Following the Cretaceous, the sea covering the south of England began to retreat and the land was pushed higher. The Weald (the area covering modern day south Surrey, south Kent and north Sussex) was lifted by the same geological processes that created the Alps, resulting in an anticline which stretched across the English Channel to the Artois region of northern France. Initially an island, this dome-like structure was drained by the ancestors of the rivers which today cut through the North and South Downs (including the Mole, Wey, Arun and Adur). The dome was eroded away over the course of the Cenozoic, exposing the strata beneath and resulting in the escarpments of the Downs and the Greensand Ridge.