some of the Tertiary rocks of southwestern Washington: US. Geol. Survey Oil and Gas Inv. Chart 00—57, 2 sheets. Reagan, A. B., 1909, Some notes on the Olympic Peninsula, Washington: Kans. Acad. Sci. Trans, v. 22, p. 131—238. Schenck, H. G., and Kleinpell, R. M., 1936, Refugian stage of Pacific Coast Tertiary: Am. Assoc. Petroleum Geologists Bull., v. 20, no. 2, p. 215—225. Smith, B. Y., 1957, Lower Tertiary Foraminifera from Contra Costa County, California: California Univ. Pubs. Geol. Sci, v. 32, n0. 3, p. 127—242, pls. 17—32. Smith, H. P., 1956, Foraminifera from the Wagonwheel forma- tion, Devils Den district, California: California Univ. Pubs. Geol. Scie., v. 32, no. 2, p. 65—126, pls. 9—16. Snavely, P. B., Jr., Brown, R. D., Jr., Roberts, A. E., and Rau, W. W., 1958, Geology and coal resources of the Centralia- Chehalis district, Washington: US Geol. Survey Bull. 1053, 159 p. Vaughan, T. W., 1945, American Paleocene and Eocene larger Foraminifera: Geol. Soc. America Mem. 9, pt. 1, 175 p., 46 pl. Weaver, C. E., 1912, A preliminary report on the Tertiary pale- ontology of western Washington: Geol. Survey Bull. 15, 80 p. Weaver, C. E., and others, 1944, Correlation of the Marine Cenozoic formations of western North America: Geol. Soc. America Bull., v. 55, p. 569—598. Wilson, E. J ., 1954, Foraminifera from the Gaviota formation east of Gaviota Creek, California: California Univ. Pubs. Geol. Sci., v. 30, no. 2, p. 103—170, pls. 12—18. INDEX [Where several page numbers appear, major references are: in italic] A Page Acknowledgments ............................ 1 udelaidana, Bolivina marginata 8, 9, 11, 19 adolphina, Nodogenerina ...................... 25 advena, Bolivim ............................ 8,13, 19 (Akti'rwcyclina) aster, Discocyclinu- 3 Alabamina ____________________________________ 22 kernemis _____________________________ 4,8, 11,22 alazammis, Gaudryirm ........ 7, 25 Aldwell formation, Foraminifera .............. 4, 15, 17, 18, 20, 21, 22, 24 paleoecology .............................. l4 stratigraphy .............................. 2 Alhambra formation ........................ 6, 10, 24 alligator, Bulimma ............................ 7, 9, 25 Allomorphina macrostoma-.. ............... 4, 8, 26 alsatica, Bulimina .................. 7, 9, 11, 18 alreata stavemia, Diecorbis. ______ 3, 25 Amphimorphina califomica. ..- 4, 5, 25 Amphimgina ..................... 22 califormca ............... 3, 4, 22 51).... .............. 4, 8 Amphisteamidae. . ________________ 22 Anauloaerina ........................... 21 hammi .............................. 4, 6, 8, 11,21 anomala, Nodosaria. 7, 25 Anomalina ___________________________________ 24 califomiensia ......................... 8, 11, 13, 24 packardi. . .. 3, 26 regina .................................... 4, 26 Anomalinidae ................................ 24 applini, Lozastomum-. 19 aster, Discocyclina ............................. 26 Discocuclina (Aktinowclina) ............... 3 Aaterigeri'na ....................... 22 crasaiformia ........................ 4, 8, 10, 11,22 Astoria formation ....................... 13, 19, 22,23 B Baavi'na tenimeneia ........................... 8, 26 Bastendorfi shale ....................... 17, 20, 21, 22 Benthonic assemblages, Crescent formation... 3 Bifarina .................................. ._ 19 nuttulli ................................... 4, 19 Bolivina ...................................... 19 advena .................... 8, 13, 19 juksommis ............................... 8, 25 marginafa udelaidana .................. 8,9, 11, 19 Bolivinopsis direrta ________ bouerme, Nonionella ........................... 16 bradburui, Bulimimz .......................... 4, 25 Bulimina ................. _ 17 alliaata .................................. 7, 9, 25 alaau'ca ............................... 7, 9, 11, 18 bradburui ..... capitata ................................... 18 corrugata .......................... 4, 7, 10, 17, 18 lirata .......... 4, 7, 18 ovaia .................... .. 4, 7, 13, 25 pupm‘dea ________________ .... 25 jacksonemis- ..- 5 schmcki ......... .. 3, 5,8, 11,18 sculptilis .............. 18 sculptilis laciniata. 8, 11, 18 Bulimimzlla... .-.. , 17 subfusiformis .......................... 7, 9, 11, 17 Page Bulimlnidae .................................. 17 bulloides, Panama" 0 calcar, Robulue ........................... 7,9,11, 15 califomica, Amphimorphina- . 4, 5, 25 Amphistegimz ..... Silicosiamoilina. . . califomiensis, Anomalina. Cancris ..... _.-. 22 joaqumensta ......................... 4,8,9, 11,22 Canoes siltstone member, Kreyenhagen shale. 6 capitata, Bulimimz.... ...- 18 Cassidulina ............... 23 craasipunctata ...................... 8, 9, 11, 12, 23 alaboaa ............................ 4, 6, 8,9, 11, 23 subglobosa- . 8 Cassidulinldae ................................ 22 Caaridulinoides ............................... 23 --- 8,10, 11,23 celelgrus, Cibicides ...................... 3, 4, 8, 11,24 Ceratobulimina washburm' ..................... 8, 26 Chilostomella oolina ............ 4, 8, 26 churchi, Uviaerim... Cibicidea ........ celebrm. elmaemu. haydom. hodgei howell:.. lobatus .......... mcmastmi ................................ 3, 26 martimzemis ......................... 4, 8 marh‘mzensis mallorw'. ................ 11,24 vemzuelanua ............................. 4, 8, 26 sp .................................... 3, 4,8 ciervoensis, Eponides dupm' .................... 8, 26 Clallam formation, Foraminifera ....... 13, 16, 19, 21 stratigraphy .............................. 2 Clallam syncline ............................. 2 Coaledo formation ............................ 10, 21 Coast section, Twin River formation ......... 9 cocoaemis, Ellipeomdosaria ................... 8,25 Uvigerina ........ ' .................... 8 , 11, 12, 20 colei, Dentalina ............................... 7,25 Tritazz‘lina ............................... 4. 7, 15 Collecting localities ........................... 26 colliculus, Rotobinella ....... 3,26 candom’, Gyroidina ...... 8,26 comcripta, Lagena ...... 7, 25 comobrina, Dentalina. ._ 7,25 conform, Korrm’ella ..... 7, 25 cooperensis, Valvulineria ...... 3,25 corrugata, Bulimina ..... . 4, 7, 10, 17, 18 costata, Lagena ........ 7, 25 coatiferum, Nonion.. .. 13, 16 Cowlitz formation .................... 15,21 Cozy Dell formation ...................... 18 crassiformis, Aeterigerina.. . 4, 8,10, 11,22 crassipumtata, Cam'dulina ............. 8,9,11,12,23 Crescent formation, Foraminifera ..... 3, 17, 18, 22, 24 paleoecology ................ 13 stratigraphy .............................. 2 curta, Vulvulina. ............................. 7,25 Cushman, J. A., quoted ...................... 3 D Page Deep Creek section, Twin River formation.-. 9 deliciae, Nodosaria ............................ 7 L‘ " colei.. 7, 25 conaobn'na ................................ 7, 25 dueenburyl ............................... 4, 7, 25 7, 25 4 7, 25 7, 25 25 7 depressa, Valvulinm'a .- 13,25 directa, Bolivinopsis.... . 4, 7, 25 Disaggregation of samples. . .__. - 1 Discocyclina (Aktinocyclina) aster. 3 eater ...... 26 mile .............. 3,26 Discorbis alveata atavemis .............. 3, 25 humilia ........................... duprei ciervoemis, Epom'des. ‘ ‘ yi, L‘ " ________ E Eagerclla sp ................................... 7 Elkton siltstone .............................. 17 Elli, " ia ' 8, 25 ellisorae, Epom'dea ............................ 8, 26 elmamst‘s, Cibicides .......................... 4, 8,26 Elphidium ........................ 16 munutum-.- ..- 7, 9, 11, 12, 13, 16 sp .................... 3 Entosolenia. .......... 19 sp ....................... 8, 9, 11, 19 eocem'ca, Epistemina. . ........ 8, 26 Epiatomina eocenica.-- 8, 26 Epiatomimlla perm. . 5 Epom'dea ........... 21 dupm' cimoemis .................... 8, 26 elliaorae ................................... 8,26 kleinpelli. 5 mamfieldi. .. ...-. 21 mamfieldi areaommia ....... 8, 9, 11, 13, 21, 22 umbonatua ............................. 4, 8, 26 yeauaemia ............................. 4, 8, 26 sp ........................................ 3 F Faults ........................................ 2 Faunal units, Twin River formation ........ 10 Fieldwork .................................... 1 Folds ......................................... 2 Foraminifera, Aldwell formation-. 4 Clallam formation.. 13 Crescent formation ..... 3 Twin River formation.. 6 frankei, Guttulina ......... 7, 25 frizzelli, Siphonodosaria ....................... 8,25 G gallowaui, Uvigerina ........................ 8, 9, 20 garzaemfs, Uvegerina ...... 12, 20, 21 Gaudrw'na alazammis ..... 7, 25 sp ................................ 4 Goviota formation ...................... . 12, 26 Geology ...................................... 1 G31 G32 oilboei, Triloculina ......... 7, 25 Globigm'no _______________ Globigerinids ................................. 3 Globo'lulimmo pacifica ......................... 25 Globorotalids _________________________________ 3 Globorotolia sp _____________ 4 globoso, Cassidulina" ....... 4, 6, 8, 9, 11, 23 Globotruncanlds ................ 3 noodspeedi, Quinqueloculiua ............. 7, 10, 11, 15 gracilis, Plectofrondiculario ..................... 17 Guttulina fronkei ....... hantkem’ ..... irregularie. _ . pacifico ................................... 7, 25 problema ................................. 7, 25 Gyrm'rli'nn _ - 21 condom’ ....................... 8,26 orbicularis planata- ..- 4, 8, 12, 13,21 sp ........................................ 3 ................... 7,25 4, 6, 8, 11, 21 hantkmi, Guttulina ___________________________ 7, 25 haudoni, Cibicidea ____________________________ 8,26 Heterohelicidae ................... 16 hexagonal rcaloriformia, Lagena. . __ -. 25 hodaei, Cibicidea ......................... - 4, 8,26 . . 1 ,,-,y F f 1 , howelli, C’ibicides ...... humilis, Discorbis ______ 8, 25 I imperious, Quinqueloculino...._ .............. ~ 7, 25 impolata, Um'aerinella obsea... 25 imisa, Nom‘tm. ______ 16 Noniom'na.. ...... 16 incisom, Nom‘on ....................... 7,9, 11,13, 16 indiscriminata, Valvulinerio ........... .... 3,25 inflata. Pseudoglondulina.-. 4, 5, 7, 25 irregularis, Guttulino .......................... 7,25 J ' ' , B " ' ... - 8,25 Bulimiua ____________________________ 5 Voluulimria. . 25 jocksonensis perszmtlis, Valvulimna. . 8,10 .jenkinsi, Plectofrondiculoria .................. 5, 7, 25 joaquimmiS, Concris .................... 4, 8, 9, 11, 22 K Karreriella comm-ta ........................... 7, 25 washingtonensis ___________________________ 7, 25 Keasey formation ............................. 20, 22 kernensia, Alabamma ......... ..- 4, 8, 11, 22 "',lli,E,. ". -- 5 Kreyenhagen shale ......................... 6, 10, 15 L locim‘ato, Bulimina sculptilis" . 8, 11,18 Sculptilis ............. .. 9 Lagena comeripta ............................. 7, 25 costata ____________________________________ 7, 25 hexagona scalariformis..- 25 ' ‘ 3,7, 25 suhstriato _______________ 7, 25 Lagenidae .......... 15 latejuyota, Nodosario ....................... 3, 4, 7, 25 ligua, Pseudopolymorphina. ..... 7, 25 Lincoln formation. _ ......... 12 lirata, Bulimina ............................. 4, 7,18 INDEX Page Lithology, Aldwell formation ................. 2 Clallam formation ........................ 2 Crescent formation ........... . 2 Lyre formation ............... . 9 Soleduck formation... .. . 1 Twin River formation .................... 2 lobatus, Cibicides ....................... 3,8,10,11,24 Location ..................................... 1 Localities, collecting .......................... 26 longistagoto, N adosoria.. .. 4, 7, 25 Lotostomum opplim'. . .. _________ 19 Lyre formation, paleoecology. _________ 14 stratigraphy .............................. 2 Lyre River section, Twin River formation..._ 6 M McIntosh formation ______________________ 6,15,17 mcmastersi, Cibicides __________________________ 3,26 Mabury Reef sandstone, correlated with Cres- cent formation .................... 4 macrostomo, Allomorphina... malloryi, Cibvcides martinezensts ..- 11,24 mansfieldi, Epom'des .......................... 21 mamfieldi oregonensis, Epém’des ..... 8, 9, 11, 13, 21, 22 marginato udelaidanu, Bolivina. . _____ 8,9, 11,19 Marginulina subbullata. . . . 4, 7, 25 martinezemia, Cibicides ..... .. 4, 8 mortimzensis malloryi, Cibicides ............... 11, 24 mmloensia, Valvulineria ...................... 8,25 Miliolidae ....................... 15 minutum, Elphidium _____ ... 7, 9, 11,12,13, 16 multilineata, Plutofrondiculorm packardi. . 4, 7,16, 17 N Nestncca formation ......................... 6, 10, 17 Nodogemrim adolphina. .. _____ latejuoota ........................ 3, 4, 7, 25 longistaaatu ..................... 4, 7, 25 Nonion ________________ 16 costiferum ................................ 13, 16 inciso ..................................... 16 imusum ................ .. 7,9,11,13,16 pompilioides ............... .... 7,9,12,16,24 N ' 77 L — 16 Nonionidae .................................. 16 Nonionimz inciso.............._.....-.....,... 16 Nummoloculi'ml sp ............................ 7 nuttalli, Bifarina ______________________________ 4,19 Nye mudstone ......................... 13, 19, 22, 23 0 obsea impolata, Uvigerimlla ___________________ 25 ooli'oa, Chilostomello ................. 4,8, 26 orbicularis plonata, Gyroidina ........... 4, 8, 12, 13, 21 oregonensis, Eponidea monsfieldi ..... 8, 9, 11, 13, 21,22 ovata, Bulimino...-....-....-.-... ........ 4, 7, 13, 25 P pacifica, Globobulimino ________________________ 25 Guttulina _________ packardi, Anomalino .......................... 3, 26 Plectofrondiculoria ........................ 17 Plectofrondiculario packardi ________ . 7,11,17 packardi multilimam, Plectofrondicularia.. 4,7,16, 17 packardi pockardi, Plectofrondiculario ........ 7, 11, 17 Paleoecology, Aldwell formation .............. 6,14 Clallam formation ________________________ 13 Crescent formation .................. 13 interpretations based on Foraminifera. _.- 13 Lyre formation .................... 14 Twin River formation .................... 12,14 parua, Epistominella .......................... 5 persimilis, Valvulimrio jocksomnsis.. ._- 8,10 planata, Gyroidma orbiculuris __________ 4,8, 12, 13,21 Planktonic assemblages, Crescent formation.. 3 , Page Plectofrondicularia ............................ 16 gracilis ................................... 17 jenkinsi. packardi... pukardi multzlmeato .................. 4, 7,16,17 packordi packordi ....................... 7, 11,17 oaugham' .................................. 7 Pleurostomella sp . .- 4 Point Arguello profile. . 6 Point of Rocks formation ..................... 18 pompilioz’des, Nom'on ................... 7,9,12,16,24 Poway conglomerate ......................... 18 problema, Guttulino ...... 7, 25 Pseudoclaoulina sp--. ...... . . 7 Pseudoglondulina inflota _________ 4, 5, 7, 25 Pseudopolymorphino liguo .................... 7, 25 pseudoschencki, Sigmomorphino ............... 7, 25 , ’ ac,P*’~.- - 4,25 psilo, Discocyclina. . 3, 26 Pullem'o bulloides 8, 26 salisburyi ................................ 4, 8, 26 pupoides, Bulimina ........................... 25 P111110 sp ...................................... 7 Q quadrulata, Dcntulino ......................... 7,25 Quinqueloculina ........... .- 15 aoodspeedi” ........ 7, 10, 11, 15 imperious" ..-. .- 7, 25 triangularis _______________________________ 7, 25 weaveri ............................... 7, 9, 11,15 sp ........................................ 3 R reqim, Anomalino ............................ 4, 26 Regional correlation, Twin River formation. . 10 Robulus. - _ _ ..... - - 15 colour... 7, 9, 11,15 holcombcmia ............................. 4, 7, 25 pseudovortez .............................. 4, 25 S solieburvi, Pullem‘a .......................... 4,8, 26 San Lorenzo formation.. scalariformis, Lagena heragono ................ 25 schencki, Bulimina ...................... 3, 5, 8, 11, 18 Sigmomorphinu ........................... 5 sculptilia, Bulimim.... 18 aculptilie locim'ata, Bulimi'luz--. ......... 8,9,11, 18 Sierra Blanca limestone, correlated with Crescent formation ............... 4 Sigmailina tennis ............................. 7, 25 Sigmomorphina pseudoachemki. _ 7, 25 schemki .................... 5 Silicosigmoilino califomico .................... 4, 7, 25 Si,‘ ‘ iu frizzelli.. 8, 25 Skookumchuk formation ..................... 15 Soleduck formation, stratigraphy. ._._ 1 structure ........ ...- 2 Sphaerm'dino..- ...- 23 variobilis ................................ 9, 11, 23 Spiroloculina temnus ......................... 7, 25 Spiroplectamz'na sp ....... ...- 7 stavensis, Discorbis alveata.. ...... 3, 25 Stratigraphy ................ 1 Structure ............ 2 subbullata, Marginulina ...................... 4, 7, 25 subfusiformis, Buliminella- .. 7, 9, 11,17 subglobosa, Cossidulina-.. ...... 8 substriata, Logena.... .-.. 7, 25 aulcato, Logeno .............................. 3, 7, 25 Synonymy ................................... 15 T Tejon formation ........... Temblor formation ........................... 20, 23 uninoemis. Baggina .......................... 8,26 tennis, Sigmailina .......... .._- 7,25 tezanus, Robulus ......... .... 7,25 Spiroloculina. . ........ 7, 25 Toledo formation ............ 6, 10, 12, 17, 19, 22 triangularis, Quinqueloculina ...... 7,25 Triloculi'na ailboei .............. -_._ 7, 25 sp ..................... .... 13 Tritazilina. _... _-__ 15 colei ................................... 4, 7, 15 sp ........................................ 3 Tumey formation .................. 12, 17, 20 a. , ’is, V ' 7' ia._______ _- 4,8, 25 Twin River formation, Foraminifera _________ 6,15, 17, 18,19, 20, 21, 22, 23, 24 paleoecology ............. 14 stratigraphy ....... 2 Tyee formation _______________________________ 17, 24 U umbonatua, Epom'dee ________________________ 4,8, 26 Umpqua formation .................. 17, 18, 19, 22, 24 LIN DEX Page Uviaerina ..................................... 20 churchi .................................. 4, 8, 20 cocoaemis ............................ 8, 11, 12, 20 gallowaui _____________ 8, 9, 20 aarzamis. ________ 4, 8, 12, 20, 21 yazooenaia. . . _ _ 5, 20 Um’gerinella obsea impolata ____________________ 25 V V ,' m, __________ _ 4,5,25 Vaginulinopsis vacavillensia .................. 4, 5, 25 Valvulineria cooperemis ....... . 3, 25 depresaa._ ...... . __ 13, 25 indiscriminate. ...... _ 3, 25 jacksonemia ............................... 25 jacksonensis persimilic _____________________ 8,10 menloensis ............ tumeyensia .......... willapuemw. Sp ________________________________________ Valvuiinidae _________________________________ l5 Vaqueros formation .......................... 20, 23 0 G33 Page mriabilis, Sphaeraidimz .................... 8, 9, 11,23 Vaughan, T. W., quoted.-. 3 vauyhani, Plectofrofldiculariar _____________ 7 venezuelanua, Cibz’cides..-_ ........ 4, 8, 26 Verdun formation ____________________________ 22 Virgulz‘mz Sp .................................. 8 Volcanism .................................... 3 Vulnulina curta _______________________________ 7, 25 sp. B ..................................... 7 W Wagonwheei formation ____________________ 12, 20, 22 washbumi, Ceratobulz'mina... ......... 8,26 washingtonensis, Karreriella _________ 7,25 weaveri, Quinqueloculina .................. 7, 9, 11,15 welchi, Robulus ........................... 4, 7, 10, 15 w‘" r ', V 7 7' ia. .._. 8,26 Y Yamhill formation ____________________________ 6, 17 Yaquina formation ___________________________ 19, 22 yazoaensis, U0igerina. ________ . 5,20 yeguaemis, Epanides" __________ 4,8, 26 Globz'germa ______________________ 4, 6, 8, 11, 23, 24 FIGURE 1. 10. 11. 12. 13. 14. 15. 16. 17. PLATE 5 [All figures X 60] Quinqueloculina goodspeedi Hanna and Hanna (p. G15). USNM 626982. USGS f11874, Twin Riyer formation. a, Side View; b, opposite side view; c, apertural View. . Trituzilina colei Cushman and Siegfus (p. G15). USNM 626981. USGS f11884, Twin River formation. . Quinqueloculz’na weaveri Rau (p. G15). USNM 626983. USGS f11793, Twin River formation. a, Side View; b, opposite side View; 0, apertural view. . Robulus cf. R. calcar (Linné) (p. G15). USNM 626984. USGS f11754, Twin River formation. a, Side View; b, periph- eral View. Nonion costiferum (Cushman) (p. G16). USNM 626986. USGS f11891, Clallam formation. a, Side View; b, periph- eral view. . Robulus welchi Church (p. G15). USNM 626985. USGS f11726, Aldwell formation. a, Side View; b, peripheral View. . Nonion' cf. N. pompilz‘oides (Fichtel and Moll) (p. G16). USNM 626988. USGS f11749, Twin River formation. a, Side View; b, peripheral View. . Elphidium cf. E. minutum (Reuss) (p. G16). USNM 626989. USGS f11891, Clallam formation. a, Side view; b, peripheral View. . Nom'on incisum (Cushman) (p. G16). USNM 626987. USGS f11731, Twin River formation. a, Side View; b, peripheral View. Bulimina schencki Beck (p. G18). USNM 626997. USGS f11875, Twin River formation. Bulimina corrugata Cushman and Siegfus (p. G17). USNM 626993. USGS f11886, Twin River formation. a, Side View; b, apertural View. Buliminella subfusiformis Cushman (p. G17). USNM 626992. USGS f11867, Twin River formation. Plectofrondiculafla packardi packardi Cushman and Schenck (p. G17). USNM 626991. USGS f11876, Twin River formation. Bulimina of. B. alsatica Cushman and Parker (p. G18). USNM 626996. USGS £11815, Twin River formation. a, Side View; b, apertural View. Plectofrondicularz'a packardz’ multilineata Cushman and Simonson (p. G16). USNM 626990. USGS f11736, Twin River formation. Bulimina alsatica Cushman and Parker (p. G18). . USNM 626995. USGS f11749, Twin River formation. a, Side view; b, apertural view. Bulimina lirata Cushman and Parker (p. G18). USNM 626994. USGS f11873, Twin River formation. a, Side View; b, apertural View. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-G PLATE 5 14a FORAMINIFERA FROM THE NORTHERN OLYMPIC PENINSULA, WASHINGTON FIGURE 1. 10. 11. 12. 13. 14. PLATE 6 [All figures X 60] Bulimina sculptilis laciniata Cushman and Parker (p. G18). USNM 626998. USGS f11865, Twin River formation. a, Side View; b, apertural View. . Entosolem'a sp. (p. G19). USNM 626999. USGS f11751, Twin River formation. a, Side View; b, apertural View. . Bifarina nuttalli Cushman and Siegfus (p. G19). USNM 627002. USGS f11728, Aldwell formation. . Bolivina advena Cushman (p. G19). USNM 627000. USGS f11749, Twin River formation. Uvz'gemi'na cocoaensis Cushman (p. G20). USNM 627004. USGS f11862, Twin River formation. a, Side View; b, aper- tura view. . Uviyen'na garzaensz’s Cushman and Siegfus (p. G20). USNM 627006. USGS f11748, Twin River formation. a, Side View; b, apertural View. . Uvigerina gallowayi Cushman (p. G20). USNM 627005. USGS f11748, Twin River formation. a, Side View;b, aper- tural View. . Bolivina marginata adelaidana Cushman and Kleinpell (p. G19). USNM 627001. USGS f11869, Twin River formation. . Uvigerina churchi Cushman and Siegfus (p. G20). USNM 627003. USGS f11728, Aldwell formation. Gyroidina orbicularis planata Cushman (p. G21). USNM 627008. USGS f 11749, Twin River formation. a, ventral view; b, dorsal view; c, peripheral View. Angulogerina hannai Beck (p. G21). USNM 627007. USGS f11886, Twin River formation. Epom‘des mansfieldi oregonensis Cushman, Stewart and Stewart (p. G21). USNM 627009. USGS f11791, Twin River formation. a, ventral View; b, dorsal view; c, peripheral View. Canon's joaqm’nensis Smith (p. G22). USNM 627010. USGS f11862, Twin River formation. a, ventral View; b, dorsal view; 0, peripheral view. Asterigerina crassiformis Cushman and Siegfus (p. G22). USNM 627011. USGS f11726, Aldwell formation. a, ventral view; b, dorsal view; 0, peripheral view. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 -G PLATE 6 10a 12a FORAMINIFERA FROM THE NORTHERN OLYMPIC PENINSULA, WASHINGTON FIGURE 1. 10. 11. 12, 13. PLATE 7 [All figures X60 except l2 and 13, X20] Alabamina kernensis Smith (p. G22). USNM 627013. USGS £11862, Twin River formation. a, ventral view; b, dorsal view; c, peripheral view. . Cassidulinoides sp. (p. G23). USNM 627016. USGS £11869, Twin River formation. . Cassidulina crassipunctata Cushman and Hobson (p. G23). USNM 627014. USGS f11796, Twin River formation. a, Side View; b, peripheral view. . Cassidulina globosa Hantken (p. G23). USNM 627015. USGS f11843, Twin River formation. a, Side view; b, apertural view. . Globegerina of. G'. yeguaensis Weinzierl and Applin (p. G23). USNM 627018. USGS f11729, Aldwell formation. . Amphistegina californica Cushman and M. A. Hanna (p.G22 ). USNM 627012. USGS f11720, Crescent formation. . Sphaeroidina variabilis Reuss (p. G23). USNM 627017. USGS f11815, Twin River formation. a, Side view; b, apertural view. . Anomalina califomiensis Cushman and Hobson (p. G24). USNM 627019. USGS f11876, Twin River formation. a, Side view; b, peripheral view. . Cibicides lobatus (d’Orbigny) (p. G24). USNM 627021. USGS f11882, Twin River formation. a, ventral view; b, dorsal View; 0, peripheral view. Cibicides celebrus Bandy (p. G24). USNM 627020. USGS f11874, Twin River formation. a, ventral view; b, dorsal view; c, peripheral view. Cibz'cides martinezensis malloryi Smith (p. G24). USNM 627022. USGS f11799, Twin River formation. a, ventral View, b, dorsal View; c, peripheral view. Thin section of reddish argillaceous limestone from the Crescent formation showing globorotalids and globigerinids. USNM 627023. USGS f11714. GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 4G PLATE 7 FORAMINIFERA FROM THE NORTHERN OLYMPIC PENINSULA, WASHINGTON Jammd'ham A UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY ~ U S G S Species Age Stage Formation Lzzztligzer collec'cion _ I I ‘ locality 1 2 3 4 6 7 8 9 101112 1314 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6'1- 61.2 63 64 65 66 67 68 69 5...: "3' ' «v.— . E'EEEE 8':in \ \ \ \ \I\ I). I \II I \ I I r? \I__\~ gO-—a: fli8|5 \ \ \ \ \ X \ \ X \ \ \ \ \ \ ’ \ \ \ - fig- mm \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ I I \ \ I. \_. V man \ I \ X \ . :I:::: I I I I I ” § \ I “I Inga? \ ’I- \i’ \I \ \ \ I I I I: \I ~ 2:23: \ ; . \ 1 \ ‘- .\ I. 5°°°L~-~ mszu \ \ \ X ' X \ X X \ 7 \ \ \.' .. X '\' \ ' L mszs \ \ x \ \ \ \ x \ x x , \ 8 - . , .. E , a.) _ _ . ' . E f|l826 \ \ \ \ \ \ X \ \ \ \ \ X " \ \ m327 \ \ 7 \ \ \ \ \ \ \ g '1 I; msza \ ‘ 3 \ a; I §§ mszs \ \ \ \ \ v '\ \ \ \ ‘ ' :— L. g; a. ”T: :2 E msao , ? \ \ \ ? \ X g; g meal I \ \ \ \ \ \ \ \ ,, g 33 I I . LLJ § :. o ”Ml—I" ''''' maaz \ \ \ \ \ \ \ \ \ msaa \ \ \ \ \ 7 7 \ I x mszu I 7 I I \ mass I \ X \ \ I 7 7 \ mass \ 7 7 \ \ \ I I \ X 7 \ \ \ I I ' I I I “1337 I I ' \ \ \ \ I '1 ' 7 \ \ \ ‘I \ \ ' I I I I mess I 7 7 X \ I \ 7 \ \ I ‘ I I I ._ I I' . - 8 I . '5 fll839 I ' \ I ? \ X 'I \ \ E mauo I I . \ X I 7 X I \ x \ X 7 x \ I I ' I ‘I I I I I . I ' I I l maul I I I I I IX XI X I\ I I I \ \ \ \ \ I I ‘ I : I I I ‘ I I I I msuz I I\I I I\ \ I \ I I I I I \ ' \ \ I\ \ maua I I I I ‘ \ \ I I V ' I \l I I\ \ \ X 3000’— menu I I I \ \ I ' I I I I \ I \ \ \ A I I ‘ I . I I \ \ g; “ISIS I I I \ I ‘ I I 7 X \\ \ \ 2 5 main I I \ \ 7 \ \ I I \ 7 \ X \ \ \ \ . a mans I I I \ 7 7 I j I I \ \ \ I 7 \ "7” CE 0‘ '2 ' ' ' ' ' “’0- E g ' I I I ' I I 'EIE E E f|l8|49 \ I I I \ I I I \ I \ “3.3 maso I I I ? I I I I I \ I I I 7 \ “v I I g I I I I I «'5 I I ' ' I I x I I I I ' 0 I I I ' I I g fll85l j I ? 1 \ \ \ \I I \I‘ I I \ \ X \ \ ‘5 masz 7 7 \ 7 \ I \I I I \ I x \ \ X 3.” mess I 7 \ \ I I I I I I \ \ x \ x \ mssu \ I \ \ 7 1 \ X \ I I I ‘ I I I \ I x \ \ \ I I I I I- I j I I I 1 I. . I I IIziIII‘I I II .= 1.: ‘ I I I I I I I 1 ' “ 2000—5. I I I I I I l ." ‘-‘_ " I I I I I I I I I * I I I I I I I I I I I I I I I I I . I ' I I ‘ I I I I I I I I : I I I I I I I I I I I _____ 7,_-_- . I I I I I I I I ‘I I I I I I I I L I i a) I - I .0 I "u E I I I I I I E E I I I I 8 I I I I I I I I I I I I I I I ’ I‘ .. I I ' I I 1 loooL" I I I I I I I I , I ‘ I I I I I I I I 1.: I ' I I Cg ‘ I ‘g— /fl|855 \ \ \ 7 \ \ ’ 7 \ \ \ 1 \ \ N '- I ';f ; fl|856 \ 7 \ \ \ I I 7 \I I x 'I 7 \ 7 \ \ 7 \ 7 mo 3 I ‘ I z: 3 I ' I I £ I I I I V _'——fI|857 ? I . I I \ 7 \ I I I I I mass \ 7 \ 7 3 I \ \ ‘l \ \ \ 7 I f||859 \ 7 7 \ 7 FORAMINIF ERA FROM A PART OF THE TWIN RIVER FORMATION ON THE LYRE RIVER IN THE NORTHERN OLYIWPIC PENINSULA, WASHINGTON PROFESSIONAL PAPER 374—0 PLATE 2 KEY TO COLUMN HEA'D‘IN (Arranged _taxonom1 cal 1y) . Involutina sp. ‘ A . Spiroplectanina? up. VGaudryina cf. G. olazanensls Cushman. .Psuedoclavulina s .Karre‘niello cf. K.’ caritartct Be.ck Karre'riqlla washingtonéasis Ran. . ,Quinqueloculina taperid-lis Hannah“ Quinquelocu'lym waltz/pr: Ra'u. Quinéuelaculina sp. ; Signoiltna tennis {C'pj ek) , ‘ . 7 v: Thloqulrna cf. T. 31.1560“. B‘eek :‘Pyrs'd .51? I' . .‘Robulus cf. . Ical' dr (Linhe') > ..Robulus holconbens’is Raul; ‘ . Dentalinia dusenburyr" B'e'ék. . ' , ‘De'ntalina cf. D q'uadrjulotaé Cushm‘fin and Lininmg .'- Dentalina sp. (1%qu Rau‘, 19483- , . v_ v . '. Dentalina sp. D [of Rau,‘1948‘]. “ " I. I ' ..Dentalina‘ spp. I1 'Nodosaria cf. N. gnouala Reugp- ' “1. -Nodosa.ria longistagata d’Oi‘b . 22 tPsgudoglandulmnd of P. infld' 3-.Pseudoglandulina aff. P. infl - Lagena conscripta Cushmim. and Bark da'fle’ ' - Lagena hexagorla scalarifornis ‘(WllIfamson) - Lagena substriat’a. Willi.a‘mson- y -, Lage'na sulaatu (Walker and Jacob). Guttulina irregulari's' (d’ Otbigny). _ ‘. ., .' thtulin'a cf. 6 pacified (Cushman and - Guttulina problem: d Orbigny. .' - Nonion incisun (Cushman)- " ‘Nonion cf: N. poupilioides (Fichtel an'd M611) _‘ ,I Plectafrbndicular'ia packa'rdi nultill'ncuta Cush'man ahd- Simonson. I Pléciofrondicularia pacqudi packardi Cu‘shman and Schenck. Plectafrondvzc‘qlaria vuugbani Cushman. . I W'Nodogenerinu of N. adolphiniu (d' Orbigny'). ' uli'nina of iica Cus'hi'nan and Parker.’ - , u’l inindvc‘ alsatica Cushman and Parker .. ~ Bulinina c . . pupoidcs d'Orbigny. 'BuliI—ina schgnchi'; Beck. ’ __ ' Bulinin culptil's laciniata Cushman and Parker. '42, (Globabu Maya, ‘ca Cushman. Entosolemia's 1" ' Uvig‘erina coo‘éaeusi‘s Cushman. -I___Uvigerina gartqensis ICushman and Siegfus. . Siphonodosaria friztelli Rau. ' .,.4n5ulogerina hannai Beck. ~ . ., '=E:’lfi1psonodosuria cf. E. cocoaensis (Cushman). w, 3:,VuL-Ivruliner'ia tulleyensis Cushmnn and Simonson. ' . Valvulinerm willapaensis Rau. . ' ' , '-' Gyroidé condoni (Cushman and Schenck) ' ~ JGyPOiqiin ‘ i“. ...- AA... V. ,. l 2 , 3‘ 4 s. 6. ,7 I, 8‘ 9. orbicularis planata Cushman. , - Epistonina eocenicq (Cushman and Hanna). . Cancris 'jaaquinensis Smith. - Alabon‘iria kernensfis Smith. - Cassidulina globosa Hantken' Cassidulina s‘ubglobasa Brad' , Cassiziulinoides. sp. «4- . .Allauorphina ndcrostima Kari-er. ' ‘-..Chilost0iiie-lla -;c£.. C.‘ holinal Schwager. "2‘--»Pullenia sundae-s;- (d' '0rbigny).- . Sphacrowldi 'vaflfibllls Housm. « . Globiger'thd s'p. - . Globigerina’ sp. C.- - . tAno-mlina caltfornien’su Cushman a'n_d Hobson. . p. .339: z; fiongldmekafie? ' Sandstone Silty sandstone Sandy siltstone Concretionary siltstone Mudstone X Abundant to common \ Few to rare ? Questionably identified NOTE: Collection localities shown on plate 1 678-833 0 - 64 (In pocket) No. 2 . PROFESSIONAL PAPER 574—G E8 DEPARTMENT OF THE INTERIOR ‘ PLATE 1 GEOLOGICAL 8U RVEY UNITED STAT EXPLANATION I Clallam formation 48°15’ 7-333.“ § ‘.~.-‘.-'. r Olynwpic Peninsula 1 / 0 O ‘b Miocene /"A‘\\ Twin River formatiom V k\ Lyre formation Eocene and Oligocene f1 1743—45 Y TERTIARY S 7134 1 T ||||fl||| Undifferentiated rocks 0 p 'IAIdweII formation .,, A JU AN DE FUCA Q 2 :9 m {I} Z ‘ CD a . ‘ 3 c): I j ‘4 . . 1 Z Eocene Crescent formation g A ' J f11788—90 Crescent. “1718 . ' ' f11791 ”1793 “1796 f11802—10 Tcr Bay r11719 ,,», . 1‘1'1' 11.". .".-'.-l".".r3‘1'i's. .. ..... '. f11797—f11801 NR , 5.1.: ............................... f11792'.‘ '. .. .. _..f1-1864.:.j.f11717 .. ‘ .fi‘ 2 ...... . . . . . . . . . . . . . . . .' INDEX MAP My“? ., '; Soledqckoforma'tionrflo ‘5‘ Reagan',‘(1909)1 ~';1 -‘-'f”.~'.-'.~C”.-TI-I':C-IC‘ ~~~~~~~ x-. ....................................... ...‘xi- {- w ........................... (11.794. ............................. . 'f11754—60. ”1787 .................... .......................... \ 5.; “1812 TC? f 1720 Freshwater Bay / 1 // Observatory Point AND TERTIARY Ed-‘Z HOOk o “ '-:-:-:-:-:-:~:-.- ...... (woo -. _. \ ........................ “1867 f11869—71 Upper Cretaceous(?) ' (ind Paleocend?) CRETACEéIIsm Contact -1'?“:f~:--:3'3'1‘3:3:?§3:3:3‘31?13131323135555? -:3:3:r~ -. .. -:-:' ~:- :‘_-.- :. ~, : '1‘; """" . PORT ANGELES .1 , _ " :_ , MWWW”‘09???d’"" Q“ ' ' -.-§ ....... .-.~.~-.-Tt -.. . .. . -- . ....- ..~ ~. . - . ' .- -w..;; <§~ 3:5. .......................... ' 1.1.1.} ......... :,:_ . _ , In, . — *_ ”WWW" """"""""""" ' """""""""""""""""" 5‘3 "3-513 -... .0 ~~ .~:-:» " ............................ ;-:.§.;: ‘ " ‘ 22:2: ; ; syncune ‘ (I Approximately éooqfted .e._. *1 -.~1-.;Ij-1ijlji;3':r1182913'3‘3132'-~~-.Z 5.373735'7-“11‘1539-1- ' ‘ ‘ . .r11881. . . -. ----.f11§§p‘ “1372‘... ......... Kw... a. . PITT???:':"'."‘.'.4'.":‘:':' ... f 1.187.6'1‘ 1.x f117é6 .‘I 1;? IiIAw'W‘vT 3-1; :31; Alfizgsg§wgglle0tionqlocafity 1: A 1 V :I’ I”; ‘ ‘ ‘V ‘ M "19): 9’ I 7- ,. .-... . A ______ \ f11724 .9: . f11716 . ‘ ‘ % 4"}? ' i r: ,e ' Crescent ‘ 5331.133? I333} ‘ mass I Soleduck “mug u'yifn v ‘ '1 AF‘I‘RQXIaflATE MEAN I .i“ > f oeummfion 1962 No geology shown south of Soleduck River ' 48°oo' ' ‘ . , , 3" 123°15I . ‘ . Geology generaIiZ‘ed’ from Gower (1960) ’ - and Brown and others (1960) . _ . , 124' 15 . I 1 .« - ,' ,lvp ' A". Base from US Dept. Angcu turer I -, .. .‘_ .. é Forest Service, map ofvthe Olympic ? , National Forest, Washmgton: 1948 48°00' ,3. GENERALIZED GEOLOGIC N SHOWING U.S. GEOLOGICAL SURVEY COLLECTION LOCALITIES IN THE NORTHERN OLYMPIC PENINSULA, WASHINGTON ' i 2 Wfsébfi’z}Unpacket)No.1 2 I 0 2 4 6 MILES I I I J I I J UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Age Stage of Kleinpell (1938) Formation Deep Creek section U S G S collection locality UI OLIGOCENE Upper Zemorrian Lower Zemrrian Upper member member TWIN RIVER Middle Lowe r membe r 2000’4' Iooo’.: '- soooL.” f||773 f||77ll f|l775 f|l776 PROFESSIONAL PAPER 374—G PLATE 5 KEY TO COLUMN HEADING (Arranged taxonomically) Involutina sp. Gaudryina cf. G. alazanensis Cushman. Pseudoclavulina sp. Karreriella cf. K. contorta Beck. Karreriella washingtonensis Rau. Quinqueloculina imperialis Hanna and Hanna. Quinqueloculina weaveri Rau. Quinqueloculina sp. Spiroloculina texanus Cushman and Ellisor. . Sigmoilina tennis (Czjzek). . Nummolaculina sp. . Triloculina of. T. gilboei Beck. . Pyrgo sp. . Robulus cf. H. calcar (Linné). . Robulus spp. NH—u—n—H—H—u—u-u—n—u—I Oxomqoxmpwmwoxomdoxmpwmw . Dentalina . Dentalina . Dentalina . Dentalina . Nodosaria . Nodosaria dusenburyi Beck. cf. D. quadrulata Cushman and Laiming. sp. C [of Ban, 194$. spp. cf. N. anomala Heuss. longistigata d’Orbigny. NNN wNH /'x /'/z,/ /’// 1/ // /’,z ,/ /’// /’// /’,/ / FORAMINIF ERA FROM A PART OF THE TWIN RIVER FORMATION ON DEEP CREEK IN THE NORTHERN OLYMPIC PENINSULA, WASHINGTON . Pseudoglandulina cf. P. inflate (Bornemann). . Pseudoglandulina aff. P. inflata (Bornemann). - Lagena sulcata (Walker and Jacob). . Guttulina frankei Cushman and Ozawa. . Guttulina cf. G. pacified (Cushman and Ozawa). . Guttulina problema d'Orbigny. . Pseudopolymorphina cf. P. ligua (Roemer). . Sigmomorphina 3p. . Nonion incisum (Cushman). . Nonion cf. N. pompilioides (Fichtel and Moll). . Plectofrondicularia packardi multilineata Cushman and Simonson. . Plectofrondicularia vaughani Cushman. . Buliminella subfusiformis Cushman. . Bulimina alsatica Cushman and Parker. . Bulimina cf. B. alsatica Cushman and Parker - Bulimina cf. B. ovata d’Orbigny. . Bulimina pupoides d’Orbigny. . Globobulimina pacified Cushman. . Entosolenia sp. . Bolivina cf. B. jacksonensis Cushman and Applin. . Balivina marginata adelaidana Cushman and Kleinpell. . Uvigerina gallowayi Cushman. . Uuigerina garzaensis Cushman and Siegfus. . Ellipsonodasaria cf. E. cacoaensis (Cushman). Valvulineria willapaensis Rau. . Gyroidina condoni (Cushman and Schenck). . Gyroidina orbicularis planata Cushman. . Eponides mansfieldi oregonensis Cushman and R. E. and K. C. Stewart. . Eponides umbonatus (Reuss). . Epistonina eocenica (Cushman and Hanna). . Cassidulina cassipunctata Cushman and Hobson. . Cassidulina subglabosa Brady. . Cassidulinaides sp. . Chilostomella cf. C. oolina Schwager. . Pullenia bulloides (d'Orbigny). . Sphaeroidina variabilis Reuss. . Globigerina sp. A. . Globigerina sp. B. . Globigerina sp. C. . Anomalina califarniensis Cushman and Hobson. . Cibicides elmaensis Rau. EXPLANATION Conglomerate Sandstone Silty sandstone Sandy siltstone Concreflbnary siltstone M m M I Mudstone X. Abundant to cornmon \ Few to rare 7 'Questionably identified .v . ,,. . » NOTE: Collection-localities shown on plate 1 678-833 0 — 64 (In pocket) No. 3 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Stage Sectio‘lbetgeen U S G S Species of - mout s o 11 5 Age Kleinpell F°“"a“°“ East Twin River C‘l’ocj‘fi:3“. 21 22 23 (1938) and Murdock Creek 1 2 .(top fau'lted) :::::"-- ' 3°"’°"::...::: . “frnas \ \ -._ ' ni797~ \ “179a msoo X \ .~ f|180| X \ ' zooo'.‘ 5 _ g L ‘2‘ ’- g 8 DJ 3 .. g Q g t! E H _. 8 N 2 L ' msoz \ x \ \ 3 L ; 3 maou \ \ \ \ O 8 "' g macs \ X X \ a \ :2 msos \ msos \ \ ‘ male. IoooL mso7 , 6 I ‘ I; msos \ macs _ \ \ \ fl|8l| \ \ (base faulted) 0’ wrvv M W [ordia HAP‘P‘H‘hdhdhud O\o «SQ-1" RI Ede name Supai was used in earlier reports but was not accepted by Baker and ee 9. