THE PARALLEL ROADS OF GLEN ROY 239 



The streams from the mountains right and left of Glen 

 Gluoy would pour their waters into that glen, forming 

 a lake, the level of which would be determined by the 

 height of the col at A, 1,170 feet above the sea. Over 

 this col tbe water would flow into Glen Roy. But in Glen 

 Roy it could not rise higher than 1,150 feet, the height 

 of the col at B, over which it would flow into Glen 

 Spey. 



The water halting at these levels for a sufficient time 

 would form the single road in Glen Gluoy and the highest 

 road in Glen Roy. This state of things would continue 

 as long as the ice dam was sufficiently high to dominate 

 the cols at A and b; but when through change of climate 

 the gradually sinking dam reached, in succession, the 

 levels of these cols, the water would then begin to flow 

 over the dam instead of over the cols. Let us suppose 

 the wasting of the ice to continue until a connection was 

 established between Glen Roy and Glen Glaster, a com- 

 mon lake would then fill both these glens, the level of 

 which would be determined by that of the col c, over 

 which the water would pour for an indefinite period into 

 Glen Spean. During this period the second Glen Roy 

 road and the highest road of Glen Glaster would be 

 formed. The ice subsiding still further, a connection 

 would eventually be established between Glen Roy, Glen 

 Glaster, and the upper part of Glen Spean. A common 

 lake would fill all three glens, the level of which would 

 be that of the col D, over which for an indefinite period 

 the lake would pour its water. During this period the 

 lowest Glen Roy road, which is common also to Glen 

 Glaster and Glen Spean, would be formed. Finally, on 

 the disappearance of the ice from the lower part of Glen 



