142 



University of California Publications. 



[Geology 



Sing-ats-e Range is that of an anticlinal fold, with granitic axis 

 and sedimentaries, largely limestone, resting on the flanks. Meta.- 

 morphism of the calcareous rocks is extreme, and has resulted in 

 the formation of the well-known copper deposits of the Yerington 

 district. These copper ores are entirely similar in character and 

 origin to those near Carson and Genoa. The pre-Tertiary rocks 

 are therefore at a lower elevation in the Pine Nut and Virginia 

 ranges than further east in at least the one range noted. This 

 condition may be due to three causes, in part to original, hypso- 

 metric differences, in part to relative elevation of the Sierra 

 Nevada and Sing-ats-e with the associated Nevada ranges, and 

 in part to the depression due to the great weight of the Tertiary 

 lavas in the Virginia and Pine Nut ranges. All this is of im- 

 portance to the present paper in helping to establish a close con- 

 nection between the Sierra Nevada and the first ranges to the 

 east. 



The roof of the granitic batholith is very probably not far dis- 

 tant from the upper limit of the pre-volcanic rocks. The ques- 

 tion of its exact position and history is one of the many interest- 

 ing problems yet to be solved. The question of origin of the hot 

 water of the Comstock mines is of interest in this connection. 

 Becker has assumed that the older schists outcropping in the 

 Sierra Nevada to the west were the water-carrying strata. But 

 the schist occurs mainly in isolated areas or thin remnants not 

 carrying water where exposed. Moreover, the contact of schist 

 and intrusive plutonic is distinctly water-bearing near Carson, 

 and not the schists themselves. These facts, taken with the 

 further one of a broad synclinal axis beneath the Virginia and 

 Pine Nut ranges, rather point to the roof of the batholith as the 

 source of the Comstock water. This is compatible with either 

 view of the age of the diorite of Mt. Davidson, if it be assumed 

 that, if the diorite be of pre-Tertiary age, it is also younger than 

 the granodiorite or granite. The presence of a small spot of por- 

 phyritic granitic rock has already been noted in this connection. 



If, then, the Virginia and Pine Nut ranges be of such close 

 relationship to the Sierra Nevada, and separated from it by 

 flat-bottomed valleys and distinct fault planes, it follows that 

 Washoe, Eagle, and Carson valleys lie upon the summits of 



