EVOLUTION OF COASTAL DRAINAGE OF ESSEX. 41
Thus, the fault line running north-east to south-west through
the Southend district is inferred from a group of borings to the
west with figures ranging a dozen or so feet above and below
400 ft., whilst to the east a number of figures show a similar
range around the 500 ft. mark. Further support is forthcoming
from the fact that the downthrow side shows a steady slope
away from the inferred fault.
The chalk follows the regional dip to the south-east in
descending from the northern rim of the London Basin; the
strike following, for the most part, a north-east to south-west
trend. This smooth slope, however, is disturbed by several
interruptions. Running parallel with the strike through the
central part of south-east Essex is the feature known as the
Tiptree Line. North of the Blackwater Estuary the Line is
represented by a fault—in this case the downthrow being on
the northern side—a reversed fault. The Line is continued
on through the Chelmsford and Barstable Hundreds by a
syncline ending apparently against a north-west to south-east
fault, bringing to an end a feature conspicuous in the geology,
relief and drainage of Essex. It is succeeded to the south-west
by a gently inclined surface with a mean height of 130 ft.
stretching from Havering to East Ham (fig. 1).
Other structures run parallel to the Tiptree Line both north
and south. In the former case a normal fault, with a southerly
downthrow of about a hundred feet, may be discerned passing
across the north-west of the County. The intervening tract is
traversed only by minor anticlines and synclines conforming with
the same trend. To the south-east of the Tiptree feature
there appears to be a third important fault passing across the
County near Southend; reference has already been made to it.
Though there is no definite proof, the great depth of the Chalk
in Foulness (greater than 600 ft.) seems to lend support to the
idea that this fault may be continued throughout the Dengie
Hundred to the extreme north-east of Essex. The steep coast
in the latter district may be, in part, due to this feature. On
the south-east, or downthrow side, the Chalk reaches its deepest
level (below 500 to 600 ft.). The entire surface of the land in
these vicinities is below 25 feet, and much of it is inclined to
become marshland.
The tract of Chalk lying between these two last-mentioned