Geology and Mineralogy. 311 



Of the above mentioned rocks, those found in western America 

 include, under I, granite and urranit ••-]>< .:;.|; \r_\-. felsitc-porphvrv, 

 syenite; under LI, dioryte, hombkoide-pnrpiiy'ry. pmpylyn-. .jiiarf'z- 



Cpylyte, hornblende-anclesyte, dacyte, trachyte, rhyulytc, dia- 

 e, melaphyre, gabbro, augite-andesyte, basalt ; under IV, leu- 



The volume is chiefly devoted to the description of these rocks 

 from different localities, after a study of microscopic sections, and 

 comparisons with similar rocks of other countries ; and mum-mus 

 very singular and interesting facts are brought out, besides impor- 

 tations of the relations and mode of origin of the rocks. 

 W e add some notes respecting them, following the order in this list. 



Propylyte is the most prominent rock of the Washoe district, 

 constituting the entire Virginia range. It is a grayish- 

 green rock, consisting mostly of a ic feldspar, 



m small crystals or grains, and hornblende, the latter disseminated 

 in minute points or crystals through the former, and often in part 

 changed to chlorite or epidote. Apatite is sometimes present, and 

 occasionally biotite. I a 



from dioryte, the silica, according to the analyses given, amounting 

 to 64 to 66 per cent. It is of Tertiarv age, and hence it is not 

 called dioryte ; but, in ad rally more of the aspect 



of a modern igneous rock. A quart zifef. us variety is the quartz- 

 propylyte. 



Andesyte has, according to Zirkel, the constitution essentially of 



Fopylyte, that a of a plagioclase feldspar and 



Hornblende; and the physical differences drawn out on page 133— 

 such as a purer gray color, the hornblende in coarser crystalliza- 

 tions, etc. - are feeble in kind and decree. The analyses, however, 

 g!ve it about 60 or 61 per c - ™uld make the 



teldspar of the rock to contain four to five per cent less of silica. 

 Andesyte, moreover, has sometimes a pasty or semi-glassy ground- 

 mass. It occurs with the propylyte at various localities. 



JJacyte is a quartz-andeoyte, and this variety also occurs at 

 VVashoe and elsewhere. The color varies from firirt gray to 

 dark blackish -brown. The ground -mass, is often rbyohtic and 

 sometimes ephera ■>*' andesyte and 



Propylyte. The analyses show that th< Ispan ontains relatively 

 "ttle hme, and therefore must he, in the main, andesyte or ohgo- 

 clase. ^ The quart ... . ' . *hows no fluid- 



^chisions when microscopically examined. > 



trachyte is described as occurring in the vicinity ot Washoe, 

 a nd between there and Pyramid Lake. The rock consists of san- 

 «Jw ot glassy ortl " — the older — contains a 



Plagioclase feldspar also, and thus graduates toward andesyte. 

 ^"dymitewas observ. I n th i-oun- i n I . te in thm 6-sided 

 P^tes grouped together in <*reat numbers. A " hall'-glassy-lookmg 

 r?°k'' f rom the ° Cou UiiT^. hetweei Sheep Corral Canon and 

 2 adsworth, of dark brownish-black color, containing samdin and 

 a| so pale green augite with gome pi a gi clase feldspar and horn- 

 AM - Jou «- Scl-Thikd Sbbies, Vol. XIII, No. 76.-Afril, 1877. 



