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
The Undercliff The Undercliff The Undercliff is the name of several areas of landslip on the south coast of England. They include ones on the Isle of Wight; on the Dorset-Devon border near Lyme Regis; on cliffs near Branscombe in East Devon; and at White Nothe, Dorset. All arose from slump of harder strata over softer clay, giving rise to irregular landscapes of peaks, gullies and slipped blocks, that have become densely vegetated due to their isolation and change of land use. The Kent coast at Folkestone and Sandgate also has similar undercliff areas. The Undercliff on the Isle of Wight skirts