CORAL-REEFS. 



129 



injurious effects of the sediment and fresh water borne 

 down from the land were consequently lessened, the 

 greater number of the channels, with which the reef in its 

 fringing state must have been breached, especially those 

 which fronted the smaller streams, will have become choked 

 up with the growth of coral : on the windward side of the 

 reef, where the coral grows most vigorously, the breaches 

 will probably have first been closed. In barrier-reefs, 

 therefore, the breaches kept open by draining the tidal 

 waters of the lagoon-channel, will generally be placed on 

 the leeward side, and they will still face the mouths of the 

 larger streams, although removed beyond the influence of 

 their sediment and fresh water; — and this, it has been 

 shown, is commonly the case. 



Referring to the following diagram, in which the newly 

 formed barrier-reef is represented by unbroken lines, instead 

 of by dots as in the former woodcut, let the work of 

 subsidence go on, and the doubly pointed hill will form two 



, A' ' i^a*. C - A" 



^^ -;:r,.. B j HB j H ...„.,,...— »<■ ST 



[No. 5.] 



A'A'— Outer edges of the barrier-reef at the level of the sea. The cocoa-nut 

 trees represent coral-islets formed on the reef. 



CC — The lagoon channel. 



B'B'— The shores of the island, generally formed of low alluvial land and of 

 coral detritus from the lagoon-channel. 



A" A" — The outer edges of the reef now forming an atoll. 



C — The lagoon of the newly formed atoll. According to the scale, the 

 depth of the lagoon and of the lagoon-channel is exaggerated. 



874 



