Sect. I. KEELING ATOLL. 15 



reef, the channels and hollows become filled up with 

 fragments cemented together by calcareous matter ; and 

 the surface of the reef is converted into a hard smooth 

 floor (G of wood-cut), like an artificial one of free- 

 stone. This flat surface varies in width from 100 to 

 200, or even 300 yards, and is strewed with a few large 

 fragments of coral torn up during gales : it is uncovered 

 only at low water. I could with difficulty, and only 

 by the aid of a chisel procure chips of rock from 

 its surface, and therefore could not ascertain how 

 much of it is formed by the aggregation of detritus, 

 and how much by the outward growth of mounds of 

 corals, similar to those now living on the margin. No- 

 thing can be more singular than the appearance at low 

 tide of this ' flat ' of naked stone, especially where it is 

 externally bounded by the smooth convex mound of 

 JSTulliporse, appearing like a breakwater built to resist 

 the waves, which are constantly throwing over it sheets 

 of foaming water. The characteristic appearance of 

 this ' flat ' is shown in the foregoing wood-cut of Whit- 

 sunday Atoll. 



The islets on the reef are first formed between 200 

 and 300 yards from its outer edge, through the accu- 

 mulation of a pile of fragments, thrown together by 

 some unusually strong gale. Their ordinary width is 

 under a quarter of a mile, and their length varies from 

 a few yards to several miles. Those on the S.E. and 

 windward side of the atoll, increase solely by the addi- 

 tion of fragments on their outer side ; hence the loose 

 blocks of coral, of which their surface is composed, as 

 well as the shells mingled with them, almost exclu- 



