Il8 MR. F. W. HARMER ON THE GLACIAL DEPOSITS 
The ice to which the latter deposit was due was much the 
stronger, as it prevented the chalky drift from overspreading 
the plain (see contour map), forcing it against the western 
slopes of the Wolds, along which it is bedded in ridges 
parallel to the latter, attaining a maximum height of 450 
feet above sea level. The separation of the white and blue 
boulder-clays is well marked, and may often be ascertained 
by the colour of the land alone ; one passes, moreover, 
abruptly from the one to the other. 
These facts have an important bearing on the study of 
Norfolk glaciology. Phenomena similar to those of Lincoln- 
shire may be observed in our own county. Referring once 
more to the contour map, we may see that the lines separating 
the North Sea drift of Lincolnshire from the intensely chalky 
clay, and the latter from the Kimeridgian drift, which are 
interrupted by the Fenland depression, reappear in our own 
county. 
It will be noticed that the chalk escarpment which runs 
southward from Hunstanton towards Swaffham is broken 
by a gap, about twenty-five miles in width, extending from 
the latter place to a point north-east of Newmarket, where 
the chalk hills of the Gog Magogs commence. This gap forms 
the entrance to a wide trough, probably of pre-glacial origin, 
running continuously from west to east from the Fenland to 
the Suffolk coast, the joint basin of the Little Ouse and 
Waveney. 
Through this gap the Chalky boulder-clay ice poured in 
great volume from the Fenland, fanning out afterwards to 
the east and south-east, and covering an area of something 
like a thousand square miles with boulder-clay which in 
places approaches 100 feet in thickness, and has a maximum 
elevation of more than 300 feet above sea level. The boulder- 
clay of this district is generally of a dark indigo colour, its 
matrix being almost entirely composed of ground-up Kimeridge 
shale. It contains many large blocks of Kimeridgian septaria, 
and of hard Lincolnshire chalk and grey tabular flint. Frag- 
ments of Oolitic limestone and of other Jurassic rocks are 
not infrequent, but its predominant character is Kimeridgian. 
