PLEISTOCENE GEOLOGY OF THE THAMES VALLEY. 343
(1.) WESTERN PORTION.
(a.) Tunnel Cement Works. A good section of the Middle
Terrace Drift as represented in the western portion of the district
is exposed in the quarry of the Tunnel Cement Works. This
section exhibited, in 1900, the drift piled up against the old chalk
cliff which formed the bank of the Pleistocene Thames at this
stage in its development.
The beds shown in the section are :—
1. Surface soil and "wash gravel," about 4 feet.
2. Stiff brown loam, about 4 feet.
3. Finely laminated sand, with occasional seams of argillaceous material.
Two well-marked bands of pebbles were exposed, occupying respectively the
top and bottom surfaces of the middle third of this series. The lower pebble
band consisted chiefly of well rounded flints, but in the upper bed in addition
to these were many small fragments of chalk, mostly well rounded, and a few
unworn chalk flints. Towards the base of the series large chalk pebbles
became more abundant, until at last near the junction with the chalk cliff
they formed two-thirds of the total detritus. This portion of the series,
however, was easily distinguished from the underlying chalk-rubble by its
perfect stratification and the well rounded character of the included fragments
of chalk. As the beds approached the south, i.e., as they receded from the
old bank so the pebbles of chalk became fewer, until not one could be found
in the basal portion. In places the beds are somewhat indurated, this condi-
tion probably arising from contraction during drying. The arenaceous con-
stituents appear to have been wholly derived from the Thanet Sands of the
neighbourhood. The total thickness of the beds included in this division is
from 16 to 20 feet.
4. Chalk rubble, angular and unstratified, about 6 feet,
5. Chalk.
Mr. W. J. L. Abbott, F.G.S., described this section in 1890
(60) and recorded several species of the usual larger Pleistocene
Mammalia and also seven species of Mollusca. The species are
all included in our general list from Grays Thurrock.
(b.) Pit west of Milwood Lanc. Proceeding eastwards
along the London Road, the next exposure of the brickearths is
that seen in the tramway cutting of the quarry belonging to
Messrs. Gibbs. The section was briefly described by Mr. W.
Whitaker, F.R.S., in 1889, in the "Geology of London," (59),
and he figures it as it was in 1872. Since that time it has been
deepened, but no further detail of much importance is to be
seen. The section resembles that seen in the Tunnel Pit in
showing the drift piled against an old chalk cliff. The details