72 THE STORY OF LIFE IN THE SEAS. 



Corals on the shores of the island of Krakatoa 

 which is situated in the Sunda straits, and was 

 the seat in 1884 of one of the most violent 

 volcanic eruptions of historical times. After the 

 eruption the sea-bottom round the island was 

 found to consist of a fine volcanic mud, in which 

 it may be believed no Coral embryos could find a 

 secure foothold. Now it is known that living 

 Corals give rise to a number of very minute 

 larvae which for a period of time swim freely in 

 the water, eventually settling down on some solid 

 stone or shell to give rise by growth and budding 

 to the Coral blocks. These larvse frequently 

 settle down on a piece of floating pumice-stone 

 and after a time grow to such a size that they 

 sink it. If, in sinking, they fall upon the bottom 

 in shallow water they form together a sub- 

 stratum on which other larvae can settle and 

 flourish. This is apparently the manner in 

 which Coral clumps are beginning on the slopes 

 of Krakatoa and these will undoubtedly give 

 rise in time to a more or less complete Fringing 

 reef. 



Any further discussion on this point would 

 lead us into subjects beyond the scope of this 

 book, but enough has been said to indicate to 

 the reader the manner in which the countless 

 Coral-polyps may, in the course of time, change 

 the position of the reefs on Coral shores, thereby 

 altering the set of the tides there, changing the 

 position of the sand-banks, affecting the rate of 

 erosion of the cliffs, and in other ways causing 

 important modifications of the coast-line. 



I have mentioned that the ground on the 



