SOCIETY ISLANDS. 305 
which is a crystalline feldspathic rock, very similar to a grayish- 
white feldspathic rock that was observed passing into basalt in New 
Holland. | 
The most striking feature of the northwestern islands is the depth 
of the bays. I shall hereafter show that this fact is connected with a 
greater amount of subsidence than has been experienced farther south. 
The extent of the shore plains, and the large lakes in some places 
cut off from the sea, evince the accumulating force of the waves, act- 
ing along with the growth of coral reefs. ‘There are many places be- 
sides those mentioned, where embankments have been thus thrown up 
by the sea, inside of which are marshy areas. They also appear to 
indicate, more decidedly than anything observed on Tahiti, a rise of 
several feet since the preceding era of subsidence ceased. 
The great amphitheatre of Himeo appears to be analogous to that 
west of Orohena in Tahiti. Yet a more particular examination is re- 
quired before we can safely base upon it all the deductions which it 
seems to authorize. The descriptions carry us at once to the volcanic 
regions of the Canaries, and the walled amphitheatres there; but we 
forbear urging the comparison. 
We have little evidence with regard to the progression in the fires 
that once burned along the Tahitian range. Still the character of the 
rocks and the features of the surface lead us to the opinion that the 
fires were first extinct at the northwest end of the line, and last at the 
southeast. This corresponds with the course in the Sandwich Islands, 
and is the reverse of that in the Navigators. 
