LOWER CHALK — NORTH-EAST OF FRANCE 
237 
D’Orbigny points out that his Cenomanian stage consists of 
quartzose sand in Sarthe and Loire, of “ craie chloritee ” (chalk with 
glauconite grains), in Normandy and the Pay du Bray, of compact 
or marly white chalk in the Aube Yonne and north-east of France ; 
and he remarks, “ it is easy to see from these great differences at one 
and the same geological horizon what conclusions we should reach 
if we relied on mmeralogical characters to distinguish the Creta¬ 
ceous stages ; that differences of opinion and of classification should 
exist cannot astonish us ; but when we abandon that deceptive 
character and substitute for it, as we have done, palaeontological 
characters, everything will be simplified ; horizons will show them¬ 
selves clearly, and we shall see the stratigraphy agreeing accurately 
everywhere with the palaeontological results.” (Op. ait., p. 638.) 
Things are not quite so simple as d’Orbigny supposed they would 
be, and his stratigraphic correlations are not all correct, but he 
was unquestionably right in believing that the palaeontological 
method would give better results than a purely stratigraphical 
or lithological method. In this he was only carrying out the dictum 
of William Smith that “ strata can be identified by the fossils 
they contain.” 
The following are the Cephalopoda and some of the other fossils 
given by d’Orbigny in 1852 as characteristic and widely distributed 
members of his Cenomanian fauna : — 
Belemnitella vera (=plena). 
Nautilus triangularis. 
Ammonites varians. 
„ falcatus. 
„ rotomagensis. 
„ Mantelli. 
Scaphites sequalis. 
Baculites baculoides. 
Turrilites costatus. 
Avellana cassis. 
Area passyana. 
Corbis rotundata. 
Inoceramus striatus. 
Pecten asper. 
„ elongatus. 
Pecten (Neithea) sequicostata. 
Spondylus striatus. 
Discoidea cylindrica. 
Everyone will recognise these as species which are characteristic 
of our Lower Chalk (including Chloritic Marl) ; none of them range 
above it, and though some of them do range downward into a bed 
which we class as Upper Greensand, yet that bed is only a few feet 
thick, and may be regarded as a passage bed. 
Some French geologists now include the whole or a part of the 
zone of Ammonites rostratus in their Cenomanian, but the pro¬ 
priety of such an arrangement does not concern us here, for in this 
chapter we are dealing with the French equivalents of our Lower 
Chalk and not with any particular conception of the Cenomanian 
stage. 
Stratigraphical Details. 
Boulonnais .—The only coast section of the Chalk in the north¬ 
east of France is that of Blanc-nez, which corresponds to that of 
Kent, near Dover. This has been described by M. Chellonneix and 
Prof. Barrois, and the following account of it is adapted from that 
of the latter*: — 
* 
Proc. Geol. Assoc., Vol. vi. pp. 28, 29 (1879). 
