Innumerable similar problems still await solution. Some of us have been engaged in trying with pick and crowbar to engineer a way into the swallets above Castleton, which send their waters through the heart of the hills down to the caves in the dale of Hope. One of these, which we have penetrated to a distance of 350 feet, may turn out to be the entrance to as wonderful a chain of caverns as those of Eastwater. Long Kin Hole, Helln Pot, and other tremendous cavities in the Ingleborough district, still promise good sport. Of all the varieties of cave forms these vertical holes are the most impressive, and also the most perilous to explore. No exploit stands out more finely in the record of that intrepid explorer, M. Martel, than his single-handed descent into Gaping Ghyll, the first ever accomplished. In the Cevennes, however, he has reached the bottom of abysses still more profound, though without the unpleasant accompaniment of falling water. One of the most awkward of the descents described by him is that of the Aven de Vigne Close (Ardèche), 190 mètres in depth. This strange pit is almost a corkscrew in shape, comprising five perpendicular drops, the bottom of one being a few feet from the top of the next. To manage the final pitch, with a chain of rope ladders 40 mètres too short, it was necessary to get six men down to the "Salle à Manger" at the foot of the fourth stage, others remaining as sentinels at the head of the various stages. Some of these waited on their narrow perches for eleven hours, in the dark, with nothing to do but listen to the distant noises of their comrades at work. One man, hanging at the end of a rope, succeeded single-handed in fastening a pulley to the free end of the second ladder, and so let down the third ladder to the required extent. This critical operation was carried out under grave difficulties, the nerves of the whole party having been shaken a few minutes earlier by the accidental fall of a heavy lamp, which was within an inch of killing the men beneath.