On the Fossil Shells of the Paris Basin. 211 



logical periods, such as those which we know to have hap- 

 pened in Europe. 



The comparison of the species of tertiary beds with those 

 of the secondary, of which we have just now spoken, having 

 afforded the important result that none of the species of the 

 secondary deposits lived at the same time with those of 

 the most inferior tertiary beds, it was curious to examine 

 whether these inferior tertiary beds contained any species 

 which might be identified with those which now live. This 

 identity is incontestably established, but only in regard to a 

 small number of species, which is sufficient, we think, to 

 connect the tertiary epoch with the present, and this con- 

 nexion is so much more remarkable, as we have seen the 

 number of analogues augment in proportion as we pass from 

 the more ancient to the more recent beds. 



Yet within these few years geologists assimilate the whole 

 of these beds, which they believe to be of the same age, 

 and represent them parallel, bed for bed, to those of the 

 Paris basin. But we have seen in the tertiary beds not 

 a parallelism, but a true succession, and at the same time 

 we have made use of the analogy of fossil species to dis- 

 tinguish between them, where they are limited to a very 

 small number of those tertiary basins of the same geologi- 

 cal epoch with that of Paris. We have had occasion in the 

 course of this work in giving the localities of the species, to 

 mention two of these tertiary basins which are of the same 

 age with ours ; we refer to that of London, and to that of 

 Belgium, as more extensive and considerable than we are in 

 the habit of supposing. 



The little tertiary basin of La Manche, in the environs of 

 Volognes ; the calcareous beds of Bas-medoc, which are de- 

 posited below, and on either side of the vast basin of 

 Gironde ; on one part of the valley of Ronca, near Verona ; 

 the limestones of Castel- Comberts ; the beds singularly mo- 

 dified in the Alps, and which are met with particularly in 



