414 



THE AMERICAN NATURALIST 



[Vol. LII 



many contrasts with those of the true lagoons and outer 

 reef rims. All of the pure- sea-water-requiring organisms 

 are wholly absent or rare, and in their places one finds a 

 large series of brackish water and silt-loving forms. The 

 generalization is quite accurate for the Kaneohe and Pearl 

 Harbor inner reefs that 



The main distinction between the inner and outer reefs consists in the 

 less fragmentary character of the rocks in the former case, the less fre- 

 quent accumulations of debris on their upper surface, and the more 

 varied features and slopes of the margins. . . . There is to be found 

 about inner reefs, over large areas, solid white limestone, showing 

 internally no evidence of its coral origin, and containing rarely a shell 

 or other imbedded fossil. It is a result of the consolidation of the fine 

 coral sand or mud that is made and accumulated through the action of 

 fV. Q K,»V.f i_ ■ » 



3. Channels or seas within barriers, which may receive 

 detritus either from the reefs, or from the shores^ or from 

 both these sources combined. These channels correspond 

 to the lagoons of the fringing reef, except that the chan- 

 nels are much larger. The Hawaiian lagoons are gen- 

 erally floored with coral sand, indicating that reef erosion 

 is more rapid than coast erosion. 



4. Beaches and beach formations, produced bv coral 

 accumulations on the^hore through the action of the sea 

 and winds. Beaches and dunes of coral sand are com- 

 mon on the islands of Molokai, Oahu, Kauai, Laysan, Mid- 

 'vny, < >rean, etc. 



^ Of the three great classes of coral reefs— fringing, bar- 

 rier, and atoll-the first and last only have representation 

 m the Hawaiian Archipelago. The fringing reefs are 

 platforms of coral limestone which extend but a relatively 

 short distance from the shore. The seaward edge of the 

 platform is characteristically somewhat higher than the 

 inner portion, and is usually awash at low tide. The reef 



the light waves that work over 

 consist of branching corals, v 

 small fragments; for even in 



ae inner reefs. Other portions of reef 

 h the intervals filled in by sand and 



