330 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



THE CAROLINE ISLANDS. 



Plates 18-2, Jigs. 3, 4; 183-193, 235, 229-232; 233, fiys. 1-3. 



* 



We visited among the Carolines the islands and atolls of Kusaie, Pingelap, 

 Ponapi, Andema, Losap, Nama, the Royalist group, Truk, and Namonuito, 

 obtaining thus an excellent survey of the high volcanic islands of the group 

 from our examination of Kusaie, Ponapi, and of Truk, while the others 

 represent the structure of the low atolls ; some of them have probably a 

 volcanic basis, and others a tertiary limestone foundation, but neither were 

 observed at any of the low islands we visited. 



Of the eastern Carolines, Kusaie and Ponapi are volcanic islands, and 

 of the western, Yap and the Pelew group are also volcanic. The reefs of 

 the Pelew group have been well described by Professor Semper.^ 



The barrier reefs of the volcanic islands of the Carolines are similar in 

 character to those of the Society Islands, though some features, such as the 

 great width of the platforms of submarine erosion of Truk, Ponapi, and of 

 Kusaie, and the development of a border of mangrove islands at the base 

 of the volcanic islands, are not found in the Society Islands. 



The Truk Archipelago is perhaps the most interesting of the island 

 groups of the Carolines ; it is the only group of volcanic islands surrounded 

 by an encircling reef I have thus far seen in the Pacific which at first 

 glance seems to lend any support to the theory of the formation by sub- 

 sidence of such island groups as Truk. I can well imagine that an investi- 

 gator, seeing for the first time coral reefs in this group, would describe the 

 islands as the summits, nearly denuded, of a great island that had grad- 

 ually sunk. But a closer examination readily shows, I think, that Truk is 

 not an exception to the general rule thus far obtaining in all the island 

 groups of the Pacific we visited during this trip ; that we must look to 

 submarine erosion and to a multitude of local mechanical causes for our 

 explanation of the formation of atolls, of barrier and encircling reefs, and 



' Die Naturlichen Existenzbedingungen d. Thiere, v. Karl Semper, Leipzig, 1880, I!<). TI., p. 39. 



