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
Cave Diving Group Neath River Cave. Progress and development of equipment and techniques have always come in phases, and with this progress, although still hoping to discover dry caves, came diving of a purely exploratory nature. This has led to advances at Wookey Hole and Cheddar Gorge caves in Somerset. In Derbyshire a great deal of effort has produced significant discoveries in the Peak Cavern/Speedwell Cavern system. In South Wales many kilometres of Daren Cilau were first trodden by cave divers; and the link with Elm Hole and Pwll y Cwm was another major feat. In the north of England, divers have made