THE KOCKS OF THE WASHOE DISTRICT. G3 



a blue-gra}-, not unlike "teinte neutre," tlie aiigite-andesites are <,renerally 

 a much deeper, somewhat, brownish-bhie. Certain glassy angite-andesites 

 strongly resemble the glassy hornblende-andesites, Avhile another variety is 

 pinkish-gray, and bears no supei-ficial resemblance to anything else in the 

 District. Some gray vesicular modifications have a basaltic look. The 

 crystalline augite-andesites greatly predominate over the glassy ones 

 Hornblendes occur in a majority of specimens, but in very small numbers 

 as compared with the augites, probably not one per cent, while mica is met 

 with only often enough to justify the assertion of its occurrence. 



Augite. — I'he augite is of precisely the same character as that of the 

 hornblende-andesites. Its color is always a more or less brownish-yellow, 

 which varies somewhat in shade but not in character, and is very like that 

 of bamboo. I have not observed a single case of pinacoidal cleavage, while 

 there is a decided tendency to the suppression of one of the prismatic cleav- 

 ages. In some specimens the proportion of augite is small, and the crystals 

 are then very well developed. In other cases they are very numerous and 

 occur in groups in which, owing apparently to interference, the crystallo- 

 graphic outlines are imperfectly developed. They frequently contain glass 

 inclusions, which sometimes assume the form of negative crystals, and 

 sometimes spheroidal shapes; but embedded microlites of other minerals 

 are rare. Besides the porphyritical crystals, the augite often appears to 

 form a portion of the groundmass, and microlites of it are common in the 

 feldspars. In one rock, which has been classified as a hornblende-ande- 

 site, an augite was noted piercing an ilmenite. These facts point to a very 

 wide range of time for the crystallization of the augite, which would seem 

 to have been among the first, and among the last, minerals to assume a 

 crystalline form. This is a strong contrast to the occurrence of hornblende, 

 but in conformity with the results of experiment, for, as is well known, 

 augite has been artificially reproduced under a variety of conditions; whereas, 

 so far as I am aware, the efforts to repi-oduce hornblende have hitherto 

 proved unsuccessful. The augites very exceptionally show a trace of the 

 black border, so commonly accompanying hornblende. 



Other minerals. — The homblcnde is precisel}' similar to that of the horn- 

 blende-andesites. It usually occurs in minute crystals, with heavy black 



