CONCLUDING REMARKS. | 199 
division of the Crag, which has for so many years been assumed, must, in my opinion, be 
abandoned. The Paleontological difference between the Walton bed and the newest 
part of the Red Crag, the Scrodicularia portion, or even the Butley portion, is far greater 
than any which exists between these latter and the Fluvio-marine Crag or Chillesford 
beds; and whether, as discussed at pp. ix and x of the Introduction to this ‘Supplement,’ 
the Fluvio-marine Crag of Bramerton (and, of course, the deposits at the other Fluvio- 
marine Crag localities of Suffolk and Norfolk also) be coeval with the newer part of the 
Red Crag, or posterior to it, it is sufficiently clear that, from the oldest or Walton Red 
Crag deposit up to the Chillesford clay itself, all the beds of the English Crag which are 
posterior to the Coralline are portions of the same geological formation, during the 
-accumulation of which only very slight oscillations in the relative position of the sea and 
land occurred. 
The synoptical list which follows these remarks will show what species of Mollusca 
have occurred in the Fluvio-marine Crag that have not yet been detected in the Red. 
With three or four exceptions these are shells that from their minuteness or fragility 
would only be preserved under exceptional circumstances in so roughly accumulated a 
deposit as the Red Crag, and their not having been detected in that formation need not 
surprise us. ‘The most important among these three or four exceptions is the arctic 
species, Astarte borealis, which occurs sparingly in the Fluvio-marine Crag of Bramerton, 
but is common in the Chillesford bed at the same place, as well as in all the successive 
glacial deposits. It is, however, significant that while thus common in the Chillesford 
bed where it overlies the Fluvio-marine Crag, this shell has not been detected in these 
same Chillesford beds where they overspread the Red Crag ; thus indicating, apparently, 
that its absence from the Red Crag was due to a localisation of the species rather than to 
any difference in age between the two deposits. The occurrence of a bed of land and 
freshwater shells in the Red Crag at Butley has, in my opinion, no bearing upon the 
question of the synchronism between the Red and Fluvio-marine Crags, but is due to the 
causes referred at p. 4 of this ‘Supplement.’ 
T have not attempted to correlate the British Crag beds with the Crag of Antwerp, 
or with the Monte Mario, or Sicilian formations, because I feel satisfied that unless I had 
the means of comparing the specimens themselves from those formations with my own 
specimens from the English beds, any results that might be published would be more or 
less illusory. It is not sufficient for reliable identification to look over collections abroad ; 
the specimens from the respective formations must be placed side by side and compared 
with each other. or this purpose extensive collections from these foreign beds would 
require to be made; and as I have not the opportunity at my advanced years of forming 
such, I have thought it best to leave the task of making a satisfactory correlation to other 
observers. J have therefore confined my tabular lists to the successive beds of the Crag, 
the Glacial, and Post-glacial series in that portion of England to which I have confined this 
Supplement, having had the means, except in the few cases expressly mentioned in the 
