granite; the mica schists, for example, of mica--the quartz rocks, of
quartz, &c.? For this there are both chemical and mechanical causes.
Suppose that a river has a certain quantity of material to carry
down, it is evident that it will soonest drop the larger particles,
and carry the lightest farthest on. To such a cause is it owing that
some of the materials of the worn-down granite have settled in one
place and some in another. {52} Again, some of these materials must
be presumed to have been in a state of chemical solution in the
primeval seas. It would be, of course, in conformity with chemical
laws, that certain of these materials would be precipitated singly,
or in modified combinations, to the bottom, so as to form rocks by
themselves.

The rocks hitherto spoken of contain none of those petrified remains
of vegetables and animals which abound so much in subsequently formed
rocks, and tell so wondrous a tale of the past history of our globe.
They simply contain, as has been said, mineral materials derived from
the primitive mass, and which appear to have been formed into strata
in seas of vast depth. The absence from these rocks of all traces of
vegetable and animal life, joined to a consideration of the excessive
temperature which seems to have prevailed in their epoch, has led to
the inference that no plants or animals of any kind then existed. A
few geologists have indeed endeavoured to shew that the absence of
organic remains is no proof of the globe having been then unfruitful
or uninhabited, as the heat to which these rocks have been subjected
at the time of their solidification, might have obliterated any
remains of either plants or animals which were included in them. But
this is only an hypothesis of negation; and it certainly seems very
unlikely that a degree of heat sufficient to obliterate the remains
of plants or animals when dead, would ever allow of their coming into