PLEISTOCENE CLASSIFICATIONS.
279
of any prehistoric industry which would more precisely date
the deposits of the Humber district, the suggestion remains open
to question.
So far as south-eastern England is concerned, I believe that
the most important interglacial break is that between the
Chalky Boulder Clay and the Ponders End deposits, during
which the Boyne and Taplow Terraces of the Thames were laid
down. The "Middle Glacial" seems to me less satisfactory
but as very probably representing extensive, if only partial,
melting of the ice.
One does not question the fact that there is sand and gravel
at all horizons in the Boulder Clays. But if we find a particularly
vast quantity of such clean-washed material at some one particu-
lar horizon it does seem to suggest an unusual amount of ice-
melting (due to a rise of temperature) at that particular stage.
The Pre-Chellian stage will need critical examination in the
future when more comparative evidence is available. One
could discuss it extensively, but at the moment I could not
suggest a conclusion.
To the Chellian stage belongs, of course, the Boyne, or
100-foot Terrace of the Thames, while the oldest basement
gravels of the Taplow, 50-foot or Middle Terrace, are referable
to the Late Chellian. These represent the river-bed when the
Boyne Terrace was the flood-plain.
The Acheulian stage comes between the Chellian and the
Mousterian, but changes in the application of the term have
rather confused the issue. In the first instance, de Mortillet
applied the term Acheulian (38) to the whole of the Lower
Palaeolithic, or River Drift period of Evans. Subsequently, the
same author (39) re-named the major part of this period as
Chellian in place of Acheulian, and restricted the latter term to a
comparatively brief intermediate epoch before the Mousterian.
For many years this remained the accepted view, but more
recently there has been a growing tendency to push the Acheulian
boundary backwards at the expense of the Chellian and thus
to revert nearer to its original usage.*
The Proto-Mousterian tortoise-core industry is found on the
floor of a later episode of the Taplow Terrace. The true Mous-
terian industry is well seen on a buried flood-plain of the Taplow
Terrace in the Stoke Newington district. The problem of the
Mousterian ice age has already been discussed.
There is not much to be said about the Upper Palaeolithic
* For instance, one of our most familiar English types of the Chellian industry (identified
as such by de Mortillet) is the celebrated Grays Inn Lane specimen of A.D. 1690. In the new
edition of Ancient Hunters, published since the above was written, this specimen again becomes
a type of the Acheulian, as it was before 1883.