158 RAMBLES AND REVERIES. 



surface of the water. The action of the surf, hurling 

 up fragments of the rock, shells and various debris, 

 would do the rest, bringing the reef at length above 

 the surface and so forming an islet. Inside the reef 

 there would be a shallow lagoon communicating 

 here and there with the outside ocean. Thus is 

 formed the Atoll or true Coral island with its 

 interior lagoon. 



Humboldt has given such a clear and intelligible 

 outline of Darwin's hypothesis that I cannot do 

 better than quote it : "An island mountain closely 

 encircled by a coral reef subsides, while the fringing 

 reef that had sunk with it is constantly recovering 

 its level, owing to the tendency of the coral animals 

 to regain the surface by renewed perpendicular 

 structures; these constitute, first, a reef encircling 

 the island at a distance, and subsequently, when the 

 enclosed island has wholly subsided, an atoll. 

 According to this view, which regards islands as the 

 most prominent parts or the culminating points of 

 the submarine land, the relative position of the 

 coral islands would disclose to us, what we could 

 scarcely hope to discover by the sounding-line, viz. 

 the former configuration and articulation of the land " 

 ( Views of Nature, p. 262). 



Admirably as this theory fits into the conditions 

 of the case, it is open to the objection that it 

 requires many thousands of square miles of ocean 

 bed to be continually sinking, with consequences 

 that would naturally be looked for in other places. 



Dr. John Murray, of the Challenger, has put 

 forward another explanation. He suggests that 



