84 HISTORY OF THE EARTH. 
noceros, hippopotamus, tapir, &c.,) that are from time to time 
found enveloped in the soil of northern countries, also point to 
similar conclusions in regard to the mean temperature in very 
ancient times of the regions in which they occur. The animal 
and vegetable fossils brought by Capt. Parry from Melville Is- 
land, in latitude 75°, bear an intimate resemblance to those of Eng- 
land and the United States. 
At the present day, the climate of every part of the earth's sur- 
face is determined principally by its latitude. The facts just 
stated, indicate a different condition of things at the period when the 
secondary and tertiary strata were deposited ; that there was then 
a nearer approach to uniformity of temperature in all parts of the 
world; such as could have been derived only from a common 
focus or source of heat beneath the surface ; the remains of that 
by which the solid rocks were once held in a state of fusion. 
45. Of the present temperature of the interior parts of the 
earth. — Observations made in mines in the western part of Eu- 
rope and in Mexico, indicate an increase of temperature as we de- 
scend. When this fact was first announced, the greater heat 
found in the deeper strata was attributed to other causes, and es- 
pecially to chemical changes proceeding there, such as the con- 
version of the metallic sulphurets into sulphates, the animal 
warmth given out by the workmen, the combustion of numer- 
ous lamps and candles employed in lighting the mine, and of 
gunpowder used in blasting the rocks, — also to the compression of 
the air produced by the lengthening of the atmospheric column — 
rather than to a permanent elevation of temperature in the cen- 
tral mass of the globe. M. Cordier collected and compared the 
results obtained by preceding observers, and added others, the 
fruit of his own researches. In these last also, such precautions 
were taken to avoid the causes of error which were supposed to 
have vitiated the earlier experiments, that it is very difficult to 
avoid the conclusions to which they seem to lead. 
The tin and copper mines of Cornwall have been wrought to 
a considerable depth beneath the level of the sea. They are drain- 
ed through an adit or tunnel, commencing at that level, upon the 
coast, and carried into the heart of the mining district. Into this 
all the water that collects in the mine, whether flowing from the 
higher parts, or raised by the steam engine from greater depths, 
is conveyed along the channels cut for the purpose, and finally 
discharged at the mouth of the adit at the rate of 16S0 cubic feet 
per minute, or 2S7,000 hogsheads per day. Its temperature at 
this point is 19 degrees above the mean temperature of the air 
and earth at the surface. It is calculated that the heat created by 
the respiration of the workmen, by the combustion of lamps and 
candles and other causes, would not be sufficient to raise the tem- 
perature of such a mass of water more than a single degree. 
Results corresponding to these have been obtained wherever 
observations have been made in mines of considerable depth -> by 
