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



Pecten asper' such as P. asper itself, P. Galliennei, and Catopygus 

 carinatus ; some of the Lower Chalk, such as Ammonites varians, 

 A. Mantelli, and Scaphites cequalis ; near the base, too, a peculiar 

 large coralloid polyzoan (Ceriopora ramulosa) is not uncommon. 

 Tbe upper bed has fewer fossils, but the same ammonites occur 

 with, occasionally, Scaphites cequalis. These two beds are well 

 marked off from those above and below, and may be called the zone 

 of Ammonites Mantelli. 



The upper surface of No. 4 is always a layer of brown phosphatic 

 nodules ; these are now ' welded ' on to this bed, but the interstices 

 between them are filled with the material of the overlying bed. 

 This bed, No. 5, is full of large grains of quartz and glauconite, but 

 has a chalky matrix, and is much more friable than the bed below. 

 Setting aside the derived phosphatic fossils, of which there are 

 many, the commonest fossil in bed 5 is Rhynchonella Wiestii, a 

 species which is closely allied to Rh. Cuvieri. With it are 

 found Belemnitella plena and Discoidea cylindrical so that, looking 

 to the fossils, the bed would seem to be the equivalent of the 

 Belem-mieUa-marls of Dorset and other counties. Physically, how- 

 ever, it is the base of the Middle Chalk or Turonian, for it passes 

 up into the hard glauconitic chalk which contains only Turonian 

 species. 



As to the succeeding yellowish nodular chalk, there can be no 

 doubt regarding its age ; it has some resemblance to the Melbourn 

 Rock, and may be regarded as its equivalent. We think, therefore, 

 that the Middle Chalk has here a basement-bed of gritty glauconitic 

 chalk, containing derived fossils, which bears the same relation to 

 the Melbourn Rock as the basement-bed in Dorset does to the 

 Chalk Marl. 



If the above inferences are correct, the only beds which can be 

 regarded as the equivalents of the Lower Chalk in this section are 

 Nos. 3 and 4. Mr. C. J. A. Meyer saw these beds in 1895, and at 

 once recognized No. 3 as a union of the 10 and 1 1 of his Beer 

 Head section, 1 No. 4 as his bed 12, and the overlying beds as his 

 13 and 14. He is now, however, prepared to agree with our cor- 

 relation of these beds. 



Group M, the zone of Ammonites Mantelli, can be followed above 

 the landslips of the coast-line between Lyme Regis and Axmouth 

 running out near the top of Haven Hill, above the mouth of the Axe. 



West of Seaton the Greensand and Chalk are brought in again 

 by a fault and a syncline, an excellent section being exposed along 

 the face of Whitecliff. The details of this will be given in the 

 Survey Memoir, and it is only necessary to notice here that the 

 glauconitic chalk (No. 5) is absent, the hard nodular yellowish 

 chalk (No. 6) resting directly on the zone of A. Mantelli. The 

 latter, moreover, forms one massive bed from 2 to 3 feet thick, 

 though careful examination shows that beds 3 and 4 enter into its 

 composition. 



The Upper Greensand is about 160 feet thick, including a sandy 



1 Quart. Journ. Geol. Soc. vol. xxx. (1874) p. 369. 



