218 



THE WORLD OF LIFE 



CHAP. XI 



that occurred, and, more especially, the almost total ex- 

 tinction of the lower or earlier types just when they appear 

 to have reached their highest and most varied structure, 

 their greatest size of body, and their almost world-wide 

 distribution. Before attempting a solution of this difficult 

 problem an outline must be given of the latest, and in some 

 respects the most interesting, of the geological eras — the 

 Tertiary, or, as more frequently termed by geologists, the 

 Cainozoic. 







