432 



N. H. DARTON PALEOZOIC AND MESOZOIC OF WYOMING 



in which the term Permian is used in the Mississippi valle}^ The Forelle 

 limestone may possibly represent the Embar formation. 



Permian-Triassic ? 



CHVaWATER RED BEDS 



General relations. — The Chngwater formation ranges in thickness from 

 900 to 1,200 feet and consists of sandy shales or soft, massive sandstones, 

 nearly all of bright red color. Gypsum deposits occur in most places. 

 There are extensive exposures along the lower northeastern slope of the 

 "Wind Eiver mountains, in the Owl Creek, Bridger, and Eattlesnake up- 

 lifts, in the flexures south of Casper and Douglas, aljout Alcova, in the 

 Shirley and Freezeout hills, in the anticlines north and east of Medicine 

 Bow, and along the east side and across the south end of Laramie basin. 

 It appears also at intervals along the east slope of Laramie mountains. 

 In the greater part of the south-central Wyoming region the Chugwater 

 formation lies on Tensleep sandstone, but in the southern end of the 

 Laramie basin it lies on red beds of the Casper formation, from which in 

 places it is not easily separated. 



Wind River uplift. — The Chugwater formation outcrops along the 

 northeast slope of the Wind Eiver uplift, excepting for a short distance 

 near Dinwoody lake, where the Tertiary overlaps across to the older rocks. 

 It also appears in three areas along the anticline which passes east of 

 Fort Washakie, Lander, and Dallas. In this region the formation is 

 about 1,250 feet thick, and consists mostly of red shales and red sand- 

 stones. The upper beds are pinkish and contain much gj'psum and lime- 

 stone. Some of the sandstone beds are 50 feet thick and in part of gray 

 color. On Sage creek, west of Fort Washakie, the formation is the same 

 as at Lander, but has 4 feet of dolomite in the middle. South of Circle 

 the formation has at top a ledge of rusty sandstone for a short distance. 

 Other ledges of sandstone occur below. 



Owl Creek uplift. — The Chugwater outcrops extensively along both 

 sides of the Owl Creek uplift, and it appears again in Thermopolis anti- 

 cline. Exposures of considerable width extend along the south side from 

 North fork of Muddy creek to Black moiintain. The thickness averages 

 800 feet, with but little local variation, and the rocks do not vary greatly 

 in character in different portions of the uplift. Toward the top and bot- 

 tom red shales predominate, while in the middle soft sandstones and alter- 

 nations of sandstones and shales are the principal features. jSTear the 

 base there is usually a thin bed of piirplish gray limestone from 18 inches 

 to 3 feet thick, and in some portions of the area two such limestones 



