CORAL REEFS OF THE INDIAN OCEAN. 13 



Life in different Positions) — Lagoon Coral Reefs (Distribution, Description, 

 dead Reefs, etc.) — Deep Water — Sec. 5. The History of Minikoi as an 

 Atoll — Elevation — A Perfect Atoll — Gain and Loss — A Century Ago (native 

 Evidence) — Reconstruction of Land and Reef. 



{To he continued.) 



CHAPTER I. 



The Coral Reefs of the Indian Ocean. 



The topography of the Indian Ocean gives but little aid to the student in attempting 

 to determine the character of the foundations of the various island groups. Far less indeed is 

 this the case here than in the Pacific Ocean, where the trend ot each of the larger groups 

 has a tendenciy to run somewhat parallel to that of others and to continental land, sug- 

 gesting that they lie on lines of weakness of the earth's crust, lines of former volcanic 

 activity. The two oceans are alike in that the western part of each is almost bare of 

 coral islands, the Pacific absolutely so, the Indian Ocean with Cocos-Keeling' and Christmas 

 islands" alone. Of these the former is the type, on which descriptions of most atolls have 

 been moulded, and the latter is an ancient atoll, which has undergone great elevation, the 

 only one indeed in the whole Indian Ocean. This lack of raised reefs is remarkable, as 

 compared with the Pacific Ocean, and can only be taken as an indication of the absence 

 of any considerable volcanic activity in modern times, at any rate between Madagascar and 

 India. 



There are only two changes in the past in connection with the topography of the 

 Indian Ocean, about which there is any general consensus of opinion, i.e. a former water 

 connection with the Atlantic Ocean, and a land connection between Madagascar and Africa. 

 The permanency since the Jurassic period of the Arabian Sea and of the great basin between 

 Chagos and Rodriguez on the one hand and Australia on the other has not been seriously 

 impeached, so that there is only left a belt between S. Africa and S. India, and it is in 

 this that all the considerable coral reefs lie. The general depth of the whole Indian Ocean 

 is remarkably uniform, about 2500/ (fathoms), a single sounding only of over 3000/. (3097 

 to the S.W. of Christmas island) having been obtained. What however is still more notice- 

 able is, that not a single sounding N. of the line between Cape St Mary (S. Madagascar) 

 and Cape Leeuwin (S.W. Australia) has been run of less than 2000 / except near continental 

 land, or close to islands and shallow reefs, the existence of which is known at the present 

 day. The soundings, such as they are, although not quite close enough, give strong in- 

 dications, that the belt between Madagascar and India is cut by a depth of over 2000/ 

 in three places, i.e. between the Maldives and Chagos, between the latter and Saya de 



' Vide ''The Structure and Distribution of Coral Reefs," ^ Vide "A Monograph of Christmas Island, Indian 



by Chas. Darwin (1889) and "The Cocos-Keeling Islands" Ocean." British Museum (1900). 

 by H. P. Guppy, Scottish Geo. Mag. (1889). 



