LETTER 363. TO C. LYELL. Down, February 7th [1866].

I am very much obliged for your note and the extract, which have interested me extremely. I cannot disbelieve for a moment Agassiz on Glacial action after all his experience, as you say, and after that capital book with plates which he early published (363/1. "Etudes sur les Glaciers"; Neuchatel, 1840.); as for his inferences and reasoning on the valley of the Amazon that is quite another question, nor can he have seen all the regions to which Mrs. A. alludes. (363/2. A letter from Mrs. Agassiz to Lady Lyell, which had been forwarded to Mr. Darwin. The same letter was sent also to Sir Charles Bunbury, who, in writing to Lyell on February 3rd, 1866, criticises some of the statements. He speaks of Agassiz's observations on glacial phenomena in Brazil as "very astonishing indeed; so astonishing that I have very great difficulty in believing them. They shake my faith in the glacial system altogether; or perhaps they ought rather to shake the faith in Agassiz...If Brazil was ever covered with glaciers, I can see no reason why the whole earth should not have been so. Perhaps the whole terrestrial globe was once 'one entire and perfect icicle.'" (From the privately printed "Life" of Sir Charles Bunbury, edited by Lady Bunbury, Volume ii., page 334).) Her letter is not very clear to me, and I do not understand what she means by "to a height of more than three thousand feet." There are no erratic boulders (to which I particularly attended ) in the low country round Rio. It is possible or even probable that this area may have subsided, for I could detect no evidence of elevation, or any Tertiary formations or volcanic action. The Organ Mountains are from six to seven thousand feet in height; and I am only a little surprised at their bearing the marks of glacial action. For some temperate genera of plants, viz., Vaccinium, Andromeda, Gaultheria, Hypericum, Drosera, Habenaria, inhabit these mountains, and I look at this almost as good evidence of a cold period, as glacial action. That there are not more temperate plants can be accounted for by the isolated position of these mountains. There are no erratic boulders on the Pacific coast north of Chiloe, and but few glaciers in the Cordillera, but it by no means follows, I think, that there may not have been formerly gigantic glaciers on the eastern and more humid side.

In the third edition of "Origin," page 403 (363/3. "Origin," Edition VI., page 335, 1882. "Mr. D. Forbes informs me that he found in various parts of the Cordillera, from lat. 13 deg W. to 30 deg S., at about the height of twelve thousand feet, deeply furrowed rocks...and likewise great masses of detritus, including grooved pebbles. Along this whole space of the Cordillera true glaciers do not now exist, even at much more considerable height. "), you will find a brief allusion, on authority of Mr. D. Forbes, on the former much lower extension of glaciers in the equatorial Cordillera. Pray also look at page 407 at what I say on the nature of tropical vegetation (which I could now much improve) during the Glacial period. (363/4. "During this, the coldest period, the lowlands under the Equator must have been clothed with a mingled tropical and temperate vegetation..." ("Origin," Edition VI., 1882, page 338).)

I feel a strong conviction that soon every one will believe that the whole world was cooler during the Glacial period. Remember Hooker's wonderful case recently discovered of the identity of so many temperate plants on the summit of Fernando Po, and on the mountains of Abyssinia. (363/5. "Dr. Hooker has also lately shown that several of the plants living in the upper parts of the lofty island of Fernando Po, and in the neighbouring Cameroon Mountains, in the Gulf of Guinea, are closely related to those on the mountains of Abyssinia, and likewise to those of temperate Europe" (loc. cit., page 337).) I look at [it] as certain that these plants crossed the whole of Africa from east to west during the same period. I wish I had published a long chapter written in full, and almost ready for the press, on this subject, which I wrote ten years ago. It was impossible in the "Origin" to give a fair abstract.

My health is considerably improved, so that I am able to work nearly two hours a day, and so make some little progress with my everlasting book on domestic varieties. You will have heard of my sister Catherine's easy death last Friday morning. (363/6. Catherine Darwin died in February 1866.) She suffered much, and we all look at her death as a blessing, for there was much fear of prolonged and greater suffering. We are uneasy about Susan, but she has hitherto borne it better than we could have hoped. (363/7. Susan Darwin died in October 1866.)

Remember glacial action of Lebanon when you speak of no glacial action in S. on Himalaya, and in S.E. Australia.

P.S.--I have been very glad to see Sir C. Bunbury's letter. (363/8. The letter from Bunbury to Lyell, already quoted on this subject. Bunbury writes: "There is nothing in the least NORTHERN, nothing that is not characteristically Brazilian, in the flora of the Organ Mountains.") If the genera which I name from Gardner (363/9. "Travels in the Interior of Brazil," by G. Gardner: London, 1846.) are not considered by him as usually temperate forms, I am, of course, silenced; but Hooker looked over the MS. chapter some ten years ago and did not score out my remarks on them, and he is generally ready enough to pitch into my ignorance and snub me, as I often deserve. My wonder was how any, ever so few, temperate forms reached the mountains of Brazil; and I supposed they travelled by the rather high land and ranges (name forgotten) which stretch from the Cordillera towards Brazil. Cordillera genera of plants have also, somehow, reached the Silla of Caracas. When I think of the vegetation of New Zealand and west coast of South America, where glaciers now descend to or very near to the sea, I feel it rash to conclude that all tropical forms would be destroyed by a considerably cooler period under the Equator.