The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

98 ~ ECONOMIC GEOLOGY coast towns were provided with fresh-water by sea, and sold at the price of often 5 gallons for a penny. The nitrate may be recognized by its inflammability on burning wick. According to tradition the deposits were discovered owing to the ground catching fire; the alarmed Indians took some to a priest to expel the evil spirit, which he recognized as nitrate. In the eighteenth century it was used instead of saltpetre (KNOg) for gunpowder, but the modern trade dates from the discovery by a Scottish settler near Iquique, that the white soil made his garden extremely fertile. He sent some to Scotland where its nature was determined, and the first nitrate works were established at Iquique in 1826. In 1830, 8300 tons were exported; the amount increased to 2§ million tons in 1913, fell to 1 million tons in 1922, but had risen to 24 million in 1925. The nitrate deposits or ‘‘ saltreras are generally on the edge of salt pans or ‘ salares.” The sequence of deposits is usually as follows. At the surface are a few inches of decomposed *‘ porphyry; below is a conglomerate which is cemented by sulphates of lime, potash, and sodium, with a little sodium nitrate; next a layer of sand and clay con- taining salt and anhydrite. This layer and the conglomerate are together from 1-3 feet in thickness; and beneath them is the caliche, the main bed of sodium nitrate; it varies in thickness from a few inches to 6 feet; the average of nitrate in the material mined is between 20 and 30 per cent.; and less than 17 per cent. usually does not pay. The caliche rests upon sand and clay containing salt and gypsum, below which may be a second nitrate layer, the banco. TrEORIES OF ForMaTioN—The origin of sodium nitrate has given rise to an unusual variety of hypotheses. It was attributed to the decay of seaweeds and fish in an arm of the sea which had been raised above sea-level (Darwin, 1846, Geol. Observ. S. Amer., Chap. 111; C. Noellner, ¥. prakt. Chem. cii, 1867, p. 461). The main argument for this theory was the presence of marine shells, and it was discredited when they were found to be derived from the underlying Cretaceous rocks. = According to a second theory the nitrate was derived from guano, either deposited by birds on the shores of lagoons (Penrose, 1910) or blown inland from the coast {Ochsenius, 1888, Z.d.g.G., x1, pp. 153-65). A third

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