st_, Because, however little of the wood is left unpenetrated, the
division is always distinct between the injected part and that which is
not penetrated by the fluid flint. In this case, the flinty matter has
proceeded a certain length, which is marked, and no farther; and, beyond
this boundary, there is no partial impregnation, nor a gradation of the
flintifying operation, as must have been the case if siliceous matter
had been deposited from a solution. 2_dly_, The termination of the
flinty impregnation has assumed such a form, precisely, as would
naturally happen from a fluid flint penetrating that body.

In other specimens of this mineralising operation, fossil wood,
penetrated, more or less, with ferruginous and calcareous substances,
has been afterwards penetrated with a flinty substance. In this case,
with whatever different substances the woody body shall be supposed
to have been penetrated in a state of solution by water, the regular
structure of the plant would still have remained, with its vacuities,
variously filled with the petrifying substances, separated from the
aqueous menstruum, and deposited in the vascular structure of the wood.
There cannot be a doubt with regard to the truth of this proposition;
for, as it is, we frequently find parts of the consolidated wood, with
the vascular structure remaining perfectly in its natural shape and
situation; but if it had been by aqueous solution that the wood had been
penetrated and consolidated, all the parts of that body would be found
in the same natural shape and situation.

This, however, is far from being the case; for while, in some parts, the
vascular structure is preserved entire, it is also evident, that, in
general, the woody structure is variously broken and dissolved by the
fusion and crystallization of the flint. There are so many and such
various convincing examples of this, that, to attempt to describe them,
would be to exceed the bounds prescribed for this dissertation; but such
specimens are in my possession, ready for the inspection of any person
who may desire to study the subject.

We may now proceed to consider sulphureous substances, with regard to
their solubility in water, and to the part which these bodies have acted
in consolidating the strata of the globe.

The sulphureous substances here meant to be considered, are substances
not soluble in, water, so far as we know, but fusible by heat, and
inflammable or combustible by means of