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Letter 2996A

Lyell, Charles to Darwin, C. R.

24 Nov 1860

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    CL has calculated that elevation and subsidence of certain formations in Sweden and Norway take place at the rate of 2 1/2 feet per century. He now proposes to estimate the age of a bed by including a conjecture that pauses occur in the oscillations in the ratio of 4 periods of stasis to one of movement. Applying this formula to Scotland, the last subsidence and re-elevation would be 590,000 years and the age of the beds with human implements would be 20,000 years.

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Nov. 24 1860.

My dear Darwin,

In former editions in speculating on age of Uddevalla & still more elevated beds of glacial period in Norway & Sweden, I have assumed an average rate of rise as 212 feet in a century. see Manual. p. 119.— 125 feet take 5000 years to rise or to sink. I wish to keep to my old standard or estimate unless shown to be objectionable as applied to countries like Greenland & Sweden in full movement. a mere guess at an average rate. at p. 120 I give 27,500 years for 700 ft of upheaval in recent times. But I expressly guard myself in same page by saying I make no allowance for pauses or for oscillations of level (of the minor kind.)

What I want to do in the new edition is to make another conjecture & to allow for the pauses. When the amount is reversed as if (which I believe with Trimmer Ramsay Jamieson & others) Scotland & Wales have moved first down & then up again 2200 feet or more, then I conceive the chief pauses would be before the downward was converted into an upward movement. Successive sea-beaches & terraces & inland cliffs mark long pauses. Smith of Jordanhill thinks he has a cliff which took more than 100,000 years to cut, subsequently to the glacial re-elevation in Scotland.

Now I propose to conjecture keeping on the safe side & not exposing myself to the charge of exaggerating the probable time, that 4 parts of Europe are stationary for one which moves at the rate of 212 feet in a hundred years, or that the stationary area exceeds that in motion as 4 to 1. & 4 expresses the period of rest or the pauses where 1 in a given region expresses the movement. Therefore if Scotland has first gone down 2250 feet after the period of land glaciers, as I believe this would take 90,000 years & the re-elevation rather more because it went up higher than it's present level, say 100,000 years, but then I must give 400,000 additional (in round numbers) for the intervening periods of rest.

Thus the last oscillation is about 50 feet in Scotland in each direction, since the 2 vast movements of 2250 down & up. But when we try to estimate the time required for the 2 movements we encounter, as Smith of Jordanhill observes, 2000 years since the Romans built the Pictish wall & find that we do not get back to the close of the last oscillation.

Then I regard this 2000 years (and we know not how many 1000 before) as a part of the great excess of stationary condition.

I also consider the successive beaches cut at Glasgow in the canoe-bearing sands all before the era of the Roman Wall as portions of the same excess of 4 to 1.

I am aware that the North Cape moves, or is said to move, 5 or 6 feet in a century & D Forbes thinks that Chili has gone up from 40 to 60 feet in 350 years, but then north of Arica, he thinks there has been a subsiding area, & about Arica, a stationary one as proved by Indian tumuli & mummies buried near the old shore level & elevated since.

But I look on S. America as rather exceptional. It would be balanced by other more inactive regions of oscillation. The average in Scandinavia would not I think exceed 212 feet. I am however much more in doubt as to the comparative areas of rest, contrasted with those of movement. I once made them as 9 to 1. If I could stimulate the geographers to make objections it would do good.

Perhaps the contemporaneous inland oscillations, especially in mountain chains, may be greater than the sea-coast ones. But we may leave those speculations out for the present.

There may be scarcely any areas in an absolute state of rest but we cannot yet take account of minute quantities. I wish you to reflect on my principle, & if possible say if 4. to 1. is a reasonable conjecture.

Large plateaux of denudation & inland sea cliffs are monuments of immense pauses.

[table]

During this period the whole of the glacial period & the present establishment of provinces of species has occurred— the mammalian fauna greatly changed, but the shells very little

The last oscillation of Scotland of about 50 feet in each direction wd take 4000 years & for pauses 16.000 more which would give 20,000 years. The Glasgow canoes & polished celts come into this brief era, but the Somme valley flint implements probably into some part of the great period of reelevation—during which in Scotland the erratic boulder clay was getting denuded & my Forfar gravel beds manufactured.

Chas Lyell

    Footnotes Add

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    f1 2996a.f1
    C. Lyell 1855, p. 119.
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    f2 2996a.f2
    The new edition of Lyell's Manual of elementary geology, retitled Elements of geology, was published in 1865 (C. Lyell 1865). CD's copy of the work is in the Darwin Library--Down. Although Lyell alluded to these points in his new edition, they were in fact discussed in greater detail in his book on the antiquity of man (C. Lyell 1863, chaps. 3, 13, and 14).
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    f3 2996a.f3
    Trimmer 1853, Ramsay 1852, and Jamieson 1860. See letter from Charles Lyell, [before 20 November 1860].
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    f4 2996a.f4
    James Smith, commonly known as Smith of Jordanhill (Scotland), wrote to Lyell about this point (Wilson ed. 1970, pp. 502--5). Lyell copied the information into his scientific journal immediately preceding the draft of this letter to CD. Smith had established himself as an acknowledged expert on the elevation of Scottish coastlines with the publication of an influential paper on the subject in 1836 (J. Smith 1836).
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    f5 2996a.f5
    The `Picts' wall' (OED) was the common name of the great wall built by the Romans between AD 120 and 130 (EB 1970); it is now commonly known as Hadrian's Wall. Running through Cumberland and Northumberland, it was constructed to help defend Roman Britain from the Picts and the Scots.
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    f6 2996a.f6
    The discovery of ancient canoes buried in the silt around Glasgow was described by John Buchanan in 1855 and discussed by Lyell in C. Lyell 1863, pp. 48--9. Lyell thought some of them might date from the Bronze Age.
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    f7 2996a.f7
    David Forbes, recently returned from a geological expedition to Bolivia and Peru, read a paper on the geology of the area at a meeting of the Geological Society on 21 November 1860. The figures given by Lyell in the letter were probably ascertained in conversation with Forbes. Forbes's results were published in D. Forbes 1861. The geology of the area near the town of Arica, in Peru, is discussed in D. Forbes 1861, p. 11.
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    f8 2996a.f8
    This figure is repeated in C. Lyell 1863, p. 58.
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    f9 2996a.f9
    Lyell discussed the point in C. Lyell 1865, pp. 158--60.
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