„ XXXIV, „ 74. A fringing reef in sandstone, Cape Verde Islands „ 110 „ XXXIV, „ 75. Embryo reef near Alexandria „ „ „ XXXV, Figs. 76 and 77. Cliffs of “coral rag” in Zanzibar „ 112 Diagram 6. Formation of atoll by direct growth. (From Fowler’s _Science of the Sea_: J. Murray) 115 „ 7. Formation of a rift valley 122 „ 8. Atoll growing on summit of a volcanic mound. (From Fowler’s _Science of the Sea_: J. Murray) 124 Fig. 78. Coast of the Anglo-Egyptian Sudan 126 Pl. XXXVI, Fig. 79. Yemêna oasis on the maritime plain _to face_ 128 Pl. XXXVII, Figs. 80 and 81. Corals on summit of Jebel Têtâwib „ 129 „ XXXVIII, „ 82 „ 83. Two views in Yemêna ravine „ 131 Fig. 84. Map of reefs off Port Sudan 137 Diagram 9. Section through Rawaya and Makawar 138 Fig. 85. Map of Rawaya, etc 139 Diagram 10. Levelling action of the sea 140 Pl. XXXIX, Figs. 86 and 87. Two views on Rawaya _to face_ 140 Diagram 11. Reefs off Ras Salak 142 Pl. XL, Fig. 88. In a fault ravine of Abu Shagarato _to face_ 143 Fig. 89. Sketch of Jebel Têtâwib, coral and gypsum beds 144 Diagram 12. Three steps on side of Red Sea Rift Valley 145 Figs. 90 and 91. Types of harbours 147-8 ERRATA p. 88. _For_ Hydniopora _read_ Hydnopora. p. 120. Halaib is a name unknown to natives, who call the place Olê. From this the official name is derived through Arab orthography probably. The Arabic alphabet is the best possible for its own language, and the worst for any other. PART I CHAPTER I THE SUDAN COAST