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 system that is formed within the Dolomitic Conglomerate is characterised by shallow loops linking low bedding chambers, or tall narrow passages, known as 'rifts', developed by phreatic solutional enlargement of fractured rifts. The streamway in the inner part of the system formed within the limestone is characterised by deep phreatic loops reaching depths as much as , with the water flowing down-dip along bedding planes and rising up enlarged joints. In the far reaches of the cave the passages descend to below sea level. Witcombe suggests that the name "Wookey" is derived from the Celtic (Welsh) for 'cave', ""Ogo"" or