FRYER— FORMATION OF ALDABRA, ETC. 413 



and rather more so near Picard Island, though much of the sand in the west disappears in 

 the calm season and collects again in the south-east trade season. Under these conditions 

 the forms of life usually found on a coral reef were naturally scarce : at low tide the most 

 conspicuous animal was an eel (Murcena mudivomer sp. ?) which crawled about with its 

 mouth wide open, biting with great ferocity at whatever came in its way. A second eel 

 (Murcena chilospilus) burrowed in the sand with astonishing rapidity, and it was noted 

 that it could burrow backwards as well as forwards. On one occasion a sea-snake was 

 seen but not captured. In the sand were found various polychaets, gephyreans, burrowing 

 Crustacea and, where coral rubble was overlaid by a layer of sand, there lived a large 

 species of Balanoglossus (9 inches long), which gave out the characteristic smell of 

 iodoform to a marked degree ; owing to the fact that it lived in the rubble rather than in 

 the sand it was most difficult to obtain unbroken. The cliffs formed the haunt of a 

 large number of molluscs among which a chiton was prominent, while a small fish 

 (Periophthalmus sp. ?) frequented the rock pools, often lying outside on the bare rock 

 and jumping from pool to pool with great agility when pursued. In the cliff face boring 

 animals were not uncommon, a small sipunculid being sufficiently numerous to assist the 

 sea materially in its work of destruction. 



As a whole, however, the fringing reef was disappointing in comparison with the 

 reefs I had visited in the Seychelles in company with Professor Stanley Gardiner, and 

 the reason is probably to be ascribed to the presence of such large quantities of sand, 

 while the mud of the lagoon must also contaminate the waters round the atoll to some 

 extent. 



The characters of the Aldabra fringing reef at first found no explanation, but the 

 reefs on the sides of Grande Passe and Passe Houareau yielded a clue. Before I left 

 I was quite satisfied that the fringing reef was merely a ledge of the elevated coral rock, 

 piled with rubble, and protected to seaward by lithothamnia and corals. As in the case 

 of the reef by the sides of the passes the rock below low water-mark is protected from 

 speedy erosion, while that above is continually washed away. The fringing reef therefore 

 is not a sign of the growth of the atoll seawards but of the amount of its loss of land due 

 to erosion. Whether the outer edge of the reef is holding its own or slowly receding is 

 impossible to say, but I am inclined to believe the latter, from the fact that it follows the 

 present conformation of the coast line so closely. 



A final problem to be dealt with is the presence of so much sand on the south coast. 

 The destruction of rock round the whole coast has already been pointed out: the result 

 of this disintegration is the production of sand. Owing to the fact that the current flows 

 from east to west, and the prevalent winds are south-east, this destruction of land is 

 greatest in the east of the atoll, and indeed it seems very probable that the shallow hank 

 to the south-east is the site of lost land. The sand produced in this process is driven 

 along the reef by the current and on the north coast the greater part is washed away : on 

 the south coast, however, the south-east winds drive it inshore and pile it on the reef and 

 against the cliffs, which in the region of the dunes are low and become almost covered up, 

 the beach being sandy and sloping gradually up to a height of 60 ft. In other places it 

 has formed numerous small sand " lances," and in the west of Picard lias been heaped up 

 SECOND SERIES— ZOOLOGY, VOL. XIV. 53 



