172 J. D. Dana — Origin of Coral Beefs and Islands. 



possible to find direct proof of subsidence," recognizing the fact 

 that subsidence, unlike elevation, puts direct testimony out of 

 sight. But still it has left evidence which he perceived and 

 thought convincing: and this stands, whatever virtue there 

 may be in other explanations. 



Moreover, we have now direct testimony for subsidence, from 

 the facts brought forward (for another purpose) by Mr. Murray, 

 as is set forth beyond. 



III. The occurrence of cases of elevation in regions of atolls and 



barrier reefs. 



The fact that elevated reefs and other evidences of elevation 

 occur at the Pelews, a region of wide barrier reefs and atolls, 

 has been presented by Prof. Karl Semper,* after a study of 

 those islands, as an objection to the theory of subsidence ; for we 

 have thereby (in the words of the Address), " a cumbrous and 

 entirely hypothetical series of upward and downward move- 

 ments." Prof. Semper reports the existence of reefs raised 

 200 to 250 feet above the sea-level in the southern third of the 

 larger of the islands, while the other two thirds exhibit evi- 

 dence of but little, if any, elevation. 



a. Such facts are of the same general character with those of 

 other elevated reefs and atolls discussed in §§ 12, 13, 16 of 

 Part I, and the same explanation covers them. The Pelew 

 region is one of comparatively modern volcanic rocks and this 

 renders local displacements a probability. 



o. The occurrence of great numbers of large and small masses 

 of coral rock, in some places crowded together, upon the tuest- 

 ern or leeward reef of the several Pelew islands, and of none on 

 the eastern reef, is mentioned as evidence against subsidence 

 and in favor of some elevation : because, Professor Semper says, 

 the strongest wind-waves on the western side are too feeble to 

 break off and lift on the reef so large masses, some of them (as 

 his words imply rather than distinctly state) ten feet thick. 



But the difficulty does not exist in fact; for earthquakes 

 may have made the waves. The region just west of the Pelews 

 is one of the grandest areas of active volcanoes on the globe. 

 Tt embraces the Philippine Islands, Krakatoa and other volcanic 

 islands of the Sooloo sea, Celebes, etc. The agents that could 

 do the work were there in force. To the eastward, in contrast, 

 lie the harmless islands of the Caroline Archipelago, mostly 

 atolls, serving, perhaps, as a breakwater to the Pelews. 



The small elevation referred to is therefore not proved by the 



* First in 1868, Zeitschr. Wissensch. Zool., xiii, 558 ; additions in Die Philippinen 

 und ihre Bewohner, Wurzburg, 1869; and still later m his "Animal Life" pub- 

 lished in Appleton's International Scientific Series in 1881. 



