been deposited at the bottom
of the sea, as exhausted of their water, and as communicating with the
surface of the earth impregnated with water. Here again we have the
power of gravity to operate in carrying down water to that place which
had been before exhausted by the power of heat; and in this manner, by
alternately employing those two great physical agents, we cannot doubt
that nature may convey soluble substances from above, and deposit them
below for the purpose of consolidating porous bodies, or of filling with
saline and earthy matter those interstices which had been originally
filled with water, when the strata were deposited at the bottom of the
sea. How far any marks of this operation may be perceived, by carefully
examining our mines and minerals, I know not; I can only say that, on
the contrary, whenever those examined objects were clear and distinct,
with the concomitant circumstances, so as to be understood, I have
always found the most certain marks of the solid bodies having concreted
from the fluid state of fusion. This, however, does not exclude the case
of infiltration having been previously employed; and I would intreat
mineralists, who have the opportunity of examining the solid parts of
the earth, to attend particularly to this distinction. But do not let
them suppose that infiltration can be made to fill either the pores or
veins of strata without the operation of mineral heat, or some such
process by which the aqueous vehicle may be discharged.

Not only are mineral philosophers so inconsiderate, in forming
geological theories upon a mere supposition or false analogy, they
have even proceeded, upon that erroneous theory, to form a geological
supposition for explaining the appearances of strata and other stony
masses in employing a particular physical operation, which is, that
of _crystallization_[37]. Now crystallization may be considered as a
species of elective concretion, by which every particular substance, in
passing from a fluid to a solid state, may assume a certain peculiar
external shape and internal arrangement of its parts, by which it is
often distinguished. But, to suppose the solid mineral structure of the
earth explained, like an enigma, by the word _crystallization_, is to
misunderstand the science by which we would explain the subject of
research; and, to form a general mineral theory thus upon that term,
is an attempt to generalise without a reason. For, when it were even
adm