Formation of Caverns

Abstract

IN NATURE of 21st April, Mr. W. Boyd Dawkins, writing of caves in Yorkshire, tells us:—“All have been at one time or other subterranean water-courses.” In the Popular Science Review for October 1869, the same gentleman writes:—“The ceiling, at the time of its deposition, must have been supported by a layer of cave earth.” With your permission I will explain the character of a phenomenon, which I have published in my “New Pages of Natural History” (Newby, 1868), which may suggest to Mr. Dawkins the manner in which the caves at Streddle and Kent's Hole were formed. In the province of Poona, Bombay, the Ghar Nuddee (white river) has, in the mountains near its source, several lime formations spanning its level. In the dry season the river runs below as a subterranean stream; in the Monsoon it runs over this sheet of lime, which varies in thickness from a few inches to two feet along the centre or crown of the cavity, increasing in thickness towards the sides; there are several fissures on the surface; the hole at the upper end is smaller than that at the lower; the whole formation is in layers, and is due to water containing vast quantities of lime in solution. Originally there was a dip or hollow place on the spot, which gradually filled with all sorts of materials, till they grew nearly to the level of the dry season stream. In this condition the first thin sheet of lime was deposited on them, till by successive seasons the formation grew into a substantial covering composed of yearly layers. As there were perishable materials down below, they subsided, so that the lime covering, having in places no support, gave way to the force of the water, or to the weight of boulders hurled upon it, and water found admission between the lime sheet and the buried materials; as these were more moveable than the covering, they gradually washed out, and left the river to resume its ancient course beneath a covering of its own formation. Of course subterranean streams may excavate caverns; but if these streams owe their origin to percolation only, no large organic remains will be found in the caverns. If these are formed after the fashion of the Ghara caves, some organic remains may still be found, though waters have washed through them for years. When these lime formations withstand all the forces to which they are subjected, and have grown into large hills, the materials which formed the mould of the cave are still in situ, the perishable portions have changed into an oily, loamy soil; but bones, pebbles, and other materials are there mixed up with the stalagmite, which originally forming upon the surface of these materials, sunk and broke up as the supports failed, and remain, as Mr. Dawkins found them in Kent's Hole.