Dr. D. Woolacott—The Interglacial Problem. 23 
that ice-retreat does not necessarily imply an Interglacial period, 
and in the second place that sweeping generalizations have been 
made before the phenomena in different areas, due to the intervals 
of ice-retreat, have been correlated. If, however, this question is 
to be finally solved it will only be by the working out of deposits, 
etc., due to the episodes of ice-retreat in each area and their careful 
correlation, that it will be found if such intervals are so widespread 
as to be really Interglacial in character. 
I would therefore suggest that until this problem has been more 
fully investigated the term ‘“ Interval-in-the-Glaciation ” of an area 
be used when only a limited extent of ground is being studied and 
not Interglacial period to designate epochs of ice-retreat, and that 
the term “‘ Interval-deposit ’’ be applied to beds formed during such 
periods, until by an accumulation of evidence they. are proved to 
be really Interglacial in character. This would tend to define 
the problem clearly, and to do away with the assumption that any 
deposits which are not of direct glacial formation in the Drift are 
Interglacial. The chief difficulty in the acceptance of a series of 
Interglacial periods is found in the fact that it is difficult to correlate 
the phenomena that have been taken to mark such episodes in 
different areas; indeed, it has appeared to some geologists that a 
change in the foci of ice accumulation and consequent direction of 
maximum movement might explain most of the phenomena, rather 
than a succession of Interglacial epochs. I the term “ Glaciation- 
interval’? was adopted, and the effects produced in such intervals 
were gradually worked out as regards their relative importance 
and extent, and afterwards, if possible, correlated in different districts 
and later in different countries, it would ultimately be possible to 
find out whether any intervals were of such extent and importance 
as to constitute true Interglacial periods. Time alone is not the 
factor, as an “ Interval-in-the-Glaciation”’ might be as prolonged as 
an Interglacial period, but it might, however, only be of short 
duration. No ‘Interval-deposit” or ‘‘ Interval-denudation ”’ 
should be accepted as Interglacial until it is definitely proved to 
be so. Only in some such way will a really sound general idea of 
the Glacial deposits be obtained, and it be settled whether they are 
the result of one continuous glaciation, or of a succession of Glacial 
epochs. 
The subject is further complicated by the difficulty of distin- 
guishing true Glacial from Interglacial deposits, and both of these 
from beds laid down during an Interval-in-the-Glaciation. ' Some 
geologists‘ have regarded the thick sands and gravels occurring 
in the boulder-clay of the North of England as Interglacial, 
but some of them may not even be _ Interval-deposits. 
They may only be of fluvio-glacial origin, and have been formed 
during periods of periodic and seasonal ice-melting. There are, 
however, some beds which may be Interval- or even Interglacial 
deposits, and their inclusion as such may bear no relation to their 
