[DanaC]

The cliffs themselves were formed at the same time as the Strait of Dover, by ice-age floods.
The cliffs are mainly soft white chalk with a very fine-grained texture, composed primarily of coccoliths, plates of calcium carbonate formed by coccolithophores, single-celled planktonic algae whose skeletal remains sank to the bottom of the ocean during the Cretaceous and, together with the remains of bottom-living creatures, formed sediments. Flint and quartz are also found in the chalk.[8] White cliffs like those of Dover are also found on the Danish islands of Møn and Langeland and the island of Rügen in Germany. The chalk cliffs of the Alabaster Coast of Normandy, France, are part of the same geological system as Dover's cliffs.