and across the Atlantic ridge one might have walked to the New
World dry-shod.[12] In similar wise the northwestern corner of America
has repeatedly been joined to Siberia through the elevation of Bering
Sea.

[Footnote 12: See, for example, the map of Europe in early
post-glacial times, in James Geikie's _Prehistoric Europe_.]

There have therefore been abundant opportunities for men to get into
America from the Old World without crossing salt water. Probably this
was the case with the ancient inhabitants of the Delaware and Little
Miami valleys; it is not at all likely that men who used their kind of
tools knew much about going on the sea in boats.

[Sidenote: Waves of migration.]

Whether the Indians are descended from this ancient population or not,
is a question with which we have as yet no satisfactory method of
dealing. It is not unlikely that these glacial men may have perished
from off the face of the earth, having been crushed and supplanted by
stronger races. There may have been several successive waves of
migration, of which the Indians were the latest.[13] There is time
enough for a great many things to happen in a thousand centuries. It
will doubtless be long before all the evidence can be brought in and
ransacked, but of one thing we may feel pretty sure; the past is more
full of changes than we are apt to realize. Our first theories are
usually too simple, and have to be enlarged and twisted into all manner
of shapes in order to cover the actual complication of facts.[14]

[Footnote 13: "There are three human crania in the Museum,
which were found in the gravel at Trenton, one several feet
below the surface, the others near the surface. These skulls,
which are of remarkable uniformity, are of small size and of
oval shape, differing from all other skulls in the Museum. In
fact they are of a distinct type, and hence of the greatest
importance. So far as they go they indicate that palaeolithic
man was exterminated, or has become lost by admixture with
others during the many thousand years which have passed since
he inhabited the Delaware valley." F. W. Putnam, "The Peabody
Museum," _Proceedings of the American Antiquarian Society_,
1889, New Series, vol. vi. p. 189.]

[Footnote 14: An excellent example of this is the expansion and
modification undergone durin