NORWICH CRAG. 
193 
tic regions. As a rule, the lamellibranchiate molluscs have 
both valves united, and many of them, such as Mya arena- 
ria^ stand with the siphonal end upward, as when in a living 
state. Tellina halthica^ before mentioned (Fig. 116) as so 
characteristic of the glacial beds, including the drift of Brid¬ 
lington, has not yet been found in deposits of Chillesford and 
Aldeby age, whether at Sudbourn, East Bavent, Horstead, 
Coltishall, Burgh, or in the highest beds overlying the Nor¬ 
wich Crag proper at Bramerton and Thorpe. 
Norwich or Fluvio-marine Crag. —The beds above alluded 
to ought, perhaps, to be regarded as beds of passage be¬ 
tween the glacial formations and those called from a pro¬ 
vincial name ‘‘ Crag,” the newest member of which has been 
commonly called the “Norwich Crag.” It is chiefly seen 
in the neighborhood of Norwich, and consists of beds of in¬ 
coherent sand, loam, and gravel, which are exposed to view 
• on both banks of the Yare, as at Bramerton and Thorpe. 
As they contain a mixture of marine, land, and fresh-water 
shells, with bones of fish and mammalia, it is clear that these 
beds have been accumulated at the bottom of a sea near tlie 
mouth of a river. They form patches rarely exceeding twen¬ 
ty feet in thickness, resting on white chalk. At their junc¬ 
tion with the chalk there invariably intervenes a bed called 
the “ Stone-bed,” composed of unrolled chalk-flints, commoii- 
Fig. 118. 
Mastodon arvernensis, third milk molar, left side, upper jaw; grinding surface, natural 
size. Norwich Crag, Postwick, also found in Red Crag, see p. 197. 
ly of large size, mingled with the remains of a land fauna 
comprising Mccstoclon arrernensis^ Elephas meridionalis^ and 
an extinct species of deer. The mastodon, which is a spe¬ 
cies characteristic of the Pliocene strata of Italy and France, 
is the most abundant fossil, and one not found in the Cro- 
9 
