b 



i'ERMIAN-TRIASSIC ? 437 



gypsum overlying Forelle limestone. This evidence throws light o)i the 

 probable continuity of the Forelle limestone across the south end of Lara- 

 mie basin. 



In the Centennial valley the gypsum measures are represenlod hy a 

 lliiii, gypsifei'ous limestone bed, separated from the supposed Forelle 

 limestone by red shales. They are overlain by alternations of red sliales 

 and soft, red sandstones. The upper part of the formation includes the 

 "monument" sandstones, as in the region southeast. 



East side of Laramie mountains. — In the foothills of the western part 

 of Laramie county the Chugwater formation is about 900 feet thick. Jt 

 comprises 375 feet of red sandy shale and soft red sandstones, 50 feet of 

 gypsiferous beds, thin limestones, and red shales, and at the top 450 to 

 500 feet of red sandstone and shale. On the south prong of Horse creek 

 the formation is 1,000 feet thick. About 100 feet above its base are 15 

 feet of slabby limestone resembling the Minnekahta limestone. On South 

 fork of Horse creek there is a 50-foot bed of massive, gray sandstone at 

 the top of the formation — a feature often seen in Colorado ; possibly this 

 member may belong to the Sundance formation. In Horse Creek canyon, 

 where the beds are vertical, the basal red shale and thin-bedded sandstone 

 thicken to 260 feet. Next above is a 20-foot bed of dolomitic limestone 

 which gives rise to a small but prominent ridge extending some distance 

 north. It is massive above and thin-bedded and purplish below. Next 

 are 70 feet of red shale, 4 feet or more of porous dolomite, 100 feet of red 

 shale, 5 feet of fine-grained, massive, pure white limestone and 660 feet 

 of red shales capped by 40 feet of reddish gray sandstone. Just south of 

 North fork of Horse creek the formation has a limestone member about 

 100 feet above its base, probably a continuation of the 20-foot bed on the 

 main creek, and the underlying red shale member is less thick. 



About Iron Mountain station the formation is between 700 and 800 

 feet thick in a section measured in beds dipping from 43 to 78 degrees. 

 The rocks are mostly red sandy shales grading into red sandstones, most 

 of which contain considerable clay. Near the middle of the formation 

 are two thin layers of limestone and at the base the following beds: 



Section of Loiver Beds of Vlnigioatcr FoniKilioii just \ort]i of Iron Mountain 



Station, Wyoniinu 



Feet 

 Brownish red, soft, massive sandstone (under tliicic iiuiss of 



red beds) H) 



Limestone, white, massive 5 



Brownish red sandstone, moderately soft, mnssivo 40 



Tliiu-bedded limestone C> 



Brownish red sandstone •"{ 



Jjimestone with Pennsylvanian fossils Many 



