536 Mr. Charlesworth on the Crag, and on ascertaining 
of British tertiary fossils,states that he has collected 450 species 
of shells from the crag: of these more than 200 were peculiar 
to the coralline, 80 peculiar to the upper bed, and 150 were 
found in both deposits. 
Before any conclusions are drawn from this statement, it is 
of the utmost importance to bear in mind the circumstances 
under which the fossils of one formation may, by the natural 
process of degradation, have been imbedded in another. I 
have before alluded to the fact of secondary shells occurring 
in the red crag where that deposit is in contact with the chalk; 
and if causes similar to those now in action were operating at 
eras antecedent to the present, there is nothing to excite our 
surprise in this phenomenon. I have been particularly struck 
with the appearance presented by the fossils in those remark- 
able masses of transported or protruded chalk which are seen 
on the beach for a few miles east of Cromer. Many of these 
enormous fragments are half buried in the stratum of blue 
clay forming the beach, to which level the elevated portion is 
by the action of the tides gradually reduced. A platform of 
chalk is thus formed, which is frequently studded in every di-+ 
rection with Belemnites and Terebratule. As its surface wears 
away the fossils are brought out in relief, and at length being 
entirely removed are deposited with the recent Mollusca. The 
point principally deserving notice here is the introductien of 
these fossils into the present deposits completely detached from 
the matrix in which they were imbedded, and which being re- 
moved in a finely divided state, would not at a future period 
be recognised in the form under which it formerly existed. 
The secondary shells in the crag of Norfolk have probably 
been removed from their original bed by a process similar to 
that just described. We see no indications of a more violent 
operation ; there are no nodules of chalk accompanying the 
fossils, which are themselves so completely freed from an 
adherent matrix that they can only be distinguished from the 
more recent Mollusca with which they are associated by an 
attention to specific distinctions, and by the chalk locked up 
within the cavity of the bivalves. 
At the time the formation of the red crag was going for- 
ward, the surface of the chalk to a great extent was protected 
from abrasion by overlying deposits, and wherever this was 
the case the superior stratum would be the one exposed to 
denudation, and from which organic remains would be trans- 
ported. In this way, undoubtedly, have the fossils of the co- 
ralline crag, along with those of the chalk, been introduced 
into a more recent deposit, and the difficulty is now to ascer- 
tail the probable amount of admixture. Connected with this 
