48
THE ESSEX NATURALIST.
in the Thurstable Hundred. The reason for their presence
is largely a matter of deduction, but they must have existed
then (i.e. Binfield stage) or earlier, for capture has obviously
taken place in the following stage before glacial material hid the
evidence of the wind-gaps. Reference to figure 1 will show those
parts of existing streams that conform to the dip of the Chalk
pavement. In this map the riverless Salcott Channel appears
in alignment with the middle Pant; Goldhanger Creek, Cressing
Brook and the upper Pant forming a second line. The major
upper portions of the rivers Brain and Chelmer may be extended
in a south-easterly direction as though joining the main stream
near Lawling Creek and the head of the Crouch Estuary. These
four "recovered" secondary consequents are the streams indi-
cated in figure 4.
Up to the junction of the Chelmer and the main stream
this course of the Proto-Thames in late Pliocene times has been
traced with some degree of confidence, but beyond this point its
course is largely a matter of inference from rather doubtful
evidence. On the right bank, beyond the Rayleigh Hills, no land
reaches to the 200 ft. level. We therefore have no evidence
that would justify the drawing of the main river north of the
Dengie Heights as has been done in the map. These heights do,
however, reach to above 170 ft. and slope to the north. On
the left bank borings fail to give satisfactory evidence of a
200 ft. platform, since the river course has now reached beyond
the zero-isobase that passes through Braintree and is therefore
in the region liable to recurrent warping. In the Tendring
Hundred, however, and north of a line passing from the coast to
Thaxted are remnants of Red Crag, and of other marine beds,
indicating invasions of the sea in Pliocene times. It seems,
therefore, not unreasonable to suppose that the river might have
flowed towards this district by way of Clacton rather than across
the Dengie district. If this latter alternative had taken place,
and bearing in mind that fact that the later courses of the Proto-
Thames continue the south-eastern migration, we should expect
to find some remnants of the northern bank within the Dengie
Hundred. Since, however, the height of that district reaches
only about 170 ft. it seems more probable to suppose the river
took its course to the north-west following the trend of the present
Blackwater Estuary.