view of the doctrine now
controverted, if we consider what would happen were a globe of
homogeneous composition placed under circumstances analogous, in regard
to the distribution of heat, to those above stated. If the whole planet,
for example, were composed of water covered with a spheroidal crust of
ice fifty miles thick, and with an interior ocean having a central heat
about two hundred times that of the melting point of ice, or 6400
degrees F.; and if, between the surface and the centre, there was every
intermediate degree of temperature between that of melting ice and that
of the central nucleus--could such a state of things last for a moment?
If it must be conceded, in this case, that the whole spheroid would be
instantly in a state of violent ebullition, that the ice (instead of
being strengthened annually by new internal layers) would soon melt, and
form part of an atmosphere of steam--on what principle can it he
maintained that analogous effects would not follow, in regard to the
earth, under the conditions assumed in the theory of central heat?[754]

M. Cordier admits that there must be tides in the internal melted ocean;
but their effect, he says, has become feeble, although originally, when
the fluidity of the globe was perfect, "the rise and fall of these
ancient land tides could not have been less than from thirteen to
sixteen feet." Now, granting for a moment, that these tides have become
so feeble as to be incapable of causing the fissured shell of the earth
to be first uplifted and then depressed every six hours, still may we
not ask whether, during eruptions, the lava, which is supposed to
communicate with a great central ocean, would not rise and fall sensibly
in a crater such as Stromboli, where there is always melted matter in a
state of ebullition?

_Whether chemical changes may produce volcanic heat._--Having now
explained the reasons which have induced me to question the hypothesis
of central heat as the primary source of volcanic action, it remains to
consider what has been termed the chemical theory of volcanoes. It is
well known that many, perhaps all, of the substances of which the earth
is composed are continually undergoing chemical changes. To what depth
these processes may be continued downwards must, in a great degree, be
matter of conjecture; but there is no reason to suspect that, if we
could descend to a great distance from the surface, we should find
elementary substances differ