LIMESTONE AND MARBLE. 143 



innumerable hosts of mollusks, the still larger hosts of 

 foraminifera and coral-polyps, as well as the corallines and 

 other sea-plants are waiting for it. In the West Indian seas, 

 where coral islands abound, it is disposed of so rapidly that 

 the water contains less lime than elsewhere. 



And now as to the way in which these animal and vege- 

 table remains may be converted into rock and marble. 



The first part of the process may be well observed in the 

 Bermuda Islands, which are surrounded for twenty miles by 

 fine coral sand which the waves have ground from the coral 

 reefs. Some of this, no doubt, is washed into the cracks and 

 crevices of the reef, and helps to consolidate it, and some 

 may be re-dissolved. But much of it is washed on shore, 

 dried by the wind, and blown into hills forty or fifty feet high, 

 which are driven farther and farther inland, and unless their 

 progress is arrested by the planting of shrubs, &c., often 

 overwhelm both gardens and houses (Fig. n). 



Exposure to the air deprives the sand of the animal 

 matter mixed with it, and then, like any other carbonate of 

 lime, it is readily dissolved by water and carbonic acid. 

 When rain falls, therefore, a little of the lime is taken up, 

 sinks with it through the sand, and, as the water evaporates, is 

 deposited as a cement which binds the loose grains together. 

 This process being constantly repeated, at last converts the 

 sand into rock of various degrees of hardness, some being so 

 compact as to be almost like marble, and capable of taking 

 a fair polish. 



All the sand is not equally affected, for the rain seems 

 frequently to follow certain particular channels which it keeps 

 open and hardens, and this, together with the fact that all the 



