326 HARMER : THE PLEISTOCENE DEPOSITS OF EAST ANGLIA. 
satisfactorily explained. The Chalk escarpment, which runs 
southwards for about 20 miles from near Hunstanton, at the 
north-west angle of Norfolk, presents, as a rule, a more or less 
abrupt face towards the west. Where the Chalk outcrop crosses 
the southern part of Sheet 65 and the northern part of Sheet 51, 
however, that is, between SwafTham and Newmarket, the line 
of tlie escarpment is broken, the N. — S. alignment of the outcrop 
is interrupted, and purjhed back some miles to the east in the 
form of a hay. 
From this area a shallow trough cut out of the Chalk, the 
lowest part of which does not exceed 50 feet above sea-level, 
extends from the Fens eastwards, its bottom forming an inclined 
plane, gradually ascending in the first instance from west to east. 
Although this depression was no doubt deepened and widened 
during the (Jlacial epoch, conditions more or less similar to those 
of the present had been established there previously to the Chalky 
Boulder-clay period, as it is occupied hy that deposit. Through 
this gap in the Chalk range, and along this easy gradient, partly 
the cause and partly the effect of its movement, the ice poured 
from the Fens in greater volume than over any other part of 
the counties of Norfolk and Suffolk, as is shown by the fact 
that it carried its moraine across Sheets 50 and 66 towards 
Yarmouth, nearly twice as far from the normal position of the 
Chalk escarpment, as it did over the region extending from 
Sheet 51 to Sheet 48 (see Fig. 4). The progress of the ice was 
checked in the latter case by the Chalk hills to the east of Cam- 
bridge. Further to the S.W., as near Royston, the crest of the 
escarpment is still higher, and this again, together with the 
high land between Dunstable and Fenny Stratford, obstructed 
the ice-flow, blocking it out from the southern portion of Sheet 
46. Across Sheet 52, however, along the basins of the Ouse 
and the Nene, follo^^ing the strike of the Oolitic rocks, the ice 
travelled a considerable distance to the S.W. beyond Buckingham 
in one direction, and Northampton in another. The area of 
Sheet 53 was protected from its incursion by high ground, but 
owing to the pressure of glaciers descending from the Pennines, 
boulder-clay was piled upon the still higher region of Sheet 63 
to an elevation which, as before stated, exceeds 700 feet (Fig. 4). 
