190 On Coral Reefs and Islands. 
emplified, for the view is a good transverse section of either of 
them. 6’ b’” are sections of the distant enclosing barrier, and 
ec” ce”, and other intermediate spots, the water within. 
The supposed similarity’ between these ideal sections and ex- 
isting islands is fully sustained by actual comparison. Fig. 2 
is a sketch of the island of Aiva in the Feejee Group. There 
are two peaks in the lagoon precisely as above; and although we 
have no soundings of the waters in and about it, nor sketches 
of peaks, facts observed elsewhere authorize in every essential 
point the transverse section given in figure 3, resembling closely, 
as is apparent, that in figure 1. The section is made through 
the line 6b, b’ b’, of figure 2. It is unnecessary to add other 
illustrations. ‘They may be made out from any of the eastern 
groups of the Feejees, the Gambier Group of the Paumotus, or 
Hogoleu in the Carolines. Wallis’s Island is another example of 
reef-grounds, or in other words, that show evidence of subsidence 
during the growth of the reefs. Broad channels, and even opel 
seas within, as in Nanuku and the Exploring Isles, are therefore 
to be received as results of the subsidence, for which explana~ 
tions should be sought. 
tween them. These channels it is true, are filled in part —_ 
the outer reefs, but proportionally less from them than from the 
