Dr. Mac Culloch on the Parallel Roads of Glen Roy. 335 



side, which according to my information extends far towards the 

 bottom of the glen, and is therefore continuous with that one which 

 I examined from its mouth. The principal question with regard 

 to this line is, whether it corresponds with the uppermost or with 

 the second of Glen Roy. I attempted to determine it by the spirit 

 level and by the barometer. The former observations were so 

 much impeded by the weather that I am unwilling to place any 

 reliance on them, since the vertical difference of these two lines 

 being little more than 80 feet, considerable nicety would be re- 

 quired in carrying on the levels. From the barometric observations 

 it appears that the difference of level between this upper line of 

 Glen Gloy and that of Glen Roy is only 12 feet, a difference that 

 may fairly be attributed to errors of observation. It is probable 

 therefore that these two are on the same level, while there seems 

 abundant reason to conclude, from the general similarity of pro- 

 portion between the intervals of those in Glen Gloy and those in 

 Glen Roy, that the former have originated from the same cause as 

 the latter, and admit of the same general train of reasoning which 

 will hereafter be applied to these. If any doubt should remain, in 

 consequence of the want of more positive evidence, it must be 

 remembered that the lines of Glen Roy have been shown to enter 

 Glen Spean, and also to be prolonged through the common wide 

 valley in which both these rivers terminate ; that the situation of 

 Glen Gloy is by the intervention of Glen Lochy analogous to that 

 which Glen Roy holds to the common valley of the Spean and 

 Roy ; and that on a calculation of chances it is almost infinitely 

 improbable, that the apparently corresponding proportions of the 

 three lines of Glen Gloy are not actually corresponding, and suf- 

 ficient to prove, if not a former continuity between the levels of 

 the different vallies, at least a common cause for all. 



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