Mr Thomson on the Parallel Roads of Lochaber. 57 



trated farther into Glen Gluoy than it did when at the higher 

 level. Now the question arises, — Is it likely that this could 

 have been the case ? Perhaps light may be thrown on the 

 subject by some curious circumstances connected with the 

 Lac de Combal. The glacier which occasions the damming 

 up of this lake has actually retired a considerable way down 

 the glen in which the lake is situated, since the deposition of 

 that part of its moraine which now retains the water ; and 

 yet the surface of the glacier is some hundreds of feet higher 

 than that of the lake. Besides this, the glacier, at a point 

 farther from the head of the glen, threatens to overwhelm 

 with its moraine the channel of the river by which the super- 

 fluous water of the lake is at present discharged. How immi- 

 nent the prospect of this occurrence really is, may be judged 

 from the fact, that it is necessary annually to remove the 

 debris thrown down by the glacier on the road which, toge- 

 ther with the river, winds through the bottom of a deep 

 ravine, enclosed on the one side by the moraine of the glacier, 

 and on the other by the continuation of the hill which forms 

 a side of the glen containing the lake. Should the glacier 

 force itself even a very little farther in this direction, the 

 surface of the lake would not only be raised above its present 

 level, but its horizontal extension towards the lower part of 

 the glen would be increased. The beach of the lake at pre- 

 sent existing, together with that of the new one thus formed, 

 would therefore exhibit exactly the peculiarities which, ac- 

 cording to the representation of Mr Milne, appear to exist in 

 the two shelves of Glen Gluoy. This fact is enough to make 

 the difficulty appear to be not insuperable. The simplest 

 view, however, to take of the subject may, perhaps, be to 

 suppose that the glacier which occasioned the formation of 

 the higher of the Glen Gluoy shelves, had at some period 

 protruded a terminal moraine as far up the glen as the 

 terminations of the lower shelf; that on the final retiring 

 of the glacier this old moraine served as a barrier to dam 

 up the water to the level of the lower shelf, and that it 

 has been subsequently washed away by the river flowing 

 over it. 



I have thought it right to point out the foregoing difficulty 



