shanty-boat"
people of the western rivers of the United States. They are the gypsies
of our streams, nomads who float downstream with the current, tying up
at intervals along the bank of some wooded island or city waterfront,
then paying a tug to draw their house-boat upstream. The river furnishes
them with fish for their table and driftwood for their cooking-stove,
and above all is the highway for the gratification of their nomad
instincts. There is no question here of trade and overpopulation.

[Sidenote: Reclamation of land from the sea.]

Pile dwellings and house-boats are a paltry form of encroachment upon
the water in comparison with that extensive reclamation of river swamps
and coastal marshes which in certain parts of the world has so increased
the area available for human habitation. The water which is a necessity
to man may become his enemy unless it is controlled. The alluvium which
a river deposits in its flood-plain, whether in some flat stretch of its
middle course or near the retarding level of the sea, attracts
settlement because of its fertility and proximity to a natural highway;
but it must be protected by dikes against the very element which created
it. Such deposits are most extensive on low coasts at or near the
river's mouth, just where the junction of an inland and oceanic waterway
offers the best conditions for commerce. Here then is a location
destined to attract and support a large population, for which place can
be made only by steady encroachment upon the water of both river and
sea. Diking is necessitated not only by the demand for more land for the
growing population, but also by the constant silting up of the drainage
outfalls, which increases the danger of inundation while at the same
time contributing to the upbuilding of the land. Conditions here
institute an incessant struggle between man and nature;[596] but the
rewards of victory are too great to count the cost. The construction of
sea-walls, embankment of rivers, reclamation of marshes, the cutting of
canals for drains and passways in a water-soaked land, the conversion of
lakes into meadow, the rectification of tortuous streams for the greater
economy of this silt-made soil, all together constitute the greatest
geographical transformation that man has brought about on the earth's
surface.[597]

[Sidenote: The struggle with the water.]

Though the North Sea lowland of Europe has suffered from the serious
encroachment of the se