80 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Calcium Magnesium Insoluble 
Height. Carbonate. ~ Carbonate. Residue. 
268’ 92.1 6.0 1.90 
251’ 94.4 4.3 ‘2.31 
248” 93.3 4.6 2.09 
Reef 95.3 3.6 1.06 
Microscopical. 268'.— A foraminiferal consolidated “mud,” in which 
Amphistegina is common. Insoluble material can be recognized in the 
section. 
251! A cavernous, crystalline rock, containing Gypsina, Carpenteria, 
and rotaline forms of Foraminifera. 
Reef. — A very crumbling rock, made up of fragments of Lithotham- 
nion, Carpenteria, and Amphistegina in a matrix consisting partly of 
“mud,” but mainly of crystalline calcite. 
Be Niue. 
Niue or Savage Island is a small mass entirely composed of raised 
coral limestone, situated in latitude 19° 10’ S., longitude 169° 47’ W., 
about 350 miles east of the Tonga or Friendly Islands. Besides the 
living reef there are three well-marked raised reefs or terraces at 80, 
120, and 200 feet respectively. The highest point of the island is a 
little over 200 feet, and there is a well-marked central depression or 
lagoon. Iam indebted to Professor David for a description and sketch 
of the structure of the island. At one part a natural ravine occurs, 
cutting through the first raised reef into a mass of coral rubble, dipping 
at 40° and forming the basis on which the second raised reef rests. 
Professor David, besides collecting specimens from the first, second, and 
third raised reefs, obtained specimens at intervals of five or six feet up 
to 70 feet from the ravine of rubble rock. . 
Chemical. — All the rocks are limestones, with a small quantity of 
magnesium carbonate, varying in amount from 3 to 8.8 per cent. 
Gravimetric analysis of a specimen of rubble rock at 53 feet shows that 
nearly 13 per cent of soluble organic matter is present, and since all the 
rocks are comparatively unaltered, it is probable that some organic 
matter is present in all the specimens. Since the magnesium carbonate 
is estimated by difference, this will have the effect of making the results 
for that compound slightly too high. Insoluble inorganic matter is 
present only in minute quantities, and the same remark holds good of 
the amount of calcium phosphate present in the rocks. 
Microscopical. 80'. First Terrace.— A transverse section of a large 
compound reef-forming coral (Figure 1.). The coral is very fresh, show- 
