DARWIN'S VIEWS. 233 



by the combined action of internal and external causes. For 

 those forces on which Dana relies for his argument in no way 

 depend on the particular nature of the corals or of the reefs 

 formed by them. Hence we have to deal exclusively with the 

 original unaltered view of Darwin. 



There are two modes which may be adopted in contravening 

 or criticising a generally accepted theory. In the first place, 

 its general fundamental basis may be attacked, or, in the 

 second, its value or worthlessness may be tested in a special in- 

 stance. I shall here adopt this latter method, and am prompted 

 to do so by several reasons. First of all, in this way only i- it 

 possible to set in the clearest light the intimate connection 

 between the main subject of this section and the form assumed 

 by reefs, that is to say the direct influence of a constant current 

 on the growth of the reef. But I do so in the second place, in 

 order to oppose the idea that in this particular instance it is 

 difficult or even impossible to test and criticise a general theory 

 by individual examples. Darwin himself, it is true, says that 

 it would be exceptionally difficult to draw any conclusion as to 

 any particular small group of islands or separate atoll or 

 barrier-reef, even when the depth of the sea outside the reef, 

 and the angle at which the enclosed land slopes, are well 

 known. But ought this difficulty more imaginary than real 

 to withhold us from making the attempt 1 I think not. It is 

 usually assumed, and with justice, that the theory which must 

 always lie at the bottom of an hypothesis appears to be soundest 

 when it can be successfully applied in explaining particular 

 cases of difficulty. But this is granting, on the other hand, that 

 we do not simply set aside such difficulties as facts or observa- 

 tion seem to oppose to the theory, because it has already been 

 proved by cumulative evidence. On the contrary, we should 

 rather require that each new difficulty that arises, if only be- 

 cause it is a difficulty, should be applied to test it. The fol- 

 lowing attempt to refer 'the reefs of the Pelew Islands in the 

 Pacific which I myself have thoroughly studied to their origi- 

 nating causes will plainly show that certain facts, easily ex- 

 plicable according to my theories, present insurmountable diffi- 

 culties to Darwin's hypothesis. 



