CORAL-REEFS. 171 



chapter on fringing-reefs. The northern extremity of Mada- 

 gascar is described by Capt. Owen 1 as formed of madreporitic 

 rock, as likewise are the shores and outlying islands along an 

 immense space of Eastern Africa, from a little north of the 

 equator for 900 miles southward. Nothing can be more vague 

 than the expression "madreporitic rock"; but at the same time 

 it is, I think, scarcely possible to look at the chart of the linear 

 islets, which rise to a greater height than can be accounted for 

 by the growth of coral, in front of the coast, from the equator 

 to 2 S., without feeling convinced that a line of fringing-reefs 

 has been elevated at a period so recent, that no great changes 

 have since taken place on the surface of this part of the globe, 

 Some, also, of the higher islands of madreporitic rock on this 

 coast, for instance Pemba, have very singular forms, which 

 seem to show the combined effect of the growth of coral round 

 submerged banks, and their subsequent upheaval. Dr. Allan 

 informs me that he never observed any elevated organic remains 

 on the Seychelles, which come under our fringed class. 



The nature of the formations round the shores of the Red 

 Sea, as described by several authors, shows that the whole of 

 this large area has been elevated within a very recent tertiary 

 epoch. A part of this space in the appended map is coloured 

 blue, indicating the presence of barrier-reefs : on which circum- 

 stance I shall presently make some remarks. Ruppell 2 states 

 that the tertiary formation, of which he has examined the organic 

 remains, forms a fringe along the shores with a uniform height 

 of from 30 and 40 feet from the mouth of the Gulf of Suez to 

 about Lat. 26 ; but that south of 26 , the beds attain only the 

 height of from 12 to 15 feet. This, however, can hardly be quite 

 accurate ; although possibly there may be a decrease in the 

 elevation of the shores in the middle parts of the Red Sea, for 



1 Owen's Africa, vol. ii. p. 37, for Madagascar; and for S. Africa, 

 vol. i. pp. 412 and 426. Lieutenant Boteler's narrative contains fuller 

 particulars regarding the coral- rock, vol. i. p. 174, and vol. ii. pp. 41 

 and 54. See also Ruschenberger's Voyage round the World, vol. i. 

 p. 60. 



2 Ruppell, Reise in Abyssinien, Band. i. s. 141. 



