6 NOTES ON AN ALLUVIAL DEPOSIT IN THE CANN VALLEY,
At several places in the right bank of the brook (which is now
being eaten away) may be seen a stratum, apparently of an interme-
diate nature between the clay (b) and the shell-marl (e). It is a
somewhat bluish clay, but of a chalky nature, and contains a fair
number of shells, notably Cyclostoma elegans. Patches of it may be
seen for about 80 yards down the brook, below the main deposit,
and where there is no overlying black earth (d).
This completes the account of the different beds to be seen at this
place; but about 100 yards further down the river is a very low,
damp spot, which, until ditches were dug to drain it a few years ago,
was little better than a bog, and was known as "Rushy Bottom." I
have only explored this spot very superficially, but at least two of the
beds already described as occurring in the main deposit seem also to
be represented here :—
(e) The white chalk-marl, as before, and containing a few similar species of
shells. Its upper surface is about on a level with the water of the brook, and it
seems only to exist as a strip, perhaps ten yards broad, along the bank. It is
overlaid by
(d) A black-earth, similar to that in the main deposit, but not quite so
dark, and containing much fewer shells. It extends beyond the area of the
stratum below, and fills a hollow of perhaps one-fifth of an acre.
A few years ago, whilst draining a meadow on the left bank of the
brook, perhaps half a mile further down, lumps of hard cellular
travertine or tufa were turned up, with some specimens of Cyclostoma
elegans.
The origins and relationships of these different beds are, of
course, difficult to determine precisely, but it seems probable that all
are of fluviatile origin, the gravel (a) being resorted Glacial gravel;
the clay (b) washed from the Boulder Clay slopes. The peat and
black earth require a different explanation, and seem likely to have
originated in a bog or lake. Mr. Clark suggests the possibility of
their having been due to a Beaver-dam, and Mr. Dalton has pointed
out to me that bones of two species of Beaver occur in the Copford
deposits; but Mr. Dalton himself is inclined to believe that these
peaty beds have originated in a bog formed by springs on the spot.
However, as the great majority of the contained shells belong to
species which do not inhabit such situations, there can be no doubt
that they, at least, have been carried to the spot by the brook during
its occasional floodings.
Coming now to the consideration of the various species of Mol-
lusca contained in these beds, it may be observed that, as a general