26 BULLETIX: MUSEUM OF COMPAKATIYE ZOOLOGY. 



the rear of the beach at Rukua on the west side of ^Ibengha. Similar 

 volcanic breccia bluffs are characteristic of many points in Fiji. 



In aditiou to the main island there are tliree other islands. Moturiki 

 and Stuart, which are small satellites of Mbengha, and Yanutha, a lai-ger 

 island near the western edge of the lagoon. Tliese islands have the 

 same geological structure as that of Mbengha. (Plate 8.) 



Mbengha is on the eastern point of the lagoon, separated fi-om the 

 inner edge of the outer reef by a channel varying in width from a half to 

 one and a quarter miles, wath 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 tlu-ee quarters of a mile in Avidth, 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 lagooa 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 Pieefs, those 

 upon which the low sandy Storm Island is placed, and the Nanuku Eeef. 

 There are several passages available for vessels on that side of the lagoon. 

 The iJ^anuku, 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 Eeef, 

 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 

 Passacre the Yanutha Pieefs 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 Ptocks, which form the western 

 spit of the wide opening on the northern side of the lagoon. As will be 

 seen from the cliart, the bottom of the ^Mbengha liagoon is most irregular ; 

 it is very uneven, varj'ing 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 ]\Ibengha when it ex- 

 tended over the gi-eater part of the area now enclosed by the outer reef. 



