covered with grass as a New England hayfield. On closer
examination, however, the growth is seen to consist of individual
bunches which can easily be pulled up, so that among the southern
tribes the fields did not become filled with grass as they did in
the north, for the women had relatively little difficulty in
keeping out this kind of weed as well as others.

In this survey of aboriginal America we have been impressed by
the contrast between two diverse aspects of the control of human
activities by physical environment. We saw, in the first place,
that in our own day the distribution of culture in America is
more closely related to climatic energy than to any other factor,
because man is now so advanced in the arts and crafts that
agricultural difficulties do not impede him, except in the far
north and in tropical forests. Secondly, we have found that,
although all the geographical factors acted upon the Indian as
they do today, the absence of metals and beasts of burden
compelled man to be nomadic, and hence to remain in a low stage
of civilization in many places where he now can thrive. In the
days long before Columbus the distribution of civilization in the
Red Man's Continent offered still a third aspect, strikingly
different both from that of today and from that of the age of
discovery. In that earlier period the great centers of
civilization were south of their present situation. In the
southern part of North America from Arizona to Florida there are
abundant evidences that the Indians whom the white man found were
less advanced than their predecessors. The abundant ruins of
Arizona and New Mexico, their widespread distribution, and the
highly artistic character of the pottery and other products of
handicraft found in them seem to indicate that the ancient