J. F. BLAKE ON THE KIMMERIDGE CLAY OF ENGLAND. 197 



The names Astartian and Pterocerian seem to be without substan- 

 tial objection ; but the upper portion has had no corresponding name 

 generally assigned to it. In the Kimmeridge Clay, however, though 

 the various portions are well separated by their general assemblage 

 of fossils, yet many fossils which in one locality are highly cha- 

 racteristic of a particular portion, are absent in that portion in another 

 locality, and characterize instead a higher or a lower zone. Thus 

 Exogyra virgula in the Jura bernois and elsewhere is characteristic 

 of the upper portion ; at the Cap de la Heve it occurs throughout ; 

 and in England it is wanting only in the upper part, or sometimes, as 

 in Lincolnshire, appears to be absent entirely. So, again, RhyncJio- 

 nella inconstans, which is the characteristic species of the lowest beds 

 in England, in the environs of Montbeliard * is found in all but the 

 lowest, and most frequently at the top, and has not been met with 

 in the Subwealden boring. On account of this peculiarity of the distri- 

 bution of Kimmeridgian fossils, it is better to use the more general 

 terms — lower, middle, and upper. 



I am not, however, attempting in this paper to correlate our Eng- 

 lish Kimmeridge Clay with the many subdivisions of that formation 

 adopted by foreign authors, but rather to show into what palseonto- 

 logical and lithological subdivisions it may naturally be separated by 

 a study of its features in the field. 



I hope to be able to show that there are only two series of beds 

 sufficiently distinct to justify their separation under different titles, 

 the upper of which agrees with that of Dr. Waagen, but the lower 

 includes his middle region and part of his lower, while the re- 

 maining part of his lower region, and possibly part of his zone of 

 Cidarisflorigemma, constitute a series of beds which from their con^ 

 taining as much of a Corallian as of a Kimmeridgian fauna, I desig- 

 nate as the Kimmeridge passage-beds. 



The different divisions I now proceed to describe. 



Uppee Kimmeridge. 



The Upper Kimmeridge Clay (Virgulien of foreign authors) is 

 distinguishable both lithologically and palseontologically from the zones 

 below. It is here exclusively that the bituminous shales, paper- 

 shales and cement-stones occur, except in the Subwealden boring, 

 where they occur throughout. They contain a comparative paucity 

 of species, but an infinity of individuals. In the thin paper- shales 

 each leaf is covered with the white compressed shells of an Ammo- 

 nite, Distinct latissima, and Lucina minuscula ; and there cannot be 

 less than 20 leaves to an inch. This is more especially seen in Lin- 

 colnshire, as at Pulletby ; for in Dorsetshire the fossils are more often 

 comminuted, though the layers are thinner. Whatever length of 

 time we may assign to the deposition of each layer, with its separate 

 shells, the whole mass, when traced along the shore, cannot fail to 

 give an extended idea of the total amount of time involved in its 

 formation. 



These laminated and bituminous clays are more limited in extent 

 * Contejean, 'Etude de l'etage Kimme>idien,' 1859. 



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