STRUCTURAL FEATURES 263 



there was found a sort of vein deposit of a yellowish material. The 

 locality is about 15 miles southwest of Silver Peak. A sample of the rock 

 was treated chemically with the following results : 



Analysis of yellow Mineral, Specimen Number 391 



George Steiger, Analyst 



Insoluble, less Si0 2 ; soluble in Na 2 C0 3 after treatment with HC1 51.5 



Si0 2 after treatment with HC1 19.0 



Fe 2 3 soluble in HC1 13.5 



CaO soluble in HC1 3.4 



MgO soluble in HC1 5 



Alkalies none 



H 2 calculated by difference 9.5 



C0 2 calculated from CaO 2. 6 



100.0 



Leaving out CaO, C0 2 , and insoluble less silica soluble in Na 2 C0 3 , and calculating 

 to 100 per cent : 



Si0 2 44.8 



Fe 2 3 31.8 



MgO 1.2 



H 2 22. 2 



100.0 



The yellow mineral removed from the impurities thus corresponds 

 closely with chloropal. 



Structural Features 



It appears probable that the valleys of the region are in part or perhaps 

 largely of orographic origin ; that is to say, they represent subsided areas. 

 Elevation of ranges and subsidence of valleys may be presumed to go on 

 simultaneously. Such movements are usually accompanied by normal 

 faulting, and there is good evidence outside of the topography that 

 normal faulting has taken place in the quadrangle. 



One of the demonstrated fault-planes lies at the north base of the 

 Silver Peak range, and the steep north slope is ascribed to uplift along 

 this fault. It is perhaps hardly correct to call this steep slope and other 

 similar slopes a faultscarp, for the original scarp has long since been 

 removed by erosion. Figure 2, plate 9, is a view of this scarp from 

 the north. The rocks of the scarp are in large part rhyolitic tuffs and 

 massive rhyolite. Ordovician sediments form a portion of the western 

 part of it. To the north of the scarp are the lake beds (Esmeralda 

 formation). These consist here largely of sandstone containing coal 

 seams. At the contact with the scarp these beds are highly contorted 



XXIII — Bull. Geol. Soc. Am., Vol. 20, 1908 



