UNCONFORMABLE ELEVATED REEFS 511 



tioii shows reef 1 formed during a movement of subsidence, which is 

 then continued so rapidly that no other reef is formed until, after a pause, 

 upheaval sets in ; reefs 2 and 3 are thus formed above reef 1. Continuous 

 submergence followed by a similar emergence might produce such a struc- 

 ture as section E ; continuous emergence followed by similar submergence 

 might result in a structure like section S. It is easy enough to deduce 

 these and other expectable conditions; it is a difficult matter to apply 

 them in the examination of uplifted reefs, where clear sections are rarely 

 exposed; but the difficulty of examination is certainly lessened if the 

 critical points are thought out beforehand. 



The numerous elevated fringing reefs of the New Hebrides seemed to 

 offer good opportunity for detecting their structure ; a few of them oh the 

 island of Efate were therefore examined, in company with E. C. Andrews 

 of Sydney, on my journey of 1914, with the problem as here stated in 

 mind. The results gained will be set forth in my final report; while not 

 conclusive, they gave much reason for thinking that the reefs are uncon- 

 formable, and that some of them at least were formed during the subsi- 

 dence of their foundation previous to the later movement of elevation. 



ACCOUNTS OF UNCONFORMABLE REEF CONTACTS 



It is not, however, only in Darwin's writings that the unconformable 

 contact of reef limestones with their foundations is overlooked, both as a 

 manifest fact of occurrence and as an inevitable consequence of the theory 

 of subsidence, Nearly all other writers on the coral-reef problem have 

 past over this significant structural matter in silence. Among the few 

 who have mentioned it are Richthofen, w^ho many years ago explained an 

 uplifted reef on the south coast of Java, 40 feet above sealevel, as a bar- 

 rier reef that had been built during subsidence on the worn edges of hori- 

 zontal Tertiary strata (1874, 246) ; Walther, who explicitly recognized 

 the importance of unconformable contacts as proving subsidence, in his 

 study of uplifted coral reefs in the Red Sea (1888) ; Lister, who described 

 the unconformable contact of elevated reef limestones on their founda- 

 tion in the island of Eua, a small southeastern member of the Tonga 

 group (1891) ; Brouwer, who describes Roti, a small continental island 

 near Timor, in the East Indies, as composed of deformed strata, uncon- 

 f ormably covered with terraced limestones which form the greatest heights 

 (214 meters) ; hence this island is an elevated atoll with visible, non- 

 volcanic, unconformable foundation (1914) ; and Molengraaff, who has 

 described unconformable elevated reefs in the small island of Letti, in the 

 same region (1915). 



