low the surface and the barrier reef would now be an 

 atoll, by continuation of its upward growth. 



Figure 7. oections illustratinq the formation of barrier reefs and oiolls 

 according to Darwin's theory. 1, 2, 3, successive stages in the sinking of 

 land beneath the water. 1, Fringing reef. 2, Barrier. 3, Atoll. 



Geologic evidence to support this theory was dis- 

 covered in the general appearance and topography of 

 many of the islands with barrier reefs by the American 



29 



