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Letter 3483F

Jamieson, T. F. to Darwin, C. R.

24 Mar 1862

    Summary Add

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    Writes with an important fact about the parallel roads of Glen Roy. The watershed at Makoul corresponds with the lowermost of the Glen Roy lines. Over a stretch of 20 miles from east to west the lowermost of the Glen Roy lines is near parallel with the present sea level.

Transcription

Ellon Aberdeensh.

24 March 1862

My Dear Sir,

I have just lighted upon what I consider an important fact with reference to the parallel roads of Glen Roy & wh. may probably interest you.

In the letter I wrote you after my return from Lochaber I think I mentioned that owing to the impossibility of tracing the lowermost line along the shores of Loch Laggan with any degree of certainty I felt somewhat in doubt as to the fact of the outlet at Makoul coinciding with that line— I afterwards wrote to both Mr. Chambers & Mr. Milne Home on the subject but failed to elicit anything certain on the subject.

I had however little doubt in my own mind that Loch Laggan had formerly discharged its waters E,ward by that channel from the circumstance of the great old delta of the Gulban which fills the S.W. corner of the lake & rises high above its present level.

—But by the greatest good fortune I find that the ordnance survey had run a line of spirit levelling up Glen Spean on to Dalwhinnie. and from the record of the engineers it appears that the water shed at Makoul just coincides with the lowermost of the Glen Roy lines— Thus, the height of said line found by the spirit levelling of an engineer employed for Mr. R. Chambers is 847 feet above the sea   it is not stated whether this refers to high water or mean sea level, but most of these surveyors usually take high water mark. and the summit level of the road at the water-shed of Makoul according to the Ordnance surveyors is 850 feet above the mean sea level.

—Now if the sea level taken by Mr. Chambers' surveyor was high water mark it wd. make the Glen Roy line up somewhat over 850 feet— something also would depend upon what part of the line the surveyor took as the line of terrace is generally several feet in vertical height.

Anyhow the coincidence is too close to be accidental—

I am inclined to think however that the level of the outflowing water at Makoul had been at one time fully 860 feet. judging from some measurements wh. I made of the height of the old delta at the S. W. corner of L. Laggan. & also from my remembrance of the beds of waterworn pebbles &c at the Makoul outlet wh. rise some feet I think above the summit level of the road. —Whether this is owing to some inequality in the level of the land that has occurred since the period of the Glen Roy roads—or whether it is owing to some discrepancy in the levellings I cannot say—

But I think it is evident that over a stretch of 20 miles from E. to W. this lowermost of the Glen Roy lines is wonderfully near if not altogether parallel to the present sea level, and I think there can be now very little doubt that it coincides with this outlet & has been determined by it.

If you think Sir C. Lyell wd. be interested in this communication I should feel much obliged if you wd. show it him as it wd. save me writing it over again.

I am | My dear Sir | Your very obed servt | Thos. F. Jamieson

C. Darwin Esq | F. R. S | &c &c &c

    Footnotes Add

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    f1 3483f.f1
    The so-called `parallel roads' of Glen Roy are three terraces that run parallel to one another along the sides of Glen Roy in Lochaber, Scotland. In the nineteenth century several attempts were made to account for their formation; in a paper published in 1839 (`Parallel roads of Glen Roy'), CD argued that the roads were the remains of beaches formed by the sea as the landmass of Scotland rose in graduated steps. By contrast, Jamieson believed that during a great `Ice Age' ice-flows trapped a series of lakes in the glen and that the roads represented the shorelines of three of these former lakes. M. J. S. Rudwick's account of what CD regarded as his `gigantic blunder' in relation to Glen Roy details the major explanations proposed during the first half of the nineteenth century to provide this celebrated phenomenon with a natural history (Rudwick 1974).
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    f2 3483f.f2
    See Correspondence vol. 9, letter from T. F. Jamieson, 3 September 1861. Loch Laggan is in Glen Spean, a glen adjacent to Glen Roy. The lowermost of the Glen Roy roads continues out of Glen Roy and around Glen Spean.
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    f3 3483f.f3
    Robert Chambers and David Milne-Home.
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    f4 3483f.f4
    Jamieson conducted an extensive correspondence with Charles Lyell on the subject of Glen Roy in 1861 (see Correspondence vol. 9, Appendix IX).
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