Arkell.1956.Jurassic..

3°6
EAST AFRICA
BATHONIAN AND CALLOVIAN, 400 m.
Lower Antalo Limestone. Marly grey limestone, hard, compact, like
Lias, with Trigonia pullus Sow., Modiolus imbricatus Sow., Eopecten
aubryi Douville, Rhynchonella morierei Davidson, Rh. lotharingica, Rh.
edwardsi, etc. Nautilus (Paracenoceras) calloviensis (Oppel) was sent me
by Professor E. Nilsson, collected by him in 1950 in the ravine of the
R. Walaka, tributary of the Blue Nile, no miles north of Addis Abbaba.
UNDATED
Abai Beds, 200 m. Crystalline yellow limestone with layers of granular
gypsum and dolomitic limestone, and casts of small indeterminable
lamellibranchs referred to by H. Douville (1886, p. 239) as 'Corbules',
by Furon (1950, p. 293) as 'Cyrenes'.
Adigrat Sandstone, 500 m. White and blue sandstones, often micaceous,
with layers of green and vari-coloured clay.
While the absence of Oxfordian may be due to collection-failure, it is
nevertheless remarkable that the apparent superposition of Lower Kimeridgian
on Callovian repeats the arrangement in the northern Lebanon
range in Syria, attributed above to wedging out of the intervening formations
against the margin of the trough of deposition. The two stages,
Bathonian and Kimeridgian, moreover, are those already noted as transgressive
in Egypt, Syria and southern Arabia. Which extended farthest to
the west or north-west in Abyssinia remains to be determined. The answer
awaits discovery along the Blue Nile and its tributaries. The mapping of
these valleys and of the western edge of the volcanic plateau is still in a
rudimentary state. The latest synthesis is that of part of the country
falling within the Sudan map compiled by Andrew (1948). Future
research will no doubt prove whether the sandstone shown on this and
preceding maps as cropping out between the Tertiary lavas and the pre-
Cambrian is wholly a continuation of the Adigrat Sandstone as indicated
on Stefanini's splendid map (1933) or in part Cretaceous and the continuation
of the true Nubian Sandstone. If the latter, then the Jurassics have
wedged out between the sandstones under the plateau. The most westerly
exposures of Antalo Limestone at present known are in the Abai valley
37 0
57' E., and a limestone (in both places associated with chert) has been
found south of Suakin in Khor Langeb 36 0
35' E., 17 0
16' N. (Andrew,
1948, p. 98.)
ERITREA (DANCALIA)
South of Annesley Bay, south of Massawa, the Red Sea rift valley
forks, one branch continuing to the Straits of Bab el Mandeb and Aden,
the other following the foot of the Abyssinian plateau edge southwards,
to become later the Great African Rift Valley. Between the two forks in
Eritrea alongside the coast lies Dancalia, or the Danakil Horst of Gregory
(Alpi Dancale of the Italians), consisting of pre-Cambrian basement
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