28o CORALS AND CORAL ISLANDS. 



(p. 127). A large amount of siihsidence is indicated by the 

 extensive reefs in every portion of the group, but it was 

 greatest beyond doubt in the north-eastern part. The sub- 

 sidence, where least, could hardly have been less than 2,000 

 to 3,000 feet. 



Ladrones, — The Ladrones appear to have undergone their 

 greatest subsidence at the northern 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 

 islands of the group have wide reefs, which show that they 

 participated to some extent in the subsidence; and this is 

 further indicated by the islands lying to the south-west, in the 

 line of the Ladrones. 



We have thus followed around the borders t'f the coral 

 area ; and, besides proving the reality of the limits, have as- 

 certained some facts with reference to a gradual diminution 

 of the subsidence toward, and beyond, these limits. A line 

 through tlie Hawaian Group would pass along the northern 

 boundary line of the area ; and taking the soutl:iern boundary 

 as given on page 273, the oblong area narrows eastward. An 

 axis nearly bisecting this space, drawn from the eastern Pau- 

 motus toward Japan, passes through the region of greatest 

 subsidence, as above determined, and may be considered the 

 line of greatest depression for the great area of subsidence. 



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

 greatest depression., coincides in direction with the mea7i 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 boundajy 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 south-eastward 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 



