GEOLOGY. 51 
is the Kern River district, including White River between 
35° and 36° on the western slope of the Sierra Nevada. There 
are gold diggings on the San Gabriel and Santa Anita Rivers, 
and in the San Francisquito cafion in Los Angeles county. In 
the Colorado valley, fifty miles above Fort Yuma, gold has 
been found. Nearly every one of the coast counties has more 
or less gold: it has been found in the valleys of Russian River, 
Putah Creek, Soquel Creek, Coyote Creek, the Salinas River, 
and in the earth in which the city of San Francisco is built. 
§ 37. Auriferous Lodes.—Gold is found fastened in stony 
veins, and loose in earthy matter: the latter called placer dig- 
gings, the former auriferous quartz lodes. 
It is the accepted theory among geologists that all gold was 
once enclosed in quartz lodes, and that the gold in the placer’ 
was obtained from the disintegration or breaking up of the 
lodes. The surface of the earth was once all rock4 the earthy 
matter was formed by the action of air and water on this 
rock. The earthy matter was then deposited in diluvium, 
among which was the gold that had existed in the rock pre- 
vious to its disintegration. 
Gold is sometimes found in granite, syenite, limestone, slate, 
and other rocks; but the auriferous lodes, regularly worked, 
are all of quartz. Most of the quartz veins run parallel with 
the main-divide of the Sierra—that is, north-northwest and 
south-southeast—are from a line to thirty feet thick, and are 
nearly perpendicular, dipping to the eastward. They are be- 
tween two thousand and six thousand feet above the sea. The 
general color of the rock is white, occasionally bluish, fre- 
quently reddish-brown, the color of iron-rust, derived from the 
decomposition of iron pyrites. In some veins the rock is com- 
pact, and then it is usually very white; in others it is full of 
cracks and crevices, and ready to break into small pieces with 
alittle pounding. Most of the veins hive gold in them; only 
afew have enough to pay for working. The gold is in par- 
ticles, of irregular shape, but with some regularity of size, scat- 
tered through the rock. The particles are seldom larger than 
