56 SCIENTIFIC SURVEY OF NORWICH AND DISTRICT 
of which prove that the sea was rather colder than the southern part of 
the North Sea at the present day. About 100 species of mollusca and 
ostracoda have been found, the best collection of them being preserved 
in the Norwich Castle Museum. 
Next in order of formation was the Great Chalky Boulder Clay, with 
its accompanying outwash sands, gravels and brickearths. Such were 
the characteristic features of its matrix and erratics that F. W. Harmer 
considered that it originated with the advance of the Great Eastern 
Glacier. Essentially, the boulder clay is composed of ‘ home-grown’ 
material—of rocks derived by glacial advance over the outcrops of the 
rock-formations of the east of England (or their extension on the bed of 
the North Sea) from the Fen district to Lincolnshire, Yorkshire, or even 
the north of England. The matrix, like the erratics, varies in different 
parts of Norfolk. In the central and western parts of the county, the 
fine material is buff or whitish and largely composed of chalk, the erratics 
including hard chalk, grey chalk, tabular Lincolnshire flint, red chalk, 
Spilsby sandstone, phosphatic Neocomian sandstone with Terebratula 
rex, etc. This is the Chalky-Neocomian Boulder Clay. In north-eastern 
and southern Norfolk and in most of the area of Suffolk, the boulder clay 
has a dark bluish-grey matrix derived from the Jurassic Clays, and its 
erratics include rocks from the Chalk, Jurassic deposits, Trias, Carboni- 
ferous and older systems. This Chalky-Jurassic Boulder Clay in the 
main lies side by side with the Neocomian type. The contact between 
the two types is well seen in the cliffs at Scratby, five miles north of 
Yarmouth. i 
The succession of glacial deposits in the neighbourhood of Cromer 
must now be considered. Correlation with the sequence of beds found 
farther south and described above is not easy. The lowermost deposit 
seen in the coastal sections is the Cromer Till, a dark grey clay containing 
erratics which are more numerous, on the whole, than those of the 
Norwich Brickearth. The erratics include Scandinavian types, but 
British rocks predominate. ‘The presence of the former has led to the 
correlation of the deposit with the Norwich Brickearth, the two boulder 
clays being included in the general term North Sea Drift. From Happis- 
burgh to Mundesley two beds of Cromer Till have been described, the 
Upper Till and the Lower Till (of Dr. J. D. Solomon), separated by very 
fine sandy beds known as the Mundesley Sands. Resting on these is a 
series of laminated clays with wisps of sand, the ‘ Intermediate Beds’ of 
C. Reid. In turn, the laminated clays are succeeded by a white or buff 
boulder clay, containing little else but debris from the chalk—the ‘ Marly 
Drift’ of older writers. The stratigraphical position of this deposit has 
been the subject of much discussion, F. W. Harmer regarding it as the 
western equivalent of the Cromer Till, and H. B. Woodward (and, more 
recently, Dr. J. D. Solomon) as a variant of the Great Chalky Boulder 
Clay. It also forms part of C. Reid’s Contorted Drift. The succeeding 
deposits consist of sands and gravels, often containing outwash material 
from the Marly Drift. 
All the deposits from the Cromer Till to the Marly Drift have been 
involved, together with the various Pliocene divisions and the Chalk, in 
