, or such
judicious observations with regard to the nature of siliceous substance,
as a compound thing; no person reasons more distinctly in general, or
sees more clearly the importance of his principles; yet, with regard to
mineral concretions, how often has he been drawn thus inadvertently
into improper generalization! I appeal to the analogy which, in this
treatise, he has formed, between the stalactical concretions upon
the surface of the earth, and the mineral concretions of siliceous
substance. As an example of the great lights, and penetrating genius, of
this assiduous studier of nature, I refer to the judicious observations
which he has made upon the subject of aluminous earth, in this
dissertation.

I am surprised to find this enlightened naturalist seeking, in the
origin of this globe of our earth, a general principle of fluidity or
solution in water, like the alkahest of the alchymists, by means of
which the different substances in the chemical constitution of precious
stones might have been united as well as crystallised. One would
have thought, that a philosopher, so conversant in the operations of
subterraneous fire, would have perceived, that there is but one general
principle of fluidity or dissolution, and that this is heat.]

Besides this proof for the fusion of siliceous bodies, which is
indirect, arising from the in dissolubility of that substance in water,
there is another, which is more direct, being founded upon appearances
which are plainly inconsistent with any other supposition, except that
of simple fluidity induced by heat. The proof I mean is, the penetration
of many bodies with a flinty substance, which, according to every
collateral circumstance, must have been performed by the flinty matter
in a simply fluid state, and not in a state of dissolution by a solvent.

These are flinty bodies perfectly insulated in strata both of chalk and
sand. It requires but inspection to be convinced. It is not possible
that flinty matter could be conveyed into the middle of those strata, by
a menstruum in which it was dissolved, and thus deposited in that place,
without the smallest trace of deposition in the surrounding parts.

But, besides this argument taken from what does not appear, the actual
form in which those flinty masses are found, demonstrates, _first_,
That they have been introduced among those strata in a fluid state, by
injection from some other place. 2_dly_, That they have been disperse