238 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



remains. In this country it is equally well distinguished by structure 

 and physical characters ; whereas the absence of distinctive physical 

 phsenomena in the equivalent series in France has tended to mask 

 the palaeontological distinctiveness which there also equally charac- 

 terizes this group of strata. 



The series next above the London Tertiary group I would term 

 " the Paris Tertiary group," of which, in France, the centre in time 

 is the Calcaire grossier, and in this country the Bracklesham Sands. 

 Of the relations of the deposits of this period and the one next suc- 

 ceeding I purpose to treat in the next part of this paper. My reason 

 for taking as the base of this Paris group the Lits Coquilliers and 

 the Sables divers*, or rather the Glauconie moyenne of M. Graves, 

 is founded chiefly on the palaeontological evidence ; notwithstanding 

 that, in mineral characters and in the absence of any well-defined 

 base-line, they seem as much, or even more in regular sequence with 

 the underlying than with the overlying series f. In this country, 

 on the contrary, there is no fossil fauna to distinguish the beds of 

 this age (the Lower Bagshots), but in lithological characters and 

 structure they form one consecutive series with the overlying beds 

 of the Bracklesham sands and clays. No passage exists between 

 the Bagshot Sands and the London Clay. It is true that there is no 

 strongly marked line of separation — only occasionally is a band of 

 pebbles spread over the surface of the London Clay. In Flanders and 

 Belgium the division is again less marked. But although an eroded 

 surface, a conglomerate bed, or a sudden alteration of mineral cha- 

 racter form palpable and useful adjuncts indicative of distinct periods 

 and of altered times, yet such corroborative evidence is by no means 

 indispensable. When these phsenomena occur, some geological 

 changes are generally indicated, but it by no means follows that these 

 phsenomena must necessarily be attendant upon all such changes. If 

 the movements of the earth's surface at that time took place at a 

 distance, — or if the encroachment of the sea, after its retirement from 

 the land during a long period, were gradual, and the materials drifted 

 to form the newer beds were derived from the same source again as 

 formerly, — then the peculiarity alone of the new fauna would form the 

 test of its independence, as the physical distinctions would necessarily 

 be in a great measure faint and obscure. 



One cause possibly of the difference of the faunas of the Calcaire 

 Grossier and Lits Coquilliers and of the London Tertiaries is the 

 connexion apparently of the former vdth forms generally considered 

 to belong to more southern and hotter climates, and of the latter with 

 the forms usually inhabiting more northern seas. Commencing with 

 the Thanet Sands, a sea open to the north extended probably over 

 the south-east of England, Belgium, and the north of France ; whilst, 

 to the south of that area, dry land, including the greater part, if not the 

 whole, of the Paris Tertiary district, prevailed and continued to prevail 



* With possibly some portion of conglomerate beds. 



+ M. Raulin, however, seems to imply that the base-line between the Glauconie 

 moyenne and the " Sables des Lignites " is generally well defined. Bull. Soc. Geol. 

 2nd ser. vol. viii. p. 461. 



