328 CORALS AND CORAL ISLANDS. 



It is worthy of special note, that this axial line, or line 

 of greatest depression, coincides in direction, with the mean 

 trend of the great ranges of islands, it having the course N. 

 52° W. ; and it also corresponds approximately with the axial 

 line of the Pacific ocean. 



The southern boundary line of the coral area, as we have 

 laid it down, lies within the area of subsidence, although near 

 its limits. This area has been prolonged southeastward in 

 some places beyond the boundary line. One of the regions of 

 this prolongation lies between the Samoan or Navigator 

 Group and the Feejees and Tonga Group ; another is east of 

 Samoa, along by the Hervey Group. Each of these extensions 

 trends parallel with the groups of islands. It would seem, 

 therefore, that the Society and Samoan Islands were regions 

 of less change of level than the deep seas either side of them; 

 that, therefore, instead of a uniform subsidence over the 

 subsiding area, shading off toward the borders, there were 

 troughs of greater subsidence, whose courses were parallel to 

 the ranges of islands ; that, in other words, there were in 

 the ocean's bottom, a few broad synclinal and anticlinal 

 flexures, having a common direction nearly parallel to the 

 axial line of the Pacific. The Marquesas and Fanning Groups 

 lie in a common line, and thus may mark the course of a 

 great central anticlinal in the oceanic basin. 



The Hawaian range has experienced its greatest subsidence 

 to the northwest, where the islands are all atolls, and show, some 

 evidences of recent sinking ; and this northwestern extremity 

 of the range is nearer to the axis of the area of subsidence, 

 above laid down, than is the southwestern. 



What is the extent of the subsidence indicated by the coral 

 reefs and islands of the Pacific % It is very evident that the 

 sinking of the Society, Samoan, and Hawaian Islands has 



