Yol. 52.] A DELIMITATION OF THE CENOMANIAN. 171 



coeval with Upper Greensand in the west. They are merely- 

 different lithological facies of one group of deposits, and in the 

 systematic classification of the future a new name will have to be 

 found for this combined Gault-and-Greensand formation. It is 

 much more developed in England than in France, and its name 

 should be taken from some English locality. 



On the other hand, we claim to have shown in this paper that 

 when we pass from the Upper Greensand to the Lower Chalk wo 

 find that the change in the nature of the deposit corresponds with a 

 great change in the fauna. This change is particularly conspicuous 

 in Dorset and the Isle of Wight, where the base of the Chalk is 

 always marked by the abundance of ammonites belonging to the 

 species varians, Coupei, curvatus, and Mantelli, with Turrilites 

 tuberculatus and T. Morrisii. 



It is true that in Wiltshire there is a more gradual passage from 

 Greensand to Chalk, and that some of these cephalopods do appear 

 in the sand just below the Chloritic Marl, but this only shows that 

 where the record is more complete we find a few forerunners of the 

 Chalk Marl fauna coming in locally before the time when these 

 species spread over the whole marine province. 



We are, therefore, very decidedly of opinion that in England 

 there is only one plane of division in this series of beds which can 

 possibly be taken as separating one natural group of deposits from 

 another. Further, seeing that England and Northern France 

 formed part of one and the same area of deposition, we should be 

 much surprised if a change of conditions which introduced a new 

 assemblage of cephalopoda over the whole of Southern England did 

 not show itself just as clearly in the North of France. 



Before passing over to France, however, we described the sections 

 to be seen in the cliffs of East Devon, where the Chalk Marl is 

 represented by glauconitic and quartziferous limestones, rich in 

 fossils and yielding an assemblage of species which more closely 

 corresponds with the Cenomanian fauna of the Sarthe than with any 

 other local English fauna. Moreover, the position of these beds is 

 perfectly clear, for they are plainly marked off from the Upper 

 Greensand, which is at the same time fully developed, and they are 

 overlain by a complete Middle Chalk or Turonian stage. Here, 

 therefore, on English ground we have a diminutive ' Cenomanian ■ 

 deposit, part of which has an arenaceous character and a peculiar 

 shallow-water fauna connecting it very closely with the typical 

 Cenomanian of the Sarthe. 



Our next study was that of the fine section exposed in the cliffs 

 near Havre (Seine Inferieure). Our object was simply to see and 

 decide for ourselves how much of it corresponded to the Gault-and- 

 Greensand stage and how much to the Lower Chalk. We have 

 indicated what seem to us the obvious and natural divisions of the 

 series near Havre, and have pointed out that our interpretation of 

 the section agrees closely with that of M. Lennier, who has studied 

 and described it more carefully than any other French geologist. 



The fact that the same bed is taken both by M. Lennier and by 



