PREFACE. Xlll 



'. 



of the third ; and Ischia and the Val di Noto, of the 

 fourth. I was also convinced that I had seen proofs, 

 during my tour in Auvergne, Tuscany and Sicily/ of 

 volcanic rocks contemporaneous with the sedimentary 

 strata of three of the above periods. 

 I On my return to Paris, in February, 1829, I com- 

 municated to M. Desnoyers some of the new views to 

 which my examination of Sicily had led me, and my 

 intention to attempt a classification of the different 

 tertiary formations in chronological order, by reference 

 to the comparative proportion of living species of 

 shells found fossil in each. He informed me, that 

 during my tour he had been employed in printing the 

 first part of his memoir, not yet published, ' on the 

 Tertiary Formations more recent than the Paris basin,' 

 in which he had insisted on the doctrine 'of the suc- 

 cession of tertiary formations of different ages/ At 

 the end of the first part of his memoir, which was 

 published before I left Paris*, he annexed a note on 

 the accordance of many of my views with his own, 

 and my intention of arranging the tertiary formations 

 chronologically, according to the relative number of 

 fossils in each group, which were identifiable with 

 species now living. 



At the same time I learned from M. Desnoyers, 

 that M. Deshayes had, by the mere inspection of the 

 fossil shells in his extensive museum, convinced him- 

 self that the different tertiary formations might be 



* Ann. des Sci, Nat., tome xvi. p. 214. 



