to the most
enormous depth or thickness. This is the situation and condition of
things in which nature is to operate; and we are to find the means of
consolidating those strata, and concreting every species of substance
in almost every possible composition, according to some known physical
principle. Here is an operation which is limited; for, we must reason
strictly, according to the laws of nature, in the case which we have
under consideration; and we cannot suppose nature as ever transgressing
those laws.

It is acknowledged, that, by means sometimes of an aeriform, sometimes
of an alkaline, perhaps also of an acid substance, calcareous matter is
dissolved in the earth, and certain metallic substances, such as lead
and iron. This solution also, upon particular occasions, (where the
proper conditions for separating the solvent from the dissolved
substance exist), forms certain concretions; these are sometimes a mere
incrustation, as in the case of the siliceous incrustation of Giezer,
sometimes again in a crystallised or sparry form, as in the case of
stalactical concretions. But here is no question of those cases where
the proper conditions may be found; first, of dissolving the substance
which is afterwards to be concreted; secondly, of separating the
menstruum from the dissolved substance; and, lastly, of removing the
fluid deprived of its solution, and of supplying a new solution in its
room; the question is, how far those concretions are formed where those
conditions do not take place. Now, this last case is that of almost all
mineral concretions.

It must not be here alleged that certain concretions have been found in
mines posterior to these having been worked by man; consequently, that
those concretions have been formed by nothing but the infiltration of
water. In those cases, where such concretions are truly found, I am
persuaded that all the conditions proper to that operation will also
be found; and it is only, I believe, in those cases where such proper
conditions may be found, that this aqueous concretion ever appears. Now,
if we shall except calcareous stalactite, and the bog ore of iron, How
seldom is it that any appearance of those aqueous mineral concretion
ever is found? Those very few cases in which they are found, afford the
strongest proof against these being operations general to the globe, or
proper mineral concretions; because it is only where all the necessary
conditions conspire in each co