90 Capt. F. W. Hutton on the Origin of the 



condensation of snow by the mountains would be therefore 

 very much in excess, and consequently the glaciers much 

 larger than at present " *. This hypothesis is similar to one 

 long ago proposed to account for the former extension of the 

 Swiss glaciers by the submergence of the Sahara. But in 

 our case it has been shown that the hot north-west winds, as 

 well as the cold south-west winds, are parts of westerly 

 cyclones f, and that they are saturated with moisture when 

 they reach New Zealand. That our north-west winds owe 

 their heat and dryness to local causes and not to the arid plains 

 of Australia has been explained by Dr. Knight J and by Mr. 

 Barkas § . The subsidence of Central Australia might possibly 

 decrease their temperature and therefore decrease the amount 

 of aqueous vapour held by them ; but this could not possibly 

 increase the amount of snow on the mountains. 



The plateau hypothesis was proposed many years ago by 

 Rendu to account for the former extension of the glaciers of 

 Switzerland ; but it never obtained many adherents. It was 

 shown that the effect of plateaux is to diminish, not to increase, 

 the size of glaciers ; and Prof. J. D. Forbes cites in proof the 

 fact that, while the snowfall in both places is about the same, 

 il the largest glacier in Norway (Lodal) may be rudely esti- 

 mated to have only one seventh of the surface of the Aletsch 

 glacier of Switzerland, tributaries in both cases being exclu- 

 ded ; but the snow-field connected with it may cover 40>> 

 English square miles at least, which probably exceeds in 

 extent anything in the Alps. The perpetual snows of the 

 Fondalen are much larger, and those of Sulitelma not in- 

 ferior " || . The size of glaciers therefore is not proportional 

 to the size of their snow-fields, as supposed by the advocates 

 of the plateau hypothesis. Neither is the denuding power of 

 the snow so great as supposed. Of course the snow-fields 

 themselves preserve the rocks that lie below them ; it is only 

 when the snow gets pressed into ice and begins to descend 

 the valleys that any erosion can take place ; but even this 

 erosion has, I think, been greatly over-estimated by the advo- 

 cates of the plateau hypothesis. On this point I gladly avail 

 myself of the opinion of Sir A. Ramsay, whom no one will 

 accuse of underrating the amount of glacier erosion. In a 

 discussion at a meeting of the Geological Society of London 



* Trans. N. Z. Inst. vi. p. 385. 



f " On the Principles of New Zealand Weather Forecast," by Com- 

 mander Edwin, R.N., Trans. N.Z. Inst, xii p. 40. 

 X Trans. N. Z. Inst. vii. p. 470. 

 § N. Z. Journ. of Science, i. p. 576. 

 II ' Norway and its Glaciers,' p. 232. 



