The differences of opinion between Hrdli[vc]ka and other students is probably more a question of nomenclature than of fact. The eastern Asiatics and Polynesians are mixed peoples, and if there were numerous migrations from Asia, spread over a very long period of time, people of different stocks would have found their way into America. "It is indeed probable," Hrdli[vc]ka adds, "that the western coast of America, within the last two thousand years, was on more than one occasion reached by small parties of Polynesians, and that the eastern coast was similarly reached by small groups of whites; but these accretions have not modified greatly, if at all, the mass of the native population[750]." The inhabitants of the plains east of the Rocky Mountains and the eastern wooded area are characterised by a head which varies about the lower limit of brachycephaly, and by tall stature. This stock probably arrived by the North Pacific Bridge before the end of the last Glacial period, and extended over the continent east of the great divide. Finally bands from the north, east and south migrated into the prairie area. The markedly brachycephalic immigrants from Asia appear to have proceeded mainly down the Pacific slope and to have populated Central and South America, with an overflow into the south of North America. It is probable that there were several migrations of allied but not similar broad-headed peoples from Asia in early days, and we know that recently there have been racial and cultural drifts between the neighbouring portions of America and Asia[751]. Indeed Bogoras[752] suggests that ethnographically the line separating Asia and America should lie from the lower Kolyma River to Gishiga Bay. Owing to these various immigrations and subsequent minglings the cranial forms show much variation, and are not sufficiently significant to serve as a basis of classification. In parts of North America the round-headed mound-builders and others were encroached upon by populations of increasingly dolichocephalic type--Plains Indians and Cherokees, Chichimecs, Tepanecs, Acolhuas. Even still dolichocephaly is characteristic of Iroquois, Coahuilas, Sonorans, while the intermediate indices met with on the prairies and plateaux undoubtedly indicate the mixture between the long-headed invaders and the round-heads whom they swept aside as they advanced southwards. Thus the Minnetaris are highly dolicho; the Poncas and Osages sub-brachy; the Algonquians variable, while the Siouans oscillate widely round a mesaticephalous mean.