566— Notices of Memoirs—W. H. Hudleston— 
other at a moderately high temperature, the result being a deposit 
of binoxide of tin or cassiterite. The liberated hydrofluoric acid, 
besides helping to form such minerals as schorl and other fluo-silicates 
and fluorides, would enter into the general circulation of the rocks, 
and thus tend to facilitate that kaolinization of the felspars which 
has produced so much china-clay on the south-west side of Dart- 
moor, and in the mass of the Hensbarrow granite. 
It is also worth noting in this connection that, according to 
Dr. Le Neve Foster, the great flat lode of Carn Brea, near Redruth, 
is in the main a band of altered rock, and he is inclined to suspect 
that half the tin-ore in Cornwall is obtained from tabular masses of 
altered granite. In such cases there is no regular lode, but very fine 
cracks in the rock have evidently given access to stanniferous 
solutions, which have deposited oxide of tin more or less abundantly 
in the vicinity of such cracks, and materially changed the nature of 
the original granite. 
The phenomena in connection with these impregnations of tin-ore 
appear to favour Daubrée’s views; but such points are to be com- 
mended to the notice of local geologists, who alone can test their 
suitability to explain the facts which come before them. I would 
merely remark that too much stress should not be laid on such cases 
as those of deer’s antlers having been found partly replaced by 
cassiterite in the old river-gravels. This has been effected at 
ordinary temperatures, most probably by the aid of alkaline carbonates 
arising from the atmospheric decomposition of felspars, and proves 
that the most insoluble minerals may be successfully attacked by 
agencies now or lately in operation, and their metallic element moved 
from point to point, but only in very small quantities. 
It is to be feared that chemical questions such as these possess but 
little interest for the members of the Association, and I apologize for 
having introduced them, however briefly, before a general audience. 
But there are certain conclusions which we are able to draw with- 
out any special reference to chemistry. In the great metalliferous 
lodes we see the roots of old mineral springs and geysers, which 
spouted their water and steam into the air, and perhaps covered the 
surface of the ground with siliceous sinter. That was a time when 
the volcanic forces of this remarkable region were on the wane, and 
after the great outpourings of lava had taken place upon a surface 
of which every trace, perhaps, has been swept away. How long 
these hydrothermal agencies continued to be active we cannot tell; 
but it is by no means improbable that they were in operation 
throughout a considerable part of Mesozoic time, during which 
period the spoils of this western land, brought down by the ceaseless 
forces of denudation, partly found their way into the eastern sea, 
and thus helped to build up the deposits which were afterwards to 
be fashioned into the Secondary rocks of England. 
