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 V. Mineral fuels

Collection:: Economics Books

COAL AND ITS CLASSIFICATION 271 1S Ie y le a +t 3 n It 1 } stage and the main agents in the conversion of peat or vege- table tissue into coal are heat and pressure in the absence of air. Wood immersed in a peat bog becomes hard and black, and resembles jet. The heat of a burning coal seam converts mine timber in an open position into charcoal, but timber buried in sodden ground becomes hard, black, and brittle like coal. Coal has been artificially prepared by E. Bergius (¥. Soc. Chem. Ind., xxxil, 1913, pp. 4626) by heating peat to 584° F. in the presence of water at the pressure of 5000 atmospheres. The carbon percentage in the artificial coal depends upon the temperature and length of treatment. Coal with 84 per cent. carbon (excluding ash and moisture) required 229 hours at 500° F., but was obtained in 21 hours at 644° F. Bergius therefore calculated that peat under pressure in the presence of water at 50° F. would be converted into bitu- minous coal in 8 million years, and into anthracite in a still longer period. Rogers in 1858 (Geol. Pennsylvania, ii, pt. 2, pp. 996-7) maintained that anthracite was formed from ordinary coal by debituminization, as he termed it. De la Beche (1848) had adopted that view for South Wales, since the coals are more anthracitic in the lower part of the Coal Measures. Strahan and Pollard (*‘ Coals of South Wales,” Mem. Geol. Surv., 1908) on the contrary hold that anthracite cannot have been formed from bituminous coal, as seams of both are interbedded and must have been subject to the same physical conditions. Strahan and Pollard re- gard anthracite and bituminous coals as formed from dif- ferent kinds of vegetation. The general evidence is however in favour of the formation of anthracite from bituminous coal. It is true that anthra- cite is not dependent upon igneous intrusions, which are absent from the Pennsylvanian fields, and in South Wales are older than the Coal Measures, nor upon faults which are often later than the change into anthracite. Nevertheless the deeper seams which have been under greater pressure and subject to higher temperature, generally contain less volatile matter than the upper seams; fields which have undergone especially severe dislocation yield anthracite, e.g. in Belgium, France, the Alps, and the Cretaceous coal- fields of New Zealand, The fossil plants of the anthracitic

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