The Peopling of America and the Early Man of North America

"The immigrations, in America as in Europe, have been intermittent, and separated sometimes by centuries. America has been peopled as if by a great human river, which, rising in Asia, has traversed the continent from north to south, receiving along its course a few small tributaries. This river resembles the torrent streams of which we have examples in France. Usually, and occasionally for years at a time, their bed is nearly dry.
Then some great storm comes, and a liquid avalanche descends from the mountains where their sources lie, covers and ravages the plain, turning over the ancient alluviums, stirring up and mixing the old and new materials, and carrying farther each time the débris it has torn up on its passage. Like this has been the career of our ethnological river. Its floods have, besides, often been diverted to the right or left, and it has opened new derivations.
It has also had its eddies. But its general direction has not changed, and we can trace it down to the present..."