464 
SILUKIA. 
[Chap. XIX. 
The public of Australia have also, through the Reports of the Mining Commis- 
sioners of Victoria, Professor M'Coy, Mr. Selwyn, and other gentlemen *, been 
made acquainted with the manner in which gold chiefly occurs in the original 
quartz-veins of the Lower Silurian rocks, whether they be in the proximity of 
granite or diffused in the gravel derived from such rocks. 
While these Reports extended very largely the areas over which it is reason- 
ably inferred that the golden detritus will be found to extend, whether in de- 
pressions or on the slopes of the old slaty Silurian rocks (an extent which can 
only be precisely measured off when adequate geographical maps shall have been 
prepared), the Commissioners pointed out the reckless and ignorant manner in 
which many speculators were sinking shafts in proximity to each other in the so- 
called ' quartz-reefs,' and often missing the vein, — whilst one successful shaft 
sunk in the right direction, with an adit, would serve the purposes of several 
proprietors. 
They also showed that the evidence given before a select committee of the 
House of Legislature had been sustained, to the effect that " auriferous drifts 
must from their very nature be quickly worked out in any one spot." The Com- 
missioners added that they had taken great pains to investigate these points on 
the gold-fields, and the result had been the most complete confirmation of the 
evidence alluded to. Some of the old alluvial gold-fields, in full prosperity 
when that evidence was given, were comparatively deserted when the last edi- 
tion of this work appeared; and there can no longer be any difference of opinion 
respecting that class of drifted gold-deposits. 
With regard to the evidence touching the yield of gold from deep mining into 
the ' quartz -reefs,' concerning which there was the greatest scepticism, the same 
result seemed at first to follow the local inquiries of these Commissioners, who, 
in a Report signed by their Chairman, said that experience in every country 
had proved that the yield of gold decreases with the depth where mining in 
the solid rock had been attempted. An enumeration by name was indeed made 
of several working shafts which had been abandoned in consequence of finding 
the gold diminish downwards, — in some cases at a few feet only, in others 
ceasing entirely, and, again, in a third class continuing downwards in small 
quantities to about 300 feet. It was then concluded that enough had been stated 
to vindicate the scientific inference that deep mining in the solid quartz-rock is 
for the most part unprofitable, — a conclusion which was in unison with my 
opinion founded on knowledge derived from other gold-countries, as published 
many years before gold was worked in Victoria : this opinion was again ex- 
pressed in the first edition of ' Siluria ' f. - 
The knowledge, however, which I subsequently obtained, induced me to modify- 
that view, and particularly as respects the Colony of Victoria. In 1858 I 
was made acquainted with the opinion of Sir H. Barkly, then the Governor 
of the Colony, as based upon extensive inquiries and personal observation, 
which went to show that a much greater supply was then derived from mining 
in the ( quartz-reefs ' than I had supposed to be the case. Again, copies of 
other Despatches from Sir H. Barkly, with Reports from Mr. Selwyn, accom- 
panied by coloured geological maps and sections prepared by that able geologist, 
whose observations extend over many years, have led me to think that, if the 
* See Keport to the Surveyor-General and the 
Chief Secretary on the Mining Kesources of the 
Colony of Victoria, 1856-7, &c. 
t It has recently been found profltable to ex- 
tract gold at some spots from the veinstones at 
greater depths ; but the gold is more finely and 
sparsely disseminated than in higher parts of the 
same veinstones. It is believed that much gold 
in old detrital accumulations will yet be found 
under the basaltic coverings of certain tracts, both 
in Australia and California.— January 1867. 
