58 



GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



Comparison with Eureka and Washoe dacite* and rhyolites. It is important 

 to ascertain the position of the Tonopah rocks with reference to (1) dacites and 

 rhyolites which have been described by Becker and by Hague and Iddings from the 

 neighboring and closely related districts of Washoe and Eureka (for these districts 

 and their rocks will often be compared with Tonopah in the present report), and 

 (2) to the system of igneous rocks as a whole. The comparison with the Washoe 

 and Eureka rocks is shown by the following analyses," which are arranged 

 according to silica content. 



Analyses of rlacite and rhi/olite from Tonopah ami other districts in Nevada. 



1. Dacite, Eureka, Nev. 



2. Dacite, Washoe, Nev. 



3. Brougher dacite, Brougher Mountain, Tonopah (specimen 359). 



4. Tonopah rhyolite-dacite, Tonopah (specimen 661). 



5. Brougher dacite, Butler Mountain, Tonopah (specimen 368). 



6. Rhyolite, Washoe, Nev. 



7. Rhyolite, Eureka, Nev. 



8. Rhyolite, Eureka, Nev. 



9. Brougher dacite, Golden Mountain, Tonopah (specimen 388). 



10. Rhyolite, Rushton Hill, Tonopah (specimen 376). 



11. Rhyolite, Eureka, Nev. 



12. Rhyolite, Mount Oddie, Tonopah (specimen 337). 



There is a close relation between Nos. "2 and 3, dacites from Washoe and 

 Tonopah (Brougher Mountain). The.se rocks are plainly almost identical, and 

 suggest the general correlation of the dacites of the two districts, although the 

 high silica content of No. i, dacite from Tonopah (Golden Mountain), has caused 

 it to )>e placed in the table l>etween a Eureka rhyolite and a Tonopah rhyolitr. 



Retetitum of t lie tit'in dacite. The analyses represent a series of closely related 

 rocks which show a transition from No. 1, which has nearly the composition of an 



"The Eureka und Waahoe analvxes are taken from Mon. I'. 8. Geol. Survey, vol. 20. pp. 261, 



