CORAL REEFS, AND ISLANDS. 281 



produce some given effect, and yet that effect may 

 not be due to it, but to some other. Subsidence 

 would, or might, account for the lagoons, and for the 

 protected seas, and yet it may not be subsidence 

 which has actually produced them. 



" Darwin's theory took into full account two of the 

 great forces which prevail in nature, but it took no 

 account of another, which is comparatively incon- 

 spicuous in its operations, and yet is not less power- 

 ful than the vital energies, and the mechanical 

 energies, which move and build up material. Darwin 

 had thought much and deeply on both of these. 

 He called on both to solve his problem. To the 

 vital energy of the coral animals he rightly ascribed 

 the power of separating the lime from the sea-water, 

 and of laying it down again in the marvellous struc- 

 tures of their calcareous homes. In an eloquent and 

 powerful passage, he describes the wonderful results, 

 which this energy achieves, in constructing break- 

 waters, which repel and resist the ocean, along 

 thousands of miles of coast. On the subterranean 

 forces which raise, and depress, the earth's crust he 

 dwelt, at least enough. But he did not know, 

 because the science of his day had not then fully 

 grasped, the great work performed by the mysterious 

 power of chemical affinity, acting through the cog- 

 nate conditions of aqueous solution. Just as it did not 

 occur to him that a coral reef might advance steadily 



