skip to content

Darwin Correspondence Project

To Charles Lyell   1 April [1862]1


April 1st

My dear Lyell.

I am not quite sure that I understand your difficulty, so I must give what seems to me the explanation of the glacial-lake-theory at some little length.2 You know that there is a rocky outlet at the level of all the shelves.— Please look at my map:3 I suppose whole valley of Glen Spean filled with ice; then water would escape from outlet at Loch Spey & the highest shelf would be first formed. Secondly ice began to retreat, & water would flow for short time over its surface; but as soon as it retreated from behind hill marked Craig Dhu, where the outlet on level of 2d shelf was discovered by Milne, the water would flow from it, & the second shelf would be formed.4 This supposes that a vast barrier of ice still remains, under Ben Nevis, along all the lower part of the Spean. Lastly I suppose the ice disappeared, everywhere along L. Laggan, L Treig & Glen Spean, except close under Ben Nevis, where it still formed a Barrier, the water flowing out at level of lowest Shelf, by the pass of Muckul at head of L. Laggan.— This seems to me to account for everything. It presupposes that the shelves were formed towards close of Glacial period.—

I come up to London to read on Thursday short paper at Linn. Soc.y 5 Shall I call on Friday morning at 912 & sit half an hour with you? Pray have no scruple to send a line to Q. Anne St to say “no”—if it will take anything out of you.—6 If I do not hear, I will come.—

Yours affect | C. Darwin


The year is established by the reference to CD’s reading a paper at the Linnean Society (see n. 5, below).
CD refers to the map accompanying his paper, ‘Parallel roads of Glen Roy’.
Milne 1849, p. 398.
CD read his paper, ‘Three sexual forms of Catasetum tridentatum, before the Linnean Society of London on 3 April 1862 (Journal of the Proceedings of the Linnean Society of London (Botany) 6: lxiv). According to Emma Darwin’s diary (DAR 242), CD left for London on Wednesday 2 April and returned home on Friday 4 April 1862.
CD’s brother Erasmus Alvey Darwin lived at 6 Queen Anne Street, London.


‘Parallel roads of Glen Roy’: Observations on the parallel roads of Glen Roy, and of other parts of Lochaber in Scotland, with an attempt to prove that they are of marine origin. By Charles Darwin. [Read 7 February 1839.] Philosophical Transactions of the Royal Society of London 129: 39–81. [Shorter publications, pp. 50–88.]

‘Three sexual forms of Catasetum tridentatum’: On the three remarkable sexual forms of Catasetum tridentatum, an orchid in the possession of the Linnean Society. By Charles Darwin. [Read 3 April 1862.] Journal of the Proceedings of the Linnean Society (Botany) 6 (1862): 151–7. [Collected papers 2: 63–70.]


Explains how melting of ice in Glen Spean could have successively freed two lower cols, thus establishing the water-levels that determined the two lower shelves in Glen Roy.

Plans to read a paper to the Linnean Society ["Sexual forms of Catasetum", Collected papers 2: 63–70].

Letter details

Letter no.
Charles Robert Darwin
Charles Lyell, 1st baronet
Sent from
Source of text
American Philosophical Society (Mss.B.D25.275)
Physical description
ALS 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 3491,” accessed on 2 March 2024,

Also published in The Correspondence of Charles Darwin, vol. 10