OF ORGANIC NATURE. 41 



very plain sailings, indeed, to say tliat they did ; and yet 

 there is no proof of anything of the kind. As the 

 former Director of this Institution, Sir H. De la Beche, 

 long ago showed, this reasoning may involve an entire 

 fallacy. It is extremely possible that a may have been 

 deposited ages before b. It is very easy to understand 

 how that can be. To return to Fig. 4; when A and B were 

 deposited, they were substantially contemporaneous ; 

 A being simply the finer deposit, and B the coarser of 

 the same detritus or waste of land. Now suppose that 

 that sea-bottom goes down (as shown in Fig. 4), so that 

 the first deposit is carried no farther than a, forming 

 the bed A^ and the coarse no farther than b, forming 

 the bed BS the result will be the formation of two con- 

 tinuous beds, one of fine sediment (A A') over-lapping 

 another of coarse sediment (B B^). Now suppose the 

 whole sea-bottom is raised up, and a section exposed 

 about the point A^ ; no doubt, at this spot, the upper 

 bed is younger than the lower. But Ave should ob- 

 viously greatly err if we concluded that the mass of 

 the upper bed at A was younger than the lower bed 

 at B; for we have just seen that they are contem- 

 poraneous deposits. Still more should we be in error 

 if we supposed the upper bed at A to be younger than 

 the continuation of the lower bed at B^ ; for A was 

 deposited long before B^ In fine, if, instead of com- 

 paring 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 



