362 "ALBATROSS" TEOPICAL PACIFIC EXPEDITION. 



Pelew Islands rise to 2000 feet, a greater height than that of the islands 

 of the Truk lagoon. Within a radius of one hundred and fifty miles of 

 Truk are a number of low islands and atolls eroded to the very level of 

 the sea, such as Namonuito, the Hall, the Mortlock Islands (PI. 232), and 

 the numerous islands and islets lying between Namonuito and Wolea, 

 none of which rise far above the level of the sea. Of course there is 

 no proof that the base of the low atolls to the east and to the west of 

 Truk is composed of volcanic rocks ; it is only by analogy that we can 



Native Canoes, Mokn, Truk, Cau. .lines. 



venture to say that some of the low islands of the Carolines are underlaid 

 by a volcanic base. 



On the other hand, the existence of islands composed of elevated coral- 

 liferous limestone, such as Nama, of San Augustin in the Oraluk group,' 

 said to be 110 feet high, of Feys (PI. 233, fig. 2), as well as the presence 

 of elevated reefs of tertiary age in the .southern Pelew Islands,^ makes it 

 probable that some of the low coral atolls of the Carolines may rest upon a 

 foundation of tertiary limestones, as is the case in the Paumotus, the Fiji 

 and Tonga groups, and other isolated islands in the Pacific. 



1 A. Chart 982. 



■■' Semper, C. Die Palau Tnseln, pp. 17, 155, 277, 285; Zeits. f. Wiss. Zool., 18fi8, XITI., p. 555: 

 Die Natiirlieben E-xistenzlieilingungen d. Thiere, 1880, II., p. 39. A. Wichraan, Ziir Geolog. Keiintniss 

 'i. Palau Inseln, Jour. d. Mus. Godeffroy, Heft VIII., p. 123. 



