Geography of Dorset is the Blackmore Vale, a relatively low-lying area of clays and limestones of Jurassic age. The south-east of the county forms part of the Hampshire Basin, an asymmetric syncline covered in sands and gravels of Paleogene age. The main rivers in the county are the Stour, Frome and Piddle. The Stour is the county's largest river, although its source is in the neighbouring county of Wiltshire. The Frome and Piddle both lie wholly within the county. The whole of Dorset's coastline is designated part of the Jurassic Coast World Heritage Site, and contains examples of many different coastal landforms, reflecting
Heritage coast column of the tables below. Designations for nature conservation (as opposed to landscape, e.g. SSSI, Special Area of Conservation and Special Protection Area) of parts of Heritage Coasts are too numerous and complex to easily list here. South Wales, Devon and Cornwall have more heritage coastline per mile than other regions, including over 50% of the coast between Cardiff and St Davids, about 55-60% of Cornwall's coast, and around 60-65% of Devon's coast. This contrasts with the coasts of North West England, where St Bees Head is the only heritage coast, or the south-east stretch of the English Channel which