proves by astronomical observation that it is eight
hundred miles thick. Lyell affirms that at twenty-four miles deep there
can be no solid crust, for the temperature of the earth increases one
degree for every forty-five feet, and at that depth the heat is great
enough to melt iron and almost every known substance. But then there is
a difference between philosophers about this last test of
solidity--those who believe in Wedgewood's Pyrometer, which was the
infallible standard twenty years ago, asserting that the heat of melted
iron is 21,000 deg. Fahrenheit; while Professor Daniells demonstrates by
another infallible instrument that it is only 2,786 deg. Fahrenheit;[374]
which is rather a difference. In one case the earth's crust would be
over two hundred miles thick, in the other twenty-four. But then comes
the great question, What is below the granite? and a very important one
for any theory of the earth. It evidently underlies the whole foundation
of speculative geology, whether we assume with De Beaumont and Humboldt,
that "the whole globe, with the exception of a thin envelope, much
thinner in proportion than the shell of an egg, is a fused mass, kept
fluid by heat--a heat of 450,000 deg. Fahrenheit, at the center, Cordier
calculates--but constantly cooling, and contracting its dimensions;" and
occasionally cracking and falling in, and "squeezing upward large
portions of the mass;" "thus producing those folds or wrinkles which we
call mountain chains;" or, with Davy and Lyell, that the heat of such a
boiling ocean below would melt the solid crust, like ice from the
surface of boiling water--and with it the whole theory of the primeval
existence of the earth in a state of igneous fusion, its gradual cooling
down into continents and mountains of granite, the gradual abrasion of
the granite into the mud and sand which formed the stratified rocks, and
all the other brilliant hypotheses which have sparked out of this great
internal fire. Instead of an original central heat he supposes that "we
may _perhaps_ refer the heat of the interior to chemical changes
constantly going on in the earth's crust."[375] Now if the very
foundations of the science are in such a state of fusion, and floating
on a _perhaps_, would it not be wise to allow them to solidify a little
before a man risks the salvation of his soul upon them?

The various theories are contradictions. The igneous theory assault the
aqueous theory with the greatest