140 
WEYBOURN CRAG. 
with a true marine deposit, and not with flints left by the sub¬ 
terranean dissolution of the surface of the Chalk through the 
agency of percolating water. The mode of origin of a stone-bed 
can be well studied in the shallow sea off Cromer, where such 
a deposit forms the fishing ground on which crabs and lobsters 
occur so abundantly. The soft Chalk is readily bored by Pholas, 
Baxicavay and various annelids, which cause it gradually to 
crumble away and to leave behind nothing but the flints, mixed 
with a certain proportion of stones from the beach. This ju'o- 
cess is not confined to the area between tide marks, but will 
go on at any depth at which the Chalk may happen to be 
exposed, and in places where there are no currents sufficient 
either to move the flints or to erode the Chalk, 
Immediately succeeding the stone-bed on this part of the coast 
is found a mass of falsebedded gravelly sand, either grey or red, 
with seams of clay. This deposit is full of shells, which are 
particularly well-preserved in the unweathered bluish sands, but 
often much decayed in the oxydized portion. It was from a 
mass of iron-grey Crag, found on the shore a quarter of a 
mile south-east of East Runton Gap, that the largest number 
of Weybourn Crag shells were obtained during the Survey; 
in fact this locality has yielded every known species belonging 
to the horizon (except the delicate Thracia papijracea)^ and a 
good many unknown elsewhere. The large number of species 
obtained was, however, largely due to the loose sandy nature 
of the deposit, which elsewhere is usually too much mixed with 
clay, or cemented with iron, to allow a sieve to be used. The 
fauna is a littoral one, and the shells are a good deal rolled. 
Mixed with them, as in the Norwich Crag, is found a consider¬ 
able number of land and fresh-water species, together with a 
. few bones of land-mammals. 
The higher portion of the Weybourn Crag seems here generally 
to be cut out by the gravelly Forest-bed; but where preserved 
it consists of alternations of clay and sand, with seams of 
mussels, and abundance of single valves of cockle, Tellina, and 
Donax. The commonest shells are the littoral sand-loving forms, 
those inhabiting muddy shores, such as Scrobicularia and Hydrobia, 
being scarce. The total thickness of the Crag on this part of 
the coast nowhere reaches fifteen feet. 
From West Runton to Sherringham the strata retain the same 
character, and the Chalk gradually rises to the level of high- 
water. There seem never to be more than a few feet of Crag 
beneath the Forest-bed, and in some places the Forest-bed rests 
immediately upon the Chalk. The principal interest of this part 
of the section is the occasional occurrence of P/ic/fls-borings in 
the Chalk beneath the stone-bed. 
West of Sherringham the Chalk continues to rise, till it forms 
a low cliff 20 feet high at Weybourn. As it rises the surface 
becomes more irregular and piped, so that the overlying deposits 
are often a good deal disturbed, especially close to Weybourn. 
A section near Weybourn (Fig. 34) will explain better than any 
words the relation of the different strata to each other. 
