50 SCIENTIFIC SURVEY OF NORWICH AND DISTRICT 
of approximately 120 to 150 ft. above O.D., this plateau declines in 
height towards the east, where it gives place to the low-lying flat district 
of the Norfolk Broads, 20 to 30 ft. above O.D. Between Norwich and 
the north Norfolk coast, and nearer the latter, there intervenes the Cromer 
Ridge (or, more accurately, a series of gravelly and clayey ridges) of morainic 
origin, reaching to a height of 300 ft. and alined from east-north-east to 
west-south-west. The elevation of the surface of the country determines 
to some extent the character of the coast-line: between Lowestoft and 
Yarmouth the plateau of Glacial Drift and Pliocene deposits meets the 
sea in the cliffs of Corton and Hopton, but north of Yarmouth the plateau 
almost disappears, and the flat area of the Broads is continued as a low 
marshy coastal belt. At the north-western limit of this stretch of coast- 
line lies Eccles, long famous since Lyell’s observation in 1839 of the 
inland advance of the sand-dunes and overwhelming of the church, the 
destruction of which was completed by the sea in 1895. From Happis- 
burgh, a few miles farther westwards along the shore, the sea cuts obliquely 
across the Cromer moraine, disclosing cliff-sections of Glacial Drift 
which display the tectonics of ice-action in such a manner and on such a 
scale that the locality has become known all over the world. The cliffs 
continue from Paston westwards as far as Weybourne, a distance of 
16 miles. 
Il. THe CHAtLk. 
The bed-rock of the district is formed by the Upper Chalk, but it is 
exposed only in the deeper valleys, such as those of the rivers Yare, 
Wensum and Bure, and on the sea-coast. When the contours of its 
surface are plotted from the data provided by exposures and boreholes, 
that surface is found to be a plane dipping gently eastwards at about 
g ft. to the mile, until it is covered by Eocene deposits (see p. 51), when 
the gradient increases to 50 ft. to the mile. As the dip of the various sub- 
divisions, or zones, of the Chalk is about 18 to 35 ft. to the mile, the zones 
crop out on the surface as belts of approximately north-north-west to south- 
south-east trend, the lowest appearing farthest towards the west. The 
Middle and Lower Chalk appear only in the westward-facing escarpment 
overlooking the Wash, but the zones of the Upper Chalk (in ascending order, 
those of the Holaster planus, Micraster cor-testudinarium, M. coranguinum, 
Marsupites, Actinocamax quadratus, Belemnitella mucronata and Ostrea 
lunata) crop out on the eastern slopes of the cuesta. Around Norwich and 
near the coast at Blakeney, the zone of Belemnitella mucronata (120 to 150 ft. 
in thickness) is well exposed, and the sections have long been famous as 
the best collecting-grounds in England for fossils from this horizon. 
Many collections contain specimens from the ‘ Norwich Chalk,’ and it 
is possibly on this account that T. H. Huxley, at the last meeting of the 
British Association at Norwich (in 1868), chose for the subject of his 
famous address to working-men ‘ A Piece of Chalk.’ To geologists there 
is the added interest that in Norfolk is to be found the highest portion of 
the zone exposed in England; at Thorpe and Whitlingham, east of 
Norwich, the characteristic high-zonal sea-urchins, ‘ Epiaster,’ Micraster 
(of an advanced coranguinum type), and the very large domed variety of 
