CAMBRIA X SYSTEM 409 



in the Casper range and in the ridges to the southeast appears to be a 

 shore deposit of the Casper formation. 



Rattlesnake mountains. — Tlie Deadwood formation outcrops along a 

 portion of the crest of Eattlesnake moimtains west of Oil City. It is 

 about 800 feet thick. At the base and near the middle are 25 to 40 feet 

 of brown to buffi fossiliferous sandstone and the basal beds are somewhat 

 quartzitic. Sand}^ gray shale with thin gray sandstone layers constitute 

 the greater part of the formation, but there is a small amount of impure 

 slabby limestone and reddish shale near the top. Glauconite is a con- 

 spicuous ingredient in most beds. 



Wind River mountains. — On the northeast slope of "Wind Eiver moun- 

 tains the Deadwood formation is about 750 feet thick, and it presents all 

 the features which are characteristic in the Bighorn and other ranges 

 northeastward. Its presence was recognized by Comstock" and its distri- 

 bution was shown in part on maps of the Hayden Survey.^ 



The basal member, which lies on granite, is about 100 feet thick and is 

 the usual hard, brownish sandstone. Next are sandy shales and slabby 

 limestone, the latter including more or less of the typical tiat peblile con- 

 glomerate of gray limestone pebbles covered with glauconite. The top 

 layer of this limestone contains many trilobites. At the top of the for- 

 mation is a hard, coarse, fossiliferous sandstone. 



Oivl Creek mountains. — Extensive exposures of the Deadwood forma- 

 tion extend along the upper slopes of Owl Creek mountains and in the 

 canyon of Bighorn river. It also appears along Crow creek northeast of 

 Circle and in Owl Creek canyon. The thickness is 900 feet and the suc- 

 cession of rocks is similar to that in the Bighorn and Wind River moun- 

 tains. At the base is hard, coarse-grained, reddish brown sandstone, 

 locally conglomeratic below and lying on a remarkably smooth plain of 

 the pre-Cambrian rocks. It varies from 50 to 100 feet in thickness and 

 is succeeded by 200 to 300 feet of sandy shales and thin-bedded sand- 

 stones, with a prominent bed of sandstone in their lower portion. In 

 Bighorn canyon this bed is 50 to 60 feet thick and of bright reddish 

 brown color. The medial member is 400 feet or more of soft greenish 

 gray shale with a conspicuous gray to buff limestone in its lower part. 

 This limestone, usually 50 feet thick, consists partly of flat pebble lime- 

 stone conglomerate. Southwest of Embar it is 30 feet thick and 300 feet 

 above the base of the formation. At the head of j\Iuddv creek it is 40 



^Report on Reconnaissance of Northwestern Wyoming. 1873, by W. A. Jones (War 

 Department), 43d Congress, 1st session. House of Representatives Kxecutlve Document 

 no. 285. Wasliington, 1874. 



"Twelfth Annual Report U. S. Geological and Geographical Survey of the Territories 

 for 1878, Atlas. Washington, 1883. 



