Atlantic and Pacific routes of migration were continued along the northern latitudes into the Western Hemisphere. Toward the northwest, the British Isles then formed an integral part of the European continent, and from this peninsula, land-connections were in all probability extended through Iceland and Greenland to America. In the far northeast, Asia was likewise joined with America by what geologists call the Miocene bridge, which probably lasted into quaternary times; and after the Behring strait finally broke through, the Aleutian island chain still linked the two continents together along the Pacific. As far as climate and topography were concerned, during these interglacial epochs there was nothing, therefore, to prevent the Mediterranean and Malaysian emigrants from pushing northwestward through Europe and northeastward though Asia into America.
As the glaciers advanced successively from the arctic and antarctic regions, the climate and topography of the Northern and Southern Hemispheres varied in this way at least three times. After the third glacial epoch, however, the changes were less marked, until towards the close of the ice age, the configuration of the earth gradually assumed its historic form and the globe became divided as at present into temperature zones. The possibilities of dispersion during the glacial, interglacial and post-glacial periods may, accordingly, be generalized as follows: Each time the Northern Hemisphere was glaciated, the migrations of men must have been confined for the most part within the Indo-Mediterranean-Malaysian belt and the southern peninsulas of the Old World. During the genial epochs that intervened between the three great glacial movements from the north, the continental area was open to incursion on either side, the climate of the Northern Hemisphere was everywhere equable, and the topographic conditions were such as to encourage migration along the Atlantic and Pacific shores of the Eurasian continent into the arctic peninsulas of the New World. As the arctic glaciers became more and more restricted to the northern regions, primeval men were probably able to hold their own in the continental area and migrate east and west across Eurasia. But after the third glacial epoch, if not before, the Atlantic land-bridge was broken; so that henceforth access to America was only possible along the Pacific, by means of the Aleutian island chain.
Cave deposits, kitchen-middens and fossil remains mark the course of the dispersion of mankind in these different directions. The aboriginal inhabitants of the now separated continents and isolated islands of the globe also preserve certain distinguishing characteristics by which the lines of their respective ancestries can be traced back along these several routes to more or less definite points of departure about the Indo-Malaysian abode. There is archeological and ethnological evidence, therefore, to show that primeval men migrated