310 PROBABLE FLUCTUATIONS OF CLIMATE. 



than two from orchideous parasites, and within a single degree 

 of tree-ferns."* The reindeer in America makes, we know, 

 very extensive annual migrations, but a heavy animal like the 

 hippopotamus could hardly do so. I am, therefore, rather 

 disposed to believe that the presence of the hippopotamus, 

 the E. antiquus, and R. leptorhimis, indicates that the climate 

 of the quaternary period was not uniformly severe, but con- 

 tained at least one interval of exceptional mildness. 



The late M. Morlot, well known as an excellent and careful 

 observer, was, I believe, the first to point out that, in Switzer- 

 land, there were two periods of great extension of the glaciers, 

 separated by an epoch of comparative warmth. And in Great 

 Britain also there is strong geological evidence of the existence 

 of several such warm interglacial periods.")" 



We shall also see presently that if the cold of the glacial 

 epoch was due to the astronomical causes pointed out by M. 

 Adhemar and Mr. Croll, the period of extreme cold must have 

 been followed by one of unusual warmth, or rather there must 

 have been several oscillations of climate from unusual heat to 

 extreme cold. 



I am disposed then, on the whole, to consider that the 

 quaternary fauna consists of two distinct groups, belonging 

 to different periods and to two different conditions of climate, 

 one warmer than the present, the other colder. The whole 

 subject, however, while of great interest, is also one of ex- 

 treme difficulty, and I shall return to it more at length in a 

 subsequent chapter. On many points we must be contented 

 to suspend our judgment, but we may at least regard it as 

 proved that, since the appearance of man, there have been 

 great changes in the fauna of Western Europe, which then 

 contained several important species, either now altogether 

 extinct or existing only in distant parts of the world. 



* Researches in Geology and Natural History, p. 285. 

 f Geikie, The Great Ice Age. Croll, Climate and Time. 



