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 littoral belt has suffered elevation or subsidence.  When the inshore sea rests upon an uplifted bottom, the contour of the coast is smooth and unbroken, because most of the irregularities of surface have been overlaid by a deposit of waste from the land; so it offers no harbor except here and there a silted river mouth, while it shelves off through a broad amphibian belt of tidal marsh, lagoon, and sand reef to a shallow sea.  Such is the coast of New Jersey, most of the Gulf seaboard of the United States and Mexico, the Coromandel coast of India, and the long, low littoral of Upper Guinea.  Such coasts harbor a population of fishermen living along the strands of their placid lagoons,[447] and stimulate a timid inshore navigation which sometimes develops to extensive coastwise intercourse, where a network of lagoons and deltaic channels forms a long inshore passage, as in Upper Guinea, but which fears the break of the surf outside.[448]

The rivers draining these low uplifted lands are deflected from their straight path to the sea by coastwise deposits, and idly trail along for miles just inside the outer beach; or they are split up into numerous offshoots among the silt beds of a delta, to find their way by shallow, tortuous channels to the ocean, so that they abate their value as highways between sea and land.  The silted mouths of the Nile excluded the larger vessels even of Augustus Caesar’s time and admitted only their lighters,[449] just as to-day the lower Rufigi River loses much of its value to German East Africa because of its scant hospitality to vessels coming from the sea.

[Sidenote:  Embayed coasts.]