328 NATURAL SCIENCE. 



JULY, 



one of the Seychelles group. The report was written at the request 

 of the Governor, by Thomas James Spurs, the lessee, who takes 

 considerable interest in the structure of the island and in the preser- 

 vation of its fauna and flora. Mr. Spurs remarks on the more 

 abundant vegetation of Aldabra, compared with Astore, Cosmoledo, 

 or Assumption. The island is covered with trees and stunted shrubs, 

 is very green, and contains mangroves as much as 55 feet in height. 

 As, however, the bush is inhabited by myriads of mosquitoes, few 

 venture therein. Aldabra is flat, 20 miles long, trending north-west 

 to south-east ; its shape is crescentic, and a line of three islands 

 between the horns encloses a lagoon, access to which is only obtained 

 at low water by one of the four channels. The narrowness of the 

 channel and the strength of the currents render it practicable only 

 for steamers. In some valuable notes on the structure of Aldabra, 

 Mr. Spurs says at first sight it seems extraordinary that an island 

 essentially madreporic, and so vast, should not be interspersed with 

 sandy plains ; when, however, it is known how strong the currents 

 and surf are, it is easily explained. The sea, bursting with great 

 violence on the reef, has swept off all the calcareous detritus, and 

 imparted to the growing coral an extraordinary strength. Mr. Spurs 

 notes that the predominating coral in Aldabra is a great " porite " ; 

 he has not found it in the other islands, and has been unable to find 

 it in a living state. The decomposition of the coral rock yields a 

 yellow mould of great fertiHty, but, unfortunately, there is very little 

 of it. The writer laments the destruction of the larger trees, which 

 he considers partly due to the hurricane of 1889, and mainly to the 

 mephitic exhalations from the soil. He quotes a note of Commander 

 Needham's, written in i8go, as to the "rising of jets of vapour of 

 large quantity from the water, which appeared around it to be 

 depressed as in a whirlpool," and goes on to state that " the inference 

 is that Aldabra is still liable to volcanic action." After some interest- 

 ing meteorological notes, Mr. Spurs remarks that thirty species of 

 trees and shrubs exist, but all are of small size, as they hardly find 

 sufficient nourishment. Of the fauna, the large tortoises were very 

 numerous, but owing to the reckless destruction by the harpooners, 

 they have diminished in numbers. Referring to Picard Island, the 

 writer has taken means to restock the place and to destroy the rats, 

 which are the greatest enemies of young tortoises. He remarks on 

 the activity and swiftness of these great chelonia, and says that they 

 retire to the bush from May to September, and come out in October 

 with the first rain. It is then that they couple, and the female lays 

 from six to eight eggs in November, in January, and in February. 



The sea turtles are numerous, but the males alone inhabit 

 the bay. As soon as a female has attained the age of producing 

 (20 to 25 years) she disappears — whither no one knows. When they 

 return to the coast to lay eggs, they are covered with barnacles of two 

 or three weeks' growth. The females are more valuable than 



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