CORAL AND CORAL REEFS 409 



even the peak. The coral, still growing up, will cover 

 the surface of the land, and you will have an atoll reef ; 

 that is to say, a more or less circular or oval ring of coral 

 rock with a lagoon in the middle. Thus you see that 

 every peculiarity and phenomenon of these different forms 

 of coral reef was explained at once by the simplest of all 

 possible suppositions, namely, by supposing that the land 

 has gone down at a rate not greater than that at which 

 the coral polypes have grown up. You explain a Fringing 

 Reef as a reef which is formed round land comparatively 

 stationary ; an Encircling Reef as one which is formed 

 round land going down ; and an Atoll as a reef formed 

 upon land gone down ; and the thing is so simple that 

 a child may understand it when it is once explained. 



But this would by no means satisfy the conditions of 

 a scientific hypothesis. No man who is cautious would 

 dream of trusting to an explanation of this kind simply 

 because it explained one particular set of facts. Before 

 you can possibly be safe in dealing with Nature who is 

 very properly made of the feminine gender, on account 

 of the astonishing tricks which she plays upon her admirers I 

 I say before you can be safe in dealing with Nature, you 

 must get two or three kinds of cross proofs, so as to make 

 sure not only that your hypothesis fits that particular 

 set of facts, but that it is not contradicted by some other 

 set of facts which is just as clear and certain. And it so 

 happens, that in this case Mr. Darwin supplied the cross 

 proofs as well as the immediate evidence. You have all 

 heard of volcanoes, those wonderful vents in the surface 

 of the earth out of which pour masses of lava, cinders and 

 ashes, and the like. Now, it is a matter of observation and 

 experience that all volcanoes are placed in areas in which 

 the surface of the earth is undergoing elevation, or at any 

 rate is stationary ; they are not placed in arts of the 

 world in which the level of the land is being lowered. They 

 are all indications of a great subterranean activity, of a 

 something being pushed up, and therefore naturally the 

 land either gives way and lets it come through, or else is 

 raised up by its violence. And so Mr. Darwin, being 

 desirous not to merely put out a flashy hypothesis, but 

 to get at the truth of the matter, said to himself, " If my 

 notion of this matter is right, then atolls and encircling 

 reefs, inasmuch as they are dependent upon subsidence, 

 ought not to be found in company with volcanoes ; and, 



