SUBSIDENCE IN PACIFIC CORAL REGIONS. 275 



Paumotu Archipelago there are about eighty of these atolls. 

 Going westward, a little to the north of west, they are found to 

 dot the ocean at irregular intervals ; and at the Kingsmill or 

 Gilbert Group, the Marshall Group, and the Carolines, com- 

 prise seventy-five or eighty atolls. 



If a line be drawn from Pitcairn's Island, the southernmost 

 of the Pauniotus, by the Gambler Group, the north of the 

 Society Group, the Navigators, and the Salomon Islands to the 

 Pelews, it will form nearly a straight boundary, trending N. 70° 

 W., running between the atolls on one side and the high 

 islands of the Pacific on the other, the former lying to the 

 north of the line, and the latter to the south. 



Between this boundary line and the Hawaian Islands, an 

 area nearly two thousand miles wide and six thousand long, 

 there are two hundred and four islands, of which ojily three are 

 high, exclusive of the eight Marquesas, and the Ladrones, with 

 Yap, Hunter's, and Los Matelotas in the line of the Ladrones 

 and Pelews. These three are Kusaie or Ualan, Ponape, and 

 Truk or Hogoleu, all in the Caroline Archipelago. South of 

 the same line, within three degrees of it, there is an occasional 

 atoll ; but beyond this distance there are none, excepting the 

 few in the Friendly Group and one or two in the Feejees. 



If each coral island scattered over this wide area indicates 

 the subsidence of an island, we may believe that the subsidence 

 was general throughout the area. Moreover, each atoll, could 

 we measure the thickness of the coral constituting it, would 

 inform us nearly how much subsidence took place where it 

 stands ; for they are actually so many registers placed over the 

 ocean, marking out, not only the sight of a buried island, but 

 also the depth at which it lies covered. We have not the 

 means of applying the evidence ; but there are facts at hand 

 which may give at least comparative results. 



a. We observe, T^r J-/, that the barrier reefs are, in general, 

 evidence of less subsidence than atoll reefs (p. 229). Conse- 

 quently, the great preponderance of the former just below the 

 southern boundary line of the coral island area, and farther 

 south the entire absence of atolls, while atolls prevail so 



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