292 THE WONDERS OF GEOLOGY. Lect. III. 



progression, circumscribed by no other limits than the 

 duration of the world. Time performs the office of inte- 

 grating the infinite small parts of which the progression is 

 made up — it collects them into one scene, and produces 

 from them an amount far greater than any that can be 

 assigned from human observation." * 



Thus the tertiary epoch displays to us a state of the 

 globe replete with life : the physical constitution of the 

 earth's surface, and the condition of the land and sea, being 

 adapted to the habits and economy of beings of the same 

 types of organization as those which exist at the present time. 

 In the most ancient periods certain forms of life prevailed, 

 and gradually became extinct, and were succeeded by others 

 which in their turn also passed away ; and in tracing the 

 varying types of vitality from the earliest ages, we perceive 

 a gradual approach to the present condition of organic 

 nature, in the contemporaneous existence of extinct forms 

 with those which now exist ; the grand line of separation 

 between the present and the past being the creation of the 

 human race. From that era, in proportion as Man has 

 extended his dominion over the earth, many races of animals 

 have been either exterminated, or modified, by his caprices 

 or necessities ; and it cannot be doubted, that in the lapse 

 of a few thousand years, vast changes will be effected by 

 human agency alone, in the geographical distribution and 

 relative numerical proportion of many of the existing genera 

 and species of animals. 



* Illustrations of the Huttonian Theory. 



