EUEEKA AND WASHOE. 281 



synchronous in age, since the succession of all subsequent lava-flows for the 

 feldspathic rocks in both localities may be said to be the same hornblende- 

 mica-andesite, dacite, rhyolite. Analyses show the homblende-mica-ande- 

 site rocks of Eureka to carry slightly more silica than the corresponding 

 rocks at Washoe, the most acid members of this group from the latter locality, 

 coming just within the range of the basic members of the series at Eureka. 



When it comes to the pyroxenic rocks following the rhyolite the 

 sequence of events does not appear so clearly established at Washoe, as 

 there no such grand exposui-es occur as at Eureka. In the immediate 

 region of the Comstock Lode only a few isolated patches of basalt are 

 exposed. Small outbursts of pyroxene-andesite, similar to those of Rich- 

 mond Mountain, have broken out only a short distance from Mount David- 

 son, but the relations between these two pyroxenic lavas are unknown. A 

 few miles northward in the same range of mountains large flows of 

 both pyroxene-andesite and basalt may be seen superimposed upon horn- 

 blende-mica-andesite and rhyolite. Taken together the Washoe District 

 and the region of Truckee Canyon present a sequence of lavas and a 

 geological history of volcanic events similar to that found at Eureka. 



The subjoined table presents a seiies of twelve chemical analyses rep- 

 resenting the volcanic rocks of Washoe arranged according to their 

 basicity :' 



1 On the development of crystallization in the igneous rocks of Washoe, Nevada; with notes on the 

 geology of the region. Bull. U. S. Geol. Survey, No. 17, p. 33. 



