130 JIR. F. W. HARMER ON THE GLACIAL DEPOSITS 
THE ORIGIN OF THE VALLEYS OF CENTRAL NORFOLK. 
Sections to the north-east of the river at Norwich, with 
others facing them, formerly existing near the Victoria 
railway station, have shown that when the ice sheet of the 
earlier glaciation travelled south-eastward from the Cromer 
coast to Loddon and Beccles, the North Sea drift extended 
continuously over what is now the valley of the Wensum, 
at present about half a mile wide, and more than a hundred 
feet in depth. The section, fig. 4, will show that the Wensum 
valley has been cut out of the Norwich brickearth (j), the 
Contorted Drift in an uncontorted form, as well as out of the 
overlying sands ( 4 ), which I associate with it. The North 
Sea brickearth never occurs, moreover, as a valley deposit. 
On the other hand, although the Chalky boulder-clay, the 
moraine of the later and inland ice-stream, covers a great 
part of the higher land with a more or less continuous sheet, 
it constantly warps over into the valleys, being often found 
within them, as, for example, at Trowse, Thorpe, Cringleford, 
Bowthorpe, and elsewhere, the Chalk upon which it rests 
always showing evidence of glacial disturbance. These valleys, 
therefore, were excavated in the interval between the retreat 
of the North Sea ice from Norfolk, and the arrival of the 
inland glacier. 
The position frequently occupied by the Cannon-shot 
gravels near the margin of the valleys, in positions where 
they could not have originated under existing conditions, is 
both interesting and significant. 
No better illustration of this could be given than that of 
the great sheet which caps Household Heath. Standing on 
the edge of the steep northern bank of the river Wensum 
one looks down to the lower ground where 100 feet below, 
Chalky boulder-clay (5 of fig. 4) rests on the valley bottom. 
This boulder-clay has been always regarded however, as 
older than the Household gravel (< 5 ). How then, it may be 
asked, could the latter have been accumulated ? But two 
explanations seem possible ; either these plateau gravels 
are older than the Chalky boulder-clay, a view which in the 
