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. 



