LA VAS IN THE GREA T BASIN REGION 623 



thrown out according to their supposed superposition, the order 

 being, therefore, regularly from acid to basic lavas. 



king's work and its later modifications 

 The first careful work on the lavas of the Great Basin was 

 done during the 40th Parallel Survey, the field-work of which 

 was done chiefly by Messrs. Hague and Emmons, while the 

 petrographic work was by Professor Zirkel, and the general 

 results and deductions were made by the director, Mr. Clarence 

 King. 1 Mr. King accepted in general the law of succession of 

 volcanic rocks, as laid down by Richthofen, but subdivided the 

 lavas of each member of the succession, and united the fourth 

 and fifth members — the rhyolite and basalt 2 — under a gen- 

 eral term, " Neolite." The natural order, as interpreted by 

 King, was as follows: 



Order Subdivision 



( a. Hornblende propylite. 



1 . Propylite < b. Quartz propylite. 



c. Augite propylite. 



a. Hornblende andesite. 



2. Andesite ■( b. Quartz andesite (Dacite). 



( c. Augite trachyte. 



( a. Hornblende-plagioclase trachyte. 



3. Trachyte < b. Sanidine trachyte (quartziferous). 



( c. Augite, trachyte. 



XT ,. ( a. Rhyolite. 



4. Neolite { 7 ' , 



J b. Basalt. 



As regards the laws maintained by Richthofen and King for 

 the Great Basin, it is necessary to observe first of all that the 

 first member — propylite — was proved by Mr. George F. Becker 3 

 to be simply a decomposed phase of the andesite in the Washoe 

 district, instead of a separate rock, as supposed by Richthofen 



'Geological Explorations of the 40th Parallel, Vol. I, p. 545 et seq. 



2 This colligation of rhyolite and basalt was made by King on the basis of their 

 close association in the field. His explanations of this fact, however, were essentially 

 different from later ones, now generally accepted, and first advanced by Mr. Hague, 

 Mon. XX, U. S. Geol. Surv. 



3 Geology of the Comstock Lode, Washoe District, Mon. Ill, U. S. Geol. Surv., 

 p. 88. 



