52 DESCRIPTIVE gp:ology. 



]3etvveen the north and soutli branches of Crow Creek, along the base 

 of the range, the Palaeozoic strata are the only rocks that occur well 

 exposed, the later Tertiaries encroaching upon the upper members. Just 

 south of the north branch occurs one of the high ridges or bluffs which is 

 so characteristic of the Laramie Hills above Wahlbach Spring, the eastern 

 face exposing the grayish-white Carboniferous limestone, which is-*always 

 found at the top of the series, and may be so easily recognized for long 

 distances across the plain. On the upper side of South Crow Creek, the 

 beds of the Coal-Measure series stand nearly vertical, the lower rock, con- 

 sisting of a hard compact conglomerate, separated from the red, dense 

 granite by a short narrow canon. The Palaeozoic rocks appear quite thin, 

 and it would seem as if the lower members were wanting; at least, the con- 

 glomerate closely resembles an interstratified layer high up among the 

 Carboniferous limestones. In one or two localities, limestones may be seen 

 lying in isolated patches directly upon the granite. Tertiary beds form 

 the banks of Crow Creek Valley, extending close up to the Carboniferous 

 rocks, resting directly against the conglomerate formation, and, as these 

 upper Tertiary strata consist of a hard coarse sandstone almost a conglom- 

 erate, the two sets of beds, lying nearly at right angles to each other, pre- 

 sent a somewhat singular appearance. South of Crow Creek, the horizontal 

 Tertiary rests directly on the Archaean. 



Crow Creek has worn out for itself a broad valley, which has cut 

 down deeply into the Pliocene strata, in several places exposing remnants 

 of Mesozoic formations, probably Cretaceous, but which lack distinctive 

 characters sufficient to determine their horizon. A pure white, soft, friable 

 rock, cropping out near the stream-bed, indicated a strike of north 35° 

 east, with a dip of 20° east. Occasionally the steep Pliocene bluffs along 

 the valley will be cut by ravines and gullies, at right angles to the creek, 

 formed by the washing-out of the soft sand rocks during heavy rains and 

 torrents, leaving near the mountains the lower unconformable rocks exposed. 

 In one of these ravines, Capt. A. L. Varney, U. S. A., procured some Rep- 

 tilian remains, imbedded in hard, dusty-gray sandstone, which Prof 0. C- 

 Marsh identified as belonging to Lestosaunts, a genus of Mosasauroid Rep- 



