Geoscience Reference
In-Depth Information
Flints are a common feature in the upper layers of the Chalk, and are the major
component of the river and beach gravels of Norfolk. They have been abundantly used
in the building of many walls and houses. The flints formed in the first place by min-
eral growth within the soft muddy sediment that was later to become the Chalk. They
grew when silica was precipitated from the water in the minute spaces and cracks that
are always present in young sediment, replacing the calcium carbonate that was present
before. In areas close to the coast, flint walls often show the flints with their rounded,
sometimes white exterior crusts, whereas elsewhere flint walls consist of 'knapped'
flints with a flatter, black face outwards, created by cracking open the flint before
mounting it in the wall.
The scenery of the coastal zone of northwest Norfolk is much younger than the
valleys and slopes visible inland. This is because the sea has only arrived at its present
position within the last few thousand years, since the general melting of the Earth's ice
cover that took place at the end of the Devensian, about 20,000 years ago (see Chapter
2).
Hunstanton (
c1
) is the only place in the whole of East Anglia where tough, over-
hanging sea cliffs occur. This is because there are no other localities where hard bed-
rock has become directly exposed to the attack of storm waves.
Hunstanton is also famous for the three differently coloured layers of bedrock in
its cliffs: a layer of Late Cretaceous white Chalk overlies an Early Cretaceous layer of
brown sandstone (Carstone), with a thin layer of red Chalk between them (Fig. 297).
The detached and fallen blocks of white chalk at the base of the cliff show that the
cliffs are collapsing and moving inland all the time. The regular rows of weed-covered
Carstone blocks in the lower part of the beach show how the storm waves have created
a wave-cut platform with a regular system of
joints
(cracks). These joints were formed
during an early and widespread phase of stressing of the bedrock.
East of Hunstanton the coastline is characterised by spits, beach ridges and bar-
riers, often with salt marshes divided up by the tidal channels that are typical of this
coastal stretch. The Burnham Flats are an offshore area of unusually shallow sea, north
of Scolt Head (
c2
), that produce the special coastal scenery of this area. The Flats ex-
tend some 25 km out to sea before the depth at low tide becomes greater than 10 m.
This means that when the sea level was rising due to melting of the Devensian ice,
the sea must have flooded over this area of land extremely rapidly. More importantly,
the flatness and shallowness of the Burnham Flats has allowed vigorous attack on the
sea bed by storm waves, moving considerable quantities of sediment and constructing
beach barriers with their associated salt marshes.
