236 GEOLOGY. 



Beautiful illustrations of this kind of erosion can be seen along the 

 streams flowing eastward from the Laramie Hills. South of the 

 Union Pacific Railroad, west of Cheyenne, the Pliocene beds form 

 irregular terraces, which often change or are prolonged into curious 

 sharp escarpments. South of Cheyenne, and eastward, the upper 

 beds are often made up of light, creamy limestone, sometimes ex- 

 ceedingly brittle, intercalated with small veins of chalcedony. Still 

 further eastward, north and south of the Union Pacific Railroad, 

 the Pliocene beds become arenaceous, but fine-grained, beds of clay 

 and marl being interlaminated. The Chug water is bordered for a 

 long distance with abrupt cliffs of Pliocene rocks, often forming 

 escarpments which have been cut out by lateral ravines and small 

 canyons. At Scott's Bluffs, near the western line of Nebraska, 

 there is a fine exposure of the Pliocene rocks, which are here made 

 up of sandstones, marls and whitish and yellowish white clays. 

 Along Lodge Pole Creek, the Pliocene rocks have assumed more 

 the forms of bluffs. Here, and occasionally on the upper Republi- 

 can, the thin, marly members sometimes contain thin masses of 

 jasper-like rocks, which occasionally contain dendritic markings, 

 produced by oxides of the metals. Among these, moss agates are 

 occasionally found. On the Niobrara and Loup rivers there is, in 

 many places, at the top, an immense amount of loose or at least in- 

 coherent sand, or loosely compacted sand. The decomposition of 

 these Pliocene beds in these regions has produced the famous sand 

 hills. Next below, are beds of compacted gravel and sand. Then 

 come calcareous and arenaceous concretions, combined with or en- 

 closed in whitish and yellowish grits. Greenish and greenish gray 

 sand comes next. Arenaceous marl, shading from deep yellow to 

 dull red, lies below the last. At the bottom is observed a grit of 

 yellowish hue, often highly calcareous, and sometimes containing 

 limestone more or less concretionary, from one to seven inches thick. 

 The following section, beginning at the top, I have taken about 

 75 miles above the mouth of the Key a Paha: 



1. Light brownish sand of undetermined thickness. 



2. Incoherent gravel and sand 25 feet. 



3. Yellowish white grit, with calcareous concretions 19 " 



4. Greenish and grayish sand. 27 " 



5. Reddish and yellowish sandy marl 35 " 



f>. Yellowish gray calcareous grit, containing layers of concre- 

 tionary limestone 42 " 



Total 148 " 



