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 nominated property on the World Heritage List and sometimes defers or refers the decision to request more information from the country which nominated the site. There are ten selection criteria – a site must meet at least one of them to be included on the list. Up to 2004, there were six criteria for cultural heritage and four criteria for natural heritage. In 2005, this was modified so that there is now only one set of ten criteria. Nominated sites must be of "outstanding universal value" and meet at least one of the ten criteria. These criteria have been modified