WITH ESPECIAL REFERENCE TO THOSE OF ESSEX. 23
such a district. For, on the one hand, there are many square miles
of country near that estuary in which superficial beds only are seen,
and in which their nature and distribution are of immensely greater
practical importance than those of the underlying formations. To
ignore the drift in such a case is necessarily absurd. But, on the
other hand, the areas in which the lower rocks appear, being few and
far between, and, in addition, of very small extent, the disposition of
the rocks forming the solid geology cannot be properly shown on
maps in which they appear as mere dots of colour in the midst
of drift. Consequently, for the proper display of these lower
rocks we need a separate map on which the superficial beds
are wholly or partly ignored. As it gradually became obvious that
there were districts of England in which the superficial beds were at
least as important as those below them, and in which the various
drifts could be shown on maps only by the use of distinct colours,
the late Sir Roderick Murchison decided that a series of maps should
be prepared to illustrate the nature and distribution of the super-
ficial deposits, on account of their agricultural importance. Many
drift maps have since been issued, that of the environs of London
being among the first. And the Geological Survey, which began its
work in the mining and mountainous districts, ignoring the super-
ficial beds, has lately found that in East Anglia maps showing the
various drifts are alone worth publishing.
For in no part of England have drift maps greater advantages over
driftless maps than in Norfolk, Suffolk and Essex, as may be illus-
trated in the following way. We may suppose that a geologist from
some remote part of Great Britain wants to see something of the
Cretaceous and Tertiary Beds of South-eastern England, and that he
proposes to visit for that purpose the coasts of Kent, Sussex,
Hampshire, and the Isle of Wight, on the one hand, and then to
cross the Thames and travel round the shores of Essex, Suffolk and
Norfolk, to the Wash, carrying, as geological guide, Sir Andrew
Ramsay's Geological Map of England and Wales, on which, from its
scale, the glacial and other drift is necessarily ignored, or only indi-
cated by dots. In his southern journey, from Herne Bay or Margate
to the Isle of Wight, he will find his map as perfectly accurate and
trustworthy as a map of its scale can be. Where, as in the Isle of
Thanet, the country between Deal and Folkestone and at Beachy
Head, chalk is indicated, there he finds the cliffs are chalk, and the
Wealden or Tertiary beds appear just where the map would lead