Much turns on the period assigned to the first appearance of man in this region; for that he is indigenous is highly improbable, if only because no anthropoid apes are found here.
The racial type, which, with the exception of the Eskimo, and possibly of the salmon-fishing tribes along the north-west coast, is one for the whole continent, has a rather distant resemblance to that of the Asiatic Mongols.

Nor is there any difficulty in finding the immigrants a means of transit from northern Asia.

Even if it be held that the land-bridge by way of what are now the Aleutian Islands was closed at too early a date for man to profit by it, there is always the passage over the ice by way of Behring Straits; which, if it bore the mammoth, as is proved by its remains in Alaska, could certainly bear man.
Once man was across, what was the manner of his distribution?
On this point geography can at present tell us little.

M.Demolins, it is true, describes three routes, one along the Rockies, the next down the central zone of prairies, and the third and most easterly by way of the great lakes.

But this is pure hypothesis.