ld, is to be repaired.

So far from employing heat or subterraneous fire as an agent in the
mineral operations of the earth, the volcanic philosophers do not
even attempt to explain upon that principle the frequent nodules of
calcareous, zeolite, and other spatose and agaty substances, in those
basaltic bodies which they consider as lavas. Instead then of learning
to see the operation of heat as a general principle of mineral
consolidation and crystallization, the volcanic philosophers endeavour
to explain those particular appearances, which they think inconsistent
with fusion, by aqueous infiltration, no otherwise than other
mineralists who do not admit the igneous origin of those basaltic
bodies. Thus, that great agent, subterraneous heat, has never been
employed by geologists, as a general principle in the theory of the
earth; it has been only considered as an occasional circumstance, or as
the accident of having certain mineral bodies, which are inflammable,
kindled in the earth, without so much as seeing how that may be done.

This agent heat, then, is a new principle to be employed in forming a
theory of the earth; a principle that must have been in the constitution
of this globe, when contrived to subsist as a world, and to maintain
a system of living bodies perpetuating their species. It is therefore
necessary to connect this great mineral principle, subterraneous fire
or heat, with the other operations of the world, in forming a general
theory. For, whether we are to consider those great and constant
explosions of mineral fire as a principal agent in the design, or only
as a casual event depending upon circumstances which give occasion to an
operation of such magnitude, here is an object that must surely have its
place in every general theory of the earth.

In examining things which actually exist, and which have proceeded in a
certain order, it is natural to look for that which had been first; man
desires to know what had been the beginning of those things which now
appear. But when, in forming a theory of the earth, a geologist shall
indulge his fancy in framing, without evidence, that which had preceded
the present order of things, he then either misleads himself, or writes
a fable for the amusement of his reader. A theory of the earth, which
has for object truth, can have no retrospect to that which had preceded
the present order of this world; for, this order alone is what we have
to reason upon; and to