It is profitable to examine a little more in detail some illustrations of Darwin’s scientific theorizing. The great central doctrine of evolution, with its buttressing support of natural selection, will fill our next chapter, but there are several lesser developments of speculation which deserve notice. I need hardly say that we are not in any way discussing the validity of the theories in the abstract, but simply Darwin’s fashion of framing, holding, and sustaining them. There is first the theory as to the formation of coral reefs. At an early period in his career Darwin conceived the idea that these reefs were produced by the subsidence of the ocean bed and the steady building up of the coral insects toward the surface. He himself admits that this theory was the most deductive of all that he ever urged and the least founded in the beginning upon a wide and careful investigation of fact. Alexander Agassiz, who, after extensive research, was not disposed to accept it, wrote: ‘Darwin’s observations were all theoretical, based upon chartographic study in his house, a very poor way of doing, and that’s the way all his coral reef work has been done.’[359] And the theory has met with strenuous opposition from many quarters, though one critic says in regard to it: ‘Be it true or not, be it a competent explanation or not, no matter. In influence on geology it has been as far-reaching as the doctrine of natural selection has been on biology.’[360] But Darwin himself clung to it to the end, meeting objections with vast ingenuity and reiterating his positions with ampler and more penetrating arguments. Yet through all the persistence there is the readiness at any moment to see the other side. ‘I must still adhere to my opinion, that the atolls and barrier reefs in the middle of the Pacific and Indian Oceans indicate subsidence, but I fully agree with you that such cases as that of the Pellew Islands, if of at all frequent occurrence, would make my general conclusions of very little value. Future observers must decide between us.’[361] And he writes frankly to Alexander Agassiz: ‘If I am wrong, the sooner I am knocked on the head and annihilated so much the better.’[362]