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es 



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H 



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u. 



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V4 



iho ^ 



Une 



with tie 



•▼ be ©*!.' 



'nna. 



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in 



•Tlie cireukr 

 tk:' "3 in the 



D 



ITl 



* notidii? more 

 in the earlier 



gboot to shoT 



-5-iiuuiy 



active 



4 Uijtin 

 •just 



;n - :iie 



■•; W 



as tt« 



r: niade th^J 



, circ 



s 



1- ,.tlaD^' 



alar 



u 





^w 





i«r- i=;;.,.,Tii 



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L-r 



'1 



? 



. 



Ch. XLIX.] 



CirvCULAE FOEM OF COEAL ISLANDS, 



591 



jnst as the ring' of dry coral recalls to onr minds the rim 

 of a volcanic crater. More lately, indeed, Mr. Darwin has 

 shown that the nmnerons volcanic craters of the Galapagos 



them 



many 



if they were submerged and incrusted with coral, they would 

 resemble trne atolls in sliape."^ 



Another argument which I adduced when formerly de- 

 fendinp* this doctrine was derived from Ehrenbersr's statement. 



some 



many others were ribbon-like strips, with flat to23S, and with- 



Since, therefore, all the genera and many of 



out lagoons. 



the species of zoophytes in the Red Sea agreed with those 

 which elsewhere construct lagoon islands, it followed that the 

 stone-making zoophytes are not guided by their own instinct 

 in the formation of annular reefs, but that this peculiar shape 

 and the position of such reefs in the midst of a deep ocean 

 must depend on the outline of the submarine bottom, which 

 resembles nothing else in nature but the crater of a lofty sub- 

 merged volcanic cone. The eno 



mous 



atolls 



me 

 ma^ 



and which had often been appealed to as a serious objection 

 to the volcanic theory. That so many of them were of the 

 same height, or just level with the water, did not present a 

 difficulty so long as we remained ignorant of the fact that the 

 reef-building species do not grow at greater depths than 

 25 fathoms. 



May he explained hy subsidence. 



Mr 



formations 



globe, was induced to reject the opinion that their shape 

 represented the form of the original bottom. Instead of 

 admitting that the ring of dead coral rested on a circular or 

 oval ridge of rock, or that the lagoon corresponded to a pre- 

 existmg cavity, he advanced a new opinion, which must, at 

 first sight, seem paradoxical in the extreme : namely, that 

 the lagoon is precisely in the place once occupied by the 



^ Darwin, Volcanic Islands, p. 113. 



. 



