[Sidenote: Nature of primitive movements.]

This movement is and has been universal and varied. When most
unobtrusive in its operation, it has produced its greatest effects. To
seize upon a few conspicuous migrations, like the _Völkerwanderung_ and
the irruption of the Turks into Europe, made dramatic by their relation
to the declining empires of Rome and Constantinople, and to ignore the
vast sum of lesser but more normal movements which by slow increments
produce greater and more lasting results, leads to wrong conclusions
both in ethnology and history. Here, as in geology, great effects do not
necessarily presuppose vast forces, but rather the steady operation of
small ones. It is often assumed that the world was peopled by a series
of migrations; whereas everything indicates that humanity spread over
the earth little by little, much as the imported gypsy moth is gradually
occupying New England or the water hyacinth the rivers of Florida. Louis
Agassiz observed in 1853 that "the boundaries within which the different
natural combinations of animals are known to be circumscribed upon the
surface of the earth, coincide with the natural range of distinct types
of man."[128] The close parallelism between Australian race and flora,
Eskimo race and Arctic fauna, points to a similar manner of dispersion.
Wallace, in describing how the Russian frontier of settlement slowly
creeps forward along the Volga, encroaching upon the Finnish and Tartar
areas, and permeating them with Slav blood and civilization, adds that
this is probably the normal method of expansion.[129] Thucydides describes
the same process of encroachment, displacement, and migration in ancient
Hellas.[130] Strabo quotes Posidonius as saying that the emigration of the
Cimbrians and other kindred tribes from their native seats was gradual
and by no means sudden.[131] The traditions of the Delaware Indians show
their advance from their early home in central Canada southward to the