74 
FRINGING REEFS. 
Ch. III. 
tour round the Mauritius seems to have met with a 
structure of this kind : he says, * J’observai que la, oil 
la mer etale independamment des rescifs du large, 
il y a a terre une espece d’effoncement, ou chernin 
couvert naturel. On y pourrait mettre du canon,’ 
&c. In another place he adds, ‘ Avant de passer le 
Cap, on remarque un gros banc de corail eleve 
de plus de quinze pieds : c’est une espece de res- 
cif, que la mer a abandonne : il regne au pied 
une longue flaque d’eau, dont on pourrait faire un 
bassin pour de petits vaisseaux.’ But the margin of 
the reef, although the highest and most perfect part, 
from being most exposed to the surf, would generally 
during a slow rise of the land be either partially or 
entirely worn down to that level at which corals could 
renew their growth on its upper edge. On some parts 
of the coast-land of Mauritius there are little hillocks 
of coral-rock, which are either the last remnants of a 
continuous reef, or of low islands formed on it. I 
observed two such hillocks between Tamarin Bay and 
the Great Black Biver ; they were nearly 20 feet 
high, about 200 yards from the present beach, and 
about 30 feet above its level. They rose abruptly 
from a smooth surface, strewn with worn fragments 
of coral. They consisted in their lower part of hard 
calcareous sandstone, and in their upper of great 
blocks of several species of Astrtea and Madrepora, 
loosely aggregated ; they were divided into irregular 
beds, dipping seaward, in one hillock at an angle of 8°, 
and in the other at 18°. The upraised reefs round 
