SUBSIDENCE IN PACIFIC CORAL REGIONS. 321 



There are two epochs of changes in elevation which may 

 be here distinguished and separately considered. 1. The sub- 

 sidence indicated by atolls and barrier reefs. 2. Elevations 

 during more recent periods. 



H SUBSIDENCE INDICATED BY ATOLLS AND BARRIER 



REEFS. 



Looking at atolls as covering buried islands, we obsereve, 

 that through the equatorial latitudes, such marks of subsidence 

 abound, from the Eastern Paumotu to the Western Carolines, 

 a distance of about six thousand geographical miles. In the 

 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 

 comprise seventy -five or eighty atolls. 



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

 most of the Paumotus, by the Gambier 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 only 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 occa- 



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