GEOLOGY OF THE DISTRICT AROUND DAGENHAM BREACH. 143 



Romford. This broad plain of river-gravel varies in height from 

 about 12 to 15 feet above Ordnance Datum at its southern margin to 

 more than loo feet along the course of the new railway between 

 Upminster and Romford, and around North Ockendon. About llford, 

 Dagenham village, and Rainham it is below 50 feet. The old river- 

 gravel not only rises above, but also extends below the alluvium of 

 the marshes, as the following sections from Whitaker's " (ieology of 

 London and of part of the Thames Valley " show. North of Dagen- 

 ham Lake a boring pierced (vol ii., p. 279) : — 



22 feet. 



24 feet. 



The amount of peat and driftwood in the alluvium varies very much 

 from place to place, but is usually very considerable. The propor- 

 tion of drift wood- j:>eat to peaty material resulting from the decom- 

 position of reeds, etc., which have grown i/i situ is also very variable. 

 At Tilbury Docks driftwood appeared only in a thin bed below two 

 others composed chiefly of the remains of reeds ; while at Albert 

 Dock the thick peaty bed was chiefly made up of driftwood, the 

 limits of the later being much more variable and ill-defined than 

 those of the Tilbury beds. The most common mammalian remains 

 in the alluvium appear to be those of red deer and oxen. Among 

 the trees are trunks of oak, birch, alder, hazel, and yew. The peaty 

 beds, as the sections given show, are interbedded with seams of 

 marsh clay or mud, the whole series resting upon sand and gravel, 

 river-deposits mainly of older date. 



Beneath these river deposits are either Chalk or Tertiary Beds. 

 At the north-eastern corner of Albert Dock there is Chalk, while at 

 Barking and Dagenham village there is London Clay. Chalk, again, 

 was found below seventy feet of river beds at Marshfoot Farm, a mile 

 N.W. of Purfleet. Crossing the Thames, we find that at Crossness 

 and Belvedere, on Erith marshes, Chalk could only be reached after 

 passing, not only through the river deposits, but through the whole of 



