247
THE PLIOCENE PERIOD IN WESTERN ESSEX
AND THE PRE-GLACIAL TOPOGRAPHY OF
THE DISTRICT.
By S. W. WOOLDRIDGE, M.Sc., F.G.S.
(With Two Text Maps.)
[Read 27th November, 1926.]
1. Introduction. The Lenham Beds.
IT has long been known that portions of the London Basin
were submerged beneath an early Pliocene sea, and that
this was the last major submergence suffered by the area. The
deposits of this sea (the Lenham Beds) were recognized near
Lenham, on the North Downs, where recognizable marine
mollusca were obtained, and again farther to the east round
Paddlesworth and on the Folkestone Cliffs. Beds of the same
age occur beyond the Straits of Dover on the Chalk Downs
of France, where they appear to be remnants of a sheet of sand
and shingle inclined northwards towards the lowlands of the
Netherlands, beneath which their equivalents occur.
In recent years it has come to be recognized that the records
of the Lenhamian episode in our own country are much fuller
and more widely spread than was formerly thought. It has
been conclusively shewn that masses of sand and shingle in
Surrey, formerly dismissed as "of doubtful age," are true Lenham
Beds. Not the least striking of the evidences for correlation
was the fact that the beds, in common with those of East Kent
yielded a highly distinctive suite of heavy accessory minerals
—perhaps the most distinctive suite recorded anywhere in
Britain.1 By means of this suite and of the physiographic
relations of the beds, it has been possible to trace them far and
wide. Outliers occur throughout the terrane of the North Downs,
from Folkestone to Aldershot. For the most part they rest
upon a distinct wave-cut platform at elevations from 550-600
ft. O.D., but the platform descends gently northward at 15-20
ft. per mile and at Shooters Hill in North Kent true Lenham
Beds occur at slightly over 400 ft. O.D. Here, and in the region
south of London in general, the deposits are of sub-littoral type,
1 G. M. Davies, Proc. Geol. Assoc., vol. xxviii. (1917), p. 49.
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