QUANTITY OF SEDIMENT IN RIVER WarEn.—Very few satis- factory experiments
have as yet been made to enable us to determine, with any degree of accuracy, the mean quantity of earthy matter dis- charged annually into the sea by some one of the principal rivers of the earth. Hartsoeker computed the Rhine to contain, when most flooded, one part in a hundred of mud in suspension. By several observations of Sir George ttaunton, it appeared that the water of the Yellow River in China contained earthy matter in the proportion of one part to two hundred, and he calculated that it brought down in a single hour, two million feet of earth, or forty-eight million daily; so that, if the Yellow Sea he taken to be one hundred and twenty feet deep, it would require seventy days for the river to convert an English square mile into firm land, and 24,000 years to turn the whole sea into terra firma, assuming it to be 125,000 square miles in extent. Manfredi, the celebrated Italian hydo- grapher, conceived the average proportion of sediment in all the running water on the globe, which reached the sea, to be TIT, and he imagined that it would require 1000 years for the sediment carried down to raise the general level of the sea about one foot. "A glass of water," says Major Rennell, " taken out of the Ganges when at its height, yields about one part in four of mud. No wonder, then, that the subsiding waters should quickly form a stratum of earth, or that the delta should encroach on the sea ! " The same hydrographer computed with much care the number of cubic feet of water discharged by the Ganges into the sea, and estimated the mean quantity through the whole year to be 80,000 cubic feet in a second. When the river is most swollen, and its velocity much accelerated, the quantity is 405,000 cubic feet in a second. Other writers agree that the violence of the tropical rains, and the fineness of the alluvial particles in the plains of Bengal, cauie the Waters of the Ganges to be charged with foreign matter to an extent wholly unequalled by any large European river during the greatest floods. We have already alluded to the frequent sweeping down of large islands by the Ganges; and Major R. H. Colebrooke, in his account of the course Of the Ganges, relates examples of the rapid filling up of some branches of the river, and the excavation of new channels, where the number of square miles of soil removed in a short time (the column of Carth being 114 feet high) was truly astonishing. Forty square miles, Cr 25,600 acres, are mentioned as having been carried away, in (me locality, in the course of a few years. But although we can readily believe the proportion of sediment in the waters of the Ganges to exceed that of any river in northern latitudes, we are abmewhat staggered by the results to which we must arrive if we +Compare the proportion of mud, as given by Rennell, with his corn. putation of the quantity of water discharged, which latter is pro- bably very correct. If it were true that the Ganges, in the flood. season, contained one part in four of mud, we should then be obliged to suppose that there -passes down, every four days, a quantity of mud equal in volume to the water which is discharged in the course of twenty-four hours. If the mud be assumed to be equal to one-half the specific gravity of granite (it would, however, be more), the weight of matter daily carried down in the flood-season would be about equal to seventy-four times the weight of the Great Pyramid of Egypt. Even if it could be proved that the turbid waters of the Ganges contain one part in a hundred of mud, which is affirmed to be the case in regard to the Rhine, we should be brought to the extraordinary conclusion, that there passes down, every two days, into the Bay of Bengal, a mass about equal in weight and bulk to the Great Pyramid.—Lyell's Geology.
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