﻿ANALYSIS OF SYNOPTICAL LIST. 



221 



exception of the Middle Glacial column of it, however, the table shows very forcibly the 

 diminishing Mediterranean aspect of the fauna as we ascend in the geological scale. 



In the Coralline Crag there are fifty-two Mediterranean forms not living in the 

 British seas, and only twenty of the converse character ; and of these twenty, two, viz. 

 Odostomia Gulsona and Psammobia tellinella, are Lusitanian. In the Walton Red Crag 

 the respective numbers are fourteen and thirteen, but in the rest of the Red Crag the 

 British species not living in the Mediterranean are in number more than double those of 

 the converse character ; while in the Fluvio-marine Crag these proportions are increased 

 five-fold, and in the Chillesford beds nineteen-fold. In the Lower Glacial there occur 

 thirteen, in the Upper Glacial twenty-one, and in the Post Glacial nineteen British 

 species unknown in the Mediterranean, but in none of these three deposits does theie 

 occur a single species of the converse character. 



Simultaneously with these features we find (as shown in notes A to I) a proportional 

 increase of the Arctic species as we ascend through the Crag and Glacial series ; and that 

 even in the Post Glacial deposits no less than four out of a total of forty-nine are Arctic 

 shells of the preceding Glacial Period which have since receded from the British 

 Coasts. 



The Middle Glacial fauna stands out in some discord with the above, since in it not only 

 do several Mediterranean species unknown to British seas reappear, but the proportion 

 which these bear to the number of British species not known in the Mediterranean is as 

 eight to twenty-one — a much larger proportion than exists in the Fluvio-marine 

 Crag, and altogether beyond the proportions exhibited by the intervening forma- 

 tions. The explanation is probably to be found in the Molluscan remains of this 

 deposit having travelled from some distance, as mentioned in the introduction to this 

 'Supplement' (p. xxiii). Altogether this Middle Glacial assemblage is a very interesting 

 one, and the most important of any of the formations succeeding the Crag. Several of 

 the species which occur in it seem to have disappeared from the British Coast during the 

 earlier part of the Red Crag ; and while some of these are not known living, others are 

 confined to the Mediterranean or other southern waters. 



I have only to add that I am equally convinced with the authors of the introduction to 

 this work that the Molluscan remains of the Middle Glacial Sand (fragmentary and worn 

 as they occur in it) are not derived from any older deposit, but are contemporaneous 

 with the sand which contains them. 



