100 MESSES. A. J. JUKES-.BEOWNE AND W. HILL : [May 1 896, 



regarding that district as the typical area of his new stage, because 

 the deposits there were of considerable thickness and were rich in 

 well-preserved fossils. 



Unfortunately d'Orbigny himself fell into error regarding the 

 deposits which should be included in his Cenomanian stage in the 

 West of France. In the Sarthe there are no Lower Cretaceous 

 strata, neither are there any beds containing a typical Albien fauna, 

 so it is not surprising that d'Orbigny included the basal clays and 

 greensands in his Cenomanian ; but he also believed that his Albien 

 stage was wanting near Havre, and that everything seen there 

 above the Kimmeridge Clay was of Cenomanian age. 1 



This belief of d'Orbigny's was doubtless one cause which retarded 

 the progress of opinion respecting the limits and components of the 

 Cenomanian stage. Another cause is certainly to be found in the 

 local and exceptional nature of the beds in the district which was 

 chosen as the type, both as regards their lithological characters and 

 the assemblage of fossils that they contain. 



A study of what has been written by French geologists con- 

 cerning the Cenomanian shows us that they have constantly found 

 a difficulty in determining what beds in other parts of the country 

 should rightly be regarded as the equivalents of the Cenomanian of 

 the Sarthe. 



In perusing the Yicomte d'Archiac's ' Etudes sur la Formation 

 Cretacee ' 2 we have been struck by the general accuracy of his 

 correlations. He evidently had a masterly grasp of the subject and 

 a keen eye for the structure of a country, and for tracing definite 

 horizons in a changeful group of beds. He anticipates d'Orbigny 

 in separating the ' groupe de la craie tufau ' of Touraine and Anjou 

 from his ' groupe du gres vert,' and he divides each of these groups 

 into three stages. It is possible that he made some mistakes in the 

 determination of his fossils, but the grouping of his beds appears 

 to be more correct, stratigraphically, than the grouping adopted 

 by d'Orbigny in his ' Cours elementaire de Pal. et de Geol. strati- 

 graphiques ' of 1852. Certainly the comparisons made in his rapid 

 traverse of the Sarthe, Orne, and Calvados are very correct, and we 

 think that he laid a sufficiently accurate basis for a more detailed 

 correlation of the Cenomanian deposits, if his successors had only 

 worked along the same lines, and had not depended so entirely on 

 the minutiae of palseontological evidence. 



Unfortunately the late Prof. Hebert, influenced probably by the 

 statements of d'Orbigny, and struck by the differences between the 

 Cenomanian faunas of Havre and of Le Mans, propounded the 

 hypothesis that the greater part of the Cenomanian of the Sarthe, 

 or Gres du Maine, as he called it, was newer than the k craie 

 glauconieuse ' of Havre, and that the former was a local deposit 

 which was not represented by anything on the northern coast. 

 This was combated and disproved by M. Guillier and M. G. Bizet, 

 who showed that chalky beds containing Eotomagian fossils occurred 



1 'Cours Elementaire, etc' vol. ii. pp. 619 & 635. 



2 Mem. Soc. Geol. France, ser. 2, vol. ii. pp. 1-148 (1846), published 1847. 



