ON SOME PLATEAU DEPOSITS AT FELSTEAD AND STEBBING. 137
which this wearing away has occurred, therefore, represents the least
time which has elapsed since the Boulder Clays were altered into loam.
Another deposit of quite a different character must now claim
our attention. This is at Stebbing Downs, a little north of the
village, or "Dunes," it might have been written, for the greater part
of the upland of that place is a large sand-dune (that is, a heap of
blown sand). Overlooking the Mount, and near to the brickyard, a
pit has been worked for sand, and a notice of the underlying Westle-
ton Gravel, etc., has already appeared in the Essex Naturalist
(vol, v., page 210). The upper six feet of sand, however, is a very
singular deposit, and its age and true character were not at first
apparent. An implement made out of a piece of conglomerate and
a fragment of Roman pottery having lately been found in it, its age
is not so uncertain.5 Indeed, until quite recent times (of improving
agriculture) the formation must have been still in progress. A close
examination of its structure and material shows the bed to be a
product of dry denudation, all of it having been drifted by the east
wind. Small pieces of chalk from the size of a shot upwards, and
almost always rounded, are collected in masses in different places.
These were supplied by the Boulder Clay, whilst the sand was
supplied by the Westleton Beds, both formations being exposed
on the somewhat higher grounds to the east and north-east. The
drifting of the sand is peculiar, and much resembles "false-bedding."
Towards the south of Stebbing village, and on the same side of the
brook, there is another upland deposit of sand differing slightly from
that of the Downs, but probably of the same age. The sand here is
cemented into masses by a ferruginous deposit.
Any attempt to judge of the ages of the three deposits of which
we have treated is affected by difficulties which concern relative as
well as absolute time. We may judge with a poor approximation of
the rate of denudation now in progress; but we cannot say that it was
the same in comparatively recent times, although times of greater
sterility as shown by the Stebbing sands. Much less can we say any-
thing of the times when those Plateau loams were made. With a
lower winter temperature there was a greater erosion during thaw; but
there were longer intervals of rest during frost, and we do not know
whether the debris was removed at the same rate as at present or not.
The same difficulty is increased in judging of the early Post
Glacial Plateau Gravels; erosion then was prodigious, but it may
5 I have (May 7th) since found a small bed of charcoal ashes under six feet of blown sand.
L