been,
at that remote period, very considerable, to judge from the various
points, many miles apart, where they have been subjected to mining
operations on almost a gigantic scale. And it may also be observed that
in but two instances the working of deep leads beneath the basaltic or
trappean coverings had been taken in hand, although "bald hills,"
capped with porous and dense basalt, and underlaid with Tertiary drifts
of as pronounced a type as at the Loddon, Ballarat, Charlotte Plains,
Creswick, &c, were frequently passed over during my peregrinations.
The ancient rivers of California somewhat resemble our deep leads, with
this difference, that, in most cases, the modern water-courses have cut
their way into the bed-rock below the older river beds, and
which latter are filled with the detritus of rocks evidently brought
along by either fluvial or glacial action. In this manner these
valuable deposits assume frequently, through the intersection of the
present drainage system of the country, the aspect of our made hills,
whereas, in reality, they are but the severed parts of a network of
ancient water channels now altogether obliterated and filled with
Pliocene gravels or drifts. In many cases the present rivers run more
than 100 feet below the old beds, thereby facilitating to a
considerable extent the economic working of these auriferous gravels.
These ancient drifts are generally of two kinds, viz., that which rests
immediately on the bed-rock presents that dark-blue color so frequently
found in our own districts, and which is mainly due to the presence of
iron pyrites ; immediately above this older gravel a seam of tough
pipeclay occurs, of a whitish color, which is in turn overlaid by a
stratum of loose reddish-white colored gravel and sand, not nearly so
coarse or containing such immense boulders as in the " blue gravel"
below. As stated before, cappings of more recent flows of lava and
volcanic muds occur, but they are not much taken notice of, on account
of the difficulties experienced in their removal by the miners, who so
systematically wash the whole of these deposits upwards of 380 feet in
height by means of powerful jets of water from nozzles and pipes. As
regards the extent of one particular channel, or ancient river, I may
state that the " lead " in question has been traced from beyond Forrest
City, Sierra County, through North Bloomfield, San Juan, Nevada City,
down to the Sacramento River, a distance of nearly 60 miles in a direct line.
Considerable interest attaches to the number of fossilized trees in
these gravels, of which some have become beautifully opalized in
texture and appearance, preserving their origin as oak, manzanite, and
cedar by means of the year rings, knots, and fibrous grain. The lower
or blue gravels contain large blocks of rock of the older volcanic
formations, very little water-worn, besides large fragments of bones
belonging to the mammalia group; the gravels above the pipeclay are
composed exclusively of completely rounded quartz boulders and gravels.
The blue gravel is richest in gold in most of these ancient rivers, but
at the Table Mountains, near Sonora, very rich deposits of fine gold
were worked in a deep-Ted colored kind of sandy clay, which is
difficult to wash, on account of its great cohesiveness, and which
resembles the red clays found in the tributaries of deep leads near
Taradale, Daylesford, Creswick, and Clunes. There remains but to be
mentioned that implements, evidently shaped by human hands, were found
in these gravels at Buckeye Hill, Sweetland, some 60 feet
beneath the surface, and that I found that the deep lead at Forrest
City measured from the surface to the bottom of the gutter not less
than 1,100 feet in depth, and, owing to the present water channels
draining the country, quite dry.