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY LOWER AND UPPER LIMITS OF THE PERMIAN SYSTEM In the Zuni uplift the lower limit of the Permian system has been placed at the base of the Abo formation (see table 1A) although it is possible that the lower- most strata in this formation are locally Pennsylvanian in age. At some points in the Zuni uplift, a thin se— quence of argillaceous limestone, shale, and sandstone beds underlies the Abo formation. These strata, al- though sparingly fossiliferous, have failed to yield ma- terial that will permit precise dating. Tentatively, they are assigned to the Pennsylvanian system. The upper limit of the Permian system in the Zuni uplift has been a subject of some discussion. Darton (1928, p. 140—142) briefly described the sequence of rocks in the Zuni uplift and referred the Permian strata to the Manzano group, which consists of the Abo formation at the base and the Chupadera formation of former usage at the top. Above this group are strata that Darton (1928, p. 143) correlated with the Moen- kopi formation. These are overlain by a conglomeratic sandstone that was identified as the Shinarump con- glomerate, and this in turn is overlain by red beds as- signed to the Chinle formation. A year later, Baker and Reeside (1929, p. 1433) re— viewed the sequence of rocks in the Zuni uplift and classified the strata that Darton had correlated with the Moenkopi formation as the upper part of the Chu- padera formation of former usage. This; assignment of the Moenkopi of Darton in the Zuni uplift to the Chupadera formation was based on the belief that in- asmuch as the Moenkopi formation does not extend east of the vicinity of St. Johns, Ariz., it is unlikely that it is present in the Zuni area. In 1941 the senior author reviewed the Zuni sequence and collected fossil plants from the unit called Moen— kopi by Darton and referred to the Chupadera by Baker and Reeside. The species noted are identical with fos- sils collected from the Chinle formation at localities near Holbrook, Ariz., and described by Daugherty (1941) . On the basis of this paleontologic data as well as on stratigraphic grounds that are outside the scope of this report, the rocks in question are here assigned to the Upper Triassic and are placed in the Chinle for— mation. The conglomerate identified as the Shinarump by Darton (1928, p. 143—144) and by Baker and Ree- side (1929, p. 1433) is also assigned to the Chinle for- mation. A conglomeratic sandstone that is locally present but which was not earlier reported lies at the base of the Chinle formation and is now correlated with the Shinarump member of the Chinle in Arizona. The upper limit of the Permian in the Zuni uplift is here placed at the top of the San Andres limestone. \ H-3 This accords with sequences farther east in New Mexico as well as those along the Mogollon Rim in Arizona (fig. 1) Where the Kaibab limestone is the youngest formation of Permian age that is preserved (Darton, 1925, p. 96, 203). There is general agreement regarding the upper and lower limits of Permian rocks in the Defiance uplift, Arizona and New Mexico. (See table 13.) The lower part of the Supai formation is classified as Permian on stratigraphic grounds that are supported by meager paleontologic data. The upper limit of the Permian in this area is at the top of the De Chelly sandstone, as defined in this report, and below the Shinarump mem— ber of the Chinle formation. This accords with the opinion of Baker and Reeside (1929, p. 1427—1428). Strata referred to the Moenkopi rby Darton (1925, p. 110) are now believed to occupy a part of the De Chelly sandstone interval, and therefore are Permian in age. The writers believe that in the Monument Valley up- warp, Utah and Arizona, Baker’s and Reeside’s pro- visional lower limit of the Permian at the base of the Rico formation should be modified to the extent of classifying the Rico as Pennsylvanian and Permian( 9). (See table 10.) It must be stressed, however, that such an age assignation should be tentative inasmuch as the problem of the age range of the Rico formation and its lithologic correlatives does not appear to have been finally resolved in all areas. The upper limit of the Permian according to Baker and Reeside (1929, p. 1422) and Baker (1936, p. 38-40) is at the top of the unit classified by them as the Hoskin- nini tongue of the Cutler formation. They recognized an apparent disconformity between the Hoskinnini tongue and the MoenkOpi formation. A result of the present investigation has been the identification of a disconformity at the base of the Hoskinnini. It is diffi- cult to evaluate these two interruptions in sedimenta- tion in terms of either a hiatus or a systemic boundary. The lithology of the Hoskinnini is generally similar to that of the Moenkopi, but the bedding structures are more similar, perhaps, to those in the Cutler formation. The authors believe that the Hoskinnini should be clas- sified as a member of the Moenkopi formation but that the age assignment of the member should be questioned. REGIONAL CORRELATIONS The locations of the Permian sections that were ex- amined are indicated on plate 1. The correlations are indicated by the line of sections on plate 2. co'm‘onwoon CREEK, NEW MEXICO, TO CANYON DEL MUERTO, ARIZONA The sequence of Permian strata in the northern part of the Zuni Mountains, N. Mex., is illustrated on plate H—4 2. These sections were measured at Cottonwood Creek (sec. 18) and in the vicinity of the settlement of Mo- Gaffey (sec. 17). At both points clastic strata that are assigned to the Abo formation at the base of the Per- mian sequence rest on metamorphic and plutonic rocks believed to be of Precambrian age. At Cottonwood Creek the contact is irregular, and the beds above it are coarse conglomerate. At McGafl'ey, similar con- ditions probably exist, although the strata at the contact are not well exposed. The Abo at the two localities ranges in thickness from 305 feet to approximately 790 feet but is similar in lithology. It consists of a monot- onous sequence of alternating brown or brownish- orange fine-grained sandstone and arkose, several beds of limestone pellet conglomerate in one zone at Cotton— wood Creek, and major intervals of siltstone. The basal contacts of sandstone on siltstone are commonly irregular, and bedding planes of the strata are marked by ripples, pits, mounds, and vague impressions of stems and leaves of terrestrial plants. The latter are charac- teristic of the Supai flora. The basal strata of the Yeso formation rest evenly on the Abo formation in the Zuni Mountains and consist of a few feet of thinly bedded brownish—red siltstone that are overlain by 80 feet or more of intricately cross- laminated and lenticularly bedded sandstone. These strata, the few feet of siltstone and the overlying mas- sive cross-laminated sandstone, constitute the basal member of the Yeso formation and are termed the Me- seta Blanca sandstone member (Wood and Northrop, 1946). This member, coarse to medium grained at Cottonwood Creek (sec. 18) and fine grained to silty at McGafl'ey (sec. 17), is generally present in northern New Mexico. Analyses of directions of dip of foreset laminae indicate a preferred orientation toward the east or southeast, which is shown on figure 1. In the north- ern part of the Zuni Mountains the Meseta Blanca is overlain by 225 to 300 feet of evenly bedded fine-grained sandstone and siltstone of similar composition, inter~ bedded with two or three thin layers of dense gray dolo- mitic limestone. At Cottonwood Creek the limestone beds have yielded poorly preserved specimens of Dio- tyoclostus sp. afl'. D. ivesi. These evenly bedded brownish-orange elastic strata and the interbedded dolomitic limestone layers constitute the San Ysidro member of the Yeso formation (Wood and Northrop, 1946), which rests conformably and apparently grada- tionally on the underlying Meseta Blanca member. Conformably overlying the San Ysidro member of the Yeso formation is a cliff-forming light-gray tan- gentially cross—laminated lenticularly bedded quartz- ose sandstone that has been correlated with the Glorieta sandstone, which is typically developed in north-central STRATIGRAPHY, PERMIAN ROCKS, ARIZONA AND ADJACENT AREAS New Mexico at Glorieta Mesa (Read and others, 1945). Earlier reports (Read and others, 1945; Kelley and Wood, 1946; Wood and Northrop, 1946; Wilpolt and others, 1946; Wilpolt and Wanek, 1951) have classified the Glorieta sandstone as a member of the San Andres limestone in northern New Mexico. Although the Glorieta grades southward into beds of San Andres lithology the distinction between the two is so great that the authors consider the Glorieta sandstone a formation. The Glorieta sandstone is 280 feet thick at Cotton- wood Creek and is 300 feet thick at McGafl'ey. The foreset laminae generally dip to the southwest, as shown on plate 1. The Glorieta is, in turn, conformably over- lain by gray medium- to thick-bedded porphyroblastic, dolomitic limestone beds that constitute the San Andres limestone. Like the Glorieta sandstone, this unit has been treated in the past as an unnamed member of the San Andres limestone (Read and others, 1945; Kelley and Wood, 1946; Wood and Northrop, 1946; Wilpolt and others, 1946; Wilpolt and Wanek, 1951), but is now recognized as formational in rank. These strata are as much as approximately 100 feet in thickness in the northern part of the Zuni Mountains, and are lim- ited above by a very irregular erosional surface that is characterized by solution breccia, steep-walled buried depressions, collapsed blocks, and other features not unlike those observed in modern karst areas. The basal strata of the Upper Triassic rest upon this old and irregular surface with profound disconformity. The sequence of strata at Black Creek (secs. 15 and 16) in the Defiance uplift, Arizona, is dominantly clastic and generally similar to that of the Zuni uplift. The pre-Permian core of the Defiance uplift is not exposed at Black Creek, and the oldest rocks are rather regularly bedded siltstone and sandstone that are chiefly brownish orange and are replete with so-called salt hoppers—sand casts and molds of halite crystals. Two thin beds of porphyroblastic, dolomitic limestone lie in the upper part of this sequence. Over-lying these strata is a cliff—forming tangentially crossbedded gray to brownish-gray quartzose sandstone with foreset laminae inclined to the southwest in most places. The Permian sequence is truncated at this level by coarsely conglomeratic strata that are assigned to the Shinarump member of the Chinle formation of Late Triassic age. The lower dominantly brownish-orange fine—grained elastic strata and interbedded dolomitic limestone of the Black Creek area are correlative with the San Ysidro member of the Yeso formation in the Zuni uplift. For geo ‘aphic reasons, they are assigned, however, to the Sufi; formation (Hager, 1924, p. 167, 423; Darton, 1925,.p. 85, 91, 207). SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY The overlying gray or brownish-gray quartzose sandstone in the Black Creek area is similarly corre- lated with the Glorieta sandstone in the Zuni Moun- tains and is classified as the upper member of the De Chelly sandstone, and the De Chelly is given forma- tion rank. The names Glorieta and De Chelly are both firmly established in the literature, and the change from one to the other takes place in the subsurface. Therefore, no serious conflict arises from the use of the two names. , At Oak Springs (sec. 14), north of the Black Creek sections, the lower part of the Supai formation is over- lain by approximately 95 feet of medium-grained highly crossbedded quartzose sandstone. This is the lower member or tongue of the De Chelly sandstone and is traceable northward throughout much of the up- lift. The dips of foreset laminae in the lower member of the De Chelly are generally southeastward, in con- trast with prevailing southwest dips in the upper member. Overlying the lower member of the De Chelly sand- stone are thickbedded and cross—laminated ledges of sandstone alternating with brownish-orange siltstone. This sequence, which is 235 feet thick, is regarded as an interfingering upper member of the Supai forma- tion. Overlying it is a sandstone ledge that is directly traceable to the Black Creek sections where it is iden- tified as all that remains of the De Chelly sandstone—— the lower member having fingered out. It is thus ap- parent that northward along the Defiance uplift a lower tonguelike member of the De Chelly sandstone appears which fuses with the more persistent upper member farther northward, as will be indicated later. At Hunters Point (sec. 13) the section is generally similar to that at Oak Springs. Geologic structure prevents measurement of the upper member of the De Chelly sandstone, but its presence was noted at the outcrop where it is similar in all respects to the sequence noted at Black Creek (sees. 15 and 16). As at Black Creek the Shinarump member of the Chinle formation rests directly on the irregularly eroded De Chelly sandstone. North of Hunters Point, Permian strata are exposed at Bonito Canyon (sec. 12) in the vicinity of Fort De- fiance. In that area quartzite classified as Precambrian crops out along Quartzite Creek and is overlain by the basal conglomerate of the Supai formation. Above this conglomerate are nearly 400 feet of fine-grained quartzose and feldspathic sandstone beds alternating with beds of siltstone. A limestone pellet conglomerate lens occurs locally in the sequence. The basal contacts of the sandstone on the siltstone beds are irregular, and laterally the strata show striking lenticularity. These H—5 ' strata are believed to be a part of the Supai formation and to be correlative with the lower parts of the se- quences exposed at Hunters Point, Oak Springs, and Black Creek. Above this sequence of irregularly bedded brownish- orange siltstone and sandstone are about 70 feet of evenly bedded brownish-orange siltstone beds contain- ing salt hoppers or halite casts. These rocks are ap- parently correlative with the upper part of the lower member of the Supai at Hunters Point and Black Creek. Beds of massive silty, fine-grained sandstone rest on the Supai formation with gradational contact. These strata are tangentially cross-laminated and grade up- ward into medium-grained quartzose sandstone that is also tangentially crossbedded. This sequence is ap- proximately 270 feet thick and is believed to represent the lower member of the De Chelly sandstone. As in- dicated on plate 1, the inclined laminae generally dip southeast in sharp contrast to the southwest dips of the laminae in the overlying sandstone. Above this massive sandstone is a thin but locally persistent layer of thin—bedded silty sandstone. An irregularly weath- ered cliff-forming sandstone that is tangentially cross laminated in very large lenticular beds overlies the thin silty sandstone. This clifi-forming sandstone is cor- related with the upper member of the De Chelly sand- stone in areas farther south. It is about 280 feet thick and is disconformably overlain by the irregularly channeling Shinarump member of the Chinle forma- tion. The upper 80 feet of this sequence is medium bedded, and some silty layers are present. These strata have been interpreted by some geologists as possibly representing a remnant of the Moenkopi formation of Early Triassic age. There appears to be no field evi- dence that the strata are other than thinner bedded phases of the De Chelly sandstone. At Buell Park (sec. 11) a few miles north of Bonito Canyon (sec. 12), the exposed sequence is similar to that just described. Irregularly bedded strata of the Supai formation are overlain by the De Chelly sandstone which is divided into a lower and an upper member. Northwest of Buell Park, Permian strata are ex- posed at Canyon de Chelly where sections were meas- ured in the walls of Monument Canyon (sec. 10) and Canyon del Muerto (sec. 9). At both places a thin in- terval of irregularly bedded conglomeratic strata that is assigned to the Supai formation is exposed in the floor of the canyons and is overlain by cross-laminated sandstone that was named the De Chelly sandstone by Gregory (1915, p. 102) from exposures in Canyon de Chelly. Both the lower and the upper members of the De Chelly can be recognized clearly at Monument H—6 STRATIGRAPHY, PERMIAN ROCKS, Canyon, and at Canyon del Muerto the identification is but slightly less certain. Contrasting dip directions of the cross laminae tend to confirm the identity of these two members. CANYON DEL MUERTO, ARIZONA, T0 NOKAI CANYON. UTAH The Permian sequence in the Canyon de Chelly area is twofold. At the base of the exposed section in the walls of Canyon del Muerto as shown on plate 2, sec. 9, are irregularly bedded and highly variable elastic rocks of the Supai formation. These are overlain by the double-ledged De Chelly sandstone. The Shinarump member of the Chinle formation of Late Triassic age rests disconformably on this sandstone. ' Northwest of Canyon de Chelly, Permian strata dip 'into the structurally depressed Black Mesa basin and reappear at the surface in the Monument Valley up- warp, approximately 64 miles distant. A partial sec tion of the Permian is exposed at South Comb Ridge (sec. 8) in the southern part of the eastern side of Monument Valley. The oldest exposed strata are a few feet of the Cedar Mesasandstone member of the Cutler formation. Resting on this is an alternating sequence of brownish-orange siltstone and thin sand- stone beds about 590 feet thick that represents a part of the Organ Rock tongue of the Cutler formation. The remaining 110 feet of the Organ Rock interval are transitional strata consisting of an alternation of silt- stone and silty sandstone. This Organ Rock sequence is overlain by a massive cross-laminated sandstone. In South Comb Ridge area the massive sandstone above the Organ Rock tongue is classified as the De Chelly sandstone member of the Cutler formation (Baker, 1936, p. 35—38), and is believed to correlate with the De Chelly sandstone in the Defiance uplift (Baker and Reeside, 1929, p. 1431; Baker, 1936, p. 35—38). Judg- ing from the prevailing southwest dips of the inclined laminae, the correlation is with the upper member of the De Chelly in the Defiance uplift. The De Chelly sandstone member is overlain by brown evenly bedded sandstone and siltstone beds containing scattered large and well—rounded grains. These strata are separated from the De Chelly sandstone member by a disconformity and are correlated with the Moenkopi formation. Northwest of South Comb Ridge the De Chelly sand- stone member thins rapidly, and a differentiation of minor units in the lower part of the Cutler formation is apparent. In Upper Gypsum Creek (sec. 7) the De Chelly sandstone member is about 200 feet thick and overlies 440 feet of brownish-orange siltstone and thin- bedded fine-grained sandstone. This, in turn, rests on a sequence of alternating gray sandstone, brownish- ARIZONA AND ADJACENT AREAS orange siltstone, and gypsiferous sandstone and silt-r stone. Lenses and platelike concretions of dolomitic limestone are present locally. In Upper Gypsum Creek the thickness of this lower unit cannot be measured. It is known, however, to overlie a brownish-red and brownish-orange unit which in turn rests on the marine Rico formation. Baker has applied the term Organ Rock tongue to the dominantly brownish—orange silty unit that under- lies the De Chelly sandstone member, and for the alter- nation of sandstone, siltstone, and gypsiferous strata underlying the Organ Rock tongue he has used the name Cedar Mesa sandstone member of the Cutler for- mation (Baker and Reeside, 1929, p. 1441; Baker, 1936, p. 33—35). The upper part of the Permian sequence is well ex- posed in the buttes and mesas in the vicinity of Monu- ment Pass in the central part of Monument Valley. At Wide Butte (sec. 6), where the sequence was measured, a few feet of brown irregularly bedded gritty sandstone that has been named the Hoskinnini tongue of the Cut- ler formation disconformably overlie the De Chelly sandstone member. The Hoskinnini tongue is, in turn, overlain with apparent disconformity according to Baker (1936, p. 38—40) by the evenly bedded brown elastic rocks of the Moenkopi formation. The Hoskin- nini is now classified as a member of the Moenkopi but its age is Triassic( '9) . The De Chelly sandstone member of the Cutler for- mation forms a vertical cliff in most of the buttes in this area and is 350 feet thick. It is a brownish—orange, tangentially cross-laminated, and medium-grained quartzose sandstone which rests with basal gradation on brownish—orange siltstone and sandstone beds of the Organ Rock tongue of the cutler formation. Inclina- tion of the foreset laminae is generally toward the south. The Organ Rock grades basally into a sequence of al— ternating siltstone and gray or brown tangentially cross-laminated fine-grained sandstone beds of the Cedar Mesa sandstone member of the Cutler formation. The laminae show a preferred inclination to the south- east. A few thin beds of nodular and tabular limestone occur in this sequence which is 360 feet thick. The Cedar Mesa sandstone member, in turn, rests conform- ably and gradationally on the Halgaito tongue of the Cutler formation, which was not measured in detail at Wide Butte. At the southeast point of Cedar Mesa, which lies north of the San Juan River in southern Utah, and in adjacent parts of Douglas Mesa (sec. 5) on the south side bf the San Juan River, a section of the lower part of the Permian sequence was measured which supple- ments that observed at Monument Pass. The Cedar SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Mesa sandstone member of the Cutler formation, which in the vicinity of Monument Pass as well as farther southeast is an alternation of gray sandstone and silt— stone, grades laterally into a more massive facies and at Cedar Mesa is a virtually uninterrupted wall of gray cross-laminated fine-grained sandstone at least 420 feet thick. Inclination of the laminae is dominantly to the east. The Cedar Mesa sandstone member grades bas- ally into 440 feet of brownish-orange siltstone, sand- stone, and limestone beds that are assigned to the Hal- gaito tongue of the Cutler formation and that rest on the marine Rico formation. The Rico, in the great meanders or Goosenecks of the San Juan River, con- sists of about 335 feet of alternating calcareous sand- stone, gray and red shale, and limestone that contain marine fossils that have reported affinities with Per- mian faunas (Baker, 1936). The Rico formation rests conformably on alternating thick beds of limestone and thin beds of shale and sand- stone which are believed to be the equivalent of the Hermosa formation. The Hermosa formation, both at the Goosenecks and to the east, contains marine fossils of Pennsylvanian age. To the southwest of Douglas Mesa (sec. 5), Permian strata are broadly exposed. At Hoskinnini Mesa (sec. 4) near Oljeto Trading Post in the western part of Monument Valley, a section of the upper part of the sequence was measured. At the top of the Cutler formation, as limited by Baker and Reeside (1929, p. 1422), are approximately 60 feet of sandy and gritty elastic beds that constitute the Hoskinnini tongue of the Cutler formation. Ac— cording to Baker and Reeside (1929, p. 1422), these are separated from the overlying Moenkopi formation by a disconformity that marks a very considerable hiatus. The writers have noted a disconformity at the base of the Hoskinnini and accordingly question the classifica- tion of the Hoskinnini in the Permian. These strata are now regarded as the basal member of the Moenkopi formation and on the basis of available data are clas- sified as Triassic( ?). The De Chelly sandstone member, which is 345 feet thick at Wide Butte, thins westward and at Hoskinnini Mesa is 250 feet thick. Inclination of the laminae is nearly due south. The De Chelly is locally discon- formable on the Organ Rock tongue of the Cutler for- mation in this area but elsewhere the contact is gradational. The Organ Rock tongue consists of characterstic red or brownish-orange siltstone and fine—grained sandstone beds that regularly alternate throughout an interval of about 440 feet. These strata overlie the upper beds of the Cedar Mesa member of the Cutler formation, H—7 which are alternating red siltstone and gray cross-lam- inated sandstone that contain calcareous nodules and tabular bodies. The De Chelly sandstone member thins to the north- west at Monitor Butte (sec. 3) and is absent near the San Juan River at Piute Farms. Just south of the vanishing point of this member a section was measured. At the top of the sequence the Hoskinnini member of the Moenkopi is overlain by brown evenly bedded silt- stone of the Moenkopi formation. The Hoskinnini rests sharply and with apparent disconformity either on the De Chelly sandstone member or directly on the Organ Rock tongue of the Cutler formation where the De Chelly is absent. The De Chelly sandstone member rests where present, on the Organ Rock tongue with a sharp contact. Sandstone dikes descend locally from the De Chelly and fill crevices in the Organ Rock tongue. The Organ Rock tongue at Monitor Butte (sec. 3) is similar to the section exposed at Hoskinnini Mesa and at Wide Butte. It apparently grades basally into the alternating siltstone and gray sandstone beds that constitute the upper part of the Cedar Mesa sandstone member. In the extreme western part of the Monument Valley upwarp, two sections provide information concerning the Permian strata as they dip westward under a broad, generally synclinal area. These sections are in the upper part of Copper Canyon (sec. 2) and at the mouth of Nokai Canyon (sec. 1) on the San Juan River. In the upper part of Copper Canyon and at the mouth of Nokai Canyon, the Hoskinnini is overlain by the upper part of the Moenkopi formation. The contact relations are reported to be those of a disconformity (Baker and Reeside, 1929, p. 1422; Baker, 1936, p. 39—40). The Hoskinnini member of the Moenkopi formation rests on the thin De Chelly sandstone member of the Cutler formation with a sharp and irregular contact and is locally disconformable on the Organ Rock tongue at both Copper Canyon and Nokai Canyon, as at Moni- tor Butte. The Organ Rock has a rather constant thick- ness (480 feet at Copper Canyon and 460 feet at Nokai Canyon) and a remarkably uniform lithology. At both localities it rests on alternating sandstone and siltstone beds that characterize the upper part of the Cedar Mesa. GENERAL CORRELATIONS OF PERMIAN ROCKS IN PARTS OF ARIZONA, NEW MEXICO, AND SOUTHERN UTAH It is, at present, impractical to establish general and reasonably final correlations of Permian strata in the Southwestern United States, but it is perhaps appro- H—8 priate to make a limited and preliminary approach to the solution in a small area. Using the central and eastern part of the Navajo Reservation as a nucleus, the authors herein make general correlations over a some- what larger area than those specifically studied in con- nection with this report. CORRELATION OF THE SEQUENCE OF PERMIAN ROCKS IN THE ZUNI UPLIFT WITH THAT IN CENTRAL NEW MEXICO The authors’ opinions regarding correlations of the Zuni sequence with those exposed in the Lucero uplift and the Nacimiento Mountains (fig. 1) are shown in table 2. The suggestion that the San Andres limestone and the Glorieta sandstone in each of the three areas are generally equivalent sequences is based on comparison of the lithologic sequences and such limited paleonto- logic data as are available. Relations of the San Andres and the Glorieta indicate both vertical and lateral gradation. In general, the San Andres grades into the Glorieta sandstone in a northerly direction. The Yeso formation in the Zuni uplift consists of the Meseta Blanca sandstone member and the San Ysidro member. These are substantially equivalent and similar in facies to the members of the Yeso formation in the Nacimiento Mountains to which these names were first applied. The Meseta Blanca sandstone member has also been recognized in the Lucero uplift where it is overlain by the Los Vallos member. The Los Vallos member, although litholog'ically dissimilar to the San Ysidro member, is tentatively correlated with it. No planes of disconformity or hiatus are believed to exist within the Yeso formation or between the Yeso and the Glorieta sandstone. In the Zuni uplift, the Lucero uplift, and the south- ern part of the Nacimiento Mountains, the Yeso forma- tion rests with a rather sharp contact on the Abo formation. This is a plane of possible disconformity and of regional angularity. However, it is not marked by a major hiatus, and despite the evidence for regional angularity, there is also some suggestion of regional lateral gradation. In fact, the entire Yeso, Glorieta, and San Andres sequence grades laterally into coarse elastic rocks of the Cutler formation in the northern part of the Nacimiento Mountains, and these cannot be readily separated from the generally similar rocks that constitute the Abo formation farther south. CORRELATION OF THE SEQUENCE OF PERMIAN ROCKS IN THE ZUNI UPLIFT AND THE DEFIANCE UPIIFT WITH THAT EXPOSED ON THE MOGOLLON RIM, NAVAJO COUNTY, ARIZONA Reconnaissance examination by the senior author, as well as a general acquaintance extending through several years, of the Mogollon Rim (fig. 1) sequence of STRATIGRAPHY, PERMIAN ROCKS, \ ARIZONA AND ADJACENT AREAS Permian rocks has led to the conclusion that the Kaibab limestone of that area is correlative with the San Andres limestone of the Zuni uplift. The Coconino sandstone is equivalent to the Glorieta sandstone. The Yeso for- mation is generally correlative with the upper and middle members of the Supai formation, and the Abo formation is correlative with parts of the lower mem- ber of the Supai (Huddle and Dobrovolny, 1945). Similarly, the upper member of the De Chelly sand- stone of the Defiance uplift is equivalent to the Coco- nino sandstone and Kaibab limestone of the Mogollon Rim. The lower member of the De Chelly sandstone is equivalent to part of the upper member of the Supai formation. The Supai formation of the Defiance uplift is then correlative with the lower part of the upper member, the middle member, and the lower member of the Supai formation of the Mogollon Rim. Problems of correlation of partly marine strata called the arkosic limestone member of the Madera for- mation (Read and others, 1945), the Red Tanks mem- ber of the Madera formation (Kelley and Wood, 1946), the lower part of the lower member of the Supai for- mation (Huddle and Dobrovolny, 1945), and the Rico formation of some areas (Baker, 1936) have not been satisfactorily resolved. All these strata represent tran- sitions between marine and continental facies. Locally they may be Permian in part and elsewhere Pennsylvanian. CORRELATION OF THE SEQUENCE OF PERMIAN ROCKS IN MONUMENT VALLEY, UTAH AND ARIZONA, WITH THAT IN GRAND CANYON, ARIZONA The authors’ general impressions are that the cor- relation of Permian rocks in Monument Valley with those of Grand Canyon (fig. 1) are not completely estab- lished. Baker and Reeside (1929) have suggested that the Cedar Mesa sandstone member, the Organ Rock tongue, the De Chelly sandstone member, and the Hoskinnini tongue of the Cutler formation coalesce into a single sandstone body. The upper part of this sand- stone grades and tongues to limestone with the result that the Kaibab limestone and the Coconino sandstone can be differentiated. The lower part of the Supai for- mation is evidently correlative with the Halgaito tongue and perhaps a part of the Rico formation. This correlation is quite reasonable, but it raises ques- tions concerning the relations of the Kaibab limestone, the Coconino sandstone, and the Supai formation in the Grand Canyon With apparent equivalents on the Mogol- lon Rim. It appears more likely that the Coconino standstone and Kaibab limestone are equivalent to a part of or all the De Chelly sandstone member of the Cutler formation and that the Supai 'is equivalent to the Organ Rock tongue, the Cedar Mesa sandstone mem- ber, and the Halgaito tongue of the Cutler formation. H—9 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY 23:25:»... A:....§.fi::o... .:n.:§..m::u... 5:25... .85.... 5:25... 32...... m :25... a»: an... M .322. 328:... .6... m H. 2.33:... 33. M w M W. ,M r . / c u H M W .h €2.25. .38 o... 3:: 5:35.... .3... 5.52.25: 22.2.3. .225 :5 a 5:. .. m .23.: 2...; :. m Mom 5 3:22. 2. .2. ou- ufi 85.53.. 5:: 2.: $58.... 52 a. 98.5... 2. an... on: .— 38.: m. $5.53.. 2. :2. M, ( W 5:2...25. .o “.5... 3 av... 55:3 .3: .o «:2. 55:8 .3: 3:35:05 .338 BEE . can :. 9:25.... 3 o:2n.uu.n..._.u.__:§_.< 5:25... 8... :5an. 3... Z I llllll 9.5.. :5 .352. 9.5» :3. , 2.9.2 23:... .352: 55.5.... 2: 5......3. 2.: 5:55 2.: 2.3.3. 2.3.2. 3:3 eggs. .15 .35.... .352. 2:3... .35... .35.: 2.33:8 .352. 22:: W 3.93:: 283:8 «:33...» 3o: .66 228:5 . . m. 8.33 5.3.: 8...: 58¢: 3:...» «:8: so: .38 822:... .36 8:25. .2...” my , u M M M m m w MI. M O 0 m. N m. l a w m. A .. A A M .M W W... m. m. W W w: m w w w m. m m. 23:: 2.22 .35.: .352. .BEoE 3:5... .8: :56 :8: E5 \ =35 9:...» :8 3...... 8.. 2...”) :8 2.5 =on .352: .23.. Jun“: I I I ||||| M m. 33mg: .......38 m u 222...: $28....» 288:8 22%...» M. W 2.:83 , 20.35 23.2w 22...... .22.»... .35.... 3.5:. m .352. W 8.55... 223.3 22mg: 2.2%:3 .82. a .3...» 2.26 on 2.25 an .322. 2.3.36 WK. 2: 3.... a a 833:... 2.2.2.... lllllll mm 2.23:... m . ._ : :. ._ , :23. “2...: :8 3.5:. 223:... a 9 ”2:2 :20. m .36.... ....:.....3.. .352. .55....3: / / W \ IA I. 522...... 25.... .: 8:352 255 3 23.2.5. 232.8 3:252 ..:...u .9 5.3.52 9.55 .9 5.2.3. 255 ... m V m ,......~:..e. 32:3: 522...... 33:8: :325. 32:8: .35... 3.22:5 .852: 9.5.2.5 E: 22:3: 2.3.; .35... 352:5 .35... 25.2.5 .35... 2.2.23 8.3 2.3 m WW . . u 3 an»... :33 to: same; :3 523w :3 52:3: to: 52.3% S 2.8.... 2.2.2 8.3: 5: 8...»: so: 8...»: to: m 5...»... En... . . E... 5:93: E... .:...N E... 28... 2.555: 25.5.3: n . 9.2.2 :5 :2: 3:... .555: 2.25 .55. 35...: W ”3.8.3.... ".85: and 32.32: .3 mag—«Eon E53 50595 3.5::an and gnuflhmnfldm was hummus.» an... 933.5. 05 5 vow—35 32.333: .3: 3 85335:“. SSE as: 5.83%, $9.23: 3...: .3 35:: S: «626:?» .5ng .8 $8.3»..s8 :36 o.§.3§§~l.m an. H—lO STRATIGRAPHY, PERMIAN ROCKS, REFERENCES CITED Baker, A. A., 1936, Geology of the Monument Valley-Navajo Mountain region, San Juan County, Utah: U.S. Geol. Survey Bull. 865, 106 p. Baker, A. A., and Reeside, J. B., Jr., 1929, Correlation of the Permian of southern Utah, northern Arizona, and south- western Colorado: Am. Assoc. Petroleum Geologists Bull., v. 13, no. 11, p. 1413—1448. Darton, N. H., 1925, A résumé of Arizona geology: Arizona Univ. Bull. 119, 298 p. 1928, “Red beds” and associated formations in New Mexico, with an outline of the geology of the State: US. Geol. Survey Bull. 794, 356 p. [1929]. Daugherty, L. H., 1941, The Upper Triassic flora of Arizona, with a discussion of its geologic occurrence by H. R. Stanger: Carnegie Inst. Washington, Pub. 526, Contr. Pale- ontology, 108 p. Gregory, H. E., 1915, The igneous origin of the “glacial de- posits” on the Navajo Reservation, Arizona and Utah: Am. J our. Sci., 4th ser., v. 40, p. 97—115. 1917, Geology of the Navajo country—a reconnaissance of parts of Arizona, New Mexico, and Utah: US. Geol. Survey Prof. Paper 93, 161 p. Eager, Dorsey, 1924, Stratigraphy—northeast Arizona—south- east Utah: California Metal and Mineral Producers Assoc, Mining and Oil Bull., v. 10, no. 2, p. 135—139, 167 ; v. 10, no. 4, p. 383~385, 423, 437—539. O ARIZONA AND ADJACENT AREAS Huddle, J. W., and Dobrovolny, Ernest, 1945, Late Paleozoic stratigraphy and oil and gas possibilities of central and northeastern Arizona: US Geol. Survey Oil and Gas Inv. Prelim. Chart 10. Kelley, V. C., and Wood, G. H., 1946, Lucero uplift, Valencia, Socorro, and Bernalillo Counties, New Mexico: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 47. Read, 0. B., Wilpolt, R. H., Andrews, D. A., and others, 1945, Geologic map and stratigraphic sections of Permian and Pennsylvanian rocks of parts of San Miguel, Santa Fe, Sandoval, Bernalillo, Torrance, and Valencia Counties, north—central New Mexico: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 21. Wilpolt, R. H., MacAlpin, A. J ., Bates, R; L., and Vorbe, Georges, 1946, Geologic map and stratigraphic sections of Paleozoic rocks of Joyita Hills, Los Pifios Mountains, and northern Chupadera Mesa, Valencia, Torrance, and Socorro Counties, New Mexico: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 61. Wilpolt, R. H., and Wanek, A. A., 1951, Geology of the region from Socorro and San Antonio east to Chupadera Mesa, Socorro County, New Mexico: U.S. Geol. Survey Oil and Gas Inv. Map OM 121. Wood, G. H., and Northrop, S. A., 1946, Geology of the Naci- miento Mountains, San Pedro Mountain, and adjacent plateaus in parts of Sandoval and Rio Arriba Counties, New Mexico: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 57. UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 374-I-I ma GEOLOGICAL SURVEY I 0. 109., PLATE I 108., I I I I I I . . , . os InnInI '- W'de -\: _ "37"|-—--—V -_ _-.—*-._I_I -‘Jfé 4XMesa' S ' fl ' 6XlButte " 1~/;I V‘ __.--— I:I——-TIXI-I—---—-¥E "-C—OLQEA—DO—-— -- — -- — __ —---——-_—.--.—--.37° I I I . I ' I ( T66_é\7”“'_ _'*—uo ”— I7“. "’3 7' ' ~I ARIZONA . NEW MEXICO ‘ ‘I I 3‘( Sm “ UD 5 //~‘A\ ' I ~\ 0..- MONUMENT' \LFXI'II’ I /,I f . Kg I I -. ' , z 8/ I I . VALLEY ' 8x 1/ I, < $5 I III ,, 2 L/“k ' I "2,. i z} w“ V I K "\o I ,- ‘ Q I_ “A I / ,6“ I I. I? - "\. '\... I «a? _ i“ I «rs - . 14‘ -‘ . \° I ‘ I I ' \ 03312:? I I I OKayenta ' v ,“I \ ""’"/ I I ‘ I '. K‘ I I. . I; I | " 9‘ , I I I I, I - I I . . I I I , /. . _ I I ‘ I l I , I, ‘\ I I l ’ 3 . I ~ ' . I I I . I o I. I ; I l | ,‘I I ' I I I ' I I _ \g I I 2 V _I “ I§ UD / x‘ I III I,‘ 2({9-‘14—// l I L‘ , I 3’3 X9 I ‘ '~ I , ' P LDVN5'1 8 I.) \ onl (fllpq I . x‘\fmmmr‘~’u\\ 1 I \ > ceVi/ z'x fix.) ‘"’"" \Jggr che (c - ../ o a: - '\ I _ UD {’31ka de ,Chelly / \ / N g I E I I I LDI" UEIIIEEOO E'g I /; ("2 \' TN ‘ I 3;; I/ I3, ‘1 m \, \ J I I ‘: ' a z I I Ir 0,, I I. ‘f (7%” ”D I __ 36“ l \ 7, :59 22(”r.:;-—»————-——;--— -— ' '—_ ‘ ' I' :/ 1)‘(I I U Buell Park I I ’-\ n-I ) \ I I I. 11 : LD N . I ‘J \ m If I Keams Canyono I 1. om l I . LDXE‘é. I I M c K I N L E Y . * a; I I A P A C H E U D Iax’igv'on Defiance I LID [V ' I cGanado f % Window Rx)ck\c l I - — - —. E :5) I l ”I (.3) I I I" I /" ,_/~« I UD 2 L =.\ I f I : 2 ~-.\, I Hunters 13~~L:- G ll / N r' LDxft X/ 3 “FjEk_._}-ux\ I . r I xx/ "ME a _ . v U? 14x Oak I /.- ...\ fl; \\ I I/Spnnzs _/ I I f I UD r" 15 I A/ ./' I I_/‘ UD I {I 6 I I/I / I7 oThoreau I I g? /l/ I U? xoMcGaffey fi’izw I 03/ .~ ‘ «C I I ? .-/ I 804/ I‘M} w "it! . 2W ,~--/ ' ’ @751“ ”D \ A N I //’T l C/ hfl <§Ic> x2< A .~ (/N M ) . ‘ K /-~~ I EXPLANATION p) is I R1V__E/~»/‘“ CIBOLA . f" I x'8 NATIONAL FOREST I ( Location of measured section /,. I Shown on [dare 2 I ”V.- I I ./ M/ ,-J ’ Direction of inclination of cmss—laminations in I ./ sandstone beds I 0/"/ ' UD I ‘2};— I Gloriem sandstone and upper member of I a“ u i 35° De Chelly sandstone .._4..L// l LD I ' Lower member of De Chelly sandstone I I Cedar Mesa sandstone member of the Cutler E I I formation (in Arizona and Utah) E M Is ' I Meseta Blanca sandstone member of the Yeso :3: J l formation (in parts of New Mexico) ’— l I _ CQ , APPROXIMAVE MUN I ' Cocomno sandstone (In parts of Anzona) DECLINATION. 1951 I I l o LO 111 ° Base fmm U S GeologIcaI Survey I 500000 maps OI Utah, AnzonaI and New MexIco MAP OF THE NAVAJO COUNTRY, ARIZONA, NEW .MEXICO, AND UTAH IO 0 10 20 MILES LLI l l l I I LJJ_I I I 595965 0 -61 (In pocket) UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY DISTANCE, 1 , IN MILES ‘ 14 ~ * 7v Nokai Canyon, Utah , I V ’ ‘iJanhQDj,10[mation Copper Canyon,” Utah; {i I (_f._——— 14 ———~————> 4f 18 3 Monitor Butte, Utah Hoskinnini Mesa, Utah H'oskinniniwmember De Chelly sandstone I of Moenkopi formation memb/(i, / of\Cutler formation Doulas Mesa, Utah I, IHoslnninI member De Clelly sandstone member of Wide Butte, Utah A 16 V 7 Upper Gypsum Creek, Utah 8 South Comb Ridge, Ariz 'Qf~MQ-eflk0pi formation‘“ Cutler formation PROFESSIONAL PAPER 574-I—I PLATE 2 9 Canyon del Muerto, Ariz |... Shinarump member of Moenkopi formation «\ Chinle formation I I I I Upper member of I I I I I I I I I I 1“” ‘‘‘‘‘ names 7 7, RIM \\ De Chelly sandstone 7 \ . / ’ YiL , ' Organ Rock tongue of Cutler formation gx~~~~~ , \_ . \\ Organ Rock tongue of Cutler formation <> Organ Rock tongue of Cutler l—-———h— winn,§\\\p\ _ \\W\\,> I L b 1: Cedar Mesa member of k formation <\l ower mem er 0 , , y \ g / fl De Chelly sandstone Cutler formation \\\\e \ ,// / ""’// 3” : \1\7\\\ ., I I I I n I I Supai Cedar Mesa sandstone member of Cutler formation I formation I I I \X I I 500 FEET 1 r \ ,, _. I» K / 400 300 _ _ Halgaito tongue of Cutler formation / \00 200 633‘ . ’ xo‘ Precambrian 100 €300 1/ . iermosa formation 0 Rico formation Rermosa formation DISTANCE, IN MILES (—-——— 10 —> x 24 \ 12 > <—-——— 6 ~——> 62—)» 4—3 —> <—-— 3 —> 1 30 A 1 12 I 9 10 11 12 13 14 15 16 17 18 EXPLANATION Hunters Black Creek Black Creek LITHOLOGY Canyon del Muerto Monument Canyon Buell Park, Ariz Bonito Canyon, Ariz Point Oak Sprins Ariz Ariz McGaffey, N. Mex Cottonwood Creek Ariz ' Ariz Ariz Ariz North South N. Mex 00°00 _ _ Shinarump member of Chinle formation Shinarump member of Chinle formation Conglomerate Sandstone, silty, arkosic, Andres IImESECEIe/f horizontally bedded Upper member of De Chelly sandstone Glorieta sandstone member of Rico formation GRAPHIC SECTIONS OF PERMIAN STRATA BETWEEN NOKAI CANYON, UI‘AH, CANYON DEL MUERTO, ARIZONA, AND / De Chelly formation Precambrian \ sandstone / SEpai formation / Precambrian /////// , I San Ysidro member of Yeso formation eso formation \ Abo formation Precambrian Meseta WE‘éfiéhm' Madera \formation \ Sandstone, fine-grained, 'lt , hiorizontally bedded Sandstone, 5' y crossbedded Sandstone, coarse-grained, horizontally bedded Sandstone, limestone pebble conglomerate Sandstone, calcareous, torizontally bedded 6P.- Sandstone, conglomeratic, horizontally bedded Mudstone Limestone, including dolomitic limestone Sandstone, silty, horizontally bedded Limestone, silty :‘<é;-‘:/;,.~.';-.’-: Sandstone, conglomeratic, a rkosic Limestone, cherty Sandstone, fine-grained, con- cave or convex crossbedded Quartzite . 