230 
THE CRETACEOUS ROCKS OF BRITAIN. 
CHAPTER XX. 
THE EQUIVALENTS OF THE LOWER CHALK IN 
THE NORTH-EAST OF FRANCE. 
French Nomenclature. 
The divisions of the Chalk in France were studied in some detail 
much earlier than they were in England. The stratigraphical 
explorations of d’Archiac, Buvignier, and Levmerie between the 
years 1838 and 1850, together with the systematic study of Cre¬ 
taceous fossils by d’Orbigny between the same dates, laid the founda¬ 
tions of the classification which has been adopted in France. 
The French have never been hampered by the idea of the litho¬ 
logical unity and indivisibility of the Chalk which led many English 
geologists to resist the innovation of dividing it into stages. Their 
country is larger, and it includes a wider and more varied series of 
Cretaceous strata deposited under different physical and bathy¬ 
metrical conditions. Moreover, then* classification had the advan¬ 
tage of being based on the evidence of fossils obtained from many 
different parts of France, and studied at the same time by the 
acute palaeontologist Alcide d’Orbigny. 
Up to the year 1843 the different portions of the French Chalk 
were known by lithological names, just as they were in England 
—namely, craie blanche , craie tufau, and craie chloritee. But in a 
paper reviewing the distribution of the Cretaceous Cephalopoda 
and Gasteropoda,* d’Orbigny proposed the name Senonien 
for the white or Upper Chalk, taking it from the location of the 
Gallic tribe of Senones (Sens in Yonne), and the name of Turonien 
for the craie tufau and craie chloritee, taking it from the tribe of 
Turones (at Tours), and the province Turonia (Touraine). 
Thus, at first, he only recognised two stages in the Chalk, which 
roughly corresponded with what were at the same time called 
Upper Chalk and Lower Chalk in England. Between 1847 and 
1852, however, he became aware that the group which he had 
called Turonien contained two distinct assemblages of species. He 
saw that his original Turonien should be separated into two stages. 
Accordingly he restricted that name to the upper portion, and 
proposed a new name, Cenomanian, for the lower portion, taking 
it from the ancient name of the town of le Mans (Cenomanum), 
where a certain type of these lower beds was well developed and 
highly fossiliferous.f 
* Bull. Soc. Geol. de France, Ser. 1., Vol. xiv. p. 480 (1843). 
t Cours Elementaire de Geologie, etc., Vol. iii. (1852) p. 631. 
