1863. J JA3IIES0X PARALLEL ROADS OF GLEX ROY. 243 



good-sized stream. It is now overgrown with swampy turf, which 

 hides the nature of the bottom. It is interesting to observe that a 

 large old delta occurs at the mouth of the Rough Burn at a level 

 corresponding with the lowest of the Parallel Roads ; the top of the 

 delta rising, however, above the line which marks the west side of it. 

 This third or lowest of the Parallel Roads of Glen Roy extends 

 into the valley of the Spean, and, passing the old delta just men- 

 tioned, seems to have stretched eastward beyond Loch Laggan to a 

 place called Makoul, where the watershed occurs that divides the 

 basin of the Spean from that of the Spey. Sir Thomas Lauder- Dick 

 first showed the connexion of the line with this watershed, pointing 

 out that here must have been the outfall for the water of the old 

 lake, when it stood at the height of the lowest Parallel Road. This 

 conjecture appears to be perfectly correct. Owing to the broken, 

 rocky nature of the ground, the line can only be traced faintly here 

 and there. Nevertheless we have this large delta at the mouth of 

 the Rough Burn. There is also another of far greater size at the 

 west end of Loch Laggan, where the entrance, of the Gulban River 

 had formerly been. This is the largest of all the deltas. It is a 

 wide- spreading mass of silt and gravel, the front of it rising about 

 twenty feet above the surface of Loch Laggan, but it slopes gradu- 

 ally backwards to a height of about fifty feet. These two deltas, 

 together with other traces, afford good evidence that a lake had filled 

 all this part of the Spean valley to the height of the lowest Glen 

 Roy line. It further appears, from levellings executed for other 

 purposes by the Ordnance Survey, that the altitude of the water- 

 shed near Makoul corresponds with that of this line. There is no 

 reason then to doubt that this was the outlet of the lake when it 

 stood at the lowest Parallel Road. Xow, when we come to examine 

 this spot, we find evidence of a large stream having flowed out there. 

 Some low rocks of gneiss, sprinkled with birches, occupy the hollow 

 bordered by a steep hill on the north side. These crags have been 

 ice-worn at a former period, as can still be perceived, but the traces 

 of subsequent water-action are unmistakeable at a level correspond- 

 ing with what had been the old outlet of the lake. The glacial 

 markings are effaced, and the rock worn into smooth, sinuous curves, 

 with something like incipient pot-holes. These water-worn ledges 

 are strewed with well-rounded balls of stone, as large as cocoa-nuts 

 — the mullers that had ground the rocky surface — lying just where 

 the eddy had left them ; and, in the recesses and sheltered bends to 

 the east or lee side of the crags, large heaps of pebbles, intensely 

 water-rolled, afford good proof that a strong brawling current had 

 long gone out here. On ascending the knolls of gneiss above the 

 level of the old outflow, these appearances vanish. No water- 

 rolled pebbles are to be seen, no washed gravel, no water-worn 

 rocks, no tendency to pot-holing, but merely a thin covering here 

 and there of coarse earth with angular bits of stone. Had this 

 watery action been due to the sea, it would not have been confined to 

 the level I have mentioned, but would have extended, at least during 

 the period of the two higher lines, to a greater elevation. 



