98 Couthouy on Coral Formations 



These outlets are by some persons supposed to designate 

 fissures in the walls of submerged craters, represented by the 

 lagoons. If we admit, however, that these islands have been 

 formed by the process which it has been attempted to describe 

 in this communication, such an explanation is rather unsatis- 

 factory, since if the coral began to grow in the fissure imme- 

 diately upon the water covering it, there is no reason why 

 the reef should not reach the surface there, as early as at any 

 other point, and the rent thus be filled up. 



In his lectures for the Lowell Institute, Prof. Lyell expres- 

 sed an opinion, that these channels were formed at a period 

 when the encircling reef was nearly on a level with the sur- 

 face of the ocean, by the rapid rush of the ebb over the lee- 

 ward side of the lagoon, whose waters at high tide were 

 raised considerably above sea level by the breakers bursting 

 into it from the windward quarter. The passage, he argu- 

 ed, once thus opened by the water forcing its way out, would 

 ever after be maintained by the same power. 



Now this might possibly have occurred, provided the rush 

 of waters had ever been directed for a length of time to one 

 particular point. But if the surface of the reef was in times 

 past, as it now is, nearly of one level throughout, which there 

 seems no reason for doubting, it is evident that the ebb would, 

 at the period alluded to by Prof. Lyell, set equally over the 

 whole leeward portion, till uniformity of level between the 

 lagoon and sea, was restored at low tide. As he had no refer- 

 ence either in his descriptions or diagrams, to the plateau 

 which I have described as extending from the beach to some 

 distance seaward ; but rather spoke as though he supposed the 

 whole space between the lagoon and surf to be a fragmentary 

 ridge ; I have sometimes thought that when he spoke of the 

 reef, as nearly on a level with the surface of the ocean at the 

 period when the passages were formed, he meant that this 

 ridge was much lower then than at present, yet sufficiently 

 high to oppose a considerable obstacle to the efflux of the 

 surplus waters of the lagoon ; or in other words, that the dif- 

 ference of level between the sea and reef, consisted in the 

 latter being a little the higher, instead of as it really is, the 

 lower of the two. If it was in fact his idea, that the lagoon 



