PREFACE. 
xiii 
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. 
! 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. 
