The Measurement of Geological Time II

Abstract

WE have now to consider an entirely distinct set of facts which have an important bearing on the probable time elapsed since the last glacial epoch. Messrs. A. Tylor, Croll, and Geikie have shown that the amount of denudation now taking place is much greater than has generally been supposed. The quantity of water discharged by several rivers and the quantity of sediment carried down by those rivers have been measured with tolerable accuracy, and allowing for the difference of specific gravity between sediment and rock, it can be easily calculated, from the known area of each river basin, what average thickness has been removed from its whole surface in a year, since. all the matter brought down by the river must evidently have come from some part of its basin. In this way it is found that the Mississippi has its basin lowered 1/6000 of a foot per annum; the Ganges, 1/2358; the Rhone, 1/1528; the Hoang-Ho, 1/1464; the Po, 1/729.