90 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



eastern face is the island of Thikombia i lau. On the southern face are 

 ^sgillangilhih, then follows the principal island of the group, Vanua 

 Mbalavu, the western shore line of which is hollowed out by a deep 

 indentation forming the western lagoon. Off its southern extremity is 

 situated Malatta, next Susui, and finally the volcanic island of Mania. 

 Vanua Mbalavu is fourteen miles long, forming a sharp angle at its 

 highest and broadest point, where the island is nearly three miles wide 

 and reaches a height of 930 feet. 



The centx'al and highest part of Vantia Mbalavu is volcanic, but 

 towai'ds the northeast and the south the volcanic rocks have lifted up 

 an ancient elevated reef which extends from opposite Avea westward. 

 The volcanic rocks (Plate 72) dip very rapidly to the north, so that 

 less than half way from Koro Mbasanga to Blackswan Point the bluffs 

 are elevated limestones. These bluffs are deeply undercut, their surface 

 pitted and thoroughly honeycombed, and full of potholes. The extent 



ISLET OFF NGILLANGILLAII. 



of the wearing of this c<3ral rock is well shown by the deep bays and 

 numberless indentations which characterize the northern coast of Yanua 

 ]\Ibalavu. When we come to the vicinity of Blackswan Point, the 

 denudation and erosion of the elevated limestone has reached its 

 maximum. Off the end of the large island lies the little island of 

 Ngillangillah (Plate 73), which is entirely composed of elevated lime- 

 stone, which here attains a thickness of 510 feet. Beyond Ngillangillah 

 there are numerous negro-heads and coral patches, some of them 

 being of considerable size; they are of ancient coral rock. The coral 

 heads and negro-heads extend along the whole length of the outer reef 



