178 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



and Bermudas the corals now growing form a thin veneer upon tlie a^olian 

 rock ledges, the remnants of the vanishing land formed from a coral 

 reef which must have flourished at the beginning of the present epoch. 



But Dana himself has even more distinctly and emphatically than 

 any other writer stated the objections to the general application of the 

 theory of subsidence for the formation of bai-rier reefs. In " Corals 

 and Coral Islands," he says (p. 347) : " The amount of subsidence deter- 

 mines in some cases the distance of barrier reefs from shore ; but it by 

 no means accounts for the diflference in their extent in different parts of 

 a single group of islands. Indeed, if this cause be considered alone, 

 every grade of extent, from no subsidence to the largest amount, might 

 in many instances be proved as having occurred on a single island. Of 

 far greater importance, as has appeared, is the volcanic character of the 

 land." The remainder of the paragraph quoted above, describing the 

 relations of volcanoes and of zoophytes as the land-making agents of 

 the Pacific, seems hardly consistent with the subsidence theory. 



Many of the observations made on elevated coral reefs do not distin- 

 guish between the elevation of a tjinn mantle on a slope to a certain 

 height, and the thickness of the reef itself. Furthermore, in such a dif- 

 ficnlt problem only the observations of trained observers can be of value. 

 Many of the data, and even many of those quoted by Dana, are the 

 records of merely casual observations of individuals with little or no 

 experience in tliis field. 



The island of Lafu, one of the Loyalty group, the geology of which 

 has been described by the Rev. W. B. Clarke,^ is one of the few elevated 

 coral islands of which we may feel certain that the highest points, two 

 hundred and fifty feet above the sea, are covered by an elevated coral 

 reef, the elevation being connected in that case, not with volcanic action, 

 but with the elevation of the adjoining island of New Caledonia. Sub- 

 sequent investigations of the Loyalty group by Balansa^ and Cham- 

 beyron have shown that other islands of the group are covered by 

 elevated coral reefs. Ouvea attains a height of a little over fifty feet, 

 with an interior lagoon ; and while Lafu shows three terraces, the neigh- 

 boring island of Mari lias five distinct terraces, attaining a height of 

 one hundred meters, with a nucleus of trachyte. 



From the interesting accounts given by Captain Chambeyron, in his 

 " Note relative a la Nouvelle Caledonie," ^ we can see how much remains 



1 Proc. Geol. Soc. London, 1846, p. 61. 



2 Bull, fie la Soc, de Geo^i., Vol. V. p. 521, 1873. 



3 Ibid., Vol. IX. p. 566, 1875. 



