140 CORAL-REEFS. 



dissevered portions ; such a tendency is very evident (as may 

 be seen in the large published chart) in the elongated reefs 

 on the borders of the two channels intersecting Mahlos 

 Mahdoo. Such channels would become deeper with con- 

 tinued subsidence, and probably from the reefs not growing 

 up perpendicularly, somewhat broader. In this case, and 

 more especially if the channels had been formed originally 

 of considerable breadth, the dissevered portions would be- 

 come perfect and distinct atolls, like Ari and Ross atolls 

 (Plate III., Fig. 2), or like the two Nillandoo atolls, which 

 must be considered as distinct, although related in form and 

 position, and separated from each other by channels, which 

 though deep have been sounded. Further subsidence 

 would render such channels unfathomable, and the dis- 

 severed portions would then resemble Phaleedoo and 

 Moluque atolls, or Mahlos Mahdoo and Horsburgh atolls 

 (Plate III., Fig. 4), which are related to each other in no 

 respect except in proximity and position. Hence, on the 

 theory of subsidence, the disseverment of large atolls, which 

 have imperfect margins (for otherwise their disseverment 

 would be scarcely possible), and which are exposed to 

 strong currents, is far from being an improbable event ; and 

 the several stages, from close relation to entire isolation in 

 the atolls of the Maldiva Archipelago, are readily explicable. 

 We might go even further, and assert as not improbable, 

 that the first formation of the Maldiva Archipelago was due 

 to a barrier-reef, of nearly the same dimensions with that 

 of New Caledonia (Plate III., Fig. 3), for if, in imagination, 

 we complete the subsidence of that great island, we might 

 anticipate from the present broken condition of the northern 

 portion of the reef, and from the almost entire absence of 

 reefs on the eastern coast, that the barrier-reef after repeated 

 subsidences, would become during its upward growth 



