INTRODUCTION. xix 



abundantly proved from the great variety of submarine platforms formed 

 at the base of volcanic islands and of elevated limestone masses throughout 

 the Pacific, the depth of these platforms being fairly indicated by that 

 of the lagoons enclosed by the encircling reefs or by that of the barrier 

 reef lagoons. 



The formation of huge masses of limestone in which occur at intervals 

 layers of corals or beds 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 while the non-coral- 

 liferous limestones were laid down at a more rapid rate at a depth greater 

 than that at which corals could grow. This process 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 first 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 comparatively 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 greater than 

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

 have continued long enough to cut the elevated limestone down, 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 connect what was the lagoon or basin at the first sea-level with the 

 lagoon or basin 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 limestone mass and of the coralliferous lime- 

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

 such an 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 or 



