2 THE CORAL REEFS OF THE MALDIVES. 



group, eighty-two in North Nilandu, one hundred and twenty-eight in South 

 Nilandu ; but in this enumeration each lagoon reef as well as each reef hat 

 was counted as a unit, and no account was taken of the many islands which 

 sometimes occur on each flat. In groups like Ari, North Male, and North 

 Nilandu, the increase in number could not be great. But in an atoll like 

 Suvadiva and such groups as South Male, South Nilandu. Mulaku, Koluma- 

 dulu, and Haddummati, where are often a great number of small islands 

 forming a chain on the extensive reef flats, then the number of islands on 

 the reef flats we have considered as units becomes very great. 



The coral reefs of the Haapai and of the Nomuka groups, the central 

 part of the Tonga Islands, is another region which may be compared to the 

 Maldives. Both the Tongan groups are independent banks separated by 

 narrow and moderately deep channels from the banks to the north and 

 south of them, and themselves separated by a channel of about five miles 

 with depths varying from three hundred fathoms in the central part of the 

 channel to three hundred and fifty and nearly five hundred at its eastern 

 and western extremities. 



The Haapai and Nomuka groups hold to each other much the same 

 relation which North and South Malosmadulu have. The plateaus of these 

 groups are well defined by the steep falling off near the one-hund red-fathom 

 line ; from their shallower parts rise secondary plateaus forming the coral 

 reefs of Nomuka and Haapai. The circular or elongated lagoon reefs of the 

 Haapai Plateau are flanked on the east and south by linear or circular reefs, 

 while the Nomuka reefs are flanked by linear reefs, only on a part of the 

 east face of the Nomuka Plateau. 1 



The Maldive Islands (PI. 7) are about four hundred miles west of 

 Ceylon. They extend north and south for a distance of about four hun- 

 dred and seventy miles ; from 7 ° north latitude to fift}^ miles south of the 

 Equator. The central part of the archipelago (PI. 1) consists of two chains 

 of groups separated by a channel, varying in width from less than ten 

 miles between Miladummadulu and North Malosmadulu to over twenty- 

 five miles between Ari and South Male. 



1 Admiralty Charts 2421, 3099, 3100, 474 ; A. Agassiz, Mem. M. C. Z. Vol. XXVIII., pp. 175, 

 192-197, Pis. 214-218. 



