Arkell.1956.Jurassic..

BORDERS OF THE MASSIF CENTRAL 75
of Middle Callovian follow 40 m. of Lower Callovian marls and dolomitic
limestones with Macrocephalites (Tintant, 1942). In western Ardeche
the Macrocephalus Zone resumes the facies of Dalle nacree as in the
east of the Paris Basin (Tintant & others, 1946). At La Voulte there is
an alternation of marls and limestones with two distinct ammonite faunas.
The upper horizon, with Macrocephalites canizzaroi (non Gemmellaro ?—
identified by Sayn & Roman, 1928, p. 152, with M. canizzaroi Couffon,
which is holotype of Dolikephalites gracilis Spath, 1928) and other small
Macrocephalitids, also Proplanulites teisseyri Tornquist, Phlycticeras,
Kheraiceras, Bomburites, Oecoptychius and many other genera (Sayn &
Roman, 1928, pp. 36-7) correlates approximately with the Koenigi Zone.
The lower assemblage (ibid., p. 33) does not appear to be much older
and probably is not basal Callovian. The true Macrocephalus Zone is,
however, represented in the Maconnais by Upper Cornbrash with
numerous Macrocephalites and large Choffatia of the subbakeriae group
and Bullatimorphites cf. bullatus (Parent, 1942). From this came the
type of M. (Kamptokephalites) maconnensis Spath (1928, Cutch, p. 190;
in Lissajous, 1912, pi. vi, fig. 7) and M. macrocephalus (Lissajous, 1912,
pi. vi, fig. 9).
BATHONIAN (C. 90 m.)
With the Bathonian the centre of interest shifts north to the Maconnais,
the subject of one of the most important monographs on Bathonian
ammonites yet published (Lissajous, 1923, posthumous). The Upper
Cornbrash, just mentioned, is immediately underlain by Lower Cornbrash
with Clydoniceras discus and Choffatia subbakeriae, just as in England
and northern France (Parent, 1942). Below come about 40 m. of marly
limestones and marls with many brachiopods, including Dictyothyris
coarctata, Ornithella digona, Rhynchonella boueti, Eudesia cardium, and
at the base an ammonite bed 1-5-2-5 m. thick, crowded with Prohecticoceras
retrocostatum (de Gross.), Oecotraustes serrigerus Waag. et spp.,
Oppelia aspidoides (Oppel), Clydoniceras discus Sow. sp. (Lissajous, 1923,
pi. xxiv, 2), Delecticeras delectum Arkell (pi. xxiv, figs. 5-7), D. cf. ptychophorum
Neum. sp. (pi. xxiii, 6), Polyplectites richei Liss., P. denseplicatus
Liss., Bullatimorphites suevicus (Roem.), various Pseudoperisphinctes,
Siemiradzkia, Choffatia (pi. xiii, 1), etc., and Epistrenoceras histricoides
(Rollier). This, the Retrocostatum Zone of Lissajous, is part of the
Aspidoides Zone and its position is at or near the base of the Upper
Bathonian (cf. Caillasses de Fontaine-Henry and Blainville in Normandy,
p. 48). Under the ammonite bed and included in the Retrocostatum
Zone by Lissajous is 9-10 m. of hard limestone called Choin, with
problematic markings but few fossils.
The lower part of the Bathonian comprises 35-40 m. of limestones
and marls with a rich ammonite fauna of great interest. Lissajous (1923,
p. 21) considered it to embrace the whole Lower and Middle Bathonian,
from Zigzag Zone to Subcontractum Zone inclusive, and he called it the
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