40 EXPEDITION OF THE "ALBATROSS," 1899-1900. 



layers of corals or of reef -building corals must have taken place in areas 

 of subsidence, — the subsidence taking place at a comparatively slow rate 

 while the coralliferous belts were deposited, and at a more rapid rate at 

 a greater depth than that at which corals could grow while the non-coral- 

 liferous limestones were laid down. Tliis proce.ss has nothing in common 

 with the formation of atolls. But when these coralliferous masses of lime- 

 stone of great thickness were elevated either suddenly or intermittently 

 to heights of more than 1000 feet, the resulting islands in the former case 

 must have represented either a bed deposited near the surface — if coral- 

 liferous — enclosing perhaps a lagoon, or a sound, or a basin of solution 

 and erosion, formed in con)paratively modern times, with recent corals 

 forming a capping of moderate thickness. In the second case, during each 

 stage of rest the elevated beds were subject to denudation and erosion 

 by the action of the sea. If each stage was an elevation of more than 

 the depth at which corals can grow, the denudation and erosion may 

 have continued long enough to cut the elevated limestone down to, or 

 nearly down to the terrace which marks the uprising of the mass. Or 

 the denudation and erosion may merely have gone far enough to open the 

 circumscribed area to the action of the sea at some points only, and 

 thus to connect what wa** the lagoon or basin at the first sea-level with 

 the lagoon or ba.sin or .sound of the second stage of rest. 



One can readily see how complicated the resultant action may become 

 when we take into account the varying height of the different stages of 

 elevation, the condition of the liuiestone mass and of tlie coralliferous lime- 

 stones after the elevation, and the action of denudation and of erosion upon 

 the elevated mass, as well as the solvent action taking place on the summit 

 and .sides, and finally the eroding action of the sea upon the interior basin, 

 .should it once break through the outer rim of the elevated basin, when its 

 lowest point has reached the level of tlie sea. This break would thus form 

 an entrance to the lagoon, much as is formed the entrance to any lagoon 

 or sound. Should this mass be elevated a second, a third, or a fourth time, 

 we may find one, or two, or more entrances to the old lagoons and .sounds 

 according to the rate of denudation and of erosion of the elevated mass 

 during the periods of rest. 



