36 ON SOME ANCIENT LAKE REMAINS AT FELSTEAD, WITH
course. This gravel furnishes oyster-shells, and a fragment of pottery
has been found in it. Beyond the transverse section made by the
present channel, we are in complete ignorance of the further course
of this bed, as it is buried under some feet of later deposits. This
gravel, from the compactness and narrowness of its bed, seems to be a
product of slow erosion, and must have been obtained from the deep-
ening rather than the widening of the channel of overflow. It may
have been that the wear of the stream took off the coating of Clay
and choked-gravel and exposed porous sands and gravel, which are
known to exist near by, and so drained the lake to an inconvenient
extent. Whatever may have been the cause, the dam was after-
wards made good at that end and the overflow was transferred to the
other end of the dam. After this alteration the gravel and shelly-
marl that we have mentioned, received no other addition but that
due to the wear and tear of the seasons, A coating of rainwash
derived from the Boulder Clay and Glacial gravel of the valley side
was slowly deposited, and entombed the ashes of the fire, the shell-
marl, and the gravel with oyster-shells. This rainwash ultimately
attained a thickness of eight feet; but it has received no addition for
a great number of years, as we shall show further on.
Turning now to the inside of the lake, we note that at some
time in its history, which does not appear to be at the beginning, a
considerable quantity of Chalky Boulder Clay was thrown into its bed.
This clay now exists with the lumps of chalk intact, and rests at one
place on lake mud with oyster-shells, and is itself overlaid by two
feet of lake mud, also with oyster-shells and a fragment of Roman
pottery, showing clearly that after its deposition the lake still existed
and was used by the inhabitants as in days gone by. The confusion
of deposits at different parts of the lake's bed is very great. The
bed seems to have consisted of gravel overlaid by peat at the time
the dam was made. In one place we now have :—