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AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 21 
Ngau. 
Plates 12, 13, 11°, Figs. 1-3. 
Negau Island is about eleven miles long, by an average of nearly four 
miles in width. It consists of volcanic rocks; a high ridge runs along 
the middle with spurs separated by deep valleys extending towards the 
east and west coast. One of these spurs forms a deep bay on the north- 
western coast. The peaks of the main ridge vary in height from 1,000 
to over 2,300 feet. Ngau is protected on the east and north by a 
broad fringing reef of a width of over three miles. At the northern 
extremity and on the east face there are a few reef boat harbors, cut out 
of the fringing reef which also extends along the whole western shore as 
a very narrow fringe. As will be seen from the chart (Plate 13), the 
small .reef harbors are without exception off the mouth of the moun- 
tain streams both on the north and east faces of the island; these in the 
rainy season bring down a large amount of mud and prevent the growth 
of corals at their mouth. From the southern end of the island extends 
in a northwesterly direction an outer barrier reef, varying in width from 
a quarter of a mile to three quarters of a mile. This reef is continuous 
being only broken in the middle by a narrow ship passage. The general 
depth of the lagoon is about twenty fathoms, with a greatest depth of 
twenty-nine. The western reef sweeps round the northern face of the 
lagoon, its eastern extension becomes broken into disconnected patches, 
and the greater part of the northeastern bay of the lagoon is filled with 
coral patches which connect it with the fringing reef of the north shore 
of the island. There are also numerous patches in the southern bight 
of the lagoon, and along the inner edge of the outer reef near the north- 
western elbow of the reef. As far as we examined the reef of Ngau the 
reef flat was covered with most extensive patches of thriving corals. 
There is a small island, Yathiwa, on the very edge of the reef forming 
the southern horn of Ngau. It holds to Ngau very much the same rela- 
tion which Kobu Island does to Nairai, but is nearer the outer edge of 
the reef, while Kobu is in the lagoon surrounded by comparatively deep 
water. 
Mambulitha Reef. 
To the south of Ngau we could see the breakers giving the outline of 
Mambulitha Reef (Plate 12), separated from Ngau by a channel having 
a depth of 750 fathoms. This reef is pentagonal in outline, about one 
mile and a quarter long, is awash, has no opening, and encloses a shallow 
