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Darwin Correspondence Project

From J. V. Carus   21 March 1876


March 21st. 1876

My dear Sir,

I come with a new difficulty. In your book on Coral-Reefs you say p. 70. l.8 from bottom “this would give to the reef a somewhat greater vertical thickness than would otherwise be possible.”1 According to my opinion it ought to be “a somewhat greater horizontal extent.” You say a few lines previously, that the coast-land is gently inclined and the soundings indicate an equally gentle slope beneath the water; there is no reason for supposing that the basis of the reef lies at a greater depth than at which the pollypfers2 could begin constructing the reef   Some allowance must be made for the outward extension of a foundation formed of sand and detritus; and this would give to the reef a greater—vertical or horizontal? extent. The foundation cannot be added to the vertical thickness of the reef, which rests on it   by this foundation the level of the basis is brought to that depth at which the polypfers could begin constructing the reef


Thus the horizontal extent of the reef is increased, but not, as far as I see the vertical thickness.

p. 68. footnote, you spell Dr. Allen, but on p.20 and 79 Allan.3 Which is right?

p 66. l. 13. read basal for basalt.4

Begging your pardon for troubling you anew I am | Yours very sincerely J. Victor Carus


Carus was translating Coral reefs 2d ed. into German (Carus trans. 1876a); see letter from J. V. Carus, 19 March 1876 and n. 1.
Polypifer: an obsolete word for polyparium, the common stem or supporting structure of a colonial cnidarian (or other colonial invertebrate), to which the individual polyps are attached (OED).
James Brands Allan.
The correction was made to the German translation of Coral reefs 2d ed. (Carus trans. 1876a, p. 49), and to Coral reefs 3d ed.


Coral reefs 2d ed.: The structure and distribution of coral reefs. By Charles Darwin. Revised edition. London: Smith, Elder & Co. 1874.

Coral reefs 3d ed.: The structure and distribution of coral reefs, with an appendix by Prof. T. G. Bonney. By Charles Darwin. London: Smith, Elder & Co. 1889.

OED: The Oxford English dictionary. Being a corrected re-issue with an introduction, supplement and bibliography of a new English dictionary. Edited by James A. H. Murray, et al. 12 vols. and supplement. Oxford: Clarendon Press. 1970. A supplement to the Oxford English dictionary. 4 vols. Edited by R. W. Burchfield. Oxford: Clarendon Press. 1972–86. The Oxford English dictionary. 2d edition. 20 vols. Prepared by J. A. Simpson and E. S. C. Weiner. Oxford: Clarendon Press. 1989. Oxford English dictionary additional series. 3 vols. Edited by John Simpson et al. Oxford: Clarendon Press. 1993–7.


A difficulty with a passage in Coral reefs about "vertical thickness", which JVC thinks should read "horizontal extent".

Letter details

Letter no.
Julius Victor Carus
Charles Robert Darwin
Sent from
Source of text
DAR 161: 104
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 10423,” accessed on 17 April 2021,

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