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GEOLOGY several feet in depth, and visitors are conveyed along it in boats. The excess of water falls over the edge of the platform with a deafening roar into the lower part of the cavern known as ' The Bottomless Pit.' This pit was explored by the Kyndwr Club in 1901, and the writer descended with the party. The vertical distance from the platform to the water surface was 63 feet, and the depth of the water was not more than 22 feet. A vertical vein of calcite nearly 6 feet in width was seen at the west end of the platform. The Blue John Mine near Castleton consists of large underground cavities connected by artificial passages. It is supposed to have been discovered accidentally in mining operations by the Romans. The Grand Cystallized Cavern is 60 feet long, 1 3 feet wide, and 45 feet high. Lord Mulgrave's diningroom is 39 feet by 36 feet, and 57 feet high. The new cavern which has been described as the ' largest, the wettest, the dirtiest and the most rugged and irregular ' of any of the series measures 100 yards in length, 16 in width. This cavern leads to the Fairy Grotto, a small cavern with delicate stalactites and stalagmites. The total distance of the winding passages is said to amount to over 3 miles. The Peak Cavern at Castleton, which has a magnificent entrance, is another example of a natural cavern connected with a system of under- ground drainage. The water enters the limestone along a line of swal- low holes near Perryfoot at the boundary of the Mountain Limestone and shales. The water is finally discharged partly through the cavern, but largely by a spring called Russett Well, and flows down the valley joining the river Noe near Hope. Eldon Hole, a chasm in the side of Eldon Hill near Peak Forest village, has been supposed to be connected by underground passages with Peak Cavern. This supposition has not been proved. The chasm is about 100 feet long and 20 feet wide at the surface. The sides are almost vertical. In December, 1900, the writer and thirteen others were lowered down this chasm by a rope. It was 180 feet deep. The bottom measured 36 feet by 29 feet. The floor is composed of loose angular blocks of limestone and slopes at an angle of 35. Climbing down we reach a low archway about 3 feet in height which opens out into a cavern. The slope of scree continues 40 feet further. The cavern is pear-shaped in a nearly horizontal section, and measures 40 feet from north-east to south-west, and 36 feet from north-west to south-east. The lowest part of the cavern is 256 feet from the surface to the ground. No stream of water was seen. Another system of underground drainage occurs near Eyam. The water enters the limestone by swallow holes and finds its way to the valley of the Derwent by way of Middleton Dale. The disappearance of the water down swallows often results in a dry valley which represents the old watercourse. Linen Dale near Eyam is one of these valleys. Great Rocks Dale through which the Midland Railway passes between Miller's Dale and Doveholes is another dry valley.