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Darwin Correspondence Project

From Daniel Mackintosh   24 December 1880

36 Whitford Road, | Tranmere, | Birkenhead

Dec. 24th 1880

Dear Sir,—

I have to thank you for lending me the American pamphlet which has caused me to add to what I have already written, the enclosed remarks of which I have retained a copy, & which you need not return.1

Mr. Strahan of the Geol. Survey, has described in some memoir (as he has informed me) somewhat similar phenomena to those on Moel Tryfan which he observed in Cheshire in thin layers of Keuper marl, and which he feels sure must have been caused by floating ice.2

Yours truly, | D. Mackintosh.

[Enclosure]

Bent and shattered edges of Slaty Laminæ

The section in which these appearances occur bears no real resemblance to some which have been found in districts where traces of ice-action are absent, in England, the United States, &c. The finely laminated sand on Moel Tryfan shews no sign of having been disturbed by the percolation of rain-water or frost, while the numerous shell-fragments arranged, along with very small pebbles, in continuous layers, have probably been preserved (as Darbishire long ago suggested)3 by the clay above the sand (which last spring was about ten feet thick) preventing the downward passage of acidulated rain-water. The erratic stones on Moel Tryfan could only have been brought by ice which must have stranded on the mountain before it could have left its erratic freight; and why have recourse to any other cause for the bending and shattering of the slates, seeing that ice not only capable of accomplishing the task, but likewise of producing the wonderful associated phenomena, must at one time have been present.

(The upper limit of the bent part of the slates inclines a very little, but not the line marking the commencement of the bending, somwhat like this—)

diagram

Footnotes

Aubrey Strahan, an assistant geologist with the Geological Survey of England and Wales, described the deposits in ‘On the lower Keuper sandstone of Cheshire’, but did not mention floating ice; he argued that the regularity of the bedding suggested ‘deposition in tranquil water’ (Strahan 1881, p. 397).
Robert Dukinfield Darbishire, in his paper ‘On the marine shells in stratified drift at high levels on Moel Tryfaen, Carnarvonshire’ (Darbishire 1863, p. 178), had suggested that the sandy clay tended to preserve the fossil shells found below.

Bibliography

Darbishire, Robert Dukinfield. 1863. On marine shells in stratified drift at high levels on Moel Tryfaen, Caernarvonshire. [Read 3 November 1863.] Proceedings of the Literary and Philosophical Society of Manchester 3 (1862–4): 177–81.

Kerr, Washington Caruthers. 1880. The gold gravels of North Carolina—their structure and origin. Transactions of the American Institute of Mining Engineers 8 (1879–80): 462–6.

Strahan, Aubrey. 1881. On the lower Keuper sandstone of Cheshire. Geological Magazine n.s. 8: 396–403

Summary

Thanks for the American pamphlet, which has caused him to write the enclosed extract on "bent and shattered edges of slaty laminae".

Letter details

Letter no.
DCP-LETT-12936
From
Daniel Mackintosh
To
Charles Robert Darwin
Sent from
Tranmere
Source of text
DAR 171: 12
Physical description
ALS 1p encl

Please cite as

Darwin Correspondence Project, “Letter no. 12936,” accessed on 22 July 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-12936.xml

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