The Elements of economic geology

Bibliographic data

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 IV. Engineering geology

Collection:: Economics Books

230. ECONOMIC GEOLOGY dangerous. These wells are shafts sunk into a porous for- mation, into which sewage is discharged and drains away. Such wells are useful in flat lowlands where there is no surface slope for the drainage. A legal decision in 1885 prohibits the use of such wells where they may contaminate the underground water supply One town is not allowed to pour its sewerage into the bed from which another town draws its drinking water; but the owner of any plot of land has the right, under both British and American law, to draw from it as much water as he can. WeLLs AND SpriNGs—The simplest condition for a spring or well is where a porous bed, such as sand, rests on an im- permeable bed. Rain-water percolates into the sand until the water-table rises sufficiently above an outlet to discharge there as a spring. Lines of springs occur along hill-sides where wet sand rests on clay. If an excavation be made at such a position water will flow into it, and it forms a shallow well or soak. The traverse of desert countries often depends on the discovery of the right positions at which to dig soaks. They are often beside pools of salt water which remain a foot or so deep where there has been no rain for many months, and evaporation removes 10 feet a year. These pools must be renewed by soakage from adjacent beds. The positions of discharge of the water may be indicated by a few rushes or microscopic alge on the ground, or on a still day by a slight tremor in the air due to the different refractive index of the moist air.- Where the ground is charged with salt the soak will only yield salt water, and a position has to be found where a soak will occur above the salt-charged level. Soaks give but small yields; for they only occur where the water percolates slowly or the supply would run away quickly, instead of oozing out for months or years. Most wells are similar in principle to soaks, though the water- bearing layer is larger, and contains more water, and the yield is larger and quicker. FLowine WeLLs—Prolific deep wells often occur (Fig. 59) where a permeable bed passes underground between two impermeable beds. The water that percolates from the outcrop is at length prevented from sinking deeper by the thinning out of the porous bed, or its becoming compact

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