SANDSTONE DIKES OF UTE PASS. 135 



different parts of the Manitou l)iisiii at the base of the 

 Potsdam, and much of the sandstone is rather coarse. 



Farther northwest the dike passes beneath a broad, 

 steep slope of talus from the granite cliffs above. It can 

 be traced, however, in an occasional prospect hole and 

 in float. Abont half a mile or so from the creek is a quite 

 conspicuous outcrop of white Cretaceous (Niobrara) 

 limestone in beds nine to fifteen inches thick with thinner 

 shaly partings. It has been quarried somewhat and 

 shows a dip to the southwest 45°. Overlying it is 

 a brown and highly fossiliferous limestone with a bitumin- 

 ous odor when freshly broken. Between this limestone 

 and the granite cliff is about two hundred feet concealed 

 by talus, but with indications that the limestone is bor- 

 dered by the sandstone dike with a breadth of one hun- 

 dred feet more or less, the Benton shales and Dakota 

 sandstone being concealed by the fault at this point. In 

 the next one-fourth mile, going west, the dike seems to 

 die out completely, no float showing in the slide ; but the 

 white limestone is exposed in several prospect holes and 

 ledges almost to the head of this valley, which extends 

 nearly a mile northwest from the creek to the summit of 

 the mesa. The dip is constantly southwest, 45° approxi- 

 mately. Probably these Cretaceous strata, like the Foun- 

 tain beds farther west, have been overturned by the 

 oblique upward thrust of the granite. 



On tracing the great sandstone dike southeast from 

 South Cheyenne Creek it is found well exposed on the 

 first spur with a breadth of one hundred to possibly two 

 hundred feet. Neither contact is exposed, but the granite 

 contact can be located within a foot or two at several 

 points. On the north are extensive but obscure expo- 

 sures of the gray fossiliferous limestone and the compact 

 white limestone. The bedding is not clearly exposed, 



