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
Geology of Dorset to erosion as the chalk was folded and forced upwards. The early deposits from this period, found across South-East England, do not occur in Dorset. The small amounts found in Devon however, coupled with the many solution holes found across the Dorset chalk, suggests that erosion may have removed them. Some of the larger solution holes, known as dolines, are found on the heaths between Dorchester and Bere Regis. Near Briantspuddle is Culpepper's Dish, 86 metres wide and over 21 metres deep. The first deposits found from this period in Dorset are the Reading Formation clays. A sub-division of the