Discusses David Milne's Glen Roy paper ["On the parallel roads of Lochaber", Trans. R. Soc. Edinburgh 16 (1849): 395–418]. Rejects Milne's theory that outlet of Glen Roy is blocked by detritus. Impressed by Milne's discovery of an outlet at the level of the second shelf. Believes this strengthens theory that lakes were formed by glacier blocking Glen Roy. Offers arguments against glacier theory.
Down Farnborough Kent
My dear Lyell
Many thanks for the Paper. I do admire your zeal on a subject
on which you are not immediately at work. I will give my opinion as briefly as I can
& I have endeavoured my best to be honest. Poor M
Imprimis, it is provoking that M
Now for business,—I utterly disbelieve in the barriers for his lakes
& think he has left that point exactly where it was in the time of Macculloch
& Dick. Indeed in showing that there is a passage at
Glen Glaster at the level of the intermediate shelf he makes the difficulty to my mind
greater. When I think of the gradual manner in which the 2 upper terraces die
out at Glen Collarig, & at mouth of Glen Roy—the smooth rounded form
of the hills there,—the lower shelf retaining its usual width where the
immense barrier stood; I can deliberately repeat
“that more convincing proofs of the non existence of the imaginary Loch Roy
could scarcely have been invented with full play given to the imagination.”
&c But I do not adhere to this remark with such
strength, when applied to the Glacier lake theory: oddly I
never was at all staggered by this theory, until now having read M
There are three chiefly hostile considerations in M
This leads me to M
Thirdly: the nature of the outlets from the supposed lakes: this appears to me
the best & newest part of the paper. If Sir James Clark would like to attend to any particular points, direct his attention to this;
especially to follow Glen Glastig from Glen Roy to L. Laggan. M
With respect to the very remarkable coincidence between the shelves & the
outlets (rendered more remarkable by M
I look at the pass of Muckul (21 ft deep, Milne) as a channel just kept open, & the head of Glen Roy (where there is a great Bay silted up) & of Kilfinnin, (at both which places, there are level-topped mounds of detritus above the level of the terraces) as instances of channels filled up at the stationary levels. I have long thought it a probable conjecture, that when a rising surface becomes stationary, it becomes so not at once, but by the movements first becoming very slow: this would greatly favour the cutting down many gaps in the mountains to the level of the stationary periods.—
Glacial Theory.— If a glacialist admitted that the Sea before the
formation of the terraces covered the country (which would account for
“land-straits” above level of terraces) & that
the land gradually emerged; & if he supposed his lakes were banked by
ice alone, he would make out, in my opinion, the best case against the marine origin of
the terraces. From the scattered boulders & till, you & I must
look at it as certain that the sea did cover the whole country; & I abide quite
by my arguments from the buttresses &c &c
that water of some kind receded slowly from the valleys of Lochaber (I presume
I fear I must have wearied you with the length of this letter, which I have not had
time to arrange properly.— I could argue at great length against
Well, I enjoyed my trip to Glen Roy very much, but it was time thrown away: I heartily
wish you would go there: it should be some one who knows glacier & iceberg
action & sea-action well: I wish the Queen would command you.— I had
intended being in London tomorrow, but one of my painful plagues will, I believe, stop
me; if I do I will assuredly call on you. I have not yet read M
Farewell, my dear Lyell, ever most truly yours C. Darwin
P.S. As you cannot want this letter, I wish you would return it me, as it will
serve as a memorandum for me—possibly I shall write to M
- f1 1116.f1The date is based on the assumption that the paper CD refers to in the letter is Milne 1847b. CD received a copy of Milne 1847b in September. See letter from Robert Chambers to David Milne, 7 September 1847, in which CD is referred to as being anxious to obtain a copy.
- f2 1116.f2Milne 1847b. The page references in the letter correspond to those of the privately printed memoir on the parallel roads of Lochaber. An annotated copy is in DAR 139: 5. References in the notes below are to Milne 1849, the version published in the Transactions of the Royal Society of Edinburgh.
- f3 1116.f3Because of Lyell's poor eyesight, his wife Mary Elizabeth frequently read to him. This letter was apparently returned to CD, as requested in the postscript, but a copy of it was also made by an unknown amanuensis, presumably for Lyell to retain. The copy is preserved among the letters to Lyell at the American Philosophical Society (APS 68).
- f4 1116.f4In the original letter CD wrote ‘Glen Roy’, with ‘p. 13.’ interlined after ‘Glen’ and ‘& Spean’ interlined after ‘Roy’. This text is followed in the copy. Later, apparently, CD deleted ‘Roy’ and the ampersand, so that the text then read ‘Glen p. 13. Spean’. However, Milne referred only to Glen Roy on page thirteen, so it appears that CD deleted ‘Roy’ and the ampersand by mistake. The deletion is ignored in the copy. In his discussion of Milne's paper CD followed a list of rough notes and comments he had made as he read it. These notes, together with a large number of others, some of which are labelled ‘Glen Roy scraps’, are preserved in DAR 50 (ser. 3): 7–30.
