156 



SEDIMENT IN RIVERS. 



tained in a certain amount of river water, by taking 

 a portion from different parts of the stream, and, 

 after evaporating the fluid part, weigh the sediment 

 In this manner it has been computed that the Rhine, 

 when most flooded, contains one part in a hundred 

 of mud in volume, and that the Yellow River in 

 China contains one part to two hundred ; and Sir 

 George Staunton calculated from a number of ex- 

 periments, that it brought down, in a single hour, 

 two million cubic feet of earth, or forty-eight mill- 

 ion daily : so that, if the Yellow Sea be taken to 

 be 120 feet deep, it would require but 70 days to 

 convert a square mile into firm land. Manfredi, the 

 celebrated Italian philosopher, conceived the aver- 

 age proportion of sediment in all the running water 

 on the globe to be one part to 175 of water, and 

 that it would take 1000 years for the sediment car- 

 ried down to raise the general level of the sea one 

 foot. Major Rennell,* of the British army, states 

 that a glass of water taken from the Ganges when 

 at its height, yields about one part in four of mud. 



Later observations by the Rev. Mr. Everest, show 

 that this calculation was erroneous, or, more proba- 

 bly, a typographical error, and that the average 

 quantity of solid matter was only l-428th part by 

 weight and l-856th part in bulk, and that the total 

 annual discharge is 6,368,077,440 cubic feet. 



" In order," says Mr. Lyell, " to give some idea 

 of the magnitude of this result, we will assume that 

 the specific gravity of the dried mud is only one 

 half that of granite (it would, however, be more) ; in 

 that case, the earthy matter discharged in a year 

 would be equal to 3,184,038,720 cubic feet of gran- 

 ite. Now about 12 1-2 cubic feet of granite weigh 

 one ton ; and it is computed that the great Pyramid 



But as these conditions vary at different seasons of the year, we 

 must make observations at different periods, and then take the 

 mean of them all. 



* Phil. Transact., 1781. 



