Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/839

Rh you find yourself in a lofty chamber; and at the further end of this all further passage is barred by a large conical talus, or shoot, of angular blocks of limestone mingled with clay, which has fallen through an aperture blocked up by the apex of the cone. In all probability the vertical shaft (fig. 1) under the ossiferous deposit in Windy Knoll ends in a similar cave, and has been blocked up in a similar fashion by the slow wearing away of the limestone.

5. A Pool formerly in the Rock-basin.—Nor could there be any reasonable doubt as to the mode in which the ossiferous clays were introduced. The Yoredale shales of Mam Tor command the lower ridges of limestone in the immediate neighbourhood; and the heavy rains have spread their weathered fragments over the boundary dividing them from the limestones. Consequently several of the swallow-holes have been lined with impervious clay, which has converted them into pools. One of these is a few yards from Windy Knoll. We may therefore infer that the clays in question were slowly accumulated in a pool in an ancient swallow-hole, and that they were derived from the Yoredales of Mam Tor, from whose precipitous sides the fragments of shale and gritstone met with in the exploration were torn by the streams.

6. Geographical Change since Accumulation.—This mode, however, of accounting for the clays of Windy Knoll implies a great geographical change in the district. At the present day Windy Knoll, as its name denotes, forms a ridge standing out from the general level of the ground, and overlooking the valley on the west, and the hollow which separates it from Mam Tor. No debris from the Yoredales could now find its way so far as the ossiferous swallow-hole, because all the streams are intercepted by the hollow. It may therefore be concluded that this has been excavated since the deposition of the clay in question.

At the time when it was being deposited also, the sides of the limestone-basin must have stood higher than now, since the imbedded blocks of limestone are the results of their being weathered away. The large mass of stalagmite also, mentioned above, and the numerous broken stalactites scattered through the clay show that there was an overhanging ledge of limestone, if not a cave, at the side of the basin, so placed that its ruins could fall into the latter. The general level of the limestone may therefore be concluded to have been lowered since the time when this was a pool at the bottom of a valley, a pool which has now disappeared along with its upper margins of limestone (fig. 1, D). We were unable to find any evidence that this denudation was brought about by the action of ice. The lowering of the limestone rocks of Windy Knoll, and the excavation of the valley separating it from Mam Tor, imply a very high antiquity for the ossiferous clays, if the present trifling rate of denudation be taken as a measure of the past.

7. The Remains of the Animals.—The remains of the animals belong to the bison, reindeer, bear ( U. ferox and U. arctos), wolf, fox, and hare, associated together in the following proportions, vertebræ and fragments being ignored:—