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endowed with habits and modes of life different from those 
of the living species, it is scarcely possible that this differ- 
ence should not have impressed itself on the skeletons which 
attest its presence in Europe. And yet the difference is so 
small between the extinct European and the existing larger 
hippopotamus, that it is scarcely appreciable. The animal, 
therefore, indicates that during the time it occupied Europe, 
the rivers were free from ice. 
This view is, however, directly opposed by the evidence of 
the whole group of Arctic mammalia, which lived in central 
and northern Europe during the Pleistocene age. It is incre- 
dible that the climate suited for the well-being of the hippo- 
potamus could at the same time have been adapted for the 
reindeer, the lemming, or the musk sheep ; for we have no 
reason to believe that the powers of resisting heat or cold 
possessed by these animals ever differed from those which they 
now possess. The evidence, therefore, afforded on the one 
hand of a warm Pleistocene climate is balanced on the other by 
that in favour of its having been as severe as that under which 
the northern group of mammalia now flourish. And the opi- 
nions of eminent naturalists are, as near as possible, equally 
divided as to its actual character. M. Lartet, fixing his atten- 
tion more particularly on the hippopotamus, inclines to the 
former view, while the latter is that taken by Dr. Falconer and 
Mr. Prestwick. The two views are, however, by no means antago- 
nistic, if we suppose that in Pleistocene Europe the climate 
was somewhat similar to that of the vast plains of Siberia, 
extending from the Altai mountains to the Arctic Sea, or to 
that offered by the inland climate of North America. In 
Siberia we meet with every gradation in climate, from the 
temperate down to that in which the cold is too severe to allow 
of the growth of trees, which gradually decrease in size as the 
traveller passes northwards, and are replaced by the grey 
mosses and lichens of the low, marshy tundras. Throughout 
the north the winter cold is intense, and in the southern por- 
tion is almost compensated for by the great summer heat, and 
its marvellous effect on vegetation. In the north countless 
herds of reindeer and elks, followed by wolves, foxes, bears, and 
gluttons, are continually on the move, in the heats of summer 
passing northwards, and avoiding the severity of the winter by 
withdrawing for shelter into the forests in the south. If the 
reindeer retreat far south, a severe winter is to be appre- 
hended ; if they remain very nearly in their usual haunts, the 
season is invariably a mild one. There is, indeed, a continual 
swinging to and fro of the Siberian mammalia; the reindeer some- 
times invading the province occupied by the elks and reddeer, 
while at others the latter animals encroach upon the province 
