Rivers as intermediaries between land and sea--Sea navigation merges
into river navigation--Historical importance of seas and oceans
influenced by their debouching streams--Lack of coast articulations
supplied by rivers--River highways as basis of commercial
preëminence--Importance of rivers in large countries--Rivers as highways
of expansion--Determinants of routes in arid or semi-arid
lands--Increasing historical importance of rivers from source to
mouth--Value of location at hydrographic centers--Effect of current upon
trade and expansion--Importance of mouth to upstream people--Prevention
of monopoly of river mouths--Motive for canals in lower
course--Watershed canals for extension of inland waterways--Rivers and
railroads--Natural unity of every river system--In arid lands as common
source of water supply--Tendency towards ethnic and cultural unity in a
river valley--Identity of country with river valley--Rivers as
boundaries of races and peoples--Rivers as political boundaries--Fluvial
settlements and peoples--Boatman tribes or castes--River islands as
protected sites--River and lake islands as robber strongholds--River
peninsulas--River islands as sites of trading posts and colonies--Swamps
as barriers and boundaries--Swamps as regions of survivals--Swamps as
places of refuge--The spirit of the marshes--Economic and political
importance of lakes--Lakes as nuclei of states--Lakes as fresh-water
seas.