CORAL REEFS 



167 



animals, and the surf grinds them down to fragments of all sizes, 

 from large blocks to the finest and most impalpable mud. The 

 process is the same as with the ordinary rocks of the coast, only 

 the material differs, and thus are formed boulders, pebbles, sand 

 and mud, all of coral fragments. The many animals which feed 

 upon coral greatly facilitate this work, partly by boring into the 



Fig 



Patch of corals on the Great Barrier Reef of Australia. (Savile Kent.) 



masses, partly by grinding the smaller fragments into fine powder. 

 Considerable masses of calcareous debris are added by the shells 

 and tests of the various animals which live in and about the reef, 

 and the coral-like seaweeds, called Nuttipores, contribute an im- 

 portant quota. All of this material is ceaselessly ground up by 

 the waves, distributed by tides and currents, and brought to rest in 

 quiet waters. A single deposit of two or three inches in thickness 

 has been observed to form between tides, after a gale along the 



