28
THE ESSEX NATURALIST.
approximately follow the present contour of the surface and pass
down to lower levels across the eroded edges of the channel
deposits. The estuarine deposits consist mainly of red sands,
and I have only occasionally seen fresh exposures, in which,
however, I have collected estuarine shells up to a level of about
30 feet O.D.
The same sequence of freshwater succeeded by estuarine
is seen in contemporary deposits elsewhere, even as far away as
West Wittering, Sussex.
These geological events that are recorded in the Clacton
channel in a thickness of some 40 feet of deposit, are crowded
together in the Lion Point channel within a thickness of scarcely
one foot. The Lion Point channel differed from the Clacton
channel in not being silted up with freshwater deposits ; it
remained an open river channel with a bed of shelly sand that
now constitutes the Lion Point shell bed. This thin bed includes
the actual change-over from fresh to salt water, and it is only
to be expected that the freshwater portion of the shell bed
should have been somewhat rearranged and confused by the
salt-water conditions that supervened directly upon it.
This epoch of submergence, accompanied by the invasion
of the river valleys by salt water to a height of 30 feet, or
perhaps more, above present sea level, may well have left behind
it many deposits that violate the normal sequence of relative
levels in river erosion. This submergence must have been very
near to the date of the Dovercourt industry, but there is no
reason for supposing that the estuarine waters ever reached so
high as that site.
Colonel Underwood records12 the finding of the clavicle of a
halibut at a depth of 31/2 feet (that is, well into the Palaeolithic
gravel) in the Dovercourt pit. If this really be contemporary,
a point on which one cannot help feeling some doubt, it would
certainly suggest the proximity of the sea.
The records of the succeeding events of alternate emergence
and submergence are hidden below sea-level in our district. One
can say, however, that the remains of mammoth and other
mammalia that have been dredged in such large numbers from
the submerged land surface of the Dogger Bank belong to a
12 Proc. Pre. Soc. E. Anglia, vol. i., 1913, p. 368.