Dr. Mac Culloch on the Parallel Roads of Glen Roy. 361 



on Glen Spean and Glen Gloy. If the solitary line of Glen Spean 

 was produced by the action of a current, it is difficult to conceive 

 that of the three separate lines marked in Glen Roy by one common 

 to both glens, only a portion of the lowest, and that for a short 

 space, should be visible in Glen Spean. 



The case of Glen Gloy is still more difficult. I have shown that 

 the head of this valley, by which it communicates with Glen Roy, 

 is obstructed by such a rise as to exclude a free communication at 

 this junction, of the whole of the lines of the latter. No current 

 could therefore pass from Glen Roy into Glen Gloy, since its bot- 

 tom, as I have also shown, is of ancient and hard rock, not a recent 

 formation. If then there was a current common to both these 

 vallies, the communication must have been formed by the opening 

 of Glen Gloy through the intervention of Loch Lochy. A stream 

 of water must therefore have run from a point where it had either 

 a free exit, or at least a wide space in which to diffuse itself, to 

 one whence there was no exit, and with a velocity as great in the 

 most difficult as in the most easy circumstances, since the lines of 

 Glen Gloy, wherever they exist, are at least as deeply impressed as 

 those of Glen Roy. 



The last inquiry to be made on the supposition that these lines 

 are the consequences of a deluge, is, into the origin of the water 

 which flowed through the valley, a subject on which I was com- 

 pelled in some measure to enter at the beginning of this argument, 

 but of which the whole difficulty could not be appreciated without 

 including Loch Laggan in the investigation ; a tract of which the 

 importance could not then have been so readily understood. The 

 views which I have formerly given of the level of this lake, and of 

 that of Glen Spean, show that this supposed point must be removed 

 far to the eastward, without which the waters could not have flowed 



