Caves of the Mendip Hills then rising up a fracture in the rock. Few caves on the Mendip Hills are more than deep or a few kilometres in length, (with some notable exceptions, such as Swildon's Hole which is over long), but a number are complex with several levels of passages which have been abandoned by the water, for example those around Cheddar. The catchment area of the Cheddar Yeo, which rises in Gough's Cave, measures . Dye marking shows that some of the water travels underground for up to , taking up to 14 days to reach Cheddar. When Banwell Bone Cave was discovered
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