22
NOTES ON DRIFT MAPS,
abode in Jermyn Street.1 But the work of De la Beche having been
felt to be advantageous by the Government, mainly or entirely on
account of its economical value from a mining point of view, and the
country first surveyed being either free from glacial drift or mining
districts in which the superficial beds were unimportant, no recognition
of the latter could have then been expected. For in the earliest days of
the Geological Survey there was more difficulty in obtaining a grant
of £1,000 for any scientific purpose than there would now be to get
£10,000. Consequently the small cost of a Survey, the rapidity of
its possible progress, and the immense value economically of the facts
gained during its progress, were then almost exclusively dwelt upon,
and these considerations were chiefly instrumental in bringing about
its establishment. Drift deposits, whether glacial or post-glacial, were
of no importance from a miner's point of view. And as regards the
rate of the Survey's progress, it must have been evident that to map
the superficial drift with as much care as the underlying rocks would
often involve the spending of as much time over a single quarter sheet
as would suffice to finish two or three times that area if attention
were confined to the "solid geology." After leaving Devon and
Cornwall the Survey did much work in Wales, both in the coalfield
and on the older rocks, and thence extended its operations eastward
and northward. It may be of interest to mention, as illustrating the
varying official views as to its affinities, that the Geological Survey was
first placed under the Board of Ordnance ; that in 1845 it was trans
ferred to the Office of Woods and Works ; and was in 1853 attached
to the Science and Art Department.
Glacial drift was first recognised by portions of a map covered by
it being dotted. Now where, as in many parts of England, the drift
seldom attains any considerable thickness, and the solid rocks beneath
are both specially important and abundantly seen in sea cliffs, river
banks and hillsides, dotting may be amply sufficient. For in such
cases it is of much more value to show clearly the disposition of the
rocks whose arrangement determines the general structure of the
district than to obscure its details with patches of another colour
showing the irregular distribution of superficial beds of comparatively
small consequence. Again, there are districts in England in which
maps showing the solid geology and ignoring the drift, and others
indicating the distribution of the various superficial beds, are about
equally necessary. The part of Cumberland nearest the Solway is
1 For these particulars I am indebted to Mr. E. Best, of the Geological Survey.