6
The Essex Naturalist
Guildford, Surrey, and Rothamsted, near St Albans, Hertfordshire. Due to uplift of
western Britain (Boulton, 1992), the sea shallowed and withdrew from the
syncline of the London Basin and rivers draining to that sea extended over the
former sea bed. The early Thames extended to cross the northern part of the Crag
basin and laid down the Kesgrave Formation, a series of gravels which record the
early alignment of the Thames from the Goring Gap in Oxfordshire across Essex
and Suffolk to Norfolk. The gravels also indicate that the Thames progressively
migrated to the south-east and with each shift of course the river cut down to a
lower level. Immediately prior to the Anglian glaciation, the Thames crossed
central Essex and went offshore, still as a river, in the Clacton area (Fig. 2a).
Fig. 2. The diversion of the Thames. (After Bridgland, 1995)
(a) The last Thames course across central Essex.
(b) The disruption and diversion of the Thames by the Anglian ice.