LA VAS IN THE GREA T BASIN REGION 635 



region Mr. King 1 notes that the rhyolitcs and rhyolite tuffs seem 

 to be Pliocene. In the Eureka district Mr. Hague 2 came to the 

 same conclusion as regards the rhyolite there. 



In western Nevada rhyolities are found jnterbedded and 

 therefore contemporaneous with the sediments of the late Plio- 

 cene Shoshone Lake in a number of localities, as, for example, 

 on the borders of the Pine Nut Range. The same relation to the 

 Shoshone Lake beds was noted on the western edge of the 

 Ralston Desert. 



In the mountains near Candelaria glassy rhyolite overlies 

 the folded Upper Eocene or Lower Miocene of the Esmeralda 

 formation. The folding which has affected these beds is the 

 same as that which has upturned the Miocene further north, 

 called by King the Truckee Miocene ; so the disturbance must 

 have been late Miocene or post-Miocene. The rhyolite in this 

 case, therefore, is probably as young as the Pliocene. 



In the Sierra Nevada Mr. Turner 3 referred the rhyolites to 

 the Upper Miocene. According to Mr. Lindgren 4 the rhyolitic 

 flows of the Sierra in the Truckee region began " toward the 

 close of the Miocene." 5 



In general, therefore, the age of the second chief rhyolite 

 eruption ranges from late Miocene well into the Pliocene. 



Basic intermediate. — In the Sierra Nevada, according to 

 Turner, 6 the pyroxene andesite is Pliocene. 



1 Explorations of the 40th Parallel, Vol. I, p. 694. 



2 Mon. U. S. Geol. Surv., Vol. XX, p. 232. 



3 Igneous Rocks of the Sierra Nevada, Jour. Geol., Vol. Ill, No. 4, May-June 

 1895, p. 406 ; Auriferous Gravels of the Sierra Nevada, Am. Geol., June 1895, p. 372. 



4 Truckee folio, U. S. Geol. Surv., p. 3. 



5 The writer was at first inclined to correlate the rhyolite of the Sierra Nevada 

 with the earliest rhyolite shown in the general correlation table (No. 1 of the general 

 succession); but a number of considerations, among others that of the comparatively 

 slight age of the Sierra Nevada rocks, as given above, induced him to class them 

 with later rhyolites (No. 3 of the general succession). In agreement with this conclu- 

 sion are Hague's views (Mon, XX, U. S. Geol. Surv., pp. 261, 281. 



6 Age and succession of the Igneous Rocks of the Sierra Nevada, Jour. Geol.. 

 Vol. Ill, June 1895, p. 408. 



