186 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 erater 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. 
- ¢. It further requires that there should be craters at least fifty 
miles in diameter, and that twenty and thirty miles should, be 4 
common size. facts give no support to such an assumption. 
_d. It supposes that the high islands of the Pacific, am the We 
¢cinity of the coral islands, abound in eraters; 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 plaust 
bility to the crater hypothesis. Pj 
Thus at variance with facts, the theory has lost favor, and 18 
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 charactet- 
Shall we suppose, with some writers, that these islands wele 
planted upon submarine banks, within one hundred and 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 cone 
tinents with elevations so uniform in height; and submerged 
banks of this kind are of extremely rare occurrence. If sud 
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 
said to prefer the declivity to the central plateau of the subme 
rine bank : on the contrary, the part nearest the surface appeals 
* 
A study and comparison of the reefs of different kinds— 
fringing, barrier, and atoll,—throughout the oceans, is the only 
Mr. Darwin has happily and successfully pursue% 
and has arrived, as we have reason to believe, at the true heoy 
of Coral Islands. It is satisfactory, because it is a simple general 
SU Jo hate get ble og enh case celal 
* Lieutenant Nelson, R. N, this hypothesis before the publication of 
Mr. Darwin's views, See Geol. : vol. v, 12; and Darwin, op. cit, p. 94 
