The English Channel Isthmus

On the subject of northern France has anyone noticed something interesting about the beaches along the English Channel? On both the French and English sides the beaches alternate between being sandy and Stony. This is because, before the last ice age, there was an isthmus connecting the two countries. Rock is broken down into sand by the action of waves, but it takes a very long time. The ice age ended about twelve thousand years ago and that is not enough time to completely break the rock into sand. In the following image, from Google Earth, the enclosed area is the approximate location of the former isthmus.

At Folkestone, near the eastern end of the English Channel on the England side, the beach is sandy.

But if we continue westward to Hastings, the beach becomes stony.

Further west, at Eastbourne, the beach is still stony.

At Brighton, the stony beach continues.

At Bognor Regis, there is still a stony beach.

But low tide at Bognor Regis reveals sandy beach further from shore.

However if we continue west to Bournemouth, past the Isle of Wight, the beach goes back to being sandy.

On the French side of the English Channel, the beach at Boulonge Sur Mer is sandy.

But if we move westward along the coast, the beach at Sainte Valery En Caux is stony.

Continuing westward, the beach at Fecamp is still stony.

But if we continue west to Le Havre, the beach goes back to being sandy.

The reason is that France and Britain were connected by land, but the last remaining isthmus between the two was swept away by moving glacial ice during the last ice age. Sand comes from the action of waves gradually breaking down rock into particles, over long periods of time. The stretches of stony beach, which is longer on the English side, are areas that only became beaches with the last ice age, which ended about twelve thousand years ago.

There has not been enough time since then for the waves to break the rocks on the beach completely down into sand. The rocks have been broken down into small pebbles, but not yet into sand. The areas of sandy beach have been beach for much longer.

The reason that there is sandy beach visible at low tide at places such as Bognor Regis is that the beach was not suddenly cut away by glacial ice there. The rock has been gradually being broken down by waves. Ice age movement of glacial ice will break loose some rock from higher ground above the beach, and the waves will proceed to gradually break it down.