ORIGIN OF TUB ATOLL. 267 



not impossible that dry land might form in certain favorable 

 spots on the reef while the subsidence was still in progress, if 

 the sinking were not beyond a certain rate. 



A cessation or diminution of subsidence, in the case of the 

 barrier reef about a high island, might result in its becoming 

 covered with verdure like the finished atoll. 



All the features of atolls harmonize completely with, 

 this view of their origin. In form they are as various and 

 irregular as the outlines of barrier reefs. Compare Angau of 

 the Feejees, with Tari-tari of the Gilbert Group (p. 165); 

 Nairai or Moala with Tarawa ; Nanuku with Maiana or Ap- 

 amama. The resemblance is close. In the same manner we 

 might find the many forms of lagoon reefs represented among 

 barrier reefs. 



We observe, also, that the configurations are such as would 

 be derived from land of various shapes of outline, whether 

 a narrow mountain ridge (as in Taputeouea, one of the Gilbert 

 Islands), or wide areas of irregular slopes and mountain 

 ranges. Among the groups of high islands, we observe that 

 abrupt shores may occasion the absence of a reef on one side, as 

 on Moala ; and a like interruption is found among corai 

 islands. Many of the passages through the reefs may be thus 

 accounted for. 



The fact that the submerged reef is often much prolonged 

 from the capes or points of a coral island, accords well with 

 these views. These points or capes correspond to points 

 in the original land, and often to the line of the prominent 

 ridge ; and it is well known that such ridge lines often ex- 

 tend a long distance to sea, with slight inclination com- 

 pared with the slopes or declivities bounding the ridge on 

 either side. 



Coral islands or reefs often lie in chains like the peaks of 



