114 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The stretch of strata of volcanic mud constituting the east shore of Viti 
Levu north of Mbau undoubtedly once extended farther east, connecting 
the main island with the islands of Moturiki and of Ovalau. This readily 
explains the changeable character of the barrier reef at different points 
along the coast of Viti Levu. Off Ovalau and Moturiki the substructure 
of the barrier reef is volcanic, and the negro-heads which crop out upon 
its surface at various points plainly indicate this. One of the most 
striking of these protrusions being a small mushroom-shaped volcanic 
rock on the barrier reef to the south of Moturiki, immediately west of 
Thangalai Island (Plate 7). This island and Leluvia, and one or two 
keys on the northern part of the great reef south of Moturiki, are small 
islets of coral sand thrown up on some of the shallower parts of the reef 
flats. The larger islands are thickly covered with cocoanuts and shrubs. 
On the southern part of the reef flats immediately north of the Tombe- 
rua Passage near the exterior edge is the island of Mumbualau. It is 
about thirty feet high, and is composed of elevated coralliferous limestone 
deeply undercut, pitted, and honeycombed, while the islands farther 
inland off Kamba Point consist of stratified voleanic mud. 
Another very striking fragment of elevated coralliferous limestone is 
that of Na Vunivatu (Plate 37), ‘on the reef flats to the south of Nasilai 
Mouth. The remnants of the elevated reef can be traced south of Tom- 
berua Passage on the Nasilai reef flats, and extend on both sides of the 
lighthouse. There are numerous heads of elevated limestone, fragments 
of former large stretches of the same material. Still farther south the 
elevated coralliferous limestone is seen to underlie the island of Nukulau 
(Plates 38-41) at the mouth of Lauthala Harbor (Plate 25), as well as 
the flats to the eastward and the island of Mokaluva with its flat (Plate 
38). The extensive mud flats forming the mouth of the Rewa River 
have to a great extent encroached upon the inner edge of the coral 
reef flats underlaid by the elevated coralliferous limestone which every- 
where crops to the surface to the south of Tomberua Passage. As far 
as the Nukulau mouth of the Rewa, the reefs are in reality fringing 
reefs growing upon flats of elevated coralliferous limestone, intersected 
by deep indentations forming reef harbors. The great extent of the flats 
skirting the shore of Viti Levu eastward from Suva Point shows the 
amount of denudation and erosion to which this part of the island has 
been subjected (Plates 24,25). From off Lauthala Bay (Plate 25) to 
Suva, the reefs are extensive barrier reef flats separated by passages 
leading into the channel running between the barrier and the shore 
(Plate 7). Some parts of the barrier flats are more than a mile wide, 
