AT WINDY KNOLL, CASTLETON, DERBYSHIRE. 727 



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 con- 

 verted them into pools. One of these is a few ) T ards 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 pre- 

 cipitous 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 geogra- 

 phical 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 im- 

 bedded 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 evi- 

 dence that this denudation was brought about by the action of ice. 

 The lowering of the limestone rocks of Windy Knoll, and the exca- 

 vation 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. ferooc and U. arctos), wolf, 

 fox, and hare, associated together in the following proportions, 

 vertebras and fragments being ignored :— 



3b2 



