Dr. Mac Culloch on the Parallel Roads of Glen Roy. 323 



for a certain space ; and as this rule is general, it is unnecessary 

 either to describe the spots or to mark the exceptions, but the fact 

 itself is important. They are often ploughed across or obliterated 

 by torrents obviously recent ; and they sometimes also terminate 

 abruptly in more ancient torrents ; but still the two upper ones 

 continue generally traceable and commonly very well marked : for 

 the rest I must again refer to the plan.* From these appearances 

 we can often ascertain the relative difference of age between the 

 hollow or torrent and the line : and we can also in some cases dis- 

 tinguish that a part of one hollow is prior and a part posterior to it. 

 It may be remarked generally that the lines are best marked on the 

 straightest sides, or on those slopes which lie in a straight or a 

 slightly curved plane, while they are most obscure where the most 

 numerous sinuosities, torrents, irregularities, or rocky faces occur. 

 Among the best marked are the two uppermost ones on the right 

 hand above Glen Turit, one of those at the head of Glen Turit, and 

 the three above Glen Fintec on the same side. About two miles below 

 the head of lower Glen Roy, a semi-circular cory or hollow opens 

 on the right, giving rise to a considerable stream and falling gra- 

 dually into Glen Turit. The two upper lines (for as yet there are 

 no more) enter it a little way and then disappear. On its opposite side, 

 or that which adjoins to Glen Turit, appear three marks offering 

 the only considerable anomaly in the whole course of these lines. 

 The two uppermost, which on a superficial view seem to be the con- 

 tinuation of the two before described, will be found more distant 

 from each other than these, and on applying the spirit level to 

 them it is seen that the lowest is continuous with the upper one of 

 Glen Roy, but that the highest is a supernumerary one, although 

 of the same apparent dimension and form, and that it terminates 



* Plate 18. 



