170
THE ESSEX NATURALIST
faults. The combined effect of the folding and faulting produced
a general easterly dip conforming with the present land surface
and the reduction in altitude of the Bagshot outcrop further to
the south. Along the High Street, shop reconstruction has shown
that even at the highest part of the area bedded Bagshot Sands
are in places at the present surface. The base of the Gravel there-
fore varies in level over some 20 feet (6 m). The remaining
exposures in Pebble Gravel serve to emphasize the uniformity of
the deposit and to allow local delimitation of the outcrop.
3. Glacial Deposits
Locality 4 showed the base of the Pebble Gravel at about
310 feet (94 m). Here the gravel outcrop is separated by Bagshot
Sands from a second drift deposit at about 300 feet (91 m) O.D.
This later deposit consists of mottled clay, sand and sandy clay
with scattered pebbles identical with those of the pebble gravel.
These are intermingled with very large unworn highly fossiliferous
nodular flints. Similar deposits occur at the same altitude at
locality 5, though here the mottled clay and sand lacks nodular
flints and pebbles and rests on an ochreous clay with flint and
quartzite pebbles. Identical yellowish clay with pebbles of flint,
quartzite and chalk was exposed south of Norsey Wood (locality
(j) and this is near strongly leached gravel containing small nodular
flints and quartzites. All these deposits are almost certainly
glacial and may be attenuated high level equivalents of the Han-
ningfield Till of its associated glacial gravel. The Till proper
(Clayton, 1957) was exposed in trenches around the junction of
Potash Road and Stock Road and this succession is shown in
Fig. 3D.
Mention should also be made of a deposit that obscures much
of the Bagshot outcrop. This consists of very fine pebbly sand
derived largely from the Eocene sands. In places the scattered
pebbles are identical with those found in the Pebble Gravel but
elsewhere there are angular flints and quartzites of obvious glacial
affinities. The outcrop of this material is shown in Fig. 1, but it
may be much more widespread than indicated. Its age and origin
are not clear, but it may well be regarded as head.
South of Billericay there is an extensive spread of gravel that
is at least in part glacial. Temporary exposures show that this
sheet extends to a higher altitude than was previously supposed
—it rises to just above 300 feet (91 m) O.D. at its northern limit.
Analysis of the pebble content and matrix shows that the sheet
can be divided into lower and upper gravels with a thin transition
zone. The lower gravel is dominated by well-rounded flint and
quartzite pebbles, that could all be reworked from the Pebble
Gravel. The upper layer has a relatively high proportion (about
10 per cent) of Bunter quartzite pebbles and the ratio of angular
to rounded flints is about three to one. In addition this layer
overlaps the lower sheet onto London Clay (Fig. 3E). Towards
the southern limit of this 'Bunter gravel a temporary excavation