Field meeting to the Romney Marsh area, Sunday 14 March 2010
Peter Allen 13 Churchgate, Cheshunt, Herts EN8 9NB
Seven members and one guest met for this traverse of Romney Marsh. Much of the
geological interest lies below ground, as would be expected, but certain features do
reflect the history of the Marsh.
The area actually comprises three marshes, Romney, Walland and Denge Marshes,
occupying an embayment between Rye and Hythe and sitting on a bedrock platform
sloping from c.20-30m below sea-level in the inner area, falling to 40m below beneath
Dungeness. During the Devensian cold stage (18,000-12,000 years ago), sea-level fell
to possibly as much as -120m OD. As the Devensian glaciers melted, sea-level rose
again and by c.10,000 years ago, the sea began to cover the bedrock platform. At this
stage, the sea could erode the cliffs behind the platform. It had been thought that the
eroded sand was worked into a long sandspit running north-eastwards from Fairlight,
near Hastings, to Rye, but this is now realised to be an oversimplification, but a barrier
of some description formed across the mouth of the embayment. Between the barrier
and the cliffs, the water would have been saline, but protected from storms, so silt and
clay or peats accumulated to form the marshes. During periods of higher sea-level, the
sea dominated and laid down silt and clay, but when the water was excluded, fen
vegetation developed and became peat. The marine nature of the silts and clays is
confirmed by the presence of Scrobicularia and other estuarine molluscs. By dating
the junctions between the silts-sands and the peats, we can build up a chronology of
when the sea dominated and when the fen formed. Carbon (C14) dating of the junction
between the clays and the overlying peat, shows that the major peat layer started forming
c.6000 years ago. This was long before human intervention could have excluded the
sea from such a wide area, so a drop in sea-level is implied. Further silts and clays
above the peat indicate a return of the sea about 3000 years ago. As these upper silts
and clays are above OD, sea-level at the time must have been higher than at present.
Subsequently sea-level dropped, so the marsh area began to be exposed. With this
drop in sea-level, the River Rother flowed from near Rye across the back of the marshes,
as a wide river or estuary, to debouch near Hythe.
By Roman times a port, Portus Lemanis (Lympne) was established on the north side of
the estuary. The remains of the Roman Fort (Stutfall Castle; TR 118342) was seen at
the foot of the slope below the more recent Lympne Castle. There was exposed marsh
on the south side. This marsh was reclaimed at various times between the Roman
period and the 11th Century, forming Romney Marsh. Because of the age of the
reclamation, exposure and farming have led to a loss of calcium, from the shells, and
to shrinkage of the peat. Thus the land surface is c. 2-3m OD, but old sand-filled river
channels have not shrunk to the same degree, so they now stand out as slightly higher
ground, by l-3m. Elevated former channels were seen at Snargate church (TQ 991287)
and again at Godhall (TR 000 289). The Rhee Wall, running through Snargate, was
originally a channel cut through from the Rother estuary, which was silting up, to
Essex Field Club Newsletter No. 62, May 2010
21