109
CORRESPONDENCE.
BOULDER-CLAY IN ESSEX.
Sir,—Referring to the paper "On the Boulder-clay in Essex" (Essex
Naturalist, vol. iv. pp. 199-201), will Mr. Monckton, or any other geologist,
adduce a single particle of evidence of the passage of anything resembling an ice-
sheet over any part of the area between Thames and Humber ?
There are hundreds, if not thousands, of sections amply disproving this
hypothetical agency, and demonstrating the deposition of the Boulder-clay in
a berg-covered sea as clearly as that of the subjacent gravels and sands in one
less charged with clayey detritus.
"An ounce of fact is worth a ton of theory," and the forcing of evidence into
harmony with conclusions drawn from observations in other and entirely different
regions has in this matter, as in others, led to the promulgation of the most
contradictory ideas.
The ice-sheet which has scored the hardest rocks of the Northern mountains,
under the impulse of a scarcely perceptible gradient, must be supposed in East
Anglia to have glided over hills of fine sand without disturbing a grain of their
surface ! Believe it who can !—Yours,
W. H. Dalton.
Derby Road, Woodford,
Sir,—In reply to Mr. Dalton I should say it is unlikely that an ice-sheet
would move over hills of fine sand without disturbing a grain of their surface,
and I should think it improbable that any one holds such a view. There is,
however, evidence to show that an ice-sheet may travel over a country without
effecting any great alteration of the surface. (See Clement Reid, "Geology of
Holderness" [1885], p. 42.)
So far as Essex is concerned, we know that, whatever the precise process may
have been, the surface of the ground over which the ice passed was to a large
extent destroyed, and the materials of the older beds re-arranged. The Glacial-
drift of Essex consists mainly of local material, chalk, clay, sand, and pebbles,
with a small proportion of foreign material intermingled, and that seems to me
the great difficulty which those who contend for the marine origin of this drift
have to meet. Thus, on the south-west of the road half-way between Ingatestone
and Frierning, there was last summer a pit in gravel composed of:—
(a). Pebbles of flint, forming the bulk of the gravel and clearly derived for
the most part from the pebble beds, remains of which still cap the high
ground at Frierning Church close at hand.
(b). Sabangular flints, many.
(c). Quartz pebbles and a block of white quartz, 5 by 31/4 inches. These must
have been brought by ice from a distance.
(d). Two large blocks of sandstone or quartzite.
Here we find a gravel on the side of a hill mainly formed of materials derived
from the top of the hill. It does not look to me like a marine bed ; it is not
the least like an old sea-beach with nothing like a sea- cliff. I might give many
more instances in support of my opinion that the Boulder-clay and Glacial-