Introduction The problem of the existence of man in America before or during the Glacial period has received fresh impetus by recent discoveries in the Missouri valley. The lively interest which these discoveries have aroused has led me to occupy the hour which is customarily allowed to the retiring President of the Society in a consideration of these new facts. Those who investigate the early history of mankind have been compared* to explorers in search of the source of one of those great streams that traverse whole continents. Where the river divides, the explorer may take the wrong branch, and at the end of his journey he may rest satisfied with the result of his search. Later explorers, perhaps after the lapse of several decades, may be led to follow up the great branch which was neglected by the pioneer explorer, and, although they soon find reason to correct . . .