Yol. 52.] IN YORKSHIRE AND LINCOLNSHIRE. 215 



■ divided), the lower being tenanted by Olcostephanns (Craspedites) 

 subditus and allies, and the upper by 0. (Pohjptychites) gravesiformis 

 and allies. These together form the 'serie Speetono-russe ' (p. 174), 

 which he shows to be equivalent to the Upper Portlandian (Purbeck 

 and Portland Stone) of the South of England, and he proposed to 

 designate these rocks the ' sous-etage Aquilonien ' (p. 192). He 

 then discusses exhaustively the correlation of this ' Aquilonian sub- 

 stage' throughout Europe, and shows that everywhere in Southern 

 as well as in Northern Europe the equivalents of this sub-stage 

 underlie the c etage Neocomien inferieur,' which upon various con- 

 siderations is declared the true base of the Lower Cretaceous system. 

 He further urges in favour of this grouping that it agrees best with 

 the older definitions and traditions of the science, and concludes his 

 argument thus : — ' Si nous replacons l'ancienne limite entre les 

 deux systemes nous nous privons d'une limite tres nette, paleonto- 

 logiquement tres bien definie, et qui, grace a la transgression 

 remarquable de la faune meridionale vers le Nord, peut-etre 

 observee dans une vaste region, circonstance qui nous fait considerer 

 cette limite comme tres heureusement choisie par les coryphees de 

 la science et comme tres precieuse au point de vue de la strati- 

 graphie comparee. Cette limite a ete tracee par la nature meme 

 • comme une limite ay ant fixe l'epoque d'un evenement geologique 

 remarquable, savoir la disparition d'une partie considerable du con- 

 tinent portlandien et le commencement de la migration de la faune 

 meridionale vers le Nord, et reciproquement peut-etre.' (' Argiles 

 de Speeton,' sep. cop. p. 199.) 



But to establish this classification it became necessary to carry 

 down into the Jurassic system not only the whole of the Berriasien 

 of South-eastern France, but also the so-called Wealden and the 

 Hils Conglomerate of North-western Germany, and in doing this 

 Pavlow is at variance with the opinions of several geologists of the 

 Continent, so that the subject must be considered as still under 

 discussion. Indeed, in a later paper, ' On the Mesozoic Hocks of 

 the province of Hiasan, Russia' (Moscow, 1894), 1 if I rightly 

 understand the brief final resume in French, Prof. Pavlow seems 

 inclined to grant that recent discoveries have shown that the 

 ' Petchorian sub-stage,' capping the 'Aquilonian,' with Ohostephanus 

 stenomplialus in the lower part and Polyptychites KeyserJingi in the 

 upper portion, may in that region correspond to the Lower Neocomian 

 of Central Europe. In his forthcoming notes on the subject Prof. 

 Pavlow will no doubt discuss this new evidence, and show its exact 

 bearing on the question at issue. 



So far as the classification of the English strata is concerned, it 

 must, I think, be admitted that the limit of the Lower Cretaceous 

 and Jurassic systems is more or less arbitrary and conventional, 

 often without reality in the field, and is therefore to be treated on 

 a basis of general convenience and historical priority. 2 And this 



1 Scient. Mem. (TJtcheniya Zapiski) Imp. Univers. Moscow, vol. xi. p. 1. 



2 See H. B. Woodward, Geol. Surv. Mem. ' Jurassic Rocks of Britain/ vol. v. 

 p. 3. 



