ORIGIN OF FORTY-FATHOM BANKS 557 



forms of the intertropical banks. The differences of from 30 to 50 fath- 

 oms liere disclosed between the depths of banks that should, according to 

 the Glacial-control theory, be closely comparable are not easily explained 

 without the aid of miequal subsidence. 



Second, the strong cliffs cut in the resistant volcanic rocks of the cen- 

 tral islands on these reefless extratropical banks show that the waves of 

 the lowered ocean, which abraded the platform around these islands, were 

 abundantly capable of cliffing the intertropical volcanic islands, now sur- 

 rounded by fringing or by close-set barrier reefs, provided the reef -build- 

 ing organisms were killed while the ocean was lowered; and as those 

 islands are not clift, we find here again reason for rejecting the assump- 

 tion that the reefs were dead. We are thus fortified in the conclusion, 

 which may have been lost sight of by the reader during the discussion of 

 the possible truncation of the Macclesfield and other banks on earlier 

 pages, that submarine banks can not be the result of abrasion and in the 

 associated belief that their present unequal depths are due to subsidence. 



Third, the considerable extent of some of the banks on the border of 

 the coral seas — the bank around Norfolk Island measures 55 by 20 miles 

 in extent and the banks around some of the northwestern members of the 

 Hawaiian group are of similar dimensions — makes it improbable that 

 they are due chiefly to the abrasion of still-standing volcanic islands by 

 the lowered Glacial ocean; and the record of "coral" in some of the sound- 

 ings suggests that part of the banks may be made of reefs. It is therefore 

 w^orth considering whether these banks may not have been inclosed by 

 extensive barrier reefs during the last inter-Glacial epoch, which is be- 

 lieved on good grounds to have been warmer and longer than the present 

 post-Glacial epoch ; for, if so, we should most appropriately have here, on 

 the border of the present coral seas, precisely the consequences deducible 

 from the Glacial-control theory, including the cliffing of central islands 

 as well as the truncation of reefs ; and in the association here of those two 

 elements we should have proof that the theory does not apply within the 

 coral seas of today, where clift central islands are of rare occurrcjice. 



Fourth, the depths of about 40 fathoms, which characterize the outer 

 margin of the extratropical banks above named, are, like similar marginal 

 depths elsewhere, in my opinion more reasonably explained as the result 

 of wave and current agencies working on loose sediments with respect to 

 present sealevel than as a mark of any former lower level of the sea; for 

 the various indications of recent upheavals and subsidences found in other 

 islands, such as Oahu and New Zealand, not far from the banks in ques- 

 tion, make it altogether improbable that the banks have long been sta- 

 tionary; and if they have moved either up or down, some agencies such 



