Has the globe within it such an active power as fits it for the
renovation of that part of its constitution which may be subject to
decay? Are those powerful operations of fire, or subterraneous heat,
which so often have filled us with terror and astonishment, to be
considered as having always been? Are they to be concluded as proper to
every part upon the globe, and as continual in the system of this earth?
If these points in question shall be decided in the affirmative, we can
be at no loss in ascertaining the power which has consolidated strata,
nor in explaining the present situation of those bodies, which had their
origin at the bottom of the sea. This, therefore, should be the object
of our pursuit; and in order to have demonstration in a case of physical
inquiry, we must again have recourse to the book of nature.
The general tendency of heat is to produce fluidity and softness; as
that of cold is, on the contrary, to harden soft and fluid bodies. But
this softening power of heat is not uniform in its nature; it is made to
act with very different effect, according to the nature of the substance
to which it is applied.
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