RED AND NORWICH CRAGS. 
115 
Coitisliall, and Liidham^ there are good jambs ” of claj,"^ from 
3 or 4 to 15 or 18 feet in thickness. These possess almost iden¬ 
tical characters. But at the typical localities of Thorpe, Post¬ 
wick, and Bramerton, there is no conspicuous development of 
clay, and where seams are present they do not always possess the 
lamination said to be characteristic of the Chillesford Clay. One 
who visited the before-mentioned localities in succession would 
undoubtedly go away convinced that the Chillesford Clay was a 
well-marked horizon in Norfolk. But if he endeavoured to trace 
out these clays on the ground, noticing the intermediate sections, 
and the behaviour of the clays themselves, he would become con¬ 
vinced that while such laminated clays are characteristic of the 
Pliocene beds of Norfolk, they are not confined to one horizon, 
they were not all deposited at one particular time, and their 
absence is not necessarily the result of denudation. 
The sections at Coltishall and Hartford Bridge, as well as 
those at Thorpe Hamlet, Hellesdon, and Hamlington, demonstrate 
that these clays are intimately connected by false-bedding with 
the pebbly gravels that often overlie them, and that they pass 
occasionally by interbedding in their horizontal extension into 
sand and gravel. In some sections we find two or more bands of 
clay, any one of which might on lithological grounds be termed 
the Chillesford Clay. 
Turning now to the divisions based on organic remains, it is a 
fact that the two beds at Bramerton Common present some differ¬ 
ences of local interest. But these two beds are merely separated 
by a few feet of false-bedded sand, which contains shells spar¬ 
ingly, And while the lower bed includes a larger assemblage 
of species, only three rare forms found in the upper bed have not 
been obtained in the lower. The lower bed has been termed 
by Lyell the Fluvio-marine Crag, because containing a mixture of 
marine, land, and freshwater shells, with bones of fishes and 
mammalia, it was clearly accumulated at the bottom of the sea near 
the mouth of a river. The influence of freshets is seen in the 
varieties and monstrosities of the Purples and Periwinkles 
(Fig. 25). But the deposit itself and the majority of the organic 
remains are so decidedly marine, 
that the term Fluvio-marine is 
rather apt to mislead. While 
numbers of freshwater shells 
from the Crag may be seen in 
Museums and private collec¬ 
tions, they are exceedingly rare 
in the deposit. Borings of 
Pholas and marine Annelides 
occur in the Chalk at the base 
of the Stone Bed, and among 
the boulders and sometimes in crevices of the Chalk there occur, 
* The term “ jamb ” is applied to any impersistent, and generally lenticular 
mass of clay, marl, or brickearth-—it is a bed “ jammed between other strata.”^— 
iNall.') Some of these beds of clay are shown on the Geological Survey Maps. 
H 2 
Fig. 25. 
Littorina littorea, distorted. 
