INTRODUCTION. xix 



as in Tiladummati and Miladummadulu, the circulation beconaes almost 

 oceanic. The reef and islands of portions of each bank will show the effect 

 of the greater or more limited circidation. This is admirably shown by the 

 condition of the reefs and heads described by Mi\ Gardiner' as existing 

 in the "jungle of reefs" in North Malos. 



Gardiner calls attention to the contrast of the slight growth of corals off 

 a reef in an enclosed atoll or clusters like Haddummati or Kolumadulu to 

 the luxuriant growth off a reef in open banks like Miladummadulu. This, 

 in such large, comparatively open atolls, is often due quite as much to many 

 minor local causes as to the prevailing oceanic conditions. 



In the Maldives the increase in size of the islands on the outer land rim 

 of atolls goes on much as we have observed it in the Gilbert, Ellice, Marshall, 

 and Paumotu Islands. Small islets or islands on the same reef flats are 

 gradually united by the formation of sand spits on the lee face of the islands, 

 thus forming bays on the sea face of an atoll ; the spits gradually approach, 

 become connected, and the filling up of the bay from the sea face unites 

 adjacent islands; their former disconnected state is merely indicated by a 

 difference in the growth of the vegetation, a distinction which gradually 

 disappears with years. The bay may also be formed on the lee side by the 

 throwing up on the sea face of a bar on the edge of the reef flat between 

 separate islands, and the bay may then be filled up both from the lee and 

 weather side and thus unite separate islands or sand-bars. 



The existence of lagoons completely shut off from the sea in some of the 

 atolls of the northern part of the Maldives is readily explained by their mode 

 of formation ; this can be traced in all its stages, from the time the atoll con- 

 sists of a crescent-shaped island occupying only a portion of the reef flat of 

 the ring, the remainder of the reef flat of the ring still enclosing a compara- 

 tively deep lagoon sometimes with six to seven fathoms of water. The 

 island throws out spits from the horns of the crescent until there is only a 

 narrow pass left between them, and finally this gap is closed by a sand or 

 shingle beach and we have the ideal atoll, — a closed ring of land enclosing 

 a deep lagoon, which exists so rarely but is always the atoll to which one 

 refers when discussing the coral-reef question. These phenomena are well 



1 hoc. cit., p. 166. 



