Urstrom into another route. When the Scandinavian and Scottish ice caps first met, the Urstrom (unless it found a way northwards under the ice) would have backed up into a huge lake in the southern North Sea, which finally found an outlet southwards over the Weald-Artois Anticline and helped to cut the valley of the Strait of Dover: see Strait of Dover#Geological formation. See also Dogger Bank for map and links to similar places Timeline of glaciation References Benn, D.I. & Evans, D.J.A. Glaciers and Glaciation (1998) Cameron, Crosby, Balson, Jeffery, Lott, Bulat & Harrison. The Geology of the Southern North Sea (1992) Glennie, K.W. Lower Permian - Rotliegend in ed. Glennie Introduction to the Petroleum Geology of the North Sea. (1990) Imray, Laurie, Norie & Wilson pub. East Coast of England: Orfordness to Blythe marine chart (1980) Landforms of the North Sea