ARTICLES 425 



time on it, or if an old barrier-reef were destroyed and 

 submerged, and new reefs became attached to the land, 

 these would necessarily at first belong to the fringing class." 1 

 Such is, I believe, the origin of the fringing reefs around 

 Tutuila in the Samoan group, Fauro in the Solomon group, 

 and elsewhere ; for they border strongly eroded volcanic 

 islands. 



In the case of most sea-level reefs, the amount of erosion 

 that took place during the period of emergence antecedent to 

 submergence and reef-growth is, to the best of my judgment, 

 greater than could have been accomplished during the Glacial 

 epochs of lowered sea-level. It is not simply the erosion of 

 valleys, now embayed, that is to be accounted for, but the 

 general erosion of a volcanic island or of a continental island 

 or coast, whereby the form of the reef foundation was pro- 

 foundly altered before the reef limestones were deposited upon 

 it. Fauro in the Solomon group is a case in point, for it is 

 described by Guppy as a volcanic wreck, greatly reduced from 

 its original dimensions. Furthermore, the depth to which the 

 pre-submergence erosion proceeded, as inferred not from the 

 present depth of embayments, which has been lessened from 

 the original measure by post-submergence deposits, but from 

 the size and form of the embayments as well as from the form 

 of the spurs between them, appears in certain cases to have 

 been two or three times greater than the maximum amount 

 of lowering that the ocean could have temporarily suffered in 

 consequence of the withdrawal of its waters to form the con- 

 tinental ice sheets of the Glacial period. Hence subsidence of 

 the reef foundations, and not merely a change or an oscillation 

 of ocean level, is demanded. 



It is not only sea-level reefs that give this geological evi- 

 dence for subsidence. Elevated reefs exhibit unconformable 

 contacts with their foundations even more clearly than non- 

 elevated reefs : indeed, in the case of certain elevated reefs 

 that I have seen, the depth to which antecedent erosion pro- 

 gressed beneath the level to which the foundations were sub- 

 merged during the formation of reef and lagoon limestones, 

 measures 600 or 800 ft. The first example of the kind that 

 came under my observation is on Vanua Mbalavu of the Fiji 

 group : the vertical measure of the unconformity there seen is 



1 Coral Reefs ; 1842, p. 124. 

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