THE ELEPHANT-BED OF CLACTON-ON-SEA. 33
Dogger Bank, which was undoubtedly a land surface, as is shown
by the peat beds which have been described in our journal.2
Rivers cannot cut their valleys appreciably below sea-level ;
but when further emergence of the land occurs, the river system
is rejuvenated, and in soft strata the valley is soon excavated
to a new and lower base-level. The Boyne Terrace river had
reached base-level and had a broad valley with a very gentle fall.
Then, during Taplow (= 50-foot = Middle) Terrace times,
emergence and rejuvenation occurred, and a deep new channel
was excavated over what is now the bed of the North Sea, the
deep inlets of the Essex coast being the submerged tributary
valleys of this stage.
The elephant-bed of Clacton represents a very small stream
or backwater, which became completely silted-up ; in fact, it
evidently formed a trap, which collected the abundant debris
of bones, wood, etc., and allowed even the forest timber to become
water-logged and to settle, instead of being swept out to sea as
in an open swiftly-flowing river.
I was at first rather puzzled by one of the features of the
flint industry of the men who lived on the banks of this stream
and whose artefacts are found in great abundance and in quiet
fresh and unrolled condition. Much of the flint used in this
industry was either Bullhead3 or fresh Chalk flint, and these
materials are not obtainable anywhere near Clacton at the
present time. My first thought was that they must have brought
their raw material from Kent by water transport, but this did
not appeal to me as being at all probable. I think the explana-
tion lies in the deep river channel, now submerged under the North
Sea.
The underground surface of the Chalk is somewhat undulating,
and the nearest record I have found among published well
sections is at Harwich, where the Chalk was touched at 55 feet
below mean sea level.4 Thus the deep river channel that we
have inferred, which probably ran quite near to the present Essex
coast, would bring the raw material of the flint industry within
easy walking distance of our site. Some special circumstance
evidently made the site a particularly attractive one to our an-
2 Essex Naturalist, xvi., 1912, pp. 51-60, and xix., 10:1, pp. 242-250.
3 The Bullead bed consists or a layer of flints at the base of the Tertiaries resting on the
subterranean surface of the chalk.
4 Another record, at Felixstowe, is given by P. G. H, Boswell, Journ. Ipswich and District
F.C., vol. v., 1916, p. 25, showing Chalk at 56 feet below O.D.
C