Sbct. III. MALDIYA ATOLLS. 45 



perfectly shown : in the large published charts of Tilla- 

 dou- Matte, the appearance of these rings, from stand- 

 ing 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 little 

 lagoon within these small annular reefs is generally from 

 five to seven fathoms, but occasionally more ; and in Ari 

 atoll many of the central ones are twelve, and some 

 even more than twelve fathoms deep. These rings rise 

 abruptly from the platform or bank on which they 

 stand ; their outer margins are invariably bordered by 

 living coral, 1 within which there is a flat surface of 

 coral rock ; on this flat, sand and fragments have in 

 many cases accumulated and been converted into islets 

 clothed with vegetation. They are indeed larger, and 

 contain deeper lagoons than many true atolls standing 

 in the open sea; and I can point out no essential 

 difference between these little ring-formed reefs and 

 the most perfectly characterised atolls, excepting that 

 they are based on a shallow foundation, instead of on 

 the floor of the ocean, and that instead of being 

 scattered irregularly, they are grouped closely together 

 with the marginal rings arranged in a rudely-formed 

 circle. 



The perfect series which can be traced from a linear 



1 Captain Moresby informs me that Millepora comjplanata is one of 

 the commonest kinds on the outer margin, as it is at Keeling atoll. 



