28 THEORY OP THE EARTH* 



2. Plan of this Essay. 



What I now offer comprehends but a few of the 

 facts which must enter into the composition of this 

 ancient history. But these few are important; 

 many of them are decisive ; and I hope that the 

 rigorous methods which I have adopted for the 

 purpose of establishing them, will make them be 

 considered as points so determinately fixed as to 

 admit of no departure from them. Though this 

 hope should only be realized with respect to some 

 of them, I shall think myself sufficiently rewarded 

 for my labour. 



In this preliminary discourse I shall describe the 

 whole of the results at which the theory of the 

 earth seems to me to have arrived. I shall men- 

 tion the relations which connect the history of the 

 fossil bones of land animals with these results, and 

 the considerations which render their history pe- 

 culiarly important. I shall unfold the principles on 

 which is founded the art of ascertaining these 

 bones, or, in other words, of discovering a genus 

 and of distinguishing a species by a single frag- 

 ment of bone, an art on the certainty of which 

 depends that of the whole work. I shall give a ra- 

 pid sketch of the results to which my researches 

 lead, of the new species and genera which these 

 have been the means of discovering, and of the 

 different strata in which they are found deposited. 



