Arkell.1956.Jurassic..

46 THE PARIS BASIN
UPPER OXFORDIAN (40-56 m.)
Zone of Ringsteadia anglica. From the 'Calcaires coquillers' at Cap
de la Heve there are in Le Havre Museum four species of Ringsteadia,
several in an ironshot mudstone exactly like that in which they are
commonest on the Dorset coast and at Westbury (Arkell, 1937, p. 55).
Below these beds at la Heve are sometimes seen up to 5 m. of clay with
Ostrea delta, devoid of recognizable ammonites; probably the Sandsfoot
Clay.
Zone of Decipia decipiens. The same clay is exposed on the south side
of the Seine estuary, the Argile (or-Marne) de Villerville (13-17 m.),
which is the highest bed clearly seen in the long line of Jurassic cliffs
on the south coast of the Baie de la Seine. Inland, near Lisieux, the
Argile de Villerville seems to pass laterally into the Sables de Glos
(35 m.), famous for their marvellously preserved gastropod and pelecypod
fauna, still retaining colour-banding (Bigot & Brasil, 1904; Bigot, 1950).
The only ammonites known are Prionodoceras glosensis and Decipia
tranchandi Bigot & Brasil sp. (1904, pi. iv); the former occurs in the
Dorset Red Beds, the latter in the later Calcaire du Mont des Boucards
in the Boulonnais (above, p. 42).
Zone of Perisphinctes cautisnigrae. Calcaire (or Gres) d'Hennequeville
(4-2 m.). Sandy limestones, partly silicified and cherty, some bands
packed with Trigonia clavellata (Sow.) and T. bronni Ag. Formerly in
Caen University Museum were specimens of Perisphinctes durnovariae
Arkell, P. boweni Arkell, and P. cf. variocostatus (Buckland) from these
beds, which accordingly correlate with the Red Beds of Dorset (Arkell,
1937, p. 53). At Trouville a thin coral rag develops on this horizon.
Probably of much the same age is a coral-and-Diceras reef at Belleme,
Orne (Dangeard, 1951a).
Zone of Perisphinctes plicatilis. Oolithe de Trouville (beds H 17-33)
(17-25 m.). The upper part consists of white and grey oolites and oolitic
marls resembling the Osmington Oolite; the lowest 4-8 m. is an ironshot
oolite marl like Elsworth Rock. The Dorset, Wiltshire and Cambridgeshire
facies of the Plicatilis Zone are here combined. The ammonite
fauna is almost identical with that of England, except that Cardioceratidae
are scarcer. The dominant species are large Perisphinctids such
as P. chloroolithicus, P. maximus, P. cotovui, P. plicatilis, P. antecedens,
with Euaspidoceras perarmatum, E. catena, E. crebricostis; also Cardioceras
excavatum and a solitary C. densiplicatum (Arkell, 1948, pp. 386-9).
Inland the oolites pass laterally into coral rag with coral reefs and Diceras
reefs up to 40 m. thick (Dangeard, 1950, pp. 143-4) inseparable from those
just mentioned.
LOWER OXFORDIAN (34 m.)
Zone of Cardioceras cordatum. Oolithe ferrugineuse (7-78 m.). Bands
in clay and ironshot marly limestone with abundant ammonites, especially
of the lowest 2-2 m. (bed Hi5). In this the dominant forms are
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