AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 21 



Ngau. 



Plates 13, 13, 11% Figs. 1-3. 



Ngau Island is about eleven miles long, by an average of nearly four 

 miles in width. It consists of volcanic rocks; a high ridge runs alouo- 

 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 pi'otected 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 baj^ of the lagoon is tilled 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 Xgau 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 soutliern 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 