3/5): a} Sandstone, coarse-grained, / concave or convex crossbedded Gneiss Sandstone, arkosic, crossbedded COTTONWOOD CREEK, NEW MEXICO 595965 0 ~61 (In pocket) Yampa C nyon in the Uinta Mo ntains Colorado Yampa Canyon in the Uinta ‘Mountains Colorado By]IHJAN'D.SEARS SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 37$J ‘ A study of some unusna/features and t/ze possz'o/e origin and development of Me canyon UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of DOCuments, US. Government Printing Oflice Washington 25, DC. CONTENTS Page Page Abstract ___________________________________________ I—l Observed features—Continued Introduction _______________________________________ 3 Lower section of Yampa Canyon—Continued Purpose of the report ____________________________ 3 Topography of canyon walls _________________ I—12 Usage of two terms _____________________________ 3 Topography of adjoining uplands _____________ 13 Sources of information ___________________________ 4 South of canyon ________________________ 13 Earlier investigations ________________________ 4 North of canyon ________________________ 13 Newer sources ______________________________ 4 Geology ___________________________________ 14 Geologic map in present report _______________ 4 Warm Springs scar—an exception _____________ 14 Acknowledgments _______________________________ 5 Suggested explanation of the features __________________ 15 Observed features ___________________________________ 5 Concepts of 1922—23 ____________________________ 15 Yampa Canyon as a whole _______________________ 5 Original extent and thickness of Browns Park forma- Statistical details ___________________________ 5 tion _________________________________________ 16 Relation to Yampa fault and other faults _______ 5 Area of maximum thickness __________________ 17 Yampa fault ___________________________ 5 Browns Park formation in Lily Park __________ 17 Red Rock fault _________________________ 5 Possible Browns Park material on Douglas Mitten Park fault _______________________ 6 Mountain ________________________________ 17 Graben between Red Rock and Mitten Browns Park formation near Elk Springs ______ 18 Park faults __________________________ 6 Nearness of Browns Park formation to east end Three-part division of canyon- _ _ _ _ _ - _ - _ ._ _____ 6 of Yampa Canyon ________________________ 19 Upper section of Yampa Canyon _________________ 6 Possible Browns Park material on Blue Moun- Middle section of Yampa Canyon _________________ 7 tain _____________________________________ 19 River pattern and direction __________________ 7 Possible Browns Park material on Harpers Topography of canyon walls _________________ 7 Corner __________________________________ 19 South wall _____________________________ 7 Possible Browns Park material west of Lodore North wall _____________________________ 7 Canyon __________________________________ 19 Topography of adjoining uplands _____________ 8 Summary __________________________________ 20 South of canyon ________________________ 8 Possible development of the canyon—a chronological North of canyon ________________________ 8 outline ______________________________________ 20 Geology ___________________________________ 9 First step __________________________________ 20 South of river __________________________ 9 Second step ________________________________ 20 North of river __________________________ 9 Third step _________________________________ 21 Meander-migration scars _____________________ 9 Fourth step ________________________________ 22 Anderson Hole scar _____________________ 10 Fifth step __________________________________ 24 Tepee Hole scar ________________________ 10 Sixth step __________________________________ 25 Browns Hole scar _______________________ 11 River development in Morgan formation__ 26 Bower Draw scar _______________________ 11 River development in Weber sandstone-__ 27 Five Springs Draw scar __________________ 11 Seventh step _______________________________ 28 “Half-turn district”———an exception ____________ 11 Effect of Mitten Park and Red Rock faults ________ 28 Lower section of Yampa Canyon __________________ 12 Selected bibliography ________________________________ 30 River pattern and direction __________________ 12 Index _____________________________________________ 33 ILLUSTRATIONS PLATE 1. Geologic map of Yampa Canyon and vicinity, Uinta Mountains, Colorado _______________________________ In pocket Page FIGURE 1. Entrance to Yampa Canyon ___________________________________________________________________________ 1—6 2. Upper section of Yampa Canyon ________________________________________________________________________ 7 3. Sharpened spur between Tepee Hole (second) and Browns Hole (third) scars ________________________________ 11 4. “Tiger Wall” in lower section of Yampa Canyon _________________________________________________________ 12 5. Lower section of Yampa Canyon. Intricate meanders in Weber sandstone __________________________________ 13 6. Warm Springs (sixth) scar ____________________________________________________________________________ 15 7. Map of eastern Uinta Mountains and vicinity, showing part of the mapped Browns Park formation ____________ 18 8. Hypothetical course of Yampa River between points B and C when cutting through Browns Park formation- ___ 25 9. Possible former high-level channel of lower part of Yampa River ___________________________________________ 30 III SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY YAMPA CANYON IN THE UINTA MOUNTAINS, COLORADO By JULIAN D. SEARS ABSTRACT Yampa Canyon, northwest Colorado, was incised in the south- ern flank of the Uinta Mountain arch by Yampa River. Modern topographic and geologic maps and aerial photo- graphs of the canyon and vicinity have disclosed unusual fea- tures, among which are: natural division of the canyon into three sections; marked change in river pattern from the mid- dle to the lower section; in the middle section, radical differ- ences in topography and geology on its two sides; also in the middle section, but only north of the river, several scallop- shaped erosion surfaces or scars partly rimmed by cliffs and with moderately sloping floors; in the lower section, still dif- ferent topography and general absence of scars; geographic and geologic relations between Yampa River and the Yampa, Red Rock, and Mitten Park faults. The observed features give further clues to the origin and development of the canyons and anomalous courses of Green and Yampa Rivers across the Uinta Mountains. South of and crudely paralleling Yampa Canyon is the Yampa fault and its branch the Red Rock fault, both with downthrow on the north. Apparently the Red Rock fault ends at the Mitten Park fault, which has downthrow on the south- east. Thus the Yampa River joins the Green within a west- ward-pointing triangular graben between these two faults. The upper section of Yampa Canyon, nearly 2 miles long, cuts stratigraphically downward through the Weber sandstone and Morgan formation, both of Pennsylvanian age, at right angles to the northeast strike and against the southeast dip of about 12° that mark the end of the Uinta Mountain arch. The river’s course is fairly simple, and topography and geology on the two sides are similar. The middle section of the canyon is nearly 20 miles long; its fall is 333 feet, an average of about 17 feet per mile. Near the point where the middle section begins, the strike of the beds swings sharply to a direction north of west, parallel to the axis of the arch; the dip is predominantly 6° SW. This changed structure extends westward to and beyond the end of the canyon. The lower section of Yampa Canyon is nearly 24 miles long. Descent of the river surface is 176 feet, an average of less than 71/5 feet per mile. ‘ In the middle section the river’s course is marked chiefly by open meanders and straight stretches. An exception is a “half-turn” meander, convex southward. The south wall is prevailingly simple and uniform—a steep slope ending upward in a cliff. Its height and width average a quarter of a mile each, and it follows and fits closely each curve of the river. is sharp. Except in the “half-turn district,” the north wall is wider, less steep, and of irregular shape. It consists chiefly of ad- joining scallop-shaped erosion surfaces or scars. Southward, however, these moderately sloping surfaces end in a steeper slope down to the river, making a break in slope convex up- ward. The Untermanns’ geologic map of Dinosaur National Monu- ment shows conspicuously that the south wall serves as a formation boundary. The upper part of the south wall and the upland immediately south of it consist of the Weber sand- stone, about 900 feet thick, which is loosely cemented and highly jointed. The lower part of the south wall, the north wall, and the adjoining belt of upland expose beds of the next older Morgan formation (except in the “half-turn district” where the Weber sandstone remains). The Morgan is about 1,200 feet thick, of sandstone and limestone; the lower part is more resistant to erosion. The hypothesis is advanced that the scallops north of the river are “meander-migration scars" formed by the progres- sive downdip (southward) migration and lowering of early meanders of Yampa River, by an unusual form of homoclinal shifting on more resistant beds in the lower part of the Mor- gan formation. In the middle section of the canyon five such scars are distinguished; because they differ somewhat from each other they are named and separately described. The lower section of the canyon differs markedly from the middle section in several ways, the most striking and signifi- cant of which are: (a) A notable change in river pattern. Meanders are more numerous and more intricately curved. (b) Topography of canyon walls and of adjoining uplands generally different from the two types in the middle section. Cross profiles are asymmetric but alternating because of inter- locking spurs with slipoff slopes. (c) An abrupt change in the relation between river and geology. The canyon is predomi- nantly cut in- the Weber sandstone, whose contact with the underlying Morgan is mostly north of the river. ((1) An al- most complete lack of “meander-migration scars.” The excep- tion is the Warm Springs (sixth) scar where the Morgan formation is again exposed to and along the river. I am convinced, for the following reasons, that at one time the site of the present Yampa Canyon was buried under the Browns Park formation of Miocene(?) age: (a) The thickest deposits of the Browns Park formation, perhaps 1,700 feet of which still remain, were in the southeastern half of Browns Park and its extension to Little Snake River. (b) Continu- I—l Its intersection with the adjoining upland 1—2 ous outcrops of known Browns Park formation extend to the upstream end of Yampa Canyon on both sides of the Yampa River. (c) The rest of the canyon site is almost surrounded by patches of conglomerate and whitish tuffaceous sandstone of Browns Park lithology. (d) In September 1959 the Unter- manns found sands similar to those of the Browns Park at four places between the Yampa River and the Yampa fault. My hypothesis of canyon origin and development is offered as a chronologic outline involving seven steps. First step—After the Uinta Mountain arch was greatly up- lifted during Laramide orogeny, it was extensively eroded and the detritus was laid down in the flanking basins and around its southeastern end. Repeated small uplifts accompanied this deposition. In late Eocene or early Oligocene time, arching was renewed and extended southeastward as the Axial Basin anticline. At this time the Yampa, Red Rock, and Mitten Park faults may have begun, but proof of this seems lacking. Second step—In middle Tertiary time, uplift virtually ceased, but continuing erosion reduced the mountain mass to mature topography. The resulting surface may have been what A. D. Howard called a pediplane. Along the mountain crest were high residual peaks, between which the erosion surface formed nearly horizontal pediment passes. North- ward and southward these passes opened out into a pediment, cut on the. upland rocks through retreat of the mountain front and sloping away from the ridge with gradually decreasing gradient. On the south flank this pediment truncated the older, southward-dipping rocks at an angle less than their dip, and also cut across the Yampa and other faults if then exist- ing. The surface was at places rather smooth and at others undulating, with low residual hills. The pediment also wrapped around the southeastern end of the arch. On this south flank the evidence now remaining near Yampa Canyon may record only a single erosion surface. Third step—During the Miocene(?) the widespread and varied Browns Park formation was laid down on the pedi- plane. At least as far east as Little Snake River the water- borne part of this material is thought to have come from the Uinta Mountains themselves. The basal conglomerate found at many places is prevailingly composed of the reddish quartz- itic sandstone of the Uinta Mountain group of Precambrian age; locally, however, fragments of Red Creek quartzite of Precambrian age" or of limestone of Mississippian age predom— inate. The upper, much thicker part of the formation con- sists partly of white or light-gray sandstone thought to have come from the Uinta Mountain group through leaching of its reddish cement; this was greatly augmented by windborne volcanic tuffs. Upper beds of the formation presumably overlapped west- ward up the Browns Park valley and also laterally on its walls; concurrently, sand from residual peaks along the crest washed down into the pediment passes and some of it was carried down the north flank, where it met and mingled with the material rising in the valley. At the same time, some of the sand from the passes, and sand and some cobbles from the crest as the mountain mass retreated, were carried down the south flank, where they filled hollows and blanketed the beveling surface, perhaps to a depth of 200 or 300 feet above the canyon site. Fourth step.——Chiefly after—but to a small amount during— deposition of the Browns Park formation, the eastern part of the Uinta Mountain arch collapsed, as a graben. Probably this took place in many small movements. Above the site of Yampa Canyon and its environs, a long narrow trough on the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY surface of the Browns Park was formed thus: (a) In a nar- row zone along the Yampa fault (repeated by the branching Red Rock fault), steep north dips, caused by drag, in the Browns Park cover and the truncated older beds that previ- ously dipped southward. (b) North of the drag zone, a zone 4 to 9 miles Wide in which the surface of the Browns Park formation was virtually flat in a north-south direction but (through tilt) sloped gently about N. 80° W. (c) Still farther north, to the crest of the ridge, a zone in which the south- ward, depositional slope of the Browns Park formation re- mained because the broad central part of the graben had gone down almost vertically. This trough probably continued, with gradually rising floor, far to the east above and north of the Axial Basin anticline, for the graben movement had extended in that direction, though with diminishing force and effect. I now suspect that, east of Little Snake River, the westward slope of its floor was erosional and depositional, hence original, rather than due to tilting and reversal as we earlier thought. Fifth step—Presumably somewhat overlapping the fourth step, during the fifth step the trough began to affect the loca- tion and direction of drainage. Streams flowing from the Continental Divide down the depositional slope of the Browns Park formation came together in the graben and, augmented farther on by other streams, were guided westward down the trough as a new Yampa River. At first the river was rather straight, but later it established incipient meanders. Being wholly in the Browns Park formation, the river at any one time should have had a pattern and gradient essen- tially uniform throughout. Above the present middle section of the canyon the channel perhaps became located along the outer, northern edges of what are now called the first to fifth scars. Above the present lower section (with a probable meander around the outside of What is now the Warm Springs scar) the river pattern presumably was like that farther up- stream rather than one of intricate meanders as today. At length the river at some point cut through the Browns Park formation to the underlying rocks. Sixth step—Superposition commenced when the river’s course began to be affected by the differing lithologic compo- sition and structure of the undermass. It is tentatively sug- gested that the river first cut through the Browns Park for- mation at the mountainward ends of the meanders curving around the sites of the present first and sixth scars. Initially this caused some decrease in the rate of downward erosion at those points and created temporary baselevels upstream from them. However, only a thin cover of the Browns Park formation then remained elsewhere along the river, hence the undermass was relatively soon reached at all points. Because of the structure of the undermass, when the river cut through the cover it ran on the Weber sandstone or the Morgan formation. In what is now the middle section it was on the upper beds of the Morgan, except in the “half-turn dis— trict” where it was on the Weber. In contrast, in what is now the lower section it ran on the Weber, except for the northward meander around the site of the present Warm Springs scar where it was again on the upper beds of the Morgan. Further development that brought today’s conspicu- ous differences in river pattern must have been influenced chiefly by differences in the way those two formations affected erosion. The upper part of the Morgan was more resistant than the soft beds of the Browns Park. In that upper part, down- ward rather than lateral erosion became dominant and cliffs YAMPA CANYON, UINTA MOUNTAINS, COLORADO perhaps 200 feet high were out. Then at the north ends of its meanders the river reached even more resistant limestones in the lower part of the Morgan while elsewhere it was still in upper beds. Direct vertical erosion practically ceased at the points of greatest stratigraphic penetration; but as the tendency to cut the channel down to lower altitudes persisted, least resistance was found in a gradual downdip shifting on top of the older, stronger beds. At first the curving north ends of the meanders were flattened along the strike, and then the meanders themselves slowly migrated, cutting floors that sloped southward and rims whose bases grew lower in that direction. Between the Tepee Hole and Browns Hole scars a conspicuous sharpened spur was developed. Concurrently, the meanders grew smaller and the river be- came shorter and of larger gradient. By its constant en- croachment against the less resistant upper beds, the south wall was kept narrow, steep, and in conformity with the riv- er’s curves. In contrast, where the river flowed on Weber sandstone it now has a pattern of rounder and more intricate meanders, with asymmetric cross sections and interlocking spurs having slipoffs slopes. I believe that this greatly changed and more complex pattern was developed after superposition began; that it resulted from jointing and erodibility of the Weber; and that the river’s length in what is now the lower section be- came greater and its gradient smaller. Seventh step—Late in the canyon cutting some rejuvena- tion probably took place. Otherwise, it is difficult to explain how and when the more resistant beds in the lower part of the Morgan were breached and a steeper slope was cut near the river, looking like a “valley-in-valley." This suggested process less satisfactorily explains the steeper banks near the river below “treads" in the slipoff slopes on spurs in the lower section; for those “treads” appear to be related to struc— ture and to harder beds in the Weber. Efiect of Mitten Park and Red Rock fauna—An apparent old high-level channel suggests that in its last few miles the Yampa was once farther north than today; that it joined the Green at the east end of the Mitten Park fault; and that the enlarged Green River flowed westward for more than a mile along that fault until it established its course and was able to leave the fault plane and continue farther west on the up- throw side. If this hypothesis is correct, then because of southward dip and of jointing in the Weber, subsequent ero- sion of new deeper channels may have formed the elongated canyon of the Green around Steamboat Rock and diverted the lower part of the Yampa ‘to its present junction with the Green. INTRODUCTION PURPOSE OF THE REPORT A detailed office study of modern topographic and geologic maps and aerial photographs of Yampa Can- yon and its environs in the Uinta Mountains has brought to my attention some striking features, one of which is very unusual or (so far as I know or can ascertain) even unique. Among the more outstanding features are: 1. A natural division of the 45—mile canyon into three parts—a short upper section, and a middle and a lower section of roughly equal length. 1—3 2. A marked change in river pattern from the mid— dle section to the lower section. 3. In the middle section, radical differences in t0- pography and geology on the two sides of the river. 4. Also in the middle section, but only on the north side of the river, several curious scallop-shaped ero- sion surfaces now partly rimmed by cliffs and with moderately sloping floors; these surfaces, perhaps the most striking feature of the entire canyon, are herein called “meander-migration scars.” 5. In the lower section, where the canyon is incised chiefly in the next younger formation, topography different from the two types in the middle section, and (with one significant exception) an absence of the meander-migration scars. 6. The relations (geographic and geologic) between the Yampa River and the Yampa, Red Rock, and Mitten Park faults. The features observed in this area, apparently not widely known, should be of interest to geologists and geomorphologists, and should offer intriguing prob— lems both in themselves and as clues to further un- raveling 0f the geologic history of the Uinta Moun- tains and the origin and development of the courses and spectacular canyons of the Yampa and Green Rivers. They are therefore presented, described, and illustrated in this report. The descriptions are fol- lowed by suggestlons offered in possible explanation of the cause and significance of the major features. USAGE OF TWO TERMS The term “meander” is used in this report a little more broadly than is customary. Most writers restrict the term to rather systematic smooth curves or loops of a river whose course may be called serpentine. The somewhat broader application herein is adopted partly for convenience and partly to emphasize the progres— sive development by which initial irregularities in a river’s course tend almost immediately to begin growth, by lateral erosion, into larger and more sys- tematic curves until they fully deserve to be called meanders. This progressive change was particularly well analyzed and described by Davis (1914, p. 4—7), who, however, carefully refrained from indicating the exact point of development at which the initial irregu— larities (his “bends or turns”) become “meanders.” The term “incised” (with its related noun “inci- sion”) is herein used with its simple meaning of “cut into.” It is intended to be noncommittal as to process of origin, cycle, and shape of cross section (symmetric or asymmetric). The word “incised” and other terms such as “intrenched” (or entrenched), “inclosed,” and “ingrown,” have been used by numerous writers with I—4 either general meaning or varying specialized signifi— cance; but as there has been no uniformity or full acceptance they seem confusing rather than helpful. SOURCES OF INFORMATION EARLIER INVESTIGATIONS The geologic history of the Uinta Mountains, the origin of the anomalous courses of Green and Yampa Rivers, and the age relations and significance of the Bishop conglomerate and the Browns Park formation have been subjects for much study and many debates for nearly a hundred years. Among the pioneer stu- dents of these problems were J. W. Powell and S. F. Emmons; after the turn of the century, important contributions were made by several geologists, among them J. L. Rich and E. T. Hancock. My own acquaintance with these problems began in the summers of 1921 and 1922 when I surveyed geol- ogy and oil and gas prospects in northwestern Colo- rado (Sears, 1924b). Interest was intensified and broadened in scope during the second season when, progressing westward, W. H. Bradley, James Gilluly, and I reached the Uinta Mountains and had some op- portunity to examine parts of Browns Park, Cold Spring Mountain, and their environs. We realized that our observations and conclusions with regard to the mountain-and-river problems were incomplete, for we could reach only a small fraction of the pertinent region and had to study most of that fraction rather hastily as a sideline to our main assignment. Fur- thermore, we were handicapped by the lack of satis- factory topographic maps of our area (the one ac— companying Powell’s classic report on the geology of the eastern portion of the Uinta Mountains, 1876, be- ing quite inadequate for our purpose) and of course the lack of aerial photographs, which would have been invaluable. Nevertheless, our concepts took form and were brought together in a report published 2 years later (Sears, 1924a). During the subsequent decade Bradley spent three seasons in extending fieldwork westward on the north flank of the Uinta Mountains and far out into the basins to the north and northeast. This additional work enabled him to modify and expand our earlier concepts and to assemble his views in a comprehensive report (Bradley, 1936). NEWER SOURCES Since publication of Bradley’s report in 1936, much new material bearing directly on the area here dis— cussed has become available. In What was almost wholly an office study, I have derived information particularly from the following sources: SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1. Aerial photographs of Dinosaur National Monu- ment, scale 1 :31,680; taken chiefly in 1938 for the Soil Conservation Service, U.S. Department of Agriculture. . Topographic map of Dinosaur National Monument, Colorado—Utah: U.S. Geo]. Survey. Scale 1:62,500; contour interval 50 feet. Surveyed in 1941. 3. Untermann, G. E., and Untermann, B. R., 1954, Geology of Dinosaur National Monument and vicinity, Utah-Colorado: Utah Geol. and Miner- alog. Survey Bull. 42. 4. Topographic maps of Hells Canyon and Canyon of Lodore South quadrangles, Colo.: U.S. Geol. Survey, 1954. Scale 1:24,000; contour interval 40 feet. 5. Aerial photographs for the quadrangles named in item 4, scales 1:28,400 and 1:17,000; taken in 1951 for the U.S. Geological Survey. 6. High-altitude aerial photographs of the eastern part of the Uinta Mountains and vicinity; taken in 1953 for the Army Map Service. 7. Topographic map of the Vernal 2-degree quadran— gle, Utah-Colorado: Civil edition reprinted by the U.S. Geological Survey from V502 military edition compiled by the Army Map Service in 1955. Scale 1:250,000; contour interval 200 feet. 8. Finally, during a brief reconnaissance of the east- ern part of the Uinta Mountains (spring of 1959) in the company of D. M. Kinney and W. R. Hansen of the Geological Survey, J. M. Good of the National Park Service, and Mr. and Mrs. G. E. Untermann of Vernal, Utah, several days spent in the immediate neighborhood of Yampa Canyon. [0 GEOLOGIC MAP IN PRESENT REPORT Yampa Canyon and its environs, as discussed in the present report, occupy nearly half of Dinosaur Na- tional Monument. Hence the base for the map (pl. 1) of the area is taken from the Geological Survey’s topographic map of the Monument, listed above as item 2. Geologic data—the boundaries of the Weber sand- stone and the Morgan formation, the strike—and-dip symbols, and the positions of the Yampa, Red Rock, and Mitten Park faults—are taken wholly from the map forming plate 2 in the report by G. E. and B. R. Untermann listed above as item 3. Though transfer .of these data was done as carefully as possible, me- chanical difficulties doubtless caused some departures from absolute precision, especially in the true altitude of formation boundaries on steep slopes where con— tour lines are very crowded. However, I believe that YAMPA CANYON, UINTA MOUNTAINS, COLORADO these departures are too slight to cause any injustice to the authors of the original map; certainly they are without significance to the problems herein discussed. ACKNOWLEDGMENTS Special obligation and gratitude are felt to Mr. and Mrs. G. Ernest Untermann of Vernal, Utah, for their generous permission to use freely the data in their report on Dinosaur National Monument and for many courtesies and helpful information given later, both in person and through correspondence. The National Park Service, through Mr. Jess H. Lombard, Superintendent, Dinosaur National Monu- ment, kindly loaned negatives and authorized use of several photographs as illustrations. Mr. Byrl D. Carey, Jr., and The California Co. furnished valued data on the thickness of the Browns Park formation obtained through drilling. Dr. Arthur D. How rd, Stanford University, helped me with several discussions on special problems of geo- morphology. To Mr. John M. Good, geologist for the National Park Service, thanks are due for information given by correspondence and during our visit to the Uinta Mountains in the spring of 1959. Finally, I am grateful to Wilmot H. Bradley, Doug- las M. Kinney, and Wallace R. Hansen, of the US. Geoogical Survey, who shared with me their knowl- edge and varied interpretations of Uinta Mountain geology. OBSERVED FEATURES The Yampa River, which rises in the Park Range, was described by Hancock (1915, p. 184), who then fully analyzed the development of its middle course across the Axial Basin anticline and Juniper and Cross Mountains by superposition from the Browns Park formation. The present report deals primarily with that part of the river downstream from Hancock’s area. YAMPA CANYON AS A WHOLE STATISTICAL DETAILS Yampa Canyon begins at point A (see pl. 1) where the river, after crossing the low ground at the mouths of the Vale of Tears and of Disappointment Creek, cuts into southeastward-dipping Weber sandstone. This is about 0.7 mile upstream from (southeast of) the point where the river crosses the eastern bound- ary of Dinosaur National Monument. The canyon ends at the mouth of Yampa River (point D), where it joins Green River just east of Steamboat Rock. 6185510—62—2 I—5 From the upper end of the canyon to its mouth the airline distance, in a direction N. 78° W., is about 241/3 miles; but because of the meandering course the distance by river is nearly twice as great, or about 45% miles.1 At the upper and lower ends of the canyon (points A and D) the altitudes of the river surface are re- spectively about 5,589 and 5,064 feet; the river thus falls 525 feet within the canyon, an overall average of more than 11.6 feet per mile. The maximum depth of canyon noted is about 1,715 feet; this is at a point opposite Warm Springs Draw, 4 miles upstream from Green River, where the Yampa surface is at 5,085 feet and the top of Warm Springs Clifl' on the south side (less than 200 yards horizon- tally away from the river) is at about 6,800 feet. RELATION TO YAMPA FAULT AND OTHER FAULTS YAMPA FAULT Crudely paralleling Yampa Canyon, but south of Yampa River at all points, is the Yampa fault. The Untermanns (1954, p. 151—152) describe it as the larg— est fault in Dinosaur National Monument, of the nor— mal type with its fault plane dipping to the north at angles of 50° to 75°. They add, “East of Johnson Draw, at the foot of Tanks Peak, Precambrian (Uinta Mountain group) occurs against lower Triassic (Moen- kopi), producing a vertical displacement of between 3,600 and 4,000 feet, maximum for faults of the Mon- ument area.” The geographic and geologic relations of the Yampa fault to the ancient and present courses of Yampa River had a significant bearing on the views devel- oped by Bradley, Gilluly, and me, and presented (Sears, 1924a) as a part of our general concept. Those relations, now known with more details and more cer- tainty than in 1922, form an essential base for the hypothesis herein presented. RED ROCK FAULT As briefly described by the Untermanns (1954, p. 152), “The Yampa fault has several branches; the largest, which the writers have called the Red Rock fault, begins at Red Rock Draw and runs in a north-_ westerly direction beyond Pool Creek where it possibly intersects the Mitten Park fault.” The downthrow side is to the northeast. From their map the Red Rock fault has been drawn on plate 1, herewith. Its junction with the main Yampa fault, the repetition of beds that it caused, and flames in miles, beginning at the mouth, and altitudes of the river surface are shown on the “Plan and Profile of Yampa River, Colorado,” from Green River to Morgan Gulch, 1924, U.S. Geol. Survey. I—6 the steep northeastward dips on both faults, due to drag, are all conspicuous on aerial photographs. MITTEN PARK FAULT As mapped by the Untermanns, the Mitten Park fault follows a generally northeastward but curving course. Downthrow is on the southeast side; where the fault crosses Green River downstream from Steam— boat Rock, the displacement as estimated by the Un~ termanns (idem, p. 154) is between 1,500 and 2,000 feet. At the north end of Steamboat Rock the beds on both sides of the fault are greatly steepened by drag. To the east, in the canyon of Green River up— stream from its junction with the Yampa, the fault appears to die out sharply and turn into a flexure whose magnitude diminishes eastward. GRABEN BETWEEN RED ROCK AND MITTEN PARK FAULTS A glance at plate 1 shows that between the Red Rock and Mitten Park faults is a graben or structur— ally depressed area with the shape of a westward- pointing triangle. This is perhaps the feature to which Powell (1876, p. 202 and pl. 5) referred as the “Echo Park sag.” This triangular graben is added upon and accentu— ates the depression effect of the major graben to which Powell (1876, p. 209) called attention with the theory that after Browns Park deposition the eastern end of the Uinta Mountain arch collapsed. Because of the concept that Bradley, Gilluly, and I formed in 1922, the collapse and the major graben were discussed at length and then summarized in the following words (Sears, 1924a, p. 291—303) : “The collapse was caused by a single large fault [the Yampa fault] on the south, by flexures and dis- tributive faulting on the north, by tilting and some faulting on the east, and by tilting on the west.” That Yampa River flows in this major graben, near and roughly parallel to its southern margin, is there— fore not a new idea. Because of the later and more detailed mapping by the Untermanns, however, I wish to emphasize that in its lower course Yampa River runs into, and joins Green River within, the added depression or triangular graben between the Red Rock and Mitten Park faults—a complicating problem to be discussed under the last heading of this report. THREE-PART DIVISION OF CANYON As mentioned in item 1 of the Introduction, the 45- mile Yampa Canyon is naturally divisible into three parts—a short upper section, and a middle and a lower section of roughly equal length. It is therefore both logical and convenient to di- vide the detailed description of the canyon under sep- arate headings for those three sections. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY UPPER SECTION OF YAMPA CANYON The upper section of the canyon, as herein desig- nated, extends from point A (pl. 1), the beginning of Yampa Canyon in sec. 20, T. 6 N., R. 99 W., down- stream about 1% miles to point B, just southwest of the high, sharp westward-jutting spur north of the river in the SE. cor. sec. 18, T. 6 N., R. 99 W. Within this section the river’s course is rather simple, form- ing an almost straight line in the upstream half and three small open meanders in the downstream half. In contrast to the longer middle and lower sections of the canyon, this short upper section is noteworthy in that the topography and geology on the two sides of the river are so nearly identical. Topographically, cross sections of the canyon are almost symmetric; small differences in the angle of slope of the two walls suggest, however, that the meanders may have been slightly enlarged during 1nc1s1on. Geologically, the upper parts of both walls and the upland behind them expose Weber sandstone, and the lower (parts of the walls expose beds of the Morgan formation. (See pl. 1; figs. 1, 2.) As the beds here strike northeastward and dip about 12° SE, the river in its general northwesterly course flows at right an- gles to the strike and against the dip, cutting strati- graphically down from the top of the Weber into the lower part of the underlying Morgan. It should be emphasized, however, that structurally the beds exposed in this upper section of the canyon represent only the lower part of a wider zone of southeastward-dipping rocks Whose stratigraphic se- quence along the river is shown by the Untermanns (1954, pl. 2) to include a dozen formations. At some point in Lily Park (perhaps near the junction of Little Snake River with the Yampa, several miles upstream from and east of Dinosaur National Monu- . 2. g $1 .; W ‘ FIGURE 1.—Entrance to Yampa Canyon; view downstream. Dip slope tis on Weber sandstone. (National Park Service photograph.) YAMPA CANYON, UINTA MOUNTAINS, COLORADO Upper part of Morgan formation; probably some Weber sandstone at top FIGURE 2.