M.K. HOWARTH AND N.J. MORRIS 



A 



SAUDI 





ARABIA 



RED^, 

 SEA 



' T ^ 



Sana'a , I 



e 



i'Djibouti ^.^..^-^^ 



\Berhera / 

 Harar» ^-^^ y / 



ETHIOPIA /^( 



/ J 



"^ial al Milh 

 \^^^31intaq 



LJ 1 , 1 1 1 



1 



50kni 



N 



MUKALLA ,; 









Joba '-V^ 



Sidara^ 



■^^^^ Al Gool 



NX 









Fuwa // 





AI Ma'abir)\ tt^ 







Bum my/ 



/J 





1 X 



/j 





-^^^~^^ 



BirAli ^,,--' 



/Sifal 







Balhafl: 



.^.^^y^'^ 







10km 

 J I I I I I I I 



Fig. 1 A, location map of the southern part of the Arabian peninsula and north-east Africa. B, Wadi Hajar west of Mukalla extends from its mouth near 

 Sifal to beyond the three salt domes of Mintaq, Joba and Sial al Milh, 90 km to the north-west. C, geological map of the lower part of Wadi Hajar from 

 Al Ma'abir to Jebel Billum and Wadi Arus, showing the outcrop of Jurassic and basal Cretaceous rocks (hatched). The dashed lines on Figs IB and IC 

 are roads. 



pushed largely vertical by the rising core of the salt dome. The 

 present paper, which deals with the lithostratigraphy and 

 biostratigraphy, will be followed by papers describing the ammo- 

 nites, brachiopods, echinoids and some of the bivalves. 



PREVIOUS INVESTIGATIONS 



Little, 1925 



O.H. Little and H.M. Heald travelled up Wadi Hajar in Febniary and 

 March 1920 at the instigation of the Sultan of Shehr and Mukalla, 

 mainly to investigate mineral deposits and agricultural methods. 



Accompanied by a retinue of 80-90 people, including 25 soldiers of 

 the Sultan's private army for protection, they experienced great 

 difficulty in passing through the formidable river gorge between 

 Naifa and the mouth of Wadi Arus, at a time before the unmetalled 

 road was constructed around the southern side of Jebel Billum. They 

 penetrated Wadi Hajar as far as Jawl Bahawa (= Jol Ba Hawa; also 

 the present Al Gool), but political and tribal reasons prevented them 

 from going farther up the wadi to El Sidara and thence to Mintaq. 

 Nevertheless, Little made geological observations on the Jurassic 

 outcrops at Naifa Cliff, Wadi Arus and near Hisn Baqirdan (= Husn 

 Ba Qirwan). The results were given in his paper (Little, 1925: 109- 

 1 14). Three fragments of ammonites and three belemnites obtained 

 from Naifa Cliff, and five bivalves and six brachiopods from Husn 

 Ba Qirwan, were figured in the same paper by Stefanini (1925: 144— 



