174 THE SEAS 



Again there would have to have been great numbers of 

 islands dotted about in the first place to provide the neces- 

 sary basis for the countless atolls. 



Sir John Murray, of whom we have already heard in 

 connection with the investigation of the bottom deposits 

 of the ocean, was the first to bring forward an alternative 

 theory of any general application. The real crux of the 

 problem is how to account for the presence of these plat- 

 forms of land covered with not more than about thirty 

 fathoms of water, from which alone, barring the subsidence 

 of pre-existing land, corals could grow to the surface. 

 Murray thought these were produced by a raising of the 

 sea bottom. This might take place as a result of a sub- 

 marine volcanic eruption throwing up a great mound of 

 debris (these things do frequently happen, islands being 

 occasionally thrown up above the surface of the sea in this 

 way, the light material of which they are composed being 

 usually washed away very quickly afterwards). It might 

 also be brought about by the accumulation of great banks 

 formed from the skeletons of the animals and plants of the 

 floating life in the surface waters which are responsible for 

 the greater part of the deposits on the bottom of the 

 sea. 



Now as soon as a platform is formed in this manner, reef 

 building corals would be able to establish themselves and to 

 begin growing upwards until they reached the surface, 

 as shown in Figure 37. Clearly those in the centre, at the 

 highest point, would reach the surface first and the pre- 

 liminary indication of the beginning of an atoll, according 

 to this theory, would be the appearance of a small circular 

 reef flat. But the corals in the centre, being unable to 

 grow upwards any further would die, while those on the 

 fringes would grow outwards, extending the flat in all 

 directions. Now, as in the case of the fringing reefs 



