OF THE THAMES VALLEY.
75
channel and transversely across it in the extreme northern
face. The latter is of great importance ; it shows con-
clusively that not only do the beds occupy a distinct
channel in the Thanet Sand, which trends from north to south,
but that the latter rests regularly upon the Chalk without the
slightest trace of subterranean dissolution at the junction of the
two beyond the universal dissolution which has resulted in the
formation of the Bull's Head bed. There is certainly no
evidence in the sections to warrant the supposition that the
deposits in question have been let down by this cause so as to
form the apparent channel. The only evidence of derangement
by dissolution is in the southern portion of the section, where
the Thanet Sand is either very thin or absent altogether, and
where slipping and "piping" would naturally be looked for
Moreover the channel in the Thanet Sand is clearly one of
surface erosion, such as would only result from the degrading,
action of a stream. At one point this erosion has been checked
by a number of sarsens, certain of the blocks weighing many
hundredweights each, which occur towards the base of the Thanet
Sand, and upon these the gravel and sand immediately
repose. Just at this junction Mr. Chadwick, who was in
company with one of us, obtained a rude Palaeolithic implement,
and several others have been obtained by Mr. W. L. Reid and
ourselves from the deposits of the channel.
We have lately come across some further published evidence
relating to this old channel. In the second part of his paper on
"The newer Pliocene period in England," Mr. Searles V. Wood
gave a figure of this channel as it was exposed in the large quarry
some time prior to 188212. This figure shows clearly how the
Thanet Sand rests regularly on the Chalk and is cut almost
through by the channel. The lower part of the channel contained
gravel and sand, the upper part being filled with brickearth,
which Mr. Wood referred to his Cyrena formation. Mr. Whitaker
appears to have seen this channel still earlier, for in the Geology
of London, Vol. i., p. 416, he says :—
" My own note of the Drift in this pit was taken in 1872, when there were, at
the northern and highest part, hollows of gravel, sand and loam, in the Thanet
sand. The largest of these hollows, in the northern face of the pit (probably the-
sams as the one noticed by Prof. Hughes) was very long, and so deep in the
middle as to cut through the Thanet sand to the chalk. [Italics ours.] Its
12 Searles V. Wood, Q. J. Geol Soc, Vol. xxxviii., p. 695, Pl. xxvi , fig. 23.