Dr. Mac C'ulloch on the Parallel Roads of Glen Roy. 319 



Glen Roy, or the division between the upper and lower vallies, is 

 seen projecting at right angles to the right hand side of the glen, 

 and then turning westward so as to form a promontory parallel to 

 that side ; having a cul de sac on one hand and giving passage to 

 the river on the other. No line is visible on the rock itself, but 

 from its junction with the side of the valley (as the plan will show)* 

 the two lines commence, and are seen running on far along the 

 face of the hill, the uppermost one being precisely even with the 

 flat parts of the surface of the rock just described. It is proper 

 here to remark that the surface of this rock rises higher in some 

 places than that line, yet it is not marked by any corresponding 

 one. The drawings accompanying this paper will render intelli- 

 gible that which words alone cannot describe ; and I must here 

 premise once for all, that this minuteness of description, however 

 superfluous it may at first sight appear, is absolutely required, as 

 the circumstances thus dwelt on will be of essential use in investi- 

 gating the cause of the appearances under discussion. It is by an 

 attention to circumstances which at the first glance appear trivial, 

 that abstruse truths are often discovered ; and it is precisely where 

 leading and obvious phenomena offer no due to guide us, that a 

 ray of light will often be thrown on the subject from appearances 

 at first neglected. Had the greater features of Glen Roy been 

 capable of explaining the singular phenomena which it exhibits, 

 this paper would have perhaps been altogether superfluous, since 

 all observers would have been agreed respecting their causes. 



These level and parallel lines are scarcely to be seen in this place, 

 except by looking from .below upwards, a position by which they 

 are foreshortened to the spectator's eye. They may sometimes 



* Plate 18, 



2s 2 



