| → would have been 1866 |
| must have been 1859 1860 1861 |
| would be 1869 |
| will have been 1872 |
|
| → took 1859 1860 1861 1866 |
| must have taken 1869 1872 |
|
| → been liable to become 1866 |
| become 1859 1860 1861 1869 1872 |
|
| → Europe and N. America. 1866 1869 1872 |
| the two Worlds. 1859 1860 1861 |
|
| → some still 1866 1869 |
| many 1859 1860 1861 |
| some closely allied, still 1872 |
|
| → of some tertiary closely allied 1866 1869 |
| tertiary representative 1859 1860 1861 |
| extinct tertiary 1872 |
|
|
the New and Old Worlds,
south of the Polar Circle, they
→would have been
completely cut off from each other. This separation, as far as the more temperate productions are concerned,
→took
place long ages ago.
the plants and animals migrated southward, they
→been liable to become
mingled in the one great region with the native American productions, and
had to compete with them; and in the other great region, with those of the Old World. Consequently we have here everything favourable for much modification,— for far more modification than with the Alpine productions, left isolated, within a much more recent period, on the several mountain-ranges and on the arctic lands of
→Europe and N. America. Hence it has come, that when we compare the now living productions of the temperate regions of the New and Old Worlds, we find very few identical species (though Asa Gray has lately shown that more plants are identical than was formerly supposed), but we find in every great class many forms, which some naturalists rank as geographical races, and others as distinct species; and a host of closely allied or representative forms which are ranked by all naturalists as specifically distinct. |
|
| As on the land, so in the waters of the sea, a slow southern migration of a marine fauna,
during the Pliocene or even a somewhat earlier period, was nearly uniform along the continuous shores of the Polar Circle, will account, on the theory of modification, for many closely allied forms now living in
completely sundered. Thus, I think, we can understand the presence of
→some still
existing and
→of some tertiary closely allied
on the eastern and western shores of temperate North America; and the still more striking
of many closely allied crustaceans (as described in
admirable work),
|
