294 FAUNA OF THE 



not move the blocks. The Deus ex machina has not only 

 been called in most unnecessarily, but, .when examined, turns 

 out to be but an idol after all. 



Driven, then, to seek some other explanation of the diffi- 

 culty, Mr. Prestwich falls back on that of floating ice. 

 Here we have an agency which would satisfactorily explain 

 all the difficulties of the case. The " packing " and pro- 

 pelling action of ice would also account for some irregulari- 

 ties in the arrangement of the beds which are very difficult 

 otherwise to understand. We are, indeed, irresistibly re- 

 minded of the figure given by Sir Charles Lyell* from a 

 view taken by Lieut. Bowen, of the boulders drifted by ice 

 on the shores of the St. Lawrence. Sir C. Lyell's work 

 is in the hands of almost every geologist, and it will, 

 perhaps, therefore, be unnecessary for me to quote the 

 accompanying description, accurately as it portrays what 

 must, we think, have been taking place in the valley of the 

 Somme thousands of years ago, just as it does in that of the 

 St. Lawrence at the present time. Nor is it the physical evi- 

 dence only, which points to an arctic climate during the period 

 now under consideration ; the fauna also tells the same tale. 

 The mollusca, indeed, do not afford much evidence, but 

 though mainly the same as those now living in the country, 

 they have northern tendencies, 34 out of 36 species being 

 at present found in Sweden, f while 29 occur in Lombardy. 

 These latter, however, are principally species having a very 

 wide range, and we shall see still more clearly that the 

 leaning of the molluscan fauna is towards the north, if we 

 remember that out of 77 Finland species, 31 have been 

 found in the upper level gravels, while of 193 Lombard 

 species only 29 have as yet occurred. 



The evidence derived from the mammalia is more con- 

 clusive. The presence of the reindeer is itself a clear indi- 



* Principles, 1853, p. 220. f Proc. Roy. Soe., 1862, p. 44. 



