270 M. Marcel de Serres on the Deposition of 



and to the south-west of that city, near St Jerom's Mill, tliere 

 are observed under the diluvium, 



1st, Tertiary marine sands, characterized by numerous re- 

 mains of marine shells, mixed with fresh-water Mussels, large 

 Helices, and Cyclostomce. 



^d, A hard calcaire moellon, with numerous marine shells, 

 small oysters, and some individuals of Ostrtta crassissima. 



3d, A marly fresh-water limestone, with small paludinse, in 

 contrasting position with reference to the calcaire moellon which 

 lies above it. 



The most remarkable thing about this limestone, is its being 

 perforated in situ by modioli, and other boring shells. Now, 

 as the connection between the calcaire moellon and the fresh- 

 water limestone is as intimate as direct, both must have been 

 deposited in the same fluid, that is to say, in the basin of the 

 ancient sea ; for, were it otherwise, there would be found on the 

 fresh- water limestone some deposits produced during the retreat 

 of the Mediterranean, while this basin was occupied by fresh 

 water only, and inhabited by land animals. No trace of conti- 

 nental surface existing between these two deposites, and the 

 second marine limestone being mingled or alternating with the 

 fresh-water limestone, as, for example, in the basins of Pezenas 

 (Herault), and Lasfoux (Gard), it must be admitted that both 

 have been precipitated in the same fluid, inasmuch as the ma- 

 rine deposites often contain fluviatile and terrestrial organised 

 bodies, as the fresh-water deposites contain marine fossils, the 

 latter being even occasionally perforated by sea-shells, whether 

 in situ, as at Aix, or rolled, as at Montpellier. 



To recapitulate, and, at the same time, having reference to 

 your observations, it appears to me, 



1st, That at least, after the deposition of the lias, the climates 

 being already separated, there existed on the earth different 

 zones, inhabited by peculiar animals, and covered with vege- 

 tables, to which the temperature of these zones corresponded. 



2dly, That, when there has been no transportation of ani- 

 mals and vegetables from one zone to another, their remains are 

 still found in the places which they originally occupied ; but that 

 when there has been displacement, a mixture has been produced 



