Caves of the Mendip Hills caves are listed below Caves of the Mendip Hills The caves of the Mendip Hills are formed by the particular geology of the Mendip Hills: large areas of limestone worn away by water makes it a national centre for caving. The hills conceal the largest underground river system in Britain. The hills consist of anticlines of Carboniferous Limestone lying over Devonian Old Red Sandstone, with the sandstone exposed on the summits. When a surface stream running off the sandstone reaches the limestone it sinks below ground through a "swallet", (also known locally as a "slocker"), continuing on its way down
Wookey Hole Caves is of what is described in the guide book as "magnificent" river passage, high and wide, which finishes at a cascade falling from a long lake. There are also more than of high level passages above the river. The way on continues underwater for some reaching a depth of before surfacing in the 25th chamber – called the Lake of Gloom because of its thick mud deposits. The sump at the end of this has been dived for to a maximum depth of before gravel chokes prevented further progress. The end is located about northeast of the entrance. Wookey Hole