176 



THE SEAS 



manner, Murray thought that a fringing reef could be 

 converted into a barrier reef. 



This theory has many points in its favour, notably in that 

 it does not demand any general subsidence of the land over 

 the tropics. It has been supported by many more recent 

 investigators of coral reefs, though often with qualifying 

 statements and additions. The most important criticisms 

 are concerned with the formation of the lagoon, for many 

 scientists think that these are at present being filled up with 

 sediment and not, as Murray's theory demands, gradually 

 increasing by further erosion and solution, and that, in any 

 case, they were originally formed by the scouring action of 

 the sea and by the action of boring animals and plants, 

 rather than by the dissolution on which Murray laid so much 

 stress. 



Clearly a definite proof of the origin of atolls might be 

 hoped for if borings were made through the coral rock down 

 into the lower layers. If the substance of the atoll was 

 found to be of coral origin to great depths, then we should 

 have strong evidence in favour of Darwin's theory, the 

 coral limestone below about thirty fathoms being that 

 which had been carried down by the subsidence of the land ; 

 if, on the other hand, a surface layer of coral limestone 

 some thirty fathoms in thickness was found resting on a 

 layer of solidified bottom deposits, of volcanic fragments, 

 or similar material, then that would afford evidence that 

 Murray's views are correct. With this end in view ex- 

 peditions led by Professor Sollas of Oxford and Professor 

 Sir Edgeworth David of Sydney, were sent out under the 

 auspices of the British Association about the end of the last 

 century. The object of these expeditions was to make 

 borings through the atoll of Funafuti, one of the Ellice 

 Islands in the middle of the Pacific. They succeeded after 

 much hard work in boring through the atoll to a depth of 



