552 W.L. UGLOW AND W. A. JOHNSTON.

the leaching of the silver content, for it is evident that the nuggets
have been but little leached. There is no evidence that the placer
gold is, as a rule, of greater fineness than the vein gold.

ACCRETION OF GOLD IN THE GRAVELS.
The view held by some writers, that nuggets are formed by the

rolling together or welding of gold particles by the action of the
stream gravels and the comparison which is made with the easy
welding of gold in dentistry do not appear applicable, for, in
order to secure good welding, it is necessary to use pure gold
free from surface film. Placer gold is never pure and the parti-
cles usually have a surface film which would prevent welding.
Moreover, the structure of the nuggets shows that they are not
formed by the welding together of particles, but rather, by de-
position from solution.

The formation of part of the placer gold by deposition from
gold solutions in the gravels is possibly suggested by the occur-
rence of crystals and crystal groups, which are apparently too
well formed to have been transported by the streams, by sub-
angular and rounded pieces of quartz with thin platings or films
of gold encasing them, and by the occurrence, in one of the hy-
draulic pits, of a rusty iron nail, to the side of which was firmly
attached a small rounded piece of gold. In the latter case it is
not certain that the gold was deposited from solution. What
probably happened was that the piece of free gold was pressed or
hammered against a roughened surface of oxidized iron, by the
action of the stream gravels. On the other hand, the gold crystals
are usually somewhat worn, and, as has been pointed out above, it
is possible that gold crystals may have been derived from the
oxidized parts of the quartz veins and included in the gravels with-
out having been much worn. Fractured quartz cemented by gold
may have been the source of the gold-plated pieces of quartz.
The large accumulations of placer gold in places where the bed-
rock is favorable for retaining gold and around boulders, as
pointed out by Atkin,° shows that the concentrations were the

8 Tbid., page 516.

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