1^ 





t 





Ui 



i, 



•Hate'./- 



■"■'ale 

 ' ^ coral alon. 



i 



I. 



li«L 



ui ate 

 atiieon 





f 



L 



UC^ p 



» is cairied dowH- 



Qg tL -^np 





t^ E«^ too rapii 



n 



rt«o 



the sDi&f*' 



_* * ' 



5(« 



u^rc till in '-•■ ■ 



'^' ^^ 



oil 



Tf 



pfH- 



tflt 



^ 



,•1 "" 



Ch. XLIX.l 



OIIIGIN OF TIIEIE FOEM. 



595 



of a lagoon, and, lastly, to tlie perfect atoll, having a lagoon 

 several liundred feet deep, surrounded bj a reef rising deeply 

 from an unfatliomed ocean. 



If we embrace these views, it is clear, that in regions of 

 growing coral a similar subsidence must give rise to\arrier 

 reefs along the shores of a continent. Thus suppose A 



(fig. 157) to represent the north-eas tportion of Australia, and 

 I c the ancient level of the sea, when the coral reef d was 

 formed. If the land sink so that it is submerged more and 

 more, the sea must at length stand at the level e f, the reef 

 in the meantime having been enlarged and raised to the 



Fiff. 157- 



point a. 



f: 



reef g, is now much greater than originally between th<? 



shore c and the reef d, and the longer the subsidence 



con- 



m 



When 



the first edition of this work appeared in 1831 

 several years before Mr. Darwin had investigated the facts 



come 



that the land was subsiding at the bottom of those pa,rts of 



numer 



perceive that such a subsidence, if conceded, would equally 



solve the enigma as to the form both of annular and barrier 



reefs. 



i> 



I shall cite the passage referred to, as published bv me in 



^1 . < T4- ,• _ _ Tin . . - *^ 



1831: 



circumstance 



be so vast an area in Eastern Oceanica, studded with 

 minute islands, without one single spot where there 



IS a 



wider extent of land than belongs to such islands as Otaheite, 

 Owhyhee, and a few others, which either have been or are 

 still the seats of active volcanos. If an equilibrium only 

 were mamtamed between the upheaving and depressing force 

 ot earthquakes, large islands would very soon be formed in 

 the Pacific; for, in that case, the growth of limestone, the 



