THE AGE OF MAMMALS 



of the Atlantic ; and lastly followed the great extension 

 of the land towards the north, the great withdrawal of 

 the sea of Pliocene times, and the growing cold which 

 led to the glacial era of the Pleistocene period. In 

 Europe and in Asia we may note that the great 

 areas which are now covered by the Alps and the 

 Himalayas were at the beginning of the Tertiary 

 period still under water and only a few signs (in the 

 form of islands) of these mighty ranges were beginning 

 to appear. 



Pre-eminently the age which comprises all these 

 periods is the Age of Mammals. But one of the 

 changes which European geologists first noticed was 

 the surprising change which took place in the marine 

 fossils. The animals of the sea which were familiar 

 during the Chalk period nearly all disappeared and were 

 replaced by new ones. The great saurian reptiles, from 

 the monsters of the land to the mososaurus serpents of the 

 sea, disappeared, and most other reptiles showed profound 

 changes, showing a revolution in the animals of the 

 land corresponding to that of the sea. Lastly, in this 

 first period, the Eocene, mammals suddenly appear in 

 force and occupy the first place among the animals. 

 The vegetation did not change so much as might have 

 been expected. 



Whence came the mammals? That, again, is one of 

 the questions which time alone can completely answer. 

 But the opinion of most geologists is that they arose 

 and developed in Asia first of all, and then spread to 

 other continents. The rise of the mammals, which, 



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