86 



THE SHORE 



exist, while on their western shores, as, for instance, 

 to the east of Africa and Australia, they attain great 

 dimensions. Their shape and appearance wherever 

 they exist is quite characteristic, a flat, almost level 

 with the surface of the sea at low tide, on which the 

 ocean pounds down, even in the calmest weather, with 

 great breakers upon at least one face. The water at low 

 tide flows over the flat for some distance, only to rush 



FIG. 22. CORAL OOLITE. FIG. 23. CORAL BRECCIA. 



These are formed by the grinding down of coral boulders, the frag- 

 ments being cemented together by the deposition of lime at 

 different grades of fineness. Both found abundantly on the 

 shores and in the islands of atolls (" Blake "). 



back by countless fissure-like channels in the edge of 

 the reef. This area, the reef flat, as it is termed, is 

 marked off on its inner side by a band of boulders, 

 generally small masses of reef rock or coral colonies, 

 which have been hurled up from inside or outside of 

 the'reef ; hence is derived its name of the boulder zone. 

 Instead of these boulders we may have a land, per- 

 chance formed by them, perchance of elevated coral 



