624 /. E. SPURR 



This conclusion was corroborated by subsequent investigators 

 in different parts of the world, so that the term has passed out 

 of use. It has also been proved by Mr. Becker's studies, and 

 later by those of Messrs. Hague and Iddings, 1 that the trachytes 

 of Richthofen and of the 40th Parallel Survey, as determined 

 by Zirkel, are mainly andesites — ■ in part hornblende-mica ande- 

 site, and in part hypersthene-augite andesite (the latter rock 

 corresponding more nearly to the augite -trachyte of Zirkel), 

 while a smaller proportion are dacites, and some are probably 

 rhyolites. It has been determined by these investigators that 

 trachyte is conspicuously absent in the province of the Great 

 Basin. The reason for Zirkel's false classification was the lack 

 of means at that time to determine the feldspars, so that the 

 plagioclases were determined as sanidine, since they showed lit- 

 tle or no striation. 



SUCCESSION OF LAVAS PREVIOUSLY DESCRIBED IN THE GREAT 

 BASIN AND VICINITY 



Eureka district. — In the course of a careful study of the vol- 

 canic rocks of the Eureka district in Nevada, Mr. Hague 2 

 arrived at the following succession of lavas at this center of 

 volcanic activity: 



1. Hornblende andesite. 



2. Hornblende-mica andesite. 



3. Dacite. 



4. Rhyolite. 



5. Pyroxene andesite. 



6. Basalt. 



Washoe district. — In the Comstock or Washoe district, at the 

 southern end of the Virginia Range, Mr. Becker 3 found the fol- 

 lowing succession of igneous rocks : 



1. Granite. 



2. Diorite. 



3. Quartz-porphyry. 



^'Volcanic Rocks of the Great Basin," Amer. Jour. Sci., June 1884^.453. 

 Geology of the Eureka District, Mont. XX, U. S. Geol. Surv., p. 230 et seq. 



2 Mon. XX, U. S. Geol. Surv., p. 290. 3 Mon. Ill, U. S. Geol. Surv., p. 380. 



