472 
SILUKIA. 
[Chap. XIX. 
in its unaltered original matrix, it seems to follow that certain rocks of igneous 
origin must have been the gold-producers, by impregnating with the metal the 
contiguous sedimentary matter which they metamorphosed. I further believe 
that, even in tracts which are largely auriferous, and in which the granites and 
igneous rocks have only here and there risen to the surface (as in Victoria and 
the Ural Mountains), the auriferous quartz-veins are the results of the same 
igneous action. 
Conclusions. — The facts and arguments insisted upon in the preceding 
pages lead to these conclusions : — 
1. That, looking to the world at large, the auriferous veinstones in the 
Lower Silurian rocks contain the greatest quantity of gold. 
2. That where certain igneous eruptions penetrated the Secondary de- 
posits, the latter have been rendered auriferous for a limited distance only 
beyond the junction of the two rocks. 
3. That the general axiom before insisted upon remains, that all Secon- 
dary and Tertiary deposits (except the auriferous detritus in the latter) not 
so specially affected never contain gold. 
4. That as no unaltered purely aqueous sediment ever contains gold, the 
argument in favour of the igneous origin of that metal is prodigiously 
strengthened ; or, in other words, that the granites and diorites have been 
the chief gold-producers, and that the auriferous quartz-bands in the 
Palaeozoic rocks are also the result of heat and chemical agency. 
In reviewing the facts already elicited respecting the origin and age of 
the various metals most useful to man, I am led to believe that iron is the 
oldest as well as by far the most diffused in nature. In fact, it occurs 
plentifully in the most ancient of all known aqueous deposits, the Lau- 
rentian rocks, and has continued to be abundant throughout all the strata 
up to the formation of the bog-ore of the present day. Copper was, 
I think, the next in age, since, unlike the diffused iron, it is found in 
veinstones which have traversed the ferruginous Palaeozoic rocks long after 
their consolidation. Lastly, judging from the evidences presented to us 
over such an enormous area as that which is occupied by the Permian 
deposits in the western or European flank of the Ural Mountains (p. 458), 
and knowing that they contain much copper-ore mixed up with the debris 
of the Palaeozoic and igneous rocks of that chain (but without a trace of 
gold or silver in them), I conclude that those noble metals could not have 
been then evolved in that chain. 
Now, if in disparagement of this view it should be alleged that these 
and other metals were occasionally met with in the same veinstone, and 
that therefore they may have been formed simultaneously, I reply that 
such collocation may be easily explained. Assuming that these ores have 
been connected with igneous agency acting from beneath, it necessarily 
follows that in their emission the last-formed ores of gold and silver would 
occasionally intermix in their passage with the ores of iron and copper 
