| → under a more favourable climate for intermigration, 1866 |
| for intermigration under a more favourable climate, 1859 1860 1861 |
| under a more favourable climate 1869 1872 |
|
| → I attribute a considerable degree of uniformity in 1866 |
| I attribute the necessary amount of uniformity in 1859 1860 1861 |
| for intermigration, will account for the supposed uniformity of 1869 1872 |
|
| → large, but partial 1859 1860 1861 1866 1869 |
| great 1872 |
|
|
freedom
→under a more favourable climate for intermigration,
→I attribute a considerable degree of uniformity in
the sub-arctic and
temperate productions of the Old and New Worlds, at a period anterior to the Glacial epoch. |
|
| Believing, from reasons before alluded to, that our continents have long remained in nearly the same relative position, though subjected to
→large, but partial
oscillations of level, I am strongly inclined to extend the above view, and to infer that during some
and still warmer period, such as the older Pliocene period, a large number of the same plants and animals inhabited the almost continuous circumpolar land; and that these plants and animals, both in the Old and New Worlds, began slowly to migrate southwards as the climate became less warm, long before the
of the Glacial period. We now see, as I believe, their descendants, mostly in a modified condition, in the central parts of Europe and the United States. On this view we can understand the
with very little identity, between the productions of North America and Europe,— a relationship which is
remarkable, considering the distance of the two areas, and their separation by the
Ocean. We can further understand the singular fact remarked on by several
that the productions of Europe and America during the
tertiary stages were more closely related to each other than they are at the present time; for during these warmer periods the northern parts of the Old and New Worlds will have been almost continuously united by land, serving as a bridge, since rendered impassable by cold, for the
of their inhabitants. |
|
| During the slowly decreasing warmth of the Pliocene period, as soon as the species in common, which
|
