FIGURE 37. MAP OF ATOLLS IN THE CAROLINE GROUP. LAND IN SOLID BLACK. 

 DEPTHS IN FATHOMS. 



300 feet, which is practically the depth of wave-base. The 

 billiard-table flatness of the lagoon floors is the product of cut- 

 and-fill by the waves, and the excess of 50 fathoms over the 

 lagoon depth can be reasonably ascribed in large part to in- 

 cipient filling of the lagoon by shells and skeletal fragments 

 derived from the organisms that thrive on reef and over lagoon 

 floor. 



Yet clearer is the fact that the actual flatness of floor can 

 have been developed only during prolonged stillstand of the 

 volcanic foundation, that is, during a long period of crustal 

 stability, including the present time. 



The main living reefs stand wall-like on the borders of the 

 lagoons, and 200 to 250 feet above the lagoon floors. From 

 their classic studies, Charles Darwin and James Dwight Dana 

 concluded that the living reefs project upward in this way 

 because the reef foundations slowly sank and continue to sink 

 slowly. Their theory, made before adequate soundings had 

 been made in the tropical belt, has serious defects. There is a 



