To J. D. Hooker   [6 May 1847]

My dear Hooker

You have made a savage onslaught,¹ & I must try to defend myself. But first let me say that I never write to you except for my own good pleasure; now I fear that you answer me when busy & without inclination (& I am sure I sh^d. have none, if I was as busy as you): pray do not do so, as if I thought my writing entailed an answer from you nolens volens, it would destroy all my pleasure in writing.—

Firstly: I did not consider my letter as reasoning, or even as speculation, but simply as mental rioting & as I was sending Binney’s paper I poured out to you the result of reading it.—

Secondly, you are right indeed in thinking me mad, if you suppose that I would class any ferns as marine plants:² but surely there is a wide distinction between the plants found upright in the coal beds & those not upright & which might have been drifted. Is it not probable that the same circumstances which have preserved the vegetation in situ, sh^d. have preserved drifted plants? I know calamites is found upright, but I fancied its affinities were very obscure like Sigillaria. As for Lepidodendron I forgot its existence, as happens when one goes riot & now know neither what it is, or whether upright. If these plants, ie calamites & Lepidodendron have very clear relations to terrestrial vegetables,, like the ferns have, & are found upright in situ, of course I must give up the ghost. But surely Sigilliria is the main upright plant, & on its obscure affinities I have heard you enlarge.—

Thirdly, it never entered my head to under=value botanical relatively to zoological evidence; except in so far as I thought it was admitted that the vegetative structure seldom yielded any evidence of affinity, nearer than that of families, & not always so much: & is it not in plants, as certainly it is in animals, dangerous to judge of habits without very near affinity. Could a Botanist tell from structure alone that the mangrove family, almost or quite alone in dicots:, could live in the sea—& the zostera family almost alone amongst the monocot^s:? Is it a safe argument, that because algæ are almost the only, or the only, submerged sea-plants, that formerly other groups had not members with such habits; with animals such an argument would not be conclusive, as I c^d. illustrate by many examples;—but I am forgetting myself, I want only to some degree to defend myself, & not burn my fingers by attacking you.— The foundation of my letter, & what is my deliberate opinion, though I daresay you will think it absurd, is that I would rather trust, cæteris paribus, pure geological evidence than either Zoolog. or Botan. evidence: I do not say that I w^d sooner trust poor geolog. evidence than good organic: I think the bases of pure geological reasoning is simpler, (consisting chiefly of the action of water on the crust of the earth, & its up & down movements) than bases drawn from the difficult subject of affinities & of structure in relation to habits.

I can hardly analyse the facts on which I have come to this conclusion; but I can illustrate it: Pallas’ account³ would lead anyone to suppose that the Siberian strata with the frozen carcasses had been quietly deposited & hence that the embedded animals had lived in the neighbourhood: but our zoological knowledge of 30 years ago, led everyone falsely to reject this conclusion.

Tell me that an upright fern in situ occurs with Sigilliria & Stigmaria, or that the affinities of Calamites & Lepidodendron (supposing that they are found in situ with Sigilliria) as so clear that they could not have been marine, like, but in a greater degree, than the mangrove & sea-wrack, & I will humbly apologise to you & all Botanists, for having let my mind run riot on a subject on which assuredly I know nothing. But till I hear this, I shall keep privately to my own opinion, with the same pertinacity & as you will think with the same philosophical spirit, with which Kœnig⁴ maintains that Cheirotherium-footsteps are fuci.

Whether this letter will sink me still lower in your opinion, or put me a little right, I know not, but hope the latter. Anyhow I have revenged myself with boring you with a very long epistle.

Farewell & be forgiving— Ever yours C. Darwin

When will you return to Kew? I have forgotten one main object of my letter, to thank you much for your offer of the Hort. Journal, but I have ordered the two numbers with Herbert,⁵ whose writing I always like.—