Wookey Hole Caves then passes through major cave systems such as Swildon's Hole, Eastwater Cavern and St Cuthbert's Swallet, around Priddy, but 95% is water that has percolated directly into the limestone. The southern slopes of the Mendip Hills largely follow the flanks of an anticline, a fold in the rock that is convex upwards and has its oldest beds at its core. On the Mendips the crest of the anticline is truncated by erosion, forming a plateau. The rock strata here dip 10–15 degrees to the southwest. The outer slopes are mainly of Carboniferous Limestone, with Devonian age Old Red Sandstone exposed
Cheddar Gorge When this melted during the summers, water was forced to flow on the surface, and carved out the gorge. During warmer periods the water flowed underground through the permeable limestone, creating the caves and leaving the gorge dry, so that today much of the gorge has no river until the underground Cheddar Yeo river emerges in the lower part from Gough's Cave. The river is used by Bristol Water, who maintain a series of dams and ponds which supply the nearby Cheddar Reservoir, via a diameter pipe that takes water just upstream of the Rotary Club Sensory Garden, a public