iSgj. RESULTS OF '' CHALLENGER " EXPEDITION. 19 



chief among which we may mention those of Sir Archibald Geikie 

 (Proc. Edinh, Roy. Phys. Soc, vol. viii., 1883, p. i.) and of the late 

 Professor James D. Dana {Amer. Jouvn. ScL, 3rd ser., vol. xxx., 1885, 

 pp. 89, 168; also in Phil. Mag., ser. 5, vol. xx., 1885, pp. 144, 269). 

 During the last few years additional interest has been added to the 

 discussion upon coral-reefs, in their geological aspect, by the discovery 

 of a number of undoubted deep-sea organic deposits, such as 

 Globigerina ooze and Radiolarian ooze, among the rocks of the earth's 

 crust, some of which, though of late Tertiary age, have been elevated 

 several thousands of feet above the sea-level. These facts have, of 

 course, tended to confirm the views of those geologists who maintain 

 that great interchanges must have taken place in past times between 

 the continental and oceanic areas of the globe. 



Within the last two years two most important monographs on 

 coral-reefs have made their appearance, Mr. W. Saville Kent's " The 

 Great Barrier-Reef of Australia," and Professor Alexander Agassiz's 

 admirable description of the Bahamas^ the authors arriving at very 

 opposite conclusions on the general question of the origin of coral- 

 reefs, from their careful and detailed studies of these interesting 

 examples. 



In connection with the latter of these memoirs, a melancholy 

 interest attaches to the circumstance that it was the perusal and 

 notice of his friend's monograph that occupied the distinguished 

 x\merican naturalist, James Dwight Dana, during the last few days of 

 his hfe. From the charming and judicious sketch of his father's life and 

 career, written by Professor E. S. Dana, we learn that the notices of 

 books in the May number of the A mevican Journal of Science were the last 

 literary work undertaken by the great naturalist, and the views that he 

 enunciates as the final result of his wide experience and his latest 

 reflections on these important questions deserve to be widely known. 

 We shall not, therefore, apologise for transferring them to these 

 pages. 



" Professor Agassiz, in discussing the origin of coral-reef lime- 

 stones, states objections to the subsidence-theory of Darwin. With- 

 out touching here on the special arguments in its favour, two or three 

 general facts may be stated. 



" In geological history, many limestones have been made 

 exceeding 1,000 feet in thickness, which show by their fossils that 

 they are not of deep-water origin. Whether derived from coral and 

 shell sediment like coral-reef rock, or from shell sediment chiefly, 

 makes no difference ; subsidence was required. 



" Subsidences of one or two scores of thousands of feet in depth 

 have taken place in past times over the region of the Appalachians, 

 Alps, and other mountain regions ; and in the sinking trough, 

 sediments were formed successively at the water's level, or not far 



1 "A Reconnaissance of the Bahamas and of the Elevated Reefs of Cuba, in the 

 steam yacht ' Wild Duck,' January to April, 1893," with 47 plates. Btdl. Mus. 

 Comp. Zool. Vol. xxvi. Number i ; December, 1894. 



C 2 



