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Letter 602

Darwin, C. R. to Lyell, Charles

6 [July 1841]

    Summary Add

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    Discusses various types of coral reefs on which he has been collecting notes. Views of C. G. Ehrenberg. His conception of the formation of Bermuda.

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    Pessimistic about the effect of his poor health on his scientific work.

Transcription

Shrewsbury.

Tuesday 6th

My dear Lyell

Your letter was forwarded me here.— I was the more glad to receive it, as I never dreamed of your being able to find time to write now that you must be so very busy, and I had nothing to tell you about myself, else I should have written— I am pleased to hear how extensive & successful a trip you appear to have made— you must have worked hard & got your Silurian subject well in your head to have profited by so short an excursion— How I should have enjoyed to have followed you about the coral-limestone— I once saw close to Wenlock, something such as you describe, & made a rough drawing, I remember, of the masses of coral— But the degree in which the whole mass was regularly stratified & the quantity of mud, made me think, that the reefs could never have been like those in the Pacific, but that they most resembled those on the East coast of Africa, which seem from charts & descriptions to confine extensive flats & mangrove swamps with mud—or like some imperfect ones, about the West Indian Islds within the reefs of which there are large swamps— All the reefs I have myself seen could be associated only with nearly pure calcareous rocks—. I have received a description of a reef lying some way off coast near Belizes (Terra Firma) where a thick bed of mud seems to have invaded & covered a coral reef—leaving but very few islets yet free from it— But I can give you no precise information without my notes (even if then) on these heads—

I will think of your suggestion of a neutral tint for such coral-reefs, as I am uncertain about, but I almost doubt whether it will be worth while— I shall of course enumerate them.— (N.B. Coral reefs extend along nearly whole line of both coasts of Red Sea) I advise you to leave the Red Sea quite uncoloured, for I have not yet considered all the data I have collected— If Ehrenberg's account of the constitution of the land be correct (as I am inclined to believe) then from Capt Moresby's accounts & charts all ought to be coloured red, for the true reefs certainly are mere fringes to singularly formed land— I much suspect that ancient barrier & encircling reefs, formed by subsidence, have since, within pleiocene period been uplifted & often worn down by surf, & are now only fringed by living reefs— This will I believe make Ehrenbergs, Moresby's & other accounts all harmonize— I doubt whether I shall make any allusion to this view, as it will appear so hypothetical—though to you & your pupils, as a mere theoretical case, it might have been expected to have somewhere occurred.—

The reefs in the West Indies are also obscure in some parts, owing to the accumulation of sediment & the large upward movement, wh has gone on there: the symmetry of reefs seems greatly disturbed every where except in open ocean, or near open ordinary coast-lines: I have not finally considered my portfolio of notes on the West Indies.

Bermuda differs much from any other isld, I am acquainted with;—at first sight of a chart, it resembles an atoll: but it differs from this structure essentially, in the gently shelving bottom of sea all round to some distance;—in the absence of the defined circular reefs, & as a consequence of the defined central pool or lagoon,—and lastly in the height of the land.— Bermuda seems to be an irregular circular flat bank, encrusted with knolls & reefs of coral, with land formed on one side. This land seems once to have been more extensive, as on some parts of the bank, furthest removed from the islds— there are little pinnacles of rock of the same nature, as that of the high larger islds— I cannot pretend to form any precise notion, how the foundation of so anomalous an isld has been produced; but I am sure its whole history must be very different from that of the atolls of Indian & Pacific Oceans—though, as I have said, at first glance of charts there is considerable resemblance—

I remember now, that Bermuda is very like the Bahama banks & Isls & these I believe have been formed by elevation (wh is certain) of ordinary submarine sand banks, with their windward edges, solidified by the growth of some coral: at Bermuda, the wind has heaped more sand & the sea acted more as a destroyer.

My health has improved a good deal, since I have been in the country, & I believe to a stranger's eyes, I should look quite a strong man, but I find I am not up to any exertion, & I am constantly tiring myself by very trifling things.

My Fathers scarcely seems to expect, that I shall become strong for some years— it has been a bitter mortification for me, to digest the conclusion, that the “race is for the strong”—& that I shall probably do little more, but must be content to admire the strides others make in Science— So it must be, but I shall just crawl on with my S. American work & be as easy as I can.—

I hope I shall just see you, before you start, —but it is not quite certain, though I think we shall return about 15th or 16th— I heartily wish you all the great success, your zeal deserves— How large an area you will have geologised i<n> the old & new World together! If we do not meet, give my kindest farewell to Mrs Lyell, & accept my warm thanks for all the friendship you have shown me— My wife is not here, but comes to day, as I left her a few days ago at Maer— if she were here, she would heartily join in her remembrances to you both.—

My dear Lyell | Believe me your's most sincerely | C. Darwin

If I do not return to London on the 16th; I will let you hear from me a few days before, in case by chance you should want to ask me any questions about Coral-Masses
Shrewsbury

    Footnotes Add

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    f1 602.f1
    In June 1841 Lyell travelled to Aymestry in Radnorshire, Wales, where he examined the corals of the Wenlock limestone, a Silurian formation. See Wilson 1972, pp. 515–16.
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    f2 602.f2
    Wenlock Edge, a limestone ridge south of Shrewsbury, the standard geological sequence for part of R. I. Murchison's Silurian system. CD's notes, made in July 1838, are in DAR 5 (ser. 2): 21–2. The drawing is on pp. 119–20 of his Glen Roy notebook (DAR 130).
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    f3 602.f3
    Described in Coral reefs, pp. 188–91.
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    f4 602.f4
    Ibid., pp. 196–205.
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    f5 602.f5
    Plate III (a world map) in Coral reefs is coloured as follows: dark blue for atolls and submerged annular reefs, pale blue for barrier reefs, pale red for fringing reefs, and bright red for volcanoes. Uncoloured coasts signify no reefs, reefs of an irregular form, reefs not based on coral foundation, and certain unusual reefs in the Red Sea (Coral reefs, pp. 119–23).
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    f6 602.f6
    Ehrenberg 1834.
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    f7 602.f7
    Robert Moresby, a naval officer who carried out surveys in the Red Sea and Indian Ocean. For this information the editors thank J. D. Brown, Naval Historical Branch, Ministry of Defence. Moresby provided CD with extensive descriptions of coral reefs (see Coral reefs, pp. 22, 83, 191–6).
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    f8 602.f8
    The Lyells were preparing to leave on a year's trip to America.
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