174 



CORAL AND ATOLLS 



to sand particle, just as the surf of the ocean is always con- 

 solidating the larger fragments together. 



Just as round the sand nucleus of the ocean barrier 



Fig. 57. 



The Western End of Pulxj Tikus, 



Showing the Avorn coral masses that are piled on the beach by the 



waves. The presence of the large rounded boulders is due to the 



strong currents rushing out of the lagoon entrance. 



calcium carbonate is ever being deposited, so on the lagoon 

 beaches this nuclear increment is ever being added. The 

 whole question of the formation of breccia turns on the con- 

 sideration of the welding force of the waves and the materials 

 with which they have to work. On the ocean side the frag- 

 ments are wedged together, sand is driven home, and by the 

 cementing action of deposited calcium carbonate the whole is 

 consolidated into a massive mosaic. On the lagoon shore 

 the materials are in a fine state of division, and the force is 



