Ch. III. FKINGING KEEFS. 73 



more or less perfect, occur on other coasts. In these 

 cases I suspect that the shallow channel, (which no 

 doubt during storms is occasionally obliterated,) is 

 scooped out by the flowing away of the water thrown 

 beyond the line on which the waves break with the 

 greatest force. At Pernambuco the bar of hard sand- 

 stone, before alluded to, has the same external form 

 and height as a coral reef, and extends nearly parallel to 

 the coast ; within this bar currents, apparently caused 

 by the water thrown over it during the greater part of 

 each tide, run strongly, and are wearing away its inner 

 wall. From these facts it can hardly be doubted that 

 within most fringing reefs, especially within those 

 lying some distance from the land, a return stream 

 must carry away the water thrown over the outer edge; 

 and the current thus produced would tend to prevent 

 the channel being filled up with sediment, and might 

 even deepen it under certain circumstances. To 

 this latter belief I am led, by finding that channels are 

 almost universally present within the fringing reefs of 

 those islands which have undergone recent elevatory 

 movements ; and this could hardly have been the case 

 if the conversion of the very shallow channel into land 

 had not been counteracted to a certain extent. 



A fringing reef, if elevated in a perfect condition 

 above the level of the sea, would present the singular 

 appearance of a broad dry moat bounded by a low wall 

 or mound. The author 1 of an interesting pedestrian 



1 Voyage a l'lsle de France, par un Officier dn Eoi, Part i. pp. 

 192, 200. 



