182 
DISTRIBUTION OF CORAL-REEFS. Cn. VI. 
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 running in front of the coast from the equator far 
southward, and rising to a greater height than can be ac- 
counted for by the growth of coral, without feeling con- 
vinced 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, are singularly shaped, apparently showing 
the combined effect of the growth of coral on submerged 
banks, together with 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 
Bed Sea, as described by several authors, proves that the 
whole of this large area has been elevated within a very 
recent tertiary epoch. A part of this space in the ap- 
pended map is coloured blue, indicating the presence of 
barrier-reefs ; on which circumstance I shall presently 
make some remarks. Riippell 1 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 to 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 
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. GO. 
1 Itiippell, Reise in Abyssinien, Band i. s. 141. 
