hence, other things being equal, the inhabitants of a country whose greatest length lay east and west, would intermingle more readily than those whose territory extended north and south.
That the eastern hemisphere attained a higher degree of civilization than the western, may be partly due to the fact, that the former presents wider spaces of uniform climate than the latter. The climatic zones of the New World, besides being shorter, are intersected by mountain barriers, which tend to retard the intercourse that would otherwise naturally follow. Thus the Mexican table-land, the seat of Aztec civilization, is a tierra fria situated above the insalubrious tierra caliente of either coast and the healthful tierra templada of the slopes, but below the mountain ranges which rise from this table-land, forming a tierra frígida, a region of perpetual snow. To this day, the natives of the Mexican plateau cannot live on the sea-coast, though less than a day's journey distant.
Between the climatic zones which extend through Europe and Asia, there are contrasts as marked and changes as sudden, but these differences are between the different zones rather than between longitudinal sections of the same zone. Hence, in the old world, where climatic zones are separated by mountain ranges which make the transition from one to the other sudden and abrupt, we see a greater diversity of race than in America, where the natural barriers extend north and south and intersect the climatic zones, thereby bringing the inhabitants along a meridian in easier communication than those who live in the same latitude but who are separated by mountains, table-lands and large rivers. That is, if color and race are dependent on climate, America should offer greater varieties in color and race than Europe, for America traverses the most latitudes; but the mountain barriers of America extend north and south, thereby forcing its people to intermingle, if at all, in that direction, while the chief ranges of the eastern continent extend east and west,
