21
NOTES ON DRIFT MAPS, WITH ESPECIAL
REFERENCE TO THOSE OF ESSEX.
By T. V. HOLMES, F.G.S., M.A.I.
[Read November 28th, 1885.]
While some of the Geological Survey maps of Essex, showing the
Chalk, Eocene, and Pliocene Beds, have been published many years,
maps showing the superficial beds or drift, in addition, are of much
later date. The drift edition of Sheet 47, for example, is one of the
publications of this year, and it includes within its boundaries about
one third of Essex. Fortunately for persons interested in the geology
of this county, the whole of it, together with small portions of others
on its borders, is contained in Sheets 1, 2, 47, and 4S. These maps,
placed side by side, make an excellent wall-map about 6 ft. 6 in. by
4 ft. 6 in. The sheets mentioned include, on the south, a portion of
North Kent, from Greenwich to Sheerness, on the north-east a con-
siderable piece of Suffolk, around Ipswich and Hadleigh, and on the
north-west and west small tracts of Cambridgeshire, Hertfordshire,
and Middlesex.
In these remarks I do not intend to touch upon the geology of
Essex to any greater extent than may be necessary in order to point
out the great practical advantages of a drift map as compared with
one showing only the underlying beds, or, in other words, the "solid
geology." And, in the first place, a few words may be useful to show
how the drift, or superficial beds, so important in this part of England,
came to be so long neglected. The explanation is to be found in the
circumstances accompanying the birth of the Geological Survey.
In the first thirty years of this century the late Sir Henry, then Mr.,
De la Beche did much excellent work as a private geological surveyor
in Devonshire and Cornwall, either personally or with the help of
assistants paid at his own expense. The usefulness of the maps thus
produced was recognised in 1832 by a Treasury grant of £300 to
defray part of the expenses incurred. The publication of De la
Beche's maps, and of the accompanying Report on the Geology of
Cornwall, Devonshire, and W. Somerset, led to a recognition of the
importance of a Geological Survey on a more extended scale, and to
its institution in (or about) 1835, with De la Beche as Director. Its
staff has been from time to time enlarged, and the illustrative collec-
tion of fossils, formed during the progress of the Survey, and at first
housed in Craig's Court, was moved, at a later period, to its present