Geoscience Reference
In-Depth Information
Pliocene molluscan fauna of the Crag Sea and eventually may have exterminated a
greater part of it. Although communication with the saline waters of the Atlantic
Ocean was subsequently re-established by the retreat of the ice sheet in the late
Pleistocene and the cutting of the Strait of Dover in postglacial times, the mol-
luscan fauna of East Anglian waters has never regained the richness and variety it
possessed during the earlier stages of the Pliocene epoch.
3.4 The Pleistocene Epoch in East Anglia
By compiling and analysing a collective of accounts made by glaciologists in
England and Wales, the origin and movement of the ice streams associated with
the glacial deposits of East Anglia was determined by Harmer and illustrated by
means of a contoured map. This was the first detailed cartographic attempt to show
the distribution of erratics and drift in England and Wales in which a system of
symbols was employed to indicate the respective sources of these features (Harmer
1928
).
Among the geologists who first attempted to resolve the nature of East Anglian
drifts, several notable pioneers can be included such as William Buckland
(1784-1856), who noticed the presence of Norwegian erratics (1823), R.C. Taylor
who called attention to contortions in the coastal sections (1824), C.B. Rose who
identified boulders from Mountain Limestone and various Jurassic strata in the
'diluvium' (1835), and Joshua Trimmer (1795-1857), who recognised two types of
boulder-clay in the cliff section at Gorleston, the lower identified by Scandinavian
blocks and the upper by Oolitic detritus, which he had traced towards the west.
Despite these early 19th century findings, Harmer and others realised that
comparatively little had been discovered about the distribution or stratigraphy of
the clay, sand and gravel beds which comprised the glacial deposits, as well as the
conditions under which they had originated. The only map to show glacial deposits
then in existence was one published by Samuel Woodward in 1833 and although
the relation of the Crag and 'Diluvium' (an early 19th-century term applied to
superficial deposits then believed to be due to a catastrophic biblical deluge) of the
coast between Cromer and Great Yarmouth to the underlying chalk had been
correctly shown, no attempt had been made up to that time to map the glacial
deposits over an extended area, either in East Anglia, or, as far as it was known, in
any other part of the world (Figs.
3.21
,
3.22
,
3.23
and
3.24
).
