xviii INTRODUCTION. 



culties in ascertaining the lateral rate of increase on the outer slope 

 of a coral reef where it depends so largely upon local conditions within the 

 bathymetrical range at which corals grow. There is great difference in the 

 method of growth of corals on the reef flats or slopes of lagoons and 

 of the exterior faces of coral reefs. The method of solidifying is quite 

 different from the amount of sand on the flats within a lagoon, the excess 

 of encrusting Nullipores on the sea faces, and the mass of coral fragments 

 in constant movement on that face. 



The rate of growth of branching corals is quite rapid, as is readily seen 

 in the channels, cleared out every few years by the natives, leading through 

 the outer reefs to the canals existing between them and the land. Mr. 

 Gardiner has calculated from his observations that the coral reefs of 

 Hulule might grow at the rate of a fathom in sixty years.' On a bank 

 of twenty-five to thirty fathoms depth ^ patches of corals would grow over 

 its surface wherever conditions were especially advantageous, and the outer 

 patches might, according to the direction of the current, form a rim, such 

 parts as were lower forming the passages through the encircling reef. This, 

 according to him, would account for such atolls as Addu, Goifurfehendu, 

 Gaha Faro, Makunudu, Wataru, Rasdu, as well as for atolls of greater size, 

 like Felidu, Ihavandiffulu, Mulaku, and others of the central Maldives 

 where the corals built up also small atolls on the rims ; while on the great 

 Tiladummati-Miladumraadulu Bank the oceanic conditions prevailing have 

 maintained the individuality of the separate faros. 



Mr. Gardiner says no faro has reefs or shoals. This cannot be said 

 of Rasdu, of the many faros of the northern part of Tiladummati, from 

 Hanimadu to Kelai and to Gafuri ; they are full of small shoals and banks 

 and sand-bars. Gardiner is right in looking upon the condition of the shoals 

 and reefs of the bank as greatly influenced by the extent of the circulation 

 of the water. If the bank is I'epresented by a small lagoon it is of course 

 limited, but if by a great lagoon as Suvadiva, or a more or less open bank 



1 Loc. cit., p. 332. 



2 It seems to me that the presence of such genera as Lophohelia on deep banks does not necessarily 

 imply that they play so important a part in building up the deep coral banks of the Atlantic as to raise 

 them from four hundred and thirty-five to fifty fathoms, the depth Mr. Gardiner assumes as the upper 

 limit of growth of reef corals. 



