156 . Letter X. 
rising of the group confirmed as far as these islands are con- 
cerned. 
We come now to the third class of formations exhibited by 
the islands of the group,—the volcanic. Nearly all the islands 
belong to this class, and are evidently of the same formation, 
Aniwa being the only purely coral island in the group. 
A 
Ly ae 
//, a 
These volcanic islands are surrounded by coral reefs. The 
reefs, however, are seldom any distance from the shore—in 
most cases they merely run out from the beach fifty or a hundred 
yards, as a flat rocky platform. Sometimes they are not visible 
at all. It is very evident to any observer that the coral reefs 
have been formed first, and that the volcanic matter has broken 
violently up and flowed over it to a great extent—in some cases 
burying it altogether. In the above section, a represents the 
water-line, c the original foundation upon which the coral reef D 
has been built. Then through c a violent eruption, or many erup- 
tions, have taken place; the matter B being thrown up, and 
flowing down, has approached closely to the edge of the reef 
on one side, and has buried it altogether on the other. On 
various parts of Aneityum and Tana, there may be seen quite 
distinctly, volcanic matter lying on the top of the coral bed, 
twisted and liquid-like, appearing as if it had just run down the 
mountain side a day or two ago. 
The presence of three active volcanoes on the group, 
and the traces of many extinct ones, show that there has been 
