JAMES DWIGHT DANA 261 



an arrangement which is strongly suggestive of a subsidence pro- 

 gressively increasing towards the middle of the ocean. The asso- 

 ciation of fringing reefs with active volcanoes and of barrier reefs 

 with extinct volcanoes, as pointed out by Darwin, indicates that 

 in some way the different kinds of coral formations are correlated 

 with hypogene actions; and it is probable that the explanation of 

 that relation lies in the theory that crustal elevation in any region 

 diminishes the pressure on the rock masses in a condition of po- 

 tential liquidity a few miles below the surface, thus lowering the 

 melting-point, so that actual liquefaction takes place, and the 

 molten materials find their way to the surface. The active volca- 

 noes should therefore be in regions where the crust has been re- 

 cently undergoing elevation, while in subsiding areas the volcanoes 

 should be extinct. The lagoons in the larger atolls often show a 

 depth much greater than the limiting depth of coral growth. This 

 is probably evidence of subsidence, since there are very strong ob- 

 jections to Murray's notion that the lagoons are extensively widened 

 and deepened by the solvent action of the sea-water. The core 

 brought up from a bore eleven hundred feet deep, recently made 

 on the island Funafuti in the Ellice group, is said to show no im- 

 portant change of character through its entire length. It appears, 

 therefore, probable that a true coral reef rock extends down to the 

 bottom of the bore and we know not how much farther. Such a 

 thickness of reef could of course be formed only by subsidence. 

 For these and other reasons it seems probable that Darwin and 

 Dana were right in believing that the multitudinous barriers and 

 atolls of the Pacific are evidence of subsidence of a vast area. It 

 is hardly necessary to say that Dana's conception of the drowning 

 of a multitude of oceanic volcanoes is more probable than Dar- 

 win's conception of the drowning of a continent. 



Next to the study of the coral formations, the most important 

 geological work done in the Exploring Expedition was in the study 

 of volcanoes. Especially important was the detailed investigation 

 of the Hawaiian volcanoes, though numerous extinct volcanoes 

 were also studied in the course of the expedition. Dana's work 

 contributed, with that of Scrope and Lyell, to the demolition of 



