542 PROF. PAVLOW ON THE CLASSIFICATION OF THE [Aug. 1 896, 



32. On the Classification of the Strata betiveen the Kimeridg-ian 

 and Aptian. By Dr. Alexis P. Pavlow, For. Corr. G.S., 

 Professor of Geology in the University of Moscow. (Read 

 March 25th, 1896.) 



[Plate XXVII.] 



Contents. 



Page 



I. Schemes of Classification 542 



II. On the English and German Species of Aucella 549 



III. General Considerations 551 



I. Schemes of Classification. 



In the paper on the Speeton fauna, forming a part of the work 

 which I wrote in conjunction with Mr. G. W. Laniplugh, I attempted 

 to correlate the Upper Jurassic and the Lower Cretaceous horizons 

 of Speeton with their equivalents in Russia and in different parts 

 of Europe, and to give a general scheme of classification of these 

 beds. This scheme may be briefly stated as follows. 



The Kimeridgian zone of Hoplites pseudomutabilis and Aspido- 

 ceras acanthicum is common to different countries of Europe. Above 

 this zone in the Meridional province repose the marine beds of the 

 Tithonic stage, terminating the Jurassic. These beds comprise two 

 substages — the Lower Tithonic, which contains two fossil-zones ; 

 and the Upper Tithonic, also containing two zones. To this Tithonic 

 stage corresponds in Southern England the Portland stage sensu 

 lato, including the Lower marine series (Portland, sensu stricto, or 

 Bononian Series), and the Upper freshwater Portland or Purbeck. 

 In Northern France and partly in Southern England three fossil- 

 zones can be distinguished in the marine Portland, namely, the zone 

 of Ammonites portlandicus and Bleicheri, the zone of Virgati, and the 

 zone of A. giganteus. In Yorkshire the equivalents of this series 

 are condensed, and moreover the freshwater Purbeck is replaced by 

 marine beds with Belemnites lateralis, deposited in a separate boreal 

 marine basin. To designate these uppermost horizons of the 

 Jurassic in its marine development, I proposed the name ' Aquilonian' 

 stage or substage, including in this term the zone or zones of Ammo- 

 nites fragilis and nodiger and the zone of Polyptychites (Keyserlingi, 

 gravesiformis, etc.). The last-mentioned zone, being the uppermost 

 of the Tithonic stage, was described as being characterized by the 

 presence in its fauna of many Cretaceous elements. 



In Russia the equivalents of the marine Portland of France and 

 the Aquilonian stage are well represented and rich in cephalopoda — 

 those most trustworthy guides in the deductions of comparative 

 stratigraphy. To the zone of Polyptychites Keyserlingi, gravesi- 

 formis, etc., with its many Cretaceous fossils, the name of ' Petchorian ' 

 was applied, and in the general scheme this was placed at the top 



