FOSSIL ESSEX MOLLUSCS
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ever, that the gravels are only the topmost member of a sequence of varied
sediments. The sequence has a surface level of 50 ft O.D. and has its
junction with the chalk bedrock at circa 22 ft O.D. The precise junction
is difficult to determine, because the surface of the underlying chalk is
badly broken up to form a rubble of chalk and flint. The gravel spread lies
on the north side of the Thurrock anticline, being banked against the
chalk. The deepest deposits are therefore on the north face of Greenlands
Pit. The section which is described in this paper is now extremely difficult
to approach, as subsequent operations have left the section high above the
quarry floor. However, further section of the same deposits can be seen
in another pit, Bluelands (TQ 570797), lying on the north side of the lane
dividing the two pits. The section on the south face of this pit is similar
in nature to the main section, but contains far fewer fossils and it is
evident that the high concentration of fossils occurring in the Greenlands
section is very localised.
Stratification
Level Ft. Ins.
20 1 0 Surface humus
19 3 6 Clay
18 3 6 Gravel
17 4 0 Clay with sand lenses
16 2 5 Gravel
15 1 Sand
14 4 Grey sand with shell
13 9 Brown sand with shell
12 2 As 13 but less shell
11 5 3 Shell bed with sand
10 1 4 Brown sand
9 2 Weathered (?) clay
8 7 Laminated clay
7 8 Grey clay with shell
6 3 Crushed shell
5 5 Grey clay
4 6 Laminated clay
3 1 6 Brown sandy gravel
2 3 1 Flint and chalk rubble
1 Chalk bedrock
The section shows a series of gravels, clays and sands, approximately
30 feet thick. Many levels are highly fossiliferous; indeed level 11 is in
parts composed of a solid mass of bivalves (Unio tumidus). In the lower
part of level 11 and in the upper part of level 10 well-rounded black flint
pebbles occur similar to those found in the Blackheath Pebble beds. At the
base of the series (level 2) the rubble consisting of flint, chalk and a small
quantity of sand contains a few shells and small chalk pebbles which have
been encrusted with a heavy coating of re-deposited lime. The lime has
probably been leached out of the shell bed above and then been re-
precipitated when it reached the highly alkaline conditions in the rubble
bed. The clays making up levels 4 and 8 are interspersed with sandy layers,
the resultant structure resembling varves, although the author would not