THE UNDULATIONS OF THE CHALK IN ESSEX. 115
It will be seen that about Ware, at Bishop's Stortford, Sudbury,
and Ipswich, the Chalk boundary is very sinuous, whilst between
those points it forms curves for the most part broad and smooth.
That is simply due to our knowledge at the points mentioned, and
our ignorance as to the intervals. We do not know what sinuosities
are present under the pall of drift, and we can only carry the hypo-
thetical line between sections that prove the absence of Tertiary beds
to the north, and their presence to the south. Lately a well sunk
northward of the boundary assumed in the Geological Survey map
at Little Sampford proved the further extension of the Tertiaries.
Such corrections (or their converse, the reduction of the hypothetical
area of Tertiary beds) are most welcome and useful. The general
strike is E.N.E. from Ware to Sudbury, and thence E. to Bramford.
Beyond the limits of the map, it runs N.E. to Saxmundham, and N.
to Yarmouth.
The base of the Chalk is approximately parallel to this line, and
so is the the great faulted undulation of Tiptree Heath, which I
described several years ago.3
That important flexure has quite recently been again proved at
Messing, and its course through Suffolk is traceable at Shelly, Ipswich,
Woodbridge, and Lowestoft. Along Tiptree ridge it is a faulted
anticlinal for several miles. From Wickham Bishop it is traceable
with less distinctness by Danbury to the south-west, its effects being
complicated by a series of obliquely-transverse flexures and fractures
in a manner defying verbal description. The parallel fault from
Walton to Prittlewell, the anticlinal of Mersea and Burnham, and
the bold flexure at Royston (where the Chalk dips at 400 to N.N.W.)
point to some general agency affecting a wide area, and in like
manner the east and west fractures from Greenwich to Erith, and
Walthamstow to Burnham, are probably of the same age and origin as
the parallel anticlinals of the Stour estuary (not shown by the contours),
and that in which Bentley occurs (as indicated by the zero-line.)
The lines of flexure and fault of N.W.-S.E. trend are less regular,
of shorter continuance and variable direction, and appear to be the
result of transverse strains at the time of the later of the previously-
mentioned movements in a district weakened by the earlier series.
It seems probable, for instance, that the triangular bit of country
between Chigwell, Havering and Romford was crushed into its
present structure of anticline and syncline by pressure from the
3 Trans Essex Field Club, vol. ii, pp. 15-18, 1881.