218 THE GEOLOGY OF SOUTH ESSEX.
vial flats north of the river below London testify, has been mainly
employed for a long time in cutting its way further southward. The
heights against which the Glacial Drift ended might then have been
a mile or two south of Romford—where the broad flat of old river
gravel now spreads—and yet south of the Thames as it then flowed.
As the river deposited gravel on its northern shore, so it would eat
into and destroy the high ground on its (then) southern bank.
The River Drift is described at some length in chapters 20 to
25, and there is a review of the literature treating of these beds which
is of great interest in illustrating the evolution of geological thought
on the question of river-valleys. The inexperienced geologist will
read with much astonishment the extraordinary variety of opinions
which have been expressed from time to time, by men of more or
less eminence, about the formation of the Thames Valley, and the
ages of certain of its deposits. He will discover that this proceeds
mainly from the excessively high value attached to certain kinds of
evidence familiar to the writer, and the comparative neglect of others
of equal or greater importance of which he knows little, and there-
fore underestimates. In such matters the sanity of Mr. Whitaker
renders him an excellent guide. And when we reflect that these old
river drifts contain the ancient flint implements—discoveries of which
Mr. Worthington Smith has so often announced in the publications
of the Essex Field Club—in addition to the remains of mammalia,
either extinct or non-existent in Britain, during the historical period,
it is not surprising that they have been much discussed, or that they
occupy 125 pages of this memoir.
Chapter 26 is devoted to the recent alluvium, together with shore
deposits, greywethers, &c., and is succeeded by others on the physi-
cal and economical geology of the district. The last chapter treats
of the petrological, mineralogical and chemical characteristics of the
various rocks : analyses are also given of the water obtained from the
wells sunk in them.
There are more than one hundred figures of sections, and each
volume contains a carefully drawn up index.1
T. V. Holmes.
1 "Geology of the London Basin," Part I. Though this older memoir has now been almost
entirely superseded either by the work here noticed or by others, mostly of smaller size, describing
separate sheets, it may be useful to state that, in addition to the sheets already mentioned, the
"Geology of the London Basin" contains a description of the greater part of sheet 3 (East Kent),
of a small part of sheet 14 (Wiltshire), and of a considerable portion of sheets 46 and 47 (Bucks,
Herts, and N. Essex). North Essex is now fully described in separate memoirs treating of
sheets 47 and 48 respectively.