EUEEKA AND WASHOE. 281 



syiiclironous in Jiye, since the succession t)t" all subsequent lava-flows for the 

 tVldspatliic rocks in both localities may lie said to be the same — hornblende- 

 niica-andesite, dacite, rhvolite. Analyses show the hornblende-mica-ande- 

 site rocks of Eureka to carry slightly more silica than tlic 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 rhvolite the 

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

 there no such grand exposures occur as at Eureka. In the immediate 

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

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

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

 sou, but the relations Ijetweeu these two pyroxenic lavas are unknown. A 

 few miles north «-ard in the same range of mountains large flows of 

 both pvroxene-andesite and liasalt ma^" be seen siqierimprise'd ujion liorn- 

 blen<le-mica-andesite and rluolite. Taken together the Washoe District 

 ami the region of Truckee Canyou present a sequence of la%'as and a 

 geological history of vohtanic events similar to that found at f^ureka. 



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

 resenting the volcanic rocks of Washoe arranged according to their 

 basicity :' 



' On the development of crystallization in the igneou.s rocks of Washoe, Nevada ; with notes on the 

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



