Arkell.1956.Jurassic..

THE BRITISH ISLES 2$
and that of the Upper Callovian there is a conspicuous change of the
ammonite fauna. In particular, no Kosmoceras crosses the boundary.
UPPER CALLOVIAN (Middle Oxford Clay, Hackness Rock)
Zone of Quenstedtoceras lamberti (Sowerby). Where best known, at
Tidmoor Point, Dorset, the clays contain great numbers of pyritized
ammonites of at least forty species (Arkell, 1947, p. 31). Among the
commonest are Quenstedtoceras (Lamberticeras) lamberti (Sow.), Q. (Q.)
leachi (Sow.), Q. (Eboraciceras) ordinarium (Leckenby), Distichoceras
bicostatum (Stahl), Kosmoceras (K.) spinosum (Sow.), Hecticoceras (Putealiceras)
puteale (Leckenby), H. (P.) punctatum (Stahl), H. (P.) pseudopunctatum
(Lahusen), but Peltoceras athleta (Phillips) also occurs, with
several other Peltoceratidae. The same fauna occurs in Oxford Clay
at Oxford (New Bodleian Library, Arkell, 1938), but at Woodham
brick-pit it is condensed in a band of argillaceous limestone or mudstone,
1 foot thick, packed with ammonites. On the Yorkshire coast the fauna
occurs in the Hackness Rock, and in east Scotland some elements are
found in the Fascally Sandstone of Brora. The Lamberti Zone could be
classed as a subzone of the Athleta Zone.
Zone of Peltoceras athleta (Phillips). In the south of England the
Quenstedtoceras assemblage is confined to the top of the Upper Callovian,
and although Peltoceras athleta and its allies range up into the same beds
they are more characteristic of some 12 m. of clays below the range of
Quenstedtoceras. In these lower beds the characteristic Kosmoceratids
are K. proniae Teisseyre and its allies, but K. spinosum occurs also, as
do some of the Hecticoceratids and other ammonites. From the Athleta
beds in Dorset come Pseudopeltoceras chauvinianum (d'Orb.) and Reineckeia
(Reineckeites) stuebeli Steinmann, R. (Kellawaysites) multicostata
Petitclerc; but some giant Reineckeids of the genus Collotia occur in
the Lamberti Zone at Woodham and also in the Athleta Zone of Dorset
and Oxford. In Yorkshire the two zones or subzones are represented
in the condensed Hackness Rock. In Scotland the Athleta Zone is
represented by the Fascally Shale.
MIDDLE CALLOVIAN
Zone of Erymnoceras coronatum (d'Orb.). To this zone belongs the
bulk of the Lower Oxford Clay, the bituminous shales used in the modern
brick-making techniques at Peterborough, Bletchley, and Stewartby,
where there are many huge sections. The shales are crowded with
crushed shells of Kosmoceras spp., chiefly K. castor and K. pollux with
(especially in the lower part) K. stutchburii and K. obductum. Erymnoceras
spp. are usually scarcer, but are sometimes preserved uncrushed in
septaria: many such have been obtained at Chickerell near Weymouth.
The zone is present in the same facies in Yorkshire (inland, at Peckondale
Hill, not on the coast), and in Scotland, where it is worked as the Brora
brick clays and shales. Callomon (1955) recognizes an upper subzone
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