266 CORALS AND CORAL LSLAWDS. 



are sufficient evidence of subsidence to one who has studied 

 the character of the Pacific islands ; for these indentations cor- 

 respond to valleys or gorges formed by denudation, during a 

 long period while the island stood above the sea. 



The manner in which a further subsidence results in pro- 

 ducing the atoll is illustrated in the upper of the following 

 figures. Viewing V as the water line, the land is entirely 

 submerged ; the barrier, V", V"' ', then encloses a broad area 

 of waters, or a lagoon, with a few island patches of reef over 

 the peaks of the mountains. A continuation of the subsi- 



SECTION ILLUSTRATING THE ORIGIN OF ATOLLS. 



dence would probably sink beneath the waters some of the 

 islets, because of their increasing in height less rapidly than 

 the barrier ; and this condition is represented along the upper 

 line of the above figure, VI, subsidence having taken place to 

 that level. The lagoon has all the characters of those of atoll 

 reefs. 



Should subsidence now cease, the reefs, no longer increas- 

 ing in height, would go on to widen, and the accumula- 

 tions produced by the sea would commence the formation of 

 dry land, as exhibited in figure 2. Verdure may soon after 

 appear, and the coral island will finally be completed. It is 



