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Darwin Correspondence Project

To Leonard Horner   18 [March 1855]1

Down Farnborough Kent


My dear Mr Horner

I daresay I am going to trouble you quite uselessly, but as you seem, (or give the impression) in your Nile Paper2 to quite believe Russegger’s statement about the baked upper sandstone deposit,3 I thought I would just state that from what I have seen myself at the C. of Good Hope & Australia4 (& from what I know has been observed in India & the Malayan archipelago) I cannot avoid a total disbelief of the whole account. But please let me premise that if Russegger shows by his observations that he is a mineralogist as well as a geologist,—if in his baked rocks he has measured any crystals of feldspar or augite &c or even tryed the rock under the blowpipe, or examined the grains of quartz & seen their edges under the microscope fused I withdraw with humble apologies to you & him, my doubts. But if he has not, I would not in my own case quote his observations as in the least trustworthy.

In the countries above specified I have seen great areas coated with from 1 or 2 to (I think) 10 or 12 feet of dark brown, & black & angularly vesicular rock, having a most curious vitrified appearance, but which certainly was owing to a curious modification of the oxides of iron contained in it. Certainly there had been no heat from below, & certainly the whole deposit is simply superficial, & alluvial: I cannot explain its origin. To show its appearance, a most intelligent young officer in the Beagle, who had read Lyell & had seen plenty of real lavas, came rushing to me to say that he had found a most splendid stream of recent lava in the mountains near False Bay:5 I knew what it wd. turn out, & so it did.—

I had the greatest doubt whether I wd trouble you with this; but I felt sure you would forgive me, & wd. perhaps like to hear of the possibility of a very great blunder being quoted as worthy of consideration in a memoir which will have value for the next, no one can tell, how many centuries.

I will be still more presumptuous, & say that I think a little shortening in the purely geological introduction would not injure the Paper.— As you will be surprised at all this, I may as well say that I have had to Report on your paper; but have of course made none of these remarks in the Report.6 Indeed I wish I had not just said that the geological introduction wd not be injured by being shortened, for it only just occurred to me as a passing suggestion.— In 50 years, the Geology will probably be all passè, whereas the whole rest of the Paper will be permanent: is not this putting new wine in old Bottles?7

How very curious your account (p. 58)8 of the non-lamination of the mud: it interests me, as I feel sure that the great upheaved Pampean mud deposit9 was formed by slow deposition of mud in an estuary, & yet it is not in the least laminated; & rarely, when splendid sections are exhibited, the slightest variations in bands of colour can be most obscurely be distinguished: Al. d’orbigny has argued from this want of lamination that the whole vast Pampean deposit was thrown down all at once by a debacle.10

Will you forgive my presumption & believe | My dear Mr Horner | Your’s very sincerely & humbly | Ch. Darwin

at p. 25 of your M.S. wd. it not be well to insert some one word instead of “Thus” to show that, you do not suppose the difference of the rise of the Nile at Rhoda & Rosetta is a measure of the amount of evaporation, as the width of the Nile & current are not the same at the two places.—11


Dated on the basis of nn. 2 and 6, below.
Horner’s paper on the results of excavations and boreholes made through the alluvial deposits of the Nile basin (Horner 1855) had been read at the Royal Society on 8 and 15 February 1855.
Russegger 1841–8, vol. 1, pt 2, pp. 752–800, described the geology of the area. It appears that Horner removed the passage that CD commented on before his paper was published (Horner 1855, pp. 109–11). There is no reference to ‘baked sandstone’. The upper sandstone is identified only as a Tertiary rock similar in mineral composition to another, lower sandstone which made up most of the Libyan range of hills. No fossils were found in the formation, and it was the prevailing rock throughout the isthmus of Suez (p. 111). See also letter to Leonard Horner, 27 April [1855].
Volcanic islands, pp. 150–2, 130–3.
Cape of Good Hope, South Africa. The rocks were not described in CD’s account of the area in Journal of researches, pp. 577–8.
CD was a referee for Horner’s paper for the Royal Society (see letter to the Royal Society, 19 March 1855).
The introduction to Horner 1855, pp. 105–9, described the value of correlating recent changes in the geological structure of the earth with secular chronology as derived from historical records such as ancient monuments. Horner believed that work such as this would help to ‘find a link connecting historical and geological time’ (p. 106).
The reference is to a manuscript page number. Horner described the absence of lamination in the Nile sediments in Horner 1855, p. 137.
See South America, pp. 98–103.
Alcide Charles Victor Dessalines d’Orbigny’s theory is in the volume G’{eologie} of his Voyage dans l’Am’{erique Méridionale} (Orbigny 1834–47). CD argued against it in South America, p. 98.
Horner 1855, p. 116.


CD has been a referee for LH’s Nile geology paper [Philos. Trans. R. Soc. Lond. 145 (1855): 105–38]. Praises the work but offers criticism not in his report: Joseph Russegger’s statement about the baked Upper Sandstone deposit cannot be believed; LH’s paper is too long.

Letter details

Letter no.
Darwin, C. R.
Horner, Leonard
Sent from
Source of text
Lady Lyell (private collection)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 1649,” accessed on 19 January 2017,