466 
SILURIA. 
[Chap. XIX. 
cient conglomerate, they have been swept from the hill-tops into adjacent 
valleys by former great rushes of water. In a country like Australia, which, in 
the later Pliocene period, it is believed, must have been covered by broad sheets 
of water, and at the same time replete with evidences of intense volcanic action 
posterior to the formation of gold, we can well imagine that such evolutions 
may well have been accompanied by rushes of water having great translating- 
power. 
The opinions of such a geologist as Mr. Selwyn, with extensive experience in 
Britain and Australia *, on the gold- veins and detritus of regions which he has 
sedulously explored during many years, have had great weight with me, and in- 
duced me to modify in the second edition an opinion expressed in the first edi- 
tion of this work. But, whilst gold-mining downwards to comparatively small 
depths in the solid veinstones of Victoria may for some years be a profitable 
business, it by no means follows that adequate profit is there to be maintained 
at very great depths. The continuous working of deep mines (the law of the 
downward impoverishment of the metal being admitted) must depend upon 
the cost of extraction. Thus, in Transylvania and Hungary, where the gold 
was formerly visible near the surface, the lower portions of the same veinstones 
now worked afford a very minute quantity only of gold, which (acording to 
Warington Smyth) would not be worth extraction but for the agency of power- 
ful crushing-mills and the very low wages of the miners. 
After showing that the vast areas of granite which in Victoria have been pro- 
truded through those old stratified auriferous rocks have had no influence upon 
their meridional (north and south) direction, or upon their upheaval and contortion, 
and stating his belief that the cracks and fissures in which the gold-quartz-reefs 
occur have not been mineralized by any process different from that which has 
operated in other mineral veinstones, Mr. Selwyn remarks that, " although no very 
reliable evidence exists of their increasing downwards very greatly in richness, 
neither is there any evidence whatever in Victoria which would enable us to state 
that any vein rich at the surface will die out or suddenly become unprofitable." 
" There is undoubtedly good evidence," he adds, "that those upper portions 
of the gold-quartz -veins which have been naturally removed by denudation, and 
now form the gold-drifts, were often far richer than any we now find at the 
surface ; but in drawing conclusions from this evidence we should not forget 
that in all probability many hundreds of vertical feet of quartz-veins have been 
thus naturally broken up, crushed, and washed ; and the fact of the veins (so 
abraded) being still frequently very rich on their present surface goes far, I 
think, to prove that the diminution of yield in depth, even though admitted to 
be true on a large scale, is still so slow as not to be appreciable within any 
depth to which ordinary mining- operations are carried." 
Giving several illustrations confirmatory of his views, and showing that the 
deepest shaft in which a quartz-vein was proved productive reaches to 400 feet, 
Mr. Selwyn concludes by expressing his opinion " that the extraction of gold 
from quartz -reefs, if properly conducted, may be regarded as an occupation 
which will prove as permanently profitable in Victoria as tin- and copper- 
mining have been in Great Britain" f. 
* It gives me great pleasure to reflect that Mr. 
Selwyn, who has so well executed the important 
task confided to him, is a scion of the Geological 
Survey of the British Isles, who greatly distin- 
guished himself in elaborating the difficult rela- 
tions of the different members of the Silurian and 
associated igneous rocks in North Wales in com- 
pany with Professor Eamsay and others. 
t It may be here mentioned that the gold-fields 
of Victoria have afforded tin, a mineral unknown 
in Eussia, which is found not only in the form of 
sand, but also in small lumps and highly coloured 
crystals. The reader who wishes to obtain a ge- 
neral view of the most important of the Australian 
gold-diggings, and acquire an insight into the 
statistics and social condition of the wonderful 
