Dove valley and Biggin Dale: SK 157506, SK 147595
Dove Dale is the most extensive and spectacular active limestone gorge in Britain. The main river maintains its permanent flow across the limestone outcrop because of its large external catchment area, while the tributary valleys are by contrast entirely dry. The meandering pattern of the river valley and gorge is uniquely controlled by resistant reefs within the limestone, which are so hard that the river has cut around rather than through them. Geologically, the reefs are of great interest since, unlike most reefs, they are without obvious 'frame builders' – the marine organisms such as corals which build up the reef by their growth and by accreting lime and other organisms around them. The origin of these unbedded reefs is a controversial and still unresolved subject and Dove Dale will undoubtedly feature in future research to resolve this problem.
Source: SSSI citation, English Nature