SKEATS: CHEMICAL COMPOSITION OF LIMESTONES. 101 
West Waitt Breacu. — The rocks here form a low cliff between the 
heights of 250 and 380 feet. 
Chemical. — Three analyses show that magnesium carbonate is present 
in amounts varying from 2.1 to 5.7 per cent, while the fourth limestone 
from 300 feet contains 11.2 per cent of magnesium carbonate. 
Calcium Magnesium Insoluble 
Number. Height. Carbonate. Carbonate. Residue. 
303 375 95.5 4.5 
372 300’ 88.8 11.2 
305 280° 94.3 5.7 .04 
3871 250’ 97.9 ‘2.1 
Microscopical. No. 372. Figure I1I. — A fragmental limestone con- 
taining corals, gastropods, echinid spines, Orbitolites, Lithothamnion, and 
Halimeda. The coral has aragonite crystals in optical continuity with its 
own fibers, while scalenohedra incrust the Lithothamnion. All the or- 
ganisms are cemented with fibrous calcite radiating from each organism, 
and interfering with the deposit from an adjacent fragment, so as to pro- 
duce a polygonal effect in the rock section. 
- Souta Enp or East Coast. Chemical. — One analysis from a height 
of 400 feet yields 16.9 per cent of magnesium carbonate. 
Calcium Magnesium 
Number. Height. Carbonate. Carbonate. 
131 400° 83.1 16.9 
Microscopical. — A dolomitic limestone whose matrix consists largely 
of rhombohedral crystals with cavernous spaces. The organisms consist 
almost entirely of Polytrema miniaceum. 
III. Chemical Summary. 
In attempting to summarize the chemical results obtained from a study 
of limestones from fifteen raised coral islands, it is found that the facts 
group themselves most naturally round three points. These are : — (A) 
The distribution of magnesium carbonate in the limestones, (B) the 
amount of calcium phosphate they contain, and (C) the extent to 
which insoluble residue is associated with them. 
A. Chemical analysis shows that certain of the islands have been 
dolomitized from top to bottom. WNgillingillah and Vatu Vara belong 
to this class. Only one limestone from Yathata has been analyzed, and 
one from Kambara, but both are found to be highly dolomitic. Exami- 
nation of several islands fails to show any appreciable dolomitization. 
