306 FAUNA OF THE LOW LEVEL GRAVELS. 



have been fitted to flourish in an arctic climate. But there 

 is some difference of opinion as to its occurrence : it has not 

 yet been found in the " diluvium " of Germany,* and though 

 remains of it have undoubtedly occurred in the drift-gravel 

 of the Somme, there is some reason to believe that they are 

 not in quite the same condition as the bones of the elephant 

 and rhinoceros ; it is just possible, therefore, that they may 

 belong, as Dr. Falconer has suggested, to an anterior period. 

 Until lately, we should haye regarded the tiger as an essen- 

 tially tropical animal ; yet it is well known to be common in 

 the neighbourhood of Lake Aral, in the forty-fifth degree of 

 north latitude : and " the last tiger killed, in 1828, on the 

 Lena, in lat. 52 J, was in a climate colder than that of 

 St. Petersburg and Stockholm." t Finally, the Cyrena flu- 

 minalis now lives in the Nile ; but, on the other hand, it is 

 found also in the rivers of Central Asia. 



While admitting these difficulties, it is still, I think, felt 

 by most Palaeontologists, that though the presence of one 

 arctic species would scarcely perhaps justify any very decided 

 inference as to climate, still that the co-existence of such a 

 group as this the musk ox, the reindeer, the lemming, the 

 Myodes torquatus, the Siberian mammoth, and its faithful 

 companion the woolly-haired rhinoceros decidedly indicates, 

 even though it may not prove, the continued existence of a 

 climate unlike that now prevailing in Western Europe. 



Finally, the lowest portion of the valley is at present oc- 

 cupied by a bed of gravel, covered by silt and peat, which 

 latter is in some places more than twenty feet thick, and is 

 extensively worked for fuel. These strata have afforded to 

 the antiquaries of the neighbourhood, and especially to 

 M. Boucher de Perthes, a rich harvest of interesting relics 

 belonging to various periods. The depth at which these 



* Sir C. Lyell, Supplement to Manual, p. 8. 

 t Lyell's Principles, p. 77. 



