of the Mississippi begin.
It is not possible to give, with complete exactness, the outlines of the immense valley drained by the Mississippi, yet, with the assistance of accurate surveys, we can make an approximation, to say the least, which will convey some idea of the physical necessity of the river to the vast area through the centre of which it takes its course.
We will say:
Within this extensive limit we find, from surveys, the following aggregate area in square miles, estimated by valleys:
As a natural consequence of the drainage of this immense area, the Mississippi receives into its waters a large amount of suspended earthy matter. This, however, does not very strikingly appear on the upper river, its own banks and those of its tributaries being more of a gravelly character and less friable than lower down. The gravity of particles, therefore, worn from the bed and sides of the channel above, unless the current be exceedingly strong, is greater than the buoyant capacity of the water, and falls to the bottom, along which, sometimes, it is forced by the abrasion of the water, until it meets some obstruction, which gathers the particles into shoal formations. This fact causes much inconvenience in the navigation of the upper rivers.
It is not until we reach the confluence of the streams of Southern Illinois and Missouri, that the sediment of the river becomes striking. Those streams, freighted with the rich loam and vegetable matter of the prairies of the east and west, soon change entirely the appearance of the Mississippi. Above the Missouri, the river is but slightly tinged; and indeed, after that great current enters, for some distance the two run side by side in the same channel, and yet are divided by a very distinct line of demarcation. It is only after the frequent sinuosities of the channel, that the two waters are thrown into each other and fairly blend. The sedimentary condition of the Missouri is so great that drift floating upon its muddy surface, by accretion becomes so heavily laden with earthy matter that it sinks to the bottom. This precipitation of drift has taken place to such an extent, that the bed of the Missouri is in many places completely covered to a great depth by immense fields of logs. Of all the silt thrown into the Mississippi, the Missouri furnishes about one third.
After receiving the Missouri, next enters the Ohio. The water of this river is less impregnated than the Missouri, though not by any means free from silt. The country through which it flows is mountainous, and the soil hard, and does not afford the same facility of abrasive action as that of the other rivers.
From the mouth of the Ohio, the Mississippi pursues a course of nearly four hundred miles, when it receives the turbid waters of the White and Arkansas Rivers. In the intervening distance a large number of small currents, more or less largely sedimentary, according to the character of the country through which they run, enter the Mississippi, in the aggregate adding materially to the sediment of the receiving stream. The White and Arkansas carry in their waters a large amount of unprecipitated matter. In this vicinity, too, sets in that singular system of natural safeguards of the surrounding country, the bayous. The country here also changes its appearance, becoming flat and swampy, and in some parts attaining but a few feet above the flood of the river, whereas in other parts, as we approach the Gulf, the country is even lower than the river.
The miasmatic and poisonous water of the Yazoo next enters, about ten miles above Vicksburg. This river is more deeply impregnated with a certain kind of impurities than any other tributary of the Mississippi. The waters are green and slimy, and almost sticky with vegetable and animal decomposition. During the hot season the water is certain disease, if taken into the stomach. The name is of Indian origin, and signifies 'River of Death.' The Yazoo receives its supply from bayous and swamps, though it has several considerable tributaries.
Below the Yazoo, on the west side, enters the Red. The name indicates the peculiar caste of its water. This river carries with it the washings of an extensive area of prairies and swamps, and is the last of the great tributaries. Hence the tendency of streams is directly to the Gulf, and that network of lateral branches, of which we will hereafter speak, begins.
We have only considered the most prominent tributaries: the sediment also brought down by the numerous smaller streams is very great, and makes great additions to the immense buoyant matter of the Mississippi.
The river itself from its own banks scours the larger portion of the sediment it contains; and in so gigantic a scale is this carried on, that it can be seen without the exercise of any very remarkable powers of sight. It is not by the imperceptible degrees usually at work in other streams, but often involves in its execution many acres of adjoining land. It will be interesting to consider this more fully.
By a curious freak of nature, the tendency of the channel of the Mississippi is always toward one or the other of its banks, being influenced by the direction of its bends. The principle is one of nicely regulated refraction. If the river were perfectly straight, the gravity and inertia of its waters would move in a right line, with a velocity beyond all control. But we find the river very sinuous, and the momentum of current consequently lessened. For example, striking in an arm of the river, by the inertia of the moving volume, the water is thrown, and with less velocity, upon the opposite bank, which it pursues until it meets another repellent obstacle, from which it refracts, taking direction again for the other side. Above the Missouri, the river is principally directed by the natural trough of the valley. Below this, however, the channel is purely the work of the river itself, shaped according to the necessities of sudden changes or obstructions. This is proven by the large number of old and dry beds of the river frequently met with, the channel having been diverted in a new direction by the accumulation of sediment and drift which it had not the momentum to force out.
Where the gravity of the greatest volume and momentum of water falls upon the bed of the river, there is described the thread of the channel, and all submerged space outside of this, though in the river, acts as a kind of reservoir, where eddies the surplus water until taken up by the current. And it always happens, where the channel takes one bend of the bed, a corresponding tongue of shallow water faces the indenture. Where the river, by some inexplicable cause, has been thrown from its regular channel, or its volume of water embarrassed by some difficulties along the banks, the effect is immediately perceived upon the neighboring bank. The column of water thus impinged against it at once acts upon the bank, and, singularly enough, exerts its strongest abrasive action at the bottom, undermining the bank, which soon gives way, and instead of toppling forward, it noiselessly slides beneath the water and disappears. Acres of land have thus been carried away in an incredibly short time, and without the slightest disruption of the serene flow of the mighty current.
This carrying away of the banks, immense as is the amount of earth thrown into the waters of the river, has no sensible effect in blocking or directing the current, though it imperceptibly raises the channel. The force of the water does not permit its entire settlement in quantities at any one place, but distributes it along the bottom and shores below. Were this not the case, it is easily to be seen, the abrasion of the river banks would be greatly increased, and the destruction of the bordering lands immense.
A singular feature resulting from the above may here be mentioned. By pursuing the course of the river, a short distance below, on the opposite bank, it will be seen that a large quantity of the earth introduced into the current by the falling of the banks, has been thrown up in large masses, forming new land, which, in a few seasons, becomes arable. That which is not thus deposited, as already stated, is transported below, dropping here and there on the way, until what is left reaches the Gulf, and is precipitated upon the 'bars' and 'delta,' at the mouth. It not unfrequently happens that planters along the river find themselves suddenly deprived of some of their acres, while one almost opposite finds himself as unexpectedly blessed with a bountiful increase of his domain.
From causes almost similar to those given to explain the sudden and disastrous changes of the channel of the river, are also produced those singular shortenings, known as 'cut-offs,' which are so frequently met with on the Mississippi. At a certain point the force of the current is turned out of its path and impinged against a neck of land, that has, after years of resistance, been worn down to an exceedingly small breadth. Possibly the river has merely worn an arm in its side, leaving an extensive bulge