48 J. STANLEY GARDINER. 



the whole lagoon with dredgings without finding any trace of such. In its southern half 

 this deeper area is covered with extremely fine sand with delicate shells and Halimeda 

 leaflets. This gradually gives place northwards to an area of broken coral fragments in 

 process of decay, studded perhaps with small colonies of Polyzoa. Towards the passage 

 Polytrema and nullipores begin to appear, and the bottom consists largely of their rounded 

 masses, 1 or 2 inches in diameter, each on a coral core. The depths in the Admiralty 

 Chart are to ail intents accurate, but the 2 fathom area is greater, as also is the 5 fathom. 

 The latter indeed occupies the whole centre, and in the middle of it is an elongated pit 

 with 7 to 9 fathoms. Dredging in this part of the lagoon is extremely unproductive. 

 No fixed organisms other than those already mentioned were obtained. For the rest 2 

 Gastropods, 1 Lamellibranch, an Asymmetron, a Carib and a few sand-loving Macrura alone 

 were obtained in any considerable numbers. 



Section .5. The History of Minikoi as an Atoll. 



In the foregoing I have been at some pains to show that an elevation of at least 

 24 feet must be allowed for the whole atoll. I do not myself consider that the change 

 of level has been much greater than this. Therein I am supported by the general appearance 

 of the corals in the conglomerate, which indicates a formation in shallow water. The point 

 may seem a small one, but it gains in importance from the wide distribution of absolutely 

 similar conglomerate on the atolls both of the Indian and Pacific Oceans. Yet I cannot 

 maintain that an ocean reef at a depth of 10 or even 15 fathoms, swept, as is probable, 

 by a strong current, would not if elevated to the same height have in its conglomerate a 

 similar structure. The sea has now been quite sufficiently explored in the tropics to show 

 that relatively few reefs exist of such a character, most having at least grown into true 

 atoll reefs awash. The reef, too, would have had to have been caught by the elevation 

 at just the right period, for with pure oceanic conditions — the most favourable, if judgement 

 may be based on the more perfect forms of atolls, afar from land, — it could only take a 

 relatively very short time for the reef to rise from 10, or even 20 or 30 fathoms to the 

 surface. The rocky area of the land lies obviously on reef. Remembering both this fact 

 and the regularity of the existing reef, I may point out that such deep shoals have not 

 usually perfect rims, but merely here and there peaks and banks approaching the surface. 



It appears to me then a fair assumption that the atoll existed as such when the change 

 of level took place. In further support of my contention that the elevation has been but 

 small, I would point out that the conglomerate appears to have been of very recent forma- 

 tion, a character fully supported by the same rock in the whole of the Maldive Archipelago. 

 Coral-rock, when elevated in any great thickness, soon loses its distinct, organic structure, 

 assuming a hard, uniform, crystalline character by rain-water solution and the reprecipita- 

 tion of its line. This may be seen in the Fijies, Tonga, Pelews, Solomons, Christmas 

 island and West Indies, indeed wherever reefs of any considerable thickness have been 

 elevated above the waves. The island of Viti Levu, Fiji, is perhaps an exception, but the 

 conditions are peculiar here, in that there must have been several elevations and subsi- 

 dences, in which the coral-rock was covered with the practically impervious so-called 

 "soapstone^" Of course the argument depends on the assumption with which I started, 



' Vide Proc. Camb. Phil. Soc, vol. ix., p. 453. (1898.) 



