Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/434

Rh separate fragments, great and small, which shall roll and bound down the steeps, and shatter in repose in the lower valleys thousands of feet below their former positions. Hooker's admirable description of the earthquake he experienced in the Sikh Himalaya, is the best instance on record of the latter.

The alterations of water courses, of which such exaggerated notions have been rendered current, by the account of the Calabrian shock of 1783, given by the Neapolitan Academy, reduce themselves, in reality, to the consequences of such slipped masses of earth, or fallen heaps of shattered rock, when precipitated into the beds of running waters.

Thus the masses of rock precipitated at the gorge of Campostrina into the bed of the Tanagro, at first almost completely dammed across its channel; its waters were ponded above the dam, and judging from the masses, in the state in which they were when I examined them some six weeks afterwards, the waters may have reached, perhaps, at some one time, 12 or 15 feet in depth above the dam. The latter was nowhere water-tight, and great leakage took place through the rocky fragments at the coarser side, nearest the toe. Partial debacles, also, turned over and gradually removed, more and more of the intruded masses, and after a very moderate time—less than a month—the regimen of the river for ordinary discharge, was re-established, though with a certain amount of change of form of channel at the point. The first great flood would further enlarge this, and soon no trace of change be left.

The turbid discolouration of the waters of the same river issuing from St. Michael's Cave at Pertosa, is a matter quite as simple. The water of the river entering