CHAPTER XIX.

DENUDATION OF THE CHALK AND WEALDEN.

Physical geography of certain districts composed of Cretaceous and Wealden strata--Lines of inland chalk-cliffs on the Seine in Normandy--Outstanding pillars and needles of chalk--Denudation of the chalk and Wealden in Surrey, Kent, and Sussex--Chalk once continuous from the North to the South Downs--Anticlinal axis and parallel ridges--Longitudinal and transverse valleys--Chalk escarpments--Rise and denudation of the strata gradual--Ridges formed by harder, valleys by softer beds--Why no alluvium, or wreck of the chalk, in the central district of the Weald--At what periods the Weald valley was denuded--Land has most prevailed where denudation has been greatest--Elephant bed, Brighton 238