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great length. It is certainly much more in accordance with the facts to consider the great lakes as so many connected reservoirs of which the St. Lawrence is the final outlet.

This river is an immense stream, about 700 miles in length, and expanding near its mouth into an estuary 100 miles wide. If we consider the chain of the great lakes as forming a part of the river, its length reaches 2,000 miles. About one-third of the amount of water passes to the Atlantic through the channel of the St. Lawrence that reaches the gulf of Mexico through the channel of the Mississippi. It has a basin whose area is about 298,000 square miles, nearly one-third of it being covered with water.* Rapids in the river above Montreal obstruct navigation, and for four months in the year it is completely closed by ice.

The level of rivers is subject to changes which are either regular or irregular. The former are diurnal, semi-annual, and annual. The daily change is caused by the tides which flow up a river sometimes to a great distance. The yearly and half-yearly changes occur in rivers situated within the tropical regions, and are the effects of the heavy rains which take place during the wet seasons in those parts of the earth. The irregular changes arise from casual heavy rain-falls which produce floods in streams otherwise insignificant, and to other temporary causes, such as heavy winds blowing up a river, which retard the downward progress of the water. A strong easterly wind will raise the level of the St. Lawrence, though it is scarcely affected by rain or drouth. This is doubtless owing to the fact that so large a part of its basin is covered with water, and the great lakes serve as reservoirs to retain it, while the water finds some difficulty in passing out rapidly. It necessarily passes very slowly through the great lakes.

The Mississippi, the “Father of Waters," is the great river of North America. It rises on the southern portion of

Somerville's Phys. Geog., p. 246.

the table-land at a height of only 1,500 feet above the level of the gulf of Mexico. It flows from north to south through more degrees of latitude than any other, and over a space of nearly 1,400 miles. Whether the Mississippi runs up hill or not is a question that has sometimes been discussed even by good scholars. We know that in the ordinary sense of the term it cannot; but its mouth is actually about two and onehalf miles further from the center of the earth than its source, owing to the spheroidal form of the globe. But up and down are only relative terms, the former meaning above the level of the surface of equilibrium, and the latter below it. The source of the Mississippi is 1,500 feet above this level.*

The tributaries of the Mississippi are very numerous, and some of them very large. The Missouri, the Ohio, the Arkansas, and the Red are all of them rivers of the first order. The Mississippi is navigable for 2,000 miles up to the Falls of St. Anthony. The Missouri is much superior to the Mississippi in magnitude where it enters it. The Missouri is rather turbulent and muddy, and its volume of water is so great that it impresses its own character on the Mississippi after the junction. Temporary sand islands form in the former, and the channel is continually changing, so that boats are piloted through it with some difficulty. The Missouri is navigable up to the great falls at the base of the Rocky mountains. The length of the Mississippi is about 2,400 miles, and that of the Missouri about the same; but from the source of the latter to the gulf of Mexico is 3,700 miles, giving by about 200 miles the longest river in the world. The meanderings of these rivers, or the difference between the direct distance from sources to mouths and the actual distance through the channels of the rivers, is estimated at about 2,000 miles.

See, on this subject, the Annual of Scientific Discovery for 1857, pp. 179-82, where there is some account of a discussion of this question by Horace Mann and Professor Lovering, owing to the former stating that the centrifugal force resulting from the earth's rotation could not produce such a result as actually takes place in the Mississippi.

Chambers' Encyclopedia, vol. vii., p. 274.

The breadth of the Mississippi nowhere corresponds with its length. At its confluence with the Missouri it is about threequarters of a mile, and it remains the same after it receives the waters of the Ohio. A steamer may ascend it from Balize for a distance of about 2,000 miles without any perceptible difference in its width. At its mouth it is 168 feet deep. The river is very rapid, and carries down an immense amount of mud; and its violent floods, caused by the melting of snow in the higher latitudes, sweep away whole forests, by which the navigation is rendered very dangerous. The trees, and whatever else may be attached to them, are carried down and deposited over the delta at the mouth, and over the gulf of Mexico for many hundreds of square miles around.

