166 J.D. Dana on Changes of Level in the Pacific Ocean. 
elevation. Yet various parts of the ocean bear evidence of chan- 
ges confined to particular islands or groups of islands. While 
the former exemplify one of the grander events in the earth’s his- 
tory, in which a large segment of the globe was concerned, the 
latter exhibit its minor changes over limited areas. The instan- 
ces of these changes are so numerous and so widely scattered, 
that they convince us of acessation in the previous general sub- 
sidence. 
The most convenient mode of reviewing the subject is to state 
in order, the facts relating to each group. 
a. Paumotu Archipelago.—T he islands of this archipelago ap- 
pear in general to have that height which the ocean may give to 
the materials. Nothing was detected which satisfied us of any 
general elevation in progress through the archipelago. 
large extent of wooded land shows only that the islands have 
been long at their present level: and on this point our own, ob- 
servations confirm those of Mr. Darwin. ‘There are examples 
elevation in particular islands however, some of which are of un- 
usual interest. The instances examined hy the Expedition, were 
Honden (or Henuake), Dean’s Island (or Nairsa), Aurora (or Me 
tia), and Clermont Tonnerre. Beside these, Elizabeth Island has 
been described by Beechey, and the same author mentions cel- 
tain facts relating to Ducie’s Island and Osnaburgh, which afford 
some suspicions of a rise. : 
Honden or. Dog Island.—This island is wooded on its differ 
ent sides, and has a shallow lagoon. The beach is eight feet 
high tide, there were numerous shells of ‘Tridacna lying 
ties in the coral rock, precisely as they occur alive on te shore 
reef. As these Tridacnas evidently lived where the shells re 
main, and do not occur alive more than six. or eight inches, of 2 
foot at the most, above low tide, they prove, in connection wi 
the other facts, an elevation of twenty inches or two feet. F 
lairsa or Dean’s Island.—The south side of Dean’s ee 
the largest of the Paumotus, was coasted along by the Peacoe a 
and from the vessel we observed that the rim of land consis! ; 
for miles of an even wall of coral rock, apparently six or eight feet 
above high tide. This wall was broken into rude columms, OF 4 
cavated with arches and caverns; in some places the sea a of 
ried it away from fifty to one hundred rods and then there follow’ 
again a line of columns and walls, with occasional ren 
fore. The reef, formerly lying at the level of low tide, had 
raised above the sea, and subsequently had undergone deg 
tion from the waves. The standing columns had some ag A 
blance in certain parts to the masses seen and there on © 
