’ 
60 Dr. D. Woolacott—The Interglacial Problem. 
much attrition; but, on the other hand, its specific identity is far 
from proved. With this possible exception there is nothing in the 
Hchinoids to suggest that the limestone from which they came 
is older than the P. asper zone; while positive evidence (C. 
columbarius and N. lacunosus) and negative evidence (D. subuculus) 
agree in suggesting an horizon even higher than the uppermost 
Selbornian. 
Note inserted in proof—Mr. Woods has sent me six radioles of 
Cidaris from Shenley. Three of these certainly belong to 
C. bowerbanki, a “Grey chalk” species. The other three probably 
represent the same species. Dr. Kitchin has sent a specimen of 
? Cardiaster or Holaster (Mus. Pract. Geol., Nos. WM 4741 and 4742) 
from the nodules in the mammullatus-zone near Leighton Buzzard. 
This specimen agrees exactly with No. D above, both in form and 
matrix. Itis not specifically determinable. 
The Interglacial Problem and the Glacial and Post- 
glacial Sequence in Northumberland and Durham. 
By Davip Wootacortt, D.Sc., F.G.S. 
(Concluded from p. 32.) 
HE features of the Glacial deposits and associated phenomena 
just discussed are in general so clear that most observers would 
arrive at the same conclusion regarding them, but there are some 
other features about which, either due to their controversial 
nature or the conflicting character of the evidence, there is 
not yet such general agreement. These are (a) the evidence for 
Interglacial Periods in the Drift of these counties, (6) the 
raised beaches of East Durham, (c) the origin of the leafy clays, 
(d) the explanation of the distribution of fragments of certain rocks 
—Flint, Chalk, Magnesian Limestone—in the Superficial Deposits. 
1. The evidence for Interglacial Periods. In my paper on the 
Superficial Deposits of the Northumberland and Durham Coalfield, 
I state that “as far as the available evidence goes there does not 
seem to be anything pointing to an Interglacial Period or Periods ”’,* 
and Dr. Smythe in his study of the Glacial Geology of 
Northumberland has evidently arrived at the same conclusion as 
regards the whole of that county, as he states that “* No classification 
of the boulder-clays of Northumberland seems possible, though 
locally there is frequently evidence of two clays of different origin ”.? 
In his description of the glacial deposits of South-East Durham 
T Quart. Journ. Geol. Soc., vol. lxi, 1905, p. 68. I also state that “ some 
of the thicker deposits (of sand and sandy clay found intercalated in the boulder- 
clay) may represent epochs when the ice was melting quicker than others, but 
whether they can be considered in any sense as ‘ Interglacial’ is very 
doubtful” 
2 Glacial Geology of Northumberland, op. jam cit., p. 93. 
