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The Antiquity of Man by Sir Charles Lyell
page 40 of 604 (06%)
Since the first introduction of the terms above defined, the number
of new living species of shells obtained from different parts of
the globe has been exceedingly great, supplying fresh data for
comparison, and enabling the palaeontologist to correct many
erroneous identifications of fossil and Recent forms. New species
also have been collected in abundance from Tertiary formations of
every age, while newly discovered groups of strata have filled up
gaps in the previously known series. Hence modifications and
reforms have been called for in the classifications first proposed.
The Eocene, Miocene, and Pliocene periods have been made to
comprehend certain sets of strata of which the fossils do not
always conform strictly in the proportion of Recent to extinct
species with the definitions first given by me, or which are
implied in the etymology of those terms. These innovations have
been treated of in my "Elements or Manual of Elementary Geology,"
and in the Supplement to the fifth edition of the same, published
in 1859, where some modifications of my classification, as first
proposed, are introduced; but I need not dwell on these on the
present occasion, as the only formations with which we shall be
concerned in the present volume are those of the most modern date,
or the Post-Tertiary. It will be convenient to divide these into
two groups, the Recent and the Pleistocene. In the Recent we may
comprehend those deposits in which not only all the shells but all
the fossil mammalia are of living species; in the Pleistocene those
strata in which, the shells being Recent, a portion, and often a
considerable one, of the accompanying fossil quadrupeds belongs to
extinct species.

Cases will occur where it may be scarcely possible to draw the line
of demarcation between the Newer Pliocene and Pleistocene, or
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