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1859
1860
1861
1866
1869
1872

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1860
1861
1866
1869
1872

on the prodigious 1859 1860 1861 1866
and on the great 1869 1872

only then first immigrated into that area. It is
well-known,
well known,
for instance, that several species appeared
some-what
somewhat
earlier in the palæozoic beds of North America than in those of Europe; time having apparently been required for their migration from the American to the European seas. In examining the latest deposits
in
of
various quarters of the world, it has everywhere been noted, that some few still existing species are common in the deposit, but have become extinct in the immediately surrounding sea; or, conversely, that some are now abundant in the neighbouring sea, but are rare or absent in this particular deposit. It is an excellent lesson to reflect on the ascertained amount of migration of the inhabitants of Europe during the
glacial
Glacial
period;
epoch,
period,
which forms only a part of one whole geological
period:
period;
and likewise to reflect on the
great
great
changes of level, on the
extreme
inordinately great
change of climate, on the prodigious lapse of time, all included within this same glacial period. Yet it may be doubted
whether,
whether
in any quarter of the world, sedimentary deposits,
including
including
fossil
fossil
remains,
remains,
remains ,
have gone on accumulating within the same area during the whole of this period. It is not, for instance, probable that sediment was deposited during the whole of the glacial period near the mouth of the Mississippi, within that limit of depth at which marine animals can
best flourish:
flourish;
for we know
that
what
great
vast
geographical changes occurred in other parts of America during this space of time. When such beds as were deposited in shallow water near the mouth of the Mississippi during some part of the glacial period shall have been upraised, organic remains will probably first appear and disappear at different levels, owing to the
migrations
migration
of species and to geographical changes. And in the distant future, a
geologist,
geologist
examining these beds,
would
might
be tempted to conclude that the average duration of life