130 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



at Bracklesham. Whereas the freshwater marls at the top of the 

 Calcaire grossier have their maximum development in the east of 

 the Paris area, and gradually thin out as they range westward, disap- 

 pearing nearly, if not altogether, before we reach its western confines ; 

 wherefore the absence of like conditions in the English area is thus 

 a priori shown to be probable. 



In Belgium there was neither the amount of subsidence expe- 

 rienced in England nor the extent of silting up going on as in France ; 

 the Bruxellian System with even less vertical dimensions than its 

 French equivalent, and a fauna less extensive than its English equi- 

 valent, exhibits throughout the same marine characters as the latter. 

 Also the land seems to have been at a greater distance : there are re- 

 mains of a land-vegetation, but composed of specimens which seem 

 to have been drifted from a distance ; for it is the harder fruit (Nipa- 

 dites) and not the more delicate leaves of the Palm which there 

 occur ; and they are often drilled by TeredincBt as though they had 

 long floated out at sea. 



The next change is, in the French area, one of a very marked 

 character : marine strata of entirely different composition to the Cal- 

 caire grossier overlie that deposit, and at the base of this upper de- 

 posit are scattered here and there the debris and wreck of the older 

 tertiary beds and of the chalk. A sudden change, I believe, here 

 took place : the aestuaries, bays, and gulfs of the Calcaire grossier 

 were invaded by the sea. That the movement was sudden, and of 

 some considerable force, I infer from the circumstance that the con- 

 solidated beds of the Calcaire grossier, including even its upper fresh- 

 water marls with the chert beds, together with the solid beds of 

 the Glauconie moyenne and Glauconie grossiere, were partially 

 broken up and denuded ; for rolled fragments of all these beds are 

 found in places at the base of the Sables moyens, and at a consider- 

 able distance from where the lower beds rise from beneath the Cal- 

 caire grossier. With these rock-debris are also found the harder and 

 larger rolled shells of the Sables de Bracheux, and the shells of the 

 Argile plastique ; whilst well-worn small flint-pebbles form the main 

 part of this conglomerate-bed — pebbles probably formed on the 

 shores of the Calcaire grossier sea, and scattered at this subsequent 

 period. Once spread over the bed of the sea, and the state of tran- 



sea-bed, temperature, depth, &c. — whether these causes have not operated to 

 a greater extent than is here allowed. In these instances the conditions are so 

 strongly marked, that they lead me to believe that such an amount of variation 

 may have been thereby produced as might, viewing each area separately and in- 

 dependently, cause some varieties to assume the permanence and importance of 

 specific differences ; and I therefore think it not improbable that eventually there 

 will be found a greater number of species common to the two countries. 



Until the exact synchronism of any deposit is established, the palaeontologist 

 cannot in each case take the actual value of these causes into full and suflScient 

 consideration, and many admirable monographs on Tertiary fossils have neces- 

 sarily been founded simply upon the differences actually apparent and persistent 

 in the fossils of the several areas, after allowing for such differences as do take 

 place in each respective area separately. The limits of variations require, how- 

 ever, to be studied for the several areas conjointly. 



