THE CORAL-REEF PROBLEM. 75 



there is no evidence to show that these submerged atoll-like 

 banks are not really banks of subsidence, rather than of up- 

 Avard growth, and in their general features they do not differ 

 from the Chagos Bank which Mr. Darwin considered to repre- 

 sent a half-drowned atoll. Until a satisfactory explanation is 

 furnished of the origin of these central lagoons, so long must 

 any theory bearing upon the formation of coral structures be 

 considered merely tentative. In the case of the Bermuda 

 Islands, which limit the field of my own investigations in this 

 direction, I am confident that, whatever may have been the 

 original construction of the region, the present lagoon features 

 have been brought about through subsidence ; and this con- 

 clusion was reached before me by Prof. Rice, who seems to 

 have been amply satisfied with the subsidence theory ! 



On one point in connection with his recent survey Mr. 

 Agassiz furnishes important testimony, and that is as to the 

 actual thickness of the coral-made rock, or, at least, the depth 

 beneath the surface at which this rock occurs. This has been 

 determined by the artesian borings made in the vicinity of 

 Honolulu, and elsewhere. At various points the bore pierced 

 coral-rock at depths of 100-500 feet beneath the sea-level. In the 

 well of Mr. James Campbell, near the Pearl River Lagoon (?), 

 28 feet of white coral was struck at a depth of nearly 1000 feet 

 below high-water mark (p. 153), and again at " Waimea, Oahu, 

 900 feet was drilled through hard ringing coral rock " (p. 152). 

 In these facts, however, Mr. Agassiz sees no evidence of sub- 

 sidence. He prefers to account for the great thickness of the 

 coral rock " by the extension seaward of a growing reef, active 

 only within narrow limits near the surface, which is constantly 

 pushing its way seaward upon the talus formed below the liv- 

 ing edge. This talus may be of any thickness, and the older 

 the reef, the greater its height would be, as nothing indicates 

 that in the Hawaiian district there has been any subsidence to 

 account for such a thickness of coral rock in its fringing reef", 

 (p. 154). But where are the evidences which support this ex- 

 planation ? I must confess that I fail to see any. The assump- 



