WITH ESPECIAL REFERENCE TO THOSE OF ESSEX.
25
and disadvantages as the site of a building of any kind, a driftless
geological map must be worse than useless. This view receives
confirmation, if we turn from Mr. Clement Reid's coast section to
inspect one drawn by Mr. F. W. Harmer, across Norfolk from
Hunstanton to Norwich and Yarmouth.2 Mr. Harmer is probably
as fully acquainted with the details of Norfolk geology as the
geological surveyors themselves, for some years before they entered
Norfolk he had, in conjunction with the late Mr. Searles Wood,
mapped very carefully a large portion of East Anglia. Turning
then to Mr. Harmer's section, we see that above the chalk—which
was found to be 1,152 ft. thick in a well at Norwich—there is scarcely
anything but Glacial Drift to be seen. A thin band of Pliocene
appears here and there between Acle and Norwich, intervening
between the chalk and the drift; but this thin bed is not shown
anywhere west of Norwich, and it is of no practical importance
whatever, though geologically interesting from the fossils it contains.
On the whole we gather from Mr. Harmer's section across Norfolk
what we learned from Mr. Clement Reid's coast section, viz.,
that while chalk may sometimes be seen in the valleys, and here
and there the Pliocene band may also be observed above it, yet that
by far the greater part of the surface consists of Glacial and other
Drift varying in thickness, but not unfrequently exceeding 100 ft.,
resting on Chalk. And we thus learn that the accuracy of Sir
Andrew Ramsay's map in Kent and its apparent deficiencies in
Norfolk are the result, not of the comparative want of knowledge of
the geology of the latter county, but of the consistent ignoring of
the superficial beds equally in Kent, where they are unimportant,
and in Norfolk, where they cover the greater part of the surface to
a depth of from 20 to more than 100 ft. For it being inadmissible
to represent the Glacial Drift by a separate colour, the only colours
that could be used in Norfolk, as elsewhere, were those marking the
highest of the underlying beds; in other words, those indicating
Chalk and Pliocene.
Though the glacial drift is, on the whole, decidedly the most im-
portant of the superficial formations of Essex, many beds of post-
glacial date occupy considerable areas, and are, like the glacial drift,
omitted on maps showing only the solid geology. On these last are
the Chalk, the Eocenes, comprising the Thanet Sand, Woolwich and
Reading Series, London Clay and Bagshot Beds; and the Pliocene,
2 "Testimony of the Rocks in Norfolk." By F. W. Harmer, F.G.S.