54 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Vatu Vara or Hat Island (Plate 19) is one mile and a quarter in 
diameter. Its summit is flat, and falls off on all sides in steep cliffs. 
It attains an altitude of 1,050 feet. The cliffs consist of elevated lime- 
stone standing out conspicuously through the dark foliage which covers 
the island from base to summit. Up to the very summit of the island 
the exposed rocks are seen to consist of limestone. The island is 
surrounded by a fringing reef nearly a mile in width on the west coast. 
On the east and north sides the sea breaks against the nearly vertical 
limestone cliffs. They are deeply undercut. On the northwest side two 
separate masses of limestone stand out midway between the base of the 
cliffs and the outer edge of the reef. An incipient lagoon, open to the 
north, is forming along a part of the west coast of the island. 
Yathata and Kaimbo. 
Plate 19. 
The islands of Yathata and Kaimbo (Plate 19), which rise respectively 
to the height of 840 and 150 feet, are composed of elevated limestone 
rock. A fringing reef encloses them both. It attains a width of over 
half a mile where it connects the islands, and is nearly a mile wide 
off the north of Yathata. Off that shore a number of small islets and 
heads stand out between the island and the outer edge of the reef. Else- 
where the fringing reef is narrow. Between the islands in the middle of 
the fringing reef stands out the islet of Nuku Levn, 90 feet in height, 
and a few heads. There appears to have been a secondary elevation on 
the south side of Kaimbo, where the undercut ledge has been raised about 
twenty feet above high water mark. 
Iam informed by Captain R. Cocks that Katavanga is composed of 
elevated limestones. 
Aiwa. 
Plates 21, 22°, Figs. 13-15. 
Aiwa consists of two small elongated islands, the western one of which 
is not quite a mile in length (Plate 21). Both are composed of elevated 
limestone, pitted and honeycombed, forming low vertical bluffs along 
their southern faces. The highest points of the islands are respectively 
210 and 200 feet. They are connected by a coral reef awash at low 
tide. The islands are in the middle of the southern face of the outer 
reef flat, which encloses an elongate narrow triangular lagoon nine miles 
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