38 



coverall the lower plains, form the divides, and extend up to the foot- 

 hills. These beds consist of loose, fine-grained, whitish sandstones, clays, 

 and gravel, the debris of older rocks. They have been gathered from 

 the surrounding heights, and deposited in horizontal layers, extending 

 continuously over the whole bed of the lake. The results of erosion which 

 has taken place since that time are to be seen here on a grand scale- 

 Canons and wide valleys have been cut out, and whole areas removed, 

 leaving isolated buttes, pyramids, and mounds of various shapes, like 

 ancient ruins scattered over the plain. Crow Heart Butte, a weird and 

 gloomy-looking pile of disintegrating rock, several hundred feet in 

 height, is a remnant of these lake deposits which serves to mark the 

 depth of their original thickness, while the surfaces planed down around 

 it indicate the enormous amount that has been w r orn off by erosion .and 

 swept away. 



In passing from the valley' toward the mountains the underlying 

 rocks come to the surface in the following order of succession : 



Cretaceous beds, gray or brownish sandstones and clays, with seams 

 of lignite and iron concretions. 



Jurassic limestones and various colored calcareous and arenaceous 

 marls, with vast quantities of gypsum. 



Triassic red sandstones. 



Carboniferous beds, mainly limestones. 



Potsdam, loose bedded brownish sandstone. 



Gneisses with seams of feldspar and quartz and dark, slaty schists, 

 gold and silver bearing. 



Granite, gray and reddish, to black quartzites and granites. 



The latter form the nucleus of the mountain ranges against which the 

 outlying beds recline at gradually decreasing angles from the Potsdam 

 sandstone to the Cretaceous series without much indication of uncon- 

 formability. This arrangement is shown in the accompanying diagram 

 (Fig. 1) of a section through South Pass and lied Canon to the mouth 

 of Wind Kiver, points at which the several layers are particularly well 

 exposed by the erosion which has followed the uplift of the mountains, 

 and will serve to illustrate the general facts in the geology of the whole 



region. It is probable that between the carboniferous and met amorphic 



rocks there are, in places, detached portions of other members of the 

 Silurian series, but these are not apparent at the point of section, 



The feldspathic gneisses and slaty schists above mentioned, are .tin 

 gold and silver bearing rocks at South Pass, and, aa they extend along 

 the whole range into the mountains beyond, they are no doubt the 

 source of gold in the river drift, which we shall And on the western 

 side of the divide. The South Pass mines are in the same stagnant 

 condition as when visited by Captain Jones ten years ago, and the 

 description then given will apply now. The gold' is found in quartz 

 veins in a free state, easily worked. The silver is distributed between 

 the plates of mica slate in beautiful frosted scales. The Jura -sic and 



