Geoscience Reference
In-Depth Information
Mousehole Heath has been cut into by the Wensum, immediately northeast of the city-
centre bend. Mousehole Heath is underlain by an extensive sheet of gravel and sand
that seems to have been left there by northward-flowing rivers draining from a tongue
of ice that existed to the south at some time during the Anglian cold spell. Ice-laid ma-
terial to the south of Norwich, particularly near Poringland, reaches an elevation of 75
m, which is high for this area.
Landscape D: Late Tertiary Crag hills and the Broads
This Landscape is defined by the presence of Late Tertiary bedrock, generally known
as the Crag, resting upon the Late Cretaceous Chalk. Chalk is exposed on the shore at
West Runton near Sheringham (
d1
), but the Late Tertiary Crag is exposed above this
over most of eastern Norfolk and Suffolk. Of special interest are coastal exposures of
the Cromer Forest Bed, which forms a very important and remarkably extensive layer
sporadically visible for more than 60 km from Cromer (
d2
) in the north to Happisburgh
(
d3
) and as far south as Pakefield (
d4
). The Cromer Forest Bed consists of a variety of
mudstones and sandstones, often carbonate-rich and full of fossil remains. The fossils
represent temperate climatic conditions and are overlain by distinctive glacial deposits
representing a return to a much colder climate. Understandably, great interest has fol-
lowed the recent discovery of flint artefacts, convincingly made by early people, both
at Happisburgh and at Pakefield. These are thought by some to represent the oldest
evidence of early humans so far found in lands north of the Alps. However, the Cromer
Forest Bed deposits and the overlying glacial deposits are complicated, involving many
local episodes, and their dating is still open to doubt and expert disagreement. Some
workers believe that the glacial deposits represent a pre-Anglian glaciation, and that
the flint implements beneath them must therefore be some 700,000 years old. Others
feel that the glacial deposits are of Anglian age and that the flint implements are more
likely to be ≈500,000 years old, an age more consistent with the currently accepted
date of settlement at these latitudes.
The cliffs in the foreground of Figure 310 are actively collapsing by land-slipping
under the attack of North Sea winter storms. They provide a cross-section through
the Cromer Ridge, one of the highest hill features in Norfolk, reaching 90 m above
sea level just inland of Sheringham (
d1
), and extending more than 10 km towards
the southwest. The ridge is thought to have been deposited by ice sheets and contains
gravel and sand, along with contorted blocks of mixed sediment tens of metres across.
Much of this appears to have been dumped, folded and fractured by ice sheets of
the Anglian cold episode, which came from a northerly direction some 450,000 years
ago (see Chapter 2). The deformation of the material suggests that the ice margin re-
peatedly advanced and retreated, scraping up and bulldozing its earlier deposits in front
