| ↑ 1 blocks not present in 1859 1860 1861 1869 1872; present in 1866 |
| We might of course speculate on the land having been formerly higher than at present in various parts of the tropics, where temperate forms apparently have crossed; but as the lines of migration have been so numerous, such speculations would be rash.
|
|
| → do not doubt that 1859 1860 1861 |
| am forced to believe that in certain regions, as in India, 1866 |
|
| → had migrated some 1859 1860 1861 |
| in Europe had migrated over at least 1866 |
|
| → from their native country 1859 1860 |
| from their native country, 1861 |
| OMIT 1866 |
|
| → six or seven 1859 1860 1861 |
| from five to six 1866 |
|
| → I suppose that 1859 1860 |
| OMIT 1861 1866 |
|
| → as 1859 1860 1861 |
| at the height of four or five thousand feet, as so 1866 |
|
|
even crossed the equator. The invasion would, of course, have been greatly favoured by high land, and perhaps by a dry climate; for Dr. Falconer informs me that it is the damp with the heat of the tropics which is so destructive to perennial plants from a temperate climate. On the other hand, the most humid and hottest districts
have afforded an asylum
the
natives. The mountain-ranges north-west of the Himalaya, and the long line of the Cordillera, seem to have afforded two great lines of invasion: and it is a striking fact,
communicated to me by Dr. Hooker, that all the flowering plants, about forty-six in number, common to Tierra del Fuego and to
still exist in North America, which must have lain on the line of march. ↑
I
→do not doubt that
some temperate productions entered and crossed even the
of the tropics at the period when the cold was most intense,— when arctic forms
→had migrated some
twenty-five degrees of
→from their native country
and covered the land at the foot of the Pyrenees. At this period of extreme cold, I believe that the climate under the equator at the level of the sea was about the same with that now felt there at the height of
→six or seven
thousand feet. During this the coldest period,
→I suppose that
large spaces of the tropical lowlands were
with a mingled tropical and temperate vegetation, like that now growing with strange luxuriance at the base of the Himalaya,
→as
graphically described by Hooker. |
|
| Thus, as I believe, a considerable number of plants, a few terrestrial animals, and some marine productions, migrated during the Glacial period from the northern and southern temperate zones into the intertropical regions, and some even crossed the equator. As the warmth returned, these temperate forms would naturally ascend the higher mountains, being exterminated on the
|
