PRELIMIXARY EEPORT. 41 



The coralliferous limestone rings would be foirly continuous in case of 

 a slow rate of denudation and erosion ; if broken through by the action 

 of the sea and with a rapid rate of denudation, only disconnected patches, 

 more or less numerous, according to the rate of erosion, would indicate the 

 former ring; and finally, with a very rapid denudation and erosion, both of 

 the exterior face and interior of the lagoon, or sound, nothing would be 

 left of the elevated mass except the submerged reef-ring. This becomes 

 still more complicated when the limestone mass, while elevated, has been 

 broken through by the underlying volcanic rocks, and when they have dis- 

 placed portions of the coralliferous limestone beds and left them more acces- 

 sible to the effects of denudation and of erosion, especially when this action 

 has taken place on the outer face of the elevated mass, and left broken 

 cuts and openings forming connections between the outer sea and the inte- 

 rior basins, which would thus soon be transformed into great sounds or 

 lagoons. The erosive as well as the solvent action of the sea would soon 

 level the outer rim to the plane of the sea level, the further disintegra- 

 tion being stopped by the growth of recent corals or of coralline algaa 

 upon the surface of the coralliferous or massive limestone eroded to the 

 level of the sea or below it. With the more rapid erosion and denudation, 

 both atmospheric and marine, of the limestones, they would rapidly dis- 

 appear, and there would be left only the volcanic mass which had uplifted 

 the limestones, with here and there a remnant of them to indicate the 

 proba])le course of events. Of course, when the volcanic masses come up 

 without elevating any limestone beds the conditions are much simpler, 

 and it becomes only a question of the mode of formation of the recent 

 corals around the base of the elevated volcanic mass. 



The want of continuity of the atolls of the eastern Paumotus of -the 

 Ellice, Gilbert, and Marsliall Islands, their separation by considerable dis- 

 tances and great depths, would seem to preclude the idea of the forma- 

 tion of the Tertiary limestones over great areas. The existence of these 

 limestones on disconnected and isolated islands would suggest the forma- 

 tivin of the limestones upon mounds or ridges elevated to very different 

 heights below the surface of the ocean, — these mounds and ridges con- 

 sisting of volcanic or other rocks elevated by the volcanic agencies which 



