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



Rakaia valley at the time when the limestone was deposited. 

 If therefore any great lateral denudation had taken place since 

 that time, the line of junction ought to stand out as a promi- 

 nence. But, on the contrary, it is in a valley, apparently 

 much in the same position with regard to the other parts of 

 the valley as when the limestone was formed. Consequently 

 no great plateau on the south of the Rakaia can have been 

 removed. 



Many other instances could be cited, but this one must 

 suffice, for it alone is sufficient proof that the denudation 

 which has taken place during the comparatively short time 

 that has elapsed since the commencement of our last great 

 glacier epoch cannot have affected the shape of the mountains 

 to such an extent as to make it worth while to take this cause 

 into consideration, even if it acted in the direction supposed. 

 That the large river-valleys were more or less filled to a height 

 of 3000 or 4000 feet above the present sea-level by Tertiary 

 rocks, most of which have been since removed, is no doubt 

 true ; but as this is below the line of perpetual snow, which 

 is estimated by Dr. von Haast and Mr. M'Kerrow to be 

 between 7000 and 8000 feet, this filling up of the valleys, if 

 it affected the level of the snow-line at all, would raise it by 

 radiation in the same way that the plateau of Thibet raises 

 the height of the snow-line on the northern slopes of the 

 Himalaya. 



As therefore both the subsidence- and the plateau-hypo- 

 theses are quite untenable, we must fall back on elevation of 

 the land as the main if not the only cause of the former 

 extension of our glaciers ; and it is strongly confirmatory of 

 this hypothesis that the two earlier glacier epochs each 

 occurred at a time when we have independent proof that the 

 land stood at a far greater height than at present. With 

 regard to the last glacier epoch, it has been estimated that an 

 elevation of between 3000 and 4000 feet would be quite 

 sufficient to bring back the glaciers to their former dimen- 

 sions *. 



But if our last glacier epoch was caused by elevation of the 

 land, it is easy to prove that it must be of an older date than 

 the glacial epoch of Europe, because while our islands are 

 separated by a strait only 500 feet deep, the difference between 

 their floras and faunas is far greater than the difference be- 

 tween the floras and faunas of England and Europe, which 

 were separated in the Pleistocene period immediately after the 

 glacial epoch. In the South Island we have six different 

 kinds of birds represented by different species in the North 

 • Trans. X. Z. lust. xiii. p. 385. 



