Back in the Eocene, some 50 million years ago (MYA), as mammals exploded in number and variety, the English Channel did not exist. England and France were a continuous land mass and the current region of the Channel was underlaid by a layer cake of early Tertiary, Mesozoic and Paleozoic sediments (top to bottom) that sat atop the Precambrian basement. Then, in the Oligocene (about 30 MYA), in concert with the Alpine Orogeny, the crust buckled, producing a broad ridge that stretched from southern England to northernmost France.
Known to geologists as the Weald-Artois anticline, the ridge is oriented ENE to ESE. Erosion has uncovered the layered sediments that warp across the ridge; along the central axis (known today as the Weald), Jurassic and early Cretaceous sandstones and shales are exposed while, on the north and south flanks, late Cretaceous chalk forms escarpments that face inward. Now known and the North and South Downs, the soft chalk has eroded into swaths of low hills and ridges that parallel the axis of the anticline.
During the final quarter of the Pleistocene (less than 500,000 years ago), at least two glacial floods scoured the region, opening the English Channel and its narrow Dover Strait, thereby connecting an arm of the Atlantic with the North Sea and separating England from the primary land mass of Europe. Along the southeastern coast of England and the northern tip of France, cliffs of the late Cretaceous chalk now rise above the Channel, widely known as the White Cliffs of Dover. Indeed, the Cretaceous Period was named for these beautiful cliffs and the other chalk outcrops of northern Europe (creta is Latin for chalk).