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
Coastline of the United Kingdom the coastline of the main island, Great Britain, as 11,072.76 miles rounding to 11,073 miles (17,820 km). The British Cartographic Society points out that "The true answer is: it depends!". If the larger islands are added, the coastline as measured by the standard method at Mean High Water Mark rises to about 19,491 miles (31,368 km). According to the "CIA Factbook", the length of the UK coastline is around 12,429 km or 7,723 miles, although no details are provided about how this figure was calculated. On the basis of EU Marine Strategy Framework Directive boundaries, the UK coastline can be