GEOLOGICAL AND PREHISTORIC TRAPS. 9
Vertical crossed by diagonal lines represent the original Clacton
deposit, which differs markedly from the rest in containing
vegetable remains in great abundance : it is evidently the result
of settlement in a stagnant backwater cut off from the flowing
stream. Circles indicate the overlying estuarine horizon, which
includes fossil oyster beds below the present O.D. level.
Temporary excavations in the west cliff in May, 1939, revealed
the base of the estuarine series with marine shells immediately
overlying a layer of Unio littoralis at about 8 feet above O.D.
Finally, the sign i3 indicates London Clay, which forms low
ridges between the channel deposits. The main channel at
Butlins has been proved down to a level of 6 feet below O.D.
without reaching the base.
I shall have more to say in the next section about channel
deposits, but I might also mention the pit of the Lea Valley
Sand Co. at Hallsford, near Ongar. This is in ferruginous
Glacial sands, and a channel of re-arranged, leached, sand
with vegetable remains can be clearly traced. In the latter I
recently found a mammoth molar which might easily have been
recorded as from Glacial sand, and no suspicion of error would
have arisen, although in fact it would have been quite wrong.
The "Forest Bed" near Harwich and the Essex
Coastal Plateau and its Gravels and Crag.—For nearly
40 years I have, at frequent intervals, examined the gravels
of the Essex coastal plain, which lies at about 70 to 80 feet above
O.D., with a gentle rise inland. Yet it is only now that I have
found a key to suggest something of their true character.
During the summer of 1939 a sewer trench was cut along the
road through the village of Little Oakley, 3 to 31/2 miles south-west
of Harwich. This revealed a sandy river deposit, not unlike
that of the Jaywick channel, but too high in level to be associated
with it. The thickness of the deposit itself lay between 60
and 70 feet above O.D. (the surface being about 75 feet O.D.
at the lowest point), and I have reason to believe that it extends
5 or 10 feet higher in places.
It was very rich in shells, which I submitted to Mr. A. Santer
Kennard, who later joined me on the site to collect for himself.
I also secured a number of deer antlers, Microtine remains, and
other bones. The results, so far as at present worked out, are