31
THE GRAVELS OF EASTERN ESSEX
In this centennial year of the Essex Field Club, it is
pleasing to report that significant progress has been
made in interpreting the gravels of eastern Essex, a
problem that has exercised many geologists during the
past century. Various gravels of eastern Essex,
between the estuaries of the Thames and Stour (Fig. l),
haue been studied and results haue been obtained which
throw considerable light on their origin and on the
history of the major rivers of south-east England.
To establish whether the gravels of eastern Essex were
of Thames, Medway or even glacial origin, the technique
of stone counting was applied to samples of 300+ stones
in each of various size ranges, collected from quarry
faces or from specially dug trial holes. This technique
involved the identification of each stone and the
calculation of the proportions of the different types of
material represented in the gravels. To assist the
identification of the stone types, a type collection of
likely source rocks was built up from samples collected
from the Weald and the West and South Midlands and from
local drift, including glacial, deposits. Samples were
also collected from the Tilbury area and the Hoo Peninsula
(North Kent) to establish pebble suites typical of the
lower Thames and Medway respectively (Table la,1b).
The higher gravels of the Southend and Dengie peninsulas,
e.g., in the Rayleigh Hills, were found to be indisting-
uishable from those of Medway origin from North Kent and
to lack the exotic component of the Thames gravels. It
is suggested that these gravels represent an extension of
the Medway across eastern Essex before the Thames occupied
its present valley through London. The higher gravels
of the Clacton area show a lateral change from west to
east. To the west of St. Osyth the gravels are identical
to those of an early, pre-glacial, Thames traced across cen-
tral Essex to St. Osyth by Rose, Allen and Hey (1976)
(Table lc). To the east, the gravels show an increased
Greensand chert content and a decrease in exotics (Table le)
and have been referred to as the Holland Gravels since
they underlie the towns of Clacton and Holland-on-Sea