6 THE CORAL REEFS OF THE MALDIVES. 



its northern extension, Cardamum Bank, which equal in depth and nearly 

 equal in size the largest plateaus of the Maldivian groups, for Bassas de 

 Pedro is seventy miles in length, and the Piti Bank about forty. Three of 

 the larger banks have no islands or lagoon reefs, the others culminate in 

 coral reefs, having the structure of atolls ; some of the small banks are no 

 larger than many lagoon reefs or faros in the Maldives. 



The soundings (PI. 7) also indicate a narrow swale from fifteen to twenty 

 miles wide, limited by the one-thousand-fathom line, as uniting Ihavandiffulu 

 in the northern Maldives with Minikoi. A similar ridge has been sketched 

 out by the Valdivia,' south of Addu, towards Diego Garcia, a distance of 

 nearly three hundred miles ; but Addu and Diego Garcia are separated by a 

 much deeper channel, of twenty-five hundred fathoms in depth (PI. 7), fully 

 as great a depth as the average of the Indian Ocean to the east and west of 

 the supposed Addu ridge. 



A long ridge bounded by the one-thousand-fathom line seems to unite 

 Kalpeni with Suheli Par with a somewhat deeper channel between it and 

 the Laccadives to the north, of a greatest depth of over twelve hundred 

 fathoms ; while a much broader and deeper channel separates this rise 

 from Minikoi and the small banks immediately to the north with a greatest 

 depth of nearly thirteen hundred fathoms. 



The fifteen-hundred-fathom line of the great tongue of the ocean (PI. 7), 

 between Ceylon and the Maldives, extends north as far as the ninth degree 

 of north latitude, to the east of Minikoi and the Laccadives about halfway 

 between them. On the west of the Laccadives and Maldives the fifteen- 

 hundred-fathom line runs close to the western shore of the latter off Ari ; 

 it is not more than eight miles from the one-hundred-fathom line to the 

 west of the Laccadives ; it runs in a northerly direction thirty miles west 

 of Agatti to west of Cora Divh. 



' Wissenshaftliche Ergebnisse d. Deutschen Tiefsec Expedition auf d. Dampfer " Valdivia." 

 Erster Band, Oceanographie ... v. Dr. G. Schott, 1902, p. 117., Taf. HI. 



The soundings on which the existence of this ridge are based are so widely separated that it is not 

 possible to determine if the deep soundings of twenty-five hundred fathoms to the west of the Une run by 

 the " Valdivia " do not e.xtend across it as a deep valley fully as deep as the oceanic depths, both to the 

 east and west. It seems somewhat far-fetched to speak, as does Dr. Schott, of the Carolines, Marshall, 

 and Gilbert Islands as connected by a plateau with a depth of four thousand metres ; and to speak of 

 coral island districts as generally connected by such plateaus. 



