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became dry land, now named Doggerland (after the Dogger Bank). As the
shoreline moved northwards, so the proto-Thames and other major rivers such as
the Rhine flowing into the Crag Sea extended across the former sea bed. The
molluscan shells of the Red Crag indicate a cooling of the climate compared to
previous stages and this formation is sometimes considered to mark the onset of
the last Ice Age.
This is in accordance with the re-classification since Harmer's time of the East
Anglian Crags in the geological column, whereby it is now generally agreed that
whilst the Coralline Crag should remain in the Pliocene Epoch, the Red Crag and
Norwich Crag should be designated to the Pleistocene (Challinor 1978 ). Thus
today the division between the Pliocene and the Pleistocene epochs in Britain is
placed at the boundary between the Coralline Crag and the Red Crag of East
Anglia. At this point there is a relatively clear stratigraphical break, a marked
increase in the proportion of modern forms of marine mollusca and mollusca of
northern aspect, as well as the first arrival (in the Red Crag) of the antecedents of
today's fauna species such as the elephant and horse.
References
Challinor, J., 1978: A Dictionary of Geology (Cardiff: University of Wales Press).
Harmer, F.W., 1914-1919: A Monograph of the Pliocene Mollusca of Great Britain, being
supplementary to Searles V. Wood's Monograph of the Crag Mollusca, Volume I, (London:
Palaeontographical Society).
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