OBJECTIONS TO THE THEORY OF SUBSIDENCE. 281 
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. It 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. 
Professor Semper has other steps in his theory which are 
considered beyond. 
The idea of elevation as a requisite is not suggested by 
the atolls of the ocean. In the Paumotu Archipelago, cover- 
ing four hundred and fifty thousand square miles, the nearly 
uniform height of the land, eight to ten feet, in the seventy 
to eighty atolls, with the shore platform a hundred yards or 
more wide near third tide-level, does not favor the assump- 
tion that elevation had put them into their present uniform 
positions. 
1. The talus-theory. — Mr. John Murray, one of the able 
naturalists of the Challenger Expedition, has proposed the 
following theory: that shore-reefs extend themselves out 
within coral-growing depths on the basement of debris de- 
rived from the growing margins. 
The fact that reefs widen by the process here mentioned 
when subsidence ceases is recognized in the author’s Expedi- 
