The coast a zone of transition--The inner edge--Shifting of the inner edge--Outer edge in original settlement--In early navigation--In colonization--Inland advance of colonies--Interpenetration of land and sea--Ratio of shore-line to area--Criticism of the formula--Accessibility of coasts from hinterland--Accessibility of coasts from the sea--Embayed coasts--Contrasted coastal belts--Evolution of ports--Influence of offshore islands--Previous habitat of coast-dwellers--Habitability of coasts as a factor in maritime development--Geographic conditions for brilliant maritime development--Scope and importance of seaward expansion--Ethnic contrast between coast and interior peoples--Ethnic amalgamations of coastlands--_Lingua franca_ a product of coasts--Coast-dwellers as middlemen--Differentiation of coast from inland people--Early civilization of coasts--Progress from thalassic to oceanic coasts--Importance of geographic location of coasts--Historical decline of certain coasts--Complex interplay of geographic factors in coastlands. CHAPTER IX. OCEANS AND ENCLOSED SEAS The water a factor in man's mobility--Oceans and seas the factor of union in universal history--Origin of navigation--Primitive forms--Relation of river to marine navigation--Retarded and advanced navigation--Geographic conditions in Polynesia--Mediterranean versus Atlantic seamanship--Three geographic stages of maritime development--Enclosed seas as areas of ethnic and cultural assimilation--Assimilation facilitated by ethnic kinship--Importance of zonal and continental location of enclosed seas--Thalassic character of the Indian Ocean--Limitations of small area in enclosed seas--Successive maritime periods in history--Contrasted historical roles of northern and southern hemispheres--Size of the ocean--Neutrality of the seas--_Mare clausum and Mare liberum_. CHAPTER X. MAN'S RELATION TO THE WATER The protection of a water frontier--Pile villages of ancient times--Modern pile dwellings--Their geographic distribution--River-dwellers in old and popular lands--Man's encroachment upon the sea by reclamation of land--The struggle with the water--Mound villages in river flood-plains--Social and political gain by control of the water--A factor in early civilization of arid lands--The economy of the water--Fisheries--Factors in maritime expansion--Fisheries as nurseries of seamen--Anthropo-geographic importance of navigation. CHAPTER XI. THE ANTHROPO-GEOGRAPHY OF RIVERS