only then first immigrated into that area. It is well known,
for instance, that several species appeared 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 in 1866 1869 1872 | of 1859 1860 1861 |
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
period; period; 1866 | period, 1859 1860 1861 | epoch, 1869 1872 |
which forms only a part of one whole geological period;
and likewise to reflect on the great
changes of level, on the 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, 1866 1869 1872 | whether 1859 1860 1861 |
in any quarter of the world, sedimentary deposits,
including
including
1859 1860 1866 1869 1872 | including 1861 |
fossil
fossil
1859 1860 1866 1869 1872 | fossil 1861 |
remains
,
remains
,
1859 1860 1866 1872 | remains, 1861 |
remains,
1869 |
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 flourish;
for we know what
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 migration
of species and to geographical changes. And in the distant future, a
geologist, geologist, 1866 1869 1872 | geologist 1859 1860 1861 |
examining these beds,
would would 1866 1869 1872 | might 1859 1860 1861 |
be tempted to conclude that the average duration of life
|