320 Gold in California. [July, 
The present average cost of treating gold quartz in California is 
estimated to be about as follows— 
acid 
In Water Mills, water free, per ton of 2,000 lbs. .. .. 4 10 
Be » water purchased te” os, ee ae Oe 
» steam ,, 5 befae| 
Although a very large amount of the gold annually collected in 
California was doubtless originally derived from the disintegration 
of auriferous veins, not more than one-third of the precious metal 
now annually brought into the market is procured from that source. 
The other two-thirds is derived from alluvial diggings, in which it 
is separated by washing from the clay, sand, and gravel with which 
it is associated. 
These gold-bearing drifts belong to at least two distinct geo- 
logical epochs, both comparatively modern, although the later period 
is distinctly separated from the former; its materials being chiefly 
derived from the recent disintegration and re-distribution of the 
materials of the older. 
The more ancient deposits are in all probability referable to a 
river-system different from that which now exists, flowing at a higher 
level, or over a less elevated continent and not unfrequently nearly 
at right angles to the main valleys of the present period. In many 
localities the older deposits, or “deep placers,” are covered by a thick 
capping of lava, and in some places this eruptive matter occurs in 
the form of basaltic columns, beneath which are found the layers of 
sand, gravel, and boulders with which gold is associated. 
In many localities, and particularly between the middle and south 
forks of the Yuba river, these auriferous gravels have, where exposed 
to denudation, a thickness of 120 feet; and of more than 250 feet 
where they have been protected by a volcanic capping. ‘These vast 
auriterous beds are composed of rounded masses of all the crystalline 
and metamorphic rocks which occur above them in the Sierra. As 
a general rule, the lower portions are composed of larger boulders 
than the upper, although large rounded water-worn masses of rock 
occasionally make their appearance among the middle and upper 
members of the series; water-worn gold is more or less disseminated 
throughout the whole mass of these deposits, although not with equal 
uniformity, but always in greater abundance in the immediate vicinity 
of the “bed-rock.” The materials of which these deep deposits are 
composed are frequently consolidated into a sort of hard concrete, 
by being firmly bound together by crystalline iron pyrites, and some- 
times this cementing material partially consists of carbonate of lime 
and amorphous silica. The wood which occurs in these deep gravel 
beds is either beautifully silicified or is replaced by iron pyrites. 
In such localities a piece of wood will frequently be met with, of 
which one end had been converted into lignite, whilst the other re- 
mained unaltered, but the whole having subsequently become silici- 
