74 FRINGING REEFS. Ch. III. 



tour round the Mauritius, seems to have met with a 



structure of this kind : he says, 4 J'observai que la, ou 



la mer etale independamment des rescifs du large, 



il y a a terre une espece cVeffoncement, ou chemin 



couvert naturel. On y pourrait mettre du canon,' &c. 



In another place he adds, ' Avant de passer le 



Cap, od 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 Grreat Black Eiver ; 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 Astrsea and Madrepora, 



loosely aggregated; they were divided into irregular 



beds, dipping seaward, in one hillock at an angle of 8°, 



