Dr. Mac Culloch on the Parallel Roads of Glen Roy. 321 



which these two lie. It is here necessary to say that the two lines 

 on the right now described are parallel to each other, and corre- 

 spond precisely in level with the fragments of the two upper ones 

 visible on the opposite side. 



As we proceed down the glen a river is seen entering at the left 

 hand equal in size to the Roy, and falling into it by a cascade which 

 rushes over a rocky bed. Here a great series of terraces is found, 

 forming a large terreplein at the top of this glen which I have 

 called lower Glen Roy. These terraces are of different levels, as 

 may be seen both in the section* and in the views that accompany 

 this paper, j" The highest of them will hereafter be proved to lie on 

 a level with a third line, to be described in the course of this in- 

 vestigation. It falls off however by many successive stages of 

 terraces, and numerous smaller ones are also to be seen descending 

 down to the very bed of the river, skirting its banks and accom- 

 panying its course. The bottom of the glen is here an alluvial flat, 

 as the above mentioned section will show. Between the two upper 

 lines on the right hand an intermediate one now becomes visible 

 for a space of about half a mile: I did not measure it, but to the eye 

 it appears equidistant from both. At this point the two lines now 

 described suddenly quit the rocky face described on the right hand, 

 and continue their courses along the alluvial slopes of the declivities 

 which follow; where also they acquire their greatest breadth and 

 distinctness. 



I forbear giving the breadths in all the places where I measured 

 them, because it is not important. The profiles will show the 

 principal varieties.^ In detailing their measures I must remark that 

 it would be impossible to describe the precise geographical point 

 measured, and such often is the curvature at the entering and salient 



* Sect. L, Plate 21. + Plate 14> 15. J Plate 18. 



