128 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
reef, its character is similar to that of Viti Levu, the substratum of 
the reef flats being either hard volcanic rocks, or stratified volcanic 
mud, or remnants of elevated limestone. The northern shore of Vanua 
Levu from Cape Undu (Plate 4) west is flanked by wide extensive 
stretches of barrier reef patches ; between them and the shore exists a 
broad navigable channel full of islands and islets, and the whole of the 
shore is also indented by deep bays separated by prominent promontories 
almost isolated from the larger island ; plainly indicating that the flats 
and patches occupy areas formerly covered by large islands or by former 
slopes of spurs from Vanua Levu itself, which have been eroded and de- 
nuded and separated from the larger island. The outer flats and patches 
of the barrier reef, which as it extends westward beyond the Mali Pas- 
sage forms the Great Sea Reef, and is nearly thirty miles distant off the 
western point of Vanua Levu. The islands and islets off the north coast 
of Vanua Levu form a broad belt of islands separated by islets, rocks, 
aud patches ; on the western extremity of the belt is Yendua Island and 
the islets extending westward. 
The existence of fringing reefs inside of barrier reefs is a very strik- 
ing feature of the Fiji coral islands. Their absence in some localities 
has been explained by Dana? on the supposition that the conditions 
are more favorable to the growth of corals on a barrier than on an 
interior fringing reef. Yet in some of the wide lagoons of Fiji the 
corals of the fringing reef grow quite as luxuriantly and to the same 
depth as those on the outer edge of the barrier reef, and are often 
more abundant than those of the lagoon slope of the barrier reef. 
Depths of five to six or seven fathoms are those of the most vigorous 
growth of corals on the outer face of such barrier reefs or encircling reefs 
as I have examined in Fiji, a depth corresponding to that observed in 
the Bahamas in similar positions. 
Some of the reefs on the northwestern face of Vanua Levu (Plate 4) 
apparently illustrate admirably the formation by denudation and erosion 
of small reef flats awash, and of reef flats destitute of islands or with 
islands encircling a shallow lagoon. It will be noticed that these flats 
and pseudo atolls rise from a comparatively shallow platform, — nine to 
twenty fathoms, — and evidently represent the different stuges of denu- 
dation and of erosion of islands which have been left on one side of the 
reef flat, or have disappeared, leaving an irregular enclosing reef, or have 
beach along Savu Savu, as well as Waikava and the adjacent islands, consists of 
coral upheaved to a height of thirty feet. 
1 Corals and Coral Islands, pp. 138, 278. 
