s entertain with regard to the system of nature, in which may
be perceived no ineffectual operation, nor any destructive intention,
but the wise and benevolent purpose of preserving the present order of
this world. But, though thus misled with regard to the cause of things,
naturalists are every where making interesting observations in the
mineral kingdom, I shall therefore avail myself of that instructive
information, for the confirmation of my theory.

It may now be proper to consider what must be required, in order to have
a geological and mineral theory established upon scientific principles,
or on such grounds as must give conviction to those who will examine
the subject; for, unless we may clearly see that there are means for
attaining that desirable end, few philosophers will be persuaded to
pursue this branch of knowledge.

A theory is nothing but the generalization of particular facts; and, in
a theory of the earth, those facts must be taken from the observations
of natural history. Nature is considered as absolutely true; no error or
contradiction can be found in nature. For, if such contradiction were
truly found, if the stone, for example, which fell to day were to rise
again to-morrow, there would be an end of natural philosophy, our
principles would fail, and we would no longer investigate the rules of
nature from our observations.

Every natural appearance, therefore, which is explained, _i.e._ which is
made to come into the order of things that happen, must so far confirm
the theory to which it then belongs. But is it necessary, that every
particular appearance, among minerals, should be thus explained in
a general theory of the earth? And, is any appearance, which is not
explained by it, to be considered as sufficient to discredit or confute
a theory which corresponded with every other appearance? Here is a
question which it would require some accuracy to resolve.

If we knew all the powers of nature, and all the different conditions in
which those powers may have their action varied, that is to say, if we
were acquainted with every physical cause, then every natural effect, or
all appearances upon the surface of this earth, might be explained in a
theory that were just. But, seeing that this is far from being the case,
and that there may be many causes of which we are as yet ignorant, as
well as certain conditions in which the known action of powers may be
varied, it must be evident, that a theory o