has laid down;" and
in like manner the Mississippi, by the continual shifting of its course,
sweeps away, during a great portion of the year, considerable tracts of
alluvium, which were gradually accumulated by the overflow of former
years, and the matter now left during the spring-floods will be at some
future time removed. After the flood season, when the river subsides
within its channel, it acts with destructive force upon the alluvial
banks, softened and diluted by the recent overflow. Several acres at a
time, thickly covered with wood, are precipitated into the stream; and
large portions of the islands are frequently swept away.

"Some years ago," observes Captain Hall, "when the Mississippi was
regularly surveyed, all its islands were numbered, from the confluence
of the Missouri to the sea; but every season makes such revolutions, not
only in the number, but in the magnitude and situation of these islands,
that this enumeration is now almost obsolete. Sometimes large islands
are entirely melted away; at other places they have attached themselves
to the main shore, or, which is the more correct statement, the interval
has been filled up by myriads of logs cemented together by mud and
rubbish."[359]

_Rafts._--One of the most interesting features in the great rivers of
this part of America is the frequent accumulation of what are termed
"rafts," or masses of floating trees, which have been arrested in their
progress by snags, islands, shoals, or other obstructions, and made to
accumulate, so as to form natural bridges, reaching entirely across the
stream. One of the largest of these was called the raft of the
Atchafalaya, an arm of the Mississippi, which was certainly at some
former time the channel of the Red River, when the latter found its way
to the Gulf of Mexico by a separate course. The Atchafalaya being in a
direct line with the general direction of the Mississippi, catches a
large portion of the timber annually brought down from the north; and
the drift-trees collected in about thirty-eight years previous to 1816
formed a continuous raft, no less than ten miles in length, 220 yards
wide, and eight feet deep. The whole rose and fell with the water, yet
was covered with green bushes and trees, and its surface enlivened in
the autumn by a variety of beautiful flowers. It went on increasing till
about 1835, when some of the trees upon it had grown to the height of
about sixty feet. Steps were then taken by