J.D. Dana on Changes of Level in the Pacific Ocean. 163 
We have thus fo.owed around 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 Pitcairns to 
Bird in the Hawaiian Group appears to have a corresponding po- 
sition on the northeast 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 Pitcairns towards 
Japan, actually passes through the region of greatest subsidence, 
as We have before determined it, and may be considered the arial 
line or line of greatest depression for the great area of subsidence. 
It is worthy of special note, that this avial line or line of 
reatest depression coincides in direction with the mean trend of 
the great ranges of islands, it having the course N. 529° 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 farther than elsewhere. One of these regions lies be- 
tween 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 8toups of islands; and with the part of the line east of Ta- 
hit. 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 
lands has been small compared with that required to submerge 
test. One, two, or five hundred feet could not have buried 
the sea; and can we believe it possible that throughout this large 
“tea, when the two hundred islands now sunk were above the 
Waves, there were none equal in altitude to the mean of these 
heights? "That all should have been within nine thousand feet 
in elevation, is by no means. probable. However moderate our 
*stimate, there must still be allowed a sinking of several thou- 
Sand feet: and however much we increase it within probable 
bounds, we shall not arrive at a more surprising change of level. 
* our continents show that they have undergone. 
Between the New Hebrides and Australia the reefs and islands 
mark out another area of depression, which may have been simul- 
Neously in progress. The long reef of one hundred and fifty 
Tules from the north cape of New Caledonia and the wide barrier 
