130 ON CORAL REEFS AND ISLANDS. 



Christmas Island, still farther to the southeast, according to 

 the description of Cook, its discoverer, had the rim of land in 

 some parts three miles wide. He mentions narrow ridges lying 

 parallel with the sea-coast, which "must have been thrown up 

 by the sea, though it does not reach within a mile of some of 

 these places." The proof of a small elevation is decided, but its 

 amount cannot be determined from the description. The ac- 

 count of P. D. Bennett, (Geographical Jour., vii, 226,) represents 

 it as a low coral island. 



Jarvis Island, as seen from the Peacock, appeared to be eigh- 

 teen or twenty feet in height, which, if not exaggerated by re- 

 fraction, (we think it not probable,) would show an elevation of 

 six or eight feet. This island is a sand flat, with little vegetation, 

 and is but two hundred miles south of Christmas Island. 



Maiden, two hundred and fifty miles southeast of Jarvis, near 

 latitude 4° S. and longitude 155° W., visited by Lord Byron, is 

 described as not over forty feet high ; but this may be the whole 

 height, including the height of the trees. 



e. Tonga Islands and others in their vicinity. 



All the islands of the Tonga group about which there are reefs, 

 give evidence of elevation : Tongatabu and the Hapai islands 

 consist solely of coral, and are elevated atolls. 



Una, at the south extremity of the line, has an undulated, 

 mostly grassy surface, in some parts eight hundred feet in height. 

 Around the shores, as was seen by us from shipboard, there is 

 an elevated layer of coral reef-rock, twenty feet thick, worn 

 out into caverns, and with many spout-holes. Between the 

 southern shores and the highest part of the island, we observed 

 three distinct terraces. Coral is said to occur at a height of three 

 hundred feet. Prom the appearance of the land, we judged that 

 the interior was basaltic ; but nothing positive was ascertained 

 with regard to it. 



Tongatabu (an island visited by us) lies near Eua, and is in 

 some parts fifty or sixty feet high, though in general but twenty 

 feet. It has a shallow lagoon, into which there are two entrances ; 

 some hummocks of coral reef-rock stand eight feet out of water. 



Namuka and most of the Hapaii cluster, are stated by Cook 

 to have abrupt limestone shores, ten to twenty feet in height. 

 Namuka has a lagoon or salt lake at centre one and a half miles 

 broad ; and there is a coral rock in one part twenty-five feet 

 high.* 



Vavau, the northern of the Group, according to Williams, is a 

 cluster of elevated islands of coral limestone, thirty to one hun- 

 dred feet in height, having precipitous cliffs, with many excava- 

 tions along the coast.f 



* Cook's Voyage. — Williams, p. 296. \ Williams, p. 4.21. 



