120 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
the line of breakers is riddled with holes and channels gouged out by the 
Echinometra common on the reef. These channels look like short wind- 
ing drill holes extending in all directions, or merely small potholes in 
which the Echinometre live protected 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 Astreans and of 
Goniastreans or Mezandrinas, a few of these are also found scattered 
on the inner part 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 Fiji, 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, Vatu 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 dne 
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 portious constitute the so called barrier and fringing 
reefs. This certainly is not generally 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 from 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 breadth of the inner 
waters or channels, and the direction and force of the currents.” 
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 Ngillangillah we came upon 
1 Corals and Coral Islands, p. 149. 
2 Loc. cit., p. 131. 
