Arkell.1956.Jurassic..

316 EAST AFRICA
1914, pi. iii, fig. 3), Dichotomosphinctes (P. gallarum Dacque) and Discosphinctes
(P. arussiorum Dacque). Revisionary remarks on these forms will
be found in Arkell, 1937-39, Monograph of the Ammonites of the English
Corallian Beds, pp. xlvii, liv, lx, lxii, lxiii.
Dogou and Ganame: Three Perisphinctids figured by Scott as Lithacoceras
are of doubtful age and generic position, though probably Upper
Oxfordian, but his Perisphinctes vokesi and P. spathi are unquestionably
Upper Oxfordian, as are also Ringsteadia africana Scott and R. daua Scott.
Diredaua (NW. of Harrar): Ringsteadia daua Scott occurs at this locality
only, also a ? Dichotomoceras and Dichotomosphinctes (Scott, 1943, pp.
68, 69).
UPPER OXFORDIAN (Transversarium Zone)
Diredaua: Dacque (1914, p. 12) records but does not figure badlypreserved
Perisphinctids which he compares to P. rota Waagen and
P. subrota Choffat, forms suggesting that he had them from an exposure
of the Plicatilus Zone, which is developed in Kenya (with Kranaosphinctes).
With them occurs Somalirhynchia.
BATHONIAN
Cottreau (1924) recognized Isastraea cf. limitata McCoy, Rhynchonella
morierei Dav., Modiolus plicatus Sow., M. cf. imbricatus Sow. and Ceromyopsis
tenera (Sow.) among fossils collected from three localities south
and SE. of Harrar, and inferred the presence of the Bathonian as in Shoa.
Since then some of the echinoids found in the Lower Bihen Limestone
at Bihendula have been recorded from localities in the Harrar Province
(Currie in Barnum Brown, 1943).
UNDATED
Adigrat Sandstone with basal conglomerate rests as usual on the
crystalline basement. It appears to thicken northwards and towards the
base passes into arkose and sandy limestones (Lamare, 1930, pp. 5, 58-9).
JUBALAND
This term is used in its geographical rather than political sense for the
whole basin of the Juba River south of about latitude 6° N., and of its
principal western tributary, the Daua. The Daua joins the Juba at
Dolo, near the present meeting-place of the frontiers of Kenya, Ethiopia
and Italian Somaliland. Into and through this huge basin the Jurassic
limestones spread southward continuously from the Harrar region, on a
front nearlysix degrees wide (between longitude 39 0
and 4S°E.), overlapped
irregularly both east and west by Cretaceous sediments and on the west
in part by Tertiary lavas. Before reaching the coast the Jurassic outcrop
narrows to a tongue along the Juba River and finally disappears about
i° north of the equator and the sea, beneath Pleistocene and Holocene
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