204 



FOUNDERS OF OCEANOGRAPHY 



corroborated Darwin's views — which are now frequently- 

 referred to as the Darwin-Dana theory. 



In course of time, however, other observers pointed 

 out that atolls were sometimes found on areas that had 

 obviously undergone elevation, and that old-established 

 fringing reefs, indicating stationary conditions, might be 

 found along with barrier reefs or atolls, which were supposed 

 to indicate subsidence. Thus Semper's observations in the 

 Pelew Islands showed the co-existence of atolls and other 

 types of reef in the same archipelago, and Agassiz and 

 several other more recent investigators threw grave doubt 

 upon the vahdity of Darwin's theory to explain the structure 

 and distribution of the reefs they had observed. Thus the 



Lagoon 



Lagoon 



(Darwin) 



Volcania!/ 

 El sv at J on 



(Murray) 



Fig. 11. — Theories of the Fobmation op Coral Atolls. 



matter became controversial — but no adequate rival theory 

 was put forward until Murray's views, based on the " Chal- 

 lenger " observations, appeared in 1880. 



A strong point in favour of Darwin's theory was that it 

 had got over the difficulty of supplying an enormous number 

 of suitable platforms in shallow water scattered over vast 

 areas of the deep sea. By slow subsidence of a tropical 

 continent or archipelago every peak and every island in 

 succession would naturally come within the range of reef- 

 building corals, and so form a suitable platform for what 

 would eventually become an atoU. Granted the assumption 

 of innumerable peaks and islands sinking slowly in an 

 oceanic area suited to the life of the coral polypes, then 

 the result will follow in accordance with Darwin's theory ; 



