42
THE ESSEX NATURALIST.
parallel features exhibits a new feature in a series of disturbances
that run roughly parallel to the dip. North of the Blackwater
Estuary a curving anticline can be discerned running from the
Tiptree fault to the neighbourhood of Brightlingsea. This
anticline is succeeded by a small subsidiary syncline, and that
in its turn by the anticline to the north of the River Stour
beyond the County boundary. South of the Blackwater is a
more complex area, but one where the structure has an im-
portant effect on the surface relief. The major feature here
is the Rayleigh anticline, followed to the south by a steep
synclinal fold running east to west beneath Canvey Island.
This feature terminated at the west in what is apparently a
north to south faulted monocline. The evidence of boreholes
in the neighbouring areas also suggests the probability of parallel
"ripples." Finally a strongly marked feature is seen in the
east-to-west anticline of Grays and Purfleet which brings the
Chalk up to the surface.
Such an extensive survey of the Chalk basement would
be purposeless if that foundation did not largely exercise its
influence on the surface of Essex. Mention has already been
made of the submerged palaeozoic floor underlying the area,
and it seems probable that the tectonic features associated with
this foundation have made themselves felt on the comparatively
soft and accommodating Eocene rocks of the surface through
the agency of the chalk pavement, because the majority of the
structural lines spoken of in describing this pavement have
been found represented in some form or other on the surface
of the country. A further coincidence between the Chalk
pavement and the surface is to be noticed in the three coastal
areas where the Chalk is downfaulted on the seaward side.
These three districts correspond to the main areas of coastal
marsh. Thus, the region around Fobbing and Canvey is de-
limited by a monocline and fault throwing down the Chalk to
below 300 ft. on the west, and a syncline reaching depths below
400 ft. on the north. Again, the Southend fault seems responsible
for the marshy area in the vicinity of Foulness and the south-
east of the Dengie Hundred. The marshy region surrounding
Horsey Island also seems to owe its inception to the presence
of a neighbouring fault.
Our consideration of the Chalk pavement will have demon-