Chapter 5

1846. ft. in. ° A. B. May 21 10 11 72 6.66 7.00 " 25 10 11 73 9.08 9.12 " 27 10 10 78 7.80 9.00 " 29 11 0 74 7.30 8.10 June 2 11 1 75 4.80 5.45 " 4 11 1 75 7.87 6.10 " 6 11 4 75 4.60 4.90 " 8 11 4 75.5 5.48 5.60 " 10 10 4 76 6.70 6.80 " 12 10 8 76 6.50 6.30 " 14 10 5 76.5 6.00 6.00 " 16 10 4 76.5 6.47 6.15 " 20 10 4 77 7.08 7.40 " 22 10 2 77 9.88 9.00 " 24 9 8 77 8.40 8.48 " 26 8 9 77.5 8.25 8.78 " 28 8 0 79 9.10 9.58 July 1 7 2 79.5 9.15 9.25 July 3 7 2 79.5 9.63 10.00 " 6 6 2 81 8.20 7.57 " 8 6 0 81 7.30 6.96 " 10 6 1 81 6.12 6.28 " 13 5 9 82 7.72 7.30 " 15 5 10 82 6.67 6.60 " 17 5 10 82 4.45 4.57 " 20 5 4 82 6.07 5.75 " 24 3 10 84 5.76 5.72 " 27 3 1 84 4.77 4.60 " 29 3 11 84.5 4.28 4.13 Aug. 1 2 6 85 4.40 4.44 " 3 2 0 84 3.18 3.34 " 5 1 9 83 3.56 3.40 " 7 1 5 83 2.85 2.85 " 10 1 6 83 3.03 2.92 " 13 2 8 84 2.97 3.00

The mean average of column A. is 6.32. " " " " " B. is 6.30.

Transcriber's note: This table has been reproduced exactly as in the original.

'By comparison with distilled water,' says the same, 'the specific gravity of the filtered river water we found to be 1.823; pint of such water at 60° weighs 7,297.40.' Engineer Forehay says the sediment is 1 to 1,800 by weight, or 1 in 3,000 by volume.

Professor Riddell also comes to the following conclusions, after an analytic investigation of the sediment. He took one hundred grains from the river margin, dried it at 212° Fahrenheit, before weighing, and found it to contain:

_Grains._

Silica, 74.15 Alumina, 9.14 Oxide of iron, 4.56 Lime, 2.08 Magnesia, 1.52 Manganese, 0.04 Potassa,} not determined Soda, } Phosphoric acid, 0.44 Sulphuric acid, 0.07 Carbonic acid, 0.74 Chlorine, 0.01 Water, 3.12 Organic matter, 3.10 ----- Total, 98.97

The existence of so large a quantity of sediment in the water of the Mississippi, leads to divers formations in its bed. These formations are principally 'bars' and 'battures.' The banks are also much affected.

When the water of the river, aided by the current, has attained its full capacity of buoyant earth, as we have already said, the excess falls to the bottom. Instead, however, of remaining permanently where it first lodged, which would soon fill up the channel and cause the river to overflow, the scouring of the water on the bottom forces a large portion along with the current, though it be not suspended. Pursuing its course for a while, some irregularity or obstruction falls in the way--a sunken log, perhaps. This obstacle checks the progress of the moving earth--it accumulates; the next wave brings down more--the accumulation becomes greater; until, in the course of a few years, there is a vast field of deposit, and a 'bar' is formed. These 'bars' often divert the channel, and occasion the immense washings before alluded to.

Bars are generally found close to the banks, though there are examples in which they extend in a transverse direction to the current. Bars of this kind very much embarrass and endanger navigation in low water. At Helena, Arkansas, there is an instance of a transverse bar, upon which, in October, the water is less than six feet. These bars are formed of sand, which seems to have been the heavier and less buoyant of the components of the earth thrown into the current by abrasion, the lighter portions having been separated by the water and carried off.

It will not be necessary to consider further the subject of bars in the river, but those at its mouth deserve some attention. The subject is one that has led to much theorizing, study, and fear--the latter particularly, from an ill-founded supposition that they threaten to cut off navigation into the Gulf.

