fluctuate appreciably. The prevailing isostatic equilibrium of the interior conti- 

 nental platform of both East and West Antarctica (Woollard, 1962) supports Hollln's 

 conclusion. 



The advance and retreat of the Antarctic Ice sheet over a peripheral zone 

 would cause isostatic depression and rebound of this zone . Assuming no crustal 

 shear strength, Weertman (1961) proposed an isostatic crustal depression of 330 

 meters for every 1,000 meters of overlying ice of large ice caps. But, as the earth's 

 crust does have shear strength, the area of depression would be spread to about 65 

 miles beyond the loaded area (Gunn, 1943, 1949). Therefore, the zone of isostatic 

 movement of the periphery of Antarctica would be less than that calculated when 

 neglecting crustal shear strength. 



Hollin (1962, p. 89) referred to "Isostatic restraint," a factor whereby isostatic 

 depression by the advancing ice front would cause a relative rise of sea level which 

 would in turn tend to counteract the eustatic drop of sea level which Initiated the 

 ice advance. Hollin assumed that the time lag between glacial adjustment to sea 

 level and isostatic compensation is small compared to the periodicity of the fluc- 

 tuations . He thereby objected (p . 187) to Voronov's contention that the Ice ad- 

 vanced all the way to the continental shelf edge - "isostatic restraint" would limit 

 the ice advance to lesser distances . 



Fairbridge (1961, p. 127), however, on the basis of paleoshorellne studies, 

 age-dating, and geodetic and gravity measurements found that "complete" isostatic 

 adjustment would take about three times as long as complete glaclation . Heiskannen 

 and Vening Meinesz (1958, p. 369) gave the formulae: 



t = AA 



(where tr is the relaxation time in thousands of years during which the deviation 

 from isostasy diminishes to 1/e of its value over an infinitely long depression of 

 width L in thousands of kilometers) and 



(where the second horizontal dimension iSjM in thousands of kilometers). Taking 

 20,000 years as the time elapsed since the last glacial maximum (Fairbridge, 1961; 

 Curray, 1961), this writer estimates, from the above formulae, that the coastal 

 zones of glacial Isostatic depression are now only about 35 percent compensated. 

 Broader areas of ice fluctuations such as the Ross embayment are now accordingly 

 about 60 percent compensated . 



The above calculations and Falrbrldge's dating of the Pleistocene cycles 

 (circa 22,000 year half-cycles) lead the author to believe that the peripheral 



17 



