AGE OF MAMMALS. 261 



our earth. But this power was specially active when, 

 in the great and extensive changes effected at times in 

 the earth's crust, as was often the case, life was largely 

 destroyed. And when the destruction was complete in 

 the two gaps that have been mentioned, there succeeded 

 an entirely new creation of plants and animals. 



CHAPTER XVIIL 



AGE OF MAMMALS. 



367. Transition from Mesozoic to Cainozoic Time. 

 "We now come to a period in the earth's history in which 

 there is a decided resemblance to the present time in 

 the general surface of the eartfe, and in its vegetables 

 and animals. The surface had become diversified with 

 numerous mountains, valleys, and rivers, though by no 

 means as largely as now, for this diversification was com- 

 pleted only when man was to be ushered upon the scene. 

 The endogens and exogens, the great sources of food for 

 man and beast, were quite predominant in the vegeta- 

 tion of the earth. In the animal kingdom, the marsupi- 

 als, which are allied at the same time to reptiles and to 

 birds, gave way to mammalia of the higher orders. In 

 the previous ages the most striking displays of animal 

 life were mostly in the ocean, in huge fishes, and mol- 

 lusks, and reptiles ; but now the land was to surpass the 

 sea in this respect. 



368. Divisions of Cainozoic Time. A common division 

 of the Cainozoic age is into the Tertiary and Post-terti- 

 ary the Tertiary occupying the time up to the Glacial 

 period, when, as you will see, the agency of ice was ap- 

 plied over a large portion of the earth to produce im- 

 portant results, and the Post-tertiary, extending thence 

 on to the advent of man. The term tertiary is an old 

 geological term, which the progress of discovery has 

 shown to be inapplicable. It was adopted when it was 



