Il6 THK UNDULAIIONS 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 Hishop 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 



i 



