Arkell.1956.Jurassic..

THE BRITISH ISLES
Pleuroceras spinatum, and thicker sands and micaceous shales below,
corresponding to the Zone of Amaltheus margaritatus, with some early
Hildoceratids, Paltarpites and Arieticeras (Buckman, Type Am. ii, 1913,
pi. LXXIV, iv, 1923, pis. CCCLXII-III, vi, 1927, pi. DCXCVIII).
M. K. Howarth (1955), as the result of a thorough restudy of the cliffsections
in Dorset, Yorkshire and the Hebrides, has established the
following subzones:
ZONES SUBZONES
Pleuroceras spinatum (Brug.) . | Pleuroceras spinatum (and P. hawskerense)
Pleuroceras apyrenum
Amaltheus margaritatus Montfort . -j
Amaltheus margaritatus (and A. gibbosus)
Amaltheus subnodosus
Amaltheus stokesi
For monographic treatment of the ironstones, see Whitehead & others,
1952. Some of the brachiopods have been revised by Ager (1954).
LOWER PLIENSBACHIAN (upper part of Lower Lias, or Carixian, up to
54 m. in Dorset)
In Dorset this substage is represented by the Green Ammonite Beds
and Stonebarrow Beds or Belemnite Marls (Lang, Spath & others,
1928, 1936). Spath (1938) has monographed the Liparoceratid ammonites
and (1942) recognizes the following subzones :
ZONES SUBZONES
Prodactylioceras davoei (Sow.) J
(= Capricornus Zone auct.) 1
Tragophylloceras ibex (d'Orb.) (
(= Henleyi Zone auct.) \
Uptonia jamesoni (Sow.) . j
Oistoceras figulinum
Androgynoceras lataecosta
Androgynoceras maculatum
Beaniceras centaurus
Acanthopleuroceras valdani
Uptonia jamesoni (with U. bronni)
Platypleuroceras brevispina
Phricodoceras taylori
SINEMURIAN (middle part of Lower Lias, 104 m. in Yorkshire)
Almost everywhere in England the Sinemurian is well developed as
shales, with numerous local ammonite horizons. In Dorset the stage
corresponds to the Black Ven Marls, Shales-with-Beef and top of the
Blue Lias Limestones (Lang, Spath & others, 1923, 1926). In Somerset
and Glamorgan a littoral facies is developed and there is slight
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