412 N. H. DARTON PALEOZOIC AND MESOZOIC OF WYOMING 



leti Clarke; Actinoceras cf. remotiseptum Clarke. This fauna is regarded 

 as late Black Eiver and earty Trenton by Mr Ulrich, for identical or 

 closel3r related forms occi;r in Black Eiver and Trenton rocks in New 

 York. He correlates the horizon with the lower massive limestone and 

 its imderl}dng sandstone in the Bighorn mountains and with the Harding 

 sandstone and the lower (Galena-Trenton) portion of the Fremont lime- 

 stone of the Canyon City region in Colorado. The hiatus at the top of 

 the Bighorn limestone represents a part of Ordovician and all of Silurian 

 and Devonian time, but there are no marked features of a great uncon- 

 formity in the contact of the Bighorn and Madison limestones. 



Cakboniferous System 

 madison limestone 



General relations. — The Madison limestone is very prominent in the 

 Bighorn, Wind Eiver, and Owl Creek mountains and it is distinct in the 

 Battlesnake mountains and the region south of Alcova. It disappears in 

 the Laramie mountains where the Casper formation lies directly on the 

 pre-Cambrian rocks. 



Wind River mountains. — Northwest of Lander the Madison limestone 

 is from 250 to 300 feet thick, and it constitutes the crest and part of the 

 long eastern slope of the prominent foothill range. The rock is light 

 gray, pure and very massive in its upper portion, but darker, more slabby, 

 and with considerable chert in its lower member. 



Owl Creeh mountains. — The Madison limestone outcrops in the higher 

 portion of the Owl Creek uplift, ordinarily constituting a prominent 

 flanking ridge and causing high cliffs in the canyon walls. It averages 

 from 500 to 600 feet thick and consists of moderately thick-bedded gray 

 limestones with an upper member of massive light colored limestone 

 which weathers to a light dove color. This upper member is cavernous 

 and in many places weathers in pinnacles and castellated forms. Exten- 

 sive exposures appear in and near Bighorn canyon and at intervals in the 

 higher ridges to the west, notably in the vicinity of Phlox mountain. Owl 

 Creek canyon, and Black mountain. 



RattlesnaJce mountains-Shirley hills. — The Madison limestone is 250 

 feet thick on the north slope of Eattlesnake mountains, where it outcrops 

 for 7 or 8 miles. The rock is a massive, light gray limestone, presenting 

 most of the features observed in other regions and yielding distinctive 

 fossils. In the canyon of Platte river, l^etween Pathfinder and Alcova, 

 the limestone again appears, but the precise thickness was not ascer- 

 tained. It lies between sandstone below and red shale of Amsden forma- 

 tion above. These features appear again southeast of Pathfinder and 



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