J. D. Dana — Origin of Coral Reefs and Islands. 179 



Near longitude 180°, as the map of the Central Pacific 

 (see Part I) illustrates, the equator is crossed by the long Gil- 

 bert (or Kingsmill) Group, at an angle with the meridian of 

 25° to 30°, and not in the direction of the Pacific current which 

 is approximately equatorial. This obliquely crossing chain of 

 atolls is continued northward in the Ratack and Ralick Groups 

 (or the Marshall Islands), making in all a chain over 1200 

 miles long ; and, adding the concordant Ellice Islands on the 

 south, and extending the Ratack line to Gaspar Rico its northern 

 outlier, the chain is nearly 2000 miles long. Nothing in the 

 direction of the long range, excepting local shapings of some 

 of the points about the atolls, can be attributed to the Pacific 

 currents. Moreover, the diversified forms of the atolls have 

 no sufficient explanation in the drift process. 



d. Further : drifting by currents may make beaches and 

 inner channels whether subsidence is going on in the region or 

 not, and are not evidence for, or against, either a movement 

 downward or upward. Sandy Hook, the long sandy point off 

 the southern cape of New York harbor, has been undergoing 

 (as the U. S. Coast Survey has shown) an increase in length, or 

 rather variations in length, through the drifting of sands by an 

 outside and an inside current ; and this is no evidence that 

 Professor G. H. Cook is wrong in his conclusion that the New 

 Jersey coast is slowly subsiding. 



e. But even in this region of Florida we have strong evidence 

 of a great subsidence during the coral-reef era, and all the subsi- 

 dence that the Darwinian theory demands. 



In a very valuable paper by Mr. Agassiz, published in 1879 

 in the Bulletin of the Museum of Comparative Zoology,* the 

 author points out that the South American continent, in com- 

 paratively recent geological times, had connection with the 

 West India islands through two lines : (1) one along a belt 

 from the Mosquito Coast to Jamaica, Porto Rico and Cuba ; 

 and (2) the other through Trinidad to Anguilla, of the Wind- 

 ward Islands. He sustains the conclusion by a review of the 

 soundings made by the Steamer Blake under the command of 

 J. R. Bartlett, U. S. N., and a consideration of the facts con- 

 nected with the distribution of marine and terrestrial species. 

 As the soundings show, the former of the two connections re- 

 quires for completeness an elevation of the region amounting 

 to 4060 feet over the part south of Jamaica, 4830 feet between 

 Jamaica and Hayti, and 5240 feet between Hayti and Cuba. 

 The other line of connection requires an elevation of 3450 

 feet. An open channel, as he observes, would thus be left be- 

 tween Anguilla and the Virgin Islands, where there is now a 

 depth of 6400 feet. The close relations in the existing fauna 

 * An abstract of the paper is contained in this Journal, III, xviii, 230, 1880. 



