This was unexpected; it was thought to be quite remarkable, and it added greatly to the difficulty of deciding the question, which, of course, at once arose, in respect to the origin of these plants and animals and men, and to the manner in which they came in possession of a continent thus cut off apparently from all intercourse and connection with the rest of the world.

For the American continent is entirely separated from the old. The nearest approach which it makes to it in any part is at Behring's Straits, on the north-west, where it is divided form the Asiatic continent by a channel about forty miles wide.

Means of Communication With the Old World.

Some animals and perhaps some plants, and most certainly man, may be supposed to have been transported across such a channel of water as this of Behring's Straits, either by boats made by the savages living on the coasts, or possibly by means of ice, either upon moving fields driven by the wind, or upon the solid surface, at some time when the whole channel was entirely frozen over.

There is also at some distance south of Behring's Straits a remarkable chain of islands, called the Aleutian Islands, which extend in a regular and continuous line from the American to the Asiatic shore. These islands are nearly all inhabited, and the natives navigate the seas around them in boats made of a frame-work of wood or bone, covered externally with seal skins.

These islands are volcanic. They contain now numerous volcanoes, some active and some extinct, and also hot springs and other indications of subterranean fire. They bear no trees, but they produce a great variety of animals. They look, upon the map, like a row of stepping stones, placed on purpose to enable men and animals from the old world to make their way to the new.