34 James D. Dana, Esq., on Coral Reefs and Islands. 



of a lake prevail within, aflfording safe navigation for the 

 tottling canoe sometimes through the whole circuit of an 

 island ; and not unfrequently, ships may pass, as by an in- 

 ternal canal, from harbour to harbour around the island. 

 The reef is covered by the sea at high tide, yet the smoother 

 waters indicate its extent, and a line of breakers its outline. 

 Occasionally a green island rises from the reef, and in some 

 instances a grove of palms stretches along the barrier for 

 miles, where the action of the sea has raised the coral struc- 

 ture above the waves. 



The sketch annexed conveys soi^e idea of the peculiar 

 features presented by a Pacific island, and its encircling 

 reefs, though in order to fill out the scene, the jagged heights 

 and deep gorges of the islands should be covered with 

 forests, and the shores with groves and native villages. The 

 coral platform which borders the shore is represented with 

 its usual uneven line, — its broad harbours with a narrow 

 entrance, — and to the left, an irregular ship-channel running 

 between the inner or fringing reef, and the outer or barrier. 

 At a single place the sea is faced by a cliffy, and here, owing 

 to the boldness of the shores and the depth of the waters, 

 the reef is wanting. To the right there is only a fringing 

 reef. 



Coral Islands. — Coral islands resemble the reefs just de- 

 scribed, except that a lake or lagoon is encircled instead of 

 a mountainous island. A narrow rim of coral reef, generally 

 but a few hundred yards wide, stretches around the enclosed 

 waters. 



In some parts it is so low that the waves are still dashing 

 over it into the lagoon ; and in others, it is still verdant with 

 the rich foliage of the tropics. The coral-made land, when 



