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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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

212 ECONOMIC GEOLOGY by Erdmann, who thinks that the deposits were laid down in a depression that held the last waters of an isolated Permian Sea which continually received river-water. It has also been rejected by Walther, who holds that the salts were not de- posited directly from sea-water, but were leached from older marine deposits and concentrated on the beds of salt lakes. One section of the German salt fields covers 24,000 square miles, and is estimated to contain 3} million million tons of potash salt and vastly larger supplies of rock-salt. A sea large enough to have supplied so much salt should have maintained a moist atmosphere and prevented continuous and complete evaporation. The bar theory, suitably adapted appears best to fit the facts; for it explains how water from the outer ocean could be continually poured into a basin undergoing evaporation and receiving large supplies of lime from rivers. Evaporation of sea-water does not explain intrusive salt masses and the salt domes around the Guif of Mexico. The first well-established salt dome was found at Rang-el-Melah in Algeria, 14 miles NW, of Jelfa. It was described by Ville (Ann. Mines (5), xv, 1850, pp. 366-73, pl. III) and is a circular mass bounded on one side by Lower Cretaceous rocks and on the other by middle Kainozoic. The beds dip away from it, and are in places inverted. They include breccia with thin veins of copper and iron pyrites. Some adjacent salt beds are ordinary marine deposits; but Ville concluded that this mass was intruded as a saline clayey magma, which forced its way through the Cretaceous and Kainozoic beds. The Jennings oilfield near New Orleans beside the Gulf of Mexico was discovered as some shallow salt lakes had persistent films of oil and escapes of gas. Bores sunk beside these salt lakes in search for the source of the oil led to the startling discovery below them of vertical pillars of salt. A bore into Anse la Butte, about 100 miles W.N.W. of New Orleans, passed through 2263 feet of almost pure salt, then through 70 feet of sediments, and ended in an unknown thickness of salt. Adjacent bores proved that the salt is a cylindrical mass 1000 feet in diameter, with the sides so steep that a bore 300 feet away from it passed through up-tilted sand and clay, and met with no salt. Horizontal tongues of

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