FORMATION OF CORAL REEFS AND ISLANDS. 237 



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dure. The small island of Makin, just north of Tari-tari, is 

 the breakwater which has protected the reef referred to from 

 the heavier seas. 



Coral island accumulations have an advantage over all 

 other shore deposits, owing to the ready agglutination of cal- 

 careous grains, as explained on a following page. It has been 

 stated that coral sand-rocks are forming along the beaches, 

 while the reef-rock is consolidating in the water. A defence 

 of rock against encroachment is thus produced, and is in con- 

 tinual progress. Moreover, the structure built amid the 

 waves, will necessarily have the form and condition best fitted 

 for withstanding their action. The atoll is, therefore, more 

 enduring than hills of harder basaltic rocks. Reefs of 

 zoophytic growth but "mock the leaping billows," while 

 other lands of the same height gradually yield to the assaults 

 of the ocean. There are cases, however, of wear from the 

 sea, owing to some change of condition in the island, or in 

 the currents about it, in consequence of which, parts once 

 built up are again carried off. Moreover, those devastating 

 earthquake- waves which overleap the whole land, may occa- 

 sion unusual degradation. Yet these islands have within 

 themselves the source of their own repair, and are secure 

 from all serious injury. 



The change of the seasons is often apparent in the distri- 

 bution of the beach sands covering the prominent points of an 

 island. At Baker's Island (near the equator, in long. 176° 

 23', W.), this fact is well illustrated. J. D. Hague states 

 (Am. Jour. Sci., II., xxxiv, 237), that the shifting sands 

 change their place twice a year. "The western shore of the 

 island trends nearly northeast and southwest; the southern 

 shore, east-by-north. At their junction there is a spit of sand 

 extending out toward the southwest. During the summer, 



