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. 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 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 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 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 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 
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 the 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. 
