552 PPvOE. PA.VLOW ON THE CLASSIFICATION OF THE [Aug. 1 896, 



seems to have taken place at this time, during which the Virgatites- 

 beds were destroyed so as to leave only a band of phosphatic 

 nodules, with fragments of Virgatites and Belemnites. 



At the end of the Jurassic period in the region of Southern 

 England, Northern (and Central) France, and Northern Germany 

 well-marked 'geocratic' movement took place, and, as the result 

 of this, the Purbeck continent arose and separated the northern 

 (Aquilonian) from the southern (Tithonic) Sea. This event, how- 

 ever, did not occur simultaneously throughout this large region; 

 the German part of it seems to have- emerged earlier than 

 the rest, probably at the beginning of the virgatus-age. Some 

 parts of Russia (the southern part of the government of Nijni- 

 Novgorod and the northern part of the government of Simbirsk) 

 likewise emerged approximately at the same time, and remained 

 dry land until the epoch of the Lower and (in some places) of the 

 Upper Neocomian ; but no freshwater beds were deposited there. 

 In other parts of Russia the sea did not disappear until later (at 

 the catenulatus-nodiger age), and reappeared in Upper Neocomian 

 time (Simbirsk). 



In the district of Syzran there is a region where the Aquilonian 

 beds seem to pass, without any noticeable break, into the Lower 

 Neocomian (Petchorian), the beginning of which is marked by the 

 appearance of new ammonites of the stenomphalus-growp. Last 

 of all there is a region in Russia where the first traces of the 

 submergence of the Purbeck continent at the end of Aquilonian 

 time (in some localities, it would seem, at a somewhat earlier time) 

 can be observed, and this event is marked by the sudden appearance 

 of ammonites of the Hoplites riasanensis-gYOU^ amidst the typical 

 Aquilonian fauna in the governments of Riasan and of Moscow. 

 But that was only a short and local episode in the life of this fauna, 

 and soon afterwards a boreal Lower Neocomian fauna with ammo- 

 nites of the stenomphalus-growp (Aucella volgensis, A. Keyserlingi, 

 Belemnites subquadratus, etc.) coming from the east and north-east 

 took possession of the Riasan region. 



At the same time — that is, a little later than in Central Russia — 

 the Lower Neocomian boreal sea stretched over Germany, where 

 it accumulated the lowermost beds of the Neocomian with Ammo- 

 nites Gevrilianus and A. Marcousanus and penetrated to Central 

 England (depositing the beds with Aucella volgensis, A. Keyserlingi, 

 Ammonites stenomphalus). This seems to be the first zone laid 

 down after the partial disappearance of the Purbeck continent 

 of Western Europe. The next zone of the boreal Neocomian, that 

 of Polyptychites Keyserlingi, gravesiformis, Beani, etc., possesses 

 a, very wide extension — from Yorkshire and Lincolnshire, through 

 Germany and Central Russia, far into the North-east. In Central 

 Russia this zone bears a very well-marked littoral character, being 

 represented by sands and conglomerates, and being in some places 

 absent. During the deposition of this zone, but apparently not until 

 towards the end of it, and therefore much later than in Central 

 Russia, we find in England, and probably in Germany also, the 



