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Darwin Correspondence Project

From Edward Forbes   [25 February 1846]1

3 Southwick Street | Hyde Park.


Dear Darwin

To answer your very welcome letter so far from being a waste of time is a gain for it obliges me to make myself clear & understood on matters which I have evidently put forward imperfectly & with obscurity. I have devoted the whole of this week to working & writing out the flora question, for I now feel strong enough to give my promised evening lecture on it at the R. Institn. on Friday2 & moreover wish to get it in printable form for the Reports of our Survey. Therefore at no time can I receive or answer objections with more benefit than now. From the hurry & pressure which unfortunately attends all my movements & doings I rarely have time to spare in preparing them for publication to do more than give brief & unsatisfactory abstracts, which I fear are often extremely obscure.

Now for your objections3 —which have sprung out of my own obscurities.

I do not argue in a circle about the Irish case, but treat the botanical evidence of connection & the geological as distinct. The former only I urged at Cambridge,4 the latter I have not yet publickly maintained.

My Cambridge argument was this—that no known currents whether of water or air, or ordinary means of transport would account for the little group of Asturian plants—few as to species but playing a conspicuous part in the vegetation—giving a peculiar botanical character to the South of Ireland. That as I had produced evidence of the other floras of our Islands (i.e. the Germanic—the Cretaceous & the Devonian ((these terms used topographically not geologically) having been acquired by migration over continuous land (the glacial or alpine flora I except for the present—as ice-carriage might have played a great part in its introduction)) I considered it most probable & maintained that the introduction of that Irish flora was also effected by the same means. I held also that the character of this flora was more southern & more ancient than that of any of the others,—& that its fragmentary & limited state was probably due to the plants composing it having (from their comparative hardiness—heaths, Saxifrages &c) survived the destroying influence of the glacial epoch.

My geological argument now is as follows: Half the Mediterranean Islands or more are partly—in some cases (as Malta) wholly—composed of the upheaved bed of the Miocene sea: so is a great part of the south of France from Bourdeaux to Montpellier: so is the west of Portugal, & we find the same corresponding beds with the same fossils (Pecten latissimus &c) in the Azores. So general an upheaval seems to me to indicate the former existence of a great post-Miocene land, the region of what is usually called the Mediterranean flora. (Every where these Miocene islands &c bear a flora of that type) If this land existed it did not extend to America (for the fossils of the Miocene of America are representative & not identical): where then was the edge or coastline of it, Atlantic-wards?

Look at the form & constancy of the great fucus-bank & consider that it is a Sargassum bank & that the Sargassum there is in an abnormal condition & that the species of this genus of fuci are essentially ground-growers.—& then see the probability of this bank having originated on a line of ancient coast. (see diagrams) I cannot admit the Sargassum case to be parallel with that of Confervae 5 or Oscillatoria

Now, having thus argued independantly 1st on my flora & 2d on the geological evidences of land in the quarter required: I put the two together to bear up my Irish case.

I think I have evidence from the fossils of the boulder formations in Ireland that if such Miocene land existed, it must have been broken up or partially broken up at the epoch of the glacial or boulder period.

This diagram may explain my meaning better than a hundred words diagram 6 —all objections thankfully received:—7 ever most sincerely | Edward Forbes.

You’ll be sorry to hear that poor Cumming8 has been suddenly struck with paralysis & is in a very precarious state.

CD annotations

crossed pencil
5.6 to indicate … post-Miocene land] scored pencil
5.7 (Everywhere … type) 5.8] scored pencil
Beside diagram: ‘Why not drifted away?’ ‘Azores not actually united’ ‘is there Post-eocene’ pencil


Dated from the reference in the letter to Forbes’s Royal Institution lecture on 27 February 1846.
CD’s letter to Forbes is missing, but see letter to J. D. Hooker, [13 March 1846], for some of his objections to Forbes’s theories.
E. Forbes 1845. The paper was read at the British Association meeting of 1845 in Cambridge.
This was an answer to one of CD’s objections, see letter to J. D. Hooker, [13 March 1846], on the question of Fucus and Confervae. The sentence was written in the margin.
Joakim Frederik Schouw, who divided the vegetation of Europe into twenty-two botanical regions in Schouw 1823, pp. 501–24.
With Forbes’s letter in DAR 164 is a note by CD: Forbes arguments from several Spanish plants in Ireland, not being transported not sound, because sea-currents and air-d[itt]o and migration of birds in same lines.— I have thought not-transportation the greatest difficulty—now we see how many seeds every plant & tree requires to be regularly propagated in its own country, for we cannot think that the great numbers of seeds superfluous, & therefore how small is the chance of here & there a solitary seedling being preserved in a well-stocked country.—


Forbes, Edward. 1845. On the distribution of endemic plants, more especially those of the British Islands, considered with regard to geological changes. Report of the 15th meeting of the British Association for the Advancement of Science held at Cambridge, Transactions of the sections, pp. 67–8.

Forbes, Edward. 1846. On the connexion between the distribution of the existing fauna and flora of the British Isles, and the geological changes which have affected their area, especially during the epoch of the Northern Drift. Memoirs of the Geological Survey of Great Britain, and of the Museum of Economic Geology in London 1: 336–432.

Schouw, Joakim Frederik. 1823. Grundzüge einer Allgemeinen pflanzengeographie. Berlin.


Answers CD’s objections with botanical and geological arguments supporting the existence of an ancient post-Miocene land extending over what is now the Mediterranean and past the Azores in the Atlantic [EF’s "Atlantis" theory in "On the connexion between the distribution of the existing fauna and flora of the British Isles and the geological changes which have affected their area", Mem. Geol. Surv. G. B. 1 (1846): 336–432].

Letter details

Letter no.
Edward Forbes
Charles Robert Darwin
Sent from
London, Southwick St, 3
Source of text
DAR 164: 151
Physical description
ALS 4pp †, CD note

Please cite as

Darwin Correspondence Project, “Letter no. 956,” accessed on 15 April 2024,

Also published in The Correspondence of Charles Darwin, vol. 3