136 SEVENTH REPORT—1837. 
water from more considerable depths, and the difference between 
a and / to their relative proximity to the lode. The tempera- 
ture of 85°°3 is at least 35° above the mean of the climate, and, 
therefore, it gives a ratio of increase equal to one degree in 
49°6 feet, if calculated from the surface; and Levant Mine, 
which was 80° at the bottom, one degree in 46 feet, or they give 
one degree in 48 and 44 feet respectively, if estimated from ten 
fathoms under the surface. . 
The thermometers were likewise placed in holes, as before, 
in a superior level in the Consolidated Mines, 130 fathoms be- 
low the surface, when No. 1 indicated a temperature of 61°, 
and No. 2 of 61°°6. This difference in favour of the short ther- 
mometer was probably due to the influence of ascending currents 
of warm air and vapour on the surface of the rock; and such an 
explanation is not inconsistent with the opinion that the general 
temperature of the upper parts of the mine had undergone a dimi- 
nution of its criginal amount, in consequence of the excavations 
below having interfered with the ascent of warm water, and pro- 
moted the drainage from above of that which was comparatively 
cold. For these reasons, and from the results obtained at the 
deepest parts of mines of various depths, I consider that the 
temperature of 61° is much below what it would have been had 
there been no inferior excavations ; and I have evidence that in 
1822, when the mine was only 150 fathoms deep, the water at 
the bottom of one shaft was at 76° and of another at 80°. 
It is clear, I think, from all the experiments which have been 
made on the temperature of mines, that causes which are more 
or less local, and exist in the earth itself, have a powerful influence 
in modifying its degree, and in producing those anomalous results 
which have always characterised observations on subterranean 
heat. When it is considered how much the crust of the earth 
abounds with fissures or faults, and that warm water has a con- 
stant tendency to ascend through cooler portions of that fluid, 
and thus to produce upward and downward currents in the fis- 
sures and veins, it would indeed be surprising if such discrepan- 
cies did not exist even in the same vicinity, to say nothing of the 
greater or less influence of water percolating from the surface. 
Upon the whole, I am strongly of the opinion that the effect of 
the simple conducting power of rocks on the temperature, at 
depths hitherto attained, is very much superseded by that of the 
transporting property of water to which I have alluded. Indeed, 
I have long taken this view of the subject, and it has appeared 
to me to account very satisfactorily for the fact of the more 
compact rocks, ,such as granite, having been often found at 
rather a lower temperature than “killas” at given depths, and 