- f5 1116.f5In ‘Observations on the parallel roads of Glen Roy’ CD stated that the marine theory of the origin of the roads ‘appears to me demonstrated’ (Collected papers 1: 118). Milne, in his paper, regretted that CD ‘should have expressed himself in these very decided and confident terms, especially as his survey was incomplete’ (Milne 1849, p. 400).
- f6 1116.f6MacCulloch 1817 and Dick 1823.
- f7 1116.f7CD alludes to the lack of any remnants of earthen barriers.
- f8 1116.f8Collected papers 1: 98.
- f9 1116.f9According to Louis Agassiz and William Buckland, the parallel roads were formed as a result of a glacier damming up the valley and forming a glacial lake, of which the roads were former beaches. See Agassiz 1840b, 1840c, and 1842b, pp. 237–40. CD rejected this theory mainly because of the absence of a known outlet for the lake, except over the glacier itself. CD could not accept the possibility that a glacier could have existed at a particular level long enough to create a ‘road’ without having been worn down by the waterflow over it. See Correspondence vol. 2, letter to Charles Lyell, [9 March 1841].
- f10 1116.f10The four figures were obtained by four different observers in Glen Gluoy and Glen Roy (see Milne 1849, p. 397). CD wrote ‘Glen luy’, but Milne's text makes clear that ‘Gluoy’ was intended.
- f11 1116.f11On the assumption that the roads were of marine origin, the height should have been the same. See Collected papers 1: 116 and Milne 1849, p. 401.
- f12 1116.f12Collected papers 1: 111–14.
- f13 1116.f13See Milne 1849, pp. 402, 414–17, and Collected papers 1: 111–13.
- f14 1116.f14Bravais 1845, in which Auguste Bravais stated the need for accurately measured levels of ancient coast lines, and described a method of measuring them based on present mean sea-levels, in turn determined by the upper range of littoral algae. He discussed the problems of measurement at Glen Roy (pp. 542–4). See also Milne 1849, p. 396, which refers to Bravais 1845.
- f15 1116.f15James Clark, physician to Queen Victoria and friend of Lyell, was probably accompanying the Royal family on their visit to a Highland lodge located on the shores of Loch Laggan, in the vicinity of Glen Roy and Glen Spean. The visit took place from 11 August to 17 September, see Annual Register 1847, Chronicle pp. 116–18.
- f16 1116.f16CD argued that icebergs floating in a narrow strait were capable of scraping and polishing the sea bottom. See Journal of researches, pp. 617–25.
- f17 1116.f17Milne 1849, p. 399; for his discussion of the river courses, see pp. 398–400. The Pass of Mukkull is at the eastern end of Glen Spean.
- f18 1116.f18Milne had discovered a col in adjacent Glen Glaster (not ‘Glastig’, as CD has it) at the level of Glen Roy's middle shelf. Earlier supporters of the lake hypothesis, as well as CD, had overlooked it. This discovery of a likely drainage point removed a powerful objection to the lake theory (see Milne 1849, p. 398).
- f19 1116.f19Collected papers 1: 115. CD's argument, which he hoped would render any coincidences of height between ‘roads’ and cols irrelevant, was that the cols were ‘land straits’, which emerged between branches of the sea as the land rose and which were maintained just at the level of the water through choking by littoral deposits.
- f20 1116.f20CD described Kilfinnin in Collected papers 1: 92, 132 n. 10. See also CD's map of the Glen Roy area, p. 87.
- f21 1116.f21CD observed that these ‘buttresses’ had been formed at various levels on the sides of the valley. Some of them were associated with, and formed extensions to, the shelves, while others were smaller and unconnected with any shelf. The buttresses were found along the courses of streamlets descending the valley, which led CD to conclude that they had been formed by the deposition of detritus when the descending stream met the edge of the lake filling the valley. If the water-level in the valley had stayed constant for a long period, both shelves and buttresses would have been formed; if it had remained at the same level for a shorter period then buttresses alone would have been formed. See Collected papers 1: 102–4.
- f22 1116.f22At this point (presumably after the letter was returned, see n. 3, above) CD added in pencil, ‘Have Lakes much more power with ice’.
- f23 1116.f23Louis Agassiz reported many evidences of glaciers at Glen Roy and neighbouring valleys, including polished rocks and moraine deposits (Agassiz 1842b, pp. 222, 236–9).
- f24 1116.f24Milne 1849, pp. 404–9.
- f25 1116.f25See South America, p. 24 n. CD described these ‘fiords’ as much shallower at their mouths than further inland. He attributed this to the accumulation of sediment formed by the wearing of the rocks exposed to the open sea. Such ‘sea channels’ resemble CD's conception of Glen Roy's ancient waterways, and this resemblance allowed CD to attribute any accumulation of detrital matter, such as those described by Milne (1849, p. 405), to the action of the sea.
- f26 1116.f26The last section of Milne 1847b is devoted to showing that Scotland ‘to the depth of at least 1200 feet, has been recently immersed in the ocean, and for a very long period’ (p. 25). Milne concluded, however, that if a survey revealed that raised beaches along the coasts of Scotland, Ireland, England, and France were continuous and horizontal, the cause of these and of the parallel roads would be changing levels of the ocean rather than of the land (p. 54).
- f27 1116.f27Letter to Robert Chambers, 11 September 1847.