133
CORRESPONDENCE.
BOULDER-CLAY IN ESSEX.
Sir.,—Mr. Monckton regards it as improbable that anyone holds that an ice-
sheet can traverse hills of fine sand without denuding them. But this absurdity
is essential to his assertion of an East Anglian ice-sheet, for the bedding of the
Boulder-clay is conformable to that of the finely-stratified sands on which it often
rests. That the Glacial Drift of Essex consists largely (I quite deny the "mainly")
of local material is further evidence against the said ice-sheet, and how a well-
stratified gravel, such as is exhibited by the pit Mr. Monckton refers to, can be
regarded as anything like a moraine, or due in any way to continuous ice, passes
my imagination. If Mr. Monckton goes to sections in Essex with a mind pre-
judiced by accounts of the northern drifts (which were produced by confluent ice)
as indicating conditions prevalent throughout West Europe, he cannot expect to
see evidence of marine action. Fossil evidence may be dispensed with (in the
Thaxted case, the shells indicate Crag, in place or nearly so). Stratification, seen
in every exposure worth calling a section, settles the question against ice as
forming the East Anglian drifts, though their material, chiefly of Lincolnshire and
Midland origin, indicates flotation by ice from those regions, in which there is
ample evidence of the action of coast ice as a powerful engine of erosion, when
Essex was mainly if not wholly submerged.
Of the authors quoted, no one who knows anything of the first values his con-
tributions to the literature of the subject, and I wholly dissent from the conclu-
sions drawn from the facts recorded by the others.
W. H. Dalton.
Derby Road, S. Woodford.
Sir,—With reference to the letters of Messrs. Dalton and Monckton on the
above subject in the last number of the Essex Naturalist (ante, p. 109), may I
be permitted to submit some original observations, which although limited to a
small area, are probably typical of much to be found over the northern half of
Essex.
In the railway cutting, between Braintree and Bulford stations, the Boulder-
Clay lies immediately on gravel and sands of "Westleton" age. The line of
division is very sharply drawn. There is no disturbance of the gravel or sand
traceable on the minutest examination, neither has either deposit entered by means
of a "tongue" or otherwise into the domain of the other. The inference is that
the deposition of Boulder-Clay came about there by a quiet process, and not under
the pressure and abrasion of land-ice.
At Blewitt's pit, one mile N.E. of Stebbing village, where similar deposits
occur, the line of division is again sharply marked, and there is also the complete
absence of any disturbance of the underlying bed. In the railway cutting, one
mile west of Dunmow Station, the same beds with the same phenomenon are con-
spicuous, and in Professor Prestwich's paper on the "Westleton Beds" (Quart.
Journ. Geol. Soc. vol. xlvi.), quoting from a previous paper of Mr. Woodward's,
he says "the line between the undoubted pebbly gravels and the overlying
Glacial Drift is generally sharply defined."
Where the Boulder-Clay rests on "Middle Glacial Gravel," the transition is
much less abrupt, and it is often difficult to say where the one formation leaves