172
THE ESSEX NATURALIST
that subsequent changes may have taken place associated with
the glacial episodes. The base of the Hanningfield gravels rests
on surfaces a few feet lower in altitude that the Pebble Gravels
and clearly ice tongues or sheets, at some time, exceeded that
altitude. Certainly the area must have been subject to intense
and repeated permafrost conditions. Such conditions might
explain, for example, the absence of bedding in the gravels and
the production of the strongly oxidised zone in the upper layers
of the underlying Bagshots. Most of the mixing of gravel and
Bagshot material along the contact zone may also be due to
freeze-thaw conditions. The faults beneath the Channels, how-
ever, seem to point to loading of some kind, and the small folds
and faults that cause the Bagshots to dip eastwards off the high
ground may be the result of distortion of pre-existing topography
under glacial load. Thus it is tentatively suggested that the
channels were initiated by the scouring action of densely loaded
currents flowing into a regressional sea, and then modified during
glaciation such that their cross section became deeper and strongly
symmetrical.
References
Clayton, K. M. (1957). Some Aspects of the Glacial Deposits of Essex.
Proc. Geol. Ass., Lond., 68: 1-21.
Middlemiss, F. A. (1955). Field Meeting at Brentwood and South Weald.
Essex. Proc. Geol. Ass., Lond., 66: 317-319.
Wooldridge, S. W. (1923). The Geology of the Rayleigh Hills, Essex
with Report of Excursion, Saturday, June 23rd, 1923. Proc. Geol.
Ass., Lond., 34 : 314-322.
Wooldridge, S. W. (1926). The Pliocene Period in Western Essex and the
Pre-Glacial Topography of the District. Essex Nat., 21: 247-268.
Wooldridge, S. W. (1960). The Pleistocene Succession of the London
Basin. Proc. Geol. Ass., Lond., 71 : 113-129.
APPENDIX
Temporary Exposures at Rayleigh
By J. T. Greensmith
The contact of the Pebble Gravels and underlying Bagshot
Sands at Rayleigh, 8 miles (12.8 km) to the east of Billericay, is
at 225 ft (68 m) O.D. Up to early 1965 the contact was well
exposed on the northwest face of a shallow quarry at Hambro
Hill (812920) and could be observed to be one of marked dis-
cordance with the pebble deposit cutting down in the form of a
channel some 2 feet (.6 m) into underlying finely-laminated, cross-
bedded sand (Fig. 4B). This exposure does not now exist. The
pebble layer, up to 4 feet (1.2 m) thick consisted of an admixture
of well rounded flints up to 3 inches (7.6 cm) in diameter and
angular unworn flints and cherts (some of jasper aspect) up to
9 inches (22.8 cm) by 7 inches (17.7 cm) by 3 inches (7.6 cm) set