EVOLUTION OF COASTAL DRAINAGE OF ESSEX. 67
quent stream. The connecting dip valleys had also become
established. It will be noticed, moreover, that the main river
by this time had migrated to the right arm of the "Y"-shaped
depression already mentioned. The Tendring area then, as now,
remained outside the region of the rectangular pattern.
In the later Pleistocene period (i.e. after glacial times) a river
system supervened whose main lines are suggested in figure 6.
This system, approximating in outline to the existing river
pattern, is deduced from the evidence of the remains of the
100 ft. or Boyn Hill terrace. From the gravels on the latter it
Fig. 6. The Probable River-System of Essex in the Later
Pleistocene: the "100 Foot" Terrace Period.
would appear that the Proto-Thames followed a meandering
course curving south of the present Canvey Island, and flowed
by way of Southend across the Rochford and Dengie Hundreds
to the Blackwater. The cause of this shifting is not apparent,
although it seems highly probable that the main stream had
forsaken the right arm of the "Y"-shaped or Hanningfield
depression as the land to the north-west rose owing to isostatic
readjustment consequent upon the melting or withdrawal of the
ice-sheet.
The rivers to the north-west of the district must have flowed
very much as they do to-day. Fed by generous supplies of