1872.] KICOL — P-IEALLEL EOADS OF GLEN ROY. 239 



known breakers, brought to the surface, there can be little doubt 

 that the sea-level would rise perceptibly both on the coast of 

 Caithness and among- the Orkney Islands. It must, however, be 

 remembered that I ascribe the roads not directly to this rise of the 

 sea-level, but to the virtual pause or halt it occasioned during the 

 uniform riso in the land. The duration of this halt would be 

 determined by the rapidity of the rise of the land, and the difference 

 between high and low tide. If the land rose, as in some parts of 

 Scandinavia, only three feet in a century, then the sea-level might 

 remain nearly permanent for the same or even a longer period. 

 But a very few years might suffice to form well-marked lines ; and 

 probably a more rapid rise might conduce to their preservation. 

 Might it not be possible, from the breadth of these roads, to esti- 

 mate the rate at which the land was rising during the time of their 

 formation ? 



There are a few special points that require to be noted when 

 applying this theory to the diiferent glens and roads. Glen Gloy is 

 very deep and narroAV near the top, but has a wide open mouth 

 towards Loch Lochy on the west. The pass at its head to Glen 

 Roy, though not broad, still bears a considerable proportion to the 

 dimensions of the glen, so that the height of the water would be 

 greatly affected by its being closed. In this glen there is no second 

 col to form another line ; and as it has no direct connexion with 

 Glen Eoy or Glen Spean, the changes in them did not influence it, 

 and the lower lines consequently do not appear in it. The line 

 seen is also more marked on the western than on the eastern side 

 of the glen, the latter having been more exposed to the open sea. 



Glen Hoy, again, has a wide, open mouth, and contracts gradually 

 towards the top. The pass there to Glen Spey has considerable 

 breadth and a flat horizontal bottom, so that by its being closed a 

 great outflow of water would be suddenly checked. The second 

 col in this valley, or that of Glen Glaister, lies so near the foot of 

 the glen that it might be thought that the shutting it would 

 produce little effect on the level of the western waters. But there 

 is another col almost on the same level on the south-west declivity 

 of Craig Dhu, where a small hill projects from it into Glen Spean, 

 greatly contracting the width of this latter glen (Spean). Hence 

 the second line continues further down Glen lioy than the first, and 

 is more distinct towards Glen Spean. The shutting of the Pass of 

 Maccoul would affect the level of the water both in Glen Spean and 

 Glen Eoy. Hence the greater extent of the third or lowest Glen- 

 Eoy line, both in that glen and in Glen Spean, where it stretches 

 from beyond Loch Laggan on the east, till it dies out on the de- 

 clivities of Ben Kevis, then washed by the open western sea. 



This view of the mode of origin of these parallel roads thus fully 

 meets the objections stated to the marine theory. The agreement 

 in level of the lines and cols is no mere chance coincidence, but the 

 direct result of existing conditions. The roads only occur in these 

 valleys and in particular portions of them because in these only 

 were the conditions essential to their formation found. Such valleys, 



