246 James 1). Dana, Esq.. on 



and the Feejees, are near the northern limits of the area, 

 pointed out. Twenty-five miles to the north of Tahiti, within 

 sight from its peaks, lies the coral island Tetuaroa, a register 

 of subsidence. Tahiti itself, by its barrier reefs, gives evi- 

 dence of the same kind of change ; amounting, however, as we 

 have estimated, to a depression of but two hundred and fifty 

 or three hundred feet. The north-western islands of the group 

 lie more within the coral area, and correspondingly, they have 

 wider reefs and channels, and deep bays, indicating a greater 

 amount of subsidence. 



Samoa. — The island of Upolu has extensive reefs, which 

 in many parts are three-fourths of a mile wide, but no inner 

 channel. We have estimated the subsidence at one or two 

 hundred feet. The volcanic land west of Apia declines with 

 an unbroken gradual slope of one to three degrees beneath the 

 sea. The absence of a low cliff is probable evidence of a de- 

 pression, as has been elsewhere shewn. The island of Tutuila 

 has abrupt shores, deep bays, and little coral. It appears 

 probable, therefore, that it has experienced a greater subsi- 

 dence than Upolu. Yet the central part of Upolu has very 

 similar bays on the north, which would afford apparently the 

 same evidence ; and it is quite possible that the facts indicate 

 a sinking which either preceded the ejections that now cover 

 the eastern and western extremities of Upolu, or accompanied 

 this change of level. Sovnii has small reefs, from which we 

 gather no certain facts bearing on this subject. East of 

 Tutuila is the coral island, Rose. It may be, therefore, that 

 the greatest subsidence in the group was at its eastern ex- 

 tremity. 



Feejee Islands. — We have already remarked upon this 

 group. A large amount of subsidence is indicated by the reefs 

 in every portion of the group, but it was greatest beyond 

 doubt in the north-eastern part. 



Ladrones. — The Ladrones appear to have undergone their 

 greatest subsidence at the north extremity of the range, the 

 part nearest the centre of the coral area ; for although the 

 fires at the north have continued longest to burn, the islands 

 are the smallest of the group, the whole having disappeared 

 except the summits, which still eject cinders. The southern 





