196 J. P. BLAKE ON THE KIMMEKIDGE CLAY OF ENGLAND. 



14. On the Kjmmekidge Clay of England. By the Bev. J. F. Blake, 



M.A., F.G.S. (Bead January 13, ] 875.) 



[Plate XII.] 



The boring of the Subwealden Exploration has brought into promi- 

 nence the antiquity of our information concerning the Kimmeridge 

 Clay of England, both as to its subdivisions and as to its thickness. 

 The only recent work done upon it is that of a foreigner, Dr. Waagen, 

 who, studying it on the southern coast at Bingstead Bay and at Wey- 

 mouth, proposed a new classification, which has been followed by 

 Mr. Judd in his valuable paper on the Speeton clay. "With this 

 exception we have to go back to the days of Conybeare and Buck- 

 land for information on the subject; and it has been impossible for 

 foreign authors to correlate satisfactorily their Kimmeridgian beds 

 with ours. Dr. Waagen's paper is brief and incomplete ; and there 

 thus seemed room for useful observation on this subject. Both the 

 above-named authors, as well as Professor Phillips and Mr. Damon, 

 have made additions to our list of fossils ; but the two latter have 

 only indicated local subdivisions in the beds. 



On the Continent, though much diversity exists in the arrange- 

 ment of these beds (each separate locality having palseontological 

 features which, to a certain extent, render unavailable the classifi- 

 cation founded on others), the general result is their separation into 

 threezones — the lowest thatofAstarte swpracorallina, ortheAstartian, 

 and the middle that of Pterocera Oceani, or the Pterocerian. On thes« 

 two there is considerable uniformity of opinion ; while the upper, more 

 or less developed in various localities, is either included in the zone 

 of Trigonia gibbosa, or the Portland strata, or separated as the zone 

 of Exogyra virgula, or the Yirgulian. Oppel, in his ' Juraformation,' 

 p. 727, while correlating the English Kimmeridge Clay in general 

 with the zone of Pterocera Oceani, states that he recognizes some of 

 the beds at the base as belonging to the Astartian zone, but without 

 further particularizing them. He, however, recognized no horizon 

 in the Kimmeridge Clay above that of Pterocera Oceani, but called 

 his next zone that of Trigonia gibbosa. 



Waagen to a certain extent follows this classification, assigning 

 500 feet, or the main mass, to the middle region, to which he 

 assigns a new name, that of the Zone of Ammonites mutabilis and 

 Exogyra virgula. He marks off in the section at Sandsfoot Castle, 

 near Weymouth, certain beds as Astartian, or, as he calls it, the 

 Begion of Ammonites alternans and JRhynchonella inconstans, and 

 makes the advance of separating the upper portion as a distinct 

 zone. He seems to regard this as higher than the Yirgulian or equi- 

 valent beds, and as characterized by the absence of Eocogyra virgula. 

 This classification, from its adoption by Mr. Judd, may be considered 

 that at present accepted. Detailed observations in Lincolnshire 

 and on the coast of Dorset have suggested to me some necessary 

 alterations. 



