and barren places that are scarcely accessible or habitable, and thereby
extends the inhabited area of the earth long before mere pressure of
population would have stretched it to such limits. We find these refugee
folk living in pile villages built over the water, in deserts, in
swamps, mangrove thickets, very high mountains, marshy deltas, and
remote or barren islands, all which can be classified as regions of
retreat. Fugitives try to place between themselves and their pursuers a
barrier of sea or desert or mountains, and in doing this have themselves
surmounted some of the greatest obstacles to the spread of the human
race.

Districts of refuge located centrally to several natural regions of
migration receive immigrants from many sides, and are therefore often
characterized by a bizarre grouping of populations. The cluster of
marshy islands at the head of the Adriatic received fugitives from a
long semi-circle of north Italian cities during the barbarian invasions.
Each refugee colony occupied a separate island, and finally all
coalesced to form the city of Venice. Central mountain districts like
the Alps and Caucasus contain "the sweepings of the plains." The
Caucasus particularly, on the border between Europe and Asia, contains
every physical type and representative of every linguistic family of
Eurasia, except pure Aryan. Nowhere else in the world probably is there
such a heterogeneous lot of peoples, languages and religions. Ripley
calls the Caucasus "a grave of peoples, of languages, of customs and
physical types."[172] Its base, north and south, and the longitudinal
groove through its center from east to west have been swept by various
racial currents, which have cast up their flotsam into its valleys. The
pueblos of our arid Southwest, essentially an area of asylum, are
inhabited by Indians of four distinct stocks, and only one of them, the
Moquis, show clearly kinship to another tribe outside this
territory,[173] so that they are survivals. The twenty-eight different
Indian stocks huddled together in small and diverse linguistic groups
between the Pacific Ocean and the eastern slope of the Sierra Nevada and
Cascade Range[174] leave the impression that these protected valleys,
similar to the Caucasus in their ethnic diversity, were an asylum for
remnants of depleted stocks who had fled to the western highlands before
the great Indian migrations of the interior.[175] Making their way
painfully and at great cos