WITH A LIST OF THE MOLLUSCA OCCURRING THEREIN. 5
and contains only a very few small flints, except near the bottom, where it rests
on the gravel and contains some fair-sized flints, although the change from clay
to gravel is sudden. It is very heavy, and dries very hard. Sections near the
brook show its thickness to be about 4 feet; but, as it seems to rest on a fairly
level bottom, and only showed a thickness of about 2 feet at D (Fig. 1), I
conclude that it thins out as it recedes from the brook. Examination under a
microscope, or washing, shows fine sand to be present. There can be little
doubt that it is in some way derived from the Chalky Boulder Clay, which is
largely developed over the whole of the district through which the brook passes ;
but, as it scarcely effervesces when treated with acid, the proportion of chalk
must be very small. The only organic remains it contains are decayed sedge-
roots from the peaty layer above, which penetrate almost to its bottom.
(c) This is a layer of peat about 4 inches thick, overlying b, and consisting of
two kinds intermixed. One kind is loose and soft, and is formed of many roots
(apparently of sedge), not much decayed ; it contains very few shells. The other
kind is harder, denser, more granular, and the composing matter is so decayed
as to be almost unrecognizable. It becomes very hard when dry, and contains
a great number of both land and fresh-water shells, many of which are in frag-
ments and look as if they had been exposed to pressure. I have not found
this peat extending beyond the area over which the black earth shows at the
surface.
(d) is a bed of very dark, fine, dry, loose, rubbly earth, reaching to 3 feet
thick. The underlying stratum passes gradually into it; it contains a number
of both land and fresh-water shells, of which I have detected 52 species.
Worms avoid it, but, as already stated, it is a rabbit's paradise. Mr. Clark
says : "Upon igniting two grammes of this, and keeping it at a dull-red heat
for half-an-hour, about half (49 per cent.) of the original amount was left.
It had a red look from burnt clay, and lime was of course present from the
shells." At the surface it is partly bare (perhaps on account of the working of the
rabbits), and is partly covered by the ordinary loamy surface-mould. In it I
have found several pieces of bone, but rabbits are, as Mr. Clark observes,
"ruthless mixers," and as the surface has been cultivated, very little can be
learnt from them. One piece, however, which I found at B, about 18 inches
from the surface, appeared to be in place.
(e) The next bed is, for this district, a less common one, consisting of almost
pure chalky matter, wonderfully white and clean, and very light and crumbly
when dry, thus contrasting strongly with the bluish clay b. It does not seem
to contain a particle of sand, but some iron is present; when treated with acid,
it effervesces violently. It contains a few shells, especially near the top,
including Cyclostoma elegans, which, except at one spot, is rare in d. I am in
doubt as to its extent, which seems to be small; but it seems to range in a
band along the brook-side of the other deposits, though it does not extend to
the bank by by 8 or 10 yards, this space being occupied by common
alluvial soil. I presume, therefore, that it is banked against some, at least,
of the older deposits. I do not know what sort of a junction it has with
the other beds. At first I presumed that it was in some way derived, like
bed b, from the destruction of the Boulder Clay, but Mr. Dalton says, "It is
probably a pure shell-marl, more recent than the peat, and of wholly organic
origin." It contains no sedge roots.
(f) The brown loam forming the surface, as already mentioned.