|
of transport, during the long lapse of geological time, whilst
island was being
and
before it had become fully stocked with inhabitants. On almost bare land, with few or no destructive insects or birds living there, nearly every
which chanced to arrive,
→if fitted for the climate, would
germinate and survive. |
| The identity of many plants and animals, on mountain-summits, separated from each other by hundreds of miles of lowlands, where
Alpine species could not possibly exist, is one of the most striking cases known of the same species living at distant points, without the apparent possibility of their having migrated from one
the other. It is indeed a remarkable fact to see so many
the same
living on the snowy regions of the Alps or Pyrenees, and in the extreme northern parts of Europe; but it is far more remarkable, that the plants on the White Mountains, in the United States of America, are all the same with those of Labrador, and nearly all the same, as we hear from Asa Gray, with those on the loftiest mountains of Europe. Even as long ago as 1747, such facts led Gmelin to conclude that the same species must have been independently created at
distinct points; and we might have remained in this same belief, had not Agassiz and others called vivid attention to the Glacial period, which, as we shall immediately see, affords a simple explanation of these facts. We have evidence of almost every conceivable kind, organic and inorganic,
within a very recent geological period, central Europe and North America suffered under an
climate. The ruins of a house burnt by fire do not tell their tale more
than do the mountains of Scotland and Wales, with their scored flanks, polished surfaces, and perched boulders, of the icy streams with which their valleys were lately filled. So greatly has the climate of Europe changed, that in Northern Italy, gigantic moraines, left by old glaciers, are now clothed by the vine and maize. Throughout a large part of the United States, erratic
and
scored
→rocks
plainly reveal a former cold period. |
| The former influence of the glacial climate on the distribution of the inhabitants of Europe, as explained
→OMIT
by Edward Forbes, is substantially as follows. But we shall follow the changes more readily, by supposing a new glacial period
→slowly to come
on, and then pass away, as formerly occurred. As the cold came on, and as each more southern zone became fitted for
→the inhabitants of the north, these
would take
→places of the former inhabitants of the temperate regions. The
→latter,
|
