th scarcely any
apparent increase of its width, although here and there it expands to a
breadth of 1-1/2, or even to 2 miles. On arriving at New Orleans, it is
somewhat less than half a mile wide. Its depth there is very variable,
the greatest at high water being 168 feet. The mean rate at which the
whole body of water flows is variously estimated; according to Mr.
Forshey the mean velocity of the current at the surface, somewhat
exceeds 2-1/4 miles an hour when the water is at a mean height. For 300
miles above New Orleans the distance measured by the winding river is
about twice as great as the distance in a right line. For the first 100
miles from the mouth the rate of fall is 1.80 inch per mile, for the
second hundred 2 inches, for the third 2.30, for the fourth 2.57.

The alluvial plain of the Mississippi begins to be of great width below
Cape Girardeau, 50 miles above the junction of the Ohio. At this
junction it is about 50 miles broad, south of which it contracts to
about 30 miles at Memphis, expands again to 80 miles at the mouth of the
White River, and then, after various contractions and expansions,
protrudes beyond the general coast-line, in a large delta, about 90
miles in width, from N. E. to S. W. Mr. Forshey estimates the area of
the great plain as above defined at 31,200 square miles, with a
circumference of about 3000 miles, exceeding the area of Ireland. If
that part of this plain which lies below, or to the south of the
branching off of the highest arm, called the Atchafalaya, be termed the
delta, it constitutes less than half of the whole, being 14,000 square
British miles in area. The delta may be said to be bounded on the east,
west, and south by the sea; on the north chiefly by the broad
valley-plain which entirely resembles it in character as in origin. The
east and west boundaries of the alluvial region above the head of the
delta consists of cliffs or bluffs, which on the east side of the
Mississippi are very abrupt, and are undermined by the river at many
points. They consist, from Baton Rouge in Louisiana, where they
commence, as far north as the borders of Kentucky, of geological
formations newer than the cretaceous, the lowest being Eocene, and the
uppermost consisting of loam, resembling the loess of the Rhine, and
containing freshwater and land shells almost all of existing species.
(See fig. 23.) These recent shells are associated with the bones of the
mastodon, elephant, tapir, mylodon