until the first underground chamber is reached. The undermined archway of rock is less able to withstand the agents of denudation, and the cliff front recedes apace. Such is the present stage at Wookey Hole, the chamber whence the river Axe issues being still in process of destruction. Thus the work goes on slowly, yet none the less surely, until along the whole course of the subterranean river the roof of the cavern is destroyed, perhaps effectually hiding the stream under huge blocks of Limestone, such as those of Ebbor Gorge, near Wells, or until the water finds another course for itself, as at Cheddar, to begin the whole story over again. Every stage is abundantly illustrated by our Mendip swallets and caves. The large swallets of Eastwater, three and a half miles from Wells, of Swildon's or Swithin's Hole, a half-mile nearer Priddy, and the more recent swallet of Stoke Lane, half-way between Wells and Frome, are excellent examples of streams engulfed on the summit of Mendip. The whole of the country surrounding the two first-named caverns is dotted with innumerable small pits and hollows. The great swallet of Hillgrove, three miles north of Wells, in the exploration of which we are at present engaged, in an endeavour to penetrate the labyrinth of ways to which it will undoubtedly afford access, is a fine example of an intermittent swallet. Here three ways, carved deeply through the stream-borne sands and clays of some uncertain epoch of geological history, converge in a deep glen, beautiful with its tropical wealth of ferns. In the bottom of the glen huge spurs of Limestone stand up boldly, dipping towards the Old Red Sandstone exposed to the south, and pointing to a great fault, along the line of which the Limestone water is bound to accumulate in a huge triangular reservoir, the outflow from which may account for the summer flow of the Axe when the majority of the swallets are dry. In winter the converging torrents here find ingress into the Limestone, but, though pits and hollows abound on every hand, no foot of man has ever yet trod the hidden ways beneath. At a depth of 10 feet we have reached the first open channel, only to have it blocked subsequently by a fall of the treacherous gravel through which we have been working.