106
THE ESSEX NATURALIST
caused by man as a result of cutting mill races and other arti-
ficial works, whether for corn mills, fulling mills, powder mills
or for other purposes. The name Cornmill Stream still persists
in more than one place. Also the fact that the channel was
becoming silted up may have given rise to excavations for
navigation purposes. It is obvious that this theory will not be
acceptable until it has been supported by adequate historical
evidence, an investigation which is beyond the scope of this
paper. Further it appears that these disturbances took place
before the river had quite abandoned its old channel.
The Grey Loams. These, on the other hand, are quite dis-
sociated from the earlier deposits. The map on page 109 shews
the deposits at Fishers Green and indicates a substantial
distance between the grey loam and the earlier shell marls.
It appears to be coincidental that at Carthagena Lock the one
deposit is capped by the other for, a little to the south, in the
pit on the site of the former Broxbourne Aerodrome, the Grey
Loam is found to rest directly on gravel. Furthermore, it
occupies a narrowly defined band or "channel" which was
mapped by augering. This channel was found in the extreme
northwest corner of the pit and crossed another small pit in the
angle of the old and new Nazeing roads. The deposits of a
similar channel were found in a pit to the south formerly
worked by Eastwoods Ltd., but this is now worked out and the
writer has been unable to give it detailed examination. The
area illustrates two facts :
a. The Grey Loams do occupy a clearly defined channel, and
b. They are geographically independent of the shell marls of
the earlier substage.
Both the Grey Loams and the later Marsh Clays were dealt
with in some detail in the original paper [1957a] and further
discussion is unnecessary here. It may be mentioned, however,
that it is rare to find Unios and other characteristic molluscs of
the Canal Phase in the Marsh Clays. Owing to the brief
lifetime of that phase these shells are usually found only in the
alluvial muds of existing streams from which they are removed
by dredging. A number have been found in the Marsh Clay in
the region of the Walthamstow Reservoirs.