36 ON CORAL REEFS AND ISLANDS. 



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 grand- 

 est Alpine scenery. There is but little soil, yet the island is cov- 

 ered 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 grow- 

 ing 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 consequently 

 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 those visited by the Expedition. But 

 the similarity among them is so great, and their peculiarities are 

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

 cession of repetitions. And moreover the facts will be found in 

 the geographical report by Captain Wilkes, and are to a great ex- 

 tent well exhibited on the map of the Paumotus and on the other 

 valuable charts of the Expedition. The characters of a few 

 briefly stated will suffice in this place. We commence with the 

 smallest. 



Jarvis's Island.— (Fig. 4, page 23.) Lat. 0° 22' S. Long. 

 159° 3T W. Length If miles trending east and west. No 

 lagoon. Shape triangular. A low sandy flat, eighteen or twenty 

 feet high, without trees, and partly covered with small shrubs. 

 A high sloping beach continuous around. Trends east and west. 

 We did not land on this island. 



■BirmVs.— Lat. 3° 35' S. Long. 171° 39' W. Four-fifths of a 

 mile by one-third, trending northwest. No lagoon. A sandy flat 

 about ten feet high, except near the north-northeast extremity, 



descriptions of caverns in the elevated coral rock of Atiu, one of the Hervey Group.* 

 In one, he wandered two hours without finding a termination to its windings, pass- 

 ing through chambers with " fretwork ceilings of stalagmite and stalactite columns, 

 which, 'mid the darkness, sparkled brilliantly with the reflected torch-light." This 

 author remarks, " that while the madrepores, the brain, and every other species of 

 coral are full of little cells, these islands, (including those resembling Atiu,) appear 

 to be solid masses of compact limestone, in which nothing like a cell can be detected" 

 Beechey, in his description of Henderson Island, another of this character, speaks 

 of the rock as compact, and having the fracture of a secondary limestone. 



* Wateoo of Cook. 



