skip to content

Darwin Correspondence Project

To Basil Hall   15 March 1840

12 Upper Gower Street

Sunday 15th March 1840

My dear Sir

I much regret, that from the state of my health I am incapable of answering your question at the length which I should much wish to do.—1 I forget what I said to Mr Lyell,2 but I remember that from your description I had expected a much larger valley. If the valley be considered as bounded by the mountains of granitic rocks its width is between 3 & 4 miles. But the width of the valley in which the river flows is only about a mile.— I have not a copy of your work, & I am unable to leave the house, but I think you have considerably overstated the distance up the valley, to which the terraces extend,— at least as far as I could discover. There are five terraces, of which three, as you observe, are best characterized.—3 The height of the edge of the upper plain close behind the town of Coquimbo is 364 feet. This upper plain slopes, down but insensibly to the eye, towards Herradura Bay, where it is chiefly formed of calcareous rock, in the place of gravel & its height is only 252 feet. This calcareous rock contains recent marine shells.—

On the lower terraces I, also, found existing shells.— The upper plain, (whose edge is 364 feet close behind Coquimbo,) rises (but insensibly to the eye), in its course up the true valley of Coquimbo, & at two miles up the valley is 420 feet above the sea,—that is 55 feet higher. than behind town of Coquimbo. The sketch I have given in my Journal of Researches of the theory of their origin, is, I believe accurate.— You will understand it better, if you will be so good as to read, what I have written about the plains of Patagonia at p. 200 to 2084

When I wrote p. 423 of my Journal, I had not visited Glen Roy.5 I now consider the cases as somewhat different.— The appearances at Glen Roy are almost entirely due to the cumulative power of the sea, on steep slopes during a period of rest. The terraces of Coquimbo and Patagonia are due to the abrading action of the sea on gently inclined surfaces during such periods.—

The parallelisms of the terraces are consequently far less exact, than those of the ‘Roads’ of Glen Roy.— If you think it worth the trouble to read my Glen Roy Paper in Philosoph Transact.6 you will perceive that the formation of terraces by the abrasion of the matter, accumulated in a gentle slope in the valleys during the rising, is a somewhat complex action.— The upper terrace or plain of Coquimbo I believe is strictly analogous to the fringe of stratified alluviums in Glen Roy, described at p. 50 in my paper.—its origin explained in the hypothesis given at p. 59. The successive terraces at Coquimbo I believe are analogous to some appearances in the mouth of the Spean,7 which I have just alluded to at p. 67.—

Glen Roy & Coquimbo or Guasco offer two grand instances of slight modifications of the action of the sea on land, during periods of rest, in its gradual elevation.—8

I much fear this note will be scarcely intelligible: I should have much enjoyed conversing with you on this subject, but I am not at present capable of such exertion.— If the subject is worth your attention, I am sure you will fully comprehend all I know, by comparing what I have written on Glen Roy & Patagonia at 200 to 208.— I should feel extreme interest in hearing your judgment on this theory I have proposed to account for the whole class of appearances under question.—

Believe me My dear Sir | Yours very truly | Chas. Darwin.

P. S. | I think you will be pleased to hear, that traces of ‘Parallel Roads’ have been discovered in other parts of Scotland since I published my paper.— And I have received several private communications on the subject.—9

Footnotes

No letter from Hall has been found. According to B. Hall 1840, p. 77, CD had been asked to comment on Hall’s interpretation of the phenomenon of terraces along the sides of valleys, and to state the analogy existing between the phenomona at Coquimbo, and those of Patagonia, and also to point out the parts of his recent paper on the parallel roads of Glen Roy in Scotland (‘Parallel roads of Glen Roy’) that bore most directly on this question. CD was unwell from January to 26 March 1840 (see Correspondence vol. 2, Appendix II).
Charles Lyell.
Hall had described riding up the valley of Coquimbo, Chile, in his Extracts from a journal written on the coasts of Chili (B. Hall 1824, 2: 6–11); he described the centre of the valley as being six or seven miles wide, and compared the horizontal beds he observed on the side of the valley to those of Glen Roy. CD had visited the valley of Coquimbo on 9 May 1835 during the voyage of HMS Beagle (R. Keynes 2001, pp. 331–2); he described the terraces he saw there in Journal of researches, p. 425, but made no mention of the width of the valley. There was a copy of B. Hall 1824 in the Beagle library (see Correspondence vol. 1, Appendix IV). Hall was evidently asking CD for information before publishing the sixth edition of his ‘extracts’. In this edition, Hall added a footnote to his comment about the width of the valley, stating that CD’s more careful measurements showed that the valley was three or four miles wide (B. Hall 1840, p. 75 n.); he also published CD’s letter in its entirety with a few alterations (ibid., p. 77).
In Journal of researches, p. 423, CD stated that the terraces in the valley of Coquimbo were formed in the same way as the plains of Patagonia, and that the presence of fossil marine shells embedded in the strata of the terraces confirmed Lyell’s view that the land was gradually rising. The plains and terraces were formed by sea currents that wore away the land and produced cliffs in periods when the gradual elevation of the land was interrupted (ibid., p. 205).
CD visited Glen Roy in the summer of 1838 (see Correspondence vol. 2, letter to Charles Lyell, 9 August [1838]).
‘Parallel roads of Glen Roy’ was published in 1839 in the Philosophical Transactions of the Royal Society of London. Hall amended his views after reading this paper and CD’s account of the plains of Patagonia in Journal of researches, pp. 200–8, as well as Lyell’s Principles of geology (C. Lyell 1830–3). Prior to this, Hall thought that the terraces might be the result of sudden and violent submarine elevations of a size and velocity great enough to produce waves that submerged the land; the resulting lakes might then have broken through successively lower barriers of rock over time, forming beaches at each new level (B. Hall 1840, pp. 76 and 77).
The River Spean originates in Loch Laggan in Glen Spean; the lowest terrace of Glen Roy (the valley of the River Roy, a tributary of the Spean) extends out into Glen Spean.
In Journal of researches, p. 423, CD noted that the phenomenon was ‘strikingly seen’ in the seven horizontal terraces in the valley of Guasco. Guasco is on the coast of Chile, and was described by Hall as a village (B. Hall 1824, p. 18).
See, for example, Correspondence vol. 1, letter from J. G. Malcolmson, 2 January 1840.

Summary

Discussion of the geology of Coquimbo, Chile.

Letter details

Letter no.
DCP-LETT-558F
From
Charles Robert Darwin
To
Basil Hall
Sent from
12 Upper Gower Street, London
Source of text
Musée royal de Mariemont, Belgium (Aut. 1061/1)
Physical description
9pp

Please cite as

Darwin Correspondence Project, “Letter no. 558F,” accessed on 4 July 2020, https://www.darwinproject.ac.uk/letter/DCP-LETT-558F.xml

Also published in The Correspondence of Charles Darwin, vol. 24 (Supplement)

letter