2l6 CHALLENGER 



shallow reef-building corals to grow; for at greater depths these 

 polyps cannot remain alive, and in Darwin's theory they are pre- 

 sumed to continue growing upwards on a platform of dead and 

 dying coral. 



The Coral Reef Committee during their various visits to Funa- 

 futi made a series of borings, the most successful of which had 

 reached a depth of 1 1 14 feet on the main island, not far from the 

 village. Borings to any great depth within the lagoon itself had 

 proved technically too difficult. 



Analysis of the cores obtained from these borings showed coral 

 rock of a shallow water type to their greatest depths. At first 

 this seemed to support Darwin's theory, for if Murray was correct, 

 rock other than limestone would have been encountered at com- 

 paratively shallow depths. The borings were, however, near the 

 seaward edge of the whole atoll structure, and followers of the 

 new theory claimed that such borings were almost entirely 

 through the talus or slope of coral debris which was being con- 

 stantly broken from the edge of the reef by the unceasing pounding 

 of the breakers. Such material would certainly fall down the steep 

 slopes towards the ocean floor and would form a sort of coral 

 rubbish dump to great depths. 



What was needed to clinch either theory was a boring in the 

 centre of the lagoon, a wildly expensive and technically difficult 

 task. However, the seismic apparatus in Challenger was well suited 

 for this work, for it had been used successfully to measure the 

 thickness of the sediment layers upon the floor of the ocean and 

 could be used similarly in the lagoon at Funafuti to measure 

 the thickness of the coral limestone, overlying something 

 harder. 



The technique was similar to that which the ship had used at 

 sea, but within the lagoon she lay at anchor using her photographic 

 device to record the times of the returning sound signals from 

 the floor of the lagoon initiated by the firing of charges from the 

 ship's boats at varying distances from the anchored ship. These 

 returning signals were picked up by the sono-buoy hydrophones, 

 the buoys themselves being anchored on a line between the ship 

 and the far-away boat. 



The Captain went ashore to see the village and to tell the people 

 of Funafuti what was happening. An old man remembered the 



