XI PHENOMENA OF ORGANIC NATURE 845 



In fine, if, instead of comparing immediately 

 adjacent parts of two beds, one of -which lies upon 

 another, we compare distant parts, it is quite 

 possible that the upper may be any number of 

 years older than the under, and the under any 

 number of years younger than the upper. 



Now you must not suppose that I put this 

 before you for the purpose of raising a paradoxical 

 difficulty ; the fact is, that the great mass of 

 deposits have taken place in sea-bottoms which 

 are gradually sinking, and have been formed 

 under the very conditions I am here supposing. 



Do not run away with the notion that this 

 subverts the principle I laid down at first. The 

 error lies in extending a principle which is per- 

 fectly applicable to deposits in the same vertical 

 line to deposits which are not in that relation to 

 one another. 



It is in consequence of circumstances of this 

 kind, and of others that I might mention to you, 

 that our conclusions on and interpretations of the 

 record are really and strictly only valid so long as 

 we confine ourselves to one vertical section. I do 

 not mean to tell you that there are no qualifying 

 circumstances, so that, even in very considerable 

 areas, we may safely speak of conformably super- 

 imposed beds being older or younger than others 

 at many different points. But we can never be 

 quite sure in coming to that conclusion, and 

 especially we cannot be sure if there is any break 



