(b) sedimentary volcanic layers ; or
(c) lava; or finally, in some places,
(d) marine formations.
Granite.—The
granite occurs in the extreme northwestern part of the State,
disappearing in the northeastern under the extensive lava beds,
reappearing in Butte and Plumas counties, and continuing to increase in
amount of exposure toward the south, until in Fresno and Tulare
counties it forms territorially by far the greater part of the belt,
extending from the crest almost down to the plain.
Auriferous Slate Formation.—The
auriferous slate formation, consisting chiefly of metamorphic,
crystalline, argillaceous, chloritic and talcose slates, appears with,
but subordinate to, the granite in the northwest. It appears again in
Plumas and Butte counties, increasing in importance as the overlying
lava decreases. North of the American River it occupies nearly the
whole width of the western slope of the Sierra, with occasional areas
of granite enclosed in it. Going south, it gradually contracts in
width, being of but little importance south of Mariposa County. In the
extreme south, at the junction of the Sierra and the Coast Ranges, it
reappears and continues in San Bernardino and San Diego counties in
connection with the granite.
The
strata of this formation are elevated very considerably, often in a
nearly vertical position. Speaking in very general terms, it may be
said that the strike of the slates is usually parallel with the axis of
the range and the dip in the southern portion of the belt is generally
to the east.
Gold Quartz Veins.—
In this formation occur almost exclusively the veins of quartz which
carry gold in amounts which pay for working. While such veins occur
also in the granite, and likewise, as has been mentioned, in some of
the Coast Range formations, the paying gold quartz is rarely found
outside of the auriferous slate formation. Some of these veins are of
very great size,
