551.77(44) 19:; 



V 



The Delimitation of the Albian and Cenomanian 



in France 



^J^HE nomenclature of the English Cretaceous System is based 

 -L upon the lithological differences exhibited by its members, 

 the only division which from the beginning had a name of different 

 origin being the Wealden. Such a basis of nomenclature is bad 

 because lithological differences are local or provincial accidents. 



French geologists have often expressed surprise at the con- 

 servatism of Englishmen in retaining a nomenclature which only 

 perpetuates errors and cannot be made to express the true relations 

 of the component parts of the Cretaceous System. They are quite 

 right: it has perpetuated the error that the Gault as a whole is older 

 than the Upper Greensand as a whole, and has prevented us from 

 recognising long ago that they were to a large extent merely 

 different lithological facies of one formation. 



There can be no question that the distribution of species affords 

 a better basis of grouping than the lithological characters of deposits. 

 Put in this way it seems a truism, but it is nevertheless a fact that 

 our existing system of nomenclature ignores this principle, and does 

 actually separate deposits which ought to be grouped together; 

 while it suggests a connection between ' Lower ' and ' Upper ' 

 Greensand which has no existence in reality. 



The French method of nomenclature is free from this reproach, 

 and it has been preferred to our own by most other European 

 nations. The French completely ignore lithological differences, and 

 their subdivisions or stages include all deposits which yield a similar 

 assemblage of fossils. 



D'Orbigny says that his principal object in undertaking the 

 ' Paleontologie Francaise " was the application of palaeontology to 

 the natural classification of the formations, and it is to him 

 that the French owe their nomenclature of the Jurassic and 

 Cretaceous systems. He found that of the Cretaceous system in 

 dire confusion, but when he had examined 593 species of Cretaceous 

 Cephalopoda and Gasteropoda he felt himself justified in dividing 

 the whole system into five distinct stages, each containing a special 

 fauna. This was in 1843, and, abandoning the lithological names 

 which were then current in France, he proposed new names for his 

 stages, taken from those of towns or districts where each stage was 

 well developed and specially fossiliferous. These five stages were 

 Senonian, Turonian, Albian, Aptian and N^ocomian. In 1852 

 he added a sixth, having recognised that the group which he called 

 Turonian in 1843, really comprised two stages with essentially differ- 







