241 



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

 those of the same denomination now contain, since their disinte- 

 gration took place at so early a period/' 



On this supposition, Mr. Kirwan proceeds to say, "I think the 

 formation of coal-mines, and most of the circumstances attending 

 them, may naturally be accounted for. 



" And, first, as to the seams of coal themselves, and their at- 

 tendant strata; they must have resulted from the equable dif- 

 fusion of the disintegrated particles of the primitive mountains, 

 successively carried down by the gentle trickling of the numerous 

 rills that flowed from those mountains, and in many cases more 

 widely diffused by more copious streams. By this decomposition, 

 the felspar and horn blend were converted into clay ; the bitumi- 

 nous particles, thus set free, reunited, and were absorbed, partly 

 by the argil, but chiefly by the carbonaceous .matter with which 

 they have evidently the greatest affinity ; since they are separable 

 by boiling water from the former, and scarcely, by the strongest 

 heat in close vessels, from the latter ; and even in an open fire, only 

 by a heat much superior to that of boiling water. The carbonic 

 and bituminous particles, thus united, being difficultly miscible 

 with water, and specifically heavier, sunk through the moist, pulpy, 

 incoherent, argillaceous masses, and formed the lowest stratum, 

 unless in cases where their proportion to the argillaceous particles 

 was so small, that the latter had subsided and coalesced, before 

 the former could have been reunited ; in that case the clayey par- 

 ticles formed the lower stratum of indurated clay. But if the 

 petrol were in the greatest proportion, it frequently sunk first, in 

 the form of a soft bitumen, carrying with it the clay, and forming 

 beds of shale, or bituminous shale, according to its proportion. 

 By oxygenation it becomes specifically heavier than water *." 



* Geological Essays, p. 330. 

 VOL. I. II 



