DYNAMICAL GEOLOGY. 24! 



ing its physical and chemical constitution, its palaeontology, 

 geological occurrence, and geographical distribution, was pub- 

 lished by C. F. Zincken in 1865. 



Fossil peat-deposits occur, so far as at present known, only 

 in the post-Tertiary or Quaternary formation. The black- 

 coal deposits of the old formations were frequently compared 

 in geological literature with brown-coal, but the homogeneous 

 structure and the rarity of good plant-remains in black coal, 

 threw great doubt upon this explanation of its origin. Agricola, 

 in 1544, explained it as condensed petroleum, and his opinion 

 still found favour with Voigt in his special work on Coal- 

 deposits (1802) and with Buckland (1822). 



Kirwan, the opponent of Hutton, even explained coal as a 

 product of the chemical decomposition of Archaean rock, while 

 Andreas Wagner supposed it to represent condensed and de- 

 oxidised carbonic acid derived from an atmosphere super- 

 saturated with carbon dioxide. Many of the geologists in the 

 eighteenth century upheld the correct explanation; amongst 

 others Scheuchzer in 1706, Beroldingen in his work on Contro- 

 versial Points in Mineralogy (1778), and James Hutton in 

 Great Britain (1785). But it was not until the microscope 

 was applied to its investigation that the origin of coal from 

 plant-growth in situ was securely established. In 1848, the 

 German botanist, Dr. Heinrich Goeppert, proved that the 

 vascular cryptogams and conifers whose remains accompany 

 coal-formations had supplied the material of the deposit. 

 His results were corroborated by Dawson in 1859; but 

 even after this date erroneous conceptions from time to 

 time were advanced with regard to the kinds of vegetation 

 which had given origin to the coal-deposits. A decisive 

 paper on the subject was contributed by Giimbel to the 

 Bavarian Academy of Sciences in 1883, wherein he gave 

 microscopic sections showing the fine textures of the various 

 plant-remains in peat, brown coal, black coal, and anthracite. 



The transformation of decayed plant-remains into coal takes 

 place under the fundamental condition of limited access of 

 air, and is promoted by heat and pressure. There is little 

 doubt that all three factors have contributed to the origin of 

 the deposits of black coal, and Bischof suggested that the 

 characteristic chemical and physical constitution of the 

 varieties of coal had been determined by definite relations in 

 the amount of air admitted and in the accompanying heat and 



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