15
III. The Blackwater Valley, Essex.
By W. H. Dalton, F.G.S., of H.M. Geological Survey.
[Read March 26th, 1881.]
Plate I.
The lower part of the valley of the Blackwater offers some
marked peculiarities of geological, and therefore geographical,
structure, and it has occurred to me that a sketch of it might
form a useful illustration of some general principles of those
sciences.
From the range of the Chalk hills overlooking Royston the
surface of the country slopes gently to the south-east as far
as Witham and Chelmsford, and then rises in the bold ridge
of Tiptree Heath and Danbury, separated by the estuary of
the Blackwater.
Part of this area is drained northward by the Cam, which
has cut its way back through the escarpment of the Chalk
at Saffron Walden ; the western part is drained by the Lea,
and the north-east by the Stour and the Colne, whilst the
central part, extending from Dunmow to Coggeshall, may be
termed the Blackwater Basin, though the rivers traversing it
bear the names of Cann, Chelmer, Ter, and Guith, the
easternmost stream only being termed Blackwater. The
course of all these is, roughly speaking, south-eastward, down
the general slope, into which they cut more or less deeply.
On reaching the ridge mentioned above, they flow along its
foot from either end, successively combining with each
other, and passing into the estuary near the middle. I need
not enter into the subordinate deviations of these rivers from
their general course, but may remark, in passing, that the
upper part of the Blackwater proper, called the Pant, is in
the direct line of the Guith from Shalford to Bocking, and then
passes by a more easterly course to Coggeshall and Kelvedon.