vol. 69.] upper jprassic strata of england. 431' 



Discussion. 



Dr. A. Mokley Davies said that all who were working at the 

 Upper Jurassic rocks would welcome this contribution to the 

 difficult subject of their zonal correlation. His first comment, on. 

 the zonal table exhibited was that it proved more clearly than 

 before that the term ' Oxfordian ' would have to be abolished. 

 While several of the zones on the Authors list could at once be 

 recognized, others had unfamiliar names, and among these he failed 

 to identify such well-marked faunal horizons as those of Amcebo- 

 ceras (alternans zone) and Physodoceras (orthocera zone). The 

 paper would, however, doubtless remove these difficulties, and 

 explain why other index-fossils had been chosen. 



Dr. F. L. Kitchin expressed satisfaction that he had given 

 encouragement to the Author to lay before the Society the first 

 fruits of his work in England. He considered that the paper made 

 a great advance in our knowledge of the strata with which it deals: 

 previous accounts of these rocks became thereby desirably supple- 

 mented by a detailed investigation, conducted from the purely zonal 

 standpoint. The speaker regarded the Author as especially qualified 

 to undertake this work, equipped as he was with sound palaeonto- 

 logical knowledge and wide experience of typical Continental 

 sections. He believed that the Author had conducted his field- 

 observations with exemplary care, and that his results might, 

 therefore, be accepted as substantially accurate, providing a sound 

 basis for future work. It gave him pleasure to report that the 

 Author hoped to return to this country next year, in order to con- 

 tinue these researches. Thanks were due to Mr. Buckinan for 

 bringing before the meeting this first valuable contribution. 



Mr. G. W. Lampmjgh said that the sequence of ammonite-zones 

 demonstrated by the Author could not fail to prove of service to 

 students of the British Upper Jurassic rocks. The succession and 

 correlation seemed to be firmly based, and, so long as this was the 

 case, the method adopted for grouping the zones into formations 

 was of secondary consequence. The Author had followed the usual 

 Continental grouping, which was not convenient for stratigraphical 

 purposes in this country, where the use of Kimmeridge Clay as 

 a descriptive lithological term could hardly be displaced. 



The Author's discovery of the true horizon of the inflated 

 gravesianus forms in the Kimmeridge section was of peculiar 

 interest, because of the difficulties which had arisen through the 

 original confusion of these forms with the Polyptychites of the 

 Speeton Clay. The speaker desired to know by what features the 

 species of this group are distinguishable when they are crushed flat. 

 He mentioned that he had recently found specimens of Aulaco- 

 steplianus in the Kimmeridge Clay of Filey Bay, at about the 

 horizon indicated in the Authors scheme. 



Mr. W. F. Gwinnell referred to the occurrence of ammonites in 

 some of the Upper Jurassic zones under consideration, in the 

 Northern Highlands of Scotland, on both the eastern and the 



