216 On the Fossil Shells of the Paris Basin. 



4. The constant proportions (3 per cent. 19 per cent, and 

 52 per cent.) in the number of living species determine the 

 age of the tertiary beds. 



5. The tertiary beds are in superposition, and not in pa- 

 rallellism as had been supposed. 



6. The beds, from their zoological contents, appear to be 

 divided into three groups or stages. 



About the month of August 1831, we proved the ex- 

 istence of these groups, and indicated the places where 

 the observations were made ; geologists have since con- 

 firmed these results, and separated the tertiary rocks ac- 

 cordingly. 



The latest and most superficial tertiary strata have been 

 deposited when the temperature of Europe was almost the 

 same as it is at present ; here are the proofs. 



The tertiary beds of this age, of Norway and Sweden, of 

 Denmark, of Saint Hospice near Nice, of a portion of Sicily, 

 contain in a fossil state, all the species of the corresponding 

 seas, and amongst others, those which in most places best 

 represent for us the temperature. These fossils present the 

 same series of varieties with the living species which an- 

 nounces most positively, that the beds referred to have been 

 deposited under circumstances similar to those in which their 

 existence is still maintained. These same beds in the South 

 of France, subject to the Mediterranean, of Spain, of Italy, 

 and of Sicily, of the Morea, of Barbary, (Algiers,) contain a 

 large proportion of the species still living in the Mediterra- 

 nean, but they contain also those whose analogues do not 

 exist, or are distributed in small numbers in the warmer 

 regions of the Atlantic, and the Seas of India. To afford a 

 correct idea of the tertiary period in Italy, we must distin- 

 guish three sorts of fossil species. 



1. Those whose analogues are still living in the Medi- 

 terranean. 



2. Those in small number, whose analogues are not found 



