9 8 THE SHORE 



indistinguishable from the shoreward part of a reef. 

 If organisms commence to grow on the outer edge 

 of such a platform, its surface appearance is in 



A" 



FIG. 29. SECTIONAL DIAGRAM TO ILLUSTRATE FORMATION OF 

 ATOLL AND BARRIER REEFS BY SUBSIDENCE. (ADAPTED FROM 

 DARWIN'S " CORAL REEFS.") 



A, A, Sea-level of island, with fringing reef in black ; A', A', the 

 same after some subsidence island, with barrier reef shaded ; 

 A", A", the same after the island has been submerged atoll 

 reef dotted. The vertical scale, as in the next figures, is many 

 times the horizontal scale. 



\ 



FIG. 30. SECTIONS TO SHOW FORMATION OF REEFS BY ABRASION 

 OF LAND. 



i, Ongea Levu, Fiji, an elevated coral island ; 2, Wakaya, Fiji, a 

 volcanic island ; A, supposed former sections of land ; B, present 

 sections of land and reef. 



every respect that of a true reef. This is especi- 

 ally the mode of formation where the land is com- 

 posed of elevated coralline limestone, as is frequent 



