any known to exist elsewhere, and it requires a special explanation to account for it. Only one explanation is possible. The Conglomerate is here filling in some great pre-existing valley in the Mountain Limestone. That is just what I should expect. The great Limestone cavern formed by the action of the swallet streams in early Triassic times collapsed, and formed a Limestone ravine, into which was rolled a great accumulation of fragments of the Limestone derived from the slopes and crags above. With the whole of this part of England these beds were subsequently submerged, remaining so during the deposit of the whole of the Secondary beds; and on their emerging once more from beneath the sea the lines of drainage were re-established along the old courses, where these had not been choked with sedimentary material. Forcing a way through the Conglomerate which then impeded its flow, the river formed those cavities which we see. Indeed, it may well be that the successive levels cut by the Axe through the Conglomerate may represent stages in the uplifting of the land, the lowest channel being the last and largest, as it has been formed during an extended period of stability. But we are not without evidences of another sort as to the existence of some of our swallet ways at that remote period. The cavities found in the Holwell quarries, near Frome, filled in with Rhaetic material containing bones and teeth of fishes; those of Gurney-Slade, near Radstock; and numbers which from time to time are laid bare in the Limestone quarries, all filled in with Triassic sediment, show that penetrating waterways of considerable size then existed. There was, too, at Charterhouse-on-Mendip, north of Cheddar, a fissure, possibly a swallet, which, being open, received an infilling of Liassic material that is known to extend to a depth of 300 feet. Had these channels been closed by a narrow aperture temporarily blocked, no infilling but by water would have taken place when the land sank beneath the waters of the Triassic and Liassic seas.