No. XIX.— THE STRUCTURE AND FORMATION OF ALDABRA AND 

 NEIGHBOURING ISLANDS— WITH NOTES ON THEIR FLORA AND 

 FAUNA. 



By J. C. F. Fryer, B.A., Balfour Student in the University of Cambridge. 



(Plates 22—29 and Text-Figures 1—3.) 

 (Communicated by Prof. J. Stanley Gardiner, M.A., F.R.S., F.L.S.) 



Read 3rd November, 1910. 

 TABLE OF CONTENTS. 



I. Introduction ... ... ... 397 IV. 



Reasons for the Expedition — History of V. 



the Aldabra regions — Topography of 

 the Aldabra regions. VI. 



II. Aldabra ... ... ... ... 400 VII. 



A. Physical features. VIII. 



B. Land topography. IX. 



C. Structure : (a) Coralline limestones ; X. 

 (b) Abnormal rocks (phosphatic lime- 

 stones). 



III. Aldabra. Lagoon and Passes, and their 



Fauna ... ... ... ... 408 



Aldabra. Fringing Reef — Reef Fauna 412 

 Aldabra. The Land Flora and 



Fauna... ... ... ... 414 



Astovk ... ... ... ... 426 



Cosmoledo ... ... ... 428 



Assumption ... ... ... 431 



Farquhar, Providence and St Pierre 433 

 The Formation and Future of the 



Islands ... ... ... 434 



Bibliography ... ... ... 440 



Description of Plates ... ... 441 



I. INTRODUCTION. 



Volumes xii. and xiii. (Ser. 2, Zool.) of the Transactions of this Society contain a 

 series of papers dealing with the various biological problems of the Indian Ocean, and 

 constituting the results of the Percy Sladen Trust expedition in H.M.S. " Sealark," under 

 the leadership of Professor J. Stanley Gardiner. In a previous expedition Stanley Gardiner 

 had investigated the Maldive and Laccadive Archipelagoes, and, before turning to what 

 may perhaps be considered the last expedition of the series, it is necessary to refer in 

 greater detail to its forerunners. 



The Maldive and Laccadive expedition was mainly devoted to an elaborate investiga- 

 tion of the formation of those archipelagoes, and the results show that their islands were 

 formed by the elevation of flourishing coral reefs, and that the bases, on which these reefs 

 grew, consist of the remnants of a continental bridge, which connected India and Africa 

 approximately from carboniferous to tertiary times. 



The two problems thus involved, that of the formation of coral reefs and of the conti- 

 nental land connection, were considered of such importance that the " Sealark " expedition 

 was organised largely, though not entirely, for their further consideration ; many of the 

 islands in the western Indian ocean had never been visited by scientific observers, and 

 their structure in most cases was but vaguely known. 



The results of the " Sealark " expedition, taken in conjunction with those of the 

 SECOND SERIES— ZOOLOGY, VOL XIV. 51 



