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Darwin Correspondence Project

To Charles Lyell   21 April [1856]1

Down Bromley Kent

April 21st

My dear Lyell

Your case seems to me most perplexing;2 I have never seen or heard of anything like it, & have been puzzling my brains quite in vain. One thing I quite see & agree with you, that it is a strong argument against the angle of (say) 12o having been produced by upheavement, for it is manifestly impossible that the columns in a flat field of lava could have been all formed at angles inclined from the centre of the island, so as to become vertical when the beds were upturned 12o. The cause must (I shd. think) be connected with the lava not having absolutely ceased its downward tendency when the shrinking which produced the columns & fissures was first superinduced.

Would it not be worth while to ask Hopkins or some such man,3 whether in a body of very viscid matter just before all motion ceased, whether there could be any vertical sliding movement in closely approximate planes tending to make (not really making) steps like these; [DIAGRAM HERE] Lava Streams for if so I can well fancy such tendency might have guided the planes of division of the columns.— I know I have seen some columnar lava with columns directed in manner for which I could conceive no cause, but I cannot remember where.—

I have seen very narrow, very convex streams of lava, (which must have been very viscid) with the proper radiating columnar structure beautifuly displayed.— [DIAGRAM HERE]

Have I not read of Glaciers, coming down a very steep slope, breaking up into vertical steps?

Do make the local areas crowded with parallel dikes a prominent feature, though I daresay you are very wise & safe in allowing some central elevation of the whole. What a deal of interesting work your Madeira expedition has given you!4

Yours most truly | Ch. Darwin

I supposed you observed your facts in Madeira & not from drawings alone.— I have been drawing the angles on paper & in thin beds of lava, I shd. have thought the difference wd. not have been conspicuous; in thick beds it undoubtedly would

Has not Forbes,5 or Hopkins or some one given figure of some very viscid substance flowing down slope, with plane of division, something like this? — [DIAGRAM HERE] A A A A A A A A A A I have some vague idea I have seen such— The planes AA, if ever so obscure, might well guide the formation of adjoining columns, & then the rest of the columns.

The more I think the more inclined I am to think that some such view must be cause of your, as it seems to me very important & extraordinary fact.— The longitudinal planes of division in a lava-stream, could have no effect, I shd think, on the dip of the columns.—

Footnotes

Dated by the subject of the letter, a topic that was discussed during Lyell’s visit to Down House, 13–16 April 1856 (see n. 2, below).
Lyell had recently visited CD at Down House (Wilson ed. 1970, p. xliii). An unpublished letter from Lyell to Georg Hartung, dated 11 and 15 April 1856, indicates that Lyell and CD had discussed the geology of Madeira in great detail, with particular reference to the angle at which molten lava could solidify (the editors thank Lady Lyell and Leonard G. Wilson for this information). The point was crucial in the debate, at that time still continuing, between Lyell and Christian Leopold von Buch and Jean Baptiste Armand Louis Léonce Élie de Beaumont. Lyell held the view that volcanic cones were built up gradually, layer by layer, through the accumulated outpourings of lava, a theory proposed in detail in C. Lyell 1850; Leopold von Buch considered that lava could not solidify on slopes and that the beds must at first have been horizontal and only subsequently elevated and inclined. CD had discussed Lyell’s argument at length in 1849 (see Correspondence vol. 4, letter to Charles Lyell, [1 November 1849], and subsequent letters).
William Hopkins was an expert in mathematical geology (C. Smith 1989).
Charles and Mary Elizabeth Lyell, accompanied by Frances Joanna and Charles James Fox Bunbury, visited Madeira and the Canary Islands in the winter of 1853–4 to study the volcanic phenomena of the islands. Some of the results of Lyell’s observations were incorporated into the fifth edition of his Manual (C. Lyell 1855, pp. 515–22). The paper on the volcanic geology of Madeira and the Canaries, which Lyell and Georg Hartung were preparing, was ultimately abandoned. Lyell discussed the question, in part, in C. Lyell 1858. Hartung later published, with Lyell’s permission, the results of their work (Hartung 1864).
James David Forbes had analysed the physical properties of glaciers in 1845 and considered that they moved primarily though acting as a viscous mass. CD had corresponded with him about the similarity of movement in glaciers and lava (see Correspondence vol. 3, letters to J. D. Forbes, 11 October [1844] and [November? 1844]). Forbes was at that time engaged in a bitter controversy with William Hopkins, who had opposed the viscous theory with his own theory of motion based on sliding. CD’s reference in the letter indicates that he meant Forbes’s work rather than Hopkins’s (C. Smith 1989). There are several diagrams similar to the one in this letter in J. D. Forbes 1845, pp. 368–436.

Summary

Speculates about cause of inclination in unusual columns of lava. Suggests CL check with William Hopkins about sliding movements in viscid matter.

Comments on CL’s expedition to Madeira.

Letter details

Letter no.
DCP-LETT-1855
From
Charles Robert Darwin
To
Charles Lyell, 1st baronet
Sent from
Down
Source of text
American Philosophical Society (Mss.B.D25.126)
Physical description
8pp

Please cite as

Darwin Correspondence Project, “Letter no. 1855,” accessed on 16 September 2019, https://www.darwinproject.ac.uk/letter/DCP-LETT-1855.xml

Also published in The Correspondence of Charles Darwin, vol. 6

letter