8 SCIENTIFIC SURVEY OF NORWICH AND DISTRICT 
invader, and a source of anxiety to the defenders. Within such a region 
bounded by forest, fen and sea, human occupation may be traced from 
prehistoric times.? ‘ Yet although these beginnings go far back, the 
Anglo-Saxon period not only duplicated certain features of early invasion, 
but was a restart from which all subsequent development has been 
direct.’ The invasions of the Anglo-Saxons took place along the river | 
valleys. "They worked their way inland by the way of the coastal inlets 
and the Fenland rivers, but on the whole they did not penetrate into the 
woodlands of the boulder clay interior. In their endeavour to hold their 
isolated kingdom the Anglo-Saxons stoutly defended both the Devil’s 
Ditch, which stretched for seven and a half miles from fen to forest 
transversely across the open chalky downland ; and the outer defence of 
Fleam Dyke—earthworks which in all probability they themselves con- 
structed. The line of the River Stour formed a natural frontier on their 
southern limit. 
The geological boundaries enabled the kingdom to possess an essential 
unity, and groups of settlements near Norwich and Ipswich indicate a 
beginning of the importance of these sites as the principal centres for 
the North Folk and the South Folk respectively. Within the kingdom 
itself, along the line of the Little Ouse and the Waveney, is a shallow 
trough which breaks across the chalk ridge in the west and divides High 
Suffolk from Norfolk, forming a natural subdivision of the kingdom and 
fostering a distinction between its northern and southern inhabitants. 
Later developments show that Norwich became the capital of this isolated 
region and that its influence was even more pronounced in the land which 
was the home of the North Folk, a region which now calls for treatment 
in some detail. 
Chalk, undoubtedly the most important solid geological formation of 
Norfolk, has bestowed many benefits on the inhabitants. It yields an abun- 
dant supply of excellent water, and at certain levels are those lines of flint 
which furnished prehistoric man with a durable material for his imple- 
ments and provided the folk of the Middle Ages with a building stone. 
A hard form of chalk called clunch which occurs in some parts of the west 
and middle west has been used as a building stone too. The marl 
derived from chalk provided a dressing for the light soils, and many old 
pits with derelict kilns testify to a widespread utilisation of the chalk as a 
material for lime. ‘The character, age, thickness, height and slope of the 
surface of the chalk vary considerably from west to east. On its western 
margin the chalk is much thinner, the older lower horizons are exposed, 
and the surface is comparatively free from later deposits, while the surface 
slope is but 8 to g ft. per mile. ‘The strike between the Wash and the 
Little Ouse—Thet gap is north-north-west—south-south-east, and shows a 
change in direction from the Chalk ; (a) on the other side of the Wash 
where it is north-west-south-east, and (6) in Suffolk where the strike is 
north-south. The junctions of these two changes in direction reveal 
3 H. C. Darby, ‘The Domesday Geography of Norfolk and Suffolk.’ Geog. Jour. 
May, 1935. 
4 P. G. H. Boswell, ‘ On the Surface and Dip of the Chalk in Norfolk.’ Tvans. 
Norfolk and Norwich Naturalists’ Soc., 1919-20. 
