44 DR. J. W. GREGORY ON THE GEOLOGY AND [Feb. I9OO, 



Our knowledge of the faunas of these five limestones is unfor- 

 tunately scanty, and further collections would be welcomed from 

 the limestones of Bur Dab, Artalla, Wagga, Abdullah Ismail, and 

 especially from the highest beds above the Miriya Pass, also from 

 the limestones associated with the gypsum-beds of Kirrit, Eyk, and 

 the Duban. But the evidence of the present collections is sufficient 

 to show that a Neocomian limestone occurs both on the summit of 

 the Somali plateau and on the floor of the Guban, and that some 

 marine limestones of probably Lower Tertiary (Eocene) age also occur 

 on the plateau. 



It seems therefore probable that the foundering of the Aden Gulf 

 is post-Eocene in age. 1 



EXPLANATION OF PLATES I & II. 

 Plate I. 

 Fig. 1. Sti/lophora frondosa, sp. nov. Duban, north of the foot of the Rugga 

 Pass. Coll. Mrs. Lort Phillips. a = part of the surface of the 

 corallum, X 3 diam. ; b = a horizontal section through part of the 

 same, X 6 diam. ; c = a vertical section through part of the same, 

 X (i diam. (See p. 30.) 



2. Stylina subtabu/afa, sp. nov. Dobar Limestone : Dobar, south of 

 Berbera. Coll. Mrs. Lort-Phillips. a = part of a horizontal section, 

 X 2 diam. ; b = part of a vertical section through the same specimen, 

 X 2 diam. (See p. 31.) 



3. Calamophyllia Aylmeri, sp. nov. Uradu Limestone, near Uradu. 

 Coll. Mrs. Lort Phillips. Part of a horizontal section, X 3 diam. 

 (See p. 31.) 



4. Facia somaliensis, sp. nov. Uradu Limestone, Ura du. Coll. Mrs. Lort 

 Phillips, a = part of the corallum, showing some calices as seen from 

 the surface, and others in section, nat. size ; b = transverse section 

 across one coral lite, x 4 diam. (See p. 35.) 



Figs. 5 & G. Priouastrcea crassisepta, sp. nov. Dobar Limestone, Dobar, 

 touth of Berbera. Coll. Mrs. Lort Phillips. Fig. 5 b = transverse 

 section of part of a oojalium, nat. size ; fig. 5 a — upper surface of a 

 corallite from the same specimen, showing columella, X 2 diam. ; fig. b' = 

 part of a vertical section through another specimen, showing columella, 

 walls, and dissepiments ; this figure is inverted. (See p. 34.) 



Plate II. 



Figs. 7-9. Columnastrcea bicoronata, sp. nov. Uradu Limestone, near Uradu, 

 south of Dobar, and in the Duban. Coll. Mrs. Lort Phillips. Fig. 7 = 

 part of the surface of a specimen from the Duban, X 2 diam. ; fig. 8 == 

 part of a horizontal section of a specimen from Uradu, X 2 diam. ; 

 fig. 9 — part of a horizontal section of a specimen from the Duban, 

 X 2 diam. (See pp. 32-33.) 

 Fig. 10. Columnastrcea Phillipsice, sp. nov. Uradu Limestone, Uradu. 

 Coll. Mrs. Lort Phillips. Part of a horizontal section, X 3 diam. 

 (See p. 33.) 



1 [This probability is based on three lines of evidence: the agreement in 

 direction of the movements which have caused the Aden Gulf and the Somali 

 Plateau ; the absence of Lower Kainozoic deposits in the Red Sea, except 

 towards the north, where, as in the Gulf of Akaba, their fauna is of Mediter- 

 ranean affinities ; and the recent date of the separation of Arabia and Africa, 

 as indicated certainly by zoological evidence, and probably by the local 

 traditions. For the last see my ' Great Rift Valley,' 1896, chapts. xii & xiii. — 

 December 22nd, 1899.] 



