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
World Heritage Site disasters, pollution, poaching, or uncontrolled urbanization or human development. This danger list is intended to increase international awareness of the threats and to encourage counteractive measures. Threats to a site can be either proven imminent threats or potential dangers that could have adverse effects on a site. The state of conservation for each site on the danger list is reviewed on a yearly basis, after which the committee may request additional measures, delete the property from the list if the threats have ceased or consider deletion from both the List of World Heritage in Danger and the World Heritage List.