THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE II. VOL. IX. 



No. IV.— APRIL, 1882. 



OiaiG-IIT-A.Ij .A.iaTIOIl.ES. 



I. — Contributions to the Paleontology op the Yorkshire 



Oolites. 

 By Wilfrid H. Hudleston, M.A., F.G.S., Pres.G.A. 



No. 2. Gasteropoda of the Oxfordian and Lower Oolites. 



IT was stated in the general introduction to these Contributions 

 (Geol. Mag. June, 1880), that the divisions to be adopted would 

 be regarded more as a matter of convenience than from any other 

 point of view. It might, perhaps, seem more philosophical to have 

 treated the whole of the Lower and Middle Oolites as one section of 

 the subject qua the Gasteropoda. By commencing at the base of the 

 series the true sequence in time would have been followed, and the 

 various " species " or their derivatives traced throughout. Had all 

 the collections examined by me existed under one roof, this might 

 have been practicable, as it would certainly have been desirable. 



Again, it may seem somewhat odd, when drawing the line, to 

 draw it through the very middle of the perarmatus-zone ; but the 

 fact is that from the Corallian to the very base of the Dogger no 

 one line stands out very pre-eminent in a palgeontological sense. 

 Nor is there any very mai'ked physical break other than what might 

 result from a change of sediment between the top of the Cornbrash 

 at Scarborough and the base of the Corallian Limestones (Passage- 

 Beds). The palfeontological break between the Cornbrash and the 

 succeeding " Kelloway Rock," as regards Cephalopoda, is tolerably 

 complete (see table), but not otherwise. There is a more marked 

 discordance between the general fauna of the Cornbrash and of the 

 Scarborough Limestone, which latter is in many respects allied with 

 the two lowest zones. 



On the whole, therefore, although the division adopted parts the 

 Coral-bearing section of the zone of A. perarmatus from the rest, 

 and thus adds a slice of quasi-Oxfordian Beds to the Corallian 

 group, yet the additional species of Gasteropoda scored to the latter 

 is so slight as scarcely to affect the lists. Even without such aid the 

 Coralline Oolite and Coral Rag, i.e. the Upper Limestones of the 

 Survey, afford a list of Gasteropoda not very far shoi't of that pro- 

 duced by the aggregate of the beds below, whilst in numbers of 

 individuals they infinitely exceed them. -This arises in a great 

 measure from the very limited vertical sections in the lower beds 

 which yield Gasteropoda in recognizable condition. 



One point of interest presented by the fine sections on the coast 

 is the approximate position of the division between the Brown Jura 



DECADE II. — VOL. IX, — NO. IV. 10 



