92 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



the contrary, many of the heads lying off the central parts of the east 

 coast of Yanua ]\Ibalavu are undoubtedly of volcanic origin, aud are 

 merely covered with a thin veneer of growing corals. Some of the small 

 volcanic rocks and islets oflF the east central part of the east coast of 

 Vanua Mbalavu are deeply undercut and eroded into mushroom-shape. 

 By far the finest example of marine erosion of volcanic rocks is seen on 

 Plate 62, which represents an eroded shore line with mushroom-shaped 

 rocks oflF the shore, indicating a slight recent elevation. Plate 62 is 

 taken from a photograph given us by Mr. E. G. Jones, and taken in Lau ; 

 unfortunately I am unable to state the exact locality. The islets of Yana 

 Yanu forming the harbor of Lomaloma consist of a yellow volcanic mud 

 full of rounded pebbles, and some of the spits of the east coast of Vanua 

 Mbalavu are composed of bedded volcanic mud (soapstone) similar to 

 that found at Suva and its vicinity. The condition of the islands and 

 islets and rocks, both of those composed of elevated coral reefs and of 

 volcanic rock, clearly indicates the great denudation and erosion which 





VOLCANIC HILLS BACK OF LOMALOMA. 



have taken place, to leave only such fragmentary remains of the land 

 •which must have once occupied the area of the lagoon. It is possible 

 that the age of the elevated limestone found at so many points in Fiji 

 may be comparatively great, and that the ancient limestone forming the 

 substructure of the reef of the present day may have been deposited in 

 late tertiary times, immediately before the present epoch. ^ 



As has been observed, the dip of the lagoon is to the eastward, or 

 rather, in a general way, towai'd the slopes of the deep tongue of water 

 forming the American Passage (Plate 19). This would seem to be the 

 natural result of the elevation of the great flat of tertiary limestones 



^ See the report of Dr. Dall, referred to in another part of tliis Bulletin. 



