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Darwin Correspondence Project

From Andrew Crombie Ramsay   29 December 1858

46 North St. | St Andrews

29 Dec. 1858

My dear Sir

I recd your note late last night, & shall gladly do what I can to help you, for I know you never act without good reason, & make good use of any information that can be given.1

The enormous thickness given to the Cambrian of the Longmynd I more than doubt.2 The beds stand nearly on end, & I suspect them to be doubled up if not more frequently strongly contorted, the tops of the curves being denuded [DIAGRAM HERE] Lower Siln x Caradoc &c Llandeilo and Lingula flags Cambrian fault Dot the fault up at any reasonable angle & prolong the Silurian line x up to it & you get a fault of 100000 ft or so,3 under impossible conditions when all the Geology of the country is considered. Besides it is too big to be believed.

In North Wales the extreme thickness of the Cambrian is in Merionethshire about 7000, or 8000 feet, & then you do not get to the bottom.

In Merionethshire Selwyn makes the Lingula flags about 6000 ft. & it looks well.4 5000 might be I think safely taken.

11000 to 12000 for the Llandeilo & Bala or Caradoc beds

2000 ft of the Pentamerus or Llandovery beds, & Pale slate or Tarannon shale. (New names adopted by the Survey & Murchison, being sort of passage beds from Lower to Upper Silurian).5 I fear these are a great deal more in thickness in districts where they have not yet been properly tracked, & are likely to remain so.

Denbighshire flags at the base of the Wenlock shale 2000 feet Wenlock shale & lime 1800 ft Ludlow Rocks I think 3500, but I write from memory & may be far wrong. I think you will find it in De la Beches heavy memoir on the deposits of South Wales in the Survey Memoirs.6 We measured it together near Builth. Old Red Herefordshire 8000. I measured it myself.

There are no measurements in Devonshire that I ever heard of & I do not think they exist. Nor yet in Scotland. People have heretofore contented themselves with the words ‘prodigious, enormous, astounding’ & such like.

Carboniferous Limestone of S. Pembrokeshire, Gower &c, 2500 ft. I was at the measuring in Pembroke & in Glamorganshire it was done by Logan.7 Coal Measures of Glamorganshire by Logan doubtfully ranging between 12000 & 14000 ft. See (I think) De la Beches Memoir as above. In Nova Scotia at the South Joggins I think Logan & Dawson measured 14000 ft of Coal Measures.8

In S. Wales the Millstone grit is included in the C.M. It is 1000 ft where thickest.

The Permian of the Magnesian limestone districts, as far as I know is yet unmeasured. The Permian marl & conglomerates believed to be of Older date round the Central Coal fields from 800 to 1000 ft.

Sedgwick gives sinkings through the limestones for Coal.9 Phillips gives for it about 350 feet.10

In Thuringia near Eisenach I was at a place where they sank 2500 ft through the Rothtodteliegunde for Coal.11 20 miles off it was scarcely 20 ft thick.

Bunter sandstone of Central Counties 1500 ft & probably 2000 further north, the central beds being thick waterworn conglomerates of quartz & quartz rock.

Keuper Marl & Sandstone 1500 ft

Lias clay & lime, I have known them go 900 ft through it without getting to the bottom. None of our sections are so thick

Marlstone 150 feet

Upper Lias clay 200 feet Phillips

Sand (Lias Sand of Wright) See his paper in Geological Journal a year or two ago on Frocester Hill.12

Inferior Oolite Cheltenham 264 ft by Hull13

Fullers Earth 150–200?

Great Oolite—200?

Cornbrash— 40?

Oxford Clay 600

Coral reef 150?

Kimeridge clay 600?

Portland stone 100 ft


Weald unknown.

Lr Greensand may be obtained from Bristows Isle of Wight sections.14

Gault 100 to 200 ft but said to be of much greater undetermined thickness N.E. of Oxford.

Upper Greensand 138 ft

Chalk 1200 ft. Probably more Tertiaries from Prestwich & Bristows Isle of Wight sections & Forbes Memoir on I. of W.15 This however will give no true idea of the London area.

Clay I know nothing about.

Drift gravel I know 200 ft of in Shropshire, & 600 ft of in the State of New York.

