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Letter 1004

Darwin, C. R. to Lyell, Charles

[3 Oct 1846]

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    Discusses A. C. Ramsay's article ["On the denudation of South Wales", Mem. Geol. Surv. G. B. 1 (1846)]. Mentions his own paper ["Volcanic phenomena in South America", Collected papers 1: 53–86]. Emphasises that sedimentary deposits are not ordinarily preserved.

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My dear Lyell

I have been much interested with Ramsay; but have no particular suggestions to offer: I agree with all your remarks made the other day. My final impression is, that the only argument against him, is to tell him to read & reread the Principles, & if not then convinced to send him to Pluto.— Not but what he has well read the Principles! & largely profited thereby.— I know not how carefully you have read this paper, but I think you did not mention to me, that he does p. 327 believe that the main part of his great denudation was effected during a vast (almost gratuitously assumed) slow Tertiary subsidence & subsequent Tertiary oscillating slow elevation.— So our high-cliff argument is inapplicable. He seems to think his great subsidence only favourable for great denudation, I believe, from the general nature of the off-shores sea's bottoms, that it is almost necessary: do look at two pages p. 25 of my S. American Vol. on this subject, when out next week.—

The foundation of his views viz of one great sudden upheaval, strikes me as threefold.— 1st to account for the great dislocations; this strikes me as the odder, as he admits that a little northwards, there were many & some violent dislocations at many periods during the accumulation of the palæozoic series.— If you argue against him allude to the cool assumption that petty forces are conflicting: look at Volcanos; look at recurrent similar earthquakes at same spots; look at repeatedly injected intrusive masses. In my paper on Volc. Phæn. in Geolog. Transact, I have argued (& Lonsdale thought well of the argument, in favour, as he remarked, of your original doctrine) that if Hopkins views are correct, viz that mountain-chains are subordinate consequences to changes of level in mass, then, as we have evidence of such horizontal movements in mass having been slow, the formation of mountain chains (differing from volcanos only in matter being injected instead of ejected) must have been slow.—

Secondly, Ramsay has been influenced, I think, by his alpine insects: but he is wrong in thinking that there is any necessary connection of Tropics & large insects; videlicet Galapagos. Arch. under the Equator. Small insects swarm in all parts of Tropics, though accompanied generally with large ones.—

Thirdly, he appears influenced by the absence of newer deposits on the old area, blinded by the supposed necessity of sediment accumulating somewhere near (as no doubt is true) & being preserved;—an example, as I think, of the common error, on which I wrote to you about. The preservation of sedimentary deposits being, as I do not doubt, the exception, when they are accumulated during periods of elevation or of stationary level; & therefore the preservation of newer deposits would not be probable, according to your view that Ramsay's great palæozoic masses were denuded, whilst slowly rising — Do pray look at end of II. Chapt at what little I have said on this subject in my S. American volume.

I do not think you can safely argue that whole surface was probably denuded at the same time to the level of the lateral patches of Magnesian conglomerate.—

The latter part of paper strikes me as good, but obvious. I shall send him my S. American Vol. for it is curious on how many similar points we enter, & I modestly hope it may be a half oz: weight towards his conversion to better views. If he wd but reject his great sudden elevations, how sound & good he wd be.— I doubt whether this letter will be worth the reading.

Ever your's | C. D.

    Footnotes Add

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    f1 1004.f1
    Andrew Crombie Ramsay, who was employed by the Geological Survey. CD's comments apply to Ramsay 1846, a copy of which is in the Darwin Library–CUL.
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    f2 1004.f2
    CD had made a trip to London with Emma which he recorded in his Account Book (Down House MS) on 30 September.
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    f3 1004.f3
    Ramsay 1846 dealt with evidence for marine denudation revealed by the work of the Geological Survey in Wales. In South America, p. 25–6, CD had argued that the cliffs on St Helena were formed by subsidence of sloping volcanic strata, allowing the ocean to cut away at successively higher levels of the slope while depositing detritus underwater. Ramsay considered slow subsidence an important aid to the process though not a necessary one (Ramsay 1846, pp. 326–7).
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    f4 1004.f4
    Ramsay (1846, pp. 314–17) believed that the convoluted strata appearing over much of South Wales had been produced by a single great catastrophe occurring near the end of the Carboniferous.
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    f5 1004.f5
    Ramsay (1846, p. 314) had noted pre-Carboniferous disturbances in North Wales.
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    f6 1004.f6
    Ramsay (1846, p. 317) argued that in view of the enormous lateral pressure required to fold strata thousands of feet thick, no such result ‘could have obtained from the conflicting action of petty forces working at various times’. Lyell was apparently considering Ramsay's argument in connection with revisions for C. Lyell 1847. Lyell did not follow CD's suggestions however, adding only a footnote to his volume commenting on the short time-span allowed by Ramsay (see C. Lyell 1847, p. 168 n.).
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    f7 1004.f7
    As assistant-secretary of the Geological Society, William Lonsdale oversaw the refereeing of CD's paper. See Correspondence vol. 2, letters to William Lonsdale, [15 May 1838], [c. June 1838], and [8 March 1839]. CD had cited William Hopkins (1838) in his discussion of the slow elevation of mountain chains (‘On the connexion of certain volcanic phenomena in South America’, Collected papers 1: 76–80).
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    f8 1004.f8
    Ramsay had cited the conclusion of Peter Bellinger Brodie (1845), that the small size of most fossil insects in British Secondary strata indicated a cool or temperate climate. This conclusion seemed to contradict the tropical character of many Secondary fossils, but Ramsay argued that Brodie's insects constituted evidence for the continued existence of a temperate highland region existing side by side with tropical lowlands throughout the Secondary period. Thus, the extensive denudation which eroded the once massive formations of South Wales had not occurred until the Tertiary (Ramsay 1846, pp. 324–5). The presumed thickness of these formations had, of course, been part of Ramsay's argument that only a great catastrophe could have folded them.
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    f9 1004.f9
    South America, pp. 135–9. Here CD argued that substantial sedimentary deposits were not likely to accumulate in periods of elevation because of the denuding action of the breakers. He used this argument to account for the absence of fossiliferous Tertiary strata on the west coast of South America. He used it again in the Origin (pp. 172–3, 290–2) as a partial explanation of the absence of transitional forms in the fossil record.
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