AGASSIZ : FIJI ISLANDS AND CORAL REEFS. 39 



rine erosion from the former extension of the slopes of the rim or of its 

 spurs. These have been more or less connected together by the subse- 

 quent growth of the corals which have found a footing upon them. 

 Kini Kini and the other islets about Totoya, as well as the negro-heads 

 on the reef flats and patches, all show the volcanic substructure upon 

 which has grown and is thriving now a thin crust of corals. 



TOTOYA FROM THE NOKTHEAST, DISTANT FIVE MILES. 



It has been difficult to explain the great depth in some of the lagoons 

 of some atolls (60 fathoms). It seems to me that the conditions occur- 

 ring in an island like Totoya give us a simple explanation of what such 

 depths mean in coral districts situated in volcanic regions. Provided 

 that we assume that these lagoons are in a region of elevation, as are the 

 Fiji Islands, and that its volcanic peaks or ridges and volcanoes have 

 been denuded and eroded, and that nothing has been left to indicate 

 their former existence beyond the reef flats upon which the corals of the 

 present day are growing. Remembering also that the corals can form 

 but an insignificant crust upon the slopes and flats which have been pre- 

 pared for their growth by the processes of elevation and of subsequent 

 erosion and denudation, and that the features characteristic of the 

 existing state of things was not brought about by the growth of the 

 coral reefs of to-day except in a very secondary manner. We are not 

 discussing the question of the formation of great limestone banks by 

 subsidence to attain the proper depth at which corals may begin to grow. 

 We are only trying to give an explanation of the conditions which must 

 have preceded and have led to the existing state of things. 



The deepest water in the crater basin of Totoya is thirty-five fathoms, 

 and it certainly cannot be held that a lagoon of such a depth has been 

 formed by subsidence after the coral reefs have begun to grow. Let 

 us now follow what would have become of Totoya had the denudation 

 and submarine erosion which have brought it to its present state been 

 continued during a longer period of time. A very few fathoms more, and 

 we should have the rim divided into three large islands, — an eastern 



