OMBE MOUNTAINS. 497 



down. A chemical examination shows the rock to be nearly pure silica: 



Silica 94.93 



Water ' 0.17 



95.10 

 with less than 5 per cent, of alumina and alkalies. 



On the south flanks of Pilot Peak, the heavy dark-blue limestones, 

 which rise between 1,500 and 1,800 feet above the valley, have 'been 

 referred to the Upj)er Coal-Measure horizon. From these beds were 

 obtained the following forms: 



Productus pundatus. 

 Spirifer cameratus. 



North of Patterson Pass, both the quartzites and limest(.)nes appear, 

 lying conformably upon the granite body. Here, as well as on the south 

 side, the beds stand up above the granites several hundred feet. At the 

 pass, they dip gently to the westward, the limestone beds extending down 

 to the valley-deposits. The quartzites strike a few degrees east of north; 

 their boundaries, however, along the eastern base were not well determined, 

 while the limestone body extends along the west side of the range for 5 or 6 

 miles, until it passes beneath the Tertiary volcanic outflows. It forms all 

 the higher summits of the ridge. It is much disturbed and broken, having 

 undergone considerable faulting and folding, and may be seen dipping in 

 nearly all directions. Here may also be observed low, irregular hills and 

 bosses of granite protruding above the limestone, the latter having suffered 

 considerable erosion near the points of contact. 



In this limestone have been found many well-defined but narrow veins 

 of ore, and considerable time and money have been expended in exploring 

 and opening the most promising mines. The ore is galena, carrying silver, 

 associated with carbonates and other oxidized products, so frequent an occur- 

 rence throughout the mountain limestone formations of Nevada. Special 

 interest, from a scientific point of view, however, is attached to this district, 

 which has become quite famous as a locality for wulfenite (molybdate of 



lead). In other localities in Nevada and Utah, the presence of wulfenite in 

 32 D G 



