198 SUPPLEMENT TO THE CRAG MOLLUSCA. 
Medial Tertiary shells, depends upon the correctness of the identifications themselves, and 
this I have not had the means of examining. 
A list of extraneous fossils was given by myself in a paper published im the ‘ Quart. 
Journ. Geol. Soc.,’ 1859, but this would now require to be much added to. ‘These are, 
however, undoubted derivatives, but I have been greatly embarrassed with specimens 
that do not belong, so far as I know, to any described species, and to which a strong 
suspicion attaches that they come from some older Tertiary formation. In such cases, as 
well as in those of known older Tertiary species, where the mineral condition of the 
specimen does not of itself indicate that it is derivative, I have figured the specimens, but 
im the synoptical list which follows I have distinguished all such as clearly derivative. 
There are besides these many shells in the Red Crag which I am disposed to regard as 
only present in that formation as derivatives.’ The number of these is greater than was 
the case when the ‘ Crag Mollusca’ left my hands in 1856, and I have distinguished them 
in the list as possibly or probably derivative. In one instance I have been compelled to 
regard as a genuine fossil of the period what I had before treated as derivative. ‘This is 
Voluta Lamberti. In other instances, such as Cassedaria bicatenata and Trophon elegans, 
which were then only known from the Red Crag, I have satisfied myself not only that 
they are Cor. Crag species, but that their presence in the Red is due only to derivation. 
The only part of the Red Crag which is genuine and free from derivatives is that of 
Walton Naze (where Voluta Lamberti that I had wrongly regarded as derivative does 
occur), all the rest of the formation being more or less leavened with derivatives from the 
Coralline Crag, and from older formations, as well as with shells from older beds of Red 
Crag age, such as Walton, as explained at page vil of the Introduction to this Supplement. 
It is unfortunate that we get only this one deposit of Walton with a genuine fauna, since 
from the change in climate and consequent introduction of many northern forms into the 
newer parts of the Red Crag (as explained in the Introduction) the Walton fauna, though 
genuine, does not show what was the true fauna during the Jafer stages of the Red Crag 
formation. 
The elimination from the Red Crag fauna of the additional derivatives from the 
Coralline tends to increase the Paleontological distinction between those deposits, while 
on the other hand the discovery, since the ‘Crag Mollusca’ left my hands, of some few 
Coralline Crag species among the genuine Red Crag fauna pretty well balances this 
increment. I, however, see no reason to modify the opinion I have always entertained as 
to the complete separation of the Coralline and Red Crags, although the fauna of the 
oldest part of the Red Crag has a greater Mediterranean affinity than that of the newer, as 
pointed out by me in the 22nd volume of the ‘ Quarterly Journal of the Geological Society,’ 
p. 542. With respect, however, to the Red and Fluvio-marine Crags, and their over- 
lymg Chillesford clay and sand, they can, in my opinion, be regarded as only one deposit, 
constituting in England the upper Crag, as the Coralline does the lower; and the triple 
' The phosphatic nodule excavation in the Red Crag at Waldringfield is quite a museum of derivatives. 
