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AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 43 
fathoms and an average depth of over twenty, except to the east of 
Lauthala, where the outer reef joins the fringing reef which skirts 
Lauthala and Ngamia. There are a number of coral patches all through 
the lagoon, but they are most abundant along the inner edge of the 
southern line of the outer reef. 
Ngamia and Lauthala are both volcanic ; the former rises to a height 
of 1,000 feet. Both are indented with deep bays. 
Along the shore of Thurston Point we found a conglomerate in course 
of formation, composed of rounded pebbles of lava cemented together 
with broken fragments of coral. 
ELEVATED ISLANDS COMPOSED OF CORALLIFEROUS 
LIMESTONES. 
Negele Levu. 
Plates 17, 17°, Figs. 5-12, and Plates 95-99. 
Negele Levu is an elongated pear-shaped atoll, somewhat constricted 
at a few points (Plate 17). Its length is fourteen miles and its greatest 
breadth seven. The lagoon is enclosed by a continuous outer reef, 
varying in width from a quarter of a mile to over a mile. The western 
face of the outer reef is broken into patches leaving excellent deep 
passages for ships. The depth in the lagoon is quite uniform, the bot- 
tom being very level, varying in depth from about five to nine fathoms 
at the eastern extremity, and sloping very gradually to fifteen or sixteen 
at the western entrance. The bottom is composed of coralline alge, 
broken shells, and coral sand, as’ well as masses of dead corals derived 
from the disintegration of the former elevated coralliferous limestone 
which once covered the whole area of the lagoon. The lagoon is free 
from coral patches except at the eastern end, which is studded with 
heads of old coral and patches of living coral. These heads also form 
a belt of considerable width along the inner side of the outer reef flats. 
The reef flats are made up of elevated coralliferous rock which has 
been planed off to the level of the sea, and scooped ont below it to 
form the lagoon. At the southern of the western entrances there is a 
small sand key, and at the northeast end there are three islands, Ngele 
Levu, Tai ni Mbeka (Plate 96), and Taulalia (Plate 95). The outer 
faces of these islands form the sea face of the outer reef, there being no 
outside reef flats. These islands are entirely composed of elevated 
