of Zoological characters in Geology. 237 



Before then I employ them alone and as most important, 

 their value should be again examined. 



It had long been remarked that diflFerences were almost 

 always found between the shells that now live in the seas, 

 and those found fossil in all countries. This has been con- 

 firmed by a more detailed examination, and has gradually 

 Jed to another rule, that the deposites of organic remains 

 buried in the beds of the globe have been formed, as it 

 were, in successive generations, so that all the debris of the 

 same deposite possess with each other a certain sum of re- 

 semblances, and with superior and inferior deposites a gene- 

 ral sum of differences ; it has been also thought that the 

 latter sum becomes larger, or the dift'erences greater, the 

 more these deposites are distinct, or at greater distances 

 from each other in a vertical direction. This rule, at first 

 laid down timidly, and only for certain localities (as should 

 always be done when rules are to be established which can 

 only result from the observation of numerous facts) — this 

 rule, I say, may apparently be applied to all places observed 

 in different parts of the globe, and to all the organic remains 

 buried in its beds, whether they belong to the animal or 

 vegetable classes. Up to the present time, the objections 

 that have been offered have either vanished before a more 

 scrupulous examination, or have been explained by the dis- 

 covery of peculiar circumstances that have given rise to 

 them. This rule, reduced to the general exposition of it 

 we have just given, does not appear to be susceptible of any 

 real objection, and all geologists are now agreed that the 

 generations of organized bodies which have successively in- 

 habited the surface of the earth, differed the more from the 

 present, in proportion as their remains were found buried 

 deeper in the beds in the earth, or what is nearly the same, 

 as they lived at epochs farther removed from the present. 



Consequently if no other difference were observable in 

 the beds which compose the crust of the globe than the dis- 

 tinct succession of generations of organic bodies, that alone 

 would be sufficient to establish (as has been remarked by 

 M- Cuvier) that this crust has been formed ia successive 

 depositious, at different periods. 



