CORAL-REEFS. gi 



The Maldiva Archipelago is 470 miles in length, with an 

 average breadth of about 50 miles. The form and dimen- 

 sions of the atolls, and their singular position in a double 

 line, may be seen, but not well, in the greatly reduced chart 

 (Fig. 2) in Plate III. The dimensions of the longest atoll 

 in the group (called by the double name of Milla-dou-Madou 

 and Tilla-dou-Matte) have already been given ; it is 88 miles 

 in a medial and slightly curved line, and is less than 20 

 miles in its broadest part. Suadiva, also, is a noble atoll, 

 being 44 miles across in one direction, and 34 in another, 

 and the great included expanse of water has a depth of 

 between 250 and 300 feet The smaller atolls in this group 

 differ in no respect from ordinary ones ; but the larger ones 

 are remarkable from being breached by numerous deep- 

 water channels leading into the lagoon ; for instance, there 

 are 42 channels, through which a ship could enter the 

 lagoon of Suadiva. In the three southern large atolls, the 

 separate portions of reef between these channels have the 

 ordinary structure, and are linear ; but in the other atolls, 

 especially the more northern ones, these portions are ring- 

 formed, like miniature atolls. Other ring-formed reefs rise 

 out of the lagoons, in the place of those irregular ones which 

 ordinarily occur there. In the reduction of the chart of 

 Mahlos Mahdoo (Plate III., Fig. 4), it was not found easy to 

 define the islets and the little lagoons within each reef, so 

 that the ring-formed structure is very imperfectly shown : in 

 the large published charts of Tilla-dou-Matte, the appearance 

 of these rings, from standing further apart from each other, 

 is very remarkable. The rings on the margin are generally 

 elongated; many of them are three, and some even five 

 miles, in diameter; those within the lagoon are usually 

 smaller, few being more than two miles across, and the 

 greater number rather less than one. The depth of the 



