The precise elevation of this contemporary horizontal platform is 

 a matter of considerable importance. From my own and others' 

 observations (see Macfadyen, 1930 ; Kuenen, 1933 ; Fairbridge, 1948 ; 

 Fairbridge and Gill, 1947 ; and many others) it is claimed that the 

 " normal " platform forms at the level of low-water springs. Exceptions 

 are known ; pre-existing cavities in the rock (karst caverns and holes), 

 lenticles of soft sand in the country rock, collapse structures, and so on, 

 may all cause segments of the reef to be " abnormal." The occurrence 

 of hard rock bands, gently dipping, may come by differential erosion 

 to almost conform to the ideal reef height and shape, but may exhibit 

 a gentle dip in one direction or another ; the effect being to institute 

 considerable confusion (see, for example, the Sydney benches in gently- 

 dipping Trias sediments — Jutson, 1939). Very exposed positions may 

 result in shore " ramps," where the bench slopes gently up on the 

 inside owing to the nature of the swash profile. However, when viewed 

 overall, the " abnormalities " find local explanations, while the " normal " 

 bench elevation tends finally to the height of low-water spring tides. 



An interesting problem in this connection was first described from 

 New Zealand by Bartrum (1916, 1935), where his " Old Hat " bench 

 was already recognized by Dana and by Hochstetter. Its elevation 

 is just below high-water level. Bartrum assumed that this is a 

 contemporary bench, formed at the present stand of the sea, but in rocks 

 of a particularly favourable sort and in fairly protected places ; the 

 rock below high-water level is supposed to be always saturated in 

 protective sea-water, while the overlying rock is subaerially weakened 

 and prepared for removal by quite gentle waves. I cannot agree with 

 this interpretation, and feel that the base-level of subaerial erosion is 

 not high-water, but low-water, springs ; also the major role played b}' 

 inter-tidal chemical processes should not be forgotten. Personally, 

 I regard the " Old Hat " type of bench as a perfect example of the 

 10 ft. eustatic platform which was actually formed only about four 

 thousand years ago, and is thus preserved in a surprisingly fresh state 

 in favourable locations. 



Admittedly, if we had not had the privilege of examining the 

 phenomenon on many occasions under ideal conditions on limestone 

 shores we might very well have failed to realize that there had been 

 multiple eustatic stands of the sea-level during the last few thousand 

 years, which have had the result of producing platforms a few feet above 

 the present one — that is, at 2-3, 5-6, and 10-11 ft. above datum (for 

 example, the present low- water spring-tide level (see Kuenen, 1933 ; 

 Fairbridge, 1947a, 1947b, 1948, 1949 ; Teichert, 1947, 1948) ). 



It may thus be readily perceived that in regions of considerable 

 tidal range, as in New Zealand around Auckland, all three of these 

 higher benches would still be subjected to marine erosion to-day, and, 

 in fact, may be very easily attributed to the effect of the sea at its 

 present stand. In this way de Lapparent in France (1906), Jardine in 

 Queensland (1925), Jutson in New South Wales (1939), Edwards in 

 Victoria (1941), and Bartrum in New Zealand (1926, 1935) all speak 

 of marine erosion as if it were selective at different heights of the tide 

 and states of weather. At low tide we are supposed to get a " normal " 

 or " ultimate " bench, at mid to high tide we find an " Old Hat " 

 type of bench, and, finally, at storm-wave swash-height we see a notch 

 called a "storm- wave " bench. In a quiet bay in Western Australia, 

 however, I believe I could demonstrate all jour levels in one and the 



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