THE HISTORICAL STAGE IN THE LEA VALLEY 105
3. DISCUSSION OF THE HISTORICAL STAGE
In a recent paper I argued that the Rammey Marsh Stage
continued to within a century or so of 1000 A.D. All deposits
subsequent to that date are placed in the Historical Stage.
When this was defined it was divided into two sub-stages, a pre-
Canal Phase and a Canal Phase, the linkage of the Lea with the
canal system early in the 19th century causing an influx of new
molluscan species. Field work which has been carried out since
the original descriptions has done much to clarify the relation-
ships between the various horizons, and the following table,
which should be read from the bottom upwards, lists the sub-
divisions :
THE HISTORICAL STAGE
B. CANAL PHASE
(circa 1800 A.D. 4. Marsh Soils, Marsh Clays (part)
onwards) and alluvial muds.
3. Marsh Clays (part).
A. PRE-CANAL PHASE 2. Grey Loams.
(circa 1000 A.D.
to 1800 A.D.) 1. Shell Marls with much re-sorted
material.
The Shell Marls. When these were first examined at Cartha-
gena Lock, it was clear that they contained much derived
material. Futher proof of this Was obtained from the Brox-
bourne section. It now seems that this state of affairs was
rather widespread in the valley and that the deposits are linked
very closely with those of the previous Stage.
At Fishers Green the calcareous concretions of the Rammey
Marsh Stage were found to underlie a bed of shell marl similar
to that examined elsewhere [see map on p. 109]. At Forest Bd.,
Walthamstow [Hayward, 1957b] the band of shelly material
in situ was very thin and impersistent whereas the base of the
Marsh Clay above it was rich in shells which had clearly been
derived.
In a previous paper [1957a] the writer stated ". . . at various
times the river changed its course in such a way as to cut
through one or more of its previously abandoned channels."
He now believes that this changing of channel was largely