2 SCHARFF : DISTRIBUTION OF BRITISH L. AND F. MOLLUSCA. 



by ice during that period, but Mr. Quilter — following Mr. Wallace — 

 inclines to the belief that the British Molluscan fauna was destroyed 

 by the subsequent submergence rather than by the ice action. 



The evidence of an enormous submergence of the British 

 Islands, after the height of the glacial period, seems to rest chiefly 

 on the occurrence of a bed of marine shells on Moel Tryfaen in 

 Wales, and one on the Three Rock Mountain near Dublin. As has 

 been shown, however, by Mr. Bell,* the occurrence of these shells 

 at a height of over 1,000 feet above sea-level does not necessarily 

 prove such a great submergence, and the utter absence in other parts 

 .of the British Islands of recent marine deposits at such heights 

 should, at any rate, make us careful in accepting this theory. 



It is enough for our purpose to note that there exists a certain 

 amount of doubt as to whether the British Non-Marine Mollusca 

 were exterminated or not during Pleistocene times, and this fact 

 must encourage us in searching for a satisfactory explanation of their 

 present distribution, and especially for the presence of so many 

 southern species of shells in these islands. 



The important contributions of Mr. B. B. Woodwardt show that 

 most of the existing Land and Freshwater Mollusca which now 

 inhabit the south-eastern portion of England lived in the same 

 district before the glacial epoch also. If we look through the list of 

 land shells which have been found in the more recent deposits of 

 the south-east of England, we find there are no signs of the typical 

 southern European forms, such as Helix pisana, revclata and acuta, 

 Testacella maugei, Pupa anglica, and Geomalacus maculosus ever 

 having been there, although I believe it has been generally assumed 

 that migration after the Glacial period from the Continent to Great Britain 

 took place by a land connection somewhere in the neighbourhood of 

 Dover. On the other hand, almost all these forms occur in the more 

 westerly parts of the British Isles — most of them being found in 

 Ireland — which, according to geologists, was only for a very short 

 time, if at all, connected with England in post-glacial times. 



The late Prof. E. Forbes;]; maintained that the two great primary 

 causes influencing the distribution of pulmoniferous mollusca, were 

 climate and soil. He believed that individuals multiplied to a much 

 greater extent on calcareous and sandy soils, than on slate, clay, or 

 granite, but that the influence even of limestone could be completely 



* Phenomena of the glacial epoch. Trans. Geol. Soc. Glasgow, vol. i.\., 1891. 



t On the Plei*tocene(Non-Marine) Mollusca of the London District. Proceed. Geol. Assoc, vol. xi. 



t Report on the Distribution of Pulmoniferous Mollusca in the British Isles. British 

 Association Report, Birmingham, 1839. 



