J. D. Dana — Origin of Coral Reefs and Islands. 173 



evidence adduced ; and yet it may be a fact without affecting 

 the theory of Darwin, as I have fully illustrated.* 



It is important to have in mind that the coral-reef era prob- 

 ably covered the whole of the Quaternary and perhaps the Plio- 

 cene Tertiary also, and hence the local elevations that have 

 taken place in the ocean were not crowded events of a short 

 period. 



Moreover, these local elevations in coral seas are spread over 

 an area of 25,000,000 square miles. As an example of the 

 long distances: the Paumotu Archipelago, consisting of more 

 than eighty atolls and two barrier-islands, and covering about 

 450,000 square miles, contains only three or four atolls that are 

 over twelve feet high ; and of these, Metia is 250 feet in height, 

 Elizabeth, 80 feet, Dean's probably where highest, 15 or 20 

 feet. Metia is one of the westernmost, near 148° 13' W. and 

 15° 50' S. ; Dean's is 60 miles to the north-northeast of Metia, 

 and Elizabeth is far to the southeast, in 128° W. and 25° 50' S., 

 or nearly 1450 miles distant from Metia. Locate these points 

 on a continent, and Pacific distances and the length of Pacific 

 chains of atolls will be appreciated. 



IV. — No ancient coral reefs have the thickness attributed by the 

 subsidence-theory to modern reefs. 



An argument against the subsidence-theory is based by Prof. 

 J. o. Kein f on the alleged fact that the thickness attributed to 

 modern reefs is far beyond that of any such reefs in earlier 

 time ; that is, the thickness is unprecedented. The argument 

 decides nothing. The question is one of geological fact, not to 

 be settled by a precedent. Whether, then, there are precedents 

 or not it is not necessary to consider. 



Besides this, it implies a distinction between coral-made and 

 shell-made rocks which does not exist. The coral-reef rock is 

 largely made of shells, and the process of formation for a lime- 

 stone of shallow-sea origin is essentially the same whether 

 shells or corals are the predominant or the sole material. No 

 thick formation of any kind of rock was ever made, or could be 

 made, by shore or shallow-sea operations without a slowly 

 continued subsidence or a corresponding change of water-level. 



* Mr. Semper's objection to the theory of subsidence based on the coexistence 

 of all kinds of reefs in the Pelews, atoll, fringing and barrier, with no reefs about 

 one island, and from the relative steepness of the submarine slopes on the 

 east and west reefs of an island have been sufficiently met in Part I 



•f Dr. Rein's first memoir on Bermuda appeared in the Senckenberg Ber. natur- 

 forsch. Gesellschaft, 1869-70, p. 157, and the later in the Verhaudlung des I. 

 deutsch. Geographentages, 1881, Berlin, 1882. The above argument is from the 

 latter paper, and is given here from the citation by Dr. Geikie, the publication 

 not being accessible to the writer. 



