Yol. 52.] A DELIMITATION OF THE CENOMANIAN - . , 173 



but encloses large lumps or doggers of calcareous stone. From this 

 point southward a similar bed or a layer of such glauconitic marly- 

 stone seems everywhere to form the base of the Cenomanian. 



A section near Lisieux shows the Gault on the point of dying 

 out, and beyond this place what we have called ' the Greensand ' 

 forms the base of the Cretaceous series. This is the ' Glauconie ' of 

 M. Paul Bizet, which in the east of the Orne may be 30 feet thick. 

 "We believe that the greater part of it corresponds to the Gaize of 

 Havre, but the occurrence of Pecten asper in the upper part of it at 

 Notre Dame de Courson, south of Lisieux, suggests the possibility of 

 its also including a thin local representative of the Pecten asper-zone. 

 At Yimoutiers, however, the thickness of this ' greensand ' is small 

 (only 10 feet), and the only fossil found is Ostrea vesiculosa, so that 

 zonal subdivision becomes impossible. The important point is that 

 it lies beneath the bed which we take to represent the Chloritic 

 Marl, and consequently that it is of the age of our Upper Green- 

 sand. 



At and south of Yimoutiers the Cenomanian proper is divided by 

 French geologists into (1) zone of Ammonites Mantelli and (2) the 

 1 Craie de Rouen,' or zone of Ammonites rotomagensis. There can be 

 no doubt that these two zones are roughly equivalent to the lower 

 and upper portions of the Cenomanian near Havre and Eouen, and 

 here we are in complete agreement with French geologists. 



Lithologically, however, there is a considerable difference between 

 the Cenomanian of Yimoutiers and that of Havre ; the lower part 

 has ceased to be a ' craie glauconieuse,' and has become a fine 

 glauconitic and slightly chalky sand, while the upper part has become 

 a still less calcareous and more micaceous sand. Still farther south 

 the lithological differences become more and more marked, till we 

 arrive at the purely arenaceous type of Le Mans. 



It is not suprising, therefore, to find that the fauna of these 

 arenaceous beds differs considerably from that of our Lower Chalk 

 and Chalk Marl ; the physical and bathymetrical conditions under 

 which these Cenomanian deposits were formed were evidently 

 similar to those under which the highest part of our Upper Green- 

 sand was deposited, and hence many of our Upper Greensand 

 molluscs and echinoderms continued to exist in these Cenomanian 

 waters. Besides these, however, there is a certain number of species 

 which are peculiar and do not occur either in our Upper Greensand 

 or in the Chalk Marl, nor in the 'Craie glauconieuse' of Havre; 

 but some of them do occur in the Cenomanian of Devon. 



The beds which we have termed the ' Cenomanian of Devon ' 

 offer some special points of comparison with that of France, besides 

 the striking resemblance between the two faunas. The minute 

 structure of the bed numbered 11 by Mr. Meyer and of the upper 

 and less arenaceous part of Bed 10 is similar to that of some beds 

 in the lower part of the Cenomanian of Cape La Heve and of 

 Yimoutiers (see p. 140). 



Bed 13 of the Devon series has, however, no analogue in France, 

 unless it is to be found in the famous fossiliferous bed near the top 



