194 CORALS AND CORAL LS LANDS. 



In the Alcyonia family, which inckides semi-fleshy corals, 

 and in the Gorgoni^e, the lime is often scattered through the 

 polyps in granules \ and the process of death sets these cal- 

 careous grains free, which are constantly added to the coral 

 sands. The same process has been supposed to take place in 

 the more common reef corals, the Madrepores and Astrseas, 

 and it is possible that this may be to some extent the case. 

 Yet it would seem, from facts observed, that after the secretion 

 has begun within the polyp, the secretion of lime going on 

 takes place against the portions already formed and in direct 

 union with them, and not as granules to be afterward 

 cemented. 



The iimd-Uke deposits about coral reefs (pp. 113, 149, 167) 

 have been attributed to the causes just mentioned, but with- 

 out due consideration. There is an unfailing and abundant 

 source of this kind of material in the self-triturating sands of 

 the reefs acted upon by the moving waters. On the seaward 

 side of coral islands, and on the shores of the larger lagoons, 

 where the surface rises into waves of much magnitude, the 

 finer portions are carried off, and the coarser sand remains 

 alone to form the beaches. This making of coral sand and 

 mud is just like that of any other kind of sand or mud. It 

 takes place on all shores exposed to the waves, coral or not 

 coral, and in every case the gentler the prevailing movement 

 of the water, the finer the material on the shore. In the 

 smaller lagoons, where the water is only rippled by the winds, 

 or roughened for short intervals, the trituration is of the 

 gentlest kind possible, and, moreover, the finely pulverized 

 material remains as part of the shores. Thus the fine material 

 of the mud must be constantly forming on all the shores, 

 for the sands are perpetually wearing themselves out ; but the 

 particles of the fine mud, which is washed out from the beach 

 sands, acaunulates only in the more quiet waters some distance 

 outside of the reef, and within the lagoons and channels, 

 where it settles. This corresponds exactly with the facts ; and 

 every small lake or region of quiet waters over our continent 

 illustrates the same point. 



