178 Recent Views regarding Coral Reefs. [Sess. 



than dead coral, unless, of course, subsidence lowers the reef 

 and permits of the growth of a layer of new coral on the top of 

 the old. Now a reef is a porous structure, — at all events in 

 its earlier stages, — so that water, both rain-water and sea- 

 water, readily finds its way into the reef. The sea- water, 

 indeed, surges up and down with each great undulation of the 

 sea outside. So a solvent action commences, and soon begins 

 to make its action manifest upon the parts of the reef that 

 have been longest open to attack. By slow degrees these 

 older corals rot and go to pieces, and crumble away to such 

 an extent under the chemical action of these waters that the 

 fragments are easily washed out during a storm, or may even 

 be removed by the winds. So in time it happens that a pool 

 is formed over the part where the ancestral corals of the reef 

 first came to the surface. It follows, therefore, that while the 

 outer corals are steadily building their way seaward, the 

 margins of a gradually enlarging and deepening pool or lagoon 

 of sea-water follow up in their rear. The process forcibly 

 reminds one of the growth of the well-known fairy-rings of 

 our pastures. If the initial stages of the coral reef were 

 commenced as a fringe to a large mass of land, the lagoon 

 becomes a long strip parallel to the coast. If, on the other 

 hand, the reef started on a submerged mound, the reef itself 

 will grow into the shape of a ring, and the central pool will 

 be roughly circular. It is this latter case which most people 

 have in mind when thinking of the coral reefs of our 

 story-books. 



One of the commonest features noticeable in connection 

 with coral reefs is the presence of masses of coral, in every 

 respect like those which are forming now below the sea, at 

 various levels high and dry above those which are now living. 

 The elevated position of these upraised coral reefs is due, not 

 to any fall in the level of the sea, but to intermittent uprises 

 of the sea-floor upon which the corals grew. Our Scottish 

 raised beaches, which are so well seen on the West Coast, or 

 at Elie, or at Granton, are records of similar changes of level 

 here within geologically-recent times. In Scotland the rise 

 has been intermittent, with long pauses between each uplift. 

 This appears to be the rule in most cases of the kind. But 



