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. 2 a ee