188 ADDEESS. [>ect. 



Avon — with animals which are now to be found only in 

 remote regions, or which are altogether extinct. It is 

 sufficiently surprising to reflect that on this very spot 

 where we are now assembled there once ranged large 

 herds of those strange and gigantic animals ; but another 

 most interesting consideration is, that when we come to 

 consider them more closely, we shall find that they con- 

 stitute in reality two distinct groups. The hippopotamus, 

 for instance, and probably the hyena, extended into 

 Great Britain, the porcupine into Belgium, the African 

 elephant into Spain and Sicily ; facts all indicating a 

 climate warmer than the present. On the other hand, 

 the mammoth and the long-haired rhinoceros, the rein- 

 deer and the marmot, the arctic hare and fox, the ibex, 

 chamois, and the musk-sheep, point decidedly to arctic 

 conditions. The musk-sheep indeed has the most northern 

 range of any known mammal. 



Passing over for the present those mammalia which 

 seem to indicate a tropical climate, let us consider what 

 may be called the arctic group, and I may observe in 

 passing that the existence of a very cold climate during 

 the latest geological period had been inferred from other 

 considerations, even when our knowledge of the mam- 

 malian fauna was much less considerable and consequently 

 less suggestive. Various theories have been suggested to 

 account for the fact that at a period, geologically speak- 

 ing so recent, the climate of Europe should have been 

 so different from what it is at present, and the best 

 authorities seem now to consider that the true explana- 

 tion is to be found in astronomical causes. If the plane 

 of the equator coincided exactly with that of the ecliptic, 

 every day would be succeeded by a night of equal length. 



