142 CLIMATE OF THE LOWER GRAVELS. CHAP. vm. 



sight to imply that the climate had not altered since the flint 

 tools were fabricated ; but it appears that all these species of 

 mollusks now range as far north as Norway and Finland, and 

 may therefore have flourished in the valley of the Somme 

 when the river was frozen over annually in winter. 



In regard to the accompanying mammalia, some of them, 

 like the mammoth and tichorhine rhinoceros, may have 

 been able to endure the rigours of a northern winter as well 

 as the rein-deer, which we find fossil in the same gravel, it 

 is a more difficult point to determine whether the climate of 

 the lower gravels (those of Menchecourt, for example) was 

 more genial than that of the higher ones. Mr. Prestwich 

 inclines to this opinion. None of those contortions of the 

 strata above described (p. 138) have as yet been observed in 

 the lower drift. It contains large blocks of tertiary sandstone 

 and grit, which may have required the aid of ice to convey 

 them to their present sites; but as such blocks already 

 abounded in the older and higher alluvium, they may simply 

 be monuments of its destruction, having been let down suc 

 cessively to lower and lower levels without making much 

 seaward progress. 



The Cyrena fluminalis of Menchecourt and the hippo 

 potamus of St. Eoch seem to be in favour of a less severe 

 temperature in winter ; but so many of the species of 

 mammalia, as well as of the land and fresh-water shells, are 

 common to both formations, and our information respecting 

 the entire fauna is still so imperfect, that it would be prema 

 ture to pretend to settle this question in the present state of 

 our knowledge. We must be content with the conclusion 

 (and it is one of no small interest), that when man first 

 inhabited this part of Europe, at the time that the St. Acheul 

 drift was formed, the climate as well as the physical geography 

 of the country differed considerably from the state of things 

 now established there. 



