204 J. h\ BLAKE ON THE KIMMERIDOE CLAY OE ENGLAND. 



Portland rock. The number of those that pass upwards is no doubt 

 really greater where the two sets of beds are fully developed. 



It thus appears that the upper portion of the Kimmeridge Clay 

 can be satisfactorily marked off by lithological and palaeontological 

 characters into one connected series, and has therefore good claim 

 for recognition. The sequel will show how far it is distinct from the 

 beds below. 



Lower Kimmeridge. 



The lower series consists of thick beds of clay, offering little 

 lithological distinction, except in the neighbourhood of the Coral 

 Rag ; and if they are divided at all, it must be palseontologically. Dr. 

 Waagen does this, including in the Lower Kimmeridge some feet of 

 the clays at the base, and calling the rest Middle Kimmeridge ; and 

 Mr. Judd, in his paper on the Speeton Clay*, follows him for the 

 strata of Filey Bay, and indicates the Lincolnshire pits which he 

 considers to belong to either region. 



The only positive indication of the nature of the Middle Kimme- 

 ridge, which Dr. Waagen states at 500 ft. thick, and which therefore 

 ought to be the main mass and most often met with, is his list of 

 12 fossils, which, he says, are such as are commonly met with on the 

 Continent in the zone of Pterocera Oceani. Of these, however, 4 (viz. 

 Amm. mutabilis, Panopcea tellina, Opis suprajurensis, and Eocogyra 

 nana) he himself records from the lower beds also. Of the remainder, 

 Amm. Berry eri and Lucina Elsgaudim (substriata) occur in the lowest 

 beds at Weymouth ; the PTioladomyce (2) are so badly preserved in 

 the Kimmeridge Clay, as well as scarce, that it is impossible to 

 place much reliance on them. Cardium pseudoaxinus is quoted by 

 Thurmann from the lower zone also, and is certainly rare. Exogyra 

 virgula occurs throughout. 



There are left Bostellaria nodifera and mosensis, the latter of 

 which is certainly most common in the upper portion ; but they do 

 not appear to be universally characteristic of the zone of Pterocera 

 Oceani. 



There is therefore nothing special about this collection of fossils 

 which would justify the separation of the beds from those below ; 

 in fact, the different species are so united by occurring together in 

 various localities, that two different faunas cannot be made out ; and 

 though minor zones may be recognized, as in the Upper Kimmeridge, 

 they are often very local. 



Judging, as we must do, for the general correlation of the beds, by 

 the general assemblage of the fossils, it appears to me that the Middle 

 Kimmeridge (that is, a series of beds containing a special Middle 

 fauna, as exhibited elsewhere) is absent from England, although, the 

 deposition of the beds having been continuous, some of them must 

 be undoubtedly contemporaneous with the Middle period. The 

 special fauna is that which abounds in Gasteropods of the genera 

 Pterocera, Nerinwa, Natica, and Chemnitzia, together with many 

 varieties of Panopcea and Pholadomya, and in some cases various 

 * Quart. Journ. Geol. Soo. vol. xxiv. p. 240. 



