EFFECTS OF OCEAN WAVES. 2C7 



these islands. I hope thus to succeed in showing that in this 

 particular iastance every difficulty vanishes which can be raised 

 by the hypothesis of subsidence. 



In Kriangle the boat-canal cut through the eastern reef, 

 and the large coral blocks lying at the south-west point are 

 easily explained by upheaval, as also the structure of the 

 eastern reef. On the western side the current attacks the reef 

 at an angle ; hence it must grow upwards perpendicularly. 

 Thus, by degrees, the corals elevated above the level of the 

 living reef must die out ; they remain standing, however, and 

 are slowly destroyed by wind and weather, the softer parts first 

 and the harder portions later, and these naturally endure the 

 longest where they are least and most rarely exposed to waves 

 and storms. This in Kriangle is the case precisely in the 

 spot where the highest blocks lie on the outer margin of the 

 reef. On the eastern side, on the contrary, the ocean drift, 

 combined with the constant current to the westward, falls 

 perpendicularly upon the reef; the billows are still further 

 increased on this side by the gentle slope of the sea-bottom, so 

 that a strong, and above all an unremitting, wearing-down 

 process is exercissd on the reef. Here, on the weather side, it 

 is said that the largest thrown-up blocks ought to be found ; 

 but this is not the case, and it is easily explained. If we 

 suppose that such blocks were actually thrown up for once, 

 they must soon have been destroyed by the incessant action 

 of the waves beating directly on the reef; and the same is the 

 case naturally with all corals which have been lifted above the 

 highest storm tides during a slow elevation of the outer margin 

 of the reef. 



One objection only can be raised. The lagoon, that is to 

 say, which is enclosed by the reefs, might with apparent justice 

 be adduced as evidence against an upheaval. And this would 

 in fact prove a great obstacle to my views if it were necessary 

 to assume a very I'apid elevation of the whole archipelago. But 

 as the case is precisely the reverse we must assume a very slow 

 upheaval, and it is easy to offer an explanation of the origin 

 of a lagoon, in spite of a slow rising of the bottom. Reflect for 

 a moment on the instance, discussed in the previous chapter, of 



