198 R. B. Newton — Cretaceous Zones in Dorset. 



II. — On thk Identification of the Acanthoceras mammillatum 



AND HOPLITES INTERRUPTUS ZONES AT OkEFORD FlTZPAINE, 



Dorsetshire. 



By R. Bullen Newton, F.G.S. 



SOME raolluscan and other remains obtained by Miss Forbes and 

 Miss Lowndes from a brick -pit exposure at Okeford Fitzpaine, 

 near Sbillingstone station, Dorsetshire, have recently been submitted 

 to me for determination. They comprise two series of specimens 

 indicative of the well-known Cretaceous zones of Acanthoceras 

 mammilla turn and Hoplites interruptus. Those from the former or 

 earlier horizon were collected about nine years ago, whereas the 

 others were obtained within the last few weeks. It will be con- 

 venient to name the species identified from the Acanthoceras 

 mammillatum zone first, then to describe the beds constituting the 

 whole of the section, and lastly to give a list of the fauna from the 

 Hoplites interruptus zone. 



(A) The Acanthoceras mammillatum Zone. 



Acanthoceras mammillatum, 1 Schlotheim, sp. 

 Hoplites Benettianus, J. de C. Sowerby, sp. 

 Pleuromya plicata, J. de C Sowerby, sp. 

 Cucullcea carinata, J. Sowerby, sp. 

 Ostrea Leymeriei (Deshayes MS.), Leymerie. 

 Exogyra sinuata, 2 J. Sowerby. 



The matrix surrounding these shells is mostly of an argillaceous 

 sandy character, slightly micaceous, and of a brown, grey, or 

 yellowish colour. That associated more particularly with the 

 specimens of Ostrea and Exogyra exhibits an oolitic structure, the 

 grains of which are heavily charged with hydrated oxide of iron. 

 This fossiliferous bed, containing also some small siliceous pebbles, 

 has a thickness of five feet, and lies about twenty -eight feet from the 

 surface ; beneath is a deposit of pure sand, having a depth of three 

 feet, which reposes on a stiff blue claj r of, probably, Kimeridge age ; 

 at the base of this occurs a sandy rock-formation which possibly 

 belongs to the Corallian period. Immediately above the deposit 

 containing the shells is a seam of brown sandy rock, four feet in 

 depth, .succeeded by fifteen feet of a grey-coloured sandy clay (of 

 a bluish tint when damp), with phosphatic nodules interspersed 

 (a section of one showing veins of calcite) ; both these bear a Lower 

 Gault fauna, characterized by Hoplites interruptus, etc. Then follow 

 two unfossiliferous bands — one of brown clay, five feet thick, the 

 other of yellow clay with angular fragments of chert, three feet 

 thick ; a foot of subsoil occurring above this completes the section. 



1 This name has heen incorrectly written mammillaris by many authors, though 

 its original rendering was [Ammonites J mammillatus. 



2 E. sinuata (synonymous with E aquva of Continental authors) is not to be con- 

 founded with E. Couloni, Defrance (—subsini/ata, Leymerie), the latter differing not 

 only in specific details, but characterizing a lower horizon, viz. the Hauterivien stage, 

 or the upper part of the A T eocomian strata. 



