118 PERCY SLADEN TRUST EXPEDITION. 
the Bamboo Mountains and which form an alluvial plain a mile and a half across. To 
the south of this the lava reoccurs at Battery Point, Point d’Esny, and Point Cocos. 
Prom Mahébourg we explored the neighbourhood, paying attention more particularly to 
its reefs and islets. Some small cliffs 50 feet in height to the north, known as Terre 
Rouge, proved to have been formed of material from the hills above together with rounded 
masses of basalt, showing concentric weathering, which have fallen out and lie piled at 
their base. The line of vegetable (humic acid) decomposition at about 8 feet below the 
summit was everywhere most marked. From there we went to Treize Cantons, where 
there was a small mound to some degree isolated from the slopes of the Bamboo 
Mountains behind. It was about 65 feet in height and consisted of a thickness of about 
18 feet of the same red earth at its base, overlaid by coral-rock. This earth, being very 
soft, has washed away in many places, with the result that the coral-rock has been 
undercut, and large masses have fallen off and lie at an angle with the earth forming 
small caverns. In one place masses of the coral-rock had fallen on either side, but in the 
centre it was overhanging for 10 to 15 feet, forming a roof over the strand which in 
Mauritian legends was the site of a noted duel. The earth is such as forms the coast-flat 
everywhere within Grand Port, while the coral-rock is made up of similar materials to 
those which cover the surface of its barrier-reef, ¢.e. sand consisting of foraminifera, 
broken-up corals, Lithothamnia, Halimeda, and such-like débris. It is, however, much 
metamorphosed and contains large crystals of calcite, and will form the subject of a 
separate report by Dr. Cullis. 
From here we sailed backwards and forwards over the channel and reefs, the scene of 
a famous frigate action in 1810 in which, owing to the intricacies of the channel and 
unfavourable winds, we lost four fine vessels, though the ‘ Néréide’ covered herself with 
slory. Ile Singe, on which we found the remains of a small fort, and Ile des Rats both 
proved to be of coral much weathered and undercut at the sea-level. Ile de la Passe, 
for the possession of which the above action was fought, was likewise formed of lime- 
stone as well as were the other islands on its reef. Ile Aigrette, the highest (45 feet) 
and largest of all (about 80 acres), was also visited, proving to be a dome-shaped mass 
of coral-rock undercut for 6 to 8 feet at its base in a manner similar to so many of the 
Lau Group of Fiji. By the kindness of the customs officer at Mahébourg, we obtained 
rock-specimens from the other reef-islands in the neighbourhood. All these were like- 
wise of coral-formation. Bird, Fous, and Marianne were evidently once parts of a single 
island, the horns of which had been cut off, leaving the two smaller islets absolutely on 
the reef-edge and the larger, Marianne, further back with a fringing-reef in front. 
Fouquets and de Ja Passe also are situated on the reef-edge. 
The weather was unfortunately too stormy for us to visit the outer parts of the reefs, 
but from Mahébourg we sailed across and across the south passage into Grand Port and 
over its reefs on either side in a pirogue. The latter is a long flat-bottomed canoe-like 
craft which is commonly used in the western part of the Indian Ocean. It is made of 
soft wood, so it cannot be sunk, and, as it draws only a few inches of water, is particularly 
suitable for work on the reefs. The latter are exposed at low spring-tides, and behind 
their seaward edge, which is similar to that of coral-reefs in general, muddy flats are 
formed, covered with more weed than we have ever found on reefs of pure limestone, 
