, horse, ox, and other quadrupeds,
most of them of extinct species.

I have endeavored to show in my Second Visit to the United States, that
this extensive formation of loam is either an ancient alluvial plain or
a delta of the great river, formed originally at a lower level, and
since upheaved, and partially denuded.

[Illustration: Fig. 23.

VALLEY OF THE MISSISSIPPI.]

The Mississippi in that part of its course which is below the mouth of
the Ohio, frequently washes the eastern bluffs, but never once comes in
contact with the western. These are composed of similar formations; but
I learn from Mr. Forshey that they rise up more gently from the alluvial
plain (as at _a_, fig. 23). It is supposed that the waters are thrown to
the eastern side, because all the large tributary rivers entering from
the west have filled that side of the great valley with their deltas, or
with a sloping mass of clay and sand; so that the opposite bluffs are
undermined, and the Mississippi is slowly but incessantly advancing
eastward.[357]

_Curves of the Mississippi._--The river traverses the plain in a
meandering course, describing immense curves. After sweeping round the
half of a circle, it is carried in a rapid current diagonally across the
ordinary direction of its channel, to another curve of similar shape.
Opposite to each of these, there is always a sand-bar, answering, in the
convexity of its form, to the concavity of "the bend," as it is
called.[358] The river, by continually wearing these curves deep,
returns, like many other streams before described, on its own track, so
that a vessel in some places, after sailing for twenty-five or thirty
miles, is brought round again to within a mile of the place whence it
started. When the waters approach so near to each other, it often
happens at high floods that they burst through the small tongue of
land, and insulate a portion, rushing through what is called the
"cut-off," so that vessels may pass from one point to another in half a
mile to a distance which it previously required a voyage of twenty miles
to reach. As soon as the river has excavated the new passage, bars of
sand and mud are formed at the two points of junction with the old bend,
which is soon entirely separated from the main river by a continuous
mud-bank covered with wood. The old bend then becomes a semicircular
lake of clear water, inhabited by large gar-fish, alligators, and wild
fowl, which the steam-boats have n