THE NEOZOIC AGES. 279 



from colder regions. Some, perhaps, in the course 

 of generations, become dwarfed in stature, and 

 covered with more shaggy fur. Permanent snow at 

 length appears upon the hill-tops, and glaciers plough 

 their way downward, devastating the forests, en- 

 croaching on the fertile plains, and at length reaching 

 the heads of the bays and fiords. While snow and 

 ice are thus encroaching from above, the land is 

 subsiding, and the sea is advancing upon it, while 

 great icebergs drifting on the coasts still further 

 reduce the temperature. Torrents and avalanches 

 from the hills carry mud and gravel over the plains. 

 Peat bogs accumulate in the hollows. Glaciers heap 

 up confused masses of moraine, and the advancing 

 sea piles up stones and shingle to be imbedded in mud 

 on its further advance, while boreal marine animals 

 invade the now submerged plains. At length the ice 

 and water meet everywhere, or leave only a few green 

 strips where hardy Arctic plants still survive, and a 

 few well-clad animals manage to protract their exist- 

 ence. Perhaps even these are overwhelmed, and the 

 curtain of the Glacial winter falls over the fair scenery 

 of the Pliocene. In every locality thus invaded by an 

 apparently perpetual winter, some species of land 

 animals must have perished. Others may have mi- 

 grated to more genial climes, others under depaupe- 

 rated and hardy varietal forms may have continued 

 successfully to struggle for existence. The general 

 result must have been greatly to diminish the nobler 

 forms of life, and to encourage only those fitted 



