The “Longues Pièces” lies on an area of sedimentary deposits dating from the Senonian period (secondary), made up of white chalk formed from flint. Fine and porous, this chalk is particularly visible on the top of the cliffs at Cap Blanc Nez. This sheet then gives way to a layer of white chalk from the upper Turonian stage which can be distinguished by the fossils embedded in it. The average thickness of this layer is 10 metres.