Near its entrance into the Gulf, the Mississippi distributes its waters through five outlets, termed passes, and consequently has as many mouths. These are termed Pass à l'Outre, Northeast, Southeast, South, and Southwest. They differ in length, ranging from three to nine miles. They also all afford sufficient depth of water for commercial purposes, except at their mouths, which are obstructed by bars. The depth of water upon one of these is sufficient to pass large vessels; a second, vessels of less size; and the rest are not navigable at all, as regards sea-going vessels. These bars, too, are continually changing, according to the winds or the currents of the river. It is a rather singular fact that when one of the navigable passes becomes blocked, the river is certain to force a channel of navigable depth through one of the others, previously not in use; so that at no one time are all the passes closed.

In looking into the past, and noticing the changes, it is recorded that in 1720, of all the passes the South Pass was the only one navigable. In 1730, there was a depth of from twelve to fifteen feet, according to the winds, and at another time even seventeen feet was known. In 1804, upon the statement of Major Stoddard, written at that date, the East Pass, called the Balize, had then about seventeen feet of water on the bar, and was the one usually navigated. The South Pass was formerly of equal depth, but was then gradually filling up. (This pass, at present, 1864, is not at all navigated.) The Southwest Pass had from eleven to twelve feet of water. The Northeast and Southeast Passes were traversed only by small craft. Since 1830 the Southwest Pass has been gaining depth. This and Pass à l'Outre are now the only two out of the five of sufficient depth to admit the crossing of the larger class of vessels. The former, however, is the one in most general use. All the other passes, with the exception of the two mentioned, have been abandoned.

In regard to the changes and numerous singular formations at the mouths of the Mississippi, we give a statement made by William Talbot, for twenty-five years a resident of the Balize. He says:

'The bars at the various passes change very often. The channel sometimes changes two and three times in a season. Occasionally one gale of wind will change the channel. The bars make to the seaward every year. The Southwest Pass is now the main outlet used. It has been so only for three years, as at that time there was as much water in the Northeast Pass as in it. The Southeast Pass was the main ship channel twenty years ago; there is only about six feet of water in that pass now; and where it was deepest then, there are only a few inches of water at this time. The visible shores of the river have made out into the Gulf two or three miles within my memory. Besides the deposits of mud and sand, which form the bars, there frequently rise up bumps, or mounds, near the channel, which divert its course. These bumps are supposed to be the production of salt springs, and sometimes are formed in a very few days. They sometimes rise four or five feet above the surface of the water.' He 'knew one instance when some bricks, that were thrown overboard from a vessel outside the bar, in three fathoms of water, were raised above the surface by one of these banks, and were taken to the Balize, and used in building chimneys. In another instance, an anchor, which was lost from a vessel, was lifted out of the water, so that it was taken ashore. About twenty years ago, a sloop, used as a lighter, was lost outside the bar in a gale of wind; several years afterward she was raised by one of these strange formations, and her cargo was taken out of her.'

We may say the bumps of which Mr. Talbot speaks are termed 'mud bumps,' from the fact of being composed of sediment. They present a curious spectacle as seen from a passing steamer. They are undoubtedly the result of subterranean pressure, but from what cause, whether volcanic, or the influence of the sea or river, or both, has not been determined. Many speculations have been entered into in regard to these phenomena, but as yet without fruitful result.

Leaving this digression, we proceed to notice that the theories set up to explain the causes of the bars at the mouth of the river, have been numerous and various. Some suppose them to be the result of the water of the river meeting the opposing force of the Gulf waves, checking the current, and causing a precipitation of the suspended sediment. Others are of the opinion that the bars are entirely the effect of marine action, and endeavor to show that the immense inward flow of the Gulf washes up from its bed the vast accumulations that are continually forming in the way of navigation.

