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Darwin Correspondence Project

To James Croll   9 August 1877

Down, Beckenham, | Kent

Aug. 9, 1877.

My dear Sir,

I am much obliged for your essay which I have read with the greatest interest.1 With respect to the geological part, I have long wished to see the evidence collected on the time required for denudation, and you have done it admirably.2 I wish some one would in a like spirit compare the thickness of sedimentary rocks with the quickest estimated rate of deposition by a large river, and other such evidence. Your main argument with respect to the sun seems to me very striking.3

My son George desires me to thank you for his copy and to say how much he has been interested by it.4

I remain, my dear Sir, | Yours very faithfully, | Charles Darwin.


CD’s annotated offprint of Croll’s article ‘On the probable origin and age of the sun’ (Croll 1877) is in the Darwin Pamphlet Collection–CUL.
CD scored several passages where Croll calculated the time required for aerial denudation (see Croll 1877, pp. 313–14).
Croll had theorised that the source of the sun’s heat could have been motion in space, noting that the collision of two bodies, each half the mass of the sun, moving towards each other at 476 miles per second would generate heat for fifty million years (Croll 1877, p. 319).
In his paper, Croll had referred to calculations by George Howard Darwin regarding the effect of geological changes on the earth’s axis of rotation (Croll 1877, p. 324; see also G. H. Darwin 1876b).


Croll, James. 1877. On the probable origin and age of the sun. Quarterly Journal of Science n.s. 7: 307–26


Comments on JC’s paper ["On the tidal retardation argument for the age of the earth", Rep. BAAS (1876): 88–9].

Letter details

Letter no.
Charles Robert Darwin
James Croll
Sent from
Source of text
DAR 143: 356
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 11097,” accessed on 27 October 2021,