It seems to me that we have abundant evidence of great oscillations in the level of the land or sea; but not of such vast changes in the position and extension of our continents, as to have united them within the recent period to each other and to the several intervening oceanic islands.

I freely admit the former existence of many islands, now buried beneath the sea, which may have served as halting places for plants and for many animals during their migration.

In the coral-producing oceans such sunken islands are now marked by rings of coral or atolls standing over them.