LARAMIE PLAINS. 85 



end of the range, circling around the spurs of Rock Mountain. They con- 

 sist of coarse, friable sandstones, usually of a reddish-brown or yellow- 

 color, with occasional layers of harder brown beds; all of them lying 

 nearly horizontal, or with a gentle dip to the eastward. On the south 

 bank of Mill Creek, not far from the Archaean mass, and almost completely 

 surrounded by Quaternary deposits, occurs a body of brownish-gray 

 sandstone, probably belonging to the Fox Hill group, which carries a layer 

 of rich carbonaceous shales, with thin seams of coal cropping out along 

 the exposed bluff; the shales exhibiting a thickness of 3 feet between the 

 sandstone layers. These sandstones were searched for organic remains, 

 but tliey only yielded a few imperfect impressions of deciduous leaves. 

 The strike of the sandstone is north 35° to 40° east, with a dip of north 

 55° to 60°. 



Between Mill and Cooper Creeks, numerous ■ small stream-beds cut 

 deeply into the sandstones, but offer no exposures of special interest. 

 Cooper Creek, a very considerable stream, which debouches through a 

 narrow canon in the mountains, has worn out by erosion a broad valley in 

 the softer Cretaceous rocks, leaving high banks upon each side, composed 

 of coarse sandstones. The valley for several miles from the mountains is 

 remarkable for the large amount of coarse detrital material, which every- 

 where covers the surface ; the large Archaean boulders lying high up on the 

 benches and ridges. At its lower end, the valley cuts through the Colorado 

 beds, which, farther up the stream, are overlaid by the Fox Hill group. 

 This formation apparently extends up to the Archaean ridges; at least, no 

 structural or palaeontological evidence was obtained of any later formations, 

 all organic remains collected from a number of localities in the exposed 

 banks being forms decidedly characteristic of the Fox Hill divisions, prin- 

 cipally of the genus Inoceramus. 



On the ridge, which forms the south side of Cooper Creek Valley, just 

 above tlie upper wagon-road, and but a short distance from the Archaean 

 foot-hills, was found a new species of the genus Axincea, which Professor 

 Meek, in his report, has described under the specific name of 



Axincea Wyomingensis. 



