Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/154

94 glaciated stones and a few boulders), which is quite as persistent as the sand and gravel, but which has not yet been clearly traced to a height of more than a few hundred feet above the present sea-level. The first indicates a cold period, the second a comparatively mild period, and the third, I believe, a second cold period, though this has been disputed by Professor Hughes and Mr. Kinahan. Believing with Professor Ramsay that the great glacial submergence commenced before the ice-sheet or ice-sheets disappeared from the country, that the lower Boulder-clay (so far as it is of marine origin) was accumulated while the land was sinking, and that the sand and gravel formation was deposited while the land was rising—and likewise believing in an interglacial period, during the first part of which the land was still submerged, dry land prevailing during the second part, it follows that there must have been a second submergence, during which the upper Boulder-clay was deposited. It is possible that the pebble-bed in the Pont-newydd cave may have been deposited as the land was rising out of the interglacial or Middle-Sand-and-gravel sea, and that pebbles and loam may then have been introduced into the Cefn cave; but as the neighbourhood could not have been inhabited by land animals until after the emergence of the land, the bones, teeth, and fragments of wood which were found associated with the lowest deposit in the Cefn cave may have been washed in by rain through fissures in the roof. After the accumulation of the stalagmite, more bones must have been introduced, and the cave may have been temporarily inhabited by the hyæna. This state of things may have been brought to a close by the submergence of the cave beneath the waters of the Upper-Boulder-clay sea, which filled the cave nearly (if not, in many places, quite) to the roof. The sand with sea-shells may have been introduced through fissures in the roof while the plateau above the cave was gradually rising above the sea-level.

The above imperfect explanation is the best I can offer concerning the mode in which the different and very dissimilar deposits in the Cefn and Pont-newydd caves were accumulated.

P.S.—As may be learned from his paper read before the Anthropological Institute, Professor Hughes found Palæolithic flint implements and a human tooth, which he believed came from the bed I have called Upper Boulder-clay, in the Pont-newydd cave.