I9I1.] STEVENSON— FORMATION OF COAL BEDS. 79 



when broken up by atmospheric agencies, yield a hard rather plastic 

 material, resisting plant growth, yet they are as black as those of 

 the mur. The theory of origin from peat would require that, in 

 the mur, the quantity of carbon increase as it approaches the coal, 

 as it must contain roots of plants ; while in the toit the carbon should 

 decrease gradually as one recedes from the coal. There is no 

 abrupt change from coal to shale in the roof, so that the latter should 

 be richer in carbon than the mur. 



It is necessary to see how transformation of vegetable matter 

 into coal is explained by each theory. This necessity is felt by de- 

 fenders of the transport theory, because the flowing water furnishes 

 only a mass of wood, bark, leaves whereas according to the theory 

 of peat bog origin, the change of vegetable matter into peat is 

 associated with the deposition. 



In passing from vegetable matter to coal, there is great loss in 

 hydrogen and great enrichment in carbon. Either the plant ma- 

 terials were changed into peat, lignite and the rest successively, or 

 the organic matter was converted at once into its present state with- 

 out passing through the intermediate stages. The latter explanation 

 rests chiefly on Fremy's experiments, which showed that vegetable 

 matter, subjected to high pressure and a temperature of 200° to 

 300° C. for a long time, becomes converted into a material very 

 closely resembling bituminous coal. A fundamental objection to 

 this theory is that no evidence exists suggesting that any such 

 temperature prevailed, and nothing is less established than -the con- 

 ception that time could compensate for deficiency in heat. 



However this may be, it is evident that, according to the doctrine 

 of transport, the change going on in materials between the shales 

 requires that specimens of shale collected at equal distances in re- 

 ceding from the coal, should show the carbon and hydrogen varying 

 in a determinate manner ; in proportion as one recedes from the 

 coal the shale should have less of carbon and more of hydrogen 

 as the more volatile hydrocarbons would go farther. But the doc- 

 trine of peatbog origin leads to a contrary condition. 



A determination of the carbon and hydrogen in shales near 

 coal beds may aid in answering the question as to whether the 



79 



