NOTES ON THE NATURAL HISTORY OF ALDABRA, ASSUMPTION 

 AND GLORIOSO ISLANDS, INDIAN OCEAN. 



BY 



Dr. W. T.. Abbott.* 



The atoll of Aldabra lies 220 miles iiortliwest of tlie uortli point of 

 Madagas(;ar, in latitnde 9'^ 25' south, and longitude 4(P east. It is about 

 22 miles long- by 8 miles in extreme width, the long- axis lying- east and 

 west.t It is entirely of coral formation, and forms ;in oval ring- of land, 

 broken at several ])oints by channels, and inclosing- a lagoon. The ring- 

 of dry land is widest at the southeast and northwest corners, where it is 

 nearly 3 miles across. The Grande Terre, or main island, forms three- 

 fifths of the circumference of the ring. It includes (from midway on 

 the western side of the ring) the whole southern and eastern sides 

 to a point ou the north shore, being' 35 miles long-. It is separated 

 by Pass Hourreau, 200 yards wide, from ISTorth or Middle Island. This 

 is 12 miles long-, forming- the north shore as far as Grand Pass. This is 

 the principal oj)ening- into the lagoon. It is 400 yards wide, and 8 to 10 

 fathoms deep. West of this lies lie Picard, or Northwest Island, 

 foiniing the northwestern corner of the atoll. It is about 5 miles long. 

 Between the south eiul of lie Picard and the northwest end of Grande 

 Terre, lie half a dozen small islands and as many shallow channels. 

 The lagoon is about 20 miles long and G miles in width. Excepting in 

 the northwestern corner near Grand Pass and in a few (diannels, it is 

 very shallow, half of it being nearly dry at low tide. Grand Pass is 

 the only inlet deep enough to allow the passage of a large vessel, and 

 through this the current runs with gre;it rapidity, 5 to 7 knots, so that 

 it is dangerous for sailing vessels except at the turn of the tides. At 

 Pass Hourrean there is a narrow channel, through which a small 

 vessel might pass. . The inner or lagoon shore of the land is everywhere 

 bounded by mangrove swamps, intersected by numerous channels. 

 During the northwest monsoon a heavy swell rolls in through Grand 

 Pass and breaks upon the reef within the lagoon. It is very danger- 

 ous to boats at such times, and the pass can not be traversed. There 

 are numerous islands scattered about the lagoon, the longest being lie 

 Sepoj', about 5 miles from Grand Pass and directly opposite to it, and 

 ile Michel, opposite to Pass Hourreau, and close to the southern side 



^^ Edited by Frederick W. True,, with the assistance of other curators of the 

 Museum. No identifications of .species were included in ]")r. Abbott's manuscript. 

 tTlie island was com]»letcly surveyed by H. M. S. Alert, in 1882. 

 Proceedings Natioiiiil Museuiii, \'ol. X VI — Is'o. 97:t. 



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