PEELIJIINARY KEPORT. 37 



cas tlie Ellice and Gilbert, seem to be somewhat higlier than the Paumotus, 

 but this difference is only apparent, and is due to the difference in the 

 height of the tides, which is very small in the Paumotus, while in the 

 former groups it may be five, and even six feet. 



From Jaluit 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 idea of the character 

 of the high volcanic islands of the group from our examinations of Kusaie 

 and of Ponapi, while the others represent the conditions of the low atolls, 

 having probably a volcanic basis, but this was not observed at any of 

 those we examined. 



The reefs of the volcanic islands of the Carolines are similar in char- 

 acter to those of the Society Islands, though there are some features, 

 such as the great width of the platforms of submarine erosion of Ponapi 

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

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



The Truk Archipelago was perhaps the most interesting of the island 

 groups of the Carolines, and it is the only group of volcanic islands sur- 

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

 which at first glance lends any support to the theory of the formation of 

 such island-groups as Truk by subsidence. This group was not visited 

 by either Darwin or Dana ; and I can well imagine that an investigator 

 seeing this group among the first coral reefs would readily describe the 

 islands as the summits, nearly denuded, of a great island which had 

 gradually sunk. But a closer examination will readily show, I think, 

 that this group is not an exception to the general rule thus far obtaining 

 in all the island groups of the Pacific I have 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 and of 

 barrier and encircling reefs, and that, on the contrary, subsidence has 

 played no part in bringing about existing conditions of the atolls of the 

 South and Central Pacific. 



Nowhere have we seen better exemplified than at Truk how important 

 a part is played by the existence of a submarine platform in the growth 



