148 W. H. S'udkston — On tJie Yorkshire Oolites. 



and White Jura of the Germans, or between what the Swiss geolo- 

 gists might term tlie " Dogger " and the " Malm." This line would 

 probably run somewhere in the great unfossiliferous masses of the 

 tipper part of the " Oxford Clay." For further remarks on this 

 subject, with reference to stratigraphical details and other matters, I 

 must refer to the " Yorkshire Oolites." ' 



The distribution of the several zones which contain the Gastero- 

 poda are more or less known to most geologists ; yet I am persuaded 

 to say a few words on this subject, partly to explain the accompany- 

 ing table, and partly because, in spite of what has been written on 

 the Geology of East Yorkshire, one is every now and then reminded 

 that the mistakes of half a century ago possess a strange fascination 

 for those who have but a cursory acquaintance with the district. 



Although the beds below the Corallian probably exceed in the 

 aggregate 1000 feet in thickness (taken at their maxima), yet the 

 shelly horizons occupy but a limited space, and those which contain 

 Gasteropoda in decent condition and quantity are still more limited. 

 Adopting the coast sections in the main as our types, there ai'e seven 

 principal fossiliferous zones or horizons between the striatulus-heds 

 — zone of Ammonites Jurensis — and the Corallian Eocks, whose 

 Gasteropoda have been already described, (See Table on pp. 146-147.) 



1. First or lowest zone. This is known as the Dogger. Including 

 the grey sands (Lingula-heds), the yellow sands, and the Dogger 

 proper, a thickness of 80 feet may be assigned to the group, where 

 most fully developed, as at Peak (Blue Wyke).^ The remains of 

 Gasteropoda are almost wholly confined to a shell-bed 18 inches 

 thick, which occurs about 8 feet below the top of the series at Peak, 

 but nowhere else in Yorkshire. The matrix is very characteristic. 

 The substance of the shells has been largely replaced by spathic iron, 

 whilst their exterior is lined with a thin skin of dark brown oxide. 

 From the abundance of Nerincea cingenda this band has been named 

 the Nei-ingea-hed. It contains nearly half the species enumerated in 

 this Memoir (No. 2). Some 300 feet of "estuarine" sands and 

 shales, with at best only irregular traces of marine shells, succeeds, 

 and then we arrive at 



2. The second zone, known as the Millepore-Bed, which is best 

 seen on the north horn of Cloughton Wyke at Sycarham, where the 

 thickness may be about 12 feet. This is also a kind of sandy iron- 

 stone, but more gritty and calcareous than the Dogger. The Gas- 

 teropoda are mostly limited to one bed, whilst Conchifera are 

 abundant throughout. Some portions of the matrix contain more 

 carbonate of iron than of lime, and there is just sufficient iron 

 peroxidized to impart a reddish-brown tint to the mass, which is 

 much flecked by a white substance allied to Kaolin. This peculiarity 

 is less noticeable in the bed where the univalves are mostly found. 

 The Millepore-Bed is well developed south of Scarborough, where it 

 becomes thicker. It forms an important scar in Gristhorpe Bay. 

 In the interior the fawn-coloured sandy limestones of the Howardian 



1 Proc. Geol. Assoc, vols. iii. and iv. ; see also Fox Strangways, Siu'vey Mem. 

 Geol. of Scarborough ; and "Wright, Quart. Journ. Geol. Soc. vol. xvi. p. 1 et seq. 



2 Cf. "Yorkshire Oolites," part i. Proc. Geol. Assoc, vol. iii. p. 294. 



