BY PROFESSOR GRIFFITH TAYLOR, DSC, B E., B.A., F.G.S. 193 



In my brief report (4) on the glaciology which I made 

 in February, 1919, I wrote as follows: — 



"In the early days of the Ice Age a great drift of 

 "snow occupied a shallow valley where now is Lake Seal.. 

 "Freezing and thawing took place continually around 

 "this snow-drift, and broke down the structure around 

 "the drift. Small streams surrounded the drift, and not 

 "only supplied the ice wedges, but carried aWay some of 

 "the debris. The sapping extended outward by slow 

 "degrees as the snow-drift increased, and gradually a 

 "flat valley was eroded, much like the embryo cirque on 

 "the 4,300-foot level above (and south of) Lake Seal. 

 "(See Fig. 5 at A.) The deepening process would ad- 

 "vance into the hill at the foot of the snow-drift and 

 "would be especially strong during the dwindlnig of the 

 "ice-slab (into which the snow would soon be converted) 

 "as the Ice Age passed away." 



It is important to realise that the oncoming and waning 

 •of the Ice Age were both gradual. Hence the controls de- 

 termining the erosion varied more or less continuously. The 

 major control was, of course, the temperature; and the point 

 is not sufficiently stressed in glacial literature, that there is 

 an optimum temperature as far as frost-action is concerned. 

 It is obviously near the melting point of ice, and probably 

 from 32 deg. to 35 deg. F. (or around 34 deg. F.) is about 

 the most favourable temperature. One of the most striking 

 results of my Antarctic investigations was to find that the 

 temperature in the Antarctic is too cold for the maximum 

 glacial erosion. There is infinitely more of this erosion going 

 on in New Zealand than in latitude 78 deg. South. 



We must therefore imagine this layer of favourable 

 temperature slowly settling down on to the plateau as the 

 Ice Age is ushered in. At present the temperature layer 

 of 34 deg. F. lies at 6,000 feet above sea level and about 

 3,000 feet above Lake Seal. Here we may assume an average 

 annual temperature of about 44 deg. F. at the present time. 

 (See Fig. 4.) 



If now we imagine a cooling of about 10 deg. F. at the 

 maximum of the Ice Age, this "nivation-layer," as we may 

 term it, will descend to the level of Lake Seal, and the maxi- 

 mum amount of frost action will occur at this level. Above 



(4) A report prepared for the Tasmanian Government Tourist 

 Bureau. 



