FISH CKKHK .MOUNTAINS. 21 



faulting present a contornialjle series of sediments inclineil throughout their 

 entire thickness at angles seldom less than 75°. 



From the axis of the anticline, near the summit, on the west side of 

 Prospect Peak, to the Iloosac fault along the eastern base of the ridge, 

 there is exposed a series of strata measuring nearly 10,000 feet in tliickness, 

 and wholly made up of Cambrian and Silurian rocks. The axis of this 

 fold occurs in the Prospect Mountain quartzite, the underlying member of 

 the Cambrian, and is in turn overlain successively by the Prospect Moun- 

 tain limestone. Secret Canyon shale, Hamburg limestone, Hamburg shale, 

 Pogcmip limestone, and Eureka quartzite. Along the Iloosac fault the 

 Eureka (juartzite is well exposed at Caribou Hill, McCoy's Ridge, Iloosac 

 Mountain, and the narrow ridge east of Round Top. 



Prospect Ridge affords the grandest section of Caml)rian rocks yet 

 recognized in the Great Basin, and with the exception of one or two insig- 

 nificant exposiu-es of slight inq)ortance east of the Sien-a tault, the rocks of 

 this period are confined to this orographic block. Section CD-EF (atlas 

 sheet xiii), constructed across the central portion of the Em-eka Mountains, 

 intersects Prospect Ridge about 3,000 feet to the north of the peak at a 

 point well chosen to bring out the anticlinal structure of the uplifted block 

 and its relations to the fault lines. There is represented on PI. ii, Fig. 4, a 

 geological section drawn at right angles to the strike of" the beds across the 

 culminating point of Prospect Peak, from Spring Valley to the Hoosac 

 fault. The Prospect Mountain limestone is here shown capping the peak 

 and the entire east slope, and it is again exposed at the base of the ridge on 

 the west side of the anticline, rising above the detrital material of Spring 

 Valley. In Fig. 3 of the same plate will be found a section of the same 

 strata across Ruby and Adams Hills. Here the beds are inclined at a much 

 lower angle, otherwise the structural featui-es and succession of strata are 

 nearly identical. Ruby Hill corresponding to Prospect Peak and Adams 

 Hill to the Hamburg Ridge, with the intermediate Secret Canyon shale 

 occupjnng a depression between them. 



Fish Creek Mountains.— To the soutliwcst of tlic Sierra fault the character 

 of the country changes, and a confused and intricate series of ridges come 

 in, presenting a strong contrast to the adjacent region. In place of the 



