322 J. STANLEY GARDINER. 



of change in the sea-water. The currents of the two monsoons are important as well as 

 the tidal current over the whole bank. With the banks close together and having deep 

 passages these largely pass directly through the atoll basins. They thus sweep out small 

 particles in suspension as well as frequently renew the water, so that the total amount of 

 lime removed is greatly increased. The want of protection by land is important, for, whereas 

 Addu lagoon with a westerly gale was quite calm and the water clear to 10 or 12 fathoms, 

 Goifurfehendu and Bodu-faro (N. Mahlos) basins — both as completely enclosed by surface 

 reefs — with not heavier winds were so churned up that the bottom was scarcely visible at 

 6 fathoms. The sea in rough weather was noticed to be quite milky even some miles off 

 Suvadiva, Haddumati and North Male, while immediately off Addu it was comparatively 

 clear. Even in calm weather the meshes of our tow-nets tended in passages to get blocked 

 up with dead organic matter and fine mud in suspension, showing what enormous effect 

 this sweeping out might have with a moderately rough sea. This movement of organic 

 matter has another, an indirect effect in the formation of lagoons of infinitely more 

 importance than its direct effect, i.e. in driving mud against the living reefs and corals, 

 causing the extinction of small coral colonies and larvae, and enormously hampering the 

 growth of larger masses. This effect of mud I have already drawn attention to in the 

 Pacific. In the Maldives I had abundant opportunity of confirming my observations, and 

 I would only here emphasise what I then wrote'. 



Important as the outwash of detritus really is, I cannot for a moment consider that 

 it apjjroaches solution in its effects in deepening lagoons after the reefs on a bank have 

 assumed the definite atoll condition. On banks such as Suvadiva, Felidu, Kolumadulu and 

 Haddumati considerable areas of the bottom must — owing to the perfection of these atoll- 

 forms — be affected to an insufficient degree to greatly stir up their deposits, while probably 

 the currents and winds would give an amj)le circulation for solution by the sea-water. That 

 this is the case is clearly shown by the presence in protected situations of deposits of soft 

 mud. Any deposit of the lagoons, however clean it may appear, has always a distinct 

 amount of organic matter in the process of decay, this providing carbonic acid gas for the 

 solution. The absence generally of deposition of calcium carbonate in dead coral masses in 

 the larger lagoons — common in many of the smaller atolls and faro — would go to prove 

 that there is no supersaturation by the lime, and hence that there is free circulation of 

 the water. 



Some of the muds are being examined by Sir John Murray, and will form the subject 

 of a separate report. I however made a series of analyses to ascertain the silica (SiOa) 

 in a number of samples'-. The analyses of 14 surface sands and rocks gave an average 

 percentage of ■047 of silica, while three samples of mud from 40 — 50 fathoms fi-om Suvadiva 

 lagoon gave 2"441, the latter thus having about 50 times as much silica as is found in 

 the surface rock. To put the matter in another way — admitting solution — about 50 volumes 

 of the sand and rock from the reef and land would have to be dissolved to give the 

 amount of silica found in 1 volume of the Suvadiva mud. No doubt some of the excess 

 of silica in the latter may be explained by special causes, influencing its formation. Never- 

 theless I fail to see that any complete explanation can be afforded that does not take into 

 consideration the solvent action of the sea. 



1 Loc. cit. p. 484, et seq. Chemical Laboratory of Gonville and Caius College at my 



2 I am indebted to Mr M. M. Pattison Muir for placing the disposal during the Easter vacation for these analyses, and 



