LA VAS IN THE GREA T BASIN REGION 643 



aware that these complementary forms constitute an acid-grow- 

 ing series, transitional between the andesite No. 4 and the rhyo- 

 lite which is complementary with No. 5, and that this series 

 appears to be in general contemporaneous with the basic-grow- 

 ing series between the andesite and the basalt. As an example 

 of this acid-growing series consecutively observed, the section 

 described in Meadow Valley Canyon is highly interesting; here 

 we have a transition from pyroxene andesite through interme- 

 diate phases to Pleistocene rhyolite, which is complementary 

 with Pleistocene basalt. 



Between the andesite No. 2 and the olivine-basalt which is 

 coupled with the rhyolite No. 3, we have not found such satis- 

 factory transition phases, but this is perhaps due to the remoter 

 age of this group of lavas. 



We may, therefore, write the general succession and relation 

 of the lavas of the Great Basin, as follows : 



I. BlOTlTE RHYOLITE AND TORDRILLITE. 



r Pyroxene-hornblende andesite. 



/ 



Hornblende-pyroxene andesite. 



/ 

 Hornblende andesite. 



/ 

 Biotite andesite. 



/ 

 Hornblende quartz-andesite. Pyroxene andesite (?) 



Dacite. 



/ 

 Latite (P) 1 



- / 

 3. Biotite rhyolite. Olivine-basalt. 



1 Compare some of the analyses of the earlier andesites and dacites at Eureka 

 (e. g., Mon. XX, U. S. Geol. Surv., p. 264, Nos. 4, 5, and 6), with those of latites 

 given by Dr. Ransome (Bull. 89, U. S. Geol. Surv., p. 66). 



2.-f 



