Cuvier and Brongniart on Paris Basin 2 1 7 



from its historical importance in the annals of science : 

 " The means which we have employed for the recognition, 

 among so many limestones, of a bed already observed in a 

 distant quarter, has been taken from the nature of the 

 fossils contained in each bed. These fossils are generally 

 the same in corresponding beds, and present tolerably 

 marked differences of species from one group of beds to 

 another. It is a method of recognition which up to the 

 present has never deceived us. 



" It must not be supposed, however, that the difference 

 in this respect between one bed and another is as sharply 

 marked off as that between the chalk and the limestone. 

 The characteristic fossils of one bed become less abundant 

 in the bed above and disappear altogether in the others, or 

 are gradually replaced by new fossils, which had not 

 previously appeared." l 



The authors then proceed to enumerate the chief groups 

 of strata composing the Calcaire Grossier, beginning at 

 the bottom and tracing the succession upward. It is not 

 necessary to follow them into these details. We may note 

 that, even at that time, the prodigious richness of the lower 

 parts of this formation in fossil shells had been shown by 

 the labours of Defrance, who had gathered from them no 

 fewer than 600 species, which had been described by 

 Lamarck. It was noted by Cuvier and Brongniart that 

 most of these shells are much more unlike living forms 

 than those found in the higher strata. These observers 

 also drew, from the unfossiliferous nature of the highest 

 parts of the formation, the inference that while the Calcaire 

 Grossier was deposited slowly, layer after layer, the number 



1 Journal des Mines, xxiii. p. 436. 



