in it, and it becomes merely the rim of the sea; for its inhabitants the sea means food, clothes, shelter, fuel, commerce, highway, and opportunity.  Now the coast is dominated by the exuberant forces of a productive soil, so that the ocean beyond is only a turbulent waste and a long-drawn barrier:  the coast is the hem of the land.  Neither influence can wholly exclude the other in this amphibian belt, for the coast remains the intermediary between the habitable expanse of the land and the international highway of the sea.  The break of the waves and the dash of the spray draw the line beyond which human dwellings cannot spread; for these the shore is the outermost limit, as for ages also in the long infancy of the races, before the invention of boat and sail, it drew the absolute boundary to human expansion.  In historical order, its first effect has been that of a barrier, and for the majority of peoples this it has remained; but with the development of navigation and the spread of human activities from the land over sea to other countries, it became the gateway both of land and sea—­at once the outlet for exploration, colonization, and trade, and the open door through which a continent or island receives contributions of men or races or ideas from transoceanic shores.  Barrier and threshold:  these are the roles which coasts have always played in history.  To-day we see them side by side.  But in spite of the immense proportions assumed by transmarine intercourse, the fact remains that the greater part of the coasts of the earth are for their inhabitants only a barrier and not an outlet, or at best only a base for timorous ventures seaward that rarely lose sight of the shore.

[Illustration:  GERMAN NORTH SEA COAST.]

[Sidenote:  Width of coastal zones.]

As intermediary belt between land and sea, the coast becomes a peculiar habitat which leaves its mark upon its people.  We speak of coast strips, coastal plains, “tidewater country,” coast cities; of coast tribes, coast peoples, maritime colonies; and each word brings up a picture of a land or race or settlement permeated by the influences of the sea.  The old term of “coastline” has no application to such an intermediary belt, for it is a zone of measurable width; and this width varies with the relief of the land, the articulation of the coast according as it is uniform or complex, with the successive stages of civilization and the development of navigation among the people who inhabit it.

Along highly articulated coasts, showing the interpenetration of sea and land in a broad band of capes and islands separated by tidal channels and inlets, or on shores deeply incised by river estuaries, or on low shelving beaches which screen brackish lagoons and salt marshes behind sand reefs and dune ramparts, and which thus form an indeterminate boundary of alternate land and water, the zone character of the coast in a physical sense becomes conspicuous.  In an anthropological sense the zone character is clearly indicated by the different uses of its inner and outer edge made by man in different localities and in different periods of history.