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, parallel with climatic zones, thereby forming in themselves distinctly marked lines between peoples, forcing the African to remain under his burning sun, and the northmen in their cooler latitudes; so that in the several climatic zones of the old world, we see the human race distinctly marked, Aryan, Semitic, and Turanian--white, black, and yellow--while throughout the two Americas, from Alaska to Tierra del Fuego, type and color are singularly uniform. * * * * * Who can picture the mighty tide of humanity, which, while the eastern hemisphere has been developing so high a state of culture, in America has ebbed and flowed between barbarisms and civilizations? Through what long and desperate struggles, continuing age after age through the lives of nations, now advancing, now receding, have these peoples passed? Asia, from its central position and favorable climate, would seem naturally to encourage a redundant population and a spontaneous civilization; the waters of the Mediterranean invite commerce and intercommunication of nations, while the British Isles, from their insular situation and distance from hypothetical primitive centres, would seem necessarily to remain longer in a state of barbarism. In the Pacific States of North America we find the densest population north along the shores of the ocean, and south on the cordillera table-land, from the fact that the former offers the best facilities for food and locomotion until the latter is reached, when the interior presents the most favorable dwelling-place for man.