462 DIVISIONS OP SO-CALLED 'JURASSIC ' TIME. [Aug. 1898^ 



VII. Summary. 



This paper contains the following : — 



(1) An argument that chronological divisions in geology should 

 depend on faunal features. 



(2) The proposition that 'Jurassic ' chronology should be governed 

 by the phenomena of ammonite-development. 



(3) The opinion that the ' Jurassic ' Period should be divided 

 into two epochs, xirietidan and Stepheoceratidan, and that the first 

 should commence with the Asteroceratan Age and end with the 

 Ludwigian. 



(4) A hemeral time-table whereby species may be dated. 



(5) A genealogy of some ' Jurassic ' ammonites to illustrate the 

 chronological remarks. 



(6) j^otes on certain generic names and the proposal of some 

 new generic titles. 



(7) A list of the genera to which reference has been made, 

 arranged under families. 



Discussion. 



Mr. H. B. Woodward remarked that most geologists would agree 

 that two sets of divisional names were needful : one to indicate 

 chronology, and the other to indicate the stratigraphical formations. 

 Stratigraphical names could not be interfered with by Mr. Buckman's 

 paper. He need only refer to Prof. Lapworth's detailed work in 

 the Southern Uplands to show how important were stratigraphical 

 names ; and he had no doubt that they would last for ever. The 

 changes of grouping proposed by the Author were such as should 

 be considered over a wide area. A worker paying special attention 

 to BeJemnites would probably arrive at very difi*erent conclusions. 

 Moreover, the diagram exhibited by the Author showed no special 

 reason for making chronological divisions at any one stage more 

 than another. He felt strongly that the paper was one that should 

 have been submitted to the International Geological Congress, 

 rather than to the Geological Society. 



Prof. Seeley regarded the Author's labours in endeavouring 

 to trace the phylogeny and affinities of ammonites as a valuable 

 contribution to palseontology. The attempt to classify the Lower 

 Secondary strata by this evidence might be less important than the 

 diagrammatic demonstration of the periods of time during which 

 characters of external form and internal structure were distributed 

 in the ammonite-tribe. It was usual to find that species appeared 

 prior to the physical changes which brought in the rocks which 

 those species distinguished by their abundance. He trusted that 

 the Author would maintain the familiar nomenclature of the 

 Oolites as the basis for his stratigraphical language, since the paper 

 appeared to be an attempt to trace the influence of stratigraphical 

 conditions on the distribution of palseontological characters in an 

 important group of fossils. 



The President also spoke. . 



