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Letter 2716A

Jukes, J. B. to Darwin, C. R.

27 Feb 1860

    Summary Add

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    Believes in the "perfect indefiniteness & frequently the vast length of the interval" between consecutive geological formations. Thus has little respect for arguments against CD based on the absence of transitional forms in the geological record. States that species found through series of beds do vary: some Silurian species have many synonyms which are really varieties of greatly differing ages. CD's theory accounts for the progressive inprovement, multiplication and increase in complexity that can be seen, but which may often be only relative.

Transcription

(Febry 27. 1860)

I beleive in the perfect indefiniteness & frequently the vast

length of the interval between the formation of any one bed & that which rests upon it

I beleive any amount of beds may be intercalated almost any where not only between any two formations, but anywhere in any formatn. & that the ordinary ideas of Geologists as to contemporaneity will have to be greatly expanded—

I am therefore prepared to treat with very little respect the argument agt. you derived from missing links.

When you have anything approaching to a continuous series of beds you have the links, moreover, when you get species ranging through a great series of beds they do vary. Calymene Blumenbachii for instance is found in both Upper & Lower Silurian, but Salter says that those found in Lower Silurian vary so much from the Wenlock ones that he has doubted their being the same species & was inclined to give them another name. So Baillie & I have arrived at the conviction that Spirifer Verneuilli. S. disjunctus & S. strictus are mere varieties of one species, that found in the Lower beds having been christened Verneuilli. So Terebratula hastata has about 30 synonyms & it is very likely that some of the varieties are of greatly difft. ages.

Your theory accounts for just so much of progressive improvement as we see has taken place i.e. an improvement & a multiplication & a complexity in the whole but not necessarily absolute in every step or every instance, & relative but not always absolute—

    Footnotes Add

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    f1 2716a.f1
    The date as given in Charles Lyell's journal, into which the letter was copied. See also Wilson ed. 1970, p. 361.
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    f2 2716a.f2
    Jukes refers to arguments against transmutation that pointed to the absence of transitional forms in the geological record.
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    f3 2716a.f3
    John William Salter, palaeontologist to the Geological Survey of Great Britain, was an expert on the fossils of older rocks like the Silurian (Secord 1986). He had worked with Jukes on the classification of the Devonian and Carboniferous formations of the south of Ireland in the early 1850s.
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    f4 2716a.f4
    William Hellier Baily worked with Jukes on the staff of the Geological Survey in Ireland. He was a specialist in the palaeontology of ancient formations.
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    f5 2716a.f5
    Spirifer and Terebratula are brachiopods. Because of their common occurrence in geological deposits beginning with the Lower Cambrian, they are frequently used for dating strata. CD had attempted to gain information on the variability of species of fossil shells in 1856. See Correspondence vol. 6, letter from S. P. Woodward, 2 May 1856, and letter to S. P. Woodward, 27 May 1856.
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