DRAINAGE SYSTEMS AND THE GLACIAL PERIOD. 239 



The evidence first regarded by scientific men to be 

 demonstrative of the formation of extensive lakes durino- 



o 



the Glacial period by the direct influence of ice-dams 

 exists in the Parallel Roads of Glen Roy in Scotland. 



Fig. 62.— Parallel roads of Glen Eoy. 



According to the description of Sir Charles Lyell, 

 " Glen Roy is situated in the western Highlands, about 

 ten miles north of Fort William, near the western end of 

 the great glen of Scotland, or Caledonian Canal, and near 

 the foot of the highest of the Grampians, Ben Nevis. 

 Throughout nearly its whole length, a distance of more 

 than ten miles, three parallel roads or shelves are traced 

 along the steep sides of the mountains, each maintaining 

 a perfect horizontality, and continuing at exactly the same 

 level on the opposite sides of the glen. Seen at a distance 

 they appear like ledges, or roads, cut artificially out of the 

 sides of the hills; but when we are upon them, we can 

 scarcely recognize their existence, so uneven is their sur- 



