roportion
to those now living, as the whole human race who have lived and died
upon the earth, to the population at the present time. Again, at each
epoch, the whole earth was no doubt, as now, more or less the theatre of
life, and as the successive generations of each species died, their
exuviae and preservable parts would be deposited over every portion of
the then existing seas and oceans, which we have reason for supposing to
have been more, rather than less, extensive than at present. In order
then to understand our possible knowledge of the early world and its
inhabitants, we must compare, not the area of the whole field of our
geological researches with the earth's surface, but the area of the
examined portion of each formation separately with the whole earth. For
example, during the Silurian period all the earth was Silurian, and
animals were living and dying, and depositing their remains more or less
over the whole area of the globe, and they were probably (the species at
least) nearly as varied in different latitudes and longitudes as at
present. What proportion do the Silurian districts bear to the whole
surface of the globe, land and sea (for far more extensive Silurian
districts probably exist beneath the ocean than above it), and what
portion of the known Silurian districts has been actually examined for
fossils? Would the area of rock actually laid open to the eye be the
thousandth or the ten-thousandth part of the earth's surface? Ask the
same question with regard to the Oolite or the Chalk, or even to
particular beds of these when they differ considerably in their
fossils, and you may then get some notion of how small a portion of the
whole we know.

But yet more important is the probability, nay almost the certainty,
that whole formations containing the records of vast geological periods
are entirely buried beneath the ocean, and for ever beyond our reach.
Most of the gaps in the geological series may thus be filled up, and
vast numbers of unknown and unimaginable animals, which might help to
elucidate the affinities of the numerous isolated groups which are a
perpetual puzzle to the zoologist, may there be buried, till future
revolutions may raise them in their turn above the waters, to afford
materials for the study of whatever race of intelligent beings may then
have succeeded us. These considerations must lead us to the conclusion,
that our knowledge of the whole series of the former inhabitants of