AMERICAN GEOLOGY DECADE OF 1840-1849. 423 



ied in the tenth volume of the reports of the expedition, a royal octavo 

 of 75b' pages, with a folio atlas of 21 plates. Many of 



Dana and the Wilkes , , . . . ., . , n , , 



Exploring the conclusions given in this volume were nrst pub- 



lished in the columns of the American Journal of 

 Science, and have already received attention. 



One of the earliest results of Dana's work, as here chronicled, was 

 the establishment of the principle that temperature influences the 

 growth and distribution of corals. A claim to priority in this discov- 

 ery was made by James P. Couthouy, and brought about a personal 

 controversy somewhat bitter between the two authors. This has been 

 alluded to elsewhere (p. 373). 



The existence of harbors about the coral-bound reefs Dana attrib- 

 uted largely to the action of tidal and local marine currents, though 

 the presence of fresh-water streams may have contributed toward the 

 same end. 



He rejected the then popular theory of the formation of coral reefs 

 and atolls through the gradual subsidence of volcanoes, the crater cor- 

 responding to the lagoon and the rim to the belt of land, though 

 believing that, beyond question, a subsidence had taken place through- 

 out a large part of the Pacific, and hence that subsidence must form 

 a part of any true theory of the origin of the reefs. 



He believed that the atoll once formed a fringing reef about a high 

 island. This, as the island subsided, became a barrier reef, which 

 continued its growth while the land slowly disappeared. The area of 

 waters within finally contained the last sinking peak, which itself 

 finally disappeared, leaving only the barrier at the surface and an 

 islet or two of coral in the inclosed lagoon. 



These were essentially the views put forward independently by Dar- 

 win. The recent work of the younger Agassiz has shown them to be 

 not wholly correct. 



From the actual extent of the present coral reefs and islands Dana 

 inferred that the whole amount of high land lost to the Pacific by this 

 subsidence was at least 50,000 square miles, probably much greater, 

 though he would not go so far as to conclude that a continent once 

 occupied the place of the present ocean, or indeed of a portion of it. 



In the discussion of the Hawaiian volcanoes it was noted that no 

 apparent connection existed, so far as indicated by the phenomena of 

 eruption, between Mount Loa and Kilauea, 16 miles distant and more 

 than 10,000 feet lower. It was therefore concluded that the two 

 conduits, which he assumed were once connected by a fissure, had 

 become isolated through the solidifying of the lava between them, each 

 conduit being possibly a separate branch of some deep-seated channel. 



The wide difference in the height of the columns of lava in two vol- 

 canoes so near together as those noted above caused him also to doubt 

 the statement so commonly made by writers of that day to the effect 

 that volcanoes were safety valves. 



