a 
AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 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 average 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, Mzeandrinas, 
Fungiz, 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 reef, — 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. 5, 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 south 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 this part of the Fiji group. 
A more detailed view of the appearance of the volcanic rocks of 
Mbengha is given in Plate 47, an eroded shore bluff immediately in 