—Upper section of Yampa Canyon; view upstream. in distance. (National Park Service photograph.) ment and the east edge of the Untermanns’ map) the soft lower beds of the mile-thick Mancos shale of Cretaceous age begin the southeastward dip and north— westward rise that here mark the southeast end or nose of the Uinta Mountain arch (Sears, 1924b, pl. 35). From that point the Yampa cuts downward into successively older beds, at last reaching the Weber sandstone and the Morgan formation, whose relative hardness, thickness, and attitude have permit- ted the erosion of a deep continuous canyon. MIDDLE SECTION OF YAMPA CANYON The middle section of the canyon, as herein desig- nated, extends from point B downstream for about 19% miles to point C at the mouth of Big Joe Draw in Starvation Valley. (See pl. 1.) The altitudes of the river surface at points B and C are respectively 5,573 and 5,242 feet; thus in this section the Yampa falls 333 feet, an average of more than 16.9 feet per mile. In the vicinity of point B, the structure of the rocks in and on both sides of the canyon begins to change in a pronounced manner. From the north- eastward strike and southeastward dip that charac- terize the upper section, the strike swings rather sharply to a direction somewhat north of west (rang- ing approximately from N. 65° W. to N. 75° W.) and the dip is prevailingly 6° SW. (with an observed range of 3° to 10°). This changed structure, with these strikes and dips, extends westward to and be- yond the junction of the Yampa with the Green; I—7 southward from Yampa River, generally for 1 to 3 miles, until the Yampa fault is approached; and northward for a number of miles as a part of the south flank of the Uinta Mountain arch. The north-of-west strike just described is fairly close to the overall direction of flow of Yampa River which, as previously stated, is N. 78° W. for the air- line from point A to point D. RIVER PA'I'I‘ERN AND DIRECTION Within the middle section the course of the river is marked by large- and medium-sized meanders inter— spersed with a few almost straight stretches a mile or more in length. With a single exception, all the meanders are of the open type. The exception is the meander in sees. 22 and 27, T. 6 N., R. 100 W., which is convex southward and is about half a mile long and three-tenths of a mile wide; it is of the type called by Davis (1914, p. 23—24) “half-turn.” Be- cause this meander and its environs north of the river are exceptional in several other ways as well, they will be mentioned and discussed repeatedly; for brevity, these environs will be referred to in this re- port as the “half—turn district.” TOPOGRAPHY 0F CANYON WALLS SOUTH WALL The south wall of Yampa Canyon is very simple and uniform. Except for a few short reentrants where in- terrupted by side streams, the wall is virtually con- tinuous as a steep slope ending upward in a sheer clifl’. The height and width of the south wall in this section average roughly a quarter of a mile each. At places (particularly in sec. 20, T. 6 N., R. 100 W., and in secs. 13, 14, and 15, T. 6 N., R. 101 W.) the clifl“ at the top is complicated by very small crenulations, but as a whole it is simple. Thus the cliff and slope follow and fit into each curve of the river with noteworthy preciseness. Almost without a break, the 6,000-foot contour ex- tends along the upper part of the south wall, at vary- ing distances below its top (which ranges in altitude from about 6,300 to about 6,875 feet). The intersection between the canyon wall and the upland adjoining it is sharp and nearly at right an— gles, and shows little if any trace of rounding by ero— sion. Indeed, many knolls and larger hills on the edge of the present upland are partly sheared by the cliff. noun WALL Except for about 31/2; miles along the river in the “half-turn district,” the north wall differs radically from the south wall, particularly in being much I—8 Wider, much less steep, and of very irregular shape. Its width, in contrast to the nearly uniform quarter of a mile for the south wall, averages approximately a mile and ranges from about 34 to 11/2 miles. Only in a general way do the bends of its upper rim cor- respond to the present curves of the river. As the greater width, more moderate slope, and irregular shape of the north wall are related to what are herein designated as meander-migration scars, they will be more fully discussed under a heading dealing with those scars (p. I—9). Another feature of the north wall is of geomorpho— logic significance. Southward the moderately sloping floors of the scars are terminated by a much steeper slope down to the river, making a convexity upward. This break in slope is conspicuous on the aerial pho— tographs. However, conditions here are somewhat anomalous and puzzling. The photographs show tonal and other differences suggesting that the break in slope is related to some variation in the resistance of rock layers. (The horizon of tonal and presum- ably lithologic change is discernible also across the river; but the south wall is in general so narrow and steep that at only a few spots is there even a faint trace of any break in slope.) This apparent relation between break of slope and stratigraphic horizon seems to be borne out by two other observations: (a) around each meander the steeper slope looks to be a little wider horizontally and a little higher vertically northward updip; and (b) as a whole the steeper slope is somewhat wider horizontally and higher vertically downstream as the river falls. The rim or sheer cliff that caps the north wall has some resemblances to and some differences from the one that. caps the south wall. Along its top the low- est points, like those on the south wall, are at an alti— tude of about 6,300 feet. The highest points, how- ever, reach an altitude of about 7,250 feet, as con- ’ trasted with a maximum of 6,875 feet on the south. The north rim is less continuous, being interrupted at the north ends of the meander—migration soars (as discussed later). However, where it exists, the north rim resembles the south rim in its sharp angle of in— tersection with the upland surface behind it, and in its abrupt shearing through knolls and larger hills on that surface. TOPOGRAPHY 0F ADJOINING UPLANDS SOUTH OF CANYON The upland south of the middle section of the can- yon is rather level and smooth on its eastern half, forming areas called East Cactus Flat and West Cac- tus Flat. \ SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Farther west, the surface of this upland is much more irregular. Here and there, altitudes are a little higher near the canyon and tend to be somewhat lower within 1 or 2 miles to the south, beyond which they rise fairly steadily to the Yampa fault and Blue Mountain behind it. With this southward rise of the surface, the 7 ,000-foot contour lies at or south of the Yampa fault as mapped by the Untermanns, except for a stretch of about 11/2 miles in secs. 28 and 29, T. 6 N., R. 101 VV., north of Tanks Peak. (See pl. 1.) Because this exception, if valid, seems here to pre- sent an anomalous relation between structure and topography, the aerial photographs of this vicinity were scrutinized with extra care. These photographs give some indications that a second fault exists here parallel to and about half a mile north of the Yampa fault as mapped; and that it compares and perhaps even connects with the northern of the 2 faults 6 miles farther east. The irregular topography of the upland between Yampa Canyon and the Yampa fault is accompanied by a no less irregular drainage pattern. Most of the numerous streams (all shown as intermittent) begin on Blue Mountain and extend northward across the Yampa fault for a couple of miles. Thereafter they assemble in a few principal channels which (for no reason obvious on the topographic map, but perhaps related to the jointing in the Weber sandstone) fol- low pronounced eastward or north-of—westward courses for 2 to 5 miles until a further swing allows them to find their way to the river. To these middle courses are added a few short southward-flowing streams. Especially noteworthy are two that begin at the very edge of the upland above the canyon wall, flow south- ward and then together eastward until joining the stream in Dry Woman Canyon just before it slips down the steep south wall and into Yampa River. NORTH OF CANYON The upland north of the canyon differs tOpographi- cally from that on the south in several ways. For one thing, it is substantially higher. As already de- scribed, the south upland between the canyon and the Yampa fault (with the questionable exception of a small stretch north of Tanks Peak) is lower than 7,000 feet in altitude. In contrast, the 7,000-foot co’n- tour line north of the Yampa crudely parallels the river a couple of miles away and also surrounds many headlands and hills in the zone southward to the can- yon wall. Still higher land lies to the north, on the flank of Douglas Mountain; a short fragment of the 8,000-foot contour line is seen on the map at the head of Buck Draw, in sec. 16, T. 7 N., R. 101 W. YAMPA CANYON, UINTA MOUNTAINS, COLORADO Between the main 7 ,OOO-foot contour and the out— liers of that contour around hills and headlands to the south is a zone of somewhat lower altitudes. A number of the longer streams, which prevailingly rise on the high flank of Douglas Mountain and flow south- ward to the Yampa River, have distinct, short or long, right or left bends in their middle courses where crossing this lower zone, in a manner suggesting stream piracy. The outliers have a general cuesta form; their upper surfaces, eroded into somewhat steplike topography, show southward gentle dip slopes on several beds; whereas their northern, northwest- ern, and northeastern edges are steep slopes or es- carpments cut downward across the dip to the vale (the zone of lower altitudes described above) and face the main 7,000—f00t contour to the north, which lies on the southern dip slopes of still older beds. This feature is particularly well shown in the east-west ridge in sec. 11, T. 6 N., R. 100 W. Still farther north, the older formations below the Morgan are cut by the streams in such a way that they tend to form flatirons dipping gently southward and pointing northward. GEOLOGY Perhaps the most conspicuous and hence first-noticed feature shown on the Untermanns’ map (1954, pl. 2) is the way in which (within what is here termed “the middle section”) the south wall of Yampa Canyon serves as a formation boundary. This feature cannot be fortuitous. Not only is it one of the criteria by which the middle and lower sections of the canyon have been differentiated, but also it is intimately re- lated to the geomorphology of the river. SOUTH OF RIVER Except for a very short distance in sec. 27, T. 6 N., R. 100 W., where the top of the south wall of the canyon near the “half-turn” meander is now cut back to the Yampa fault, the upland adjoining the canyon in a belt of varying width is mapped as wholly devel- oped in the Weber sandstone, dipping about 6° a lit- tle west of south. The Untermanns (1954, p. 36) describe the Weber as a uniform, well-sorted, buff to White or gray, medium- to fine- grained quartz sandstone. * * * Most of the cementing mate- rial is calcareous although it becomes quartzitic locally. * * * The poorly cemented and highly jointed nature of the Weber accelerates its erosion, producing characteristic deep steep- walled gorges and resulting in extremely rough topography. They add that the thickness of the Weber sandstone in the eastern portion of Dinosaur National Monu- ment is 850 to 900 feet. I—9 The boundary of the Weber with the underlying Morgan formation lies almost continuously high up along the south wall of Yampa Canyon. Because of the steepness or verticality of the upper part of that wall, and because of blurring in black-and-white re— production of the Untermanns’ topographic-geologic map, it was impossible to determine at each point pre- cisely the altitude of the contact or the thickness of Weber sandstone that now remains above that contact at the edge of the upland; fortunately, however, these details are of little if any significance for the prob— lems herein discussed. From the foregoing description it follows that the lower, major part of the south wall of Yampa Can- yon throughout the middle section exposes beds of the next older Morgan formation. NORTH OF RIVER The north wall of Yampa Canyon and (again with the exception of the “half-turn district”) the belt of upland adjoining it are mapped as wholly developed in the Morgan formation, next older than and dip- ping under the Weber sandstone south of the river. According to the Untermanns (1954, p. 33—34) : The contact between the Weber and Morgan formations was placed at the base of the massive Weber sandstone and at the top of the first limestone bed below it. * * '* The sandstone beds in both formations are very similar, consisting of uni- form fine-grained quartzitic to calcareous quartz-sandstones. The upper part of the Morgan appears to be transitional into the Weber. The light buff to gray color of the Weber is char- acteristic of the upper sandstone beds of the Morgan, although both formations contain some red sandstones. * * * The upper third of the Morgan consists of thin layers or compact, often very cherty, gray limestones which weather red. They alternate with thick fine buff to terra cotta-colored sandstone beds, occasionally somewhat cross-bedded * * * which may exceed 100 feet in thickness. In their measurements for the Hells Canyon area (a few miles farther west, near the middle of what is herein termed “the lower section of Yampa Can- yon”) the Untermanns (idem, p. 160—161) give a thickness of approximately 1,200 feet for the Morgan formation. MEANDER-MIGRATION SCARS Again with the exception of the “half—turn district,” the entire north side of the middle section of Yampa Canyon from point B to point C is made up of ad- joining large scallops, each of which is partly rimmed by cliffs or very steep slopes and has a floor that de- scends with moderate slope nearly to the river. These scallops are herein referred to as meander- migration scars because they are believed to result from and record the progressive downdip (southward) I—lO migration and lowering of early meanders of Yampa River. The unqualified term “meander scar” has apparently been used but rarely in the literature, and then (whether the meanders are on flood plains or are in- cised) only with expressed or implied reference to the trace left as an oxbow after a cutoff. (For example, see Thornbury, 1954, p. 130—131.) Cotton (1949, p. 250) uses the term “meander-scar” as an adjective qualifying alternate terraces developed during side—to-side swinging of a meander belt. These meanings and applications are mentioned here to emphasize that the term “meander-migration scar” is intended to have a quite different meaning (which, though partly anticipating suggested explanations of- fered later in this paper, is indicated at this point for convenience) . The cliffs that are so conspicuous on the sides of these scars are now interrupted and absent at their upper or inner (north) ends. I find on aerial pho- tographs and on the topographic map no conclusive evidence as to whether or not the cliffs once were al- most continuous. However, I am disposed to think that they were (though probably low at their upper ends); and that later their northern parts were dis- sected and obliterated by the streams which, rising on the flanks of Douglas Mountain, flowed southward farther and farther to join the migrating river. As far as I know, these meander-migration scars, all on the north side of Yampa River, have not hith- erto been observed or at least have not been men- tioned in a published statement. Indeed, rather wide reading, search of maps, and conversations have not brought to my attention any good example of such an extensive feature elsewhere or any clear and specific description of the feature or of the process by which it evolved. As the meander—migration scars in the middle sec- tion of Yampa Canyon differ from each other some- what in size, shape, and other ways, they are separately but briefly described below. ANDERSON HOLE SCAR The Anderson Hole (first) scar begins at point B, which has been selected as marking the boundary be- tween the upper and middle sections of the canyon. On the east the scar adjoins the upland lying north of the upper section, where the beds dip toward the southeast. On the west it adjoins the “half-turn district,” where the upland includes a substantial outcrop of Weber sandstone—the only remnant of that formation north of the middle section. This scar, with its rimming cliffs and low inner floor, forms a protected hollow that is known as Anderson Hole. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY The conspicuous cliffs that face each other on the east and west sides of the scar are almost 2 miles apart near the river and almost 11/2 miles apart at their present north ends. In this instance the south ends of both cliffs are very close to the river. North- ward the tops of the cliffs rise in altitude, whereas the cliffs themselves become lower and gradually turn into steep slopes. (The northward—facing steep slopes east of point M and west of point N on plate 1 are be- lieved not to be part of the scar rim described above, but to be a product of the later cuesta development discussed on page 1—9.) I picture these rimming cliffs or steep slopes as once extending farther and con— necting in a gentle curve that formed the low north rim of the scar, later worn down and obliterated by the streams that now cross its site. (Admittedly, however, the former existence of such north rim, as well as its location, height, and degree of continuity, seem to be questions for deduction and not susceptible of proof. As a collateral question: if such a north rim existed when a meander of the river was at that altitude and position, were there then three tributaries flowing into that meander, and were those tributaries extended as the meander migrated southward down the dip? or did the tributaries begin at some later stage? I would lean to the first alternative.) The floor of the scar, between the east and west cliffs and the hypothetical north rim, now has con- siderable relief through dissection by present streams, but overall it has a moderate slope southward nearly to the river, dropping some 1,100 feet in about 11/2 miles. An interesting feature, discernible on the topo- graphic map but more conspicuous on aerial photo— graphs, is a low concentric supplementary rim and part of a second, in the middle of the scar. Only partial traces of similar supplementary rims are de- tectable in any of the other scars. TEPEE HOLE SCAR The Tepee Hole (second) scar, whose floor forms what is called Tepee Hole, is sufliciently like the Anderson Hole scar that most of the same description would apply. The chief differences are as follows: (a) The east cliff (rather than the west) adjoins the “half-turn district”; and the south end of this east cliff is close to the river. (b) The south end of the west cliff is nearly half a mile from the river. (0) Between the west clifl' of the Tepee Hole scar and the east cliff of ‘the Browns Hole scar is an upland that terminates in a spectacular southward-pointing sharp- ened spur. (See fig. 3.) (d) The position of the hypothetical north rim is less clear than that in the Anderson Hole scar; for it depends on whether YAMPA CANYON, UINTA MOUNTAINS, COLORADO “,3, p. e ‘” FIGURE 3.——Sharpened spur between Tepee Hole (second) and Browns Hole (third) scars. View northward across canyon. West Cactus Flat and Hay-tack Rock in foreground. the east cliff should be considered to reach point Q (pl. 1) or whether the part northeast of point P is instead the product of, or has been modified by, the later cuesta development discussed on page 1—9. BROWNS HOLE BOAR Browns Hole is the name given to the sloping floor of the third scar. In many ways this scar resembles the two farther up the river, but it differs from them in other ways that are of interest and significance. For one thing, in horizontal plan the scallop is much shallower—that is, its north-south distance is much shorter than that from east to west. Even more sig- nificant, its rimming cliff is much more continuous and complete, being broken only at its northern curve by the gorge (about 1,500 feet wide) through which flows this stream that drains Browns Draw and on its north- west side by an even narrower gorge through which flows the unnamed stream, one of whose upper branches drains Iron Mine Basin. The greater con— tinuity and the curve of this clifi' seem to me to illus- trate and support the concept, discussed above, that the Anderson Hole and Tepee Hole scars also once had north rims. The stream that cuts through the cliff on the north- west side is itself unusual; for of all the streams that interrupt the side cliffs in all five scars, it is the only one that flows for any considerable distance on the upland before reaching the clifl’. However, its un- usual length was perhaps not original but caused by piracy; this is suggested by the sharp bend 0f the stream (elbow of capture?) about 1 mile northwest of the gorge and by the lowness of the divide between that bend and the west fork of Browns Draw. I—11 BOWER DRAW SCAR The Bower Draw (fourth) scar (which may be identified by the name of the principal channel, Bower Draw, that crosses it) is much less distinct. Indeed, its size and shape are such that its nature might have gone unsuspected had not the other scars been noticed and analyzed. Perhaps it might more logically be divided into 3 merging scars—2 short and very shal- low ones at the east and a larger one up Bower Draw at the west; but this would seem to be an undesirable complication. The general continuity of its clifl", the moderate slope of its floor toward the river, and the approximate accordance of its cliff pattern with the present curves of the river—all together appear to me to be ample evidence that it too was formed by the lateral downdip migration of meanders. I think that the difference was caused by the greater straightness and lack of large meanders in the early as well as the present course of the river through most of this stretch. FIVE SPRINGS DRAW SCAR The Five Springs Draw (fifth) scar (identifiable by Five Springs Draw, which crosses it) is the last scar in this section of the canyon. The southwest end of its northwest clifl' is close to the river near point C, which has been selected as marking the boundary be- tween the middle and lower sections of the canyon. The Five Springs Draw scar is much like the An- derson Hole and the Tepee Hole scars, and therefore will not be described in detail. However, it may be well to emphasize that the aerial photographs of the Five Springs Draw scar as well as those of the Bower Draw scar show clearly the break in slope and upward convexity near the river, as discussed on page 1—8 under “North wall.” “HALF-TURN DISTRICT—AN EXCEPTION At several places, mention. has been made of ways in which the “half-turn district” differs sharply from the rest of the north side of the middle section. As these differences are thought to be very significant, for convenience they are assembled and repeated here in a single place, as follo11s: (a) The “half— turn” mean— der contrasts with the “open” type of meander and the almost straight stretches seen elsewhere through- out the middle section. Furthermore, at the “half- turn” meander the narrow upland spur projecting into it shows clearly a slipofl' slope at its south end and on its west (downstream) side. (b) Around the “half- turn” meander, and upstream and downstream from it, for a total river distance of about 31/2 miles, the north wall of the canyon is very narrow and steep. (c) The “half-turn district” forms the only interruption to an otherwise continuous series of adjoining scallops I—12 (meander-migration scars) on the north side of the river. ((1) The upland in the “half-turn district” in- cludes a substantial outcrop of Weber sandstone—the only remnant of that formation north of the river in the middle section. L Taken together, these marked differences cannot plausibly be explained as due to coincidence. The “half-turn district” not only is exceptional in the mid- dle section; it also shows conditions closely resem~ bling those predominant in the lower section of the canyon, to which it is presumably related. Hence the lower section will next be described, before the “half- turn district” is further discussed. LOWER SECTION OF YAMPA CANYON As herein designated, the lower section of the can- yon extends from point C (pl. 1), at the mouth of Big Joe Draw and of Starvation Valley, downstream for about 23% miles to point D, where the Yampa joins the Green east of Steamboat Rock._ The river surface has an altitude of 5,240 feet at point C and of 5,064 feet at point D. Thus in the lower section the river falls 176 feet, an average of nearly 7.4 feet per mile, which is less than half of the gradient of 16.9 feet per mile in the middle section. As previously stated, the lower section differs mark- edly from the middle section in a number of ways, which will be discussed in detail in the pages that follow. V RIVER PATTERN AND DIRECTION It will be recalled that in the middle section, ex— cept within the “half-turn district,” Yampa River fol- lows a course of open meanders interspersed with a few almost straight stretches. The average direction of that part of the river is N. 82° W., which is close to the regional strike of the rocks. The lower section of the canyon differs notably from the middle section in its river pattern. First, near point C the river turns in a general southwesterly di- rection to the lower end of Bull Park (an airline dis- tance of about 21/; miles), before resuming its overall northwestward course to its junction with Green River at point D (pl. 1). Second, and more striking, the river’s course is much more intricate and meandering; upland spurs alternate on the two sides of the river, and many of the meanders are so curved and inter— locking as to be of the type called by Davis (1914, p. 23—24) “dove-tail.” TOPOGRAPHY OF CANYON WALLS In a general way the two walls of the canyon in the lower section resemble each other. But during their SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY incision the meanders were not cut straight down- ward, for most cross sections of the canyon are asym- metric. Evidently lateral erosion and lateral move— ment of meanders have taken place, for in general the projecting ends and downstream sides of the spurs show slipoff slopes, whereas the upstream sides of the spurs and the walls on the outer side of meander curves show very steep slopes or even undercut and overhanging cliffs. (See figs. 4, 5.) Furthermore, meanders have become much more rounded during in- cision. However, the meander belt is still quite nar- row and curving, the slipoff slopes occupy only parts of their respective spurs, and the bottom of the can- yon is still very narrow and without conspicuous flood- plain scrolls. On a number of the interlocking spurs (such as the eight small spurs just downstream from Harding Hole and the several spurs just upstream from Warm Springs) the slipoff slopes are seen on the aerial pho- A tographs to be interrupted part way down by crude “treads” of somewhat less slope. The so-called parks and holes (Bull, Harding, Burro, and Castle) in this section of the canyon are merely small, mostly steep floored, open spaces near the river, and are not comparable to Anderson, Tepee, and Browns Holes in the first, second, and third meander- migration scars of the middle section. The depth of the canyon in the lower section, as measured from the river surface to the top of the cliff on the south side, differs through a Wide range. As already described, the greatest depth observed is FIGURE 4.—“Tiger Wall," an overhanging cliff of Weber sandstone in lower section of Yampa Canyon. graph.) (National Park Service photo- YAMPA CANYON, UINTA MOUNTAINS, COLORADO 1—13 FIGURE 5.-—\Lower section of Yampa Canyon. Intricate meander: in Weber sandstone. View northward near Harding Hole. (National Park Service photograph.) - about 1,715 feet, at Warm Springs Clifi', 4 miles up- stream from Green River. This clifl' appears to ex- pose the upper two-thirds of the Morgan formation, the full thickness of the Weber sandstone, and a few feet of the Park City formation that caps it. The least depth noted (excluding the small reentrants at the mouths of side streams) is 235 feet near the west end of Castle Park. Here, because of the southwest- ward dip of the beds and the large southward mean- der of the river, the south wall exposes only the upper part of the Weber sandstone just below its top. TOPOGRAPHY OF ADJOINING UPLANDS SOUTH OF CANYON The small area of upland from Schoonover Pasture across Johnson Canyon to East and West Serviceberry Draws is merely the western tip of the upland south of the middle section of the canyon, the topography of which has already been fully described. The upland west and northwest of East and West Serviceberry Draws has its own characteristic topog- raphy. In general the upper beds of the Weber sand- stone are exposed only in a narrow, irregular belt at the edge of the upland along the canyon; this belt is augmented here and there by exposures of the Weber up theside streams. Much of the upland is veneered by the overlying Park City formation, which at a number of places approaches, or even is the very top of, the canyon wall and extends southward and south- westward for distances up to a couple of miles. The Park City forms a resistant dip slope, the surface of which is rather smooth but, especially toward the west, is marked by a great number of very shallow chan- nels and a few slightly larger ones draining south- westward down the dip. At or near the bottom of this dip slope these channels gather into larger chan- 618551 0—62——3 nels extending northwestward or southeastward ap- proximately along the boundary between the Park City and the next younger Moenkopi formation. In turn these larger channels empty into the few major streams (in Hells, Red Rock, and Sand Canyons) that suc- ceed in flowing against the dip and joining Yampa River. (This topography and stream pattern are well shown on the topographic map and even better on the aerial photographs for the upland on the two sides of Sand Canyon.) It is interesting to note that between the combined Serviceberry Draw and point D, a river distance of nearly 20 miles, only 7 streams enter the south side of the Yampa—the 3 named above, and 4 others too small to be named on the topographic map. - NORTH or canyon Beginning near the river about half a mile down- stream from point C, a high ridge extends northwest- ward to the east edge of the Warm Springs (sixth) scar, approximately parallel to and about half a mile southwest of Starvation Valley and the upper part of Warm Springs Draw. For most of its length the top of this ridge is higher than 7,000 feet; the highest point noted is marked “7365” on the topographic map. West of the Warm Springs scar the ridge resumes (though with a maximum altitude marked “6962”) and extends westward for 1 mile to the edge of Lodore Canyon of Green River. This ridge serves as a drainage divide, for it is not crossed by any of the streams that come from the high country still farther north. On the contrary, all those streams are deflected southeastward or north— westward along its northeastern base and together find a passage to Yampa River or the Green, or join Warm Springs and Iron Mine Draws, which extend down the Warm Springs scar. 1—14 The many streams that originate on the southwest- ern flank of the ridge extend southward and south- westward, down the dip, across a belt which, because of the river’s sinuous course, ranges in width from 1/2 t0 3 miles. The topography in this belt has been jus- tifiably called by the Untermanns and others “fantas— tic.” (See fig. 5.) Erosion in the poorly cemented and highly jointed Weber sandstone has produced a bewildering maze of sharp, narrow gorges. Most of these gorges begin at the ridge in deep, rounded or pointed amphitheaters; descend steeply, at places over hard ledges; and some finally drop abruptly to the river over dry “waterfalls” many feet in height. A few patches of the thin overlying Park City for- mation are found at high spots on the ridge and in the belt south of it. From its beginning near the river, northwestward for a distance of about 2 miles, the ridge is generally sharp crested and its northeastern flank is conspicu- ously crenulated. Farther northwest, the northeastern flank is much smoother. The boundary between the Weber sandstone and the underlying Morgan formation follows very closely the base of the northeastern flank of the ridge and the adjoining southeastward- and northwestward-flowing streams described above. Still farther away from Yampa River, in the Mor- gan and older formations, the topography is similar to that in the lower part of the Morgan and beds be- low it north of the middle section of the canyon, with many flatirons rising and pointing toward the north. GEOLOGY The most conspicuous and significant difference in geology between the middle and lower sections of Yampa Canyon is that, whereas in the middle section the boundary between the Weber sandstone and the underlying Morgan formation lies almost continuously high up along the south wall of the canyon, in the lower section that boundary lies predominantly at a substantial distance north of the river. As already described, near point C Yampa River turns in an overall southwesterly direction to Bull Park, several miles away. This direction is down the dip, but as the gradient of the river is much less than the angle (6°) of dip, the amount of the Morgan for— mation exposed in the canyon dwindles rapidly down— stream and ceases just below the mouth of Johnson Canyon. If this dwindling wedge of exposed beds of the Morgan is ignored, we may consider that near point C the VVeber-Morgan boundary crosses from the south wall to the north side of Yampa River. Thence it extends northwestward up the floor of Starvation SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Valley and on to Lodore Canyon of Green River in a general course that is interrupted only at the Warm Springs scar, where the Morgan formation is again exposed southward to Yampa River. Stated in a more summary way: the middle section of Yampa Canyon is eroded chiefly in the Morgan ' formation; the lower section, chiefly in the Weber sandstone. Brief descriptions of the Weber and the Morgan, quoted from the Untermanns’ report, are given on page 1—9. It seems desirable to add here only the comment that on aerial photographs the jointing in the Weber sandstone, with a principal direction es- sentially that of the strike, is generally much more conspicuous in the lower section than in the middle and upper sections of the canyon. As already indicated, a veneer of the thin Park City formation, lying above the Weber sandstone, holds up a fairly extensive dip slope south of the river and remains in a few patches north of the river in the lower section. According to the Untermanns (1954, p. 38), the Park City consists of “light gray to yel- low, frequently silty or cherty, calcareous shale * * *. Gray thinly bedded cherty fossiliferous limestone and calcareous sandstone occur in the lower portion * * *. [In] the vicinity of Dinosaur National Monument headquarters, [the Park City] is only about 50 feet thick.” WARM SPRINGS SCAR—AN EXCEPTION Just as the “half-turn district” is an exception to the topographic and geologic conditions that prevail in the middle section of Yampa Canyon, so the Warm Springs scar (see fig. 6) is an exception to the topo- graphic and geologic conditions that predominate in the lower section. The Warm Springs scar also is on the north side of the river. In size, shape, and degree of preservation, it somewhat more closely resembles the first and sec- ond scars than the other three. However, its south- ward-sloping floor is smoother, and the two streams that flow down it to the river—in Iron Mines and Warm Springs Draws—run in very shallow channels. Like the five scars in the middle section, the Warm Springs scar is eroded in the Morgan formation, which it exposes southward to the river (and, still farther downdip, in the bottom of the canyon for several miles both upstream and downstream). Perhaps the most noteworthy difference between this scar and the other five is that both the east and west rims of the Warm Springs scar, in their southern half, include a substan- tial thickness of Weber sandstone above the Morgan formation. YAMPA CANYON, UINTA MOUNTAINS, COLORADO 1—15 FIGURE 6.—Warm Springs (sixth) scar on north side‘of lower section of Yampa Canyon. (Aerial photograph for Soil Conserv. Service, U.S. - Dept. Agriculture, by Fairchild Aerial Surveys, Inc., 1938.) SUGGESTED EXPLANATION OF THE FEATURES CONCEPTS OF 1922—23 As the result of fieldwork in 1922 and of office re- search and discussions during the following winter, W. H. Bradley, James Gilluly, and I reached certain concepts about the origin and development of the Yampa and Green Rivers in their anomalous course and spectacular canyons (Sears, 1924a). In our reading we had found particular significance in Powell’s conclusion (1876, p. 201, 209) that [chiefly] after the deposition of the Browns Park beds the eastern part ofthe Uinta Mountain arch collapsed to form a great graben; and in Hancock’s summation (1915) of earlier conflicting Views and of his reasons for believing that the middle part of Yampa River had established its course by superposition from the Browns Park formation. 1—16 Inasmuch as my present suggestions to explain the features of Yampa Canyon in the Uinta Mountains are basically in accord with our concept of 1922—23 about Yampa River, for convenience the pertinent parts of our “Summary of geologic history” (Sears, 1924a, p. 301—304) are quoted in the next five para- graphs. . \ _ * * * At some time after the close of Eocene deposition the Uinta Mountain arch was further uplifted. * * * the axis of the Uinta Mountain arch was continued far southeastward as the Axial Basin anticline. * * * At this time or possibly a little later the Axial Basin anticline was further deformed by the sharp domes of Cross and Juniper Mountains. A long period of quiescence followed, during which the east- ern Uinta region was eroded to mature topography. Moun- tains and ridges were comparatively low and the total relief probably did not exceed 3,000 feet. Strata on the southern flank of the Uinta Mountain arch were beveled * * *. Climatic changes or, more probably, regional uplift caused a rejuvenation of the streams, which began a vigorous attack on the red quartzite core of the Uintas. * * * There resulted a great outpouring of red quartzite boulders, which were laid down as conglomerate eastward to Little Snake River * * *. On the south flank of the arch the hollows were filled and the beveled surfaces were partly covered. As time went on, streams lost some of their carrying power and brought white sand derived from the quartzite. Browns Park became filled with a great thickness of this sand, which spread up the val— ley by headward overlap beyond the earlier deposits of con- glomerate. Overlap also gradually covered the slopes of the hills and mountains eastward to and including Cross and Juniper Mountains, until in all the, eastern part of the Uinta Range only the highest remnants of the older rocks pro- truded above the cover of white sand. * * * In Browns Park time, * * * tilting on the south side of Cold Spring Mountain served as the forerunner of a new type of movement, and after deposition was complete the east- ern end of the Uinta Mountain arch collapsed, forming a great graben. The collapse was caused by a single large fault on the south [the Yampa fault], by flexures and distributive faulting on the north, by tilting and some faulting on the east, and by tilting 0n the west. Along the margins of the graben the Browns Park formation was given an inward dip by upward drag on the faults. As far east as Cedar Moun- tain, the Browns Park formation was tilted westward toward the drag syncline which lies just ‘north of the Yampa fault. Guided by this sloping surface and this syncline, the drainage of the Axial Basin anticline naturally formed a westward- flowing major stream—Yampa River. Its course over the covered portions of Cross and Juniper Mountains was acci- dental. ill it it at it With the courses of the rivers once firmly established in the Browns Park beds, only time was needed to lower their chan— nels and carve out their‘wonderful canyons. Although it relates to an area east of the Uinta Mountains and does not have an immediate bearing on the origin of Yampa Canyon, a part of one asser- tion quoted above now seems to me incorrect: “As far east as Cedar Mountain, the Browns Park formation . formation derived from the Uinta Mountains. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY was tilted westward * * *.” In 1923, no deposits spe- cifically identified as belonging to the Browns Park formation were known east of Cedar Mountain or to the north and south of the area affected by the graben movement. Despite a marked change in the lithology of the basal conglomerate of the Browns Park forma- tion east of Little Snake River (Sears, 1924b, p. 295), the generally uniform nature of the main sandstone body and the continuity of outcrops led us to infer that the whole formation had been derived from the Uinta Mountains (except the tuffaceous component, which came from unknown volcanic vents elsewhere) and that it had reached Cedar Mountain down east- ward-flowing drainage. As the lowest part of the Browns Park formation is now at an altitude roughly a thousand feet higher at Cedar Mountain than at the junction of the Little Snake and Yampa Rivers, a later reversal of the slope by westward tilting seemed a logical view. Since then, however, the Browns Park formation has been mapped at many places to the north and much farther northeastward, beyond Saratoga, Wyo., crossing the Continental Di- vide at present altitudes of more than 8,000 feet. If that identification is correct, much of the Browns Park formation probably had its source in and near the present Continental Divide; and a part of its mate- rial was moved southwestward past Cedar Mountain until, in a zone somewhere near the Little Snake River, it met and mingled with the part of the Browns Park On that basis I am now inclined to postulate: (a) that when the upper part of Yampa River established its course on the Browns Park formation it flowed on a surface already sloping to the southwest; (b) that the graben effect near and southwest of Cedar Moun- tain, although enough to cause the Browns Park for- mation to haVe a general synclinal attitudeabove the Axial Basin anticline, was weaker than farther west; and (c) that only westward from the approximate vicinity of Cross Mountain where the graben move- ment was more pronounced, “the Browns Park for- mation was tilted westward toward the drag syncline which lies just north of the Yampa fault.” OBIGINAL EXTENT AND THICKNESS 0F BROWNS PARK FORMATION Our concept of 1922—23 and mine of today both re- quire that at one time the site of the present Yampa Canyon (including its meander-migration scars) was buried at an unknown altitude and to an unknown thickness by deposits of the Browns Park formation. Until discoveries by the Untermanns in the late summer of 1959, this picture of former presence and YAMPA CANYON, UINTA MOUNTAINS, COLORADO burial had been only a deduction. Before then, so far as I am aware, no Browns Park material was known within this specific area. During our recon- naissance in the spring of 1959 (see p. 1—4) a day’s careful but unsuccessful search was made on \Vest and _ East Cactus Flats on the south side of the river, where possible remnants had been suspected from aerial pho- tographs. Nevertheless, I felt confident that Browns Park material once covered this specific area. Such former cover seemed a necessary factor in a logical explanation of the course of the river and the evolu— tion of its canyon. Other reasons, based on observa- tions in surrounding areas, pointed more concretely to the former extension and presence of Browns Park deposits in the area'here discussed. Corroborating evidence from thevUntermanns (writ— ten communication, Sept. 21, 1959) of the presence of Browns Park in this area was most welcome. Dur- ing a further visit they discovered at four places within the graben, between Yampa River and the main Yampa fault, substantial outcrops of material of Browns Park lithology like that which we had seen at many places nearby during our reconnaissance in the spring of 1959. AREA OF MAXIMUM THICKNESS In 1922 we felt that the Browns Park formation in and near the Uinta Mountains had its maximum origi-‘ nal thickness approximately in the area comprising the southeastern half of Browns Park (beginning near the junction of Vermilion Creek with Green River) and its extension southeastward to Little Snake River. Although not fully proved, that feeling has been strengthened by later evidence. The old and the newer data bearing on the place of greatest original thickness include the following points: 1. Southeast of Vermilion Creek in T. 9 N., R. 101 W., we calculated that about 1,200 feet of the Browns Park formation now remains, including several hundred feet of basal conglomerate mostly of red quartzite boulders. 