27G MALDIVA ARCHIPELAGO. 



a map of them Avithout believing that they were 

 once more intimately related ; and in this same 

 archipelago, Mahlos-Mahdoo atoll is divided by a 

 bifmxating channel, from 100 to 132 fathoms in 

 depth, in such a manner that it is scarcely possible 

 to say whether it ought strictly to be called three 

 separate atolls, or one great atoll not yet finally 

 divided. 



I will not enter on many more details ; but 1 

 must remark that the curious structure of the 

 northern Maldiva atolls receives (taking into con- 

 sideration the free entrance of the sea through 

 their broken margins) a simple explanation in the 

 upward and outward growth of the corals, original- 

 ly based both on small detached reefs in their la- 

 goons, such as occur in common atolls, and on 

 broken portions of the linear marginal reef, such 

 as bounds every atoll of the ordinary form. I can- 

 not refrain from once again remarking on the sin- 

 gularity of these complex structures — a great sandy 

 and generally concave disk rises abruptly from the 

 unfathomable ocean, Avith its central expanse stud- 

 ded, and its edge symmetrically bordered with oval 

 basins of coral-rock just lipping the surface of the 

 sea, sometimes clothed with vegetation, and each 

 containing a lake of clear water ! 



One more point in detail : as in two neighbour- 

 ing archipelagoes corals flourish in one and not in 

 the other, and as so many conditions before enu- 

 merated must affect their existence, it would be an 

 inexplicable fact if, during the changes to which 

 earth, air, and water are subjected, the reef-build- 

 ing corals were to keep alive for perpetuity on any 

 one spot or area. And as by our theory the areas 

 including atolls and barrier-reefs are subsiding, we 

 ought occasionally to find reefs both dead and sub- 

 merged. In all reefs, owing to the sediment being 



