From Charles Lyell   [28–31 March 1862]1

My dear Darwin

I have had what is called the “Shingles” a troublesome though not serious complaint & which seems to come & go no one knows how or wherefore.

I was very glad to hear of you & envy you being so near out. I have printed more than half.2 Just as I got your letter I was upon Glen Roy & glad to get Jamieson’s last but I have got myself into a puzzle which I should be much indebted to you to help me out of as I suspect you will be able to do & make me wonder why I did not see the explanation before—3

Assuming ice-blockages, they may alter in height from year to year without that variation affecting the permanency of the level of the shelves because the level of each shelf is determined not by the height of the ice-dam, but by the “col” or parting ridge—

Now I perfectly understand that there may first have been a blockage which caused the lowest of all the shelves common to Glen Roy & Spean, then a separate ice-dam for Glen Roy which made the waters stand higher & escape over a higher “col”.

But how in one & the same Glen like Glen Roy could there be two shelves one above the other & coextensive caused by the blocking up by ice of the waters of the Roy? How can it happen that the lower of the two cols does not always prevent the water from rising to the level of the upper one?

Is there not this advantage in the marine theory over that of ice-blockages, that the sea sinking leaves the uppermost & thus the 2d. & then the 3d shelves & does not meddle with them any more, whereas in the glacier lake hypothesis the lowest shelf must be made first? & thus the water must rise without injuring the beach first made & afterwards sink again from the uppermost level & not damage the inferior ones as it goes down?

But this I could grant if my other difficulty were removed— If it be said that the two upper shelves of Glen Roy were caused the highest by a “col” & the 2d. by the ice-dam which was lowered I should have a difficulty in supposing a long permanent level due only to ice—4

Please return this note as if I have to write to Jamieson after getting your answer it may save me trouble as I shall be then on some quite different subject.

I have heard from your brother of your child’s illness & was very sorry for it—5

believe me | ever affecty yrs | Cha Lyell

1
Dated by the relationship to the letter to T. F. Jamieson, 27 March [1862] (Correspondence vol. 30, Supplement), and to the letter to Charles Lyell, 1 April [1862].
2
CD completed the manuscript of Orchids in February 1862, and thereafter spent some weeks correcting proofs (see letter to John Murray, 9 [February 1862], and letter to H. W. Bates, 27 February [1862]). Orchids was published on 15 May 1862 (Freeman 1977, p. 112). Lyell’s Antiquity of man (C. Lyell 1863a) was published on 6 February 1863 (C. Lyell 1863b, p. vii).
3
CD’s letter to Lyell has not been found; with it was apparently forwarded the letter from T. F. Jamieson, 24 March 1862. Lyell refers to the so-called ‘parallel roads’ of Glen Roy, a series of parallel terraces running along the sides of a glen in Lochaber, Scotland. Thomas Francis Jamieson had visited the area in August 1861, since which time, CD, Jamieson, and Lyell had pursued a three-way correspondence discussing the various theories about the formation of the roads (see Correspondence vol. 9). Lyell discussed Glen Roy in C. Lyell 1863a, pp. 252–64.
4
There were a variety of competing explanations of the origin of the parallel roads of Glen Roy. The first published geological accounts postulated that the roads were the shorelines of a former lake impounded by debris. In a paper on the phenomena, published in 1839 (‘Parallel roads of Glen Roy’), CD argued that the roads were marine beaches formed during intervals in the rise of the landmass. Jamieson rejected CD’s marine theory and adopted the lake hypothesis, though invoking glaciers as the containing barriers rather than debris. For a detailed discussion of the various interpretations of Glen Roy, see Rudwick 1974.
5
Lyell refers to CD’s brother, Erasmus Alvey Darwin, and to CD’s youngest child, Horace Darwin, who had been ill since the beginning of the year (see letter to W. E. Darwin, 14 February [1862]).

Please cite as “DCP-LETT-3463,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-3463