2. Carey (1955, p. 48) later mentioned our figure, but added: “* * * a thickness in excess of this esti— mate has been penetrated in drilling within the Uinta Mountain graben. The estimate by Powell (1876, p. 40) of 1,800 feet for the total thickness of the formation appears to be fairly representa- tive for northwestern Colorado.” I have since learned from The California Company (written communication, March 1959) that the drilling mentioned by Carey referred to a hole in the northeastern part of T. 8 N., R. 100 W., which I—17 passed through about 1,550 feet of the Browns Park formation, including its basal conglomerate. 3. The present altitude of the lowest beds of the Browns Park formation exposed at, river level along Green River at the mouth of Vermilion Creek is about 5,350 feet. For some 20 miles southeastward from that point the present sur- face of the formation rises to the drainage di— vide between the Green and Little Snake Rivers. The present divide is at an average altitude of about 6,680 feet; but this divide and the surface of the Browns Park formation that holds it up rise southwestward to the contact (and apparent Overlap) of that formation against the Uinta Mountain group in Douglas Mountain (about 21/2 miles east of Smelter Ranch) where the pres- ent altitude is more than 7,000 feet (see fig. 7 ). If small‘ structural irregularities and possible faults in the Browns Park formation between the southwest end of this divide and Green River are ignored and essential horizontality of bedding is . assumed—an assumption that appears fairly rea— sonable—then the difference in present altitudes points to a maximum thickness of some 1,700 feet for the Browns Park formation now remain— ing. BROWNS PARK FORMATION IN LILY PARK The continuous exposures of the Browns Park, de- scribed above, extend across Little Snake River and far to the east nearly to Craig. They also wrap around Lone Mountain and, west of the Little Snake, extend southward in Lin Park to the SE. cor. sec. 13, T. 6 N., R. 99 W., within a mile of Yampa River (see fig. 7). The latter extension of Browns Park material (with a 100-foot basal conglomerate of gray limestone and red— dish quartzite fragments lying on the truncated edges of Older beds) rises westward high up the southeast— ward-dipping nose of the Uinta Mountain arch, reach- ing a present altitude of more than 7,000 feet at a point northeast of the upper part of Sawmill Canyon. POSSIBLE BROWNS PARK MATERIAL 0N DOUGLAS MOUNTAIN As the divides between the northward- and south- eastward-flowing streams on the eastern part of Doug- las Mountain stand at present altitudes of less than 7,200 feet (some less than 7,000 feet), the Browns Park formation is envisioned as formerly continuous across the lower parts of Douglas Mountain, even though higher hills and interstream ridges remainedunburied. This picture is supported by our unmapped Observa- tions in the spring of 1959 (see p. 1—4) that at several 1—18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY \l 8 Q 7“ m BLUE 6V MOUNTAIN UTAH _____,.___' COLORADO T. 5 N. 1 o (i) ? MILES E u )o‘o DATUM IS MEAN SEA LEVEL w l I LLM l I R103 W. R.102 W. R.101W. R,IOO W. R99 W. R498 W. Topographic contours and drainage from Geology by J. D. Sears, (3. E. Untermann. Army Map Serwce 1250.000 sheet and B. R. Untermann EXPLANATION S E U _ _ _ 7000 E < D ——— 5500 --—— § I: Fault Topographic contour lines 5 Browns Park formation 0: Dashed where approximately located. U, upthrown E side; D, downthroum side Contact A —1——_ Upstream end of Yampa Canyon Axis of Uinta Mountain arch FIGURE 7.—Map of the eastern Ulnta Mountains and vicinity, showing part of the Browns Park formation. places along drainage lines high on Douglas Mountain outcrops of white tuffaceous sandstone lithologically resembled the identified Browns Park. BROWNS PARK FORMATION NEAR ELK SPRINGS The Browns Park formation, continuously exposed from Little Snake River toward Craig, also extends southward across Yampa River upstream from Cross Mountain, thence southward and westward around that mountain, and toward the upper part of Disappoint- ment Creek. (See fig. 7.) Near Elk Springs the out- crops near their southern edge show the topographic and structural form of a partial shallow bowl, slop- ing northward; and the basal conglomerate, here largely composed of gray limestone boulders, makes a low but fairly conspicuous ridge. (This bowl- shaped structure is interpreted as being caused by a northward sinking into the graben, which, however, is much less pronounced here than farther west be- YAMPA CANYON, UINTA MOUNTAINS, COLORADO cause the Yampa fault, near Disappointment Creek, turns into a flexure decreasing in magnitude south- eastward.) From Elk Springs the formation con- tinues westward, but less and less of the upper sand- stone is preserved; finally, as Disappointment Creek is approached, only the basal conglomerate remains as a capping of isolated hills. NEARNESS 0F BROWNS PARK FORMATION T0 EAST END OF YAMPA CANYON Special attention is here called to the fact that, if a straight line is drawn between the westernmost ends of the mapped outcrops of known Browns Park for- mation in Ts. 5 and 6 N., R. 99 W., on the two sides of the river, that line will cross Yampa River just a short distance above point A, where the canyon begins. Thus, known Browns Park deposits are preserved next to, and point toward, “the site of the present Yampa Canyon” as herein defined. POSSIBLE BROWNS PARK MATERIAL ON BLUE MOUNTAIN Farther southwest (and farther away from the Yampa fault and the river) at several low places in the eastern part of Blue Mountain we found, in the spring of 1959, outcrops of white tufl'aceous sand- stone, which, like the outcrops on Douglas Mountain, closely resemble the material in the Browns Park formation. POSSIBLE BROWNS PARK MATERIAL ON HARPERS CORNER In discussing the Bishop conglomerate, Powell (1876, p. 169—170) stated: “On the south side of the Uinta Mountains a fragment is found west of Echo Park resting on Carboniferous beds.” This outcrop of conglomerate was also shown on Powell’s geologic map; its areal extent was exaggerated in a northwest— southeast direction, but its location was unquestionably the northeastern, narrow part of the ridge now known as Harpers Corner. In the autumn of 1958 I was told indirectly that John M. Good, geologist for the Na- tional Park Service, reported material similar to the Browns Park on Harpers Corner at a present altitude of more than 7,000 feet. During our reconnaissance in the spring Of 1959 (See p. I—4) the six of us spent half a day examining the Harpers Corner ridge. For at least 1 mile at its northeastern end the narrow crest of the ridge is strewn with rounded cobbles and sub- angular fragments mostly of reddish quartzite. TO- ward the southwest, where the ridge widens, the con- glomerate becomes prevailingly of gray limestone cobbles. This seems to pass southwestward under grayish-white tufi’aceous sandstone, in part bedded. This sandstone, apparently on the upthrown northwest I-19 side of the Mitten Park fault, was seen at a present altitude of about 7,550 feet (according to Good) near the junction of the Harpers Corner and Iron Springs roads in the NW. cor. sec. 15, T. 4 S., R. 25 E. In lithologic appearance it is like much of the type—area Browns Park material; we agreed that in all prob— ability it is part. of the Browns Park formation and that the conglomerate is its basal conglomerate—such as is seen, for example, near Vermilion Creek. POSSIBLE BROWNS PARK MATERIAL WEST OF LODORE CANYON The Untermanns (1954, p. 180) record the follow— ing occurrences: The writers have observed a small deposit of white chalky sandstone resembling the Browns Park formation on Diamond Mountain, south of the Pot Creek area and west of Lodore Canyon, in the vicinity of Diamond Springs, at an elevation of 7500 feet. In addition to this exposure, other remnants lithologically similar to the Browns Park have been observed along Pot Creek and on Wild Mountain by J. L. Kay (personal communication). These deposits have not been carefully studied and their significance is not yet fully understood. In a statement which includes references to the afore- said occurrences or to others apparently similar nearby, Kinney (1955, p. 115—116) independently wrote: On Pole Mountain, Mosby Mountain, and Lake Mountain, the lower bed of the Bishop is a characteristic basal conglomer- ate, 25 to 40 feet thick, composed of well-rounded boulders of limestone, chert, and sandstone in a matrix of medium- to coarse-grained sand. Overlying this basal conglomerate is a chalky-white tuifaceous sandstone, 25 to 100 feet thick, which, in turn is overlain by light-tan to buff conglomerate with a sand matrix. * * * in the escarpment formed by equivalent beds on Diamond Mountain, the conglomerate appears as streaks or thin beds, and medium-grained, partly tuffaceous, light-gray sandstone comprises most of the formation. * * * As mapped along the south flank of the Uinta Mountains, the Bishop conglomerate grades eastward from very coarse- grained quartzitic conglomerate t0 medium-grained tuffaceous sandstone with lenses and thin beds of boulders. At inter- mediate positions, and near the base of the formation, beds of chalky-white tuffaceous sandstone are found interbedded with conglomerate, thus suggesting an interflngering of fa- cies. The tuffaceous sandstone superficially resembles the Browns Park formation of northwestern Colorado. These occurrences, with a basal conglomerate (here- tofore identified as Bishop) intertongued with or overlain by grayish-white sandstone, in part tuifa- ceous, seem quite like the already described deposits on Harpers Corner. In view of these outcrops described by the Unter- manns and Kinney, we spent several days in June 1959 in reconnaissance of numerous drainage courses high in the Uintas, from the vicinity of Lodore Can— yon westward for more than 25 miles. At many places 1—20 we noted, but did not map, exposures of a grayish- white sandstone, that is partly tuffaceous, resembles lithologically the sands of the Browns Park forma- tion, and occurs under conditions like those of the similar outcrops observed previously on Douglas Mountain. SUMMARY As thus outlined, the area of the present Yampa Canyon is immediately adjoined at its east end, on ' both sides of the river, by parts of the continuous, mapped Browns Park formation and is virtually sur- rounded elsewhere by patches of material that, be- cause of its lithologic character, may well belong to that formation. _ ' These observed conditions were felt to warrant the deduction that “at one time the site of the present Yampa Canyon * * * was buried at an unknown alti- tude and to an unknown thickness by deposits of the Browns Park formation.” Inasmuch as the Unter- manns have now found material similar to the Browns Park at four places between Yampa River and the main Yampa fault, this View will be assumed correct, as a basic factor in the hypothesis of canyon develop- ment that. follows. POSSIBLE DEVELOPMENT OF THE CANYON—A CHRONOLOGICAL OUTLINE Thus far this report has consisted chiefly of de- scriptions of the features observed in and near Yampa Canyon. Possible explanations of some of the fea- tures have been given or implied. There remains to be offered a more orderly chronologic outline of the processes and events by which the canyon may have originated and developed to its present form. Dat- ing by periods and epochs is recognized as only ap— proximate; the sequence and nature of events are regarded as of more significance in this study. A number of the suggestions are not susceptible of proof; and some of them may not be acceptable to all. Cer- tainly the suggestions are made with varying degrees of conviction. Some of the problems remain problems, and possible explanations are offered only tentatively. FIRST STEP Major uplift of the Uinta Mountain arch as a part of the Laramide orogeny had been followed during the Eocene by extensive erosion of the mountains, and by deposition of much of the resulting material in the Uinta and Green River Basins to the south and north and also lapping around the eastern end of the arch over the site of the later Axial Basin anticline. Con- currently, there had been repeated but presumably small further uplifts of the main arch, for the moun- tainward edges of the formations of Eocene age in SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the basins show varying amounts of tilting and overlap as well as local deposits of coarser material. In late Eocene or early Oligocene time, possibly after an interval of quiescence, uplift was renewed— this time extending far southeastward, so as to cause arching of the Axial Basin anticline and, then or later, the sharper localized upthrusts at Cross and Juniper Mountains. During these times of uplift there may have been the beginning of the Yampa, Red Rock, and Mitten Park faults and some movement on them; but I do not know of any positive evidence that proves or dis- proves this possibility. SECOND STEP During middle Tertiary time—perhaps extending from early Oligocene into the Miocene—uplift largely or even completely ceased. Erosion of the Uinta Mountain arch went on actively, however, until at last the mountain mass (though presumably still well above sea level) was reduced to mature topography. The erosion surface. was regarded by the Atwoods (1938, p. 964) as a part of the very Widespread “Rocky Mountain Peneplain.” Bradley (1936) described and analyzed in detail the processes and their topographic and geologic results along the crest and on the north flank of the Uinta Mountains. He pictured a great erosion surface, a pediment formed under arid or semiarid conditions, which sloped gently northward and northeastward for many miles out into the Green River Basin and rose in the other direction, with increasing gradient, to the foot of the high residual mountain peaks, between which at places it passed in flatter, narrow strips and began a gentle southward slope on the opposite flank. Bradley named this widespread subsummit surface the Gilbert Peak surface, and described it as now covered at many places by remnants of the Bishop conglomer- ate. Hundreds of feet below the Gilbert Peak surface, according to Bradley’s concept, was the later Bear Mountain erosion surface, of less areal extent, also developed under arid or semiarid conditions. Part of this surface, he thought, formed the floor of Browns Park, which, as a wide, rather flat bottomed, east- ward-draining valley, was eroded below the Gilbert Peak surface in the quartzitic sandstone of the Uinta Mountain group at the same time as the higher, shal- lower “Summit Valley” of Powell. The Bear Moun- tain surface, Bradley believed, was later buried under the Browns Park formation, including at places a basal conglomerate that resembles the Bishop con- glomerate. , Later field studies by Kinney (1955) on the south flank of the mountains near Vernal and by Hansen YAMPA CANYON, UINTA (1955, 1957) along the upper Green River, together with their observations during our reconnaissance trip (already mentioned) in the spring of 1959, have brought into question (Kinney, Hansen, and Good, 1959) some phases of Bradley’s concept, particularly certain relations between the Gilbert Peak and Bear Mountain surfaces and between the Bishop conglom- erate and the Browns Park formation. I have seen too little of the region as a whole to pass judgment on their questions and wish to emphasize that the pic- ture offered in this suggested outline is not intended to be a broader judgment but merely my own Views as to conditions and development. in the area above and adjoining the site of Yampa Canyon. More spe- cifically, I feel that the evidence now available indi- cates that in this Yampa Canyon area there was only a single pediment erosion surface (whether it be iden- tified as the Gilbert Peak or the Bear Mountain) and a single covering deposit, the Browns Park forma— tion, as described in the paragraphs that follow. If in this area there was once a second surface, covered with a separate Bishop conglomerate, all evidence for it seems to have been destroyed. , My concept of the erosion surface on the south side of this part of the Uintas accords essentially with the pattern discussed by several authors and described more fully by Howard (1942). No attempt is made herein to give a general summary of Howard’s very complete analysis of the processes suggested by others and his conclusions reached from that analysis and from his own observations; but a few points are em- phasized. Because of some existing ambiguities, he proposed (Op. cit., p. 11) “the term ‘pediplane’ as a general term for all degradational piedmont surfaces produced in arid climates which are either exposed or covered by a veneer Of contemporary alluvium no thicker than that which can be moved during floods.” To the inner or mountainward zone of the pediplane, underlain by upland rocks and hence formed in con— sequence Of the retreat of the upland front, he applied the unmodified term “pediment.” For the outer, peripheral zone of the pediplane, beveling the younger, less consolidated materials deposited in a flanking basin during previous aggradation, he suggested the term “peripediment.” In describing the mountainous parts of his pediments, Howard quoted Davis (1933) as saying that “a two-sided mountain mass retreating * * * will, after first acquiring more or less indented and embayed margins and later narrowing to an ir- regular ridge with a serrate crest, be worn through in graded passes * * *.” For the “graded passes” of Davis, Howard used Sauer’s term “pediment passes.” Applying the pattern thus described by Howard, I MOUNTAINS, COLORADO I—21 picture the erosion surface developed during the sec- ond step in this area as a pediplane sloping south— ward from the crest of Douglas Mountain and from the still higher crest west of the present Lodore Can— yon, to an unknown distance out into the Uinta Basin. Along those crests were the rather flat pediment passes that lay between higher residual hills and ridges and that connected with the northward-sloping pediplane on the Opposite flank of the range. (These pediment passes seem to correspond to the passes farther west where, as described by Bradley (1936, p. 171), “* * * smooth portions of the Gilbert Peak surface cross the range and slope southward, being the headward rem- nants of that surface which once flanked the south side of the range”) Southward these pediment passes opened into the wider and more sloping embayments which, in turn, opened further and merged into the main part of the pediment. This pediment truncated the older southward-dipping rocks of the Uinta arch at an angle much less than that of their dip; it also cut across the incipient Yampa, Red Rock, and Mit- ten Park faults if by that time they had come into existence. The surface of this main part of the pedi- ment is pictured as rather smooth at places and gently undulating, with perhaps a few low residual hills, at other places. Presumably the pediment reached the contact be- tween the older, “upland” rocks and the Eocene de- posits in the Uinta Basin. Presumably, also, a flank- ing peripediment beveled those Eocene deposits and extended for an unknown distance out over them. However, no trace of that surface is now known in the Uinta Basin, possibly for reasons mentioned by Bradley (1936, p. 169) in comparing the Uinta and Green River Basins. The pediment is visualized as also extending east- ward and wrapping around the southeast end of Douglas Mountain and of the Uinta Mountain arch; for the surface on which lies the Browns Park for- mation bevels sharply the steeply dipping Older beds in Lily Park on both sides Of Little Snake River. In appearance, the pediplane on the south and east sides of the mountains presumably resembled the Gil- bert Peak surface on the north flank as pictured by Bradley (1936, pl. 38A). THIRD STEP During the Miocene(?) there was laid down the widespread and varied material known as the Browns Park formation. Bradley (1936, p. 178, 184) ascribed the deposition of the Bishop conglomerate 0n the Gil- bert Peak surface and of the Browns Park formation on the Bear Mountain surface to a moderate increase in aridity, and gave several reasons for that View. I 1-22 have no new evidence to offer on this explanation. The varied composition and the source of these beds in the western part of Browns Park were concisely described by Hansen (1957) as follows: This formation contains rocks of diverse textures and lithol- ogies including finely laminated olive-drab clays; pale orange, friable, poorly sorted siltstones and sandstone; chalky white, loose to compact bedded t‘uffs and tuffaceous sandstones; and variously sorted loosely cemented conglomerates, some ex- ceedingly coarse and bouldery. The source of the tuffs is un- known, but most of the remaining material—at least the coarser fraction—was locally derived. Broad fans, consisting chiefly of pebbles and cobbles of red quartzite derived from the Uinta Mountain group but containing also Paleozoic lime- stone and older Precambrian metamorphic rocks, built out intermittently from the highlands enclosing Browns Park. From time to time the fans were buried by falls of vitric volcanic ash, some of which was reworked into tuffaceous sandstone. Periodically, much of Browns Park was flooded by lake waters that deposited blankets of sand and clay. The result is a complex interbedding of conglomerate, sand, tuff, and clay. The tuffs and clays retain remarkable uniformity over considerable distances, but the sands and conglomerates thin markedly from the sides toward the axis of the valley. According to my concept, the Browns Park forma- tion in and near the eastern part of the Uinta Moun- tains was deposited on the previously developed pedi- plane, including the Browns Park valley and the “Summit Valley” of Powell. On pages 1—17—20 are listed a number of observations about the Browns Park formation and about unmapped outcrops of material lithologically resembling it. The observations are there described in support of my belief that at one time the site of the present Yampa Canyon * * * was buried at an unknown altitude and to an unknown thickness by deposits of the Browns Park formation. More specifically, in this particular region I be- lieve— 1. That the thickest part of the formation occurred in the eastern part of the Browns Park valley by filling of this deep valley of erosion. 2. That the sedimentary material of the formation was derived chiefly from the exposed core of the Uinta Mountains, but that it was greatly augmented by tufl' from an unknown outside source. (Hansen has informed me that in this area tufl', tufl’aceous sandstone, and montmorillonite clays make up 50 to 55 percent of the exposed stratigraphic section.) 3. That variations in the kinds of rock in the basal conglomerate where present were determined by the lithologic nature of those formations exposed where serving as local sources of the detritus. Thus, boulders of light—colored quartzite and re- lated rocks from the locally exposed Red Creek quartzite are common in the western end of SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Browns Park; the basal conglomerate in the rest of Browns Park eastward to Little Snake River and on the north side of Cold Spring Mountain near Vermilion Creek is mostly composed of red- dish quartzitic sandstone derived from the Uinta Mountain group exposed on and north of the crest of the range; and boulders of gray limestone predominate on the east end and south flank of the arch because of the continuous outcrop of limestone of Mississippian age from Lone Moun- tain southward and thence far to the west. 4. That, as valley filling progressed, the sandy major upper part of the formation (augmented by the wind-borne volcanic tuffs) overlapped westward up the Browns Park valley and also laterally high up against the valley walls—for example, high against the Uinta Mountain group on the north flank of Douglas Mountain. 5. That, simultaneously, sand derived from the Uinta Mountain group in local residual peaks and ridges along the crest washed down into the pediment passes, and then some of it was carried down the north flank, presumably meeting and mingling with that part of the formation rising in the valley. 6. That sand and scattered cobbles from part of the crest and the retreating mountain mass moved down the south flank and, augmented by tufi's, came to rest as a blanket filling hollows and cov- ering the beveling surface of the pediplane to some unknown distance southward. The thick- ness of this blanket also is unknown; but it is surmised to have been of the order of several hundred feet on the outer part of the pediment, above the site of the present canyon. FOURTH STEP The ensuing collapse of the eastern part of the Uinta Mountain arch has been repeatedly and rather fully described. Apparently it was first noted and announced by Powell (1876) who, however, left some room for uncertainty as to just when he thought it happened. At one place (p. 201) he stated: The Uinta uplift in the region of Brown’s Park was at one time several thousand feet greater than we have represented it to be, but after the deposition of the Brown’s Park beds it fell down that much * * *. At three other places (p. 169, 206, 207) he at least implied the same time for the movement. Yet at a fifth place (p. 208—209) he wrote: Let us now consider the effect which the reverse throw along the great Uinta fault and the throw along the Yampa fault has had on this valley. * * * Thus it is seen that the great block between these two faults has fallen down from YAMPA CANYON, UINTA MOUNTAINS, COLORADO 1,000 to 5,000 feet in its different portions. Prior to this downthrow there was a great elevated valley drained into the Green River. When the downthrow commenced it is prob- able that the Brown's Park beds were not yet deposited, but after it had continued for some time the region was so de- pressed that the waters of the stream were ponded and a lake formed. In this lake, then, the Brown’s Park beds were accumulated. We know that the Brown’s Park beds were involved in a part at least of this downthrow, and hence were deposited before the downthrow was accomplished, because the beds themselves were involved in the displacement; they are sev- ered by faults and bent by fractures where they are seen to overlap or extend beyond the area of downthrow. Hence it is seen that Brown’s Park is not a valley of dis- placement or of subsidence, but was originally formed as a valley of degradation—an elevated valley in a mountain re- gion. It subsided or fell down as a part of a greater block. Pre-Browns Park faulting in the Uinta Mountains was widespread. However, I lean toward the view that Powell’s collapse or graben movement of the arch (whether by new faults or by reversal of throw on earlier faults) did not. start before deposition of the Browns Park formation began. Field evidence for some graben movement during Browns Park time has been presented (Sears, 1924a, p. 296 and fig. 8); in 1921—22 we observed additional but somewhat less clear evidence of the same kind on Spring Creek in T. 7 N., R. 95 W., northeast of Maybell. But I believe that by far the greater part of the graben movement took place after deposition of the Browns Park for— mation was complete. Powell’s wording also left some room for uncertainty whether he pictured the collapse as virtually a single rapid movement or as caused by many small move— ments over a long period. I think however that he held, and intended to express, the latter concept. A postulate of intermittent, cumulative graben move— ment seems to be more logical, though in this area not susceptible of clear proof; collapse of such magnitude in a single movement or a. very few movements would be well-nigh incredible. The aggregate effect of the sinking in the southern part of the graben, above the site of the present Yampa Canyon and its environs, is pictured as follows: 1. In a narrow zone along the Yampa fault, rather steep northward dips in the Browns Park forma- tion (as well as in the underlying truncated older beds that previously had dipped to the south) were caused by drag. Where the Red Rock fault branches northwestward this zone of steep dips is repeated. 2. North of and flanking the narrow drag zone was a wider zone (perhaps ranging in width from 4 to 9 miles) in which the surface of the Browns Park formation was essentially horizontal in a north— I—23 south direction but, because of tilt, sloped gently toward the west-northwest. 3. Still farther north, extending to the crest of the ridge, was a zone in which the depositional south- ward slope of the Browns Park formation had remained undisturbed because the broad central part of the graben had gone down almost ver— tically. My picture, then, is of a trough on the surface of the Browns Park formation, some 4 to 9 miles wide, essentially flat in a transverse north-south direction but extending with gentle slope in a direction about N. 80° \V. This trough was bounded on its south side by a rather steep northward slope and on its north side by a gentler though perceptible southward slope. This trough, however, was not restricted to the area of the present Yampa Canyon. On the contrary it continued, with gently rising floor, far to the east and northeast above and north of the Axial Basin anti- cline. The graben movement had extended in that direction, though with force and effect diminishing eastward; this was deduced from the present attitude of the Browns Park formation (a flat-bottomed, steep- edged syncline lying unconformably above an anti- cline) and from the faults and flexures observed along the present margins of that formation. (See Sears, 1924a, p. 287—288, 291—292.) It is only fair to point out a present—day structural anomaly near the mouth of Little Snake River which, if not due to some later warping or fault movement, lays open to question my picture of a continuous trough passing that vicinity. The south side of the graben and of the trough here conforms to the general pattern; south of Yampa River (opposite the mouth of the Little Snake) the beds of the Browns Park form a gentle topographic half—bowl that slopes to- ward the Yampa and that, east and west of Elk Springs, is rimmed on the south by a crude hogback 0f the basal conglomerate rising to a higher altitude and dipping more steeply northward. (See Sears 1924b, pl. 35.) The north side of the major graben (op. cit., pl. 35) lies along the north edge of the Browns Park outcrops in T. 8 N., Rs. 97—99 W. The north side of the inner trough, with dips approxi- mately southward, might here be expected somewhat farther south; this would make Yampa River in its course from the canyon through Cross Mountain to Yampa Canyon follow the floor of the trough. How- ever, as shown by the northward dips west of the Little Snake in Lily Park (op. cit., pl. 35) and as observed by Kinney, Hansen, Good, and me during our reconnaissance in the spring of 1959, the pre- Browns Park beveling surface and the basal conglom- 1—24 erate and overlying sandy beds of the Browns Park formation not only rise toward Douglas and Cross Mountains but also rise from the bridge across the Little Snake in sec. 20, T. 7 N., R. 98 W., southward toward the Yampa. This apparent anomaly requires further study and consideration. Unfortunately, large-scale topographic maps are not available (the locality is just east of the Dinosaur National Monu- ment topographic sheet); and in this neighborhood our field work in 1922 consisted only of a few pace traverses without the carrying of elevations. But be— cause of the very large fault on the west side of Cross Mountain and the steep dips of the truncated older beds forming a sharp, plunging syncline between that fault and the southeast end of the Uinta Mountain arch, it is not. difficult to imagine that, perhaps long after its creation, the trough was here somewhat warped and dislocated by a little renewed movement. FIFTH STEP It seems probable that the fifth step overlapped the fourth to some unknown amount. If the collapse took place by a series of small movements over a pro— longed period, and if the resulting trough began to take form at. some time during that period, then the incipient trough—long before its full development—- should have started to affect the location and direc- tion of drainage. Also, perhaps during the fifth step or perhaps after its close, the amount of drainage increased greatly. Both Blackwelder (1934, p. 561—562) and the At- woods (1938, p. 968—969) have postulated that late in Tertiary time there began a very widespread and very great uplift of the entire Rocky Mountain re- gion and adjacent provinces, which gradually brought about. much augmented rainfall and runoff. But regardless of these problems of timing, the ef— fect of the trough may be deduced. Therefore I suggest that streams flowing westward and southwestward from the Continental Divide down the depositional slope of the Browns Park formation began to be influenced by the graben, perhaps in the general vicinity of Cedar Mountain, and gathered into a new Yampa River. Joined successively by other streams farther west, this growing river was guided down the trough. It was restrained from major deflections to the north or south by the steeper dips on the edges, but was relatively free to swing laterally within the zone in which the floor of the trough was essentially level in a crosswise direction. Presumably its course was at first fairly straight, but by lateral erosion the initial irregularities were cut, enlarged, and smoothed into incipient meanders. As long as the river was flowing on or in the soft SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY cover of the Browns Park formation it was in no way affected by the structure or varying lithology of the buried older rocks, and thus it had no cause to depart from uniformity. Hence the slow develop- ment from irregularities to incipient meanders should have proceeded at about the same rate throughout, so that in shape and gradient all parts of the river’s course at any one time would resemble each other. Surely there was no pronounced and striking differ- ence in pattern from place to place such as charac- terizes the river’s course today. During this period, lateral erosion was accompanied by a certain amount of downcutting. Through com- bination of the two processes, presumably there was shallow incision with long low slipofi' slopes on the ends and downstream sides of spurs and with low cutbanks on the outside of curves and the upstream sides of spurs. But because the Browns Park for- mation in this area was relatively thin—perhaps a few hundred feet at most—incision in it and further enlargement and smoothing of incipient meanders could not go on indefinitely. When this fifth step came to a close, the river had not yet widened its valley floor to the point of free swinging and the creation of flood—plain scrolls, and had accomplished little down-valley sweep. In plan, the river at the close of this period is vis- ualized as having a very different shape or pattern from that developed later, and as occupying a differ- ent geographic position. In the part corresponding to what is herein called the middle section of the canyon, except for the stretch through the “half-turn district,” the river is pictured as then following the course marked by the dashed line in figure 8. Comparison of this figure with the map, plate 1, shows that the dashed line is drawn along the outer edges of those later features that are herein interpreted as meander-migration scars. If this position was correct, the river distance between points B and C would then have been about 261/2 miles instead of 19% miles as at present; and if the differ- ence in altitude, 333 feet, between those two points has remained unchanged, the average gradient of the river from point B to point C was then about 12.5 feet to the mile instead of the present 16.9 feet. In the part corresponding to what is herein called the lower section of the canyon, a meander is pictured as extending northward to the north end of the site of the Warm Springs scar. Through the rest of this part the river’s course is thought to have been simi- lar in pattern to that in the middle part—that is, in more angular incipient meanders as contrasted with the intricate dovetail meanders of today. For the l YAMPA CANYON, UINTA MOUNTAINS, COLORADO Present course of Yampa River NOTE: Reference points B and C shown on Plate 1 2 MILES 1—25 FIGURE 8.—Hypothetical course of Yampa River between points B and C just before cutting through Browns Park formation. reason given in the fourth paragraph above, uni- formity of pattern at that time in the several parts of the river seems logical. Moreover, in this lower part the shape and location of the spurs and upper walls of the present canyon (as seen on the aerial photo- graphs and on the Dinosaur National Monument to- pographic sheet) indicate ample leeway for the type of course just described. However, subsequent ero- sion of the canyon brought such great modifications that the drawing of a hypothetical course would not be justified. But I am confident that the river dis- tance from point C to point D was then substantially less than the present 23% miles, hence that the gradi- ent between those points was steeper than the present averaged 7 .4 feet per mile—perhaps of the order of the 12.5 feet per mile suggested for the middle part. The fifth step came to an end when at some point the river first cut through the Browns Park forma- tion to the underlying older rocks. S I XTH STEP Change from the fifth step to the sixth step is seen as involving not a change in process but a differing effect on the river’s course through differences in structure and lithology from the covering Browns Park formation to the underlying rocks. Superposi- tion and its attendant phenomena began. The forces that had led to downcutting, lateral cutting, and a small amount of downstream sweep continued to oper- ate, but with varying results. I It has been suggested that, when the river cut through the Browns Park formation to the more re- sistant older rocks, further downward erosion would have depended on rejuvenation, perhaps through up- lift (with or without some tilting). Such uplift should have left some local physiographic traces; if so, none have come to my attention, though perhaps because they were destroyed by subsequent erosion. However, I am inclined to believe that there was no uplift at this time, and that the river still had ample power for further downcutting. The point at which the river first cut through the Browns Park formation to the older rocks in this area is not known and is not thought to be susceptible of proof. But several clues afford grounds for specula- tion and a tentative conclusion. 1. The pediment (pre-Browns Park surface) was de- scribed as sloping gently southward at an angle definitely less than the angle of southward dip of the older beds that it truncated. 