Comments on cool-period MS. Still believes geographical changes principal cause of former changes of climate.
53 Harley Street:
March 10, 1866.
My dear Darwin,—
Your precious MS. has arrived safe. I will return it
registered in a few days. I am much obliged to you for the privilege of reading it; and
in regard to the notes prepared for the new edition, I am amused to
find how many of the topics are the same as those treated of in the letters of yourself,
Hooker, and Bunbury, in commenting on the observations by Agassiz of marks of glaciation
in the Organ Mountains. By the way, you allude to Hooker's discovery
of moraines in the Sikhim Mountains, which I believe are only about 7
I have been doing my best to do justice to the astronomical causes of former changes of climate, as I think you will see in my new edition, but I am more than ever convinced that the geographical changes are, as I always maintained, the principal and not the subsidiary ones. If you snub them, it will be peculiarly ungrateful in you, if you want to have so much general refrigeration at a former period. In my winter of the great year, I gave you in 1830 cold enough to annihilate every living being. The ice now prevailing at both poles is owing to an abnormal excess of land, as I shall show by calculation. Variations in eccentricity have no doubt intensified the cold when certain geographical combinations favoured them, but only in exceptional cases, such as ought to have occurred very rarely, as paleontology proves to have been the case.
Ever most truly yours, | Charles Lyell.
- f1 5031.f1CD had sent Lyell the manuscript for chapter 11 of his `big book' on species (Natural selection, pp. 534--66), and notes for additions to editions of Origin (see letter to Charles Lyell, 8 March  and nn. 8 and 9; see also letter to Charles Lyell, [3 March 1866] and n. 6).
- f2 5031.f2Lyell refers to notes for additions to the fourth edition of Origin (see n. 1, above).
- f3 5031.f3Lyell refers to the letters from C. J. F. Bunbury to Charles Lyell, 3 February 1866 and 20 February 1866, the letters to Charles Lyell, 7 February , 15 February , and 22 February , and the letter from J. D. Hooker, 21 February 1866. Lyell had sought comment from CD, Joseph Dalton Hooker, and Charles James Fox Bunbury on Louis Agassiz's claim that he had found evidence of former glacial action in the Organ Mountains of Brazil (see letter to Charles Lyell, 7 February ).
- f4 5031.f4In the manuscript that he sent Lyell (see n. 1, above), CD wrote, citing J. D. Hooker 1854: `Looking south we find in the Himalaya abundant evidence of the former much lower descent of the Glaciers, which have left behind them enormous Moraines' (DAR 14: D16 v.; see also Natural selection, p. 545 and n. 5). Hooker had described moraines and other evidence of former glaciation in valleys in Sikkim and elsewhere in the Himalayas in J. D. Hooker 1854, 1: 248, 380. The mountains of Sikkim are near latitude 28
oN, and the Organ Mountains of Brazil are near latitude 23 oS (Times atlas).
- f5 5031.f5CD sent Lyell Hooker's letter of 9 November 1856 (Correspondence vol. 6) with the manuscript of chapter 11 of his `big book' on species (see n. 1, above).
- f6 5031.f6The publication of Origin was precipitated by a letter from Alfred Russel Wallace to CD containing Wallace's manuscript `On the tendency of varieties to depart indefinitely from the original type'. See Correspondence vol. 7, letter to Charles Lyell, 18 [June 1858] and n. 3, and Appendixes III and IV.
- f7 5031.f7CD had expressed the view that geographical changes were subsidiary causes of former climate change (see letter to Charles Lyell, 8 March  and nn. 6 and 7). In C. Lyell 1867--8, Lyell considered the geographical causes of former changes in climate in chapter 12; the corresponding astronomical causes are considered in chapter 13.
- f8 5031.f8Lyell refers to CD's manuscript (see n. 1, above), in which CD's theory of geographical distribution was based upon the premise that glaciation had at some stage affected the whole earth or `a few great meridional belts' (DAR 14: D20, D34; see also Natural selection, pp. 548, 557). In Origin, the causes of the glacial period were first considered in the fifth edition, in which CD referred to James Croll's astronomical theory of glaciation (Origin 5th ed., pp. 451--2); in the sixth and final edition, CD referred briefly to Lyell's theory that glaciation was caused by changes in the relative positions of land and water and related it to Croll's theory (Origin 6th ed., p. 336; see also Peckham ed. 1959, pp. 593--4).
- f9 5031.f9Lyell thought that the earth's climate varied according to great cycles of change; in the first edition of Principles of geology, published between 1830 and 1833, a complete cycle was termed the `great year', during the winter of which `not only land as extensive as our existing continents, but immense tracts of sea in the frigid and temperate zones, would … present a solid surface covered with snow' (C. Lyell 1830--3, 1: 116--23; quotation from pp. 119--20). For commentaries on Lyell's concept of the `great year', see Secord 1997, pp. xviii--xix, and Leeder 1998, p. 108.
- f10 5031.f10In the tenth edition of Principles of geology, Lyell argued that the current proportion of land to sea in polar regions was greater than it once had been, and that consequently the temperature of the earth as a whole was cooler (C. Lyell 1867--8, 1: 247--8).
- f11 5031.f11Croll had recently estimated the dates of recurrent glacial periods as a function of periods of maximum eccentricity in the earth's orbit (Croll 1866a). Lyell challenged these estimated periods of glaciation on the grounds that palaeontological evidence indicated that some coincided with long periods of equable temperatures (C. Lyell 1867--8, 1: 299--300).