To Robert Chambers1   11 September 1847

Extract from Letter from C. Darwin to R. Chambers 11 Sept 18472

I hope you will read the first part of my paper before you go (to Glen Roy)3 & attend to the manner in wh. the lines end in Glen Collarig.4 I wish Mr. Milne had read it more carefully. He misunderstands me in several respects, but suppose it is my own fault, for my Paper is most tediously written. Mr. Milne fights me very pleasantly & I plead Guilty to his rebuke about “demonstration”.5 I do not know what you will think: but Mr. Milne will think me as obstinate as a Pig, when I say, that I think any Barrier of Detritus at the mouth of Glen Roy, Collarig & Glastig6 more utterly impossible than words can express. I abide by all that I have written on that head—

Conceive such a mass of detritus havg been removed, without great projections being left on each side, in the very close proximity to every little delta7 preserved on the lines of the shelves, even on the Shelf 4, wh. now crosses with uniform Breadth, the spot where the Barrier stood with the Shelves dying gradually out &c. To my mind it is monstrous. Oddly enough, Mr. Milne’s description of the Mouth of Loch Treig (I do not believe that valley has been well examd in its upper end) leaves hardly a doubt that a Glacier descended from it,8 & if the Roads were formed by a Lake of any kind, I believe it must have been an Ice Lake. I have given in detail to Lyell my several reasons for not thinking Ice-lakes probable;9 but to my mind, they are incomparably more probable than detritus of rock barriers.

Have you ever attended to Glacier action? After having seen N. Wales, I can no more doubt the former existence of gigantic glaciers, than I can the Sun in the Heaven. I could distinguish in N. Wales to a certain extent Iceberg from Glacier Action—10 (Lyell has shown that Icebergs at the present day score rocks,)11 & I suspect that in Lochaber the two actions are united, & that the scored rock on the water sheds, when tideways, were rubbed & bumped by half stranded Icebergs. You will no doubt attend to Glen Glastig. Mr. Milne I think does not mention, whether Shelf 4 enters it,12 wh. I shd. like to know; & especially he does not state, whether rocks worn, on their upper faces, are found on the whole 212 vertical course of this Glen, down to near L. Laggan or whether only in the upper part:—nor does he state whether these rocks are scored, or polished, or moutonnés,13 or whether there are any “perched” Boulders there or elsewhere. I suspect it wd. be difficult to distinguish between a River Bed & Tidal channel. Mr. Milne’s description of the Pass of Mukkul expanding to a width of several hundred yards 21 feet deep, in the shoalest part, & with a worn Islet in the middle sounds to me much more like a tidal channel than a River Bed.14 There must have been in the latter view plenty of fresh water in those days.

With respect to the coincidence of the shelves with the now water sheds, Mr. Milne only gives half of my explanation Please read p 65 of my paper. I allude only to the head of Glen Roy & Kilfinnin as silted up. I did not know Mukkul Pass; & Glen Gluy15 was so much covered up, that I did not search it well as I was not able to walk very well. It has been an old conjectural belief of mine, that a rising surface, becomes stationary, not suddenly but by the movement becoming very slow. Now this would greatly aid the tidal currents cutting down the passes between the mountains just before & to the level of the stationary periods. The current in the fiords in T. del Fuego in a narrow crooked part are often most violent; in other parts ⁠⟨⁠    ⁠⟩⁠ they seem to silt up16

Shall you do any levelling?17 I believe all the levelling has been in Glen Roy, nearly parallel to the Great Glen of Scotld. For inequalities of elevation, the valley of the Spean, at right angles to the apparent axes of Elevation, wd. be the one to examine. If you go to the head of Glen Roy, attend to the apparent Shelf above the highest one in Glen Roy, lying on the South side of Loch Spey, & therefore beyond the Water shed of Glen Roy. It would be a crucial case.18 I was too unwell on that day, to examine it carefully, & I had no levelling Instrument. Do these fragments coincide in level with Glen Gluoy Shelf?

