Dr. D. Woolacott—The Interglacial Problem. 65 
have removed all such evidence as well as the greater portion of the 
drift of the earlier period. The superposition of these two drifts is, 
however, quite explainable on the hypothesis of a continuous 
glaciation, without a Glaciation-interval or Interglacial period, as 
the ice-streams coming from the west may have reached the coastal 
region before they were diverted southwards by the pressure of the 
Scandinavian ice in one continuous glaciation ; thus boulder-clay 
with western erratics would later be overlaid by drift containing 
northerly derived material. Further evidence would seem to be 
necessary before an “‘ Interval-in-the-Glaciation”’ can be taken to be 
proved in the deposition of the purely British drifts of Northumber- 
land and Durham. 
In connexion with the Interglacial Problem there are three 
deposits of special interest apart from those already discussed. 
These are (1) the Sewerby Raised Beach near Bridlington, (2) the 
deposit at Horsebridge Head, north of the mouth of the Wansbeck, 
and (3) that at the Lyne Burn. 
(1) Trechmann has stated that the evidence for the Preglacial 
age of the raised beach at Sewerby, near Bridlington, is not con- 
clusive,! and if it is eventually proved that there are Glaciation- 
intervals in the formation of the Drifts of the North of England it 
would seem possible that it could have been formed in such a period. 
(2) The gravel deposit at Horsebridge Head, which rests on the 
rock surface beneath boulder-clay,? has been thought by some 
observers to be a Preglacial raised beach *; but Dr. Smythe after a 
very careful examination regards it as the deposit of an early Glacial 
stream.’ The evidence obtained from an examination of the 
boulders is not conclusive. Chalk, flints, fossiliferous magnesian 
limestone, Cheviot porphyrite, igneous and metamorphic rocks all 
occur init.” Bullerwell also records a fragment of a shell (Ostrea 2) 
from it. There seems to be material from several sources, including 
Scotland, the Cheviots, the Magnesian Limestone (whose present 
outcrop is several miles further south), and from Cretaceous strata. 
It is rather a puzzling formation, but it certainly seems to afford 
evidence of a passage of ice from the north before the deposition of 
the more westerly derived boulder-clay overlying it, and it is possible 
that it is an Interval-deposit or even a true Interglacial bed. 
(3) A deposit containing very much the same admixture of material, 
including greywacke and garnetiferous mica-schist (Pitlochrie 2), 
occurs a few miles to the north at the mouth of the Lyne Burn; it, 
however, rests on reddish prismatic clay below which is typical 
boulder-clay, and is covered by blown sand. This deposit again might 
1 Op. jam cit., p. 190. 
* There is a photograph of this deposit in my paper on the Superficial 
Deposits, op. jam cit., p. 68. 
* e.g. Bullerwell, “‘ Section of the Cliffs near Newbiggen by the Sea, etc. ” : 
Nat. Hist. Trans. Northumberland; etc., vol. iv, pt. 1, 1914, pp. 61-6. 
* Glacial Geology of Northumberland, ibid., pp. 98-9. 
° Bullerwell regards some of the granites as being from Aberdeen. 
VOL. LVIII.—NO. II. 5 
