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C. Doment ). D. Huker.

Down. July 30th, 1856. VT ILAR HOCKER, - Your letter is of much value to me. I was no: atle to get a definite answer from Lyell,* as you w see in tre enclosed letters, though I inferred that he thought cothing of my arguments. Had it not been for this correspondence, I should have written sadly too strongly

. You may rely on it I shall put my doubts moderately. There Diever was such a predicament as mine : here you continental extensionists would remove enormous difficulties opposed to me, and yet I cannot honestly admit the doctrine, and must therefore say so. I cannot get over the fact that not a fragment of secondary or palæozoic rock has been found on any island above 500 or 600 miles from a mainland. You rather misunderstand me when you think I doubt the possibility of

* On the continental extensions of Forbes and others.

1856.)

CLASSIFICATION.

439

subsidence of 20.000 or 30,000 feet ; it is only probability, considering such evidence as we have independently of distribution. I have not yet worked out in full detail the distribution of mammalia, both identical and allied, with respect to the one element of depth of the sea ; but as far as I have gone, the results are to me surprisingly accordant with my very most troublesome belief in not such great geographical changes as you believe ; and in mammalia we certainly know more of means of distribution than in any other class. Nothing is so vexatious to me, as so constantly finding myself drawing different conclusions from better judges than myself, from the same facts.

I fancy I have lately removed many (not geographical) great difficulties opposed to my notions, but God knows it may be all hallucination.

Please return Lyell's letters.

What a capital letter of Lyell's that to you is, and what a wonderful man he is. I differ from him greatly in thinking that those who believe that species are not fixed will multiply specific names : I know in my own case my most frequent source of doubt was whether others would not think this or that was a God-created Barnacle, and surely deserved a name. Otherwise I should only have thought whether the amount of difference and permanence was sufficient to justify a name: I am, also, surprised at his thinking it immaterial whether species are absolute or not : whenever it is proved that all species are produced by generation, by laws of change, what good evidence we shall have of the gaps in formations. And what a science Natural History will be, when we are in our graves, when all the laws of change are thought one of the most important parts of Natural History.

I cannot conceive why Lyell thinks such notions as mine or of ‘Vestiges,' will invalidate specific centres. But I must not run on and take up your time. My MS. will not, I fear, be copied before you go abroad. With hearty thanks.

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P. S.-After giving much condensed, my argument versus continental extensions, I shall append some such sentence, as that two better judges than myself have considered these arguments, and attach no weight to them.

C. Darwin to J. D. Hooker.

Down, August 5th (1856)

. I quite agree about Lyell's letters to me, which, though to me interesting, have afforded me no new light. Your letters, under the geological point of view, have been more valuable to me. You cannot imagine how earnestly I wish I could swallow continental extension, but I cannot ; the more I think (and I cannot get the subject out of my head), the more difficult I find it. If there were only some half-dozen cases, I should not feel the least difficulty; but the generality of the facts of all islands (except one or two) having a considerable part of their productions in common with one or more mainlands utterly staggers me.

What a wonderful case of the Epacridæ! It is most vexatious, also humiliating, to me that I cannot follow and subscribe to the way in which you strikingly put your view of the case. I look at your facts (about Eucalyptus, &c.) as damning against continental extension, and if you like also damning against migration, or at least of enormous difficulty. I see the ground of our difference (in a letter I must put myself on an equality in arguing) lies, in my opinion, that scarcely anything is known of means of distribution. I quite agree with A. De Candolle's (and I dare say your) opinion that it is poor work putting together the merely posssible means of distribution; but I see no other way in which the subject can be attacked, for I think that A. Dc Candolle's argument, that no plants have been introduced into England except by man's agency, of no weight. I cannot but think that the theory of continental extension does do some little harm as stopping investigation of the means of dispersal, which, whether negative or positive, seems to me of value; when negatived, then every

1856.]

SPECIFIC CENTRES.

441

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one who believes in single centres will have to admit continental extensions.

... I see from your remarks that you do not understand my notions (whether or no worth anything) about modification; I attribute very little to the direct action of climate, &c. I suppose, in regard to specific centres, we are at cross purposes; I should call the kitchen garden in which the red cabbage was produced, or the farm in which Bakewell made the Shorthorn cattle, the specific centre of these species ! And surely this is centralisation enough!

I thank you most sincerely for all your assistance; and whether or no my book may be wretched, you have done. your best to make it less wretched. Sometimes I am in very good spirits and sometimes very low about it. My own mind is decided on the question of the origin of species; but, good heavens, how little that is worth! ..

[With regard to “specific centres," a passage from a letter dated July 25, 1856, by Sir Charles Lyell to Sir J. D. Hooker ('Life,' ii. p. 216) is of interest :

"I fear much that if Darwin argues that species are phantoms, he will also have to admit that single centres of dispersion are phantoms also, and that would deprive me of much of the value which I ascribe to the present provinces of animals and plants, as illustrating modern and tertiary changes in physical geography."

He seems to have recognised, however, that the phantom doctrine would soon have to be faced, for he wrote in the same letter : “Whether Darwin persuades you and me to renounce our faith in species (when geological epochs are considered) or not, I foresee that many will go over to the indefinite modifiability doctrine."

In the autumn my father was still working at geographical distribution, and again sought the aid of Sir J. D. Hooker.

A Letter to Sir J. D. Hooker (Sept., 1856). “In the course of some weeks, you unfortunate wretch, you will have my MS, on one point of Geographical Distribu

tion. I will, however, never ask such a favour again; but in regard to this one piece of MS., it is of infinite importance to me for you to see it; for never in my life have I felt such difficulty what to do, and I heartily wish I could slur the whole subject over.”

In a letter to Sir J. D. Hooker (June, 1856), the following characteristic passage occurs, suggested, no doubt, by the kind of work which his chapter on Geographical Distribution entailed :

“There is wonderful ill logic in his (E. Forbes'] famous and admirable memoir on distribution, as it appears to me, now that I have got it up so as to give the heads in a page. Depend on it, my saying is a true one, viz., that a compiler is a great man, and an original man a commonplace man. Any fool can generalise and speculate ; but, oh, my heavens ! to get up at second hand a New Zealand Flora, that is work."]

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C. Darwin to IV. D. Fox.

Oct. 3 (1856). I remember you protested against Lyell's advice of writing a sketch of my species doctrines. Well, when I began I found it such unsatisfactory work that I have desisted, and am now drawing up my work as perfect as my materials of nineteen years' collecting suffice, but do not intend to stop to perfect any line of investigation beyond current work. Thus far and no farther I shall follow Lyell's urgent advice. Your remarks weighed with me considerably. I find to my sorrow it will run to quite a big book. I have found my careful work at pigeons really invaluable, as enlightening me on many points on variation under domestication. The copious old literature, by which I can trace the gradual changes in the breeds of pigeons has been extraordinarily useful to me. I have just had pigeons and fowls alive from the Gambia! Rabbits and ducks I am attending to pretty carefully, but less so than pigeons. I find most remarkable differences in the skeletons of rabbits. Have you ever kept any odd breeds

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