ntributing its part, that the effect is
accomplished; and this is a thing which cannot possibly take place in
the aquiform strata below the surface of the sea. But, without attending
to this clear distinction of things perfectly different, naturalists are
apt to see false analogies, and thus in generalising to form the most
erroneous theories.

I shall now give an example of this fallaceous manner of reasoning; it
is in the case of certain mineral appearances which are erroneously
considered as stalactical concretions.

The only true stalactical bodies are of a calcareous substance; they are
formed by water containing this substance in a dissolved state; and the
principles upon which this particular concretion is formed are well
known. It is therefore easy to compare other concretions, which may have
some superficial resemblance to these stalactical bodies, in order to
see if they have proceeded upon the same principle of concretion from
a dissolved state, or by water depositing its dissolved substance in a
similar manner.

There are two different mineral substances which give appearances of
this sort. These are certain concretions of calcedony, and also of
iron-ore, which are thought to have such resemblance to stalactical
concretions as, by some superficial observers, to be reckoned of the
same kind. It is now proposed to show that those conclusions are not
well founded; and that, in this case of calcedony and iron-ore, it could
not be upon the principle of stalactical concretion that the bodies now
in question had their forms.

The principle upon which calcareous substance is dissolved in water, and
made to concrete by the evaporation of the acid substance, or fixed
air by which it had been dissolved, is too well known to require any
explanation in this place; we are only to consider the sensible effects
of those operations of which we know so well the proper conditions.

There are just two distinct views under which we may consider all
stalactical concretions formed; these are the incrustation of
the calcareous substance concreting upon a foreign body, and the
incrustation of the same substance upon itself. By the first any manner
of shape may be formed, provided there be a solid body, upon the surface
of which the calcareous solution is made to pass. By the second, again,
we have various forms; but we know the principles upon which they had
been made. These are the shape and motions of the fluid which gives th