sources of the Mississippi do not reach the Delta
before the beginning of August, about 100 days
after the breaking up of winter, and more than
a month after the inundation has been abating.
The average height of the floods, below the
mouth of the Missouri, is 15 feet. Erom the
Missouri to the Ohio it rises 25 feet, and for a
great distance below the mouth of the Ohio it
l'ises 50 feet. Before reaching Natchez, the height
of the floods begins to decline. At Baton Rouge
it seldom exceeds 30 feet, and at New Orleans
12. This gradual diminution in the flood, in the
lower part, has been supposed by some to result
from the draining through the numerous effluxes
of the river, conveying away such considerable
portions of its waters by separate channels to the
sea. So greatly does the quantity of snow and
rain differ in different years, that it is quite im-
possible, even for those who have had the longest
experience, to anticipate, with an approach to
certainty, the elevation which the flood will attain
in any given year. Some years the waters do
not rise above their channels, and no inundation
takes place. As the banks of the river in the
Delta, from the cause above noticed, are higher
than the general level of the country, constituting
an alluvial margin of from half a mile to a mile
and a half wide, it becomes important to protect
some of the more valuable tracts in the rear from
the annual overflow of the river, from which they
could not easily be drained. For this purpose
an artificial embankment has been raised at great
expense upon the margin of the river, called the
Levee. On the E. side this embankment com-
mences 60 miles above New Orleans, and extends
down the river more than 130 miles. On the W.
side it commences 172 miles above New Orleans.
The vast trade of the valley of the Mississippi
centres at New Orleans. Vessels are often from
5 to 30 days ascending the river to this port, un-
less they employ the steam tow-boats, though
they will often descend with a favorable wind in
12 hours. Before the introduction of steam-
boats it required 8 or 10 weeks to go to the mouth
of the Illinois. The use of steamboats has nearly
superseded all other vessels for ascending the
river. Boats of 40 tonS ascend more than 2000
miles, to the Falls of St. Anthony. The passage
from Cincinnati to New Orleans and back has
been made in 19 days. The first steamboat on
the western waters was built at Pittsburg in 1811,
and there are now over 300 on the Mississippi
and its tributaries, many of them of great bur-
den. By the opening of the Illinois Canal from
Chicago to the head of navigation in the Illinois
River, a connection has been formed between the
waters of the River St. Lawrence and the Mis-
sissippi, of sufficient draught to admit the passage
of small vessels, laden with their cargoes of mer-
chandise. Some time in the autumn of 1849, the
first vessel was reported at New Orleans as hav-
ing arrived from the St. Lawrence, via the Wel-
land Canal, the great lakes, the Illinois Canal
and River, and the Mississippi. Returning by
the Atlantic coast, she might then have circum-
navigated the United States.

Mississinewa River, la. and O. This river rises
in the N. W. part of Dark co., 0., flows N. W.
into la., and empties into the Wabash River in
Miami co.

Missouri River. The sources of this great
river take their rise in the Rocky Mts., and some
of their springs are within a mile of other springs
which discharge themselves W., through the Co-
lumbia River, into the Pacific Ocean. The three
principal streams which constitute the head
waters of the Missouri are the Jefferson, the
Madison, and the Gallatin, which unite at the
same point in lat. 45° 10' N., and Ion. 110° W.
From their confluence at this point, the river
takes the name Missouri, and flows onward,
receiving numerons tributaries in its course,
through a distance of more than 3000 miles, to
its junction with the Mississippi, in lat. 38° 51'
N., and Ion. 90° W. Its course is at first N.
and N. E., to the mouth of White Earth River,
lat. 47° 25'; thence S. E., about 220 miles, to the
Mandan villages, or Indian settlements. From
this point, the river takes a S. course, through a
distance of several hundred miles; and then,
being inflected more to the E., it pursues this
general direction to the Mississippi. Although it
loses its name at its confluence with the Missis-
sippi, it is, before it reaches this point, much the
longest and largest river of the two, and, phys-
ically considered, is entitled to be denominated
the principal, rather than the secondary. The
Missouri is already a very large river, when it
approaches and passes the sources of its very
inferior rival. If it be ranked according to
physical preeminence, as including the Missis-
sippi from its confluence with that river to its
mouth, it has an entire length of about 4350
miles, and is probably the longest river of the
earth. Ranking it as a secondary to the Missis-
sippi, and having reference to the area drained by
its channel, it is the largest river of that class in
the world. A direct line drawn along its valley,
from its junction with the Mississippi River to
the head of Maria's River, one of its most N. W.
sources, is nearly 1400 miles in extent, and the
width of the upper valley of the Missouri, as that
part is called which is above the confluence of
the Yellowstone, is not less than 600 miles across
the sources, and has a mean of 300 miles in the
general direction of the streams. The entire
valley, drained by the Missouri proper, includes
an area of 523,000 square miles, or a surface more
than double that of the whole Atlantic slope of
the United States. The upper valley of the Mis-
souri presents a surface, on the W. side, broken
by mountains, and gradually spreading into
plains, as the rivers descend in their courses.
The whole face of the country, with partial ex-
ceptions along the rivers, is open prairie, exhibit-
ing a strong resemblance to the steppes of Asia,
in nearly the same latitude. The surface of the
lower valley is also extensively occupied with
prairie, the alluvial and fertile soil on the rivers
not having a very great breadth. The first
large tributary of the Missouri is the Yellow-
stone. This river, 800 yards wide at its mouth,
and probably the largest tributary of the Mis-
souri, enters it on the S. W. side, about 1800
miles from its junction with the Mississippi.
The Yellowstone, at its junction, is as large as
the Missouri. Steamboats ascend to this point,
and can ascend farther by either branch. After
their junction, the united waters of the Yellow-
stone and Missouri form a river as large in
volume, and as wide and deep, probably, as at
its entrance into the Mississippi. Chienne River,
400 yards wide at its mouth, enters the Missouri
on the S. W. side, 1310 miles from its mouth:
White River, 300 yards wide, enters it on the
S. W. side, 1130 "miles from its mouth; Big