258 H. W. TURNER GEOLOGY OF THE SILVER PEAK QUADRANGLE 



Such rocks are abundant in the quadrangle. The largest flow is that of 

 Piper Peak ridge. This basalt differs from the other flows in being 

 rather coarse in grain and in containing more hyper stliene than olivine. 

 Chemically this rock is richer in silica than most basalts, as may be seen 

 in the following analysis : 



Partial Analysis of the Basalt of Piper Peak, N umber 590 

 George Steiger, Analyst 



Silica "54.78 



Magnesia 3 . 55 



Lime 7 . 48 



Soda 3.28 



Potash 2.44 



Most of the basalts of the quadrangle are of the ordinary olivinitic 

 type. They are dark heavy rocks, often scoriaceous, usually showing 

 minute yellow grains (olivine) to the unaided eye. 



The Pleistocene basalt of the Clayton Yalley crater is largely in the 

 form of lapilli; that is, more or less rounded, scoriaceous fragments. 



The Succession of the Lavas 

 in general 



The oldest lavas observed in the region are the meta-rhyolites and 

 associated lavas of the Cambrian and Ordovician periods. 



Between Paleozoic and Tertiary time there appears to have been a 

 cessation of volcanic activity. 



In the Tertiary era the quadrangle was the scene of frequent and pro- 

 longed eruptions, and the lavas and tuffs of this era are so related to 

 the deposits of the Esmeralda formation that the age of some of the 

 eruptions has been in part definitely ascertained. 



OLDER BASALT 



What are perhaps the oldest lavas are certain basalts which form 

 narrow bands near the supposed base of the Esmeralda formation in Ice 

 House canyon and vicinity, associated with red conglomerate beds. 



OLDER ANDESITE 



South of the Cave Spring road, at the west base of the Silver Peak 



range, are dikes and intruded sheets of altered andesites in the there 



hardened sandstones. These may be as old as the basalts above re- 

 ferred to. 



OLDER DACITE 



In the Miocene sandstones and slates near the coal mines are inter- 

 bedded layers of a dacite-tufr". This is composed of crystals, broken or 



