In such masses, (for example of flint and agate,) we find
included shells and coralline bodies. Consequently, there must be a
natural operation in the globe for consolidating and hardening its soft
and loose materials. It is concerning the nature of this consolidating
operation that we are now to inquire.
There are just two ways in which porous or spongy bodies can be
consolidated, and by which substances may be formed into masses of
a natural shape and regular structure; the one of these is simple
_congelation_ from a fluid state, by means of cold; the other is
_accretion_; and this includes a separatory operation, as well as that
by which the solid body is to be produced. But in whichever of these
ways solidity shall be procured, it must be brought about by first
inducing fluidity, either immediately by the action of heat, or
mediately with the assistance of a solvent, that is, by the operation
of solution. Therefore, fire and water may be considered as the general
agents in this operation, which we would explore.
Heat has been already mentioned as a general power, and as acting in all
the different parts of the globe; I would now wish more particularly to
call the attention of the reader to subterraneous fire, or heat, as
a powerful agent in the mineral regions, and as a cause necessarily
belonging to the internal constitution of this earth.
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