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GEOGRAPHICAL BOUNDARIES.
The boundary zone in Nature--Oscillating boundaries of the habitable area of the earth--Wallace's Line a typical boundary zone--Boundaries as limits of expansion--Boundary zone as index of growth or decline--Breadth of boundary zone--Broad frontier zones of active expansion--Value of barrier boundaries--The sea as the absolute boundary--Natural boundaries as bases of ethnic and political boundaries--Primitive waste boundaries--Alien intrusions into border wastes--Politico-economic significance of the waste boundary--Common boundary districts--Tariff free zones--Boundary zones of mingled race elements--Assimilation of civilization in boundary zones--Relation of ethnic and cultural assimilation--The border zone of assimilation in political expansion--Tendency toward defection along political frontiers--The spirit of colonial frontiers--Free border states as political survivals--Guardians of the marches--Lawless citizens deported to political frontiers--Drift of lawless elements to the frontiers--Asylums beyond the border..