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1833 (39) Salinas

crystals of Gypsum 1594. 1595. They are lying on & partly imbedded in the fetid dark sand. It is very remarkable, that these crystals contain some such sand in their centres. & from their geological position it is an certain, they have been deposited in every respect similar to the common salt & Sulp. of Sosa, excepting perhaps its annual re-solution. — I have never seen such crystals in any of the beds. — The Gauchos call this "madre del sal" — & say that in all the neighbouring salinas (b), these [projective] salts are found (a). — There are four great salinas to the north of the R. Negro, & one to the south. — In one of the former, the salt to the thickness of 2 or 3 feet forms a floor at all times beneath the lake. — this one is at least 3-4 times as big as the one described; it occurs in the high sandstone plain. —

I am told there is a small salina in the low alluvial plain in the valley of the R. Negro. — it is occasionally worked. — I omitted to state, that the Gauchos say in the first one, all the water which flows in during heavy rains is fresh; but that there is a salt spring even during summer, on the northern side of the lake. — It is by such agency that I can alone account for these salinas especially in such a situation, as the valley of the a river. — We have seen, that some beds contain at the R. Negro, saline matter, which doubtless would be dissolved, whenever water filtered through the soft stone. How salt has been deposited in earthy layers, from a sea, which

25 verso

(a) There are great numbers of smaller ones, some of which I saw between R. Negro & Colorado

(b) This relation of salt & gypsum seen in their modern present deposits is interesting, as compared with what is seen in the New Red Sandstone.

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1833 (40) Salinas

contained living animals, & therefore not saturated it is hard to guess. —

Salitrales

There is another class of saline depositions, called by the Gauchos salitrales, from containing much saltpetre. — These I have seen, far most abundantly at B. Blanca. The whole of the low basin abounds with these salts, which would appear to me to be composed of nitrates, muriates & sulphates. —

After some fine weather I saw one snow-like expance several miles long; but the encrustation is scarcely 1/4 of an inch thick. — These salitrales, almost invariably lie over deep mud; & in appearance they exactly resemble a swamp occasionally overflowed by the sea; quite barren excepting small detached clumps of succulent saline plants. They abound at very low levels. (but yet ele several feet above high water) & the soil is so impregnated with salt, that even after a shower of rain, the water in the cart rills is not fit to drink. The salt is not simply deposited at bottom of shallow pools, &c &c. but encrusts or effloresces, (like hoar frost) on the surface of the broken earth, leaves & roots of vegetables. — or rather, what I mean is that the salt does not appear invariably to be most thickly deposited in the lowest level of any plughole. — I obtained in a few minutes a bottle full of this salt from the grass 761 tin label, surrounding a puddle in the impure Tosca plain, which I have supposed to have been only elevated during the last upheaval. — Saltpetre occurs in the Detritus plain, on which the Fort stands, & which is about 30 or 40