Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/169

Rh The gravel here includes some enormous blocks of limestone, which have fallen into it from the rock above. When this stream of gravel reaches the mouth of Bacon Hole, it turns sharp round into the cave in a northerly direction, the angle of deposition changing to 25° N., the floor of the cave being about 30 feet above high water. The limestone-gravel is covered with the black bone-earth in which so many remains of Elephant and Rhinoceros have been found in the cave, and is mixed with marine shells of species now living on the coast and in the sea-sand. The whole is covered with stalagmite, from 2 to 3 feet thick, also sloping northwards at an angle of 25° N. There are layers of stalagmite included within the limestone-breccia (proving changes in the conditions of deposition at intervals) in the cave; but the gravel, although so much higher on the side of the cliff to the west, does not fill up the whole of the cave.

Looking at Dr. Buckland's drawings of caves, I think there is evidence that much of the loose materials which have formed the cave-deposit have passed downwards from the subaerial gravels on higher levels, and continued through and over the caves as far as the level of the sea, lake, or river below them.

All English bone-caves are at levels within 150 feet of running water at the present time, or of the sea; and the great majority are within the limit of 70 or 80 feet, their fossiliferous contents corresponding in level with all the known fossiliferous gravels containing mammalian remains, including the Crag.

In the period referred to, water ran apparently in the bottom of the valleys which are now dry.

All bone-caves seem, at the time of the deposition of their contents, to have been in situations where water traversed them from fissures above, and flowed into them from the side streams flowing along the valleys in which they are situated, and they offer evidence of an immense rainfall at the period of the deposition of the cave-gravels. The very washed condition of the materials found in bone-caves, and the manner of accumulation, indicate that their contents were more derived from above than below; and the enormous pieces of limestone which have fallen into the gravel at Kent's Hole and Bacon Hole show that there must have been not only the action of running water thereon, but the force of a column of water upon the cave to dislodge the pieces from the roof.

There are in all caves apertures in the roof, evidently worn by water coming through it. I observed a good instance of this in the Paviland Cave at Gower (close as it is to the sea), and another in Brixham Cave. Some years since, I believe, it was remarked by Dr. Buckland that there were always at least three openings in bone-caves, two of them from higher levels than the mouth.

The subaerial gravel comes down the steep slopes of the limestone cliffs at Gower from a great height, and falls into a stratified marine deposit, just as it falls down the steep cliffs into the Hopes-Nose raised beach, near Torquay, where it is mingled with the sea-sand, pebbles, and shells deposited almost horizontally on the limestone rock.