nature of the rocks over which it flows. Will a stream deepen its
channel more rapidly on massive or on thin-bedded and close-
jointed rocks? on horizontal strata or on strata steeply inclined?

DEPOSITION

While the river carries its invisible load of dissolved rock on
without stop to the sea, its load of visible waste is subject to
many delays en route. Now and again it is laid aside, to be picked
up later and carried some distance farther on its way. One of the
most striking features of the river therefore is the waste
accumulated along its course, in bars and islands in the channel,
beneath its bed, and in flood plains along its banks. All this
alluvium, to use a general term for river deposits, with which the
valley is cumbered is really en route to the sea; it is only
temporarily laid aside to resume its journey later on. Constantly
the river is destroying and rebuilding its alluvial deposits, here
cutting and there depositing along its banks, here eroding and
there building a bar, here excavating its bed and there filling it
up, and at all times carrying the material picked up at one point
some distance on downstream before depositing it at another.

These deposits are laid down by slackening currents where the
velocity of the stream is checked, as on the inner side of curves,
and where the slope of the bed is diminished, and in the lee of
islands, bridge piers and projecting points of land. How slight is
the check required to cause a current to drop a large part of its
load may be inferred from the law of the relation of the
transporting power to the velocity. If the velocity is decreased
one half, the current can move fragments but one sixty-fourth the