232 H. W. TUKNEB GEOLOGY OF THE SILVER PEAK QUADRANGLE 



parallel streaks. Such of the grains as have not been granulated are 

 fractured and rounded and the quartzes usually show undulous extinc- 

 tion. Lines of mica foils, chiefly finely divided muscovite, contribute 

 greatly to the formation of the schistose structure. "While the two types 

 of schists here described are very different in chemical composition — the 

 granite-augen-schist having the composition of granite or of arkose, and 

 the lime-rich extreme of the calcareous augen-schists the composition of 

 an impure limestone — at numerous points schists representing transitions 

 from one to the other may be found. Such a series, all taken from one 

 bluff about 1 mile southeast of Xorth spring, shows transitions from a 

 typical granite-augen-schist composed of lines of minute grains of quartz 

 and feldspar and of minute muscovite foils in which are imbedded large 

 grains of feldspar and quartz and muscovite foils with little or no car- 

 oate to a granite-augen-schist similar to that just described, but with 

 lines of carbonate granules in addition. The calcareous augen-schists 

 may represent thin bedded limestone and lime shales thoroughly injected 

 and infiltrated with granitic material. 



Analyse* of calcareous Augen-Schists and of Granite-Augcn-schists 



ge (Steiger, Analyst 





Number 



7^7 



Number 



Number 



744. 



Number 



, 33. 



Number 



734. 



KiO 



22.45 

 34.46 



.54 



1.87 



23.13 



30.31 



29.35 



.86 



2.15 



21.51 



62.59 

 5.00 



3.70 

 2.07 



3.20 



71.48 

 1.50 



3.35 

 3. vi 

 1.03 



73.46 



( "al > 



■ - 



Na,0 



K,0 



CO . 



4.26 

 2.80 



.23 







Numbers 787 and 730 are of the type designated calcareous augen-schists. 

 and numbers 744. 733. and 734 are typical granite-augen-schists. 



THE WHITE GRANITE 



The white granite ( alaskite of Spurr ) was nowhere observed certainly 

 intrusive in fossiliferous Cambrian or later sediments. It is usually a 

 coarse grained rock, composed of orthoclase or potash-feldspar, with 

 some albite or soda-feldspar and frequently some muscovite. but it is 

 often nearly destitute of black mica. By the loss of quartz it grades over 

 into syenite. There is sometimes plagioclase present. The following 

 partial analyses of white granite (alaskite) by George Steiger indicate 

 the chemical composition: 



