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 100 feet along the course of the new railway between
Upminster and Romford, and around North Ockendon. About Ilford,
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 "Geology of
London and of part of the Thames Valley" show. North of Dagen-
ham Lake a boring pierced (vol ii., p. 279): —
Again, south of the lake, we find :—
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 driftwood-peat to peaty material resulting from the decom-
position of reeds, etc., which have grown in 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