2. The Browns Park formation was pictured as thick— ening slightly southward, its basal beds of course having a dip that corresponded to the slope of the pediment surface and its upper beds having a somewhat smaller southward dip. 3. During the graben movement, the zone that be- came the crosswise flat floor of the trough was tilted slightly northward, thereby decreasing a little the southward dip of the basal beds of the Browns Park and the southward slope of the buried pediment surface. If these seemingly plausible conditions were true, then the northern ends of the incipient meanders had a somewhat lesser thickness of the Browns Park for- mation to penetrate than the rest of the river, though the difference was probably very small. In the ab— sence of a more tangible or more verifiable hypothe— sis, this picture is tentatively assumed to be correct. On this basis, I would suggest that the river first cut through the Browns Park formation at the mountain- ward ends of the meanders curving around the sites of the present Anderson Hole and Warm Springs I—26 scars. (A line drawn between those two places lies north of, or updip from, the ends of the other as- sumed meanders.) The immediate effect of reaching the older, more resistant rocks should be some decrease in the rate of downward erosion at those points and the creation of temporary or local baselevels upstream from them. However, if the thickness of the soft Browns Park cover then remaining elsewhere along the river was as small as pictured, only a relatively short time should be required to reach the undermass through— out. Because the strike of the older rocks was a little north of west, and their clip was predominantly about 6° S.VV., the intersection of the Weber-Morgan bound- ary with the old truncating pediment surface was roughly parallel to that strike; the younger formation (the Weber sandstone) lay south of that boundary intersection and the older (the Morgan formation) lay north of it. As soon as the river cut through the Browns Park cover, it ran on those two formations. In the middle part of the river (between points B and C) its course was on the upper beds of the Mor- gan, except for the stretch through what is herein called the “half-turn district” where it ran on Weber sandstone. In the lower part of the river (between pOints C and D) its course was on Weber sandstone except for that northward-extending meander around the site of the Warm Springs scar, where it was again on the upper beds of the Morgan. Inasmuch as the attitude (strikes and dips) of the Morgan and Weber was essentially uniform through- out the middle and lower parts of the river (from point B to point D), it seems obvious that the further development, which brought the conspicuous differ- ences in river pattern from place to place, must have been influenced chiefly by differences in the way those two formations affected erosion. RIVER DEVELOPMENT IN MORGAN FORMATION The alternating sandstone and limestone beds of the upper one-half or two-thirds of the Morgan forma- tion were more resistant than the soft material of the Browns Park. Where and while the river was run- ning in those upper beds of the Morgan its course is pictured as not shifting widely. Lateral erosion was retarded somewhat by greater rock resistance in the banks but was sufficient to cut those banks into cliffs whose height increased during continued downcutting. After incision had progressed to a further depth of perhaps 200 feet, the river at the north ends of its meanders reached the even more resistant limestones in the lower part of the Morgan while elsewhere it was still in the upper beds. Direct vertical erosion SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY practically ceased at those points of greatest strati— graphic penetration; the river as a whole continued its tendency to slowly cut down its altitude, but at those points found less obstacle in a gradual south- ward, downdip shifting on top of the still more re- sistant beds. Such a process of meander shifting bears little re— lation to that by which the VV ell- known slipoff slopes are formed on the convex ends and downstream sides of alternating spurs in one type of more normally in— cised meanders. On the other hand, the suggested process would seem to be closely related to that which was early (and perhaps first) described by Salisbury (1898, p. 146) as follow:s “Flowing along the strike of dipping beds, streams do not usually sink their channels vertically, but shift them down dip at the same time that they are deep- ened. This process is known as monoclinal shifting.” This process was described also by Tarr (1914, p. 547), by Dake and Brown (1925, p. 106), and by Von Engeln (1942, p. 142) under the same name; by Cot— ton (1949, p. 89—90) and by Thornbury (1954, p. 112) under the name “homoclinal shifting”; by Wooldridge and Morgan (1937, p. 159) and by Lobeck (1939, p. 191) under the name “uniclinal shifting”; and by Worcester (1948, p. 187) without name. I think that in all these cited descriptions the authors had spe- cifically in mind only the lateral, downdip shifting of first- cycle strike- -valley streams with concurrent shift— ing of divides—a well- known phenomenon. However, their names and the process itself appear to be ap- plicable also to the lateral, downdip shifting of in- cised meanders herein postulated under unusual con— ditions favoring such a shift. 1 The initial effect of the shifting was to straighten and flatten the arcuate north ends of the meanders to a shape more nearly in accord with the strike of the beds. This effect is recorded in the present pattern of contour lines (see particularly those in the Anderson Hole, Tepee Hole, and Warm Springs scars on pl. 1). Then, as more and more of the river cut down to the more resistant low er beds, increasingly large parts of the meanders shifted bodily southward down the dip, to ever lower altitudes. As the river thus shifted its position, its progressively abandoned channel became the growing southward sloping meander- -migration scars. The shape of the scar floors indicates continu- ous cutting and shift; no traces of cutoffs and mean- der cores are seen. On their sides the scars are rimmed with cliffs whose bases are in generalat pro- gressively lower altitudes southward. At the north ends of the longer scars, however, such rimming cliffs as may once have existed have been essentially oblit- YAMPA CANYON, UINTA MOUNTAINS, COLORADO erated through erosion by the intermittent streams that came from Douglas Mountain to the early meanders; these streams were extended southward during the migration and have since cut into and modified the floors of the scars. By some lateral erosion and spur trimming, the rim- ming cliffs on the west side of the Tepee Hole scar and the east side of the Browns Hole scar were cut back to form a southward—pointing, conspicuously sharpened spur (fig. 3). As part of the river migration thus postulated, the meanders grew smaller (though not more rounded), the river was shortened, and presumably its gradient was increased. On its southern side the shifting river was con— stantly encroaching against and eroding or even un— dermining the updip edges of the higher beds. Through this relation and process the south wall was kept steep and narrow throughout, and its top was kept in close conformity with every bend and turn of the river. In this way, too, the boundary between the Morgan and the overlying Weber sandstone came to lie almost continuously high along the south wall. In time the spurs between the meanders, as well as the interstream divides forming the uplands on both sides of the river, were stripped of all or almost all their earlier Browns Park cover, and also were some— what further lowered by “erosion. Maintenance of a sharp angle between the top of the cliffs and the up- land surface was perhaps the result of aridity. RIVER DEVELOPMENT IN WEBER BANDSTONE In its lower part (except for the meander around the present Warm Springs scar), and presumably also in the “half-turn district” of the middle part, the river is Visualized as cutting through the Browns Park cover to the Weber sandstone rather than to the Morgan formation. Reasons have already been given why the river is thought to have had a uniform pattern of incipient meanders throughout its middle and lower parts just before passing through the Browns Park formation. Yet wherever superposition began on the Weber sand- stone the river now has a general pattern of rounder and more intricate meanders, many of which form what are often called “goosenecks.” Furthermore, in those portions the present canyon has asymmetric cross sections and interlocking spurs with distinct slipotf slopes. (See pl. 1.) Inheritance of the present curving intricate pattern through uplift and rejuvenation is ruled out because, as indicated above, such a pattern presumably did not exist here on the Browns Park formation. My belief that uplift did not accompany the beginning of super— I—27 position has already been stated. Early writers seemed to take for granted that incised meanders could result only through inheritance of such a course established during a previous cycle; but, perhaps first influenced by Winslow (1893), many writers have pointed out that incised meanders may form within a first cycle through lateral erosion during incision. The conclusion seems to me inescapable that the present pattern of incised meanders was developed after superposition began, and that the conspicuous differences of pattern between the parts of the can- yon cut in the Weber and the parts cut in the Morgan reflect directly the different ways in which those two formations afl'ect erosion. In their description of the Weber sandstone the Untermanns (1954, p. 36) said: “The poorly cemented and highly jointed nature of the Weber accelerates its erosion, producing characteristic deep, steep-walled gorges and resulting in extremely rough topography.” The joints in the Weber, particularly those approxi- mately parallel to the strike, show very plainly on the aerial photographs. With a high degree of confidence, therefore, I pos- tulate that during incision in the Weber many incipi- ent meanders were more and more eroded laterally to complex, rounded meanders, with concurrent growth of slipoff slopes on the spurs. During this develop- ment there may have been some quick, local shifts in the position of the channel, for here and there on the north side of the river are features that somewhat re- semble high-level cutofls and meander cores; but these are uncertain because the topography has been so greatly modified through later erosion by side streams. With much less confidence, I suggest the possibility that during incision there may also have been some larger scale, more general changes of the river’s course to positions farther south. However, if such changes actually happened, their cause and results were very different from those of the gradual shift that brought about the meander—migration scars in the Morgan. The possibility is mentioned here for three reasons: the shape of the sloping land north of the river as visualized from the topographic map; the fact that sheer or even sharply undercut cliffs of Weber sand- stone (see fig. 4) are much more numerous on the south side of the river; and (approached through a still different line of thought) the suggestion made in the closing section of this report that such changes in canyon channel may have taken place around and east of Steamboat Rock. But regardless of whether such larger scale changes in position were or were not possible, the development of much more intricate meanders during incision is 1—28 pictured as having considerably lengthened the river between points C and D, thereby proportionately re- ducing its gradient. SEVENTH STEP Some rejuvenation probably took place at a fairly late time in the incision. On page 1—8 the southward—sloping meander-migra- tion scars in the middle section of the canyon are de— scribed as terminated near the river by a break to a steeper slope, which causes an upward convexity. If, as I believe, the floors of the scars were cut during migration of the river down southward-dipping more resistant beds in the lower part of the Morgan, then an explanation must be sought as to why those beds were at last breached and why the canyon was eroded below them. The breaching of these more resistant beds, and the appearance of the steeper slope as the north side of a valley-in-valley, together seem to be most logically at- tributed to rejuvenation that led to the cutting of a V-shaped inner gorge. Such rejuvenation may have been the result of uplift, with or without some tilting; of increase in stream flow; or of some other cause. Von Engeln (1942, p. 176) has stressed the very great increase in cutting power that can result from a very small increase in velocity of flow. The somewhat anomalous vertical and horizontal position of the present break in slope can perhaps be explained as follows. When the river had come vir- tually to its present location, rejuvenation caused more vigorous downcutting. At first the northern part of each meander was still flowing on the more resistant lower beds of the Morgan; hence the inner gorge there began at once to be cut into those beds. On the other hand, because of the southward dip the southern part of each meander was still flowing on somewhat higher and less resistant beds of the Morgan; hence the up- per part of the inner gorge was there cut first into those less resistant beds, and the river did not reach and cut down into the more resistant lower beds until progressively later; after that, the beds above them were eroded away. On page 1—12 the slipoff slopes on the interlocking spurs in the lower section of the canyon are described as interrupted part way down by crude “treads” of somewhat less slope. Below these “treads” the banks are steep. It would be natural to assume that the steep banks below are a continuation of the valley-in- valley postulated for the middle section and therefore were cut at the same time and by the same process. Of that continuity, time, and process, however, no clear evidence is seen on either the topographic map or the aerial photographs. , SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The “treads” lie at successively lower altitudes to- ward the south, without regard to whether that direc— tion is upstream or downstream on the several mean— ders. This fits the picture of their relation to lithol- ogy and dip. Perhaps they were formed when and where downcutting of any slipofl' slope was slowed by locally reaching a slightly more resistant bed; and then, when downward and lateral erosion cut through that bed in its particular meander, cutting of a steeper bank below it was resumed. EFFECT OF MITTEN PARK AND RED ROCK FAULTS The foregoing chronologic outline presents the seven steps that may have led up to and caused the devel- opment of the winding, deeply incised Yampa Canyon in the Uinta Mountains. The outlined steps bring the river and the canyon to the point of their junction with the Green. (No discussion is here given about possible later regional uplift that may have brought mountains and rivers to present altitudes.) But no explanation has yet been suggested for a problem relating partly to Yampa Canyon and partly to the course and development of Green River down- stream from the junction, although the problem was briefly mentioned on page 1—6: Because of the later and more detailed mapping by the Un- termanns * * * I wish to emphasize that in its lower course Yampa River runs into, and joins Green River Within, the added depression or triangular graben between the Red Rock and Mitten Park faults—-a complicating problem to be dis- cussed under the last heading of this report. The problem includes chiefly two puzzling questions: (a) What is the origin of the spectacular hairpin- shaped meander of Green River around Steamboat Rock? (b) How did the combined rivers get out of the extra depression and across the Mitten Park fault with its large downthrow on the upstream side? If the Mitten Park fault came into existence and if all or much of the movement on it was accomplished prior to the cutting of the pediment, to the deposition of beds of the Browns Park, and to the forming of the graben and the trough—that is, prior to the second, third, and fourth steps of the chronologic outline— then I find it difficult to account for the great dif- ference in present altitudes of the conglomerate and material similar. to the Browns Park high on Harpers Corner ridge and of the material similar to the Browns Park found by the Untermanns low in the graben be- tween the Yampa fault and the Yampa River. On the other hand, if all or most of the movement on the Mitten Park fault happened as part of the gen- eral graben movement and trough formation, then the upthrow (northwest) side of the Mitten Park fault would apparently have formed a barrier to the river YAMPA CANYON, UINTA MOUNTAINS, COLORADO flowing down the trough. In that case it would be natural to infer that water from the two rivers would be ponded on the upstream side of the barrier until it grew deep enough to overflow that barrier and begin to cut a channel through and west of it. Such pond- ing may have taken place; but, if it did, no traces of it seem to remain and it would be out of harmony with some other steps in my hypothesis. An alternative is here suggested as a possible way out of the dilemma; as a possible explanation for the course of the Green around Steamboat Rock; and also as a possible explanation of three features that are yet to be described. The alternative suggestion is that early in the can- yon cutting, at a higher level, the last few miles of Yampa River (west of the southern part of the mean- der in the Warm Springs scar) may have been some- what farther north than at present; that the Yampa may have joined the Green at or near the east end of the Mitten Park fault; and that the enlarged Green River may have flowed for more than 1 mile westward along the fault (whose throw increases in that direc- tion) until it firmly established its course and was able to leave the fault plane and continue farther west on the upthrow side. The features that give rise to that suggestion are as follows: 1. East and west of the north end of Steamboat Rock are two nearly straight stretches of Green River, one of which is about 0.6 mile long, and the other about 0.3 mile. If those two stretches are ex- tended and connected by an imaginary line that is slightly arcuate northward, the line thus ex- tended intersects the north end of Steamboat Rock at its present lowest spot (seen on the Dinosaur National Monument topographic map to be at an altitude between 5,750 and 5,800 feet). 2. The greatly curving Mitten Park fault, after pass- ing Harpers Corner and crossing Green River, cuts across the north end of Steamboat Rock at or very near the lowest spot. Thence it reaches Green River again and, low in the canyon, ex- tends along the upstream straight stretch. How- ever, its throw here diminishes so sharply that the fault itself apparently ends in the east wall of the curving canyon and passes eastward into a flexure. On special large-scale (1217,000), very detailed aerial photographs, that flexure is indi- cated rather clearly for about 2 miles by a locally increased southward dip of some lighter colored beds of the Weber exposed at the surface (see also the more closely crowded topographic con- 1—29 tours on pl. 1, just south of the altitude marked “6962”); but the flexure is only faintly Visible and seems to be almost gone in the southern part of the floor of the Warm Springs scar. 3. The slope between the flexure just described and Yampa River from Warm Springs to point D is now greatly dissected by short streams that drain to the Yampa. But within that small district are three higher hills still capped with patches of the southward-dipping Park City formation. From the eastern (largest) and the middle patches the ground slopes northward until, about 0.3 mile from each patch, it forms a smooth concave curve and then merges with and starts to rise as the slope of the southward-dipping flexure. At the low point of each of those curves the present alti- tude is between 6,240 and 6,280 feet as shown on the Canyon of Lodore South sheet (which, being newer and of larger scale, brings out the topog- raphy more clearly for this study). On each side these curving surfaces have been encroached upon and eroded into by the heads of young streams. But as seen on topographic maps and on aerial photographs and as later viewed from Harpers Corner (see fig. 9), these two smooth concave curves look like remnants of an old high-level round-bottomed channel. Moreover, if these curves do indicate an old channel, its course in both directions can be deduced. Upstream, its floor may be represented by a crude “shelf” shown by contours farther apart; if so, its north wall here also is the steeper south slope of the flexure, but its south wall has now been entirely cut away. Downstream, the possible channel might have been along a line which, if drawn between the low points of the two concave curves and extended northwestward with a gentle swing, would cross the present rim of Lodore Canyon through a comparably low gap and meet Green River near the east end of the fault. Taken separately, any one of the three features de- scribed may seem to be either due to chance or without significance. Taken together, each strengthens the others and makes coincidence more improbable. If this alternative suggestion seems to explain plausibly these features and the passing of the Mitten Park fault, a corollary appears: subsequently, because of southward dip and of jointing in the Weber sand- stone, the erosion of new deeper channels cut Green River southward to form its narrow, elongated can- yon around Steamboat Rock and also diverted the lower part of Yampa River to the present junction at point D. I—30 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FIGURE 9.—-Possible former high-level channel of lower part of Yampa River. Green River at left, Yampa River at extreme right. eastern and middle hills capped with Park City formation. Park Service photograph.) SELECTED BIBLIOGRAPHY Atwood, W. W., and Atwood, W. W., Jr., 1938, Working hy- pothesis for the physiographic history of the Rocky Moun- tain region: Geol. Soc. America Bull., v. 49, no. 6, p. 957— 980. Bates, R. E., 1939, Geomorphic history of the Kickapoo re- gion, Wisconsin: Geol. Soc. America Bull., v. 50, p. 819— 880. Blackwelder, Eliot, 1934, Origin of the Colorado River: Geol. Soc. America Bull., v. 45, no. 3, p. 551—566. Bradley, W. H., 1936, Geomorphology of the north flank of the Uinta Mountains: U.S. Geol. Survey Prof. Paper 185—I, p. 163499, pls. 34—45. Carey, B. D., Jr., 1955, A review of the Browns Park forma- tion, in Intermountain Assoc. Petroleum Geologists, Guide- book, 6th Ann. Field Conf. 1955, p. 47—49. Cotton, 0. A., 1949, Geomorphology: 5th ed., revised, New York, John Wiley & Sons, 505 p. Dake, C. L., and Brown, J. S., 1925, Interpretation of topo- graphic and geologic maps: New York, McGraw-Hill Book 00., 355 p. Davis, W. M., 1914, Meandering valleys and underfit rivers: Assoc. American Geographers Annals, v. 3, p. 3—28. 1933, Granitic domes of the Mohave Desert, California: San Diego Soc. Nat. Hist. Trans, v. 7, p. 211—258. Emmons, S. F., 1877, Descriptive geology: U.S. Geol. Explor. 40th Parallel (King), v. 2, p. 191—206, 222—227, 271—290. At right, (National View eastward from Harpers Corner. Engeln, 0. D. von, 1942, Geomorphology, systematic and re- gional: New York, The Macmillan 00., 655 p. Forrester, J. Donald, 1937, Structure of the Uinta Mountains: Geol. Soc. America Bull., v. 48, p. 631—666, 4 pls., 1 fig. Hancock, E. T., 1915, The history of a portion of Yampa River, Colorado, and its possible bearing on that of Green River: U.S. Geol. Survey Prof. Paper 90—K, p. 183—189, pls. 20—21. Hansen, W. R., 1955, Geology of the Flaming Gorge quadran- gle, Utah-Wyoming: U.S. Geol. Survey Geol. Quad. Map GQ—75. 1957, Geology of the Clay Basin quadrangle, Utah: US. Geol. Survey Geol. Quad. Map GQ—101. Howard, A. D., 1942, Pediment passes and the pediment prob- lem: Jour. Geomorphology, v. 5, no. 1, p. 3—31; no. 2, p. 95—136. Johnson, Douglas, 1932, Streams and their significance: Jour. Geology, v. 40, no. 6, p. 481—497. Kinney, D. M., 1955, Geology of the Uinta River—Brush Creek area, Duchesne and Uintah Counties, Utah: US. Geol. Survey Bull. 1007, 185 p. Kinney, D. M., Hansen, W. R., and Good, J. M., 1959, Distri- bution of Browns Park formation in eastern Uinta Moun- tains, northeastern Utah and northwestern Colorado [abs]: Geol. Soc. America Bull., v. 70, no. 12, p. 1630. Lobeck, A. K., 1939, Geomorphology, an introduction to the study of landscapes: New York, McGraw-Hill Book 00., 731 p. YAMPA CANYON, UINTA MOUNTAINS, COLORADO Mahard, R. H., 1942, The origin and significance of intrenched meanders: Jour. Geomorphology, v. 5, no. 1, p. 32—44. Moore, R. C., 1926a, Origin of inclosed meanders on streams of the Colorado Plateau: Jour. Geology, v. 34, no. 1, p. 29—57. 1926b, Significance of inclosed meanders in the physio- graphic history of the Colorado Plateau country: Jour. Geology, v. 34, no. 2, p. 97—130. Powell, J. W., 1876, Report on the geology of the eastern por- tion of the Uinta Mountains: U.S. Geol. and Geog. Survey Terr, 218 p., atlas. Rich, J. L., 1910, The physiography of the Bishop conglom- erate, southwestern Wyoming: Jour. Geology, v. 18, no. 7, p. 601—632. 1911, Gravel as a resistant rock: Jour. Geology, v. 19, no. 6, p. 492—506. 1914, Certain types of stream valleys and their mean- ing: Jour. Geology, v. 22, no. 5, p. 469—497. Salisbury, R. D., 1898, The physical geography of New Jer- sey: New Jersey Geol. Survey, Final Rept. 4, p. 1—187. Sears, J. D., 1924a, Relations of the Browns Park formation and the Bishop conglomerate and their role in the origin of Green and Yampa Rivers: Geol. Soc. America Bull., v. 35, p. 279—304, 11 figs, 1 pl. I—31 Sears, J. 1)., 1924b, Geology and oil and gas prospects of part of Moffat County, Colorado, and southern Sweetwater County, Wyoming: US. Geol. Survey Bull. 751—G, p. 269— 319, pls. 35—37. Tarr, R. S., and Martin, Lawrence, 1914, College physiography: New York, The Macmillan 00., 837 p. Tarr, W. A., 1924, Intrenched and incised meanders of some streams on the northern slope of the Ozark Plateau in Missouri: Jour. Geology, v. 32, no. 7, p. 583—600. Thornbury, W. D., 1954, Principles of geomorphology: New York, John Wiley & Sons, 618 p. Untermann, G. E., and Untermann, B. R., 1954, Geology of Dinosaur National Monument and vicinity, Utah-Colo- rado: Utah Geol. and Mineralog. Survey Bull. 42, p. 1—221, pls. 1—3. Winslow, Arthur, 1893, The Osage River and its meanders: Science, v. 22,. p. 31—32. Wooldridge, S. W., and Morgan, R. S., 1937, The physical basis of geography: New York, Longmans, Green & 00., 445 p. Worcester, P. G., 1948, A textbook of geomorphology: 2d ed., New York, D. Van Nostrand 00., 584 p. INDEX Page Acknowledgments ............................................................ 5 Aerial photographs, as sources of information ........ 4, 11, 13,14, 29 Anderson Hole scar ................. 10, 27 Axial Basin anticline ........................................................ 20 Basal conglomerate, Browns Park formation .................................. 22 Bishop conglomerate. _ . _ ._.- ....... 20 Bower Draw scar _____________________________________________________________ 11 Browns Hole scar ............................................................. ll, 27 Browns Park formation, discoveries in area ................................... 17—20 drilling data. .. .. _.- 5 erosion surface below. . - 20 Miocene deposition of .................................................... 21—22 recent extensions of area .................................................. 16 stripping of ...... ...- .. 24, 25, 26, 27 superposition of drainage pattern from .................................... 15, 16 Canyon walls, topography and geomorphology of ............................. 7 Douglas Mountain ........................................................... 8-9 Five Springs Draw scar ....................................................... 11 Geologic map, discussion ..................................................... 4—5 Geology, lower sani‘inn 14 middle section .......... 9 upper sonflnn _ 6 Geomorpholdgy .............................................................. 7, 3, 9 Graben between Mitten Park and Red Rock faults, formation of ............. 22-23 influence on late Tertiary drainage ................................. relation to river course ......................... Green River, course below mouth of Yampa River ........................... 28—29 Half-Tum district .................................................. 7, 9, 11—12, 24, 27 Harper’s Corner ridge, Browns Park formation .............................. 29 Incised, definition ............................................................ 3—4 Mancos shale ....... 7 Meander, definition. . . - 3 Meander-migration scars ..................................................... 3 definition and description ................................................. 9-12 in Morgan formation __________________ Meanders, in Browns Park deposits .............. in Morgan formation. _ . . _. in older rocks _____________________________________________________________ 24—26 in Weber sandstone ...................................................... 27—28 shifting of .......... Middle Eocene erosion. Mitten Park fault ........... effect on river development position .................................................................. 4 relation to Yampa River. .. 3 Morgan formation _________________________________________________________ 6, 7, 9, 14 boundaries ............................................................... 4—5 meander-migration scars in ________ .. 28 river development in .................................................. 26—27, 28 O Page Park City formation __________________________________________________________ Pediment, erosion in. . Pediment passes .................... 21 Pediplane .......................... 21 Peripediment. 21 Previous work ................................................................ 4 Red Rock fault ......................................................... 3, 4, 5, 20, 21 effect on river development. ........ .._- 28-29 position ............................ 4 relation to Yampa River .................................................. 3 Slipofi slopes and treads .................................................... 9, 12,28 Steamboat Rock, river flexure at ........................................... 27—28, 29 Structure, upper section .............. 6-7 Superposition, relation to river course ................................... 15, 16, 24, 27 Tepee Hole scar ........................................................... 10—11, 27 Topographic maps, as sources of information .................................. 4 Topography, canyon walls .................................................... 7—8 lower section ............................................................. 12 middle section _____ 12 uplands ............. 7, 8-9 upper section ............................................................. 6 Uinta Mountain arch .................................................. 6, 7,15, 20, 21 collapse of .......... Uplands, topography ....... Uplift, late Eocene-Oligocene. late Tertiary .............................................................. 24 Warm Springs scar ..................................................... 24, 26, 27, 29 Weber sandstone. ._ ..... 6, 7, 9, 14 boundaries.._.-..._ .................. 4—5 river development in .................................................. 26, 27—28 Yampa Canyon .......................................................... 6, 7, 12, 13 development above junction with Green River ........................... 19-28 explanation of features ......................... 15-29 location and extent. ........ 5 lower section ................... 12—14 late Tertiary river course ............................................. 24 middle section ............................................................ 7—12 geology ......... __._ 9 late Tertiary river course. 24, 26 location and structure. . . 6 meander-migration scars .............................................. 10 river pattern and direction ............................................ 7 three-fold character ......... 3, 6 upper section ................ 6-7 Yampa fault ..................................................... 3, 4, 5, 7, 9, 19, 20, 21 position .............. 4 relation to Yampa River .................................................. 3 Yampa River, middle course. 5 migration ................................................................. 26-27 pattern and direction.-. ............................................. 6, 7, l2 rejuvenation of _____ ‘ 28 relation to faults .......................................................... 3 I—33 108°30’ PROFESSIONAL PAPER 574-1 PLATE 1 EXPLANATION 40’ 45' RiOZ W. 55’ 109°00’ GEOLOGICAL SURVEY R.i 04 W. UNITED STATES DEPARTMENT OF THE INTERIOR Dashed where approximately located. U, upthrow'h stde D downthmwn Side —'|'_‘ 6 Strike and dip of beds ‘ C WDOKMHZZOmdeu ii) Z<_Z<>I_>mZZm_n_ i Dashed where approximately located P w Weber sandstone IPm Morgan formatlon RiiOi W. iifl‘ (n ‘‘‘‘‘ Significant points in canyon (discussed in text) Reference points of scars (discussed in text) Contact ‘\~. in \ —-30’ —40°25’ 108°30’ Geoiogy from G. E. Untermann and B. R. Untermann N. 5 T. R99 W. 1954, pl. 2) 61187 ( EOLOGICAL. SURVEY. WASHINGTON. D. C a INTER IOR— 35’ R.IO3 W, I .1» 0 a E A Lu 2 u v S APPROXIMATE MEAN DECLINATION, I951 , R.IO4 W. Pm Browns Hole swawmw SNESN Pw le 8000’ 7000’ 40' R.iOIW. 3 MILES 45’ SCALE 1:62 500 CONTOUR INTERVAL 50 FEET DATUM iS MEAN SEA LEVEL HI—‘IHHI—l. 50' GEOLOGIC MAP AND CROSS SECTION OF YAMPA CANYON AND VICINITY, UINTA MOUNTAINS, COLORADO 55’ Rocks older than Morgan formation 109°00’ \ \ 6000’ 5000’ Base from U. S. Geological Survey Dinosaur National Monument topographic map, 1950 40°25'— Armstrong and Gressman—THE BANNOGK THRUST ZONE, SOUTHEASTERN IDAHO—Geological Survey Professional Paper 374-J' EART“ ..—— sciENCES .\/" LiBRARY The Bannock Thrust Zone Southeastern Idaho GEOLOGICAL SURVEY PROFESSIONAL PAPER 374—J Preparea'partgy on oefialf of Me U .S. Atomic Energy Commission r,._mev~"'”‘W‘w " ‘ , A : * r :‘ , x The Bannock Thrust Zone Southeastern Idaho A By FRANK C. ARMSTRONG and EARLE R. CRESSMAN ‘ SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PR:OF§ESSIONA§=L PAPER 374-] Preparedpizrtiy on ore/mg" of Me U.S. Atomic Energy Commission UNITED STATES GOVERNMENT PRINT.ING OFFiI}C§E, WASHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART 7L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, DC. CONTENTS Page \ Abstract ___________________________________________ J1 Introduction _______________________________________ First interpretation of the structure of southeastern Idaho- The Bannock overthrust _____________________________ Original interpretation ___________________________ Mansfield’s final interpretation ___________________ Extent ____________________________________ Displacement ______________________________ Folding____--___-______-__-_--__________-'_- Age___----_-_______--_--_-_-__-_______,___ Extrapolation of the Bannock overthrust_ _ _ - _ '_ _ _ _ _ The Bannock thrust zone : present interpretation ________ Area east and north of Georgetown ________________ Left Fork of Twin Creek and Georgetown Canyon __________________________________ Slug Creek _________________________________ Syncline underneath Snowdrift Mountain ______ Crow Creek fault zone _______________________ Bear River Valley ______________________________ Area northwest of Nounan ___________________ O‘clflkhhlhfiwwlONNI-I 4415165650! The Bannock thrust zone—Continued Bear River Valley—Continued Threemile Knoll ____________________________ East border of Bear River Valley _____________ Ages of thrusting-_-----------------------., _____ Paris thrust fault ___________________________ Thrust faults between Crow Creek and Snake River Plain ______________________________ Thrust faults in western Wyoming ____________ Time of folding of thrust surfaces _________________ Amount of displacement _________________________ Comments on extrapolations of the Bannock _______ Northern extensions _________________________ Southern extensions _________________________ Structure and structural evolution of a part of south- eastern Idaho ____________________________________ References cited ____________________________________ ILLUSTRATIONS [Plates are in pocket] PLATE 1. Simplified maps showing changes in the interpretation of the geologic structure of southeastern Idaho and parts of adjoining Utah and Wyoming. Geologic structure maps of area near Georgetown, Idaho. Simplified structural map of southeastern Idaho and adjoining parts of Utah and Wyoming. FIGURE 2. 3. Geologic map and section of the Left Fork of Twin Creek and Georgetown Canyon area, Idaho. 4. 