ON CHANGES OF LEVEL IN THE PACIFIC OCEAN. 121 



b. The subsidence producing an atoll, when continued, gradu- 

 ally reduces its size, until finally it becomes so small that the la- 

 goon is obliterated ; and consequently a prevalence of these small 

 islands is presumptive evidence of the greater subsidence. We 

 observe, in application of this principle, that the coral islands 

 about the equator, five or ten degrees south, between the Paumo- 

 tu.s and the Tarawan Islands, are the smallest of the ocean : sev- 

 eral of them are without lagoons, and some not a mile in diame- 

 ter. At the same time, in the Paumotus, and among the Tara- 

 wan and Marshall Islands, there are atolls twenty to fifty miles 

 in length, and rarely one less than three miles. It is probable, 

 therefore, that the subsidence indicated was greatest at some dis- 

 tance north of the boundary line, over the region of small equa- 

 torial islands, between the meridian of 150° W. and 180°. 



c. When after thus reducing the size of the atoll, the subsi- 

 dence continues its progress, or when it is too rapid for the grow- 

 ing reef, it finally sinks the coral island, which, therefore, disap- 

 pears from the ocean. Now it is a remarkable fact that while the 

 islands about the equator above alluded to indicate greater subsi- 

 dence than farther south, north of these islands, that is, between 

 them and the Hawaiian Group, there is a wide blank of ocean 

 without an island, which is near twenty degrees in breadth. 

 This area lies between the Hawaiian, the Fanning and the Mar- 

 shall islands, and stretches off between the first and last of these 

 groups, far to the northwest. 



Is it not then a legitimate conclusion that the subsidence which 

 was least to the south beyond the boundary line, and increased 

 northward, was still greater or more rapid over this open area ; 

 that the subsidence which reduced the size of the islands about 

 the equator to mere patches of reef, was farther continued, and 

 caused the total disappearance of islands that once existed over 

 this part of the ocean ? 



d. That the subsidence gradually diminished southwestwardly 

 from some point of greatest depression situated to the northward 

 and eastward, is apparent from the Feejee Group alone. Its 

 northeast portion, as the chart shows, consists of immense bar- 

 riers, with barely a single point of rock remaining of the sub- 

 merged land ; while in the west and southwest there are basaltic 

 islands of great magnitude. Again, along to the north side of 

 the Vanikoro Group, the Salomon Islands, and New Ireland, there 

 are coral atolls, though scarcely one to the south. 



In view of this combination of evidence, we cannot doubt that 

 the subsidence increased from the south to the northward or 

 northeastward, and was greatest between the Samoan and Ha- 

 waiian Islands near the centre of the area destitute of islands, 

 about longitude 170° to 175° W. and 8° to 10° N. 



16 



