From Daniel Mackintosh   1 December 1867

20 Sussex Street, | Winchester,

1st Dec. 1867.

Sir,

Having some idea of the extent to which your time must be occupied, I should not have troubled you with acknowledging the receipt of your very kind and considerate letter,1 were it not that for some time past I have been longing for an opportunity of consulting you on one or two points connected with Denudation.2

You may, perhaps, have noticed a number of articles by me in the Geological Magazine which have given rise to a rather warm controversy on the origin of escarpments, valleys, and plains.3 With the exception of a little assistance from Mr Hull (of the Ord. Survey) and Mr Kinnahan (Irish Survey) I have been left to fight the battle with the Subaërial school singlehanded.4 In endeavouring to answer opponents, I have been gradually led not to place too much reliance on sea-coast action, and after allowing a certain amount of influence to ice, I have been driven to oceanic currents, periodically increased in intensity by sudden upheavals or depressions of the earth’s crust, as the main excavators of valleys.5

My object in writing is to take the liberty of asking if you have published any thing, or know of any thing that has been published, on the excavating power of currents, and whether you think that their action on the chalk of the south of England (with or without ice) would be sufficient to explain the hollowing, rounding scoring, escarpmenting, and terracing, which form so striking a feature of the chalk downs.6 For upwards of a year I have been wandering among these downs with the view of generalizing all the facts connected with the terracing and scoring of their slopes. When I ventured a short time ago (too inconsiderately) to assert that there were raised beaches among the chalk downs, Mr. Poulett Scrope ridiculed the idea in the Geological Mag., and referred all the terraces to the action of the plough.7 I think I can now demonstrate that, however much the terraces may have been either enhanced or defaced by cultivation, there are thousands which are of natural origin. The most puzzling characteristic is their very frequent want of horizontality and parallelism, which at first might suggest the idea of currents rather than sea-coast action. But I have noticed a similar absence of horizontal parallelism among the smaller terraces of the North of Scotland & elsewhere. Would you kindly inform me if this be a characteristic of any of the terraces you have discovered in S. America, and whether unequal upheaval, or irregular formation during oscillations of the land, would offer an explanation.8 The finest series I have seen is near Stockbridge, on the side of the Andover and Romsey Railway.9 They are parallel, but gently inclined longitudinally. They are covered with fractured flints, mixed with thoroughly rounded pebbles.

I enclose the very rough & imperfect sketch I took on the spot.10

Hoping you will kindly excuse the liberty I take in asking for a hint or two on these subjects when you happen to have a little leisure, | I am, Sir, | Your very obliged & humble Sert., | D. Mackintosh

This will be my address for more than a week to come—afterwards Chichester

P.S. I shall gladly embrace the first opportunity of seeing the work you refer to, and shall call attention to the fact probably in the Geological Magazine.11

1
CD’s letter has not been found. See letter from Daniel Mackintosh, 8 December [1867] and n. 2.
2
CD had written about denudation in two periodicals in the 1840s (see Correspondence vol. 2, letter to Charles Maclaren, [15 November – December 1842] (also published in Collected papers 1: 171–4), and ‘On the transportal of erratic boulders from a lower to a higher level’ (Collected papers 1: 218–27)). CD also considered denudation in Origin, pp. 285–7, 308, estimating the rate of its action in the formation of the Weald (see Correspondence vol. 12, letter from A. C. Ramsay, 10 July 1864 and n. 3).
3
See Mackintosh 1865a, 1865b, 1866a–d, and 1867a–c, in which Mackintosh argued that greater recognition should be given to the effect of marine influences on the surface geology of Britain. In response to Mackintosh’s papers, various writers, notably Joseph Beete Jukes, George Maw, George Poulett Scrope, and William Whitaker, published articles in the Geological Magazine during 1866 and 1867. These authors emphasised the importance of subaerial denudation, that is, erosion resulting from fluvial and glacial action rather than marine action (Challinor 1978). For a more detailed contemporary account of subaerial denudation, see Greenwood 1866. See also Correspondence vol. 13, letter to J. D. Hooker, [29 July 1865], n. 11.
4
Mackintosh refers to Edward Hull and George Henry Kinahan and to the Ordnance Survey and the Geological Survey of Ireland. For Hull’s views on denudation and their relevance to the controversy surrounding Mackintosh’s papers, see E. Hull 1867. Kinahan emphasised the similar appearances of geological features formed by marine and subaerial agencies, including ice (Kinahan 1867).
5
See, for example, Mackintosh 1867a, pp. 137–8.
6
CD considered the action of sea currents in excavating coastal land forms, though not specifically chalk, in South America, chapters 1–3. CD wrote on the denudation of Wealden chalk by coastal erosion in Origin, pp. 285–7; the Weald is a district bounded by the North and South Downs in Hampshire, Surrey, Sussex, and Kent. In 1865, CD wrote to Charles Lyell, approving of the account of the denudation of the Weald in the sixth edition of Lyell’s Elements of geology (C. Lyell 1865), which included an argument for marine erosion as the main agent in the formation of the Weald (see Correspondence vol. 13, letter to Charles Lyell, 21 February [1865], n. 5).
7
Mackintosh had claimed that thousands of raised beaches were to be found in the chalk downlands of southern England (see Mackintosh 1866a, p. 69, and Mackintosh 1866b, p. 155). Scrope challenged Mackintosh’s view of the marine origin of terraces on the chalk downs in Scrope 1866.
8
CD had interpreted inclined terraces at Coquimbo, Chile, as raised beaches on ground that had subsequently undergone unequal elevation (South America, pp. 41–5).
9
The terraces, on the south-west side of the village of Stockbridge, between the towns of Andover and Romsey, Hampshire, are described in Mackintosh 1869, pp. 86–8.
10
The enclosure has not been found; the terraces at Stockbridge are illustrated in Mackintosh 1869, p. 87.
11
The work CD refers to has not been identified. Mackintosh acknowledged CD in the preface to his book on the scenery of England and Wales, and claimed CD as a supporter of his views on marine weathering (Mackintosh 1869). For more on Mackintosh’s views in the context of nineteenth-century geology in England, see Oldroyd 1999.

Please cite as “DCP-LETT-5703,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5703