1 . Diagram illustrating progressive decrease in age of thrust faults from west to east ......................... _. III Page WWW“ 14 16 16 16 17 18 19 20 Page J15 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY THE BANNOCK THRUST ZONE, SOUTHEASTERN IDAHO By FRANK C. ARMSTRONG and EARLE R. CRESSMAN ABSTRACT The Bannock overthrust in southeastern Idaho and north- central Utah was originally described by Richards and Mansfield (1912) as a single large thrust fault that formed at the close of the Laramide orogeny and was folded by renewed compression near the end of Pliocene time. Later Mansfield expanded and revised his interpretation of the Bannock over- thrust so that at least the northern part of the overthrust was thought to be a thrust zone in which the individual faults originated in a folded sole thrust. Detailed mapping in areas critical to Richards and Mansfield’s interpretations has shown that the faults thought by them to be parts of one large thrust are separate faults, and that, although some of the thrust surfaces are curved, they were ' not folded in Pliocene time but probably were folded during a late stage of the thrusting. Extensions of the Bannock thrust to the north, south, east, and west based upon extrapolation of a single large folded thrust surface are not warranted. The Bannock overthrust is reinterpreted as a westward-dip- ping imbricate thrust zone possibly several tens of miles wide extending at least from southwestern Montana to north-central Utah. It is recommended that the name “Bannock overthrust” no longer be used, and that this zone of imbricate thrusts in the southeast corner of Idaho be called the Bannock thrust zone. The thrusts range in age from Late Jurassic to post- Early Cretaceous and are progressively younger from west to east; strong regional compressive forces do not appear to have been active in the area as late as Pliocene time. The upper plates of the thrusts moved to the northeast in response to an unknown force. Steep eastward-trending tear faults formed during thrusting probably in response to differential movement among the eastward-moving thrust plates. In Tertiary and Quaternary time block faulting was extensive; it formed the northward-trending graben valleys seen in the area today. INTRODUCTION Laws regulating the disposal of public lands require that the lands be classified as to their character before disposal, and the responsibility for this classification was given to the United States Geological Survey in its organic act of 1879. Accordingly, in December 1908 the Secretary of the Interior withdrew from entry large areas of public land in southeastern Idaho and adjacent parts of Utah and Wyoming, pending an examination of their phosphate resources. In order that the phos- phate deposits, which became known later as part of the western phosphate reserve, might be developed under the mineral-leasing laws, classification of these lands was started by the Survey in 1909. Hoyt S. Gale was in charge of the work from 1909 to 1910;_R. W. Rich- ards, from 1910 to mid-1912; and George Rogers Mans- field, from mid-1912 to about 1936. Although classifi- cation of these lands has continued intermittently to the present time, the major job of classification was done under Mansfield’s guidance during the period 1909—36. The final results of this work appeared in Geological Survey Professional Papers 152 and 238 by Mansfield, and Geological Survey Bulletins 430 by Gale and Richards, 470 and 577 by Richards and Mansfield, 713 and 803 by Mansfield, and 923 by G. B. Richardson. The geologic maps and descriptions published in these reports not only contributed greatly to an understand- ing of the geology and structural evolution of the Rocky Mountains, but effectively guided exploration for min- able phosphate deposits in this area. Early in their work, Richards and Mansfield found several rather widely separated individual thrust faults of large displacement. As the work progressed, they found evidence that led them to conclude that these thrusts were parts of a single large folded thrust fault which they named the Bannock overthrust (1912‘). In 1947 the Geological Survey started a new study of the western phosphate field. This work was under- taken on behalf of the Division of Raw Materials of the United States Atomic Energy Commission because uranium was known to occur in small amounts in the phosphate rock and in the phosphatic shale associated with it. As it seemed apparent that uranium could be produced economically from these deposits only as a byproduct of phosphate mining, a study was also made of the amount, grade, and distribution of the phosphate deposits and the vanadium and other minor constit- uents of the phosphatic rocks that might be recovered as byproducts in an integrated operation. The work in- cluded detailed stratigraphic studies and geologic mapping. During this study much of the area in south- eastern Idaho covered by the previous land-classifica- tion work was reexamined, some of it being remapped; in addition, an area west of the earlier work was mapped J1 J2 \ SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY for the first time. Some of the findings of this later work have already been published and the rest are be- ing prepared for publication. The new study, as one of its results, indicates that interpretation of the Bannock overthrust requires modi- fication. Although the new work confirms most of the findings of the earlier investigation, it shows that indi- Vidual faults that were thought to be parts of a single folded thrust are in reality separate imbricate thrusts and that these thrusts were not all formed at the same time. The purpose of this paper is to describe some of these faults, to give the evidence that they are not parts of one fault and that they are of different ages, and to discuss the implications of the new data and interpre- tation in relation to the structural evolution of this part of the Rocky Mountains. In order to make clear the differences between the old and new interpretations and the reasons for them, Mansfield’s concept of the Bannock overthrust is reviewed in some detail at the outset. From a review of Mansfield’s changing Concept of the Bannock overthrust, it is possible to speculate that had Mansfield lived and cjmtinued to work in southeastern Idaho, he may have, come to many of the same conclusions We have. Like the original paper on the Bannock overthrust, this paper is a byproduct'of w rk on the phosphate deposits. It is based on detailed geologic mapping in restricted areas and on reconnaissance in southeastern Idaho and adjacent parts of Utah and Wyoming dur— ing several field seasons. Alt ough our work has covered only part of the area nally interpreted by Mansfield to be involved in the Bannock overthrust, a large part of the mapping was in the area where the concept of the Bannock overthrust originated and in other areas which are critical to that interpretation. We have not solved all the problems, and the structure of some cOmplex areas is open to alternative interpre- tations, yet the new data sugges ‘ a reinterpretation of the thrust structure in southeastirn Idaho. Cressman is responsible for the main structural interpretations in an area of about 180 square miles that extends about 15 miles northward from the south end of Snowdrift Mountain and lies between Crow Creek on the east and the town of Georgetown, Idaho, on the west. Armstrong is responsible for all other data and interpre- tations in the report. We acknowledge with thanks the benefit of discus- sions with a number of our Survey colleagues, many of whom have contributed to a better understanding of the geology of southeastern Idaho. We are particularly indebted to William W. Rubey (Who at the start of our work pointed out some of the weaknesses of the concept of the Bannock overthrust as a single feature) for his counsel in the field, and his discussions of the strati- graphy and structure of southeastern Idaho and western Wyoming. We are also indebted to Mr. Rubey and to Steven S. Oriel for information on the ages of thrust faults in Western Wyoming, and particularly for dis- cussion of evidence in western Wyoming that has a bearing on the interpretation of the “structural evolu- tion of southeastern Idaho. 9 FIRST INTERPRETATION OF THE STRUCTURE OF SOUTHEASTERN IDAHO Geologic mapping in southeastern Idaho and the ad- joining part ofnorthern Utah in the summers of 1909 and 1910 by geologists of the U.S. Geological Survey disclosed the presence of several thrust faults that crop out in the ranges adjacent to Bear River and Bear Lake Valleys (Gale and Richards, 1910; Richards and Mans- field, 1911) . As used in this paper, “Bear River Valley” refers to the geographic feature that is the almost unin- terrupted northward continuation of Bear Lake Valley and that extends from Georgetown to Threemile Knoll. Between Georgetown and Nounan low hills of Triassic and Tertiary rocks indistinctly separate Bear Lake Valley from Bear River Valley. At the end of the 1910 field season the structure of the area was interpreted as shown on plate 1A. Several discontinuous, separate thrust faults were recognized. The thrust fault west of Bear Lake Valley was thought to continue northward past Nounan at least as far as Threemile Knoll, where a patch of quartzite boulders on top of the knoll was mapped as an outlier of the thrust (Richards and Mansfield, 1911, p. 400). A steep normal fault, with the downthrow on the west side, was mapped from a point northeast of Threemile Knoll southward along the east side of Bear River and Bear Lake Valleys to a point near the Utah-Idaho boundary. Numerous springs, hot and cold, and travertine deposits along most parts of the projected course of this fault were interpreted as indicating the position of the fault where it was poorly exposed Or covered (Richards and Mansfield, 1911, p. 398). Another normal fault that branches from the first one south of Georgetown was mapped southward along the west, side of Bear Lake Valley. Downthrow on this fault is on the east side. Bear Lake Valley thus was interpreted as a graben tapering northward (Richards and Mansfield, 1911, p. 398—399), but no mention was made of the structure of Bear River Valley. THE BANNOCK OVERTHRUST ORIGINAL INTERPRETATION ‘As the result of mapping east and northeast of Georgetown, Idaho, in the summer of 1911, the struc- THE BANNOOK THRUST ZONE, SOUTHEASTERN IDAHO J3 tural interpretation of southeastern Idaho was revised. A sinuous thrust fault was recognized that extended from the Left Fork of Twin Creek on the west, across Georgetown Canyon, around the south end of Snow- drift Mountain, and into Crow Creek on the east (pl. 2A). The western part of the trace of the fault is con- vex to the north, and the eastern part concave to the north; the dip along the trace is to the north side of the fault. From the outcrop pattern and direction of dip, two northward-plunging folds were interpreted in the thrust surface, an anticline on the west and a syncline on the east; the sinuousity of the fault was believed to result principally from folding of the thrust surface. Recognition of two folds raised questions as to whether there might be other folds in the thrust, and led to the interpretation that the known folds continued to the west in another syncline and anticline. From this 1n— terpretation it was deduced that the known thrust faults of the area, rather than being separate and discon- tinuous as previously believed, were all parts of one large folded overthrust. This thrust fault was de- scribed and named the Bannock overthrust after Ban- nock County, Idaho, from its exposures in the eastern part of the county (Richards and Mansfield, 1912). In 1919 the original Bannock County was divided into Bannock County on the west and Caribou County on the east; consequently the exposures from which the fault took its name are now in Caribou County. As a result of this later interpretation, faults were connected that would not otherwise be thought of as the same fault. Faults dipping in opposite directions, as well as those with flat or steep'dips, could thus be interpreted as parts of the same feature. The sinuous, disconnected thrusts exposed in southeastern Idaho were therefore supposed to result from erosion of a single folded thrust surface. The outcrop pattern and amount and direction of dip of any part of this master fault would therefore depend not only on topography and the original dip of the fault, but also on the later folding of the thrust surface and the position of the outcrop on a later fold. Consequently, faults inter- preted as thrusts could have any dip and the direction of dip had no relationto the direction of movement (Richardsand Mansfield, 1912, p. 697). This expanded and revised structural interpretation (Richards and Mansfield, 1912) is shown in plate 18. Two major changes from the interpretation of 1910 (pl. 1A) should be noted: (a) the normal \fault along the east side of Bear River Valley was interpreted as a thrust fault; and (b) Bear River Valley was considered to be a window in the thrust surface. MANSFIELD’S FINAL INTERPRETATION As more of southeastern Idaho was mapped, details of the thrusting were worked out and the folded— thrust interpretation was amplified and extended to apply to a larger area (Richards and Mansfield, 1914; Mansfield, 1920, 1921, 1927, 1929, 1952; Richardson, 1941). The concept of the Bannock overthrust thus grew and Changed so that its final form, although preserving the idea of a folded thrust, was different from that first presented, The early mapping covered the southern part Of the Bannock and in this area it was considered to be a single thrust fault (Richards and Mansfield, 1912, p. 695; 1914, p. 35). Textbooks on structural geology (Willis and Willis, 1934, p. 181; Nevin, 1942, p. 111; Billings, 1942, p. 183; Hills, 1943, p. 120; Eard- ley, 1951, fig. 184) ordinarily refer only to the earliest and simplest interpretation of the Bannock overthrust: the single folded thrust fault in the southern part of the area. Later, as mapping progressed northward, the Bannock was recognized at some places as a single fault and at other places as a fault zone made up of several branch faults (Mansfield, 1921, p. 451 ,1927, p. 150, 151, 152; 1929, p. 55). Finally, 1n the northern part of the area, a broad zone of thrust faults was recognized that was believed to be the northward continuation of the Bannock (Mansfield, 1952, p. 61). In this area the Bannock overthrust was considered to be made up of “three principal branches * * * and several minor faults that * * * are conceived as originating in a sole, or great thrust fault * * * shallow enough to permit its exposure at the surface where affected by gentle folding or fault- ing” (Mansfield, 1952, p. 67). It thus appears to us: (a) that Mansfield finally inter- preted the northern part of the Bannock overthrust as an imbricate thrust zone originating in a concealed folded sole thrust, and the southern part in Bear River and Bear Lake Valleys as a single large folded thrust fault; and (b) that this single fault is the exposed sole of the zone to the north. Mansfield’s final interpreta- tion of the Bannock overthrust (1952, p. 64—68), and its extensions as suggested by other geologists is shown in plate 10. EXTENT As finally interpreted (Mansfield, 1952, p. 66), the Bannock overthrust extended from Woodrufl' Creek, Utah, to the southeast edge of the Snake River Plain southeast of Idaho Falls, Idaho, an airline distance of about 140 miles and a distance along the major traces of the fault of about 270 miles. J4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY DISPLACEMENT The Bannock overthrust was thought to have been formed by northeast-southwest compressional forces that pushed the overriding block northeastward. A horizontal displacement of at least 12 miles and possibly slightly more than 35 miles was postulated (Richards and Mansfield, 1912, p. 703—704; Mansfield, 1921, p. 447; 1952, p. 64). The stratigraphic throw on the Bannock, that is, the stratigraphic throw on the sole fault or the sum of stratigraphic throws on branch faults in the thrust zone, ranges from about 1,000 feet to perhaps as much as 20,000 feet (Mansfield, 1927, p. 158). The points of minimum and maximum stratigraphic throw are about 15 miles apart near the East and West Stump branches of the Bannock (pl. 10). Proximity of the points of minimum and maximum throw was explained by the fact that stratigraphic throw at any point on the thrust is not a true measure of movement on the fault. Prior to the thrusting, the sedimentary rocks were folded into a series of anticlines and synclines, Then the Bannock cut obliquely and irregularly through the folds and moved folded upper plates over folded lower plates, so that the stratigraphic throw at any one point represents only chance juxtaposition, at the time thrusting ceased, of previously folded formations. Amount of strati- graphic throw thus varies widely. FOLDING An important feature of the Bannock overthrust interpretation, in both its first and final forms, is the folding of this originally nearly horizontal and rather regular thrust surface (Richards and Mansfield, 1912, p. 704; Mansfield, 1921, p. 451; 1927, p. 159; 1952, p. 65). Renewed compressional forces, acting in the same direction as the original thrusting, folded the fault surface into anticlinal and synclinal folds, some of which were locally overturned to the northeast. In the southern part of the area four folds, two anticlines and two synclines, were recognized in the sole thrust (Richards and Mansfield, 1912, fig. 2; Mansfield, 1927, pl. 37) (pl. 2A). The western anticline arches over Bear River Valley ; the syncline next east passes beneath the Aspen Range and the towns of Georgetown and Montpelier; the crest of the eastern anticline is exposed in Georgetown Canyon, on the Left Fork of Twin Creek, and in the Slug Creek window; the eastern syn- cline passes beneath Snowdrift Mountain. Folding of the thrust surface brought the crests of the anticlinal folds close enough to surface so that sub- sequent erosion could cut through the overlying block, expose the underlying block, and thereby form windows in the thrust. Two such windows, the Bear River Val- ley and Slug Creek windows, were thought to have been formed on the crests of the anticlines in the sole thrust (Richards and Mansfield, 1912, fig. 2; Mansfield, 1927 , pls. 1, 37) (pl. 2A) ; farther north two other win- dows were mapped (Mansfield, 1952, p. 65, fig. 25) (pl. 10). Recognition of folds and windows in the thrust sur- face led to the interpretation that a large folded thrust fault underlay a large part of southeastern Idaho. If the presence of a folded thrust were accepted, then it became possible to interpret other folds and windows in the thrust from evidence that in itself was inconclusive. As is suggested below (p. J17), the Portneuf and Para- dise Valley windows are perhaps two such windows. AGE The Bannock overthrust was believed to have formed during Late Cretaceous or early Tertiary time (Rich- ards and Mansfield, 1912, p. 704), probably'near the end of the Laramide orogeny (Mansfield, 1921, p. 465; 1952, p. 73). The youngest rocks involved in the thrusting are those of the Upper Cretaceous (and Lower( ?) Cretaceous) Wayan formation (Mansfield, 1927, p. 151, pls. 2, 4, 5, 11; 1952, p. 44, 6'8, pls. 1, 2). The oldest rocks concealing the trace of the fault are those of the Eocene Wasatch formation, probably the lower part of the Wasatch (Richards and Mansfield, 1911, p. 394, pl. 16; Mansfield, 1927, p. 109, 155, pl. 9). In the southern part of the area, where the Bannock is interpreted as a single thrust fault, all the now-isolated parts of that once continuous thrust were considered to be of the same age. Another important feature of the Bannock overthrust interpretation is that the thrust surface was thought not to have been folded until late Pliocene or post- Pliocene time, long after thrusting had ceased (Mans- field, 1921, p. 465; 1927, p. 203; 1929, p. 62; 1952, p. 73). It was believed that the shape of the folds and degree of folding in the thrust surface resemble the low dips and open folds in the Salt Lake formation (Pliocene( ?)) and some of the associated lavas, and that these similari- ties indicated that all had been folded at the same time. EXTRAPOLATION OF THE BANNOCK OVERTHRUST In the original paper on the Bannock overthrust, the possibility was recognized that the Bannock and “known thrust faults of probably identical age” in southeastern Idaho and nearby Wyoming and Utah might all be parts of one fault which are now isolated by erosion (Richards and Mansfield, 1912, p. 7 06—707 ). There can be little doubt that “known thrust faults of probably identical age” included all thrusts from the Willard on the west to the Darby on the east. Since 1912 several more specific extensions of the Bannock THE BANNOCK THRUvST ZONE, SOUTHEASTERN IDAHO . ' J5 have been suggested, all of which greatly increased its possible length and horizontal displacement. These ex- , trapolations of the Bannock were based on, and made possible by, the assumption that a large folded thrust underlay the area. Various extensions of the Bannock overthrust to the north were proposed. Originally the Putnam over- thrust was mapped as a separate fault (Mansfield, 1920, p. 62), but later it was interpreted, as a branch of the Bannock that connected with the main overthrust to the southeast along a line passing through the Portneuf window (Mansfield, 1929, p. 56) (pl. 10). Southeast of Idaho Falls the Bannock passes beneath Tertiary lava and sediments of the Snake River Plain. North of the plain along the projected strike of the Bannock is the Medicine Lodge thrust, and it has been suggested that it is the northWard continuation of the Bannock (Kirkham, 1927, p. 27; Mansfield, 1929, p. 58; 1952, p. 67). A westward extension of the northern part of the Bannock was postulated by Ludlum (1943, p. 984—985) . He suggested that the Putnam-Bannock fault emerged somewhere between the Putnam overthrust and the Bannock Range, arched over the range, and descended again to the west. According to this interpretation, the Bannock Range is in a large window in the Putnam- Bannock fault, and the root’of the fault is somewhere west of the range. The Auburn and Star Valley faults were suggested as possible eastward extensions of the Bannock (Mans- field, 1927, p. 159). As the master fault was believed to be folded, eastward dips of the Auburn and Star Valley faults were explained by those faults’ being on the eastern flank of an anticlinal fold in the master fault. According to this interpretation, the area between the Auburn and Star Valley faults and the Bannock fault is a window whose boundaries are not completely known. Originally the Bannock was interpreted as connect- ing southward with a thrust near the southeast corner of Bear Lake (Richards and Mansfield, 1912, fig. 1), but later it was interpreted as connecting with a fault near the southwest corner of Bear Lake (compare pls. 112 and 10). Beyond this point the Bannock was projected southward to connect with the thrust exposed along Woodrufl' Creek, Utah (Richards and Mansfield, 1911, p. 397; Mansfield, 1929, fig. 2; 1952, fig. 25; Richardson, 1941, fig. 2). The possibility that the Bannock connects withthe Willard thrust South and west of Woodruif Creek was recognized early (Richards and Mansfield, 1912, p. 707), and fieldwork, though at first contradictory (Black- 649984—63—2 welder, 1910), later suggested that such a connection was probable (Blackwelder, 1925). Still later work suggested that the trace of the probable connection between the two thrusts is about as shown on plate 10 (Eardley, 1944, p. 866-872; 1951, figs. 185, 189; Crit- tenden, 1959, fig. 1; 1961). THE BANNOCK THRUST ZONE: PRESENT INTERPRETATION We have traced the development of the interpreta- tion of the Bannock overthrust from its original to its final form, and have shown how the overthrust has been interpreted to extend beyond its original suggested limits. Let us now examine that interpretation and its extrapolations in the light of recent field work. Although the new mapping confirms most of the earlier mapping, certain important differences require modifications of some of the previous structural interpretations. AREA EAST AND NORTH OF GEORGETOWN East and north of Georgetown, where the Bannock overthrust interpretation originated, remapping con- firms ~the presence of flexures (pl. 28) in the surfaces of several thrust faults, but it seems probable that the flexures were formed during the later part of the same orogeny that produced the thrusts, rather than in late or post-Pliocene time, and that the thrust fault does not continue many miles to the north. Evidence from key areas that supports these conclusions is given in the following sections. LEFT FORK OF TWIN CREEK AND GEORGETOWN CANYON The structure of the Left Fork of Twin Creek and Georgetown Canyon area is complex, and because of incomplete exposures some of the details may never be correctly deciphered. Several intimately and complexly related thrust faults occur there (pl. 3). The thrust surfaces have been bent and broken, and the abrupt bend in the thrust originally interpreted as an anti- clinal fold in the thrust surface (Richards and Mansfield, 1912, p. 697; Mansfield, 1927, p. 153) is at a point where the thrust is cut by a later, nearly vertical fault. Only that part of the geology on plate 3 that immediately concerns the Bannock overthrust interpre- tation will be mentioned. A short distance southwest of Shale Spring (pl. 3) an anticline in the Twin Creek limestone is cut at its north and south ends by thrust faults that join farther southwest to form one thrust. Displacement on the southern branch brings Twin Creek limestone over Nugget sandstone and Upper Triassic rocks; displace- ment on the northern branch is within the Twin Creek. J6 lSHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY [The southern branch is probably the main thrust sur- face; the upper plate probably buckled from continued compression and finally broke along the northern branch to form a small imbricate thrust above the main fault. A little northwest of these thrusts, a larger thrust brings Carboniferous rocks over Jurassic and Triassic rocks, and near its southwest end the larger thrust covers the thrust between the Twin Creek and Upper Triassic rocks (pl. 3). West of Shale Spring the upper plate of the large thrust is broken by a tear fault and by a small imbricate thrust fault that probably formed in the same manner as the earlier imbricate thrust in the Twin Creek. About three quarters of a mile east of Shale Spring 21. straight steep fault cuts the large thrust, and on the west, near the south end of Dairy syncline, an- other fault cuts both thrusts (pl. 3). The faults that cut the thrusts have much in common; along both, Brazer limestone (Mississippian) is in contact with Twin Creek limestone (Jurassic). The northern part of the western fault, however, separates Wells forma— tion (Pennsylvanian and Permian) from Madison limestone (Mississippian) , and the northern projection of the eastern fault is within the Brazer. Insufficient movement occurred along these faults, therefore, to ex- plain the large stratigraphic throws shown along some parts of their traces. Most of this large stratigraphic throw is clearly a result (if thrusting; Brazer rocks of the upper plate of the large thrust have been dropped down along the east and west faults so that Brazer is in contact with Twin Creek and other Mesozoic rocks of the lower plate. Between the Left Fork of Twin Creek and George- town Canyon and along the south side and at the west end of Georgetown Canyon are areas of Madison lime- stone that also are interpreted as parts of the upper plate of the large thrust (pl. 3). Although the nature of the fault that separates Carboniferous rocks on the west from, Mesozoic and Carboniferous rocks on the east near the mouth of Georgetown Canyon cannot be stated with certainty, it is interpreted as a later range-front fault similar to the fault that cuts the thrusts near .he south end of Dairy syncline. A similar fault along he range front is the east boundary of a small area of adison a third of a mile southeast of the Left Fork f Twin Creek. The thrust pattern thus is not simple, but one in which hrust plate is thrust on thrust plate, each bending and reaking to form a complex imbricate structure. Cut- ing this complex thrust pattern are later faults. The steep fault three-quarters of a mile east of Shale pring was not mapped by Richards and Mansfield, and the sharp bend where the thrust meets the steep fault was interpreted as an anticlinal flexure (Richards and Mansfield, 1912, p. 697) in the thrust surface. In the critical area to the north, exposures are sparse and a displacement of several hundred feet in the Brazer could go undetected. The fault was not found during remapping of this critical area, but the bend in the trace of the axial plane of the Summit View anticline, which probably was caused by ofl'set on the steep fault, may mark its northward continuation. The steep fault served only to modify the thrust pat- tern, for if the rocks are restored to their positions prior to movement on the steep fault east ofShale Spring, an anticlinal bend in the thrust surface still seems neces- sary to allow the thrust to pass under Snowdrift Moun- tain. Had this bend in the thrust surface resulted from folding after thrusting had ceased, there should be a similar bend in the rocks above the thrust. No such fold was recognized, however, in remapping the rocks of the upper plate of the thrust. The absence of such a fold in the rocks above the thrust suggests that the bend in the thrust surface was not formed after thrust- ing had ceased, and that this bend, like the others in the area, was formed at the time of thrusting. SLUG CREEK Recent mapping in the area of the Slug Creek window (Cressman and Gulbrandsen, 1955, pl. 27), about 6 miles north of Shale Spring, shows that the faults bordering the east and west sides of the winddw are normal and that the west sides dropped downward (pl. 23). The eastern fault has a stratigraphic throw of only a few hundred feet at its north end and cannot be traced the length of the window with confidence; the western fault also has a stratigraphic throw of only a few hundred feet, but it can be traced north and south of the limits of the window. If a fault is present along the south margin of the window, it is of small displace- ment; the fingerlike projection of Wells formation (Pennsylvania and Permian) at the south end of the window that Mansfield (1927, pl. 6) showed overlying Rex chert. (Permian) is now interpreted as Tertiary gravel that lies on top of the Rex chert member of the Phosphoria formation. The absence of the window eliminates its use as corroborative evidence for the northward continuation of the thruSt fault on the Left Fork of Twin Creek. SYNCLINE UNDERNEATH SNOWDRIFT MOUNTAIN Richards and Mansfield traced what they believed to be a single thrust fault from the Left Fork of Twin Creek southeastward around the south end of Snow- drift Mountain and from there to the northeast into Crow Creek valley where Mansfield (1927, pl. 1) showed THE BANNOCK THRUST ZONE, SOUTHEASTERN IDAHO J7 the thrust dividing into several branches. The faults dip toward Snowdrift Mountain (pl. 2A). Remapping of this area shows that the thrust along the southwest side of Snowdrift Mountain, which has a stratigraphic throw of about 14,000 feet, splits into several branches near the south end of Snowdrift Mountain. East of where the branching occurs, the stratigraphic throw is distributed among the branches and decreases progres- sively toward the northern end of each branch (pl. 23). No stratigraphic throw was found along Preuss Creek, but at this locality complex structure within the Twin Creek limestone necessitates an extension of a thrust fault around the southeast end of Snowdrift Mountain to join with one of the faults in Crow Creek valley. Although the accompanying map (pl. 3) of the Georgetown Canyon-Snowdrift Mountain-Crow Creek area differs in some details from that of Richards and Mansfield, it supports their main interpretation: the curving fault trace around the south end of Snowdrift ’Mountain can be interpreted as the surface expression of a north-plunging gentle synclinal fold in the fault surface. . CROW CREEK FAULT ZONE In contrast to the fault along the southwest side of Snowdrift Mountain where all the throw is on one fault, the thrust fault zone in Crow Creek valley con- sists of discontinuous, branching, subparallel thrust faults (Mansfield, 1927, pl. 7; Cressman, 1957). Stratigraphic throw on the individual thrusts exceeds 1,500 feet at only a few places. A fault zone consisting of branches of the Bannock overthrust was shown as extending north of Crow Creek for about 12 miles and then‘northwestward for about 55 miles to the Snake River Plain (pls. 10 and 2A) (Mansfield, 1927, pl. 1; 1952, pl. 1). The ranges west of the fault zone were thus thought to be part of the Bannock overthrust plate. For about 30 miles north ’ and northwest of Crow Creek, however, the branches of the thrust lie for the most part between formations that are adjacent in the/stratigraphic column; perhaps some of the thrusts would not have been mapped if their presence had not been required by the regional struc- tural interpretation; Furthermore, the East Stump and West Stump branches of the Bannock (pl. 10) appear from their traces to dip steeply eastward (Mansfield, 1927, pl. 5); possibly they are normal faults. The character of the faults from the head of Crow Creek to the East and West Stump faults and the absence of the Slug Creek window suggest to us that individual thrusts are not continuous from Crow Creek to the Snake River Plain, and that the thrust beneath Snow- drift Mountain and the southern parts of Dry Ridge and the Aspen Range dies out northward. Much of the horizontal movement on this thrust may have been taken up along tear faults such as those in Crow Creek valley (pl. 23). The Blackfoot fault, about 23 miles north of Georgetown (pl. 4), whose south side has moved east nearly 2 miles (Young, 1953, p. 83), and a similar but smaller fault about 3 miles north of the Blackfoot fault (V. E. McKelvey, written communication, 1958) are other tear faults along which movement may have been taken up. BEAR RIVER VALLEY Recent mapping of critical areas shows that Bear River Valley is a graben and that the thrust fault along the west side of the valley and that on the Left Fork of Twin Creek are not parts of one large thrust fault. Data supporting these conclusions are discussed in the following paragraphs. AREA NORTHWEST OF NOUNAN Northwest of Nounan, Brigham quartzite (Cam- brian) has been thrust over Thaynes formation (Lower Triassic) along a westward-dipping thrust fault. Richards and Mansfield (1911, p. 426, pl. 14) originally mapped the quartzite as Brigham, but later Mansfield (1927, p. 155, pl. 6) showed the quartzite as Swan Peak (Ordovician). Remapping of a small part of this area confirms the quartzite as Brigham and shows that the thrust, which has a stratigraphic throw of about 20,000 ”feet, is cut by at least two steeply eastward-dipping normal faults which strike north-northwest (pl. 23). Where examined, the traces of the normal faults are marked by linear outcrops of intensely brecciated quartzite and eastward-facing, scarps, and on aerial photographs they form moderately straight lineaments, locally marked by scarps, which can be traced on the photographs about 2 miles north and about 8 miles south. These faults and other similar, approximately parallel lineaments roughly mark the topographic western border of Bear River Valley. ‘ West of Liberty, Brigham quartzite is thrust over Thaynes formation along a westward—dipping thrust fault, as it is northwest of Nounan. The similarity of geologic structure suggests that these thrusts are parts of the same fault and connect under cover along the west side of Bear River Valley in a manner similar to that shown on plate 23. The possible northward con- tinuation of this thrust is discussed in the next section. THREEMILE KNOLL On top of Threemile Knoll a patch of large quartzite boulders overlies Thaynes formation] Originally the quartzite was thought to be Cambrian, probably Brigham (Richards and Mansfield, 1911, p. 404), but J8 , ‘SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY later was referred to the Ordovician Swan Peak (Mans- field, 1927 , p. 234, pl. 44). The supposed similarity of the structural relations at Threemile Knoll to the thrust fault northwest of Nounan (that is, Cambrian or Ordovician quartzite overlying Thaynes at both places) led to the interpretation that the quartzite boulders were erosional remnants or an outlier of a thrust plate that once extended over the top of Threemile Knoll (Richards and Mansfield, 1911, p. 404; Mansfield, 1927 , p. 156). Remapping of Threemile Knoll and the surrounding area confirms the identification of the quartzite boulders as Swan Peak. The quartzite occurs as conspicuous white boulders, cobbles, and pebbles. Although quartz- ite of the Swan Peak formation makes up most of the “erosional renmant,” relatively inconspicuous cobbles and (pebbles derived from other Paleozoic formations are also present. All the fragments lie in a red sandy matrix locally calcite-cemented and are of the same resistant rocks that commonly occur as fragments in Tertiary (?) gravels nearby; they could have been de- rived by erosion from nearby hills. Patches of this bouldery material occur also on the flanks and along the base of Threemile Knoll, as well as nearby (pl. 23) , and on the crest and west flank of the north end of the Bear River Range. The material on top of Threemile Knoll is therefore interpreted to be a Tertiary( ?) gravel, and not an outlier of the Nounan thrust—a pos- sibility that Mansfield (1927 , p. 234) considered but, on the basis of the evidence then available, rejected as the less probable of the two interpretations. The large thrust fault near Nounan continues north- westward under cover for an unknown distance. Mans- field (pls. 10, 2A) projected it from near Nounan to a point a short distance west of Threemile Knoll and thence to the Portneuf window and beyond. Although the thrust may extend as far as Threemile Knoll, we be- lieve that it dies out northwest of Nounan and that it probably extends no farther than Tenmile Pass, about 20 miles northwest of the outcrop near Nounan (pl. 4). The geologic structure of the Chesterfield Range north of Tenmile Pass, although partly concealed by Tertiary cover, appears to contrast strongly with the structure of the Soda Springs Hills and the north end of the Bear River Range, south of the pass. North of the pass, Paleozoic rocks are folded and faults are not abundant. South of the pass, Paleozoic rocks that dip moderately and uniformly eastward are cut by two sets of steeply dipping faults; one set strikes about north, the other nearly east. The eastward-trending (tear?) faults have a cumulative left-lateral offset probably in excess of 10,000 feet. We think that the eastward- trending faults partly absorbed the movement along the thrust and that they probably indicate the northern end of the thrust plate. Moreover, north of Tenmile Pass in the area between the Portneuf window and Reservoir Mountain (pl. 10), the presence of a large thrust fault is not necessary to a logical explanation of the geologic structure. On the contrary, if a large thrust fault is projected through this area, it must be projected beneath cover, for no such thrusts were seen where Paleozoic and Mesozoic rocks are exposed (Mansfield, 1927, pl. 3; 1929, pl. 1). The improbability of the existence of the Portneuf win- dow is discussed below (p. J17). EAST BORDER OF BEAR RIVER VALLEY Remapping the east border of Bear River Valley shows that a steeply westward dipping normal fault, or series of faults, extends along the west front of the Aspen Range between Georgetown and Threemile Knoll. Mapping near Soda Springs indicates that in this area springs and travertine deposits similar to \ those that are numerous along the east side of Bear River and Bear Lake Valleys are associated with recent block faults and not with thrust faults. New mapping in the Aspen Range immediately east of Bear River Valley shows that, although a few thrust faults are present, they have only minor displacement and that many of the thrusts previously mapped in this area “do not exist or are better interpreted as normal faults” (Gulbrandsen and others, 1956, p. 16—17). The presence along the east side of Bear River Valley of a westward-dipping normal fault, instead of an eastward-dipping thrust fault as previously believed, and the absence of an outlier on Threemile Knoll elim- inate the basis for the postulation of the western syn- clinal and anticlinal folds in the Bannock overthrust and also of the Bear River Valley window. Bear River Valley is thus a graben bounded on the east and west by normal faults. The thrust along the east side of Bear River Range, best exposed west of Paris (pl. 4), and'the one in the Georgetown Canyon area, well ex- posed near Meade Peak (pl. 213), are separate thrusts. To emphasize their separate nature they are here named ‘ the Paris and Meade thrusts, respectively. AGES 0F THRUSTING- Probable differences in age among the thrust west, . and those east and northeast of Georgetown support the conclusion that they are not parts of one large thrust. , PARIS THRUST FAULT The Paris thrust cuts Thaynes formation (Lower Triassic) and the trace of the thrust is covered by _ age. THE BANNOCK THRUST ZONE, SOUTHEASTERN IDAHO " J9 Wasatch formation 1 (Eocene) (Mansfield, 1927, pl. 9). A more precise dating of the thrust is suggested, how- ever, by fragments in rocks mapped as Ephraim con- glomerate on Red Mountain in the Gannett Hills (pl. 23). At its type locality in the Gannett Hills (pl. 23) the Gannett group (Lower Cretaceous) is between 3,000 and 3,500 feet thick and has been divided into five for- mations, from bottom to top: Ephraim conglomerate, Peterson limestone, Bechler conglomerate, Draney limestone, and Tygee sandstone. Lower Cretaceous fresh-water faunas have been found in the Peterson and Draney limestones (Mansfield, 1927, p. 101—105; Moritz, 1953, p. 63—68). To the north and east the Gannett group thins rapidly, becomes finer grained, and con- tains only a few feet of conglomerate in the entire sec- tion; its five formations lose many of their distinguish- ' ing characteristics, and consequently recognition of the different formations is somewhat uncertain (Moritz, 1953, p. 66—68; Wanless and Gray, 1955, p. 53—57; Rubey, 1958). On Red Mountain (pl. 2) exposures of rocks mapped as Ephraim conglomerate (Mansfield, 1927, pl. 9) con- sist of numerous outcrops of thick resistant beds of poorly sorted red conglomerate separated by areas of red soil in which are small sparse outcrops of red sand-' stone. Although most outcrops are conglomerate, \ conglomerate beds make up probably less than half"vthe total stratigraphic thickness at this local- ity. The Ephraim on Red Mountain can be divided roughly in half into a lower and an upper part on the basis of the character of the conglomerate beds present. The lower part of the Ephraim is characterized by beds of pebble conglomerate that contain dark-colored 1The Wasatch group near Evanston, Wyo., was divided by Veatch (1907, p. 87—96) from bottom to top into the Almy, Fowkes, and Knight formations. The Knight, conglomeratic and otherwise lithologi- cally similar to the Almy, was thought to overlie the other two fema- tions unconformably. Fossils from all three formations were considered Eocene, and a close stratigraphic relation was recognized between the Evanston formation (then tentatively