GRANITE. 141 



The arcose character of tlie sandstones of the Coast Ranges has been 

 described. In the Sierra Nevada granite is abundant, even in the foot-hills. 

 The higher Sierra, where not masked by lavas, consists chiefly of this rock. 

 From the main Sierra range the granite extends to Steamboat Springs and 

 Washoe Lake. Here it disappears under the eruptive rocks of the Virginia 

 Range, but reappears on the eastern side of this range near the southern 

 end of the Comstock lode. 



The lithological character of the granites examined, from the Washoe 

 district to the Farallone Islands, does not greatly vary, the chief difference 

 being in the proportion of hornblende present. Some of the granite from 

 the neighborhood of the Comstock carries little or no hornblende, while at 

 Washoe Lake hornblende is particularly abundant. A moderate amount 

 of hornblende occurs in the granite of Steamboat Springs and on the west- 

 erly slope of the main Sierra. The Rocklin granite, from the western base 

 of the range, is also hornblendic. In the central Coast Ranges hornblende 

 is not abundant in the granite, only a portion of the specimens showing 

 this mineral and none a very large amount. 



At the Comstock and at Steamboat Springs, as well as on the eastern 

 slope of the Sierra, the granite immediately underlies strata at least as old 

 as the Mesozoic. In the Coast Ranges, also, Neoeomian beds rest upon it. 

 No distinctly intrusive granite of Mesozoic or Tertiary age has been rec- 

 ognized in the present investigation. That such exists, as asserted by Pro- 

 fessor Whitney, I by no means deny; but there is at least some ground 

 for supposing that the main part of the rock is Arcluean. 



Granite of Steamboat Springs. — Tlils is a ratlicr coarso-graincd, gray rock, the 

 grains averaging 1.5'"™ to 2™'" in diameter. Plainly visible are quartz, feld- 

 spar (in part triclinic), dark-green hornblende, and black mica. Under the 

 microscope are seen quartz, oligoclase, orthoclasc, dark-brown, uniaxial 

 biotite, dirty-green hornblende, and accessory minerals. These last are 

 apatite, titanite, zircon, mag-netite, chlorite, epidote, and ferric oxide. The 

 quartzes are in large part composite grains and of course contain fluid in 

 elusions. The feldspars show m many cases undulous extinction and very 

 often also zonal structure The crystals of primary consolidation are bet- 

 ter distinguished from those of secondary consolidation than is usual in 



