﻿1XXX PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I905, 



Kent to Antrim, we should find a belt of sediments marked by the 

 abundance of glauconite running obliquely to the planes which 

 define synchronous deposits. 



Turning to belts characterized by definite organisms in this 

 Same Cretaceous system, we recollect that it is maintained by 

 Mr. Jukes-Browne that the beds of the zone of Pecten asper in 

 France are of later date than those of the same zone in Britain ; 

 and Mr. Jukes-Browne, Mr. H. Woods, and Dr. W. I\ Hume have 

 shown the occurrence of a particular type of fauna at different 

 horizons in the Upper Cretaceous rocks of the British Isles. 



Many other examples might be given, but the foregoing are 

 sufficient for our purpose. 



In an ideal classification, therefore, of the sedi- 

 mentary rocks we require a triple nomenclature, in 

 order to subdivide the rocks according to lithological 

 characters, organic contents, and periods of formation. 

 It is true that, in some cases, the groupings based on each of these 

 will be identical, but in others they will differ. The agreement, or 

 want of agreement, of the groupings can only be determined as the 

 result of detailed work. 



The necessity for this triple classification has long been tacitly 

 recognized, and has indeed been largely carried out in the case of 

 the Mesozoic rocks, but no definite scheme of nomenclature has 

 been adopted for the whole of the sedimentary rocks, although it is 

 clearly required. 



Such a scheme, to be acceptable, must not necessitate a violent 

 change from the nomenclature at present in use. It is my wish 

 to point out that the scheme which has been practically adopted in 

 the case of the Mesozoic rocks is generally applicable to rocks of 

 other ages, and does not demand any marked departure from the 

 existing nomenclature. 



The lithological names proposed by William Smith were, at one 

 time, largely used as chronological names also ; but, as the result of 

 fuller work, they have been almost entirely superseded for the latter 

 purpose by other expressions, which are, it is true, in many cases 

 modifications of the original word : for instance, we speak of a 

 particular lithological group as the Kimmeridge Clay, but the rocks 

 of the age of the Kimmeridge Clay are known as Kimmeridgian. 

 I would suggest that the names adopted in a scheme of classification 

 of strata divided according to their ages should always 

 end in ' ian,' the termination adopted in the case of the time- 

 subdivisions of the Mesozoic rocks. 





