222 The Heat of the Comstock Mines. [March, 
of the shattered rock that composes them is noticeably cold 
to the touch, and cools down the air of the drift. Such a 
wet, cold belt of rock exists on the 800 feet level of the 
Justice Mine, and there is a very decided change of temper- 
ature in passing from one to the other side of it. Water 
drips from the rock in numerous places in these as in most 
mines, and that usually it is hot, or at least warm. 
Other cold belts are found in the mines which are not so 
cool as that in the Justice, but are perceptibly cooler than 
the rock at a short distance from them. They complete a 
well-linked chain of heat phenomena, extending from rocks 
that are sensibly cold to the touch, and may not have a tem- 
perature above 50° or 6o° F., through rocks that have the 
average atmospheric temperature, and those which are as 
hot as surface rocks ever become in Nevada, to those which 
have a temperature of 157 0 F. 
Finally, in the chain of testimony relating to this pheno- 
menon is to be noted the condition of the rock. Wet places 
have been spoken of, but the rock cannot be considered as 
generally wet. There are water-ways, and many of them 
appear to reach the surface, but they are of limited breadth, 
like the belts of hot rock. This water is usually hot, but 
sometimes cool or tepid. 
Very often, usually in fadt, the rock is perfectly dry, 
though very hot : that is the case in all the mines. Wet 
rock is the exception, and dry rock the rule, through the 
whole lode. In the drifts cut through this hot, dry rock, 
the walls of the freshly exposed surfaces are painful to the 
hand, and the air is often filled with dust. The rock is both 
hard and tough, but, in spite of its strength, it gives an im- 
pression of fine porosity to the touch, due probably to its 
trachytic character. It often has the odour of clay, but not 
always. It may be slightly adherent, or the impression of 
dryness upon the tongue may be due to its heat, or to the 
fine dust which covers every fragment. 
The heat in the Comstock and other mines similarly 
situated is quite generally spoken of as the feeble remnant 
of a temperature that once reached the point of rock fusion, 
but the fadts observed have led the author to refer the high 
temperatures encountered in the mines not to the internal 
heat of the earth, nor to the residual heat of the rocks, 
which were once melted, but to chemical action now main- 
tained in the erupted rocks. 
This adtion is not a combustion, for the oxidisable mine- 
rals in the lode and its accompanying rocks, the metallic 
sulphides, are little altered. In fadt, the total quantity of 
