324 THE CAMBRIAN. (bull. 81. 



The diameter of the strata forming the Cambrian about the Big Horn 

 Mountains will be spoken of iu connection with the extension of that 

 range in Wyoming. The Gallatin section of the Cambrian includes 

 1,250 feet of strata, of which 835 feet are limestone, resting upon 415 

 feet of sandstone. Conformably subjacent to the latter, there are 5,000 

 feet of alternations of conglomeritic, micaceous sandstones, with bands 

 of siliceous limestones and indurated clay shales, referred to the Algon- 

 kianby Dr. A. C. Peale. 1 



A more detailed manuscript section, that Dr. Peale kindly prepared 

 at my request, is as follows : 



' Pebbly limestones 145 feet. 



(fossils, Leptama melita, Ophileta sp. f 



Triplesia cahifcra, Ptychoparia sp. ? 

 Ptychoparia (E.) aflinis). 

 Dry Creek shales 30 feet. 

 Mottled limestones 160 feet. 



( fossils, Ptychoparia sp. ? Hyolithes sp. ?) 

 Gallatin limestones 835 feet. .. <( Obolella shales 280 feet. 



(fossils, Obolella sp. ?) 

 Trilobite limestones 120 feet. 



(fossils, Lingulella sp., Acrotreta gemma. 



Kutorgina sculptilis, Agnostus bidens. 

 Hyolithes gregaria, Olenoides serrutus. 

 Ptychoparia gallatinenses. 

 Bathyuriscus? haydeni). 



['Gallatin shales 290 feet. 

 Gallatin sandstones 415 feet. . . J ^^' %$&&£. ft*"""" ^ ? 



^Gallatin quartzite 125 feet. 



It is probable that the 5,000 feet of strata referred to the Algonkian 

 in the published section will ultimately be referred to the Lower Cam- 

 brian as they occupy the stratigraphic position of the Bow Eiver series 

 to the north in British Columbia through the upper 3,000 feet of which 

 the Olenellus fauna has been found to range. 



The section near the mouth of the East Gallatin Eiver was studied 

 in detail by Dr. Peale in 1884, and two lithologically well denned groups 

 determined and characterized as follows : 



To the lower one, which was carefully searched, without success, for organic re- 

 mains, the name of East Gallatin group has been provisionally applied. It is com- 

 posed of a series of alternations of green and greenish gray micaceous sandstones and 

 clay slates (almost argillites), with thin bands of laminated limestones ; 2,300 feet of 

 these beds were sectionalized iu detail without any traces of fossils being found. 



The sandstones are in heavy beds and present a somber appearance, weatheriug on 

 exposed surfaces to steel-gray aud almost black colors and frequently breaking into 

 cubical blocks. The slates are blue, yellowish, olive-green, and at some places red. 

 In the limestone a concretionary structure is frequently noticed. For the upper 

 group, lying above a well defined pink quartzitic sandstone, we have retained the 

 name Potsdam. Green and dark purplish red micaceous shales, mostly arenaceous, 

 with occasional thin bands of limestone, make up this group, and many of the beds 

 are highly fossiliferous. The collections have not been carefully studied yet, and wo 

 therefore simply refer to them in this general way at this time. 2 



1 Report of Dr. A. C. Peale (on the Montana division of geology). U. S. Geol. Surv., 10th Ann. Hep., 

 1890, p. 131. 

 a Hayden, F. V.: Report Montana Division. U. S. Geol. Surv., 6th Ann. Rep., 1884-'85, 1885, p. 50. 