My memory fails me abt some of the Oolites, but it is to be got from some of our Survey sections, & I could get the thicknesses for you when I go to town or if you are in town & call Mr. Best will measure them for you.16

I must think about the faults & reply to that query again

Ever truly | Andw C Ramsay

CD annotations

‘55’added brown crayon
Top of first page: ‘22’17 brown crayon
Bottom of last page: ‘167531pencil


CD was preparing chapters 9 and 10 of his ‘abstract’ (Origin, pp. 279–311, 312–45) on the topics ‘On the imperfection of the geological record’ and ‘On the geological succession of organic beings’. See ‘Journal’ (Appendix II), where CD refers only to ‘Geological Succession’. From Ramsay’s letter, it seems that CD had asked him to gauge the depth of various geological deposits in order to estimate the time it must have taken, and the extent of denudation required, to form the sediment that characterised them. An earlier note in Ramsay’s hand pertaining to the depth of deposits of the Weald in Kent, dated by CD ‘March 1857’, has several extensive annotations by CD calculating the time needed for the Weald’s denudation (DAR 205.9 (3): 346). CD also noted ‘In about year will know more’: CD seems to have written to Ramsay, as planned, to gain further information. See also Correspondence vol. 3, letter to A. C. Ramsay, 10 October [1846].
These strata in Wales were the lowest in which traces of life had been detected. See Origin, p. 307.
Ramsay added the dotted lines he describes in the letter, extending his diagram into the text of the manuscript. It has not been possible to reproduce these lines.
Alfred Richard Cecil Selwyn had geologised in Wales as a member of the Geological Survey, 1845–52. He then became director of the Geological Survey of New South Wales (Flett 1937, p. 56). Ramsay probably refers to Jukes and Selwyn 1848.
Ramsay had joined the Geological Survey in 1841 and spent much of his career studying the geology of Wales. Roderick Impey Murchison was director of the survey.
Henry Thomas De la Beche was the first director of the Geological Survey until his death in 1855. Ramsay refers to De la Beche 1846.
William Edmond Logan had geologised with De la Beche in Wales before returning to Canada. He was appointed the first director of the Geological Survey of Canada in 1842.
John William Dawson had geologised in the South Joggins district of Nova Scotia in 1842 and again in 1852. His results were published in Dawson 1855.
Adam Sedgwick.
John Phillips.
Ramsay refers to the geological deposits known as the Rothtodtliegende, or Rothliegende, group in Prussia.
Wright 1856.
Henry William Bristow had been a geologist with the Geological Survey since 1842. His map of the geology of the Isle of Wight was issued in 1855 (Flett 1937, p. 63).
Joseph Prestwich studied the Isle of Wight formations in 1846 (see Prestwich 1846). Ramsay also refers to Forbes 1853.
Edward Best was appointed assistant geologist with the Geological Survey in 1855. CD used the information given in this letter to calculate the combined thickness of British strata, giving an approximate total of 72,584 feet. In Origin, p. 284, he wrote: ‘the lofty pile of sedimentary rocks in Britain, gives but an inadequate idea of the time which has elapsed during their accumulation; yet what time this must have consumed!’ There are two notes in CD’s hand pertaining to Ramsay’s information in DAR 205.9 (3): 341 and 348. The first is dated 23 December 1858 and calculates the time required for the denudation of the Weald (see n. 1, above), a subject that CD discussed in Origin, pp. 285–7. The second tabulates the maximum thickness of British strata using Ramsay’s figures and those of others. The page was apparently sent to Ramsay, for it includes several annotations and corrections in his hand. It was marked ‘22’ in brown crayon (see n. 17, below).
The number of CD’s portfolio on palaeontology and extinction, including notes on geological faults.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Dawson, John William. 1855. Acadian geology: an account of the geological structure and mineral resources of Nova Scotia, and portions of the neighbouring provinces of British America. Edinburgh.

De la Beche, Henry Thomas. 1846. On the formation of the rocks of South Wales and south western England. Memoirs of the Geological Survey of Great Britain and of the Museum of Economic Geology in London 1: 1–296.

Flett, John Smith. 1937. The first hundred years of the Geological Survey of Great Britain. London: His Majesty’s Stationery Office.

Hull, Edward. 1857. Memoir of the geology of the country around Cheltenham. Memoirs of the Geological Survey of Great Britain and of the Museum of Practical Geology. (To accompany Sheet 44 of the Geological Survey.) London.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Prestwich, Joseph. 1846. On the Tertiary or supracretaceous formations of the Isle of Wight as exhibited in the sections at Alum Bay and White Cliff Bay. Quarterly Journal of the Geological Society of London 2: 223–59.


Responds to CD’s queries about the thickness of various geological formations. [See Origin, p. 284.]

Letter details

Letter no.
Andrew Crombie Ramsay
Charles Robert Darwin
Sent from
St Andrews
Source of text
DAR 205.9: 398
Physical description
8pp †

Please cite as

Darwin Correspondence Project, “Letter no. 2387,” accessed on 18 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 7