From Daniel Mackintosh   8 December [1867]1

20 Sussex Street, | Winchester

8th Dec.

Sir

I am truly obliged by your kind letter received a few days ago, and am looking forward with great pleasure to reading your work at the Geol. Society.2

I am glad to find there are “inclined terraces” in South America.3 The inclination of the terraces of many parts of the Chalk downs, is one of the principal objections to their having been made for agricultural purposes.4

I can never give in to the escarpments of Sussex & Kent having been formed by Rain & Streams. The plains at their bases, in many places cutting equally through the gault & chalk, are inexplicable by an agent which can only act by deepening; and making V-shaped valleys5

Kent, near Maidstone6

diagram

Your definition of the distinctive offices of the sea (widening) & freshwater (deepening) seems to me to furnish the Key to the whole subject7

Near Royston & elsewhere in the E. Central Counties the valleys at the base of the chalk escarpments have been cut down, through chalk, to the Gault, not excavated along the Gault (Mr. Searles Wood.)8

diagram

In the number of the Geological Magazine for the present month there are three letters on Denudation in answer to Mr. Whitaker, which shew the present state of the Controversy.9

With many thanks for your kindness, I beg to remain, | Sir, Your very faithful & | obliged Sert., | D. Mackintosh.

1
The year is established by the relationship between this letter and the letter from Daniel Mackintosh, 1 December 1867.
2
The letter has not been found in the Darwin Archive–CUL. Mackintosh probably refers to South America (see letter from Daniel Mackintosh, 1 December 1867 and n. 8). CD’s first published comment on terraces in South America were in ‘Observations of proofs of recent elevation on the coast of Chili’, p. 49 (Proceedings of the Geological Society of London 2 (1838): 446–9; see also Collected papers 1: 43).
5
Mackintosh’s belief in the sea as an agent of erosion had been challenged by others who believed in subaerial denudation, that is, erosion resulting from fluvial and glacial action rather than marine action (Challinor 1978). See also letter from Daniel Mackintosh, 1 December 1867 and n. 3. In his book Rain and rivers, George Greenwood argued that these agents had determined the physical character of Wealden Sussex and Kent (Greenwood 1866, pp. 57–61). See also letter from Daniel Mackintosh, 1 December 1867, n. 6. In earlier letters to CD, Joseph Beete Jukes had offered a similar interpretation (Correspondence vol. 10, letters from J. B. Jukes, 25 May 1862 and 30 May 1862).
6
The sketch is derived from figure 2 in Foster and Topley 1865 (see Mackintosh 1869, p. 102).
7
For CD’s early view of the physical characteristics of valleys formed by rivers, see Correspondence vol. 5, letter to Charles Lyell, 18 February [1854] and n. 3.
8
The reference is to Searles Valentine Wood’s description of a geological section through parts of Cambridgeshire and Hertfordshire (Wood 1867). According to Wood, a chalk scarp near Royston, Hertfordshire, resulted from a trough several miles wide ‘cut down on both sides from the Chalk and Upper Glacial clay into the Gault’ rather than from weathering (Wood 1867, pp. 401–2). See also Mackintosh 1869, pp. 102–3.
9
The references are to E. Hull 1867, Kinahan 1867, and Mackintosh 1867c, which appeared in the Geological Magazine for December 1867, prompted by an article by William Whitaker (Whitaker 1867).

Please cite as “DCP-LETT-5711,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5711