It is in this way that geologists suppose the material from which coal beds were formed to have been formed, only the facts seem to require that the deposits be made in peat swamps which existed at the mouths of large rivers. We are to look for analogies, says Professor Le Conte, “among the river swamps of the Mississippi.” Such peat swamps exist—some of them of great extent-at this time on the margin and in the delta of the Mississippi. According to Mr. Lyell, the peat swamps of the Mississippi, although annually flooded by the river water, are entirely untouched by the river mud. The reason of this is, that those spots are surrounded, particularly on the sides next the river, by dense vegetation, which acts as a sieve to strain the water of its mud before it reaches the peat swamp. “The water of these swamps is therefore pure; pure peat has been quietly depositing there for ages."*

Mr. Lyell observes that “the prodigious quantity of wood annually drifted down by the Mississippi and its tributaries is a subject of geological interest, not merely as illustrating the manner in which abundance of vegetable matter becomes, in the ordinary course of nature, imbedded in submarine and estuary deposits, but as attesting the constant destruction of

* See Smithsonian Report for 1857, p. 136.

soil and transportation of matter to lower levels by the tendency of rivers to shift their courses. Each of these trees must have required many years, some of them many centuries, to attain their full size; the soil, therefore, whereon they grew, after remaining undisturbed for long periods, is ultimately torn up and swept away."* It has been calculated that this mean annual amount of solid matter brought down by the waters of the Mississippi is about one three thousandth of its volume, being equal to about 37,000 million cubic feet, which would cover over eleven square miles one foot deep.

The mean descent of this great river is little more than one foot in a mile. This is sufficient, if there were no friction, to give it a velocity of eight feet in a second, supposing it uniform at the end of the first mile. Its actual velocity is much less than this.

The hydraulics of rivers, until a very recent period, were in a very imperfect state. In 1851 a survey of the Mississippi was undertaken, but after a suspension for some years it was resumed in 1858, and carried to its completion. The magnitude of this great river, it is evident, renders it a very suitable stream to test the mainly hypothetical laws and formula which have heretofore been supposed sufficient for river hydraulics. But its power has heretofore set at naught all arbitrary laws. “Lesser streams, in their occasional outbursts of disobedience, when they roar defiance at the artificial laws set up to govern their behavior, though they may embarrass and annoy, yet, from their inferior force and volume, fail so utterly to astound the unhappy engineer whom they set at naught, as this monster, the Mississippi.”

The labors of the eminent engineers who have submitted this report have entirely revolutionized, “if in fact they may

Lyell & Principles of Geology, vol. ii., pp. 183-4.

| Report upon the Physics and Hydraulics of the Mississippi River ; upon the Protection of the Alluvial Regions against Overflow ; and upon the Deepening of the Mouths. By Capt. A. A. HUMPHREYs and Lieut. H. L. ABBOT. Submitted to the Bureau of Topographical Engineers, War Department, 1861. 4to., pp. 456 and cxlvi.

not,” says Professor J. A. P. Barnard, "probably be said to have created it."* We here give a few of the results to which observation has led, as condensed from the report by Professor Barnard :

“In a uniformly flowing stream, the maximum velocity of the water in any vertical plane parallel to the current is not found at the surface, but at a point situated a little more than three-tenths of the depths below the surface. • “To whatever cause it may be owing, there is a resistance to the flow of water at the surface similar in kind to that which takes place at the bottom, though usually less in degree. The resistance is propagated downward, according to a law of diminution similar to that with which the resistance at the bottom is propagated upward.”+

There are several other propositions given, but we need not reproduce them here. Measurements of the daily discharge of the river were made for twelve months at Carrollton, Louisiana, for eleven months at Columbus, Kentucky, for ten months at Vicksburg, and for a month and a half at Natchez. Similar observations were made upon other rivers. We need only state further, in relation to the matter, that the results are of the most important character, and will serve as a basis for extending our knowledge of river hydraulics for all future time. The laws which control the water of the “ Father of Waters ” must control that of all other rivers, local causes excepted. With respect to running water we may here notice this fact, which is well exemplified in the Mississippi, namely, that the volume of water does not seem to be increased by receiving the water of other and even larger rivers. The reason is that the momentum of the greater body of water carries it forward with increased rapidity, by enabling it to overcome resistances with greater facility.

If North America possesses the longest river—the Missouri and the Mississippi—South America has the largest one on the globe. The Amazon rises in Peru, and drains the chain of • Silliman's Jour., vol. xxxvi, p. 16.

+ Ibid, p. 21. For further information respecting the Mississippi, about the mouth and the delta, see Coast Survey Reports for 1851, 1852, and 1857. See also Jefferson's Notes on Virginia for a sketch of the river as then known.

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