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
Alyn Valley Woods and Alyn Gorge Caves helleborine and wayfaring tree. There are also areas of calcareous grassland with plants such as bloody cranesbill and lesser meadow-rue. Much of the site lies on an escarpment of Carboniferous limestone and there are three cave systems: Ogof Hesp Alyn, Ogof Hen Ffynhonnau and Ogof Nadolig. Lead ore, zinc ore, limestone and calcite were formerly mined in the area. Alyn Valley Woods and Alyn Gorge Caves Alyn Valley Woods and Alyn Gorge Caves is a Site of Special Scientific Interest on the border of Flintshire and Denbighshire in north Wales. Most of the site is also designated as the Alyn