SKEATS: CHEMICAL COMPOSITION OF LIMESTONES. 69 
frequently employed to express the appearance of the finest calcareous 
detrital material and is not intended to convey the idea of an argil- 
laceous sediment. In this part of the work I have endeavored to record 
the facts so far as I have been able to observe them, leaving any theo- 
retical bearing these may have to be dealt with at the conclusion of 
the paper. 
II. Chemical and Microscopical Results. 
1. Paciric OcEAN. 
A. The Fiji Group (Eastern or Lau Division). 
Manco. — Mango is an island subcircular in shape, and about 34 miles 
in diameter, situated in latitude 17° 25’ S. and longitude 179° 10’ W. 
Mr. E. C. Andrews’s published descriptions,! with maps and sections, give 
a good idea of the general structure of the island. It consists of an 
elevated ring of limestone, with bold cliffs often over 400 feet in height. 
Patches of recently raised reefs occur here and there on the lower slopes, 
while along the inland cliffs old reefs are met with at levels of 50 and 
250 feet, and traces of a terrace occur up to 200 feet in the cliffs on the 
northern and southern limits of the island. The ring of elevated lime- 
stone is now not continuous all round the island, but has been broken 
through at the north-western and south-eastern margins by very exten- 
sive andesitic flows proceeding from two volcanic centers, one in the 
south-east of the island, the other north-west of its center. The lime- 
stone is still further obscured over the central depression by the forma- 
tion of a considerable deposit of volcanic alluvium. On the north-east 
of the island there is a small lagoon, connected by a narrow channel with 
the sea. This depression probably represents a former means of com- 
munication between the outer sea and the central lagoon. The limestones 
which I have examined were collected by Mr. E. C. Andrews from.among 
the older unbedded limestones of the sea-cliffs at definite heights above 
high-water mark. They are all younger than the basal limestones which 
are exposed here and there. These basal limestones dip at 15°-20°, 
and are interbedded with “ soapstone.” 
Chemical. — Most of the rocks consist of highly dolomitic limestones ; 
but at a few points, notably, at 370, 310, and 298 feet, limestones occur 
with only 4.9, 9.7, and 10.7 per cent of magnesium carbonate respec- 
1 Bull. Mus. Comp. Zodl., 1900, Vol. XXXVIIL., pp. 17-20. 
