94 



University of California Publications. 



[Geology 



lineated by lines of dark-colored minerals. The whole was evi- 

 dently in a state of great movement and circulation just previous 

 to the time of solidification. Titanite and magnetite are the 

 important accessory constituents, both in an unusually large 

 amount. Titanite is commonest near the metamorphic contacts, 

 where the yellow crystals invariably attract the eye. Magnetite 

 is usually found in the hornblende crystals, and averages prob- 

 ably nearly 2% of the whole. Quite a few tons of magnetite 

 sand can be found on the eastern beaches of Lake Tahoe near 

 Glenbrook. Aplitic and pegmatitic dikes of prevailing pink tint 

 are very common throughout the granitic mass. 



In some small areas these dikes are so common that the sur- 

 face is composed almost entirely of their fragments. Tourmaline 

 is common in the pegmatite veins. Quartzose phases of the peg- 

 matites are likewise frequently found, small fragments of which 

 look, upon casual inspection, like ordinary vein quartz. The 

 granodiorite contains a large volume of basic inclusions, a further 

 reference to which will be made. 



Schists. — Petrographieally the schists cover a wide range. 

 Lindgren 4 describes those of the Truckee quadrangle as "sedi- 

 mentary rocks metamorphosed to hornfels, quartzites, and knotty 

 schists." This character applies well to certain portions of the 

 Carson area, best near Lakeview, east and west. But beside the 

 altered sediment there is a great development of metamorphosed 

 volcanic rocks, including flows and tuffs. These are best exposed 

 in the large area west of Carson, and are chiefly andesitic in 

 character. Those areas immediately north and south of Carson 

 are likewise metamorphic andesite, but in the spur from the Vir- 

 ginia Range south of Washoe Lake the sedimentary character 

 again is in evidence. On Prison Hill a large amount of meta- 

 morphic agglomerate shows near the contact with granite, here 

 a fault line. On Mt. Tallac, metamorphic andesites are again in 

 large amount. Peavine Mountain, near Reno, is noteworthy in 

 showing a large amount of altered acid volcanics. In all areas 

 the old sedimentaries are characterized by a well-developed 

 schistosity ; the volcanics by little or, at times, none. The schists 

 are usually hornblendic, from dark blue-gray to black in color, 



* W. Lindgren, Truckee Folio, United States Geological Survey Text. 



