194 Mrs. McKenny Hughes—Pleistocene Mollusca. 
has been offered for observing the relative position of the beds in 
which the different species were more or less abundant. None of 
the shells were confined to definite zones; nor were they distributed 
through beds bearing any constant relation to one another; but, at 
varying horizons, and in different parts of the field, lenticular 
masses and pockets occurred, in which certain species were very 
abundant, while others were absent there which were common above 
or below, or at the same horizon close by; whereas, not far off they 
would be found mixed together in the same bed. In former excava- 
tions, in one part of the field, plant-remains were found in abund- 
ance near the base of the gravel. Among these were a few Chara 
spores and a quantity of leaves and twigs which are considered by 
Mr. Clement Reid to belong to one species of Salix—probably 
S. repens. From the recent diggings very few plant-remains have 
been obtained ; only an obscure fragment here and there. 
It is clear that gravel-pits of inconsiderable size opened in closely 
adjoining parts of the field might yield a very different group of 
fossils; but the removal of the whole showed that this depended 
upon small local variations of the same set of deposits. For instance. 
there were, in one case associated with Mammoth near the top, and 
in another resting on the Gault at the very base of the deposits (see 
Fie. 1.—Section seen by Ancient Well North of Ruin, on site of Barnwell Abbey. 
Scale—10 feet to 1 inch. 
a, Surface soil, ete.; 4, Irregular gravel; c, Fine sand and marl: d, Reddish sand ; 
e, Coarse gravel consisting in places of large subangular flints with a few 
boulders derived from the drift and passing horizontally into fine beds of chalky 
gravel and marl full of shells, chiefly Bythinia, Corbicula, Unio, Valvata, 
Planorbis, etc.; f, Gault. 
Section Fig. 1), lenticular marly beds containing shells and opercula 
of Bythinia in great abundance. In some places no specimen of 
Corbicula (Cyrena) could be found; still more often Unio litoralis 
was absent, although these shells occurred somewhere at every 
horizon. Except, therefore, in the case of very extensive excava- 
tions, generalizations, especially where founded largely on negative 
evidence, must be considered only as tentative. 
In the gravel-pits at the other side of the Newmarket Road no 
shell-bearing beds are now exposed, although a few years ago Unio 
litoralis occurred abundantly in the N.W. corner of the pit, but 
lower than the level of the present workings. 
Following the gravel due north we come to the brick-pit at 
