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Darwin Correspondence Project

From James Croll   23 June 1869


June 23d. 1869.

Dear Sir,

Please to accept of my warmest thanks for the copy of the new edition of your Origin of Species which you were so kind as to present me with.1 I trust that you will not consider me vain for saying that I am very much gratified with the complimentary way in which you have referred to my papers.2 I am particularly interested in the section on alternate glacial periods in north and south.3 I had no idea of this application of the theory when engaged on the subject or I might have brought out the point more clearly than I have done, that when the northern hemisphere, for example, is under a glacial period the line of highest temperature will not be at the equator but will lie a very considerable distance to the south of the equator. And again when the glacial period is transferred over to the southern hemisphere the line of greatest heat will move over to as great a distance to the north of the equator. Your idea that the temperate climate plants will move up the mountain side while this line of greatest heat is being transferred from the one hemisphere to the other is most ingenious as it is natural.

I am, | Yours very truly | James Croll

Charles Darwin Esq. M.A; F.R.S.


The fifth edition of Origin was published in the week beginning 22 June 1869; presentation copies were sent out earlier (see letter from Robert Cooke, 22 June 1869).
CD added a number of references to Croll’s work on subaerial denudation and glacial periods to Origin 5th ed. (see ibid., pp. 349, 352, 379, 451).
See Origin 5th ed., pp. 450–61. CD used Croll’s hypothesis of alternating glacial periods in the northern and southern hemispheres to help to explain the survival of tropical species, and the distribution of temperate ones.


Origin 5th ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 5th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1869.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.


Thanks for presentation copy of Origin [5th ed.].

Clarifies his point on north and south glacial periods. Supports CD’s view that temperate plants will move up mountains during the alternation.

Letter details

Letter no.
James Croll
Charles Robert Darwin
Sent from
Source of text
DAR 161: 265
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 6799,” accessed on 18 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 17