536 GEOLOGY. 



tion, the Chinese in Asia, between the tropics and the parallel of 40° 

 N. Lat., and between the desert on the west and the sea on the east; 

 the Mexican in North America, between similar latitudes and in a 

 similar atmospheric environment; and the Peruvian of South America, 

 in equivalent physiographic surroundings. From these more advanced 

 centers of evolution there was a gradation in all directions, and 

 through various stages of partial civilization, to nomadic tribes, scat- 

 tered hunting-bands and isolated families of limited attainments. 



(2) A second and much inferior movement to the southeast, reach- 

 ing into the southern hemisphere, gave rise to the Australioid and 

 associated races which have thus far failed to rise to the higher civiliza- 

 tions, or to develop notable power. 



(3) To a third movement to the southwest is assigned the peopling 

 of Africa south of the Sahara with the negroid and associated races, 

 which have had a voluminous but not powerful development. 



(4) The fourth movement was northwestward across or around 

 barriers of desert and mountain, to Western Asia, Europe, and North 

 Africa, and gave rise to the most virile and progressive branches 

 of the human family, the Xanthochroic (fair- white) and the Melano- 

 chroic (dark- white) races of Huxley's classification. The more or less 

 decayed trunks of these branches still remain in Western Asia. Three 

 chief passageways across the barriers seem to have been utilized in 

 this movement, and in these passageways the most notable of the 

 early civilizations developed, in transit as it were, and lingered for 

 long periods. These passageways were (1) the Red-Sea-Nile- valley 

 avenue, in which the dark- white and the Ethiopian races mingled, (2) the 

 Euphrates valley, the central avenue of the Semitic races, and (3) the 

 intermontane tracts of the Iranian plateau, the probable pathway of 

 the ancestral Aryan races, and quite certainly the pathway of the 

 later backward migration of the Aryans that gave the Brahminical 

 elements to India's early civilization. 



Ignoring the feeble Australian movement, the three great diver- 

 gencies in the Old World were suggestively related to the physiographic 

 features of the region, particularly to the great desert tract that stretches 

 from the Sahara to the Gobi, having the Ethiopians on the south, the 

 Mongoloids on the southeast and east, and the Caucasians on the north 

 and west. While inferences from physiographic relations may easily 

 be pushed too far, there is little doubt that they were very influential 



