A Treatise on Rivers and Torrents Author:Paolo Frisi Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAP. H. ON THE SUBSTANCES BROUGHT DOWN BY RIVERS. We remarked, in the preceding chapter, the regular gradation in which, when descending the bed of any ri... more »ver, we meet with, first, large and rough masses of stones; afterwards, round stones, smaller in succession ; then, large and small gravel; and, last of all, sand and pure earth. This gradation is a fact every where constantly observed : it remains that we assign for it an adequate cause. Guglielmini, in the sixth chapter of his work, treating on the nature of rivers, is of opinion that the sands are nothing but stones pulverised, just as stones are often composed of sands bound together. He has besides observed, that stones, impelled by the impetuosity of the water, rolling over and striking each other, must break and continually wear away. He considered the polish, which gravels take in streams, as a manifest sign of their abrasion; and, that the incessant murmur that is heard in the beds of rivers, which carry gravels, was less the effect of the mutual shock of the waters, than of the continual striking of the stones against each other. In a word, he asserts that stones, by their mutual collision and friction, become round, constantly diminish in bulk, become by degrees either large or small gravel, and are at last ground down and reduced to common sands. As for myself, I am of opinion, that round stones, gravels, and sands, are substances originally prepared by nature, and spread all over the globe : that stones, turning and rolling on the bed of a river, may there receive a greater degree of polish, and sands may possibly become smaller; but that stones and gravels, striking and rubbingagainst each other, however great may be the force, can never be converted into sand; and, finally, that the constant diminution...« less