Umbgrove, J. H. F. (1946) : Origin of Continental Shelves. Bull. Amer. Assoc. 



Petv. Geol., Vol. 30, pp. 249-253. 

 Wentworth, C. K. (1927) : Estimates of Marine and Fluvial Erosion in Hawaii. 



Joiirn. of Geol., Vol. XXXV, No. 2, pp. 117-133. 

 Whitaker, W. (1867) : On Subaerial Denudation, and on Cliffs and Escarpments 



of the Chalk and Lower Tertiary Beds. Geol. Mag., Vol. 4, pp. 447-454 and 



483-493. 

 ■VON Zahn, W. (1909) : Die zerstorende Arbeit des Meeres an Steilkiisten. Mitt. 



Geogr. Gesell. Hatnbufg, Vol. 24, pp. 193-284. 



Summary OF Discussion 



Dr. Shepard commented that steps across the continental shelf 

 seemed from the study of a large number of charts to be practically the 

 same in most parts of the world. As to storm-wave benches, tidal-wave 

 investigations in Hawaii in 1946 had shown actual cuts 10 ft. or 20 ft. 

 above normal sea-level. This was admittedly in soft material. But with 

 repetition the same occurrence might take place in harder material. 

 In general, said Professor Bartrum, there could be no doubt that 

 surrounding platforms were uplifted. 



Professor Bartrum replied to criticism by Dr. Fairbridge of his own 

 results by commenting on a series of slides, including many New Zealand 

 examples, confirming the conclusions of Gulliver and Fenneman. He 

 pointed out that Dr. Fairbridge showed inconsistencies with his later 

 argument, in attempting to homologize platforms 2 ft. to 8 ft. above 

 sea-level with those below. The examples of " Old Hat " structure were 

 illustrated. Such phenomena were encountered only in certain con- 

 ditions, where the rocks were impermeable, free from close-spaced joints, 

 amenable to weathering, and in sheltered waters. A local example was 

 illustrated of a 96 ft. wide platform developed in Parnell Grit, having a 

 gentle slope. The rocks were quite resistant when wet, but broke into 

 pieces very readily on alternate wetting and drying. A series of other 

 New Zealand examples was shown. 



Professor Cotton attempted to sum up the conflicting points made by 

 Dr. Fairbridge and Professor Bartrum. Everywhere that erosion 

 occurred, he stated, two platforms were tentatively developed — one 

 towards the sea showed normal sloping profile, while the high- water 

 platform of Bartrum was also present, making its way in towards the 

 land. In certain rocks the top platform gets ahead in its development 

 and we find the " Old Hat " type of erosion. In other cases the lower 

 platform develops at the greater rate, and w"e find the normal shore-line 

 profile. 



Comments by J. A. Bartrum, Auckland University College 



Dr. Fairbridge's observations of shore platforms in rocks other than 

 limestones, which have abnormal solubility compared with most other 

 rocks, appear to be limited. On New Zealand shores there are hosts 

 of examples of wide, gently-sloping subaqueous platforms which have 

 the profile demanded by Fenneman, Gulliver, and others of their school. 

 He also minimizes the corrosive potentialities of waves as compared 

 with subaerial processes, but any observer can readily satisfy himself 

 that, in normal rocks, given suitable tools, waves are extremely capable 

 ■corrosive agents. 



If, as Dr. Fairbridge maintains, the types of beach that I have termed 

 the " Old Hat " and " Storm-wave " shore-platforms, which differ at 

 times as much as 10 ft. in height, are to be referred to one and the same 



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