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Darwin Correspondence Project

From Edward Forbes   [9 May 1845]1


Dear Darwin

I have been too busy to look over your list with requisite consideration until yesterday.

I have marked on the lists their probable depths judging from the associations of the genera.2 My marks are within wide ranges.

I could come however to more likely conclusions were two points noted

1st—the average size of the specimens & species found in each locality.

2d The comparative abundance of specimens of each species, & their state, as indicating life & death &c

Thus the Huafo list might indicate twice the depth if the species are all very small & the specimens of Turritella few.

All such calculations, at any rate, must be only provisional, until we know the range in Depth of mollusca in the neighbouring seas.


Dated from CD’s reply, 13 May [1845].
The lists of shells from different localities are in DAR 43.1: 51–2. The localities are Port Saint Julian, Santa Cruz, Huafo Island, Navidad, Copiapó, and the Cordillera of central Chile. Fuller identifications of the shells are given in lists throughout South America. CD used Forbes’s estimates of the depths at which these species lived to demonstrate the amount of sea-bed subsidence that must have occurred at Copiapó and the Cordillera of central Chile (South America, pp. 193, 196).


South America: Geological observations on South America. Being the third part of the geology of the voyage of the Beagle, under the command of Capt. FitzRoy RN, during the years 1832 to 1836. By Charles Darwin. London: Smith, Elder & Co. 1846.


Has marked probable depths of the specimens on CD’s list of S. American shells. Asks for details which would provide more precise conclusions. [See South America, p. 226.]

Letter details

Letter no.
Edward Forbes
Charles Robert Darwin
Sent from
Source of text
DAR 43.1: 50
Physical description
†, CD list 4pp †(by EF)

Please cite as

Darwin Correspondence Project, “Letter no. 866,” accessed on 17 November 2019,

Also published in The Correspondence of Charles Darwin, vol. 3