of the chief forces impelling people to migrate and cover the
earth.

Among the primitive men who were pushed outward from the Asian
deserts during a period of aridity, one group migrated
northeastward toward the Kamchatkan corner of Asia. Whether they
reached Bering Sea and the Kamchatkan shore before the next epoch
of glaciation we do not know. Doubtless they moved slowly,
perhaps averaging only a few score or a hundred miles per
generation, for that is generally the way with migrations of
primitive people advancing into unoccupied territory. Yet
sometimes they may have moved with comparative rapidity. I have
seen a tribe of herdsmen in central Asia abandon its ancestral
home and start on a zigzag march of a thousand miles because of a
great drought. The grass was so scanty that there was not enough
to support the animals. The tribe left a trail of blood, for
wherever it moved it infringed upon the rights of others and so
with conflict was driven onward. In some such way the primitive
wanderers were kept in movement until at last they reached the
bleak shores of the North Pacific. Even there something--perhaps
sheer curiosity--still urged them on. The green island across the
bay may have been so enticing that at last a raft of logs was
knotted together with stout withes. Perhaps at first the men
paddled themselves across alone, but the hunting and fishing
proved so good that at length they took the women and children
with them, and so advanced another step along the route toward
America. At other times distress, strife, or the search for game
may have led the primitive nomads on and on along the coast
until a day came when the Asian home was left and the New World
was entered. The route by which primitive man entered America is