the Mesozoic, from hundred and
fifty to sixty-five million years ago ,under a
warm and damp climate , not
only did the dinosaurs but many other species become extinct among
ammonites and sea urchins constituting the marine plankton. It is the
sedimentary accumulation of their calcareous remains that created the
cliffs that we can admire today.
The one hundred and thirty kilometres of chalk cliffs along the coast, called the alabaster coast , are a unique setting highly sensitive to erosion.
the effect of the swell, frost, water seepage,
and other factors linked to the constitution of the chalk itself, the
eroded of about twenty centimetres a year. The blocks that fall down on
strand release chalk and flint.
chalk is rapidly dissolved in the sea while the flint is rolled and
the sea and eventually becomes a pebble.
into an offshore bar which constitutes a natural
barrier which protects the
bottom of the cliffs against direct
attacks from the waves.
phenomenon is common to all the cliffs along the Channel coasts
, so this
is what happens in Sussex with the Seven Sisters for example.
has made this natural environment change.
Indeed, the economical development of ports induced the building of
sea walls in order to allow an easy access to bigger and bigger boats .
setting up of heavy equipment, such as the oil rig at Antifer or the
power stations around Dieppe, changed the coastal landscape and
erosion and the recession of the cliffs. ( from half a meter to a meter
. Huge sections fall down into the sea causing
the collapse of houses built on top of the cliffs .
are also a valuable industrial resource.
The traditional collecting of pebbles on the beaches of Dieppe and Le
was forbidden in 1985 in order to preserve the stock of pebbles and
protection of the cliffs . This activity increased however in the area
Somme mouth where the stock of pebbles is important.
pebble , made of ninety-nine per cent of silica , is exported to
countries over the world because it can be used in industry in three different ways :
regular-shaped pebbles are used to crush fragile chemicals in
pharmacology. Their purity do not alter the products.
- In spite of their hardness, pebbles can be crushed into grains of different sizes which are then used as gas or water filters or come into the making of glass-paper
- When the pebble is brought to a temperature of one thousand and six hundred degrees centigrade, it changes into a white powder which is used to make earthenware and ceramic, such as the famous English Wedgwood or the French Luneville. The burnt pebble also comes into the making of toothpastes, road-paints or architectural coatings.