No geologist disputes that great mutations of level have occurred within the period of existing organisms.

Edward Forbes insisted that all the islands in the Atlantic must have been recently connected with Europe or Africa, and Europe likewise with America.

Other authors have thus hypothetically bridged over every ocean, and united almost every island with some mainland.

If, indeed, the arguments used by Forbes are to be trusted, it must be admitted that scarcely a single island exists which has not recently been united to some continent.