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 III. Earthy minerals

Collection:: Economics Books

(82 ECONOMIC GEOLOGY which absorbs carbon dioxide from the air and is deposited as carbonate of lime in the interstices of the stone and thus strengthens it. The process failed at Westminster because the decay had gone too far, and the new crust flaked away. The restora- tion of building stone which has undergone thorough decay has proved so far economically impracticable. II. Roap METALS The suitability of stones for road construction depends on qualities different from those required in building and varies with the climate and traffic. A good road metal must be sufficiently tough to withstand the traffic; the powder formed by its wear and tear should act as a cement and form a smooth impermeable surface; and the stone and its powder should hold by surface-tension the water mixed with it, and the tar or bitumen added as binding material. The selection of road metal depends primarily upon trafic. A comparatively soft stone will carry light vehicles if its powder binds well; hence limestone, volcanic tuff and laterites, though weak and friable, form excellent country roads. Massive granite setts may be necessary to carry heavy lorries near docks and factories. For such setts hardness alone is inadequate, for a quartzite would become slippery and make a good slide but a bad pavement; rocks are used which have constituents of different hardness, such as granite, as the felspars wear more readily than the quartz, and the surface keeps rough and gives a good grip. As a rule, however, the constituents of a stone should be nearly 2qual in hardness. Paved roads were built by the Romans, and are still used in China; they are suitable for pack animals, but not for wheeled traffic, as adjacent slabs inevitably settle at different levels and the fall of the wheel on to a lower slab drives it lower and may break it. Most modern roads have a surface of macadam, so called from the adopted name of its inventor : it consists of pieces of tough stone of uniform size, about I or 2 inches in diameter, mixed in some binding material ; this layer rests upon a foundation which admits of some vibration, so that the surface is elastic and yields slightly to a heavy shock.

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