STRUCTURE OF CORAL ISLANDS. 159 



appear to be solid masses of compact limestone, in wJiidi nothing 

 liize a cell can be detected T 



Beechey, in his description of Henderson Island, another 

 of this character, speaks of the rock as compact, and hai'ing 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 narrow 

 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 of 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 : — 



farvis's Island. — (Fig. 3, page 135.) Lat. o°2 2'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 are 

 distinguishable in it. Its surface is a low sandy flat, eighteen 

 or twenty feet high, without trees, and partly covered with 



