1898.] Funafuti, Rotuma and Fiji. 501 



but few small spots of verdure" is "probable evidence of sub- 

 sidence now in progress," and the existence of barrier reefs, atolls 

 or submerged atolls, is an evidence of subsidence ; altogether it is 

 clear that Dana, with the present charts before him, would 

 consider that the Fiji Group is, or has been up till a very recent 

 period, subsiding. Support, however, is scarcely lent to this by 

 the broad fringing reefs especially to the south-east of Viti Levu. 

 At this part the Rewa river, after a tortuous course of nearly 

 130 miles, opens into the sea. I estimated the area of its mud 

 deposits and its delta at about 80 square miles, all of which would 

 be completely submerged by a subsidence of about 8 feet. A 

 small river, the Navua, has a delta of about 20 square miles, and 

 like the Rewa, is also largely fed by a region of soapstone ; 

 accordingly they might be equally supposed perhaps to form their 

 deltas somewhat rapidly. But the Ba river in Vitu Levu and the 

 Ndre Keti and Lambasa rivers in Vanua Levu draining only areas 

 of volcanic rock would require a vast period of time to form their 

 large deltas. The sand flats at Wakaya, Taviuni, and Fulanga, as 

 noticed before, are very considerable, while by Nateva Bay and to 

 north of Viti Levu they are in places 1 — 1^ miles broad ; these 

 would only be formed in a period of rest, and their formation can 

 be but slow, so that they also point to the probability that move- 

 ments of elevation and subsidence have not occurred throughout 

 the whole group for a considerable period. 



In the next place it is necessary to consider what are the 

 foundations of atolls. Here I can only emphasize still further 

 Admiral Wharton's views, when he says 1 : — " I would venture to 

 suggest the cutting down of volcanic islands by the action of the 

 sea and that this action has a far greater share in furnishing coral 

 foundations than has been generally admitted." While agreeing 

 mainly with these views, I do not know that the sea would have 

 in all these cases merely a bank of cinders and ashes to act upon ; 

 lava might well rise to a certain height and then burst its way 

 out above or below the water. The lava, when it first met the 

 water, would probably burst up into cinders and ashes, but 

 beneath these a crust would form and the lava might continue 

 to flow 2 . 



At the same time I consider that mounds can be, and are 

 being, built up to the requisite height for the reef-building 

 organisms by the skeletons of marine animals. But what is the 

 requisite height ? The chief building organism is Lithothamnion, 

 the bathymetrical zone of which must be limited to a large degree 

 by the extent to which light can penetrate sea water. On this 



1 Loc. cit., p. 392. 



a Geology. By A. H. Green. Part i., 1876, p. 224. 



