RECORD: Darwin, C. R. Geological diary: Salitrales (1833) CUL-DAR34.27-28 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/).

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrected and edited by John van Wyhe 1.2011. RN1

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text.

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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.

See the introduction to the Geological Diary by Gordon Chancellor.


27

1833 (41) Salitrales.—

Salitrales

feet above the level of the great swamp.

I also saw some on the high Tosca rock plain, it here occurred in a little valley, & coated some vegetable mould, with fragments of Tosca rock. — We have seen it in the cellars of the houses at the R. Negro; also encrusting a well in the low sandstone plain. —

It is said to occur on bare patches in the valley of the R. Negro. — & I saw it in the valley, near the Colorado; here a large swamp was covered with salt-loving plants, & in summer is white with saltpetre. —

I should imagine this plain, must occasionally be overflowed by the river, anyhow it is clearly alluvial. — there are lines of sand-dunes in the midst of these, which (& other reasons) make me believe that at some remote period the sea entered this valley or aestuary. —

In several of the above particulars, these salitrales essentially differ from the deposition of salt in the salinas. — In the almost universal occurrence in low, modern or alluvial plains (a), in contra distinction of an elevated depression, in forming only a very thin crust & this over deep mud (I allude except in both cases, particular instances, such as salitra on the high Tosca rock plain). — in the manner of encrustation, instead of plain deposition. — From the local position & appearance of the salitrales it gives one the idea of being actually formed in the mud. — We should be obliged almost to come to some such conclusion, if the

27 verso

(a) The salitrales occur in level plains, where the whole soil appears to be impregnated with salt, & a depression of an inch causes a thin coat to be seen after rain. — Salinas occur where you might expect springs. —

We may conjecture salt in the latter case, that the salt owes its chief origin to deep seated beds; In the other case have we salts decomposed by vegetables & nitric acid formed by the mud.!!?!

28

1833 (42) Salitrales.—

the fact, which I believe the Gauchos asserted (a), that the salitrales were occasionally overflowed by the R. Colorado.—

To the South, at Port Desire, I found in a low muddy flat valley, in the great oyster formation an encrustation of saline matter, which I believe is of same nature with that of B. Blanca. —

At S. Cruz (1633) [crosswise]

Falkner states (P 37)1 that the saltpetre district extends from between Vinulean & St Anthony to Corriates, Rioja & Catamarca, that is in the great Tosca formation. — Now in the low plains between the Ventana & P. Salado though of same orig geological nature, there is very little saltpetre. — I saw however one white patch about 35 miles to the south of the Salado, but I did not see it again till near B. Blanca. — Falkners southern limits are therefore wrong. —

At Corrientes & in the North it seems especially abundant & pure. — In this district we have Sulp. of Magnesia at Melincu√®. (Arica). —

It is said there are saltpetre tracts near B. Ayres (b) & I heard of them in Entre Rios. — Perhaps it also occurs, (but very rarely) in the superficial Tosca of B. Oriental:

During the gran Seco, some of the smaller streams had a salt taste. —

Humboldt in Mexico2 talks of a saline efflorescence which probably is of somewhat a similar nature. —

1 Falkner 1774.

2 Humboldt 1811.

28 verso

(a) Again I believe the salitrales in the valley of the R. Negro must have been overflowed during the floods & Easterly gales of (1826?). —

(b) About Rockas (71 miles W by N of Luxan) much saline efflorescence. — Miers Chili. —1

(or F. of Rosas)

1 Miers 1826, vol. 1, p. 39 describes a journey near Roccas: "There was a succession, for a considerable distance, of reedy swamps; the higher parts of them were covered with a saline efflorescence. The grass was also strongly saline."


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