That there are, in other countries, evident marks of volcanos which
have been long extinguished, is unquestionably true; but naturalists,
imagining that there are no other marks of subterraneous fire and
fusion, except in the production of a lava, attribute to a volcano, as
a cause, these effects, which only indicate the exertion of that power
which might have been the cause of a volcano.
If the theory now given be just, a rock of marble is no less a mark
of subterraneous fire and fusion, than that of the basaltes; and the
flowing of basaltic streams among strata broken and displaced, affords
the most satisfactory evidence of those operations by which the body of
our land had been elevated above the surface of the sea; but it gives no
proof that the eruptive force of mineral vapours had been discharged in
a burning mountain. Now, this discharge is essential in the proper idea
of a volcano.
Besides this internal mark of an unerupted lava in the substance of the
stone or body of the flowing mass, there are others which belong to it
in common with all other mineral strata, consolidated by subterraneous
fire, and changed from the place of their original formation; this is,
the being broken and dislocated, and having veins of foreign matter
formed in their separations and contractions.
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