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 Farr a few days later for at a maximum depth of to emerge in the 25th chamber, a desolate, muddy place named "The Lake of Gloom". The 25th chamber represents the furthest upstream air surface in Wookey Hole Cave. From here the River Axe rises up from a deep sump where progressive depth records for cave diving in the British Isles have been set: firstly by Farr () in 1977, then Rob Parker () in 1985, and finally by John Volanthen and Rick Stanton () in 2004. The pair returned again in 2005 to explore the sump to a depth