THE EARTH. 41 



never find them? We know that lakes, and lands also, h;iv« 

 produced animals that are now no longer existing ; why, there- 

 fore, might not these fossil productions be among the number? 

 I grant that this is making a very harsh supposition ; but I can- 

 not avoid tliinking that it is not attended with so many embar- 

 rassments as some of the former, and that it is much easier 

 to believe that these shells were bred in fresh water, than thut 

 the sea had for a long time covered the tops of the highest 

 mountains. 



CHAP. VI. 



OF THE INTERNAL STRUCTURE OF THE EARTH. 



Having, in some measure, got free from the regions of con- 

 jecture, let us now proceed to a description of the earfh as we 

 find it by examination, and observe its intenial composition, as 

 tar as it has been the subject of experience, or exposed to human 

 inquiry. These inquiries, indeed, have been carried but to a verv 

 Jittle depth below its surface, and even in that disquisition men 

 have been conducted more by motives of avarice than of curiosit)'. 

 The deepest mine, which is that at Cotteberg in Hungary,' 

 reaches not more than three thousand feet deep ; but what pro- 

 portion does that bear to the depth of the terrestrial globe, down 

 to the centre, which is above four thousand miles? All, there- 

 fore, that has been said of the earth, to a deeper degree, is 

 merely fabulous 'ir conjectural : we may suppose, with one, thai 

 it is a globe of glass ;' with another, a sphere of heated iron ;* 

 with a third, a great mass of waters;* and with a fourth, one 

 dreadful volcano :' but let us at the same time show our con- 

 Bciousness, that all these are but suppositions. 



Upon examining the earth, where it has been opened to any 

 depth, the first thing that occurs, is the different layers or beda 

 of which it is composed ; these all lying horizontally one over 

 tlic other, like the leaves of a book, and each of them composed 



8 Boyle, vol. iii p. 210. 3 BufTon. 4 WhUton. 



6 Buri.et. 6 l-'xc! cr. 



