288 pRocEEDiNas OP THE GEOLOGICAL SOCIETY, [May 12, 



have no hesitation in affirming that it would be a physical impos- 

 sibility for a river like the Roy to ilovp" over and down such decli- 

 vities and leave no notch behind. I have seen a stream which had 

 during a flood changed its course, cut out in a few days a channel 

 which centuries would fail to efface. In uncultivated ground such 

 inequalities of surface are very slowly obliterated. In such places 1500 

 or 1600 years of neglect have done little to efface the old Roman roads 

 or camps ; the still older British hill-circles and vitrified forts are still 

 distinctly marked ; and there is no reason to believe these river-beds 

 more perishable. The Glen-Roy lines are the best proof how dura- 

 ble such markings are in such conditions. In Glen Roy itself there 

 is much curious evidence both of the effects of river-action and the 

 durability of the marks it leaves. The delta-terraces formed where 

 the streams fell into the old bays on the level of the lines, as at the 

 entrance to Glen Turrit, were of course immediately cut into by the 

 rivers when laid dry by the retiring of the waters. Many of these 

 old watercourses, which had been cut out by the Turrit and other 

 streams before they finally settled down into their present beds, are 

 still easily seen. Some of these are nearly as old as the line they 

 accompany, and older than the lower lines — and thus prove that there 

 has been no surface-change here sufficient to obliterate the former 

 river- channels, had they ever existed. 



I might now leave the question to be decided on the evidence ad- 

 duced ; but tbere are a few other facts corroborating the same views 

 that may be mentioned. And first, though these lines are in some 

 respects unique in character, there are other indications of the 

 former presence of the sea in this region. Thus in the valley of 

 the Spean there is, as it were, a continuous series of terraces con- 

 tinuing the lines at intervals down to the sea-level. Such wide 

 terraces, or shingle beaches, are well seen along the Spean from Roy 

 Bridge downwards. Another similar terrace is seen at the mouth 

 of Loch Treig on the level of the third or lower line. The sea has 

 stood here for a long period, as the hills above this sheet of detritus 

 are washed very bare, and in some places a well-marked shore-cliff 

 has been cut immediately above it. The detritus here, however, 

 has not come down Loch Treig, as might at first sight be imagined, 

 but from the Corry Laire to the west, and has then been swept 

 eastwards by the tidal currents, and even up into Loch Treig, on 

 which it abuts with a bold, almost vertical end. In many other 

 places in this part of Glen Spean there is similar evidence of a cur- 

 rent from the west flowing up the valley. Thus the lower or western 

 sides of the knolls and rocks are bare, and the detritus accumulated in 

 long mounds or tails behind (that is, above them) to the east. This 

 could not have occurred in an inland lake, wheie there are no currents, 

 but must have taken place in a marine channel open from sea to sea. 



Further, there is a vast amount of evidence of the former pre- 

 sence of the sea at various levels between the upper and lower 

 Glen-Roy lines in all the surrounding region. This evidence also 

 is specially distinct in the valley of the Spey, and thus on the other 

 side of the watershed and in the very valleys into which the lakes 



