112
NOTES ON A MAP INCLUDING THE GREATER
PART OF SOUTH-EASTERN ENGLAND.
RECENTLY ISSUED BY THE GEOLOGICAL SURVEY.
By T. V. HOLMES, F.G.S (Vice-President).
[Read February 8th, 1896.]
THIS map, which is known as Index Sheet No. 12, is the first
issued by the Geological Survey which has been colour-printed
and not coloured by hand. The results of this alteration are greater
accuracy than is possible with hand-coloured maps, and a reduction
of price from 10s. 6d. to 2s. 6d., which brings it within the reach of
all persons interested in the district within a radius of fifty or sixty
miles from London. The scale of the map is four miles to the inch,
and, as the railways and chief roads are marked, it furnishes (if
mounted to fold), apart from the geological information it gives, a
useful guide to the traveller by railway.
Of course, on a map of this scale it has been found necessary to
omit various superficial deposits for the sake of greater general clear-
ness. Those not shown are the Glacial Drift, and the patches of
gravel and loam to be found here and there in various positions,
from our hill tops to our river valleys, which are all post-Pliocene in
age, and almost all newer than the Glacial Drift. To have added
these would have been to introduce obscurity, especially in Essex,
where, over a large portion of the county, the underlying Tertiary
rocks would have appeared only as small irregular spots. South of
the Thames the obscurity would have been much less, owing to the
absence of the Glacial Drift, but as these superficial beds everywhere
lie indiscriminately on rocks of various ages they would, even in
Kent and Surrey, have made many geological boundaries indistinct
which are now obvious at a glance.
The area included in Index Sheet No. 12 is that of the whole of
the counties of Essex, Hertford, Middlesex, Surrey, and Kent, with
the greater part of Sussex, and portions of Hampshire, Berkshire,
Buckinghamshire, Bedfordshire, Cambridgeshire, and Suffolk. The
coast-line extends from Orford in Suffolk to Rye and Winchelsea in
Sussex.
Some years ago (Essex Naturalist, vol. ii., pp. 21-33) I took
an opportunity of pointing out the great advantages of drift maps