151
ON SUBSIDENCE OF THE THAMES ESTUARY
SINCE THE ROMAN PERIOD, AT
SOUTHCHURCH, ESSEX.
By A. G. FRANCIS, O.B.E., B.A., F.R.C.S., F.S.A
(With 2 Plates and 1 Text Figure.)
(Read October 31st, 1931.)
IN 1885 and subsequent years Mr. F. C. J. Spurrell [1]* stated
that:—(a) There is no certain evidence that the Romans
constructed embankments in the Thames Estuary to keep out
the tide. (b) As the level of Roman occupation is far below
Trinity High Water mark (121/2ft. above Ordnance Datum), the
land surface between London and the mouth of the Thames
must have been several feet higher at that time. (c) A gradual
subsidence of this area has taken place during and since the
Roman period.
These views have been endorsed, and additional evidence
given, by other writers; but there is some difference of opinion
concerning the point at which tidal action ceased.
Mr. Spurrell thought that the estuary began at East Tilbury
or Gravesend and that there was fresh water above this point.
On both sides of the river there was formerly a large forest
with many yew trees; it has been traced in the marshes of
Long Reach and nearer London, at Dagenham, Rainham,
Dartford, Erith, Plumstead and Crossness; the stubs of large
yews appear in both banks in Long Reach and on the foreshore
at low tide between Purfleet and Grays [2]. The forest grew at a
level which is now 121/2ft. below T.H.W.; as this is the average
level of Roman occupation in this area the forest was probably
in existence at this period. The yew is intolerant of water and
cannot live in salt; therefore, the land must have been upwards
of 13ft. higher and tidal action ceased below Grays. In the
region of Tilbury and Gravesend the outcrop of chalk and large
patches of river gravels offered sites suitable for habitation and
an easy passage across the Thames from prehistoric times
onwards; in the early part of the Roman period there was
extensive occupation of both sides of the river and probably a
ford or ferry [3] at this point.
* For figures in brackets see references on p. 168.