Arkell.1956.Jurassic..

498 RUSSIA AND THE EUROPEAN ARCTIC
of the Middle Callovian, with Kosmoceras jason, not in the overlying beds
with K. castor and K. pollux as in western Europe.
LOWER CALLOVIAN
Nikitin (1884a) divided the Middle and Lower Callovian between two
zones of Cadoceras milaschevici and C. elatmae. It is difficult to determine
at what level the division falls in terms of west European zones, but probably
it is somewhere in the Koenigi-Calloviense Zones. The Russian
Callovian is famous for its variety of forms of Cadoceras (e.g. Nikitin,
1882, pi. xi, figs. 20, 21, pi. xii, figs. 26-29; I
88i, pi. iii) and there are also
many forms of Macrocephalites (1882, pi. x, figs. 15-18), Kepplerites such as
K. lahuseni Parona & Bonarelli, 1897 (type Lahusen, 1883, pi. vi, fig. 8)
and Gowericeras (figs. 5, 6, 7), Proplanulites, Chamoussetia, Grossouvria,
etc. When a detailed stratigraphical succession comes to be worked out,
interesting comparisons with NW. Europe and especially England are to
be expected.
On the middle Volga, in places, Lower Callovian ammonites are only
found rolled in a conglomeratic bed of the Coronatum Zone, which rests
directly on the Permian; in other places there are sands similar to the
underlying Permian (Pavlow, 1884; 1885; 1897, p. 5), which may be
basal Callovian or older. Arcticoceras is recorded near Kuibyshev (Zonov,
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? BATHONIAN
In the Samara bend of the middle Volga the Permian and Carboniferous
are transgressively overlain by 25-30 m. of white sands, with basal pebble
bed and lenses up to 4-5 m. thick of laminated clays at or near the base and
filling pockets in the Palaeozoic platform. These beds are attributed by
Russian geologists to the Bathonian. (Boutrov, 1937, pp. 38-9; Zonov,
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BASIN OF THE PETCHORA RIVER
Between the northern Urals and the Timan Range lies a wide triangular
basin drained by the Petchora River, which crosses the Arctic Circle and
flows into the Arctic Ocean. The greater part of the basin is filled with
Quaternary marine beds, but beneath much of it there is a sheet of Cretaceous
and Jurassic strata, which come to the surface between the river and
the flank of the Timan Range. The best exposures are on the River
Pishma and at the headwaters of the River Ishma, two tributaries of the
Petchora. Near the confluence of the Pishma and Petchora, Murchison
(1845, p. 417) already noted 'large masses of grey calcareous sandstone
subordinate to clays and charged with ammonites and fossil wood',
passing down to thick grey clays and shales with Posidonia, resting on
Devonian limestone.
Ammonites were brought back and figured by Keyserling (1846)
and a number of later explorers. The assemblages all fall, in age, between
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