LA VAS IN THE GREA T BASIN REGION 629 



Sweetwater Range. — The Sweetwater Range may next be 

 considered, since it lies south of the Pine Nut Range and shows 

 very nearly the same rocks. It is separated from the Pine Nut 

 Range only by the Walker River Valley, while at its southern 

 end it connects with the Sierras, of which it may thus be con- 

 sidered a spur. 



The observed succession of lavas in this range is as follows : 



1. Rhyolite (closely connected and perhaps contemporaneous with 



granites of similar composition). 



2. Hornblende-pyroxene andesite. 



Epoch of erosion and subsequent formation of Shoshone Lake. 



3. Hornblende-pyroxene andesite, tuffs and breccias. 



4. Hornblende-biotite latite. 



5. Basalt. 



Gabb's Valley Range. — In the lavas of Gabb's Valley and 

 the Gabb's Valley Range, which lies just east of Walker Lake, 

 the following succession was made out : 



1. Biotite andesite. 



2. Biotite rhyolite. 



3. Hypersthene-hornblende aleutite. 1 



4. Augite basalt. 



A granular rock, which had every appearance of being 

 effusive, was also found in Gabb's Valley, and on examination 

 proved to be a hornblende-biotite quartz-monzonite. This, how- 

 ever, is not included in the list, since its exact position is uncer- 

 tain. It is very likely earlier than all the others and is perhaps 

 contemporaneous with the biotite-hornblende quartz-monzonite, 

 which forms the oldest rock in the Walker River Range, being 

 more ancient than the granite. 



Silver Peak Mountains. — Mr. H. W. Turner, who has studied 

 the volcanic record in the Silver Peak district, has kindly sup- 

 plied the writer with the preliminary statement that in general 

 the succession of lavas here is as follows : 



1. Rhyolite. 



2. Andesite. 



3. Basalt. 



'See American Geologist, April 1900, p. 230. 



