Page:The American Cyclopædia (1879) Volume XI.djvu/679

 MISSISSIPPI PJVER 661 rectly represent many of the mud banks and channels or bayous around the Balize, which is the station of the pilots at the mouth of the river. Here only,- for a distance of 100 m. from the gulf, is the river seriously obstructed by bars. Over these the depth of water is some- times only 15 f t. ; but this is very changeable, as the channels are shifted by the floods in the river and the gulf storms. These bars are com- posed of blue clay mud, through which vessels drawing 2 or 3 ft. more water than the actual depth can be taken by steam tugs. Great ef- forts have been made by the government to re- move these obstructions by dredging, and the depth of water has been increased thereby to 21 f t. ; but owing to the difficulty of maintain- ing such a great depth with dredges, congress has appointed a board of engineers to investi- gate the subject and report a plan. The sedi- ment of the lower Mississippi is chiefly a fine clayey matter, so universally suspended in the water as to give it a thick muddy appearance. The Upper Mississippi is clear, but the Missouri pours into it a vast amount of whitish muddy matter, which renders the water so turbid that at St. Louis one cannot see through a tumbler filled with it. This, however, does not prevent its being generally used for drinking, and for culinary purposes. The Ohio adds to it a green- ish current, and the Arkansas and Red rivers pour in the red ochreous sediment already re- ferred to ; while the Mississippi itself excavates its alluvial plain and sweeps down, intermingled with the rest, vast quantities of vegetable soil that falls in the banks of the river. The coarser pebbles and sands accumulate in the bends and eddies, forming bars, and the lighter materials are deposited in the gulf of Mexico. Accord- ing to the report of Capt. (now Gen.) Hum- phreys and Lieut, (now Gen.) Abbot, a com- parison of the results of many observations during a long period leads to the belief that the weight of the sediment of the Mississippi is T^ that of the water, and its bulk ^fa ; and if the mean annual discharge of the river be assumed to be 19,500,000,000,000 cubic feet, it follows that 812,500,000,000 pounds of sedi- mentary matter, constituting one square mile of deposit 241 ft. in depth, are yearly trans- ported to the gulf. In addition to the amount held in suspension, the Mississippi pushes along large quantities of earthy matter. No exact measurement of this can be made, but from the yearly rate of progress of the bars into the gulf, it appears to be about 750,000,000 cubic feet, which would cover a square mile about 27 ft. deep. The total yearly contributions from the river to the gulf amount then to a prism 268 ft. high, with a base of one square mile. The uniformity of width of the Mississippi is very remarkable. At New Orleans it is about 3,000 ft. wide, and from this it varies little for a distance of nearly 2,000 m., except that in the bends it swells out to 1 or even 1 m. The junction of its principal branches pro- duces no increase in the width. The depth is very variable, sometimes reaching 150 ft., but the maximum is more commonly from 120 to 130 ft. The mean depth at high-water mark is about the same at Carrollton and at Natchez, 300 m. further up. A section of the river at Carrollton, made at high-water mark in 1858, comprises 184,000 square feet, and at Natchez 221,000. The mean rate of descent varies at low water from -005 of a foot per mile at the head of the passes, to -578 of a foot at Cairo, and in high-water from -115 of a foot to '497 of a foot per mile. The velocity varies at Carrollton from 1-45 to 2'61 m. per hour, ac- cording to the stage of the water and the di- rection of the wind. The Mississippi, like the other great rivers of the west, is continually gathering into its current numbers of trees, as the banks upon which they grew are under- mined. They are frequently left in the main channels, their roots fixed to the bottom, and their tops pointing down stream. In this con- dition they are known as snags and sawyers, and present to boats ascending the river, espe- cially at night, a most dangerous obstruction. But continual care is now given to the removal of these obstructions. The accumulations of the drift materials in the arms of the river have sometimes been so great as to bridge these over and extend for miles up the current. The obstruction is then known by the name-of raft. From about the year 1778 such an accu- mulation had been gathering in the Atchaf alaya, until in 1816 it had extended to full 10 m. in length, over 600 ft. in width and about 8 ft. in depth. Though rising and falling with the water, it afforded a soil for the growth of bushes and of trees, some of which reached the height of 60 ft. In 1835 the state of Louisiana took measures to have it removed, and this was finally accomplished at a heavy cost in the course of four years. The Red river raft is still more famous for the large sums which have been appropriated by congress to effect its removal, the work upon which has been carried on with great success of late years, and is now almost completed. The appropriations made from time to time by congress for the Mississippi river comprise the following items : Mouth of Mississippi river, from 1886 to 1856 $690,000 " 1856 to 1875 1,224,850 Mississippi river, between Illinois and Ohio rivers. 665,000 Des Moines rapids 3,028,200 Rock Island rapids 1,039,650 Upper Mississippi river, including falls of St. An- thony 677,640 Mississippi river, including rapids (1886 to 1856). . . 465,000 Total $7,789,840 For a full statement of measurements, all the phenomena, physical elements, and laws relating to this great river, see the " Report upon the Physics and Hydraulics of the Mis- sissippi River," prepared by Capt. A. A. Humphreys and Lieut. H. L. Abbot, U. S. army (4to, Philadelphia, 1861), and also the official reports of the chief of engineers to the war department. The first European explorer