THE EARTH. 47 



also, have produced animals that are now no 

 longer existing ^ why, therefore, might not these 

 fossil productions be among the number ? I grant 

 that this is making a very harsh supposition ; but 

 I cannot avoid thinking, that it is not attended 

 with so many embarrassments as some of the for- 

 mer ; and that it is much easier to believe that 

 these shells were bred in fresh water, than that 

 the sea had for a long time covered the tops of 

 the highest mountains. 



CHAPTER VI. 



OF THE INTERNAL STRUCTURE OF THE EARTH. 



HAVING, in some measure, got free from the re- 

 gions of conjecture, let us now proceed to a de- 

 scription of the earth as we find it by examina- 

 tion, and observe its internal composition, as far 

 as it has been the subject of experience, or ex- 

 posed to human inquiry. These inquiries, in- 

 deed, have been carried but to a very little depth 

 below its surface, and even in that disquisition 

 men have been conducted more by motives of 

 avarice than of curiosity. The deepest mine, 

 which is that of Cotteberg in Hungary,* reaches 

 not more than three thousand feet deep ; but 

 what proportion does that bear to the depth of 

 the terrestrial globe, down to the centre, which 



* Boyle, vol. iii. p. 240. 



