STRUCTURE OF CORAL ISLANDS. 189 



Royal Geographical Society, vol. v., p. 398 ; and another on 

 this group by J. J. Horsburgh, and W. F. W. Owen, in the 

 the same journal, vol. ii., pp. 72 and 81. As stated by Mr. 

 Darwin, the archipelago has a length of 470 miles, with an 

 average breadth of 50 miles ; and it consists for the most of 

 its length of two parallel lines of atolls. The large atoll at 

 the north end has a length of 88 miles, while Suadiva, one of 

 the southernmost, is 44 miles long from north to south, and 

 34 miles across. 



The point of special interest in their structure is the oc- 

 currence of atolls or annular reefs within the larger atolls 



% IWells Is 4 



zoo .&, 





St g^* sbofanindvioaTrdle. 



,^pto^fvgorsbur^i Atoll 



MAHLOS MAHDOO ATOLL, WITH HORSBURGH ATOLL. 

 *Sca?« 1-20 o/" an inch to a mile. 



The islets of the lagoon and those of the encircling reef, are 

 in many instances annular reefs, each with its own little lake, 

 Gems within gems are here clustered together. 



