116 THE UNDULATIONS OF THE CHALK IN ESSEX.
north-west acting obliquely to the earlier fracture between Waltham-
stow and Romford, so that, whilst a deep trough was formed from
Wickham Bishop to Havering, a transverse fracture was produced at
the latter place. The ground to the south-west of this, being forced
into the angle, yielded along a line passing through Chigwell, and
there produced a faulted synclinal of much greater importance than
the slight depression passing southward from Havering. Between
these synclines the Chalk rises in Hainault Forest to the sea-level,
whilst to east, west and south it is from two to three hundred feet
lower.
In like manner the shallow depression between Horndon-on-the-
Hill and S. Ockendon becomes a sharp and deep fold between Rain-
ham and Dagenham, is unrecognisable near Barking, but re-appears
with its normal east and west trend from East Ham to Canning
Town. Probably the synclinal of Benfleet is part of the same fold,
though obliterated at Fobbing and Vange by predominant pressure
oblique to the original flexuring.
I do not think it necessary to describe in words the course of the
several contours, as the map supersedes any verbal account, and the
rest of the county calls for no special notice. Altogether the Essex
Chalk shows a range of elevation of about 1200 feet from its greatest
depression at Fowlness, over 600 feet below the sea-level, to the 600
feet above sea which, but for denudation, it would exceed in the north-
western corner of the county.
I believe one is expected to conclude a summary of facts such as
the foregoing with a little theorising as to the causes of the phenomena
described. I would suggest for the N.E.-S.W. folds, a slipping of
the Chalk and Tertiary beds towards the line of main depression of
the London Basin, probably over the surface of the Gault, but
pinching up some of it into the folds. This slipping could only
occur after great erosion of the upper beds. The limits of the
Boulder-clay indicate a great bank or land-area as existing in South
Essex late in the Glacial period ; over,' at any rate, the Essex half of
the Thames valley. What was then a hill-range above the level of
the Glacial sea is now South Essex, with the Thames, Crouch and
Blackwater estuaries, proving enormous denudation (or differential
subsidence) in early Post-glacial times. Such reduction in thickness of
the Tertiary deposits might, I venture to suggest, result in a series of
undulations in the Chalk by gravitation, without invoking Messrs.
Vulcan & Co., the agents generally credited with all such