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Show IMBEDDING OF ORGANIC REMAINS [Ch. XIII. vation of some organic relics which have become mingled in a common tomb with those of older date. Fissures are very common in calcareous .rocks, and these are usually, in the course of ages, fill:d up m p~rt by small angular fragments of limestone, wlnch scale off under the influence of frost and rain.. Vegetable earth and land-shells are washed in at the same time, and the whole mass often becomes cemented together by calcareous matter dissolved by rainwater, or supplied by mineral springs. In an uncultivated country the edges of such fissures are usuall.y overgrown with bushes, so that herbivorous animals, espee1ally when chased b beasts of prey, or when carelessly browzing on the shrubs, a;e liable to fall in and perish. Of this kind is a fissure still open in Duncombe Park, in Yorkshire, where the skeletons of dogs, sheep, goats, deer, and hogs, have been found, lodged upon different ledges that occur at various depths in a rent of the rock descending obliquely downwards*. Above the village of Selside, near Ingleborough in Yorkshire, a chasm of enormous but unknown depth occurs in the scarlimestone, a member of the-carboniferous series. ''The chasm,', says Professor Sedgwick, '' is surrounded by .grass~ shelving banks, and many animals, tempted towards 1ts brmk, hav.e fallen down and perished in it. The approach of cattle 1s now prevented by a strong lofty wall, but there can be no doubt that, during the last two or three thousand years, great masses of bony breccia must have accumulated in the lower parts of the great fissure, which probably descends through the whole thickness of the scar-limestone, to the depth of per-haps five or six hundred feet 1- ." . . . A fissure in the limestone of the Cmron, m France, 1s seen on the high road between Aubenas and Ville-Dieu, filled with a breccia' consisting of angular fragments of the rock. an.d land-shells cemented together. The mode of its formation 15 * Buckland Reliquiro Diluvianro, p. 55. t Memoir on the Structure o£ 1 the Lake Mountains of the North of England, &c., read before the Geological Society, January 5, 1831, Ch. XIII.] IN THE MUD OF CAVES AND FISSURES. admirably. illustrated by the rapid growth of a similar deposit not far distant. At the pass of Escrinet, on the northern esca~·pment of the Coiron hills, near Aubenas, a tabular mass of hmestone is seen disintegrating into innumerable anD"ular fragments, which are transported by the rain to the foot :r th declivity, where they have accumulated at one spot, in a talu: fifty ~eet in thickness and five hundred yards wide. The upper part Is composed for the most part of loose fragments, on which numer.ous land-shells are seen living; the lower portion is consolidated by stalagmite into a compact mass which serves for mill-stones. The calcareous cement has a red tinge, but not of so deep a colour as most of the Mediterranean breccias*. By the decomposition of the calcareous rocks near Nice '1. 'a s?1 .Is produced of a blood-red colour; and red breccias, con- Sisting of fragments of rock and land-shells cemented torrethcr are contm. ua 11 y forming. If the mountains here were r°e nt b ' e~rthquakes, ';e ~ight expect the fissures to be gradually fille~ w1th red brece1as hke those of higher antiquity so celebrated in many parts of the Mediterranean. !(often happens that fissures communicate with subterranean caverns, a fact somewhat confirmatory of the views of those geologists who attribute the origin of limestone caverns in great part to the movements and dislocations of the strata In t~is case th: fissure may serve for ages as a natural pit-fali to ammals passmg by, and their bones, with all the earth sand an d fragments of rock that fall through these passages' , may' be washed down or subside by their own weight, so as to reach the cavern below where thick deposits may be amassed. Oftentimes when the bones of animals are strewed along the bottom of fissures or caves which they may have inhabited, they become covered over with mud introduced by land-floods, and are thus preserved from decomposition. Thus on the floor of. many caverns mentioned by Dr. Buckland, in the Mendip ~Ills and Derbyshii·e, sedimentary mud has been left in recent times rlming floods. * I examined this spot in the year 1828, accompanied by Mr. Murchison. |