AGASSIZ: FIJI ISLANDS AND CORAL EEEFS. 25 



is not more than 300 feet high, and is joined to the rest of the island by 

 a comparatively low neck. The depth of the Wakaya Lagoon is greater 

 on the average than that of Makongai ; it reaches a maximum depth of 

 thirty-six fathoms, with a general avei'age depth of over twenty. There 

 are comparatively few patches in the lagoon. The bottom consists of 

 coralline sand and shells. We entered through the northern passage 

 and crossed the lagoon, and on our way out examined the reef patches 

 forming the boat passages to the south of it. On the shore of the bay, 

 near the boat passage, we found a good deal of pumice. We found 

 traces of elevation on the neck connecting the point on which Lieutenant 

 Langdale's house is built. 



We could not examine the corals on the weather face of the weather 

 reef, but on the inner side and on the lee reef we found corals flourishing 

 most luxuriously, mainly Madrepores, Pocillopores, Astreans, Mieandrinas, 

 Fungise, and a few Gorgonians. They form a belt mainly between two 

 and seven or eight fathoms, beyond which there seem to be only coral 

 sand and corallines both on the inner and outer faces of the lee reef. 

 With the disappearance of Wakaya through denudation and erosion, we 

 should have an atoll with a substratum of volcanic rocks which very 

 likely might be covered to a limited depth with islets of coral sand blown 

 up from the encircling I'eef, — an atoll in no way to be distinguished by 

 outward appearances from the theoretical atoll built up by corals and 

 by subsidence. 



Mbengha. 



Plates 8, 11*, Fig. 6, and Plates 46-49. 



Mbengha Island is irregularly shaped, with three deep indentations, 

 one on the western side, the others on the eastern, nearly cut off the 

 high point forming the eastern side of Malumu Bay from the main body 

 of the island. (Plate 48.) The principal ridge, running nearly north 

 and sontli across the central part of the island, rises abruptly from the 

 south to a height of over a thousand feet, and has several peaks at- 

 taining heights varying between 1,200 and over 1,400 feet. The secon- 

 dary ridge to the east of Malumu Bay is somewhat less than a thousand 

 feet. On the east face to the south of Solianga are exposed some fine 

 bluffs consisting of volcanic conglomerate breccia. (Plate 46.) They 

 are perhaps as good examples as we have seen of the great erosion and 

 denudation which have taken place in tliis part of the Fiji group. 



A moi-e detailed view of the appearance of the volcanic rocks of 

 Mbengha is given in Plate 47, an eroded shore bluff immediately in 



