254 CORAL AND ATOLLS 



harrier. Where large fragments lie piled in uneven masses, 

 smaller fragments will collect, and fill in the interspaces ; the 

 waves will wedge them home, and tend to make the whole 

 thing solid. Upon the lee of these elevations, grains of coral 

 sand and lighter particles will collect, and find their way into 

 the chinks left in the rock piles. A very important action 

 now begins to take place, for around each small coral particle, 

 as a nucleus, a crystalline deposition of calcium carbonate 

 takes place ; particle is held to particle, and the fine sand that 

 has been driven by the force of the waves into every tiny 

 interspace becomes a cement that holds the coarser fragments 

 firmly together. The result of this action is that a con- 

 glomerate is made of irregular fragments, broken branches, 

 and coral sand ; the whole mass cemented by a deposition 

 of calcium carbonate around the particles. The deposition of 

 calcium carbonate is not confined to an encrusting layer around 

 the particles ; it takes place in the dead coral itself, and the 

 individual fragments become harder and heavier than they 

 were during life. 



A breccia mass, as hard as concrete, is thus formed 

 about the fragments which some chance storm first cast upon 

 the rim of the reef. It is obvious that, since the process is 

 the outcome of wave action, it will start first of all upon the 

 windward side of the reef; and at the point of maximum wave 

 action we may expect to see the first piling up of the boulders 

 that will afterwards form the barrier. Ultimately, other 

 portions of the ring will be affected — probably in the first 

 instance during storm weather — and the piled-up rim will 

 spread, as a horse-shoe, around the rim of the reef. The 

 sequence is, in all probability, somewhat as follows. A time 

 of storm brings waves that are abnormally powerful across 

 the reef spot; upon the windward side their feet will be 

 caught, and during the height of the storm some boulders of 

 massive corals will be lifted and cast upon the top of their 

 neighbours, where they will come to rest. Under more normal 

 conditions of wind and wave, accumulations will take place 

 about these dislodged boulders, and they, by their own growth, 



