246 
THE CRETACEOUS ROCKS OF BRITAIN. 
Critical Remarks.— It will be seen from the preceding account 
and from that previously given of the Gault and Gaize in Volume I. 
that the Albian and Cenomanian in the north-east of France form 
a \ery complex series of beds, and that it is difficult to assign the 
several members of the series to their correct zonal horizon. 
The general correlation proposed by Professor Barrois in 1878 . 
for the Departments of Aisne and Ardennes was as follows : — 
Zone of Bel. plenus.—White and grey marls. 
Hoi. subglobosus.—Wanting 
Am. laticlavius.—Glauconitic marls. 
55 
55 
Pecten asper. {® ables f ’ a . Hardo > re ’ 
1 (Marne de Givron. 
We must remember that by the zone of Belemnites plenus he 
means an equivalent of some 60 feet of chalk at Wissant and Dover, 
and not merely the band of marl to which we apply the name in 
England. His zone of Holaster subglobosus includes the Wissant 
zones of Am. rotomagensis and Am. varians (116 feet thick) ; in 
1878 he considered this to be absent, but we have reason to think 
he would not maintain this view now. We strongly dissent from 
it both on the ground that there is no sign of a break of any kind 
but a complete passage from glauconitic marl to the whitish marl, 
and because we doubt the reference of the former to the zone of 
Am. laticlavius. 
By the zone of Am. laticlavius Professor Barrois means what 
we have called the subzone of Stauronema Carteri , the true Chloritic 
Marl of Folkestone and the Isle of Wight. Now it does not appear 
that he found a single specimen of Ammonites laticlavius at 
any locality in the departments of the Ardennes, Aisne, and Nord, 
and that fossil is not in England confined to the Stauronema. 
zone. Further, he only mentions two specimens of Stauro¬ 
nema, and these are preserved in black phosphate and may 
have been derived. We do not think this evidence is sufficient. 
No doubt Professor Barrois was also influenced by the presence 
of phosphatic nodules and by the occurrence of Pecten asper , but 
neither of these facts can be allowed to have much weight. This 
has practically been admitted by Professor Barrois himself, who 
notes the occurrence of P. asper at Bois des Haies in the Ardennes 
many feet above the bed which he regards as the zone of Am. lati¬ 
clavius, and he appends this note:—“ This is not the first time 
that Pecten asper has been recorded from above the greensand 
with P. asper. M. Hebert has recorded it from Vitry-le-Francais, 
and I have recognised it at Saully (Yonne) in the zone of Holaster 
subglobosus.” 
The opinion of Mr. W. Hill and myself was expressed in 1896,* 
when we showed that the beds containing P. asper at Cap la Heve 
represented the lower part of our Lower Chalk, i.e., of what Professor 
Barrois calls the zone of Holaster subglobosus. 
* Delimitation of the Cenomanian, Quart. Journ. Geol. Soc., Vol. lii. 
p. 170, and Ann. Soc. Geol. Nord., Tom. xxiv. p. 227. 
