1863.] JAMIESON PARALLEL ROADS OF GLEN ROY. 237 



§ 2. The different Theories. 



a. General review of the theories. — It was scarcely possible in the 

 first examination of such a subject to escape errors, and some of 

 those Dr. Macculloch fell into greatly enhanced the difficulty at- 

 tending it, so that although both an able geologist and an acute 

 reason er, and believing a lake to be the cause, yet he found himself 

 quite baffled to account for either its existence or disappearance. 

 Sir Thomas Lauder-Dick, himself a very excellent observer, and 

 aided by the local knowledge of Mr. Macdonell of Insch, had made 

 a nearer approach to the true conditions of the problem, but was 

 unable to offer any more probable explanation as to how the lakes 

 were retained or emptied, than was to be got by supposing some 

 great displacements or dislocations of the adjoining district. But 

 there is not a jot of evidence that any such have taken place since 

 the period of these lakes. No fault has anywhere been detected in 

 the lines ; and they are so horizontal and undisturbed that, even apart 

 from many other objections, these circumstances alone are incom- 

 patible with the notion of great convulsions having rent the sur- 

 rounding district. 



Another theory is that which appeals to diluvial agency. A great 

 inundation, it has been said, flowing over the country from the west, 

 might have left these marks as it gradually subsided. This was Sir 

 George Mackenzie's idea* ; and very recently Mr. H.D. Rogers f, Pro- 

 fessor of Natural History in the University of Glasgow, has suggested 

 something similar, only that he thinks it was during the rise of this 

 great inundation that the thing was done. A great heave of the 

 Atlantic's bed might have sent a volume of water across Scotland, 

 and as it poured through the glens it might, it is said, have grooved 

 these lines on their sides. In support of this, Professor Rogers states 

 that the lines consist of deep grooves in the earthy covering of the 

 hills, and are most distinctly and deeply indented in the sides that 

 look down the valley, disappearing altogether in the recesses or 

 deeper corries that scollop the flanks of the mountains ; and, further, 

 that certain traces of what is called false bedding, or oblique lami- 

 nation, in the gravel-beds indicate a current flowing in the required 

 direction. 



So far, however, from the lines being faintest on the N.E. faces 

 of the hills, or being absent in the side recesses, it so happens that 

 these are often the places where they are most beautifully seen. 

 This is remarkably the case on the hill of Bohuntine, in the lower 

 part of Glen Roy, where all the three lines are strongly marked on 

 the N.E. face of the hill, the two upper vanishing entirely round 

 the other side, which looks down the valley. And in the side re- 

 cesses of Glen Turrit the shelves are as clearly seen as anywhere else. 

 Indeed, Professor Rogers seems to have overlooked the fact that, in 

 regard to the two lower lines, there is no outlet for this current at 

 the head of Glen Roy ; for, owing to the rise of the ground, they 



* Edin. Phil. Journ. January 1848. 



f Lecture before the Royal Institution. March 22, 1861. 



