120 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



the line of breakers is riddled with holes and channels gouged out by the 

 Echiuometra common on the reef. These channels look like short wind- 

 ing drill holes extending in all directions, or merely small potholes in 

 which the Echinometree live pi'otected from the action of the breakers 

 (Plate 30). In the same belt corals begin to grow in greater profusion, 

 mainly Pocillopores, Madrepores, and small heads of Astraeans and of 

 Goniastrseans or Mseandrinas, a few of these are also found scattered 

 on the inner pai't of the reef flat. The corals living upon the outer edge 

 of the reef flat form merely a thin crust, between the patches of which 

 the substratum of elevated limestone crops out. Similarly, at a great 

 many other points in Eiji, the outer edge of the reef flat, when exposed 

 at the very lowest stages of tide, is seen to be edged with a belt of rocks 

 identical in structure to that which forms the substratum of the reef 

 flat platform. I may mention Mango, Yatu Leile, and a number of the 

 islands of Fiji which have been described. The slope of the outer edge 

 of the reef flat falling off" more or less rapidly has little to do with the 

 recent reef crust growing upon it ; that only modifies its slope, possibly 

 to twenty fathoms. The general slope of the sea face of the reef is due 

 to conditions which antedate the formation of the coral reefs of the 

 present day. 



Dana^ says that beneath the channels (basins) lies in general the 

 coral rock of the reef region, the inferior part of the great reef forma- 

 tion, whose upper portions constitute the so called barrier and fringing 

 reefs. This certainly is not genei'ally the case : see the description of 

 the flats between Ovalau and Mbau. Dana himself cites a number of 

 examples which do not accord with his views when describing great 

 admixtures of coral and of material derived fi-om the mountains adjoin- 

 ing, and as he well says : " When the materials from both sources, the 

 shore and the reef, are mingled, the proportion will necessarily depend 

 on the proximity to the mouths of streams, the bi'eadth of tlie inner 

 waters or channels, and the direction and force of the cui'rents." 



As has already been observed by Dana, *' At low tide the breakers 

 often cease, or nearly so." ^ It is frequently possible a short time before 

 the turn of the tide to examine the corals growing on the outer face of 

 a reef. At Komo we had an opportunity to photograph coral reef flats 

 where the corals were growing upon a substratum of volcanic rocks 

 (Plate 65) just as they are growing upon a basement of tertiary lime- 

 stone at the entrance of Suva Harbor. At Xgillangillah we came upon 



1 Corals and Coral Islands, p. 149. 



" hoc. cit., p. 131. , 



