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



tion 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 subsi- 

 dence ; for we have thereby (in the words of the Address) 

 " a cumbrous and entirely hypothetical series of upward and 

 downward movements/' 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 evidence 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. 



b. The occurrence of great numbers of large and small 

 masses of coral-rock, in some places crowded together, upon 

 the western or leeward reef of the several Pelew Islands, and 

 of none on the eastern reef, is mentioned as evidence against 

 subsidence and in favour of some elevation; because, Professor 

 Semper says, the strongest wind-waves on the western side 

 are too feeble to break off and leave on the reef such 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. It embraces the Philippine Islands, Krakatoa and 

 other volcanic islands of the Sooloo sea, Celebes, &c. 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 evidence adduced ; and yet it may be a fact without 

 affecting the theory of Darwin, as I have fully illustrated f. 



It is important to have in mind that the coral-reef era 

 probably covered the whole of the Quaternary and perhaps 

 the Pliocene Tertiary also ; and hence the local elevations that 



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

 Philippinen und ihre Bewohner, Wiirzburg, 1869 ; and still later in his 

 6 Animal Life/ published in Appleton's International Scientific Series in 

 1881. 



t Mr. Semper's objection to the theory of subsidence based on the co- 

 existence of all kinds of reefs in the Pelews — atoll, fringing, and barrier — 

 with no reefs about one island, and from the relative steepness of the 

 submarine slopes on the east and west reefs of an island, have been 

 sufficiently met in Part I. 



