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
West Bay, Dorset a World Heritage Site which stretches for and includes most of the Dorset coastline. West Bay also lies within the Dorset Area of Outstanding Natural Beauty. West Bay is sited on deposits of river alluvium that indicate a former estuary. There are beaches and cliffs on either side of the harbour. The beaches were previously of a similar size—in terms of their seaward extent—but now East Beach is considerably larger, due to accumulation of finer sediment. East Beach is also designated a Site of Special Scientific Interest, and forms one end of Chesil Beach, a barrier beach which extends southeast