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Darwin Correspondence Project

From David Forbes   1 March 1872

11, York Place, | Portman Square, | London. W.

1 March 1872

Dear Mr Darwin

As you know that I rather pride myself on being systematic—I was annoyed today that I could not at once lay my hands on the analyses of chalk, I found them the moment you left1—the difficulty in doing so before being because I had entered them under the head of investigations of the Atlantic mud2

I enclose herewith the results of 2 analyses which you can take as representatives only to show the components of the true chalk which contains the flints—and of the most impure or grey chalk (chalk marl)—lowest in the series

Yours very truly | David Forbes

White chalk– with flints
Carbonate of Lime – 98·40
    —     of Magnesia 0·08
Insoluble (silicious rock debris) 1·10
Alumina(with Phosporic acid 0·42
Grey chalk. beds resting on greensand
level of low water Folkestone
Carbonate of lime 94·09
    —     of Magnesium 0·31
Insoluble (rock debris) 3·61
Phosphoric acid traces
Sea }Chloride of sodium 1·29
Water 0·70

CD annotations

Top of letter: ‘Worms’3red crayon


Forbes analysed chalk samples in order to compare them with samples of Atlantic mud collected on the Lightning and Porcupine expeditions (see Quarterly Journal of the Geological Society 27 (1871): xlviii–xlix n., and Thomson 1873, pp. 467 ff.).
CD cited the results of Forbes’s analysis of chalk in Earthworms, pp. 299–300.


Earthworms: The formation of vegetable mould through the action of worms: with observations on their habits. By Charles Darwin. London: John Murray. 1881.


Sends information on composition of chalk at Shoreham and Folkestone.

Letter details

Letter no.
David Forbes
Charles Robert Darwin
Sent from
London, York Place, 11
Source of text
DAR 164: 149
Physical description
ALS 2pp †

Please cite as

Darwin Correspondence Project, “Letter no. 8233,” accessed on 13 July 2024,

Also published in The Correspondence of Charles Darwin, vol. 20