10 STEVENSON— FORMATION OF COAL BEDS. [April;.!. 



of a series, the latter having been derived from the former by the 

 influence of heat, which itself was the agent by which vegetable 

 matter was converted into coal. Fuliginous matter is given off 

 when vegetable materials are burned and it is just what is needed 

 to compose coal beds. There are many charred coal beds, which 

 have lost their volatile or fuliginous matter through subterranean 

 heat. The volatile matter, diffused through the water, aided in 

 formation of the strata, while smoke from burning bodies on the 

 land found its way to the sea where it settled to the bottom. But 

 this was not the only source. The rivers of Scotland carry brown 

 water from the bogs ; there must be some agency causing precipita- 

 tion of this browMi material, otherwise the sea would be impregnated 

 with oily substance. The constant perishing of plants and animals 

 would give a supply of oily or bituminous matter to the ocean, which 

 would become pure coal unless earthy stuffs be in the water, which 

 would render the coal impure. If the mixture be perfect and the 

 subsidence uniform, a homogeneous substance resembling cannel 

 would be formed. 



Therefore, witli regard to the composition of mineral coal, the theory 

 is this, that inflammable vegetable and mineral remains, in a subtilized state, 

 had subsided in the sea, being mixed more or less with argillaceous, calcare- 

 ous and earthy substances in an impalpable state. Now the chymical analysis 

 of fossil coal justifies this theory: for in the distillation of the inflammable 

 or oily coal, we procure volatile alkali, as might naturally be expected. 



Kirwan,^"' indignant at Hutton's generally iconoclastic views, 

 entered the lists evidently determined to annihilate the new doc- 

 trines as well as their author. He rejects the hypothesis that pit coal 

 is merely earth or stone impregnated with petrol or asphalt, for Kil- 

 kenny coal contains neither petrol nor any other bitumen. He 

 recognizes the vegetable origin of wood coal but maintains that it 

 is chemically different from mineral coal, so different as to show 

 that the latter was not derived from wood deposited in or out 

 of the sea. As further arguments, he notes features in the mode 

 of occurrence. Beds of mineral coal are uniform in thickness within 

 great areas, beds of wood coal are not ; beds of mineral coal show 

 parallelism, which is unknown in wood coal beds ; wood coal mines 



" R. Kirwan, "Geological Essays," London, 1799, pp. 315-349. 



10 



