156 Dr. J. D. Dana on the Origin of 



winian theory, that the subsidence increases much in amount 

 westward. The western end of the chain is about a degree 

 nearer the equator than the eastern. 



In the Samoan Islands, the largest island, Savaii, is the 

 westernmost; and from there the islands decrease in size east- 

 ward, and end in an atoll, Rose Island. The group is like Tahiti 

 in gradation as to increase of subsidence, but the direction is 

 the reverse ; and this fact points apparently to a much deeper 

 area between them *. Moreover, although such broad barrier- 

 reefs as those of Raiatea and Bolabola do not occur in the 

 Samoan group, bold shores do in Tutuila and Manua, and 

 indicate the participation of these islands in the subsidence, 

 notwithstanding their contracted reefs. Further, the reef of 

 Upolu is broad enough to be proof of little change in the 

 region of that island; and there was little, probably, at Savaii, 

 the larger island west of it. The evidence of increased sub- 

 sidence to the eastward is strong, and narrowness of reef is no 

 objection to it. 



At the Sandwich Islands the case is similar and yet dif- 

 ferent ; similar in the fact that the largest island of the chain, 

 Hawaii, makes one of its extremities, the eastern, and a series 

 of coral-islands the other — the whole length being 2000 miles; 

 but different in that no great reef exists about the shores of 

 either of the eastern islands to prove that the subsidence there 

 was small or none. The elevated reefs are only a local phe- 

 nomenon, and do not prove the absence of subsidence during 

 the era preceding the elevation. 



But we have other evidence of importance, derived from 

 soundings about the group by the ' Challenger ' in 1875 and the 

 'Tuscarora' in 1874, 1875. These soundings show that the 

 deep-sea area of 3000 to 4000 fathoms comes up quite closely 

 to the eastern end of the chain. It was found within 300 

 miles of north-eastern Hawaii and 250 of south-western, and 

 within 80 miles of north-eastern Oahu ; and a sounding but 

 125 fathoms less than 3000 was obtained by the ' Challenger ' 

 within 40 miles of eastern Hawaii (or half its diameter). To 

 the westward, along the north side of the chain, the deep-sea 

 area appears to be two or three times more distant, according 

 to the ' Challenger ' results ; the condition on the south side is 

 uncertain. It would seem from the great depth near Hawaii, 

 that the region of this great island, although it is now actively 

 volcanic and has little growing coral about it, had undergone 

 more subsidence than the coral-reef end of the chain, and 



* The distance between the remote extremities of these two groups is 

 nearly 2000 miles, and the interval between the nearer over 800 miles. 



