1879*] The Heat of the Comstock Mines. 221 
ture of 157 0 F. On the contrary, the water in other places 
is much less hot, but it is as a rule always hotter than the 
air, and in many cases it appears to be hotter than the rock 
is found to be, except in especially hot spots. 
The East cross-cut of the Crown Point 2000 feet level, 
which was temporarily abandoned and boarded up on ac- 
count of the heat, gave an air temperature of 150° F., the 
thermometer being thrust through a crack in the boarding. 
At the head of this cross-cut the heat was proved to be 
higher than this. 
Another hot spot is in the Imperial Consolidated Mine. 
In this mine the Black Dyke splits, sending a shoot off to 
the north-east, and a drift has been run on the 2000 feet 
level, along the eastern side of this branch dyke. 
This proved to be a very hot spot indeed. Rock, air, and 
water were all so much above the usual limits of tempera- 
ture, even in these hot mines, that the work of cutting the 
drift must have been extremely severe. 
The Belcher south incline has a hot belt of rock, quite 
narrow, a short distance above the nineteen hundred station, 
and similar hot places are found in most of the mines. 
The author inclines to the opinion that, as a general rule, 
these hot areas lie in belts, and are not irregular or promis- 
cuously placed in the mass of East country rock. Where 
this seems to be disproved by the distance run in the 
superheated rock, it will, he thinks, probably be found 
that the drift, or incline, and the hot belt have the same 
direction. 
Hot belts are also found at the contact of the diorite and 
propylite in the Virginia mines. The diorite is itself in 
adtive decomposition, and mines which have carried drifts 
in or near it are very hot. The Julia has explored a quartz 
seam, which appears to lie entirely in the diorite, and this 
has proved to be one of the hot belts. 
This apparent concentration of the heat in the line of 
contadt of two rocks is not supposed to be due to any 
thermal or eledtro-thermal adtion, but to depend merely upon 
the fadt that in this neighbourhood the ground is more 
broken and the surfaces of the rock increased. These con- 
ditions are obviously favourable to the adtion of atmospheric 
waters. 
Belts of excessively hot ground are not the only notice- 
able phenomena in these mines. More remarkable still are 
the belts of unusually cold rock : these are fewer in number 
than the hot belts, but they are strongly marked ; they are 
always wet, and the water that drips through the crevices 
