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Letter 1599

Darwin, C. R. to Sharpe, Daniel

12 Nov [1854]

    Summary Add

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    Regrets he cannot come to hear DS's paper ["On the structure of Mont Blanc", Q. J. Geol. Soc. Lond. 11 (1855): 11–27]. Has a lively interest in the subject.

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    Edward Forbes has misrepresented his view on foliation and cleavage [Athenæum 30 Sept 1854].

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    CD is convinced DS's view will replace Huttonian and Lyellian view of metamorphic schists.

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    Recommends H. C. Sorby's paper [probably "On the origin of slaty cleavage", Edinburgh New Philos. J. 55 (1853): 137–50].

Transcription

Down Farnborough Kent

Novr 12

My dear Sir

I have been to London just lately & am compelled very soon to go again, & I really cannot screw up my courage to go up for Wednesday, though I shd like it extremely. Moreover I am not at all sure that I could go, as I have guests in the house, & I do not know on what day they depart.— I am really very sorry to miss your paper, as I feel a lively interest on the subject. I observed in the Athenæum that Forbes at the Brit. Assoc. has been observing on this subject, & slightly mis-represents my views in calling foliation identical with cleavage, for I believe I have always called it the same process or action carried to an extreme.

Have you considered Mr Sorby's paper; I have only seen a notice of it? I wish you success, the day will come, when little if any of the metamorphic schists will be considered on the Huttonian & Lyellian view as mere metamorphosed layers of different ingredients, I feel profoundly convinced.—

Dear Sharpe | Yours very truly | C. Darwin

    Footnotes Add

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    f1 1599.f1
    Sharpe's paper ‘On the structure of Mont Blanc’ (Sharpe 1855) was read at the Geological Society meeting of 15 November 1854. Sharpe discussed the relationship of the foliation of the crystalline rocks to the cleavage of the surrounding stratified slates.
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    f2 1599.f2
    The Athenæum, no. 1405, 30 September 1854, pp. 1172–82, carried a report of the British Association for the Advancement of Science meeting in Liverpool. Edward Forbes was president of section C (geology).
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    f3 1599.f3
    In his paper, Forbes stated that CD considered foliation in mica slate ‘identical with cleavage, and due to the same cause,—the one passing into the other’ (Athenæum, no. 1405, 30 September 1854, p. 1178, later published as Forbes 1854b). In Forbes's opinion foliation was ‘a superinduced structure quite distinct from cleavage or lamination’ (Forbes 1854b, p. 82).
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    f4 1599.f4
    Sorby 1853. Henry Clifton Sorby presented observations that supported a mechanical origin for the cleavage in the slate rocks of North Wales. He suggested ‘there is abundance of evidence to prove that rocks having slaty cleavage have been greatly compressed in a line perpendicular to cleavage, and elongated to a certain extent in the line of its dip’ (Sorby 1853, p. 144).
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    f5 1599.f5
    The view of Charles Lyell and his predecessor, James Hutton, was that the lines of what CD and Sharpe called cleavage and foliation represented different layers of the original deposits which had been contorted and metamorphosed by later geological action. According to the Athenæum account, Lyell's comment on Forbes's distinction (see n. 3, above) was that ‘Plutonic action … often left the planes of stratification still visible. The unaltered sedimentary beds were frequently affected by irregularities as great as those of the altered rocks… . If these were rendered metamorphic, there would be danger of attributing to chemical action peculiarities which existed whilst the beds were yet unaltered.’ (Athenæum, no. 1405, 30 September 1854, pp. 1178–9). Lyell, apparently influenced by the papers of Sharpe and Sorby, revised his view in favour of the mechanical explanation of cleavage in the fifth edition of the Manual of elementary geology (C. Lyell 1855, pp. 607–17). In his preface, outlining the principal alterations and additions in that edition, he stated: ‘New proofs are cited in favour of attributing cleavage to mechanical force, p. 610., and for inferring in many cases a connection between foliation and cleavage, p. 615. At the same time, the question—how far the planes of foliation usually agree with those of sedimentary deposition, is entered into, p. 614.’ (ibid., p. ix).
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