I9II.] STEVENSON— FORMATION OF COAL BEDS. 11 



have sudden elevations or depressions, not found in those of 

 mineral coal ; slips or dikes abound in true coal but do not occur 

 in wood coal : wood coal is frequently, genuine coal never found 

 in plains. Mineral coal is of distinctly inorganic origin. 



Aly opinion, therefore, is that coal mines or strata of coal, as well as 

 the mountains or hills in which they are found, owe their origin to the 

 disintegration and decomposition of primeval mountains, either now totally 

 destroyed, or whose height and bulk, in consequence of such disintegration, 

 are now considerably lessened. And that these rocks, anciently destroyed, 

 contained most probably a far larger proportion of carbon and petrol than 

 those of the same denomination now contain, since their disintegration took 

 place at so early a period. 



The seams of coal and their attendant strata must have resulted 

 from the equable diffusion of the disintegrated particles of the 

 primitive mountains carried down by the " gentle trickling of the 

 numerous rills " and more widely dift'used by more copious streams. 

 The important sources of material for the coal beds were granite 

 and trap, as those rocks contain natural carbon and hornblende, the 

 latter mineral being an extremely important source. Kirwan's argu- 

 ments are extremely ingenious and he finds no difficulty in explain- 

 ing all known phenomena by means of his " supposition." 



Playfair^* attacked Kirwan's doctrine and defended that of 

 Hutton. He regarded Kirwan's suggestions as deserving only 

 ridicule. He showed that both wood and mineral coal occitr in the 

 same bed and that most of Kirwan's postulates were not in accord 

 with fact. The quantity of hornblende and silicious schist to be 

 decomposed in order to yield the coal would be vastly greater than 

 Kirwan had supposed ; Playfair suggested that it would have been 

 better to imagine that the diamond existed so abundantly in the 

 primeval mountains as to constittite great rocks. A single ridge 

 might suffice to give material for coal beds of all the surrounding 

 plains. He asserted that Kirwan's hypothesis trespasses on every 

 principle of common sense. 



\'oigt^^ strenuously opposed v. Beroldingen's hypothesis that coal 



"J- Playfair, "Illustrations of the Huttonian Theory of the Earth," 

 Edinburgh, 1802, pp. 148-160. 



^'J. C. W. Voigt, " Versuch einer Geschichte der Steinkohlen, der 

 Braunkohlen und des Torfes," Weimar, 1802, pp. 42-46. 



11 



