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.