Exmoor is a dissected plateau of Devonian sedimentary rock, rising to at Dunkery Beacon. It extends into Devon but the majority of the area is in Somerset. Much of the area is a National Park. The landscape is one of rounded hills, with hogs-back cliffs at the coast due to geological movements. Because of high rainfall there are boggy areas and the part by the Chains is a Geological Conservation Review site recognised as being nationally important for its south-western lowland heath communities and for transitions from ancient semi-natural woodland through upland heath to blanket mire. The Chains provides palynological record of a mid to late Flandrian vegetation history on Exmoor. The pollen sequence in the peat is calibrated by radiocarbon dating. The Glenthorne area demonstrates the Trentishoe Formation of the Hangman Sandstone Group. The Hangman Sandstone represents the Middle Devonian sequence of North Devon and Somerset. These unusual freshwater deposits in the Hangman Grits, were mainly formed in desert conditions.