113 



recede farther and farther from its former relation to the island. 

 The Polyps, however, ever most active where most exposed to 

 the play of the waves, have grown vertically upwards at the 

 outer edge of the reef, and btiild here energetically, to regain 

 the position most favourable for their development; but this 

 subsiding island is becoming lower and smaller, and the space 

 between the edge of the reef (r, r,) and the beach, proportionately 

 broader. This is fiUed with a channel of shallow water, into 

 which masses of Coral, torn from the outer margin, are hurled 

 by the fury of the stormy waves. These become thickly coated 

 with Nulliporoe, to a thickness of 2 or 3 feet. The lagoon channel 

 is filled likewise by other debris, and crowded with other species 

 of Polypifera that luxuriate in shallow water. A section of 

 the island, after a subsidence of several hundred feet, is given 

 in rig.'4. The former Hving margin of the reef (r) is now dead 



a ^^^• 



Fig. 4. 



Coral, dragged down to a depth at which the Polyps coiJd not 

 live ; but their progeny, working onwards and upwards in 

 proportion as the land was subsiding, have maintained their 

 position, and now form the margin of the outer Coral circle 

 surrounding the land, where they form a Barrier reef, (r r) 

 separated by the lagoon channel (1, 1) from the remnant of the 

 land, (a, a, b) as already described in the case of the island 

 of Bolabola, (Fig. 2) where the Barrier reef is seen from within, 

 from one of the high peaks of the island. 



