Continental Monthly , Vol. 5, No. 6, June, 1864 / Devoted to Literature and National Policy

by Various

2. Salt water, beneath the fresh, also running out at about the same velocity.

3. A reflex flow of salt water, running in slowly at the bottom.

It is this inward current, he thinks, that produces the deposit, and in doing so carries with it no small degree of sea drift. The influx of the lower column flowing up stream, after it passes the dead point, is allowed time and opportunity for the sediment to deposit. The principle of the reflex current is somewhat that of an eddy, not only produced by the conflict of two opposing bodies of water, but also is much influenced in the under currents by the multitude of estuaries presented by the irregular sea front of the coast.

A gentleman, who seems to have taken a very statistical view of these bars, makes the following business-like and curious calculation as to their immensity: we introduce it on account of its originality. He says the average quantity of water discharged per second is five hundred and ten thousand cubic feet. The quantity of salt suspended, one in three thousand by volume. The quantity of mud discharged, one hundred and seventy cubic feet per second. Considering seventeen cubic feet equal to one ton, the daily discharge of mud is eight hundred and sixty-four thousand tons, and would require a fleet of seventeen hundred and twenty-eight ships, of five hundred tons each, to transport the average daily discharge. And to lift this immense quantity of matter, it would require about seven hundred and seventy-one dredging machines, sixteen horse power, with a capacity of labor amounting to one hundred and forty tons, working eight hours.

Another class of sedimentary formations met with along the banks of the Mississippi are the battures. There is one remarkable instance of these in front of New Orleans, which has led to much private dispute, and even public disturbance, as to ownership. Within sixty years, in front of the Second Municipality of the city, the amount of alluvial formations susceptible of private ownership were worth over five millions of dollars, that is, nearly one hundred thousand dollars per annum, and the causes which have produced them are still at work, and will probably remain so. As far back as 1847 these remarks were made upon the subject: 'The value of the annual alluvial deposits in front of the Second Municipality now is not less than two hundred thousand dollars, and, with the exception of the batture between the Faubourg St. Mary line and Lacourse street, all belongs to this municipality.' 'Such a source of wealth was never possessed by any city before. In truth, it may be said that nature is our taxgatherer, levying by her immutable laws tribute from the banks of rivers and from the summits of mountains thousands of miles distant to enrich, improve, and adorn our favored city.' There are numerous other examples of the kind going on elsewhere along the river.

But the greatest exhibition of the wonderful character of the Mississippi, and in which all its singular effects are most distinctly shown, is in its Delta. For a long succession of years the immense quantities of sediment, of which we have already spoken, had gradually precipitated upon this portion of the river until it reached the surface. Drift now lodged upon it: the decomposition of drift and the accumulation of other vegetable matter soon furnished a suitable bed for the growth of a marine vegetation, and now a vast area, a level expanse of waste land and marsh, is seen extending a great distance into the Gulf, ramified here and there by the outlets of the river. Indeed, so rapid have been these formations, that upon the testimony of history, the Mississippi River to-day is twenty-nine miles farther in the Gulf than it was in 1754.

Mr. Forshey, an engineer, remarks that 'the superficial area of the true Delta formation of the Mississippi, or below Baton Rouge, where the last bluffs are found, is about fifteen thousand square miles, constituting a region of mean width seventy-five miles, and mean length two hundred miles. Probable depth of alluvion is about one fifth of a mile, by inference from the depth of the Gulf of Mexico.' In the vicinity of New Orleans, boring to a depth of two hundred feet, fossils, such as shells, bones, etc., have been found. And at thirty feet specimens of pottery and other evidences of Indian habitation have been discovered. The foundation upon which rest the alluvial formations has been found to consist of a hard blue silicious clay, closely resembling that met with in the bed of the Mississippi. The most recent of the alluvial fields of the Delta have been constituted a parish, termed Plaquemine. In 1800, according to one authority, there were but very few acres in cultivation in the entire parish. Since leveeing above, the deposit has been extremely rapid, until now we find some excellent plantations in Plaquemine. Fifty miles below New Orleans the tillable land is nearly a mile in width; below there, it becomes gradually less, until it is lost in the Gulf. Still the accumulations are going on, and it is impossible even to surmise what changes the great river may yet effect in the future geography of this section of the American continent.

Considering the multitude of streams and vastness of area drained by the Mississippi, it is natural to suppose the river is much affected in the stage of its water by the seasons. We have seen that the meltings of the Rocky Mountain snows, the mountain rills of the Alleghanies, the waters of the valleys of the upper river, of the Missouri, of the Ohio, the Arkansas, the Yazoo, and the Red, all find outlet through this one stream. There are certain seasons in the year when all these widely distant localities are subject to a gradual approach of warmth from the south, until they arrive at a sort of climatic average. This creates a maximum of the supply of water. The inverse then takes place, and a minimum results. For instance, in the latter part of December, the lower latitudes of the Mississippi begin to experience their annual rains. These by degrees tend northward as the season advances. In March commence the thaws of the southern borders of the zone of snow and ice; and during April, May, and June, it reaches to the most distant tributary fountain head. The river now is at its highest. The reverse then sets in. All the tributaries have their excess, the heats of summer are at hand, drought and evaporation soon exhaust the surplus of the streams, and the river is at its lowest.

To meet the great annual excess of water in the Mississippi, nature has provided sure safeguards. These are termed bayous, and are found everywhere along the river, below the mouth of the Ohio. Additional preventives against inundation are the lagoons, or sea-water lakes, of the coast. Into these bayous and lagoons, as the river becomes high, the excess of water backs or flows. They are natural reservoirs, to ease the rise, and prevent the inevitable suddenness and danger which would result without them. In these reservoirs the water rises or falls with the river; and when the fall becomes permanent, the water in the bayous—the lagoons having outlet into the sea—falls with it, returning into the main stream, and finding entrance into the Gulf, from which it had been temporarily detained. Without the bayous the lands adjacent to the Lower Mississippi would, with very few exceptions, be subject to an annual overflow, and be perfectly worthless for certain agricultural purposes. In summer the bayous in numerous instances become perfectly dry, and give a very singular effect to the appearance of the country.

Below the mouth of the Red River the tributaries of the Mississippi cease, and the entire volume of the river is attained. As a protection against serious consequences arising out of such an immense mass of water, nature has again introduced a remedy. This consists in a number of lateral branches, which leave the river a short distance below the mouth of the Red, tending directly to the Gulf, through a continuous chain of conduits, lakes, and marshes.