84 DESOKIPTIVE GEOLOGY. 



of the stream have exposed some arenaceous black clays, carrying inter- 

 sti'atified narrow beds of pm-er sandstones, which dip about 1° to the 

 westward, and in their general habit closely resemble the Fort Benton 

 beds. From these clays Avere collected Ostrea congesta, and minute but 

 well-preserved fish-scales lying with their broader surfaces parallel with the 

 stratification. 



On the west side of the river, the Colorado group extends well up on 

 the steeper slopes of the Medicine Bow Range, underlying the railroad as 

 far westward as Como Lake, but affording few characteristic outcrops. 

 Between Lookout and Miser Stations, beds of argillaceous sandstones are 

 well exposed, from which were collected specimens of the genus Inoceramus. 

 A short distance east of Miser, the railroad cuts through a heavy bed of 

 brown sandstone, dipping slightly eastward, remarkable for its concretionary 

 structure. These concretions consist of coarse, reddisli sandstone^ firmly 

 held together by a ferruginous paste, which causes them to withstand 

 erosion much better than the sandstone in which they are embedded. They 

 occur of all sizes, from a few inches up to two feet in diameter, many of them 

 quite smooth and symmetrical, and having weathered out from the bluff lie 

 strewn over the surface of the plains. About one -half mile west from Miser 

 Station, the railway cuts through another ridge of hard gray sandstone, also 

 dipping east, in which were found large numbers of Colorado fossils, chiefly 

 of the genus Inoceramus, but associated with Ammonites and Saurian teeth, 

 the latter showing the enamel well preserved. 



High up, along the gentle nearly uniform slopes of the Medicine Bow 

 Range, overlying the Colorado group, occurs a very considerable develop- 

 ment of Fox Hill beds. The junction between the two series is a very 

 difficult one to trace out, the upper beds of the Colorado group being 

 highly arenaceous, passing into the Fox Hill division of coarse, reddish- 

 yellow sandstone by almost imperceptible gradations ; a lithological 

 difficulty enhanced by the absence of all marked physical boundaries, 

 and the very general accumulation of detrital material derived from the 

 elevated ridges of the range, which lies scattered over the slopes. The 

 Fox Hill beds, resting unconformably upon the Archaean rocks-, extend 

 from Mill Creek, a branch of the Little Laramie River, to the northern 



