43Q SCIENCE PROGRESS 



group have written, it is eminently possible that those islands 

 were built up above sea-level by volcanic eruptions ; that they 

 were strongly eroded during a higher stand than that of to-day ; 

 that subsidence then took place, cluring which coral reefs and 

 lagoon limestones were unconformably deposited on the eroded 

 and submerged volcanic slopes ; that a slight tilting afterwards 

 caused^the emergence of the reefs now elevated above sea-level 

 in; the southern part of the group, while permitting the con- 

 tinued upgrowth of several atolls in the northern part ; and 

 that a moderate subsidence has taken place since the tilting, 

 whereby a new barrier reef, now at sea-level, has been built 

 up around the embayed shoreline of the southern elevated 

 reefs. It is singular to note that these manifest possibilities 

 have been about as little considered by the many geological 

 authors who have quoted Semper against Darwin as they were 

 by Semper himself. 



Rein on the Origin of Atolls. — Rein first suggested the possi- 

 bility that atolls may have been formed as coral crowns upon 

 submarine banks that were built up to small depth by the 

 accumulation of organic deposits upon comparatively deep, 

 still-standing foundations * ; but the suggestion still remains 

 merely a possibility without any direct evidence in its favour, 

 as far as the stability of the submarine foundations is concerned. 

 Rein's inexperience in geological argument may be measured by 

 his statement that the elevation of marine deposits on the two 

 sides of the Atlantic, in Africa and North America, gave reason 

 for thinking that Bermuda had not subsided, as well as by his 

 failure to inquire into the structural relations of reefs elsewhere 

 than in Bermuda, and by his belief that the occurrence of certain 

 elevated reefs argued against their formation during subsidence. 



Murray on Atolls and Barrier Reefs. — Rein's suggestion as 

 to the origin of atolls was independently announced by Murray 

 in 1880, 3 whereupon it gained an undeserved popularity; for 

 although Murray had had the enviable opportunity of serving 

 on the staff of the Challenger, and of thus seeing a number of 

 coral reefs during his voyage, his preparation for geological 



1 J. J. Rein, " Beitrage zur physikalischen Geographie der Bermuda-Inseln," 

 Ber. Senckenb. naturf. Ges. 1870, 140-158; "Die Bermuda-Inseln und ihre 

 Korallenriffe " . . . Verh. isten Deut. Geogr'tag, 1881, 129-146. 



' J. Murray, " On the Structure and Origin of Coral Reefs,'' Proc. Roy. Soc. 

 Edinb. x. 1880, 505-518; "Structure, Origin, and Distribution of Coral Reefs," 

 Proc. Roy. Inst. xii. 1888, 251-262. 



