376 Dr. Mac Cull och on the Parallel Roads of Glen Roy. 



the purpose of confining the waters in this direction. If this were 

 a mass of alluvial matter occupying the strath in which the junction 

 of the Spey and Truim takes place, it is not difficult to conceive that 

 it was gradually worn down by the action of the waters of the Spey, 

 causing the drainage of the highest level in Glen Roy ; or else after 

 that drainage had taken place by the failure of some other barrier. 

 The flow of the Spey and of the Roy would then follow the directions 

 of the intermediate ground, and the present courses of these rivers, as 

 far as they were then free, would be established. If we now turn our 

 attention to the western side of Glen Roy, and examine the elevation 

 and direction of the ground at its junction with the vale of the Lochy, 

 we shall see that both Glen Roy and Glen Spean bear one common 

 water mark or'line, and unite into a common wide valley before they 

 join the vale of the Lochy. The imaginary barrier must therefore 

 be removed, at least to that part of this valley where the lines termi- 

 nate ; which is to a point beyond Teindrish. But I have shown 

 that the form of this ground, and the gradual dilatation of the 

 valley into that of the Lochy is such, that no barrier could have 

 existed here without occupying the whole present valley of the 

 Lochy. This barrier towards the sea, may therefore be removed 

 with considerable probability to some more distant point, a proba- 

 bility increased by considering the circumstances which attend Glen 

 Gloy. Although no direct continuation of level can be traced between 

 it and Glen Roy, as there is between the latter and Glen Spean, yet 

 I have shown that in both there are one or more lines at the same 

 probable altitude, and that the condition of the upper junction of 

 these glens is such, that the communication could not have taken 

 place at that point. If also we suppose that Glen Gloy was dammed 

 by a barrier of its own, independently of that which occupied the 

 common opening of Glen Roy and Glen Spean, we multiply our 



