224 The Heat of the Comstock Mines. [March, 
heat from their bodies, together with that produced by the 
burning of the large numbers of candles, could not account 
for any considerable proportion of this heat. Indeed it may 
be assumed, in the absence of calculations, that all the heat 
from these and other ordinary sources of heat in mines is no 
more than sufficient to compensate for the large amount of 
refrigeration produced by the liberation of the compressed 
air which is employed in every mine to work numerous 
underground machines. This heat absorption has not been 
taken into account in the above calculations. 
In another respeCt, also, these calculations are defective, 
and give results very much too low. Usually the air enters 
the mine dry and leaves it saturated with moisture, the 
evaporation of which indicates an amount of heat absorp- 
tion, which would probably increase the above figures 
surprisingly. 
These calculations, imperfect as they are, show that the 
source of heat is one that adts on a magnificent scale, and 
also that it cannot reside in the small quantity of pyrite 
which is oxidised. That source is probably the chemical 
alteration of the felspathic minerals of the propylite and 
other rocks. This change consists apparently in the process 
of transforming felspar to clay, technically known as 
kaolinisation, from the faCt that china clay, or kaolin, is 
produced in this way. 
With regard to the future increase of the heat it is judged 
that, until water temperatures above 154 0 F. are observed, 
nothing in the present condition of things indicates the 
certainty that the heat will ever rise to the boiling-point of 
water, 212 0 F. It is rational to suppose that the access of 
atmospheric air and water must diminish in proportion to 
the depth after a certain point is reached. At that point 
the temperature will be at a maximum. Below it there will 
be a state of equilibrium, probably for a very considerable 
depth. Below that the heat may diminish even to a point 
below that of the highest of the three zones. There must 
be some point where the absence of drainage allows the 
water to aCt like a blanket over the rocks, protedting them 
from the aCtion of air or gases from the surface. The known 
depth required for the production of a temperature amounting 
to 130° F. is so great that we may fairly doubt whether air 
or water penetrate to lower depths in quantity sufficient to 
maintain mineral decomposition with the adtivity necessary 
to obtain the boiling temperature. 
The author’s explanation of the heat phenomena connected 
with these remarkable mines supposes the existence of a 
