SURVEY AND COMPARISON 165
end of the main wall, since the whole of Two Tree Island
forms pasture-land. On the seaward side, Halimione,
Agropyron, Beta and Atriplex occur, but only in scattered
patches. It is of interest that, whereas Artemisia maritima
occurs only once near the mainland sea wall, it is found in
several places on the seaward side of Two Tree Island, and
much more frequently on Canvey and on the north Kent
coast. This suggests that a gradual spreading of this species
from the Kent to Essex coast is occurring here.
THE INNED SALT MARSHES
On the mainland, the distance from the sea wall to the
base of the escarpment varies from a quarter to nearly half
a mile. The enclosed land is extremely flat, and is divided
into fields of various shapes by drainage creeks or ditches.2
Since the area is all at one level, the main factors influencing
the vegetation are again drainage and salinity.
The drainage of the enclosed land is effected by these
ditches. Small channels in the fields carry excess water
away into the surrounding ditches. Where these have been
dug specifically as drainage channels (see Sites 2, 5 and 6),
they are usually four or five feet deep and one or two yards
wide. Many of these are unconnected with adjacent
ditches. Where creeks of the old salt marsh, which were cut
off by the building of the sea wall (see Sites 3 and 7), are
used as drainage channels, they are usually only one or two
feet deep and are much wider. There is very little move-
ment of water in most of the creeks, and there is only one
outlet to the sea, near Site 4A. This consists of a small pipe
connecting Creek 4 to one of the main creeks of the salt
marsh, and a little drainage water escapes this way. It
appears, therefore, that the main drainage system relies on
the accumulation of water in the ditches in winter and its
evaporation in summer. Most of the creeks, particularly the
narrow, specially-dug ones, do dry up completely in summer.
This seems a somewhat inadequate system, especially to the
west of the inned marshes, where water brought by streams
from near Hadleigh Castle collects, but serious flooding
rarely occurs. In the recent heavy rains some of the
2 The terras "creek" and "ditch" are interchangeable in the consideration
of the inned marshes.