472 DESCRIPTIVE GEOLOGY. 



many features that are common to all the ranges of the Nevada Plateau. 

 As regards then' geological aspect, however, each mountain-range possesses 

 much that is striking and distinctive, not only as related to their structural 

 and dynamical features, but to the age of the beds exposed and their mode 

 of occurrence. The salient features of each mountain-range will be given 

 under the detailed description of each, beginning with those uplifted ridges 

 that border upon the Great Desert, the Ibenpah and Ombe, and proceeding 

 westward as far as the Shoshone Range, which lies just to the east of Reese 

 River. 



Ibenpah Mountains. — The first elevation to the west of the Desert, 

 at the southern limit of the map, is that of the Ibenpah Mountains, a high 

 commanding range, whose principal summits, just beyond the boundary of 

 the map, attain a probable elevation of 10,000 feet or more. That portion 

 of the mountains within the area of this exploration lies entirely in the Ter- 

 ritory of Utah; the 114th meridian, the boundary -line between the State 

 of Nevada and Utah, running through Deep Creek Valley, just west of the 

 mountains. 



This higher portion of these mountains, beyond the southeast corner of 

 the map, was not visited, but shows to the east of the crest a body of granite, 

 overlaid by heavy limestone formations. These are seen at the gap through 

 which passes the old overland stage-road, where they show an anticlinal 

 structure, folding over the underlying granite core. The limestones are 

 generally dark-colored, passing from gray to blue, and considerably meta- 

 morphosed, while on the flanks toward the Desert they show some indis- 

 tinct developments of arenaceous beds and quartzites. 



Mount Horeb, the extreme northern point of the range, is formed of 

 earthy blue and black limestones, dipping 45° to the northeast. In none 

 of the beds were any fossils found by our parties, but from their general 

 lithological resemblance to the Wahsatch limestone, they have been referred 

 to the Lower Coal-Measure horizon, while it is probable that in the lower 

 exposures a careful search might reveal the Devonian and Silurian forma- 

 tions. 



The lower portion of the eastern slopes of the range toward the Desert 



