Geoscience Reference
In-Depth Information
Fig. 3.20 P680266 (1907) Construction work at Castle Meadow with wooden supports on the
slope descending from Norwich Castle; the exposure of chalk and other deposits at this city site
would have been of great interest to Harmer. (CP13/050 Reproduced by permission of the British
Geological Survey NERC. All rights reserved)
3.3.5 The Icenian Crag
The Icenian Crag (a term derived from the name of the Iceni, an ancient tribe of
East Anglia) includes the Norwich Crag, Chillesford Beds and Weybourne Crag.
Whilst the Red Crag is a shore deposit, the formations of the Icenian Crag are
believed to have been deposited in shallow waters of the Crag Sea near the estuary
of a large northward-flowing river that was probably the forerunner of the Rhine.
The suggestion that there may have been a gradual diminution in the salinity of
the Crag Sea during later stages of the Crag period would explain the decline of
molluscan fauna in the succeeding Icenian deposits, as compared with its great
variety and abundance during the preceding periods. The advance of the ice sheet
from Scandinavia in the Icenian period may have gradually obstructed and
eventually brought to an end the northern communication of the Crag Sea, while
fresh water continued to pour into the sea from the south. Such an influx of fresh
water, especially during summer, would have formed a large lake with waters
which increasingly became brackish. This might have changed the character of the
