154 THEORY OF THE FORMATION Ch. V. 



fish, turtle, and perhaps of birds : possibly, also, the bones of small 

 saurians, as these animals find their way to islands far remote from 

 any continent. The large shells of some species of Tridacna would 

 be found vertically imbedded in the solid rock, in the position in which 

 they lived. We might expect, also, to find a mixture of the remains of 

 pelagic and littoral animals in the strata formed in the lagoon, for 

 pumice and the seeds of plants are floated from distant countries into 

 the lagoons of many atolls ; on the outer coast of Keeling atoll near 

 the mouth of the lagoon, the shell of a pelagic Pteropodous animal was 

 brought up on the arming of the sounding lead. All the loose blocks 

 of coral on Keeling atoll were burrowed by vermiform animals ; and as 

 every cavity, no doubt, ultimately becomes filled with spathose lime- 

 stone, slabs of the rock would, if polished, probably exhibit the exca- 

 vations of such burrowing animals. The conglomerate and fine-grained 

 beds of coral-rock would be hard, sonorous, white, and composed of 

 nearly pure calcareous matter ; in some few parts, judging from the 

 specimens at Keeling atoll, they would probably contain a small 

 quantity of iron. I have seen a conglomerate now forming on the 

 shores of the Maldiva atolls, resembling conglomerate limestone from 

 Devonshire. Floating pumice and scoriae, and occasionally stones trans- 

 ported in the roots of trees (see my Journal of Eesearches, p. 549) 

 appear the only sources through which foreign matter is brought to coral- 

 formations standing in the open ocean. The area over which sediment 

 is transported from coral-reefs must be considerable ; Captain Moresby 

 informs me that during the change of monsoons, the sea is discoloured 

 to a considerable distance off the Maldiva and Chagos atolls. The sedi- 

 ment off fringing and barrier coral-reefs must be mingled with the 

 mud which is brought down from the land, and is transported seaward 

 through the breaches which occur in front of almost every valley. If 

 the bed of the ocean were to be upraised and converted into land, the 

 atolls of the larger archipelagoes would form flat-topped mountains, 

 varying in diameter from a few to sixty miles — for the smallest atolls 

 would probably be worn quite away; and from being horizontally 

 stratified and of similar composition, they would, as Sir C. Lyell has 

 remarked, falsely appear as if they had originally been united into one 

 vast continuous mass. Such great strata of coral-rock would rarely be 

 associated with erupted volcanic matter, for this could only take place, 

 as may be inferred from what follows in the next chapter, when the 

 area in which they were situated, commenced to rise, or at least 

 ceased to subside. During the enormous period necessary to effect an 

 elevation of the kind just alluded to, the surface would necessarily be 

 greatly denuded ; hence it is highly improbable that any fringing- 



