56 Mr Thomson on the Parallel lioads of Lochaber. 



channel, but a portion of it will flow in the opposite direction, 

 apparently up hill, till its surface comes to meet the bottom 

 of the channel at a level little, if at all, below the surface of 

 the mud at the side entrance. 



In confirmation of the views just brought forward, regard- 

 ing the possible horizontal extension of the glaciers, I may 

 refer to the evidence given by Professor Forbes, in his " Tra- 

 vels in the Alps" (page 50), of immense erratic blocks having 

 been conveyed by glaciers from the main chain of the Alps 

 across all the inequalities of the great plain of Switzerland, 

 and deposited high on the hills round the Lake of Neufchatel ; 

 the total distance travelled over being 60 or 70 miles, and 

 the total declivity due to their descent being certainly not 

 more than 1° 8', and probably not half so much. 



Glen Gluoy, in regard to its blockage, seems to have been 

 quite independent of all the other glens to which I have as 

 yet alluded. A glacier occupying the present site of Loch 

 Lochy, and receiving supplies from the various neighbouring 

 mountains, would appear to aff'ord a sufficient explanation of 

 the phenomena observed in this glen. Mr Milne has, how- 

 ever, discovered in it a shelf which is lower than the one pre- 

 viously known, and which does not appear to be in connection 

 with any summit-level. If this be the case, we may suppose 

 that, while the lake was at the level of this second shelf, its 

 discharge took place by the present mouth of the glen, thx'ough 

 an elevated channel in the moraine of the glacier. The lake 

 would therefore have resembled almost exactly the Lac de 

 Combal and the Matmark See, described and figured in the 

 work by Professor Forbes to which I have already referred. 

 (Pp. 193 and 345.) 



There is, however, a circumstance connected with this shelf 

 which seems to me to involve some difficulty. As represented 

 by Mr Milne, its terminations, on both sides of the glen, are 

 farther from the mouth of the glen than those of the shelf 

 above. In fact, the upper shelf is shewn round the sides of 

 Glen Fintec, while the lower shelf is made to stop short with- 

 out reaching the entrance to that glen. Should this repre- 

 sentation be really correct, it would appear to involve the 

 supposition, that the glacier, when at the lower level, pene- 



