256 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



practically dry stretclies of limestone witli innumerable crevices 

 into wliich the animals retreat during hot weather, and here again 

 we can come to the same conclusion as with Helix aspersa, Miill. 

 The largest examples of Arianta arbustorum (Linn.) are from Central 

 Europe, whilst the large size attained by Sitccinea putris (Linn.), 

 Limncea stagnalis (Linn.), L. palustris (Miill.), and Planorbis corneus 

 (Linn.) in Austria has often been noticed. The examples of 

 Cochlicella acuta (Miill.) from Sussex are much larger than those 

 from the West of England, whilst German examples of Helix pomatia, 

 Linn., are decidedly larger than English. 



It would thus appear that the " continental " type of climate 

 is far more beneficial to the development of the mollusca than 

 the " insular ", and it is not presuming too much to conclude that 

 the evidence derived from the Holocene mollusca points distinctly 

 to at least one period of this character. 



We have seen that the MoUuscan fauna of England has varied 

 greatly in Holocene times, and I have endeavoured to show that 

 this variation has arisen from changes of climate. From 

 archaeological and stratigraphical evidence a sequence in these 

 changes can be deduced, and it is now necessary to compare this 

 with the results obtained from other lines of research. 



Perhaps the clearest exposition of the Holocene period is that 

 given by Professor F. J. Lewis, based on the results of his work on 

 the great masses of Scotland, an investigation undertaken to ascertain 

 what changes of climate had occurred (Trans. Roy. Soc. Edinburgh, 

 vol. xli, 1905, p. 679 ; vol. xlv, 1906, p. 335 ; vol. xlvi, 1907, p. 33 ; 

 and vol. xlvii, 1911, p. 793). 



According to this author the present conditions may be con- 

 sidered as dry, and the sequence in descending order is : — 



1. Sphagnum : humid. 



2. Upper Forest Growth. 



3. Sphagnum: humid. 



4. Subarctic plants (colder). 



5. Sphagnum : humid. 



6. Lower Forest Growth. 



7. Subarctic plants. 



8. Arctic plants. 



9. Moraine. 



This differs markedly from the succession recently suggested by 

 C. E. P. Brooks {The Evolution of Climate, London, 1922, pp. 126-58). 

 This author only recognizes three principal periods : — 



1. The " Classical " Rainfall, maximum, 1800 b.c.-a.d. 500. 



2. The Forest period (dry), 3000 B.C.-1800 B.C. 



3. The post-glacial optimum, a warm period. 



There are a number of minor changes postulated, principally 

 from literary evidence, which in these matters is always doubtful. 



Our facts, however, strongly support the views of Professor 

 Lewis, whilst the occurrence of two forest growths separated by 



