250 THE POPULAR SCIENCE MONTHLY. 



elevations toward the sea-level. Again, the reef-building coral will 

 grow upon its own debris — rising, as men, morally and spiritually, 

 ai-e said by the poet to do, " on stepping-stones of their dead selves to 

 higher things." This small error told for much ; for if coral could 

 grow on dcL'p-sea deposits when lifted up, and if it could also grow 

 seaward, when once established, upon its own dead and sunken 

 masses, then submarine elevations and not submarine subsidences 

 might be the true explanation of all the facts. But what of the 

 lagoons and the immense areas of sea behind the fringing reefs? 

 How could these be accounted for? It was these which first im- 

 pressed Darwin with the idea of subsidence. They looked as if the 

 land had sunk behind the reef, leaving a space into which the sea 

 had entered, but in which no fresh reefs could grow. And here we 

 learn the important lesson that an hypothesis may adequately account 

 for actual facts, and yet nevertheless may not be true. A given 

 agency may be competent to 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 inconspicuous in its operations, and yet is not less 

 powerful 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 sea-water, and of laying it down again in 

 the marvelous structures of their calcareous homes. In an eloquent 

 and powerful passage he describes the wonderful results which this 

 energy achieves in constructing breakwaters 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 cognate conditions of 

 aqueous solution. Just as it did not occur to him that a coral reef 

 might advance steadily seaward by building ever-fresh foundations on 

 its own fragments when broken and submerged, or that the vigorous 

 growth of the reefs to windward was due to the more abundant supply 

 of food brought to the reef-building animals from that direction by 

 oceanic currents, so did it never occur to him that it might melt 

 away to the rear like salt or sugar, as the vital energy of the coral 

 animals failed in the sheltered and comparatively stagnant water. 

 It was that vital energy alone which not only built up the living 

 tubes and cells, but which filled them with the living organic matter 

 capable of resisting the chemical affinities of the inorganic world. 



