and the Evidence of the Funafuti Borings. 85 



these steep slopes are several which are at much lower angles. 

 These steep walls most probably represent the outer parts of 

 the growing reef at various stages of development while the 

 methods of formation of the intervening flatter slopes may be 

 more debatable. The important point to note is that in the 

 development of the Funafuti atoll we have evidence in the 

 submarine profiles that there has been a centripetal not a cen- 

 trifugal shift of the outcrop of the reef since the more deeply 

 buried submarine steep walls representing former positions of 

 the outer reef-face are further from the center of the island 

 than those of more recent origin and shallower depth. An 

 appeal to the facts as shown in the submarine profile of Funa- 

 futi indicates, therefore, that the development of that atoll is in 

 general accordance with the diagrams of atoll growth origi- 

 nally published by Darwin and by Dana while Yon Lendenfeld's 

 and Daly's views and diagrams are clearly inapplicable to that 

 particular atoll. 



The I^illing of the "Lagoon-moat". 



Daly* attaches much importance to the mechanism of the 

 filling of the " lagoon moat " in atolls. He claims that, accord- 

 ing to the subsidence theory of atoll formation, the fairly 

 shallow and relatively flat lagoon floors which are commonly 

 met with, imply advanced filling of the lagoon to depths of 

 scores, hundreds or possibly thousands of meters. The fill- 

 ing mechanism according to Daly involves two factors, sedi- 

 ment and active transportation of that sediment. On this basis 

 he claims that the lagoon floors should not be flat but should 

 slope away from the sources of supply of sediment, i.e. the reef- 

 face and the central island in the case of barrier reefs in course 

 of development to atolls. Further he claims that the supply of 

 sediment is quite insufficient unless in the case of all atolls a 

 very prolonged pause has followed subsidence. He favors the 

 view that the "lagoon moats" really represent wave-cut sur- 

 faces or rock platforms developed by the erosion of pre-existing 

 islands while the sea level stood lower than it does at present. 

 Davisf has criticised this theory of wave-cut platforms as the 

 support for modern atolls from the point of view among others 

 that enormous periods of time would be necessary to develop 

 level rock platforms in the case of islands some of which must 

 have been 20 to 30 miles in diameter. The writer is more 

 particularly concerned with Daly's criticism of "moat" filling 

 previously stated above. It will be noted that although Daly 

 quotes Darwin's view that the "moat" is slowly filled through 

 the accumulation of detritus and shells and skeletons of organ- 

 isms inside the reef, in his discussion of the mechanism of 



* E A. Daly. Proc. Nat. Acad. Sci., ii, pp. 664-670, 1916. 

 fW. M. Davis, Bull. Am. Geogr. Soc, xlvi, p. 646, 1914. 



