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Darwin Correspondence Project

To W. E. Darwin   [1 March 1872]1

9 Dev: St—


My dear Wm

It was a capital thought of yours, to get the chalk analysed.2 Immediately on getting your note I called on David Forbes, who is the one man in England who has carefully analysed many specimens of chalk.3 He says that from 1 to 2 per cent of earthy matter is ⁠⟨⁠a⁠⟩⁠ fair average for the upper chalk with flints. In the lowest & most earthy beds of chalk without flints there is as much as 4 or 5 per cent. Therefore he concludes that the specimens analysed by Capt Parsons must certainly have become penetrated with surface mud.4 This seems to remove the wonderful difficulty of the layer of mould not being thicker at the bottom of your valley. I suppose the chalk about Winchester must be very pure, or unusually porous; for about Down the residue from the dissolved chalk evidently accumulates on the surface, & does not to any great extent percolate into the solid mass—

yours affecty | Ch Darwin


The date is established by the relationship between this letter, the letter from W. E. Darwin, [29 February 1872], and the letter from David Forbes, 1 March 1872. In 1872, 1 March was a Friday.
CD was in London from 16 February to 21 March 1872 (CD’s ‘Journal’ (Appendix II)).
CD described the chalk samples found by W. E. Darwin and Robert Mann Parsons in Earthworms, p. 299.


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


David Forbes thinks WED’s chalk samples have been penetrated by surface mud.

Letter details

Letter no.
Charles Robert Darwin
William Erasmus Darwin
Sent from
London, Devonshire St, 9
Source of text
DAR 162: 103
Physical description
L(S) 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 8216,” accessed on 16 July 2024,

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