THEORY' OF THE EARTH. 5 



depends that of my whole work, I shall give a 

 rapid account of the new species, and of genera 

 previously unknown, which the application of 

 these principles has led me to discover, as well as 

 the different kinds of deposits in which they are 

 contained. And as the difference between these 

 species and those which exist at the present day 

 is bounded by certain limits, I shall show that 

 these limits much exceed those which now distin- 

 guish the varieties of the same species. I shall 

 therefore make known to what extent these va- 

 rieties may go, whether from the influence of time, 

 or from that of climate, or, lastly, from that of do- 

 mestication. 



In this way I shall be enabled to conclude, and 

 to induce my readers to conclude with me, that 

 great events were necessary to produce the more 

 considerable differences which I have discovered. 

 I shall next mention the particular modifica- 

 tions which my researches must necessarily intro- 

 duce into the hitherto received opinions regard- 

 ing the revolutions of the globe; and, lastly, I 

 shall inquire how far the civil and religious his- 

 tory of different nations corresponds with the re- 

 sults of observation with regard to the physical 

 history of the Earth, and with the probabilities 

 which these observations afford concerning the 

 period at which societies of men may have found 

 fixed places of abode, and fields susceptible of 



