MODIFICATION OF THEORY EXAMINED. 89 



extent of high land." Were it not for these extensive 

 highlands and lofty mountains, Greenland and the 

 Antarctic regions, according to Mr. Wallace's theory, 

 would be free from permanent snow and ice. He, 

 however, nowhere, so far as I can find, offers any proof 

 for the conclusion that those regions possess extensive 

 high lands, elevated plateaus, and lofty mountains 

 sufficient to account for these icy mantles. In the last 

 chapter the subject has been discussed at considerable 

 length, and the conclusions arrived at are diametrically 

 the opposite of those advocated by Mr. Wallace, 

 viz., that Greenland, and probably the greater part of 

 the Antarctic regions, consists of land probably not 

 much above sea-level, and that the mass of ice under 

 which they are buried must be due to some other 

 cause than elevation of the land. 



Permanent Ice may originate without Perpetual 

 Snow. — It is not necessary that, in order to have 

 permanent ice, there should be perpetual snow. If 

 snow softens or becomes partially melted and after- 

 wards re-freezes, it is then far more difficult to melt 

 than it was in its original condition. Half-melted 

 snow, when re-frozen, resists the summer sun long 

 after the loose snow has disappeared. We have a good 

 example of this amongst our Scottish mountains. In 

 many places the frozen half-melted snow is permanent; 

 and were the climate from any cause to become 

 deteriorated its amount would yearly increase. In 

 fact, it might go on increasing till not only all our 

 Highlands but the greater part of the surface of 

 Scotland might be covered with ice, long before the 

 snow-line had descended below the level of the summit 

 of Ben Nevis. 



