Cheddar Complex the Pleistocene period. Cheddar Caves contain both active and fossil systems. The active cave system is one of the most heavily studied karst systems in Britain with reference to the conduit and diffuse flow characteristics of its hydrology. Charterhouse Caves include four major swallet caves that provide an indisputable record of Pleistocene landform development in the Mendips and surrounding area. Sun Hole Cave provides a varied fauna radiocarbon-dated to the end of the Late Devensian Cold Stage. Several types of limestone including Clifton Down Limestone, Cheddar Limestone and Cheddar Oolite are visible in the Gorge and surrounding areas with pale
Somerset Valley and to the south, on the clay substrate, are broad valleys which support dairy farming and drain into the Somerset Levels. There is an extensive network of caves, including Wookey Hole, underground rivers, and gorges, including the Cheddar Gorge and Ebbor Gorge. The county has many rivers, including the Axe, Brue, Cary, Parrett, Sheppey, Tone and Yeo. These both feed and drain the flat levels and moors of mid and west Somerset. In the north of the county the River Chew flows into the Bristol Avon. The Parrett is tidal almost to Langport, where there is evidence of two