SKEATS : CHEMICAL COMPOSITION OF LIMESTONES. CE 
Microscopical. 1000’. — A fine-grained cavernous dolomite, whose 
cavities have been filled subsequently with clear secondary calcite, 
reducing the proportion of magnesium carbonate to 25.5 per cent. The 
organisms present are Lithothamnion, and possibly Polytrema, while 
meandrine strings of dolomite crystals, filled in with secondary calcite, 
suggest the former presence of corals. 
650’. A very porcellanous-looking fine-grained dolomite, whose cavi- 
ties and cracks are filled with secondary calcite. No organisms are 
recognizable. 
500’. A fine-grained silty dolomite, whose organic contents, very 
much altered, consist of decomposed Lithothamnion and casts of Orbito- 
lites. Cavities in the rock are lined with clearer crystals of dolomite. 
Namuxa.— This island is 4} miles long, and consists of a narrow 
undulating ridge, rising in places to a height of 240 feet.! 
It is formed wholly of elevated limestone, and is situated in latitude 
18° 50’ S., longitude 178° 35’ W. It forms one of the most southerly 
islands of the Eastern or Lau group of the Fiji Archipelago. 
Chemical. — Only three limestones were available for analysis, of 
which two were found to be dolomitic. The uppermost specimen, from 
a height of 162 feet, is a limestone containing only 2.5 per cent of 
magnesium carbonate, but has .78 per cent of insoluble residue, a high 
value for a coral limestone unassociated with rocks of other than coral 
origin. Ata height of 75 feet the magnesium carbonate has increased 
to 17.7 per cent, while no less than 34.5 per cent is found in the lowest 
rock from a height of 30 feet. 
Calcium | Magnesium | Insoluble NAMUKA. 
Height. | carbonate. | Carbonate. | Residue. 
162’ 96.7 2.5 78 
OD 
Z 
15 82.3 V7 — Z 
30’ 65.5 34.5 == | % om 
Microscopical. 162'.— A fine-grained consolidated ‘“ mud,” formerly 
full of organic fragments, a few of which remain (Lithothamnion), but 
nearly all have been replaced by calcite pseudomorphs. The rock is much 
cracked, the sides of the cracks being lined first with an iron staining 
and then completely filled from solution by crystals of calcite, projecting 
1 Bull. Mus. Comp. Zoél., 1899, Vol. XXXIIL., p. 57. 
