These two species of bodies, therefore, the siliceous and the
sulphureous, may now be examined, in relation to the causes of their
concretion, with a view to determine, what has been the general
concreting or consolidating power, which has operated universally in the
globe; and particularly to show, it has not been by means of any fluid
solution, that strata in general have been consolidated, or that those
particular substances have been crystallized and concreted.
Siliceous matter, physically speaking, is not soluble in water; that is
to say, in no manner of way have we been enabled to learn, that water
has the power of dissolving this matter.
Many other substances, which are so little soluble in water, that their
solubility could not be otherwise detected of themselves, are made to
appear soluble by means of siliceous matter; such is feld-spar, one of
the component parts of rock-granite.
Feld-spar is a compound of siliceous, argillaceous, and calcareous
earth, intimately united together. This compound siliceous body
being, for ages, exposed to the weather, the calcareous part of it is
dissolved, and the siliceous part is left in form of a soft white earth.
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