Changes of Level in the Pacific Ocean. 247 



islands of the group have wide reefs, but they afford no good 

 evidence of any great extent of subsidence since the reefs 

 began to form. 



We have thus surveyed the borders of the coral area, and 

 besides proving the reality of the limits, have ascertained 

 some facts with reference to a gradual diminution of the subsi- 

 dence towards and beyond these limits. A line from Pitcairn's 

 to Bird in the Hawaiian Group appears to have a correspond- 

 ing position on the north-east with the southern boundary line 

 of the coral area ; the two include a large triangular area. An 

 axis nearly bisecting this triangular space, drawn from Pit- 

 cairn's toward Japan, actually passes through the region of 

 greatest subsidence, as we have before determined it, and may 

 be considered the axial line, or line of greatest depression 

 for the great area of subsidence. 



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. 



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

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

 its limits. 



There are places along this line where this area has been 

 prolonged further than elsewhere. One of these regions lies 

 between Samoa and Rotuma, and extends down to the Feejees 

 and Tonga Group ; another is east of Samoa, reaching towards 

 the Hervey Group. Each of these extensions trends parallel 

 with the groups of islands, and with the part of the line east of 

 Tahiti. It would seem, therefore, that the Society and Samoa 

 Islands were regions of less change of level than the deep 

 seas about them. 



What may be the extent of the coral subsidence ? — It is 

 very evident that the sinking of the Society, Samoan, and 

 Hawaiian Islands, has been small compared with that required 

 to submerge all the lands on which the Paumotus and the other 

 Pacific atolls rest. One, two, or five hundred feet could not 

 have buried all the many peaks of these islands. Even the 

 1500 feet of depression at the Gambier Group is shewn to be 

 at a distance from the axis of the subsiding area. The groups 

 of high islands above mentioned contain summits from 4000 to 



