Davis. — Si(jiilfini nf Fcalnrcs of K( rf-liardf red Coasfs. 25 



Suess was somewhat more warranted in ascribing the emergence of a 

 number of Pacific atolls to a sinking of ocean-level, for, according to the 

 records that he quoted, their altitudes were about alike ; but a closer 

 examination of the facts shows not only that the altitudes of these emerged 

 islands vary greatly, but also that the amount of post-emergence erosion 

 that they have suffered is very unlike. Hence their present altitudes 

 must be explained by local upheavals, varying in date as well as m 

 measure. 



Diverse Measures and Dates of Submergences and Emergences. — Local 

 diiieiences in the measures and the dates of emergences and submergences 

 are the best indications of local movements, and evidence of such differences 

 is found on islands in many parts of the Pacific and Indian Oceans. In 

 Fiji, for example, the uplifted limestones, which reach an altitude of 650 ft. 

 on Vanua Mbalavu, in the eastern part of the group, are greatly dissected ; 

 Vatu Vara, an elevated atoll thirty miles to the west, is hardly dissected 

 at all, though its height is 1,030 ft. ; Naiau, another elevated atoll, 580 ft. 

 in altitude, forty miles to the south, is also little dissected ; several other 

 barrier-reef islands, one hundred miles or more to the west, show no 

 signs of elevation. 



Again, Viti Levu and Vanua Levu, the two largest islands of the Fiji 

 Group, show fringing or close-set barrier reefs in association with slightly 

 elevated reefs on parts of their southern coast, while to the north-west 

 they have distant barrier reefs, enclosing broad lagoons. The barrier reef 

 on the north-west of Viti Levu is well formed near the island, but fails to 

 reach the sea-surface farther away, where the lagoon has the unusual depth 

 of 58 fathoms. Such a combination of features can hardly be explained 

 without assuming a gentle tilting of the islands. 



A similar tilting would seem to be demanded by the features of the 

 Pelew Islands as described long ago by Semper, although that zoological 

 observer, who knew nothing of embayed shore-lines or of unconformable 

 reef contacts, thought tilting too improbable a process to be believed in. 

 New Caledonia shows abundant signs of recent submergence to some such 

 measure as 80 or 100 fathoms, while the Loyalty Islands, not far away 

 to the north-east, are recently elevated atolls. In the Solomon Group, 

 Fauro, previously mentioned, is surrounded by a submarine platform which 

 appears to represent a submerged barrier reef, while New Georgia, farther 

 east in the same group, is bordered for part of its circuit by a remarkably 

 good example of an emerged barrier reef. 



It thus appears clear that diverse emergences and submergences at 

 different dates are indicated in various island groups. Hence, even if 

 changes of ocean-level from any cause have from time to time produced 

 universal and synchronous emergences and submergences of moderate 

 measure, local movements of much greater measure are also demanded 

 by the features of various islands, and these local movements are probably 

 the chief causes of the strong submergence which the drowned valleys 

 and outstanding barrier reefs of many volcanic islands call for. Further 

 observations on many reef-encircled islands should be made in order 

 to learn the relative values to be assigned to the various causes of 

 emergence and submergence ; and from what has thus far been said 

 it is clear that the observations should, in this aspect of the coral-reef 

 problem also, be directed more to the islands tlian to the reefs which 

 encircle them. 



