THE NATURE OF THE INTERIOR OF THE EARTH. 
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1. The results of a large number of experiments, made in 
mines and boreholes in various parts of the world, affording 
conclusive evidence that the temperature of the earth, as deep 
down as has yet been explored from the surface, increases in 
direct ratio as we descend towards its centre. 
It has been found a matter of much difficulty, owing, as might 
be expected, to the interference of local causes, to determine with 
exactitude the true general rate of such increase in temperature 
downwards, but all observers agree in regarding it as somewhere 
between 1° and 2° Fahrenheit for every hundred feet in depth 
from the surface. 
2. Numerous observations of the temperature of hot and deep- 
seated springs and Artesian wells, which prove that the tempera- 
ture of the water increases with the depth of its source, and 
confirm the results of the experiments made in mines. 
3. The great currents of molten lava emitted from the vol- 
canic orifices in all quarters of the globe, which, as in the space 
enclosed between America, Asia, and Australasia, may present 
one vast scene of volcanic activity, covering a large area of the 
face of the globe, and bearing testimony to the vast accumula- 
tion of molten matter which must necessarily exist in its interior. 
4. The numerous analyses of the lavas and other products 
of volcanoes, which prove them to be quite analogous in mine- 
ralogical and chemical constitution, without reference to what 
parts of the world, however distaut from one another, in which 
they may have been ejected, and lead to the inference that they 
must all have proceeded from some one great hypogene source, 
and not be products of any mere local action. 
5. The evidence afforded by geological observation that 
eruptions of rock masses, resembling those of our modern 
volcanoes, have, since the earliest periods, played a similar part 
in the geological history of the earth. 
6. The occurrence of great faults (more or less vertical), 
formed by the elevation and depression of large areas of the 
rock formations which constitute the external crust of the earth. 
These latter phenomena lead to the inference that the external 
crust itself cannot, in depth, rest upon an unyielding mass of 
matter in the solid state, but that it must be superposed upon 
some more or less fluid substance, which, by its mobility, can, 
when some one portion of the crust above has subsided or been 
let down, become displaced and make room for itself by elevating, 
or, as it were, floating up, some other part of the same. 
As far as explorations have as yet been carried down into the 
earth, the direct increase of temperature with the depth has 
been fully established ; and, as no facts are known at present 
which can invalidate the supposition that the same, or a some- 
what similar, ratio holds good in still greater depth, it is perfectly 
