EVOLUTION OF COASTAL DRAINAGE OF ESSEX. 43
strated that many of its characteristics are reflected in the
present-day landscape. It may also be noticed in figure 2 that
many of the existing streams have features that can only be
explained by a consideration of this pavement, and may be looked
upon as vestiges of the Mid-Pliocene riverine pattern. In
figure 2 the existing rivers show some indication of the influence
of the Chalk sub-stratum. The roughly parallel or fanlike river
nexus to the north-west is at once apparent, the streams making
for the country of a central broad valley, which is partly occupied
by the Blackwater Estuary. Only the Colne and the Stour,
however, are successful in reaching this, their apparent objective.
The tributaries of the Blackwater terminate as subsequent
streams along the first broad valley at the margin of the Boulder
Clay plateau.
Apart from this north-western drainage system the re-
maining Essex rivers appear to be connected with the Crouch
valley, or small, disconnected, coastal, marshy brooks. The
Crouch, it may be noticed, is not apparently connected with
the north-western series of streams but flows west to east, with
the Roach as its main tributary—an entirely different drainage
direction.
It has been stated above that the older river system, in-
augurated "consequently" upon the surface of the last uplift
(early Pliocene) could be reconstructed by a consideration of the
existing rivers and the Chalk pavement. With this idea in
mind the rivers, or portions of those rivers, that flow in accor-
dance with the slope of the buried Chalk surface were entered
upon a map of the district (figure 1).
From this map the task of grasping the scheme of the Essex
streams becomes easier. The water-parting dividing the area
drained by the Thames' tributaries and that drained by inde-
pendent streams flowing direct to the sea is seen to correspond
approximately with a crest of the underground Chalk surface.
This crest traverses the western district before it begins to dip
towards the basins of the Roding, Ingrebourne, etc. It will
be seen that many of the existing river basins correspond to
similar areas in the sub-surface relief of the top of the Chalk.
A further examination of the eastern watershed reveals two
major stream trends apparently related to the Chalk—a northern
one following a north-west to south-east direction, whilst to the