278 S. HAZZLEDINE WARREN,
value upon either side, I think they are against, and not for, the
acceptance of the very early alleged industries of our pre-human
ancestors.
Biology demands a pre-human ancestor, but one must not
confuse that with the claim that Biology demands a pre-human
flint industry of manufactured artifacts. Flaked flints of unknown
origin must be determined by the comparative anatomy of flint
flakings of known origin, and not by introspective arguments.
The divergence of view upon this subject of flint-flaking
determinations is a serious disadvantage of the method with
which I am experimenting, namely, that of taking the human
industries, so far as these are available, as the basis of the time-
scale of the Pleistocene. One can only use what one believes
to be reliable, and to be in conformity with the truth of Nature.
Turning again to the Table of Classifications, I would class
with the Lower Boulder Clays, the North Sea Drift and the
Contorted Drift of Cromer, and the Norwich Brickearth ; as
also the Scandinavian Boulder Clay of the Yorkshire coast.
It is not possible here to discuss the stratigraphy of the
glacial deposits ; I can only say that on general lines there does
seem to me to be a cumulative weight of evidence pointing to
the conclusion that there were at least two important glacial
episodes with a break of some sort between them. It further
would appear to me a reasonable proposition to think that the
' Middle Glacial " sands of East Anglia represent extensive
melting of the ice, but I am very far from thinking that every
local patch of glacial sand and gravel, which has Boulder Clay
below it and Boulder Clay above it, can be considered truly
" Middle Glacial." The glacial deposits are very variable,
very mixed, and very difficult to classify.
With the Upper Boulder Clays I would group particularly
our Chalky-Kimmeridgic Boulder Clay and the Purple Boulder
Clay of Yorkshire.
The celebrated interglacial beds of Kirmington (33), etc.,
come between the Purple Boulder Clay below and the Hessle
Boulder Clay above. If the correlation of the Hessle Clay with
the Ponders End stage and the Magdalenian be sound, then
these interglacial beds of Lincolnshire and Yorkshire are con-
siderably later than one has thought. It appears irresistible
to correlate the evidences of submergence at the following
localities, as it seems to have occurred at about the same date,
namely:—Clacton (see ante p. 275), West Wittering, etc.
(Sussex) (34), Woodston, etc. (near Peterborough) (35), the
March and Nar Valley district (see also ante p. 275), possibly
Ilford (36), and perhaps Mersea Island (37).
It is tempting to throw the marine and estuarine deposits
of Kirmington, etc., into the same group, but in the absence