144 Couthouy on Coral Formations 



the impending shelf of the surface plateau, which from their 

 being torn off now presents at its edge only a steep slope. 

 That this shelf could not have been formed while the plateau 

 was at its present elevation, is apparent not merely from the 

 fact that the surf would prevent its construction, but because 

 as the appearance of the whole reef testifies, it is not covered 

 with a depth of water adapted to the operations of the poly- 

 pes on such a scale. The fragments must also have been re- 

 moved to the locality they now occupy, while the reef was 

 at a lower level, since the surf at present scarcely reaches 

 them except during heavy gales. That a considerable re-ele- 

 vation has taken place since they became fixed where we find 

 them, is evinced by the manner in which their sides and faces 

 have been hollowed out by the action of the waves. Had no 

 change of level occurred, we should naturally expect to see 

 the greatest excavation near their union with the subjacent 

 reef, where they are unceasingly exposed to the flux and re- 

 flux of the tide, whereas it is frequently near their upper 

 third, and a portion of it above high water mark, giving to 

 the smaller masses a great variety of configuration, as may 

 be seen in the following sketch of a cluster on the reef at 

 King's island. 



"mf^ iiiiir„jir. ii...MJi 



7Jii:riiir""jirL::;^'zrifX"i 



The interrupted line in this and the preceding cut indicate 

 the line of high water in ordinary tides. 



I incline to a belief that the fissures described as existing in 

 the thin shelves of coralline limestone surrounding some 

 islands, should be included among the evidences of re-eleva- 

 tion. The character of their stratification shows that these 

 were originally deposited on a horizontal plane, and their pres- 

 ent dip of 5*^ or 6"^ seaward, may have been occasioned by 

 the upward pressure of the submerged summit below the bed 

 of the lagoon, which would also be likely to cause in strata of 

 their extent and tenuity, such rents as I have mentioned. 

 This is certainly the case with similar formations on the east- 



