Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/838

726 of 21 feet, through the whole of which bones were scattered, but in far greater quantity below than above. In one part the remains of fox, wolf, bison, and reindeer were all matted together; and in another on the west side there was a stratum of bones, mostly decayed, which measured 4x3x2 feet. On the west side also, close under the rocks, the bones were soldered into a compact breccia by the infiltration of carbonate of lime. Close to this two perfect skulls of bison lay crosswise, the one over the other. Ultimately the rock-basin began to narrow, and the ossiferous clay to disappear; we traced it downwards until it rested on loose angular fragments of limestone which filled a vertical shaft (fig. 1). We cleared it out on every side except the north; and into that we tunnelled for 5 or 6 feet, till further excavation became dangerous. The rock also reappearing at the surface (figs. 2 & 3) showed that it did not extend far in that direction, and rendered further work unnecessary.



4. The Rock-basin a Swallow-hole.—It was obvious (see section and plan, figs. 1 & 3) that the bottom of the rock-basin ended in a vertical shaft, and that it belonged to the class of "swallow-holes," "chaudrons du diable," or "katavothra," which are to be found in most limestone regions, and which have been formed by the convergence of water charged with carbonic acid on a point of weakness in the rock offered by the intersection of two or more systems of joints. In the immediate neighbourhood of Windy Knoll these swallow-holes abound; and through them the drainage of the upland valley to the west passes into the series of caverns that underlies the limestone ridges, averaging 1600 feet high, separating it from the valley of Hope and Castleton to the east. In the quarry close by, a cavern has been discovered of very considerable size, in which one of these swallow-holes may be studied from the underside. On descending through a small hole, just big enough to admit a spare and agile explorer,