respect is neither better, nor worse, than any other similar attempt founded on the rate at which a valley is being excavated, or alluvium being deposited, or on the retrocession of a waterfall, such, for example, as Niagara. It is merely valuable as enabling us to form some sort of idea of the high antiquity of the neolithic men who left these remains behind in the cave. As the trench (see Figs. 20, 21) begun on the outside passed into the entrance of the cave, the accumulation of stones above the neolithic stratum disappeared, and the latter became intermingled with the Brit-Welsh layer above, so that it would have been impossible to distinguish the one from the other had not the talus marked the interval in the plateau outside. The talus also above the Brit-Welsh stratum ceased at the entrance, although here and there large blocks of stone, fallen from time to time from the roof, rested on its upper surface. _The Grey Clays._ Immediately below the neolithic stratum, a deposit of stiff grey clay of unknown depth occupies both the entrance and the inside of the cave (Figs. 20, 21), containing fragments of limestone and large angular blocks which had fallen from the roof. A shaft sunk to a depth of twenty-five feet near the entrance failed to arrive at the bottom, but presented the following section in descending order: stiff grey clay with layer of stalagmite six feet thick; a finely laminated calcareous clay twelve feet thick; and below, a similar bed of clay to that on the surface. In a second shaft sunk to the depth of twelve feet farther within the cave, the base of the grey clay was not reached.[72] [Illustration: FIG. 29.--Section below Grey Clay at entrance.] A third shaft, at the entrance, however, penetrated the clay, No. 1 of Figs. 20, 21, 29, at a depth of about five feet, and revealed the existence below of a reddish-grey loamy cave-earth (Fig. 29, A), containing bones and teeth of the same animals as those from the caverns of Kent’s Hole, Wookey Hole, and others, which belonged to a group that invaded Europe before the glacial period, and that inhabited the region north of the Alps and the Pyrenees in pre- and post-glacial times.[73] We subsequently discovered the cave-earth to be from three to four feet thick, and that it rested on an accumulation (Fig. 29, B) of large blocks of limestone, the interstices between which were filled with clay, sometimes laminated and at others homogeneous, as well as with coarse sand. Below this we broke into an empty passage, one side of which was formed by the solid rock, and the other of blocks of stone imbedded in the clay.