On Coral Reefs and Islands. 191 
inner. The extent of reef-grounds within a barrier, raised by 
accumulations at the same time with the reefs, is often fifty 
times greater than the area of the barrier itself. Owing to these 
causes the rate of growth of the barrier may be at least twice 
more rapid than that of the inner reefs. 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 sub- 
sidence between the two mentioned, would sink the inner reefs 
more rapidly than they could grow, and cause them to disap- 
A wide flat reef, continuous over so-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 
production of inner currents, destroying growing corals over the 
interior parts of the coral reef; so that whatever the rate of sub- 
sidence, 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-exis- 
tence is incompatible with the mode of action going on. They 
afford the strongest support to the theory. 
rom these considerations it is evident that a barrier reef 
three hundred square miles; and the outline of the former land 
is indicated by the course of the enclosing reef. A still greater 
n 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 
Principles or probabilities, to suppose them once to have 
