Caves of the Mendip Hills 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 towards sea level by
Wookey Hole Caves of , setting a new British Isles depth record for cave diving. This record was broken in 2008 by Polish explorer Artur Kozłowski on a dive in Pollatoomary in Ireland. During 1996–1997 water samples were collected at various points throughout the caves and showed different chemical compositions. Results showed that the location of the "Unknown Junction", from where water flows to the static sump in the 22nd chamber by a different route from the majority of the River Axe, is upstream of the sump in the 25th. There are old legends of a "witch of Wookey Hole", which are still