270 TllKUKY Ol' CUUAL-JiEEFcJ. 



margin of the reef, will soon regain the surface. 

 The water, however, will encroach little by litiie 

 on the shore, the island becoming lower and smaller, 

 and the space between the inner edge of the reef 

 and the beach proportionally broader, A section 

 of the reef and island in this state, after a subsi- 

 dence of several hundred feet, is given by the 

 dotted lines. Coral islets are supposed to have 

 been fonned on the reef; and a ship is anchored 

 in the lagoon-channel. This channel will be more 

 or less deep, according to the rate of subsidence, 

 to the amount of sediment accumulated in it, and 

 to the growth of the delicately branched corals 

 which can live there. The section in this state 

 resembles in every resjiect one drawn through an 

 encircled island : in fact, it is a real section (on the 

 scale of '388 of an inch to a mile) through Bola- 

 bola in the Pacific. We can now at once see why 

 encircling ban-ier-reefs stand so far from the shores 

 which they front. We can also perceive that a 

 line drawn perpendicularly down from the outer 

 edge of the new reef to the foundation of solid 

 rock beneath the old fringing-reef, will exceed by 

 as many feet as there have been feet of subsidence 

 that small limit of depth at which the effective 

 corals can live ; the little architects having built 

 up their great wall-like mass, as the whole sank 

 down, upon a basis formed of other corals and their 

 consolidated fragments. Thus the difficulty on this 

 head, which ap})eared so great, disappears. 



If, instead of an island, we had taken the shore 

 of a continent fringed with reefs, and had imagined 

 it to have subsided, a great straight banier, like 

 that of Avistralia or New Caledonia, separated from 

 the land by a wide and deep channel, would evi- 

 dently have been the result. 



Let us take our new encircling ban-ier-reef, of 



