wer or Mexican course of the Colorado River and
the Gulf of California. The Franco-British convention, which in 1898
confirmed the western Sudan to France, also conceded the principle of
making the Niger, the sole outlet of this vast and isolated territory,
an international waterway, and created two French _enclaves_ in British
Nigeria to serve as river ports.[668]

[Sidenote: Motive for canals in lower course.]

The mouth of a large river system is the converging point of many lines
of inland and maritime navigation. The interests of commerce, especially
in its earlier periods of development, demand that the contact here of
river and sea be extensive as possible. Nature suggests the way to
fulfill this requirement. The sluggish lowland current of a river, on
approaching sea level, throws out distributaries that reach the coast at
various points and form a network of channels, which can be deepened and
rendered permanent by canalization. In such regions the opportunity for
the improvement and extension of waterways has been utilized from the
earliest times. The ancient Egyptians, Chaldeans, East Indians, and the
Gauls of the lower Po for thousands of years canaled the waters of their
deltas and coastal lowlands for the combined purpose of irrigation,
drainage, and navigation. The great canal system of China, constructed
in the seventh century primarily to facilitate Inland intercourse
between the northern and central sections of the Empire, extends from
the sea at Hangchow 700 miles northward through the coastal alluvium of
the Yangtze Kiang, Hoang-ho and Pie-ho to Tientsin, the port of Peking.
Only the canal system of the center, important both for the irrigation
of the fertile but porous loess and for the transportation of crops, is
still in repair. Here the meshes of the canal network are little more
than half a mile wide; farmers dig canals to their barns and bring in
their produce in barges instead of hay wagons.[669] Holland, where the
ancient Romans constructed channels in the Rhine delta and where the
debouchment courses of the Rhine, Meuse and Scheldt present a labyrinth
of waterways, has to-day 1903 miles (3069 kilometers) of canals, which
together with the navigable rivers, have been important geographic
factors in the historical preeminence of Dutch foreign commerce. So on
the lower Mississippi, in the greatest alluvial area of the United
States, the government has expended large sums for the improvement of