38
THE ESSEX NATURALIST.
continually migrated towards the south-east, leaving, as evidence
of its former positions, widespread areas of sands and gravels,
and several partly destroyed peneplanes. It is equally fortunate
in that later transported material—the glacial clay—has in some
districts covered, and so preserved, traces of these early
peneplanes. A great deal of care, however, must be exercised
when considering these peneplanes, since orogenetic movement,
or buckling, will render their evidence useless.
A brief examination of the geological nature of the country
is necessary before we can consider the evidence afforded by
apparent peneplanation.
The geology of the County is fairly simple. Essex lies at
the north-eastern termination of the London Basin and, broadly
speaking, shows its well-known Stratigraphical sequence. At
about a thousand feet below the ordnance datum level lies a
buried palaeozoic pavement.4
It is not unlikely that a synclinal distortion of the rocks
of the floor may ultimately be demonstrated in central Essex,
but there is no actual evidence to hand at present. Borings
throughout the area indicate that the pavement rises to less
than a thousand feet along the Stour valley in the north, and
again around Fobbing and East Ham in the south of the County.
The crest of an anticline passes east to west through the extreme
south of the County, and certain borings indicate a further,
still more southerly, downfold beneath the Weald. The evidence
derived from borings to the west, and beyond the County
boundaries, indicate that the palaeozoic ridge is a continuous
feature in the west towards South Wales. It would also
appear that this submerged palaeozoic ridge is a western
prolongation of the Ardennes massif.
The above theory, which we may regard as practically proved,
has had an important bearing on the Essex coastlands, and
consequently upon the use we may make of the evidence of
peneplanes. The proximity to the surface of the palaeozoic
ridge passing east to west beneath the Thames, has given to
southern Essex a surface stability denied to the two synclines
lying north and south, for the greater thickness of relatively
unconsolidated rocks in the basins allows of greater vertical
contraction. The syncline to the south, lying beyond our area,
4 Wooldridge, S. W. Proc. Geol. Assoc., xxxix., 1928.