FORMATIONS OF THE LARAMIE RANGE 405 



The formation appears again on Chugwater and Horse creeks, consist- 

 ing of an upper series 30 feet thick of soft, slabby sandstones, gray at the 

 base and buff toward the top, with ripple-marked layers and much inter- 

 calated shale, and a lower series 50 feet thick, mostly of green and gray 

 shale, with layers of soft, thin bedded, greenish gray sandstones lying on 

 the Chugwater formation. 



MORRISON FORMA TION 



The Morrison formation appears to extend continuously along the 

 Laramie range, presenting its usual characteristics of a joint clay or 

 massive shale, mostly of greenish gray color with some portions of ma- 

 roon tint. Occasional thin beds of light colored sandstone are in- 

 cluded, and limestones are numerous in the lower portion of the forma- 

 tion, especially to the southward. In the vicinity of Casper mountain 

 the thickness is not much more than 100 feet, but on the Chugwater 

 and near Horse creek it is 300 feet. 



LAKO TA-DAKO TA 



The Morrison formation is everywhere overlain by coarse grained buff 

 sandstones, which have been designated " Dakota," but probably include 

 the Lower Cretaceous members, Fuson and Lakota. Their thickness is 

 100 to 150 feet. At the base there is usually more or less conglomerate 

 merging upward into a series of coarse sandstone ; then follows a bed of 

 shales, varying in color from dark gray to bright purplish red, strongly 

 suggestive of the Fuson formation, and at the top a thick mass of coarse 

 brown to gray sandstone often containing considerable ironstone. In 

 many of the hogback ranges there is a third sandstone member, but it 

 probably belongs in the lower part of the Benton, for it is always under- 

 lain by a considerable thickness of dark colored shales. 



THE BENTON GROUP 



The formations of the Benton group are extensively exhibited about 

 the northern end of the Laramie range and on Chugwater, Horse, and 

 Lodgepole creeks. As in other regions, they consist mainly of shale 

 of dark color, but the component formations present many of their dis- 

 tinctive features.. The Mowrie series of hard shales, which weather to 

 light gray color, are distinct throughout, lying about 500 feet above the 

 Dakota sandstone at the north end of the range and about 200 feet above 

 to the southward. As in the Black Hills region, a sandstone bed usually 

 occurs in the lower portion of the Graneros shales, a feature especially 

 conspicuous on Chugwater and Horse creeks. Here the thickness of this 

 sandstone is about 25 feet, and it is underlain by 140 to 150 feet of dark 



