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The Geology of Folkestone
The beds exposed at Folkestone belong to the
Lower Cretaceous era of the Albian stage, dating
back to approximately 113 million years.
The lowest beds exposed are the Folkestone Beds -
more commonly referred to as the Lower Greensand.
These sandy beds probably accumulated in shallow
seas under the influence of strong currents.
Few fossils are found in the main mass of sand,
but the sandstone beds and phosphatic nodules
contain a rich fauna of ammonites, bivalves,
echinoids (sea urchins), gastropods, driftwood,
fish and reptilian remains in the 60 ft. of the
formation.
Above the Lower Greensand is the Gault. The
base of this marks an important marine trans-
gression in Southern England, which swept north-
wards and westwards to the borders of Wales and
into Northern England. The gault, a shallow
water deposit, was laid down in quieter waters
farther away from the source of the sediment.
The gault consists of dark bluish grey to pale
grey soft mudstones which weather to yellow and
brown clays. The basal few feet of the formation
are commonly silty or sandy. Phosphatic nodule
beds also occur, marking brief halts in deposition
These nodule beds, together with those from the
Lower Greensand were formerly worked for
agricultural use. The gault contains a rich
fauna in which molluscs predominate.
The formation is divided into four ammonite zones:
the zones of HOPLITES DENTATUS and EUHOPLITES
LAUTUS which make up the Lower Gault correspond
to the mid Albian stage and the zones of
MORTONICERAS INFLATUM and STOLIEZHAIA DISPAR
correspond to the Upper Albian or Upper Gault.
The gault is about 130-150 ft. thick at Folkestone