250 TOILERS IN THE SEA. 



enabled better to proceed with a more minute de- 

 scription of reefs and atolls, the latter term being 

 less open to objection than islands. 



Coral reefs are accumulations of coral rock which 

 have been built up from the sea bottom around the 

 shores of islands, or the continent, in the tropics. 

 These reefs are usually entirely submerged at high 

 water, and at low water present only a flat surface of 

 rock just rising above the water level. Some islands 

 are only girt by narrow fringing reefs, whilst others 

 are wholly or partially surrounded by the distant 

 barrier reef, which may be from ten to fifteen miles 

 from the island, or islands, with a considerable channel 

 of water between the barrier and the shore ; and, in 

 other cases, one side of the island may be protected 

 by a distant barrier reef, and the other girt only by a 

 fringing reef, the relationship between the barrier 

 and fringing reef being shown to be very close. 

 Hence we may formulate the conclusion that "reefs 

 around islands may be entirely encircling, or they 

 may be confined to a larger or a smaller portion of 

 the coast, either continuous or interrupted ; they 

 may constitute throughout a distant barrier ; or the 

 reef may be fringing in one part, and a barrier in 

 another ; or it may be fringing alone. The barrier 

 may be at a great distance from the shores, with a 

 wide sea within, or it may so unite to the fringing 

 reef that the channel between will hardly float a 



