26 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the rear of the beach at Rukua on the west side of Mbengha. Similar 
volcanic breccia bluffs are characteristic of many points in Fiji. 
In adition to the main island there are three other islands. Moturiki 
and Stuart, which are small satellites of Mbengha, and Yanutha, a larger 
island near the western edge of the lagoon. These islands have the 
same geological structure as that of Mbengha. (Plate 8.) 
Mbengha is on the eastern point of the lagoon, separated from the 
inner edge of the outer reef by a channel varying in width from a half to 
one and a quarter miles, with a greatest depth of twenty-three fathoms 
closer to the island than to the reef. The channel between Yanutha 
and the outer reef is about three quarters of a mile in width, with a 
depth of from eleven to thirteen fathoms. There are in addition a 
number of patches of coral rising from a depth of from ten to twelve 
fathoms, irregularly scattered over the western part of the lagoon and 
along the inner edge of the outer reef. 
Mbengha and Yanutha Islands are enclosed within a long reef over 
thirty miles in length, forming an irregularly shaped pentagonal lagoon 
with rounded angles. The northern side is open, forming a passage fully 
five miles wide, and studded with patches. This part of the lagoon slopes 
very gradually from 17 fathoms to 130 or 140 fathoms in the centre 
of the Mbengha Passage, separating Mbengha from the island of Viti 
Levu. 
The northeastern face of the lagoon is flanked by the Pratt Reefs, those 
upon which the low sandy Storm Island is placed, and the Nanuku Reef. 
There are several passages available for vessels on that side of the lagoon. 
The Nanuku, Sulphur, and Cutter Passages with a depth of from nine 
to thirteen fathoms. The southern and southwestern sides of the lagoon 
are flanked by a long unbroken coral reef, the Mbengha Barrier Reef, 
varying in width from half a mile to over a mile and a quarter, extending 
from Cutter to Frigate Passage. There is a small sand key about the 
middle of the Mbengha Reef on its inner edge. To the north of Frigate 
Passage the Yanutha Reefs form the northwestern side of the Mbengha 
Lagoon. They are separated by broad channels ending in the reef of Bird 
Island and a long line of patches, the Nisithi Rocks, which form the western 
spit of the wide opening on the northern side of the lagoon. As will be 
seen from the chart, the bottom of the Mbengha Lagoon is most irregular ; 
it is very uneven, varying greatly in depth, and full of heads and patches 
overgrown with corals. The rocks and heads and patches are fragments 
of volcanic rock, the remnants of the island of Mbengha when it ex- 
tended over the greater part of the area now enclosed by the outer reef, 
ee 
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