180 CORAL-REEFS. 



transverse chain of mountains, surmounted by atolls, would 

 only be marked on the map by a transverse blue band. 

 But where a chain of atolls and barrier-reefs lies in an 

 elongated area, between spaces coloured red, which there- 

 fore have remained stationary or have been upraised, this 

 must have resulted either from the area of subsidence 

 having originally been elongated (owing to some tendency 

 in the earth's crust thus to subside), or from the subsiding 

 area having originally been of an irregular figure, or as 

 broad as long, and having since been narrowed by the 

 elevation of neighbouring districts. Thus the areas, which 

 subsided during the formation of the great north and south 

 lines of atolls in the Indian Ocean, — of the east and west 

 line of the Caroline atolls, — and of the north-west and 

 south-east line of the barrier-reefs of New Caledonia and 

 Louisiade, must have originally been elongated, or if not 

 so, they must have since been made elongated by elevations, 

 which we know to belong to a recent period. 



I infer from Mr. Hopkins' researches, 1 that for the forma- 

 tion of a long chain of mountains, with few lateral spurs, 

 an area elongated in the same direction with the chain, 

 must have been subjected to an elevatory movement. 

 Mountain-chains, however, when already formed, although 

 running in very different directions, it seems 2 may be 



1 "Researches in Physical Geology," Transact. Cambridge Phil. 

 Soc, vol, vi. part i. 



2 For instance in S. America from lat. 34°, for many degrees south- 

 ward there are upraised beds containing recent species of shells, on 

 both the Atlantic and Pacific side of the continent, and from the 

 gradual ascent of the land, although with very unequal slopes, on 

 both sides towards the Cordillera, I think it can hardly be doubted 

 that the entire width has been upraised in mass within the recent 

 period. In this case the two W.N.W. and E.S.E. mountain-lines, 

 namely the Sierra Ventana and the S. Tapalguen, and the great north 



