THEORY OP THE EARTH. 29 



And as the difference between these species and 

 the species which still exist is bounded by certain 

 limits, I shall show that these limits are a great deal 

 more extensive than those which now distinguish 

 the varieties of the same species ; and shall then 

 point out how far these varieties may be owing to 

 the influence of time, of climate, or of domestica- 

 tion. 



In this way I shall be prepared to conclude 

 that great events were necessary to produce the 

 more considerable difterences which I have disco- 

 vered: I shall next take notice of the particular 

 modifications which my performance should intro- 

 duce into the hitherto received opinions respect- 

 ing the primitive history of the globe ; and, last of 

 all, I shall inquire how far the civil and religious 

 history of different nations corresponds with the re- 

 sults of an examination of the physical history of 

 the earth, and with the probabilities afforded by 

 such examination concerning the period at which 

 societies of men had it in their power to take up 

 fixed abodes, to occupy fields susceptible of culti- 

 vation, and consequently to assume a settled and 

 durable form. 



3. Of the first appearance of the Earth. 



When the traveller passes through those fertile 

 plains where gently-flowing streams nourish in their 

 course an abundant vegetation, and where the 



