194 NATURAL SCIENCE [September 



ent faunas; consequently he restricted the name Turonian to the upper 

 of these stages, and gave the name of Cenomanian to the lower. 



Since 1852 these names have always been used by French 

 geologists, but in spite of much careful work on the fossils, and in 

 spite of the progress made in stratigraphical geology, the delimita- 

 tion of these stages has never been satisfactorily settled. The 

 restriction of the fossil species to the several stages did not prove 

 so complete and exact as had originally been supposed. Many 

 species were found to range from one stage to another, and where 

 there is a gradual passage from stage to stage, there is of course 

 scope for difference of opinion regarding the plane of separation. 

 Moreover in the case of the Albian and Cenomanian there are 

 special difficulties, for in the Aube whence was taken the type 

 of the Albian, the fossiliferous beds corresponding to the Lower 

 Gault are overlaid by a great series of almost unfossiliferous marls 

 (representing Upper Gault), and the Cenomanian is neither well 

 developed nor very fossiliferous. D'Orbigny, again, considered the 

 Albian to be absent from the area taken as the type of the Ceno- 

 manian (la Sarthe), and this view is still held by many French 

 geologists, though there are basement beds which some have 

 regarded as older than the true Cenomanian. 



"When the stratigraphical succession in the north-east of France 

 (Marne, Meuse and Ardennes) came to be better understood, it was 

 found that between the beds which yielded typical Albian fossils 

 and those in which only Cenomanian fossils occurred, thick deposits 

 of sandy marl and fine-grained sandstone (gaize) came in, and that 

 these beds contained a mixture of species, some being such as were 

 originally regarded as Albian and others such as are generally 

 confined to the Cenomanian. In these beds the prevalent Am- 

 monites are A. infiatus ( = rostratus) and A. auritus, and they came 

 to be known as the zone of A. infiatus. Occasionally, however, 

 they contain Ammonites of the species A. mantclli, A. varians, and 

 A. falcatus, which are essentially Cenomanian forms. 



D'Orbigny was not fully acquainted with the fauna of these beds, 

 but he was aware that the Gaize de Montblainville contained such a 

 mixture of species, and he nevertheless referred it to the Albian. 1 

 Further, he regarded the Gault of Wissant and of Folkestone as the 

 equivalent of his Albian stage, and in his " Paleontologie Francaise," 

 Ammonites infiatus, A. varicosus, A. auritus, and A. mayorianus, are 

 given as Gault {i.e. Albian) fossils. 



The Upper Gault with Ammonites infiatus continued to be re- 

 garded by most French writers as Albian, up to the year 1874, but 

 Hebert in 1864, and Barrois in 1874, preferred to consider it as 

 Lower Cenomanian, the latter giving as reasons (1) that the Gaize 



1 Vide his " PaL'ontologie et G^ologie Stratigraphique. " Tom. ii., p. 622, 1852. 



