CORAL-REEFS. 139 



The disseverment of the larger Maldiva atolls. — The 

 apparent progressive disseverment in the Maldiva Archi- 

 pelago of large atolls into smaller ones, is, in many respects, 

 an important consideration, and requires an explanation. 

 The graduated series which marks, as I believe, this process, 

 can be observed only in the northern half of the group, 

 where the atolls have exceedingly imperfect margins, con- 

 sisting of detached bason-formed reefs. The currents of the 

 sea flow across these atolls, as I am informed by Capt. 

 Moresby, with considerable force, and drift the sediment 

 from side to side during the monsoons, transporting much 

 of it seaward; yet the currents sweep with greater force 

 round their flanks. It is historically known that these atolls 

 have long existed in their present state ; and we can believe, 

 that even during a very slow subsidence they might thus 

 remain, the central expanse being kept at nearly its original 

 depth by the accumulation of sediment. But in the action 

 of such nicely balanced forces during a progressive sub- 

 sidence (like that, to which by our theory this archipelago 

 has been subjected), it would be strange if the currents of 

 the sea should never make a direct passage across some one 

 of the atolls, through the many wide breaches in their 

 margins. If this were once effected, a deep-water channel 

 would soon be formed by the removal of the finer sediment, 

 and the check to its further accumulation ; and the sides of 

 the channel would be worn into a slope like that on the 

 outer coasts, which are exposed to the same force of the 

 currents. In fact, a channel precisely like that bifurcating 

 one which divides Mahlos Mahdoo (Plate III., Fig. 4), 

 would almost necessarily be formed. The scattered reefs 

 situated near the borders of the new ocean-channel, from 

 being favourably placed for the growth of coral, would, by 

 their extension, tend to produce fresh margins to the 



