STRUCTURE OF CORAL ISLANDS. L95 



of this character, speaks of the rock as compact, and having 

 the fracture of a secondary limestone. 



The surface of the island is singularly rough, owing to 

 erosion by rains. The paths that cross it wind through nar- 

 row passages among ragged needles and ridges of rock as high 

 as the head, the peaks and narrow defiles forming a miniature 

 model of the grandest Alpine scenery. There is but little 

 soil, yet the island is covered with trees and shrubbery. 



The shores at the first elevation of the island, must have 

 been worn away to a large extent by the sea ; and the cliff 

 and some isolated pinnacles of coral rock still standing on the 

 coast are evidence of the degradation. But at present there 

 is a wide shore-platform of coral reef, two hundred or two 

 hundred and fifty feet wide, resembling that of the low coral 

 islands, and having growing coral, as usual, about its margin 

 and in the shallow depths beyond. 



In the face of the cliff there are two horizontal lines, 

 along which cavities or caverns are most frequent, which con- 

 sequently give an appearance of stratification to the rock, 

 dividing it into three nearly equal layers. 



We might continue this account of coral reefs and islands, 

 by particular descriptions of others in the Pacific. But the 

 similarity among them is so great, and their peculiarities are 

 already so fully detailed, that this would amount only to a 

 succession of repetitions. The characters of a few, briefly 

 stated, will suffice in this place. 



Jarviis Island.— (Fig. 4, page 168.) Lat. 0° 22' S. Long, 

 159° 58' W. Two miles long by one mile wide, and trending 

 east and west. No lagoon, but a basin-like depression over 

 its interior, which at bottom is seven or eight feet above the 

 sea, and in which the lagoon once existed; old beach lines 



