2o6 Stather : Dr. Rome on the Yorkshire Chalk. 



The fact that there is an essential difference between the 

 character of the zones in the Yorkshire Chalk and the better 

 defined zones of some other fossiliferous beds, for example^ those 

 in the Yorkshire Lias, must impress itself on every worker who 

 has studied zonal divisions in other formations. The limits of 

 the ammonite zones of the Lias can in many cases be verified 

 without dif!iculty even by the tyro, but the longer one has worked 

 the Yorkshire Chalk the greater has one found the difficulty in 

 defining the upward or downward limit of any particular fossil ; 

 and these limits seem to depend so largely upon the accident of 

 collecting that the same observer, working at different times, 

 will find, in our experience, that his boundaries are constantly 

 shifting. Most of the fossils are sprinkled so sparingly through 

 the mass that any particular section may give a result differing 

 by many feet at least from another section. And the zones 

 therefore fade into each other imperceptibly like the colours of 

 the spectrum. This difference between the Chalk and the Lias 

 must imply some essential difference in the conditions of deposi- 

 tion, as the only sharp boundary known to the present writer 

 in the Yorkshire Chalk represents a hiatus which is strongl}^ 

 marked both stratigraphically and palseontographically, and is 

 indicated by the band of black shale at the base of the Middle 

 Chalk. But, as Dr. Rowe has dealt only with the Chalk, his 

 idea of a zone relates to Chalk zones alone, and this should be 

 remembered by Yorkshire readers of his paper. Indeed, the 

 opening sentence of his paper shows that to him the Chalk is 

 apparently the only rock worth recognising on the coast, for he 

 says : ' The Yorkshire coast . . . . has been one which has 

 been severely left alone by zonal geologists.' 



It must strike the reader of this paper that the names of 

 some of the zones as applied to Yorkshire are scarcely well 

 adapted for the purpose. For we find on comparing the lists of 

 fossils from the various beds, that among the fossils which are 

 used to distinguish the zones some are not confined to the zones 

 they represent, while others are exceedingly rare or entirely 

 absent from the beds. However, we are glad to note that to 

 meet this difficulty, Dr. Rowe has in two cases suggested local 

 zone names, and the cases where the southern zonal name is 

 allowed to stand are always accompanied by a clear statement 

 of the exceptional conditions of distribution. But, nevertheless, 

 it is our opinion that, unless a fossil name is forthcoming that 

 fairly well represents the limits of the zone, it would be better, for 

 the time being at any rate, to fall back upon a purely arbitrary 



Naturalist, 



