MODE OF ORIGIN. 129 
barrier may be at least twice more rapid than that of the inner reefs. 
If the barrier increases twenty feet in height in a century, the inner 
reef according to this supposition would increase but ten feet; and 
any rate of subsidence between the two mentioned, would sink the 
inner reefs more rapidly than they could grow, and cause them to 
disappear. A wide flat reef, continuous over such extensive reef- 
grounds, could be formed only with an extremely slow rate of subsi- 
dence; and even then they would be liable to be cut up by the pro- 
duction of inner currents, destroying growing corals over the interior 
parts of the coral reef; so that whatever the rate of subsidence, the 
inner portions would grow less rapidly. There is therefore not only 
no objection to the theory from the existence of wide channels and 
open seas; on the contrary, their non-existence is incompatible with 
the mode of action going on. They afford the strongest support to 
the theory. 
From these considerations it is evident that a barrier reef indicates 
very nearly the former limits or extent of the land enclosed. The 
Exploring Islets (Feejee chart), instead of an area of scx square miles, 
the whole extent of the existing land, once covered three hundred square 
miles ; and the outline of the former land is indicated by the course of 
the enclosing reef. A still greater extent may be justly inferred. For 
the barrier, as subsidence goes on, gradually contracts its area, owing 
to the fact that the sea bears a great part of the material inward over 
the reefs: and, consequently, the declivity forming the outer limit of 
the submarine coral formation, has a steep angle of inclination. 
In the same manner it follows that the island Nanuku, instead of 
one square mile, extended once over two hundred square miles, or had 
two hundred times the present area of high land. Bacon’s Isles once 
formed a large triangular island of equal extent, though now but two 
points of rock remain above the water. 
The two large islands in the western part of the group, Vanua Levu 
and Viti Levu, have distant barriers on the western side. Off the 
north point of the former, the reef begins to diverge from the coast, 
and stretches off from the shores till it is twenty and twenty-five miles 
distant; then, after a narrow interruption, without soundings, the 
Asaua Islands commence in the same line, and sweep around to the 
reef which unites with the south side of Viti Levu; and tracing the 
reef along the south and east shores, we find it at last nearly connect- 
ing with a reef extending southward from Vanua Levu. Thus these 
two large islands are nearly encircled in a single belt; and it would 
33 
