398 PERCY SLADEN TRUST EXPEDITION 



previous expedition, show that the Indo-African bridge was in all probability reduced by- 

 subsidence to a narrow isthmus or chain of islands, and that then by the power of current 

 erosion it was gradually cut down below sea-level, until at the present day the Seychelles 

 archipelago alone remains above water. With the exception of the above archipelago and 

 Mauritius all the islands visited by the " Sealark " were shown to be coralline in structure, 

 and all indications as to their mode of formation, as in the case of the Maldives, favoured 

 the theory of elevation and not of subsidence. 



The "Sealark" expedition, however, found it impossible to investigate one group 

 of islands, which Gardiner*, when classifying the islands of the Indian Ocean, has termed 

 the Farquhar series, though, for reasons which will become obvious, I shall in future refer 

 to it as the Aldabra series. It contains the islands of Aldabra, Assumption, Cosmoledo, 

 Astove, Farquhar, Providence and St Pierre, of which the three latter only were visited 

 by the " Sealark." The whole series lies to the north of Madagascar between longitudes 

 45° E. and 52° E. and between latitudes 9° S. and 10 # 5° S., the component islands being 

 separated by from 20 miles (Aldabra and Assumption) to 180 miles (Astove and Farquhar). 

 Of the various islands, Astove, Cosmoledo and Assumption were practically unknown, but 

 Aldabra had become famous as the last home in the Old World of the giant land-tortoise ; 

 its land avi-fauna also was known to be peculiar, while contradictory reports made difficult 

 any conception of its structure. In 1907 the analysis of samples of guano, received from 

 the locality, pointed to the existence there of rocks other than those of reef formation, and 

 it therefore appeared possible that a further remnant of the Indo-African bridge might yet 

 be existing on Aldabra. Further investigation seemed desirable, and Professor Stanley 

 Gardiner, who with Mr Hugh Scott was planning a further expedition to the Seychelles, 

 made provision for the author to accompany the expedition and undertake the work of 

 thoroughly investigating the Aldabra series of islands. This paper gives a brief history of 

 the latter work, and the deductions made from it, though the reports of the specialists on 

 the material collected must be consulted for confirmatory or contradictory evidence. 



Before turning to the description of the expedition a few more facts of general bearing 

 on the region must be mentioned, while in addition the scanty details of history about the 

 islands may at once be disposed of. They first appear on the charts of the early sixteenth 

 century, Aldabra itself being called Alhadara on the " Carte de Madagaskar d'apres 

 Pilestrina" in the year 1511. In subsequent charts one or more of the other islands are 

 usually indicated but not sufficiently well to make sure as to which is really intended, 

 though the name Joao de Nova for Farquhar is usually constant. In different times 

 Aldabra is called Ya dArena, Y dAreo, Ilhadara and Adarno, names which appear to 

 indicate sand island — as will be seen later, a most inappropriate designation. Voeltzkow, 

 who visited Aldabra in 1895, makes the reasonable suggestion that the island was first 

 discovered by the Arabs f, who named it Al-Khadhra, " the Green," and the early European 

 navigators, the Portuguese, translated it phonetically to Al-hadara, and so obtained the 

 various names, by which it has since been known. No written records of the islands 



* Geographical Journal, Oct. 1906, p. 326. 



t Arab craft employed in the slave and other trades regularly plied between Zanzibar and the Comoros in 

 very early times. 



