The Ancient Fauna of Essex.
19
but it would be only local; considerable changes of level,
for instance, have taken place in our own Thames Valley.
Below high-water-mark, in the neighbourhood of Victoria
and Albert Docks at Plaistow, there are abundant evidences
of deposits such as I have spoken of, and a canoe has been
found, showing that primitive man was there when the
valley stood at a far higher level than now. Mr. Searles Wood
in some of his papers mentions trees in situ at many points
below the present level of the Thames, affording good evidence
that in prehistoric times the level of the Thames stood con-
siderably higher than it does now; and that savage men, if not
civilised men, at that time occupied the country.
Probably no independent geological investigator since the
early days of Buckland, Trimmer, and Morris, has paid such
careful attention to the structure of the Thames Valley, and
of its contained deposits, as Mr. Searles V. Wood, F.G.S.
Numerous papers on this subject have been communicated
by him to the 'Quarterly Journal of the Geological Society'
and to the 'Geological Magazine.'
Writing. thereon in 1866 (Geol. Mag., vol. iii., p. 59),
Mr. Wood observes : "The brick-earth of Ilford, both that
of Uphall and that of the London-road Field, is a deposit
underlying the Thames gravel, and unconformable to it."
He also speaks of it as anterior in date to the similar deposit
of Grays, which likewise contained Cyrena fluminalis and
other purely fresh-water shells.
In a letter to me (dated March 10, 1874) Mr. Wood says :—
" When I wrote the paper in vol. iii. of the Geol. Mag. (1866),
I was under the impression that, though the Grays brick-
earth was clearly newer than the main sheet of the Thames
gravel (it forming distinctly a terrace beneath it), the Cyrena
brick-earth of Ilford, and of Crayford and Erith, was anterior
to, and passed underneath, it. Some year or two afterwards,
however, I satisfied myself that this was an error as concerned
Crayford and Erith, and I wrote a letter to the 'Geological
Magazine' (Oct. 10, 1868, vol. vi., p. 534) directly, to ac-
knowledge this.
" The Ilford bed lying flush with the gravel sheet of that
part of Essex does not present the means of determination
by section ; but I cannot doubt, however, that it is identical