THE CHANGING COASTLINE OF ESSEX 81
extending northwards from Colne Point towards Brightling-
sea Creek has the natural character of the coast been
preserved, although even here in the neighbourhood of the
point itself there has been considerable working of the
shingle for road metal, etc.
In the Dengie Peninsula, bordered by the Rivers Black-
water and Crouch, the close relationship existing between
the geological formation and the topography is well
illustrated. Inland, the London Clay with its capping of
Pleistocene Gravel and Brickearth in places, forms a low,
dissected plateau rising to over 100 feet above sea level. The
clay is extended east of Bradwell to reach the present coast-
line near the site of the Roman Fort of Othona. Elsewhere,
between the clay outcrop and the shoreline, are marshes
named after the nearby settlements on the clay plateau to
the west, e.g., Bradwell, Dengie, Southminster, etc.
(Fig. 2).
Punning through the marshes northward from Holliwell
Farm to the neighbourhood of the former site of Othona is
a long narrow ridge of shelly sand and shingle. It rises
slightly above the marshes on either side, having a height
of 10 to 12 feet, compared with 3 to 8 feet in the bordering
marshes. It is also the boundary between the lower marsh
(height 3-7 feet) to the west with its irregular drainage
pattern and the enclosed upper marshland (height 7-8 feet),
with a regular pattern of ditches in the east.
This geological dividing line is reflected in the human
response, for most of the farmsteads situated in the marshes
lie along the ridge. The lower marsh is largely given over
to permanent pasture, whilst the newer upper marsh is
predominantly under arable cultivation.
To the south of the River Crouch, in the ''island
province" of Foulness, Wallasea, Potton, etc., the London
Clay is only found at depth, being overlain by 40 to 50 feet
of alluvium and sand. In Foulness Island there are a num-
ber of isolated patches of shelly sand, similar to those found
in the marshes of the Dengie Peninsula. This island is really
built up of a number of smaller islets, separated by creeks
which have now silted up, although many are still plainly
visible on the ground. Reclamation by dyke building has