THE WASHOE ROCKS. 99 



these relations at the Springs I made an examination at 

 AYashoe for purposes of comparison. On Mt. Kate, and 

 the range of hills to the southeast of it, I detected the 

 same transition rocks, in small quantities but distinctly 

 developed. This range is mostly composed of a very 

 coarse pyroxene andesite. Its structural relations had 

 always puzzled me, for while the rock of which it is com- 

 posed presents, as a whole, apparently insignificant litho- 

 logical differences from the ordinary pyroxene andesite of 

 the Comstock area, there seemed plain evidence that the 

 main mass had been much eroded, while this range seemed 

 to have suffered but little. It now appears to be the first 

 portion of the series of eruptions of w^hich the later horn- 

 blende andesite was the last, and I believe it to have been 

 much later than the main, comparatively level pyroxene 

 andesite area, though no eruptive rock, intermediate in age^ 

 has been detected. I may also mention that I have traced 

 the same passage from pyroxenic to micaceous andesite at 

 Mt. Shasta and at Clear Lake. 



Messrs. Hague and Iddings recognize that my diabase 

 preceded the older hornblende andesite. Tbey also recog- 

 nize that the later hornblende andesite was ejected long^ 

 after the earlier hornblende andesite. The pyroxene ande- 

 site of the Mount Kate range, which is connected with the 

 later hornblende andesite by transitions, must, therefore,, 

 to accord with their admissions, be younger than the rock 

 w^hich I called diabase. The discovery of these transitions, 

 thus leads inevitably to the conclusion that the pyroxenic 

 porphyries of Washoe are not substantially one eruption. 



Earlier Hornblende Andesite. — The relative age of the 

 older hornblende ^ andesite ^of AVashoe seems to me very 

 clear. It overlies both the diabase and the diorite in thin 

 sheets, and Messrs. Hague and Iddings admit that it is 

 younger than these rocks. They assert, however, that it 

 is also younger than the mass of rock laid down on my maps 

 as augite andesite. They are consequently compelled to 



