Sir,

Although I wrote the words “ideally and ignoring ablation” deliberately in my paper, I think Dr. Heinsheimer raises a useful point when he says that ablation including ice flow is in fact important. In particular I accept that the main ice sheet, when it first grew, probably took more than 15,000 yr. to do so because of the ablation at its edge—but not very many times more. Published suggestions that the Antarctic Ice Sheet grew very slowly, taking 50,000 yr. or more, should be read with caution.

What I wished to emphasize in my paper was not so much the speed with which the ice sheet first grew, as the speed with which it adjusted itself to subsequent climatic, eustatic and other changes. An example of such a speedy change is given in a calculation I have given as part of the Cambridge symposium on mass balance studies (Reference HollinHollin, 1962, p. 313).