ATOLL AND REEF FORMATION 238 



great extent. It is not true that corals live best in the 

 surf : the observation has been repeatedly made that the surf- 

 line is practically barren of living coral growth : but it is 

 true that the corals of the outer — submarine — edge of the 

 reef grow most luxuriantly, and Chamisso's ideas were in the 

 main correct. 



The structure that Chamisso erected upon an unknown 

 base requires but little elaboration when Semper, Agassiz, and 

 Murray have demonstrated the foundation to be a reality — 

 and for the making of this structure neither subsidence nor 

 solution is called upon. 



The idea that the reef corals delight in the crash of the 

 surf must be given up, and so the original suggestion of a 

 better aeration of the outer coral colonies, causing their more 

 rapid growth, has also been abandoned. Combined with this idea 

 of a more abundant supply of oxygen to the outer corals is 

 the supposition that they are also in a position to obtain more 

 food, and so to thrive better than those which get the water 

 only after it has passed over the outer rim. Semper attached 

 great importance to the currents which flow about a reef, and 

 Professor Hickson, in the Celebes, noted the effects of the 

 currents upon coral growth. Mr. G. C. Bourne, from a study 

 of Diego Garcia (Froc. Boy. Soc, 1888, p. 458), came to the 

 conclusion that currents were among the most important 

 agents in causing the shape of coral reefs, and he says, " The 

 strength and direction of currents appears to me to be the 

 main influence of coral growth ; that the behaviour of currents 

 on meeting an obstacle with sloping shores explains the super- 

 abundant growth of corals on the outer slopes of a reef, 

 whether submerged or awash ; that the growth of corals on 

 the periphery of a bank being in great excess of the growth 

 in its interior portions is sufficient to explain the formations 

 known as atolls and barrier reefs." Yet the workings of this 

 particular current influence still await an explanation. 



These views therefore agree in placing Chamisso's bank on 

 the base that Agassiz, Semper and Murray pictured ; but the 

 method of the more rapid growth of the edge is modified. 



