THE ESSEX NATURALIST.
Hill ; it may have been the former course of the Roding before
this river was captured by the head-waters of either the "Romford
River" (q.v.) or the "Nore River."
Rejuvenation.—The foregoing stage was closed by a revival
of emergence producing rejuvenation of the rivers, and this in
turn resulted in dissection of the 200-feet Platform as the valleys
were cut deeper.
It has long been known that the Roding valley was pre-
Boulder Clay down to about 150 ft. O.D.[Holmes, 1894 ; Dines
and Edmunds, 1925] near Abridge. A similar relation is true of
the small Ingrebourne as well as of many of the larger valleys
of Essex. I have new evidence which indicates that the pre-
Boulder Clay excavation of the Roding went down to within
a few feet of the present floor of the valley.
Chigwell Lane.—There is a patch of gravel here between
130 ft. and 160 ft. O.D. that is mapped as Boyn Hill Terrace of
the Roding Valley. It extends for about three-quarters of a mile
and was crossed by the anti-tank ditch N. of Chigwell Lane
station, which showed it to be a pure Pebble Gravel, thrown into
a series of festoons 6 ft. or 8 ft. deep, and not a terrace of river
gravel. Boulder Clay occurs a little higher, and clearly overlies
the gravel, which contains no trace of glacial material. I found
one piece of Greensand Chert on the dump, but quartz was
scarcely represented by anything larger than grit.
Below this site patches and pockets of pebble gravel trail
down to the floor of the valley, but these contain some mixture
of glacial material.
Hallsford.—I call the exposures here my key sections to
unlock certain of the secrets of the local geology.
There are two pits, one to the W. of the High Ongar Road
(recently closed) at about 0.35 mile S.E. across the valley from
Chipping Ongar. This reveals glacial sands, with subordinate
clay, descending to, if not below, the floor of the Roding Valley
at 130 O.D.
The other pit is that of the Hallsford Brick and Tile Works,
on the opposite side of the road and about three-quarters of a
mile S.E. of Chipping Ongar. It is owned by Mr. Noble of
Ongar, to whom my thanks are due for giving me every facility.
The deposits shown in Fig. 1 are :—1 Rainwash, of the Iron Age,
up to about 4 feet ; 2 Loess, probably of Aurignacian Age, up to
8 feet ; 3 a buried land surface with a few rare Levallois flakes ;
4 Chalky-Jurassic Boulder Clay ; 5 Glacial Sands, of hummocky
form and variable thickness ; 6 Pebble Gravel up to about 6 feet
or more. (Irregularly eroded surface) ; 7 London Clay.