regarded as Eocene) and the con- formably overlying Almy and Fawkes formations. Work by Tracey and Oriel (1959, p. 128, 129) has shown that in the northern part of the area mapped by Veatch much of the area shown as Almy is underlain by rocks more properly assigned to the Evanston formation of Late Cretaceous and Paleocene age. Diagnostic fossils have not been found at the type locality of the Almy, nor has this area been remapped; however, the stratigraphic position of the type Almy, provided it, too, is not part of the Evanston, indicates a post-Evanston and pre-Knight Fossils from the type locality of the Fawkes show it to be of late Eocene or possibly earliest Oligocene age and, therefore, to overlie the Knight. The Knight unconformably overlies the Evanston and at its type locality and elsewhere has yielded fossils of early Eocene age. Although Richards and Mansfield (1911, p. 394, p1. XVI; 1914, p. 38) originally thought that the conglomeratic beds overlying the trace of the Paris thrust southwest of Paris were correlative with the Almy of Veatch, Mansfield (1927, p. 109) later decided that it was impracticable to distinguish between the Almy and Knight in that area. Accordingly he showed the Eocene Wasatch formation overlying the Paris thrust. His usage is followed in this report. chert pebbles set in a red sandy matrix. Most of the pebbles are less than 2 inches but some are as much as 5 inches in diameter. In addition to chert, these con- glomerates also contain a small proportion of sandstone pebbles and quartzite pebbles. A second type of' con- glomerate occurs in lesser amounts in the lower part of the Ephraim. This is a cobble conglomerate and con~ tains cobbles of limestone, sandstone, chert, and quartz« ite in about equal amounts. The cobbles average about 3 inches and reach a maximum diameter of about 6 inches. In the lower part of the Ephraim, limestone fragments seem to be restricted to the cobble conglomerates. Although the precise stratigraphic sources of the peb- bles and cobbles cannot be identified with certainty, their general aspect suggests that almost all were de- rived from upper Paleozoic formations. Most pebbles in the lower part of the Ephraim are dark-colored chert. Generally the chert does not occur as large pieces; where the conglomerate is coarse, it occurs as small frag- ments among the large ones; where the conglomerate consists of pebbles about 2 inches or less in diameter, the pebbles may be almost exclusively chert. With the aid of a hand lens it can be seen that many of the chert pebbles are spicular. Examination of a thin section of a maroon chert pebble shows it to contain silicified spicules and a few individual carbonate rhombs, and to lack detrital quartz grains; that is, it strongly resembles chert from the Rex chert mem- ber of the phosphoria formation (Permian). Many Paleozoic formations in the region contain abundant chert; for example, the cherty shale and Rex members of the Phosphoria formation (Permian), the Wells, the Brazer, and the Fish Haven formations. In con- trast to the Paleozoic rocks, the only Mesozoic rock that contains significant amounts of chert is the Portneuf limestone member of the Thaynes formation, and the Portneuf contains abundant chert only in its north- westernmost part at Fort Hall, about 60 miles north- west of Red, Mountain. South and east of Fort Hall the Portneuf rapidly changes in character and the chert disappears (Kummel, 1954, pl. 38, 39). It is not pos- sible, of course, to identify the source formations of in- dividual chert pebbles, but to one familiar with the Paleozoic rocks of the region, it is apparent that all the chert pebbles could have been derived from Paleozoic formations. Because of_the abundance of chert peb- bles, the several possible Paleozoic sources, and the re- stricted possible Mesozoic sources for them, it seems highly probable that the chert pebbles were derived al- most entirely from upper Paleozoic formations. Almost all the limestone cobbles strongly resemble- Carboniferous limestones that crop out to the west :. J10 many are sandy and silty limestones similar to those in the Brazer limestone and Wells formation; a few are composed largely of flattened oolites similar to the limestones that characterize the lower member of the Wells (‘Cressman and Gulbrandsen, 1955, p. 260) ; others contain brachiopod and coral fragments and echinoid spines, and a few are coarse crinoidal limestone similar to that in the Madison limestone. A half dozen or so cobbles of the distinctive medium—brown, fine sandy and silty limestone so characteristic of the Triassic formations in the area were also found. Some of these contain large brachiopod fragments and are thought to be from the Dinwoody formation. Many of) the sandstone pebbles and cobbles can be referred to the sandy units in the Brazer and Wells formations with a high degree of certainty. One red sandstone pebble may have been derived from the Preuss sandstone (Upper Jurassic). Among the pebbles in the cenglom- erates are also a few rounded pebbles of white pure quartzite that is composed of uniformly medium—sized well-rounded frosted sand grains of high sphericity. Because of their distinctive lithology, it seems probable that these pebbles were derived from the Ordovician Swan Peak formation. . The upper part of the Ephraim on .Red Mountain, from about 7,800 altitude to the top, is characterized by beds of poorly sorted boulder conglomerate that con- tain abundant carbonate fragments. The fragments occur in a red sandy matrix similar to that of the con- glomerates in the lower part of the Ephraim. Cobbles 6 to 10 inches in diameter are common, many boulders are 20 inches in diameter, and a maximum diameter of 24 inches has been reported (Steven S. Oriel, written communication, 1959). The coarsest beds are in a zone near the middle of the upper part of the Ephraim; slightly less coarse but otherwise similar conglomerates lie stratigraphically above and below it. The main constituents of these conglomerates are cobbles and boulders of limestone; conspicuous, though ‘ less abundant, are cobbles and boulders of quartzite, dolomite, and sandstone; and even a few shaley frag- ments were found. Chert is moderately abundant but is not conspicuous as it occurs mostly as pebbles inter- stitial to the larger fragments. Most of the limestone fragments again strongly re- semble the Carboniferous limestones that crop out to the west: many are sandy and silty limestones similar to those in the Brazer and Wells formations; several contain abundant flattened oolites similar to limestones in the lower member of the Wells; a number contain brachiopods and corals similar to the Carboniferous limestones, and one is a coquina. Most of the sand- stone fragments found also resemble units in Carbonif- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY erous formations. Several fragments of medium brown, silty limestone from the Dinwoody( '9) forma- tion, a few containing brachiopods, also were found. A few red sandstone pebbles and cobbles foundin these conglomerates may possibly have been derived from the Preuss sandstone; and the single glauconitic sandstone pebble found may have come from the Stump sandstone. The chert pebbles are similar to those in the lower part of the Ephraim. One brown and tan chert cobble was found that is like the brown- and tan-weathering chert characteristic of the phosphatic chert horizon at the base of the Brazer. Thin section examination shows that it contains detrital sand grains like chert ‘ from the Brazer limestone. Cobbles and boulders of quartzite derived from the Swan Peak formation of Ordovician age are conspicu- ous and numerous throughout the upper part of the Ephraim, but they are most Conspicuous and perhaps most abundant in the coarse conglomerates near the middle part of that unit. Several quartzite fragments were found that, in addition to diSplaying the distinc- tive Swan Peak lithology, contain numerous small pits characteristic of the quartzite in the upper part of the Swan Peak formation (Armstrong, 1953),; one such boulder is 21 inches in diameter. The upper part of the Ephraim also contains num- erous cobbles and boulders of dolomite. Some are white, coarsely crystalline dolomite like many of the beds in the Laketown dolomite (Silurian); some are medium-brown, medium-crystalline dolomite similar to the Fish Haven dolomite (Ordovician) and to a few thin dolomite beds in the upper member of the Wells; and others are dark-brown, medium-crystalline, petro— liferous-smelling dolomite like the Jefferson dolomite (Devonian). With the exception of the beds in the Wells, dolomites of these types are not known to occur stratigraphically above the Jefferson in the Ephraim source area to the west. Fragments of quartzite from the Worm Creek quartzite member of the St. Charles limestone (Upper Cambrian) and Brigham quartzite (Lewer( ?) and Middle Cambrian) were looked‘for but not found. Both quartzites are easily recognized; the Worm Creek contains abundant white porcelaneous feldspar grains, and almost all units of the Brigham are characterized by a wide range in grain size. Fragments from these quartzites are conspicuous in the Evanston formation (Late Cretaceous and Paleocene) in nearby western Wyoming and in later Cenozoic conglomerates of the area. , A. number of conclusions are suggested by the char- acter of the Ephraim on Red Mountain: (a) The differences betWeen the conglomerates in the lower and THE BANNOCK THRUST ZONE, SOUTHEASTERN IDAHO upper parts of the Ephraim suggest that the source area was farther to the west or that there was less relief between the source area and Red Mountain in early Ephraim time than in late Ephraim time. (b) The lack of fragments from Mesozoic formations, particu- larly the distinctive medium-brown fine sandy limestone and limy sandstone so characteristic of the Triassic formations in the area, suggests that the Mesozoic (formations were largely stripped from the source area by the start of Ephraim time. Fragments from these Triassic formations are common elsewhere in the region in Cenozoic gravels that contain other carbonate rock fragments. (c) The lithologies of the fragments in the upper part of the Ephraim suggest that more and older Paleozoic rocks were exposed in the source area as Ephraim time progressed. (d) The apparent absence of quartzite fragments from the Worm Creek quartzite member of the St. Charles limestone and Brigham quartzite suggests that Cambrian formations had not been exposed in the source area by the end of Ephraim time. T The US. Geological Survey considers the Ephraim conglomerate, the basal formation of the Gannett group, to be of Early Cretaceous age. Although at most places the Ephraim rests with apparent conformity on the Upper Jurassic glauconitic marine Stump sandstone (Mansfield, 1927, p. 101; Moritz, 1953, p. 66), Mansfield (1927, p. 101) thought that the stratigraphic break . between the two formations might be a large one. At least locally there is a hiatus at the base of the Ephraim for about 20 miles east of Cokeville, Wyo. (pl. 4), in the southeastern part of the Cokeville quadrangle, the Stump is absent at most places (W. W. Rubey, written communication, 1960) and the Ephraim overlies the Upper Jurassic Preuss sandstone (Imlay, 1950, p. 41). The Ephraim has not yielded diagnostic fossils, but on the basis of stratigraphic position and the presence of nonmarine Lower Cretaceous fossils in the overlying Peterson limestone, it has been thought that the basal part of the Ephraim is possibly as old as late Late Jurassic and that the upper part is Early Cretaceous (Cobban and Reeside, 1952, p. 1030; Wanless and Gray, 1955, p. 55; McKee and others, 1956, p. 3). R The stratigraphic thickness of rocks mapped as Ephraim on Red Mountain is about 5,000 feet and is considerably more than was believed previously (Mansfield, 1927, pl. 12, section W—W’). The original thickness of this conglomeratic unit must have been more than 5,000 feet for that thickness is preserved in the center of an eroded syncline. Near Miller ranch, about 19 miles'north by east of Red Mountain, a meas- ured section of Ephraim is 1,025 feet thick (Mansfield, 1927, p. 103). There it is a red conglomerate that con- J11 tains some red sandstone and a few thin beds of lime- stone, and it appears to lie conformably between the Stump sandstone and the Peterson limestone. To the east and north of Miller ranch, the Ephraim thins rapidly, becomes finer grained, and contains very little conglomerate; about 40 miles northeast of Miller ranch, it is about 175 feet thick and consists mostly of silt-stone (Moritz, 1953, p. 66, fig. 2; Wanless and Gray, 1955, p. 55—56). Near Thomas Fork Canyon, Wyo., about 9 miles southeast by east of Red Mountain, the Ephraim has a maximum thickness of 800 feet (Moritz, 1953, p. 66). From Miller ranch to Red Mountain the Ephraim thickens at a rate of at least 1 foot in 25 feet hori- zontally,_and from near Thomas Fork Canyon to Red Mountain it thickens at the rate of at least 1 foot in 11. If an isopach map is constructed using the thicknesses of the Ephraim at Red Mountain, Thomas Fork Canyon, and Miller ranch, the rate of thickening normal * to the isopachs is 1 foot in 8 for a distance of about 6 miles. As these rates of thickening are rather‘large and are minimum rates, it seems probable to us that the thick conglomeratic unit underlying Red Mountain contains more than the basal Ephraim formation of the Gannett group and that stratigraphic equivalents of several formations of the Gannett group may be pres- ent. If, in addition to the Ephraim, other formations of the Gannett are present on Red Mountain, then the . fivefold division of the Gannett group disappears to the south and west as it does to the north and east. Con- sequently, only the very basal part of the conglomeratic unit on Red Mountain could be as old as latest Jurassic. The marked westward increase of thickness and grain size in the Ephraim indicates a source only a short dis- tance west of Red Mountain (Moritz, 1953, p. 66), and the 'rate of increase in grain size suggests that the source was perhaps 25 miles or less west of the Gannett Hills (Rubey in Moritz, 1953, p. 66) . The abundance of car- bonate and sandstone fragments in the conglomerates also suggests a nearby source area, if the results of Plumley’s studies (1948, p. 575, fig. 15) can be extended to include the Ephraim conglomerate. In a study of stream terrace gravels on the east flank and immediately east of the Black Hills, S. Dak, he found that in a. , stream transport distance of 30 miles, 90 percent of the limestone plus sandstone pebbles 16 to 32 mm in diam— eter were removed from the terrace gravels along Rapid Creek. A source for the fragments in the Ephraim 25 miles west of the Gannett Hills would be about 10 miles west of the east margin of the present Bear River , Range. The rocks exposed in the present Bear River Range are. early Paleozoic in age, including the Swan J12 Peak formation, of course, and occur in the upper plate of the Paris thrust. - ' The presence of the Ephraim conglomerate has long been recognized as evidence of a Late Jurassic or Early Cretaceous orogeny to the west (Mansfield, 1927, p. 194; Wanless and Gray, 1955, p. 55, 56), but the location of the orogeny and its mechanism have not been specified. The abundance of soft rock fragments in the Ephraim conglomerates, the direction and rate of increase in grain size, and the direction of thickening of the Ephraim point to an orogeny not far west of the Gan- nett Hills, and the preservation of Thaynes strata in Bear River and BearLake Valleys (Mansfield, 1927, pls. 6, 9, 44) suggest that the eastern margin of the area most affected by the orogeny approximately coincided with the east side of the present Bear River Range. The mechanism and time of orogeny remain to be established. .. Absence of major depositional breaks in the pre- Stump stratigraphic sequence of the region is evidence that deposition across the site of the ancestral Bear River Range was continuous from Cambrian to the end of Stump time. Paleotectonic studies of the rocks of the Jurassic system show that about 6,000 feet of J uras— sic strata were deposited across the ancestral Bear River Range (McKee and others, 1956, p. 1, pl. 3). Strati- graphic studies of the Triassic of this area show that about 7,400 feet of Triassic strata were deposited in the Fort Hall area several miles northwest of the Bear River Range and that at least 4,700 feet were deposited along the east side of the range near Paris, where an in- complete section that thick is exposed (Kummel, 1954, pl. 34) . Paleotectonic studies of the rocks of the Trias- sic system show that probably at least 7,000 feet of Triassic strata were deposited in the area of the ances- tral Bear River Range (McKee and others, 1959, p. 18, " pl. 5). The thickness of post-Swan Peak Paleozoic strata deposited at the site of the ancestral Bear River Range was about 9,000 feet as shown by the stratigraphy in the areas north, east, and south of the present range (Mansfield, 1920; 1927; 1929; Williams, 1948). From this depositional history it follows that the orogeny and the Paris thrust are post—Stump in age. The direction of thickening and of increase in grain size of the Ephraim and, to a lesser degree, the change from marine to continental conditions of deposition are evidence that the ancestral Bear River Range had been uplifted and was being eroded at the time of deposition of the Ephraim. That the area started to rise even be- fore the end of Stump time is suggested by grit beds in the Preuss a short distance north of Kemmerer (pl. 4) (W. W. Rubey, written communication, 1960), by the clastic nature of the Stump (Peterson, 1955, p. 79), SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY by the apparent absence of the Stump in the western- most exposures in the Wasatch Range (Stokes, 1959, p. 110), and by the presence of a few pebbly beds in the top of the Stump (Rubey, quoted in Imlay, 1952, p. 966) . The lack of Mesozoic pebbles and the abundance of upper Paleozoic pebbles in the Ephraim in the Gan- nett Hills indicate that at the time of deposition of the Ephraim at this locality about 13,000 feet of Mesozoic strata had been largely stripped from the ancestral Bear River Range; and the presence of Swan Peak pebbles in this same Ephraim is evidence that an additional thickness of about 9,000 feet of Paleozoic strata had been cut through by erosion, at least locally, to expose outcrops of Orodovician Swan Peak from which the; pebbles could be derived. The coarseness of the Ephraim conglomerate is evi- 7 dence that the source area was uplifted to form moun- tains. Between Stump and the end of Ephraim time about 22,000 feet of erosion took place in the ancestral Bear River Range, and there is some suggestion that the erosion may have been accomplished in two steps: the first slow and probably in part pre—Stump, the second rapid and post-Stump. At Threemile Knoll in Bear River Valley a few red beds occur in the Thaynes; they probably are part of the Lanes tongue of the Ankareh formation in the Portneuf limestone member in the upper part of the Thaynes. Beds that also are probably correlative with the Portneuf crop out near Paris along the west side of Bear Lake Valley (Kummel, 1954, p. 175) . These Portneuf equivalents are roughly 4,000 feet above the base of the Triassic. Outcrops of Thaynes occur elsewhere in Bear Lake and Bear River Valleys between the Paris and Threemile Knoll occur- rences. Lack of Mesozoic pebbles in the Ephraim on Red Mountain might be explained by slow gentle uplift of the source area prior to the time of deposition of the Ephraim and by the fact that during this interval the upper part (but less than 9,000 feet) of the Mesozoic rocks was slowly eroded from the source area and de- posited as fine Sediments somewhere to the east. When erosion had cut down to a point an unknown distance above the Portneuf limestone member, the source area was suddenly raised and in consequence coarse continen- tal( ?) Ephraim conglomerate was deposited directly on marine Stump sandstone. Pebbles [from the 4,000+ feet of Mesozoic rocks remaining to be eroded from the source area were either carried east of the Gannett Hills (where most such pebbles are found today) or were so diluted in the flood of Paleozoic pebbles that they do not now form a conspicuous part of the Ephraim. If the upper part of the Mesozoic rocks was not slowly eroded during a gentle uplift prior to the sudden uplift that produced the Ephraim, exclusion of Mesozoic THE BANNIOICK THRUlST ZONE, SOUTHEASTERN IDAHO pebbles from the Ephraim is even more difficult to explain and the sudden rise of the area to the west must have been even more catastrophic. The manner of uplift of the ancestral Bear River Range is suggested, and in part restricted, by the geo- logic structure of the present Bear River Range. Not all the Bear River Range has been mapped geologically, but its structure is moderately well known from the mapping that has been done (Mansfield, 1927, pls. 6, 9; Hardy and Williams, 1953; Armstrong, unpublished) and from reconnaissance by Armstrong. Gently folded Paleozoic rocks are in (Paris) thrust-fault contact with gently folded Triassic rocks along the east margin of the range. The thrust cuts folds in both the upper and lower plates. In the interior of the range the Paleozoic . rocks occur in the gently dipping limbs of an open syn- cline whose form has very nearly been destroyed beyond recognition by numerous block faults, most of which are Cenozoic in age. No thrusts other than the Paris have been recognized in the range, and no block faults older than the Paris thrust have been recognized. Folding followed by thrust faulting are thus the first deforma- tions to which the rocks of the Bear River Range were subjected. The thrust faulting in this region has been thought to be the culminating effect of the compressive forces that produced the folds (Mansfield, 1927, p. 170, 198; 1952, p. 76; Williams, 1948, p. 1158), and this idea is supported at least in part by rather Widespread occurrence of westward—dipping thrust faults of small displacement that out folds overturned eastward (pls. 2B, 3) (Cressman and Gulbrandsen, 1955, pl. 27; Gulbrandsen and others, 1956, pl. 1; Cressman, 1957). If the rocks of the Bear River Range were deformed first by folding and if the block faults in the range are younger than the Paris thrust, it seems extremely un- likely that the ancestral Bear River Range could have been raised up by block faulting. If the ancestral Bear River Range had been warped up gently without folding as in epeirogeny, it is doubtful that a conglom- erate like the Ephraim could have formed. Moreover, such an arching would have produced a dome rather than a basin in the rocks of the range. Of course, the possibility that later deformation reversed the structure cannot be completely eliminated. It seems to us that the sudden appearance in the stratigraphic column of a coarse conglomerate like the Ephraim argues for a catastrophic event to explain its presence. This argument, together with the elimination of block faulting and the probable elimination of gentle uplift as a means for raising the ancestral Bear River Range, leaves only folding and thrusting, that is, orogeny in its strictest sense, as the mechanism of uplift. Whether the ancestral Bear River Range was uplifted J13 by folding only or by folding and thrust faulting—- that is, whether the Paris thrust is significantly younger than the Ephraim conglomerate—remains to be deter- mined. We know of no evidence that can conclusively date the Paris thrust and the Ephraim, but a few gen- eral considerations suggest that they are of about the same age: (a) First, we have no evidence that they are of different ages. In many places in the region, failure by thrust faulting appears to be the final mechanism of yielding in response to the compression that pro- duced the folds. Considered in this light, at least some of the thrust faulting is the final expression of and part of the folding process. . (b) Further, the folds in the Triassic rocks in Bear River and Bear Lake Valleys are not significantly different from those in the Paleozoic rocks in the Bear River Range, yet the rocks in the ancestral and present ranges were raised at least 13,000 feet higher than the rocks in the valleys; This differ- ence in uplift cannot be explained solely by difference in degree of folding. (0) Finally, it might be argued that as the Ephraim is the coarsest, thickest conglom- erate in the Mesozoic of the area, it represents a major , tectonic event, and that, as the major structural feature in the Ephraim source area is the Paris thrust, the Ephraim is therefore a product of the same orogeny that produced the Paris thrust. The evidence, although not conclusive, suggests to us that the Paris thrust and Ephraim conglomerate are of about the same age and that the Ephraim is the product of an orogeny that in- volved folding and thrust faulting in the ancestral Bear River Range. \ To the south in central Utah, coarse conglomerates similar to the Ephraim also have been interpreted as being evidence of orogeny to the west. The Indianola , group in the Wasatch Plateau (Spieker, 1946, p. 126— 130) and the Kelvin formation in the north-central Wasatch mountains (Eardley, 1944, p. 838—840) con— tain conglomerate beds that rapidly thicken and in- crease in grain size westward. Both Eardley (1944, p. 859—860, 865, fig. 2) and Spieker (1946, p. 149—152) vis- ualized the orogeny as involving compressive forces that produced uplift, folds, and thrust faults. Although the Ephraim, Indianola, and Kelvin have not been closely dated, it seems probable that the basal part of each contains conglomerates that are correlative to the east with the Morrison formation of late Late Jurassic age (Stokes, 1955, p. 80; McKee, and others, 1956, p. 3), and that at least along their western limits the lower parts of all three areof about the same age. It thus appears probable that practically contemporaneous orogeny in Late Jurassic or Early Cretaceous time ex- tended northward from a short distance west of the Wasatch Plateau along the west margin of the north- ‘ J14 \ central Wasatch Mountains to the north end of the Bear River Range. In summary, the ancestral Bear River Range started to rise slowly, probably before the end of Stump time; as it rose, erosion kept pace and fine debris was shed to the east. Uplift was then suddenly accelerated, and this change was marked by the start of deposition of the Ephraim. Whether the Paris thrust formed at the instant uplift was accelerated or later to coincide with the coarser conglomerate in the upper part of rocks mapped as Ephraim on Red Mountain is not known, but a post-Stump limiting maximum age is certain and an immediately pre-Ephraim limiting maximum age may be indicated. If the Ephraim on Red Moun- tain contains stratigraphic equivalents of several for- mations of the Gannett group, a pre-mid-Gannett limiting minimum age for the start of movement on the Paris thrust is required by our interpretation of the rocks on Red Mountain. We cannot be certain, how- ever, that movement ceased in Gannett time. Abundant fragments from the Worm Creek quartzite member of the St. Charles limestone and the Brigham quartzite in the Evanston formation (Late Cretaceous and Paleo- cene) in nearby western Wyoming indicate that by Evanston time Cambrian formations had been exposed - in the ancestral Bear River Range. No other possible ‘ source area for these fragments is known. The absence of these quartzites in the Ephraim on Red Mountain and their presence in the Evanston suggest that the ancestral Bear River Range continued to be tectonically active after Ephraim time. This activity and perhaps movement on the Paris thrust may have continued into late Evanston (Paleocene) time. All major folding and thrust faulting in southeastern Idaho have previously been thought to have occurred in post-Wayan (Early( ?) and Late Cretaceous) time, but we believe that folding in the Bear River Range and movement on the Paris thrust started in latest Jurassic or earliest Cretaceous time. THRUST FAULTS BETWEEN CROW CREEK AND SNAKE RIVER PLAIN Overlapping of thrusts in the Left Fork of Twin Creek and Georgetown Canyon area (pl. 3) indicates slightly different ages among the thrusts, but beds necessary to date the thrusts closely are lacking. The same zone of thrusting can be traced around the south end of Snowdrift Mountain into Crow Creek and thence to the north about 10 miles, where thrusts cut Ephraim and the overlying Peterson limestone of the Gannett group, and the traces of these thrusts are covered by Pliocene( ?) Salt Lake formation (Mansfield, 1927, pl. 12 sec. 0’—0") . The Peterson is middle Early Cretace- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY one in age (Cobban and Reeside, 1952, pl. 1), and the thrusts are therefore no older than poet—middle Early Cretaceous and are no younger than Pliocene. About 20 miles northwest of this Peterson locality, in the area north and northeast of Paradise Valley window (pl. 10), thrust faults cut Wayan formation of Late Cretaceous (and Early( ’2) Cretaceous) age (Cobban and Reeside, 1952, pl. 1; Moritz, 1953, p. 72) and are overlain by Pliocene(?) Salt Lake formation (Mans- field, 1927 , pls. 2, 4; 1952, pl. 1). Between these thrusts and the Peterson locality are the East Stump and West Stump branches of the Bannock; the East Stump also was mapped as cutting Wayan (Mansfield, 1927, pl. 5). The East Stump and West Stump faults, however, are steeply eastward-dipping and may be normal faults rather than thrusts. All the thrust faults from Crow Creek to the Snake River Plain were interpreted by Mansfield as branches ‘ of the Bannock overthrust and were thought to be post- Wayan and pre-Salt Lake in age. We doubt that any one fault is continuous from Crow Creek to the Snake River Plain; it appears rather that a zone of thrust faults extends between these points. All the thrusts from Crow Creek to the Snake River Plain are older than Salt Lake (Pliocene) and younger than Peterson (middle Early Cretaceous), and many or perhaps all of them are younger than Wayan (post-Early( ‘43) and Early Late Cretaceous). All the thrusts in this zone are therefore younger than the Paris thrust. THRUST FAULTS IN WESTERN WYOMING The pattern of older thrust faults to the west and younger ones to the east is continued eastward into Wyoming (fig. 1). West and northwest of Kemmerer, Wyo., the youngest beds involved in the major deforma- tion accompanying the Absaroka thrust, but not cut by it, are in the upper part of the Adaville formation (Veatch, 1907, p. 75, 76, pls. 3, 4) of Montana to early Lance age (Cobban and Reeside, 1952, pl. 1; Dorf, 1955, p. 99, fig. 1). Mapping in the area by Tracey and Oriel (1959, p. 128) and by Gazin (1959, fig. 1) shows that basal beds of the Evanston formation of latest Cretaceous (Lancian) to earlylate Paleocene (Tiffan- ian) age are cut by (and are also affected by minor movement along) the Absaroka thrust. However, the areal distribution of most of the Evanston, which over a wide area lies with marked angular unconformity on both the overriding and underlying blocks of the thrust, suggests that most of the movement on the Absaroka was completed before deposition of the bulk of the Evanston formation (W. W. Rubey, S. S. Oriel, J. I. Tracey, J r., written communications, 1959, 1960). Most of the movement along the Absaroka fault near J15 THE BANNOCK THRUvST ZONE, SOUTHEASTERN IDAHO .umaw 3 ”.an ES“ 333 :55 no on: 5 $3226 95$“:on 93352:: SEMSQIIH :th ‘ Om. mocxo $30.. 33.: mien. :0 V\. IL... o.mm<_¢k oCOED>OE O 50—.» *0 2:: “39.59..“— \ mutt: On. 33 SEE: .3 92:3 3 l 530.. 3.580 9.22:5 EVE: 9:5“. 2032.: EC. IE 05933.. 95% {1:111 5%.: mm. £3..ch 952...: 8—9: . ., 0:2me: «mic; .obE: usage... \x\..\ \\\c\ comB—cn. w\- - -fcgos 38255 9.09 9.:me 0:38 o o 50 S us: A mmma: zEE x0090: _ a :. Eu 032.3“. .\ f_V\\ \\\ r“ \kcqficdom m2u8u4 £232? .0»; $.qu nooscozou 63> 33¢ a... 9:. 5:3 .0 £8: coSEEux *0 $0353: nah E... .u 22:: 53:: 595.353 335 9.0334 ._.m_ _\..; Arrow points in direction of movement of upper plate \ of thrust fault, queried where doubtful; all upper \\ plates but Willard in 8 moved to the east \ II2°oo‘ III°3o' III°oo‘ \ \ @IDAHO FALLS 43° 30. \ V aIDAHO FALLS A A A' \_J \\ III°3o' III°oo' IIo°3o‘ \ o .7 I9 1;; MILES \ I DATUM IS MEAN SEA LEVEL \ \ I I PUTNIAM \h x I OVERTHIRUST , \\., . I V\ (A 3% 00 EAST STUMP I ' 4 BRA I K 4 RRQ? 4214/0 NCH] I I I n \ c." ,I \\L9,\ yI—SSTAR VALLEY FAULT - 43°00 Q 9“ «3,, \W 4‘ k POCATELLO I >1]ng 2%? ‘23). : 1 ““ ,\ I Klippen ‘9’ ~‘ ' QWEST STUMP \ I \\ l . T} g I \ \l ' o BRANCH .>\ | ,5- AUBURN FAULT . I LIJ . 43v Klippe on \ I : g "o Threemlle Knoll \ I , e l I E «DJ/T ' ‘ I o TENMILE . / OIZ PASS SODA \‘-‘-. Iii ' . suite“? <1 o / ‘ 9:; x Klippe I l g . OUTLINE OF on Three — I g ' PLATES ._2A and B mile Knoll SODA q SPRIN/és I In I l I / —42°3o' I I GEORGETOWN I I LIBERTY I _.; .2 , 3 4 n . I W ’ T- ' ‘ ’, ,x MONTPELIET . _: _ M ' , ”grime-«3., / : I I ____________ID_A:I<>______- ' UTAH -——--—--—------ --——-—I—-42°oo I /, ' Q~I I w s, :e \ V“ J : I l LOGAN? I : ' 4* I? I ‘v I — I ‘b <'2 I—'o :2 >- I I; | I _ ‘ . . , x“ 'l . 4I°3o' ‘- , __ r . 1 ,7, WILLARD I WILLARD ,, HRUSRT‘Fa/V,’, . THRUST' =~ ”000 U , I ~~ fH/PUST ON I 5:“. 135”” ‘ ;W000/?UFF . ‘ '- CREEK I , , I EVANSTON % VII-EVANS‘I’VON \ . , \ I \ (Compiled from Gale and RichardsI‘ISIO" I Mansfield, I920, I927. I929, l9_52';¥' : (Compiled from Richards and Mansfield ,I9I2. Kirkham,1927; Ludlum, I943? I figs I. 2‘ 5,) Eordley. I944” - 4W00' B. THE BANNOCK OVERTHRUST AS ORIGINALLY INTERPRETED BY RICHARDS AND MANSFIELD C MANSFIELD 8 FINAL INTERPRETATIONOF THE] BANNOCK OVERTHRUST, AND CORRELATIONS OF THE BANNOCK WITH OTHER FAULTS AS SUGGESTED BY MANSFIELD AND OTHERS INTERIOR—GEOLOGICAL SURVEY WASHINGTON D C~6122I UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 374-—J 4x- I. I'MONTPELIER \‘Ik # I—u- 0 5 I I I I I Dafum is mean sea level IO MILES GEOLOGICAL SURVEY PLATE 2 "“1030, III°I5' I I i \\ 42°45' \‘o‘ ‘KII_pPepnw?<-. BEAR RIVER LEFT FORK SNOWDRIFT CROW , _'.T¥teemlle ‘ VALLEY OF TWIN CREEK MOUNTAIN CREEK f, I “9°“ . ‘ .f-tx. I 6250' . . > BANNOCK OVERTHR SODA,” \C‘ I SPRINOS \‘ I 42°3O‘ E X P LA N AT I O N X .. Patches Of Tertiary graveI referred to in text f‘ I mi \ \ ‘\ \ / ‘ ’I ‘ \ \ ‘I'f' 11-w- Tr \ \ I I \ 1 Ex ‘\ \\ I I! \ ' ‘ \\ Normal fault Lu \‘ \I I \ , »:\ Dashed where in]? rred or (concealed: (I) \ \ I \ \\\ hack/lies (m downthmum side ‘ . \ / \ MONTPE'LIER I\ LIBERTWe/ \ \ - \ \ 3 11- 1-7-1?!" Tr- \\ I Transverse fault ‘ // Dashed where Inferred 0r mm‘ealed: havhuros (m " "I c. J . (Ioumfhroum side; arrow I'Irzrl'irafes dirw‘f’ion of rein,— % r; I” ‘ ' t'iue rruIIIermm; when: direction of movenwm not known harhures and arrow omitted (Compiled from Monsfield,_ l927, pls. I,4, 6, 7, 9, ll, I2, 37) . _ w -7- A. SIMPLIFIED MAP AND CROSS SECTION OF MANSFIELD'S FINAL INTERPRETATION Thrust fault OF“ THE BANNOCK OVERTHRUST NEAR GEORGETOWN, IDAHO Dashed where inferred or (‘onceuled' queried where {5.5 doubtful; sawteeth on, side of upper plate and [mini down dip; (Ipprox’zf'nmte strafigraphir til/V011} In thou— sands offeet shown by numeral III°3o‘ III°I5‘ I; L .I - I 42°4 ‘ I=I~ ‘ T ~ I 5 i ‘X ‘ 4 _ - _ ‘ 3X Trace Of axialplane Of anticlinal fOId in thrust surface I A ,4 A I I» 4 * ———+——— I X4 ))(( \v, X :1 _ I | Trace Of axial plane Of synclinal fold in thrust surface n. Threemile ‘4 :I 4 5‘ I Knoll 4 T , I I 4 <1 i SODA IE =I / ISPRINGS I / TA 3' I as T I R/fl'm I I I} I \L ‘I 2 I I 42° 30' Lu Paris 3 thrust BEAR RIVER LEFT FORK SNOWDRIFT CROW g I 5 VALLEY OF TWIN CREEK MOUNTAIN CREEK / C I: I; ISI 0: a: < LIJ co \ \ UNITED STATES DEPARTMENTOF THE INTERIOR PROFESSIONAL PAPER 574-J GEOLOGICAL'SURVEY PLATE 5 111° ‘7' 30" // _ W//// ' ; EXPLANATION I 1,5? 4W /‘ / / » // , /' 'zv: , 31/ E _..... .;: I l‘» < _— , Qal Z Contact '- '> > E Long dashes where approximately located; short dashes Alluvium hill,wash, talus, |<—E where inferred; dotted where concealed and terrace gravel 3 O > U ___ 7/ n: D // ///? 1‘ Fault // /% E Long dashes where approximately located; short dashes S 1 L k f . Lu where inferred; dotted where concealed. U, upthrown a t a e ormation }— side; D,downthrown side 5, ”A. A. if" ' JD Thrust fault ‘I I I. ‘ Dashed where approrimately located; dotted where con— cealed; queried where doubtful; sawteeth on side of Preuss sandstone I t upper p a e U) o‘. omegc‘au— U) . , 1:, _ V. r E: Fault brecma Twin Creek limestone 2 Jr / // \\ \V Anticline Trace of axial plane and direction of plunge; dashed where u § \\ approximately located Nugget sandstone 30‘ / Overturned anticline Trace of axial plane; dashed where approximately located Ankareh and uppermost Thaynes formations, TRIASSlC / ....... / /X/ Syncline Trace of axial plane and direction of plunge; dashed where approximately located; dotted where concealed [/36 N PERMIAN Phosphoria formation Overturned syncline Trace of axial plane and direction of plunge; dashed where approximately located; dotted where concealed 30 _J_ Strike and dip of beds PENNSYL- VANIAN' Wells formation } 40 TL Strike and dip of overturned beds 42° 30' oo“ fl CARBONlFEROUS MISSISSIPPIAN W2 “3;, Madison limestone a Strike and dip of beds overturned through more than 180° HO“ 75x19; 155;; eoogy y .. ressmcn, —- 2 Miles I J I I Scale 900d 8000' 7000' GEOLOGIC MAP AND SECTION OF THE LEFT FORK OF TWIN CREEK AND GEORGETOWN CANYON AREA, IDAHO UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 574% GEOLOGICAL SURVEY PLATE 4 II3°3O’ II3°oo' II2°3O' II2°oo' IIO3o' Infoo‘ “0730‘ ‘\ I ) < E X P LA N AT I O N 7 CABIN THRUST ,r MO T __ ’,___-4. W / \IEEW’N/ \ f o - 1' H d A 44 30 I [ ”y l g \ ~ I \ A A; :4: ’\/\ 0 \ ”HEW,— k A \J E 'rr 1171111- 1? 'rr \ , ' ‘1 f”; Block fault / ' é Dashed where Inferred or eaneealed; queried where I MEDICINE LODGE‘ THRUST 1’3 (Mold/'74]; haehures an dolor/fhrou'n side; hag/(ares 3w (III/(Wed where dir'eeffon of'moI/‘ewent not known 0‘ 2 :é; O , s :2 7 ' \.\ § i 11‘ TT TI—TTI‘ 'r'r 'h' * \ i :- g g Transverse fault \\ ‘5 g Dashed where (Inferred or eoaeealed,‘ hoe/lures on \ S ; downth row" side; arrow 'i'rIdI'eates direction afrela— _ 44000‘ T X 33-); fire mouemenf; queried where d'ireet'ion is unee'rfai'n HAWLEY __, “-5. 2 3 MOUNTAIN \ \ g \ TH RUST \ I , ‘ é o \ N \ *4 _ _ -7— \ \‘ v. .2 2 WT _ (I) -’ \‘ QV g g Thrust I'ault ‘\ “R E: m. Dashed where inferred or concealed; queried where LOST ‘ Q 2 doubtful; sawteel‘h, on side, ofupper plafe and point RIVER \ g 9‘ down dip THRUST? \ *1 ,3 Q 5» E \ m r; O . Q IDAHO FALLS SE Trace of axial plane of anticline " 43 30 Q I” :~: I». s s s Q, 2 § § + é” ; g Trace of axial plane, of overturned anticline; arrows of? \k1 5 7 ” point down dip of limbs 1&3“! I \ \ A ~ ‘ K" A‘ PUTNAM ( I; “ A TH RUST q (2“ 1‘ ’$ \ a \\ y \ « kgv n M“ 4 A V V“ =I ‘1). t *N V: )‘ a » ,1 c 4 was I n x a 4 A w 1‘ Q I? o. O‘QP‘A A: f" fit” POCATELLO ‘ ‘3". A $431 ,6‘3‘; ’3“, A , A A) v» n £_r,/« k A 5. Q 1 *1 ( ‘33“ "50 2:38 W I rTo _._.__ t}— ; £4, 4 ix * 5007.” C0 Ala/000 Fj “‘9“ K TENMILEAG A?» CREEK 4 1 ‘PAssg/if & 4 N \1 4 "4 fl ‘ SODA/{V1 4:5- 4 4 4 4 SPRINGS 4 ' )/ ~ ¥ HILLS 4 :I V a a 2 v \ =1 m '4 x. V 14 a 4 #4,;- \- ~‘ 57$ AK}: i ,Q» V s SODA %-IT 33' ‘? Q. j SPRINGS TIP TOP 42030- :. ,I )I :I TAT» TOILFIELD 7 a 4% ‘? NOUNAN DARBY ‘1 3 2:5fé TH RusT n. z 4 <1 2 c: 't 4 Y I ‘ x ‘I LA BARGE I I OILFIELD 1 S ‘ 1 z 3i S O U R C E S 1 4 0 Armstrong, Frank C. (unpublished data) \/ j I "ABSAROKA THRUST Cheney, Thomas M. (wrltten communlcation, 1959) IDAHO o - :l 42 00 Cressman (1957) -- UT? <1, Cressman and Gulbrandsen (1955) 4 I Eardley (1944) I ‘I Gulbrandsen and others (1956) V I Hardy and Williams (1953) I / Howe (1955) 'I «I 1 Kirkham (1927) I / 0 Love, Weitz, and Hose (1955) KEMMERER Ludlum (1943) 1 \1 VI Mansfield (1920, 1927, 1929, 1952) =I CRAWFORD I McKelvey, V. E. (written communication, 1959) ’1 TH RUST { Richardson (1941) 1 Rubey (1958) A y \ Scholten and others (1955) ’A / :I f) Williams (1948) 1 I Young (1953) 1 I 4I°3o' Zeni (1953) ._/ I d j A ITHRUST ON I 14‘ WOODRUFF I I CREEK I X! A. E: f l X? 4 WILLARD 3 1 OGDEN THRUST I THRUST \‘L I EVANSTON A7 ’1. I % \ ’ I OGDEN 1}? .1, 4, A 4'3 DURST THRUST I 1 TAYLOR THRUST3 r; l I I INTERIORi (3 EOLOGICAL SURVEY WASHINGTON D ( 61221 SIMPLIFIED STRUCTURAL MAP OF SOUTHEASTERN IDAHO AND ADJOINING PARTS OF UTAH AND WYOMING IO M 5 I O I IO 1 2'0 3|OMILES