154: Daly — The C oral-Reef Zone. 



demand: a rule of comparatively small depth for 

 lagoons ; and flat floors for wide lagoons, at levels slightly 

 higher, on the average, than those characterizing the tops 

 of most extra- tropical banks. The theory by no means 

 excludes the occasional discovery of exceptional depths 

 even inside barrier and atoll reefs, where constructional 

 hollows — drowned valleys, fault-troughs, volcanically 

 formed depressions — have not yet been filled with detri- 

 tus. In fact, the rarity of lagoon depths greater than 50 

 or 60 fathoms strongly suggests a lack of extensive sub- 

 sidence of the sea-floor for the last hundred thousand 

 years, if not for the last million years or more. The local, 

 Recent subsidence of a Vanikoro or of part of the Tonga 

 plateau are exceptions merely proving the rule. 



Again, uplift has recently (in the late Wisconsin stage 

 or later!) shallowed some lagoons. Examples are given 

 in the writer's 1915 paper. Others are North Argo 

 lagoon and Ngele Levu lagoon of the Fijis, each bearing 

 islets of elevated limestone. These two cases have been 

 cited as evidence against the Glacial-control theory, on 

 the ground that their lagoon depths are abnormally small. 

 Since they have been recently uplifted, the lagoon floors 

 should be nearer the present sea-level than similar floors 

 which have undergone no displacement in late-Glacial or 

 post-Glacial time. In reality, the study of exceptional 

 cases here also seems to prove the rule of long-continued 

 and nearly perfect crustal stability for most of the oceanic 

 areas in the tropics. 



5. Crustal Movements in Areas Near Coral Reefs. — 

 Conclusions demanding instability in a sea area because 

 neighboring lands have recently moved up or down ought 

 to be made very conservatively. If one judged from the 

 recent, gigantic warpings proved in the Timor-Ceram 

 region by Molengraaff and others, he might be tempted 

 to deduce recent crustal uneasiness in the adjacent, 

 western part of the same "Eastern" archipelago. Yet 

 the charts show that the broad area from Java to Siam 

 and Annam has been stable nearly enough and long 

 enough for the generation of one of the greatest conti- 

 nental shelves on the globe. Molengraaff himself has 

 emphasized a long crustal stillstand in the Java Sea area, 

 as implied in his view that it suffered peneplanation. 19 



19 G. A. F. Molengraaff, Proc. kon. Akad. Wet., Amsterdam, vol. 19, p. 

 612, 1916. 



