450 
Geology of Norfolk. 
watershed, the upper or soft chalk forms the base of the crag 
and detrital deposits. The out- crop of the strata brings to the 
surface along the western edge of the watershed the lower beds 
of hard chalk, provincially called corlk, which contains much 
disseminated siliceous matter, and is sufficiently hard to be used 
as a building stone. 
From beneath this, the gault, and the representatives of the 
green sand — the red chalk and the carstone — successively emerge, 
and are succeeded by the Kimmeridge clay, which forms the 
base of the alluvial deposits of the Wash, and is not separated 
as in the south of England, by the coralline oolite from the Oxford 
clay, neither has it the Portland oolite above it. As the drift 
approaches the watershed, it gradually thins off", and loses much 
of that regularity of deposit which is observable in the Cromer 
and Gorlston coast sections, and in those of the valleys of the 
Waveney, the Wensum, and the Yare. It is found on the 
summit of the watershed, with still less regularity of stratifica- 
tion, ind, on the steep slopes of its western escarpment, has 
been much more broken by denuding action. 
Those who will take the trouble to compare the agricultural 
districts into which Young has divided Norfolk, in his map ap- 
pended to the Reports of the Board of Agriculture, with those of 
which Marshall and Kent have described the boundaries, will 
find but little accordance existing between them ; and it will be 
still more difficult to trace a connexion between any of these 
agricultural districts and the geological districts of any geological 
map extant. Neither is there any work or map descriptive of 
the geology of Norfolk which does not require correction in some 
material point. The county map of William Smith is the best. 
The diligence of local observers has been able to make few alter- 
ations in his boundaries of the chalk and the strata below it ; and 
those have been occasioned by the scrupulous accuracy which 
induced him to map only what he had actually seen, and caused 
him to represent the gault in discontinuous patches, which has 
since been traced by ]\Ir. Rose, as a narrow continuous band. 
His map of Norfolk is likewise the best agricultural map extant, 
dividing the county into the light and strong soiled districts which 
represent, with as much accuracy as possible on so small a scale, 
the general outline of the areas occupied by different members of 
the drift ; by an error, however, very excusable at the time his 
map was published, when the tertiary strata more recent than 
those of the Paris and London basins were little known, he has 
mistaken their place in the geological scale, and has referred the 
drift to the London and Plastic clay series, placing the crag be- 
low the latter. To this map I shall again have occasion to refer, 
when describing the districts into which I divide the county. Its 
