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h.River Amite. U. Atchafalaya Bay.
/. I. River Tangipao. V. Baratatia Bay.
m. m. Pearl River. W. Fausse Riviere, an old channel ol
n. Lake Maurepas. the Mississippi, now a lake.
o. Lake Ponchartrain. x. The Passage of Manchac, connect
p. Lake Borgne, a bay of the Gulf of ing Lake Maurepas with I.ake Pon
Q. Chctimache, or Grand Lake. The Rigolets, or passages connect
r. Quacha Lake. ing Lake Ponchartrain with Lake
S. Vermillion Bay. 'Borgne.
This plan, which exhibits the course of the Mississippi, from the junction of Red river to the sea, will illustrate the position of the various outlets and streams connected with it; which, in the lower part of its course, are so numerous, and so interlocked with each other, as not to be easily understood. It is necessary to explain, that the Mississippi, below Red river, and most of the other streams in the Delta, flow on the top of ridges, their waters being higher than the country immediately beyond their banks. It will be observed, accordingly, that very few of them receive any tributary streams in the space which the plan includes. On the contrary, they generally send off part of their waters by lateral courses, some of which (though rarely) return again into the parent stream lower down, while others find their way to the sea, sending off other lateral branches as they advance, and forming lakes where they meet with considerable hollows. All the streams between Teche river, on the south-west, and the lakes Maurepas and Ponchartrain, on the north-east, derive their waters from the Mississippi, either directly, by openings in its banks, or indirectly, from the moisture it diffuses through the subjacent soil; and all the country in. eluded between these limits, and extending in a transverse direction to the north-west and south-east angles of the plan, is subject to inundation, from the annual swell of the river, except where it is protected by artificial embankments, or, in a few places, by the natural elevation of the soil. This alluvial tract forms the proper Delta of the Mississippi. Its length, in a north-east and south-west direction, is above 200 miles, its breadth about 100. Its surface is almost an unvaried level; and eastward of the Lafourche it is generally a morass, of the same height as the tidewater, except on the banks of the river. Of the outlets of the Mississippi, included in this space, the Atchafalaya, the Lafourche, and the Ibberville, are the most considerable. Others are channels which are filled during the overflow, and during the season of low water are dry; while a considerable number serve as drains to cany off the surcharge of moisture from the soil, deeply impregnated with water. It will be observed also, that there are numerous cross courses and interlocking channels between these streams, which run into one another like net-work, and divide the surface of the country into numerous islands. In many of these channels, near the sea, there is no visible current, during the dry season; and at this period the tide reaches up the Atchafalaya river and the Bayou Plaquemines, within five miles of the Mississippi on the one side, and up the Ibberville, within nine miles of it on the other. The Red river, and the upper parts of the channel of the Mississippi, as far as the Ohio, have also an annual overflow, but these differ in many respects from the Lower Delta, and need not be described here.
The Mississippi river forms the eastern boundary of this state from the 38d degree of latitude to the mouth of Red river at the 31st degree, a distance of S06 miles by water; and its course thence to the Gulf of Mexico is 326; in all 632 miles. In its course through the low country this river overflows its natural banks, and the waters which pass over on the west side never return. Those which escape on the east side rejoin the parent stream, except between Baton Rouge and Manchac, where, by the channel of the Ibberville and Amite rivers, they find a passage to lakes Maurepas and Ponchartrain, which communicate with the ocean. The mean width is 880 yards, though in many places near islands and shoals it is much greater; and it is wider 1000 miles from the sea than near its mouth. At Natchez, opposite Fort Rosalie, it is 620 yards. Nine miles below the efflux of the Fourche river, the depth from the highest bank was found to be 153 feet. The difference between high and low water here is twentythree feet, which gives a constant depth of 130 feet;* but the passes, or channels, through which it discharges its waters into the gulf, have no more
* The low water level of the Mississippi at this place is found to be ten feet above the common level of Lake Ponchartrain, which has eighteen feet water. The bottom of the river here is therefore 102 feet below that of the lake; of course the idea which some have that an opening here would carry off the entire body of the river water is unfounded—Darby, p. 135.
than twelve feet at low water. A regular ebb and flow from twelve to eighteen inches takes place as high as New Orleans, 108 miles from the mouth of the river. The waters of this river, in consequence of the dissolution of the snows of the northern regions, and the fall of rains, begin to rise in January, and subside in June, though sometimes at an earlier period. In 1812 they rose to their greatest height in the month of December, which the oldest inhabitant had never before witnessed. Between the mouth of the Ohio and Natchez the waters rise fifty feet; at Baton Rouge, twenty-five; and at New Orleans, twelve. The average rise above New Orleans has been estimated at thirty feet.
Table of the mean ri.e of the Waters of the Mississippi at Natchez, from the lowest ebb to the higliest
"By William Dunbar. See 6th volume of the Transactions of the Philosophical Society of Philadelphia.