ch are readily undermined by
the washing action of the stream. In the ordinary course of events,
the river beginning, we may imagine, with a straight channel, had its
current deflected by some obstacle, it may be even by the slight
pressure of a tributary stream, is driven against one bank; thence it
rebounds and strikes the other. At each point of impinge it cuts the
alluvium away. It can bear on only a small portion of that which it
thus obtains; the greater part of the material is deposited on the
opposite side of the stream, but a little lower down, where it makes a
shallow. On these shallows water-loving plants and even certain trees,
such as the willows and poplars, find a foothold. When the stream
rises, the sediment settles in this tangle, and soon extends the
alluvial plain from the neighbouring bank, or in rarer cases the river
comes to flow on either side of an island of its own construction. The
natural result of this billiard-ball movement of the waters is that
the path of the stream is sinuous. The less its rate of fall and the
greater the amount of silt it obtains from its tributaries, the more
winding its course becomes. This gain in those parts of the river's
curvings where deposition tends to take place may be accelerated by
tree-planting. Thus a skilful owner of a tract of land on the south
bank of the Ohio River, by assiduously planting willow trees on the
front of his property, gained in the course of thirty years more than
an acre in the width of his arable land. When told by the present
writer that he was robbing his neighbours on the other side of the
stream, he claimed that their ignorance of the laws of river motion
was sufficient evidence that they did not deserve to own land.

In the primitive state of a country the water-loving plants,
particularly the trees which flourish in excessively humid conditions,
generally make a certain defence against these incursions of the
streams. But when a river has gained an opening in the bank it can,
during a flood, extend its width often to the distance of hundreds of
feet. During the inundations of the Mississippi the river may at times
be seen to eat away acres of land in a single day along one of the
outcurves of its banks. The undermined forests falling into the flood
join the great procession of drift timber, composed of trees which
have been similarly uprooted, which occupies the middle part of the
stream. This driftwood belt often has a width of th