258
A NEOLITHIC FLOOR.
after a storm, or a dam constructed by beavers, or sandbanks
forming across the river's mouth. Causes such as these have
been known to effect wide-spread alteration over large tracts
of country, and caution should, no doubt, be exercised in
looking to more powerful natural agencies to account for slight
recent changes.
Many of these river deposits, however, occur in such regularity
over a considerable area, that they seem to mark some general
succession of events, dating from the Neolithic period. This
represents a time of long duration and of momentous develop-
ment, so far as man's history is concerned, although geologically
such a lapse of time is quite insignificant, and any changes
that have occurred are too slight to be regarded save as mere
incidents during an almost stationary geological condition.
Archaeological evidence is more likely to record such slight
changes in prominent relief and to supply us with data for
gauging with greater accuracy the extent to which changes
in the physical condition have occurred in recent geological times.
Any discovery serving to throw light on this question becomes
important, and a comparison should be made with similar
occurrences elsewhere.
Much valuable information regarding the peat deposits of
the Thames has been collected by Mr. Whitaker,2 and Mr. F. C. J.
Spurrell3 has contributed some important papers on the subject,
in which he has, more than anyone else, dealt with the
archaeological side of the question. In the general section of
the course of the Thames, Mr. Spurrell shows that three dis-
tinct bands of peat are found in the bed of the river at Graves-
end. The lowest of these dies out in ascending the river, so that at
Crossness two only are found, while only one is found at London
and the higher reaches beyond. (Fig. 8).
Mr. Spurrell has obtained a great deal of evidence that the
highest of these bands was a land surface in Roman times.
Describing the section at Tilbury, he says :—
" The upper layer of the peat was comparatively thin and mainly con-
sisted of a small growth of underwood, with spreads of grass resembling
the growth on the marshes of the present day. I think it likely that
2. Memoirs of the Geological Survey, 1889. Vol. 1. Geology of London, p. 454, etc.
3. Arch. Journal, vol. xlii. 1885 "Early Sites and Embankments on the Thames
Estuary"; Proc. Geol. Assoc, vol. xi. 1889-90. "On the Estuary of the Thames and its
Alluvium," pp. 210-230 ; See also : T. V. Holmes, Trans. Essex Field Club, vol. iv. p. 135, and
B. B. Woodward, Proc. Geol. Assoc, vol. xi., No. 8.