have
been carried to a distance by water and deposited as breccia or
conglomerate of volcanic ashes or lapilli. These layers stratified,
often in alternation with gravel or clay, generally cover the gravel
deposits.
Gravel Deposits.—The
gravel deposits occur in every variety of texture, from very fine pipe
clay, through sands and gravels, to rolled pebbles and boulders
sometimes weighing tons. It is now generally accepted that they have
been laid down by the action of a system of tertiary rivers, which had
the same general course (nearly) as the present streams on the west
slope of the Sierra, but whose channels were wider and slopes greater.
The waters of these rivers, eroding the auriferous slates with the
included quartz veins, concentrated the precious metals in deposits
often three hundred and fifty to four hundred feet wide at the bottom
and sometimes several thousand feet wide on top. Their depth now
varies from a few inches to six or seven hundred feet. Volcanic
eruptions have in places covered these deposits with lava and tufa
hundreds of feet deep. Denudation and erosion ensued and the products
of volcanic activity have sometimes been covered in turn with
gold-bearing detritus. Quantities of fossil wood and numerous remains
of land and water animals have been found in the deposits and are being
constantly unearthed as the mines are being worked.*
The deep canons of the rivers of the extreme northern counties, especially the Klamath and its branches, contain
* In reference to the occurrence of gold the following note, taken from the Engineering and Mining Journal, February
10, 1877, relative to the discovery of pay gold in the New South Wales
coal measures, will be found interesting. Mr. C. S. Wilkinson, F.R.S.,
writes from the Geological Survey Office, Geelong, under date of
November' 25, to the Mining Department, as follows:
u
During my examination of the Tallawang Gold Field Reserve I observed
the important fact that the gold found in tertiary alluvial deposits at
the old Tallawang and Clough's Gully diggings has been chiefly derived
from conglomerates in the coal measures. These conglomerates are
associated with beds of sandstone and shales containing the fossil
plant of our coal measures, the glossopteris. . . . This is the
first time that gold has been noticed to occur in payable quantity in
the coal measures in the colony, and it is not unworthy of remark that we here possess one of the most ancient alluvial deposits in the world."