Macculloch talks of one in Glen Turret above the Shelf 1.19 I cd. not see it— These would be important discoveries. But I will write no more, & pray yr. forgiveness for this long ill written outpouring. I am very glad you keep to yr. subject of the terraces— I have lately observed, that you have one great authority (C. Prevost)20 that authority signifies a Getting)21 on yr. side respecting yr. heretical & damnable doctrine of the ocean falling.22 You see I am orthodox to the burning pitch—

1
A typed and edited copy of this letter, for ML 2: 177–80, is in DAR 143. It was evidently based on the handwritten copy used for the above transcription.
2
The date possibly reads ‘16 Sept 1847’.
3
Chambers made a second visit to Glen Roy in the autumn of 1847 (Chambers 1848, pp. 116–17).
4
CD claimed that the lines in Glen Collarig died out gradually (see ‘Observations on the parallel roads of Glen Roy’, Collected papers 1: 113). He concluded that the gradual disappearance of the lines was evidence for marine beaches rather than a lake shore, which presumably would terminate abruptly at a barrier. Chambers addressed this subject in Ancient sea margins, stating that the gradual disappearance of the lines presented the weakest point of David Milne’s argument for the lake theory. See Chambers 1848, pp. 112–13.
6
An error for Glen Glaster. It is likely that CD used the word ‘Glastig’ in his original letter, see letter to Charles Lyell, 8 [September 1847], n. 18, in which the same mistake occurs.
7
The reference is to CD’s ‘buttresses’, described in Collected papers 1: 102–4. See also letter to Charles Lyell, 8 [September 1847].
8
According to Milne, the rock at the outlet was ‘all smooth and rounded on the side facing the SW. or WSW’. He further noted many erratic boulders that had been carried there from the west (Milne 1849, pp. 412–13).
10
CD had visited North Wales in 1842; he published his observations, and his theory of combined glacial and iceberg activity, in ‘Notes on the effects produced by the ancient glaciers of Caernarvonshire’, Collected papers 1: 163–71.
11
See C. Lyell 1845, 2: 173–5. Lyell described a furrowed coastal ledge in Nova Scotia; a local resident told him that during the previous winter the bay had indeed been covered with a sheet of ice which the tides moved back and forth across the rocky ledge.
12
Milne 1849, p. 398. Milne in fact does state that shelf four enters Glen Glaster, at the head of which he discovered the col coincident in level with shelf three.
13
Roches moutonnées are rocks which have been subjected to glacial action and are rounded ‘like a sheep’s back’ (OED).
14
Milne 1849, p. 399. The pass of Mukkull is described as ‘the grandest exhibition of an ancient river-course’ in the area. See CD’s remarks on the subject in his letter to Charles Lyell, 8 [September 1847].
15
The transcription by Francis Darwin in ML 2: 177–80 is ‘Glen Roy’, but ‘Gluy’ in the handwritten copy is undoubtedly a misreading of ‘Gluoy’. CD had searched Glen Roy but did not enter Glen Gluoy.
17
According to Chambers (1848, p. 99), he requested a levelling survey to be made of Glen Roy. However, he does not make clear whether it was during his first or second visit to Glen Roy.
18
Shelves at separate heights in separate glens would represent strong evidence for independent lakes.
19
John MacCulloch described a ‘supernumerary’ line above the uppermost shelf within Glen Roy at the entrance to Glen Turret, but not extending into it (MacCulloch 1817, pp. 323–4). CD referred to the absence of this line in Collected papers 1: 134 n. 23.
20
Constant Prévost, professor of geology at Paris university, argued in Prévost 1840 that the sea level had fallen rather than that the land had been elevated.
21
In the typed copy of this letter used for ML, this sentence was edited by Francis Darwin to read: ‘I have lately observed, that you have one great authority, (C. Prevost) [not?] that authority signifies a [farthing?] on your side respecting your heretical and damnable doctrine of the Ocean falling.’ (ML 2: 180).
22
Chambers stated that, because of the uniformity and apparent correspondence of level of ancient sea beaches he had studied, he preferred a withdrawing sea to an upheaving earth (Chambers 1848, pp. 5–6).

Please cite as “DCP-LETT-1119,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-1119