190 LAMPLUGII : NOTES ON THE WHITE CHALK OF YORKSHIRE. 
the mass seems never to have been sufficiently deep to over-ride 
entirely tlie Chalk escarpment at Speeton, perhaps partly because of 
the abruptness of the cliffs and partly because the main current of the 
ice-flow was to some extent deflected by the Oolitic hills north of 
Scarborough. The greater part of the Eastern Moorlands and of the 
Yorkshire Wolds probably remained as low tracts of land just rising 
above the margin of the ice which in places sloped rather steeply 
towards the land, so that its morainic border was sometimes pushed 
or washed on to the edge of the Chalk plateau, forming irregular 
mounds, as at Speeton. But on the lower ground near Flamborough 
the height of the clift' was not sufficient to arrest the ice-flow which 
therefore passed across the headland into the Bay of Holderness, 
producing in its passage the varied phenomena already noted. During 
the long persistence of this Ice-sheet of the North Sea wide 
oscillations of its margin occurred, so that it sometimes filled 
up the whole of the Holderness Bay and crept well up the inner 
slopes of the Wolds, while at other times it receded many miles 
distant, and its morainic material was washed by floods and deposited 
in well -stratified sheets over the low ground east of the Wolds. 
The steady recession which afterwards set in may, as 1 have 
elsewhere suggested," at first have been due not so much to an actual 
amelioration of climate as to a diminished snow-fall, consequent upon 
the greater elevation of the Irish Sea Glacier at this period, by which 
the greater part of the moisture of the damp Atlantic air currents 
was intercepted on the western side of England. 
Thus a rather dry climate of Arctic severity seems to have marked 
the later stages of the Glacial Period in the east of England. But sub- 
sequently the average temperature rose, the ice-sheets in every part 
of the country rapidly dwindled, and the rainfall became excessive. 
At this time the scouring out of the Wold Valleys was again in 
active progress, and the great spreads of sub-angular chalky gravel 
which overlie the Drift-series at the mouths of all the Wold Valleys 
are the records of tliis period. 
The disappearance of the ice-sheet left Flamborough Head almost 
hidden under a mantle of drift, and the former bays on either side 
* Glacialists' Magazine, vol. i., p. 189. 
