THE PARALLEL ROADS OF GLEN ROT 235 



latent heat, did these winds touch the hills north of the 

 glen. 



An instructive observation bearing upon this point is 

 here to be noted. Had our visit been in the winter we 

 should have found all the mountains covered: had it been 

 in the summer we should have found the snow all gone. 

 But happily it was at a season when the aspect of the 

 mountains north and south of Glen Spean exhibited their 

 relative powers as snow collectors. Scanning the former 

 hills from many points of view, we were hardly able to 

 detect a fleck of snow, while heavy swaths and patches 

 loaded the latter. Were the glacial epoch to return, the 

 relation indicated by this observation would cause Grlen 

 Spean to be filled with glaciers from the south, while the 

 hills and valleys on the north, visited by warmer and drier 

 winds, would remain comparatively free from ice. This 

 flow from the south would be reinforced from the west, 

 and as long as the supply was in excess of the consump- 

 tion the glaciers would extend, the dams which closed the 

 glens increasing in height. By and by supply and con- 

 sumption becoming approximately equal, the height of the 

 glacier barriers would remain constant. Then, if milder 

 weather set in, consumption would be in excess, a lower- 

 ing of the barriers and a retreat of the ice being the conse- 

 quence. But for a long time the conflict between supply 

 and consumption would continue, retarding indefinitely the 

 disappearance of the barriers, and keeping the imprisoned 

 lakes in the northern glens. But however slow its retreat, 

 the ice in the long run would be forced to yield. The 

 dam at the mouth of Glen Roy, which probably entered 

 the glen sufiiciently far to block up Glen Glaster, would 

 gradually retreat. Glen Glaster and its col being opened, 



