1898] ALBIAN AND CENOMANIAN IX FRANCE 195 



cle rArgonne contains so many Cenomanian species, (2) that this 

 zone overlaps the Lower Gault, and tlms in his opinion separates 

 itself from the latter. Later in 1876 Barrois expressly included 

 the Upper Gault of Folkestone and Wissant in the Cenomanian. 

 But he made no estimate of the number of species which united the 

 zone of Ammonites inflatus at these places to the beds above, nor 

 did either of them ever discuss the relative values of the different 

 elements of the fauna of the A. inflatus zone. 



The variation and discordance of opinion in France may be 

 gathered from the change in the grouping of the zones in different 

 editions of A. de Lapparent's well-known " Traite de Geologic" In 

 his edition of 1885 the zone of A. inflatus is grouped as Albian, in 

 that of 1892 it is placed in the Cenomanian. The latter method 

 of grouping has been adopted by Mr G. Dollfus for the Service 

 de la Carte geologique de la France. At present, therefore, most 

 French geologists make a very small Albian and a very thick 

 Cenomanian, while the line of separation between the two stages 

 is drawn through the middle of the Gault of Wissant and through 

 a perfectly continuous bed of sandy clay at Havre. 



In England we have arrived at very different results ; De Ranee 

 in 1868 and Price in 1874 showed that the Gault of Folkestone 

 was separable into two divisions — a Lower Gault characterised by 

 Ammonites interruptus and A. lautus, and an Upper Gault charac- 

 terised by A. varicosus and A. rostratus. In 1876 Barrois published 

 his excellent Researches on the Upper Cretaceous Series of England, 

 and proved to us that the greater part of our Upper Greensand was 

 the stratigraphical equivalent of the Upper Gault of Folkestone. 



Subsequent investigations have led us to regard the combined 

 Gault and Greensand as a single stage or natural group of beds, to 

 abandon the names Gault and Greensand as denoting definite chrono- 

 logical divisions ; they can only be regarded as descriptive of different 

 lithological aspects or facies of the formation, and consequently as 

 serviceable only on maps that are designed to exhibit such lithological 

 variations. Hence we can recognise with Barrois a zone of Ammon- 

 ites rostratus ( = inflatus), but it is quite impossible for us to accept a 

 classification which groups this zone with the Lower Chalk and separ- 

 ates it from the Lower Gault. We base our refusal on the very 

 principle by which the French themselves profess to be guided, namely, 

 on the faunistic relations of the several zones, and especially on the 

 range and relative abundance of the different species of Cephalopoda. 



Now a classification which appears to be the best and most 

 natural expression of the facts in southern England can hardly be 

 unnatural in the north of France, and thus it became clear that 

 some study of the French sections from an English point of view 

 was greatly needed. Such a study was made by Mr W. Hill in 



