130 RELATIONSHIP OF EXTINCT TO LIVING TYPES [Cn. X. 



strata in the higher level gravels of the Seine and Somme which in- 

 dicate ice-action, such as might be caused by the freezing over of the 

 rivers in winter, as now happens in corresponding latitudes in Canada. 

 As these higher-level gravels, which contain human implements 

 mingled with remains of extinct mammalia, approach in age to the 

 glacial period in proportion as they recede to a greater distance from 

 our time, it is natural that we should discover in them some indica- 

 tions of a colder climate. Accordingly, in addition to the disturbed 

 stratification, a phenomenon to which I shall again allude in the 

 sequel, p. 156, the large dimension of many angular fragments of rock 

 buried in the higher gravel, and which have been transported from 

 great distances in the same hydrographical basins, afford corrobora- 

 tive indications of ice-action. 



If it be ashed whether the character of the fluviatile and land-shells 

 of the same post-pliocene drifts also implies a colder climate, it may 

 be said that they are generally of the same species as those now in- 

 habiting the same districts, but most of them have now so wide a 

 northward range into Norway" and Finland, that they may perhaps 

 have nourished when the cold, especially in winter, was greater than 

 now. But when we contemplate the whole of the evidence as to 

 climate derived from a wide area in Europe, we find it to be very 

 conflicting, owing possibly to post-glacial fluctuations in temperature, 

 occasioning the migrations of quadrupeds from north to south and 

 from south to north, during different seasons of the same year, or 

 during successive stages of the same era. The reindeer and the 

 musk-buffalo, Bubalus moschatus, are well known as living inhabi- 

 tants of the Arctic regions, and they both occur fossil in the valley of the 

 Thames, and in that of the Avon, near Batheaston, as well as in the 

 drift of the valley of the Oise, a tributary of the Seine. The same 

 buffalo has also been met with in the post-pliocene drift of North 

 Germany, at the gates of Berlin, where, as in England, it accompanied 

 the mammoth, Elephas primigenius, and the two-horned, or woolly 

 rhinoceros, R. tichorhinus. The last-mentioned mammalia were both 

 of them found by Pallas preserved with their flesh in the frozen gravel 

 of Siberia, and they have also been met with in the drift of North 

 Germany, near Quedlinburg, associated with the Norwegian lemming, 

 Myodes lemmus, and another species of the same family, called by 

 Pallas Myodes torquatus (by Hensel Misothermus torquatus), a still 

 more Arctic quadruped, for it was observed by Parry in lat. 82° N., 

 and is said never to stray farther south than the northern borders of 

 the woody region. 



No instance has yet occurred in North Germany of the association 

 of these lemmings, reindeer, and musk-buffalos, with the hippopotamus. 

 When the latter genus occurs in England, it is usually accompanied 

 by Elephas antiquus, and Rhinoceros hemitcechos (Falc), or sometimes 

 with Rhinoceros leptorhinus. 



At Gray's Thurrock, in Essex, on the left or north bank of the 



