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1859
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in any one region for the immigration of 1860 1861 1866 1869 1872
for the coming in of quite 1859

from other regions, 1860 1861 1866 1869 1872
by immigration, 1859

mastodons 1859 1860 1861 1866 1869
the species of mastodons 1872

series, first 1859 1860 1861 1866 1869
series,— in the first place 1872

then 1859 1860 1861 1866 1869
in the second place 1872

perfect, 1859 1860 1861 1866 1869
complete, which is far from the case, 1872

character between the forms of life above and below. We must, however, allow for the entire extinction of some preceding forms, and in any one region for the immigration of new forms from other regions, and for a large amount of
modification
modification,
during the long and blank intervals between the successive formations. Subject to these allowances, the fauna of each geological period undoubtedly is intermediate in character, between the preceding and succeeding faunas. I need give only one instance, namely, the manner in which the fossils of the Devonian system, when this system was first discovered, were at once recognised by palæontologists as intermediate in character between those of the overlying carboniferous, and underlying Silurian
systems.
system.
But each fauna is not necessarily exactly intermediate, as unequal intervals of time have elapsed between consecutive formations.
It is no real objection to the truth of the
statement
statement,
that the fauna of each period as a whole is nearly intermediate in character between the preceding and succeeding faunas, that certain genera offer exceptions to the rule. For instance, mastodons and elephants, when arranged by Dr. Falconer in two series, first according to their mutual
affinities,
affinities
and then according to their periods of
existence,—
existence,
do not accord in arrangement. The species extreme in character are not the
oldest
oldest,
or the most recent; nor are those which are intermediate in character, intermediate in age. But supposing for an instant, in this and other such cases, that the record of the first appearance and disappearance of the species was perfect, we have no reason to believe that forms successively produced necessarily endure for corresponding lengths of
time.
time:
A
a
very ancient form
may
might
occasionally
have lasted
last
much longer than a form
else-where
elsewhere
subsequently produced, especially in the case of