Geology

Excerpt: ...Sicily, having become dammed by a stream of lava flowing from Etna, succeeded, in two hundred and fifty years, in cutting through hard solid basalt a new channel for itself, which measured from twenty to fifty mètres in depth, and from twelve to eighteen in breadth. When, also, we remember the fact, that no river is absolutely free from mineral matter held in suspension, but that, on the contrary, all running water is more or less discoloured with sediment, which is merely the material derived from the disintegration of rocks, it will appear to us difficult to overestimate the power of watery erosion. To the mineral matter held in suspension, we have to add the coarser detritus, gravel and sand, which is being gradually pushed along the beds of rivers, and which, in the case of the Mississippi, has been estimated to equal a mass of seven hundred and fifty million cubic feet, discharged annually into the Gulf of Mexico. By careful measurements, it has also been ascertained that the same river carries down annually into the sea a weight of mud held in suspension which reaches the vast sum of 812,500,000,000 pounds. The total annual amount of mineral matter, whether held in Pg 53 suspension or pushed along the bottom of this great river, has been estimated to equal a mass 268 feet in height, with an area of one square mile. 64. Alluvium.