132 MR. F. W. HARMER ON THE GLACIAL DEPOSITS 
After some interval, during which this deposition of sand, 
and the erosion of the valleys took place, possibly representing 
one of the inter-glacial periods insisted on by Professors 
James Geikie and Penck, Norfolk was again invaded by 
ice, by the great inland glacier to which was due 
the well-known Chalky boulder-clay, a wide-spread deposit, 
the moraine projonde of the second glaciation, which covers 
a great part of Norfolk and Suffolk with a more or less 
continuous sheet. On the higher land it forms plateaux, 
presenting a levelled appearance, but it occurs also in 
a sporadic way within the valleys. In north-western 
and central Norfolk it is grey or whitish, and prevalently 
chalky ; in the southern part of the county and in Suffolk it 
is blue in colour, forming very stiff land, its matrix consisting 
chiefly of Kimeridgian detritus. 
This inland ice-stream, which seems to have filled the 
Fenland to overflowing, radiating thence in various directions 
as shown in fig. 4, was, in the writer’s opinion, a prolongation 
of the great glacier of Teesdale and of the Vale of York, 
reinforced by lateral ice-streams from the Pennines, and 
specially by the North Sea Ice, then lying in considerable 
thickness off the Lincolnshire coast, which overflowed the 
Wolds. 
The Chalky boulder-clay, the matrix of which varies in 
different districts in accordance with the various Jurassic 
rocks over which the ice had passed, contains much Pennine 
and Oolitic detritus, and constantly, in the greatest profusion, 
blocks of the characteristic tabular grey flint and hard chalk 
of the Lincolnshire Wolds. 
As the glacial period waned and the great ice-sheet which 
for long ages had covered hill and valley alike began gradually 
to disappear from East Anglia, it forsook the higher elevations, 
still filling depressions, however, and generally occupying 
the lower ground, the coarse plateau gravels originating near 
the margin of the retreating ice. Somewhat later, when the 
ice of the valleys became sedentary but still filled them 
nearly to the brim, sheets of gravel were accumulated 
in places along the margin of the old valleys, which may 
