DEPTH OF CORAL GROWTH. 



323 



In conclusion, it is a fail- deduction that the increase both in depth and extent in the 

 lagoons of the Maldive atolls is mainly due to solution, an important additional factor being 

 the outwash of fine matter by the tidal and oceanic currents. It is obvious, though, that 

 there are two nicely balanced sets of conditions, causing the filling in or increase in size 

 of any lagoon. A quantitative estimation of these, a comparison of the factors — analyses of 

 the water at different states of the tide and from several parts of each lagoon, estimation 

 of the amount of water entering or leaving each lagoon, areas of coral growth, etc. — would 

 be useful, and could not fiiil to throw much desirable light on this most complicated question^ 



Section III. The Bathymetrical Limits of Coral-Reef Builders. 



While the dredgings in the Maldive Archipelago were mainly taken to ascertain the 

 general characters of the bottom and its fauna and flora in diff'erent jaositions, the situations 

 were — by particular requests of various authorities on the formation of coral reefs— 

 largely chosen with the view of ascertaining the depth to which the reef corals extend. 

 Dredges of Naples and Plymouth designs and hempen swabs, 3 to 9 feet long, were largely 

 used in addition to the Otter trawl and beam trawls of various patterns. The eff'ectiveness 

 of all these in procuring corals from shallow water, where the bottom could be seen, was 

 carefully ascertained, and the trawls were additionally weighted with 2 or 4 old fire-bars for 

 deeper work. During the time I had the steamer for dredging I chose some of the roughest, 

 and hence most likely ground, between 30 and 50 fathoms, ultimately breaking or leaving 

 most of my a^jjiaratus on the bottom. Much dead coral rock was brought up, some of it 



also for giving me the assistance of trained attendants. water and dried, and the organic matter burnt off. The 

 Three to ten grams were taken of each sample after it had amount of silica (SiO.,) was then estimated. The only metals 

 been well mixed, the whole carefully washed with distilled found were Calcium, Magnesium, Aluminium and Iron. 



Remarks 



Elevated rook 



Elevated rock 



Elevated rook 



Elevated rock; the sand infiltra- 

 tion between the corals 



Elevated rock ; consolidated mud 

 between corals 



Elevated rock ; mixed corals and 

 mud 



From a freshwater pool 



A recent rock 

 A recent rock 

 Two analyses 

 Two analyses 

 Two analyses 



rove a very extensive solution for 



