ROCKS OF THE PRE-CAMBRIAN COMPLEX 233 



Analyses of the White Granite (Alaskite) 





Number 

 467. 



Number 

 259. 



Number 

 210. 





70.80 

 2.71 7 

 3.95 



3.83 



72.72 



.51 



1.65 



6.93 



73.59 





.49 



Soda 



3.62 





4.13 







Granite number 467 is from 6.3 kilometers west of north from Red mountain. 

 Collected at the edge of an included mass of marble. Dikes of this rock are 

 in the dolomitic marble. Macroscopically, a coarse grained nearly white rock, 

 apparently composed chiefly of feldspar. Microscopically, an even grained 

 rock composed of feldspar, quartz, and muscovite. The feldspar is microcline 

 and plagioclase. There are present minute zircons. Carbonate of lime is 

 rather abundant in cracks and between the grains of the primary constituents, 

 which are fresh. The rock shows evidence of crushing. The quartz is in inter- 

 locking, in part elongated, grains showing undulous extinction. 



Granite number 259 is from the lower tunnel of the Mary mine. Macroscop- 

 ically, it is a light gray granite showing white feldspar, quartz, and biotite. 

 Microscopically, it is composed of microcline and orthaclase, quartz, oligoclase, 

 biotite, muscovite, zircon, and apatite. There is a little carbonate and chlorite 

 present. The rock shows no evidence of crushing or shearing. 



Granite-gneiss number 210 is from a dike in quartz-schist 1.5 kilometers 

 northwest of the Silver Peak benchmark. This quartz-schist underlies the 

 lower Cambrian. Macroscopically, it is a white gneissic granite containing 

 muscovite. It is evidently a sheared form of white granite. Microscopically, 

 it is composed of orthoclase, albite, quartz, plagioclase, and muscovite. One 

 minute garnet was noted. The rock has been strongly sheared, the feldspars 

 and quartzes being fractured and granulated. It is now a granite-gneiss. 



Some of the pegmatite dikes seem to be genetically related to the white 

 granite, and these dikes are very clearly later than the gneisses, for they 

 cut across the gneissic banding. 



The high cliff which forms the west wall of the deep north-south 

 canyon that lies about iy 2 miles northwest of the New York canyon is 

 formed from top to bottom of alternating lenses of the white granite and 

 augen-schist. These lenses or layers lie nearly horizontally. If we sup- 

 pose the lenses of white granite to be intrusive sheets in the augen-schists, 

 their lens-character and their lack of continuity may be regarded as due 

 to pressure exerted after the intrusion. 



The gneissic and schistose structures of the pre-Cambrian gneisses and 

 schists above described are usually roughly parallel with the bedding of 



7 The high content of lime in this specimen is plainly due to carhonate of lime Infil- 

 trated into cracks, as shown by the microscope. The rock is fresh and a true granite. 



