open natural highways from the
interior to the coast. This structure has made the Atlantic side of the
Iberian Peninsula far more open than its Mediterranean front, and
therefore contributed to its leadership in maritime affairs since 1450.
So from the shores of Thrace to the southern point of the Peloponnesus,
all the valleys of Greece open out on the eastern or Asiatic side. Here
every mountain-flanked bay has had its own small hinterland to draw
upon, and every such interior has been accessible to the civilization of
the Aegean; here was concentrated the maritime and cultural life of
Hellas.[444] The northern half of Andean Colombia, by way of the parallel
Atrato, Rio Cauco, and Magdalena valleys, has supported the activities
of its Caribbean littoral, and through these avenues has received such
foreign influences as might penetrate to inland Bogota. In like manner,
the mountain-ridged peninsula of Farther India keeps its interior in
touch with its leading ports through its intermontane valleys of the
Irawadi, Salwin, Menam, and Mekong rivers.

Low coasts rising by easy gradients to wide plains, like those of
northern France, Germany, southern Russia, and the Gulf seaboard of the
United States, profit by an accessible and extensive hinterland.
Occasionally, however, this advantage is curtailed by a political
boundary reinforced by a high protective tariff, as Holland, Belgium,
and East Prussia[445] know to their sorrow.

These low hems of the land, however, often meet physical obstructions to
ready communications with the interior in the silted inlets, shallow
lagoons, marshes, or mangrove swamps of the littoral itself. Here the
larger drainage streams give access across this amphibian belt to the
solid land behind. Where they flow into a tide-swept bay like the North
Sea or the English Channel, they scour out their beds and preserve the
connection between sea and land;[446] but debouchment into a tideless
basin like the Caspian or the Gulf of Mexico, even for such mighty
streams as the Volga and the Mississippi, sees the slow silting up of
their mouths and the restriction of their agency in opening up the
hinterland. Thus the character of the bordering sea may help to
determine the accessibility of the coast from the land side.

[Sidenote: Accessibility of coasts from the sea.]

Its accessibility from the sea depends primarily upon its degree of
articulation; and this articulation depends upon whether the littor