CHAP. XI.] HANTONIAN PERIOD. 229 



others more gradually, while London Clay types modified 

 by time come in more and more. 



It is certainly difficult to explain the peculiarities of the 

 Bracklesham and Parisian faunas on the supposition that 

 there was a complete and open communication between 

 the southern and northern seas, but on the other hand it 

 is not easy to indicate the exact location of the isthmus 

 which may be supposed to have separated them. The 

 Bruxellian deposits of Belgium, however, seem to throw 

 some light on the subject ; the majority of the Bruxellian 

 species are Bracklesham and Calcaire Grossier types, but 

 with these are associated a certain number of species which 

 are peculiar to the " Sables de Cuise," and have not yet 

 been found in the Calcaire Grossier of Paris ; l so that 

 there appears to be in Belgium just that very com- 

 mingling of the north and south faunas which does not 

 occur in England. It would seem, therefore, that there 

 was a direct communication between the French and 

 Belgian areas of deposition, and it is indeed certain that 

 such a connection existed during the formation of one 

 zone (z. de Nummulites Icevigata) at any rate ; for fragments 

 of hard sandstone with the fossils of this zone are scattered 

 at intervals over the axis of Artois, and most abundantly 

 over a tract to the south of Lille by Douai, Cambrai, and 

 St. Quentin, lying, like our Sarsen stones, sometimes on 

 the Lower Eocene sands, and sometimes on the Chalk, or 

 still older rocks. 



Since, then, this zone extended completely across the 

 ridge, it is quite possible that the lower Bruxellian beds 

 did also, for the sandstone fragments have been preserved 

 in consequence of their hardness, and the fact of their 

 presence is no proof that the older beds did not have the 

 same extension. Professor Gosselet, therefore, is not 

 warranted in assuming, as he seems to have done in pre- 

 1 " Geologie de la Belgique," vol. i. p. 227. 



