STRUCTURE OF CORAL ISLANDS. 61 
are firmly imbedded in it below, and so cemented to it as to appear 
to be actually a part of the platform rock. Sketches of some of these 
masses are here given. 
Fig. 2. 
Figure 1 represents a mass on the island of Waterland, (one of the 
Paumotus,) six feet high, and about five in diameter; it was solid with 
the reef rock below, as though a part of it, and about two feet above 
its base, it had been so nearly worn off by the waters as to have 
become irregularly top-shape. Figure 2 is another mass, similarly 
attached to the reef at base, observed on Kawehe, (Vincennes Island.) 
It was six feet high above low water level, and seven feet in its 
longest diameter. Below, it had been worn like the one just de- 
scribed, though to a less extent. Another similar mass was eight feet 
high. Figure 3 represents a block six feet high and ten feet in its 
longest diameter, seen on Waterland ; 
it was unattached below, and lay with 
one end raised on a smaller block. On 
Aratica, (Carlshoff,) the same were ob- 
served. One loose mass like the last 
was eight feet high and fifteen feet in 
diameter, and contained at least a 
thousand cubic feet. Raraka also af- 
forded examples of these attached and unattached blocks, some stand- 
ing with their tops six feet above high water mark. 
These masses are similar in character to others met with among 
the fields of blocks just described, and only differ in having been left 
on the platform instead of being transported over it. Some of them 
are near the margin of the reef, while others are quite at its inner 
limit. The third mass figured above was a solid conglomerate, con- 
sisting of large fragments of Astreas and Madrepores, and contained 
some imbedded shells, among which an Ostrea and a Cyprea were 
noticed. This is their general character. The other two were 
parts of large individual corals (Porites); but there was evidence in 
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