326 JUEASsic CHRONOLoar: JjIah. [vol. Ixxiii^ 



Author appeared to disregard the alternative possibility : namely^ 

 that, in certain cases, ammonites may have had very restricted 

 horizontal ranges. It is not enough to point to ammonites as being 

 strongl3''-swimming organisms. So are fishes : yet many marine 

 fishes are strictly limited in their horizontal distribution. The 

 details of the temperature and currents along the Liassic shore-line 

 were not known sufficientl}^ for us to decide how far the ammonites 

 of any one locality would be restricted ; nor did our knowledge of 

 their bionomics enable us to sa^^ whether these or other factors 

 might have limited their distribution. 



It is extremely improbable that the Oxj^cones in the Oxynotus- 

 Bed of the Dorset Coast are derived, since, with the pyritized speci- 

 mens are found others, manifestly un-derived, consisting as they do 

 of fi.lms on the clay. 



(2) Concerning the nomenclature of stages and of zones, two 

 opposing principles are followed by different authors. According 

 to the one, the name of a stage or zone is taken, and its boundaries 

 altered, if desired. According to the other, the original con- 

 notation of the term is retained, and, if new divisions ' are 

 needed, the original stages are subdivided. Thus, Bonarelli sub- 

 divided the Charmouthian into Domerian and a lower, unnamed 

 division, which was subsecjuently termed ' Carixian ' ; but the Author 

 had meanwhile restricted the term ' Charmouthian ' to this lower 

 division, which he now subdivides. Nor was this all, for most of 

 his Kaasayan is pai't of the' Sinemurian. Therefore, it would be 

 necessary to saj^ Charmouthian of Mayer-Eymar, Charmouthian of 

 Buckman, and so on. Similarly, Wright instituted a zone of 

 A. furneri, but this is by no means the zone of A. turneri of the 

 paper now under discussion ; and instances might be multiplied. 



It would be advantageous if an agreement were to be arrived at 

 among geologists as to which principle should be adopted. The 

 speaker strongl}^ advocated the latter principle, and added that its 

 application should not reach back to old and well-established terms. 



Dr. A. M. Daties said that, for nearly thirty j'ears, the Author 

 had been developing ideas on the Jurassic Period in a series of 

 papers in the Society's Journal. Starting with the Inferior Oolite, 

 in which non-sequences could be demonstrated by stratigraphical 

 as well as palseontological evidence, he was now extending this prin- 

 ciple in the investigation of strata where only the latter was usually 

 available. While the conditions of deposition of the West Euro- 

 pean Jurassic were such as to favour local alternations of erosion 

 and deposition, it was possible that some inconsistencies of fauna! 

 sequence might be explained in another way — by alternate contrac- 

 tion and expansion of the geographical range of a genus. Even if 

 the Author's explanation should not be confirmed in eveiy case, the 

 Society ought to be grateful to hhii for bringing so many new facts 

 and suggestions before them ; and also, incidentall}", for having 

 induced Mr. Tutcher to present them with some of the results of 

 his long and careful work in the Bristol area. 