After a personal observation and investigation, and as well after frequent and free consultation with others, we are persuaded to discredit the above-mentioned theories. The resistance of the Gulf does not form the bars, though it exerts an influence. The immense volume and force of water ejected from the river receives no immediate repellent action from the Gulf, but extends into it many miles without the least signs of disturbance, as may be plainly discovered even in the most casual observation. It is known as well that the water of the river remains perfectly palatable at a very close proximity to the sea. This is a very good evidence of the superior force of the river's current. The two volumes of water mix a considerable distance out at sea.

An able engineer states that, upon examination, he found a column of fresh water seven feet deep and seven thousand feet wide, and discovered salt water at eight feet below the surface. As the result of his investigations, he divides the water into three strata, as follows:

1. Fresh water, running out at the top with a velocity of three miles an hour.

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.

The principal bayous, which exert so important a part in regulating the stage of this part of the river, are in length and distance from the Gulf as follows:

_Distance By River._ _Miles._ _Miles._

Bayou La Fourche, from the Mississippi River to the Gulf, 100 180 " Plaquemine, " " " 60 210 " Manchac, " " " 50 220 " Atchafalaya, " " " 110 300

The course of the bayous, it will be seen, have a more direct route than the river. Their average width is one thousand feet, and fall twenty-two feet. Their average velocity is about three and two tenths miles per hour. Though the rise of the river at Baton Rouge sometimes attains a height of thirty feet, so great is the relieving capacity of these lateral branches, that at New Orleans the rise never exceeds twelve feet. At Point à la Hache the difference between the highest and lowest stage is but six feet; at Fort Jackson, four feet, while it falls to low water mark when it enters the sea.

Having briefly noted the peculiarities of the Mississippi, a few facts in recapitulation may place it in a more comprehensive attitude as regards its appearance and size. In the north, after leaving the Falls of St. Anthony, the river has but the characteristics of a single stream, but below the Ohio we find it combines the peculiarities of a number. The water here begins to show signs of almost a new nature and greater density. The river develops into a much wider channel, and its peculiarities become more marked and impressive.

Strange as it may seem, the greatest mean width of the Lower Mississippi is at the confluence of the Ohio, and from this point it gradually becomes narrower, until it is but little more than half that width as it draws near the Gulf. This gives the river a kind of funnel shape, and if it were not for the numerous bayous and lateral branches, which we have explained, the most violent convulsion and devastation would arise. In the United States Engineer Reports we find this statement:

The mean width of the Mississippi River between the Ohio _Feet._ and Arkansas Rivers, 4,500

Mean width between the Arkansas and Red Rivers, 4,100

Mean width between the Red River and Donaldsonville, 3,000

Mean width between Donaldsonville and the Gulf, 2,500

Above the Red River the range between high and low water is about forty-five feet, and thence to the Gulf it gradually diminishes to zero.

The greatest velocity of current is about five and a half miles per hour during floods, and about one and a half miles per hour during low water.

The river is above mean height from January to July, and below from August to December. The greatest height is attained from March to June, and the lowest from October to November.

The mud of the Mississippi is very yielding, insomuch that an allowance of several feet is often made where the draught of a vessel exceeds the clear depth of the water. We have heard of cases where steamers have ploughed successfully through four feet of it.

It is singular, too, and exhibits still more clearly what we have said of deposits, that the lower river for the most part runs along the summit of a ridge of its own formation, and annually this ridge is becoming more elevated. The inland deposits are made by the bayous and their overflow. The lands close to the river are disproportionately higher than those farther back. The average distance from the river to the swamp is about two and a half miles. And the slope in some places sinks to a depression of eighteen feet to a mile. It is upon this strip of tillable earth that the river plantations are located. By a system of drainage even much of the swamp lands now unconverted might soon be turned to profitable use.

The numerous islands and old channels of the Mississippi are also another source of wonder to the traveller. The 'cut offs,' previously explained, are mainly the cause of both. In the first instance, the river forces its way by a new route, and joins the river below; this necessarily detaches a certain amount of land from the main shore. As for the second, after the river has taken this new route, its main abrasive action follows with it. The water in the old channel becomes comparatively quiet, sediment is rapidly deposited, and in course of time the old bed loses its identity, or becomes a beautiful lake, numerous instances of which occur between the Ohio and the Red Rivers.