382 Transactions. —Chemistry. 
may contain. Consequently the deposition of gold from solution being as we 
know unaffected, or but slightly so (comparatively), by the condition of the 
solvent, the great purity of gold deposited from these surface waters is 
explained. ; 
The above explanation of the greater purity of our alluvial or drift gold 
over gold found in the reef is, I think, much more plausible than that 
which attributes this difference to the interaction of solutions of gold upon 
the auriferous masses transported from the reef, whereby the silver of 
these masses is replaced by gold and so removed, leaving the mass corres- 
pondingly richer in gold. That this process can be continued until our 
largest auriferous masses can be thus affected throughout appears to me 
impossible when we consider the imperviousness of such metallic masses to 
liquids, and how nearly the atomic volumes of gold and silver approximate. 
That a superficial change, however, in this direction may occur is by no means 
improbable, but sucb would escape detection unless it were especially sought 
for. Thus the hypothesis advanced by Mr. Selwyn as to the manner in which 
the nuggets of our drifts may have been formed receives support upon all 
those points which appear of any importance. 
That nuggets of some size may, however, be in a few instances transported 
bodily from these matrices into the drifts or water-courses is by no means 
improbable, but in this case they would, I think, partake of the usual quality 
of the reef gold of the country about, and so would be inferior in this respect 
to gold formed in the manner above described. 
Whatever may be the origin, however, of any particular nugget, or of 
nuggets generally, when we consider the auriferous nature of many mine 
waters, also that of sea-water, together with the decomposing and aggregating 
action of metallic sulphurets upon the gold of these waters, we cannot avoid 
the conclusion that gold is now being deposited and aggregated in many of 
our drifts, and that such depositions have been going on from remotest times. 
In conclusion, the questions as to the source of the gold of our nuggets, 
the nature of the agencies by which it is dissolved, and the precise chemical 
state in which it exists in our auriferous waters, are subjects which it is not 
incumbent upon me to discuss here. I will, however, take leave to make a 
few observations upon them now. 
As regards their source I think this is rather in gold as disseminated in 
certain of our slate, sandstone, or schist rocks, than in that of our reefs, 
In reference to the nature of the solvent I have shown* that sulphuretted 
hydrogen attacks gold at ordinary temperatures, forming a sulphide of the 
metal, and we know that all the sulphides of this metal we have to this time 
formed are soluble in alkaline sulphides ; therefore, as both these agents are 
* Trans. N.Z. Inst., Vol. HE, Ark Yr 
