GRANULAR IGNEOUS ROCKS 



251 



even texture with only small porphyritic crystals in the largest area, 

 which forms the crest of the western part of the Palmetto mountains 

 and of the southern part of the Silver Peak range, but in the smaller 

 area, east of Fish Lake valley, on the western flanks of the Silver Peak 

 range, there are developed porphyritic orthoclase crystals often an inch 

 or more in length. The area 5 miles northwest of Piper peak is also of 

 this character. 



The second type of quartz-monzonite is a medium, even-grained rock 

 forming at some points considerable masses, the largest one noted being 

 on the north side of the Palmetto mountains. It is probably later in age 

 than the coarse type. The two types of quartz-monzonite just noted as 

 occurring in the Silver Peak range form the foothills of the Inyo range, 

 in the extreme southwest corner of the quadrangle, the coarse type here 

 having large porphyritic crystals of orthoclase. The medium grained 

 quartz-monzonite is present here in smaller amount and is distinctly later 

 in age, as it contains blocks of the coarse porphyritic variety. 



In the table of analyses the chemical composition of some of these 

 rocks is indicated. It will be noted that numbers 348, 349, and 653 are 

 true granites, but these appear to be merely facies of the quartz-mon- 

 zonite magna. 



Partial Analyses of Quartz-monzonite and Granite from the southern Part of 



Silver Peak Range 



George Steiger, Analyst 



Silica. 

 Lime. 

 Soda. . 

 Potash 



Quartz- 

 monzonite, 

 number 

 324. 



69.23 

 3.38 

 3.75 

 4.75 



Granite, 



Granite, 



Granite, 



number 



number 



number 



664. 



653. 



348. 



71.14 



68.50 



73.22 



2.56 



.60 



1.52 



3.65 



4.05 



2.79 



3.37 



4.83 



5.35 



Soda- 

 granite, 

 number 

 349. 



76.04 

 .46 



7.58 

 .07 



Description of the Rocks Analyzed 



Quartz-monzonite, specimen number 324. — Locality: In the Palmetto moun- 

 tains, 10.2 kilometers southwest of Barrel spring. 



Macroscopically, a light gray coarse grained granitic rock, apparently chiefly 

 feldspar. Microscopically, a coarse grained monzonite in which the orthoclase 

 exceeds the plagioclase in amount. Feldspar, quartz, pyroxene, and accessories. 



Granite, specimen number 664. — Locality: On the east side of Fish Lake 

 valley, 20.7 kilometers southwest of Piper peak. 



Macroscopically, a fine grained light gray granite. Microscopically, an 

 evenly granular rock composed of microcline and micropegmatite, plagioclase, 

 quartz, biotite, epidote, and titanite. 



