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To Daniel Mackintosh   9 October 1879

Down | Beckenham Kent

Oct 9/79.

Dear Sir.

I hope that you will allow me to have the pleasure of thanking you for the very great pleasure which I have derived from just reading your paper on erratic blocks— The Map is wonderful. & what labour each of those lines show!1 I have thought for some years that the agency of floating ice, which nearly 12 a century ago was overrated, has of late been underrated—2 You are the sole man who has ever noticed the distinction suggested by me between flat or planed scored rocks & mamillated scored rocks.—3

I do not think that I ever published any notice on the Ashley Heath Boulder—nor can I tell where to look for my memoranda of its size, when I had the ground excavated on one side & partly beneath it—but I remember that the hole was deep.—4 The block rested on rounded lumps of new Red Sandstone about as big as a child’s or man’s head; & one of these had been split into two halves & was deeply-scored, though the scores were short. I thought at the time that the boulder had fallen off floating ice, & had crushed & scored the block   If it had fallen through the air so soft a rock would have been crushed into powder—

with great admiration for your paper | I remain dear Sir. | Yours faithfully | Ch Darwin.

Copy

1
Mackintosh’s paper was ‘Results of a systematic survey, in 1878, of the directions and limits of dispersion, mode of occurrence, and relation to drift-deposits of the erratic blocks or boulders of the West of England and east of Wales’ (Mackintosh 1879); the map, ‘Shewing the positions, limits and directions of dispersion, and intercrossing of the courses of the boulders of the W. of England and eastern part of N. Wales’ is plate 22.
2
Charles Lyell had argued for the role of floating ice in the transport of rocks in Lyell 1830–3, 1: 299 and 3: 50, before Louis Agassiz presented his theory of glaciation to explain a wide range of geological phenomena (Agassiz 1837). On the reception of these two theories, and their place in CD’s thinking, see Mills 1983 and Rudwick 1969.
3
See Mackintosh 1879, p. 448, and CD’s ‘Ancient glaciers of Caernarvonshire’, pp. 186–7, where CD speculated that dome-formed rocks indicated the action of glaciation, and flat or angular rocks the action of icebergs.
4
In Mackintosh 1879, p. 442, Mackintosh noted that a boulder that he saw on Ashley Heath was probably the same as one described by CD; see also Correspondence vol. 9, letter to Charles Lyell, 10 September [1861] and n. 8. CD had written about the boulder in 1842 in his ‘Ancient glaciers of Caernarvonshire’, p. 186 n. Ashley Heath is in Staffordshire. CD’s note on the boulder, made in June 1846, when he was visiting relatives at Maer, is in DAR 5: B31–2.

Please cite as “DCP-LETT-12252,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-12252