210 PALEONTOLOGY. 



same extent by all palaeontologists, it is nevertheless one 

 which the progress of science has shown to be more general 

 than was at one time supposed. The actual state of our 

 science does not permit us to affirm that this law is without 

 exceptions, but all the probabilities accord in favour of the 

 speciality of fossils. " All the works that have been written 

 by zoologists well acquainted with the discrimination and 

 precision which palaeontology requires, have almost invari- 

 ably given as their result that fossils are different in each 

 formation." * 



If we take, for example, the fossils of the triasic, oolitic, 

 and cretaceous periods, we find them to be completely dif- 

 ferent from one another ; but it is probable that future in- 

 vestigation will show that we must go much further than 

 this, and admit that the stages or sub-divisions of each of 

 these periods possess their own special fauna. D'Orbigny 

 has shown,f that in the chalk rocks of Prance no species of 

 fossil molluscan or radiate animal is common to any two 

 of the stages into which he has sub-divided the cretaceous 

 system of that country. That is to say 



( Danien ^ 



ISenonien 

 Turonien j Each of these stages he has 



divided iiito seven stages,J -I Cenomanien } found contains its own 

 the . . . . Albien special fauna. 



I Aptien 

 ^ Neocomien j 



SECOND LAW. The differences which exist between extinct 

 faunas and living animals are greater in proportion to their 

 antiquity ; or, in other words, in the same ratio as the sedi- 

 mentary strata are more ancient, the animal debris contained 

 therein differ from the forms that inhabit the earth at the 

 present day. 



This law becomes evident when we compare the fossil 

 remains of animals of different geological epochs. If, for 

 example, we examine the shells of the tertiary strata, we 

 shall recognise in its newer divisions a majority of forms 



* Pictet, p. 64. f D'Orbigny, Palontologie Fra^aise. Ter. Cretace. 

 For the English equivalent of these stages, see the table in the chapter 

 on the cretaceous group. 



