16
THE ESSEX NATURALIST.
London Clay. I have, however, proved the continuation of the
Lion Point channel deposit inland to the north-west of this
hummock of London Clay. I think the channel probably sweeps
round in a wide curve between the two coast sites at a distance
of about 1/2 mile or more from the sea. A keen watch should
be kept on any temporary excavations along this line.
The foreshore section across the Clacton channel shows it to
be about 500 yards in width at high-water mark, and 200 yards
or more at low water. The Lion Point channel deposit is a little
more than 500 yards wide at high-water, and some 300 yards
wide at low-water level. In either or both cases the foreshore
section may be an oblique cut across the channel, and conse-
quently in excess of its true width ; on the other hand, the
original channel may have spread out to a greater width above
the level of high-water, although this is no longer visible7.
Judging from the slope of the old river bed on either side of the
two channels, I should think that the channels extend
downwards about another 4 feet below low-water, perhaps rather
more in the case of the Clacton channel. As the rise of spring
tides is about 12 feet this would give some 16 feet as the depth
of the former river below the present level of high tide.
I formerly thought that the Clacton channel deposit occupied
the floor of a small tributary valley. I now realise that instead
of being a small valley that would have a mere brook flowing
through it, we are concerned with the actual water channel of a
big river. When we take into consideration the vast quantity
of Thames-Medway material the deposit contains, the conclusion
seems inevitable that we are dealing with the actual channel
of the main Thames. At the same time we have also to explain
the unusual circumstance of the quantity of timber and other
vegetable material that the Clacton channel (but not the Lion
Point channel) contains. I think the simple explanation that
it was a meander or loop that was at one time cut off as a stagnant
backwater in which the vegetable material had time to settle
instead of being swept away, is probably the true one.
As is well known the lower part of the silting of the Clacton
channel, that is, below the present level of high-water, is purely
freshwater, but the upper portion of the silting is estuarine. In
7 In the case of the Clacton channel the eastern bank is still preserved to a wider and higher
position in the cliff.