150 Daly — The Q oral-Reef Zone. 



2. General Absence of Spur-end Cliffs. — The bays 

 caused by the drowning of valleys in pre-Glacial time had 

 no such limitations of width and depth. Soon after their 

 development, the adjacent hill spurs or capes would 

 normally be protected by fringing reefs during the late 

 Tertiary. According to the foregoing brief analysis of 

 Glacial and Recent conditions, few of these spurs should 

 now show high cliffs above the sea. The spurs were 

 defended against Pleistocene wave abrasion until much 

 time had elapsed in the scouring and re-gradation of 

 shelves, the destruction of Tertiary fringing reefs, and 

 the much slower benching of the underlying, generally 

 much more resistant, rock. Cliffs cut in the foundation 

 rock would have to be 30 to 60 or more meters high in 

 order now to appear above sea-level. From the little 

 that is known regarding the rate of cliff-recession in hard 

 lavas and granites, one may well doubt the ability of 

 Pleistocene abrasion to do so great a work in the average 

 case. If cliffs so high were generated in the first glacial 

 stage, their summits have undergone weathering and 

 wasting ever since and, unless refreshed, might have 

 already faded out more or less completely. Protection 

 by interglacial reefs is another of the problems difficult 

 to estimate. 



The essential point is that the Glacial-control theory 

 does not demand extensive benching of hard-rock islands 

 during the Glacial period, even if its total duration were 

 one million years. The widths of drowned-valley embay- 

 ments do not imply any conclusion whatever concerning 

 the amount of cliff recession on Pleistocene shores. Nor 

 is there any implied relation between the widths of 

 drowned-valley embayments and the widths of the plat- 

 forms on which the modern reefs have grown. In the 

 writer's judgment these platforms are chiefly due to the 

 smoothing and extension of banks by Pleistocene marine 

 gradation, and not to extensive wave-benching of forma- 

 tions as hard as lavas or ordinary continental rocks. 

 The broad platforms which were essentially prepared by 

 wave erosion in hard rocks must date from periods long 

 before the Glacial epoch; in these instances also the 

 Pleistocene waves and currents did little more than 

 smooth off any veneer of organic deposits or of detritus 

 lying on the wave-cut flats. In brief, Pleistocene wave 

 abrasion merely "sand-papered" structures of which 



