94 



FUNAFUTI 



is clearly the case. The first stage, in which the reef is 

 no more than 25 fathoms thick, and forms a selvage 

 accurately following the margin of the land, is repre- 

 sented by that numerous class known as "fringing" 

 reefs. The second, in which a comparatively thick reef 

 surrounds an island with an intervening saltwater chan- 

 nel, is illustrated by another class, known as " encircling " 

 or " barrier " reefs. In these, as we might expect, the 

 form of the reef is only remotely related to the contour 

 of the enclosed island, the valleys of which present 



ATOLL 



FIG. 22. Third Stage. 



that fiord-like character so suggestive of sunken land. 

 The last stage is that of the atoll itself. 



The excellence of Darwin's theory lies in this, that it 

 explains all the essential features of an atoll on one 

 simple assumption. It is inconsistent with no known 

 fact, and as additional discoveries have been made it has 

 not required to be supplemented by fresh hypotheses. It 

 is not like a Gothic structure, supported by flying 

 buttresses and other tours de force, but rather resembles 

 some noble Italian tower, which rises from its base, 

 straight, simple, and self-sufficing. It was no sooner 

 given to the world than it commanded almost universal 

 assent. 



