xxiv INTRODUCTION. 



an atoll after it has " become fairly perfect," ^ though he recognizes " the 

 outwash of mud as an important and direct subsidiary cause." ^ It has con-, 

 siderable bearing on the nature of the deposits on the outer face of an atoll. 

 The amount of detritus washed out of a lagoon depends again in great 

 measure on the position of an atoll. If sheltered or exposed to the sweep 

 of the monsoons, the amount of silt will greatly vapy with the depth of 

 the lagoon, and will be more or less detrimental to the growth of corals 

 wherever they happen to grow, on the lagoon or sea face. 



No one can cross one of the Fiji atolls of the Lau group ^ without being 

 struck with the evidence of the action of solution on the islands, islets, and 

 flats within the lagoon. Such atolls as Fulanga, Ongea, the Yangas^ cluster, 

 the Argo reef, and others of the Lau group show this effect most plainly. 

 Islands like Kambara, Vatu Leile, Mango, are on a large scale, pitted, 

 honeycombed, and under-cut by the combined wearing and solvent action 

 of the sea. But with our present knowledge it seems difficult to assign 

 to each factor its proportionate value. 



Wherever in the Maldives reef rock was examined I found it without 

 exception of the most modern character, a few exposures as horses on the 

 beaches and on the reef flats would seem to indicate a slight elevation of 

 the Maldives. If the existing conditions at the Maldives have been brought 

 about by subsidence, it is strange we should not find anywhere on this ex- 

 tensive plateau, from the northernmost atolls as far as Kolumadulu, some 

 trace, some outlier or some central rocks indicating the nature of the rocks 

 composing the underlying plateau forming the base upon which the in- 

 numerable atolls of the Maldives have been formed. The conditions are in 

 many ways similar to those of the Lau Islands on the eastern plateau of Fiji. 

 There the elevation has been considerable (to a height of one thousand feet), 

 and everywhere indications are found of the character and age of the un- 

 derlying strata. A similar condition exists in the Paumotus, where some of 

 the tertiary elevated reefs attain an elevation of about three huudred feet. 

 At the Maldives there is, however, only evidence of a very slight elevation. 



' This does not seem to hold good for Minikoi and other Laccadive atolls with shallow lagoons. 



" Loc. cit., p. 334. 



» A. Agassiz, Bull. M. C. Z., Vol. XXXIII., pp. 43, 88. 



