80 EXPEDITION OF THE “ ALBATROSS,” 1899-1900. 
indicated by long lines of narrow islets thrown up on the reef platforms, 
exactly as they are in the Paumotus. These islands and islets are usually 
well wooded, and thus give a very peculiar aspect to the barrier reef. In 
the case of Bora-Bora, Maupiti, and Aitutaki, for instance, we have a central 
volcanic peak of considerable height surrounded by a wide lagoon, the sea 
edge of which is formed by a fringe of wooded islets and islands forming a 
more than half-closed ring around the central island, which, in Bora-Bora 
and Maupiti, rise in slopes and nearly vertical walls, the former to a height 
of nearly 2400 feet, the other to about 800 feet. 
The only island of the Cook Group which we examined was Aitutaki; 
as Atiu is composed of elevated limestone, and Rarotonga is volcanic, I 
hoped we might find that atoll to be in part volcanic and in part composed 
of elevated coralliferous limestone; we found it to.be volcanic, an island 
with the structure of Bora-Bora on a smaller scale. 
We anchored at Niue, an island composed of elevated coralliferous lime- 
stone showing three well-marked terraces, the lowest of not more than five 
to ten feet, and in many places disappearing completely, the limestone cliffs 
rising vertically from the sea well into the second or even the third. ter- 
races. The vertical faces of the cliffs are dotted with caverns and deeply 
indented by small cafions extending at right angles to the face of the 
shore or forming blunt headlands separating short reaches of coral-sand 
beaches. 
The second terrace varies in height from fifty to sixty feet, the third 
from ninety to 100 feet. The second terrace is deeply undercut, and in 
the higher vertical cliffs extending into the third terrace from the sea, the 
former positions of the terraces are usually indicated by lines of caverns. 
There are corals on the sea slopes of the first terrace, extending down to 
ten or twelve fathoms, growing much as they are found at Makatea. 
From Niue we went to the Tongas, which we found a most interesting 
group. The elevated Tertiary coralliferous limestones take here their great- 
est development, and are on a scale far beyond that of their development in 
the Lau Group of the Fijis, or the Paumotus. The first island of the Ton- 
gas we visited, Kua, is perhaps the most interesting of the islands composed 
of Tertiary elevated coralliferous limestone I have visited. From Dana’s 
| 
