326 



THE GEOLOGIST. 



1st. There exist distinct and well defined limits between 

 the Faunas peculiar to each Formation or Division, as none 

 of the species of Ammonites pass from the Jurassic to the 

 Cretaceous formation. 



2nd. There have been, at each grand geological epoch, 

 not only distinct species, but a series of peculiar, and 

 generally well defined zoological forms, as w^e see in the 

 distribution of groups into separate formations. 



3rd. This change in the form of organised beings, is the 

 more strongly marked, in proportion to the space which in- 

 tervenes between important epochs ; for example, there is a 

 greater difference between the forms peculiar to the Jurassic 

 and Cretaceous formations, than between the different di- 

 visions of the Cretaceous formation itself. 



4th. The affinities which we remark between the groups of 

 the species of the divisions of the Cretaceous formation, 

 evidently prove, not only that these divisions belong to one 

 of the grand Geological periods, but that they also distinctly 

 divide them, as regards the affinity, from the divisions of 

 the Jurassic formation, which have also their general special 

 characters ; thus the Cretaceous deposits may well consti- 

 tute a Formation, distinct from the Jurassic formation. 



5th. The different divisions of the Cretaceous formation, 

 whilst presenting affinities and reciprocal passages between 

 the groups of Ammonites, have, notwithstanding distinct 

 external forms, nature having, at each epoch, varied her 

 productions, and given them a general character, or fades, 

 which at once distinguishes them. 



6th. The different divisions, independently of the general 

 appearance, have, either groups of peculiar form, or at least, 

 a predominant number of species of these groups which may 

 almost always serve to distinguish them. 



7th. In every instance, the species of Ammonites are 

 entirely distinct in each formation, and in each division of 

 the formation, and all may be applied to distinguish dis- 



