65
THE EVOLUTION OF THE COASTAL
DRAINAGE OF ESSEX.
By RUPERT COLES, B.A., Ph.D.
[Read 24th November, 1934.]
Continued from p. 49.
The main channel lying at about 150 ft. above O.D. must
have differed very little in its essential outlines from that of the
previous Binfield stage. Within the Essex area it left the
present line of the Thames near Blackwall and followed a slightly
curving line to Lawling Creek by way of Upminster. Fluvio-
glacial gravels at the appropriate altitude support the suggestion.
It is also possible to discern in the district the outlines of a trench
with flanks well above the 150 ft. level and base at 150 ft. O.D.1
It seems probable that the Proto-Darenth joined the main
river somewhere to the south of Brentwood, but the Medway,
which until this period had been a persistent feature of the
system, introduces difficulties. The ground of the Rochford
Hundred bears no gravels at the necessary height to allow us to
decide whether, or not, its ancestor crossed this district. It is
possible, however, that a river may have carved a way over the
present gap between Leigh and Fobbing, but there is no evi-
dence to support or contradict this theory. A more probable
alternative is that the Medway began its present northern
channel at this juncture; the North Sea concurrently having
increased its extent.
Of more importance to Essex were the conditions along the
left bank. The approach of the adjacent ice-sheet must have
resulted in a temporary increase in the volume of the northern
tributaries which is borne out by the fact that deep pre-glacial
buried channels occur. A further result, and one apparent in the
present relief, is the multiple river capture that seems to have
taken place at that time, perhaps aided by the rising of the
Tiptree ridge. If, however, the Tiptree ridge is considered
as of earlier date, the previously mentioned Pliocene rivers in
the Thurstable area (the Proto-Pant, Brain, etc.) must be
regarded as belonging to an antecedent system. If this was not
so (i.e., if the Tiptree ridge resulted from the capture and was.
1 South-Eastern Union of Scientific Societies. 1926. Wooldridge, S. W.