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
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