GEOLOGICAL AND PREHISTORIC TRAPS.
7
now realise that this "floor" industry is a developed Clactonian,
much earlier than the Cave Mousterian, and to some degree
at least ancestral to it.
An important line of evidence in the dating of the tundra
deposits of the Lea Valley is that they are substantially more
recent than the Stoke Newington "floor." If, as we formerly
thought, the "floor" be Mousterian, then the only known cold
phase into which the Lea Valley deposits can be fitted is the
Magdalenian. But the change in the dating of the "floor"
industry has removed any obstacle to a revision of the dating
of the tundra deposits to an earlier stage though still within the
Late Pleistocene.
The Clacton Channel Deposits.—When originally working
the Elephant-bed of Clacton, I looked upon it as filling up the
floor of a small tributary valley. But later, partly from the
abundance of Kentish Greensand chert and of the peculiar
"marbled" or "mahogany" flint from the Lower Thames
Valley, I came to regard it as the channel of the main stream of
the Thames-Medway, and this view is now generally agreed.
But during recent years much further light has been thrown
upon the details, and this is shown upon the sketch plan (Fig. 1).
Four main sources of information are included in this plan.
(1) The continuous erosion of the foreshore which is becoming
narrower and steeper owing to the effect of the sea-wall in
arresting waste along the high-water line; (2) drainage
trenches at Jaywick; (3), the scientific excavations of Dr.
Oakley and Mrs. Leakey; (4) drainage trenches and other excava-
tions at Butlin's Holiday Camp during 1938-1940.
It is now established that instead of one channel there is a
number of irregular channels, which may be of the nature of
"deeps" scoured out in the bed of a larger river, and these cover
a direct width of more than half a mile. Along the Jaywick
shore the Clacton mammalian fauna has been proved in the
channel deposits at the four points marked by arrows.
In the plan, horizontal lines indicate shallower deposits of
loamy gravel near the margin of the channels. Horizontal
crossed by vertical lines indicate the Jaywick type of sandy
and marly beds with mammalia and shells underlaid by the
river-bed gravel from which most of the flint industry is obtained.