whole globe,
with the exception of a small external shell, must be fluid, and the
central parts must have a temperature many times higher than that of
melted iron.

5thly. But the theory adopted by M. Cordier and others, which maintains
the actual existence of such a state of things, seems wholly
inconsistent with the laws which regulate the circulation of heat
through fluid bodies. For, if the central heat were as intense as is
represented, there must be a circulation of currents, tending to
equalize the temperature of the resulting fluids, and the solid crust
itself would be melted.

6thly. Instead of an original central heat, we may, perhaps, refer the
heat of the interior to chemical changes constantly going on in the
earth's crust; for the general effect of chemical combination is the
evolution of heat and electricity, which in their turn become sources of
new chemical changes.

CHAPTER XXXII.

CAUSES OF EARTHQUAKES AND VOLCANOES--_continued_.

Review of the proofs of internal heat--Theory of an unoxidated
metallic nucleus--Whether the decomposition of water may be a source
of volcanic heat--Geysers of Iceland--Causes of
earthquakes--Wavelike motion--Expansive power of liquid
gases--Connection between the state of the atmosphere and
earthquakes--Permanent upheaval and subsidence of land--Expansion of
rocks by heat--The balance of dry land how preserved--Subsidence in
excess--Conclusion.

When we reflect that the largest mountains are but insignificant
protuberances upon the surface of the earth, and that these mountains
are nevertheless composed of different parts which have been formed in
succession, we may well feel surprise that the central fluidity of the
planet should have been called in to account for volcanic phenomena. To
suppose the entire globe to be in a state of igneous fusion, with the
exception of a solid shell, not more than from thirty to one hundred
miles thick, and to imagine that the central heat of this fluid spheroid
exceeds by more than two hundred times that of liquid lava, is to
introduce a force altogether disproportionate to the effects which it is
required to explain.

The ordinary repose of the surface implies, on the contrary, an
inertness in the internal mass which is truly wonderful. When we
consider the combustible nature of the elements of the earth, so far as
they are known to us,--the facility with which their compounds may be
dec