NORWICH IN ITS REGIONAL SETTING 9 
lines of weakness which in some measure account for the depression of the 
Wash and the Little Ouse—Waveney Gap. The latter is well marked in 
the Chalk and the period of its formation was probably post-Eocene and 
pre-Pliocene. At Hunstanton the chalk passes down into the well-known 
red chalk which rests directly on the dark brown ferruginous sandstone 
called carstone or ‘ gingerbread stone,’ used locally as a building stone. 
Further south, from Sandringham to Stoke Ferry, a stratum of gault occurs 
between the Lower Greensand and the Chalk; the Greensand in turn 
resting on Kimmeridge Clay. From this line, Hunstanton to Stoke Ferry, 
the Chalk dips eastwards, the amount of true dip being about 35 ft. to the 
mile. Consequently the thickness increases, being as much as 1,150 ft. 
at Norwich. East of the line Weybourne, Reepham, Hethersett, Dickle- 
burgh, Pliocene deposits, collectively called the Crag rest unconformably 
on the Chalk, and a small outlier occurs at Guist eight miles to the west of 
this line. Further eastwards Eocene deposits have been found in borings 
between the Crag and the Chalk. From a line Woodbastwick—Beccles 
and the coast the surface of the Chalk has been bevelled off giving rise to a 
rapid increase of its slope—the fall being as much as 400 ft. in about 
four miles. It is both interesting and significant to note that the present 
surface of the Chalk is over 250 ft. above O.D. at a point a few miles to 
the north of Swaffham, 50 ft. above O.D. at Norwich, and 450 ft. below 
O.D. at Yarmouth. The whole area of Norfolk was subjected to a series 
of glacial invasions which occurred at intervals in the Pleistocene period. 
Dr. J. D. Solomon ® distinguishes four distinct periods of ice advance. 
The advancing and retreating ice sheets have been responsible for con- 
siderable alteration to the topography. They blunted the edge of the 
chalk escarpment in the west ; re-excavated the Little Ouse—Waveney 
trough ; and created the Cromer Morainic Ridge, which is so youthful 
that it is almost unmodified by erosion. The moving ice covered the 
greater part of Norfolk with a mantle of drift varying considerably in 
thickness and the composition of its materials—large plateaux of chalk 
boulder-clay, trails of sands and gravels, isolated areas, often several 
square miles, of laminated clays and loams are in the main the surface 
materials from which the soils of Norfolk are derived. Post-glacial 
deposits are almost entirely confined to the low-lying parts of the country : 
(1) valley gravels and loams in patches situated between the chalk outcrops 
and the fens ; (2) vast deposits of alluvium and peats in the fenlands to 
the west and the eastern marshlands of the lower Bure—Yare—Waveney ; 
(3) small isolated deposits of alluvium scattered here and there are to be 
found in the interior, probably the sites of old meres ; (4) materials form- 
ing the coastal marshes of the northern fringe of Norfolk situated between 
Holme-next-the-Sea to Weybourne ; (5) blown sands at intervals along 
the coast, e.g. Old Hunstanton to Holme, Brancaster to Blakeney, 
Happisburgh to Hemsby, Ormesby to Yarmouth. 
Obviously such variations in surface geology were predominant factors 
in moulding the topography and determining the drainage system of the 
region. The chalk escarpment in the west determined the line of the 
5 J. D. Solomon, ‘ The Glacial Succession on the North Norfolk Coast.’ Proc. 
Geologists’ Assn., vol. xliii, pt. 3. 
