CAMBRIAN AND LOWEE OEDOVICIAN. 127 



name, "as Fort Cassin, or Philipsburg formation, or any other appropriate name." "^ This 

 seems to the writer not only as eminently proper but really a necessary procedure. The 

 thickness and importance of this group, consisting of the upper 220 feet of division D and 

 the whole of E, is such as definitely to warrant its separate mapping in the Champlain region, 

 and the writer proposes the name "Cassin formation" for it, to make Whitfield's suggestion 

 more precise and definite. 



L 12. SOUTHWESTERN MONTANA. 



Peale originally described the Cambrian of the Gallatin section in southern 

 Montana and furnished details to Walcott,*°** who writes as follows: 



The Gallatin section of the Cambrian includes 1,250 feet of strata, of which 835 feet are 

 hmestone, resting upon 415 feet of sandstone. Conformably subjacent to the latter, there are 

 6,000 feet of alternations of conglomeratic micaceous sandstones, with bands of siliceous lime- 

 stones and indurated clay shales, referred to the Algonkian by Dr. A. C. Peale. '' 



A more detailed manuscript section, that Dr. Peale kindly prepared at my request, is as 

 follows : 



Gallatin limestones, 835 feet: 



Pebbly limestones, 145 feet. Fossils, Leptsena meUta, Ophiletasp.?, Triplesia calcifera, Ptycho- 



paria sp.?, Ptychoparia (E.) aiBnis. 

 Dry Creek shales, 30 feet. 



Mottled limestones, 160 feet. Fossils, Ptychoparia sp.?, Hyolithes sp.? 

 Obolella shales, 280 feet. Fossils, Obolella sp. ? 

 Trilobite limestones, 120 feet. Fossils, Lingulella sp., Acrotreta gemma, Kutorgina sculptilis, 



Agnostus bidens,' HyoHthes gregaria, Olenoides serratus, Ptychoparia gallatinenses, Bathyu- 



riscus? haydeni. 

 Gallatin sandstones, 415 feet: 



Gallatin shales, 290 feet. Fossils, Lingulella sp. ?, Hyolithes sp. ?, Ptychoparia sp. ? 

 Gallatin quartzite, 125 feet. 



In the report just quoted Walcott expressed the view that the 5,000 feet of 

 strata beneath the "Gallatin sandstones," which Peale assigned to the Algonkian, 

 might be Cambrian and equivalent to the Bow River group of Canada. But in 1909 

 he found that only the upper part of the Bow River is Cambrian, and it is separated 

 from the major part by an unconformity. Most of the Bow River is therefore pre- 

 Cambrian, and the equivalent in Montana is the same. 



The Gallatin sandstones of Peale in the above section were later called by him 

 Flathead formation, but the name Flathead is now restricted to the basal quartzite, 

 and the overlying shales have been named Wolsey shale. The latter two formations 

 and the overlying limestone were measured in detail on Crowfoot Ridge in the 

 Yellowstone Park by Iddings and Weed ^^^ and the result is given in their mono- 

 graph on the park. 



In the same volume Walcott ^^^^ describes the Cambrian faunas from these 

 formations. He finds that — 



The Cambrian fauna of the park includes 10 species that are referred to the upper division 

 and 21 that are referred to the middle and lower divisions of the Middle Cambrian fauna. 



The Middle Cambrian fauna * * * jg more intimately related to that of the Black 

 Hills and the upper Mississippi Valley in Wisconsin and Minnesota than to the Middle Cambrian 

 fauna of Nevada or British Columbia. There are no' indications of the Lower Cambrian or 

 OleneUus fauna. The upper-division fauna is also strongly related in its Brachiopoda to the 

 Mississippi Basin fauna. 



o Whitfield, R. P., Observations on the fauna of the rocks at Fort Cassin, Yt., with descriptions of a few new species: 

 Bull. Am. Mus. Nat. Hist., vol. 3, 1890, pp. 27-28. 



b Tenth Ann. Kept. U. S. Geol. Survey, pt. 1, 1890, p. 131. 



