148 THE CORAL REEFS OF THE MALDIVES. 



land. On the lagoon slope of Gan corals, although growing in many 

 irregular patches, yet do not seem to me to grow as vigorously as they are 

 stated to do by Gardiner in Addu. 1 In from eight to ten fathoms the 

 masses already grow somewhat apart, and gradually become separated by 

 wide lanes of coral sand. 



1 Mr. Gardiner states that Addu is filling with sand derived from the disintegration of the coral 

 growth, which, taken as a whole, he says, "quite surpasses in vigor anything in my experience elsewhere, 

 either in the Maldives or in the Pacific." This Mr. Gardiner bases on soundings taken by Mr. Cooper,* 

 and asks for a comparison of his amended chart with the Admiralty Chart, though Mr. Gardiner 

 recognizes the uselessness of isolated soundings, from the difficulty of fixing points of reference, due to 

 changes in the land ; he says, " we could get no even approximative^ fixed points for our sight." f 



Mr. Gardiner on his amended chart places the northeast point of Addu nearly half a mile more to 

 the eastward than Moresby, and thus shows a great increase in the dimensions of the northeast horn 

 flats ; this renders it impracticable to locate Mr. Cooper's soundings on the Admiralty map. Taking the 

 general trend of the lines south of Hangadu — Gardiner, loc. cit., p. 415, fig. 109 — to the western spit of 

 the southeast passage, thence towards Ilika and the line immediately south of the northwestern passage 

 with its northeastern extension to Balihura, we do not find Mr. Cooper's soundings sufficiently close to 

 the positions of Moresby's soundings to warrant his conclusions. Mr. Gardiner's soundings of thirty-one 

 fathoms, or any other, as plotted, do not come sufficiently near the thirty-nine-fathom spot of Moresby 

 to be proof of a change of level of eight fathoms. 



Granting that in Addu, being outside the influence of the trades, J the currents due. to them cannot 

 affect the circulation of its lagoon as greatly as in more open northern atolls, yet the circulation due to 

 the tides alone is sufficiently active to induce comparatively rapid change in the waters of the lagoon. 

 Mr. Gardiner ascribes the filling of the lagoon " rather to the want of solution " and decrease in depth 

 of the passages (which is not demonstrated) "than to the luxuriant growth of corals;" yet the north- 

 western horn has been shut off by corals since 1836. Against this § he sets the possible decrease of the 

 area from which the sediment is supplied, which he attributes in one case to increase of land, and in the 

 other looks upon it as an " effective source of sediment." While acknowledging the important agency 

 of solution in modifying the hydrography of a lagoon, it seems hazardous to measure its efficiency by 

 the comparative surveys made by Mr. Gardiner in the Maldives : || its existence and extent is far more 

 readily perceived in the changes which, by analogy, we may fairly estimate in such atolls as Fulanga, 

 Argo, Ongea, Yangasa, and others in Fiji. If 



Mr. Gardiner estimates** that five-sevenths of the lagoon of Addu is protected by land, and that 

 there are but ten miles of flats over which water can have access to the lagoon. It certainly is well 

 protected on the west face, and on a good part of the eastern face; but it seems to me that Mr. 

 Gardiner's estimate of the effect of this protection is altogether too great. Ten miles of flats, together 

 with two channels with only a narrow irregular ridge separating deep water from the lagoon, is an area 

 quite sufficient to allow a fair circulation of water in the lagoon, and to account for a better growth of 

 corals where the water from the flats strikes the lagoon. Mr. Gardiner speaks of the water in the 

 lagoon of Addu "as considerably clearer than in most basins." ff Our experience during our short stay 

 in Addu was quite the contrary; the water was everywhere remarkably turbid. Although the reef flats 

 of Addu average more in breadth than those of any of the other Maldive groups, yet the difference does 

 not appear important enough to sustain Mr. Gardiner's conclusions that although there has been solution, 

 now there is little solution, owing to the want of circulation, for according to his views, when an atoll 

 is more or less closed, then begins the period of solution in depth. 



* Loc. cit., p. 318. § Loc. cit., p. 321. ** Loc. cit., p. 320. 



t Loc. cit., p. 415. || Loc. cit., p. 323. tt Loc. cit., p. 320 



t Loc. cit., p. 321. T Bull. M. C. Z., Vol. XXXIII., pp. 57, 60, 62. 



