40 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



animal remains in stone coal is due to the solvent power of carbon 

 dioxide coming from the decomposing seaweeds. 



IVIuck'*'* came strongly to support of Mohr's doctrine in the first 

 edition of his work. The essential objections to the theory are: 

 (i) That great accumulations of seaweed are not likely to reach 

 the bottom; (2) that remains of seaweeds have not been found in 

 dredgings, which bring up only inorganic materials and animal 

 remains; (3) the poverty of earthy materials in stone coal; (4) the 

 absence of sea plants, and (5) the rare occurrence of sea shells in 

 stone coal. 



The answers to these objections are: 



That the first is based on supposition, originating in lack of 

 knowledge ; that, for the second, it may be well to wait for its invali- 

 dation by opposing facts ; as for the third, it stands in close connec- 

 tion with the second and so may be of narrowly conclusive value, 

 but it is to be remarked that the ash-poor glance coal alternates with 

 the often very ash-rich matt- and cannel coal, whose ash does not 

 proceed from beds intervening between the coals, but is so intimately 

 mixed with the coal stuff that it can be due in only small degree to 

 later infiltration ; as for the fourth, absence of sea plants is explained 

 by the fact that those plants, in dead or torn condition, with or 

 without access of air, undergo decay very quickly, becoming, within 

 a few weeks or months, a structureless mass, in which organic 

 remains cannot be recognized; the fifth is answered very easily, for 

 animal remains are calcareous and are removed by carbon dioxide 

 which originates during the coal making process. 



In the second edition of his work. Muck, though no longer urging 

 the theory, argued that sea plants, embraced under the trivial term 

 " Tang," oft"ered and do off'er enough material for stone coal forma- 

 tion. The disappearance of organic structure in stone coal is ex- 

 plained as easily for seaweeds as for land plants by a kind of peaty 

 fermentation. The morphological differences between seaweeds and 

 the land plants corresponds to chemical differences in composition. 



Petzholdf' gave a more than halting adhesion to this doctrine 



"' F". Muck, "Die Cheinie der Steinkolile," Leipzig, ist cd., 1880: 2d ed., 

 1891. The citations are from the second edition, pp. 162-165, 168. 



" .'\. Petzholdt, " Beitrag zur Kenntniss der Steinkohlenbildung," Leipzig, 

 1882, pp. 25, 26, 27. 



40 



