11 - Geographical Distribution
11-05 - Means of dispersal, by changes of climate and of the level of the land, and by occasional means
Sir C. Lyell and other authors have ably treated this subject.
|Sir Charles Lyell|
I can give here only the briefest abstract of the more important facts.
Change of climate must have had a powerful influence on migration: a region when its climate was different may have been a high road for migration, but now be impassable; I shall, however, presently have to discuss this branch of the subject in some detail.
Changes of level in the land must also have been highly influential: a narrow isthmus now separates two marine faunas; submerge it, or let it formerly have been submerged, and the two faunas will now blend or may formerly have blended: where the sea now extends, land may at a former period have connected islands or possibly even continents together, and thus have allowed terrestrial productions to pass from one to the other.
No geologist will dispute that great mutations of level have occurred within the period of existing organisms.
Edward Forbes insisted that all the islands in the Atlantic must recently have been connected with Europe or Africa, and Europe likewise with America.