66 TOPOGRAPHY AND GEOLOGY
notably
the "great quartz vein," which has been traced from near the centre of
Amador County through Calaveras and Tuolumne into Mariposa to the
Mariposa Estate, a distance of eighty miles. The vein attains a width,
in places, of several hundred feet.
Carboniferous Limestones.—There
are certain limestones in Shasta and Butte counties which are
carboniferous, the oldest formation known in the State, and which are
possibly the same as those found here and there throughout the
gold-mining region.
Marine Sedimentary Deposits.—
The marine sedimentary deposits of cretaceous and tertian- age occur
in the foothills all along the eastern margin of the Great Valley,
lying unconformably on the upturned edges of the auriferous slates.
Their greatest development is in Kern County, between Kern and White
rivers. The rock is lor the most part a soft sandstone, made up chiefly
of granite debris.
Lava.—The
chief lava country is in Plumas and Butte and the region north of these
counties, and east of Trinity and Klamath rivers. Here is a series of
volcanic cones, of which Lassen's Peak and Mount Shasta are the most
prominent, from which flowed, in the later tertiary or still more
recent times, the streams of lava which now cover many thousands of
square miles of northern California and southern Oregon. The limitation
of the auriferous belt at the north, in Plumas and Butte counties, is
due not to the thinning out of the gold-bearing formation, but to its
being covered by this volcanic mass.
Along
the crest of the Sierra, to the south, are numerous volcanic vents and
here and there are areas of lava, but these are comparatively small.*
Sedimentary Volcanic Layer's.—Very
frequent, and associated with the gravel deposits, are the sedimentary
volcanic layers, consisting of fragments of lava which
* As to the Tuolumne Table Mountain sec J. Ross Browne, "Mineral Resources of the U. S.,n 1867, page 25.
