CRETACEOUS SYSTEM 443 



along both sides of the Owl Creek uplift, tliu north side of llattlesnake 

 mountains, the anticlines south "of Casper and Douglas, the Shirley and 

 Freezeout hills, and the uplifts east of ^ledicine Bow and liock Creek. 

 It extends along the east side and across the south end of the Laramie 

 basin and appears at intervals in the foothills on the east side of Laramie 

 mountains. Two narroAV zones of outcrop extend along l)oth sides of 

 Centennial valle}', and the formation outcrops for 2 iiiik's along tlie east 

 slope of Jelm vallej' just east of Jelm. A small area is faulted to the 

 surface east of Sheep mountain. In Laramie basin the Morrison forma- 

 tion lies unconformably on the Chugwater red beds, liut elsewhere the 

 Sundance formation intervenes. 



The Morrison deposits are mainly hard clays or massive shales, varying 

 in color from pale greenish to maroon and having a peculiar chalky ap- 

 pearance. The prevailing tint is pale olive green. Thin beds of drah 

 limestone and occasionalbeds of light colored sandstone are included, 

 and also in places masses, 2 inches or less in thickness, of olive green to 

 dark green, brittle, siliceous rock of concretionary nature. Some typical 

 exposures are shown in plates 28 and 39. 



Wind Eiver-Oiol Creek region. — In the Wind River and Owl Creek 

 uplifts the Morrison formation outcrojDs in a zone immediately adjoining 

 the outcrop of the Sundance formation. Frequent exposures appear in 

 the slopes of the ridges due to the Cloverly sandstone along both sides 

 of the Owl Creek and Thermopolis uplifts, and in the Fort Washakie- 

 Lander region, although the formation is often covered by talus on the 

 slopes. In the Lander region the thickness is 225 feet, and the rocks 

 are mainly pale green to maroon massive shales, with thin beds of sand- 

 stone. Ordinarily the upper portion is of buff tint and the lower portion 

 partly maroon. About Fort Washakie the formation is 200 feet thick 

 and has a 4-foot bed of sandstone near the middle. In the Owl Creek 

 uplift the thickness varies from 100 to 250 feet in greater part, in gen- 

 eral diminishing from east to west. The predominating material is the 

 usual massive shale, or mixture of clay and fine sand, of pale greenish 

 gray color, merging into deeper green, maroon, pink, and red. In the 

 middle there are usually 50 feet or more of soft, fine-grained, greenish 

 gray sandstone, which is well exhibited on the north slope of the anticline 

 4 miles nortlieast of Thermopolis. It is here overlain by 40 feet or more 

 of sandy shale, in part of maroon tint; 10 feet of loosely consolidated 

 conglomerate with pebbles mostly of a very dark color, and at the top 10 

 feet of highly carbonaceous, dirty buff shale. The basal beds here are 

 reddish and greenish massive sandy shale. On ISrorth fork of IMuddy 

 creek the rock is mostlv soft, fine-grained, white, very massive sandstone, 



