It is in this mineral system that I have occasion to compare the
explanations, which I give of certain natural appearances, with the
theories or explanations which have been given by others, and which are
generally received as the proper theory of those mineral operations. I
am, therefore, to examine those different opinions, respecting the
means employed by nature for producing particular appearances in the
construction of our land, appearances which must be explained in some
consistent mineral theory.
These appearances may all be comprehended under two heads, which are now
to be mentioned, in order to see the importance of their explanation, or
purpose which such an explanation is to serve in a theory of the earth.
The first kind of these appearances is that of known bodies which we
find composing part of the masses of our land, bodies whose natural
history we know, as having existed in another state previous to the
composition of this earth where they now are found; these are the
relicts or parts of animal and vegetable bodies, and various stony
substances broken and worn by attrition, all which had belonged to a
former earth.
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