88 ON CORAL REEFS AND ISLANDS. 



same height as here supposed. Mount Loa and Mount Kea, of 

 Hawaii, present a remarkable instance of approximation, as they 

 differ but two hundred feet: but the two sides of the crater of 

 Mount Loa differ three hundred and fourteen feet in height. 

 Mount Kea, though of volcanic character, has no large crater at 

 top. Hualalai, the third mountain of Hawaii, is 4000 feet lower 

 than Mount Loa. The volcanic summit of East Maui is 10,000 

 feet high, and is a fine example of a large crater; but the wall 

 of the crater on one side is 700 feet lower than the highest point 

 of the mountain ; and the bottom of the crater is 2000 feet below 

 the rim of the crater. Similar facts are presented by all volcanic 

 regions. 



c. It further requires that there should be craters at least fifty 

 miles in diameter, and that twenty and thirty miles should be a 

 common size. Facts give no support to such an assumption. 



d. It supposes that the high islands of the Pacific, in the vi- 

 cinity of the coral islands, abound in craters; while on the con- 

 trary there are none, as far as is known, in the Marquesas, Gam- 

 bier, or Society Groups, the three which lie nearest to the Pau- 

 motus. Even this supposition fails, therefore, of giving plausi- 

 bility to the crater hypothesis. 



Thus at variance with facts, the theory has lost favor, and is 

 no longer sustained even by those who were once its strongest 

 advocates. The question still recurs with regard to the base- 

 ment of coral islands, and the origin of their lagoon character. 

 Shall we suppose, with some writers, that these islands were 

 planted upon submarine banks, within one hundred arid fifty feet 

 of the surface of the sea? As has been said, there is no author- 

 ity for the supposition. We nowhere find regions upon our con- 

 tinents with elevations so uniform in height; and submerged 

 banks of this kind are of extremely rare occurrence. If such 

 patches of submerged land existed, the lagoon structure would 

 still be as inexplicable as ever; for the growing reefs of the Pa- 

 cific show that corals may flourish alike over all parts of the 

 bank, where not too deep. The zoophyte can by no means be 

 said to prefer the declivity to the central plateau of the subma- 

 rine bank: on the contrary, the part nearest the surface appears 

 to abound in the largest species of corals.* 



A study and comparison of the reefs of different kinds, — 

 fringing, barrier, and atoll, — throughout the oceans, is the only 

 philosophical mode of arriving at any conclusion on this subject. 

 This course Mr. Darwin has happily and successfully pursued, 

 and has arrived, as we have reason to believe, at the true theory 

 of Coral Islands. It is satisfactory, because it is a simple general i- 



* Lieutenant Nelson, R. N\, suggested this hypothesis before the publication of 

 Mr. Darwin's views. See Geol. Trans., vol. v, 12 ; and Darwin, op. cit., p. 94. 





