" Geology, although it cannot prove that other planets are filled with appro- 

 priate races of living beings, has demonstrated the truth of conclusions scarcely 

 less wonderful : — the existence on our own planet of so many habitable surfaces 

 or worlds as they have been called, each distinct in time, and peopled wilh its 

 peculiar races of aquatic and terrestrial beings." 



Sir Charles Lyell. 



