Arkell.1956.Jurassic..

54 THE PARIS BASIN
CALLOVIAN (up to 60 m.)
The Callovian is especially celebrated for its wealth of well-preserved
ammonites and appears to be complete with all its zones. The ammonites
and their stratigraphy, especially those from the famous locality Montreuil-
Bellay (30 miles SE. of Angers) have been the subject of studies by
Hebert & Deslongchamps (i860), de Grossouvre (1891), Couffon (1917-19,
1934), Petitclerc (1915, 1918, 1921, 1924) and Gerard & Contaut (1936).
These works provide a wealth of excellent figures. The stratigraphy
is also well summarized by Glangeaud (1895), Welsch (1903) and Couffon
& Dolfuss (1928).
The Lower Callovian contains Bullatimorphites spp. as well as all the
usual genera, but it is doubtful whether the true Macrocephalus Zone
is represented, despite many records of this species and M. herveyi ;
if the index species does occur it seems to be associated with Kepplerites,
Reineckeia, etc., of the Koenigi and later zones. The age of the celebrated
ironstone fauna of the Chalet quarry, Montreuil-Bellay, is substantially
Middle Callovian, with late-Lower Callovian, as can be seen from Couffon's
splendid plates. The Upper Callovian contains a remarkable fauna of
the Athleta Zone (monographed by Gerard & Contaut, 1936) and locally
admits of the separation of a distinct Lamberti Zone (de Grossouvre,
1891, p. 252).
BATHONIAN (about 12 m.)
Typically, the Bathonian consists of 8-10 m. of poorly-fossiliferous
cherty limestones with thin ammonite beds above and below. At the
top is a variable series of limestones with Oxycerites aspidoides, Bullatimorphites
bullatus, etc., assigned to the Aspidoides Zone (Welsch, 1903,
pp. 841, 974, 994). At the base is a well-marked horizon (o^-i^ m.)
with a rich fauna of the Zigzag Zone, yielding all the characteristic
ammonites, such as Zigzagiceras in great variety, Morphoceras, Ebrayiceras,
Procerites schloenbachi and other spp., Parkinsonia spp., and
Oxycerites spp. (Welsch, 1894). At Lucon, Vendee, are limestones
with Cadomites which de Grossouvre (1930, p. 363) regarded as Middle
Bathonian. Although the Bathonian along the western border of the
Massif Central is often called brackish, the fauna is overwhelmingly
normal marine (Glangeaud, 1895, p. 168).
BAJOCIAN (up to 50 m.)
The Bajocian, though often thin, seems to be zonally complete. All
the zones from Opalinum to Parkinsoni have been recognized and
distinguished by their ammonite faunas (Glangeaud, 1895, 1896; Welsch,
1903, pp. 828, 986; 1928a; Couffon & Dolfuss, 1928, p. 34). Especially
valuable for world correlation is a succession of ammonite horizons,
each with a distinctive assemblage agreeing with its Dorset counterpart,
representing the Discites, Trigonalis and Laeviuscula Subzones of the
Sowerbyi Zone, and overlain by the Sauzei Zone (Welsch, 1928a). The
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